DE1446369A1 - Treatment of porous aluminum oxide coatings - Google Patents

Description

DR. F. ZUMSTEIN - DR. E. ASSMANN - DR. R. KOENIQSBER0ER

PATENT LAWYERS

TELEPHONE, «8478 MDNOHEN 2. 1446369

TELEQRAMMEi ZUMPAT BRÄUHAU88TRA88E A / m

ΡΟβΤβΟΗΕΟΚΚΟΝΤΟ: MONOHS 01189 g

BANK ACCOUNT: BANKHAUe H. AUFHÄUeER

Dr. ExpL

S / Gy 2/2/1

^ ⁶ Charles Calvin Coim, Ridge Avenue, and

Samel_Lenard_Coto _± _Crawford_Street _L _firmierend_unter Colonial Alloys Company, City of Philadelphia,

Commonwealth of Pennsylvania, USA

Addendum to patent. * (Patent application C 22 224 Vl / 48d)

The present invention relates to α treatment of porous aluminum oxide coatings according to patent. .. ♦ ...,

, Vl / 48d
Patent application C 22 224 / artificially formed on aluminum or aluminum-based alloys to improve corrosion resistance. The treatment relates specifically to the use of alkali silicates. In the following, for the sake of simplicity, aluminum and aluminum-based alloys are generally referred to as aluminum.

The porous coatings on which the treatment according to the invention Can be applied on the aluminum

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produced by anodic oxidation or by chemical treatment in a special way, that by anodic oxidation The coatings produced are stored in electrolytes such as sulfuric acid (or, in an equivalent manner, bisulfate), phosphoric acid, Chromic acid, sulfamino acid, oxalic acid or others equivalent electrolyte produced. The oxide coatings produced in this way are porous. In contrast, anodic Treatment in boric acid, ammonium bicarbonate or similar electrolytes, produces coatings of such low porosity, that the invention is not applicable.

Other porous coatings to which the present invention is applicable can be made by chemical oxidation will. Typical of such coatings are those made by using alkali metal compounds together with sodium carbonate or by using baths containing fluoride ions and chromium ions, in some cases with additives of phosphate ions, e.g. an aqueous acid bath containing chromic acid, sodium bifluoride, sodium fluoroborate and urodium phosphate contains.

The production of porous oxide coatings, both electrolytically! as well as in a non-electrolytic, chemical way is well known. It is needless to go into the details of this to describe much-used procedures. The present invention is generally applicable to porous coatings so produced applicable,

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Alkali silicates have been used to treat porous aluminum oxide coatings used to study the protection of such coatings against corrosion. Resistance to Corrosion that had been developed by the known methods was not satisfactory because it was loose, slight leave absorbable protective films, most of which can be easily stripped from the covers. A. coating valued by such a film withstands the usual insurance against corrosion resistance immediately after manufacture, but the coating is used first stripped off and then the test is carried out, the coating from which the film has been more or less removed is not sufficiently resistant. Furthermore, when using known Lethoaen using silixates, the relatively loose protective film chalky when exposed to air and the surface becomes streaky.

The main object of the present invention can be briefly as manufacturing a greatly improved protection against corrosion through the use of alkali metals. Kie silicates but are included in a manner that is not just a mere coating of the alumina coating. this is apparent from the fact that, even after thorough stripping, the coating is not only excellent in corrosion resistance but also retains its initially uniform appearance.

BATH

The present invention is characterized by the use of sequential stages. In the first stage _r developed here (which can be followed by other stages not mentioned directly according to the invention), a preliminary treatment of the porous oxide coating is effected by using a silicone solution under conditions which not only serve to produce a mere sealing action. It can be either sodium or

c c

Potassium sulfate can be used, but since sodium silicate is considerably cheaper, it is the commercial chemical. In the following, the use of sodium silicate is always referred to, it being understood that equivalent amounts of potassium sulfate can also be used. The first treatment is carried out preferably below 50 0 (1? .OF) (when successive treatments are carried out in different Siliieatbädcrn) and the best results were obtained when the temperature around room temperature to about 45 ° C (110 ⁰ P) is. The duration of this treatment should be relatively short: Λ / Ζ minute to 5 minutes. For the first treatment, the ratio of silicon dioxide to alkali oxide should be at least 2: 1. The concentration of the silicate can vary from about 1 g per liter to saturation. This range encompasses equivalent silileate concentrations from about 0.1 $ to 30-6. The maximum concentration used ' νβΑ-iiwa depends on the solubility of the SiIiXate used in detail. High concentrations are undesirable,

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when the viscosity of the silicate solution becomes high and at the same time adheres to the workpiece to be machined.

The times for treatment are not critical. In this first stage, you should take less than five minutes if possible be. Two minutes of treatment are generally sufficient; longer times are not desirable, especially if the ratio of silica to sodium oxide is low; this results in alkaline conditions which can cause undesirable corrosion «

The effect of this first stage is only presumably known, but it appears possible that aluminum silicate is formed, which causes a reduction in the pore size. It is not desirable to carry out this stage above 50 ° C (120 i ¹ ) (still based on successive treatments in different silicate baths) because hydration may then be present which prevents the desired effect of the first stage. Everything that goes on in the first stage must be complete or effective before any substantial degree of hydration can be achieved.

As an alternative to the description just given, a first

Treatment in the same silicone bath as in the second stage and is used at elevated temperature. This pail makes use of the advantage that sealing with silicate both a function of time and auoh

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the temperature is »The seal is prevented by itself

c when the coated aluminum articles are placed in a hot silijifat

solution are immersed, they are quickly removed from it and be held in the air for a short time before being re-immersed in the silifeat solution for final treatment will. The explanation is probably to be sought in that, because the articles cool very quickly on removal from the bath, the same effect occurs as if the treatment had taken place at a considerably lower temperature, ZoB.

in a sodium silicate bath, which has a ratio of silicon dioxide to sodium oxide of 2: 1, with a silicon acetate concentration of 5 g per liter and is kept at 10O ⁰ G (21O ⁰ I), a 1 Hin. or shorter soaks of the coated aluminum articles followed by air transfer for 1/2 to 1 minute or more before a second soak in the same bath has essentially the same results as previously discussed. This is obviously due to the fact that the first potting essentially only wets the article and the first step after removal is carried out at an average temperature so lowered that the sealing, which must be avoided, does not occur »

In the technical process, the 30% of the first immersion usually has a lower, upper limit of about 1/2 minute because the items that are carried on racks must be handled by elevators. The fastest immersion and removal procedures performed in this manner

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take up «times that are on the order of 1/2 minute. In other words, although a shorter immersion time would theoretically suffice, the method cannot be carried out much faster.

The advantage of using the same bath for the first and second treatments is obviously economical and makes the process easier. Preferably, in order to avoid substantial sealing in the first treatment, the only bath in such a pail is used at a relatively low temperature range in order to achieve <ute results in the second treatment, e.g. as low as 65 C (150 ⁰ P), there is more drift in the permissible immersion time during the first treatment. If the bathroom, for example, has a temperature at 65 ° C (150 ⁰ P), the first dipping may take about 5 min, compared to little more than a minute, if the bath has a temperature of 100 ⁰ C (210 ° P) Has. As can be seen in more detail below, the second treatment must be extended accordingly if the bath temperature is kept so low.

It may seem, on chance, that a double immersion in the same 3ad is a continuous immersion in the bathroom is equivalent. But this is definitely not the case. Regardless of the implementation as a result of the first immersion, it will take some, albeit a short time. The implementation must be purely suitable results

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Completed by pulling the articles out into the air, with cooling occurring before any substantial sealing effect of the silicate occurs. Try, Achieving the desired results with a single immersion was completely inconclusive.

In an alternative-η _f first treatment ε stage, the hydration of the porous oxide is effected diirch treatment with hot water, which, in the simplest part, can be done by using γόη water alone. The action which takes place in this first stage is due to wetting of the hat, but it is probable that the essential action is due to the diminution of the pore size by swelling of the oxide. The seal so produced is far from complete, so that the coating remains substantially porous, although it must be said that the porosity is substantially reduced. Generally speaking, however, it is desirable not to use pure water at this stage, but a solution which somehow enhances the effect of water. When using aqueous solutions at elevated temperatures, the water in the solution not only causes swelling and a reduction in the pore size. The solute is absorbed by the coating, which, as a result of the added absorbed substance, causes an even greater reduction in the actual size of the pores

ft

will. The aqueous solution in a second form can be a substance contained, which is reflected in the heat when applying

BATH ORIGiNAL 8 0 9809/10 59

precipitates in the pores and so to a greater reduction in their pore size due to the clogging effect of an insoluble Stoffs "contributes. Typical of this type of treatment is the use of easily hydrolyzable salts such as nickel and cobalt acetates. With a third type one like that

The aqueous solution used, finds (according to some theories) both a reaction with the aluminum oxide coating or the base aluminum as well as adsorption. Typical solutions of this type are alkali dichromates.

According to the invention, the first treatment, which is carried out in one of the ways just indicated, is followed by a second treatment by means of a fi alkali silicate in a hot, aqueous solution. Either sodium or potassium silicate can be used; but from a practical standpoint, sodium silicate is less expensive and widely used. In this second stage of treatment, the application of the first stage foM, the input

effect of an alkali silicate solution on the coating, the one

c
SiliiCat concentration of one. Grams per liter to saturation

Has; the concentration depends on the particular 'silicate used'. The silicate concentration can vary from about 0.19 to 50%. Generally speaking, the concentration of silicate in the solution is conveniently about 10 grams per liter, although this concentration is by no means critical. As regards the silicates used, they can have a ratio of silicon dioxide to alkali metal of from about 1: 1 to about 4: 1. The temperature in the treatment aoll possible over 66 ⁰ C (150 ⁰ P) lie; she

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- ίο -

can range up to the boiling point · The temperatures for this second stage can preferably range from 88 ^° C. (190 ^° F.). move to the boiling point of the solution. The treatment time for the fabrics can be between 5 and 3 minutes. If the silicon oxide to sodium oxide ratio is low, the treatment temperatures should be in the lower part of the temperature range in order to cause as few burns as possible. A treatment over 30 minutes is harmless, but it is of little use either. For practical reasons, a treatment lasting 5 to 20 minutes is very beneficial. While the last discussion relates generally to coating processes in which the first and second treatments are carried out in different baths, it will be apparent from the previous discussion that the bath for the second treatment is the same as for the first treatment, using the precautions indicated to avoid substantial sealing on the first treatment and to effect its completion while the second treatment is carried out to complete sealing. ■

In the series of specific examples given below, it can be assumed that the aluminum objects are anodized in a conventional manner in a 15% (weight percent) aqueous sulphurous acid solution with a current density of 12 amperes per 0.305 a (per square foot) alternating current for 5 and 60 minutes at 24 ⁰ O (75 ° ϊ) ül »» r »oj» n were » Mq Ö * i *» riia4 · w # rd · »4 * nn

BATH ORIGINAL 809809/1059

wash and treated according to the invention ". Although specially on a specific, anodic oxidation process has been referred to, this is for illustrative purposes and has none fundamental importance. Any method of forming an oxide layer may be used, which, as before described results in a porous aluminum oxide film. The choice of one or the other coating method becomes general determined only by the desired, particular, specific results, such as the thickness or the density of the coating.

The following examples illustrate the invention without restricting it;

example 1

Anodically porous coated aluminum articles are for 2 minutes in an aqueous solution containing 5 grams of sodium per liter, and the silicon dioxide (SiOP) to Natriumoxyd- (Na ₂ O) ratio 2: betrögt 1, eingetaueht at 49 ° C (120 ⁰ P) . The articles are then sealed (no rinsing needed), by placing them ° C (200 ⁰ P) is immersed for 5 minutes at 93 in an aqueous solution containing 10 grams of sodium per liter; the silica to sodium oxide ratio is 2: 1.

Example 2

Anodically porous coated aluminum objects are 2 Mi-

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ute in an aqueous solution containing 10 grams of sodium silicate per liter and its silicon dioxide to sodium oxide ratio 3 »2: 1, immersed. The items are then sealed by placing them in an aqueous solution for 5 minutes Solution of 93 ° C (2OO ° F) which is immersed 10 grams of sodium silicate per liter and its silicon dioxide to sodium oxide ratio 3.2: 1. For this seal, the silica to sodium oxide ratio can be any ratio be between 3.2: 1 and 1: 1 or more or less

Example 3

Anodically porous coated aluminum objects are immersed for 5 minutes in an aqueous solution at room temperature which contains 10 grams of sodium silicate per liter and whose silicon dioxide to sodium oxide ratio is 2: 1. The objects are then sealed (no rinsing required) by immersing them for 5 minutes in an aqueous solution at 88 ⁰ O (190 ⁰ F) which contains 10 grams of sodium silicate per liter and whose silicon dioxide to sodium oxide ratio is 2: 1 .

The previous examples relate to the use of separate baths for the initial and final treatments. Only ^ shall be given examples in which a consecutive Immersing the article in the same bath is done.

Example 4

Anodically porous coated aluminum objects are 1 minute

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nute immersed in an aqueous solution at 99 ⁰ O (210 ⁰ F), which contains 5 grams of sodium silicate per liter and whose SiIi-

oxide
cium dioxide to sodium / ratio is 2: 1. The items are then removed and held in the air in the bath for 1 minute; then they are again immersed in the same bath for 5 minutes.

example

Be followed the same procedure as in Example 4 with the exception that both the times of the first immersion and the time of holding the workpiece in the air practically the minimum of 1/2 minute have been shortened. The results were identical to those of Example 4.

The last procedure was carried out in a laboratory test, but the time an object was held in the air between treatments was reduced to 10 seconds. The results were still identical to those of Example 4.

The last two examples were made using aluminum items carried out, which had a porous coating, which accordingly, (1) by a conventional treatment with an aqueous solution of 170.1 g (6 ounces) per 3 »79 liters (per gallon) of sodium carbonate and 56.7 g (2 ounces») per 3 »79 liters (per gallon) of sodium chromate and (2) by conventional · Treatment with an aqueous solution containing 3.7 i / l

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Chromic acid (CrO,), 0.75 g sodium bifluoride (NaHF _2), 0.7 g of sodium fluoborate (NaBi. ¹⁾ and 1.0 g Trinataumphosphat was prepared at 26.7 ⁰ C (80 ⁰ F) for 5 minutes. The results obtained were the same as in Example 4 above.

One type of overall treatment that proves to be particularly satisfactory proved, is the one in which nickel acetate is used in aqueous solution in the first stage. Such Treatment not only gives excellent results when the coating of the coating is not, but is also advantageous «used in a coloring. The reason for that is that when a porous alumina coating is colored in the usual manner and then with a silicate solution is treated, the color goes off steadily. But if after the color of the coating is exposed to the action of a hot nickel acetate solution during the subsequent treatment the silicate solution does not remove the color. It follows that the advantageous results of the invention Method with colored coatings can be obtained.

Example 6

Anodically porous coated aluminum objects are immersed in a 0.5% nickel acetate solution. immersed for about 5 minutes at about 80 ⁰ C (180 ⁰ P). The "objects are then immersed in a sodium silicate solution with water, which is a

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-IP-

Concentration of 10 g / l and a silicon dioxide to sodium oxide ratio of 2.4: 1. The immersion is continued at a temperature of 88 ^° C (190 ^° F) for about 5 minutes. Finally, the articles are washed with water and dried. The result is a clear, dirt-free oxide coating that is resistant to both salt spray and alkali corrosion.

one
Here is £ 1 * remark on the absence of dirt

the oxide coating. The use of nickel acetate creates dirt to a remarkable extent, but this one will,

Nile
in accordance with the method of the present invention, effectively removed by treatment with silicate in all different ways of producing acceptable corrosion resistance.

Major changes may be made in the details of the preceding Treatment to be taken. The nickel acetate can

by generally equivalent amounts of other hydrolyzable Nickel salts or e.g. hydrolyzable cobalt salts are replaced. In the case of nickel acetate or equivalent hydrolyzable

Salt

Be *** can essentially have a pH range of 4.5 to 7.5

be used. The concentrations of the hydrolyzable salts are not critical} they can vary from around 0.156 to saturation move. The treatment can be carried out in a period of 2 to 20 minutes. The temperature can vary from above

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move halfway 49 ° C (120 P) to the boiling point, although a temperature of at least 66 ⁰ C (150 ⁰ P) is desirable »

The type of composition, the range of temperatures and the application time of the silicate solution can behave as already described, the temperature of the silicate solution can move from room temperature to boiling point and. the treatment time from 1/2 minute upwards.

The washing stage between the first and the direct treatment shall be explained here from the general point of view. Where the material was in solution during the first treatment with the SiIicat can react, a very thorough rinsing is desirable, as excess first solution (such as nickel acetate) with the Silicate would react to not just possibly be irregular Producing results on the workpiece, but also degradation of the silicate solution due to precipitation of an i-nickel silicate to effect. On the other hand, there are conditions for which it is immaterial whether the substance is from the first treatment may be introduced into the silicate solution if, for example, the first seal is effected by water alone or if a silicate solution is used in the first treatment, which does not change significantly in the composition differs from that used in the final treatment. The reason for the washing stage therefore lies essentially in the Prevention of unwanted reactions or contamination of the silicate solution.

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• - 17 -

Example 7

Anodically porous coated Ailuminiumgegenstände be dipped 1 minute a 5jiige, aqueous solution of Natriuraefiromat at 21 ⁰ G (70 ° P). After rinsing with water, the objects are ^{immersed for 5 to 10 minutes at 93 0} G (200 ⁰ P) in a solution which contains 10 grams per liter of sodium silicate and whose silicon dioxide to sodium oxide ratio is 2: 1.

Amendments of the last Seispiels can (70 ⁰ F) to the melting point in an aqueous sodium dichromate solution having a concentration of 0.1 $ to saturation, performed by 1 to 25 minutes of immersion at a temperature of 21 ⁰ G. The final seal can be carried out in sodium or potassium silicate solutions under any of the modified conditions discussed so far.

The Vatri's Church of this example can be replaced by another Alkali dichroate, alkali chromate or chromic acid are replaced

' Example 8 Example 7 is carried out with "11" a different execution form , by using "an latriuaaolybdate instead of the"

»Atritmdioiiroaate uses · The concentration of molybdates

j can move from 0.5t to saturation; A concentration tone Vfi is "honorable" sharing.

BA ORIGINAL 809809/1059

Example 9

Anodically porous coated aluminum articles are immersed for 2 minutes in an aqueous solution at 66 ⁰ C (150 °?) Containing 10 grams of disodium phosphate per liter · Mach rinsing with water, the articles are about 5 minutes in an aqueous solution at 93 ° 0 ( 200 ° f), which contains 10 grams of sodium silicate per liter and whose silicon dioxide to sodium oxide ratio is 2: 1.

Changes, as indicated in example 7, are also possible here.

Example 10

The process of Example 9 can be carried out by replacing the Dinatriuaphoephatlöeung with an aqueous solution, with 1 gram of tannic acid per liter, at a torrential temperature τοη 49 ⁰ O (12O ⁰ I).

Example 11

Get noticed method of Examples 9 can be carried out by dl · Dinatriumphoephatlösung araoun by a "wieerige Lö 'ung sit 1 KaliumperBiangana-t per liter ereetrt · Zweekfcääigerwelee a Tempere door at 88 ⁰ C (190 ⁰ J), and a lintauohseit of about Applied for 5 minutes.

It should be noted that bare β, hot lake waeeer for the initial treatment, if necessary, leave or eat

BATH ORIGINAL

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Near boiling point ^ can be used; to achieve the b'este'n'ilrgebnisse the temperature of the water to ⁰ Xi5O-F) should be.

The sealed coatings produced according to the preceding examples withstand a salt spray test for at least 16 hours which ^{1 is carried out with} an aqueous solution containing 5 $ sodium chloride and one gram of copper chloride per 3.79 liters (gallon). The pH of this solution was adjusted with acetic acid to 3.2 and the temperature maintained at 49 ° G (120 ⁰ F). In addition, the coatings so / generated, sealed withstand 8 to 10 minutes, when it is immersed in an aqueous 3 $ sodium carbonate solution at 27 ° 0 (80 ⁰ F). Sole tests show the high resistance to salt spray corrosion and also to alkali corrosion.

Both in terms of resistance to salt spray corrosion as well as alkali corrosion, it must be noted that in certain industries there is a considerable need for such combined resistance features have arisen. In the automotive industry, for example, detergents have for Washing the vehicles sometimes have a considerable alkalinity, which consequently tend to be anodically «coated» Attack aluminum parts. In the construction sector, the aggressive effects of types of cement and mortar are often based on a high alkalinity, being anodically coated aluminum

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is attacked.

As already indicated, a sodium silicate solution can be used for the first treatment, which, as far ^{as the} concentration and the ratio of silicon dioxide to sodium oxide is concerned, with the sodium silicate solution of the second sealing

/ Bath treatment is identical, with either the same / or different baths being used at different temperatures. If sodium silicate is used for both the initial treatment and the second sealing treatment, and the solution of the latter treatment is more concentrated than that of the first, a water rinse should be made between the first and the sealing treatments. Furthermore, if the sodium silicates of the two treatments do not have the same silica to sodium oxide ratio, a water rinse should be made between the first and sealing treatments. Bisse rinsing only prevents the composition of the second bath from being changed by dragging the first bath.

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Claims (11)

Claims 1, method of treating aluminum with a porous Oxide coating according to patent, patent application C 22 224-, characterized in that the surface with an aqueous bath under time and temperature conditions that only one Achieve partial sealing of the pores of the oxide coating, about 5 to 30 minutes and then with an aqueous one Alaklisilijfcatl solution at a temperature above about 66 C. (150 F) to complete their sealing will. 2. The method according to claim 1, characterized in that gh
one sweep- »wäüm-fre first * bath, 4a« a hot, aqueous alkali silicate solution & »% is used. 3 .. The method according to Anapruch 2, characterized in that the mentioned conditions of the mentioned first bath are chosen so that the resulting reaction is complete runs. The method according to claim 2 or 3, characterized in that after the first stage, the application of a helpfull, aqueous alkali metal licate solution, the aluminum treated in this way is cooled in order to prevent the calibration resulting reaction from being rolled out. BATH 809809/1059 -.22 - 5. Procedure according to. Claim 1 to 4, characterized in that that the mentioned successive applications of the aqueous solution are carried out with the same alkali metal silicate solution. 6. The method according to claim 1 to 5, characterized in that said first application of an aqueous alkali metal solution at a temperature not exceeding about 49 C (120 F) is carried out in a time of about 1/2 to 5 minutes. 7. The method according to claim 1 to 6, characterized in that that the aforementioned first application of an aqueous solution of an alkali metal silicate is carried out with a solution whose silicon dioxide is to alkali oxide ratio at least 1: t fc & contributes. 8. The method according to claim 1 beer 7 »characterized in that that the second application of an aqueous alkali oil solution with a solution is carried out »whose Siliciuisdloxyä zu Alkali oxide ratio is from 1 st to about 4 s 1. 9 «A method according to claim 1 characterized gekeimzeißlmet _t" that the said first bath is water at a aup feinperatiir of at least 66 ⁰ O (15Q ° F); : 7 10. The method according to claim 9, characterized gektsnzeielmet * that the second bath consists of a ψ » £> * ί? ΪΥΜβ 30 # ige» vwämxtgm. solution of an alkali silicate, in which the ratio BAD ORIGINAL "8098OS / 1059 Silica to alkali oxide range from about 1: 1 moves up to about 4: 1. 11. The method according to claim 1, characterized in that the first bath consists of an aqueous solution of a substance Group of alkali dichromates, alkali chromates and chromic acid consists. BATH ORIGINAL 809809/1059