Home

here - Labsys

1. SYNCHRONOUS i Toe err m GEAR TRAIN 0 I CLUTCH e 4 e y POINTER DIAL t PIVOT SHAFT ij CALIBRATED ja SPIRAL SPRING PIVOT CUP gt JEWELLED BEARING GUARDLEG SPINDLE gt SAMPLE CONTAINER Figure 3 1 Below the main case is the pivot cup through which the lower end of the pivot shaft protrudes A jewel bearing inside the pivot cup rotates with the dial or transducer the pivot shaft is supported on this bear ing by the pivot point The lower end of the pivot shaft comprises the spindle coupling to which the Viscometer s spindles are attached Brookfield Engineering Labs Inc 3 3 Spring Torque There are four basic spring torque series offered by Brookfield Brookfield Spring Torque Terminology dyne cm milli Newton m LV 673 7 0 0673 RV 7 187 0 0 7187 HA 14 374 0 1 4374 HB 57 496 0 5 7496 The higher the torque calibration of your instrument the higher the viscosity measurement range for a spe cific spindle The viscosity measurement range for each torque calibration and spindle combination may be found in Appendix B There are many variations of the standard spring torques Please consult Brookfield Engineering Labo ratories or your dealer with your special requirements 3 4 Viscosity Measurement Tec
2. Inner Annulus 1 45 36 83 ID x 1 259 31 98 OD S X J Shaded area depicts Stationary Stator Skirt and Cup MORE SOLUTIONS TO STICKY PROBLEMS Page 50 Brookfield Engineering Labs Inc APPENDIX B Spindle Entry Codes and Range Coefficients The Range Coefficient is a convenient tool for quickly determining the maximum viscosity that can be measured with a specific spindle speed combination Identify the spindle in use and the torque range LV RV HA HB of the Viscometer Rheometer Look up the Range Coefficient in the following table Divide the Range Coefficient by the spindle speed to determine the maximum viscosity in centipoise that can be measured E g RV Viscometer with RV3 spindle Range Coefficient is 100 000 At 50 rom the maximum viscosity that can be measured is 100 000 50 or 2 000 cP The Entry Code is the two digit number used to identify the spindle in use when operating a standard digital Viscometer Rheometer spine o v w m w Rve 93 750 1 000 000 2 000 000 8 000 000 um oa 18 750 200 000 200 000 1600 000 i a E ar a7 a75 000 9001000 8 000 000 32900000 m 98 750 7 000 000 2 000 000 8 000 000 v2 eE 30 000 820 000 640 000 2 560 000 Table continued on next page MORE SOLUTIONS TO STICKY PROBLEMS Page 51 Brookfield Engineering Labs Inc vp w e e 18 750 200 000 400 000 1 600 000 37 4
3. GEUTIONS Your Brookfi iscometer _ i 3 e Newtonian and non Newton an Fluids e Temperature Dependence of Viscosit and much more MORE SOLUTIONS TO STICKY PROBLEMS TABLE OF CONTENTS INTRODUCTION cccccceeeeeeeeseeeeeneeeeneeeeesneeeeneseeees 1 CHAPTER Iiei Feacesctencceesieeenedetecnuceeetepaecetececeneatete 2 1 1 Why Make Rheological Measurements 2 1 2 Thinking Rheo Logically eee 2 1 3 Three Schools of Thought on Viscosity Measurement ccceeeeeeeeeeeeeeeeeeeeeteeeeeeees 2 1 3 1 The Pragmatic School eeee 2 1 3 2 The Theoretical School 8 2 1 3 3 The Academic School s s s 3 CHAPTER 2 icici tice ccvscceeceectiv states sh cesencieenstterteteeett 3 2 1 Equipment for Specific Situations 3 2 2 VISCOMETESS ienes eara a 3 2 3 RNCOMECHEMS setnie aaa 3 2 4 Spindle Geometries ccceeeeeeeeeeeeeneeeees 4 2 4 1 Disc Spindles ceeeeeeeeeeseeeeeeees 4 2 4 2 Cylindrical Spindles ceeeee 4 2 4 3 Coaxial Cylinders s s s 4 2 4 4 Cone Plate Geometry eeeeee 4 2 4 5 T Bar Spindles ccceeeeeeceeeeeeeeees 4 2 4 6 Vane Spindles ceceeeeeteeeseeeeeees 5 2 5 Temperature Control ccsceeeeteeeeeteeeees 5 2 5 1 Temperature Baths eeeeee 5 2 5 2 Thermosel System ssec 5 2 5 3 Peltier Thermo electric Systems 5 2 6 Small Sample Volume ccceee
4. MORE SOLUTIONS TO STICKY PROBLEMS Page 3 interchangeable model for model in most viscosity specifications requiring Brookfield Viscometers The dial reading type is the least expensive Brookfield Viscometer and is suitable for most appli cations where samples are to be tested over a short period of time and a permanent detailed record of rheo logical behavior is not required This is due to the fact that while the Viscometer rotates continuously read ings may be made only intermittently when the pointer passes under the vision glass or when the reading is held and the Viscometer stopped Long term viscos ity tests necessitate frequent operator attention and some fast acting processes dictate continuous moni toring The Digital Viscometer with its continuous sensing and display is more suited to such situations It may be left unattended for long periods and the data out put DV II Pro may be adjusted to provide a detailed record of even the fastest rheological processes In addition many operators prefer a digital display which eliminates the interpolation sometimes necessary when reading a dial Both types offer equivalent ac curacy Brookfield Digital Viscometers excluding DV E are also available in cone plate geometry See Section 2 10 for more information on cone plate spindle ge ometry Several specialized viscometers are available which have been designed to satisfy particular industry needs These instru
5. BS designation indicates that the spindle is also available in a solid shaft configuration MORE SOLUTIONS TO STICKY PROBLEMS Page 39 Brookfield Engineering Labs Inc HT 2 Sample Chamber Dimensions C Damer en 0 750 19 05 3 062 77 77 Disposable HT 2DB chambers for use with Thermosel are available from Brookfield or an authorized dealer A 9 DIN Adapter DIN Spindle Factors and Shear Rates N RPM DIN Spindle Dimensions A HT DIN 81 6 096 154 84 125 3 18 6915 17 56 1 0373 26 35 1 237 31 42 237 31 SC4 DIN 82 5 219 132 56 125 3 18 6915 17 56 1 0373 26 35 1 237 31 42 20 Dimensions are in inches mm MORE SOLUTIONS TO STICKY PROBLEMS Page 40 Brookfield Engineering Labs Inc DIN Chamber Dimensions 1 0850 0 7540 DIA DIA Spindle No Accessory Used With HT DIN 81 7500 19 05 Thermosel SC4 DIN 82 7500 19 05 Small Sample Adapter SC4 DIN 83 500 12 7 Small Sample Adapter ULA DIN 85 DAA 1 1 0875 27 62 DIN Adapter ULA DIN 86 ULA DIN 6Y 7540 19 15 DIN Adapter sl emacs ULA DIN 87 ULA DIN 6Y 5048 12 82 DIN Adapter an QS Dimensions are in inches mm DAA 1 ULA DIN 6Y DIN CHAMBER DIN CHAMBER A 10 Helipath Stand with T Bar Spindles T Bar Spindle Factors Spindle Factors are listed as constants related to the Viscometers rotational soeed Spindle Factors are traditionally used to convert the torque
6. 008 19 48 4 TINE iini aiia ieee sieeve tien 19 4 8 5 Pressure ececcceeeeeecceeeeeeteeeeeeentenes 19 4 8 6 Previous History aene 20 4 8 7 Composition and Additives 20 4 8 8 Special Characteristics of Dispersions and Emulsions ccceceeeeeeeeeeeeneeneees 20 CHAPTER 5 iis notte te ed heen 21 APPENDIX A Specifications Ranges and 5 1 Advanced Methods for Operating Parameters cescsseeeeeeeees 30 Rheological Analysis ceeeeeeeeeees 21 A 1 Dial Reading Viscometer Spindles 5 2 Defining Operating Parameters of Various and Speeds Aorere ico havea 31 Spindle Geometries 2 0 21 A 2 Digital Viscometers Rheometers 5 2 1 Cylindrical Spindles 0 eeee 21 Spindles and Speeds eeeeeeeeeeee 32 5 2 2 Coaxial Cylinders s s s 22 A 3 Disc Spindle Information for Standard 5 2 3 Cone and Plate n 22 Viscometers Rheometers n 32 5 2 4 Disc and T Bar Spindles 22 A 4 Cylindrical Spindles for Dial Reading 5 2 5 Spiral Adapter Spindle 22 Viscometer and Digital Viscometers 5 2 6 Paddle Paste Spindles 23 Rheometers 0 eee ececeeeeeeeeeeeecteeaeeeeeeeeeeeees 33 5 2 7 Vane Spindles a se 23 A 5 Wells Brookfield Cone Plate 5 2 8 Other Special Spindles 23 Viscometers Rheomete s 0cee 35 5 3 Analyzing Time Independent A 6 Small Sample Adapter 0 c cecceee 36 Non Newtonian Flu
7. 3368 5 dyne cen timeters full scale 5XHB 5 X 57 496 287 500 dyne cm Multiplier also applies to all factors and ranges 3 Torque at any dial or display reading equals reading multiplied by full scale torque divided by 100 RVT model reading 40 torque 40 X 7187 0 100 2874 8 dyne cm 4 To calculate the upper limit of viscosity measuring range full scale range for your instrument multiply the factor by 100 after defining the spindle and speed in use see A 3 A 4 For digital mod els push the autorange button Brookfield Engineering Labs Inc Some notes about the terms appearing in this Ap to obtain viscosity in centipoise pendix For example the Spindle Factor for a 2 LV 1 Shear rate constants where given are simply mul spindle on an LV Viscometer is given as 300 N tiplied by the Viscometer s rotational speed in RPM to obtain the shear rate in reciprocal sec onds for that speed The constants are indepen dent of Viscometer model sample viscosity or temperature Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Fac tors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centi poise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading Section A 1 4 The Viscometer s ro
8. Alternatively the Viscometer can be recalibrated to compensate for the smaller container as outlined in Section 3 3 10 Also use of the Small Sample Adapter should be considered See Section 2 6 1 3 4 5 Sample Conditions The sample fluid should be free from entrapped air Air can be removed by gently tapping the container on a table top or by careful use of a vacuum apparatus The sample should be at a constant and uni form temperature This can be verified by checking the temperature at several different locations within the container Be sure to bring the sample spindle and guardleg to the same temperature before tak ing a viscosity reading Temperature uniformity can often be maintained by agitation prior to a measure ment but first determine that such agitation won t affect viscosity of the sample fluid see Section 4 7 5 Factors used to calculate viscosity values from the Viscometer readings are independent of temperature A constant temperature water bath is used to maintain the desired temperature Refer to Section 2 5 for information on recommended baths High temperature work up to 300 C may re quire use of the Thermosel accessory See Section 2 8 1 Homogeneity of the sample is also quite impor tant especially in dispersed systems where settling can occur In many cases simple stirring just prior MORE SOLUTIONS TO STICKY PROBLEMS Page 11 to the test will keep the components dispersed 3 4 6 Spindle
9. but keep this fact in mind and treat the multi point rheology informa tion as if it were In many cases this produces emi nently satisfying results and eliminates the neces sity of buying a highly sophisticated and very ex pensive piece of rheological equipment Brookfield Engineering Labs Inc 1 3 3 The Academic School The third school of thought is quite academic in nature People adhering to this school require that all measurement parameters particularly shear rate and shear stress be defined and known They need equipment with defined geometries such as cone and plate or coaxial cylinders Examples from the Brookfield line would be the Wells Brookfield Cone Plate and CAP Viscometers and the UL adapter Small Sample Adapter Thermosel Din Adapter and Spiral Adapter accessories as well as the R S and PVS Rheometers With this equipment the shear rate is defined and accurate absolute viscosities are obtained directly That then is our view of the three schools of thought on viscosity measurement You may need to think in terms of any or all of these depending on your background approach goals and type of equip ment available Brookfield Viscometer users fall into all three the following chapters present information of use to each CHAPTER 2 2 1 Equipment for Specific Situations The purpose of this chapter is to provide an over view of Brookfield s entire line of Viscometers Rhe ometers and related a
10. eter is to be used for quality control purposes and the operator is not concerned with the actual cen tipoise value of the material If your work requires that actual centipoise val ues be obtained we suggest the following proce dure if a different container is to be used or if you don t wish to use the guard leg 1 Following the procedures outlined earlier in this chapter measure the viscosity of a Newtonian fluid using a standard container as specified in Section 3 3 4 Brookfield Viscosity Standards are highly recommended for this procedure Perform this measurement carefully as the accuracy of your end result depends upon it Multiply the Viscometer reading by the appropriate Factor to determine the fluid s viscosity in centipoise Transfer the Standard to the container for which the Viscometer is to be calibrated Ensure that the fluid temperature is the same as it was during Step 1 3 Using the same spindle you intend to use for subsequent sample testing measure viscosity of the Standard in the new con tainer Note the dial or display reading and speed S1 4 The new range of measurement is deter mined by this formula pe 10m X 2 lt Where R1 is the full scale range of mea surement under the new conditions 7 is the viscosity of the Standard as measured in step 1 and x is the dial or display read ing obtained in step 3 MORE SOLUTIONS TO STICKY PROBLEMS 5 To calculate the res
11. see Section 4 4 If the bonds within the aggregates are extremely strong the system may display a yield value see Section 4 4 about plastic flow The magnitude of the yield value depends on the force required to break these bonds If a material s flocculated structure is destroyed with time as it is sheared a time dependent type of flow behavior will be observed see Section 4 5 If the shear rate is decreased after destruction of some or all of the flocculated structure the material s viscosity may be lower than it previously was at the same shear rate Since flocs begin to link together after destruction the rate at which this occurs affects the time required for viscosity to at tain previous levels If the relinking rate is high vis cosity will be about the same as before If the relinking rate is low viscosity will be lower This results in the rheological behavior called thixotropy see Section 4 5 The attraction between particles in a dispersed phase is largely dependent on the type of material present at the interface between the dispersed phase and the liquid phase This in turn affects the rheological behavior of the system Thus the intro duction of flocculating or deflocculating agents into a system is one method of controlling its rheology Shape of the particles making up the dispersed phase is also of significance in determining a system s rheology Particles suspended in a flowing medium are consta
12. where N is spindle speed in RPM 5 2 6 Paddle Paste Spindles The Brookfield KU 1 Viscometer uses a paddle spindle to measure the reaction torque when rotated at 200 RPM Unlike regular viscom eter spindles the resultant viscosity is in KU Kreb Units and g grams Because of the unique spindle shape no shear rate calculation is possible The Brookfield KU 2 Viscometer provides the same measurement capability as the KU 1 and also converts the Krebs reading into a centipoise viscosity value Since the spindle geometry is unique the centipoise reading taken with the KU 2 does not correlate with centipoise measurements from a standard Brookfield Viscometer using disc or cylindrical spindles A paste spindle is available as an option to the paddle spindle This spindle is similar to the paddle type The design consists of off set rod type vanes approximately 22 mm x 19 mm long The resultant viscosity is recorded in units of g grams It is suit able for use with high consistency materials such as roller mill pastes 5 2 7 Vane Spindles The vane spindle can be treated as a virtual cyl inder with radius and length equal to the equivalent dimensions of a single vane The equations in Sec tion 5 2 1 may apply for low rotational speeds be low 10 RPM Eddy currents at higher rotational speeds could give falsely higher viscosity values 5 2 8 Other Special Spindles Brookfield can produce special s
13. with the same spindle These measure ments are usually made at speeds that differ by a factor of 10 for example 2 and 20 RPM 10 and 100 RPM etc but any factor may be established In constructing the ratio the viscosity value at the lower speed should be placed in the numera tor the one at the higher speed in the denominator Therefore for pseudoplastic shear thinning fluids the ratio will exceed 1 0 as the degree of pseudoplastic behavior increases Conversely for dilatant shear thickening fluids the ratio will be less than 1 0 as the degree of dilatancy increases This procedure is commonly known as the thixo tropic index The name is misleading since this ratio quantifies time independent non Newtonian be havior not thixotropy which is a time dependent phenomenon Analysis of time dependent properties is detailed in Section 5 4 A similar method eliminates calculation of vis cosity and simply utilizes dial display torque read ings to derive what is known as a viscosity ratio Mx oo mo 09 Viscometer torque reading at speed x Viscometer torque reading at speed 10x other ratios may be used VISCOSITY RATIO Definitions Mx M10x 5 3 2 Graphic Methods The most basic graphic method of analyzing non Newtonian flow is constructing a plot of viscos ity versus spindle speed using the same spindle for all readings Generally viscosity is plotted along the Y axis and speed RPM alo
14. 5 minutes must be allowed for the reading to reach apparent equilibrium Usually you can just wait until the reading appears relatively constant for a reasonable time Amore repeatable procedure is to specify a defi nite number of spindle revolutions to be counted before taking a reading Since the time required for acertain number of revolutions will differ significantly with the speed in use an alternate method is to let the spindle rotate for a specified period of time You may find that the reading does not come to equilibrium but continues to oscillate This is usu ally due to the presence of an elastic as well as a viscous component in the fluid If the reading con tinually increases or decreases the fluid is prob ably time dependent and requires special tech niques to be measured successfully See Section 4 5 The torque display on the Digital Viscometer may fluctuate by 0 1 or 0 2 even after equilibrium is reached If this happens simply use the median value as the accepted reading Larger fluctuations may indicate the conditions described in the pre ceding paragraph Once a valid reading is obtained with a Dial Reading Viscometer multiply it by the Factor for the spindle speed combination you are using The Fac tor will be found on the Factor Finder supplied with the Viscometer Calculating Digital Viscometers do not require the use of a factor These viscometers will display viscosity in units of cP directly pro vi
15. A 16 CAP 2000 Viscometer The CAP 2000 Viscometer is a variable speed cone plate instrument 5 rpm to 1000 rpm with integrated temperature control Torque Range Standard 1xCAP or 181 000 dyneecm Option 1 23 CAP or 7 800 dynescm See Section A 15 for spindle dimensions Viscosity Viscosity Shear Sample Cone Cone Min Speed Max Speed 1000 Rate Volume Angle Radius 5 RPM Poise RPM Poise g CAP 01 37 5 375 0 2 2 0 13 3N sec 67 uL 1 511cm CAP 02 75 750 0 4 4 0 13 3N sec 38 uL 1 200cm CAP 03 150 1500 0 8 8 0 13 3N sec 24 uL 0 953cm N A Not appropriate for use at speeds above 400 rpm MORE SOLUTIONS TO STICKY PROBLEMS Page 47 Brookfield Engineering Labs Inc A 17 R S Rheometer amp R S Soft Solids Tester The R S Rheometer operates in either conrolled stress or controlled rate mode Controlled stress is useful for evaluation of yield behavior creep analysis and viscoelasticc response Controlled rate provides flow curve information viscosity vs shear rate or shear stress Available spindle geometries include cone plate plate plate coaxial cylinder and vane spindles R S Soft Solids Tester sense cerns tm Mm e er Sos Rage Degrees mm mL Rate sec Stress Pa Range cP Poe SSS ee SS Se aS es Tooo o ooo ao CE E E a ey Ee a a Pea a ee ee ee eS a a a Ea eS E E pe eee E re O CE al Pot Ce aie we ae Co Not Applicable Not Applicable mm mm MORE SOLUTIONS TO
16. For example the Spindle Factor for a CPE 40 spindle on an LV Viscometer is given as 3 07 N see the following Cone Spindle Factors Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 12 RPM the Spindle Factor is 3 07 12 or 7 25 Multiply all Dial Viscometer readings made with this spindle speed combination by 7 25 to obtain viscosity in centipoise N RPM MORE SOLUTIONS TO STICKY PROBLEMS Page 35 Brookfield Engineering Labs Inc ACCESSORIES FOR STANDARD VISCOMETERS RHEOMETERS A 6 Small Sample Adapter SC4 Series Spindle Factors and Shear Rates Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for an SC4 21 spindle and 13R chamber on an RV Viscometer is given as 500 N see the following SC4 Series Sindle Factors and Shear Rates Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 20 RPM the Spindle Factor is 500 20 or 25 Multiply all Dial Viscometer readings made with this spindle speed combination by 25 to obtain viscosity in
17. RPM 2 10 4 PVS Rheometer The Brookfield PVS Rheometer is a portable unit designed for measuring viscosity at high pressure and temperature It s ability to measure viscosity over a pressure range from abient up to 1 000 psi and a temperature range of 40 C to 200 C makes it ideal for applications such as oil and gas well drill ing fluids pulp and paper plastics petrochemicals and aerosol based products The PVS Rheometer operates at shear rates from 0 01 sec to 1 700 sec corresponding to speed ranges from 0 05 to 1 000 RPM The PVS Rheometer torque sensor is unaffected by changes in pressure or temperature the placement of bear ings outside the pressurized sample volume virtu ally elminates the need for maintenance 11 Defined Shear Stress R S Series Rheometer The Brookfield R S Rheometer differs from the standard Brookfield viscometers in that it is a con trolled stress or controlled torque instrument rather than a controlled rate RPM instrument Controlled stress with the R S provides many benefits such as a very broad viscosity measurement range testing for Yield properties and the ability to measure flow properties of delicate high viscosity gels The R S Rheometer is available in several mod els The coaxial Cylinder Model offers DIN geom etries with bob spindle diameters of 8 14 25 45 48 mm and double gap The Cone Plate Model of fers 1 and 2 degree cones of 2 5 5 0 and 7 5 cm diameter The Cone P
18. T bar spindle prevents the calculation of shear rate or shear stress See Section 2 12 1 Brookfield Engineering Labs Inc 2 4 6 Vane Spindles The vane spindle when immersed into a mate rial traps a portion of the test sample creating a cylinder of sample that can be used to calculate shear stress and shear rate With vane spindles well defined measurements are possible for non flowing or slow flowing fluids including yield values Four vane spindles are available and can be used with most Brookfield viscometers See Section 2 12 3 2 5 Temperature Control In order to ensure maximum accuracy and repro ducibility in many viscosity measurement procedures temperature control is highly recommended The fol lowing systems are available from Brookfield 2 5 1 Temperature Baths Constant temperature baths are suitable for most viscosity measurement applications They are available in two basic types circulating for use with jacketed devices such as the Wells Brookfield Cone Plate Viscometer Section 2 10 1 and the Small Sample Adapter Section 2 7 2 and reservoir cir culating for all applications this type can be used with jacketed devices as well as with any sample container that can be immersed in the bath s reser voir Temperature baths are generally limited to a maximum operating temperature of approximately 120 C depending on the bath fluid used and usu ally require auxiliary cooling devices for operat
19. centipoise Spindle Semple ow fv ona ne Shear Rate Chamber Size mL sec sexsinan 90 soon enon seon asen oan N RPM M 1000 A The values for the sample size mL were adjusted slightly in 2005 If unsure check the i hag fluid level in the chamber to verify that the spindle shaft is covered 1 8 inch above the p18 inen point where the cone and shaft come together MORE SOLUTIONS TO STICKY PROBLEMS Page 36 Brookfield Engineering Labs Inc SC4 Series Spindle Dimensions a Diameter Side Length Effective Length inches mm inches mm inches mm SC4 14 0 344 8 74 0 340 8 64 0 478 12 14 SC4 15 0 376 9 55 0 674 17 12 0 821 20 85 SC4 16 0 275 6 99 0 815 20 70 0 989 25 12 IN SC4 18 0 688 17 48 i SC4 21 SD 0 660 16 77 SC4 25 0 188 4 78 SIDE LENGTH SC4 27 SD 0 463 11 76 1 300 33 02 1 547 39 29 SC4 28 0 370 9 39 1 260 32 00 1 480 37 59 N A SC4 29 0 300 7 62 1 070 27 18 1 250 31 75 SC4 31 0 463 11 76 0 990 25 15 1 208 30 68 SC4 34 0 370 9 39 0 954 24 23 1 156 29 36 Refer to Section 5 2 1 The SD designation indicates that the spindle is also available in a solid shaft configuration 3 DIN geometries for the Small Sample Adapter are also available See Appendix A 9 DIAMETER hp SC4 Series Small Sample Chamber Dimensions 75
20. indicated for appli cations where extremely well defined shear rate and shear stress data is required particularly when the sample volume is relatively small Several Brookfield accessories feature coaxial cylinder geometry each also has unique advantages for specific situations These accessories are the Small Sample Adapter Section 2 6 1 the UL Adapter Section 2 6 2 the Thermosel Section 2 6 4 the DIN Adapter Sec tion 2 6 3 and the Spiral Adapter Section 2 12 2 Disposable chambers and spindle are available for Small Sample Adapter and Thermosel Please read 2 6 1 and 2 6 4 for details 2 4 4 Cone Plate Geometry Cone plate geometry offers absolute viscosity determinations with precise shear rate and shear stress information readily available The sample volumes required are extremely small and tempera ture control is easily accomplished Cone plate ge ometry is particularly suitable for advanced rheo logical analysis of non Newtonian fluids Itis avail able on the Wells Brookfield Cone Plate Viscom eters CAP 2000 Rheometer and R S Rheom eter see Section 2 10 for more information 2 4 5 T Bar Spindles Generally used in conjunction with the Helipath Stand accessory with which they are supplied as standard equipment T bar spindles make possible the measurement of non flowing or slow flowing ma terials such as pastes gels and creams Results are considered apparent since the unique geom etry of the
21. is an indirect measure of product consistency and quality Another reason for making flow behavior studies is that a direct assessment of processability can be obtained For example a high viscosity liquid requires more power to pump than a low viscosity one Knowing rheological behavior therefore is useful when designing pumping and piping systems It has been suggested that rheology is the most sensitive method for material characterization because flow behavior is responsive to properties such as molecular weight and molecular weight distribution This relationship is useful in polymer synthesis for example because it allows relative differences to be seen without making molecular weight measurements Rheological measurements are also useful in following the course of a chemical reaction Such measurements can be employed as a quality check during production or to monitor and or control a process Rheological measurements allow the study of chemical mechanical and thermal treatments the effects of additives or the course of a curing reaction They are also a way to predict and control a host of product properties end use performance and material behavior 1 2 Thinking Rheo Logically To begin consider the question Can some rheological parameter be employed to correlate with an aspect of the product or process To determine this an instinct must be developed for the kinds of chemical and physical phenomena which affect
22. measure viscosities from 5 cP to 10 000 000 cP at shear rates from 0 066 to 93 0 reciprocal seconds The Small Sample Adapter s jacketed design per mits connection to a circulating type bath for excel lent temperature control up to a recommended maxi mum of 100 C Disposable 13RD chamber is avail able for use with SSA a special water jacket is re quired for this configuration 2 6 2 UL Adapter The UL Adapter is primarily intended to allow viscosity measurements in ranges below those nor mally measurable by a particular Viscometer When used with its removable end cap in place the UL Adapter measures a sample volume of 16 0 mL For more information see Section 2 7 1 2 6 3 DIN Adapter DIN standards come from Germany and are similar in scope and purpose to ASTM standards from the United States The Brookfield DIN Adapter like the UL Adapter is designed to measure in ranges below those normally measured with a particular Viscometer The DIN Adapter utilizes additional DIN spindles for measurement ranges from 1 cP to 50 000 cP and conforms to DIN 53019 2 6 4 Thermosel System The Thermosel System allows the measurement of viscosity at temperatures to 300 C It incorpo rates coaxial cylinder spindle geometry that uses a sample volume of 8 0 to 13 0 ml depending on the spindle utilized See Section 2 8 1 Disposable chambers Part No HT 2D 100 and spindle Part No SC4 27D are available for use with Thermosel 2 6 5
23. of delicate high viscosity gels Similar to DV III Ultra it can operate in stand alone mode or under PC con trol and provides detailed data on material behavior including yield stress The CAP 2000 Rheometer is a variable speed cone plate instrument with broad shear rate capability Its rugged design makes it ideal for busy work environ ments whether running in stand alone mode or under PC control The PVS Rheometer is a pressurizable variable speed instrument used primarily to evaluate fractur ing fluids and drilling muds in the oil gas industry The relatively new YR 1 Rheometer is an inexpen sive benchtop instrument which tests the yield behav ior of materials providing a single yield stress value for better QC evaluation of products 2 4 Spindle Geometries All Brookfield Viscometers and Rheometers are sup plied with spindles suitable for most applications within the viscosity range of the instrument There are how ever situations where specialized spindle geometries are necessary to obtain optimum results Brookfield has available a wide variety of spindles and accesso ries to fulfill these needs All Brookfield spindles are constructed of 300 series stainless steel for maintenance free service in most applications some are available coated for maximum corrosion resistance Brookfield also offers dispos able spindle and chambers made of aluminum as noted in this section Please inquire about special spindle mate
24. value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for a T C spindle on an RV Viscometer is given as 10 000 N see the follow ing T Bar Spindle Factors Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 50 RPM the Spindle Factor is 10 000 10 or 1 000 Multiply all Dial Viscom eter readings made with this spindle speed combination by 1 000 to obtain viscosity in centipoise Maximum recommended rotational speed for spindle 10 12 RPM Travel Speed for Helipath drive motor which moves rotating spindle downward into sample 7 8 inch 22 2 mm per minute There is no defined shear rate for T bar spindles eons v w mA e N RPM M 1000 MORE SOLUTIONS TO STICKY PROBLEMS Page 41 Brookfield Engineering Labs Inc T Bar Spindle Dimensions Spindle Crossbar Length 1 894 48 1 41 2 1 435 36 4 1 065 27 1 CROSSBAR LENGTH Dimensions are in inches mm A 11 Spiral Adapter Spiral Spindle Factors and Shear Rate Spindle Factors are listed as constants related to the Viscometers rotational soeed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscomet
25. 00 C with the cap removed it may be used in sample containers of almost any size 2 7 2 Small Sample Adapter With some spindle chamber combinations the Small Sample Adapter permits measurement of vis cosities below the Viscometer s normal range Check the applicable range sheet for details More information on the Small Sample Adapter can be found in Section 2 6 1 2 7 3 Thermosel System With certain spindles the Thermosel System provides increased sensitivity at low viscosities check the applicable range sheet for more data The Thermosel System is discussed in more detail in Section 2 8 1 2 7 4 Wells Brookfield Cone Plate Viscometer The Wells Brookfield Cone Plate Viscometer has measurement capabilities below 1 0 cP See Sec tion 2 10 for more information on this instrument 2 8 High Temperature Measurement of viscosity at high temperature can be simple or complex depending upon the sample materials and temperature Sometimes all that is nec essary is to increase the distance between the Vis cometer and sample material through use of spindle extensions see Section 2 13 In difficult applications such as the measurement of molten glass it may be necessary to utilize a specialized furnace and crucible as well as custom designed spindles constructed of heat resistance materials consult with Brookfield En gineering Laboratories for more information on this type application Between these two extremes there is MO
26. 00 Inside DIA Standard Chamber a 8750 DIA e Disposable Chamber C orama Damer Depth SC4 6R RP 0 500 12 70 1 110 28 19 SC4 7R RP 0 501 12 73 1 745 44 32 2672 SC4 8R RP 0 515 13 08 1 584 40 23 SC4 13R RP 0 750 19 05 2 550 64 77 SC4 13RD DISPOSABLE SAMPLE CHAMBER Dimensions are in inches mm 1 The chamber is available with an optional embedded temperature probe in which case the RP designation is used E g SC4 6RP 2 Disposable chamber is available only in 13R size and comes in quantities of 100 chambers Part No SC4 13RD 100 Outside diameter is slightly larger than standard 13R chamber and requires special size water jacket Part No SC4 45YD in order to use Inside diameter and sample volume required are same as 13R chamber Contact Brookfield or an authorized dealer for information MORE SOLUTIONS TO STICKY PROBLEMS Page 37 Brookfield Engineering Labs Inc A 7 UL Adapter UL Adapter Spindle Factors and Shear Rates Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Fa
27. 00 N see the following Disc Spindle Factors Table The Viscometer s rotational soeed RPM is represented by N If the measure ment is being made at 12 RPM the Spindle Factor is 300 12 or 25 Multiply all Dial Viscometer readings made with this spindle speed combination by 25 to obtain viscosity in centipoise Disc Spindle Factors am To Tw eo ool eo an mam Toon zon soon 2 RV H 400m soom 3200 N 3 RV H 1000m 20007 8000 N 4 RV H 2o00 40007 16M N wRvH 400m sooon s2m N 6 RV H tom omy 80M N N RPM M 1000 1 RV H 1 spindle is available as an option MORE SOLUTIONS TO STICKY PROBLEMS Page 32 Brookfield Engineering Labs Inc Disc Spindle Dimensions 2 2150 56 26 2 406 61 12 2 2150 56 26 2 406 61 12 Dimensions are in inches mm Dimension A is 4 531 115 on LV spindles 5 250 133 on RV H spindles Dimension B is 125 3 2 on all spindles 063 1 65 1 062 26 97 1 938 49 21 063 1 65 1 062 26 97 1 938 49 21 063 1 65 1 062 26 97 1 938 49 21 8324 21 14 1 938 49 21 5757 14 62 063 1 57 1 188 30 17 1 938 49 21 Figure 1 8477 46 93 063 1 65 1 938 49 21 Fig 1 Fig 2 Fig 3 A 4 Cylindrical Spindles for Dial Reading Viscometer and Digi
28. 40 400 000 800 000 3 200 000 93 600 1 000 000 2 000 000 8 000 000 187 200 2 000 000 4 000 000 16 000 000 a p o e eo ae 200 Purapwes se s420 seso 73000 292 000 SC4 15 7R 46 880 500 000 1 000 000 4 000 000 SC4 16 8R 120 000 1 280 000 2 560 000 10 240 000 SC4 18 13R 3 000 32 000 64 000 256 000 SC4 21 13R 4 688 50 000 100 000 400 000 SC4 25 13R 480 000 5 120 000 10 240 000 40 960 000 SC4 27 13R 23 440 250 000 500 000 2 000 000 SC4 28 13R 46 880 500 000 1 000 000 4 000 000 SC4 29 13R 93 750 1 000 000 2 000 000 8 000 000 SC4 31 13R 30 000 320 000 640 000 2 560 000 SC4 34 13R 60 000 640 000 1 280 000 5 120 000 CPE 40 CP 40 3 270 6 540 26 160 CPE 41 CP 41 1 151 12 280 24 560 98 240 CPE 42 CP 42 42 600 6 400 12 800 51 200 CPE 51 CP 51 4 854 51 780 103 560 414 240 CPE 52 CP 52 9 300 99 220 198 440 793 760 2 456 26 200 52 400 459 600 10 404 111 000 222 000 888 000 50 146 535 000 1 070 000 4 280 000 508 954 5 430 000 10 860 000 43 4440 000 MORE SOLUTIONS TO STICKY PROBLEMS Page 52 Brookfield Engineering Labs Inc APPENDIX C ASTM Specifications The following ASTM specifications describe the use of Brookfield Viscometers and accessories Copies of these documents are available from Brookfield upon request C 965 96 C 1276 94 D 115 03 D 562 81 D 789 91 D 1076 88 D 1084 97 D 1417 90 D 1439 83a D 1824 90 D 2196 86 D 2364 85 D 2393 86 D 2556 97 D 2669 87 Practices
29. 5 Temperature Sensitivity Test 28 APPENDIX E Brookfield Locations 55 6 6 Temperature Profiling with Up Down Rala eicere 28 6 7 Static Yield Test 00 0nenn 28 6 8 Dynamic Yield Test 2 28 6 9 RECOVENY o raa EEA EEA NATAR E AONA 29 INTRODUCTION When a piece of technical equipment is marketed successfully for over 70 years it is inevitable that a large body of experience will develop from the use of that equipment Procedures are established papers are published standards are accepted and a vast in formal grapevine of advice grows amidst the commu nity of users Such is the case with the Brookfield Vis cometer Accepted as a standard of viscosity mea surement around the world the Brookfield Viscometer is the nucleus of a library of information that encom passes the experiences of thousands of users ina seemingly endless variety of applications This library however is not gathered conveniently together in any single location It is fragmented scat tered here and there in technical journals in test re ports in the notes made by technicians researchers and quality control people For many users particu larly those new to the field of viscosity measurement it is extremely difficult to gain access to information generated outside their own company or industry Brookfield Engineering Laboratories has for many years acted as a clearinghouse for this type informa tion reprinting a variety of tec
30. A 3 Disc Spindles A 4 Cylindrical Spindles Standard Cone Plate Viscometers Rheometers A 5 Wells Brookfield Cone Plate Viscometers Rheometers Accessories for Standard Viscometers Rheometers A 6 Small Sample Adapter A 7 UL Adapter A 8 Thermosel System A 9 DIN Adapter A 10 Helipath Stand A 11 Spiral Adapter A 12 Vane Spindles Special Purpose Instruments A 13 Krebs Viscometer A 14 YR 1 Rheometer A 15 CAP 1000 Viscometer High End Viscometer Rheometers A 16 CAP2000 Viscometer A 17 R S Rheometer amp R S Soft Solids Tester A 18 PVS Rheometer MORE SOLUTIONS TO STICKY PROBLEMS Page 30 Calibration Spring Torque for Standard Viscom eters Rheometers Standard Brookfield Viscometers Rheometers use a calibrated spiral spring inside the instrument to measure the resistance sensed by the spindle rotat ing in the fluid sample The following table identifies the four common spring torques available from Brookfield LV 673 7 dyne centimeters full scale RV 7187 0 dyne centimeters full scale HA 14 374 0 dyne centimeters full scale HB 57 496 0 dyne centimeters full scale Notes 1 These values apply to all models with the same prefix designation LV refers to LVF LVT LVTD LVT CP LVTDCP LVDV I LVDV II LVDV II Program mable LVDV II Pro LVDV IIl LVDV Il Ultra 2 For alternative spring torque models multiply the base spring torque by the multiplier in the model designation 5XLVT 5 X 673 7
31. Cone Plate Systems When sample volume is extremely limited it may be necessary to use cone plate geometry The Wells Brookfield Cone Plate geometry requires a sample of only 0 5 to 2 0 mL depending on spindle More data on this instrument will be found in Sec tion 2 10 1 The CAP and R S Cone Plate geometries re quire lt 1mL for sample volume See Section 2 10 for details Page 5 Brookfield Engineering Labs Inc 2 7 Low Viscosity Each Brookfield Viscometer and Rheometer mea sures a wide range of viscosities however it occa sionally becomes necessary to measure viscosities below the normal range of the instrument Several pieces of Brookfield equipment offer this capability 2 7 1 UL Adapter This accessory was specifically designed to provide greater sensitivity at low viscosities for the LV series Viscometers it can however be used on any model Brookfield Viscometer When mounted on an LVT Viscometer the UL Adapter provides a viscosity range of 1 0 to 10 0 cP and a defined shear rate of 73 4 reciprocal seconds at 60 RPM For other Viscometer models the minimum measurable viscosity with the UL Adapter in place is RVT 6 4 cP HAT 12 8 cP HBT 51 2 cP The UL Adapter features coaxial cylinder geometry with a removable polyethylene end cap for the outer cylinder With the end cap in place the Adapter holds a sample volume of 16 0 ml and can be immersed in a bath for temperature control up to a recommended maximum of 1
32. Immersion The spindle should be immersed up to the middle of the shaft indentation Failure to do so could re sult in incorrect viscosity readings In some cases the sample fluid may change its rheological structure during the act of spindle im mersion To avoid this we recommend inserting the spindle in a different portion of the sample than the one intended for measurement The spindle may then be moved horizontally to the center of the sample container This must be done before at taching the spindle to the Viscometer 3 4 7 Sensitivity and Accuracy Brookfield Viscometers are guaranteed to be accurate to within 1 of the full scale range of the spindle speed combination in use this percentage expressed in centipoise values is equal to the spindle Factor accuracy of a spindle speed combi nation with a factor of 25 would therefore be within 25 cP Repeatability is to within 0 2 of the full scale range The relative error of a particular viscosity read ing is dependent upon the actual dial or display torque reading In general relative error of the vis cosity value will improve as the reading approaches 100 This is because the tolerance of 1 of full scale viscosity applies to all readings and repre sents a smaller percentage of measured viscosity as the actual reading increases Consider the fol lowing example AnLVT Viscometer when used with a 1 spindle at a speed of 60 RPM has a spindle Factor of 1 ob
33. PM or Figure 6 5 This method shows how viscosity can change as a function of temperature time and rotational speed or shear rate MORE SOLUTIONS TO STICKY PROBLEMS Page 28 6 7 Static Yield Test Choose a vane spindle Choose a low rotational speed between 01 RPM and 0 5 RPM Record torque values at defined time intervals The maximum torque is an indication of the static yield value The maximum torque value will probably change if a different rotational speed is chosen This method is quick easy to do and may provide repeatable test data TORQUE TIME Figure 6 6 The maximum torque value can be converted into a yield stress value in Pascals or dynes cm using the formula provided with Brookfield vane spindles 6 8 Dynamic Yield Test Use coaxial cylinder or cone plate spindle geometry Run a controlled rate ramp as defined in method 6 2 One suggestion is to use the lowest possible speeds for the controlled rate ramp Record the torque values or shear stress values at defined time intervals Review the data and determine a best fit straight line through the data The dynamic yield point is where the best fit straight line intersects the torque or shear stress axis RPM or Y T or TORQUE TIME Figure 6 7 The dynamic yield stress value will probably be dif ferent from the static yield stress value Brookfield Engineering Labs Inc 6 9 Recovery This parameter characterizes how
34. RE SOLUTIONS TO STICKY PROBLEMS Page 6 Brookfield equipment for most high temperature vis cosity measurement applications 2 8 1 Thermosel System The Thermosel System is specifically designed for viscosity measurement of small samples in the temperature range of approximately 40 to 300 C It is usually sold as a complete system including Viscometer but is also available as an accessory to your present Viscometer except cone plates In addition to the Viscometer the Thermosel System consists of a special coaxial cylinder spindle and sample chamber an electric heating apparatus called a thermocontainer and a digital proportional temperature controller with RTD sensor The Thermosel System is available in three variations System 1 is a manual unit with a dial reading Vis cometer System 2 includes a Digital Viscometer and outputs for recording viscosity and temperature and System 3 which adds the capabilities of a fully pro grammable temperature controller to the features of System 2 with or without a PC control The Thermosel System requires small sample volumes 8 0 to 13 0 ml depending on spindle and its coaxial cylinder spindle geometry provides de fined shear rates in the range of 0 08 to 93 0 recip rocal seconds depending on spindle and Viscom eter model 2 8 2 Temperature Baths Brookfield Temperature Baths are also suitable for viscosity measurements at high temperature Certain models have a maximum operatin
35. SHEAR STRESS M dynes cem2 Tt 2 3 8 E nr VISCOSITY poise n F 9 Definitions o cone angle degrees r cone radius cm Cone O Plate See Section 5 2 1 for definitions of other variables 5 2 4 Disc and T Bar Spindles The standard disc type spindles provided with most Viscometer models and the T bar spindles used with the Helipath Stand accessory as well as spindles with special shapes other than cylindrical or cone configurations do not have directly defin able shear rate and shear stress values You may occasionally see the Viscometer s rotational speed referred to as a shear rate particularly when T bar spindles are used This is incorrect as math ematical models are not available for calculating vis cosity functions using T bar spindles However models are available for the disc spindles Refer to Technical Paper AR 82 available from Brookfield Engineering Laboratories 5 2 5 Spiral Adapter Spindle The Spiral Adapter has an inner threaded spindle surrounded by a concentric outer cylinder Brookfield Engineering Labs Inc This combination causes the sample to be continu ally pumped up through the Spiral Adapter cham ber The material reaches a steady state of flow during which viscosity is measured The primary assumption is to think of the screw shaped spindle as a cylinder rotating inside of the cylindrical cham ber The approximate shear rate in reciprocal sec onds is 667N
36. STICKY PROBLEMS Page 48 Brookfield Engineering Labs Inc A 18 PVS Rheometer The PVS Rheometer is a variable speed co axial cylinder geometry instrument with the capability to pressurize the samle up to 1000 psi Stator might also be called bob or spindle On the PVS Rheom eter the cup also called chamber rotates while the stator remains stationary and senses torque Viscosity Ranges and Shear Rates Bob Viscosity Stator Range cP No mPa s EE ee aaen on as e o N RPM Mz 1000 Dimensions B B B B1 B2 B5 A A A E D E D E D a C C C A B Diameter C Diameter D E Shear Cup Diameter Annulus inches mm inches mm inches mm inches mm inches mm Rate inches mm inches mm B1 4527 114 99 925 23 5 1 358 34 49 3 507 89 08 3 527 89 59 1 703N 1 45 36 83 0 046 1 168 B2 4524 114 91 925 23 5 967 24 56 3 354 85 19 3 524 89 51 0 377N 1 45 36 83 0 241 6 135 4 526 114 96 925 23 5 1 259 31 98 3 462 87 93 3 526 89 56 0 85N 1 45 36 83 0 095 2 425 N RPM Based on PVS 30 HC standard cup Larger cup is available MORE SOLUTIONS TO STICKY PROBLEMS Page 49 Brookfield Engineering Labs Inc Optional Stator Cup Geometry TA5 Used for Low Viscosity Fluids Triple Annulus Dimensions Intermediate Annulus 1 99 50 55 ID x 1 73 43 94 OD
37. This section based on information gleaned from years of customer experience is intended as a tickler to get you thinking about the mysteries your Viscometer can help you solve Keep always in mind if you compare two results in a measuring series all parameters and all treatment must be kept the same 4 8 1 Temperature One of the most obvious factors that can have an effect on the rheological behavior of a material is temperature Some materials are quite sensitive to temperature and a relatively small variation will result in a significant change in viscosity Others are relatively insensitive Consideration of the effect of temperature on viscosity is essential in the evaluation of materials that will be subjected to temperature variations in use or processing such as motor oils greases and hot melt adhesives 4 8 2 Shear Rate Non Newtonian fluids tend to be the rule rather than the exception in the real world making an appreciation of the effects of shear rate a necessity for anyone engaged in the practical application of rheological data It would for example be disastrous to try to pump a dilatant fluid through a system only to have it go solid inside the pump bringing the whole process to an abrupt halt While this is an extreme example the importance of shear rate effects should not be underestimated Brookfield Engineering Labs Inc When a material is to be subjected to a variety of shear rates in processing
38. a and product behavior the procedure can then be reversed and rheological data may be used to predict performance and behavior 1 3 Three Schools of Thought on Viscosity Measurement In our experience there are basically three schools of thought on the use of viscometers in applications rheology We present them here and invite you to de cide which you fall into remembering that there is no right one and that each has its merits 1 3 1 The Pragmatic School The first school of thought is the most pragmatic The person who adheres to this school cares only that the Brookfield Viscometer generates numbers that tell something useful about a product or pro cess This person has little or no concern about rheological theory and measurement parameters ex pressed in absolute terms Quality control and plant production applications are typical of this category 1 3 2 The Theoretical School The second school of thought involves a more theoretical approach Those adhering to this school know that some types of Brookfield Viscometers will not directly yield defined shear rates and absolute viscosities for non Newtonian fluids However these people often find that they can develop correlations of dial viscosity with important product or process parameters Many people follow this school of thought The applications rheology literature is re plete with statements along the line of I know the data isn t academically defined
39. ading at each speed This is the down curve It is best to allow a consis tent time interval between each speed change If the fluid is time independent the up curve and the down curve will coincide If they do not the fluid is time MORE SOLUTIONS TO STICKY PROBLEMS Page 25 dependent Position of the up curve and the down curve indicates the type of flow behavior if the up curve indicates a higher viscosity than the down curve the fluid is thixotropic lower rheopectic An indication of the recovery time of the fluid how quickly it returns to its initial viscosity after exposure to shear conditions can be obtained by turning off the Viscometer at the end of the down curve waiting for a given period of time restarting the Viscometer and immediately taking a reading A more sophisticated approach is to calculate the thixotropic breakdown coefficient This is a single number which quantifies the degree of thixotropy or rheopexy displayed by the sample fluid First plot Viscometer reading using a specified spindle speed combination versus log time taking readings at regu lar intervals This usually produces a straight line Then apply the following equation THIXOTROPY BREAKDOWN COEFFICIENT St St Tb F i4 In lA aa 4 Definitions St Viscometer reading at t minutes St Viscometer reading at t minutes F Factor for spindle speed comb
40. alue Determination Newer instruments from Brookfield such as the DV Ill Ultra R S and YR 1 Rheometers physically mea sure the start of flow at zero shear rate These read ings measured in Pascals Pa dynes cm or New ton m may differ from values obtained using dynamic methods see preceding section which back calcu late yield stress from flow curve data shear stress vs shear rate 5 5 Analyzing Time Dependent Non Newtonian Fluids In most cases analysis of thixotropic and rheopectic fluids see Section 4 5 involves plotting changes in viscosity as a function of time The simplest method is to select a spindle and speed preferably a low speed and leave the Viscometer running for an ex tended period noting the dial or display reading at regu lar intervals It is important to control temperature of the sample fluid carefully so that variations in tempera ture won t affect the results A change in the fluid s viscosity over time indicates time dependent behav ior a decrease signifies thixotropy an increase rheopexy or in some cases curing of the sample material A second method is to graph the Viscometer read ing versus speed using a single spindle Starting ata low speed note the reading at each successively higher speed until the reading goes off scale A graph of these readings is the up curve Without stopping the Viscometer reduce the speed incrementally to the starting point again noting the re
41. ample cups of the Wells Brookfield Cone Plate Viscometer to provide a controlled atmosphere for the sample being tested 2 14 2 Explosion Proof Construction Dial Viscometer Only When the danger of explosion is great due to the presence of flammable fumes or other factors use of approved explosion proof equipment may be required Brookfield dial reading Viscometers ex cept cone plate types are available in Underwrit ers Laboratory UL approved explosion proof ver sions These instruments are approved for Class Group D hazardous locations The Digital Viscom eters and Rheometers are not available with explo sion proof construction Electrically operated Brookfield accessories such as the Helipath Stand and the Thermosel are not available in explosion proof versions They can be used with explosion proof Viscometers some times requiring special adapters but only in non hazardous environments Brookfield Engineering Labs Inc 2 15 Process Control Practical application of viscosity data obtained in the laboratory often involves use of on line process vis cometers and viscosity controllers Brookfield manu factures a complete line of instrumentation that has been applied to a wide variety of process control ap plications Please contact Brookfield Engineering Labs for more information CHAPTER 3 3 1 Why You Should Read This Chapter The purpose of this chapter is to provide the Vis cometer user with info
42. an fluids you may encounter include Although rarer than pseudoplasticity dilatancy is fre quently observed in fluids containing high levels of deflocculated solids such as clay slurries candy compounds corn starch in water and sand water mixtures Dilatancy is also referred to as shear thickening flow behavior PLASTIC This type of fluid will behave as a solid under static conditions A certain amount of stress must be applied to the fluid before any flow is in duced this stress is called the yield stress f To mato catsup is a good example of this type fluid its yield value will often make it refuse to pour from the bottle until the bottle is shaken or struck allowing the catsup to gush freely Once the yield value is T n exceeded and flow begins plastic fluids may dis play Newtonian pseudoplastic or dilatant flow char acteristics See Figure 4 5 PSEUDOPLASTIC This type of fluid will display a decreasing viscosity with an increasing shear rate as shown in Figure 4 3 Y 7 A Y B Y Figure 4 3 Probably the most common of the non Newtonian fluids pseudo plastics include paints emulsions i A B Y and dispersions of many types This type of flow behavior is sometimes called shear thinning An easily understood model is to imagine that in the Figure 4 5 So far we have only discussed the effect of shear moment of turning the spindle in the sample the structure of molecules of the samp
43. antial increase in viscosity above a certain shear rate The material s flow behavior may be Newtonian or non Newtonian below this point Due to the relatively low shear rates at which most Brookfield Viscometers operate it is unlikely that you will encounter turbulent flow unless you are measur ing viscosities lower than 15 cP with an LV series Vis cometer or 85 cP with other models The higher the viscosity of a fluid the less likely it is to experience turbulence If turbulence is observed while measur ing low viscosity fluids it can often be eliminated by using the UL Adapter accessory 4 7 Yield Behavior Situation 1 medical ointment will not easily squeeze out of the tube when moderate pressure is applied Situation 2 salad dressing comes gushing out of the bottle with only a slight pressure squeeze The fundamental quality control problem plaguing both of the above products is a scientific term known as yield stress Simply put this is the amount of force required to get a fluid to begin flowing For tubes and squeeze bottles this translates into how easily or how hard a customer must squeeze to get fluid to begin squirting or pouring out of the nozzle There are several ways to measure this yield stress Brookfield Engineering Labs Inc in products like ointments and salad dressings Using a standard bench top viscometer the quality control technician can run an up down speed ramp and record the torque value
44. b your Viscometer and go to it They are not unfortunately as common as that much more com plex group of fluids the non Newtonians which will be discussed in the next section 4 4 Non Newtonian Fluids A non Newtonian fluid is broadly defined as one for which the relationship t is not a constant In other words when the shear rate is varied the shear stress doesn t vary in the same proportion or even neces sarily in the same direction The viscosity of such fluids will therefore change as the shear rate is varied Thus the experimental parameters of Viscometer model spindle and speed all have an effect on the measured viscosity of a non Newtonian fluid This measured viscosity is called the apparent viscosity of the fluid and is accurate only when explicit experi mental parameters are furnished and adhered to Non Newtonian flow can be envisioned by thinking of any fluid as a mixture of molecules with different shapes and sizes As they pass by each other as Brookfield Engineering Labs Inc happens during flow their size shape and cohesive ness will determine how much force is required to move them At each specific rate of shear the alignment may be different and more or less force may be re quired to maintain motion There are several types of non Newtonian flow be havior characterized by the way a fluid s viscosity changes in response to variations in shear rate The most common types of non Newtoni
45. ble under the influence of very high pressures similar to gases but to a much lesser extent Increases of pressure tend to increase the viscosity As an example The flow properties of highly concentrated slurries above 70 80 by vol Brookfield Engineering Labs Inc ume of particles where there is insufficient liquid to fill completely all the voids between the particles re sults in a three phase mixture i e solids liquids and usually air Due to the presence of air the mixture is compressible and therefore the more you compress it the greater the resistance to flow 4 8 6 Previous History What has happened to a sample prior to a vis cosity measurement can significantly affect the re sult especially in fluids sensitive to heat or aging Thus storage conditions and sample preparation techniques must be designed to minimize their ef fect on subsequent viscosity tests Thixotropic ma terials in particular are sensitive to prior history as their viscosity will be affected by stirring mixing pouring or any other activity which produces shear in the sample 4 8 7 Composition and Additives The composition of a material is a determining factor of its viscosity When this composition is al tered either by changing the proportions of the com ponent substances or by the addition of other materials a change in viscosity is quite likely For example the addition of solvent to printing ink re duces viscosity of the i
46. bubble is in the center of the target in the level indicator If you are continuing to experience problems with your viscometer follow this diagnosis section to help isolate the potential problem Perform an Oscillation Check 1 Remove the spindle and turn the motor OFF 1 Gently push up on the viscometer coupling L Turn the coupling until the red pointer reaches 5 10 on the Dial Viscometer or the torque readings reach 5 10 on the Digital Viscometer LY Gently let go of the coupling L Watch the pointer swing freely and finally rest within 0 2 of zero on the Dial Vis cometer or the torque reading returns to within 0 2 of zero on the Digital Viscom eter If the pointer sticks or the torque reading does not return to zero the unit is in need of service Perform a Calibration Check L Verify spindle speed and model selection 1 Verify test parameters temperature container volume method 1 Perform a calibration check in accordance with the procedures from the viscometer operat ing manual Verify tolerances are calculated correctly Verify calibration check procedures were followed exactly If the unit is found to be out of tolerance the unit is in need of service Please contact Brookfield or an au thorized dealer for service CHAPTER 4 4 1 Coming to Grips with Rheology Rheology is defined by Webster s Dictionary as the study of the change in form and the flow of matter embracin
47. can information on the viscosity behavior of your material change as a function of rotational speed or shear rate using a Brookfield Viscometer or Rheometer Choose the appropriate method to suit your requirements 6 3 Up Down Rate Ramp Contact Brookfield or our authorized dealer if you re Use the same method defined above in CON quire additional assistance TROLLED RATE RAMP to create the UP RAMP Upon reaching the maximum rotational speed or 6 1 Single Point Viscosity Test shear rate reverse direction and return to the start Choose a spindle ing speed or shear rate This creates the DOWN Select a rotational speed or shear rate RAMP Control temperature if required Specify how long the spindle rotates before making the measurement Make sure the torque reading is gt 10 Record the viscosity value in cP or mPass Record sample temperature in F or C 6 2 Controlled Rate Ramp Choose a starting rotational speed or shear rate Choose a maximum rotational speed or shear rate Choose in between speeds or shear rates as ap propriate Specify how long the spindle rotates before making the measurement Record data at each speed or shear rate similar to the method defined above in SINGLE POINT Try to keep the torque readings above 10 if pos sible Method Viscosity Data RPM or Y TIME RPM or Y Figure 6 1 MORE SOLUTIONS TO STICKY PROBLEMS Record viscosity and torque data at each spee
48. ccessories and to suggest ways in which these products may be helpful in solving spe cific viscosity measurement problems This informa tion will be useful to people adhering to all three schools of thought on viscosity measurement The equipment has been organized into functional groups to help you quickly zero in on the items of most interest to you Viscometers Rheometers Spindle Geometries Temperature Control Small Sample Volume Low Viscosity High Temperature Defined Shear Rate High Shear Rate Defined Shear Stress Non Flowing Sample Materials Special Accessory Items Fumes and Hazardous Locations Process Control 2 2 Viscometers Brookfield laboratory Viscometers are available in three basic types dial reading analog digital and programmable The most significant difference be tween them is the manner in which the viscosity read ing is displayed The dial reading type is read by not ing the position of a pointer in relation to a rotating dial the Digital type is read by means of a 2 line LCD display In addition the Digital Viscometer includes a 0 10mv output that may be connected to a variety of devices such as remote displays controllers and re corders In most respects dial reading and Digital Vis cometers are functionally similar The operating pro cedures for both are essentially the same they are available in the same model variations they accept the same Brookfield accessories and are generally
49. ctor for the UL spindle on an LV Viscometer is given as 6 N see the following UL Adapter Spindle Factors and Shear Rates Table The Viscometer s rotational soeed RPM is represented by N If the measurement is being made at 60 RPM the Spindle Factor is 6 60 or 0 1 Multiply all Dial Viscom eter readings made with this spindle speed combination by 0 1 to obtain viscosity in centipoise LV RV Shear Rate sec 64 N 128 N 512 N 1 224N DIN UL 11 44 N 122 N 244 N 976 N 1 29N N RPM Sample size 16 0 mL end cap on UL Adapter Dimensions T i 3 5725 90 74 3 6366 92 37 SIDE LENGTH EFFECTIVE LENGTH Spindle Effective Actual Length Diameter one Length 3 6366 92 39 3 5725 90 74 0 9902 25 15 1 0875 27 62 1 l E 0 9902 25 15 SPINDLE O D 1 0875 27 62 CHAMBER I D Dimensions are in inches mm Effective length includes correction for end effect and should be used in manual calculations for shear rate shear stress equations when using Dial Reading Viscometers Actual length is given for reference only Digital Viscometers Rheometers have a correction factor built in to the firmware of the instrument no additional calculations are required MORE SOLUTIONS TO STICKY PROBLEMS Page 38 Brookfield Engineering Labs Inc A 8 Thermosel System SC4 Series Spindle Factors and Shear Rates Spindle Factors are listed as constants related to the Visc
50. d or shear rate Try to keep the torque readings gt 10 if possible For each specific speed or shear rate observe whether the viscosity value on the UP RAMP is different from the viscosity value on the DOWN RAMP Different viscosity values indicate that the material is time sensitive to shearing action Figure 6 2 This method shows how viscosity can change as a function of both rotational speed shear rate and time 6 4 Time Sensitivity Test Choose a rotational speed or shear rate Choose a time interval to record viscosity data Observe whether the viscosity or torque values change as a function of time Page 27 Brookfield Engineering Labs Inc T or TORQUE TIME Figure 6 3 This method shows how sensitive the material is to being sheared at a fixed speed or shear rate 6 5 Temperature Sensitivity Test TEMPERATURE 6 Choose a rotational speed or shear rate Choose a starting minimum temperature and a maxi mum temperature Record viscosity values at defined time intervals while the temperature ramps up Viscosity Data TEMPERATURE Figure 6 4 Most materials exhibit decreasing viscosity behav ior with increasing temperature 6 Temperature Profiling with Up Down Rate Ramp Test This method combines the approaches described in methods 6 3 and 6 5 Choose specific temperatures of interest At each temperature run the Up Down ramp and record the viscosity data R
51. ded the spindle number has been entered refer to the instruction manual of your viscometer A note about Factors and Ranges both can be used to calculate viscosity from a given reading A Factor such as that obtained from the Factor Finder is simply multiplied by the Viscometer reading to calculate viscosity in centipoise A Range as sup plied with some Brookfield Accessories in lieu of a Factor is equal to the Factor multiplied by 100 Therefore to calculate viscosity first divide the Range by 100 then multiply by the Viscometer dial or display reading 3 4 9 A Calibration Check People are often concerned about the accuracy of their Viscometer Here are some tests of its me MORE SOLUTIONS TO STICKY PROBLEMS Page 12 chanical performance A Variations in power frequency will cause the spindle to rotate at an incorrect speed If you are in an area where electric clocks are used this factor may be immediately eliminated Voltage varia tions have no effect as long as the deviation is not greater than 10 of the nameplate voltage and the frequency remains constant Other readily apparent symptoms of improper power supply are failure of the motor to start jerky spindle rotation a wildly fluctuating pointer or inconsistent digital display readings B Damage to the pivot point or jewel bearing will adversely affect accuracy and repeatability of the Viscometer The following Oscillation Test will allow you to evalua
52. dle and speed specified after confirming that you have the correct Viscometer model When conducting an original test the best method for spindle and speed selection is trial and error The goal is to obtain a Viscometer dial or display torque reading be tween 10 and 100 remembering that relative error of measurement improves as the reading ap proaches 100 see Section 3 3 7 If the reading is over 100 select a slower speed and or a smaller spindle Conversely if the reading is under 10 se lect a higher speed and or a larger spindle If the approximate viscosity of the sample fluid is known a faster method for honing in on the right spindle speed combination is available by referring to the Factor Finder supplied with the Viscometer The goal is to select a combination whose range brackets the estimated viscosity of the sample For any given spindle speed combination the maximum range available is equal to the spindle Factor multiplied by 100 This maximum is also called Full Scale Range or FSR For Digital Vis cometers that have the AUTORANGE key select ing a speed and spindle and then depressing and holding the AUTORANGE key will cause the screen to display FSR in cP mPazss The minimum recommended range equals the Factor multiplied by 10 For example a 2 spindle on an LVT Viscometer at 12 RPM has a Factor of 25 The maximum range of this combination is 25 times 100 or 2500 cP The minimum recommended vi
53. e materials can be employed When attaching a spindle remember that it has a left hand thread and must be screwed firmly to the coupling Always lift up on the spindle coupling when attaching a spindle to avoid damage to the instrument s pivot point and jewel bearing After at MORE SOLUTIONS TO STICKY PROBLEMS Page 10 tachment do not hit the spindle against the side of the sample container since this can damage the shaft alignment A good procedure to follow is to immerse and position the spindle in the sample fluid before attaching it to the Viscometer The spindle guardleg supplied with some mod els protects the spindle from damage and is sig nificant to the Viscometer s calibration when using the 1 or 2 spindle The guardleg should be used at all times If it proves necessary or desirable to operate the Viscometer without the guardleg this fact should be noted when reporting test results It may be desirable to recalibrate the Viscometer to compensate for the absence of the guardleg Re fer to Section 3 3 10 for this procedure Note spindle guardlegs are provided only on LV and RV models of the dial reading and Digital Viscometers with standard spindles HA and HB models as well as Cone Plate models do not re quire a guardleg The guardleg is also not used in conjunction with most accessories 3 4 3 Selecting a Spindle Speed When performing a test according to an existing specification or procedure use the spin
54. e minimum range is obtained by using the largest spindle at the highest speed the maximum range by using the small est spindle at the slowest speed Measurements made using the same spindle at different speeds are used to detect and evaluate rheological properties of the test fluid These properties and techniques are discussed in Chapters 4 and 5 The Viscometer is composed of several mechanical subassemblies See Figure 3 1 for a schematic view of the major components of a basic dial reading Vis cometer MORE SOLUTIONS TO STICKY PROBLEMS Page 9 The stepper drive motor which replaced the syn chronous motor and multiple speed transmission is located at the top of the instrument inside the housing to which the nameplate is attached The Viscometer main case contains a calibrated beryllium copper spring one end of which is attached to the pivot shaft the other end is connected directly to the dial This dial is driven by the motor drive shaft and in turn drives the pivot shaft through the calibrated spring In dial reading models the pointer is connected to the pivot shaft and indicates its angular position in relation to the dial In Digital models the relative angular posi tion of the pivot shaft is detected by an RVDT rotary variable displacement transducer and is read out on a digital display lt _ HOUSING
55. eeeeeees 5 2 6 1 Small Sample Adapter 00 5 2 6 2 UL AGA pen psices sccceectiserecetitaresnseverios 5 2 6 3 DIN Adapter eesceeeeessteeeeeeenaes 5 2 6 4 Thermosel System sssr 5 2 6 5 Cone Plate Systems cceeeee 5 2 7 LOW VISCOSILY oeeie aaae ina eedan k eRe 5 2 7 1 UL Adapter sereset 6 2 7 2 Small Sample Adapter 0000 6 2 7 3 Thermosel System siessen 6 2 7 4 Wells Brookfield Cone Plate Viscom QUON hitga i a eiiiai a iaiaaeaia 6 2 8 High Temperature assseesssseesrrrnserrrresrrennns 6 2 8 1 Thermosel System s es 6 2 8 2 Temperature Baths cece 6 2 8 3 Cone Plate with Embedded Heating ccscceeessieeeeeeeee 6 2 9 Defined Shear Rate ccsceecteeeeneeeees 6 2 10 High Shear Rate cccceeeeeeeeeeeeeenteees 7 2 10 1 Wells Brookfield Cone Plate Viscom eter Rh eometer cceeeeeceeeeeesseeeeeeeneeeees 7 2 10 2 CAP Viscometer Rheometer 7 2 10 3 R S Rheometer eeceeeeeeees 7 2 10 4 PVS Rheometer ccceeeeeee 7 2 11 Defined Shear Stress 0 ccceceeeeeeeeees 7 2 12 Non Flowing Sample Materials 8 2 12 1 Helipath Stand 8 2 12 2 Spiral Adapter 0 ccceeceeeeseeeeeees 8 2 12 3 Vane Spindles siseses 8 2 13 Special Accessory tems ceeeeeeeees 8 2 13 1 Quick Connect 8 2 13 2 Spindle Extensions ceeee 8 2 14 Fumes and Hazardous Locations 8 2 14 1 Pur
56. eld or one of its dealers for this service 3 6 Viscometer Troubleshooting Specific fault diagnosis procedures are detailed in the instruction manual that is provided with each Vis cometer The chart below lists some of the more com mon problems that you may encounter while using your Viscometer along with the probable causes and sug gested cures Spindle Does Not Rotate L Make sure the viscometer is plugged in LY Check the voltage rating on your viscometer 115V 220V it must match the wall voltage 1 Make sure the power switch is in the ON posi tion 1 Make sure the speed selection is set properly and securely at the desired speed Spindle Wobbles When Rotating or Looks Bent 1 Make sure the spindle is tightened securely to the viscometer coupling LY Check the straightness of all other spindles replace them if bent 11 Inspect viscometer coupling and spindle cou pling mating areas and threads for dirt clean threads on spindle coupling with a 3 56 inch left hand tap L Inspect threads for wear if the threads are worn the unit needs service 14 Check to see if spindles rotate eccentrically or wobble There is an allowable runout of 1 32 inch in each direction 1 16 inch total when measured horizontally from the bottom of the spindle rotating in air LY Check to see if the viscometer coupling is bent if so the unit is in need of service T Check that the instrument is level Be sure that the
57. er to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for a Spiral spindle on an RV Viscometer is given as 10 500 N see the following Spiral Spindle Factors Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 30 RPM the Spindle Factor is 10 500 30 or 350 Multiply all Dial Viscometer readings made with this spindle speed combination by 350 to obtain viscosity in centipoise 984 N 10 5M N 21M N 84M N 667N N RPM M 1 000 MORE SOLUTIONS TO STICKY PROBLEMS Page 42 Brookfield Engineering Labs Inc Spiral Spindle Dimensions 825 Spiral Chamber Dimensions 500 250 DIA i Spindle Diameter Length A 12 Vane Spindles Vane Spindle Factors Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor fo
58. for Measuring Viscosity of Glass Above the Softening Point Reapproved 2002 Standard Test Method for Measuring the Viscosity of Mold Powers Above their Melting Point Using a Rotational Viscometer Methods of Testing Varnishes Used for Electrical Insulation Standard Test Method for Consistency of Paints Using the Stormer Viscometer Test Methods for Determination of Relative Viscosity Melting Point and Moisture Content of Polyamide PA Specification for Rubber Concentrated Ammonia Preserved Creamed and Centrifuged Natural Latex Test Methods for Viscosity of Adhesives Methods of Testing Rubber Latices Synthetic Methods of Testing Sodium Carboxymethyl cellulose Test Method for Apparent Viscosity of Plastisols and Organosols at Low Shear Rates by Brookfield Viscometer Test Methods for Rheological Properties on Non Newtonian Materials by Rotational Brookfield Viscometer Standard Methods of Testing Hydroxyethyl cellulose Test Method for Viscosity of Epoxy Resins and Related Components Test Method for Apparent Viscosity of Adhesives Having Shear Rate Dependent Flow Properties Test Method for Apparent Viscosity of Petroleum Waxes Compounded With Additives Hot Melts MORE SOLUTIONS TO STICKY PROBLEMS D 2983 03 D 3232 88 D 3236 88 D 3468 99 D 3716 99 D 3791 90 D 4016 81 D 4287 94 D 4402 87 D 4889 93 D 5018 89 D 5133 01 Page 53 Brookfield Engineering Labs Tes
59. found in Section 2 1 14 B Never place the instrument upside down with a fluid coated spindle attached C Do not expose the Viscometer to ambient tem peratures in excess of 40 C When measuring samples at high temperatures the use of spindle extensions or the Thermosel accessory is recom mended D Avoid applying side or down thrust to the spindle coupling this protects the pivot point and jewel bear ing which can be broken or dulled by rough treat ment Always lift the spindle coupling when attach ing or removing a spindle Do not strike the spindle against the sample container or otherwise apply side thrust to it Do not pull down on the spindle or spindle coupling E Do not drop or severely jar the instrument The Brookfield Laboratory Stand provides a convenient sturdy support If the Viscometer is intended for portable use it should be stored in its carrying case when not in use Page 13 Brookfield Engineering Labs Inc If the Viscometer is physically damaged or fails the Oscillation Test in Section 3 3 9 it should be returned for repair to Brookfield Engineering Laboratories or to the dealer from whom it was purchased The need for periodic preventative maintenance var ies with the conditions of use Under normal circum stances a yearly service should be sufficient to keep the Viscometer in top working order More severe use will necessitate more frequent service The instru ment should be returned to Brookfi
60. g elasticity viscosity and plasticity We con cern ourselves in this chapter with viscosity further defined as the internal friction of a fluid caused by molecular attraction which makes it resist a tendency to flow Your Brookfield Viscometer measures this friction and therefore functions as a tool of rheology The purpose of this chapter is to acquaint you with the different types of flow behavior and use of the MORE SOLUTIONS TO STICKY PROBLEMS Page 14 Brookfield Viscometer as a rheological instrument to enable you to conduct a detailed analysis of virtually any fluid This information is useful to all Viscometer users particularly those adhering to the Theoretical and Academic schools of thought on viscosity mea surement 4 2 Viscosity Viscosity is the measure of the internal friction of a fluid This friction becomes apparent when a layer of fluid is made to move in relation to another layer The Brookfield Engineering Labs Inc greater the friction the greater the amount of force required to cause this movement which is called shear Shearing occurs whenever the fluid is physically moved or distributed as in pouring spreading spraying mixing etc Highly viscous fluids therefore require more force to move than less viscous materials Figure 4 1 Isaac Newton defined viscosity by considering the model represented in Figure 4 1 Two parallel flat ar eas of fluid of the same size A a
61. g tempera ture of 200 C For more information see Section 2 5 2 8 3 Cone Plate with Embedded Heating CAP series Viscometer Rheometer with high temperature plate can heat samples to 325 C which is ideal for certain resins The R S Rheometer has similar capability in a special cone plate version R S CPS E which goes to 250 C Since sample size is relatively small temperature equilibrium is achieved rapidly 2 9 Defined Shear Rate For applications where viscosity data must be ex pressed in absolute terms it is necessary to use a spindle geometry for which shear rate and shear stress values can be calculated Such defined operating parameters are found in the following Brookfield in struments and accessories Consult the referenced sections for more information about these products Cylindrical Spindles 2 4 2 Small Sample Adapter 2 6 1 UL Adapter 2 6 2 DIN Adapter 2 6 3 Thermosel System 2 8 1 Wells Brookfield Cone Plate Viscometer 2 10 1 Brookfield Engineering Labs Inc CAP Viscometer 2 10 2 R S Rheometer 2 10 3 PVS Rheometer 2 10 4 2 10 High Shear Rate Brookfield Viscometers are by design relatively low shear instruments The maximum shear rate achiev able with most spindle configurations is usually less than 100 reciprocal seconds Defined shear rates in the range of up to 300 reciprocal seconds can be gen erated by some Viscometer models when used in con junction with the UL Adapter Section 2 1 6 the S
62. ge 18 value into a single purpose instrument such as the Brookfield YR 1 This type of instrument called a yield rheometer costs roughly the same as a standard bench top viscometer and provides the dedicated test capability to ensure that yield values are measured correctly The firmware algorithm detects the maxi mum torque value and calculates the equivalent yield stress In addition the instrument has the ability to specify quality control limits between which the yield value must fall when making a measurement This additional feature will save valuable time for the QC operator in making a pass fail determination on the product prior to packaging The yield measurement capability found in the YR 1 has also been included in the DV III Ultra Rneometer This enables the DV III Ultra to determine yield stress and then the flow curve viscosity or shear stress vs shear rate for a sample material 4 8 What Affects the Rheological Property Viscosity data often functions as a window through which other characteristics of a material may be ob served Viscosity is more easily measured than some of the properties that affect it making it a valuable tool for material characterization Earlier in this chapter we discussed various types of rheological behavior and how to identify them Having identified a particular rheological behavior in a material you may wonder what this information implies about its other charac teristics
63. ge Fittings 00 ee eeeeeeeeeees 8 2 14 2 Explosion Proof Construction 8 2 15 Process Control c cccceceeeeseeeeeeeeeeeneeeees 8 CHAPTER 3 cas ccc coccelezcceectoceceaanceesceccdeeter sstteceece 9 3 1 Why You Should Read This Chapter 9 3 2 How the Brookfield Viscometer Works 9 3 3 Spring Torque cceecceesseeeeeeeeeessteeeeeeeees 10 3 4 Viscosity Measurement Techniques 10 3 4 1 Record Keeping acsee 10 3 4 2 The Spindle and the Guardleg 10 3 4 3 Selecting a Spindle Speed 10 3 4 4 Sample Container Size 05 11 3 4 5 Sample Conditions ceeeeee 11 3 4 6 Spindle Immersion ceeeeee 11 3 4 7 Sensitivity and Accuracy 08 11 3 4 8 Obtaining a Viscometer Reading 11 3 4 9 A Calibration Check cceeeeee 12 3 4 10 Recalibrating the Brookfield VISCOMOUHEN iaa EAE 12 3 5 Viscometer Maintenance s e 13 3 6 Viscometer Troubleshooting 14 CHAPTER 4 icseccactecetedsceteccutoeasensszcccusecnenevsscesesstee 14 4 1 Coming to Grips with Rheology 14 4 2 VISCOSILY arerioei aia ai 14 4 3 Newtonian FIUICS seeen 15 4 4 Non Newtonian Fluids seee 15 4 5 Thixotropy and Rheopexy sses 16 4 6 Laminar and Turbulent Flow 17 4 7 Yield Behavior seeen 17 4 8 What Affects the Rheological Property 18 4 8 1 Temperature ssis 18 4 8 2 Shear Rate eese 18 4 8 3 Measuring Conditions
64. he CAP 1000 can also be configured with lower torque range and choice of lower speed for special purpose applications Torque Range Standard 1xCAP or 181 000 dyneecm Option 1 23 CAP or 7 800 dynescm STANDARD SPEEDS CHOICES FOR OPTIONAL SPEEDS Viscosity Viscosity Viscosity Viscosity Viscosity 750 RPM 900RPM 5RPM 50 RPM 500 RPM il aces Se a Poise Poise Poise Poise Poise g CAP S 01 0 25 25 0 2 2 0 37 5 375 3 75 37 5 0 375 3 75 13 3N sec 67 uL 1 511cm CAP S 02 0 41 4 1 75 750 75 75 0 75 7 5 13 3Nsec 38uL 1 200cm CAP S 03 0 83 8 3 150 1500 15 150 15 15 133Nsec 24pL 0 953cm CAP S 04 1 67 16 7 300 3000 30 300 330 CAP S 05 3 33 33 3 600 6000 60 600 6 60 3 3N sec 67 pL 0 953cm N A CAP S 09 1000 10000 100 1000 100 uL 0 953cm CAP S 10 0 67 6 7 0 5 5 0 100 1000 10 100 NA 5 0N sec 170 pL 12 1 511cm N A Not appropriate for use at speeds above 400 rpm CAP Viscometer Spindle Dimensions CEEI Tans 00 03 3 a waa ooz CAP S 08 2 075 52 71 1 190 30 23 010 0 25 CAP S 09 2 075 52 71 750 19 05 010 0 25 CAP S 10 2 075 52 71 187 4 1 190 30 23 010 0 25 010 0 28 0 0 010 7 e oo fowo 7 e e oo 025 7a sa iere 0 025 010 0 MORE SOLUTIONS TO STICKY PROBLEMS Page 46 Brookfield Engineering Labs Inc HIGH END VISCOMETERS RHEOMETERS
65. hn Wiley amp Sons New York NY PAINT FLOW AND PIGMENT DISPERSION Second Edition Temple C Patton Interscience Publishers New York NY PRINCIPLES AND APPLICATIONS OF RHEOLOGY Arnold G Fredrickson Prentice Hall Inc Englewood Cliffs NJ RHEOLOGICAL METHODS IN FOOD PROCESS ENGINEERING James F Steffe Freeman Press E Lansing MI RHEOLOGICAL PROPERTIES OF COSMETICS AND TOILETRIES Dennis Laba Marcel Dekker Inc New York NY RHEOLOGY FOR CERAMISTS Dennis R Dinger Dinger Ceramic Consulting Services Clemson SC MORE SOLUTIONS TO STICKY PROBLEMS VISCOMETRIC FLOWS OF NON NEWTONIAN FLUIDS Colemen Markovitz Noll Springer Verlag New York Inc New York NY VISCOSITY AND FLOW MEASUREMENT Van Wazer Lyons Kim Colwell Interscience Publishers New York NY ISO standards may be purchased in the United States from American National Standards Institute 11 West 42nd Street New York NY 10036 Phone 212 642 4900 Fax 212 302 1286 Outside the United States please contact ISO s member in your country or International Organization for Standardization 1 rue de Varembe 1211 Geneva 20 Switzerland ASTM test methods are available from ASTM 1916 Race Street Philadelphia PA Phone 215 299 5400 Fax 215 977 9679 Brookfield Engineering Laboratories maintains a li brary of technical papers on viscosity measurement and control Reprints are available upon request at no charge Acurrent listing of a
66. hnical papers on the subject of viscosity measurement and making them available at no cost This program has helped many people benefit from the experiences of others There is a middle ground however between the spe cific technical information provided in these papers and the basic operating procedures outlined in an instruc tion manual for your instrument We have been re quested many times over the years to publish a book that would bridge the gap between the elementary and the advanced a sort of extended user s manual that would guide the way for the person wishing to explore in greater depth the field of viscosity measurement MORE SOLUTIONS TO STICKY PROBLEMS Page 1 with an emphasis on Brookfield equipment The book you hold in your hand is the result of those requests It does not replace your instruction manual nor does it replace the specific technical papers al ready or yet to be published It is also not a textbook on rheology Rather it is a guide to help point out the way to getting more from your Brookfield Viscometer It does this in several ways by offering practical advice on the use and maintenance of the Brookfield Viscometer based on our experience and that of our customers by suggesting ways in which specific pieces of hardware may be used to solve viscosity measurement problems by explaining the basic principles of rheology and their relation to measurements made with Brookfield equi
67. hniques As with any precision instrument proper operating techniques will improve effectiveness of the Brookfield Viscometer A step by step procedure for Viscometer operation can be found in the Instruction Manual sup plied with each unit and is not repeated here Instead we present recommendations and advice gleaned from over 70 years of customer experience They form a sound foundation for a viscosity testing procedure and a starting point from which more advanced techniques can be explored 3 4 1 Record Keeping We recommend that the following information always be recorded when making a viscosity mea surement viscometer model spindle or acces sory rotational speed container size or dimensions sample temperature time of spindle rotation sample preparation procedure if any and whether or not the spindle guardleg was used Test Report Forms supplied in the instruction manual with each Vis cometer are convenient for this purpose 3 4 2 The Spindle and the Guardleg Examine each spindle before using it If it is corroded or damaged to the extent of changing its dimensions a false viscosity reading may result Since all spindles are brightly polished when new any sign of pitting dulled edges or other obvious damage should dictate the purchase of a new spindle If you have an unusual problem along these lines corrosion resistant 316 series stainless steel and Teflon coated spindles are available Also spe cial spindl
68. ids eee 23 A 7 UL Adapter asiasia 38 5 3 1 Ratio Methods n se 23 A 8 Thermosel System n se 39 5 3 2 Graphic Methods ccceeeeeee 23 A 9 DIN Adapter eeeceeceeeeeeteeeeeeennteeeeeeenaees 40 5 3 3 Template Method 24 A 10 Helipath Stand with T Bar Spindles 41 5 3 4 Dynamic Yield Value Determination 24 A 11 Spiral Adapter ccccceceeseeeeeeeeeeneees 42 5 4 Static Yield Value Determination 25 A 12 Vane Spindles n 43 5 5 Analyzing Time Dependent A 13 KU 2 Krebs Viscometer 0 44 Non Newtonian Fluids e cece 25 A 14 YR 1 Yield Stress Rheometer 45 5 6 Temperature Dependence of Viscosity 25 A 15 CAP 1000 Viscometer ceeeeee 46 5 7 Math Models carieni 26 A 16 CAP 2000 Viscometet eeee 47 5 8 Brookfield Application Software 26 A 17 R S Rheometer amp 5 9 Miscellaneous Methods ceeees 27 R S Soft Solids Tester ccceeeeeee 48 A 18 PVS Rheometer seneese 49 CHAPTER O riarena acetal ei aaaeaii 27 6 1 Single Point Viscosity Test ee 27 APPENDIX B Spindle Entry Codes 6 2 Controlled Rate Ramp ceeeeee 27 and Range Coefficients cscccssseeeeeees 51 6 3 Up Down Rate Ramp nsss 27 APPENDIX C ASTM Specifications 53 6 4 Time Sensitivity Test cceeeeeeeeees 27 APPENDIX D References ccccsseeeceeeeee 54 6
69. ination Plots of thixotropic behavior may sometimes be used to predict the gel point of a fluid One way to do this is to plot log Viscometer reading versus time using a single spindle and speed If the resulting line has a steep slope gelling is likely to occur If the line curves and flattens out gelation is unlikely Another technique is to plot time versus the recipro cal of the Viscometer reading In this method the gel point can be read from the curve intercept at a Vis cometer reading of 100 Fluids which do not gel will be asymptotic to the vertical axis 5 6 Temperature Dependence of Viscosity The viscosity of most fluids decreases with an in crease in temperature By measuring viscosity at two temperatures using a single spindle and speed it is possible to predict a flow curve representing the tem perature dependence of the viscosity of a fluid accord ing to the following relationships using the application of simultaneous equations Brookfield Engineering Labs Inc 15 n Ave hete Ne where B Tate 0m 7 A n e T Definitions T Temperature at which viscosity n was measured Temperature at which viscosity n was measured T 5 7 Math Models The analysis of viscometer data may be enchanced through the use of mathematical models Non Newtonian behavior can be simply expressed through an equation and in some cases the coefficients of a model can be used to infer performance of a fl
70. inches mm Dimension A is 4 531 115 on LV spindles 5 250 133 on RV H spindles Dimension B is 125 3 2 on all spindles few fs Fig 1 MORE SOLUTIONS TO STICKY PROBLEMS Foo Fig 2 Page 34 fe Fig 3 Brookfield Engineering Labs Inc Cylindrical Spindle Equation The following cylindrical spindle table depicts information for use with the equations presented in Section Actual Radius cm Effective Sone 1 2C Length cm Length em 1 LV 0 9421 7 493 6 510 2 LV CYL 0 5128 6 121 5 395 5 2 1 only Effective length includes correction for end effect and should be used in equations Actual length is given for reference only A 5 Wells Brookfield Cone Plate Viscometers Rheometers Cone Spindle Dimensions and Shear Rates wa o degrees Size mL sec rus N RPM Cone Spindle Factors Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise
71. ion at or below ambient temperature Refrigerated baths are also available Contact Brookfield Engineering Laboratories or your dealer for more information 2 5 2 Thermosel System This system is designed for the measurement of small samples in the temperature range of ap proximately 40 to 300 C Unlike a temperature bath the Thermosel doesn t utilize a fluid medium for temperature control For more information see Section 2 8 2 5 3 Peltier Thermo electric Systems The Cap 1000 Viscometer CAP 2000 Rheometer and the R S CPS P1 Rheometer have an embedded peltier device in the sample plate to provide rapid temperature control Small sample size less than 1 mL facilitates easy temperature profiling of materials 2 6 Small Sample Volume The standard sample container for most Brookfield Viscometers is a 600 ml low form Griffin beaker Us ers often find it desirable or necessary to measure samples of smaller volume Several Brookfield prod ucts feature small sample volumes MORE SOLUTIONS TO STICKY PROBLEMS 2 6 1 Small Sample Adapter Specifically designed to facilitate the measure ment of small samples the Small Sample Adapter SSA is a jacketed coaxial cylinder accessory that is compatible with all Brookfield Viscometers with the exception of cone plate types Depending on the model selected the Small Sample Adapter uti lizes sample volumes of 2 0 to 16 0 ml Also de pending on model the Small Sample Adapter will
72. is de signed to quickly attach or remove a spindle from a Brookfield Viscometer Rheometer resulting in time savings and elimination of cross threading The Quick Connect accessory is made of stainless steel and can be used with LV RV HA HB disk spindles cylindrical spindles as well as T bar couplings 2 13 2 Spindle Extensions Spindle extensions are suitable for applications utilizing standard disc or cylindrical spindles where distance between the Viscometer and the sample material must be increased up to 6 feet maximum Type D extensions are installed between the Vis cometer and the spindle and are suitable for appli cations where depth of the spindle immersion can be observed Type S extensions include the im mersed portion of the spindle and are used where depth of immersion is not observable 2 14 Fumes and Hazardous Locations Whenever fumes and vapors are present that could enter the Viscometer care should be taken to prevent such entry When the fumes are explosive or flam mable special precautions are required not only for protection of the Viscometer but for the safety of nearby personnel 2 14 1 Purge Fittings A purge fitting may be provided on the pivot hous ing of any Viscometer An inert gas such as nitro gen is introduced under low pressure through the purge fitting creating a positive pressure inside the Viscometer housing which prevents entry of fumes and vapors Purge fittings are also available for s
73. l lists available papers on specific application areas as well as general interest experimental techniques If you don t have the current edition let us know and we ll send one to you Ask for Data Sheet 091 C 5 8 Brookfield Application Software Brookfield offers various software programs which work in conjunction with viscometers rheometers to allow for automatic data collection analysis including use of math models and the creation of permanent test records Brookfield Engineering Labs Inc Software Instrument Required 5 9 Miscellaneous Methods RHEOCALC32 DV III Ultra Rneometer There are many other techniques available for ana DV IIl Rneometer lyzing the rheological behavior of fluids under a vari DV II Pro Viscometer ety of conditions Space doesn t permit a detailed dis WINGATHER32 DV II Pro Viscometer cussion here but more information can be obtained DV Il Programmable from Brookfield Engineering Laboratories on these and Viscometer other advanced methods DV II Viscometer CAPCALC32 CAP series Viscometers ee ats ESAR eee RHEOVISION PVS Rheometer ae j RHEO 2000 R S Rheometer Techniques for determination of extremely low shear viscosity and leveling behavior of coating materials using spring relaxation procedures AR 84 Computer analysis of certain rheological characteristics CHAPTER 6 The following methods provide various ways to obtain This method shows one example of how viscosity
74. late Model also functions as a Plate Plate Model by using flat plates ranging from 2 5 5 0 and 7 5 cm diameter The flat plate geom etries are a good choice for extremely high viscos ity fluids or where the fluid has solid particles in it R S Soft Solids Tester The R S Soft Solids Tester combines vane spindle geometry with low shear and stress provid ing viscoelastic characterization of soft solid mate Brookfield Engineering Labs Inc rials such as pastes gels waxes and slurries Brookfield Rheo 2000 software with soft solids mod ule is required 2 12 Non Flowing Sample Materials Non flowing or slow flowing sample materials such as pastes creams and gels present special problems in viscosity measurement Conventional rotating spindles tend to channel push the sample material aside resulting in a continuously decreasing Viscom eter reading that is of little value Several alternatives address this problem 2 12 1 Helipath Stand The Helipath Stand is a motorized stand to which any Brookfield Viscometer can be attached The Stand slowly raises and lowers the Viscometer at a rate of 7 8 inch per minute while a special T bar spindle rotates in the sample material The cross bar of the spindle thus continuously cuts into fresh material describing a helical path through the sample as it rotates The channeling effect of con ventional spindles is completely eliminated permit ting meaningful viscosity consi
75. le will be temporarily changed and the molecule formation will be orientated more parallel to the spindle rate on non Newtonian fluids What happens when the element of time is considered This question leads us to the examination of two more types of surface So the hindering of the spindle rotation will NON NEN TONIAD TONE STORIE ANG TRORA decrease The faster the rotation will become the more the structure is destroyed and the less the structure of molecules slide in together the lower the viscosity will be 4 5 Thixotropy and Rheopexy Some fluids will display a change in viscosity with time under conditions of constant shear rate There are two categories to consider DILATANT Increasing viscosity with an increase in shear rate characterizes the dilatant fluid see Fig ure 4 4 THIXOTROPY As shown in Figure 4 6 a thixotro pic fluid undergoes a decrease in viscosity with time while it is subjected to a constant shear rate T n n t Y 5 Y Figure 4 4 Figure 4 6 MORE SOLUTIONS TO STICKY PROBLEMS Page 16 Brookfield Engineering Labs Inc RHEOPEXY This is essentially the opposite of thixotropic behavior in that the fluid s viscosity in creases with time as it is sheared at a constant rate See Figure 4 7 n Figure 4 7 Both thixotropy and rheopexy may occur in combi nation with any of the previously discussed flow be haviors or only at certain shear rates The time ele ment is extremely variable
76. made by rotating the spindle at 200 rpm 2 125 53 98 KU1 10 3 562 90 47 188 4 77 312 7 92 1 625 41 28 KU1 75Y 3 562 90 47 188 4 77 1 688 42 88 078 1 98 1 625 41 28 There is no defined shear rate for the Krebs and Paste Spindles A 14 YR 1 Yield Stress Rheometer The YR 1 uses a unique method to apply a controlled torque ramp to the vane spindle in order to measure yield stress behavior in the sample material Standard torque ranges available for the YR 1 Rheometer are 1 4RV RV HB and 5xHB YR 1 Spindle Shear Stress Range Data Torque Range Pa 125 1 25 5 5 2 5 25 25 250 5 5 2 20 10 100 100 1000 4 40 16 160 80 800 800 8000 20 200 80 800 400 4000 4000 40000 Shear Stress Range dyne cm 1 25 12 5 5 50 25 250 250 2500 5 50 20 200 100 1000 1000 10000 40 400 160 1600 800 8000 8000 80000 200 2000 800 8000 4000 40000 40000 400000 Note 1 Pa 10 dyne cm Vane Spindle Dimensions 2 708 in 6 878 cm 1 354 in 3 439 cm A V 72 1 708 in 4 338 cm 0 853 in 2 167 cm 0 499 in 1 267 cm 0 463 in 1 176 cm 0 232 in 0 589 cm V 73 0 998 in 2 535 cm MORE SOLUTIONS TO STICKY PROBLEMS Page 45 Brookfield Engineering Labs Inc A 15 CAP 1000 Viscometer The CAP 1000 Viscometer is a high torque single speed cone plate instrument used traditionally for testing at high shear rates around 10 000 sec T
77. mall Sample Adapter Section 2 1 5 or as part of the Thermosel System Section 2 1 7 For shear rates in excess of 300 reciprocal seconds it is usually neces sary to use the Wells Brookfield Cone Plate CAP PVS Rheometer or R S Rheometer 2 10 1 Wells Brookfield Cone Plate Viscometer Rheometer The Wells Brookfield Cone Plate Viscometer will determine the absolute viscosity of small samples under conditions of defined shear rate and shear stress Its cone and plate spindle geometry requires a sample volume of only 0 5 to 2 0 mL and gener ates shear rates in the range of 0 6 to 1 875 recip rocal seconds depending on model and spindle used The instrument s sample cup is jacketed for excellent temperature control Depending on the particular model and spindle in use the Wells Brookfield Cone Plate will mea sure viscosities from 0 1 cP to 2 6 million cP al though no single instrument will cover this range the use of several spindles will allow one instrument to measure a wide range of viscosities The Wells Brookfield Cone Plate Viscometer is available in different Digital versions A tempera ture bath is optional and highly recommended for precise and reproducible viscosity measurements The cone and plate spindle geometry is avail able only on the Wells Brookfield Cone Plate instru ment it is not available as an accessory or modifi cation of other Brookfield Viscometers It is pos sible to use this instrument with standa
78. ments are unique and do not nec essarily compare to the traditional Brookfield Viscom eter The Brookfield KU 2 is designed to provide a viscosity measurement in Krebs units and is often used in the paint industry The Brookfield CAP 1000 is designed to operate at high shear rate 10 000 s 12 000 s and is often used in the resin and paint industries 2 3 Rheometers Avery important advancement in viscosity measure ment is the bidirectional DV III Ultra Rneometer and more recently the DV Il Pro Viscometer for use with PC This instrument with variable speed capability allows easy handling and programming of complicated Brookfield Engineering Labs Inc application measurements It also enables the stor age of calculated results and transfer of data to Excel or any LIMS system When used with Brookfield Rheocalc software it easily gives a graphical view of results which is especially important on flow curve in terpretations The overlay capability of the Rheocalc software gives a good possibility to compare different measured results from multiple tests The Brookfield R S Rheometer differs from the stan dard Brookfield viscometers in that it is a controlled stress or controlled torque instrument rather than a controlled rate RPM instrument Controlled stress with the R S provides many benefits such as a very broad viscosity measurement range testing for Yield properties and the ability to measure flow properties
79. n inks hee Painting and ee under 107 10 coating toilet g y bleaches Chewing and Tona x z Paints r o 2 7 Mixing and 101 10 Manufacturing stirring liquids Pumping blood OL 3 Pipe flow 10 10 flow Application of a 4 Rubbing 105310 creams and lotions to the skin Spray drying ats and 10 105 painting fuel 9 atomization Milling pigments 10 105 Paints printing in fluid bases inks High speed 108 10 Paper coating MORE SOLUTIONS TO STICKY PROBLEMS Page 19 4 8 3 Measuring Conditions The condition of a material during measurement of its viscosity can have a considerable effect on the results of such measurement It is therefore important to be aware of and to control as much as possible the environment of any sample you are testing First the viscosity measurement techniques outlined in Section 3 3 should be adhered to Vari ables such as Viscometer model spindle speed combination sample container size absence or presence of the guard leg sample temperature sample preparation technique etc all affect not only the accuracy of your measurements but the actual viscosity of the material you are measuring Second other less obvious factors that may af fect viscosity must be considered For example the sample material may be sensitive to the ambi ent atmosphere as is the case with dental impres sion materials blast furnace slag blood and mu cus It may be that a controlled atmosphere fa
80. ng the X axis Slope and shape of the resulting curve will indicate the type and degree of flow behavior For examples of this type graph see the illustrations accompany ing the discussion of non Newtonian flow types in Section 4 4 Another method is to plot Viscometer reading on the X axis as a function of speed on the Y axis If the graph is drawn on log log paper the result is frequently a straight line When this hap Brookfield Engineering Labs Inc pens the slope of the line indicating the type and degree of non Newtonian flow and its intercept with the X axis indicating its yield value if any can be used as empirical constants When shear rate and shear stress are known as with cylindrical spindles or coaxial cylinder ge ometry these values may be substituted for speed and Viscometer reading in the above methods Thus predictions of viscosity at other shear rates may be made by interpolating between or extrapo lating beyond the values available with a particular spindle geometry When using these methods with disc spindle geometries it is best to make all measurements with the same spindle An assumption that can be made with regard to shear rate is that for a given spindle the shear rate is proportional to the speed There fore the shear rate at 30 RPM for example is 10 times the shear rate at 3 RPM 5 3 3 Template Method A more sophisticated technique for the analysis of non Newtonian fluids involve
81. nk and additives of many types are used to control the rheological properties of paints 4 8 8 Special Characteristics of Dispersions and Emulsions Dispersions and emulsions which are multiphase materials consisting of one or more solid phases dispersed in a liquid phase can be affected rheologically by a number of factors In addition to many of the factors discussed previously charac teristics peculiar to multiphase materials are also significant to the rheology of such materials These are discussed below One of the major characteristics to study is the state of aggregation of the sample material Are the particles that make up the solid phase separate and distinct or are they clumped together how large are the clumps and how tightly are they stuck to gether If the clumps flocs occupy a large volume in the dispersion viscosity of the dispersion will tend to be higher than if the floc volume was smaller This is due to the greater force required to dissipate the solid component of the dispersion MORE SOLUTIONS TO STICKY PROBLEMS Page 20 When flocs are aggregated in a dispersion reaction of the aggregates to shear can result in shear thinning pseudoplastic flow At low shear rates the aggregates may be deformed but remain essentially intact As the shear rate is increased the aggregates may be broken down into individual flocs decreasing friction and therefore viscosity For more information on pseudoplastic flow
82. ntly being rotated If the particles are essentially spherical rotation can occur freely If however the particles are needle or plate shaped the ease with which rotation can occur is less predictable as is the effect of varying shear rates The stability of a dispersed phase is particularly critical when measuring viscosity of a multiphase system If the dispersed phase has a tendency to settle producing a non homogeneous fluid the rheological characteristics of the system will change In most cases this means that the measured vis cosity will decrease Data acquired during such con ditions will usually be erroneous necessitating spe cial precautions to ensure that the dispersed phase remains in suspension Brookfield Engineering Labs Inc CHAPTER 5 5 1 Advanced Methods for Rheological Analysis As mentioned in Chapter 1 those who follow the Academic school of thought on viscosity measurement have more complex needs than those who follow the Pragmatic or Theoretical schools They need viscosity data that are defined in rheological terms This usually requires a complete mathematical description of the Viscometer s operating parameters and an analysis of the rheological behavior of the fluid being studied Previous chapters have described various types of fluid behavior and their relationship to measurements made with Brookfield Viscometers Rheometers and accessories The Appendix details the significant operating
83. of viscosity implies the existence of what is called laminar flow the movement of one layer of fluid past another with no transfer of matter from one to the other Viscosity is the friction between these layers Depending on a number of factors there is a certain maximum speed at which one layer of fluid can move with relation to another beyond which an actual transfer of mass occurs This is called turbulence Molecules or larger particles jump from one layer to another and dissipate a substantial amount of energy in the process The net result is that a larger energy input is required to maintain this turbulent flow than a laminar flow at the same velocity The increased energy input is manifested as an apparently greater shear stress than would be observed under laminar flow conditions at the same shear rate This results in an erroneously high viscosity reading The point at which laminar flow evolves into turbulent flow depends on other factors besides the velocity at which the layers move A material s viscosity and specific gravity as well as the geometry of the Viscometer spindle and sample container all influence the point at which this transition occurs Care should be taken to distinguish between turbu lent flow conditions and dilatant flow behavior In gen eral dilatant materials will show a steadily increasing viscosity with increasing shear rate turbulent flow is characterized by a relatively sudden and subst
84. ometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for the an SC4 27 spindle with 13R chamber on an RV Viscometer is given as 2500 N the following SC4 Series Spindle Factors and Shear Rates Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 50 RPM the Spindle Factor is 2500 50 or 50 Multiply all Dial Viscometer readings made with this spindle speed combination by 50 to obtain viscosity in centipoise Par Tw Tm Pat Ize sec Ceo o n son asa e sorz eo eson soon ooon soon osn N RPM_ M 1000 1 The BS designation indicates that the spindle is also available in a solid shaft configuration 2 DIN geometry for the Thermosel is also available See Appendix A 9 SC4 Series Spindle Dimensions Effective Length inches mm inches mm inches mm SC4 18 1 399 35 53 i E SC4 21 1 384 35 15 SC4 27 BS 1 547 39 29 SIDELENG TH SC4 28 BS 1 480 37 59 SC4 29 BS 1 250 31 75 7 SC4 31 BS 1 208 30 68 SC4 34 BS 1 156 29 36 DIAMETER Dimensions are in inches mm Refer to Section 5 2 1 1 The
85. or use it is essential to know its viscosity at the projected shear rates If these are not known an estimate should be made Viscosity measurements should then be made at shear rates as close as possible to the estimated values It is frequently impossible to approximate projected shear rate values during measurement because these values fall outside the shear rate range of the Viscometer In this case it is necessary to make measurements at several shear rates and extrapolate the data to the projected values This is not the most accurate method for acquiring this information but it is often the only alternative available especially when the projected shear rates are very high In fact itis always advisable to make viscosity measurements at several shear rates to detect rheological behavior that may have an effect on processing or use Where shear rate values are unknown or not important a sample plot of viscosity versus RPM will often suffice Examples of materials that are subjected to and are affected by wide variations in shear rate during processing and use are paints cosmetics liquid latex coatings certain food products and blood in the human circulatory system The following table shows typical examples of varying shear rates Typical range of shear rates s Application Sedimentation of fine powders in Medicines a suspending Paints liquid Levelling due to io J Paints printing 3 107 10 surface tensio
86. parameters of this equipment and presents simplified formulas for obtaining shear rate and shear stress values However for many this information is still inadequate to perform the type of analysis they require Having identified a particular flow behavior and defined it mathematically these people need more information to understand how the fluid will react in a certain situation and how to control that reaction If is for these people that this chapter is provided In it you will find basic formulas from which the simplified shear rate and shear stress information in the Appendix was derived Also various methods for analyzing Newtonian and non Newtonian fluids are presented The information presented here represents a cross section of the most useful methods developed both by Brookfield Engineering Laboratories and by others Other specific methods usually applicable to a particular rheological problem are sometimes available Please inquire if you need more information 5 2 Defining Operating Parameters of Various Spindle Geometries In this section we present equations that define the operating parameters of spindle geometries found on various Brookfield Viscometers Rheometers and ac cessories These are organized according to the type of geometry being discussed Definitions and values not listed may be found in the Appendix A MORE SOLUTIONS TO STICKY PROBLEMS Page 21 5 2 1 Cylindrical Spindles The following equations appl
87. pindles upon request This activity is coordinated through the Sales Department at Brookfield Spindles that have come out of this type of activity include modifica tions of the Helipath Stand T bars i e multiple tines very large spindles for low viscosity liquids and spe cial materials of construction 5 3 Analyzing Time Independent Non Newtonian Fluids The equations we have presented thus far will yield precisely defined viscosity data for both Newtonian and non Newtonian fluids With Newtonian fluids this is all the analysis that is necessary since variations in shear rate will have no effect on viscosity of the fluid When the fluid is non Newtonian however the situ ation is more complicated While the equations per MORE SOLUTIONS TO STICKY PROBLEMS Page 23 mit complete definition of a reading made with a cer tain spindle at a certain speed the numbers obtained with another spindle and or speed will most likely be different Which set of numbers is the right one Both and neither These differing numbers are part of the rheological description of the fluid and therefore must be considered in the course of its analysis In this section we will outline several methods for doing this on time independent fluids as defined in Section 4 4 5 3 1 Ratio Methods Acommon method for characterizing and quan tifying non Newtonian flow is to figure the ratio of the fluid s viscosity as measured at two different speeds
88. pment by discussing factors that affect rheological behavior and how these may be controlled by outlining advanced mathematical procedures for detailed analysis of viscosity data by consolidating a variety of useful range tables formulas and specifications for many Brookfield Viscometers and accessories We hope that you will find this book useful and refer to it often It is our attempt to answer all at once many of the questions we have been asked over the years If you have any questions that are not answered here or if you want to suggest improvements or changes for future editions please feel free to contact us It was after all the input of people like yourself that made this book possible in the first place Brookfield Engineering Labs Inc CHAPTER 1 1 1 Why Make Rheological Measurements Anyone beginning the process of learning to think Rheo Logically must first ask the question Why should make a viscosity measurement The answer lies in the experiences of thousands of people who have made such measurements showing that much useful behavioral and predictive information for various products can be obtained as well as knowledge of the effects of processing formulation changes aging phenomena etc A frequent reason for the measurement of rheological properties can be found in the area of quality control where raw materials must be consistent from batch to batch For this purpose flow behavior
89. r a V 72 spindle on an RV Viscometer is given as 1 100 N see the follow ing Vane Spindle Factors Table The Viscometer s rotational speed RPM is represented by N If the mea surement is being made at 1 100 RPM the Spindle Factor is 1 100 10 or 110 Multiply all Dial Viscometer readings made with this spindle speed combination by 110 to obtain viscosity in centipoise 24 56 N 262 N 524 N 4 6M N 501 N 5 35M N 10 7M N 42 8M N 5 09M N 54 3M N 108 6M N 434 4M N N RPM M 1 000 Possibility of turbulence at speeds above 10 rpm may give artificially higher viscosity readings MORE SOLUTIONS TO STICKY PROBLEMS Page 43 Brookfield Engineering Labs Inc Vane Spindle Dimensions Vane Length Vane Diameter inches cm inches cm 2 708 6 878 1 354 3 439 A 1 708 4 338 853 2 167 998 2 535 499 1 267 463 1 176 232 589 Note Sample container diameter should be twice 2x the vane diameter when possible Sample container depth should provide clearance at the bottom equivalent to vane spindle diameter when possible SPECIAL PURPOSE INSTRUMENTS A 13 KU 2 Krebs Viscometer Spindle Dimensions Paste Spindle Standard Krebs Spindle KU1 10 KU1 75Y B A A D E E D C C MORE SOLUTIONS TO STICKY PROBLEMS Page 44 Brookfield Engineering Labs Inc The KU 2 KU 1 KU 1 Viscometer measures viscosity in Krebs units and grams The KU 2 Viscometer also reports the viscosity reading in centipoise The measurement is
90. rapidly a mate rial returns to its original condition after it has been sheared Perform the time sensitivity test described in method 6 4 At the end of the time interval during which the material is sheared set the rotational speed to 0 RPM Observe the torque signal to see what happens TORQUE TIME Figure 6 8 Some materials recover to their original condition within a very short time while others will recover only partially or not at all This behavior is observed if during the recovery period the drive is decoupled from the spindle as in the R S SST Rheometer Ifa spring torque instrument is used such as a standard Brookfield LV RV HA HB Viscometer or Rheometer then the torque will decrease as the spring unwinds MORE SOLUTIONS TO STICKY PROBLEMS Page 29 Brookfield Engineering Labs Inc APPENDIX A Specifications Ranges and Operating Parameters Appendix A is intended to provide the user of Brookfield Viscometers Rheometers and accesso ries with all the information required to perform math ematical analyses of viscosity data acquired with this equipment It includes essential dimen sions viscosity range tables and constants orga nized by product in data sheet form The following Brookfield Viscometers Rheometers Accessories Special Purpose Instruments and High End Viscom eters Rheometers are covered Standard Viscometers Rheometers A 1 Dial Reading Viscometer A 2 Digital Viscometers Rheometers
91. rd disc and cylindrical spindles however an extension for the laboratory stand is required to provide sufficient clearance under the Viscometer 2 10 2 CAP Viscometer Rheometer The Brookfield CAP series of Cone Plate Vis cometers offer high shear rates and variable speeds in an instrument optimized for R amp D and QC appli cations such as paints coatings resins inks cos metics pharmaceuticals and foods These series of viscometers have integrated temperature control for test sample volume of less than 1 mL The CAP 1000 is a single speed viscometer running at 750 RPM on 50 Hz and 900 RPM on 60 Hz generating shear rates at 10 000 or 2 500 sec at 50 Hz and 12 000 or 3 000 sec at 60 Hz de MORE SOLUTIONS TO STICKY PROBLEMS 2 Page 7 pending on choice of spindle The CAP 2000 is a variable speed instrument and has variable shear rate capability over the speed range from 5 to 1 000 RPM This instrument generates shear rates from 166 to 13 300 sec at viscosity ranges from 0 1 to 1 500 Poise 0 1 to 150 Pass The CAP Series meets industry test standards BS3900 ISO 2884 and ASTM D 4287 The CAP Viscometer offers choice of low torque or high torque capability selection is based on vis cosity range of samples to be tested 2 10 3 R S Rheometer R S Rheometer can generate shear rates up to 5 100 sec in narrow gap coaxial cylinder geom etry and up to 6 000 sec in cone plate Maximum instrument speed is 1000
92. re separated by a distance dx and are moving in the same direction at different velocities V1 and V2 Newton assumed that the force required to maintain this difference in speed was proportional to the difference in speed through the liquid or the velocity gradient To express this Newton wrote Levers A ox where n is a constant for a given material and is called its viscosity a The velocity gradient ax is a measure of the change in speed at which the intermediate layers move with respect to each other It describes the shearing the liquid experiences and is thus called shear rate This will be symbolized as Y in subsequent discussions Its unit of measure is called the reciprocal second sec The term F A indicates the force per unit area re quired to produce the shearing action It is referred to as shear stress and will be symbolized by t Its unit of measurement is dynes per square centimeter dynes cm or Newtons per square meter N m Using these simplified terms viscosity may be de fined mathematically by this formula T shear stress Y __ shear rate The fundamental unit of viscosity measurement is poise A material requiring a shear stress of one dyne per square centimeter to produce a shear rate of one reciprocal second has a viscosity of one poise or 100 centipoise You will encounter viscosity measure ments expressed in Pascal seconds Pas
93. rials and configurations for unusual applications 2 4 1 Disc Spindles Provided as standard equipment with LV spindles 2 and 3 and RV HA HB models spindles 2 through 6 these are general purpose spindles for use in containers of 600 mL capacity or larger Disc spindles produce accurate reproduc ible apparent viscosity determinations in most flu ids The results obtained can be converted into viscosity functions by a mathematical procedure outlined in Technical Paper AR 82 available from Brookfield Engineering Laboratories See Section MORE SOLUTIONS TO STICKY PROBLEMS Page 4 2 9 for information on spindle geometries that di rectly provide defined shear rates 2 4 2 Cylindrical Spindles These spindles LV 1 and 4 RV HA HB 7 provide a defined spindle geometry for calculating shear stress and shear rate values as well as vis cosity when used with the Brookfield Guard Leg In all other respects their operating parameters are similar to those of disc spindles Because their defined geometry facilitates math ematical analysis cylindrical spindles are particu larly valuable when measuring non Newtonian flu ids They are applicable to any Brookfield Viscom eter model with the use of the appropriate range sheet Cylindrical equivalents of the LV 2 and 3 disc spindles are also available See Section 2 9 for information on other defined shear rate geom etries 2 4 3 Coaxial Cylinders Coaxial cylinder geometry is
94. rmation necessary to make meaningful viscosity measurements It will describe the mechanical components of the Brookfield Viscom eter and suggest some useful operational techniques Those adhering strictly to the Pragmatic school of viscosity measurement may not wish to read any fur ther than this chapter All users however should read it before moving on a good grounding in basic Vis cometer operation will facilitate advancement to more sophisticated techniques 3 2 How the Brookfield Viscometer Works The Brookfield Viscometer is of the rotational vari ety It measures the torque required to rotate an im mersed element the spindle in a fluid The spindle is driven by a motor through a calibrated spring deflec tion of the spring is indicated by a pointer and dial or a digital display By utilizing a multiple speed trans mission and interchangeable spindles a variety of vis cosity ranges can be measured thus enhancing ver satility of the instrument For a given viscosity the viscous drag or resistance to flow indicated by the degree to which the spring winds up is proportional to the spindle s speed of ro tation and is related to the spindle s size and shape geometry The drag will increase as the spindle size and or rotational speed increase It follows that for a given spindle geometry and speed an increase in vis cosity will be indicated by an increase in deflection of the spring For any Viscometer model th
95. s 4 RVT HAT HBT Dial Reading Viscometers built before September 2001 have only eight speeds 5 RVT HAT HBT are supplied with six spindles as of September 2001 RV H 1 spindle is available as an option MORE SOLUTIONS TO STICKY PROBLEMS Page 31 Brookfield Engineering Labs Inc A 2 Digital Viscometers Rheometers Spindles and Speeds Current Viscometer No of Former Viscometer Rheometer Model Spindles No of Speeds Speeds rpm Rheometer Model 100 60 50 30 20 12 mice 5 A 3 2a 2 1 5 1 ae 2 J 100 60 50 30 20 1 100 60 50 30 20 1 RV HA HB DV I 5 4 3 2 5 2 1 5 1 LVDV II Programmable A RV HA HBDV II Programmable 01 to 250 rpm LVDV III Ultra 2 600 a a LVDV III LVDV III RV HA HB DV III Ultra 6 2 600 l 01 to 250 rom RV HA HBDV III RV HA HBDV III 1 rpm increments from 0 1 to 250 RV H 1 Spindle is available as an option A 3 Disc Spindle Information for Standard Viscometers Rheometers Spindle Factors are listed as constants related to the Viscometers rotational soeed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for a 2 LV spindle on an LV Viscometer is given as 3
96. s or milli Pascal seconds mPaes these are units of the In ternational System and are sometimes used in prefer ence to the CGS designations One Pascal second is equal to ten poise one milli Pascal second is equal to one centipoise Newton assumed that all materials have at a given n viscosity MORE SOLUTIONS TO STICKY PROBLEMS Page 15 temperature a viscosity that is independent of the shear rate In other words twice the force would move the fluid twice as fast As we shall see Newton was only partly right 4 3 Newtonian Fluids This type of flow behavior which Newton assumed for all fluids is called not surprisingly Newtonian It is however only one of several types of flow behavior you may encounter A Newtonian fluid is represented graphically in Figure 4 2 Graph A shows that the re lationship between shear stress t and shear rate Y is a straight line Graph B shows that the fluid s vis cosity remains constant as the shear rate is varied Typical Newtonian fluids include water and thin motor oils Y z Y Figure 4 2 What this means in practice is that at a given tem perature the viscosity of a Newtonian fluid will remain constant regardless of which Viscometer model spindle or speed you use to measure it Brookfield Viscosity Standards are Newtonian within the range of shear rates generated by Brookfield equipment Newtonians are obviously the easiest fluids to mea sure just gra
97. s at each speed We call this a con trolled rate method Using a best fit line typically available in standard software programs the techni cian can back calculate what the torque yield value would be This type of calculation determines what is known as dynamic yield because the yield value has been interpolated A more precise method to determine yield is to use a controlled stress rheometer such as the Brookfield R S CPS Rheometer This type of instrument employs a controlled stress ramp to gradually increase the amount of force torque on the sample until flow is initiated By using a controlled stress ramp the QC technician can determine more directly where yield begins This is known as static yield The type of spindle geometry used to obtain yield stress data is an important consideration A practical low cost approach is to use standard disk or cylindri cal spindles in a 600 mL beaker with a viscometer This approach will employ a controlled rate test method as explained earlier The use of coaxial cylinder or cone plate geometry with either controlled rate or con trolled stress mode of operation are strong alterna tives These geometries are typically considered to be more precise because the fluid is sheared evenly within a defined gap The advantage of controlled stress over controlled rate is that this is a direct method for evaluating yield behavior One disadvantage is that this type of instrumenta
98. s use of a template Its use is limited to fluids that follow the power law meaning ones that display one type of non Newtonian flow rather than shifting from one type to another as shear rate is varied For example a material that changed from pseudoplastic to dila tant flow when a certain shear rate is exceeded would not follow the power law over the full range of shear rates measured The template method is usable only with data generated with cylindrical spindles or coaxial cylin ders The data is fitted to a template to determine a constant called the STI The STI is a convenient way to characterize non Newtonian flow much like the Viscosity Index Certain parameters of the Vis cometer in use and the STI are fitted to a second template which is then used to predict the fluid s viscosity at any selected shear rate This is a useful method for predicting viscosity at shear rates not attainable by the Brookfield Vis cometer and for characterizing fluid behavior un der a specific set of conditions Acomplete descrip tion of the template method including both tem plates is available from Brookfield Engineering Laboratories as Technical Paper AR 49 5 3 4 Dynamic Yield Value Determination Some fluids behave much like a solid at zero shear rate They will not flow until a certain amount of force is applied at which time they will revert to fluid behavior This force is called the yield value and mea
99. scosity that should be measured is 25 times 10 or 250 cP Therefore if the viscosity of the sample fluid is estimated to be 4000 cP another spindle speed combination must be selected in order to Brookfield Engineering Labs Inc make the measurement If the sample fluid is around 2000 cP however this spindle and speed would be suitable With a little practice a quick glance at the Factor Finder will suffice to make an appropriate selection of spindle and speed When conducting multiple tests the same spindle speed combination should be used for all tests When a test must be performed at several speeds select a spindle that produces on scale readings at all required speeds This may necessi tate using a dial or display reading less than 10 which is acceptable as long as the reduced accu racy of such a reading is recognized 3 4 4 Sample Container Size For measurements with standard Viscometer models we recommend a container with an inside diameter of 3 1 4 inches 83 mm or larger The usual vessel for this purpose is a 600 mL low form Griffin beaker Use of a smaller container will result in an increase in viscosity readings particularly with the 1 and 2 spindle When utilizing a smaller container the simplest approach is to report the dimensions of the con tainer and ignore the probable effect on calibration As long as the same size container is used for all subsequent tests there will be no correlation prob lem
100. stency measure ments to be made Aset of six T bar spindles anda special coupling are included with the Helipath Stand 2 12 2 Spiral Adapter The Brookfield Spiral Adapter accessory is a pump type sensor that directly measures viscosity of pastes including applications such as solder paste foods cosmetics and pharmaceuticals The Spiral Adapter has an inner threaded spindle sur rounded by a concentric outer cylinder This com bination causes the sample to be continually pumped up through the Spiral Adapter The mate rial reaches a steady state of flow during which vis cosity is measured The steady state measurement is less sensitive to sample handling and minor ma terial variations than other viscosity measuring meth ods 2 12 3 Vane Spindles Vane Spindles immerse directly into the sample material without causing disturbance The material trapped between the vanes will move as the spindle rotates The net effect is that a virtual cylinder of sample material in which the vane spindle is in scribed will flow at defined rotational speeds thereby providing complete flow curve data for vis cosity analysis Vane spindles can be used with standard Brookfield Viscometers Rheometers and R S SST Rheometer 2 13 Special Accessory Items The following items can be purchased for use with Brookfield Viscometers Rheometers MORE SOLUTIONS TO STICKY PROBLEMS Page 8 2 13 1 Quick Connect The Brookfield Quick Connect accessory
101. suring it is often worthwhile Yield values can help determine whether a pump has sufficient power to start in a flooded system and often corre late with other properties of suspensions and emul sions The pourability of a material is directly re lated to its yield value MORE SOLUTIONS TO STICKY PROBLEMS Page 24 One method of determining yield value involves plotting Viscometer readings on the X axis versus speed RPM on the Y axis on standard graph paper The line thus obtained is extrapolated to zero RPM The corresponding value for the Viscometer reading represents the dynamic yield value If a cylindrical spindle is used to make the readings the yield value may be calculated from this equation YIELD VALUE vr se oR 11 yield value dynes cm2 Viscometer reading 0 RPM constant from table below Definitions y x1 fa Cylindrical Spindle ________ Model Spindle Entry Code LV RV HA HB 1 61 0 16 1 72 344 13 78 2 66 0 67 7 411 14 21 56 85 3 67 2 56 27 30 5460 218 39 4 64 12 48 133 14 266 28 1065 14 5 65 25 26 269 45 538 91 2155 63 Extrapolating the line to zero RPM is easy if the line is fairly straight This is called Bingham flow If the line is curved as in pseudoplastic or dilatant flow an estimate of X1 must be made by continuing the curve until it intersects the X axis 0 on the Y axis This estimated value of X1 is then subtracted from all the other readings that comprise the graph These new values are plo
102. t Method for Low Temperature Viscosity of Automotive Fluid Lubricants Measured by the Brookfield Viscometer Method for Measurement of Consistency of Lubricating Greases at High Temperatures Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials Reapproved 1999 Standard Specification for Liquid Applied Neoprene and Chlorosulfonated Polyethylene Used in Roofing and Waterproofing Method of Testing Emulsion Polymers for Use in Floor Polishes Standard Practice for Evaluating the Effects of Heat on Asphalts Test Method for Viscosity of Chemical Grouts by the Brookfield Viscometer Laboratory Method Standard Test Method for High Shear Viscosity Using the ICI Cone Plate Viscometer Standard Method for Viscosity Determinations of Unfilled Asphalts Using the Brookfield Thermosel Apparatus Standard Test Methods for Polyurethane Raw Materials Determination of Viscosity of Crude or Modified Isocyanates Standard Test Method for Shear Viscosity of Coal Tar and Petroleum Pitches Reapproved 1999 Standard Test Method for Low Temperature Low Shear Rate Viscosity Temperature Dependence of Lubricating Oils Using a Temperature Scanning Technique Inc APPENDIX D References References The following publications are available from the publishers listed for further reading on the subject of rheology and viscosity measurement NON NEWTONIAN FLOW AND HEAT TRANSFER A H P Skelland Jo
103. tained from the Factor Finder supplied with each instrument Since the full scale range of any spindle speed combination is equal to the Factor multiplied by 100 the full scale viscosity range in this case is 100 cP The accuracy tolerance is 1 of this range or 1 cP irrespective of the Viscometer s dial or display reading Refer to the following table to see how this affects the accuracy of various read ings taken with this spindle speed combination Viscometer Possible Relative Reading Viscosity Error Error 100 100 cP 1cP 1 50 50 cP 1 cP 2 10 10 cP 1 cP 10 The same principle applies to the repeatability of the reading As with accuracy the potential error introduced by the repeatability tolerance becomes less significant as the dial or display reading in creases 3 4 8 Obtaining a Viscometer Reading Before operating the Viscometer be sure that it Brookfield Engineering Labs Inc is securely attached to its stand and has been prop erly leveled Select a spindle and speed combina tion and attach the spindle to the Viscometer Don t mix LV and RV spindles Turn the Viscometer on and allow it to run until a constant reading is obtained Be prepared how ever for some overshoot since momentum gained by the spindle during acceleration may cause the reading to initially oscillate about the final equilib rium value A number of procedures can be employed to obtain a satisfactory reading In some cases as much as
104. tal Viscometers Rheometers Spindle Factors are listed as constants related to the Viscometers rotational speed Spindle Factors are traditionally used to convert the torque value on a Dial Reading Viscometer to a centipoise value Divide the given constant by the speed in use to obtain the Spindle Factor for that spindle speed combination This Spindle Factor is then multiplied by the Viscometer s dial reading to obtain viscosity in centipoise For example the Spindle Factor for a 1 LV spindle on an LV Viscometer is given as 72 N see the following Cylindrical Spindle Factors and Shear Rates Table The Viscometer s rotational speed RPM is represented by N If the measurement is being made at 10 RPM the Spindle Factor is 72 10 or 7 2 Multiply all Dial Viscometer readings made with this spindle speed combination by 7 2 to obtain viscosity in centipoise MORE SOLUTIONS TO STICKY PROBLEMS Page 33 Brookfield Engineering Labs Inc Cylindrical Spindle Factors and Shear Rates Shear Rate ek 1 LV 72 N 780 N 1560 N 6240 N 0 220N 2LV CYL 330 N 3350 N 6700 N 26 8M N 0 212N N RPM M 1000 Optional Item Factors are for readings made without using the guardleg Cylindrical Spindle Dimensions COLOCO 0 7418 18 84 2 563 65 1 3 188 80 97 2 LV CYL a 0 4037 10 25 2 624 66 65 3 LV CYL 0 2315 5 88 2 094 53 19 0 1250 3 2 0 536 13 61 0 1250 3 2 1 983 50 37 N A 5 LV 7 RV H Dimensions are in
105. tational speed RPM is represented by N If the measurement is being made at 12 RPM the Spindle Factor is 300 12 or 25 Multiply all Dial Viscometer read ings made with this spindle speed combination by 25 to obtain viscosity in centipoise 3 Where given Sample Chamber Diameter refers to inside diameter I D Spindle Diameters are outside diameters O D 4 All dimensions are given in inches and in millime ters in parentheses unless otherwise noted Be sure to use the metric values when required for rheological equations A 1 Dial Reading Viscometer Spindles and Speeds No of LVT Speeds rpm LVF ca ae ed ie ee acs Se ae ae ee 60 30 12 6 60 30 12 6 3 1 5 0 6 0 3 RVF RVF 100 100 50 20 10 RVT HAT HBT a i ae 100 50 20 10 5 4 2 5 2 1 0 5 This model is no longer available 20 10 4 2 Notes 1 Speed variations other than standard models listed above are identified by suffix in model designation RVT 200 fastest speed is 200 RPM All other speeds are in same proportion as standard models RVT 200 speeds are 200 100 40 20 10 5 2 1 RPM 2 RPM specifications apply to all Viscometers with same model designation LVT refers to LVT LVTD LVT CP LVTDCP etc each of these instruments has eight speeds as shown above for LVT model 3 Check with Brookfield or an authorized dealer regarding availability of non standard calibration spring torques and rotational speed
106. te the condition of these compo nents 1 The Viscometer should be mounted and lev eled with no spindle installed and the power switch in the off position for Dial Reading Viscometers Digital Viscometers should have the power on autozero performed and the motor off 2 Turn the spindle coupling to deflect the pointer or digital display upscale from its zero posi tion to a torque reading of 5 to 10 and let it swing back under its own power 3 Ifthe pointer swings freely and smoothly and returns to within 0 2 of zero each time this test is repeated the pivot point and jewel bearing are in good condition If it crawls back or sticks on the dial performance of the Viscometer will not be up to specification and it should be serviced On Digital Viscometers the digital display should fluctuate smoothly and return to within 0 2 of zero reading C We have never found a spring made of beryllium copper which showed any change in its characteristics due to fatigue even after hundreds of thousands of flexings For this reason a check of the calibrated spring is usually not necessary D Use of acalibrated viscosity standard is rec ommended as a final performance check Test the viscosity standard as you would any sample fluid carefully following any applicable instructions Brookfield Viscosity Standards calibrated to within 1 are ideal for this test The use of fluids other than viscosity standards is not recommended d
107. the rheological response For the moment assume this information is known and several possibilities have been identified The next step is to gather preliminary rheological data to determine what type of flow behavior is characteristic of the system under consideration At the most basic level this involves making measurements with whichever Brookfield Viscometer is available and drawing some conclusions based on the descriptions of flow behavior types in Chapter 4 Once the type of flow behavior has been identified more can be understood about the way components MORE SOLUTIONS TO STICKY PROBLEMS Page 2 of the system interact more information on what af fects the rheological property can be found in Section 4 7 The data thus obtained may then be fitted to one of the mathematical models which have been success fully used with Brookfield instruments Many of these models may be found in Chapter 5 Such mathematical models range from the very simple to the very complex Some of them merely involve the plotting of data on graph paper others re quire calculating the ratio of two numbers Some are quite sophisticated and require use of programmable calculators or computers This kind of analysis is the best way for getting the most from our data and often results in one of two constants which summarize the data and can be related to product or process perfor mance Once a correlation has been developed between rheological dat
108. tion can be much more expen sive than a standard controlled rate bench top viscom eter The results however are generally considered to be more accurate In addition the amount of sample required to make the measurements can be minimized with these types of spindle systems In all of the above cases the sample being tested experiences some handling prior to the start of the test Therefore there may be some adverse impact to the sample structure that could affect the test results Specifying the step by step procedure for handling of the sample is very important An alternative spindle geometry vane spindles are suitable for most fluids and are ideal for paste like materials gels fluids with suspended solids and a variety of so called soft solid materials puddings sauces Certainly salad dressings fall into this latter category The primary benefit of the vane spindle is that it imparts minimal disruption to the sample during spindle immersion The spindle can be operated in either controlled rate or controlled stress mode as explained above to determine yield value The measurement of yield stress deserves to be come a standard test method for quality control given the importance of assuring proper product behavior as illustrated in the examples at the beginning of this article To simplify the burden on QC one approach is to incorporate the QC test method for determining yield MORE SOLUTIONS TO STICKY PROBLEMS Pa
109. tted on log log paper Vis cometer reading versus speed This graph will usu ally be a straight line for power law fluids if the value for X1 was estimated accurately A curved line on this graph indicates that another estimate of X1 should be made Once a straight line is obtained the angle this line forms with the Y axis RPM is measured The power law index of this fluid can then be calculated from this equation POWER LAW INDEX 12 N tan Definitions Angle formed by plot line with Y axis of graph If 6 is less than 45 degrees the fluid is pseudo plastic greater than 45 degrees dilatant Brookfield Engineering Labs Inc The power law index can be used to calculate the effective shear rate at a given speed by using this equation SHEAR RATE 1 7 _N_ 13 eee Y 0 2095 N Power law index Viscometer speed RPM Definitions N Another method for determining yield value and plastic viscosity when a plot of Viscometer reading versus speed produces a curved line is to plot the square root of the shear stress versus the square root of the shear rate This often straightens the line and facilitates extrapolation to zero shear rate This method is most suitable for pseudoplastic flu ids with a yield value conforming to a model of flow behavior known as the Casson equation More in formation is available from Brookfield Engineering Laboratories in Technical Papers AR 77 and AR 79 5 4 Static Yield V
110. ue to the probability of unpredictable rheological be havior E If the Viscometer passes all of the preced ing tests its performance should be satisfactory Should accuracy or operation of the instrument still be suspect please refer to the troubleshooting chart in Section 3 5 3 4 10 Recalibrating the Brookfield Viscometer In many cases it is not practical to use a 600 mL low form Griffin beaker when making measurements Brookfield Engineering Labs Inc with a Brookfield Viscometer It may be desirable to use a different container if transferring the ma terial proves messy or time consuming Sometimes people also use the instrument without the guard leg to avoid the extra cleaning that would other wise be involved Either of these practices requires that a recalibration of the instrument be made if accurate results are to be obtained If measurements have been made under one set of conditions and you merely wish to establish a reference point with the same material under new conditions the following procedure will suffice 1 Measure the material in both the old and new container and or with the guard leg removed and in place Be sure that the same spindle and speed are used and that the tempera ture of the material remains the same 2 Note the new reading this is the new refer ence point corresponding to the original value This procedure may be used in establishing control methods to be followed when the Viscom
111. uid un der conditions of use Newtonian flow is defined by a proportional response in shear stress for a change in shear rate a linear relationship Non Newtonian fluids will exhibit a non linear stress rate relationship Newton s equation for viscosity has been modified many times to attempt to characterize non Newtonian behavior Some of the more widely used equations include Bingham Casson NCA CMA Casson and Power Law Bingham T To N Yy Casson VT Vi VY NCA CMA Casson lta VT 2VTo 1 a VNY Power Law t kY Herschel Bulkley T To k Y where T shear stress Y shear rate viscosity o yield stress consistency index flow index aspect ratio 9s FF as The chocolate industry utilitzes the NCA CMA ver sion of the Casson equation to evaluate chocolate prior MORE SOLUTIONS TO STICKY PROBLEMS Page 26 to final processing This equation closely approximates the plastic behavior of chocolate In addition experi ence shows that the slope term plastic viscosity indicates the chocolate s response to being moved in processing mixing pumping Also the y intercept yield stress or zero shear viscosity indicates the force required to start stop flowing molding enrobing Aparticular batch of chocolate can be modi fied to achieve the specific performance characteris tics required for the next processing step The oil drilling industry in the United States utilizes the po
112. ulting new ranges when the same spindle is operated at different speeds under the new conditions use this formula Ri S2 R2 S1 Where R1 is the range already established in Step 4 for RPM of S1 and S2 is the speed for which range R2 is to be deter mined The multiplying factor f for the new condi tions can be determined by this formula Ri 100 Where R1 is the range for the particular spindle and speed combination used as de termined in Step 4 To calculate viscosity for a Dial Reading Vis cometer therefore multiply the reading ob tained on the Viscometer s 0 100 scale by f O lt f 3 5 Viscometer Maintenance Brookfield Viscometers are highly reliable provided the instrument is handled properly Most problems are readily detected by the Calibration Check in Section 3 3 9 To prevent potential problems a few pointers are worth remembering A The forces to which the Viscometer responds are extremely small the optimum performance of the instrument depends on the elimination of all un necessary friction which may affect its sensitivity This means cleanliness Care must be taken to pre vent dust fumes liquids and other forms of con tamination from entering the Viscometer housing If it is necessary to use the instrument in such envi ronments use of the spindle extensions and or purge fittings is recommended to minimize the en try of contaminants More information on these ac cessories can be
113. under conditions of con stant shear some fluids will reach their final viscosity value in a few seconds while others may take up to several days Rheopectic fluids are rarely encountered Thixot ropy however is frequently observed in materials such as greases heavy printing inks and paints When subjected to varying rates of shear a thixo tropic fluid will react as illustrated in Figure 4 8 A plot of shear stress versus shear rate was made as the shear rate was increased to a certain value then im mediately decreased to the starting point Note that the up and down curves do not coincide This hys teresis loop is caused by the decrease in the fluid s viscosity with increasing time of shearing Such ef fects may or may not be reversible some thixotropic fluids if allowed to stand undisturbed for a while will regain their initial viscosity while others never will T n Y 5 Y Figure 4 8 The rheological behavior of a fluid can of course have a profound effect on viscosity measurement tech nique In Section 4 8 we will discuss some of these effects and ways of dealing with them Chapter 5 will present advanced mathematical techniques used in analyzing flow behavior under a wide variety of condi tions First however we will discuss the effects of MORE SOLUTIONS TO STICKY PROBLEMS Page 17 laminar and turbulent flow on viscosity measurement 4 6 Laminar and Turbulent Flow The very definition
114. vailable papers and an order form are provided in the booklet TECHNICAL PAPERS ON VISCOSITY MEASUREMENT AND CONTROL DATA LIST 091 C Page 54 Brookfield Engineering Labs Inc APPENDIX E Brookfield Locations United States Brookfield Engineering Laboratories Inc 11 Commerce Boulevard Middleboro MA 02346 Tel 508 946 6200 or 800 628 8139 Fax 508 946 6262 e mail sales brookfieldengineering com United Kingdom Brookfield Viscometers Limited 1 Whitehall Estate Flex Meadow Pinnacles West Harlow Essex CM19 5TJ England Tel 44 1279 451774 Fax 44 1279 451775 e mail sales brookfield co uk Germany Brookfield Engineering Labs Vertriebs GmbH Hauptstrasse 18 D 73547 Lorch Germany Tel 49 7172 927100 Fax 49 7172 927105 e mail info brookfield gmbh de MORE SOLUTIONS TO STICKY PROBLEMS Page 55 Brookfield Engineering Labs Inc ISO 9001 Certified 11 Commerce Blvd Middleboro MA 02346 T 508 946 6200 or 800 628 8139 USA or F 508 946 6262 Boston Chicago W www brookfie London Stuttgart Guangzhou
115. vor able to the objectives of the test must be provided see information on purge fittings in Section 2 14 Another factor which may affect viscosity mea surements is the homogeneity of the sample It is usually desirable to have a homogeneous sample so that more consistent results may be obtained Sometimes however tendency of a material to separate into non homogeneous layers is the char acteristic of most interest Care must be taken in such instances not to disturb that which you wish to study by mixing or shaking the sample 4 8 4 Time The time elapsed under conditions of shear ob viously affects thixotropic and rheopectic time de pendent materials But changes in the viscosity of many materials can occur over time even though the material is not being sheared Aging phenom ena must be considered when selecting and pre paring samples for viscosisty measurement Con sider also the fact that many materials will undergo changes in viscosity during the process of a chemi cal reaction so that a viscosity measurement made at one time in the reaction may differ significantly from one made at another time 4 8 5 Pressure Variations in pressure may cause dissolved gases to form bubbles entrained gases to change size as well as distribution and in some cases tur bulence Pressure is not experienced as often as other parameters Pressure compresses fluids and thus increases intermolecular resistance Liquids are compressi
116. wer law equation to evaluate the performance of drilling mud and fracturing fluid The latter is a ma terial forced into a non performing well to allow for ad ditional oil recovery The power law equation has been found to closely approximate its pseudoplastic behav ior In addition experience shows that the power term n flow index indicates the ability of the fluid to be moved down into the well The coefficient k consis tency index indicates low shear rate flow behavior of the mud once it is at the far reaches of the well A fracturing fluid can be modified in its storage vessel to obtain the appropriate flow characteristics prior to be ing pumped into the well In both cases described above the successful use of the math model will prevent the utilization of im proper fluid and ultimately poor performance or re jected material The math model should be utilized as a tool to better understand and interpret viscometer data The utilization of math models normally requires viscosity data collection under defined conditions of shear rate and shear stress Many spindle geometries are available for use with your Brookfield Viscometer Rheometer which will provide shear stress and shear rate data In addition Brookfield offers several soft ware packages and some instruments with the em bedded capability to analyze data sets using a variety of mathematical models Our brochure Technical Papers on Viscosity Measurement and Contro
117. y to cylindrical spindles only on any Brookfield Viscometer Rhe ometer SHEAR RATE 2 Re2 Rp2 an oe tu cf Nb 1 sec 1 Ree RA 1 SHEAR STRESS M 2 a 2 dynes cm2 t Dn Rp 2 VISCOSITY z poise n 3 y Definitions angular velocity of spindle rad sec EN N RPM Re radius of container cm Rp radius of spindle cm Xx radius at which shear rate is being calculated cm M torque input by instrument dyne cm L effective length of spindle cm see Appendix A 4 0 L gt Ro MR Note R should not exceed 2R for well defined shear rates Brookfield Engineering Labs Inc 5 2 2 Coaxial Cylinders Coaxial cylinder geometry is found in the UL Adapter Small Sample Adapter Thermosel System DIN Adapter Spiral Adapter PVS Rheometer and R S Rheometer SHEAR RATE 5 sec 1 y a o 4 i z R Rp SHEAR STRESS M 2 2 5 dynes cem2 Tt 2m Rol 5 VISCOSITY poise n ra 6 Definitions shear rate at surface of spindle sec 1 lt _ r gt See Section 5 2 1 for other definitions MORE SOLUTIONS TO STICKY PROBLEMS Page 22 5 2 3 Cone and Plate These equations may be used with all models of the Wells Brookfield Cone Plate Viscometer Rhe ometer CAP Viscometer Rheometer and R S CPS Rheometer SHEAR RATE i sec 1 You E sin 0 7

here - Labsys

Contents

Download Pdf Manuals

Related Search

Related Contents