DE2114333A1 - Coated metal and process for coating metal surfaces - Google Patents

Description

2114333 Patent attorney Dipl.-Phys. Gerhard üedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84

B 5060

THE BROKEN HILL PTY. CO. LTD., 500 Bourke Street, MELBOURNE / Australia

Coated metal and process for coating metal surfaces

The invention relates to articles made of zinc, zinc alloys or galvanically galvanized items that have an electrodeposited coating.

In general, the present invention relates to the protection of zinc surfaces of strips, wires, rods and shaped articles.

Dr.F / Ho

109842/1838

It is known that zinc coated steel surfaces in aggressive Media are subject to corrosion. This can lead to chemical processes affecting the surface of the metallic zinc transform to zinc hydroxide and zinc oxide, the protection is lost. The subsequent loss of zinc hydroxides enables progression the corrosion process, since metallic zinc is subjected to corrosion again.

The present invention relates to articles made of zinc or objects coated with zinc,

The term "zinc" used in the following description is understood to mean pure zinc and zinc compounds.

The articles according to the invention made of zinc or zinc alloys or the galvanized articles, the coating of which has been electrolytically applied, are covered by a film of chromium metal with a thickness of

2
at least 0.25 mg / m and a chromium oxide film in a thickness of

labeled at least 0.108 mg / m.

In the present invention, the chromium oxide coatings are in milligrams Chromium indicated per square meter of the coated surface.

The thickness of these films depends on the type of protection. The protection again depends on the stress to which the articles are subjected. While there is an optimal strength from the standpoint of corrosion resistance, a higher strength may be desirable if the subsequent conditions of use of the coated articles require this.

⁵⁰⁶⁰ 1 0 9 SA 2/1 8 3 8

It has been found that a surface coated according to the invention has excellent corrosion resistance. Furthermore, the coating produced according to the invention shows an excellent connection to organic coatings, e.g. B. in the form of polyvinyl chloride or acrylate polymers. The Chromoxydfilm serves to passivate the chrome finish and protects the chromium metal film to scratching and abrasion ₀ He also reinforced the corrosion resistance of the surface.

In a general form, the present invention relates to a two step process for the electrolytic coating of zinc surfaces or zinc alloys with a film of chromium and a film of Chromium oxide:

1st stage. Cathodic treatment of the surface in an aqueous solution from chromium trioxide (CrO ", chromic acid) and sulfate ions, the

The concentration of chromium trioxide is between 100 and 450 g / l The ratio of chromium trioxide / sulfate ions is 50: 1 to 200: 1 and the

2 current density is between 21, 6 and 860 amperes / dm,

2nd stage. Cathodic treatment of those coated with chrome metal Surface in an aqueous solution of chromium trioxide, the concentration being between 50 and 400 g / l and the current density 21, 6 to

ο
216 amps / dm.

The optimal parameters of the above stages are given in the following Description explained in more detail.

The first stage is preferably followed by an effective washing in hot water at temperatures of 5O ⁰ C to 8O ⁰ C.

In yet another form, the present invention relates to a single

⁵⁰⁶⁰ 1 0 9 8 /, 2/1 8 3 8

step process for electrolytic coating of a zinc surface or of zinc alloys with a chromium metal film and a film of chromium oxide, characterized by the cathodic treatment of Surface in an aqueous solution of chromium trioxide (Cr (X, chromic acid) and sulfate ions, the concentration of chromium trioxide between

between 25 and 150 g / l, the ratio of chromate oxide / sulfate ions

ο 50: 1 to 200: 1, the current density between 21.5 and 860 amperes / dm

and the electrolyte temperature is ^{27 °} C. to 66 ^{° C.}

It can be the usual lead-tin, lead-tin-antimony, lead and lead alloys can be used as anodes. On the other hand, it has been found that for coating continuously moving wire or moving Ribbons can be used as mild steel anodes. The advantages are low costs and no maintenance. When using mild steel anodes the electrolytes do not have to be readjusted in the two-stage process. However, in the one-step procedure, a substance that has the Chromium (VI) ions reduced, used to avoid the presence of To ensure chromium (III) ions and thus the formation of the coating from chromium oxide. Alcohol, glycerine, sugar and especially hydrogen peroxide can be used as suitable substances. The concentration of chromium (III) ions can be up to 20%, the effectiveness of the coating not being significantly affected.

The conditions for applying chromium metal / chromium oxide films. (Chromox) on steel surfaces are known. They hardly change either when coating galvanized steel wire or steel strips. In contrast, it has been found that when using low-grade steel anodes, this is unusual high current densities can be achieved. Old upper limit was

which is normally considered to be 86 amps / dm. On the other hand, it has been found that it is possible and also favorable to achieve current densities of up to 320 amperes / dm * to use. The current densities can be even higher, which is what im

. 1 0 9 8 <2, 1 η 3 8

Regarding the speed of plating and the plating efficiency is beneficial.

The difference in corrosion resistance of steel wire or tape, that have been coated with Chromox and of electroplated samples that have been coated with Chromox is highly significant. In the event of In the former samples, the chromox film is the steel's only protection against oxidation. The areas where regularly on the Chromox surface If water condenses, they are of course only corrosion-resistant to a limited extent. On the other hand, if the Chromox film is applied to objects that are coated with zinc, a considerable synergistic effect can be observed. The life of the Chromox zinc coating is essential greater than the added lifetimes of the zinc coating and Chromox film. This is shown by the test results, which under aggravated Corrosion conditions were carried out.

The following is the preferred embodiment of the two-step process for attaching the Chromox film. Each stage is discussed individually. With "pad-wiped" and "fully galvanized" wire identical results were obtained.

Before treatment, the galvanized surfaces can be according to one of the be cleaned using the following procedures.

1. Degreasing with trichlorethylene: Etching in 10% (V / V) sulfuric acid. Electrolyte aids can be used. Cathode current density

ο
21.5 amps / dm. Wash in warm water.

2. Trichlorethylene degreasing: electrolytic etching, cathode

current density 21.6 amps / dm, in 10% W / V sodium hydroxide solution. Wash in warm water.

109842/1838

-6- 21H333

The deposition of the chrome powder depends on the concentration of the chromic acid and the sulfate content of the electrolyte, the electrolyte temperature and the current density at the cathode.

The chrome metal is deposited electrolytically from an electrolyte, which consists of chromic acid and a sulfate catalyst.

Using an electrolyte with a CrO2 concentration of 250 g / l and a CrO ^ SO. Ratio of 75: 1 as starting values, various temperatures and current densities were tested. Indeed, it is known that these two variables affect the nature and appearance of the deposit in addition to electrical efficiency. It has been found that the electrical efficiency is significantly influenced by the increase in temperature and current density. In the current density range from 64 to 320 amperes / dm, the electrical efficiency increases with increasing current density. With the current densities listed last, values of almost 50% can be achieved. The temperature range amounts to 32 to 43 C. For all examined current densities decreases the efficiency of the Chrommetallabsclieidung when the temperature is raised above the range of 32 C to 6O ⁰ C. The decrease is particularly characteristic at current densities of 129 to 320 Am-

2 2

pere / dm. At 640 amps / dm the influence of temperature was on

the electrical efficiency only low.

With current densities of more than 107 amperes / dm, shiny chrome coatings can occur be achieved. The temperature is 32 ° C to 46 ° C. The coatings deposited at 640 amperes / dm lost their light color Metallic luster of the samples that had been generated at higher current densities and appeared slightly gray.

By changing the composition of the electrolyte, ie the

109842/1838

Chromic acid concentration and the sulfate content, the characteristics the chromium metal deposition and in particular the electrical efficiency changes depending on the temperature and the current density will.

Accordingly, tests were carried out in which the chromic acid / sulfate ion ratio and the chromic acid concentration were changed. The electrical efficiencies were measured at various current densities and temperatures. First the CrO _Q concentration was kept constant at 250 g / l. The chromic acid sulfate ion ratio was varied by adding sulfuric acid. There are chromium metal coatings in the current density range 64-320 Ampere / dm surface and in the temperature range of 32 C to 6O ⁰ C prepared. For any combination of current density and temperature, the measured electrical efficiency was approximately 5% lower than that measured at the higher 75: 1 ratio. If the ratio was increased to 150: 1, the electrical efficiency decreased significantly. The coating deteriorated in appearance and turned a dark gray. At a constant temperature of 38 C around ¹ and a relatively low current density of 64 amperes / dm, optimal efficiencies were found at a ratio of 80: 1. If the current density was increased to 320

2
pere / dm increased, the most favorable ratio gradually increased until it finally reached a value of 100: 1. With these optimal conditions, shiny metal coatings were obtained.

After determining the optimal chromic acid / sulphate ratio for chrome plating galvanized D.va'ii to 100: 1, the Influence of the chromic acid concentration on the electrical efficiency at different temperatures and currents •.! Nier.sueht ,, It was found that with an increase in the current density, the Chruiiiyauiv concentration, the maximum efficiency with itself bHn ^ l, also increased.

1 0 9 8 /. ? / 1 ■ ": 8

BATH ORIGINAL

-8- 21H333

The maximum electrical efficiency is at 64 amperes / dm

100 g / l, while at 320 amps / dm the optimal chromic acid concentration in the electrolyte is 220 g / l.

The conditions necessary for optimal electrical efficiency can be summarized as follows:

Chromic acid concentration in the electrolyte 220 g / l

CrOo / SO. Ratio in the electrolyte 100: 1

Electrolyte temperature 32 - 46 ^{0 C}

Current density at the cathode 320 amps / dm

A particular advantage is that low chromic acid concentrations at high current densities are necessary. With increasing chromic acid concentration, smoking of the electrolyte occurs. This is especially the case then This is the case when working on the cathode at high current densities. At 200 g / l smoking the electrolyte is not a problem. In the literature it was stated that at 450 g CrO “/ l excessive smoking of the electrolyte occurs, which can be hazardous to health.

Another interesting point to consider is. the relatively wide temperature range, in which a high and fairly constant electrical efficiency can be measured. To determine the optimal parameters for the application of chrome on electro-galvanized i ^ raht similar experiments carried out. It has been found that there is a slight difference in efficiency between lightly electroplated and heavily electroplated samples. However, the difference is not believed to be particularly significant. On the other hand there were considerable ones Differences in efficiency when "hot-dipped" galvanized wire compared to electro-galvanized wire was plated with chrome. Electrogalvanized wire was used

BATH ⁵⁰⁶⁰ 1098 ^ 2 / ^ 38

-9- 21U333

a clear increase in efficiency of nearly 10% at current densities observed in the range of 64 to 320 amps / dm. /

The chromium oxide is deposited in a chromic acid electrolyte influenced without the addition of sulfate ions. The amount of electrolytically applied chromium oxide depends

1. the current density at the cathode,

2. the treatment time,

3. the electrolyte concentration (CrOJ and

4. on the electrolyte temperature.

Experiments with "hot dipped" wire showed that it had an electrolyte a chromic acid concentration of 50 g / l to 300 g / l is suitable for the deposition of chromium oxide films.

_{A chromic acid concentration of 100 g CrO Q} / l was found to be suitable for applying chromium oxide films to pre-clad steel wire. It was used for comparison purposes. In the temperature range from 32 ⁰ C to 54 ° C, the current density was varied to determine the influence of temperature and the current density on the rate of Chromoxydabscheidung.

The rate of chromium oxide deposition is not linear, but decreases with time. As the temperature increases, the rate of oxide deposition decreases. Maximum separation occurs at 32 ^° C. At 54 ^° C. the rate of deposition decreases sharply. If the temperature of the electrolyte falls below 32 ⁰ C, the appears to be

⁵⁰⁶⁰ 1 0 9 8 A 2/1 8 3 8

21H333 - io-

To change the chromium oxide coating. Was it above this temperature of light, characteristic color, it now becomes green-brown in appearance and not very handsome.

In the temperature range from 32 ⁰ C to 54 ⁰ C, the Qxydabscheidung at a constant treatment time as a function of the current density is not linear. It has been found that chromium oxide deposition is much slower on pre-clad chrome-plated steel samples than on pre-clad steel samples.

There is a whole range of current density and temperature combinations, within which a desired oxide level and accordingly a colored Chromox product is obtained. There are current densities up to

up to 280 amps / dm possible. The treatment time for these dents is but extremely short. Control problems arise in industrial applications.

To the influence of the chromic acid concentration of the electrolyte on the To investigate the rate of deposition of the chromium oxide, the temperature and current density were set constant at 38 C and 138 amps / dm. The chromic acid concentration of the electrolyte was between 50 g / l and 200 g / l varies. The growth of the hydrated chromium oxy df film is greatest at 150 g / l. It decreases when the electrolyte concentration increased to 200 g / l or decreased to 100 g / l.

The parameters for the deposition of chromium oxide are wide Area. There is a chromic acid concentration range of the electrolyte from 50 to 300 g / l available. The optimal deposition rate occurs at a concentration of 150 g / l and at a tempera door of 32 ° C. The current density can be adapted to the requirements adapted to the individual situations.

4 ή ö ö /, 0 / 1R3S

Similar results are obtained with electroplated wire.

In a preferred embodiment of the one-step process Chromium is usually deposited from an electrolyte that contains chromic acid and a sulfate as a catalyst. Temperature and current density In addition to the composition of the electrolyte, they also influence the deposition of the chromium metal. Also the amount of the remaining chromium oxide, that is deposited on top of the metallic chromium is affected. In some cases the amount of oxide deposited is negligible. On the other hand, by changing the plating parameters, considerable amounts can be deposited. Lower chromic acid concentrations in the electrolyte (120g CrO “/ l) and chromic acid sulfate ion ratios in the range of 50: 1 to 150: 1 usually allow the double coating in the course of the same electrolytic treatment.

Lower temperatures favor the increase in deposited chromium oxide in Chromox coating. This applies to high chromic acid concentrations in the electrolyte too. However, this effect is not significant at chromic acid concentrations below 100 g / l.

10 9 8 4 2/1 3 8

summary

Chrome metal coating

Two-step process

variable

Galvanized
wire

Galvanized tape

Electrolyte; CrO ₃ concentration

Electrolyte;

CrO ": SO. Ratio ^ό *

Electrolyte temperature

Cathode;
Current density

optimum

Suitable area

optimum

Suitable area

optimum

Suitable area

optimum

Suitable range 220 g / l

200 g / l

100-400 g / l 100-450 g / l

100: 1

50: 1-150: 1

38 - 43 ⁰ C

32-66 ^° C

324 amps / dm

54-325 amps / dm

100: 1

50: 1-175: 1

38-43 C.

32-66 C.

21.5 - 161 _r amp / dm '

Higher current densities favor higher electrical efficiencies. However, they are not cheap because of economic considerations

Current densities above 162 amp / dm are limited. It was therefore a number characterizing the optimum is not given.

5060

10 9 8 4 2/183 8

1H333

conditions

Electrical efficiency

Galvanized Galvanized Wire Tape

Current density 324 amp / dm ^z 38 ⁰ C

CrOg concentration 220 g / l CrO „: So ,, 100: 1

O ir

Current density 54 amp / dm 38 ⁰ C

CrOg concentration 220 g / l CrO ₃ : SO _4,. 100: 1

50%

23%

20%

Chromium oxide deposition optimum Two-stage process Galvanized
tape variable More suitable
area Galvanized wire 100 g CrO ₁ vl electrolyte optimum 150 g CrO ₃ / l 50-300g CrO ₃ / l More suitable
area 50-30Og CrO _Q / l 38 ⁰ C electrolyte
temperature More suitable
area 38 ⁰ C 27 ⁰ C - 54 ⁰ C 32 ⁰ C - 54 ⁰ C 21, 6 - 2J6
amp / dm Cathode
current density 21.6 - 324 amps / dm

5060

1 0 9 S U 2 I 1 8 3 8

21H333

Chromium ox Optiirum E instage process e η variable Galvanized tape Electrolyte; CrO ₃ - More suitable
area 50 g CrO "/ l
0 concentration More suitable
area 50-15Og CrO ,, / l electrolyte CrO ₃ : SO ₄ ratio More suitable
area 50 : 1 - 150 : 1 Electrolyte temperature More suitable
area 38 ⁰ C 32 ⁰ C - 54 ⁰ C Cathode current density 21, 6-216 Amp / dm ² Corrosion test

Test pieces of "pad-wiped" galvanized wire (76 g Zn / m), who had received a Chromox coating in the laboratory were tested in a steam atmosphere. The time it took to apply the coating was measured destroy and form rust on the steel base. In the undeformed state, the Chromox coating extended the service life, the was three times that of untreated galvanized wires. In the shaped state, the wire around its own diameter had been bent (torsion test), the difference in life expectancy was only characterized by a factor of two. This result is still highly significant.

The following typical chromium oxide coatings were used for these corrosion tests:

1 0 9 8 A 2/1 8 3 8

Chromium metal coating 107.6 - 215, chromium oxide heading 10.78- 64.53 mg chromium oxide / m Samples of galvanized steel sheets "hot-dipped" with zinc stone and supplied "hot dipped" were treated with Chromox to obtain coatings with weights in the following ranges:

Chromium metal 2.15-21.5 mg chromium / m; Chromium oxide 1.08-10.76 mg Chrome / m.

Significant increases in corrosion resistance were noted. The Chromox coating increased the life expectancy of the electroplated produced coating by at least a factor of 2.5.

Experiments were also carried out in an autoclave which contained tap water of approximately 100 ^° C. under atmospheric pressure. Steel coated with Chromox and galvanized pieces coated with Chromox were used as test pieces. The water level itself did not touch the test pieces. They were taken out at certain intervals and examined for red and white corrosion products. It was found that red rust first appeared on the Chromox coated steel samples after approximately 10 hours. The Chromox coated, galvanized samples did not show red rust for less than 100 hours.

Salt spray tests were also carried out in neutral salt solutions. These also indicated that the Chromox coated electroplated samples had an unexpectedly large increase in corrosion resistance over the steel samples coated only with Chromox . Tests have also been carried out on Chromox coated galvanized products that are already on the market. They showed that after abrasion and deformation by the manufacturing process , the coating still retains its corrosion resistance.

5060 1 0 9 8 /,? / 1 ^c 3 3

.ie. 21U333

protected. In all cases the chromox coated galva * nized material is superior to normal galvanized products.

As already mentioned, a Chromox surface has excellent adhesive properties against lacquers or paints, with zinc surfaces, as they exist in galvanized products, must be applied before application surface treatment of the paint can be carried out.

The usual painting technique involves chemical pretreatment. Included a chromium phosphate is usually applied. The adhesion of the epoxy primer to the metal surface is strengthened. In the end a final coat is applied. The adhesion of the last applied paint film to the primer is particularly strong. The weakest link is the bond between the primer and the metal surface. The chemical "in-line" pretreatments are necessary to ensure adequate adhesion between the metal and the epoxy paint. The epoxy paint will be in front of the Application of the final coat applied. These pretreatments are expensive and have the following disadvantages:

The commercial chemical pretreatments have a specific one Use for 2-3 weeks. After that, they become ineffective and must be removed. This means a difficult and expensive removal the solution by pulling and removing. In contrast to this, the above-mentioned electrolytes only need to be replaced very rarely. In regular At intervals, chromium and sulfate ion depletions are compensated for.

The times of the chemical treatments are in the range of 5-15 seconds. The times for the Chromox treatment can be varied according to the existing production facilities. It is convenient in the range of 1-15 seconds.

5060 1 0 9 8 A 2/1 8 3 8

Comparative tests were carried out and it was found that that Chromox provides a surface with adhesive properties that are well above the values found for the products, which have been pretreated according to known methods. Chromox coated, electroplated samples were made with a known chemical pretreatment which is based on phosphate chromate. A transformation takes place on the metal surface. This creates a Sufficiently reactive surface is made that adheres to paints elevated.

Various variations of the Chromox coatings were tested. from three of these were applied to slate galvanized steel strips.

Samples A and B were made in a two step process. Both samples had the same chrome metal coating weight of

ο
215.2 mg / m surface. The chromium oxide concentrations were, however

2 different. Example A had a chromium oxide level of 53 mg / m, while-

2
rend sample B contained 1 ^ 4 mg / m. Sample C was made using a one-step process. The chromium metal and chromium oxide films were applied with the same electrolytic treatment. the

2 Chromium metal concentration was 215.2 mg / m and the oxide formed one

2
Coating of 21.52 mg / m. The results of the comparative tests are

shown in Table 1.

There were two pretreatments after the moisture test significant differences found. They occurred in the samples that had only received an air finishing coat (Table 1).

For the salt spray tests, the marked fields were diagonal incised so that an X ~ orange character emerged. It was lovely

109842/1838

-is- 21U333

deep enough to cut the paint film and the zinc surface to expose. These tests also showed significant corrosion resistance of Chromox samples compared to the known treatments. In contrast to the known pretreatments is the Chromox treatment suitable for applying paints using the electrophoretic method.

5060. _{A Λ ft}

H982 / 1838

Table 1 Tests for paint adhesion with known pretreatments and with galvanized fields with

Chromox had been treated

Look after the exam

test

Chromox B Well-known pretreatment

Mechanical properties of

coated, double coated Impact resistance
To bend Samples with painting
as the last layer layered samples hardness After SOO hours O
CD·
coCft (D
(2) Moisture testing After 600 hours ro ' (3) (A) CD (i) OO (ü)

(iii) After 1000 hours
(iv) After 1850 hours

Satisfactory

Satisfactory Satisfactory Satisfactory lend

dd

Il It

It Il

Not attacked Not attacked

Il Il

Occasionally
blow

Occasionally blisters

Occasionally blisters

Not attacked. Not attacked

⁺ 10% bubbles ⁺ 30% bubbles

20% bubbles 80% bubbles

50%

90% bubbles

5060

Table 1 (cont.)

CO CjJ CO

Appearance after the exam

test

mox Well-known pretreatment

(B) Painted samples with double coating

(i) After 300 hours (ii) After 300 hours

Moisture Test (cont.)

(iii) After 1000 hours (iv) After 1850 hours salt spray test

(i) (ü) (Ui)

Not attacked Not attacked η Not attacked Not attacked

After 300 hours After 600 hours After 1000 hours

Il It II.

(iv) After 1850 hours

Minor minor

accumulation of white

ßem rust on white rust

the crack on the crack

Starting white rust on the crack

Moderate accumulation of v. white rust on the crack

White rust on d. Tear mark Reinforced white rust

Lots of red and white rust on the crack

Percentage of the surface that was covered with very small bubbles.

CO

ο in

The synergistic effect evident from the above is also to be noted when the process is applied to steel strips plated with zinc.

At present the steel strips are easily available in standard goods and Quality goods classified. Standard strips are made from cold rolled steel with a low carbon content. It is split by size and painted black. Quality goods are made from steel with a medium carbon content. The steel is austenitized. He's also with lead quenched. It will then be painted green. The black paint is a type of bitumen that is soluble in xylene. The green paint is a high quality one Alky dashed.

In both cases the painting process is a continuous dipping process. The paint is then dried in an oven 3.65 m long and 13.2 m high with air circulation.

The application of a Chromox coating on a thin pre-layer Zinc offers the possibility of an improved coating system. The advantages are:

1. High line speed up to 305 m / min., Reducing the production speed is increased.

2. Considerable cost savings with improved product. So costs the black bitumen paint for painting $ 3.37 per ton. The green alkyd paint costs $ 5.91 each to coat Ton. The speed of the latter is 107 m / min. In the

in contrast to the zinc coatings (1.5 - 6.1 g / m surface area) and

2
Chromox (21.5-215.2mg / m2 surface) will add to the cost

Estimated $ 2 per ton at 305 m / min.

109842/1838

21U333

Combinations of electroplated zinc, chromium and chromox were made on standard strips of steel measuring 15.2 1, 9 χ 0.056 cm. The tested combinations are shown in Table 11. Tables III and IV show the corrosion resistance of the various coatings. The chrome metal bath had a concentration of 220 g CrO _Q / l plus _{2.2 g H 0} SO./1.· The oxide bath had a concentration of 100 g CrO / l. The cathode current density was 108 Am-

2 ··

pere / dm of the surface. The coating combinations were under the Selected from the point of view of a possible technical application. The test pieces were immersed in a 5% w / v solution of sodium chloride. The differences in corrosion resistance could be seen from the extent of the iron oxide formed. After a suitable dilution the total iron content was determined. The electroplated zinc and Chromox coated product were those with organic Far superior to coated strip products. The synergistic effect of the ultra-fine Chromox coating on a thin zinc pre-plating compared to the direct Chromox coating of the strips is clearly evident from the results.

Cost estimates were made for zinc pre-plating plus Chromox coating and the rest of the black and green coating employed. It was found that the usual black coating $ 3.37 per ton, the green $ 5.91 per ton, and the zinc pre-plating and chromox plating just $ 1.73 each Ton costs. .

5060

109842/1838

Table 11 The combinations were made in the laboratory.

zinc Cr metal Cr oxide colour g / m / 2
mg / m mg / m 1. 8.2 107.6-215.2 53.8 ■ blue 2. 8.2 53.8-107.6 53.8 ■ I! 3. 5.5 107.6-215.2 53.8 ■ I! 4th 5.5 53, 8 - 107, 6 53.8 ■ Il 5. 2.7 107.6-215.2 53.8 ■ I! 6th 8.2 53.8-107.6 53.8 ■ Il 7th 8.2 107.6-215.2 metallic white 8th. 8.2 53.8-107.6 . II 9. 5.5 107.6-215.2 Il 10. 5.5 53.8-107.6 It 11. 2.7 107.6-215.2 It 12th 2.7 53.8-107.6 Il 13th 8.2 - I! 14th 5.5 - Il 15th 2.7 - If 16. - 107.6 - 215.2 53.8 ■ blue 17th - 53.8-107.6 53.8 - Il 18th - 107.6-215.2 metallic white 19th - 53.8-107.6 It 20th Steel belt, 2
ι 21. Steel belt, - 107.6 22nd Steel belt, - 107.6 - 107, 6 - 107.6 - 10 7.6 - 107.6 - - - - - - - - - • 107, 6 • 107.6 - - uncoated starting material black coating green coating

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109842/1838

111

Immersion test with a 5% w / v sodium chloride solution 2 hours 4 hours 20 hours 45 hours ■ No corro
sion
11 No corro
sion
Il No corro
sion
dd No cor
rosion
dd Total-
iron cor
rosion
after 45
Hours. 1.
2. Il It It dd less than
0, 1
dd 3. Il ti ti Il dd 4th It 11th dd ti dd 5. dd It dd ti dd 6th Il ti Traces w r Traces w r dd 7th 11th Il ti It dd 8th. 11th Il Il Il Il P. Il 11th it dd ti 10. It It dd Tracks r r dd 11. 11th Il dd r r 0.2 12th 11th Il It r r 3.4 13th Il It Tracks r r r r 2.1 14th Il 11th r r r r 5.6 15th Il I! r r r r 7.5 16. Il It r r r r 4.6 17th r r r r r r r r 3.4 18th rr
rr rr
_rr (a) rr
rr rr
rr 6.2 19th
20th r r . r r ^ r r r r 6.9
9.4 21. No corro
sion Slightly r r . r r r r 12.3 22nd 5.9

(a) (b) worse than 18 and 19 rr = red rust
wr = white host

9 8A ⁰ MB 3 8

-25-Table IV

21U333

Field trials 2 days

3 days

4 days

8 days

16 days

1. No corrosion. No corrosion rosion

No cor- No cor- No cor- No corrosion rosion arced rosion

2. It Il It rr ti ti It Il from the test
fung removed - 3. I! ti It It Il Il Il It Il - 4th ti Il It No ti It Il dd Il - 5. Il Il very bad very
rr bad It Il It rr at the
Bend Il - 6th It It It Il Il rr spots Il - 7th Il It ti Il dd It No cor ti - No rosion Il - 8th. ti It M. Il H It from the test
fung removed - 9. Il ti Il Il H It - 10. Il It Il Il It It M. All over 11. Ii 11th It dd ti bad rr Small Fiele bend rr 12th Il ti Il ti It 11th 13th Il Il It wr & rr 14th It wr
Spots rr wr & rr It lo! Il wr & rr It dd 16. Rust stain rust stain Increase on
rust rr 17th II ti dd 18th It Il dd 19th Il It ti 20th very
bad very
bad rr rr 21. Il Il 22nd very small

Corrosion corrosion stains

rr

Si Krat- around 90 ^BC

zer
rr

Stains and scratches

5060

109842/1838.

To confirm the laboratory results and to work out the parameters, which are necessary for the production of a highly corrosion-resistant material, became pilot plants for galvanized wire and steel strips constructed.

In the pilot system used for wire coating, it was possible to to run the wire on two levels. A basic level and an upper level (10 cm above the basic level) were available. The treatment tanks were made of mild steel and lined with PVC. The lining served as protection against chemical attack and against current transfer. Initially, the wire was held in the treatment tank by small nylon dipping rollers. However, these turned out to be unsuitable because of their high abrasion. The preferred embodiment were mild steel rollers coated with plastic.

The system had a capacity of 0 to 610 m / min. At the specified The maximum speed was 73 m / min. The speed was regulated with an Eennan and Froude drive.

The mechanical system of the plant was designed for versatility Designed to move the tanks into almost any configuration. The original "payoff and take-up" systems can be direct be placed one on top of the other to allow the operation of belts on the system to enable.

The electrical system of the pilot plant consisted of two independent ones Rectifiers that allowed multiple configurations of electrical power supply to be used. The big rectifier could either Supply direct current, alternating current or alternating current and direct current. To achieve this, the one coming from the rectifier was made Electricity passed over 3 power rails. It was alternating current

10 9 8 4 2/1838 BATH ORIGINAL

.27-21H333

live, direct current positive and direct current negative / alternating current neutral. The current from this rectifier was 2500 amps in all of the configurations mentioned. The smaller one Rectifier had 2 independent supplies, the 2 AC supplies, 2 DC supplies or AC and DC could provide together. The output from this rectifier was carried over 4 rails, 2 of which were for alternating current live / direct current positive and 2 for alternating current neutral / direct current negative. The maximum levy from this Rectifier was 200 amps.

There were six 272 liter tanks for the storage solutions for the different treatment tanks were used * The tanks were off PVC made. They were heated with 2KW quartz radiators, the proved to be very useful. The radiators were via Sunvic control units regulated. The temperature measurement was carried out with thermocouples. The thermocouples were with a simple one Measuring device connected to a six-way switch.

The solutions were pumped into the treatment tanks with impeller pumps. Like most of the other system parts, the pump was made of PVC for reasons of corrosion resistance.

The smoke extraction system consisted of two flues, one with a central one Pipe were connected. There were valves at the head of each pipe. This enabled the amount of extraction to be regulated in every part of the system. It was quickly found that using a "pad wiped" galvanized wire with a diameter of 15.7 mm produced shiny oxide colors under pilot plant conditions could become. The current density for plating with chrome metal was 248 amperes / dm, while it was for plating with the oxide

109842 / 1G38

21U333

ο
166 amps / dm. It was found that by varying the speed between 15 and 46 m / min, the full range of oxide colors from rose gold to blue could be produced.

Because of this qualitative work, Chromox coatings were made produced under the following conditions, a "pad wiped" galvanized wire of 15,, 4 mm diameter was used:

Baths

Alkali cleaning chrome metal plating

Chromium oxide plating

After each treatment bath, washing was carried out with hot water. Line speed: 15m / min., 30m / min., 61m / min.

Current densities when plating with chrome metal: 75.6 amps / dm,

2 2 2

166 amps / dm, 248 amps / dm, 324 amps / dm.

Current densities when plating with chromium oxide: 32 amperes / dm,

2 2 2 2

83 amps / dm, 115 amps / dm, 166 amperes / dm, 248 amps / dm,

324 amps / dm.

Combinations of the above variables have been set. The results are shown in Tables la to Ic. The corrosion resistance is determined by tests similar to those performed in the im Laboratory-made samples, as shown in Tables 1 la to lic, were used.

⁵⁰⁶⁰

composition temperature 78 g / l NaOH 70 ⁰ C 226 g / l CrO 38 ⁰ C 2.5 g / l H ₂ SO ₄ 97.7 g / l CrO " 38 ⁰ C O, oil g / l H ₂ SO ₄

Table la line speed 15m / min.

Chromium oxide current density (Ampo / dm} Chromium metal current density (Amp «/ dm)

300

770

1070 75.6

106, 32

248, 40

324.0

No color

Cr metal mg / m Cr-Oxia mg / m

% electr. Cr metal efficiency

No.

colour

Cr metal mg / m ο Cr oxide mg / m

% electr. Cr metal efficiency

IA IG IN THE IS blue-bronze bronze blue square blue-gold 0 290.52 710.13 1645.23 30.128 30.128 33, 204 33,356 - 11.1 13.5 24.0 IB IH IN IT blue green blue green gold green-gold 59.18 333.53 828, 52 1530.20 45.192 49.498 51.648 107, 60 3.2 9.3 15.7 22.7

No color

11th

gold-purple

IO IU

gold-purple purple

Table la (cont.)

O
PO Chrome,.!.!
Current density
(Amp. / Dm / No. Cfciommotiül sir omc'iclitj (amp./ein· 248, / Q £ 24.0 IX ^! ¹ 1540 colour 7 pounds, 6 163, S2 IP IV green grey H333 Cr metal mg / m ² ID IS purple pure green 1839, 9C Cr oxide mg / m ² purple purple 793.24 1543.28 75.32
O % electr. Efficiency
Cr metal 9L, 992 376, 60 57.028 63,481 26.8 §
ίο No. 65.633 55,952 15.1 24.0 2300 colour . 5.4 10.5 IQ IW ς * I. Cr metal mg / m ² IE IK gold-green I. Cr oxide mg / m gold-green gold-green 850.04 1700.08 O Q
Z ■ % electr. Efficiency
Cr metal 98.992 398.1.20 79.62 75, 32 co
ro No. 75.32 75.32 16.1 24.8 -t- 3000 colour 5.4 11.1 IR co Cr metal mg / m IL gold-green co
CD 2
Cr oxide mg / m gold-green gold-green 828, 524 % electr. Efficiency
Cr metal 182, 92 451.92 82.852 92, 636 91.46 15.7 9.9 12, 6

Line speed 30 m / min. No. Table Ib Current density 21 (Amp. / Dm) 20th 324.0 2S 2T Chromium oxide
Current density
(Amp./dm) colour 163, 32 green Blue- 248, 40 green-gold purple-dappled dark blue C * 300 Cr metal mg / m Chrome metal 2G 215.20 2M 451.92 893.08 946, 88 Cr oxide mg / m 75.6 blue 49.5 blue 51.65 22.6 41.93 % elcttr. Efficiency
Cr metal 2A 193.68 12.2 373.60 17.1 25.3 28.5 No. bronze-blue 27.978 25.82 2U colour 0 11.0 14.3 gold-purple 770 Cr metal mg / m '3 Y, 20 2H 2N 943.88 Cr oxide mg / m - deep blue blue 49.5 1 ^ 3 % electr. Efficiency
Cr metal 2 B 215.20 451.92 26.5 _ ^
co -P *
LQ ^ ₄ ι No. blue 41.9 34 44.12 O colour 0 12, 2 17.1 co 1070 Cr metal mg / m 451.9 ro
» Cr oxide mg / m - % electr. Efficiency
Cr metal 2C OO green Blue 0 53.80

: .ί3 I'd (cont.) ^v

σ (Amp./dr./) No. Chron-metai / L 2E 163, S2 ip./Cd.i,? S24, 0 ro co 1540 colour 7 £, β green-purple 2Y o / n / n 2V ο - *
CD t>.
O
in Ca3 •O Cr metal mg / m 2D 43, 04 bronze-gold 2P gold-purple. CjJ co
co Cr oxide mg / m gold 80.70 238.72 gold-purple - CS % electr. Efficiency
Cr metal 21, 52 4.4 65.64 494, 93 65.64 No. 65, (633 2F
bronze-gold 13.4 66, 71 - ORiGiN 2300 colour 2.2 64.56 2Κ 18.8 2W I.
it I
co > Cr metal mg / m 80.70 gold-purple 2Q purple-green I. ο
Cr oxide mg / m 6.6 301.28 purple 1043, 72 % electrical efficiency
Cr metal 75.32 559.52 79.62 No.
colour 17.1 79, 62 29.6 3000 Cr metal mg / m 2L
green 21.2 2X
green-purple Cr oxide mg / m 301.28 2R
green 1035.24 % electr. Efficiency
Cr metal 80.70 538.00 87.15 17.1 89.31 30.2 20.4

O
co Line speed 61 m / min _e No. Table lc 166, 32 3H 31 (Ampo / dm) 324.0 ο - »
CD i OO Chromium oxide
Stromdich ^
(Amp _e / dm ' colour 3G bronze-gold blue-bronze 248.4 3S O
IO J ^
CO
CO 2/18 300 ρ
Cr metal mg / m gold 43, 04 43.04 3M faint blue OJ OO
OO ρ
Cr oxide mg / m 21.52 33.36 37.66 faint blue 516.48 % electr. Efficiency
Cr metal Chrome metal current density 38, 74 5.0 5.0 139.88 19.37
ι No. 75.6 2.5 25.82 30.0 colour 3A 10.8 3T 770 Cr metal mg / m no 3N Light Blue co
co Cr oxide mg / m 0 blue-bronze 473.44 % electr. Efficiency
Cr-MetaH 35.51 161.40 30.13 No. - 33.35 27.5 colour 3B 12.5 3U 1070 ρ
Cr metal mg / m faint blue 30th blue ο
Cr oxide mg / m 0 blue 494.96 % electr. Efficiency
Cr metal 39, 81 193.88 37.66 - 37, 66 28.8 3C 15.0 Light Blue 0 52, 72 -

J> IS)

Linisi-3Gcel>-7indlg!; 3it 31 m / lJIm.

Tabella lc (cont.)

Chromm «i-ill ßirü.üUleh

> i

75.6

160.3 ?,

240, 4

324.0

No.

colour

Cr metal mg / m

2 Cr oxide mg / m

% electr. Cr metal efficiency

3D

Light Blue
0
52.7

3Y

blue 21.52 49.5 2.5

3P
blue
161.40
39.81
12.5

3V blue 548.7a 51.65 31.0

No.

colour

Cr metal mg / m Cr oxide mg / m

% electr. Cr metal efficiency

3E
gold
0
67.79

3K

green-gold 75.32 59.18 8.7

3Q

green-gold
215.20
54, 80
16.6

3W gold 591, 80 65.64 34.4

No.

colour

Cr metal mg / m ο Cr oxide mg / m

% electr. Cr metal efficiency

3P

gold-purple
0
79.62

31,

gold-purple 13S _} 8 8 65ν 64 ^{ 16, 2

3R. 3X

gold'-purple gold-purple

279.76 x 613.32

65.64> 75.32

21.6 35.5

CD O

A soldering machine for steel strips was also constructed. They had the dimensions 19 χ 5.6 mm. Standard belts were continuously coated with a combination of zinc, chromium metal and chromox as shown in table purple. The results of the corrosion test are also shown in table lilac . The synergistic effect of the combination of zinc and Chromox coatings is shown again.

Chromox coated and electro-galvanized wire was also continuously manufactured in a pilot plant. Depending on the different coating weights, a corresponding high temperature steam resistance can be determined.

1 0 9 8 A? / 1 Γ? 8th

Table purple

Application in the pilot system - chromox-coated, electro-galvanized Steel belts.

Zn
/ 2
g / m Cr metal
/ 2
mg / m Cr oxide
\ ais Lr ^
mg / m • - Corrosion resistance
25 hours ASTM - Salt-
spray 3.05 60.26 62.41 no wr, no rr 1.84 33.36 76.4 Stain wr, no rr 0.91 76.4 91.46 no wr, stain rr 0.91 '45,192 38.74 no wr, no rr 0.91 73.17 81.78 no wr, no rr 0.61 88.23 86,080 no wr, no rr 1.84 182,920 - medium wr, stain rr 0.89 - - ■ heavy wr, stain rr 2.72 - difficult rr 0.45 - 100% rr Std, black 105% rr H green 75% rr

Chrome metal bath

Chromium dioxide bath

225g CrCL / 1

100g CrO./l

Table 11a

ABCDEFGHIJKLMNOPQRSTUVWX comparison, 15 m / min. series

Autoclave test hrs.

231212212211211112222121 33232232 2 211222212332231 333422432212432233433332

4 4

Salt sprayed sth.

24
32
48
72

000000100000100000000000 llOOOOlOOOOQlOOOOOlOOOOO 1110 00100000100000100000 112000100000100000100000 112111111111111111100001 Comparative samples abc d ei g hi

111111111 111111111 111111111 222222111 4 2 44 4 4444

0 - no corrosion product

1 = white corrosion products

2 = white corrosion products + red spot

3 = white corrosion products + lots of red rust spots

4 = white corrosion products + extensive red rust

O CO O

Table lib

ABCDEFGHIJKLMNOPQRSTUVWX 30m / min. Series 2

Autoclave test hrs.

45 222121221212322221222123

100 170

33212243232 2433321332333 33322 2 433323433323332343

Salt spray test hours

24 32 48 72

110000100000100000110001 110000110000100000110 00 1 110000110000100000110001 11000011000 0100000 110001 1111114110 11210000111011

0 = no corrosion product

1 = white corrosion products

2 = white corrosion products + red spot

3 = white corrosion products + lots of red rust spots

4 = white corrosion products + extensive red rust

CO CO CO

Table lic
ABCDEFGHIJKLMNOPQRSTUVWX comparison 61m / min. series

Hour
110 111111111111111111111111 2

Salt spray test Std

8 10 1100110 0 00110000000000 0

24 111100110 0001110 0 0000000 0

32 211100110010111000000000 0

φ 48 2111001100 101110 00000000 0 Ο «

7 72 414 4 0 114 111 111 110 111 111 100 0 **

Q- not a corrosion product
^ 1 = white corrosion products

^ 2 = white corrosion products + red spot

~; 3 = white corrosion products + lots of red rust spots

, 3 4 = white corrosion products + extensive red rust

Claims (1)

Claims or 1. Articles made of zinc / zinc alloys or galvanized articles, the coating of which has been applied electrolytically, characterized by a film of chromium metal with a thickness of at least 0.215 mg / m and a chromium oxide film with a thickness of at least mg / m 2. 2. Objects according to claim 1, characterized by film thicknesses of 0.215 mg or 0.107 mg / m2. 3. Objects according to claim 1, characterized by film thicknesses as they have been described in the examples in Tables la to Ic. AJ Two-stage process for the electrolytic coating of zinc surfaces or alloys with a film of chromium metal and a film of chromium oxide, characterized in that 1. the surface in an aqueous solution of chromium trioxide Chromic acid) and sulfate ions with a concentration of chromium trioxide between 100 and 450 g / l, a chromium trioxide / sulfate ratio of 50: 1 to 200: 1 and a substrate current density between 21.6 and 2,864 amps / dm is cathodically treated and 2. the surface coated with chrome metal in an aqueous solution of chromium trioxide with a concentration between 50 and 400 g / l is treated cathodically, the substrate current density 21, 6 to 216 Am] amounts to. 216 amps / dm ² and the electrolyte temperature of each stage 27 to 66 ^ΩC 5 «The method according to claim 4, characterized in that in the first Level the chromium tria ^ d concentration 100 to 450 g / l, the chronitrioxydic acid / t; 0fS 4 2710 21U333 / lat ratio 50: 1 to 175: 1, the electrolyte temperature 27 C to 66 C and ο the current density at the cathode 54 to 324 amperes / dm and for the second stage the chromium trioxide concentration 50 to 400 g / l, the electrolyte ^{temperature 27 0} C to 54 ⁰ C and the current density at the cathode 21, 6 to ο 216 amps / dm. 6. The method according to claim 5, characterized in that in the first stage the chromium trioxide concentration 200 to 220 g / l, the chromic acid / sulfate ratio 100: 1, the electrolyte ^{temperature 38 0} C to 43 ⁰ C and the ο Current density at the cathode approx. 324 amps / dm for wire items and about 162 amperes / dn for tapes and in stage 2 the chromium trioxide concentration 100 to 150 g / l, the electrolyte temperature ^{about 38 ° C} 2 and the current density at the cathode about 324 amps / dm for wire 2 items and approximately 162 amps / dm for tapes. 7. Process according to claims 4 to 7, characterized in that after de] he follows. after the first stage, a wash with hot water at 5O ⁰ C to 8O ⁰ C 8. The method according to claims 4 to 7, characterized in that Mild steel is used as the anode. 9. One-step process for the electrolytic coating of zinc surfaces or surfaces coated with zinc alloys with a film of chromium metal and a film of chromium oxide, characterized in that the treatment of the surface in an aqueous solution of chromium trioxide (CrO ₉ , chromic acid) and sulfate ions with a concentration «5 tion of chromium trioxide between 25 and 150 g / l, a chromium trioxide / sulfate ratio between 50: 1 and 200: 1 and a substrate current density between see 21, 6 and 864 amperes / dm of the surface and ^{takes place cathodically at an electrolyte temperature between 27 °} C. and 66 ° C. ⁵⁰⁶⁰ 10984 2/1 P. 38 10. The method according to claim 9, characterized in that the chromium trioxide concentration 50 to 150 g / l, the chromium trioxide / sulfate ratio 50: 1 to 150: 1, the electrolyte temperature 32 ° C to 54 ° C and the current density at the cathode 21, 6 to 216 amperes / dm. 11. The method according to claim 10, characterized in that the chromium trioxide concentration is approximately 50 g / l and the electrolyte temperature is ^{approximately 38 ° C.} 12. The method according to claims 9 to 11, characterized in that that mild steel is used as the anode and so much of a suitable amount of a reducing agent is added that the concentration of chromium (III) ions is approximately up to 20%. 13. Process for coating products made from steel strips, thereby 2 characterized that the steel strips first with at least 1.5 g / m be zinc-plated and then coated with chromium metal / chromium trioxide according to the method of claims 4 bis. 14. The method according to claims 4 to 13, characterized in that that the zinc surface is cleaned in all processes. 5060 * ^ "~ '109842/1838