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Steel for enamelling and enamelled steel User manual

1. Direction Thickness mm YS MPa TS MPa E r 90 r average n 90 DCOIEK 0 4 0 5 140 310 226 EN 10209 IF 0 5 0 7 140 290 270 390 gt 28 0 7 3 140 270 230 DCO3EK 0 4 0 5 140 280 228 AM FCE TF 0 5 0 7 140 260 270 350 230 0 7 3 140 240 232 DCO4EK 0 4 0 5 140 260 232 EN 10209 J 0 5 0 7 140 240 270 350 gt 34 0 7 3 140 220 gt 36 DCOSEK gt gt EN 10209 T 0 7 3 140 220 236 15 DCO6EK 0 4 0 5 120 230 236 EN 10209 0 5 0 7 120 210 I 270 350 21 6 0 7 2 238 120 190 2 3 214 DCO7EK 0 5 2 ei 20 19 U 90 160 270 350 240 2 3 Solfer CA 0 4 0 5 140 260 232 AM FCE T 0 5 0 7 140 240 270 390 234 0 7 2 140 220 236 Solfer 0 5 0 7 140 260 gt 32 EN 10209 li 270 370 0 7 2 140 240 234 Solfer 0 5 0 7 140 230 236 EN 10209 T 270 350 0 7 2 140 210 238 Sn T 0 5 2 280 380 360 480 220 1 The guaranteed minimum yield strength after 5 deformation and enamel firing is 300 MPa User manual Steel for enamelling and enamelled steel ArcelorMittal Mechanical properties of hot rolled steels for enamelling Direction Thickness mm YS MPa TS MPa Ego E 5 65 VSo S240EK 1 3 3 a2 i gt 240 360 430 3 6 gt 34 S300EK 15 3 280 420 225 T 360 500 3 5 2 260 420 230 User manual Steel for enamelling and enamelled steel ArcelorMittal 55 Appen
2. 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 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 break down 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 saucepans 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 913 Sanitary ware The sanitary ware market also exploits the qualities of enam elled steel The properties of the steels available nowadays make it possible to design and offer a wide range of bathtubs wash hand basins and sinks in a variety of shapes and sizes to
3. Steel SET Nickel Firing at Direct on white Strong pickling deposition 830 C enamelling Application of Degreasing cover coat i ii Firing at Conventional Light pickling s 830 C enamelling Application of ground coat Firing at Two coat one fire 830 C enamelling Firing at Ground coat 830 C enamelling without 4 4 Ready to Enamel cold rolled steel Ready to Enamel cold rolled steel enables forming without the addition of a lubricant and enamelling without surface prepara tion It is obtained by surface deposition of a dry organic coat ing It can be applied on all cold rolled enamelling steel grades DCO1EK DCO4EK Solfer Solfer CA Ready to Enamel cold ro different types of parts Hobs or cladding pane DCOGEK DCO7EK Solfer led steel can be used to manufacture s enamelled in white or colour using the two coat one fire or conventional enamelling process Oven cavities or trays anti acid or pyrolytic enamelled with ground coat enamel Other applications sanitary ware architecture etc This product is patented by ArcelorMittal User manual Steel for enamelling and enamelled steel ArcelorMittal pickling R 5 Forming of steel for enamelling 5 1 Transport and storage 5 2 Decoiling slitting and cutting 5 3 Forming 5 3 1 Bending 5 3 2 Deep drawing User manual Steel for enamelling and enamelled steel ArcelorMittal SN
4. surface of the part in particular the micro roughness on the grains and the attack on the grain boundaries Normal pickling Overpickling 16 User manual Steel for enamelling and enamelled steel ArcelorMittal 3 2 5 Acid rinsing n the case of direct on ensure good adhesion of The quantity of nickel iven temperature the that after the pickling p part is less than 1 If rinsi pH wil If the part is rinsed in wa The purpose of acid rins the part without exceedi Ni deposited no rinsing that nickel must be deposited on the white enamelli the white enam that can be de nickel depositio rocess the pH ng is not carried remain too low and insufficient ni ng we shall see later part after pickling to el to the steel posited on a part at a n time and the nickel g concentration in the bath vary according to pH The maximum quantity is achieved at a pH of 2 8 However it has been found at the surface of the out after pickling the ckel will be deposited ter the result wi ing is therefore ng the optimum rinsing in wate be the same to increase the pH of value T t Ni in the bath N gt PH User manual Steel for enamelling and enamelled steel ArcelorMittal 3 2 6 Nicke deposition Nickel plays an important part in the direct on white enamelling process in pro moting enamel adhesion If necessary it may be used in
5. 6 min m pressure current ON onran OFF applied pressure ON electrodes pressure released N electrode electrode tip indentation weld nugget sheet separation heat affected zone electrode User manual Steel for enamelling and enamelled steel ArcelorMittal weld nugget S 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 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 an wheels a b a wheels e SR v o weld nuggets d 2 38 Joining of steel for enamelling Projection welding The projections are protuberances bulges with controlled geometrical dimensions formed by deep drawing or machin ing of one of the workpieces to be joined The passage of the welding current is localised right at the protuberance Projec
6. Ana lyse the factors that influence forming steel grade component design lubrication tool design draw beads radi etc 1 S300EK thickness 1 7 mm 0 6 non drawability range drawability range 0 22 0 1 06 0 5 0 4 0 3 0 2 0l 0 0 1 0 2 0 3 0 4 0 5 Example of FLC for a steel for enamelling User manual Steel for enamelling and enamelled steel ArcelorMittal 33 34 User manual Steel for enamelling and enamelled steel ArcelorMittal User manual Steel for enamelling and enamelled steel ArcelorMittal Joining of steel for enamelling 6 1 Clinching 6 2 Lock seaming 6 3 Welding 6 3 1 Resistance welding 6 3 2 Gas shielded arc welding 6 3 3 Welding fumes 6 3 4 Reconditioning 36 36 37 37 38 39 39 35 Joining of steel for enamelling Steel for enamelling is compatible with many commonly used metal joining technigues clinching lock seaming and welding 61 Clinching Clinching is a discontinuous joining technigue in which local join ing 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
7. Transport and storage upper shaft 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 ated storage facilities to ensure that no moisture accumu ates n particular coils sheets and blanks should not be stored near windows doors etc to avoid extreme variations in temperature that could produce condensation During transport and if outdoor storage is unavoidable the upper shaft coils sheets and blanks should be protected Avoid storing the products directly on the floor lower shaft Symmetrical mounting of slitting blades 5 2 Decoiling slitting and cutting lower shaft The drive system for decoiling must be adjusted to match line speed in order to optimise product flow In extreme circum Non symmetrical mounting of slitting blades 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 front side of burrs Slitting cutting to length and shearing operations should be v reverse side 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 cut
8. 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 exceptional n ique for flat parts surface appearance It is a very efficient tech but does have a few drawbacks It is 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 the part to be enamelled The particles of enamel propelled out of the spray gun by a stream of air become nega tively charged migrate towards the part to be enamelled pos tive 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
9. defects see chapter 4 1 p time min A 900 enamel impermeable to atmospheric Oz and reaction of oxides with enamel 800 700 5 fusion of enamel solidification of enamel 600 500 400 porous enamel and reactions stop 300 oxidation of iron 200 100 0 1 2 3 4 5 6 7 User manual Steel for enamelling and enamelled steel ArcelorMittal User manual Steel for enamelling and enamelled steel ArcelorMittal Enamelling processes and associated steel grades 4 1 Hydrogen and fish scales 4 2 4 3 4 1 1 4 1 2 4 1 3 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 4 2 1 4 2 2 4 2 3 Scope of application The ArcelorMittal range of hot rolled steel for enamelling Use Enamelling on cold rolled steel 4 3 1 4 3 2 4 3 3 4 3 4 4 3 5 4 3 6 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 4 4 Ready to Enamel cold rolled steel 22 22 22 23 24 24 24 24 25 25 25 25 26 26 28 28 21 22 Enamelling processes and associat
10. form of powder obtained by grinding the frit The grinding time is determined experi has to be sieved to be rid ectromagnet to eliminate duces the steel s corrosion mel are coated with silicon here to the substrate between the applica powder obtained does not tment at the enameller and be directly used in powder spray guns It takes a great deal unit as it has to be elec financially viable However this process is more Enamel Preparation of the enamel ENAMEL MANUFACTURER grinding sieving magnetic separation enamel powder coating with silicon packaging specific additives mixing grinding ready to use sieving enamel powder magnetic separation packaging enamel frit packaging 10 User manual Steel for enamelling and enamelled steel ArcelorMittal transportation transportation transportation ENAMELLER 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 fir ing temperature the better the quality of the enamelled parts As far as the metal is concerned however the firing
11. is also a material that is very easy to recy cle It 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 pre liminary treatment User manual Steel for enamelling and enamelled steel ArcelorMittal 25 92 9 3 9 4 Uses of enamelled steel Domestic uses of enamelled steel 9 1 1 Electric water heaters 9 1 2 Domestic appliances and cookware 9 1 3 Sanitary ware Enamelled steel and the construction industry 9 2 1 Outdoor applications 9 2 2 Indoor applications 9 2 3 Recommendations for installation Other applications of enamelled steel 9 3 1 Applications in industry 9 3 2 Sign panels Summary ofthe principal uses of steel for enamelling 48 48 48 48 49 49 49 49 50 50 50 51 47 Uses of enamelled steel 91 Domestic uses of enamelled steel 91 1 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 corrosi
12. made in all areas have tended to reduce these risks 811 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 generate vapours and waste that need to be treated m nsuring that a surface treatment line of this kind complies with n urrent legislation reguires investment in a waste treatment plant which can double the operating cost of surface prepara tion ArcelorMittal endeavours to develop products that respect the environment and that are simpler to use We are therefore cur rently 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 suspension refractory colouring agents electrolytes and opacifiers This method means that the waste produced during this process must be treated and likewise the water used Enamel manufacturers have therefore developed ready to use enamels tha
13. meet the requirements of even the most demanding consum s Enamel can be decorated in a multitude of ways producing wide range of finishes But the product really excels when t comes to its hygiene and sanitary qualities It is completely inert both chemically and mechanically Besides not harbouring bacteria the enamelled surface can be cleaned very easily using even the most aggressive products If cared for properly it will ways look brand new 3 fob gp ja 22 er 121 JS Jani n name pub ther buildings as a wa tions and lifts Ename rooms JD Weather and J decora dpp Ena of t De out me or for c prefabricated ne perat Due guaranteed for 4 replaced when a any noticeab ook as if the work had been done at two d insta Enamelled steel and the construction industry ICat to the dura led steel is also a Outdoor applicat tion enamelled s ons led panels are pa bY building in bility of O even UV resistant with virtual teel is adding more traditiona the enameller question Th advantages over convent ions the idea ticu arly suitab to match Is iona 50 years enam the colours colour stability can elled pa building is being renovated or extended with e difference in colour Con sequent ifferent led steel has many applicati
14. to prevent hydration which would have the effect of reducing their electric resistance thereby preventing correct deposition of enamel on the part The gual 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 the 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 con taminated 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 tempera ture of between 70 C and 120 C Infrared radiation or con vection drying is the safest way of preparing parts for firing 3 42 Firing of enamel Firing is generally carried out at a temperature of betwee
15. two side enamelling and a guaranteed minimum level of mechanical properties after forming and firing of the enamel currently under develop ment Please contact us for further information These grades can be supplied pickled unpickled oiled or unoiled We should point out that no standards exist for this kind of steel 4 2 2 The ArcelorMittal range of hot rolled steel for enamelling Forming Bending Profiling Bending Hard profiling Light drawing Drawing Joining Enamelling process Surface treatment Enamel application Enamel firing Applications 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 Possible degreasing shot blasting Water heater bottoms 4 2 3 Use Grades S240EK and S300EK are used to manufacture water 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 Grades S240EK S300EK A o Problem fre
16. ArcelorMittal User manual User manual Steel for enamelling and enamelled steel Introduction Enamelled steel is a material with exceptional properties and has many applications in various aspects 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 of asponge The same material is used for cookware again offering an array of advantages enamelled saucepans prevent the growth of bacteria do not absorb odours are not attacked by food acids and can be used directly on the gas hob In the bathroom we find bath tubs in all shapes and colours in a matt shiny or satin fin ish and impervious to the ravages of water and time Last but not east enamelled water heater tanks prevent any water leaks Enamelled steel also has important 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 heat reflec tion properties it can be used in colum
17. Narrow punch V bending Flap bending Bending on a panel forming machine 31 32 5 3 2 Deep drawing Deep drawing is the processing operation that makes it possible to exploit the formability of sheet steel to the maximum The success of a deep drawing operation depends on the opti isation 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 initially 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 form ing 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 propert
18. Thierry Renard p 5 Philippe Vandenameele p 7 Polyvision Heysel metro station Brussels Belgium Enamelled panels designed by Jean Francois Octave 13 University of Pavia Italy architect Giancarlo De Carlo 21 Tom D Haenens 29 Jacques Van den Berghe 35 PolyVision 41 Tom D Haenens 45 PolyVision 47 PolyVision 53 PolyVision DDDD DD DT Copyright All rights reserved No part of this publication may be reproduced in any form or by any means whatsoever without prior written permission from ArcelorMittal Care has been taken to ensure that the information in this publication is accurate but this information is not contractual Therefore ArcelorMittal and any other ArcelorMittal Group company do not accept any liability for errors or omissions or any information that is found to be misleading As this document may be subject to change at any time please consult the latest information in the product document centre at industry arcelormittal com User manual Steel for enamelling and enamelled steel ArcelorMittal 61 ArcelorMittal Europe Flat Products 24 26 boulevard d Avranches L 1160 Luxembourg flateurope technical assistance arcelormittal com industry arcelormittal com n O N n l z wW D Ww D 1 x a
19. ades are chosen to withstand the strains gener ated 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 resistance to slipping in a direction parallel to the folds and a ow resistance to joint opening CT A k e ae Different single and double lock seams 6 3 Welding Resistance welding is the most common welding process though arc welding technigues 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 mechan ical 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 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 ae key parameters to check are applied pressure current tensity and welding time D 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
20. al blade clearances User manual Steel for enamelling and enamelled steel ArcelorMittal 5 3 Forming There are two main techniques for forming steel for enamelling 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 n conventional sheet steel processing bending is the most severe 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 ibrium 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 exte rior fibres tendency to elongate The neutral fibres move in the direction of the tool and the sheet becomes thinner This n u 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
21. amelling con ditions 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 steel fo on the metallurgical properties of r enamelling Cold rolled steel The production of enamelling steels must favour the eventual formation of sufficient hydrogen traps In the case of alumini um killed steel ures As iron uring cold rolli Aa n hese voids are cementite clusters tend to form iron carbide e3C during the hot rolling process at high coiling tempera carbides are very brittle their fragmentation ng will cause small voids to appear in their trail called hydrogen traps Similarly mang of cohesion wit anese sulphide precipitates reduce fish scale defects During cold rolling these are deformed causing a loss h the matrix and the appearance of small voids Other solutions that make use of hydrogen s affinity with ele ments such as boron may also be adopted Aluminium killed steel Fragmented cementite after cold rolling Hot rolling Fe3C cementite 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 c
22. ated sulphuric acid H3504 and the Hot rinsing cold rinsing and a final rinse in demineralised effect is mainly centred on the grain boundaries The pickling water if there is to be no subseguent surface treatment intensity 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 pickling is as follows iron sulphuric acid iron in solution in the acid hydrogen gas Fe 2H SO lt 88 SO Hla Standard pickling conditions are asfollows Temperature of the acid bath 70 75 C Concentration of sulphuric acid H2SO4 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 tep for obtaining good quality parts After pickling the sur face pattern observed will vary according to the iron loss meas ured The photos below show the influence of pickling on the n
23. corro sion 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 74 is tha equip 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 t it is extremely resistant to abrasion which explains why is So widely used in many fields such as domestic and sanitary ment Abrasion resistance is determined by means of a friction test VS High and low temperature stability Thanks to their vitreous nature enamelled surfaces have excel in ind Enam 60 ent t SOON emperature stability Some applications especially in the domestic appliance sector pyrolytic self cleaning ovens and ustry reguire operating temperatures of about 450 C to elled steel can also be subjected to temperatures of C without any adverse effects on the enamel we are able 7 6 to offer steels that are very resilient at this temp
24. cover coat on the visible side and possibly coil so as to leave a few mm of space between the wraps then on both sides This is suitable for producing white or coloured annealing this coil in a batch annealing process in an oxidis parts with a very good surface appearance after enamelling ing atmosphere to decarburise the steel The space between Housing panels for domestic appliances the wraps allows contact between the annealing gas water hobs covers and tops of cookers doors for built in ovens vapour and the entire surface of the steel thus facilitating microwave ovens and cookers decarburisation Bathtubs and shower trays Architectural panels Direct on white enamelling has a number of advantages over the conventional enamelling process cover coat Athinner 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 a after enamelling no bubbles or black spots and also limits steel substrate deformation at high temperatures e g during pyrolysis cycles ground coat cover coat surface treatment Steel substrate enamel film User manual Steel for enamelling and enamelled steel ArcelorMittal 25 26 Enamelling processes and associated steel grades 4 3 4 Two coat one fire enamelling Direct on white enamel
25. d pottery and Egyptian and Persian civilisa durability of this material different as steel and enamel has given rise to a material with and offering many applications the mists of time ly prized The remark jewellery found on tions testify to the been high high tech process using isticated materials and state of the art technigues Enamelled s that meets modern day reguire ngevity aesthetic gualities hygiene and respect for ils applying one or more layers of pre prepared surface of an appropriate grade of firing it at a temperature of between 780 C and s requires the involvement of three parties manufacturer either a manufacturer or a sub The earliest examples of jewellery and gold and silverware that make use of silver copper bronze come Mycenaean technique t tury BC The Celts d century BC and the 11 tine style h throughout oped in Lim hen spread to Egy eveloped the cha R century during eavily influenced the 12 century oges the technique of cloisonn enamel on The golden age of enamelling was between the 6 metal gold from Cyprus and date back to the period most likely around the 13 century BC The pt and Greece around the 6 cen mplev amp enamel method in the 3 h the Byzantine period The Byzan the whole of western production when enamel began to be devel Th ce CEA t Fi d 0 e firs
26. dices 10 2 Performance of enamelled steel The table below indicates 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 grades Cold rolled low carbon steel flat products for must meet to be defined as suitable for vitreous vitreous enamelling 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 of the panel and one coat from 75 275 um if the 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 thickness of the substrate is more than 0 75 mm The 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 adhesio
27. e atmospheres e g in the chemi handling them particularly during installation on facades or cal and agro food industries Its resistance to chemicals and walls to fermentation makes it an excellent lining for silos chemi cal reactors dryers closed tanks and other water treatment The technique for installing enamelled cassette trays on a wall is plant storage systems Furthermore because of its resistance identical to that used for any other metallic facing The cassette to high temperatures and heat reflection properties it can be tray is laid on a horizontal and or vertical framework made of used in columns and heat exchangers Its resistance to corrosion profiles in galvanised steel stainless steel or aluminium integral caused by combustion gases also makes it an excellent material with the wall to be clad The panels are then screwed to this for the manufacture of flue linings and exhaust manifolds framework The fixing system may be visible or invisible Plastic spacers and washers protect the enamel from overtightening 9 3 2 Sign panels of the screws The space thus created between the wall and the panel will also allow surface water to drain away in the case Enamelled steel is an ideal solution for indoor and outdoor sign of outdoor applications thereby preventing corrosion Further amp communication panels more there must be suf
28. e firing cycle of ground coat containing naturally coloured adhesion oxides is applied only dark colours are possible t is therefore necessary to use an enamel that does not contain any adhesion oxides as otherwise it will not be white and a This process can be used for steel with a very low carbon content in order to prevent the Oven and microwave oven cavities release of gases during firing Internal components of built in ovens or cookers inner doors dripping pans baking trays To ensure that the enamel adheres to the steel the part is pick Washing machine drums ed after degreasing in order to activate its surface and a coat ground coat ing of nickel is then applied with the aim of improving adhesion between the enamel and the steel an steel substrate lt 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 nicke coating of between 1 and 2 g m per side 4 3 2 Conventional enamelling two coats two firings The steel s low carbon content will be ensured by annealing This process is used for visible parts After performing ground open coil steel open coil annealing OCA which entails first coat enamelling one coat one fire this entails applying and running braided stainless steel wire between the wraps of the firing an enamel
29. e welding 3 By the wet or dry process At approx 830 C Water heater bodies 1 Grades that can be welded without any difficulty whatever the welding process may be TIG MIG seam welding laser 2 S240EK and S300EK are suitable for one side enamelling 3 The product is generally supplied pickled and unoiled Surface treatment may include degreasing followed by shot blasting With one side enamelling the non enamelled side is coated with borax to prevent scale formation during firing 4 Enamel is usually applied by a wet or dry process With wet application 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 3 Enamelling on cold rolled steel 4 3 3 Direct on white enamelling When enamelling visible parts conventional enamelling is a rel 4 31 Ground coat enamelling one coat one firing atively expensive process due to the need to apply two coats of enamel and have two firing cycles The aim of direct on white This process entails applying and firing one ground coat of enamelling is to achieve the same result i e a white enamelled enamel on each side of the part to be enamelled and is intended part without any visible surface defects by applying a single for semi visible and non visible parts Given that only one layer coat of enamel and performing just on
30. easily automated 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 thickness 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 linked 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 gr
31. eation time to 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 H3 volume time TH 15tg e TH gt 100 agueous solution H2SO additives T 25 C H e gt H 2H gt h H data recorder u 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 defects is measured by means of an enamelling test in a moist atmosphere or by using a low adhesive ground coat enamel sensitive ground coat 23 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 Depending on final use one or two side enamelling different steel grades exist One side enamelling hot rolled steel with a specific chemical composition that can guarantee excellent resistance to fish scale defect and the same level of mechanical properties after forming and firing of the enamel Two grades are available to match these requirements S240EK and S300EK Two side enamelling hot rolled steel with a specific chemical composition that can guarantee excellent resist ance to fish scale defect after
32. ed steel grades course of the 20 century mirroring progress in steel in the 1980s Enamelling on hot heater silo and tank applications The enumeration of enamelling processes and associa scale defects 41 Hydrogen and fish scales 411 Formation of fish scale defects As we have observed already hydrogen penetrates during the enamel firing cycle in the following manner The moisture H20 in the air in the furnace atmosphere penetrates the enamel and migrates towards the e steel interface The H20 then breaks down The oxygen is used in bonding reactions between t enamel and steel gt Er nes in the form of hydrogen gas H9 Present day enamelling processes have developed over the 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 pat ented by the Bethlehem Steel Corporation in 1958 the development of the two coat one fire enamelling process rolled substrates also devel oped in parallel to the above processes particularly for water then by ted steel grades follows this historical trend However before we outline these processes we must first mention the main parameter that will govern the metallurgy be
33. erature Thermal shock resistance enamelled panels could go for 30 years without any signs of corrosion on the metal su pstrate 7 3 Chemical resistance of enamel The chemical properties ronment in which it is to of enamel are tailored to the envi be used Enamel thus has extremely good resistance to chemicals acids apart from hydrofluoric acid alkalis detergents in kitchens or bathrooms Enamelled steel is also and organic solutions Whether used contact with a variety of foodstuffs perfumes cosmetics or cleaning products will have no effect whatsoever on the surface of these products extremely resistant to atmospheric attack Consequently rain atmospheric pollution sulphur diox ide 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 Enamel is able to withstand wide temperature variations in excess of 100 C without undergoing any damage It can there fore be used in applications where such variations are found cooking appliances domestic equipment exhaust systems 77 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 pro
34. ficient space left between the cassette trays to allow for expansion Lastly the leak tightness of the The surface will not be damaged by urban pollution weather system can be improved if necessary by using silicon sealing UV or graffiti It is fire resistant and offers a host of decorative mastic possibilities making it the best possible material for the most sophisticated graphic creations 50 User manual Steel for enamelling and enamelled steel ArcelorMittal 9 4 Summary of the principal uses of steel for enamelling Steel type Process Dedicated steels for the process Other possible steels Use Hot rolled steels Enamelling on hot rolled S240EK Water heater tanks S300EK one side enamelling process Cold rolled steels One side ground coat HC300EK Water heater tanks enamelling on cold rolled steel one side enamelling process Ground coat enamelling DCOIEK Solfer Oven cavities DCO3EK Solfer Inner doors DCO4EK Solfer CA Dripping pans DCO6EK DCO7EK Two coat two fire DCOIEK Solfer Bathtubs enamelling DCO3EK Solfer Shower trays DCO4EK Solfer CA Architectural panels DCOSEK Signage DCO6EK DCO7EK Direct on white Solfer Hobs enamelling Solfer Covers Doors Two coat one fire Solfer CA Solfer Architectural panels enamelling Solfer DCO6EK DCO7EK User manual Steel for enamelling and enamelled steel ArcelorMittal 51 52 Uses
35. galvanised steel or stainless steel variable joints enamel panels 1 5 mm thick plus backing board Fixing system used for the new Signaux Girod building A Girod nut aluminium spacer Rizoux reinforcing piece M8x60 grub screw User manual Steel for enamelling and enamelled steel ArcelorMittal Section A A Scale 1 12 B Detail of B Scale 1 3 a W N VA ev oE nylon spacer nylon washers stainless steel bolt enamel panel Fixing of flat enamel panels in a tunnel High quality stainless steel sub frame 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 frame work is designed to the dimensions of the cassette trays there are no standard dimensions framework X front view X gt SE So ide vi ae side view ae front view section mounting lug N vertical intermediate LA framework sealing joint joint cover strip User manual Steel for enamelling and enamelled steel ArcelorMittal 59 Credits Cover Philippe Vandenameele Sainte Catherine Sint Katelijne metro station in Brussels Enamelled panels designed by
36. her deep drawn sui corner deep drawing or welded The latter technique has drawback that it is always more difficult to apply enamel on of a weld Surface blemishes or pores in the enamel can ac appear on the bead or the heat a performed properly De BC tcase the top tually if welding is not ffected zone Firi them ng enamelled cassette trays at high temperature can cause This is why it may be necessary to laminate the inside of the panels so as to make them flat Various types of backing boards may be used aluminium 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 to deform backing boards on 49 Uses of enamelled steel In order to clad columns or pillars it is possible to make panels 9 3 Other applications of enamelled steel with a semi circular profile Since in this case the panel pro duced is more rigid a backing board is unnecessary 9 31 Applications in industry In view of the thickness of enamelled panels and the possi ble laminate applied they vary between 15 and 30 kg m in Enamelled steel also has important applications in industry weight All necessary precautions must therefore be taken in even in the most corrosiv
37. hind them resistance to fish the steel namel ne tomic hydrogen diffuses into the steel and then recom During this phase of rising temperatures hydrogen solubility in the steel increases 11 N VEZ ee BS Fish scale defects User manual Steel for enamelling and enamelled steel ArcelorMittal During the cooling cycle hydrogen solubility in the steel decreases The enamel since its sol and remains enamel has solidified solidifies Some of the excess hydrogen has to escape from the steel ubility decreases The hydrogen migrates towards the enamel steel interface trapped it is no longer able to escape since the Oversaturation with hydrogen therefore creates very high local pressure spots Enamel blisters are formed resulting in the defect k nown as fish scale it resembles fish scales hence its name The intensity of the phenomenon will be directly li system The crucial impo This defect is d The main paran nked to the amount of water vapour in the steel s capacity to absorb hydrogen is also of tance readed by both enamellers and end users as it only appears after a varying delay neters that tend to aggravate the formation of fish scale defects are as follows A moist firing atmosphere Inadequate process drying if the enamel is applied by the wet Use of steel that is not suitable for enamelling En
38. ies can be determined by this test Re yield strength stress level above which deformation becomes plastic and therefore permanent Rm ultimate tensile strength or breaking load A elongation at rupture Lankford coefficient plastic strain ratio which expresses 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 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 opera tion uniaxial tension User manual Steel for enamelling and enamelled steel ArcelorMittal Different deformation modes There are two deforma Expansion is charac area of the steel shee ness since the volume of which can lead to rup This deformation m ness of the materia od the drawn component Deep drawing mode the steel sheet whi ch 0 These two deformatio cess the solution is to eca int the materia ture of the steel n be seen in he figure be is caused by a co may lead to an r wri fin nkling tion modes expansion and deep drawing terised by a
39. ing on the gas or electric where the mixture is introduced at one end When it emerges it is cooled rapidly first of all by being passed e manufacture of enamel e various stages in manufacturing enamel tep is to check weigh and mix the various constitu amel up to 15 This is followed by the fusion stage The purpose of the fusion process is to render the final amor ng mposition of the enamel n common process involves using a tunnel furnace s out the other Movement through the furnace is The mixture remains in the furnace about an hour water cooled rolling mill to form a glass sheet then ler Crushing completes the cooling cycle This rapid process from a high temperature fixes the structure An alternative fusion process involves using a rotary furnace into which the constituents are poured mixed and heated liguid enamel is then poured into a pit and water guenched After cooli ng and crushing enamel frit is obtained Fusion of enamel mixer screw conveyor loading arm temperature between 11 duration 1 2 2 2 Preparation of enamel amel frit cannot be used as such It must first be mixed with furnace 00 C and 1300 C hour of lumps and various residues then passed through a magneti other constituents then ground These steps may be carried ou
40. inutes 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 a uni form 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 variation of dip coating the dip and shake method which involves mov ing 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 sprayi
41. l enamelling two coats two firings Firing at ion oft ng process generally comprises severa high temperature type of part and final appearance required g on hot rolled substrate Ground coat enamelling one coat one firing Direct on white enamelling Two coat one fire enamelling he surface of the part after forming on of the enamel ion of the enamel to the steel nomy explains the variety of enamelling processes steps enamelling processes depending on 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 Shot blasting used for enamelling on hot rolled substrate Degreasing Rinsing Pickling Acid rinsing ickel deposition mandatory for direct on white enamelling Rinsing eutralisation Drying 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 pro moted by the resulting greater contact surface area thereby increasing enamel to steel adhesion Together
42. led panel Since the colours are created using mineral pigments they dis play considerable stability over time One particular feature is User manual Steel for enamelling and enamelled steel ArcelorMittal 43 44 User manual Steel for enamelling and enamelled steel ArcelorMittal User manual Steel for enamelling and enamelled steel ArcelorMittal 8 1 8 2 Enamelled steel and the environment The production process 8 1 1 Environmental risks associated with surface treatment 8 1 2 Environmental risks associated with enamelling 8 1 3 Environmental risks associated with firing the enamel Life cycle and disposal of the enamelled product 46 46 46 46 46 45 46 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 reguired 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 dis posed 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 81 The production process Enamelling on steel is a relatively complex process and there are environmental risks associated with each stage Advances
43. ling 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 Sur face treatment is limited to degreasing only Enamel to steel adhesion is achieved by using ground coat enamel with added adhesion oxide cobalt oxide in a layer no thicker than 40 um Steel with a low carbon content must be used to prevent excessive release of gases during firing A carbon content of C 0 02 to 0 03 is usually recommended cover coat ground coat with additives steel substrates enamel film User manual Steel for enamelling and enamelled steel ArcelorMittal 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 DCOSEK and DCOGEK are in compliance with EN 10209 Grade DCOSEK was developed specially for the manufacture of bathtubs Grade DCO7EK is ntended for very deep drawing applications DCO1EK DCO3EK DCO4EK and DCOSEK are aluminium killed steels whereas DCO6EK and DCO7EK are IFS type steels decarburised in steel plants IFS interstitial free steel Solfer CA is obtained by superficial decarburisation d
44. longed 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 kitchen Thanks to everyday usage it is also widely known that enamelled steel is a food grade material that does not gi by graffiti Enamel s smooth sealed surface a can be used for cleaning purposes making it places subject to graffiti attacks 79 Colour stability Enamelled surfaces are very easy to clean especially if defaced mineral composition mean that commercially avai ess 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 ve off odours nd its exclusively able solvents much easier and Enamelled steel comes in an almost infinite range of colours patterns and textures with a gloss semi ma these images will last as long as the rest of the that they are not sensitive to UV tt or matt finish In addition it is possible to reproduce any image with extreme accuracy by screen printing e g signs posters works of art or photographs If the process is performed at a high temperature enamel
45. lossy appearance measurement angle of 60 Colour ISO 7724 Measurement 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 for 1000 hours a cycle consists of 4 hours and 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 lacguer 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 stobility 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 57 58 Appendices 10 3 Recommendations for installing enamelled architectural panels A few examples of fixing systems Omeras fixing system Fixing of a rainscreen cladding W j Q je Sub frame in hot dip
46. luble soaps mulsification fats are dispersed in fine droplets by phos hates or silicates ecrease in surface tension fat molecules are coated with rganic agents which weakens the bonds between them nd the substrate D gt m W 19 EI v o 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 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 gas es during the enamel firing cycle Enamelling of steel 3 2 3 Rinsing 3 24 Pickling Rinsing follows degreasing and is carried out in one or more The purpose of pickling is to attack the steel surface in order to steps increase its micro roughness and hence its reactivity which A single hot water rinse 60 70 C if there are to be promotes the adhesion of enamel Pickling is generally carried subsequent surface treatment procedures pickling etc out using concentr
47. lybdenum oxide MoO cobalt oxide CoO cupric oxide CuO manganese oxide MnO and most efficient adhesion agent However enamel manufactur Nickel oxide NiO is certainly the for reasons linked with food contact safety and REACH compliance Opacifiers and colouring agents which contribute visual and tactile qualities to enamel led parts Opacifiers serve to increase the opacity of enamel and are present in cover coat enamel The most common are titanium dioxide TiO antimony oxide Sb Os zirconium oxide ZrO gt and tin oxide SnO Colouring agents are obtained by combining mineral oxides User manual Steel for enamelling and enamelled steel ArcelorMittal The most 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 common procedure is for the colouring agent in the form of fine particles to be mechanically mixed with the enam el during the grinding stage before application to the substrate 22 Th za WA The first s ents of en desired co The most and come by gravity through a into a coo quenching of the glass and prevents any phase separation phous structure of the enamel uniform and to lower the fir temperature This requires the glass to be melted at a tem perature of between 1100 C and 1300 C depend
48. 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 m2 per side after meticulous degreasing especially for grades DCO6EK 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 for enamelling and enamelled steel ArcelorMittal HC300EK E 27 28 Enamelling processes and associated steel grades 4 3 6 Block diagram of enamelling processes on cold rolled substrates
49. n Enamel porosity ISO 8289 A potential difference of 1000 V is applied Maximum 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 33 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 Mohs EN 101 Surface hardness is measured by the Mohs Minimum hardness is 5 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 Thickness of substrate gt 0 75 mm Maximum deflection 0 5 in the convex direction and 0 25 in the concave direction Thickness of subs
50. n 780 C and 850 C which is well above the softening temper ature of enamel 500 600 C It can be done in a box furnace o 5 in a tunnel furnace continuous Firing time and temperature depend on the thickness of the steel and the type of enamel Fi ring is carried out in an oxidising atmosphere Box furnaces are generally used for short production runs and arly popular with independent small parts They are particu 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 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 radiation and convection 20 3 4 3 Enamelto steel adhesion mechanisms The adhesion of enamel to uncoated steel is achieved by means of chemical reactions that take place during the firing and cool ing cycles The process can be divided into four stages 1 stage up to 550 C The moisture H20 and the oxygen O2 in the air penetrate the porous enamel and oxidise the iron in
51. n constituent is silica SiO2 which is the most abundant mineral in the earth s crust Free silica exists principally in its crystallised form guartz which has a purity in excess of 99 It is also found in combined form icas In order to confer on enamelled ty silica glass has to be modified nal state Its melting point is too the enamel enamel an amorphous structure and hence mechanical strength These include for example alumi to lower the coefficient of expansion increase resistance to temperature chemicals and abrasion of opacifiers another constituent of melting point and firing temperature ient of expansion These are mainly ium tetraborate in its anhydrous form a2B407 or hydrated form Na2B407 10 H20 and alkaline oxides such as oxides of sodium Na 20 potassium K30 lithium Li O calcium CaO magnesium MgO and stron tuents produce borosilicates of sodi Icium magnesium or strontium which melting point may also be lowered by boron trioxide B203 Fluxes such rease the coefficient of expansion by ica structure Adhesion agents which are metal oxides that are involved ns to promote adhesion between the mel coating These reactions will also nin steel as well as atmospheric oxy chromic oxide Cr203 ers have banned its use gen Adhesion agents are present in ground coat enamel main ly in the form of mo
52. n increase in the surface t and therefore a reduction in thick remains the same in extreme cases the top section of ow mpressive stress in increase in the thick n modes coexist during the drawing pro d the best compromise between deep drawing mode wrinkling and expansion rupture or necking expansion 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 eguations for the behaviour of the metal in all deformation modes starting with s mple uniaxial tension By evaluating the deformation an indispensable indicator is used in this field the Forming Limit Curve or FLC Foras teel sheet of a given grade and thickness the FLC deter d mines a safety limit for deep drawing operations 1 2 range superimposed on strain values representing the deformation as a W hole This curve can be established according to various acceptance criteria necking or rupture of the steel wrinkling excess of the coating This cu Eva ve thinning of the metallic coating cracking or peeling ve allows the user to uate the safety margin for the drawn component Identify critical areas of the component where the material is subjected to severe deformation
53. nce 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 applications requires a few precautions to be taken In view g of the properties of enamel it is usually impossi fy an enamelled panel No bending cutting or drilling performed as this would damage the enamelled su tion is therefore very important for the project manager A very accurate lay face to be clad will guarantee succes and unlike other types of panels such as lacquered board th installation tolerance is very low It is therefore vital to kno in advance the exact dimensions of all the panels and also th position of all the holes that will be used to hang them from th fa ade or wall in question to modi can be face Good site prepa architect or the building out drawing of the sur a D n D PD al 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 ommended The corners may be eit
54. ng 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 a s 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 atmosphere 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
55. ns and heat exchangers Its resistance to corrosion caused by combustion gases also makes it an excellent material for the manufacture of flue linings and exhaust manifolds Finally the use of enamelled steel is a first rate solution in the con struction industry for cladding buildings or for interior decoration as it successfully combines a rigid steel substrate with an enamel coating The result is an end product that is aesthetically pleasing durable and easy to clean making it a material that will appeal to even the most demanding clients Enamelled steel can also be an appropriate option for lining tunnels as it ensures they are easier and cheaper to clean and improves fire resistance User manual Steel for enamelling and enamelled steel ArcelorMittal Introduction Definition The fusion at high temperature of two materials as noble and as quite rema enamelled s The origins but its gua ably well p sites astonishing Today enamelling steel has become a highly soph ments of lo the environ The ename enamel to t steel and then 850 C Thi A stee An enamel An enamel of ancient rkable p teel operties lities have always reserved teel is a material ment ling process enta ne manufacturer er who can be contractor A brief history of enamel of the use of enamel are lost in enamelle
56. ocess Surface treatment before enamelling 3 2 1 Shotblasting 3 2 2 Degreasing 3 2 3 Rinsing 3 2 4 Pickling 3 2 5 Acidrinsing 3 2 6 Nickel deposition 3 2 7 Finalrinse neutralisation and drying Enamel application 3 3 1 Wet application 3 3 2 Dry application electrostatic powder spraying Drying and firing of enamel 3 4 1 Drying of enamel 3 4 2 Firing of enamel 3 4 3 Enamel to steel adhesion mechanisms User manual Steel for enamelling and enamelled steel ArcelorMittal 14 Enamelling of steel 31 The enamelling process The enamelling process entails applying and firing one or more lay ers of enamel on one or both sides of a suitable steel substrate cover coat ground coat _ steel substrate class appearance adhesion C 0 004 Co 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 ieving these two properties Carbon is important to ensure ach the can adverse process of adhesion of enamel However if its content is too high this ly affect the surface appearance of enamel due to the release of gaseous CO and CO produced during fir ing tha The ename Applicat This anti t exist Preparat Preparati Drying There is a choice of severa the Enamellin Conventiona
57. of enamelled steel Market Domestic appliances Industry Construction Architecture Miscellaneous Manufactured component Self cleaning oven cavities pyrolytic catalytic Hobs Washing machine interiors Cookware Water heaters Bathtubs Flues Roof tiles US Curtain walls Exterior wall cladding Signage road traffic signs advertising etc Art Top of the range exhaust silencers Tanks and silos User manual Steel for enamelling and enamelled steel ArcelorMittal Corrosion resistance High temperature stability Abrasion resistance Impact resistance Resistance to changes in temperature Acid resistance Alkali resistance Resistance to cleaning products Colour stability Hygiene and ease of cleaning Luminosity Catalytic power Ease with which graffiti can be cleaned off Fire resistance Longevity 10 1 Mechanical properties of steel for enamelling 54 10 2 Performance of enamelled steel 56 10 3 Recommendations for installing enamelled architectural panels 58 User manual Steel for enamelling and enamelled steel ArcelorMittal 54 Appendices 10 1 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
58. old 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 Several permeation tests can be used to measure steel s hydro gen absorption capacity the Strohlein test the Dippermet test and the Helios II system Letomec SRL The Strohlein test is the one described in EN 10209 2013 It is used to measure steel s hydrogen 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 guantities 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 recombining in molecular form in imperfections within the metal When the metal is saturated the output signal changes A permeation curve is thus obtained showing the quantity of hydrogen passing into the metal as a function of time metal User manual Steel for enamelling and enamelled steel ArcelorMittal The perm
59. on Furthermore since enamel is a food grade material the water can also be safely used in the kitchen n view of the 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 or cold rolled HC300EK if the required thickness is below 1 5 mm 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 capa ble 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 t 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 esistance t is flame resistant and can withstand a high temperature t is safe for contact with food and prevents the growth of bacteria t is very resistant to steam which means it can readily be used for this cooking method t has undeniable aesthetic qualities
60. ons in construction It can be ed as a cladding for buildings or tunnels and in the interiors ic places such as train and metro stations airports and covering and for false ceilings parti n excellent material for fitting out clean ly unlimited scope for solution for outdoor e for separation walls brickwork buildings They are the exact dimensions technique has obvious financia building methods The panels can led in any weather irrespective of the outside tem ure be nels can be ly it will not times The ease with which graffiti can be cleaned off is readily dem onstrated when to graf The use of enam as it m illumination the means fire res fiti attacks istance the building is located in a n area t User manual Steel for enamelling and enamelled steel ArcelorMittal hat is prone elled steel for lining tunnels is recommended akes them easier and cheaper to clean ensures better enamelled surface reflects light well which that less investment in lighting is reguired and improves 9 2 2 Indoor applications Enamelled steel is a very popular choice for fitting out pub lic 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 Si
61. orming Bending Profiling A A A Bending Hard profiling Light drawing e A A A Drawing e S Deep drawing e e e A A A Joining Problem free welding Enamelling process Direct on white Surface treatment e o S e o e o Degreasing enamelling pickling and nickeldeposition 2 Enamel application e e e e e By wet or dry process Enamel firing e e e e e At approx 830 C Tvo eoat onefire Surface treatment e e e e Degreasing egomeling Enamel application e o e e By wet or dry process Enamel firing e e e e At approx 830 C Conventional enamelling Surface treatment Degreasing ground coat enamelling and Enamel application By wet or dry process two coat two fire E 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 loss of 25 g m2 per side Nickel coating of between 1 and 2 g m2 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
62. orr_ gt travel wire guide and contact tube nozzle gt shielding gas ON arc lt U solidified weld metal 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 t 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 JE ee id outside corner weld edge weld butt weld Different weld configurations inside corner weld 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 an
63. s and help fat produced when food is cooked There are 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 refrac tory hence porous which has the effect of increasing the contact surface between the enamel and the fat thus facilitating its elimination Cy Hy O catalyst gt xH 07 yCO7 m fficiency falls off over time as a result of progressive ockage of the pores OT 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 Cy H O 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 quality 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 12 User manual Steel for enamelling and enamelled steel ArcelorMittal 3 Enamelling of steel The enamelling pr
64. small guantities in conventional processes nickel flash The most common method used to deposit nickel is the precipi tation of metallic nickel by displacement of iron ions 2Fe NISO4 HS04 gt 2FeSO4 Ni Ho Conditions pH 2 8 temperatu time 7 mi As in the case signifi variation may cant inf ISO 4 12 5 g l E TOSE nutes of pickling the nickel deposition conditions have a uence on the guantity of nickel deposited A slight have serious conseguences on enamel adhesion To ensure that with an optimum enamel obtained and iron the direct on white enamelling process produces good adhesion and an attractive appearance combination exists between the iron loss to be the quantity of nickel deposited oss 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 poor adhesion O 44 iron loss gt g m 1 side 0 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 35 lt pH lt 4andT 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 m
65. t 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 pro cesses 8 1 3 Environmental risks associated with firing the enamel The main risks are associated with the release of small quanti ties of fluorine during the enamel firing stage though this cor rosive element is less and less likely to be present in modern day enamels Furthermore firing furnaces are now eguipped 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 material 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 dura bility Enamelled steel
66. t either by the enamel manufacturer or by the enameller to mentally The ground powder then whom the manufacturer has supplied the necessary materials separator permanent magnet or e Enamel may be applied in liguid form In this case after the any iron particles in addition of certain ingredients suspension refractory colour ate holes in the enamel which re ing agents electrolytes and opacifiers the frit is ground and protection Finally the grains of ena mixed with water to form a slurry which will be used for dip enabling them to ad coating or spraying applications Enamellers in particular manu tion and firing stages The enamel facturers of domestic appliances who do long production runs require any additives or further trea in a single colour became increasingly reluctant to prepare the can enamel themselves This led to the introduction of ready to of investment to set up a powder use powder in the 1980s to simplify the preparation of the trostatic to be slurry The powder is prepared by the enamel manufacturer economical in the long term ller the by adding specific products before grindin has only to add colouring agents optional powder with water to obtain the slurry g The ename before mixing User manual Steel for enamelling and enamelled steel ArcelorMittal the powder These particles tend to cre rolling mill glass sheet Enamel may also be applied in the
67. t utensils in en ntury and appeared the 19 century made advances in nverters in large gua evelopment of enamelling on these subs blast fur n he course of the 20 uction but also keeping ally present day en in Germany The in it possible to m amelling processes amelled cast iron date dustrial revolution in anufacture cast iron naces and then stee ntities which opened regulations pace with ever s back to the 18 development of the way for the trates have developed over century mirroring progress in steel pro tricter environmental 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 strength of the enamel to heat and cold rmal shock resistance resistance Mechanica ed surface Resistance e ire SE lygiene and ease of cleaning Multiplicity and stability of colour These characteristics will be discussed in more detail below see chap
68. tempera ture 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 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 does 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 instance 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 gt Alkali resistant properties sanitary ware washing machines by addition of ZrO Improved corrosion resistance for water heater applica tions by addition of ZrO and Al203 User manual Steel for enamelling and enamelled steel ArcelorMittal Self cleaning enamels Self cleaning enamels are u eliminate the two types of self cleaning enamels sed in domestic oven
69. ter 7 Properties of enamelled steel User manual Steel for enamelling and enamelled steel ArcelorMittal 251 DP 2 3 Enamel The composition of enamel The manufacture of enamel 2 2 1 The various stages in manufacturing enamel 2 2 2 Preparation of enamel The different types of enamel 2 3 1 Enamel and substrate 2 3 2 The different types of enamel for steel 11 11 11 Enamel 21 The composition of enamel in feldspars clays and m properties they impart to Refractories which give na A1203 whi ENSO INVOS and facilitate the action enamel Fluxes which lower the and increase the coeffic composed of borax sod tium SrO These consti um potassium lithium ca h instead of 1720 C The dding fluorine F2 or s the alkaline oxides inc illing the voids in the sil a a in chemical redox reactio steel surface and the ena involve the iron and carbo parts its properties of durabi as it cannot be used in its orig high its coefficient of thermal expansion is too low compared to that of steel and its adhesion to steel is zero Various constit uents therefore have to be added in order to obtain an enamel These can be categorised in four main groups according to the ave a lower melting point than silica approximately 1400 C namel is a glass obtained by fusion at high temperature between 1000 C and 1300 C Its mai
70. the steel This causes the formation of a layer of iron oxide at the enamel steel interface The atomic hydrogen arising from the decomposition of H O diffuses into the steel recombines as molecular hydrogen and fills the holes in the steel The solubility of H in steel increases with temperature 2 4 stage 550 830 C The enamel softens then fuses forming a semi permeable layer This reduces gaseous exchanges with the furnace atmosphere The iron oxide present at the enamel steel interface is dissolved by the enamel firing temperature C 3 4 stage around 830 C At this temperature chemical redox reactions take place between the iron oxide layer at the enamel steel interface the metal oxides in the enamel and the carbon in the steel Fe Co alloys precipitate at the enamel steel interface These are at the heart of the adhesion of enamel to steel Adhesion is promoted by the roughness of the steel The dissolved oxygen recombines with the carbon in the steel releasing gaseous CO CO gt The intensity of these releases must be monitored The quantity of hydrogen in the steel is at maximum levels 4 stage cooling The enamel solidifies stopping gaseous exchanges Hydrogen solubility in the steel decreases when the temperature falls The steel becomes oversaturated and hydrogen accumulates under the enamel coating An excessive quantity of hydrogen at the interface causes fish scale
71. ting during handling The following rules should be observed to control the location of burrs after cut ting Slitting and side trimming wheels should preferably be mounted symmetrically Burr orientation after slitting Clearances must be properly adjusted burr orientation 30 User manual Steel for enamelling and enamelled steel ArcelorMittal The slitting quality is considered to be good if Thedistorted 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 technigues is not recom mended since they produce chips and high burrs Laser or plasma cutting technigues can also be used Their advantages are high precision and the absence of burrs 6 to 8 distorted zone plastic rounding 25 to 40 shear zone 50 to 60 fracture zone little or no burr formation lt gt horizontal i clearance Morphology of the cut edges upper shaft steel sheet vertical clearance crossover steel sheet lt horizontal clearance between steel lower shaft Horizontal and vertic
72. 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 electrode 5s force sheet product weld nuggets workpiece projections force f d5 g weld nuggets weld nuggets h bolt ii User manual Steel for enamelling and enamelled steel ArcelorMittal 6 3 2 Gas shielded arc welding The principle of electric arc welding technigues is the applica tion of heat by striking a low voltage 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 COs binary Argon CO or tertiary Argon CO Oo This method can be used to join materials of a different type and of any thickness solid wire electrode shielding gas current conduct
73. trate lt 0 75 mm Maximum deflection 0 15 in both directions 56 User manual Steel for enamelling and enamelled steel ArcelorMittal 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 of exposure to salt spray 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 agueous solution of 10 citric standard 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 agueous 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 g
74. uring the continuous annealing process This steel grade is specially ntended for the two coat one fire enamelling process Nev theless it can also be used for ground coat or conventional namelling D D Solfer and Solfer are aluminium killed decarburised open coil annealed steels that are intended for direct enamel ling to give a white or coloured finish with a single coat follow ng degreasing strong pickling and nickel deposition However these types of steel can be used in two coat one fire enam ling and ground coat or conventional enamelling for enam elling pyrolytic self cleaning oven cavities if ground coat enamels are used that are suitable for the low intrinsic reactivity of these steels D These grades correspond to standardised grades DCO3ED and DCO4ED EN 10209 Grade HC300EK is a structural cold rolled enamelling stee grade with guaranteed minimum yield strength Its mechani cal properties are preserved after deformation and enamel fir ing This grade is mainly designed for the one side enamelling process Last but not least these grades offer excellent resistance to fish scale defects We can guarantee a minimum TH of 100 for grades DCO1EK DCO3EK DCO4EK DCOSEK Solfer CA Solfer Solfer and HC300EK in accordance with EN 10209 Enamelling processes and associated steel grades MO OM OM x S ge g Grades 5 8 3 3 S S 5 a a a a a a 3 a a F
75. with the chemical hydrogen traps created during steel production this improves esistance 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 and 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 he degreasing temperature which must be between 60 C and 90 C depending on the process used he concentration of degreasing agent 45 50 g l The pH of the degreasing baths he 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 pres nce of an aqueous solution of soda or potash forming o
76. y deposits oxides and foreign bodies that may have appeared during the welding process User manual Steel for enamelling and enamelled steel ArcelorMittal 39 40 User manual Steel for enamelling and enamelled steel ArcelorMittal User manual Steel for enamelling and enamelled steel ArcelorMittal 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 42 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 which 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 M2 Corrosion resistance Enamel is a coating that provides steel with excellent

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