DE2264581A1 - PROCESS FOR PRE-TREATMENT OF A STEEL SHEET TO BE FORMED AND, IF NECESSARY, ENAMELLED - Google Patents

Description

Process for pretreating a to be deformed and, if necessary steel sheet to be enamelled separation from P 22 40 767.6-45 The invention relates a method for pretreating a subsequently to be deformed and optionally steel sheet to be enamelled, in which at least one removable before deformation Cover layer is applied to the steel sheet.

Such a method is known from DT-OS 1,965,586.

This known method is based on either purely chemical, Purified electrolytically or by a combination of chemical and electrical steps Surface of the steel sheet is a layer of a water-soluble polyphosphate upset. This polyphosphate cover layer serves to protect the sheet metal surface against damage caused by a subsequent Deformation process could occur. These known cover layers made from salts of polyphosphoric acids are disadvantageous in so far as they are under attack during storage, for example decay from humidity. These decay products in the form of salts lower However, phosphoric acids are known to be highly hygroscopic, so that these too decay with increasing speed and thus an undesirable oxidation of the steel surfaces to be protected.

From US-PS 2,390,644 it is also known to promote the Drawability of steel wires used lime slurries by sodium silicate solutions to replace. According to this known method, those used for wire drawing are used Raw materials in bundle form in a 1 to 5% aqueous solution of sodium silicate immersed at about 93 ° C and after drying with the help of a suitable lubricant, such as soap powder. This well-known cover made of sodium silicate serves to neutralize acid residues from the previous pickling treatment and as a means of absorbing and absorbing the required lubricant.

In addition, the known cover of the impairment of the wire surface during the drawing process and the formation of rust on the surface of the raw material that has not yet been drawn counteract.

The invention is based on the object of a method of the above called type to create, which the generation of an against the attack of humidity insensitive, pretreated steel sheet is permitted.

This object is achieved according to the invention in that on the steel sheet a layer of water glass and a layer of wax can be applied.

According to a particularly advantageous embodiment of the invention the surface of the steel sheet prior to the application of a cover layer on a Electrolytically roughened manner explained in more detail below. With the subsequently applied water glass layer, the workpiece is completely protected against the Formation of scratches during the deformation process, for example by a press, before enamelling is carried out if necessary. It has been shown that that if a 2 to 5 micron thick layer of water glass is on the surface of the Steel workpiece applied and a liquid lubricant on the waterglass layer, For example, a press oil, is spread, the deep-drawability of the workpiece is greatly improved and the risk of scratching the workpiece during the deformation process is greatly reduced.

The mechanism by which the scratches are formed by the extremely thin Waterglass crawl on the workpiece is avoided, appears to be the following: the thin waterglass layer is so strong that? they have a very high localized pressure can withstand that caused by small waves such as those on the surface of the workpiece are inherent, or caused by waves newly formed in the course of the deformation The thin waterglass layer remains between your square and an upper one Deformation stamp and between the \ YerkstücI and a lower deformation stamp @ el or a carrier plate. The presence of such a thin layer of water glass is used between the workpiece and the effective parts of the deformation device to distribute a local concentration of the pressure on the surrounding oil, so that the scratching caused by it on the surface of the workpiece is almost is completely eliminated. When the deformation die (dielörindüse) is under pressure slides along the O'ser surface of the workpiece, the thin water glass layer be scratched by the punch, but the surface of the workpiece itself is protected as only the water glass layer is scratched. A common soft liquid film, such as a lubricant film or a press oil film, but is too weak to to withstand the high pressure lolalized on the surface of the workpiece occurs. As a result, the soft liquid film tears in the course of the deformation process and the surface of the workpiece comes into direct contact with the deformation punch or the deforming nozzle and it gets scratched when the workpiece moves relatively moved to the deformation punches.

Water glass is relatively cheap and is available on the most diverse widely used in technical fields.

It is known that an aqueous water glass solution is used as a degreasing agent egg can be used. Accordingly, an applied to the waterglass layer Oil film can be removed more easily than if it were directly on the surface of the workpiece is applied. the above is the usual, washable cover, the from an aqueous solution of a metal soap or a water-soluble polymer has been produced does not exhibit water repellency and corrosion resistance. the Water glass layer is easily soluble in water, but it ensures one high corrosion resistance, as the aqueous waterglass solution is strongly alkaline, whereby the surface of the workpiece is inactivated.

When applying water glass to a steel workpiece, e.g.

a steel sheet, a steel plate or a steel molding the surface of the water glass film in the pra @ is preferably with one against moisture resistant layer coated so as to prevent excessive absorption of moisture to prevent by the water glass. The excessive body absorption by Water glass has the effect that the water glass itself turns into whitish powder particles If latticed - once the water glass is converted into the whitish powder it loses its resistance to corrosion. The moisture absorption through Water glass also makes it more viscous.

Accordingly, the excessive moisture absorption by waterglass, if steel sheets coated with water glass have been stacked one on top of the other for a longer period of time must be stored, to the fact that the steel sheets stick to each other.

Looking for a material that will prove to be more moisture resistant Coating suitable for the water glass, it has now been found that the desired water resistance thereby aiming can be that you cover the water glass with a layer of wax coated, which is solid at room temperature. By applying such a Wax layer on the water glass layer will improve the prevention mentioned above the formation of scratches is not affected. In the cases where those with water glass If coated workpieces have to be stored for a longer period of time, it is advisable to use the to coat the outer surface of the waterglass layer with wax called the German term is in the solid phase at room temperature. The water glass layer on the surface the workpiece can be dried before being coated with the wax mentioned will.

According to a preferred embodiment of the invention, an aqueous Water glass solution, consisting of 4 parts by volume of water and 10 parts by volume of water glass, applied to the surface of a steel sheet by conventional roller coating unci dried by blowing warm air. After drying it will be with Waterglass-coated steel sheet is immersed in a wax solution that penetrates Dissolve normally solid wax in toluene in an amount of 100 wax per Liter of toluene has been produced. Instead of dipping the steel sheet in the wax solution, The steel sheet can be used to coat the waterglass cover with a layer of wax also dipped in molten wax or roller coated will. The thickness of the water glass layer to be brought onto the steel sheet is preferably 2 to 5 milerons and the solid one on the waterglass layer The wax layer should preferably be 0.5 to 1 micron thick. With a water glass layer and a wax coating of the above thicknesses becomes excellent in deep drawability achieved. Even after deep drawing, the steel sheet can be firmly adhered to it Glass enamel layer are coated. To ensure a firm bond between the steel sheet and the glass enamel layer to ensure the surface of the steelworks or the steel sheet roughened after the application of the waterglass layer.

The inventive method for pretreating the surface for the glass enamelling is carried out in such a way that first the workpiece surface, e.g. the steel sheet is roughened before the waterglass layer is applied.

With the usual glass enamelling process, the workpiece is first For example, the sheet steel, brought into the desired shape, cleaned and then by immersing it in an aqueous sulfuric acid or nitric acid solution etched.

By etching the surface of the workpiece is roughened and the finished workpiece can then be enameled from glass (fire enameling) be subjected. The etched surface of the workpiece can be applied before the glass enamelling an extremely thin nickel-cobalt, molybdenum or phosphate coating is applied, to improve the adhesion of the enamel to the workpiece. A table example of one such known pretreatment for glass enamelling is in the British Patent 763 v79 described. It is also possible to use the roughened surface to subject the workpiece to a chromate treatment. When pretreating the Steel sheets or the workpiece according to the etching process according to the invention is any Sheet steel electrolytically etched using a liquid electrolyte, which moves quickly during the etching process, so that a large number of pyramid-shaped deep holes is etched into the surface of the sheet or the workpiece.

The etching process according to the invention can be carried out while the steel sheet is laid out flat, and the etched sheet is after etching, for example by means of a press, is deformed and then the deformed sheet is subjected to glass enamelling0 This can reduce the overall efficiency of the glass enamelling process including etching can be greatly improved. With the etching according to the invention becomes a liquid Electrolyte spread on the surface of the flat Steel sheet and the steel sheet can be handled more easily than in the Case of etching by immersing the steel sheet in an electric cell.

With the usual etching before enamelling, a sheet steel or a steel plate in an electrolytic cell is anodized by cutting the sheet metal or the Plate moves relatively slowly in the electrolyte clay. In this case, the steel sheet works or the steel plate as the anode and there is a tendency that on the anode surface Hydrogen gas is trapped, which adversely affects the etching by removing the Adhesion of the glass enamel on the steel sheet or on the steel plate sch;, .. cht.

If one tries now with the usual etching process, the steel sheet To move at a relatively high speed, the electrolyte cell must be enlarged because the steel sheet to achieve the desired etching effect must be exposed to the electrolyte for a certain period of time. After several years Investigations have now been found that the above-mentioned difficulties of the usual Etching pretreatment for the glass enamelling can be avoided in that one a comparatively high relative speed between the liquid electrolyte and the steel sheet. In addition, the high relative speed serves between the liquid electrolyte and the steel sheet also add to the surface of the steel sheet to roughen to form sharp-angled projections and indentations that are densely distributed over the surface of the steel sheet. to greatly improve the adhesion between the glass enamel layer and the steel sheet and to improve the electrolotic etching process without the etching devices have to be enlarged by comparing a high relative velocity between the liquid electrolyte and the steel sheet applies.

Further details, features and advantages of the invention are apparent In the following description, he prefers embodiments with reference to the enclosed Drawings. 1A is a fragmentary cross-sectional view a rolled steel sheet covered with a water glass coating and a wax layer is provided; Fig. IB is a fragmentary cross-sectional view of a water glass coated steel sheet, which before the glass enamelling according to the invention Procedure has been pretreated; Fig. 10 is a fragmentary cross-sectional view of a steel sheet which, according to the method according to the invention, is coated with a phosphate layer and has been coated with a water glass layer; Figure 2 is a schematic diagram an electrical circuit for performing the etching process using an electrolytic cell with a rotating drum; 3 is a graphical representation, which is the relationship between the peak count and the r; I (Porcelain Enamelling Institute) index (in @) explained; Figures 4A and 5A Images of the surface conditions of steel sheets obtained using a stationary Electrolytic cell or a rotating electrolytic cell have been etched, taken on with a scanning electron microscope at a magnification of 1000 times; the figures 4B and 5B show pictures corresponding to those of FIGS. 4A and; the magnification on Has increased 3000 times; the figures 40 and 50 images corresponding to those of FIGS. 4A and 5A, but this time the magnification was increased to 10,000 times; Figures 6 and 7 a lateral View or a plan view of a device that is used to carry out the method according to the invention is suitable; and Figs. 8A, 8B and 8C are pictures the surface states one using a fast moving liquid Electrolytes in the device according to Figures 6 and 7 etched steel sheet, recorded using a scanning electron microscope at a magnification from 1000 times, 3000 times or 10 000 times.

Figure 1A of the accompanying drawings shows a fragmentary view View of a steel sheet A pretreated by the method according to the invention. The rough surface of the steel sheet A is, as in the wig. 1A indicated, with a Coated dry water glass layer 3 and located on the water glass layer B. a layer of lubricant a. Fig. 13 shows a steel sheet Al, which before Applying a dry water glass layer B and etched with a nickel layer E has been coated. On the water glass layer B there is a lubricant layer C. Fig. 1C illustrates a steel sheet Al coated with a phosphate layer D. is. On the phosphate layer D there is a lubricant layer C.

If now a rolled steel sheet, for example by means of a press is deformed before the glass enamelling, the @ellen on the sheet metal surface flattened or leveled, which may cause scratches or scuffs on the leveled surface be generated. This flattening of the turellen and the risk of scratching the flattened surface is inevitable, even if the steel sheet surface is provided with a nickel or phosphate coating is. The braided surface and the scratches weaken the bond between the Steel sheet and the glass enamel layer on it and also affect that Appearance of the enamelled moldings. Especially the one with a phosphate coating provided steel sheet must be handled carefully during the shaping so that the phosphate layer does not peel off.

The phosphate layer itself acts as a lubricant during compression set. A suitable soap material can be used with the phosphate layer. This phosphate layer should preferably also after the deformation by means of the press on the steel sheet surface to ensure a firm adhesion of the paint coating or the Glasenailijberzug on the steel sheet. However, if the Phosphate layer has scratches or during the deformation by the press remains adhering to the same, its function is impaired.

It has now been found that if a very thin layer is made the comparatively less flexible dry water glass on the sheet steel surface the roughened condition of the steel sheet surface during the the entire deformation process can be maintained by the press. Of the The reason for this improvement seems to be as follows: all small pits on the entire rough surface of the steel sheet are made by the comparative hard material, i.e. the water glass, which will open the wells, such as shown in Figures 1, 1B and 1C, and the waterglass layer takes the local Concentration of high pressure during deformation, creating a deformation the rough surface conditions, e.g. the removal of the protrusions and the filling the wells with steel from the Protrusions, prevented0 It .niide now found that with the help of the pre-treatment according to the invention, steel sheets with smooth surfaces, e.g. steel sheets with a glossy surface coating, can be deformed by means of a press without scratching the surfaces same arise. The comparatively hard water glass is placed on the sheet steel surface Applied in such a thickness that the waterglass layer itself through moving parts of a deformation device may be scratched, however the steel sheet surfaces under the water glass remain intact0 The application of Water glass on a steel plate before the glass enamelling (fire enamelling) after the process according to the invention is explained in more detail in the following examples.

Example 1 Two samples from according to the method according to the invention Protective steel sheets were made using cold rolled steel sheets a thickness of 0.8 min (with a matt surface coating of 3.0 µ Hmax), the with 5 micron or 3.5 micron thick dry waterglass layers and coating layers coated from a suitable press lubricant on the waterglass layers was.

Using the same steel sheets with a thickness of 0.8 min four comparative samples were produced without a waterglass coating, those with lubricant coatings were provided.

All samples were formed into cups in an identical manner and then the scratching and flattening effects (leveling effects) of the different samples with each other compared. Every sample cup was 55 mm deep and was made by punching out a blank with a diameter of 200mm by means of a flat surface punch with a diameter of 100 mm using a compressive load of 5 tons. The outer The surface of the drawn part was subjected to scratching and flattening. The gloss or the glow of the outer surface increased with the number of scratches and the degree of flattening increase. The shine and smoothness of the outer surface card the sample cup according to ASTM method D 523 or according to the method according to JIS Z 8741 measured. The broconis obtained in this way are shown in the table below I curled up. Small values for the gloss (smoothness) (in%). in the following Table I indicate a good protection of the rough sample surface by the protective layers, namely, since the gloss or smoothness is less, the better the protection.

Table I Surface layers gloss Gs (0 °) @ * (in three places for each sample) digit mean value 1 2 3 press lubricant alone 85.84 88.80 92.80 89.12 "75.20 89.20 90.00 84.80" 104.40 79.52 81.28 88.40 "116.24 88.00 80.80 95.04 5 @ thick waterglass layer plus press lubricant 45.60 36.24 47.20 43.04 3.5 p thick waterglass layer plus press lubricant 41.60 32.96 37.60 37.36 ------ * Gloss Gs (0 °) in%, according to JIS Z3741 As the Table I above shows the gloss of the outer surface of the cup sample reduced to about half by applying a waterglass layer to the Sheet steel compared to the cup-ron with the press lubricant alone. at the samples with the 5 micron resp.

3.5 itikron thick water looks were practically no scratches and flattened parts caused by the deformation cm see. In this way, with such protective layers, the surface conditions became of the steel sheet before the deformation by means of the press and after the deformation of the steel sheet maintained by means of the press.

When a press lubricant layer was used alone, one occurred considerable number of scratch lines and flattened parts running through the deformation had been generated on the steel sheet surface.

A typical example of the improvement in deep-drawing properties is the following: If a 1.6 now thick sheet steel is made from a grade steel SPCC (JIS) using a press after applying a 5 micron thick water glass layer plus a press sealant layer (press oil No. 620 from NIHOM KOSAKUYU KABUSHIKT K & ISLA) pulled Tyhrde, a drawdown limit L.D.R.

of 2.25 obtained. On the other hand, if the same steel sheet on the If a layer of waterglass was drawn in the same way without Vertsendurg, his was Draw ratio limit L.D.R. only 2.05. It is generally believed that the high viscosity of the press lubricant has a positive effect on the deep-drawing properties affects and that the water glass layer or a similar solid phase layer a gives very high viscosity.

Example 2 Two steel sheet samples, using the pretreatment method according to the invention subject are manufactured using cold rolled steel sheets a thickness of 1.8 mr; (with a glossy surface), the i 5 resp.

3.5 micron thick dry waterglass layers and with top layers from a suitable press lubricant. Using the The same steel sheet 1.8 mm thick was another test sample without one Made of water glass coating on which only a layer of lubricant is applied became.

All samples were drawn and scratched in the same way and the flattening effects of the various samples were compared. Each sample was made using a punch with a flat surface with a diameter of 140 mm to a depth of 85 mm drawn using a sheet (blank) with a diameter of 280 mm and using a Pressure load of 6 tons.

At the sample, which is only protected by the press lubricant layer innumerable parallel scratches were made on its outer surface in the case of the above manual deep drawing. The number of parallel scratches has been greatly reduced, when the sample was provided with a 3 micron thick waterglass layer.

The sample with the 5 micron thick waterglass layer practically occurred no scratches during deep drawing. The degree of gloss or smoothness of the individual samples were measured in the same manner as in Example 1. The one with it Results obtained are summarized in the final Table II.

Table II surface layers gloss Gs (0 °),% press lubricant layer alone 96.0 3 µ thick waterglass layer plus press lubricant layer 63.2 5 µ thick waterglass layer plus press lubricant layer 49.6 As As can be seen from Table II above, the sample exhibited only a press lubricant layer had the red sheen, not only because of the shiny surface before drawing, but also because of the formation of scratches in the course of deep drawing. It was determined, that the gloss of the samples, which had waterglass layers, was lower in spite of this the lack of scratching. The reason for this decrease in gloss is that that by sliding and rotating the crystal lattice of the steel sheet during the plastic deformation in the deformation on the steel sheet surface is small Waves arise so that the original shine of the surface of the steel sheet does not can be sustained.

However, the advantages of using the waterglass layer will be through this change in the gloss or the smoothness of the surface is not impaired.

Example 3 Two steel sheet samples obtained by the method according to the invention should be pretreated, were made by applying 5 and 3.5, respectively Give away micron thick layers of dry water glass on with phosphate coatings Steel sheets and thereon were coated layers of a suitable press lubricant upset. Using the same one coated with a phosphate coating Steel sheet, a sneeze test was made without a water glass coating which has a layer of soap applied to it. The samples produced in this way were on drawn in the same manner as in Example 1 and the results obtained are summarized in Table III below.

Table III Surface Layers Gloss Gs (00),% (in three places for each sample) Position 1 2 3 Mean soap layer alone 27.76 38.40 34.40 33.52 3.5 P thick waterglass layer plus press lubricant layer 32.16 27.20 30.40 29.92 5 p thick waterglass layer plus press lubricant layer 26.40 29.60 29.04 28,32 It was found that in the sample which had only one layer of rope, the phosphate coating was partially removed, increasing the gloss of the steel sheet. In contrast, the sample according to the invention, which has a waterglass layer the phosphate coating was not affected at all by the deep drawing and the gloss was not changed by dragging.

Example 4 Four samples of steel sheets from a steel with a Exceptionally low carbon content for glass enamelling has been treated by applying a sulfuric acid etching solution (until a weight loss of 2 g / 0.09 m² (1 ft .²)) and then plated with nickel (in a Amount of 50 mg / 0.09 m2 (1 ft2)). 3 to be pretreated according to the method according to the invention Samples were produced using the steel sheets thus pretreated a steel with a very low carbon content by applying 3.5, 2.5 and 1.5 micron thick dry waterglass layers. A test sample that doesn't have a Water glass coating was produced using that pretreated as above Steel sheet made from a steel with a very low carbon content. All on Samples prepared in this way were as in Example 1 Deep drawing tests subjected. The results obtained are summarized in Table IV below.

Table IV Thickness of the waterglass layer Adhesion strength of the glass (in Micron) enamel 0 poor 1.5 2.5 moderately good 3.5 excellent ;; ie the above Table IV shows the etched and nickel-plated surface of the steel sheet from the very low carbon steel through the), 5 micron thick waterglass layer almost completely protected, so that a very st.rle adhesion between the Sheet steel and the enamel layer was guaranteed.

In general, the surface conditions of the steel sheet are very important for achieving a good glass enamel layer (fire enamel layer) on it. Ilenn the steel surface is completely flat, it is very difficult to make a firm bond to achieve between the steel sheet and the glass enamel layer. The by applying a water glass layer on the surface of the steel sheet for the purpose of pretreatment of the steel sheet for glass enamelling are the following: (a) The steel sheet can after deformation, for example by means of a press is carried out to be easily ontfettot, because water glass itself is a degreasing agent Has an effect. After the steel sheet has the desired shape, the water glass can by washing the steel sheet with cold water, hot water or an aqueous one Solution of a suitable degreasing agent must be removed. Along with the water glass can after the specified washing process for the removal of Water glass also contains the lubricants and waxes that help ease the deformation have been applied to the steel sheet, can be removed. The following table V shows the different degreasing speeds to remove the press lubricant in the case of a steel sheet with a 3 micron thick waterglass layer on the one hand and a steel sheet without a water glass layer on the other hand. For degreasing were the steel sheets are immersed in a 2% aqueous sodium hydroxide solution at 80.degree.

Table V Surface condition Degreasing degree (after washing within the following periods at sea.) 2 5 10 30 6G 120 300 600 Press lubricant Layer alone ND ND ND ND ND ND ND D 3 micron thick waterglass chit plus press lubricant layer ND ND HD HD D CD CD CD ND = not degreased HD = halfway degreased D = almost degreased CD = completely degreased (b) The one required to dry the waterglass layer Time is much shorter than that it takes for a coating to dry out of a usual one organic matter is required. The manufacture of the water glass coating is consequently easier than the production of conventional coatings. The inventive Water glass coating is free from the risk of aging of the steel sheet, which is caused by the burning is effected.

(c) Water glass is an inexpensive material, so the entire Pretreatment process can be carried out economically.

(d) Water glass is a material that is the coating layer for the Glass enamelling is similar, so that any water glass residues are not detrimental Have effects on the glass enamel layer.

It should be noted here that the application of the water glass layer described as part of the pre-treatment process for glass enamelling has been, but that water glass itself is also suitable as protection for the free or a metal-plated surface of a steel sheet for deformation in general.

The following further practical examples serve to provide a more detailed explanation the invention.

Example 5 On the surface of a 0.8 mm thick steel sheet for the glass enamel was applied to waterglass to form a 3.5 micron thick dry waterglass layer on top of it.

A press lubricant layer was applied to the waterglass layer and the steel sheet thus protected was pulled out into a saucepan. After degreasing and washing with water, a 130 micron thick white glass enamel layer was formed applied and fired in one operation. The glass enamel layer produced in this way of the saucepan was flawless and the glass enamel layer adhered very firmly to it Sheet steel of the saucepan.

Example 6 On the surface of a steel sheet coated with phosphate waterglass was applied to form a 3.5 micron dry waterglass layer On the waterglass layer a press smear! applied and the steel sheet protected in this way was made by means of a press processed. The phosphate coating was found to be well protected and during was not scratched during processing with the press. Then it was edited that way Steel sheet provided with a paint and it was found that the paint on the Sheet steel adhered very firmly. Is painted steel sheet had a very high corrosion resistance.

Example 7 On the surface of 1.8 mm thick steel sheets Water glass applied to form a 5 micron thick dry water glass layer on each of the steel sheets. A press lubricant layer was applied to the waterglass layer applied and the steel sheets protected in this way were by means of a Press deformed. There were no scratches or scratches on the surface of the sheet steel. Scratches. After smoothing the roughened parts of the steel sheets by lightly Polishing, shiny copper, nickel or chrome plating was applied. The results obtained were satisfactory.

Example 8 An aqueous waterglass solution consisting of 4 parts by volume Water and 10 parts by volume of water glass was cold-rolled on first samples Sheets made of non-killed steel are applied by means of a roller coater forming a layer of water glass about 3 microns thick after 30 seconds Drying at 80 ° C. Each of the steel sheets coated with water glass was inserted into a Immersed wax solution, which is made by dissolving 100 g of wax in 1 1 of toluene so that a wax layer about 1 micron thick was formed thereon became. As a solvent for the wax, benzene or any other suitable solvent can be used.

After the water glass and wax coatings were applied, each The sheet steel of the first samples was formed into a cup using a press.

Separately, there was a second sample of cold-rolled steel sheet, the from the same batch of non-killed steel as the first cold rolled Steel sheets had been made using only a high quality liquid Lubricant coated and deformed in the same way by means of a press.

The workability of the first and second sheets was then tested and the results obtained are summarized in Table VI below.

Table VI first (after the second (based on common remarks according to the invention) in the same way pre-treatment method pre-loaded) sample with treated) sample of a layer made of a 3 micron thick liquid kiron layer of water and lubricant (Press oil no.

and a NIHON KOSAKUYU wax layer 1 Mi- 660 from kron KABUSHIKI KAIsw) ~~~~~~~~~~~~~~~~~ Limit of the extraction ratio- stamp with a ses (L.D.R.) 2.27 2.17 flat surface punching force and a through at one knives of 30 mm extraction ratio of 2.17 2.90 t 3.15 t scratch after scratch the outer steel surface of the cup, which is based on 100 sheet metal-shaped cups Samples that were continuously pressed onto the upper die Coating surface was wetted by corrosion test on the stem about 1.5% SO2, in an SO2 no corrosive strong corrosion relative humid atmosphere sion after within activity> 95% after the press 10 days 2 days sen deformation Removable within 120 seconds of the coating 30 seconds full-seconds removed by constantly dipping into a deformation after the press removed by 5 % solution of a non-stirred dipping in degreaser warm water (Homezarin F-180 from 600C from Kawo Selten Company) No sticking together - the liquid Smear of the specimens when sticking within medium led to longer exposure times of 30 a hardly re-load 100 kg tion days separable together per 200 mmx200 mm gluing the steel As can be seen from Table VI above, the double coating according to the invention leads to the following advantages: (a) The Application of the wax coating is easy. As to prevent scratches If a waterglass layer is already present, a very thin wax coating is sufficient to prevent corrosion and to achieve a lubricating effect, the Wax coating using a wax solution in a suitable organic Solvent or can be applied by melting on; (b) by the combined Effect of preventing scratches by the water glass layer and lubrication excellent press workability can be ensured by the wax coating will; (c) The pretreated steel sheet can last for a comparatively long time Period of time, because the wax coating is in front of the waterglass layer protects against attack by the atmosphere, so that the water glass with the air does not reacts and thus the corrosion of the steel sheet is eliminated; (d) the pretreated Sheet steel can also be stored after the press deformation because of the wax coating it protects against the humidity of the air. On the parts where the wax coating has been removed by the press deformation, the remaining waterglass layer is used to passivate the steel sheet due to the alkalinity of the water glass; (e) the coatings can easily be removed by dipping the steel sheet in warm water at a temperature above the melting point of the wax. When the wax melts, the water glass under the wax coating dissolves quickly in the warm water. In this way, the two teachers can join very easily removed from the deformed steel sheet; (f) the amalgamation of the Steel sheets can be prevented by the fact that one for the production of the wax coating a wax with a melting point above about 500C is used; (g) during press deformation no additional lubricant is required as long as the inventive Pretreatment is applied.

It has now been found that the adhesion between a steel sheet and a glass enamel layer applied thereon by roughening the surface of the steel sheet in a fast moving electrolyte relative to the steel sheet can be. In the following examples, this roughening step is shown Pre-treatment explained in more detail.

Example 9 Figure 2 of the accompanying drawings illustrates the principle the surface roughening caused by the pretreatment process according to the invention is caught. As shown in this figure, the conditions become one variable speed rotating motor 1 is controlled by a regulator 2. The power output by the engine 1 is transmitted by means of a suitable transmission, for example by means of rollers and a belt 5 on a rotating shaft 4 transfer. One end of the rotating shaft 4 is on a rotating drum 5 attached, the kenzortrosch arranged in a Z-cylindrical electrolyte cell 7 is. A cylindrical cathode 6 made of lead is between the rotary drum 5 and the inner surface of the side wall of the electrolytic cell 7 is arranged. the rotating shaft 4 is connected to a brush 8, which is connected to the positive Voltage terminal of a rectifier 9 electrically connected is. The cathode cylinder 6 is connected to the negative voltage line of the rectifier 9 connected. The rotating current 15 is selective relative to the electrolytic cell 7 movable so that the drum 5 is loaded in the cell 7 for treatment and for the attachment or removal of a steel sheet 10 from the cell 7 removed can be.

An etching solution or a liquid electrolyte made from dilute sulfuric acid and iron sulfate is poured into the cell 7 so that the steel sheet 10 immersed in the etching solution so that an electric current flows between the steel sheet 10 and the cathode 6 flows. To establish the electrical connection between the steel sheet 10 and the rotating shaft 4 become suitable conductor rings (not shown), which are electrically connected to the rotating shaft 4 and are mechanically designed so that they have the steel sheet 10 on the outer surface hold onto the rotating trcmmc-i 5.

In this way @ rkt there; Sheet steel 10 as a rotating anode in rier Electrolyte cell 7 and the electrical current between the anode and the cathode 6 acts on the surface of the steel sheet 10.

Tests were carried out using 0.8 mm thick cold-rolled sheet made of cimem steel with a low carbon content a width of 50 mm and a length of 325 mm, In Fig. 2 a 30 mm is wider Distance between the steel sheet 10 and the cathode 6, measured in the radial direction the cylindrical electrolytic cell 7 is provided. The one used in the experiments The etching solution contained iron (II) sulfate (H2SO4? H2O) in a concentration of 100 g / l and sulfur sauce (H2S04) in three different concentrations, namely in one Concentrations of 10 g / l, 20 g / l and 50 g / l.

The etching solution was kept at 80.degree. C. and its concentration became constantly monitored and within a range of # 0.1% at the desired concentration held. A current rate of 30 A / dm².30 seconds was used for each etching solution. The rotating speed of the rotating shaft 4 and the steel sheet 10 became set to 400 rpm and the tests were also carried out with one for comparison non-rotating shaft 4 and a non-rotating sheet steel '' O passed through ¢ After the treatment in the Zel 7, the steel sheet 10 was subjected to various plating conditions plated with nickel. Then, a glass enamel layer was placed on the nickel-plated steel sheet (Fire enamel layer) applied.

For each of the pretreated under the various conditions above Steel sheets was the Au number of the etching peak counts and the PEI (Porcelain Enanelling Institute) index. The results obtained are compiled in the following table VII. The etch peak count was measured using a Spitzon counter from the Bendix Company / USA and @@@ @ pit @ enzahl Table Vii below represents the number of peaks per 25.4 mm line segment on the sheet steel surface, the height of which is more than 0.5 microns. The PZ'I index (%), the diC adhesive strength between a steel sheet and one produced thereon Fire enamel coating was made according to the Japanese industry standard process JISR-4204 and ASTM method C-313-59, respectively. A PEI index of 100 % gives up a perfect adhesive strength (bonding strength) of a fire enamel layer a sheet steel.

After the steel sheet was etched, it became, as in. the fire enamelling common, plated with nickel. The nickel plating provides an iron oxide (FeO) layer, as an intermediate layer, the adhesion between the steel sheet and the fire enamel layer supports. Along with a Watt bath, four different nickel plating conditions were used applied.

Based on the data given in Table VII below is the relationship between peak count and PEI index in the graph Representation of FIG. 3 for different concentrations of sulfuric acid and for various nickel plating conditions shown. Tabel VII Etching conditions number of peaks and PEI index concentra- rotary speed electrical plated with nickel with nickel with nickel with nickel tion of the conditions plated plated plated sulfur drum (rpm) (A / dm² xsec.) at 0.5A / dm² at 0.5A / dm² at 0.25A / dm² at 0.25A / dm² acid (g / l) within within within within 100 sec. from 50 seconds from 50 seconds from 25 seconds

Number of PEI- Number of PEI- Number of PEI- Number of PEI-the index the index the index of the index peaks * (%) peaks * (%) peaks * (%) peaks * (%) 0 30 30 242 100 240 94.3 215 98.7 233 52.5 10 400 30 30 250 100 250 100 240 100 260 100 0 30 30 240 81.1 243 98.7 225 76.7 230 52.5 20 400 30 30 243 100 240 100 245 100 235 100 0 30 30 220 54.1 220 75.5 228 60.4 220 61 50 400 30 30 220 81.1 220 100 214 100 235 87.4 * Number of peaks per 25.4 mm line segment on the sheet steel surface, the height of which was more than 0.5 microns.

In Fig. 3, the filled squares indicate the etching with a rotating anode, while the non-filled squares indicate the etching with the mean stationary anode. From this Fig. 3 it can be seen that the adhesion of the fire enamel layer generally better on the steel sheets etched with the rotating anode was than on the steel sheets etched with stationary anodes. They show that too Number of peaks (peak counts). It should be noted that when the The number of peaks was greater than about 240, a PEI index of 100% without any Failure could be assumed. If the steel sheets have been etched by them when rotating anodes were used, their PEI indices were generally higher than those obtained with steel sheets that obtained using the same as stationary anodes had been etched, even if the number of their tips was relatively low.

Figures 4A, 4B and 4C of the accompanying drawings show Images of the surface conditions of a steel sheet produced using the same was etched as a stationary anode, the images using a recording Electromicroscope with a magnification of 1000, 3000 or 10000 times were taken.

Figures 5A, 5B and 5C of the accompanying drawings show similar ones Images of a steel sheet being etched using it as a rotating anode was, with the images at a magnification of 1000, 3000, or. 10,000 times were taken on. In the case of the rotating anode (FIGS. 5A to 5C), square Recesses or so-called etching scars are formed with multi-stepped side walls. On the other hand, those with the stationary anode (Figures 4A to 4C) through the Etching formed recesses simple valleys without clearly defined stepped wall parts as a result, the steel sheets those using the same when rotating anodes had been etched, countless small but deep etching pits that could not be counted by conventional peak counters.

Example 10 The effects of the rotational speed of the steel sheet acting as an anode when using a method similar to that of it has been described above with reference to Figure 2 of the accompanying drawings has been investigated, this time the rotational speed of the anode 100 and Was 200 rpm. It was found that similar improvements in the number of suen and the PEI index at lower speed of the steel sheet could be achieved, but the degree of improvement, for example the Adhesion strength of the enamel layer on the steel sheet, with increasing speed of rotation increased.

With the usual pretreatment for applying a layer of fire enamel (Glass enamel layer) in one process step, it was previously necessary to add the weight of a steel sheet by about 0.2 g / dm2 due to the etching. According to the invention Process can reduce weight loss when etching, which is necessary to achieve good adhesion all I need is to about half or less of the usual weight loss be reduced when one has a comparatively high relative speed generated between the etching solution and the steel sheet to be etched with it. In the following Table VIII is an example of such a weight improvement sve'rreduction specified.

Table VIII Chemical Composition- Revolution Etch Weight PEI Index (%), reduction of the etching solution speed current reduction twice the density change measure (rpm) (A / dmc) by etching2 ~~~ (/ dm) H2S04: 20 g / l 200 30 0.287 100 100 FeSO4.?H20: 100 g / l 0.206 99.4 100 0.131 100 100 0.097 96.2 100 400 30 0.307 100 100 0.237 100 100 0.157 100 100 0.077 100 100 Due to the lower requirements in terms of weight reduction in etching, it is possible to use a smaller electrical To use energy source and a shorter electrolyte cell in the etching device. In Example 10, the weight reduction by etching was varied the duration of the etching controlled, the nickel plating using a Watt bath at a current density of 0.5 A / dm2 over a period of 30 seconds was carried out. In the experiments of Example 10 it was found that between the etching solution and the steel sheet require a finite relative speed that is, the etching solution on the steel sheet surfaces must be stirred. Thereon a practical device for carrying out the invention has now been established Pretreatment process for fire enamelling worked out, for example is shown in Figures 6 and 7 of the accompanying drawings.

In Fig. 6, a rolled steel sheet 11 is through two pairs of Guide rollers 12 and 13 in the direction indicated by the arrow a in a Pre-treatment process for fire enamelling introduced. A Pair of stationary cathode plates 14, 14 'are arranged to face the surfaces of the steel sheet 11 with a distance d between the corresponding steel sheet surface and face the cathode 14 or 14 '. The cathode plates 14, 14 'are preferred protected by a pair of cover plates 15, 15 '. In Figures 6 and 7 is a Pair of nozzles 16, 16 'arranged so that at a high speed under pressure an etching solution into the spaces between the steel sheet 11 and the cathodes 14, 142 is injected from the opposite edges of the plate 11 ago.

Each nozzle 16 or 16 'is connected to a pump 17, Which the Supplies etching liquid under pressure. The inlet port of each pump 17 is provided with a Reservoir 18 in connection, which the etching liquid from the above Void between the steel sheet 11 and the cathode plates 14, 14 'for the recirculation by the pump 17 receives. A pair of stripping rollers 19, 19 ′ lie on the steel sheet 11 on the sides of the cathode plates 14, 14 "opposite the nozzles 16, 16 '. The stripping rollers 19, 19 'are preferably made of an acid-resistant rubber.

In the embodiment shown in Figures 6 and 7 is a another pair of anode plates 20, 20 'at suitable distances d' from the steel sheet 11 provided. Pumps 22 convey the current carrier liquid into the cavities d ' under pressure through the nozzles 21, 21 ', which the liquid towards the direct first nozzles 16, 16 '. The cathode plates 20, 20 'are through cover plates 23, 23 'protected and the liquid injected through the nozzles 21, 21' is wiped off by stripping rollers 24 before the sheet 11 reaches the first cathode plates 14, 14 'opposite. The liquid from the cavities d 'is in a storage container 25 collected for recirculation by the pumps 22 through a partition 26 is separated from the first storage container 18 The cathode plates 14, 14 ' stand with a negative voltage source (not shown) in connection, while the anode plates 20, 20 'are connected to a positive voltage source (not shown) are connected. This way it becomes a closed passage generated for a direct current through the etching solutions and the steel sheet 11. It is it is clear to the person skilled in the art that instead of the arrangement of FIGS. 6 and 7, the steel sheet 11 in the way by a stationary etching solution with a suitable electrical Power supply device can be performed that this via the nozzles 16, 16 and 21, 21 'flows off. To supply an electrical current, electrical Conductive rollers are used which are in direct contact with the steel sheet 11 stand.

In the embodiment according to FIGS. 6 and 7, a cold rolled was used Sheet metal made of a steel with a low carbon content and a width of 1 m and a thickness of 0.8 mm for fire enamelling (Gsemail1ipriiiig) by introducing desse '- = n at a speed of 5 m / sec., with an etching solution, which contained 2% sulfuric acid, which with 10 m3 / min. was recirculated, and one Current carrier liquid was used which contained 10% sulfuric acid, which with 5 m 3 / min. Recirculated 100% Each of the cathode plates 14, 14 'was about 2 m long and was spaced from the steel sheet 11 about 10 cm and the etching was carried out carried out with a DC voltage of 20 volts and a current of 8000 A.

Figures 8A, 8B and SO of the accompanying drawings show images, which the surface conditions of the etched by means of the device according to FIGS. 6 and 7 Show the steel sheet, taking the pictures with the same electron microscope as the FIGS. 4A to 40 and 5A to 5C at the respective corresponding magnifications were recorded. As can be seen from FIGS. SA to 8C, according to the method using the apparatus of Figures 6 and 7 as in the case of Figures 5A Right-angled deep scars with stepped sidewalls can be produced up to 5C.

According to the method according to the invention for fire enamelling pretreated sheet steel shows strong adhesion to a glass enamel layer (Fire enamel layer) applied with or without prior nickel plating and wherein the steel sheet has been shaped prior to enamelling. To after firing, the glass enamel layer adheres to the process according to the invention pretreated steel sheet is much more durable than in the usual way pretreated Steel sheets.

As described above, the method according to the invention it improves the pretreatment process for glass enamelling or fire enamelling and it can include electrolytic etching with a liquid electrolyte, which moves relative to the steel sheet to be etched, thereby forming deep etched pits which is the adhesion between the steel sheet and the subsequently applied The etching solution can be applied to the sheet steel surface under pressure are sprayed in the form of jet streams through nozzles, so that electrolyte cells with a shorter length can be used. The fire enamelling can thus be carried out with a compactly built device. This represents a significant technical progress.

Patent claims:

Claims (10)

Claims X method for pretreating a following to deforming and optionally enamelled sheet steel, in which before the deformation at least one removable cover layer is applied to the steel sheet is indicated by the fact that a layer is applied to the steel sheet made of water glass and a layer of wax can be applied. 2. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that the water glass layer on the previously electrolytically roughened surface of the steel sheet is applied. 3. The method according to claim 1 or 2, characterized in that g e k e n n -z e i c It does not mean that the waterglass layer is coated with the wax layer. 4. The method according to at least one of claims 1 to 3, characterized It is not noted that the material of the wax layer is a heated one Water removable wax is used, which is solid at room temperature. 5. The method according to at least one of claims 1 to 4, characterized It is not noted that the steel sheet was used prior to the application of the waterglass layer is plated with nickel on its electrolytically roughened surface. 6. The method according to at least one of claims 1 to 5, characterized it is not noted that the electrolytically roughened surface of the Steel sheet before applying the layers of water glass and wax with a Phosphate layer is coated. 7. The method according to at least one of claims 1 to 6, characterized it is not noted that the wax to be applied is in an organic Solvent is dissolved. 8. The method according to at least one of claims 1 to 7, characterized it is not noted that the electrolytic roughening of the steel surface takes place in such a way that at a distance parallel to the steel sheet connected as the anode a cathode arranged and during the passage of current through the electrodes in the gap between the steel sheet and the cathode under pressure into the gap Its rapid passage is injected with liquid electrolyte filling it. 9. The method according to claim 8, characterized in that g e k e n n z e i c h -n e t that the steel sheet is continuous during the electrolytic surface roughening is moved forward with the help of a feed and guide device and the liquid Electrolyte in a closed circuit containing a container, a pressure pump, a nozzle device and the saplt is etched between the cathode and sheet steel, and that the liquid electrolyte of the nozzle device under pressure from the Pump is fed that the electrolyte from the nozzle device into the gap between Sheet metal and cathode is injected into it. 10. The method according to at least one of claims 1 to 7, characterized it is noted that the sheet steel is continuous during the roughening process is moved forward so that there is a parallel stationary cathode happened at a distance from it, being in the gap between the cathode and sheet steel a liquid under pressure Electrolyte is injected, which the Fills gap and quickly passes through the same that parallel to the steel plate also at a distance from this in a near the cathode Place an anode, with an electrically conductive liquid underneath Pressure is injected into the gap between the latter anode and the steel sheet, which this gap fails with its rapid passage and that to the anode and the Yathede so applied a voltage that the surface of the steel sheet by an electric current flowing between the anode and the cathode through the Sheet steel flows, is etched. L e r s e @ t e