DE2264581B2 - Method for preparing a steel sheet for glass enamelling after the sheet has been deformed - Google Patents

Description

The invention relates to a method for preparing a steel sheet for a after deformation of the Sheet glass enamelling with those specified in the preamble of claim 1 above Features. Such a method is known from DE-OS 19 65 586, for example. With this one known method comprises the electrolytic treatment of the steel sheet to be coated a electrolytic fine degreasing and electrolytic pickling. In conclusion to such an electrolytic one Surface fine cleaning is carried out by electrolytic nickel plating of the steel sheet, which is why this Applying a protective coating from a water-soluble Polyphosphate connects. After removing this protective polyphosphate coating, the final Enamel coating applied.

This known process is carried out electrolytically Treatment primarily with the aim of achieving film-free sheet metal surfaces. the w electrolytic degreasing is known to be based on the fact that existing layers of fat with the help of Electrolysis evolved hydrogen gas can be lifted from the metal substrate. To this ^ development To achieve this, however, the steel sheet must act as a cathode

r>, since otherwise a discharge of H ⁺ ions on the steel sheet cannot be achieved.

The known preparatory method is disadvantageous in that it uses the electrolytic surface treatment only essentially completely fat

bo free surfaces can be achieved, although the cleanliness and in particular freedom from grease of the steel surfaces to be coated is of great importance.
Not achievable with the help of the known electrolytic

However, b ^r> see surface treatment is influencing the steel sheet surfaces so that the adhesive strength of the steel sheet is improved for the later applied enamel layer.

It is known from “Lecture Hall for Ceramics, Glass, Email”, 1961, page 465, left column, paragraph 3, “through electrochemical corrosion of the sheet metal surface and anchoring of the enamel in the resulting depressions « to make an enamel stick to sheet steel. Such anchoring depressions in the sheet steel surface however, cannot be achieved by electrolytic pickling, as pickling on the one hand and etching on the other hand, each have different process conditions. As already mentioned, the electrolytic pickling the object to be pickled can be connected as a cathode, while electrolytic Etching the object to be etched is to be switched as an anode In contrast to pickling, when etching not only the top layer is removed, the subsoil is also attacked and eroded locally.

The according to DE-OS 19 65 586 applied protective coatings of water-soluble polyphosphates are, however, associated with the disadvantage that these protective layers during storage by access by Moisture decomposes with the formation of hygroscopic decomposition products. It goes without saying that the hygroscopic decay products favor rapid oxidation of the sheet metal surfaces to be protected.

The invention is therefore based on the object of a 2Ί To train the method with the features specified in the preamble of claim 1, Jaß that Sheet steel has particularly good adhesive properties and that the removable protective coating dem Attack of moisture has grown. ) <>

This object is achieved by the features specified in claim 1.

The technical progress that can be achieved with the aid of the invention is primarily to be seen in the fact that the Etching scars caused by electrolytic etching provide an excellent primer for the enamel layer form and that the waterglass-wax layer on the one hand has an excellent lubricating effect Has deforming and on the other hand is resistant to attack by moisture.

Preferred embodiments of the invention are specified in the subclaims.

When applying water glass to a steel workpiece, e.g. B. a steel sheet, a steel plate or a Steel molding, the surface of the water glass film is in practice preferably with a counter Moisture resistant layer coated so as to prevent excessive absorption of moisture by the To prevent water glass. Namely, the excessive moisture absorption by water glass causes w the water glass itself weathered into whitish powder particles. Once the water glass is in duS has converted to whitish powder, it loses its resistance to corrosion. The moisture absorption water glass also makes it more viscous. «Accordingly, the excessive moisture absorption leads through water glass, if stable sheets coated with water glass are stacked on top of one another for a long time stored \ ver <that the steel sheets cling together. bo

According ei W preferred embodiment of the invention w'i ^f A, an aqueous water glass solution, consisting of A VaiVi'henteilen water and 10 parts by volume of water glass (lilfth conventional roll coating onto the surface TFIIIA ^ s steel sheet applied and (<- warm inflating Air-dried. After drying, the steel sheet coated with water glass is immersed in a heat dissolving agent, which has been prepared by dissolving normally solid wax in toluene in an amount of 100 g wax per liter of toluene. Instead of immersing the steel sheet in the wax solution, coating can be used of the water glass coating with a wax layer, the steel sheet can also be dipped in molten wax or subjected to a roller coating. The thickness of the water glass layer to be applied to the steel sheet is preferably 2 to 5 μm and the solid wax layer on the water glass layer should preferably be 0.5 to 1 μm thick With a water glass layer u Excellent deep-drawability is achieved with a wax coating of the above-mentioned thicknesses. Even after deep-drawing, the steel sheet can be coated with a glass enamel layer firmly adhering thereto. In order to ensure firm adhesion between the steel sheet and the glass enamel layer, the surface of the steel workpiece or the steel sheet is roughened before the water glass layer is applied.

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

In the case of the etching according to the invention, a liquid electrolyte is spread out on the surface of the flat Steel sheet sprayed and the steel sheet can be handled more easily than in the case of etching through Immersing the steel sheet in an electrolytic cell.

After several years of investigations, it has now been found that there are disadvantages of the usual etching pretreatment for the glass enamelling can be avoided by having a comparatively high applies relative velocity between the liquid electrolyte and the steel sheet. aside from that the high relative speed between the liquid electrolyte and the steel sheet also serves to roughening the surface of the steel sheet to form sharp-angled protrusions and indentations, which are densely distributed over the surface of the steel sheet. This made it possible to reduce the liability greatly improve the electrolytic etching process between the glass enamel layer and the steel sheet to improve without having to enlarge the etching devices.

The invention is described in more detail below with reference to the drawing. It shows

1A is a fragmentary cross-sectional view of a rolled steel sheet coated with a water glass coating and is provided with a layer of wax,

Figure IB is a fragmentary cross-sectional view a coated with water glass steel sheet, which before the glass enamelling according to the invention Procedure has been pretreated,

FIG. 1C is a fragmentary cross-sectional view of a steel sheet produced according to the present invention Process has been coated with a phosphate layer and a water glass layer,

Fig. 2 is a schematic diagram of an electrical Circuit for carrying out the etching process using an electrolyte cell with a rotating drum,

Fig. 3 is a graph showing the Relationship between the peak count and the PEI (Porcelain Enamelling lnstitute) index (in%) explains the

F i g. 4A and 5A pictures of the surface conditions of Steel sheets made using a stationary

Electrolytic cell or a rotating electrolytic cell have been etched, recorded with a scanning electron microscope at a magnification of 1 000 times that

F i g. 4B and 58 pictures corresponding to those of ί 4A and 5A, but this time the enlargement has increased to 3000 times that

F i g. 4C and 5C are pictures corresponding to those of Figs. 4A and 5A, but this time the enlargement was increased to 10,000 times, the ι ο

6 and 7 are a side view and a plane view, respectively Top view of a device which is suitable for carrying out the method according to the invention, and the

F i g. 8A, 8B and 8C are images of the surface conditions of a using a fast moving one liquid electrolytes in the device according to FIGS. 6 and 7 etched steel sheet, added below Use of a scanning electron microscope with a magnification of 1,000 times, 3,000 times or IO OOO-fold.

The F i g. 1A of the drawings shows a fragmentary view of a pre-treated according to the inventive method the steel sheet A. The rough surface of the steel sheet A, as indicated in Fig. IA, with a dry water glass layer B coated 2ϊ and on the water glass layer S is a lubricant layer C. IB shows a steel sheet A 1 which has been etched and coated with a nickel layer E before a dry water glass layer B is applied. On the water glass layer B, a lubricant layer is C. Figs. IC illustrates a steel plate A 1 that is coated with a Phosphatschichi D. On the phosphate layer D there is a lubricant layer C.

If a rolled steel sheet is now deformed, for example by means of a press, before glass enamelling, the waves on the sheet surface are flattened or leveled, which may cause scratches or scrapes on the leveled surface. This flattening of the waves and the risk of scratching the flattened surface are inevitable, even if the steel sheet surface is coated with nickel or phosphate. The flattened surface and the scratches weaken the adhesion between the steel sheet and the glass enamel layer thereon and also affect the appearance of the enameled molded articles. In particular, the steel sheet provided with a phosphate coating must be handled carefully during the deformation 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 be retained on the steel sheet surface even after the deformation by means of the press, in order to ensure firm adhesion of the paint coating or the glass enamel coating to the steel sheet. However, if the phosphate layer is scratched or stuck to it during the deformation by the press, its function will be severely impaired

It has now been found that if a very thin layer of the comparatively less flexible dry water glass is applied to the steel sheet surface, the roughened state of the steel sheet surface can be maintained during the entire deformation process by the press. The reason for this improvement seems to be as follows: All small depressions on the entire rough surface of the steel sheet are caused by the comparatively hard material, i.e. h the water glass, which fills up the depressions as shown in FIGS. B. the elimination of the projections and the filling of the recesses with steel from the projections is prevented.

It has now been found that with the help of the pretreatment according to the invention, steel sheets with smooth surfaces, for example steel sheets with a glossy surface coating, by means of a Press can be deformed without scratching the surfaces of the same. That comparatively hard water glass is applied to the steel sheet surfaces in such a thickness that the Water glass layer itself can be scratched by the moving parts of a deforming device can, however, that the steel sheet surfaces remain intact under the water glass.

The application of water glass to a steel sheet before the glass enamelling (fire enamelling) after The method according to the invention is explained in more detail in the following examples.

example 1

Two samples of steel sheets to be protected by the method according to the invention were produced using cold-rolled steel sheets 0.8 mm thick (with a matt Surface coating of 3.0 μ Hmax), which with 5 μΐη or 3.5 μm thick dry waterglass layers and coating layers made from a suitable press lubricant were coated on the waterglass layers.

Using the same steel sheets with a thickness of 0.8 mm, four comparison samples were made without produced a water glass coating, which were provided with lubricant coatings.

All samples were formed into cups in an identical manner and then the scratching and flattening effects (leveling effects) of the various samples were compared with one another. Each sample cup was 55 mm deep and was made by punching out a blank having a diameter of 200 mm by means of a flat surface punch having a diameter of 100 mm while applying a compressive load of 5 tons. The outer surface of the drawn part was subjected to scratching and flattening. The glossiness of the outer surface increased with the number of scratches and the degree of the flattening increase. The gloss and the smoothness of the outer surface of the sample cups were measured by the ASTM method D 523 and the method according to JIS Z 874t, respectively. The results obtained are summarized in the following table 1. Small values for the gloss (smoothness) (in%) in the following table I mean good protection of the rough sample surface by the protective layers, since the gloss or smoothness is lower by se is, the better the protection

Tabel

Surface layers

Gloss Gs (O ¹ ),% ")

(in three places on each sample)

Job
I.

Press lubricant alone 85.84 88.80

Press lubricant alone 75.20 89.20

Press lubricant alone 104.40 79.52

Press lubricant all 116.24 88.00

5μ thick waterglass layer 45.60 36.24 plus press lubricant

3.5μ thick waterglass layer 41.60 32.96 plus press lubricant

*) Gloss Gs (0 °) in%, corresponding to) IS Z 8741.

92.80
90.00
81.28
80.80
47.20

37.60

Average

89.12
84.80
88.40
95.04
43.04

37.36

As Table I above shows, the gloss of the outer surface of the cup sample was reduced to about Half reduced by applying a water glass layer to the steel sheet compared to the Cup samples with the press lubricant alone. For the samples with the 5 μm or 3.5 μm thick Water glass layers were practically no scratches and flattened parts caused by the deformation had been caused to see. In this way, with such protective layers, the surface conditions became of the steel sheet before the deformation by means of the press also after the deformation of the steel sheet maintained by means of the press. When a press lubricant layer was used alone, there was significant one large number of scratch lines and flattened parts caused by the deformation on the Steel sheet surface had been generated.

A typical example of improving deep-drawing properties is the following:

When a 1.6 mm thick steel sheet made of a steel of the SPCC (JIS) class by means of a press according to the Applying a 5 micron thick waterglass layer plus a press lubricant layer was drawn, a draw ratio limit L.D.R. of 2.25 obtained. If, on the other hand, the same steel sheet on was drawn in the same manner without using a waterglass sheet, its draw ratio limit was L.D.R. only 2.05. It is generally believed that the high viscosity of the press lubricant has a beneficial effect on the deep-drawing properties and that the waterglass layer or a similar solid phase layer gives a very high viscosity.

Example 2

Two steel sheet samples to be subjected to the pretreatment process according to the invention, were made using cold-rolled steel sheets 1.8 mm thick (with a shiny surface), which are 5 or 3.5 μm thick dry waterglass layers and coated with top layers of a suitable press lubricant became. Another test sample was made using the same 1.8 mm thick steel sheet Manufactured without a water glass coating on which only a layer of lubricant was applied.

All samples were drawn in the same way and the scratching and flattening effects of the various samples were compared with one another. Each sample was drawn using a punch with a flat surface with a diameter of 140 mm to a depth of 85 mm using a metal sheet (blank)

2 ¹ J with a diameter of 280 mm and applying a pressure load of 6 tons.

The sample, which was only protected by the press lubricant layer, produced countless parallel lines Scratches on its outer surface at that

in the deep drawing mentioned above. The number of parallel Crater was greatly reduced when the sample was provided with a 3 μm thick water glass layer. at the sample with the 5 μm thick water glass layer entered practically no scratching during deep drawing.

r> The degree of gloss or smoothness of each sample was determined in the same manner as in Example 1 measured. The results obtained are summarized in Table II below.

Table II

55

60

65 surface layers

Gloss Gs (0 °),%

Press lubricant layer alone 96.0
3 μm thick water glass layer 63.2

plus press lubricant layer
5 μm thick water glass layer 49.6

plus press lubricant layer

As can be seen from Table II above, the sample which had only one press lubricant layer exhibited the greatest gloss, not only because of the glossy surface before drawing, but also because of the scratching in the course of deep drawing. It was found that the gloss of the samples which had waterglass layers was lower in spite of the lack of scratching. The reason for this reduction in gloss is that the sliding and rotating of the crystal lattice of the steel sheet during plastic deformation causes small waves on the surface of the steel sheet when it is deformed, so that the original gloss of the surface of the steel sheet cannot be maintained.

However, the advantages of using the waterglass layer are enhanced by this change in gloss or the smoothness of the surface is not affected

Example 3

Two steel sheet samples, which were to be pretreated according to the method according to the invention, were produced by applying 5 or 3.5 μm thick dry waterglass layers to steel sheets provided with phosphate coatings, and coating layers of a suitable press lubricant were applied to them. Using the same phosphate-coated τ steel sheet, a test sample without a water-glass coating on which a layer of soap was applied was prepared. The samples produced in this way were taken in the same way as in Example 1 and the results obtained are summarized in the following Table III.

Table III

Surface layers

Gloss Gs (0 °), ° / o

(in three places for each sample)

Job

2 3

Average

Soap layer alone 27.76 38.40 34.40 33.52

3.5 μ thick waterglass layer 32.16 27.20 30.40 29.92

plus press lubricant layer

5 μ thick waterglass layer 26.40 29.60 29.04 28.32

plus press lubricant layer

The sample which had only one layer of soap was found to have partial phosphate coating was removed while increasing the gloss of the steel sheet. On the other hand there was a waterglass layer having sample according to the invention, the phosphate coating by the deep drawing not at all attacked and the gloss was not changed by the pulling.

Example 4

Four samples of steel sheets made from a steel with an exceptionally low carbon content for glass enamelling were treated by applying a sulfuric acid ^{etching solution (until a weight loss of 2 g / 0.09 m 2 was} achieved) and then plated with nickel (in an amount of 50 mg / 0.09m ² 3 samples to be pretreated according to the method according to the invention were produced using the steel sheets pretreated in this way from a steel with a very low carbon content by applying 3.5, 2.5 or 1.5 μm thick dry waterglass layers. which had no waterglass coating was produced using the steel sheet pretreated as above from a steel with a very low carbon content.All samples produced in this way were subjected to deep-drawing tests as in Example 1. The results obtained are summarized in Table IV below.

Table IV

Thickness of the waterglass layer (μιη)

Adhesion strength of the Glass enamel

bad bad moderately good excellent

As shown in Table IV above, the etched and nickel-plated surface of the steel sheet made of the very low carbon steel could be almost completely protected by the 3.5 micron thick waterglass layer, so that a very strong bond between the steel sheet and the glass enamel layer is ensured was.

In general, the surface conditions of the steel sheet are very important for obtaining a good one Glass enamel layer (fire enamel layer) on top. If the steel surface is completely flat, it is very much difficult to achieve a strong bond between the steel sheet and the glass enamel layer. The through the Application of a water glass layer to the surface of the steel sheet for the purpose of pretreating the Steel sheet for the glass enamelling achievable advantages are the following:

(a) After the deformation, which is carried out, for example, by means of a press, the steel sheet can be easily degreased, as water glass itself has a degreasing effect. After the steel sheet has the desired shape, the water glass can be removed by washing the steel sheet with cold water, hot water or an aqueous solution of a suitable degreasing agent. Together with the water glass, after the specified washing process for removing water glass, the lubricants and waxes which have been applied to the steel sheet to facilitate the deformation can also be removed. The following Table V shows the different degreasing speeds for removing the press lubricant in the case of a steel sheet with a 3 .mu.m thick water glass layer on the one hand and a steel sheet without a water glass layer on the other. The steel sheets were immersed in a 2% aqueous sodium hydroxide solution at 80 ° C. for degreasing

11 Table V 22nd ND
ND 64 581 the
60 12th specified
300 Periods
600 Surface condition ND
D. ND
CD D.
CD Press lubricant layer
alone
3 micron thick water glass
layer plus press lubricant
middle class Degree of degreasing (according to
in sec.)
2 5 to the
IO Washing inside
30th below
120 ND
ND ND
HD ND
HD ND
CD

ND = not degreased
HD = halfway degreased
D = almost degreased
CD = completely degreased

(b) The time required to dry the waterglass layer is much shorter than that required to Drying a coating of a common organic substance is required. The manufacture of the Water glass coating is therefore easier than the production of conventional coatings. The inventive Water glass coating is free from the risk of aging of the steel sheet caused by burning is effected.

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

(d) Water glass is a material that is similar to the coating layer for glass enamelling so that any water glass residues have no adverse effects on the glass enamel layer.

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

The following further practical examples serve to explain the invention in more detail.

Example 5

Water glass was applied to the surface of a 0.8 mm thick steel sheet for the glass enamelling with the formation of a 3.5 μm thick dry water glass layer on the same. A press lubricant layer was applied to the waterglass layer and the steel sheet thus protected was pulled out to a saucepan. After degreasing and Washing with water, a 130 μm thick white glass enamel layer was applied and in one operation burned. The glass enamel layer of the saucepan produced in this way was free of defects and the The enamel layer adhered very firmly to the steel sheet of the saucepan.

Example 6

Water glass was applied to the surface of a steel sheet coated with phosphate Formation of a 35 μm thick dry water glass layer A press lubricant layer was applied to the waterglass layer and that on top of it Well-protected steel sheet was processed by means of a press. It was found that the phosphate coating was good was protected and was not scratched during processing using the press. Then it became like that The machined steel sheet was painted, and it was found that the paint on the steel sheet was very firmly adhered. The painted steel sheet had very high corrosion resistance.

Example 7

Water glass was applied to the surface of 1.8 mm thick steel sheets with the formation of a 5 μm thick dry water glass layer on each of the steel sheets. On the waterglass layer was a

ίο Press lubricant layer applied and the on Steel sheets protected in this way were deformed by means of a press. On the surface of the There were no scratches or scuffs on the steel sheet. After smoothing the roughened parts of the

η steel sheets by light polishing became shiny Copper, nickel or chrome plating applied. The results obtained were satisfactory.

_w example 8

An aqueous water glass solution consisting of 4 parts by volume of water and 10 parts by volume in a water glass was applied to the first samples of cold-rolled sheet made of non-killed steel by means of a roller

4> layer applied to form an approximately 3 micron thick waterglass layer after drying for 30 seconds at 80 ° C. Each of the with water glass coated steel sheets were immersed in a wax solution obtained by dissolving 100 g of wax in 1 l

w toluene had been made so that a wax layer a thickness of about 1 micron was formed thereon. Benzene can be used as a solvent for the wax or any other suitable solvent can be used. After applying the water glass and wax coatings were used to press each steel sheet of the first samples into a cup deformed

Separately, second samples of cold-rolled steel sheet obtained from the same batch of

bo not killed steel like the first cold rolled Steel sheets had been made only coated with a high quality liquid lubricant and deformed in the same way by means of a press

b5 Then the workability of the first and Tested second panels and the results obtained are summarized in the following Table VI

Table VI

Most of the sample (pretreated according to the method according to the invention) with a 3 μm thick waterglass layer and a 1 μm thick layer of wax

Second sample (pretreated in the usual way) with one layer
from a liquid lubricant
(Press oil No. 660 from the company
NlHON KOSAKUYU
KABUSHiKI KALSHA)

Remarks

Limit of the

Extraction ratio

(LD.R.)

Punching force at one
Pull-out ratio
from 2.17

Scratches on the
Sheet steel surface

Gluing the
Coating on that
rubber stamp

Corrosion test in
an SO2 atmosphere after the
Press deformation

Removability of the
Coating after the
Press deformation

Glue together
of the samples
prolonged storage

2.27

2.90 t

no corrosion after 10 days

Completely removed within 30 seconds by immersion in warm water at 60 ^° C

no sticking together within 30 days

3.15 t

Scratches on the outside
Surface of the molded
Mug

the stamp surface became
through the lubricant
wetted

strong corrosion inside
of 2 days

removed within 120 seconds by immersion in a
5% solution of a degreaser (Homezarin
F-180 from Kawo
Sekken Company)

the liquid lubricant
hardly led to you again
separable gluing together of the steel

Stamp with a
flat surface and a diameter
of 30 mm

based on 100 samples that were pressed continuously

about 1.5% SO ₂ ,
relative humidity
> 95%

not stirred

Load 100 kg
per 200 mm χ 200 mm

As can be seen from Table VI above, the double coating of the invention leads to feed the following advantages:

(a) The wax coating is easy to apply. Since there is already a If a waterglass layer is present, a very thin wax coating is sufficient to prevent corrosion and to achieve a lubricating effect, the wax coating using a wax solution can be applied in a suitable organic solvent or by melting;

(b) by the combined effect of preventing the formation of scratches by the water glass layer and the Lubrication by the wax coating can ensure excellent press workability will;

(c) The pretreated steel sheet can be stored for a comparatively long period of time because the wax coating protects the waterglass layer from attack by the atmosphere, so that the water glass does not react with the air and thus the corrosion of the steel sheet is eliminated;

(d) The pretreated steel sheet can be stored even after the press deformation, because the wax coating protects it against the humidity of the air. At the parts from which the wax coating has been removed by the press deformation, the remaining water glass layer serves to passivate the steel sheet due to the nature of the water glass;

(e) The coatings can be easily removed by immersing the steel sheet in warm water Temperature that is above the melting point de! Wax lies. When the wax melts, it dissolves; Put the water glass under the wax coating in the warm water quickly. That way, both of them 3 coatings very lightly from the deformed steel sheet be removed;

(f) The sticking together of the steel sheets can be prevented by making them of the wax coating is a wax with a melting point

w used above about 50 ° C;

(g) no additional: lubricant is required for the press deformation, as long as the according to the invention proper pretreatment is applied.

It has now been found that the adhesion is intermediate

^r > ^r ) a sheet of steel and one applied to it!

Glass enamel layer by roughening the surface de:

Steel sheet fell in a relative to the steel sheet fast moving electrolytes can be improved. In the following examples the this «

fao roughening stage extensive pretreatment explained.

Example 9

The F i g. 2 of the drawings explains the principle de

hi surface roughening, which of the invention Ben pretreatment procedure is included. As shown in this figure, the running conditions are determined one rotating at a variable speed

Motor 1 controlled by a regulator 2. The output of the engine 1 is by means of a suitable transmission, for example by means of rollers and a belt 3, onto a rotating shaft 4 transfer. One end of the rotating shaft 4 is attached to a rotating drum 5 concentrically arranged in a cylindrical electrolytic cell 7 is arranged. A cylindrical cathode 6 made of lead is between of the rotary drum 5 and the inner surface of the side wall of the electrolytic cell 7 are arranged rotating shaft 4 is connected to a brush 8 connected to the positive voltage terminal of a The rectifier 9 is electrically connected. The cathode cylinder 6 is connected to the negative voltage terminal of the rectifier 9 connected. The rotary drum 5 is selective relative to the electrolytic cell 7 movable so that the drum 5 is loaded in the cell 7 for treatment and for attachment or Removal of a steel sheet 10 from the cell 7 can be removed.

An etching solution or a liquid electrolyte consisting of dilute sulfuric acid and ferrous sulfate, is poured into the cell 7 so that the steel sheet 10 is immersed in the etching solution, so that an electric current flows between the steel sheet 10 and the cathode 6. To establish the electrical connection between the steel sheet 10 and the rotating shaft 4 are fitted with suitable conductor rings (not shown) used, which are electrically connected to the rotating shaft 4 and mechanically designed so that they hold the steel sheet 10 on the outer surface of the rotating drum 5. On this toilet. works the steel sheet 10 as a rotating anode in the electrolytic cell 7 and the electric current between the anode and the cathode 6 act on the surface of the steel sheet 10.

Tests were carried out using 0.8 mm thick cold-rolled sheets of au-5, a steel with a low carbon content, with a width of 50 mm and a length of 325 mm. In FIG. 2, a 30 mm wide distance is provided between the steel sheet 10 and the cathode 6, measured in the radial direction of the cylindrical electrolytic cell 7. The etching solution used in the experiments contained iron (II) sulfate (H ₂ SO ₄ -7H ₂ O) in a concentration of 100 g / l and sulfuric acid (H2SO4) in three different concentrations, namely in a concentration of 10 g / l, 20 g / l and 50 g / l. The etching solution was maintained at 8O ⁰ C and their concentration was continuously monitored and maintained within a range of + 0.1% at the desired concentration. A current density of 30 A / dm ² -30 seconds was applied to each etching solution. The speed of rotation of the rotating shaft 4 and the steel sheet 10 were set at 400 rpm, and the tests were also carried out with a non-rotating shaft 4 and a non-rotating one for comparison rotating steel sheet 10. After the treatment in the cell 7, the steel sheet 10 was plated with nickel under various plating conditions. Then, a glass enamel layer (fire enamel layer) was applied to the nickel-plated steel sheet

For each of the steel sheets pretreated under the various conditions mentioned above, the number of etching peak counts and the PEI (Porcelain Enamelling Institute) index certainly. The results obtained are summarized in Table VII below: The number of etching peaks was measured using a tip counter from Bendix Company / USA and the peak number in Table VII below represents the

: s Number of peaks per 25.4 mm line segment on the steel sheet surface, the height of which was more than 0.5 microns. The PEI index (%) that represents the The adhesive strength between a steel sheet and a layer of fire enamel produced on it, was

jo de according to the Japanese industry standard process JISR-4204 and ASTM method C-313-59, respectively. A PEI index of 100% gives a perfect Adhesion (bonding strength) of a fire enamel layer on a steel sheet.

3> After etching the steel sheet, this became like Common in fire enamelling, plated with nickel. The nickel plating provides an iron oxide (FeO) layer, which, as an intermediate layer, supports the adhesion between the steel sheet and the fire enamel layer.

Four different nickel plating conditions were used in conjunction with a Watt bath.

Based on the data given in Table VII below, the relationship between the Peak number and the PEI index in the graphic

• 45 illustration of Fig. 3 for different concentrations of sulfuric acid and for various nickel plating conditions shown.

Table VII Turning electrical number of sharpen PEI- and PEI index PEI- with nickel PEI- with nickel PEI- I. speed Conditional with nickel index with nickel index flat H-rt index plated at index ι Etching conditions the drum worked plated be plated at 0.25 A / dm ² 0.25 A / dm ² I. Concentration 0.5 A / dm ² (%) 0.5 A / dm ² (%) within (%) within (%) j tion of within 100 within 94.3 of 50 sec 98.7 of 25 sec 52.5 j sulfur of 100 sec. 100 of 50 sec. 100 number 100 number 100 acid number 81.1 number 98.7 the 76.7 the 52.5 S. (A / dm ² the 100 the 100 Sharpen*) 100 Sharpen*) 100 ; ■ (Rpm) χ sec.) Sharpen*) 54.1 Sharpen*) 75.5 60.4 61 0 30 30 81.1 100 215 100 233 87.4 400 30 30 242 240 240 260 (g / i) 0 30 30 250 250 225 230 10 400 30 30 240 243 245 235 0 30 30 243 240 228 220 20th 400 30 30 220 220 214 235 220 220 50

*) Number of peaks per 25.4 mm line segment on the sheet steel surface, the height of which is more than 0.5 micron.

In FIG. 3, the solid squares indicate the etching with a rotating anode, while the open squares indicate the etching with the stationary anode. From this Figure 3 it can be seen that the adhesion of the fire enamel layer on the steel sheets etched with the rotating anode was generally better than on the steel sheets etched with the stationary anode. This is also shown by the number of peaks (peak counts). It should be noted that if the number of peaks was greater than about 240, a PEI index of 100% could be assumed without any failure. If the steel sheets were etched by using them as rotating anodes, their PEI indices were generally higher than those obtained with steel sheets using the same were etched as stationary anodes, even when the number proportionate their tips low was.

4A, 4B and 4C of the drawings show images of the surface conditions of a steel sheet etched using the same as a stationary anode, the images being taken by a recording electron microscope at a magnification of 1,000, 3,000 and 10,000 times, respectively.

Figures 5A, 5B and 5C of the drawings show similar images of a steel sheet which is made using the same was etched as a rotating anode, with the images at a magnification of 1000-, 3000 or 10000 tach were recorded. In the event of the rotating anode (FIGS. 5A to 5C) have square recesses or so-called etched pits formed with multi-stepped side walls. On the other hand, those with the stationary anode (F i g. 4A to 4C) recesses formed by the etching are simple animals without clearly defined graded ones

Table VIII

Wall parts. As a result, the steel sheets, using the same as rotating anodes had been etched, innumerable small but deep scars that were not possible with conventional tip counters could be counted.

Example 10

In addition, the effects of the rotational speed of the steel sheet functioning as an anode were added to

ίο use a similar procedure as it above with reference to FIGS. 2 of the drawings, examined, wherein this time the rotating speed of the anode was 100 and 200 rpm. It was found that similar

ι ■> Improvements in the number of tips and of the PEI index could be achieved at a lower speed of the steel sheet, but that the degree of Improvements, for example the adhesive strength of the enamel layer on the steel sheet, with increasing Turning speed increased.

With the usual pretreatment for applying a fire enamel layer (glass enamel layer) in one Process step, it was previously necessary to reduce the weight of a steel sheet by etching by about

2 ^r > 0.2 g / dm ² to decrease. According to the method according to the invention, the weight loss during etching, which is necessary to achieve good adhesion, can be reduced to about half or less of the usual weight loss if one compares

Ki seise high relative speed between the etching solution and the steel sheet to be etched with it generated. In Table VIII below is an example of such weight reduction improvement specified.

Chemical together Rotation Etching current Weight PEI index (° / 100 settlement of the etching solution speed dichlc diminish b) 100 age tion through measured twice 130 the etching 100 (Rpm) (A / dm ² ) (g / dm ² ) 100 H ₂ SO ₄ : 20 g / l 200 30th 0.287 100 FeSO ₄ -7H ₂ O: 100 g / l 0.206 100 100 0.131 99.4 100 0.097 100 400 30th 0.307 96.2 0.237 100 0.157 100 0.077 100 100

Due to the lower requirements with regard to the weight reduction during etching, it is possible to use a smaller electrical energy source and a shorter electrolyte cell in the etching device. In Example 10, the weight reduction due to the etching was controlled by varying the duration of the etching, with the nickel plating being carried out using a Watt bath at a current density of 0.5 A / dm ² for a period of 30 seconds. In the experiments of Example 10, it was found that a finite relative velocity is required between the etching solution and the steel sheet, that is to say that the etching solution must be stirred on the steel sheet surfaces. On the basis of this, a practical device for carrying out the pretreatment method according to the invention for fire enamelling has now been worked out, as shown, for example, in FIGS. 6 and 7 of the drawings.

In FIG. 6, a rolled steel sheet 11 is introduced into a pretreatment process for fire enamelling by two pairs of guide rollers 12 and 13 in the direction indicated by the arrow <x. 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 the cathode 14 or 14'. The cathode plates 14, 14 'are preferably protected by a pair of cover plates 15, 15'. In the F i g. 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, 14 'from the opposite edges of the sheet 11 is injected. Each nozzle 16 or 16 'is connected to a pump 17, which the etching liquid under Pressure supplies The inlet port of each pump 17 is in communication with a reservoir 18, dtr the Etching liquid from the above-mentioned cavity between the steel sheet 11 and the cathode plates 14, 14 'for the recirculation by the pump 17 takes up a pair of Abstreifwalzcn 19,19' is on the Steel sheet 11 at the nozzles 16, 16 'opposite Sides of the cathode plates 14, 14 '. The stripping rollers 19,19 'preferably consist of one acid-resistant rubber.

In the FIG. 6 and 7, a further pair of anode plates 20, 20 'is provided at suitable distances d' from the steel sheet II. Pumps 22 convey the current carrier liquid into the cavities c / 'under pressure through the nozzles 21,2Γ, which direct the liquid in the direction of the first nozzles 16, 16'. The cathode plates 20, 20 'are protected by cover plates 23, 23' and the liquid injected through the nozzles 21, 21 'is wiped off by stripping rollers 24 before the sheet 11 lies opposite the first cathode plates 14, 14'. The liquid from the cavities d ' is collected in a storage container 25 for recirculation by the pumps 22, which is separated from the first storage container 18 by a partition 26.

The cathode plates 14, 14 'are connected to a negative voltage source (not shown), while the anode plates 20, 20 'are connected to a positive voltage source (not shown) are. This creates a closed passage for a direct current through the etching solutions and the steel sheet 11 is produced. It is clear to a person skilled in the art that instead of the arrangement of FIGS. 6th and 7 the steel sheet 11 in the manner by a stationary replacement with a suitable electrical Stromzuführi'ngseinrichtung can be performed that this flows off through nozzles 16, 16 'and 21, 21'. To the Feeding e'ties electric current can be electric Conductive rollers are used which are in direct contact with the steel sheet 11.

In the embodiment according to FIGS a cold-rolled sheet of a steel with a low carbon content of a width of 1 m and 0.8 mm thick for fire enamelling (glass enamelling) pretreated by introducing the same at a speed of 5 m / Selc, where an etching solution containing 2% sulfuric acid with 10mVMin. was recirculated and a current carrier liquid was used, which contained 10% sulfuric acid with 5 mVMin. was recirculated. Each of the Cathode plates 14, 14 'were about 2 m long and had a distance of about 10 cm from the steel sheet 11

ίο and the etching was done with a DC voltage of 20 Volts and a current of 8000 A.

Figures 8A, 8B and 8C of the drawings show Images showing the surface conditions of the device according to FIG. 6 and 7 etched steel sheet show, the images with the same electron microscope as the F i g. 4A to 4C and 5A to 5C for the respective corresponding enlargements were recorded. As can be seen from FIGS. 8A to 8C, can after the procedure using the

Ji) the device of FIG. 6 and 7 as in the case of FIG. 5A Right-angled deep scars with stepped sidewalls can be produced up to 5C.

The steel sheet pretreated by the method according to the invention for fire enamelling has a

. '"> strong attachment to a glass enamel layer (fire enamel layer), which with or without prior Nickel plating has been applied and the steel sheet has been shaped prior to enamelling. After firing, the glass enamel layer adheres to the

in steel sheet pretreated by the method according to the invention is much more durable than in the usual way pretreated steel sheets.

As described above, the method according to the invention provides an improved pretreatment

n drive for glass enamelling or fire enamelling and it may comprise an electrolytic etch with a liquid electrolyte which is relatively iu the to be etched steel sheet moves, whereby deep etching scars are formed, which the adhesion between the

4 (i sheet steel and the subsequently applied fire enamel layer greatly improve. The etching solution can be applied under pressure to the steel sheet surface in the form of Nozzle streams are sprayed through nozzles, so that electrolyte cells are used with a shorter length

v> can be. The fire enamelling can thus be carried out with a compact device. This represents a significant technical advance.

6 BIa (I drawings

Claims (9)

Patent claims: 1. Method of preparing a steel sheet for one after deforming the sheet ensuing glass enamelling, in which the sheet metal is electrolytically treated to remove material and is provided with a protective coating removed after deformation, characterized in that that by the electrolytic treatment in the sheet metal surface a variety of Etched scars is caused, whereupon the sheet roughened in this way as a protective coating with a known thin water glass coating and a thin wax coating will. 2. The method according to claim 1, characterized in that the water glass coating in one Thickness of 2 to 5 μm and the wax coating in a thickness of 0.5 to 1 μm on the steel sheet be applied. 3. The method according to claim 1 or 2, characterized in that the material of the wax layer a wax removable with heated water is used, which solid at room temperature is. 4. The method according to at least one of claims 1 to 3, characterized in that the Steel sheet before applying the waterglass layer on its electrolytically roughened Surface is plated with nickel. 5. The method according to at least one of claims 1 to 4, characterized in that the electrolytically roughened surface of the steel sheet before the layers are applied Water glass and wax are provided with a phosphate layer. 6. The method according to at least one of claims 1 to 5, characterized in that the The wax to be applied is dissolved in an organic solvent. 7. The method according to at least one of claims 1 to 7, characterized in that the electrolytic roughening of the steel surface takes place in such a way that at a distance parallel to the than > Anode-connected sheet steel placed a cathode 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 filled with liquid electrolyte injected. 8. The method according to claim 8, characterized in that the steel sheet during the electrolytic Surface roughening continuously with the help of a feed and guide device Ii is moved forward and the liquid electrolyte in a closed circuit containing a container, a pressure pump, a nozzle device and the gap between the cathode and sheet steel, is circulated, and that the liquid electrolyte of the .'ο 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. 9. The method according to any one of claims 1 to 7, i-, characterized in that the steel sheet during of the roughening process is continuously moved forward :, so that there is one parallel to it arranged stationary cathode happened at a distance therefrom, being in the gap between «Ι cathode and sheet steel under pressure a liquid Electrolyte is injected, which fills the gap and quickly passes through the same that parallel to the steel plate also at a distance therefrom at one located in the vicinity of the cathode μ Place an anode is arranged, whereby an electrically conductive liquid under pressure into the Gap of the latter anode and the steel sheet is injected, which this gap at their rapid passage fills and that to the anode and α ", the cathode is such a voltage that the surface of the steel sheet is etched by an electric current flowing between the anode and the cathode through the steel sheet.