Home

More Solutions 2003

1. BRODKFIELD 150 9001 2000 Certified MORE SOLUTIONS TO STICKY PROBLEMS Guide to Getting More From Your Brookfield Viscometer Making Rheological Measurements Equipment for Specific Situations How the Brookfield Viscometer Works Viscosity Measurement Techniques Newtonian and non Newtonian Fluids Temperature Dependence of Viscosity and much more MORE SOLUTIONS TO STICKY PROBLEMS TABLE OF CONTENTS INTRODUCTION nne nee nennen ennn eenenneeeeenn 1 CHAPTER aaa paetara trettende cadera diiandos 2 1 1 Why Make Rheological Measurements 2 1 2 Thinking Rheo Logically rrnnnnnvvvnnnnnnn 2 1 3 Three Schools of Thought on Viscosity Measurement nnnnssvvvnnnnnnnvvnnnnnnsvnnnnnnnnsnneenn 2 1 3 1 The Pragmatic School 2 1 3 2 The Theoretical School 2 1 3 3 The Academic School 3 CHAPTER 2 ociosa liado ici 3 2 1 Equipment for Specific Situations 3 2 2 Viscometers rnnnnnannnvennnnnnnvnennnnnnnvennnnnnnenenr 3 2 3 Rheometers nnrnnnnnnnnnvnnnnnnnnvnnnnnnnnnnnnnnnnnnneenr 3 2 4 Spindle Geometries nanne 4 2 4 1 Disc Spindles rrrnnnvnnnnnvvnnnnvnnnnnnvnnnn 4 2 4 2 Cylindrical Spindles annen 4 2 4 3 Coaxial Cylinders annen 4 2 4 4 Cone Plate Geometry nn 4 2 4 5 T Bar Spindles rrnnnvnnnnnvnnnnnvnnnnnnvnnnn 4 2 4 6 Vane Spindles naan anne enenn 4 2 5 Temperature Control naaar eneen 5 2 5 1 Temperature Baths 5 2 5 2 Thermosel System aa
2. CHAPTER 5 naaar seren iere venreesnetn ardea idad 20 5 1 Advanced Methods for Rheological Analysis 25e inssenenereznoneenevennonigsninnoezenn 20 5 2 Defining Operating Parameters of Various Spindle Geometries annae vann 21 5 2 1 Cylindrical Spindles 21 5 2 2 Coaxial Cylinders en 21 5 2 3 Cone and Plate annen annen 21 5 2 4 Disc and T Bar Spindles 21 5 2 5 Spiral Adapter Spindle 22 5 2 6 Paddle Paste Spindles 22 5 2 7 Vane Spindles rrsvvnnnnnvnnnnnvnnnnnenn 22 5 2 8 Other Special Spindles 22 5 3 Analyzing Time Independent Non Newtonian Fluids annen 22 5 3 1 Ratio Methods s erennnnnvvnnnnnnnnnnenn 22 5 3 2 Graphic Methods ene 22 5 3 3 Template Method 23 5 4 Static Yield Value Determination 24 5 5 Analyzing Time Dependent Non Newtonian Fluids annen ennn 24 5 6 Temperature Dependence of Viscosity 24 5 7 Math Models rrnnnnnnnvnnnnnnnnnvnnnnnnnnvnnnnnnnnnenn 26 5 8 Brookfield Application Software 26 CHAPTER 6 mrsa anda tecdvestecs 26 6 1 Single Point Viscosity Test 26 6 2 Controlled Rate Ramp anar anneer 26 6 3 Up Down Rate Ramp nnen annen 26 6 4 Time Sensitivity Test annen aaneen 26 6 5 Temperature Sensitivity Test 27 6 6 Temperature Profiling with Up Down Rate 27 6 7 Static Yield Test annen nen eneen 27 6 8 Dynamic Yield Test nnen ane eee 27 6 9 Recovery
3. rrssvennnnnnnvevnnnnnnnvennnnnnnvnnnnnnnnner 28 APPENDIX A Specifications Ranges and Operating Parameters eenn 29 A 1 Dial Reading Viscometer Spindles and A e 30 A 2 Digital Viscometers Rheometers Spindles and Speeds 31 A 3 Disc Spindles for Dial Reading Vis cometers and Digital Viscometers Rheometers aaneen 31 A 4 Cylindrical Spindles for Dial Reading Viscometer and Digital Viscometers Rheometers aaneen 32 A 5 Wells Brookfield Cone Plate Viscom eter Factors Dimensions and Shear Ra ESE raa at ianiai soeren iets 34 A 6 Small Sample Adapter 34 A 7 UL Adapter nanne nennen eenn 36 A 8 Thermosel System nanne 37 A 9 DIN Adapter Spindle Dimensions and Shear Rates nanne nnee 38 A 10 Helipath Stand Spindle Dimensions and Factors nnn en 39 A 11 Spiral Adapter Dimensions and Shear Rate nnen aaneen 40 A 12 Vane Spindle Dimensions and Ranges umnssvvvnnnnnnnvennnnnnnnnnnnnnnnnnneennr 40 A 13 KU 1 Krebs Viscometer Spindle DIMENSIONS nnee nennen 41 A 14 YR 1 Yield Rheometer Spindle Dimensions and Ranges 41 A 15 CAP 1000 Viscometer 42 A 16 R S Rheometer amp R S Soft Solids TEST 25 75 ce ences tenen id 42 A 17 CAP Viscometer Spindle Dimensions and Shear Rates 43 A 18 PVS Rheometer Stator Dimensions and Shear Rates 43 APPENDIX B Spindle Entry Codes and Range Coefficients citan tdi 45 APPENDIX C ASTM Specifications 48 APPENDIX D References nnn eneen
4. 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 plotted 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 tan6 Definitions 6 Angle formed by plot line with Y axis of graph If O is less than 45 degrees the fluid is pseudo plastic greater than 45 degrees dilatant The power law index can be used to calculate the effective shear rate at a given speed by using this equation Brookfield Engineering Labs Inc SHEAR RATE sec Y NE 1 3 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 t
5. obtained 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 11 Viscometer Possible Reading Viscosity Error Error 100 100 cP 1 cP 1 50 50 cP 1cP 2 10 10 cP 1cP 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 3 8 Obtaining a Viscometer Reading Before operating the Viscometer be sure that it 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
6. 42 88 078 1 98 1 625 41 28 A 14 YR 1 Yield Rheometer Spindle Dimensions and Ranges YR 1 Spindle Range Data YR 1 Spindle Dimensions Torque Shear Stress Range Range Pa dyne cm V 71 RV 5 5 5 50 V 73 RV 10 100 100 1000 2 708 in 6 878 cm 1 354 in 3 439 cm v HE 397400 1 706 in 4 333 cm 0 853 in 2 167 cm V 72 HB 160 1600 V 73 HB 800 8000 V 73 0 998 in 2 535 cm 0 499 in 1 267 cm V 71 5xHB 20 200 200 2000 V 72 5xHB 80 800 800 8000 V 73 5xHB 400 4000 4000 40000 Note 1 Pa 10 dyne cm MORE SOLUTIONS TO STICKY PROBLEMS Page 41 Brookfield Engineering Labs Inc A 15 CAP 1000 Viscometer Spindle Shear Sample Cone Viscosity Viscosity Viscosity Viscosity Viscosity p Rate Volume Radius 5 RPM Poise 50 RPM Poise 500 RPM Poise 750 RPM Poise 900 RPM Poise CAP 01 13 3N sec 67 ul E 1 511cm 37 5 375 3 75 37 5 0 375 3 75 0 25 2 5 0 2 2 0 CAP 02 13 3N sec 38 ul 1 200cm 75 750 7 5 75 0 75 7 5 0 5 5 0 41 4 1 1700 ul 3 0 2 399cm 0 42 4 2 0 35 3 5 CAP 08 2 0N sec 400 ul 3 02 1 511cm 250 2500 25 250 2 5 25 1 66 16 6 1 4 14 CAP 09 2 0N sec 100 ul 3 02 0 953cm 1000 10000 100 1000 10 100 6 67 66 7 5 5 55 CAP 10 5 0N sec 170 ul 1 22 1 511cm 100 1000 10 100 1 10 0 67 6 7 0 5 5 N2 R M A 16 R S Rheometer amp R S Soft Solids Tester Ertl Degrees mm mL Rate sec Stress Pa EE EE Fe ARAS en ren eee er rem 2
7. 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 Brookfield Engineering Labs Inc 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 value into a single purpose instrument such as the Brookfield YR 1 This type of instrument
8. The use of fluids other than viscosity standards is not recommended due 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 3 10 Recalibrating the Brookfield Viscometer In many cases it is not practical to use a 600 mL low form Griffin beaker when making measurements with a Brookfield Viscometer It may be desirable to use a different container if transferring the mate rial proves messy or time consuming Sometimes people also use the instrument without the guard leg to avoid the extra cleaning that would otherwise be involved Either of these practices requires that a recalibration of the instrument be made if accu rate 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 con trol method
9. of Speeds Speeds rpm 60 30 12 6 60 30 12 6 3 1 5 0 6 0 3 100 50 20 10 RVF 100 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 LVTDGP etc each of these instruments has eight speeds as shown above for LVT model 3 Check with factory regarding availability of non standard calibration spring torques and rotational speeds 4 RVT Dial Reading Viscometers with serial number 200000 and higher have 10 speeds 100 50 20 10 5 4 2 5 2 1 0 5 ST MORE SOLUTIONS TO STICKY PROBLEMS Page 30 Brookfield Engineering Labs Inc A 2 Digital Viscometers Rheometers Spindles and Speeds TE EEE RV HA HB DV 1 RV HAVHB DV ll DV Il meme 01 to 200 rpm 01 to 250 rpm ENGINE R 2 600 1 rom increments from 0 1 to 250 01 to 250 rom ADEN 2 600 1 rom increments from 0 1 to 250 A 3 Disc Spindles for Dial Reading Viscometers and Digital Viscometers Rheometers Disc Spindle Factors me mw me ev fm ENEN ro fr rave von an om NE KEE CO monn ann oon CO ann soon renn sen ao monn zoen roe om coun sm N RPM M 1000 MORE SOLUTIONS TO STICKY
10. PROBLEMS Page 31 Brookfield Engineering Labs Inc Disc Spindle Dimensions 2 LV COCO kin 2 2 2150 56 26 908 23 06 2 406 61 12 E 821 ERA EE 2 RV 1 8477 46 93 063 1 65 1 062 26 97 1 938 49 21 1 8550 47 12 063 1 65 1 062 26 97 1 938 49 21 2 2 3 3 3 063 1 65 1 062 26 97 1 938 49 21 3 063 1 65 1 062 26 97 1 938 49 21 5757 14 62 1 938 49 21 ons are In D A Dimensi inches mm Dimension is 4 on LV spindles 5 250 133 on RV H spindles Dimension B is 125 3 2 on all spindles TT U U A B j B H B A og E ees F A D Fy Hl Ik r gii E E U an U u tek c Fig 1 Fig 2 Fig 3 A 4 Cylindrical Spindles for Dial Reading Viscometer and Digital Viscometers Rheometers Cylindrical Spindle Factors and Shear Rates dek ba Shear Rate 1 LV 72 N 780 N 1560 N 6240 N 0 220N H2LV 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 32 Brookfield Engineering Labs Inc Cylindrical Spindle Dimensions for equations used in 5 2 1 see Cylindrical Spindle Equation Table on the following page OI o F 1 LV 1 0 7418 18 84 2 563 65 1 3 188 80 97 2 LV CYL 0 403
11. Spindle Speed When performing a test according to an existing specification or procedure use the spindle 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 reading between 10 and 100 remembering that accuracy improves as the reading approaches 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 select 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 10 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 mPass The minimum recommended range equals the Factor multiplied by 10 For example a 2 spindle on an LVT Viscometer at 12 RPM
12. 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 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 20 operating 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 under
13. ars uo Definitions Mx Viscometer reading at speed x M10x Viscometer reading at speed 10x other ratios may be used 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 along 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 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 Page 22 Brookfield Engineering Labs Inc 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
14. 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 sample cups of the Wells Brookfield Cone Plate Viscometer and the Thermosel System to provide a controlled at mosphere 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 l Group D hazardous locations The Digital Viscom eters and Rheometers are not available with explo sion proof construction El
15. calculate the resulting new ranges when the same spindle is operated at different speeds under the new conditions use this formula Ri _ 82 R S 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 con ditions can be determined by this formula R1 100 Where R1 is the range for the particular spindle and speed combination used as de termined in Step 4 To calculate viscosity therefore multiply the reading obtained on the Viscometer s 0 100 scale by f al a o a f 3 4 Viscometer Maintenance Brookfield Viscometers are highly reliable provided the instrument is handled properly Most problems are readily detected by the Calibration Check in Sec tion 3 3 9 To prevent potential problems a few point ers 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 unnecessary friction which may affect its sensitiv ity This means cleanliness Care must be taken to prevent dust fumes liquids and other forms of contamination from entering the Viscometer hous ing If itis necessary to use the instrument in such environments use of the spindle extensions and or purge fittings is recommended to minimize the entry of contaminants More information on these accessories can be found in Se
16. eenen 49 APPENDIX E Brookfield Locations 50 INTRODUCTION When a piece of technical equipment is marketed successfully for almost 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 in a 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 technical 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 betw
17. falling 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 Brookfield Engineering Labs Inc Typical range of shear rates S Application Sedimentation of fine powders in Medicines a suspending Paints liquid Levelling due to 5 A Paints printing y 107 10 A surface tension inks e Painting and pda under 107 10 coating toilet g y bleaches Chewing and i 3 TO 10 102 Dip coating Mixing and 401 102 Manufacturing stirring liquids Pipe flow 10 108 Pumping blood flow Spray dying Spraying and gaa AND i i atomization atomization Application of
18. ferent from the static yield stress value Brookfield Engineering Labs Inc 6 9 Recovery This parameter characterizes how 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 28 Brookfield Engineering Labs Inc APPENDIX A Specifications Ranges and Operating Parameters Appendix A is intended to provide the user of Brookfield Viscometers and accessories with all the information required to perform mathematical analy ses of viscosity data acquired with this equipment It includes essential dimensions range tables and constants organized by product in data sheet form The following Brookfield Viscometers Rheometers accessories and special purpose instruments and High End Rheometers are covered Standard Viscometers Rheometers A 1 Dial Reading Viscometer A 2 Digital Viscometers Rheometers A 3 Disc Spindles A 4 Cylindrical Spindles High End Rheometers A 18 R S Rheometer and R S Soft Solids Tester SST Wells Brookfield Cone Plate Viscometers Rheometers CAP 2000 Vi
19. 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 2 6 1 Small Sample Adapter Specifically designed to facilitate the measure ment of small samples the Small Sample Adapter is a jacketed coaxial cylinder accessory that is com patible with all Brookfield Viscometers with the ex ception of cone plate types Depending on the model selected the Small Sample Adapter utilizes MORE SOLUTIONS TO STICKY PROBLEMS Page 5 sample volumes of 2 0 to 16 0 ml Also depending on model the Small Sample Adapter will 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 permits connec tion to a circulating type bath for excellent tempera ture control up to a recommended maximum of 100 C 2 6 2 UL Adapter The UL Adapter is primarily intended to allow viscosity measurement
20. have an unusual problem along these lines corrosion resistant 316 series stainless steel and Teflon coated spindles are available Also spe cial spindle 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 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 3 3 Selecting a
21. remains stationary and senses torque B B B1 B2 A A E E D AA Cc C B1 B2 5 inches mm inches mm inches mm inches mm 93 E inches mm 3 B5 Shear Rate Cup Diameter inches mm Annulus inches mm 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 Brookfield Engineering Labs Inc PVS Rheometer Optional Geometry TA5 Triple Annulus Dimensions Intermediate Annulus 1 99 50 55 ID x 1 73 43 94 OD immer Annulus 1 45 06 80 1D x 1259 01 88 OD T MS y Shaded area depicts Stationary Stator Skirt and Cup MORE SOLUTIONS TO STICKY PROBLEMS Page 44 Brookfield Engineering Labs Inc APPENDIX B Spindle Entry Codes and Range Coefficients To calculate the upper limit of measuring range use Table A instead of A 3 Disc Spindle Factors ino oee veen PW versen a verson ein m af or ave A IET ICI IT IAS Re 06 93 750 1 000 000 2 000 000 8 000 000 375 000 4 000 000 8 000 000 32 000 000 HAB 06 93 750 1 000 000 2 000 000 8 000 000 375 000 4 000 000 8 000 000 32 000 000 ao os es7s0 000 000 2000000 8000000 6 000 64 000 128 000 512 000 30 000 320 000 640 000 2 560 000 120 000 1 280 000 2 560 000 10 240 000 600 000 6 400 000 12 800 000 51 200 000
22. to create the UP RAMP Upon reaching the maximum rotational speed or shear rate reverse direction and return to the start ing speed or shear rate This creates the DOWN RAMP Record viscosity and torque data at each speed 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 26 Brookfield Engineering Labs Inc Y 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 temperature and a maximum tem perature Record viscosity values at defined time intervals while the temperature ramps up arma TEMPERATURE Figure 6 4 Most materials exhibit decreasing viscosity behav ior with increasing temperature 6 Temperature Profiling with Up Dow
23. 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 I 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 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 requ
24. 1 200 000 12 800 000 25 600 000 102 400 000 MORE SOLUTIONS TO STICKY PROBLEMS Page 45 Brookfield Engineering Labs Inc METE ULA DIN 81 36 500 73 000 292 000 36 500 73 000 292 000 di 420 ULA DIN 82 420 144 420 nm 6 ULA DIN 85 1 144 12 200 24 400 97 600 ULA DIN 86 36 500 73 000 292 000 ULA DIN 87 11 340 121 300 242 600 970 400 SC4 14 6R 117 200 1 250 000 2 500 000 10 000 000 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 21 4 688 50 000 100 000 400 000 SC4 25 13R 25 480 000 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 SC4 37 23 440 250 000 500 000 2 000 000 ee el eol eso IA ES 400 HEM BE MORE SOLUTIONS TO STICKY PROBLEMS Page 46 Brookfield Engineering Labs Inc Absolute Systems Shear Rate Calculation Example Cone Spindle CP 40 at 10 rpm has a shear rate of 10 x 7 5 75 s 8 8 8 8 8 1 1 1 1 2 2 2 2 2 3 3 4 4 4 UL Adapter ULA Thermosel ULA DIN 81 HT 2 DIN Adapter Set ULA DIN 85 ULA DIN 86 ULA DIN 87 M EA 8 E MEE Small Sample Adapter FE ULA DIN 82 13R KA ULA DIN 83 7R 83 SC4 14 6R Ooo SC
25. 4 15 7R HE lle ES SC4 18 13R HO SC4 21 13R 2t SC4 25 13R BEJE SC4 27 13R ER SC4 28 13R EEJ SC4 29 13R R SC4 31 13R a SC4 34 13R 84 BE ia 42 Cone Plate System CP 40 CP 41 CP 42 CAP1000 2000 01 10 167 26667 0 067 0 134 1 5 7 2 3 4 5 SC4 16 8R 6 8 1 5 7 8 9 1 4 0 1 2 MORE SOLUTIONS TO STICKY PROBLEMS Page 47 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 81 C 1276 94 D 115 85 D 562 81 D 789 91 D 1076 88 D 1084 88 D 1417 90 D 1439 83a D 1824 90 D 2196 86 D 2364 85 D 2393 86 D 2556 80 D 2669 87 Practices for Measuring Viscosity of Glass Above the Softening Point 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 Testin
26. 4 Brookfield Engineering Labs Inc flowing or slow flowing fluids including yield values Three 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 operation ator below ambienttemperature 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
27. 4_ 5 Rubbing TO creams and lotions to the skin Milling pigments 103 105 Paints printing in fluid bases inks High speed 5_ 4n6 10 107 Gasoline engines 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 favor 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 19 usually desirable to have a homogeneous sample so that more consistent results m
28. 500 N 1000 N 4000 N 0 93N SC4 21 13R MORE SOLUTIONS TO STICKY PROBLEMS Page 34 Brookfield Engineering Labs Inc SC4 Series Spindle Dimensions 0 340 8 64 0 344 8 74 SC4 15 0 376 9 55 0 674 17 12 SC4 16 0 275 6 99 0 815 20 70 SC4 18 0 688 17 48 0 660 16 77 SC4 21 SC4 25 0 188 4 78 0 520 13 21 0 463 11 76 SIDE LENGTH SC4 27 80427 1 300 33 02 SC4 28 0 370 9 39 0 300 7 62 1 260 32 00 SC4 29 1 070 27 18 N SC4 31 0 463 11 76 0 990 25 15 SC4 34 0 370 9 39 Heter to Section OG a 0 954 24 23 DIAMETER SC4 Series Sample Chamber Dimensions SC4 6R RP 0 500 12 70 1 110 28 19 SC4 7R RP 0 501 12 73 1 745 44 32 SC4 8R RP 0 515 13 08 1 584 40 23 SC4 13R RP 0 750 19 05 2 550 64 77 Dimensions are in inches mm MORE SOLUTIONS TO STICKY PROBLEMS Page 35 a Diameter Side Length Effective Length inches mm inches mm inches mm 0 478 12 14 0 821 20 85 0 989 25 12 1 399 35 53 1 384 35 15 0 697 17 70 1 547 39 29 1 480 37 59 1 250 31 75 1 208 30 68 1 156 29 36 Brookfield Engineering Labs Inc N RPM M 1000 A 7 UL Adapter UL Adapter Spindle Factors and Shear Rates LV RV Shear Rate sec L G4N 128 N 512 N 1 224N DIN UL 11 44N 122 N 244N 976 N 1 29N N RPM Sample size 16 0 mL end cap on UL Adapter Dimensi
29. 7 10 25 2 124 53 95 2 624 66 65 3 LV CYL 0 2315 5 88 1 688 42 86 2 094 53 19 5 LV 0 1250 3 2 0 596 15 14 N A 7 RV H 0 1250 3 2 1 983 50 37 N A 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 4 LV 0 1250 3 2 1 221 31 01 N A i B rT ele B mn A e A D 1 i D 11 1 c hu Hc kc Fig 1 Fig 2 Fig 3 The following cylindrical spindle table depicts information for use with the equations presented in 5 2 1 only Cylindrical Spindle Equation Radius cm Effective Actual Length cm Length cm 1 LV 0 9421 7 493 6 510 2 LV CYL 0 5128 6 121 5 395 Effective length includes correction for end effect and should be used in equations MORE SOLUTIONS TO STICKY PROBLEMS Page 33 Brookfield Engineering Labs Inc A 5 Wells Brookfield Cone Plate Viscometer Factors Dimensions and Shear Rates Cone Spindle Dimensions and Shear Rates gt mous N RPM Cone Spindle Factors N RPM A 6 Small Sample Adapter SC4 Series Spindle Factors and Shear Rates Spindle Sample Shear Rate Chamber same oe ome e ee SC4 14 6R 1172 N 12 5M N SC4 18 13R MESA EEN 30 N 320 N 640 N 2560 N 1 32N 46 88 N
30. Pa s 10 rpm inches cm inches cm V 71 RV 5 5 5 50 262 2620 V 72 RV 2 20 20 200 1110 11100 2 708 6 878 1 354 3 439 V 73 RV 10 100 100 1000 5350 53500 1 706 4 333 853 2 167 V 74 RV 100 1000 1000 10000 53500 535000 998 2 535 499 1 267 V 71 HA 1 10 10 100 524 5240 463 1 176 232 589 V 72 HA 4 40 40 400 2220 22200 V 73 HA 20 200 200 2000 10700 107000 Note Sample container diameter should be twice 2x the vane diameter V 74 HA 200 2000 2000 20000 107000 1070000 when possible Sample container depth should provide clearance V 71 HB 4 40 40 400 2096 20960 at the bottom equivalent to vane spindle diameter when possible V 72 HB 16 160 160 1600 8880 88800 V 73 HB 80 800 800 8000 42800 428000 V 74 HB 800 8000 8000 80000 428000 4280000 V 71 5xHB 20 200 200 2000 10480 104800 V 72 5xHB 80 800 800 8000 44400 444000 V 73 5xHB 400 4000 4000 40000 214000 2140000 V 74 5xHB 4000 40000 40000 400000 2140000 21400000 Notes 1 1 Pa 10 dyne cm 2 1cP 1mPars 3 Possibility of turbulence at speeds above 10 rpm may give artificially higher viscosity readings MORE SOLUTIONS TO STICKY PROBLEMS Page 40 Brookfield Engineering Labs Inc A 13 KU 1 Krebs Viscometer Spindle Dimensions Standard Krebs Spindle Paste Spindle for use with KU 1 KU1 10 Viscometer KU1 75Y B B A A D E E D C C KU1 10 3 562 90 47 188 4 77 2 125 53 98 312 7 92 1 625 41 28 KU1 75Y 3 562 90 47 188 4 77 1 688
31. ally 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 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 ve
32. any 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 50 Brookfield Engineering Labs Inc
33. ar 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 Control 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 Brookfield Engineering Labs Inc 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 Software Instrument Required RHEOCALC DV 11l Rheometer WINGATHER DV Il Viscometer CAPCALC CAP series Viscometers RHEOVISION PVS Rheometer RHEO 2000 R S Rheometer 5 9 Miscellaneous Methods There are many other techniques available for ana lyzing the rheological behavior of fluids under a vari ety of conditions Space doesn t permit a detailed dis cussion here but more information can be obtained from Brookfield Engineering Laboratories on these and other advanced methods Approximation of shear rate and shear stress values using disc type spindles AR 82 6 Techniques for determination of extremely low shear viscosity and leveling behavior of coating ma
34. ard Test Method for High Shear Viscosity Using the ICI Cone Plate Viscometer Test Method for Effect of Mold Contamination on Permanence of Adhesive Preparations and Adhesive Films 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 Standard Test Method for Low Temperature Low Shear Rate Viscosity Temperature Dependence of Lubricating Oils Using a Temperature Scanning Technique Brookfield Engineering Labs 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 John 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 VISCOMETRIC FLOWS OF NON NEWTONIAN FLUIDS Colemen Markovitz Noll Springer Ver
35. as 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 A more repeatable procedure is to specify a defi nite number of spindle revolutions to be counted before taking a reading Since the time required for a certain 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 multiply it by the Factor for the spindle speed combination you are using The Factor will be found on the Factor Finder supplied with the Viscometer Calculating Digital Viscometers does not require the use of a factor These viscometers will display viscosity in units of cP directly provided the spindle number has be
36. as 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 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 It is avail able on the Wells Brookfield Cone Plate Viscom eters CAP 2000 Rheometer and R S Rheometer 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 T bar spindle prevents the calculation of shear rate or shear stress See Section 2 12 1 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 Page
37. 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 operating tempera ture of 200 C For more information see Section 2 4 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 strumen
38. ay 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 compressible 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 ume of particles where there is insufficient liqui
39. ayer 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 materials 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 substantial increase in viscosity above a certain shear rate The material s flow behavior may be Newt
40. 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 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 data 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 basic
41. bubble orientation of the instrument If you are continuing to experience problems with your viscometer follow this diagnosis section to help isolate the potential problem Perform an Oscillation Check 4 Remove the spindle and turn the motor OFF 4 Gently push up on the viscometer coupling 14 Turn the coupling until the red pointer reaches 15 20 on the Dial Viscometer or the torque readings reach 15 20 on the Digital Viscometer 3 Gently let go of the coupling 1 Watch the pointer swing freely and finally rest on zero on the Dial Viscometer or the torque reading returns to zero on the Digital Viscometer If the pointer sticks or the torque reading does not return to zero the unit is in need of service Perform a Calibration Check 4 Verify spindle speed and model selection 4 Verify test parameters temperature container volume method 4 Perform a calibration check in accordance with the procedures from the viscometer operat ing manual 6 Verify tolerances are calculated correctly 6 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 follow the procedures outlined in the viscometer operating manual 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 embracing elasticity viscosity and plasticity We con c
42. 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 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 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 obviou
43. ccasionally 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 Brookfield Engineering Labs Inc 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 This combination causes the sample to be continu ally pumped up through the Spiral Adapter The material reaches a steady state of flow during which viscosity is measured The approximate shear rate in reciprocal seconds is 667N 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 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 s
44. cial 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 Page 7 Brookfield Engineering Labs Inc 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 consistency measure ments to be made A set of six T bar spindles and a 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 sensit
45. ction 2 1 14 B Never place the instrument upside down with a fluid coated spindle attached MORE SOLUTIONS TO STICKY PROBLEMS Page 13 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 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
46. d 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 affectthe 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 Brookfield Engineering Labs Inc example the addition of solvent to printing ink re duces viscosity of the ink 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 aff
47. des detailed data on material behavior in cluding 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 this need Many are listed in this section 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 Please inquire about special spindle materials and configurations for unusual ap plications 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
48. e 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 instrumentation can be much more expen sive than a standard controlled rate bench top viscom eter
49. e 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 Il 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 There are many variations of the standard Viscom eter models available such as intermediate spring torques Please consult Brookfield Engineering Labo ratories or your dealer with your special requirements Several specialized viscometers are available which have been designed to satisfy particular industry needs These instruments are unique and do no
50. easing viscosity with an increasing shear rate as shown in Figure 4 3 Y 5 Y Figure 4 3 Probably the most common of the non Newtonian fluids pseudo plastics include paints emulsions and dispersions of many types This type of flow behavior is sometimes called shear thinning An easily understanding model is to imagine that in the moment of turning the spindle in the sample the structure of molecules of the sample will be destroyed and the molecule formation will be orientated more parallel to the spindle surface So Brookfield Engineering Labs Inc the hindering of the spindle rotation will 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 DILATANT Increasing viscosity with an increase in shear rate characterizes the dilatant fluid see Fig ure 4 4 Y 5 y Figure 4 4 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 examp
51. ected 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 Ifthe 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 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 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 dependen
52. ectrically 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 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 Page 8 Brookfield Engineering Labs Inc CHAPTER 3 3 1 Why You Should Read This Chapter The purpose of this chapter is to provide the Vis cometer user with information 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
53. een 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 6 by offering practical advice on the use and maintenance of the Brookfield Viscometer based on our experience and that of our customers 6 by suggesting ways in which specific pieces of hardware may be used to solve viscosity measurement problems 6 by explaining the basic principles of rheology and their relation to measurements made with Brookfield equipment 6 by discussing factors that affect rheological behavior and how these may be controlled 6 by outlining advanced mathematical procedures for detailed analysis of viscosity data 6 by consolidating a
54. eld or one of its dealers for this service 3 5 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 4 Make sure the viscometer is plugged in 4 Check the voltage rating on your viscometer 115V 220V it must match the wall voltage 4 Make sure the power switch is in the ON posi tion 4 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 4 Check the straightness of all other spindles replace them if bent U 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 1 Inspect threads for wear if the threads are worn the unit needs service Brookfield Engineering Labs Inc 1 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 4 Check to see if the viscometer coupling is bent if so the unit is in need of service 4 Check the correct
55. em fam por 1 m fam mme 2 am rd EM em 1 pf 1 eos fe fee me eenn fm ee EN eos fa fo ee ve oe f e focos omme fam o Sonae mr EST mm mm Stress Pa we pf 1 4 von m aa oa vo o o poo vos mf s fam i MORE SOLUTIONS TO STICKY PROBLEMS Page 42 Brookfield Engineering Labs Inc A 17 CAP Viscometer Spindle Dimensions and Shear Rates Spindle No A B Diameter C Angle D Diameter E Shear Rate CAP S 01 2 075 52 71 187 4 75 0 27 1 190 30 23 010 0 25 13 3N CAP S 02 2 075 52 71 187 4 75 02 27 945 24 0 010 0 25 13 3N CAP S 03 2 075 52 71 187 4 75 750 19 05 010 0 25 13 3N CAP S 04 2 075 52 71 187 4 75 945 24 0 010 0 25 3 3N CAP S 05 2 075 52 71 187 4 75 750 19 05 010 0 25 3 3N CAP S 06 2 075 52 71 187 4 75 553 14 05 010 0 25 CAP S 07 2 075 52 71 187 4 75 1 889 47 98 010 0 25 CAP S 08 2 075 52 71 187 4 75 1 190 30 23 010 0 25 CAP S 09 2 075 52 71 187 4 75 750 19 05 010 0 25 CAP S 10 2 075 52 71 187 4 75 19 12 1 190 30 23 010 0 25 5 0N A 18 PVS Rheometer Stator Dimensions and Shear Rates Stator might also be called bob or spindle On the PVS Rheometer the cup also called chamber rotates while the stator
56. en entered refer to the instruction manual of your viscometer Brookfield Engineering Labs Inc Pay attention on interpretation of results when you use rotation speeds where turbulence of the samples exist 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 3 9 A Calibration Check People are often concerned about the accuracy of their Viscometer Here are some tests of its me 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
57. ent inside the housing to which the nameplate is attached The Vis cometer 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 rela tion to the dial In Digital models the relative angular MORE SOLUTIONS TO STICKY PROBLEMS Page 9 position of the pivot shaft is detected by an RVDT ro tary variable displacement transducer and is read out on a digital display 4 HOUSING SYNCHRONOUS ST s MOTOR GEAR TRAIN CLUTCH TE I 3 a de POINTER DIAL ER AG PIVOT SHAFT I CALIBRATED up SPIRAL SPRING PIVOT CUP JEWELLED Lj BEARING GUARDLEG av 1 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
58. ent 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 F o pA A lax where n is a constant for a given material and is called its viscosity iy 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 I in subsequent discussions Its unit of measure is called the reciprocal second sec Brookfield Engineering Labs Inc 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 n viscosity Y oare 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 Pass or milli Pascal second
59. ern 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 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 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 14 Vis A 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 are separated by a distance dx and are moving in the same direction at differ
60. ersus speed using a single spindle Starting at a 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 reading 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 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 24 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 interva
61. es 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 power 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 she
62. 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 the 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 Figures 3 1 fora schematic view of the major components of a basic dial reading Vis cometer The stepper drive motor which replaced the syn chronous motor and multiple speed transmission in 2000 is located at the top of the instrum
63. fortunately 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 1 y 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 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 Newtonian fluids you may encounter include PSEUDOPLASTIC This type of fluid will display a decr
64. g 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 MORE SOLUTIONS TO STICKY PROBLEMS D 2983 87 D 2994 77 D 3232 88 D 3236 88 D 3468 90 D 3716 83 D 3791 90 D 4016 81 D 4287 94 D 4300 83 D 4402 87 D 4889 93 D 5018 89 D 5133 90 Page 48 With Additives Hot Melts Test Method for Low Temperature Viscosity of Automotive Fluid Lubricants Measured by the Brookfield Viscometer Methods of Testing Rubberized Tar Method for Measurement of Consistency of Lubricating Greases at High Temperatures Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials 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 Stand
65. 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 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 In all other respects their operating param eters 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 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 h
66. geometries it is best to plot speed on the Y axis and to make all measurements with the same spindle An assumption that can be made with re gard to shear rate is that for a given spindle the shear rate is proportional to the speed Therefore 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 involves 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 conditio
67. has a Factor of 25 The maximum range of this combination is 25 times 100 or 2500 cP The minimum recommended viscosity 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 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 3 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
68. he 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 Value Determination Newer instruments from Brookfield such as the R S Rheometer and YR 1 Rheometer physically measure the start of flow at zero shear rate These readings measured in Pascale Pa dynes cm or Newton m will probably differ from values obtained using dynamic methods see preceding section 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 v
69. ing the spindle and speed in use see A 3 A 4 For digital mod els push the autorange button Page 29 Brookfield Engineering Labs Inc A note about the terms appearing in this Appendix Shear rate constants where given are simply multiplied by the Viscometer s rotational speed in RPM to obtain the shear rate in reciprocal seconds for that speed The constants are independent of Viscometer model sample viscosity or temperature Spindle factors are listed as constants related to the Viscometers rotational speed Divide the constant by the speed in use to obtain the Factor for that spindle speed Viscometer model combination This Factor is then multiplied by the Viscometer s dial or display reading to obtain viscosity in centipoise For example the Factor for a 42 LV spindle on an LV Viscometer is given as 300 N Section A 1 4 The Viscometer s rotational 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 Viscometer readings made with this spindle speed combination by 25 to obtain viscosity in centipoise Where given Sample Chamber Diameter refers to inside diameter 1 D Spindle Diameters are outside diameters O D All dimensions are given in inches and in millimeters 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 Spindles No
70. ires more power to pump than a low viscosity one Knowing its 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 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
71. is used for all subsequent tests there will be no correlation prob lem 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 3 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 using 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 Brookfield Engineering Labs Inc 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 Referto Section 2 5 for information on recommended baths High temperature work up to 300 C may re quire use ofthe 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 to the tes
72. ive 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 2 13 1 Quick Connect The Brookfield Quick Connect accessory 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 is used with LV RV HA HA disk 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 MORE SOLUTIONS TO STICKY PROBLEMS 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
73. lag New York Inc New York NY MORE SOLUTIONS TO STICKY PROBLEMS 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 available papers and an order form are provided in the booklet TECHNICAL PAPERS ON VISCOSITY MEASUREMENT AND CONTROL DATA LIST 091 C Page 49 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 Germ
74. le 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 exceeded and flow begins plastic fluids may dis play Newtonian pseudoplastic or dilatant flow char acteristics See Figure 4 5 Y n PA lt gt Y A B Y Figure 4 5 So far we have only discussed the effect of shear 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 16 non Newtonian flow thixotropic and rheopectic 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 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 n Figure 4 6 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 3 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 under conditions of con stant shear some fluids will reach their final viscosi
75. ls This usually produces a straight line Then apply the following equation THIXOTROPY BREAKDOWN COEFFICIENT S Tb In St F ty 14 7 Definitions St Viscometer reading at t minutes St Viscometer reading at t minutes F Factor for spindle speed combination 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 y MEMES Ne where B 5 In A n e T Definitions T Temperature at which viscosity n was measured Temperature at which vi
76. lso apply to SC4 BS spindles HT 2 Sample Chamber Dimensions also applies to disposable chamber HT 2DB amar ben 0 750 19 05 2 550 64 77 MORE SOLUTIONS TO STICKY PROBLEMS Page 37 Brookfield Engineering Labs Inc A 9 DIN Adapter Spindle Dimensions and Shear Rates MORE SOLUTIONS TO STICKY PROBLEMS Page 38 Brookfield Engineering Labs Inc A 10 Helipath Stand Spindle Dimensions and Factors Travel Speed for Helipath drive motor which moves rotating spindle downward into sample 7 8 inch 22 2 mm per minute T Bar Spindle Factors EEK SEKSE aye N RPM M 1000 Maximum recommended speed 10 12 RPM v CROSSBAR LENGTH T Bar Spindle Dimensions Spindle Crossbar Length 1 894 48 1 1 435 36 4 0 604 15 3 0 403 10 9 Dimensions are in inches mm MORE SOLUTIONS TO STICKY PROBLEMS Page 39 Brookfield Engineering Labs Inc A 11 Spiral Adapter Dimensions and Shear Rate Shear Rate is 667N where N is rotational speed in RPM Spiral Spindle Dimensions Spiral Chamber Dimensions i J LA pS 825 500 L 250 DIA 275 DIA Spindle Diameter Length Length A 12 Vane Spindle Dimensions and Ranges Vane Spindle Range Data Vane Spindle Dimensions Spindle Torque Shear Stress Range Viscosity Range cP Vane Length Vane Diameter Range Pa dyne cm m
77. 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 MORE SOLUTIONS TO STICKY PROBLEMS interchangeable model for model in most viscosity specifications requiring Brookfield Viscometers The dial reading type is the least expensive Brookfield Viscometer and is suitabl
78. n trolled stress or controlled torque instrument rather than acontrolled 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 Plate 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 using it with different gaps like 3 mm and so on R S Soft Solids Tester A special version of the R S Rheometer is the SST which offers special application solutions e g the creep test is a very good possibility for charac terizing samples which should not be sheared be fore measuring or which have a lumpy structure like pastes The R S Soft Solids Tester combines vane ge ometry with low shear and stress providing vis coelastic characterization of soft solid materials such as pastes gels waxes and slurries 2 12 Non Flowing Sample Materials Non flowing or slow flowing sample materials such as pastes creams and gels present spe
79. n 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 RPM or Y 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 27 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 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
80. n eneen 8 CHAPTER 3 seder eden ete van zunne etende aeara aiant 9 3 1 Why You Should Read This Chapter 9 3 2 How the Brookfield Viscometer Works 9 3 3 Viscosity Measurement Techniques 9 3 3 1 Record Keeping annen 9 3 3 2 The Spindle and the Guardleg 10 3 3 3 Selecting a Spindle Speed 10 3 3 4 Sample Container Size 10 3 3 5 Sample Conditions 10 3 3 6 Spindle Immersion aanne 11 3 3 7 Sensitivity and Accuracy 11 3 3 8 Obtaining a Viscometer Reading 11 3 3 9 A Calibration Check 12 3 3 10 Recalibrating the Brookfield Viscometer nannnvnnnnnnnnvnnnnnnnnnvnnnnnnnneer 12 3 4 Viscometer Maintenance 13 3 5 Viscometer Troubleshooting 13 CHAPTER EE 14 4 1 Coming to Grips with Rheology 14 4 2 Viscosity rnnnnnvnnnnnnnnvnnnnnnnnnvnnnnnnnnenennnnnnnenn 14 4 3 Newtonian FluidS aaneen 15 4 4 Non Newtonian Fluids annen 15 4 5 Thixotropy and Rheopexy nnn 16 4 6 Laminar and Turbulent Flow 17 4 7 Yield Behavior nnen nen 17 4 8 What Affects the Rheological Property 18 4 8 1 Temperature rnnrssnvnnnnnnnnnnnnnnnnnnennnn 18 4 8 2 Shear Rate nnn nana nanne nennen 18 4 8 3 Measuring Conditions 19 4 8 4 TIME iest tica 19 4 8 5 PreSSure annen nanannenen ennn eee enn 19 4 8 6 Previous History eee 19 4 8 7 Composition and Additives 19 4 8 8 Special Characteristics of Dispersions and Emulsions 20
81. nne 5 2 5 3 Peltier Thermo electric Systems 5 2 6 Small Sample Volume nan aren 5 2 6 1 Small Sample Adapter 5 2 6 2 UL Adapter annen ennen eenen 5 2 6 3 DIN Adapter annae eenen eenn 5 2 6 4 Thermosel System aanne 5 2 6 5 Cone Plate Systems nnee 5 2 7 Low Viscosity enen enne neneenn 5 2 7 1 UL Adapter annen eneen 5 2 7 2 Small Sample Adapter 6 2 7 3 Thermosel System aaneen 6 2 7 4 Wells Brookfield Cone Plate Viscometer annen nennen neen ennen nenenenn 6 2 8 High Temperature nanne nennen enn 6 2 8 1 Thermosel System aaneen 6 2 8 2 Temperature Baths 6 2 8 3 Cone Plate with Embedded Heating 6 2 9 Defined Shear Rate nnn anne nnen 6 2 10 High Shear Rate nnn aaneen 6 2 10 1 Wells Brookfield Cone Plate Viscometer Rheometer 7 2 10 2 CAP Viscometer Rheometer 7 2 10 3 R S Rheometer nn enen 7 2 10 4 PVS Rheometer srnnnnvvnnnnnvnnnnnvenn 7 2 11 Defined Shear Stress annen 7 2 12 Non Flowing Sample Materials 7 2 12 1 Helipath Stand ann nemen 8 2 12 2 Spiral Adapter naan annen 8 2 12 3 Vane Spindles nnn aaan eeeenn 8 2 13 Special Accessory Items 8 2 13 1 Quick Connect naaar renee 8 2 13 2 Spindle Extensions nnee 8 2 14 Fumes and Hazardous Locations 8 2 14 1 Purge Fittings nanne neen 8 2 14 2 Explosion Proof Construction 8 2 15 Process Control a
82. ns A complete 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 measuring 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 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 23 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 Wa 11 yield value dynes cm2 Viscometer reading amp 0 RPM constant from table below Definitions y x1 fa Model Cylindrical SS SS gt Spindle LV RV HA HB 1 0 16 1 72 3 44 13 78 2 0 67 7 11 14 21 56 85 3 2 56 27 30 54 60 218 39 4 12 48 133 14 266 28 1065 14 5 25 26 269 45 538 91 2155 63
83. of the Viscometer The following Oscillation Test will allow you to evaluate 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 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 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 a 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 12 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
84. of spindle The CAP 2000 is a variable speed instrument and has variable shear rate capability over the speed range from 50 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 1000 meets industry test standards BS3900 ISO 2884 and ASTM D 4287 2 10 3 R S Rheometer R S Rheometer can generate shear rates up to 4 100 sec in narrow gap coaxial cylinder geometry and up to 4 800 sec in cone plate Maximum in strument speed is 800 RPM MORE SOLUTIONS TO STICKY PROBLEMS 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 2 11 Defined Shear Stress R S Series Rheometer The Brookfield R S Rheometer differs from the standard Brookfield viscometers in that it is a co
85. onian or non Newtonian below this point Due to the relatively low shear rates at which most MORE SOLUTIONS TO STICKY PROBLEMS Page 17 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 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 values at each speed We call this a con trolled rate method Using a best fit lin
86. ons Al I i 3 5725 90 74 3 6366 92 37 SIDE LENGTH EFFECTIVE LENGTH Spindle Effective Actual Length Diameter mr Length 3 6366 92 39 3 5725 90 74 0 9902 25 15 1 0875 27 62 Y lz 0 9902 25 15 SPINDLE O D 1 0875 27 62 CHAMBER 1 D ET Dimensions are in inches mm Effective length includes correction for end effect and should be used in shear rate shear stress equations Actual length is given for reference only Digital calculating instruments DV E DV l DV Il and DV Ill have correction factor built in no additional calculations are required MORE SOLUTIONS TO STICKY PROBLEMS Page 36 Brookfield Engineering Labs Inc A 8 Thermosel System SC4 Series Spindle Dimensions Factors and Shear Rates N RPM M 41000 The above values also apply to SC4 BS series spindles SC4 Series Spindle Dimensions sorte menn ices ches om inches mm inches mm inches mm A 0 688 17 48 1 249 31 72 1 399 35 53 i 2 0 660 16 76 1 230 31 24 1 384 35 15 0 463 11 76 1 300 33 02 1 547 39 29 SIDE LENGTH 0 370 9 39 1 260 32 00 1 480 37 59 SC4 29 0 300 7 62 1 070 27 18 1 250 31 75 NA 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 DIAMETER Refer to Section 5 2 1 Dimensions are in inches mm Dimensions a
87. ontrol 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 standard 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 at 750 RPM on 50 Hz and 900 RPM on 60 Hz gener ating shear rates at 12 000 or 3 000 sec at 60 Hz and 10 000 or 2 500 sec at 50 Hz depending on choice
88. ry ex pensive piece of rheological equipment Page 2 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 accessories 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
89. s mPass these are units of the In ternational System and are sometimes used in prefer ence to the metric 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 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 5 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 15 sure just grab your Viscometer and go to it They are not un
90. s 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 18 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 When a material is to be subjected to a variety of shear rates in processing 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 due to these values
91. s 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 The 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 2 6 5 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 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 de
92. s to be followed when the Viscometer is to be used for quality control purposes and the op erator is not concerned with the actual centipoise 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 2 Brookfield Engineering Labs Inc 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 fre X Where R1 is the full scale range of mea surement under the new conditions n is the viscosity of the Standard as measured in step 1 and x is the dial or display read ing obtained in step 3 To
93. scometer PVS Rheometer A 5 A 19 A 20 Accessories for Standard Viscometer Rheometers A 8 Thermosel System A 6 Small Sample Adapter A 7 UL Adapter A 9 DIN Adapter A 10 Helipath Stand A 11 Spiral Adapter A 12 Vane Spindles Special Purpose Instruments A 13 A 14 A 15 A 16 A 17 A 18 Krebs Viscometer YR 1 Rheometer CAP 1000 Viscometer R S Rheometer amp R S Soft Solids Tester CAP Viscometer PVS Rheometer MORE SOLUTIONS TO STICKY PROBLEMS Calibration Spring Torque for Standard Dial Read ing Viscometer and Digital Viscometer Rheometer 673 7 dyne centimeters full scale 7187 0 dyne centimeters full scale 14 374 0 dyne centimeters full scale 57 496 0 dyne centimeters full scale 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 III etc 2 For alternative spring torque models multiply the base spring torque by the multiplier in the model designation 5XLVT 5 X 673 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 defin
94. scosity n was measured 7 2 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 fluid 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 ND Casson VT v vVID NCA CMA Casson 1 a VT 2V To 1 a VND Power Law t kp where T shear stress D shear rate n viscosity To yield stress k consistency index n flow index a aspect ratio MORE SOLUTIONS TO STICKY PROBLEMS Page 25 The chocolate industry utilitzes the NCA CMA ver sion of the Casson equation to evaluate chocolate prior to final processing This equation closely approximates the plastic behavior of chocolate In addition experi ence shows that the slope term vm plastic viscosity indicates the chocolate s response to being moved in processing mixing pumping Also the y intercept 2v yield stress or zero shear viscosity indicat
95. shaft comprises the spindle coupling to which the Viscometer s spindles are attached 3 3 Viscosity Measurement Techniques As with any precision instrument proper operating techniques will improve effectiveness of the Brookfield Viscometer Astep 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 65 years of customer experience They forma sound foundation for a viscosity testing procedure and a starting point from which more advanced techniques can be explored 3 3 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 Brookfield Engineering Labs Inc 3 3 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
96. signed 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 LVF or LVT Viscometer the UL Adapter provides a viscosity range of 1 0 to 10 0 cP anda defined shear rate of 73 4 reciprocal seconds at 60 RPM For other Viscometer models the minimum Brookfield Engineering Labs Inc 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 100 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 low
97. stand 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 Brookfield Engineering Labs Inc 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 5 2 1 Cylindrical Spindles The following equations apply to cylindrical spindles only on any model Brookfield instrument SHEAR RATE sec 1 VE 2 R 2 Rp2 x2 Ro Rp SHEAR STRESS M 2 ELLE 2 dynes cm 1 27 Ry 2 VISCOSITY poise n Ez 3 Definitions o angular velocity of spindle rad sec T NJ N RPM Re radius of container cm Rp radi
98. t nec essarily compare to the traditional Brookfield Viscom eter The Brookfield KU 1 is designed to provide a viscosity measurement in Krebs units and is often used in the paint industry The Brookfield CAP 1000 is de signed 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 A very important advancement in viscosity measure ment is the bidirectional DV Ill Rheometer for use Page 3 Brookfield Engineering Labs Inc with PC This instrument with variable speed capa bility allows easy handling and programming of com plicated application measurements lt also enables the storage of calculated results and transfer of data to Excel or any LIMS system lt easily gives a graphi cal view of results which is especially important on flow curve interpretations 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 of delicate high viscosity gels Similar to DV III it can operate in stand alone mode or under PC control and provi
99. t 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 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 readings to derive what is known as a viscosity ratio Mx VISCOSITY RATIO lo AS 2
100. t 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 constantly 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
101. t will keep the components dispersed 3 3 6 Spindle 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 3 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 The accuracy of a particular viscosity reading is dependent upon the actual dial or display reading In general accuracy of the viscosity value will in crease as the reading approaches 100 This is be cause the tolerance of 1 of full scale viscosity applies to all readings and represents a smaller percentage of measured viscosity as the actual read ing increases Consider the following example An LVT Viscometer when used with a 1 spindle at a speed of 60 RPM has a spindle Factor of 1
102. terials using spring relaxation procedures AR 84 Computer analysis of certain rheological characteristics CHAPTER 6 The following methods provide various ways to obtain information on the viscosity behavior of your material using a Brookfield Viscometer or Rheometer Choose the appropriate method to suite your requirements Contact Brookfield or our authorized dealer if you re quire additional assistance 6 1 Single Point Viscosity Test Choose a spindle Select a rotational speed or shear rate 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 This method shows one example of how viscosity can change as a function of rotational speed or shear rate 6 3 Up Down Rate Ramp Use the same method defined above in CON TROLLED RATE RAMP
103. ts and accessories Consult the referenced sections for more information about these products Cylindrical Spindles 2 4 2 UL Adapter 2 6 2 DIN Adapter 2 6 3 Small Sample Adapter 2 6 1 Thermosel System 2 8 1 Wells Brookfield Cone Plate Viscometer 2 10 1 CAP Viscometer 2 10 2 R S Rheometer 2 10 3 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 Small 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 Page 6 Brookfield Engineering Labs Inc 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 c
104. ty 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 Aplot 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 Brookfield Engineering Labs Inc fluids if allowed to stand undisturbed for a while will regain their initial viscosity while others never will T 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 7 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 laminar and turbulent flow on viscosity measurement 4 6 Laminar and Turbulent Flow The very definition of viscosity implies the existence of what is called laminar flow the movement of one l
105. uch 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 spindles 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 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 MORE SOLUTIONS TO STICKY PROBLEMS and neither These differing numbers are par
106. us of spindle cm x radius at which shear rate is being calculated M torque input by instrument see Appendix A L effective length of spindle see Appendix A Note R should not exceed 2R for well defined shear rates 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 MORE SOLUTIONS TO STICKY PROBLEMS Page 21 SHEAR RATE 2 sec 1 Y 2 o 4 R Rp SHEAR STRESS M 2 5 dynes cm2 Tt 37 Ro 5 VISCOSITY poise n A 6 shear rate at surface of spindle sec 1 Definitions Y See Section 5 2 1 for other definitions 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 1 vx ee sec t Y EG 7 SHEAR STRESS M dynes cm2 Tt 5 5 8 E nr VISCOSITY poise n z 9 Definitions 0 cone angle degrees cone radius cm 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 o
107. viscosity capabilities as low as 0 1 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 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 MORE SOLUTIONS TO STICKY PROBLEMS Thermosel System is

More Solutions 2003

Contents

Download Pdf Manuals

Related Search

Related Contents