Steel for enamelling and enamelled steel
Contents
1. H in steel increases with temperature 4 stage cooling 2 stage 550 830 C The enamel softens then fuses forming a The enamel solidifies stopping gaseous exchanges Hydrogen solubility in the steel decreases when the semi permeable layer This reduces gaseous exchanges temperature falls The steel becomes oversaturated and with the furnace atmosphere hydrogen accumulates under the enamel coating The iron oxide present at the enamel steel interface is An excessive quantity of hydrogen at the interface dissolved by the enamel causes fish scale defects see chapter 4 1 firing temperature C 900 enamel impermeable to atmospheric O and reaction of oxides with enamel 800 700 fusion of enamel solidification of enamel 600 500 400 porous enamel reactions stop 300 and oxidation of iron 200 100 1 2 3 4 5 6 Y User manual Steel for enamelling and enamelled steel ArcelorMittal 41 411 41 2 41 3 4 2 4 21 4 2 2 4 2 3 4 24 4 3 4 3 1 4 3 2 4 3 3 4 3 4 4 3 5 4 3 6 4 4 441 4 4 2 4 4 3 Enamelling processes and associated steel grades Hydrogen and fish scales Formation of fish scale defects Impact on the metallurgical properties of steel for enamelling Measuring steel s absorption capacity the Strohlein hydrogen permeation test Enamelling on hot rolled steel Scope of application The ArcelorMittal range of hot rolled steel for enamelling2. Vv A EN inside corner butt weld weld edge weld Different weld configurations 6 3 3 Welding fumes Welding steel entails the formation of welding fumes Conse quently the workplace should be suitably equipped to extract these fumes extractor torch extractor hood glove box etc 6 3 4 Reconditioning In general conventional welding processes produce a heat affected zone around the weld where the surface is altered It may therefore be important to clean the surface immediately after welding has been completed to remove any deposits oxides and foreign bodies that may have appeared during the welding process User manual Steel for enamelling and enamelled steel ArcelorMittal 41 Properties of enamelled steel Enamel adhesion Corrosion resistance Chemical resistance of enamel Mechanical strength of the surface High and low temperature stability Thermal shock resistance Fire resistance Hygiene and ease of cleaning Colour stability 44 Properties of enamelled steel Enamelled steel has a number of useful properties that are chiefly due to the vitreous nature of the enamel The chemical composition of enamel varies according to its end use so as to fully meet the required characteristics 71 Enamel adhesion The enamel must adhere to the substrate in order to ensure that the enamelled steel has the required properties for each end use Adhesion is determined by means of an impact test whi
3. modes starting with simple uniaxial tension By evaluating the deformation an indispensable indicator is used in this field the Forming Limit Curve or FLC For a steel sheet of a given grade and thickness the FLC deter mines a safety limit for deep drawing operations range superimposed on strain values representing the deformation as a whole This curve can be established according to various acceptance criteria necking or rupture of the steel wrinkling excessive thinning of the metallic coating cracking or peeling of the coating This curve allows the user to Evaluate the safety margin for the drawn component Identify critical areas of the component where the material is subjected to severe deformation Analyse the factors that influence forming steel grade component design lubrication tool design draw beads radii etc x Im S300EK thickness 1 7 mm non drawability range A y rang 1 N 034 drawability range x VA Oras 0 1 5 p A r Es 06 0 5 04 0 3 0 2 01 0 0 1 0 2 0 3 0 4 0 5 0 6 Example of FLC for a steel for enamelling User manual Steel for enamelling and enamelled steel ArcelorMittal 35 6 1 6 2 6 3 6 3 1 6 3 2 6 3 3 6 3 4 Joining of steel for enamelling Clinching Lock seaming Welding Resistance welding Gas shielded arc welding Welding fumes Reconditioning 38 38 39 39 40 Al Al 37 38 Joining of steel for ena
4. p 13 University of Pavia Italy architect Giancarlo De Carlo p 21 Tom D Haenens p 31 Jacques Van den Berghe p 37 PolyVision p 43 Tom D Haenens p 47 PolyVision p 49 PolyVision p 55 PolyVision Copyright All rights reserved No part of this publication may be reproduced in any form or by any means whatsoever without prior permission from ArcelorMittal Care has been taken to ensure that the information in this publication is accurate but ArcelorMittal and any other ArcelorMittal Group company do not accept responsibility or liability for any errors or any information that is found to be misleading As this document may be subject to change please consult the latest information in the Magazines and Brochures section at www arcelormittal com fce User manual Steel for enamelling and enamelled steel ArcelorMittal 63 ArcelorMittal Flat Carbon Europe 19 avenue de la Libert L 2930 Luxembourg fce technical assistance arcelormittal com www arcelormittal com fce
5. 280 2 28 OSEO 140 260 2 30 DCO3EK 270 350 214 0727 20 17 140 240 232 2 3 21 2 0 4 0 5 140 260 232 0007 140 240 2 34 DCO4EK 270 340 21 6 0727 2017 140 220 2 36 DES gt 14 0 4 0 5 140 260 2 34 DCO4ES 0 5 0 7 140 240 270 340 2 36 21 6 gt 0 18 0 7 3 140 220 2 38 0922 ey DCO5EK 140 190 270 320 gt 0 18 225 2 1 8 0 4 0 5 120 210 236 0 5 0 7 120 190 2 38 DCO6EK 270 320 2 1 6 0722 120 170 gt 40 2 3 21 4 DCO7EK lt 3 80 160 270 350 2 40 2 0 20 0 4 0 5 140 280 2 30 Solfer 0 5 0 7 140 260 270 370 232 0722 140 240 2 34 0 4 0 5 140 250 270 350 2 34 Solfer 0 5 0 7 140 230 2 36 0922 140 210 2 38 User manual Steel for enamelling and enamelled steel ArcelorMittal Mechanical properties of hot rolled steels for enamelling Thickness mm R MPa R MPa A 1 5 3 227 S240EK 2 240 360 430 3 6 234 1 5 3 2 280 225 S300EK 330 450 3 4 5 2 260 230 Mechanical properties of aluminised steels for enamelling Thickness mm R MPa R MPa A r90 n90 0 5 0 7 2 28 Alusi BEC lt 260 lt 380 gt 18 gt 0 18 0 7 3 2 30 0 5 0 7 lt 240 2 30 lt 370 Alusi BEA 0 7 1 23 gt 33 20 18 lt 230 153 lt 365 232 User manual Steel for enamelling and enamelled steel ArcelorMittal 57 Appendices 10 2 Performance of enamelled steel The table below indicates
6. 6 and the 11 century during the Byzantine period The Byzan tine style heavily influenced the whole of western production throughout the 12 century when enamel began to be devel oped in Limoges Q The first utensils in enamelled cast iron date back to the 18 century and appeared in Germany The industrial revolution in the 19 century made it possible to manufacture cast iron advances in blast furnaces and then steel development of converters in large quantities which opened the way for the development of enamelling on these substrates Finally present day enamelling processes have developed over the course of the 20 century mirroring progress in steel production but also keeping pace with ever stricter environ mental regulations User manual Steel for enamelling and enamelled steel ArcelorMittal The characteristics of enamelled steel Enamelled steel has many properties that make it a first rate material for numerous applications Its characteristics result from combining the properties of its two constituent elements steel and enamel Steel contributes mechanical strength and formability while enamel provides durability and a beautiful glossy appearance Here are just a few examples of its many properties Corrosion resistance Chemical resistance Mechanical strength of the enamelled surface Resistance to heat and cold Thermal shock resistance Fire resistance Hygiene and ease of cleaning Multipl
7. The space between the wraps allows contact between the annealing gas water vapour and the entire surface of the steel thus facilitating decarburisation Direct on white enamelling has a number of advantages over the conventional enamelling process A thinner enamel coating but offering greater impact resistance The very low carbon content of these steels makes it possible to obtain a very high quality surface appearance after enamelling no bubbles or black spots and also limits deformation at high temperatures e g during pyrolysis cycles cover coat surface treatment steel substrate User manual Steel for enamelling and enamelled steel ArcelorMittal cover coat ground coat with additives steel substrate 4 3 4 Two coat one fire enamelling Direct on white enamelling has two major drawbacks Surface preparation is complex expensive and not very environmentally friendly Decarburised steel must be used The aim of the two coat one fire enamelling process is to obtain the same result white parts with no surface blemishes with a simpler surface preparation and just one firing cycle Surface treatment is limited to degreasing only Enamel to steel adhesion is achieved by using ground coat enamel with added adhesion oxides nickel or cobalt oxide in a layer no thicker than 40 um Steel with a low carbon content must be used to prevent ex cessive release of gases during firing A carbon content of C
8. Use Easyfilm HPE and Easyfilm HFE Enamelling on cold rolled steel Ground coat enamelling one coat one firing Conventional enamelling two coats two firings Direct on white enamelling Two coat one fire enamelling The ArcelorMittal range of cold rolled steels for enamelling Block diagram of enamelling processes on cold rolled substrates Low temperature enamelling on aluminised steel substrates Aluminised steels for enamelling Alusi BEC and Alusi BEA Application Use 22 22 22 23 24 24 24 25 25 25 25 25 26 26 26 28 28 28 29 29 21 Enamelling processes and associated steel grades Present day enamelling processes have developed over the course of the 20 century mirroring progress in steel produc tion but also keeping pace with ever stricter environmental regulations Conventional enamelling on cold rolled steel was thus followed in the 1960s by direct on white enamelling thanks to the emergence of open coil decarburised steel pa tented by the Bethlehem Steel Corporation in 1958 then by the development of the two coat one fire enamelling pro cess in the 1980s and finally the introduction of enamelling techniques on metallic coated substrates at the turn of this century Enamelling on hot rolled substrates also developed in parallel to the above processes particularly for water heater applications The enumeration of enamelling processes and associated steel grades fo
9. a uniform coating thickness This process is often used for parts with a complex shape such as oven cavities One drawback of this process is that sagging of the enamel can occur A varia tion of dip coating the dip and shake method which involves moving the parts about different axes when they emerge from the bath minimises sagging and excessive thickness of the enamel coating Flow coating This process entails spraying the entire surface of the part with enamel through one or more round nozzles Air assisted spraying Enamel is sprayed on the parts to be coated using a spray gun powered by a jet of compressed air at a pressure of between 3 and 4 5 bar The process is generally carried out in a booth the parts being hung on a metal conveyor belt Manual spraying requires highly experienced operators in order to avoid sagging and excessive thickness of the enamel coating This procedure may be automated and tends to be reserved for short produc tion runs Electrostatic spraying A charge differential is applied between the negatively charged enamel and the positively charged parts to be coated The enamelling spray gun consists of a central tube through which the enamel passes surrounded by an annular nozzle through which the atomising air passes faster than the stream of enam el This difference in speed causes the enamel slurry to atomise into fine droplets At the tip of the spray gun the droplets pass through an atmos
10. cleaning oven the principle involves heating the oven cavity to a high temperature about 500 C so as to burn fats and residues deposited on the walls when food is cooked Catalytic self cleaning oven in this case cleaning takes place at normal cooking temperatures Enamel contains a catalyst that speeds up the oxidation of fats and the breakdown of residues Use of Easy to Clean ETC enamel the absence of micropores in the completely smooth surface of enamel prevents any accumulation of dirt Enamelled steel is also used for cookware enamelled sauce pans prevent the growth of bacteria do not absorb odours are not attacked by food acids and can be used directly on the gas hob They have a very smooth surface that is highly resistant to the abrasive and chemical effects of ordinary detergents and can be cleaned very easily They are also suitable for use in induction cooking which has great potential 91 3 Sanitary ware The sanitary ware market also exploits the qualities of enam elled steel The properties of the steels available nowadays ake it possible to design and offer a wide range of bathtubs wash hand basins and sinks in a variety of shapes and sizes to eet the requirements of even the most demanding consum ers Enamel can be decorated in a multitude of ways producing a wide range of finishes But the product really excels when it comes to its hygiene and sanitary qualities It is completely inert both chemically a
11. heater tanks Their mechanical properties remain unchanged after forming and firing of the enamel This has the following advantages It extends the life span of water heaters by increasing their fatigue safety margin during heating phases The thickness of the steel can be reduced thereby reducing raw materials cost of the water heater Finally after enamelling the inside wall of the tank displays excellent corrosion heat and moisture resistance 4 2 4 Easyfilm HPE and Easyfilm HFE Easyfilm HPE and Easyfilm HFE are dry non permanent films applied to hot rolled substrates and have the following advantages Corrosion protection three months protection in the case of Easyfilm HPE and six for Easyfilm HFE They are dry products which helps keep workshops clean and improves safety Suitability for welding and laser cutting Compatibility with all known lubricating oils All traces of grease can be removed by alkaline degreasing Complete absence of heavy metals Easyfilm HFE also has an excellent friction coefficient over its entire surface u lt 0 1 making it particularly suitable for creating deeply drawn or profiled parts that generally require additional lubrication during processing This has obvious eco nomic benefits for the user It simplifies the enamelling process It obviates the need to purchase lubricants for the deep drawing process It reduces cost of treating and recycling used oil These produ
12. it is cooled rapidly first of all by being passed through a water cooled rolling mill to form a glass sheet then into a cooler Crushing completes the cooling cycle This rapid quenching process from a high temperature fixes the structure of the glass and prevents any phase separation An alternative fusion process involves using a rotary furnace into which the constituents are poured mixed and heated liquid enamel is then poured into a pit and water quenched After cooling and crushing enamel frit is obtained Fusion of enamel mixer Screw conveyor loading arm temperature between 1100 C and 1300 C 2 2 2 Preparation of enamel Enamel frit cannot be used as such It must first be mixed with other constituents then ground These steps may be carried out either by the enamel manufacturer or by the enameller to whom the manufacturer has supplied the necessary materials Enamel may be applied in liquid form In this case after the addition of certain ingredients suspension refractory colouring agents electrolytes and opacifiers the frit is ground and mixed with water to form a slurry which will be used for dip coating or spraying applications Enamellers in particular manufacturers of domestic appliances who do long production runs in a single colour became increasingly reluctant to prepare the enamel themselves This led to the introduction of ready to use powder in the 1980s to
13. make use of hydrogen s affinity with ele ments such as boron may also be adopted Aluminium killed steel Hot rolling Fe C cementite Fragmented cementite after cold rolling In the case of interstitial free steel IFS titanium precipitates formed before hot strip coiling will act as traps This chemical trapping is consolidated by loss of cohesion between the matrix and the titanium precipitates during the cold rolling process Hot rolled steel In the case of hot rolled steel chemical hydrogen trapping is the only possibility and titanium carbides are the most effec tive traps However trapping is less effective in this instance than with the cold rolling process 41 3 Measuring steel s absorption capacity the Strohlein hydrogen permeation test The Strohlein permeation test is used to measure steel s hy drogen absorption capacity by determining the total volume of cavities present in the steel It makes use of hydrogen gas produced by electrolysis The solution consists of sulphuric acid plus small quantities of arsenic oxide and mercury chloride This is maintained at 25 C When a direct current is applied to the solution by a current generator the H protons in the solution trigger a reduction reaction Atomic hydrogen penetrates into and then diffuses through the metal recombining in molecular form in imperfections within the metal When the metal is saturated the output signal changes A permeation curve is
14. of the two steel sheets The electrical aspects of the process can be described as a succession of ohmic resistances the relative values of which produce local heating The strength of the contact resistance between the two sheets governs the formation of the weld nugget at the site of the spot weld The key parameters to check are applied pressure current intensity and welding time To extend the life span of the welding electrodes they must be cooled during long production runs by internally circulating cooling water at 20 C at a rate of 4 6 l min electrodes y EA Ar pressure current ON current OFF applied pressure ON pressure released electrode electrode tip indentation weld nugget sheet separation heat affected zone electrode User manual Steel for enamelling and enamelled steel ArcelorMittal weld nugget lap joint Resistance seam welding Unlike resistance spot welding resistance seam welding uses rotating electrode wheels If possible the seams should be welded discontinuously Roll Spot to limit heating of both the steel sheet and the electrodes see figure c on this page A variant of this process is to use an intermediate electrode with consumable copper wire Soudronic patent This method which calls for a fairly precise guiding system for the placement of the copper wire may be economically advantageous for long production runs because when the welding parameters
15. substrate 3 2 Surface treatment before enamelling The purpose of surface treatment is to obtain a surface that is compatible with the enamelling process Surface treatment comprises various steps The number of steps varies according to the enamelling process used hot blasting Degreasing insing ickling Acid rinsing o used for enamelling on hot rolled substrate mandatory for direct on white enamelling insing eutralisation Drying S R P Nickel deposition R N 3 21 Shot blasting Surface treatment by shot blasting of hot rolled substrates is used for example to make the bottoms and bodies of water heaters or to make gas cooker burner caps The purpose of this treatment is to increase the surface roughness of the steel This provides a better keying of the enamel as during the enamel firing cycle enamel metal chemical reactions are promoted by the resulting greater contact surface area thereby increasing enamel to steel adhesion Together with the chemical hydrogen traps created during steel production this improves resistance to the defect known as fish scale Shot blasting is carried out on an unoiled substrate so as to avoid contaminating the shot If the shot does become con taminated with oil it is less effective and soils the surface of the steel This soiling may cause the enamel to be rejected where a wet application process is to be used User manual Steel for enamelling an
16. such variations are found cooking appliances domestic equipment exhaust systems 7 7 Fire resistance A flame or any other source of heat will cause no damage to an enamelled surface In addition enamel will not give off any toxic fumes in the event of prolonged exposure to heat The fire resistance of enamelled panels is classified as A1 7 8 Hygiene and ease of cleaning The smooth hard vitreous surface of enamelled steel has no pores or cracks which prevents the growth of bacteria and the accumulation of dust Enamelled steel can therefore be used in sensitive areas such as clean rooms or kitchens Thanks to everyday usage it is also widely known that enam elled steel is a food grade material that does not give off odours Enamelled surfaces are very easy to clean especially if defaced by graffiti Enamel s smooth sealed surface and its exclusively mineral composition mean that commercially available solvents can be used for cleaning purposes making it much easier and less expensive to clean The savings made may be considerable Enamelled steel is thus a material that can be used in places where surface cleanliness is very important e g tunnels or in places subject to graffiti attacks 79 Colour stability Enamelled steel comes in an almost infinite range of colours patterns and textures with a gloss semi matt or matt finish In addition it is possible to reproduce any image with extreme accuracy by screen print
17. the furnace prevent heat loss The furnaces are mainly electric or gas fired radiant tube The heating elements are arranged on the walls and bottom of the furnace Thermal energy is transmitted to the parts by radia tion and convection 20 Enamelling of steel 3 4 3 Enamel to steel adhesion mechanisms The adhesion of enamel to uncoated steel is achieved by means 3 stage around 830 C of chemical reactions that take place during the firing and cooling cycles At this temperature chemical redox reactions take place The process can be divided into four stages between the iron oxide layer at the enamel steel inter face the metal oxides in the enamel and the carbon in 15 stage up to 550 C the steel Fe Ni Co alloys precipitate at the enamel steel interface The moisture H O and the oxygen O in the air pene These are at the heart of the adhesion of enamel to steel trate the porous enamel and oxidise the iron in the steel Adhesion is promoted by the roughness of the steel This causes the formation of a layer of iron oxide at the The dissolved oxygen recombines with the carbon in the enamel steel interface steel releasing gaseous CO CO The intensity of these The atomic hydrogen arising from the decomposition releases must be monitored of H 0 diffuses into the steel recombines as molecular The quantity of hydrogen in the steel is at maximum hydrogen and fills the holes in the steel The solubility of levels
18. the performance of enamelled panels intended for architectural use which must comply with EN 14431 Criterion Reference Brief description Quality specification standard Steel substrate EN 10209 EN 10209 describes the criteria that steel Cold rolled low carbon steel flat producis for grades must meet to be defined as suitable for vitreous enamelling vitreous enamelling and also the test methods used to determine suitability for enamelling hydrogen permeation iron loss for steel intended for direct on white enamelling and enamel adhesion test Enamel application ISO 2178 Application of at least two coats of enamel The coating thickness on the visible side varies on the visible side ofthe panel and one coat from 75 275 um ifthe thickness of the substrate of enamel on the reverse side The firing is less than 0 75 mm and from 180 500 um ifthe temperature must be at least 500 C The thickness of the substrate is more than 0 75 mm coating thickness is measured using an elcometer eddy current testing Enamel adhesion EN 10209 The sample of enamelled sheet is deformed Class 1 2 or 3 annex D using a hemispherical punch by dropping a 1 5 kg weight onto the punch from a height appropriate for the thickness of the substrate The degree of adhesion is determined by comparison with reference photos and ranges from 1 good adhesion to 5 poor adhesion Enamel porosity ISO 8289 A potential difference of 1000 V is applied M
19. thickness that needs to be used the tank is regarded as a pressure vessel and must be tested at about 12 bar the steels used for the tank are hot rolled S240EK and S300EK grades 91 2 Domestic appliances and cookware The domestic appliance market is the biggest user of steel for enamelling Enamelled steel is in fact the only material capable of withstanding the many stresses to which appliances are subjected particularly in cooking applications It has therefore become indispensable for specific applications where it is unri valled hobs oven cavities dripping pans baking trays etc Here are just some of its many useful properties Resistance to scratching and abrasion is much better than with other materials Enamelled steel neither retains nor absorbs odours so it cannot impart them It is resistant to products commonly used in the kitchen whether they be acidic e g vinegar and lemon juice or alkaline e g detergents and also has excellent corrosion resistance It is flame resistant and can withstand a high temperature It is safe for contact with food and prevents the growth of bacteria It is very resistant to steam which means it can readily be used for this cooking method It has undeniable aesthetic qualities User manual Steel for enamelling and enamelled steel ArcelorMittal Advances in enamel design in the past few years have led to the development of self cleaning oven cavities Pyrolytic self
20. thus obtained showing the quantity of hydrogen passing into the metal as a function of time User manual Steel for enamelling and enamelled steel ArcelorMittal The permeation time t is directly linked to the steel s enam elling capacity EN 10209 defines the TH value above which steel is said to be suitable for enamelling as 100 H volume A p time TH 15t e TH gt 100 aqueous solution H SO additives T 25 C Her ol 2H gt 4 H data recorder n steel thickness e This test can only be used on steel with cavities i e aluminium killed steel In the case of IFS susceptibility to fish scale de fects is measured by means of an enamelling test in a moist atmosphere or by using a low adhesive ground coat enamel sensitive ground coat 24 Enamelling processes and associated steel grades 4 2 Enamelling on hot rolled steel 4 21 Scope of application Enamelling on a hot rolled substrate entails applying one or more layers of enamel on one or both pre prepared sides and then firing at a high temperature Hot rolled steel for one side enamelling this being steel with a specific chemical composition that can guarantee Excellent resistance to fish scale defects in the enamelled parts Conservation of mechanical properties after forming and firing of the enamel 4 2 2 The ArcelorMittal range of hot rolled steel for enamelling Two grades are available to match t
21. 0 02 to 0 03 is usually recommended 4 3 5 The ArcelorMittal range of cold rolled steels for enamelling ArcelorMittal has a full range of cold rolled steels for enamelling see the table on the next page Grades DCO1EK DCO4EK DCO5EK and DCO6EK are in compliance with EN 10209 Grade DCO5EK was developed specially for the manufacture of bathtubs Grade DCO7EK is intended for very deep drawing applications DCO1EK DCO3EK DCO4EK and DCO5EK are aluminium killed steels whereas DCO6EK and DCO7EK are IFS type steels decarburised in steel plants IFS interstitial free steel DCO4ES is a cold rolled aluminium killed steel with a specific chemical composition particularly with respect to its carbon content This steel was developed specially for the two coat one fire enamelling process after degreasing only Solfer and Solfer are aluminium killed decarburised open coil annealed steels that are intended for direct enamelling to give a white or coloured finish with a single coat following de greasing strong pickling and nickel deposition However these types of steel can be used in two coat one fire enamelling and ground coat or conventional enamelling for enamelling pyrolytic self cleaning oven cavities if ground coat enamels are used that are suitable for the low intrinsic reactivity of these steels These grades correspond to standardised grades DCO3ED and Last but not least t
22. Inadequate degreasing causes surface blemishes demonstrat ing the importance of monitoring the conditions under which this procedure is performed Another thing to watch out for is the phenomenon of resinification of the oil on the part to be degreased which when exposed to light makes degreasing very difficult even impossible Lastly surface blemishes in the metal scratches pores etc may trap oil residues that may form gases during the enamel firing cycle 16 Enamelling of steel 3 2 3 Rinsing Rinsing follows degreasing and is carried out in one or more steps A single hot water rinse 60 70 C if there are to be subsequent surface treatment procedures pickling etc Hot rinsing cold rinsing and a final rinse in demineralised water if there is to be no subsequent surface treatment Normal pickling User manual Steel for enamelling and enamelled steel ArcelorMittal Overpickling 3 2 4 Pickling The purpose of pickling is to attack the steel surface in order to increase its micro roughness and hence its reactivity which promotes the adhesion of enamel Pickling is generally carried out using concentrated sulphuric acid H SO and the effect is mainly centred on the grain boundaries The pickling inten sity is measured by iron loss Depending on the enamelling process used pickling may be light iron loss 5 g m per side or strong iron loss 25 g m per side The chemical reaction triggered during
23. ance after enamel Application of the enamel and firing With Alusi BEC grade the catalytic e be applied by a wet or dry process Firi temperature of 560 C Alusi BEA grade can be enamelled wi in order to obtain a ing namel coating can ng is performed at a th a matt or glossy enamel suitable for firing at a low temperature applied by a wet or dry process It is fired at 560 C A convection oven must be used in order to guarantee a homogeneous colour after enamelling Thickness mm 0 6 1 2 2 0 Welding current kA 9 9 to 12 7 10 6 to 12 1 10 9 to 12 4 Welding latitude kA 2 8 1 5 Positioning time periods Welding time periods 10 12 24 Holding time periods Electrode pressure daN 330 550 Type of electrode Flat 6 mm Spot welding of Alusi BEC and Alusi BEA grades User manual Steel for enamelling and enamelled steel ArcelorMittal 29 51 Transport and storage 5 2 Decoiling slitting and cutting 5 3 Forming 5 31 Bending 5 3 2 Deep drawing Forming of steel for enamelling 32 32 33 2 34 31 32 Forming of steel for enamelling 51 Transport and storage Some simple yet nevertheless essential precautions should be taken for the transport and storage of steel Coils sheets and blanks should be kept in heated or venti lated storage facilities to ensure that no moisture accumu lates In particular coils sheets and blanks should not be stored ne
24. ar windows doors etc to avoid extreme variations in temperature that could produce condensation During transport and if outdoor storage is unavoidable the coils sheets and blanks should be protected Avoid storing the products directly on the floor 5 2 Decoiling slitting and cutting The drive system for decoiling must be adjusted to match line speed in order to optimise product flow In extreme circum stances on some processing lines the drive system will also eliminate jogs flapping and slippage of adjacent wraps and in the case of hot rolled steel coil break defects For slitting and other cutting operations tools should be cor rectly adjusted and sharpened so as to minimise the formation of burrs Slitting cutting to length and shearing operations should be included in process design from the outset to ensure that any burrs formed do not detract from the appearance of the parts or pose a risk of cutting during handling The following rules should be observed to control the location of burrs after cutting Slitting and side trimming wheels should preferably be mounted symmetrically Clearances must be properly adjusted User manual Steel for enamelling and enamelled steel ArcelorMittal upper shaft lower shaft Symmetrical mounting of slitting blades upper shaft lower shaft Non symmetrical mounting of slitting blades front side A y reverse side burr orientation Burr orientation after
25. aximum 5 defects m method A between the enamelled surface and an ISO 2746 electrode Sparking indicates the presence of a pore in the enamel Abrasion resistance ASTM C501 The aim of this test is to determine the weight The maximum weight loss after 1000 cycles must loss of a sample subjected to friction from an not exceed 0 1 g m abrasive wheel loaded with a constant weight Abrasive emery paper 533 Test load 1 kg Impact resistance ISO 4532 This test is conducted using an impact pistol set 24 hours after the test there must be no enamel at a force of 20 N to strike the sheet cracks larger than 2 mm in diameter right at the point of impact Surface hardness EN 101 Surface hardness is measured by the Mohs Minimum hardness is 5 Mohs scale which rates minerals according to their hardness from 1 calcite to 10 diamond Scratch test ISO 15695 The surface is scratched with needles to which The enamelled surface must be able to is applied by means of an arm a force ranging from 1 20 N withstand a force of 7 N without scratching Flatness Flatness is determined by measuring the difference in deflection of the panel in its non enamelled state and after firing The measurement is performed on the long diagonal User manual Steel for enamelling and enamelled steel ArcelorMittal Thickness of substrate gt 0 75 mm Maximum deflection 0 5 in the convex direction and 0 25 in the concave direction Thickness o
26. c Self cleaning oven cavities e e e e e e appliances pyrolytic e o e o catalytic ej e ol Hobs e e e e e e Washing machine interiors e je e oe o o Cookware e o e o o ele Industry Water heaters Bathtubs e o o o e o o e Construction Flues e Roof tiles US o e Architecture Curtain walls e o Oo o Exterior wall cladding Signage road traffic signs advertising etc Art Miscellaneous Top of the range exhaust silencers User manual Steel for enamelling and enamelled steel ArcelorMittal 101 10 2 10 3 Appendices Mechanical properties of steel for enamelling Performance of enamelled steel Recommendations for installing enamelled architectural panels 56 58 60 55 56 Appendices 101 Mechanical properties of steel for enamelling The mechanical properties of cold rolled hot rolled and aluminised steels for enamelling are shown in the table below The values refer to crosswise measurements Mechanical properties of cold rolled steels for enamelling Thickness mm R MPa R MPa A r 90 r average n 90 0 4 0 5 140 310 226 DCOIEK 080m 140 290 270 390 2 28 0 7 3 140 270 2 30 0 4 0 5 140
27. ch entails deforming a sample of enamelled sheet using a hemispherical punch by dropping a 1 5 kg weight onto the punch from a height appropriate for the thickness of the sub strate The degree of adhesion is determined by comparison with reference photos The score given ranges from 1 very good adhesion to 5 very poor adhesion UP Corrosion resistance Enamel is a coating that provides steel with excellent corrosion resistance even at high temperatures Enamelled surfaces are non porous and hence impermeable to all liquids Salt spray tests performed on enamelled parts with a cold rolled or alu minised substrate indicate that they can withstand salt spray for over 500 hours without showing any signs of red rust Tests conducted by the Porcelain Enamel Institute have shown that enamelled panels could go for 30 years without any signs of corrosion on the metal substrate 73 Chemical resistance of enamel The chemical properties of enamel are tailored to the envi ronment in which it is to be used Enamel thus has extremely good resistance to chemicals acids apart from hydrofluoric acid alkalis detergents and organic solutions Whether used in kitchens or bathrooms contact with a variety of foodstuffs perfumes cosmetics or cleaning products will have no effect whatsoever on the surface of these products Enamelled steel is also extremely resistant to atmospheric attack Consequently rain atmospheric pollution sulphur
28. crease resistance to temperature chemicals and abrasion and facilitate the action of opacifiers another constituent of enamel Fluxes which lower the melting point and firing temperature and increase the coefficient of expansion These are mainly composed of borax sodium tetraborate in its anhydrous form Na B 0 or hydrated form Na B O 10 H 0 and alkaline oxides such as oxides of sodium Na O potassium K O lithium Li O calcium CaO magnesium MgO and stron tium SrO These constituents produce borosilicates of so dium potassium lithium calcium magnesium or strontium which have a lower melting point than silica approximately 1400 C instead of 1720 C The melting point may also be lowered by adding fluorine F or boron trioxide B 0 Fluxes such as the alkaline oxides increase the coefficient of expansion by filling the voids in the silica structure Adhesion agents which are metal oxides that are involved in chemical redox reactions to promote adhesion between the steel surface and the enamel coating These reactions will also involve the iron and carbon in steel as well as atmospheric oxygen Adhesion agents are present in ground coat enamel mainly in the form of nickel oxide NiO molybdenum oxide MoO cobalt oxide CoO cupric oxide CuO manganese oxide MnO and chromic oxide Cr 0 Opacifiers and colouring agents which contribute visual and tactile qualities to enamelled parts O
29. cts are compatible with all dry enamelling proces ses subject to certain conditions User manual Steel for enamelling and enamelled steel ArcelorMittal 4 3 Enamelling on cold rolled steel 4 31 Ground coat enamelling one coat one firing This process entails applying and firing one ground coat of enamel on each side of the part to be enamelled and is intended for semi visible and non visible parts Given that only one layer of ground coat containing naturally coloured adhesion oxides is applied only dark colours are possible This process can be used for Oven and microwave oven cavities Internal components of built in ovens or cookers inner doors dripping pans baking trays Washing machine drums ground coat steel substrate 4 3 2 Conventional enamelling two coats two firings This process is used for visible parts After performing ground coat enamelling one coat one fire this entails applying and firing an enamel cover coat on the visible side and possibly on both sides This is suitable for producing white or coloured parts with a very good surface appearance after enamelling Housing panels for domestic appliances hobs covers and tops of cookers doors for built in ovens microwave ovens and cookers Bathtubs and shower trays Architectural panels cover coat ground coat steel substrate 25 26 Enamelling processes and associated steel grades 4 3 3 Direct on white enamelling Wh
30. d enamelled steel ArcelorMittal 3 2 2 Degreasing The purpose of degreasing is to remove exogenous matter present on the steel surface and originating from earlier steps rust preventing oils drawing oils and various kinds of dust Degreasing is therefore a very important step in the process of surface preparation Various parameters must be checked The type of degreasing agent The degreasing temperature which must be between 60 C and 90 C depending on the process used The concentration of degreasing agent 45 50 g l The pH of the degreasing baths The treatment time 15 minutes immersion a few minutes spraying Possible mechanical action agitation of the bath or spraying pressure Alkaline degreasing is the most common process used Alkaline solutions can have three different physico chemical actions Saponification fatty substances are dissolved in the pre sence of an aqueous solution of soda or potash forming soluble soaps Emulsification fats are dispersed in fine droplets by phos phates or silicates Decrease in surface tension fat molecules are coated with organic agents which weakens the bonds between them and the substrate Two methods are employed immersion or dipping and spraying The mechanical action agitation of the bath spray ing pressure increases the effectiveness of degreasing In the case of degreasing by immersion several baths are arranged in series
31. d with each stage Advances made in all areas have tended to reduce these risks 8 11 Environmental risks associated with surface treatment Surface treatment can sometimes be very complex and in the case of direct on white enamelling may include degreasing pickling nickel deposition and rinsing These various operations use a great deal of water energy and chemicals which gene rate vapours and waste that need to be treated Ensuring that a surface treatment line of this kind complies with current legislation requires investment in a waste treat ment plant which can double the operating cost of surface preparation ArcelorMittal endeavours to develop products that respect the environment and that are simpler to use We are therefore currently perfecting surface coatings that will make it possible to simplify or possibly dispense with surface treatment before enamelling User manual Steel for enamelling and enamelled steel ArcelorMittal 8 1 2 Environmental risks associated with enamelling When enamel is supplied to the enameller in the form of frit the enameller needs to grind the frit and prepare a suspension in water after incorporating the necessary additives suspen sion refractory colouring agents electrolytes and opacifiers This method means that the waste produced during this pro cess must be treated and likewise the water used Enamel manufacturers have therefore developed ready to use enam
32. dioxide nitric oxide salt laden marine atmospheres ultra violet radiation and sudden changes in temperature will not lead to any changes in the appearance colour or gloss of the enamelled surface User manual Steel for enamelling and enamelled steel ArcelorMittal 7 4 Mechanical strength of the surface Like glass the surface of enamelled steel is very hard which means that it is extremely resistant to scratching abrasion impact and wear Hardness is classified as between 5 and 7 on the Mohs scale One of the benefits of the surface hardness of enamelled steel is that it is extremely resistant to abrasion which explains why it is so widely used in many fields such as domestic and sanitary equipment Abrasion resistance is determined by means of a friction test US High and low temperature stability Thanks to their vitreous nature enamelled surfaces have excel lent temperature stability Some applications especially in the domestic appliance sector pyrolytic self cleaning ovens and in industry require operating temperatures of about 450 C to 500 C Enamelled steel can also be subjected to temperatures of 60 C without any adverse effects on the enamel we are able to offer steels that are very resilient at this temperature 7 6 Thermal shock resistance Enamel is able to withstand wide temperature variations in ex cess of 100 C without undergoing any damage It can there fore be used in applications where
33. drain away in the case of outdoor applications thereby preventing corrosion Furthermore there must be sufficient space left between the cassette trays to allow for expansion Lastly the leak tightness of the system can be improved if necessary by using silicon sealing mastic User manual Steel for enamelling and enamelled steel ArcelorMittal 9 3 Other applications of enamelled steel 9 31 Applications in industry Enamelled steel also has important applications in industry even in the most corrosive atmospheres e g in the chemi cal and agro food industries Its resistance to chemicals and to fermentation makes it an excellent lining for silos chemi cal reactors dryers closed tanks and other water treatment plant storage systems Furthermore because of its resistance to high temperatures and heat reflection properties it can be used in columns and heat exchangers Its resistance to cor rosion caused by combustion gases also makes it an excel lent material for the manufacture of flue linings and exhaust manifolds 9 3 2 Sign panels Enamelled steel is an ideal solution for indoor and outdoor sign amp communication panels The surface will not be damaged by urban pollution weather UV or graffiti It is fire resistant and offers a host of decorative possibilities making it the best possible material for the most sophisticated graphic creations 9 4 Summary of the principal uses of steel
34. e the nickel deposition time and the nickel concentration in the bath vary according to pH The maximum quantity is achieved at a pH of 2 8 However it has been found that after the pickling process the pH at the surface of the part is less than 1 If rinsing is not carried out after pickling the pH will remain too low and insufficient nickel will be deposited If the part is rinsed in water the result will be the same The purpose of acid rinsing is therefore to increase the pH of the part without exceeding the optimum value Ni deposited A i T t Ni in the bath no rinsing A rinsing in water gt pH 2 8 User manual Steel for enamelling and enamelled steel ArcelorMittal 3 2 6 Nickel deposition Nickel plays an important part in the direct on white enamel ling process in promoting enamel adhesion If necessary it may be used in small quantities in conventional processes nickel flash The most common method used to deposit nickel is the pre cipitation of metallic nickel by displacement of iron ions 2Fe NiSO H SO gt 2FeSO Ni H Conditions NiSO 12 15 g l pH 2 8 temperature 70 C time 7 minutes As in the case of pickling the nickel deposition conditions have a significant influence on the quantity of nickel deposited A slight variation may have serious consequences on enamel adhesion To ensure that the direct on white enamelling process pro duces enamel with g
35. e at two different times The ease with which graffiti can be cleaned off is readily dem onstrated when the building is located in an area that is prone to graffiti attacks The use of enamelled steel for lining tunnels is recommended as it makes them easier and cheaper to clean ensures better illumination the enamelled surface reflects light well which means that less investment in lighting is required and im proves f re resistance There are also other possible applications such as sound proof walls water storage tanks pipes and water treatment plant systems where the use of enamelled steel highlights its resist ance to corrosive agents and to the proliferation of bacteria User manual Steel for enamelling and enamelled steel ArcelorMittal 9 2 2 Indoor applications Enamelled steel is a very popular choice for fitting out public places Flame resistant vandal proof easy to maintain and offering virtually unlimited scope for decoration it is ideal as a wall covering and for ceilings partitions lift cars etc It is therefore used in Metro stations Train stations Airports The interior decor of ships Since it is free of bacteria and is not affected by moisture it is also the perfect solution in hospitals clean rooms and sanitary systems 9 2 3 Recommendations for installation The installation of enamelled cassette trays for both building cladding and interior decoration applicat
36. e mass deposited can in fact cause localised withdrawal of the enamel during firing The dry coating obtained is called biscuit Air drying is not recommended as the parts may become contaminated by dust particles in the air and residual moisture may remain in the enamel favouring the formation of fish scale defects Dryers or ovens must be used at a temperature of between 70 C and 120 C Infrared radiation or convection drying is the safest way of preparing parts for firing 3 4 2 Firing of enamel With the exception of the process of enamelling on aluminised sheets firing is generally carried out at a temperature of be tween 780 C and 850 C which is well above the softening temperature of enamel 500 600 C It can be done in a box furnace or in a tunnel furnace continuous Firing time and temperature depend on the thickness of the steel and the type of enamel Firing is carried out in an oxidising atmosphere Box furnaces are generally used for short production runs and small parts They are particularly popular with independent enamellers Tunnel furnaces are either rectilinear U shaped or L shaped and are suitable for long production runs They are divided into three sections pre heating firing and cooling which permits a controlled increase and decrease in temperature The parts arranged on cradles pass through these sections suspended from a conveyor Air seals located at the entrance and exit of
37. e operation and determines the steel grade to be selected During the bending process the metal is bent over the tool if there is no friction or external tension there should be equi librium between the elongation of the exterior fibres and the compression of the interior fibres But friction detracts from the compression of the latter and tension increases the ex terior fibres tendency to elongate The neutral fibres move in the direction of the tool and the sheet becomes thinner This thinning obviously results in a loss of strength and any tension applied would soon cause rupture if the resistance of the metal to deformation had not been increased by work hardening The important property is therefore its work hardening capacity indicated by the strain hardening coefficient n Different bending techniques may be used narrow punch V bending flap bending automatic panel forming or edge forming Flap bending Bending on a panel forming machine 33 34 Forming of steel for enamelling 5 3 2 Deep drawing Deep drawing is the processing operation that makes it possi ble to exploit the formability of sheet steel to the maximum The success of a deep drawing operation depends on the op timisation of manufacturing parameters and meticulous fine tuning The material itself is obviously the first of the many parameters that can be adjusted The choice of a steel grade to produce a given shape depends initiall
38. e part to be enamelled The particles of enamel propelled out of the spray gun by a stream of air become negatively charged migrate towards the part to be enamelled positive electrode and are deposited there Once the first coat has been deposited the particles start losing their attractive force A repulsive force is then generated When this becomes equal to the attractive force the particles are no longer deposited This process therefore provides a uniform enamel coating and automatically limits its thickness The particles of enamel must be coated organic envelope generally silicon in order to prevent hydration which would have the effect of reducing their electric resistance thereby preventing correct deposition of enamel on the part The qual ity of the organic coating the grain size and rheology of the powder are key factors for obtaining uniform deposition of enamel and an attractive surface appearance after firing This process is highly effective for flat parts but it is more dif ficult to enamel hollow parts e g oven cavities because of the Faraday cage effect It offers many advantages Waste reduction Material savings Uniformity of coating thickness User manual Steel for enamelling and enamelled steel ArcelorMittal 3 4 Drying and firing of enamel 3 41 Drying of enamel Drying is a vital step after the wet application of enamel Mois ture which represents 40 50 of th
39. e phenomenon will be directly linked to the amount of water vapour in the system The steel s capacity to absorb hydrogen is also of crucial importance This defect is dreaded by both enamellers and end users as it only appears after a varying delay The main parameters that tend to aggravate the formation of fish scale defects are as follows A moist firing atmosphere Inadequate drying if the enamel is applied by the wet process Use of steel that is not suitable for enamelling Enamelling conditions thus have to be strictly monitored in order to counter this defect The steel must also have an ade quate hydrogen absorption capacity which requires manufac turing it with specific metallurgical properties 41 2 Impact on the metallurgical properties of steel for enamelling Cold rolled steel The production of enamelling steels must favour the even tual formation of sufficient hydrogen traps In the case of aluminium killed steel cementite clusters tend to form iron carbide Fe C during the hot rolling process at high coiling temperatures As iron carbides are very brittle their fragmen tation during cold rolling will cause small voids to appear in their trail these voids are called hydrogen traps Similarly manganese sulphide precipitates reduce fish scale defects During cold rolling these are deformed causing a loss of cohesion with the matrix and the appearance of small voids Other solutions that
40. els that are supplied in powder form enabling this process to be dispensed with These enamels are mixed with water prior to application The enamelling booths do need to be cleaned meticulously after each application cycle in which these enamels are used The resulting waste must be disposed of The development of enamel application methods based on electrostatic powdering circumvents this disadvantage In fact 99 of the enamel ends up on the part and the rest can be recovered for re use The even thickness of the enamel coating also means that this method yields enamel savings of between 20 and 30 compared with wet application processes 8 1 3 Environmental risks associated with firing the enamel The main risks are associated with the release of small quan tities of fluorine during the enamel firing stage though this corrosive element is less and less likely to be present in modern day enamels Furthermore firing furnaces are now equipped with exhaust gas treatment systems which considerably reduce the amount of pollution discharged to the atmosphere 8 2 Life cycle and disposal of the enamelled product The qualities of enamelled steel make it a very modern mate rial that complies with the latest environmental regulations Enamel enhances steel by considerably extending its life span No other steel coating metallic organic can give steel this level of durability Enamelled steel is also a material that is very easy to
41. en enamelling visible parts conventional enamelling is a relatively expensive process due to the need to apply two coats of enamel and have two f ring cycles The aim of direct on white enamelling is to achieve the same result i e a white enamelled part without any visible surface defects by applying a single coat of enamel and performing just one firing cycle It is therefore necessary to use an enamel that does not contain any adhesion oxides as otherwise it will not be white and a steel with a very low carbon content in order to prevent the release of gases during firing To ensure that the enamel adheres to the steel the part is pickled after degreasing in order to activate its surface and a coating of nickel is then applied with the aim of improving adhesion between the enamel and the steel Pickling is usually performed using sulphuric acid The intensity of pickling is measured by means of the iron loss value Optimum adhesion and surface appearance after enamelling are achieved with an iron loss of 25 g m per side and a nickel coating of between 1 and 2 g m per side The steel s low carbon content will be ensured by annealing open coil steel open coil annealing OCA which entails first running braided stainless steel wire between the wraps of the coil so as to leave a few mm of space between the wraps then annealing this coil in a batch annealing process in an oxidis ing atmosphere to decarburise the steel
42. f substrate lt 0 75 mm Maximum deflection 0 15 in both directions Criterion Reference Brief description Quality specification standard Corrosion resistance ISO 7253 Salt spray test a sample is exposed to salt No surface corrosion defects after 500 hrs of spray for a specific period of time The degree exposure to salt spray of delamination of the coating and the proportion of rust on the surface define the level of corrosion Acid resistance ISO 2722 Acid resistance is determined by placing the Class A minimum according to the reference sample in an aqueous solution of 10 citric norm acid at room temperature for 15 minutes The measurement is performed according to a reference norm ISO 2742 Acid resistance is determined by placing the Maximum weight loss 18 5 g m sample in an aqueous solution of boiling 6 citric acid for 150 minutes Acid resistance is determined by weight loss Surface appearance The enamelled surface is observed under The enamelled surface must be free of defects natural light from a distance of 1 5 m likely to spoil the general appearance of the enamelled part Gloss ISO 2813 The specular reflection of the coated product is Generally variations in the panel must not measured using a glossometer exceed 10 gloss units agreed beforehand by the matt appearance measurement angle of 85 parties involved glossy appearance measurement angle of 60 Colour ISO 7724 Measurement
43. for enamelling Steel type Process Dedicated steels for the process Other possible steels Use Hot rolled steels Enamelling on hot S240EK Water heater tanks rolled S300EK Cold rolled steels Ground enamelling DCOIEK Solfer Oven cavities DCO3EK Solfer Inner doors DCO4EK DCO4ES Dripping pans DCO6EK DCO7EK Two coat two fire DCOIEK Solfer Bathtubs enamelling DCO3EK Solfer Shower trays DCO4EK DCO4ES Architectural panels DCOSEK Signage DCO6EK DCO7EK Direct on white Solfer Hobs enamelling Solfer Covers Doors Two coat one fire DCO4ES Solfer Architectural panels enamelling Solfer DCO6EK DCO7EK Aluminised steels Enamelling on Alusi Alusi BEC Catalytic self cleaning oven cavities Alusi BEA Hobs Covers Doors User manual Steel for enamelling and enamelled steel ArcelorMittal 53 54 Uses of enamelled steel fe o TD S e 2 5 O E 3 g A 2 a oO Ve E gt gt a 3 3 2 Yn D TU D ES S v g El E 5 B S Si ei o 3 2 Doa 3 S S oa S l 8 ee NON ES el else ee E 3 v ES o ES O S OA amp wm OA ESA IS D EA fo oO Q 2 c a A 32 5 E gt o 77 7 Gy fo Fell EE ED Si Si ES tel Se ea el eS SB ea S Sl elg DOE EE Ea EEEE S g S Ele SEL 4 D o D so area E E S aka el 5 Market Manufactured component OME a Ele la 2 S sz S S amp SE Domesti
44. for enamelling and enamelled steel ArcelorMittal 27 28 Enamelling processes and associated steel grades 4 3 6 Block diagram of enamelling processes on cold rolled substrates Steel ma gt Nickel gt Firing Direct on white Suen Ss deposition at 830 C enamelling Application of Degreasing cover coat aan Firing Conventional Light pickling gt a Application of at 830 C enamelling ground coat Firing Two coat one fire at 830 C enamelling Firing Ground coat at 830 C enamelling without pickling 4 4 Low temperature enamelling on aluminised steel substrates enamel coat Alusi steel substrate This process is performed on an aluminised steel substrate The enamels used have been modified so as to ensure good adhesion on this type of substrate The process entails applying enamel to just one side of the part to be coated with the other side being protected from corrosion by the Al Si alloy coating then firing at a temperature of about 560 C low tempera ture firing User manual Steel for enamelling and enamelled steel ArcelorMittal 4 41 Aluminised steels for enamelling Alusi BEC and Alusi BEA Aluminised steels for enamelling are coated with an alloy of 90 aluminium and 10 silicon A special enamel suitable for this type of coating must be used for enamelling Afte
45. gh temperature can cause them to deform This is why it may be necessary to laminate backing boards on the inside of the panels so as to make the flat Various types of backing boards may be used aluminiu or galvanised steel sheets wood aluminium honeycomb struc ture cardboard or polymer The choice of material used will depend on where it is to be used outdoors or indoors and the thickness of the initial panel 51 52 Uses of enamelled steel In order to clad columns or pillars it is possible to make panels with a semi circular profile Since in this case the panel produ ced is more rigid a backing board is unnecessary In view of the thickness of enamelled panels and the pos sible laminate applied they vary between 15 and 30 kg m in weight All necessary precautions must therefore be taken in handling them particularly during installation on fa ades or walls The technique for installing enamelled cassette trays on a wall is identical to that used for any other metallic facing The cas sette tray is laid on a horizontal and or vertical framework ade of profiles in galvanised steel stainless steel or alu inium integral with the wall to be clad The panels are then screwed to this framework The fixing system may be visible or invisible Plastic spacers and washers protect the enamel from overtightening of the screws The space thus created between the wall and the panel will also allow surface water to
46. have been carefully optimised this method can always guarantee excellent internal quality of the molten nuggets This technique can be used with steel thicknesses of up to 1 2 mm electrode wheels a b electrode wheels 4 weld 7 sheet weld nuggets d 39 40 Joining of steel for enamelling Projection welding The projections are protuberances bulges with controlled geometrical dimensions formed by deep drawing or machining of one of the workpieces to be joined The passage of the welding current is localised right at the protuberance Projec tion welding is an attractive alternative when welding relatively solid fittings onto a thin steel sheet since the small volume of the protuberances will reduce the amount of heat taken up by the solid component during the welding process e g mounting threaded nuts or bolts on car body parts see figures g and h below To avoid premature failure of the weld the pressure on the electrode must be controlled exactly Welding time is usually short particularly with thinner gauges of steel e flat tipped force electrode sheet product bi weld nuggets eli projections force f 9 weld nuggets A ea h bolt weld nuggets P fi i User manual Steel for enamelling and enamelled steel ArcelorMittal 6 3 2 Gas shielded arc welding The principle of electric arc welding techniques is the applica tion of heat by striking a low v
47. he requirements of different applications S240EK and S300EK These can be supplied pickled unpickled oiled or unoiled We should point out that no standards exist for this kind of steel Grades S240EK S300EK Forming Bending Profiling Bending Hard profiling Light drawing A Drawing o Joining Problem free welding Enamelling process One side Surface treatment Possible degreasing shot blasting 2 enamelling Enamel application By the wet or dry process Enamel firing At approx 830 C Applications Water heater bottoms Water heater bodies Grade that can readily be used for the process forming or enamelling A Grade that can be used with caution forming or enamelling Grade that is not recommended or is prohibited forming or enamelling 1 Grades that can be welded without any difficulty whatever the welding process may be TIG MIG seam welding laser 2 The product is generally supplied pickled and unoiled Surface treatment may include degreasing followed by shot blasting The non enamelled side is coated with borax to prevent scale formation during firing 3 Enamel is usually applied by the wet process flow coating or spraying In this case the enamel must be dried between 70 C and 120 C Electrostatic powder application is another option User manual Steel for enamelling and enamelled steel ArcelorMittal 4 2 3 Use Grades S240EK and S300EK are used to manufacture water
48. hey offer excellent resistance to fish scale DCO4ED EN 10209 defects We can guarantee a minimum TH of 100 for grades DCO1EK DCO3EK DCO4EK DCO5EK DCO4ES Solfer and Solfer in accordance with EN 10209 Y Y Y Y x x un Grades UNIS NC NS NC NS glg O O O 8 oO a a A a aa O a n n Forming Bending Profiling A Bending Hard profiling Light A A drawing Drawing Deep drawing A A Joining Problem free welding Enamelling process Direct on white Degreasing EEE Surface treatment pickling and nickel deposition 2 By wet or Enamel application e dry process 3 Sr At approx Enamel firing o 830 C Two coat one fire Surface treatment o Degreasing enamelling J Enamel application By wet or dry process Enamel firing s At approx 830 C Conventional Surface treatment Degreasing enamelling Enamel application By wet or dry process ground coat enamelling and two coat two fire enamelling Enamel firing At approx 830 C Grade that can readily be used for the process forming or enamelling A Grade that can be used with caution forming or enamelling Grade that is not recommended or is prohibited forming or enamelling 1 Grades that can be welded without any difficulty whatever the welding process may be Other joining processes clinching lock seaming may also be used 2 Degreasing pickling and nickel deposition Iron l
49. icity and stability of colour These characteristics will be discussed in more detail below see chapter 7 Properties of enamelled steel 21 22 2222 2 2 2 ZS 2 8 1 282 Enamel The composition of enamel The manufaciure of enamel The various stages in manufacturing enamel Preparation of enamel The different types of enamel Enamel and substrate The different types of enamel for steel Enamel 21 The composition of enamel Enamel is a glass obtained by fusion at high temperature between 1000 C and 1300 C Its main constituent is silica SiO which is the most abundant mineral in the earth s crust Free silica exists principally in its crystallised form quartz which has a purity in excess of 99 It is also found in com bined form in feldspars clays and micas In order to confer on enamelled parts its properties of durability silica glass has to be modified as it cannot be used in its original state Its melting point is too high its coefficient of thermal expansion is too low compared to that of steel and its adhesion to steel is zero Va rious constituents therefore have to be added in order to ob tain an enamel These can be categorised in four main groups according to the properties they impart to the enamel Refractories which give enamel an amorphous structure and hence mechanical strength These include for example alumi na Al O which serves to lower the coefficient of expansion in
50. ick High quality stainless steel sub frame plus backing board Fixing system used for the new Girod building Section A A A Scale 1 12 l E B O O J T 1 ES A Ca o So 1 T Q Q P Ka le 1 amp oY Detail of B Scale 1 3 nylon spacer Girod nut gt nylon washers aluminium spacer pacer Al Rizoux reinforcing piece N stainless steel bolt M8x60 grub screw 1 d enamel panel User manual Steel for enamelling and enamelled steel ArcelorMittal PMA fixing system for BS Cassettes The BS Cassette system comprises a supporting framework onto which are fixed the facing and specific fittings Since the framework is designed to the dimen framework X p front view X sions of the cassette trays there are no standard dimensions framework Y front view Y front view side view section mounting lug _ vertical intermediate framework sealing joint joint cover strip User manual Steel for enamelling and enamelled steel ArcelorMittal 6l Credits Cover Tom D Haenens Philippe Vandenameele p 5 Philippe Vandenameele p 7 Heysel metro station Brussels Belgium artist Jean Fran ois Octave
51. indicates the steel s capacity to harden when plastic deformation takes place These properties only represent an imperfect description of the behaviour of steel in one simple example of a forming ope ration uniaxial tension User manual Steel for enamelling and enamelled steel ArcelorMittal Different deformation modes There are two deformation modes expansion and deep drawing Expansion is characterised by an increase in the surface area of the steel sheet and therefore a reduction in thick ness since the volume of the material remains the same which can lead to rupture of the steel in extreme cases This deformation mode can be seen in the top section of the drawn component in the figure below Deep drawing mode is caused by a compressive stress in the steel sheet which may lead to an increase in the thick ness of the material or wrinkling These two deformation modes coexist during the drawing pro cess the solution is to find the best compromise between deep drawing mode wrinkling and expansion rupture or necking expansion 5 plane strain N S 7 extension deep drawing Different deformation modes in a drawn component Forming limit curves Two methods exist to express these variations in mechanical properties By evaluating the stresses various plasticity criteria Tresca Von Mises Hill etc can be used to determine equations for the behaviour of the metal in all deformation
52. inding sieving magnetic separation packaging enamel frit packaging gt enamel powder ready to use enamel powder 0 User manual Steel for enamelling and enamelled steel ArcelorMittal ENAMELLER transportation ee transportation eee transportation gt enamel powder mixing with water enamel slurry addition of colouring agents mixing addition of water grinding 2 3 The different types of enamel Enamels have different compositions depending on the type of substrate to be coated and in the case of steel depending on the enamelling process used 2 31 Enamel and substrate The composition of enamels is varied in order to match the enamel firing temperature to the substrate The higher the firing temperature the better the quality of the enamelled parts As far as the metal is concerned however the firing temperature is limited by the substrate For example phase changes in steel must be taken into account Moreover the coefficient of expansion of enamel must be compatible with that of the substrate 2 3 2 The different types of enamel for steel Ground coat enamel Ground coat enamel contains metal oxides Ni Co Cu oxides which promote enamel to steel adhesion by creating alloys with the iron in steel see 7 1 on the subject of the adhesion of enamel to steel Since metal oxides are dark in colour white ground coat d
53. ing e g signs posters works of art or photographs If the process is performed at a high tempera ture these images will last as long as the rest of the enamelled panel Since the colours are created using mineral pigments they display considerable stability over time One particular feature is that they are not sensitive to UV User manual Steel for enamelling and enamelled steel ArcelorMittal 45 8 1 8 1 1 8 1 2 8 1 3 8 2 Enamelled steel and the environment The production process Environmental risks associated with surface treatment Environmental risks associated with enamelling Environmental risks associated with firing the enamel Life cycle and disposal of the enamelled product 48 48 48 48 48 47 48 Enamelled steel and the environment The criteria associated with sustainable development are such that assessing the ecological value of a particular prod uct is not just a case of considering the materials required to manufacture the product and any associated waste prod ucts but also evaluating the environmental impact of the product itself during its lifetime and when it is eventually disposed of The environmental impact of enamelled steel must therefore be considered on two levels During manufacture of enamelled parts During their life cycle and disposal 8 1 The production process Enamelling on steel is a relatively complex process and there are environmental risks associate
54. ions requires a few precautions to be taken In view of the properties of enamel it is usually impossible to modify an enamelled panel No bending cutting or drilling can be performed as this would damage the enamelled sur face Good site preparation is therefore very important for the architect or the building project manager A very accurate layout drawing of the surface to be clad will guarantee success and unlike other types of panels such as lacquered board the installation tolerance is very low It is therefore vital to know in advance the exact dimensions of all the panels and also the position of all the holes that will be used to hang them from the facade or wall in question The thickness generally used is between 1 5 and 3 mm and the widths about 1500 mm the feasible dimensions are limited by those of the enamel firing furnace It is possible to use thick nesses as low as 0 3 mm in which case the panel is glued to a more rigid sub frame steel aluminium etc For the manufac ture of the cassette trays bending radii of about 3 mm are rec ommended The corners may be either deep drawn suitcase corner deep drawing or welded The latter technique has the drawback that it is always more difficult to apply enamel on top of a weld Surface blemishes or pores in the enamel can actu ally appear on the bead or the heat affected zone if welding is not performed properly Firing enamelled cassette trays at hi
55. ked to the grade of steel employed To guarantee the attractive appear ance of the clinched joints localised lubrication with a volatile oil may prove necessary to limit friction between the punch the surface of the steel and the die User manual Steel for enamelling and enamelled steel ArcelorMittal 6 2 Lock seaming The term lock seaming covers all the mechanical processes for producing a joint by plastic deformation of at least one of the components involved Lock seaming can be used to join steel for enamelling provided that the steel grades are chosen to withstand the strains gene rated in the folds However lock seaming is only suitable for parts with a geo metrically simple design and cannot be used for corners Lock seamed joints cannot be dismantled and have a low re sistance to slipping in a direction parallel to the folds and a low resistance to joint opening DJ U 6 Different single and double lock seams Fm Wi a Z 6 3 Welding Resistance welding is the most common welding process though arc welding techniques are used for some applications 6 31 Resistance welding Resistance spot welding This is a complex process including electrical passage of an electric current thermal dispersion of heat energy me chanical application of significant pressure and metallurgical aspects whereby the aim is to generate heat by the passage of an electric current and then the local fusion
56. l ArcelorMittal Steel for enamelling and enamelled steel User manual User manual Steel for enamelling and enamelled steel 1 Introduction 22 Enamel 3 Enamelling of steel 4 Enamelling processes and associated steel grades 5 Forming of steel for enamelling 6 Joining of steel for enamelling 7 Properties of enamelled steel 8 Enamelled steel and the environment 9 Uses of enamelled steel 10 Appendices 13 21 31 37 43 47 49 55 Introduction Enamelled steel is a material with exceptional properties and has many applications in various aspecis of everyday life In the home enamelled steel is used in the kitchen for worktops and casings for domestic appliances This has the advantage of making them resistant to any sort of everyday damage so that both hot dishes and frozen food can safely be placed on them for instance it also means that they can be cleaned with a quick wipe f a sponge The same material is used for cookware again offering array of advantages enamelled saucepans prevent the growth nd can be used directly on the gas hob In the bathroom we find athtubs in all shapes and colours in a matt shiny or satin finish O a of bacteria do not absorb odours are not attacked by food acids a b a nd impervious to the ravages of water and time Last but not east enamelled water heater tanks prevent any water leaks Enamelled steel also has i
57. llows this historical trend However before we outline these processes we must first mention the main parameter that will govern the metallurgy behind them resistance to fish scale defects 41 Hydrogen and fish scales 411 Formation of fish scale defects As we have observed already hydrogen penetrates the steel during the enamel fring cycle in the following manner The moisture H O in the air in the furnace atmosphere penetrates the enamel and migrates towards the enamel steel interface The H 0 then breaks down The oxygen is used in bonding reactions between the enamel and steel Atomic hydrogen diffuses into the steel and then recom bines in the form of hydrogen gas H During this phase of rising temperatures hydrogen solu bility in the steel increases Fish scale defects User manual Steel for enamelling and enamelled steel ArcelorMittal During the cooling cycle hydrogen solubility in the steel decreases The enamel solidifies Some of the excess hydrogen has to escape from the steel since its solubility decreases The hydrogen migrates towards the enamel steel interface and remains trapped it is no longer able to escape since the enamel has solidified Oversaturation with hydrogen therefore creates very high local pressure spots Enamel blisters are formed resul ting in the defect known as fish scale it resembles fish scales hence its name The intensity of th
58. lls off over time as a result of progressive blockage of the pores Pyrolytic cleaning takes place while the oven is empty at about 520 C Fat and residues that are deposited on the walls during cooking are burnt at this temperature leaving only a carbon deposit that can be wiped off C H 0 heat gt xC yH O This type of enamel has a softening point higher than the pyrolytic temperature It is glossy non porous and highly resistant to acids and alkalis Cover coat enamels Cover coat enamels give enamelled parts their aesthetic qua lity and also help to increase their chemical resistance Since they contain absolutely no adhesion agent they cannot be used alone on a metal substrate under any circumstances Enamels for low temperature firing These enamels for use on aluminised substrates have been developed from enamels used for aluminium by modifying the coefficient of expansion Their firing temperature 560 C is lower than that of enamels used on bare steel substrates 31 3 2 321 3 2 2 3 2 3 3 2 4 3 2 5 3 2 6 3 2 7 33 3 31 33 2 3 4 3 41 3 4 2 3 4 3 Enamelling of steel The enamelling process Surface treatment before enamelling Shot blasting Degreasing Rinsing Pickling Acid rinsing Nickel deposition Final rinse neutralisation and drying Enamel application Wet application Dry application electrostatic powder spraying Drying and firing of enamel Drying of enamel Firi
59. melling Steel for enamelling is compatible with many commonly used metal joining techniques clinching lock seaming and welding 61 Clinching Clinching is a discontinuous joining technique in which local joining points are produced by simultaneous deformation of two or more sheets of steel with the aid of a punch and die Clinched joint This process requires neither preformed holes nor additional material Since the joint does not need to be heated there is no heat affected zone Clinching is a clean process that produces no fumes or slag it is relatively quiet and uses little energy It can be easily automa ted and easily integrated into a manufacturing line Regarding the appearance of the sheets each clinched joint produces a hump and a hollow which may limit their suitability for certain applications Since the static strength of a clinch is lower than that of a spot weld 30 70 of spot weld strength a greater density of clinched joints is required The clinching tool must be perfectly perpendicular to the sheets and the punch must be very pre cisely positioned with respect to the die The following guidelines must be observed for clinching The thinner sheet should not be less than half the thick ness of the thicker sheet The maximum thickness after joining is 6 mm This maximum thickness can be decreased if the steel used has greater mechanical strength The ease of clinching of a steel sheet is directly lin
60. mportant applications in industry even in the most corrosive atmospheres e g in the chemical and agro food industries Its resistance to chemicals and to fermentation makes it an excellent lining for silos chemical reactors dryers closed tanks and other water treatment plant storage systems Furthermore because of its resistance to high temperatures and eat reflection properties it can be used in columns and heat ex h changers Its resistance to corrosion caused by combustion gases also makes it an excellent material for the manufacture of flue inings and exhaust manifolds Finally the use of enamelled steel is a first rate solution in the User manual Steel for enamelling and enamelled steel ArcelorMittal construction enamel coati ration as it successfully combines a rigid pleasing durable and easy to clean maki appeal to even the most demanding clients Enamelled steel can also be an appropriate option for lining tu are easier and cheaper to clean and improves f re resistance industry for cladding buildings or for interior deco ng The result is an end prod ng it a material that wil steel substrate with an uct that is aesthetically nnels as it ensures they Introduction Definition The fusion at high temperature of two materials as noble and as different as steel and enamel has given rise to a material with quite remarkable p
61. nally enamelled material has the advantage that it is not necessary to apply a ground coat of enamel There is direct adhesion between the enamel and the substrate Its performance during catalytic cleaning cycles is in compliance with ISO 8291 The Alusi BEA grade is designed for the enamelling of visible parts and can be used in the following fields of application Enamelled casing parts for domestic appliances hobs front and side panels Indoor architectural applications 4 4 3 Use Forming Alusi BEC and Alusi BEA grades can be formed by bending profiling or deep drawing The aluminium coating has the ad vantage of increasing the friction coefficient However great care should be taken to avoid scratching the surface of the part since this would produce surface blemishes after enam elling The use of hard polished chromium plated tools is rec ommended Joining After suitable modification of the welding parameters for cold rolled sheet Alusi BEC and Alusi BEA grades can be welded without any difficulty whatever the welding processes may be spot welding TIG MIG MAG etc Other joining processes clinching lock seaming may also be used Enamelling Surface preparation Surface preparation is very important It is crucial es pecially with Alusi BEA grade to perform meticulous alkaline degreasing followed by hot and cold rinsing using demineralised water for the final rinse good surface appear
62. nd mechanically Besides not harbour ing bacteria the enamelled surface can be cleaned very easily using even the most aggressive products If cared for properly it will always look brand new 9 2 Enamelled steel and the construction industry Enamelled steel has many applications in construction It can be used as a cladding for buildings or tunnels and in the interiors of public places such as train and metro stations airports and other buildings as a wall covering and for false ceilings parti tions and lifts Enamelled steel is also an excellent material for fitting out clean rooms 9 21 Outdoor applications Weather and UV resistant with virtually unlimited scope for decoration enamelled steel is the ideal solution for outdoor applications Enamelled panels are particularly suitable for separation walls or for cladding more traditional brickwork buildings They are prefabricated by the enameller to match the exact dimensions of the building in question This technique has obvious financial advantages over conventional building methods The panels can be installed in any weather irrespective of the outside temperature Due to the durability of the colours colour stability can be guaranteed for 40 even 50 years enamelled panels can be replaced when a building is being renovated or extended with out any noticeable difference in colour Consequently it will not look as if the work had been don
63. ng of enamel Enamel to steel adhesion mechanisms 14 Enamelling of steel Sil The enamelling process The enamelling process entails applying and firing one or more layers of enamel on one or both sides of a suitable steel sub strate cover coat ground coat steel substrate class appearance adhesion 0 004 0 05 User manual Steel for enamelling and enamelled steel ArcelorMittal Successful enamelling is characterised by Good adhesion of enamel to steel Good surface appearance after firing of enamel The carbon content of the steel can hinder the process of achieving these two properties Carbon is important to ensure the adhesion of enamel However if its content is too high this can adversely affect the surface appearance of enamel due to the release of gaseous CO and CO produced during firing This antinomy explains the variety of enamelling processes that exist The enamelling process generally comprises several steps Preparation of the surface of the part after forming Preparation of the enamel Application of the enamel to the steel Drying Firing at high temperature There is a choice of several enamelling processes depending on the type of part and final appearance required Enamelling on hot rolled substrate Conventional enamelling two coats two firings Ground coat enamelling one coat one firing Direct on white enamelling Two coat one fire enamelling Enamelling on metallic coated
64. oes not exist More reactive ground coat enamels exist containing a higher proportion of metal oxides which avoids the need to pickle the steel before enamelling These enamels are used for in stance for the two coat one fire enamelling process Ground coat enamel also protects against corrosion of the enamelled part Furthermore depending on the type of part to be enamelled other constituents will be added to obtain Acid resistant properties oven cavities dripping pans by addition of TiO Alkali resistant properties sanitary ware washing machines by addition of ZrO Improved corrosion resistance for water heater applica tions by addition of ZrO and Al O User manual Steel for enamelling and enamelled steel ArcelorMittal Self cleaning enamels Self cleaning enamels are used in domestic ovens and help eliminate the fat produced when food is cooked There are two types of self cleaning enamels catalytic and pyrolytic We therefore talk about catalytic and pyrolytic self cleaning ovens Catalytic cleaning takes place while the oven is working normally at about 200 C Enamel contains oxides that catalyse the breakdown of fat forming water and carbon dioxide Moreover this type of enamel is very refractory hence porous which has the effect of increasing the contact surface between the enamel and the fat thus facilitating its elimination C H 0 catalyst gt xH 0 VCD Efficiency fa
65. of the difference in colour of a The measuring method and the tolerated sample compared with a reference standard difference in colour are agreed beforehand by either visually the parties involved or using a colorimeter UV resistance ISO 4892 The sample is exposed to cyclical UV radiation Measurement of the colour and gloss before and for 1000 hours a cycle consists of 4 hours after the test exposure to UV radiation at a temperature of 60 C followed by 4 hours condensation without radiation at a temperature of 40 C Resistance to graffiti Cleaning of the enamelled surface It must be possible to easily clean off ink varnish lacquer and paint after they have aged for 8 days using appropriate solvents without any change in colour or gloss of the surface Reaction to fire CSTB Standardised tests to determine reaction to fire Class Al ex MO Low temperature stability Resistance to cold 60 C in so far as the steel is sufficiently resilient at this temperature High temperature stability Resistance to heat 450 C User manual Steel for enamelling and enamelled steel ArcelorMittal 59 60 Appendices 10 3 Recommendations for installing enamelled architectural panels A few examples of fixing systems Omeras fixing system Fixing of a rainscreen cladding Sub frame in hot dip galvanised steel or stainless Fixing of flat enamel panels in a tunnel steel variable joints enamel panels 1 5 mm th
66. oltage arc between an electrode and the steel sheet There are several possible methods plasma TIG MAG but MAG is recommended because it is the most productive In MAG welding the electrode is consumable and provides the filler metal The molten metal is protected from corrosion by an active barrier gas 100 CO binary Argon CO or tertiary Argon CO O This method can be used to join materials of a different type and of any thickness solid wire electrode shielding gas current conductor wire guide and contact tube solidified weld metal al travel nozzle _ shielding gas arc lt molten weld metal For MAG welding of thin sheets the most common configu ration is the superposition of the two sheets to be welded to produce a lap weld This welding method involves the addition of material to form the joint which means that the finished part is not aesthetically pleasing since the appearance of the weld itself is generally unattractive It is advisable to choose electrode wire with mechanical and chemical properties similar to those of the steel grades to be welded Moreover if the heat affected zone area around the weld is too large this may cause bubble type surface blem ishes after enamelling local modification of the metallurgical properties of the steel lap weld fillet weld gutter position weld aa da Y outside corner weld
67. ood adhesion and an attractive appear ance an optimum combination exists between the iron loss to be obtained and the quantity of nickel deposited iron loss 25 50 g m per side nickel coating 1 2 g m per side Ni 9 m 1 side A poor appearance 2 good adhesion good appearance 1 poor adhesion 0 4 E iron loss 0 25 50 9 m 1 side 18 Enamelling of steel 3 2 7 Final rinse neutralisation and drying The purpose of the final rinse is to eliminate all traces of acid still present on the surface of the part Two baths are generally used First bath 2 5 lt pH lt 3 2 and T 30 35 C for 7 minutes Second bath 3 5 lt pH lt 4 and T 25 C for 7 minutes The purpose of neutralisation is to completely eliminate any acid residues 10 5 lt pH lt 11 5 and T 70 C for 7 minutes Once surface preparation is complete the parts must be dried to prevent them rusting before enamelling User manual Steel for enamelling and enamelled steel ArcelorMittal 3 3 Enamel application Enamel may be applied using either the wet or dry process 3 31 Wet application There are several ways of applying enamel by means of the wet process Dip coating The parts to be coated are plunged into an enamel slurry mix ture of enamel powder and water the density and viscosity of which are closely monitored The parts are then suspended to allow the excess enamel applied to drip off thus ensuring
68. oss of 25 g m per side Nickel coating of between 1 and 2 g m per side 3 A 130 u coat of enamel is applied using the wet or dry method spraying electrostatic dip enamelling ETE or electrostatic deposition 4 Meticulous degreasing must be performed 5 Enamel is applied using the wet or dry method spraying or electrostatic deposition Suitable ground coat enamels with added adhesion oxides nickel or cobalt oxide must be used The thickness of the ground coat should not exceed 30 u as otherwise the reactivity will be too high The thickness of the cover coat should be 100 u 6 Surface treatment is limited to degreasing only If additive free ground coat enamel is used light pickling is recommended targeting an iron loss of 5 g m per side after meticulous degreasing especially for grades DCOGEK and DCO7EK which have a lower surface reactivity Surface reactivity can be improved by a nickel flash Pickling can be avoided by using a ground coat enamel with added adhesion oxides nickel or cobalt oxide 7 Enamel can be applied by a wet or dry process dip coating spraying or electrostatic deposition A ground coat with or without additives is applied to a thickness of about 100 u on both sides In the case of two coat two fire enamelling a cover coat is applied on the visible side to a thickness of about 130 u The enamel must be dried if applied using the wet method at a temperature of between 70 C and 120 C User manual Steel
69. pacifiers serve to increase the opacity of enamel and are present in cover coat enamel The most common are titanium dioxide TiO antimony oxide Sb 0 zirconium oxide ZrO and tin oxide SnO Colouring agents are obtained by combining mineral oxides The colour of enamel depends on the type of colouring agent its concentration in the enamel the chemical composition of the enamel and the firing conditions in the enamelling furnace User manual Steel for enamelling and enamelled steel ArcelorMittal The most common procedure is for the colouring agent in the form of fine particles to be mechanically mixed with the enamel during the grinding stage before application to the substrate 2 2 The manufacture of enamel 2 21 The various stages in manufacturing enamel The first step is to check weigh and mix the various consti tuents of enamel up to 15 This is followed by the fusion stage The purpose of the fusion process is to render the final amor phous structure of the enamel uniform and to lower the firing temperature This requires the glass to be melted at a tem perature of between 1100 C and 1300 C depending on the desired composition of the enamel The most common process involves using a tunnel furnace gas or electric where the mixture is introduced at one end and comes out the other Movement through the furnace is by gravity The mixture remains in the furnace about an hour When it emerges
70. phere that has been ionised in an electric field and become negatively charged before being deposited on the part to be enamelled Once the initial coats have been applied the droplets will be less and less attracted to the part and a repulsive force will arise This opposes the attractive force until equilibrium is reached thus controlling the thickness of the coating The resulting enamel coating is uniform and losses are minimised The ETE process Elektro Tauch Emaillierung electrostatic dip enamelling or electrophoresis The electrophoresis process is principally used for direct on white enamelling Particles of enamel in colloidal suspension in a saline solution are conveyed under the effect of an electric field They become negatively charged on the surface and are carried to the anode of the electrolytic cell which is the part to be enamelled This process results in a very uniform thickness of enamel automatic limitation of deposition and an excep tional surface appearance It is a very efficient technique for flat parts but does have a few drawbacks Itis expensive It requires the use of a cathode having the shape of the part to be enamelled Monitoring the electrical properties of the enamel slurry is complex 3 3 2 Dry application electrostatic powder spraying The principle of electrostatic powder spraying is the same as for the wet method An electric field is formed between the nozzle electrode and th
71. pickling is as follows iron in solution in the acid hydrogen gas Fe2 SO 2 H iron sulphuric acid E Fe 2H SO E gt Standard pickling conditions are as follows Temperature of the acid bath 70 75 C Concentration of sulphuric acid H SO at 7 Pickling time 10 15 minutes Concentration of iron in the bath 2 g l The slightest variation from these standard conditions may lead to a significant variation in iron loss and hence in enamel adhesion Chemical analysis of the steel is also an extremely impor tant parameter for checking iron loss Some elements such as phosphorus copper or molybdenum have a major influence on its value It is therefore vital to accurately check the concen tration of the various chemical elements in steel n the case of direct on white enamelling pickling is the key step for obtaining good quality parts After pickling the surface pattern observed will vary according to the iron loss measured The photos below show the influence of pickling on the surface of the part in particular the micro roughness on the grains and the attack on the grain boundaries Underpickled surface 3 2 5 Acid rinsing In the case of direct on white enamelling we shall see later that nickel must be deposited on the part after pickling to en sure good adhesion of the white enamel to the steel The quantity of nickel that can be deposited on a part at a given temperatur
72. r forming these steels can be enamelled at low tempera ture by means of a simpler more economical and environmen tally friendly process than the conventional method on cold rolled steel There are two grades available Alusi BEC and Alusi BEA Surface preparation of these grades consists of no more than very meticulous degreasing no pickling Only one coat of enamel with a thickness ranging between 80 and 100 um is required on one side only the other side being protected naturally by the aluminium coating which forms a highly re sistant aluminium oxide layer during firing Firing is performed at 560 C preferably in a convection oven so as to keep the temperature of the enamelled part as even as possible in order to ensure a homogeneous colour It is difficult to achieve a very glossy surface appearance after enamelling however max specular gloss 80 A wet or dry enamelling process may be used The corrosion resistance of the non enamelled side of the enamelled part is excellent it can withstand the salt spray test for over 500 hours in accordance with ISO 7253 Finally the use of aluminised steel for enamelling leads to cost savings of between 8 and 15 for the finished product com pared with the conventional enamelling process on cold rolled steel 44 2 Application The Alusi BEC grade is especially suitable for enamelled ca talytic self cleaning oven cavity walls Use of this steel rather than conventio
73. recycle lt has the advantage over other materials of being classified as a recoverable material and not as waste It does not give off toxic fumes or produce other dangerous substances when disposed of It is 100 recyclable without the need for any preliminary treatment QU 911 922 913 972 921 DD 923 9 3 981 9 3 2 9 4 Uses of enamelled steel Domestic uses of enamelled steel Electric water heaters Domestic appliances and cookware Sanitary ware Enamelled steel and the construction industry Outdoor applications Indoor applications Recommendations for installation Other applications of enamelled steel Applications in industry Sign panels Summary of the principal uses of steel for enamelling 50 50 50 50 51 51 51 51 52 52 52 53 49 Uses of enamelled steel 91 Domestic uses of enamelled steel 911 Electric water heaters An electric water heater consists of an external protective cas ing insulation an inner tank containing the water to be heated and a heating element The element converts electrical energy into heat which is conveyed to the cold water in the lower part of the water heater Water circulates in the tank by convection and its temperature is controlled by a thermostat Enamel covers the inner wall of the tank protecting it from corrosion Furthermore since enamel is a food grade material the water can also be safely used in the kitchen In view of the
74. roperties and offering many applica tions enamelled steel The origins of the use of enamel are lost in the mists of time but its qualities have always been highly prized The remark ably well preserved enamelled pottery and jewellery found on sites of ancient Egyptian and Persian civilisations testify to the astonishing durability of this material Today enamelling steel has become a high tech process using highly sophisticated materials and state of the art tech niques Enamelled steel is a material that meets modern day requirements of longevity aesthetic qualities hygiene and respect for the environment The enamelling process entails applying one or more layers of enamel to the pre prepared surface of an appropriate grade of steel and then f ring it at atemperature of between 780 C and 850 C This requires the involvement of three parties A steel manufacturer An enamel manufacturer An enameller who can be either a manufacturer or a subcontractor A brief history of enamel The earliest examples of jewellery and gold and silverware that make use of the technique of cloisonn amp enamel on metal gold silver copper bronze come from Cyprus and date back to the Mycenaean period most likely around the 13 century BC The technique then spread to Egypt and Greece around the 6 century BC he Celts developed the champlev enamel method in the 3 entury BC The golden age of enamelling was between the
75. simplify the preparation of the slurry The powder is prepared by the enamel manufacturer by adding specific products before grinding The enameller has only to add colouring agents optional before mixing the powder with water to obtain the slurry User manual Steel for enamelling and enamelled steel ArcelorMittal rolling mill furnace duration 1 hour glass sheet Enamel may also be applied in the form of powder obtained by grinding the frit The grinding time is determined experi mentally The ground powder then has to be sieved to be rid of lumps and various residues then passed through a magnetic separator permanent magnet or electromagnet to eliminate any iron particles in the powder These particles tend to create holes in the enamel which reduces the steel s corrosion pro tection Finally the grains of enamel are coated with silicon enabling them to adhere to the substrate between the appli cation and firing stages The enamel powder obtained does not require any additives or further treatment at the enameller and can be directly used in powder spray guns It takes a great deal of investment to set up a powder unit as it has to be elec trostatic to be financially viable However this process is more economical in the long term 10 Enamel Preparation of the enamel ENAMEL MANUFACTURER grinding sieving magnetic separation coating with silicon packaging specific additives mixing gr
76. slitting horizontal clearance The slitting quality is considered to be good if The distorted zone is small The shear zone is roughly a third of the thickness The fracture zone is sharp with an angle of less than 5 There are few or no burrs Cutting to length on a shearing line produces burrs oriented in opposite directions on the front and reverse sides of the steel sheet This aspect is important since it means that it is essen tial to stack the sheets perfectly vertically The use of disk cutters and similar techniques is not recom mended since they produce chips and high burrs Laser or plasma cutting techniques can also be used Their ad vantages are high precision and the absence of burrs 6 to8 g distorted zone plastic rounding A shear zone fracture zone little or no burr formation upper shaft steel sheet k vertical clearance steel sheet crossover horizontal clearance between steel lower shaft Horizontal and vertical blade clearances User manual Steel for enamelling and enamelled steel ArcelorMittal 5 3 Forming There are two main techniques for forming steel for enamel ling Bending which is mainly used for making panels architec tural and signage applications Deep drawing which is particularly used in the domestic appliance and sanitary ware industries 5 31 Bending In conventional sheet steel processing bending is the most se ver
77. y on the assumption that the prop erties of the finished part will be such that it can withstand the stress indicated in the specifications Regarding the forming it will undergo this means that the formability of the steel rheological aspect and its surface properties with respect to contact between the steel and the tool tribological aspect must be appropriate for the shape to be produced the required appearance of the final product and the expected cost The mechanical properties of steel In the context of forming steel sheets it is worth remembering that they will react very differently depending on how stress or strain is applied The most commonly used mechanical properties are those that can be determined by a uniaxial tensile test This test has the advantage of being simple to execute and providing a large amount of data at the same time The following mechanical properties can be determined by this test Ro yield strength stress level above which deformation becomes plastic and therefore permanent R ultimate tensile strength or breaking load A elongation at rupture r Lankford coefficient plastic strain ratio which expres ses the ratio of the true width strain to the true thickness strain for a given elongation usually 25 It gives a good idea of the capacity of the sheet to deform in deep drawing mode and varies according to the orientation of the sheet specimen axis n strain hardening coefficient which
Download Pdf Manuals
Related Search