US3207683A

US3207683A - Process of electrolytic surface treatment of metals

Info

Publication number: US3207683A
Application number: US170995A
Authority: US
Inventors: Hermann Georges
Original assignee: COUSSINETS STE INDLE
Current assignee: COUSSINETS STE INDLE; INDUSTRIELLE DES COUSSINETS Ste
Priority date: 1962-02-05
Filing date: 1962-02-05
Publication date: 1965-09-21
Anticipated expiration: 1982-09-21

Description

G. HERMANN Sept. 21, 1965 PROCESS OF ELECTROLYTIC SURFACE TREATMENT OF METALS Filed Feb. 5, 1962 p g gd Fig.2

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INVENTOR. Georges Hermann BY 144,44. Woe/L7 6M H/S ATTORNEYS United States Patent 3,207,683 PROCESS OF ELECTROLYTIC SURFACE TREATMENT 6F METALS Georges Hermann, Annecy, Haute-Savoie, France, as-

signor to Societe lndustrielle des Coussinets, Paris, France, a corporation of France Filed Feb. 5, 1962, Ser. No. 170,995 19 Claims. (Cl, 204-141) This invention relates to a process of electrolytic surface treatment of metals such as pickling of metals, particularly ferrous metals and alloys.

The object of the pickling in its wide sense is to clean, to dissolve or to detach the calamine, the rust or any other oxide, as well as surface coats and deposits such as paint or various metallic coatings so as to provide the metal with a surface suitable for applications which will be made of it. The pickling operation is aboslutely necessary when the metal or the metallic piece has to be coated with a coating, a paint or a film or a sheet of another metal. A satisfactory adherence can only be obtained if the metal to be covered is perfectly clean, which means free of grease, rust or oxide.

The known processes of carrying out these successive operations use different techniques for each operation. Thus degreasing is often effected by dipping the pieces into organic solvents such as trichloro-ethylene, or into hot aqueous alkaline solutions with a carbonate, silicate or sodium phosphate base, or even into a low hydrofluoric acid solution. Sometimes to alkaline solutions, tensioactive agents or moistening agents such as aromatic or aliphatic sulfonates with long chains are added. Also an electrolytic method is used, in which the metal to be degreased acts either as a cathode or preferably as an anode in order to avoid the fragility of the pieces treated owing to the adsorption of hydrogen within these alkaline solutions between 50 and 95 C.

The metal or the metallic piece thus degreased is carefully rinsed, then introduced into another bath, in order to eliminate oxides and surface deposits. Said bath generally has a. base of sulfuric or hydrochloric acid or a mixture of these acids and the process is carried out mainly between 65 and 90 C. with solutions at -30% concentration. In order to avoid an excessive attack, and thus an appreciable loss of the metal, to the acid bath are often added inhibitors formed by coloring matters or colloidal materials or various substances of high molecular weight. Also for this pickling operation the electrolytic method is used, in which the piece to be pickled forms either the anode or the cathode. It is often used in the case where the surface oxides to be eliminated are mainly formed by Fe O the dissolving speed of which is very slow in the acid solutions, even when hot.

After said operation, it is necessary to rinse abundant- 1y, then to neutralize the residual acidity and finally to rinse again. These washings often leave a very thin oxide film on the metal surface which is sometimes removed by a passage through a bath of zinc and ammonium chloride.

These processes require, therefore, an extensive plant for the successive operations with several baths. The pickled metals often show surface defects owing to pittings which are produced Within the acid baths, and which cause the known fragility owing to the adsorption of hydrogen.

The main object of the present invention is to provide a pickling process which overcomes these drawbacks. According to the present invention a process of electrolytic surface treatment of metals is provided in which degreasing and pickling and eventually polishing, are simultaneously carried out in a single alkaline bath at high conductivity, in which the electrodes are formed by 3,207,683 Patented Sept. 21, 1965 the metal to be treated, under alternating current at low voltage, said bath containing: an alkaline degreasing agent, an alkaline pickling agent, a tensio-active agent and a chelating agent, the actions and properties of which are complementary to one another.

The conductivity of the bath expressed in mho (ohm cmf depends upon its composition and its age. At a temperature of 20 C., it can be from 0.10 mho to 0.30 mho, but is preferably between 0.17 mho and 0.30 mho.

The degreasing agent may be caustic soda or preferably orthosilicate of sodium.

The pickling agent is chosen from the alkaline cyanides, sodium cyanide being preferred.

The tensio-active agent, the action of which consists in accelerating and standardizing the removal of the rust by modifying the interfacial tensions of the electroylte-rust system, must be appropriate to the alkaline medium. Alkaline salts of fatty secondary sulfonated alcohols or alcoyl-aryl-sulfonates may be used, but an alkaline salt of fatty secondary snlfonated alcohols such as, for example, the so-called Teepol is preferred.

The object of the chelating agent i to confine the alkaline-earth ions and the metal ions, such as copper, susceptible of hindering the good running of the degreasing and pickling operation. The chelating agent may be constituted by polyphosphates, specially sodium tripolyphosphate; sodium salts of ethylene diaminotetracetic acid, specially the tetrasodium salt; tertiary amino-alcohols, specially triethanolamine; polyacids-alcohols, specially tartric acid; or by the mixture of these compounds.

A composition of a preferred bath is as follows:

Sodium orthosilicate Sodium cyanide Tensio-active agent Teepol Sodium tripolyphosphate or tetrasodium salt of ethylene diaminotetracetic acid.

The concentrations of the said agents in this bath and their relative proportions may range Within predetermined limits.

Thus, the concentrations may be comprised:

For the degreasing agent between 20 g./l. and g./l. For the pickling agent between 25 g./l. and 250 g./l. For the tensio-active agent between 0.5 g./l. and 3 g./l. For the chelating agent between 5 g./l. and 30 -g./l.

In order to reduce the gelatinous precipitate of silica resulting from the hydrolysis of the orthosilicate of sodium, a predetermined amount of caustic soda, generally from 1 to 10 g./l., may be added.

The relative proportions of the agents may vary greatly. The following table shows some examples:

acid Sodium tripolyphoshate p 0 Caustic soda... Quantity necessary to 0 0. 1 0 reduce the hydrolysis of the orthosilieate of sodium which appears inttlbezform of gelatinous flocks of silicate. 0 o

Examples of compositions are given in the following table TABLE II {Grams per litre] Thus electrolytes are provided giving improved active results with bright or mat pickling.

Composition B in Table II is suitable for degreasmgpickling of fine precision pieces.

Composition C in Table II is a bath of normal activity with which satisfactory results have been obtained.

Composition F of Table II constitutes a very active bath, appropriate to the elimination of thick coats of rust or calamine.

Alternating current of the distribution system under a voltage between 5 and 30 volts with a current density between 20 and 200 amperes per dm. and preferably between 50 and 100 amperes per dm. was used.

The contact time, generally very short, is varied according to the state of the surface of the metal to be treated. On fatty and highly calamined pieces, a satisfactory result is obtained after a contact varying between 30 seconds and 2 minutes. On rusty pieces, the same result is obtained after a contact of 1 to 5 minutes. One can de-tin, de-copper the sheets plated at 2 cm. in 1 to 2 minutes.

The process is carried out at between 30 and 70 C. and preferably between 50 and 65 C.

The pH is maintained between and 13, and preferably between 12 and 13.

Finally, after pickling the metal is carefully washed and rinsed as usual.

The process of the invention presents numerous advantages. As already mentioned, it enables in a single treatment simultaneous degreasing and pickling even to a predetermined brightness. The thick layers of calamine or rust, or surface oxides, the greases, dirty oils, the films of paint and the deposits of metal, such as copper, tin, zinc, are quickly eliminated.

Since the pieces to be treated form the electrodes of the bath, it follows that, compared with direct current, the use of alternating current allows for example the simultaneous degreasing-pickling in a continuous operation of two strips destined to receive ultimately an electrolytic deposit or a stoved antifriction lining or a tinning by dipping.

The direct current applied to the metallic electrodes to be degreased and pickled, immersed in the known type of electrolytes as hereabove mentioned, does not produce effects analogous to those produced by this invention; at

"the most there will be the normal electrolytic degreasing on the cathode.

By the process of the present invention, only the alternating current at the frequency of the system and at low voltage allows the electro-chemical phenomenons as indicated by the results previously shown to be obtained. Only a transformer is required, while the pickling with direct current, for example the anodic pickling of iron in a sulphuric acid medium, necessitates the use of a current rectifier in addition to a transformer.

The process of the invention allows in a single operation followed by a rinsing, the equivalent of a degreasing -with trichloroethylene, alkaline degreasing, rinsing, acid pickling and a neutralizing rinsing to be carried out so &

that the apparatus required is considerably reduced, as are the handling operations and the time of treatments.

There is no important attack on the metal itself. Thus in a bath having the composition B of Table II, the loss of weight in metal for a sheet metal of 7 of thickness, is 1.32 g. per hour and per dm. under a current of 25 volts, cycles, 100 amperes per dm.

Submitted to the process of the invention, the metal to be treated keeps not only its subjacent polish, but acquires a particular brightness. It is more resistant against oxidation for a given time period than the metal pickled according to the hitherto known processes. This is all the more important when the pickled metal is ultimately to receive a protective coat or be plated electrolytically.

Finally, although intended more particularly for ferrous metals and alloys, the process of the invention can be applied with the same success to pickling-polishing of brasses and copper; the polish obtained is specular.

The following non-limitative examples illustrate the invention:

EXAMPLE 1 In a bath formed by the composition A in Table II at a temperature of 50 C., two strips of soft steel, 120 cm. long, 15 cm. wide and a thickness of were immersed for 5 minutes. One of the sheets was coppered (thickness of the coppering 10 microns) and the other was tinned (thickness of the tinning 20 microns). They formed the electrodes of the electrolysis cell. An alternating current at 50 cycles, 25 volts and a current density of amp./dm. was used.

After 4 minutes of contact, the two strips were withdrawn from the bath, washed abundantly, then dried. Their surfaces were perfectly clean and bright, free of any traces of copper and tin.

EXAMPLE 2 In a bath formed by composition C of Table II at a temperature of 40 C., two strips, one of them of copper, the other of brass, 10 cm. long, 10 cm. wide and a thickness of were immersed for 2 minutes, the surfaces of the sheets being oxidized, scratched, greasy and dirty. They formed the electrodes of the electrolysis cell. An alternating current at 50 cycles, 25 volts and a current density of 50 amp/rim. was used.

After 2 minutes of contact, the treated strips were withdrawn from the bath, washed abundantly, then dried. Their surfaces were perfectly deoxidized and polished. On the strip of brass, one could even observe through the microscope the boundaries of crystals.

EXAMPLE 3 In a bath formed by composition D in Table II at a temperature of 60 C., two strips 120 cm. long, 10 cm. wide and a thickness of were immersed for 2 minutes, the surface of the strips being highly calamined and greasy. They formed the electrodes of the electrolysis cell. An alternating current at 50 cycles, 25 volts and a current density of 50 amp./dm. was used.

After 1 minute, 30 seconds of contact, the two strips treated were withdrawn from the bath, washed abundantly, then dried. Their surfaces were perfectly clean and free of any oxide. It presented a very silvery aspect, which after 7 months was still maintained. These strips were ready to receive an electrolytic coppering or a tinning by dipping.

EXAMPLE 4 In a bath formed by composition E in Table II at a temperature of C., two tubes of iron, cm. long with an outside diameter of 31 mm. and an inside diameter of 26 mm. were immersed for 5 minutes, the outside surface of the tubes being greasy, covered with oil paint and calamined. They formed the electrodes of the electrolysis cell. An alternating current at 50 cycles, 25 volts, and a current density of 70 amp/din. was used.

After 5 minutes of contact, the tubes treated were with drawn from the bath, Washed abundantly, then dried. Their outside surface was perfectly clean, and the soldered joint of these tubes was itself free of any oxide.

EXAMPLE 5 In a bath formed by composition F in Table 11 at a temperature of 60 C., two very deeply rusted sheets, 50 cm. long, 10 cm. wide and a thickness of were immersed. They formed the electrodes of the electrolysis cell. An alternating current at 50 cycles, 25 volts and a current density of 50 amp./dm. was used.

After 3 minutes of contact, the sheets treated were withdrawn from the bath, washed abundantly, then dried. Their surfaces were freed of any traces of rust, except the deep cavities therein formed by heavy rust pittings.

In an alternative method of the invention, commercial sodium silicate, i.e., sodium metasilicate, was used as a degreasing agent instead of orthosilicate of soda. Triethanolamine was used as chelating agent. Cryolite was added as a suspension and attacking agent, as well as a typical tensio-active agent of either the sulphonated oil type, such as sodium sulforicinate or alkaline salt of acid sulphates of fatty alcohols such as Teepol, and by the use of sodium plombite the object of which is to retard the formation of ferrocyanide during electrolysis. The conditions of the baths were improved by using high current density and temperature and in some cases by the use of a second electrode which cannot be consumed and is inert. Moreover, worn out baths were handled more particularly to recover sodium cyanide.

The concentration of caustic soda was raised to advantage to approximately 100 g. per liter of electrolyte, but such content may be varied between 80 and 120 g./1iter. This great increase in concentration in ratio to that of the previously described process of the invention improves the electrical conductivity of the bath which increases from 0.17 mho-0.30 mho to 0.40 mho and enables a constant pH rising to about 13.5-14 to be maintained; moreover, it enables the substitution of sodium orthosilicate by inexpensive commercial sodium silicate, i.e. sodium metasilicate, and the sodium ferrocyanide in the used electrolyte can be easily separated from the other elements.

The replacement of sodium orthosilicate by commercial sodium silicate enables the price of the chemical elements forming the composition of the bath to be lowered. The low ratio of Na O to Si in the latter is compensated by the powerful concentration of caustic soda in the bath.

The chelating agents used in the process of Examples 1 to may be advantageously replaced by triethanolamine of which the moistening, emulsifying, degreasing, dissolving and complex qualities are known.

It has been discovered that when triethanolamine is mixed with an aqueous solution of alkaline hydroxide, the bath is capable of forming an electrolyte which with an alternating current of 50 cycles has a degreasing and scouring action accompanied by an intense gaseous substance being released by the iron electrodes which has the advantage of promoting scouring functions. This gaseous discharge may be increased by adding ammonia or ammonium-containing reagents. Furthermore, triethanolamine increases and extends the activity of the electrolytes of cyanide alkaline bases. Moreover, if low quantities of cryolite are added, it improves the scouring process, both as regards the semicolloidal properties of the latter and the activity of its fluorine ions. These improvements are expressed in the putting into suspension of the particles coming from cleansing and an absence of deposited iron hydroxide on the scoured surfaces. The addition of moistening agents in some cases where the quantities of fatty products on the articles to be treated are large, can prove efiicacious. It is advisable to use an anionic moistening agent such as Teepol and to use it in the proportion of 1 cc. per liter of electrolyte. How- 6 ever, where excessive froth would constitute a hindrance, it is preferable to use another moistening agent such as sodium sulforicinate which can be used to full efficacy in baths with a high pH at the rate of 1 to 5 cc. of sodium sulforicinate at 50% per liter of electrolyte.

It has also been discovered that plombite of sodium acts to retard the formation of sodium ferrocyanide without slowing down the gaseous discharge on the electrodes.

The activity of the bath in fact, is connected in part with the concentration of alkaline cyanide and one of the main processes of scouring may be regarded as being the electrolytic action which follows, which takes place only with alternating electric current.

In that reaction, the speed at which the sodium ferrocyanide is formed from the iron of the electrodes and the sodium cyanide of the electrolyte, is predicated on the current density. For a given concentration of CNNa, however, the speed at which sodium ferrocyanide is formed remains independent of the variation in the concentration of alkaline hydroxide.

The presence of sodium plombite slows up the previous reaction and thus enables the activity of the baths to be extended. The preparation of this plombite can be done by dissolving hot litharge in an aqueous solution of sodium hydroxide at 50%:

PbO+2NaOH+H 0:Pb(OH) Na A solution of 20 g./l. of Pb (in the form of plombite) may be prepared for example by dissolving 21.44 g. of

TABLE III Influence of sodium plombite on the content of the bath of free sodium cyanide (g./l. of sodium. cyanide) in terms of time %h. 1h. 1%h.|2h. 2%h.3h. 3%h.

Bath of Ex. 1 79. 1 62. 6 45. 4 28. 9 1.4. 7 6. 3 2.8 Bath of Ex. 1:

+ 0.5 gJl. Pb- 79.3 64. 2 48. 2 33. 2 20. 5 12.5 7. 6 1 g./l. P 81 67.3 52. 4 38.1 25. 5 16. 8 11. 3 2 g./] Pb 82. 6 70. 4 56. 6 43. 3 30. 8 21. 7 15 The technical conditions in the scouring operation have likewise been improved in order to reduce the cost. Thus it has been possible to reach a compromise between the quality of scouring and the duration of treatment in the bath by adjusting the current density between 20' and amperes/dm. and preferably to 30 or 40 amperes/dm.

Further, in order to avoid carbonation and decomposition of the bath, the temperature of the bath was kept at between 45 and 50 C. which further enables crystalliaztion to be eliminated.

The fitting of the electrodes may be carried out in accordance with various plans dependent on the articles being handled. The following are given as examples of a few possible alternatives illustrated in the accompanying drawings:

(1) The two electrodes are formed by two articles to be treated. This is the case where single articles of small area are concerned (continuous scouring of wire or of a narrow foil, for example) (FIGURE 1).

(2) Scouring the interior of a cylindrical container. The method shown in FIGURE 2 is used in which a central electrode A is formed by graphite.

(3) .When the articles have concave or convex surfaces (FIGURE 3) the two articles of the same surface are laid facing and form electrodes. The other surface of each article faces a graphite electrode A.

(4) In the case of scouring the back and front surfaces continuously of two very wide foils, these are joined to the same alternating current conductor and interposed between three electrodes A A A of graphite fed by the second conductor from the source (FIGURE 4). It has been found in fact that graphite, an amorphous conducting material, which does not show any gaseous polarization and does not scale during operation, even when it is of poor quality and is very porous, forms the second ideal electrode.

The concentration of the various agents may be within the following limits:

Sodium cyanide 50 to 150 g./l. Caustic soda 80 to 120 g./l. Cryolite 1 to 20 g./l. Triethanolamine 10 cc. to 100 cc./l. Silicate of soda at 36 Baum 50 cc. to 150 cc./l. Lead in the form of plombite of sodium 0.1 to 3 g./l. Pb Sodium sulforicinate at 50% 0.0 to 10 cc./l. Teepol 0.0 to 5 cc./l.

Finally, the scouring baths which are the subject of the present invention have the peculiarity when saturated in iron and thus unusable, to separate into tWo phases at the surrounding temperature:

A liquid phase poor in sodium ferrocyanide and comprising the whole of the components.

A crystallized phase rich (96%) in hydrated sodium ferrocyanide, Na Fe(CN) .12H O which it is therefore possible to separate, for instance by drying in the open.

Sodium ferrocyanide can be sold as it is, or purified by any known means. It may likewise be transformed into sodium cyanide which may again be used for making up baths. This transformation may be carried out by thermal means:

Either at low temperature (450 C.) according to the reaction:

with a theoretic yield in sodium cyanide of 83.33%;

Or at red heat in accordance with the reaction:

with a theoretic yield in sodium cyanide of 100%.

The mixture is heated in an iron crucible, or one of castmetal or graphite, precautions being taken to avoid extending the duration of heating so as not to form iron carbide (toward 600 C.). After having reacted, the material is treated with water. The iron is separated magnetically and the solution, rich in sodium cyanide, is recycled.

The following examples show the operation of the process according to the invention:

EXAMPLE 6 Sheet metal of the specification XC 10 which were greasy and oxidized, were scoured electrolytically in a bath compounded in accordance with the information given herein, the composition of which was as follows:

Sodium cyanide g 100 Cryolite g 5 Caustic soda g 100 Triethanolamine cc 25 Solution of sodium silicate at 36 Baum cc 65 Water: suflicient to make 1 liter.

After treatment, the metal had a glazed appearance like silver, and was free from any blemishes.

In operating conditions under A.C. current, 50 cycles, at a temperature of 50 C. with a current density of 30 amp./dm. the critical content of free sodium cyanide 8 was 10 g./l. Below that content the bath is no longer of any practical use.

EXAMPLE 7 The magnetic oxide covering laminated foils which were hot rolled (specification A 37) were eliminated in a bath of the following composition, in which sodium orthosilicate was used as in Examples 1 to 5:

Sodium orthosilicate g 40 Sodium cyanide g Cryolite g 10 Caustic soda g '100 Triethanolamine cc 40 Water: quantity sufficient for 1 liter.

pH-l4.

After treatment, the metal from which all traces of oxide and grease had disappeared, had an absolutely clean appearance.

Under the same working conditions as those in Example 6, the results obtained were substantially the same for a bath, but with greater labor, owing to the presence of sodium orthosilicate instead of sodium silicate of commercial use.

EXAMPLE 8 A series of 1,000 rings of specification A 42 and of an outside diameter of 321 mm. and an inside diameter of 280 mm., covered with an irregular film of magnetic oxide and oil were scoured in the following bath:

Sodium cyanide g 100 Cryolite g 5 Caustic soda g 100 Triethanolamine cc 25 Solution of sodium silicate at 36 Baum cc 65 Lead in the form of plombite of sodium g 1 Water: suflicient quantity for 1 liter.

After treatment, the original irregularities in the surface still persisted. The perfectly clean restored surfaces became amenable to the application of an electro-plating of copper Without any further treatment.

Under Working conditions identical to those in Example 6, the duration of activity of this bath was extended by 25%.

EXAMPLE 9 The baths given in the three previous examples were left to crystallize at rest at 20 C. and the residual concentration of sodium ferrocyanid'e was determined in the liquid phase. The following Table IV gives the results thus obtained. The content of sodium ferrocyanide of the clear liquid in the spent bath used in Example 1 has been given by way of comparison:

TABLE IV Bath of Bath of Bath of Bath of Ex. 1 Ex. 6 Ex. 7 Ex. 8

Grams per Liter of Sodium Ferrocyanide 47 17 11 17 volts and at a current density of substantially 20200 amperes per dmfi, said bath consisting essentially of (a) an alkaline degreasing agent selected from the group consisting of caustic soda, sodium orthosilicate and sodium metasilicate, said degreasing agent being in amounts between 20 and 200 g./l.; (b) an alkaline cyanide as an alkaline pickling agent, said pickling agent being in amounts between 25 and 250 g./l.; (c) a tensio-active agent selected from the group consisting of an alkaline salt of a fatty secondary sulfonated alcohol, an alcoylaryl-sulfonate and sodium sulforicinate, said tensio-active agent being in amounts between 0.5 and 20 g./ 1.; and (d) a chelating agent selected from the group consisting of polyphosphates, a sodium salt of ethylene diaminotetracetic acid, tertiary amino-alcohols, and polyacids-alcohols, said chelating agent being in amounts between and 100 g./l.

2. A process according to claim 1, wherein the bath consists essentially of sodium orthosilicate as a degreasing agent, sodium cyanide as a pickling agent, an alkaline salt of a fatty secondary sulfonated alcohol as a tensioactive agent, and a member of the group consisting of sodium tripolyphosphate, the tetr-asodium salt of ethylene diaminotetracetic acid, triethanolamine, tartric acid as a chelating agent.

3. A process according to claim 1, wherein the bath has a pH of to 14.

4. A process according to claim 1, wherein the temperature of the bath is between 30 and 70 C.

5. A process according to claim 1, wherein the conductivity of the bath is between 0.10 and 0.40 mho.

6. A process according to claim 1, wherein cryolite is added to the bath in amounts between 1 and g./l.

7. A process according to claim 1, wherein sodium plombite is added to the bath in amounts between 0.1 and 3 g./l.

8. A process according to claim 1, wherein the bath contains cryolite, has a pH between 13.5 and 14, and wherein the spent bath is left to crystallize sodium ferrocyanide which is removed from the bath.

9. The process of claim 1 characterized by immersing a second metal article into said bath, said two articles forming the two electrodes of said bath.

10. The process of claim 1 characterized by said bath including cryolite in amounts between 1 and 20 g./ 1., and sodium plombite in amounts between 0.1 and 3 g./l.

11. A process of electrolytic surface treatment of metals wherein degreasing, pickling and at least one of cleaning and polishing of the metal surfaces are simultaneously carried out in a single alkaline bath, said process comprising immersing a metal article and an electrode in said bath and passing an alternating current between the article and the electrode, said alternating current being used at between 5 and volts and at a current density of substantially 20-200 amperes per dm. said bath consisting essentially of an alkaline degreasing agent selected from the group consisting of caustic soda, sodium orthosilicate and sodium metasilicate, said degreasing agent being present in amounts between 20 and 120 g./1.; an alkaline cyanide as an alkaline pickling agent, said pickling agent being present in amounts between 25 and 250 g./l.; a chelating agent selected from the group consisting of polyphosphates, a sodium salt of ethylene diaminotetracetic acid, and tertiary amino-alcohols, polyacidsalcohols; said chelating agent being present in amounts between 5 and g./l.; and cryolite, said cryolite being present in amounts between 1 and 20 g./l.

12. The process of claim 11 characterized by said bath including sodium plombite which is present in amounts between 0.1 and 3 g./l.

13. The process of claim 11 characterized by immersing a second metal article into said bath, said two articles forming the two electrodes of said bath.

14. A process of electrolytic surface treatment of metals wherein degreasing, pickling and at least one of cleaning and polishing of the metal surfaces are simultaneously carried out in a single alkaline bath, said process comprising immersing a metal article and an electrode in said bath and passing an alternating electric current between the article and said electrode, said alternating current being used at voltages between 5 and 30 volts and at a current density of substantially 20-200 amperes per dm. said bath consisting essentially of an alkaline degreasing agent selected from the group consisting of caustic soda, sodium orthosilicate and sodium metasilicate, said degreasing agent being present in amounts between 20 and g./l.; an alkaline cyanide as an alkaline pickling agent, said pickling agent being present in amounts between 25 and 250 g./l.; a chelating agent selected from the group consisting of polyphosphates, a sodium salt of ethylene diaminotetracetic acid, tertiary amino-alcohols, and polyacids-alcohols, said chelating agent being present in amounts between 5 and 100 g./l.; and at least one of: (a) cryolite in amounts between 1 and 20 g./l.; (b) sodium plombite in amounts between 0.1 and 3 g./l.; and (c) a tensio-active agent selected from the group consisting of an alkaline salt of fatty secondary sulphonated alcohol, an alcoyl-aryl-sulphonate and sodium sulpho ricinate, said tensio-active agent being in amounts between 0.5 and 3 g./l.

15. The process of claim 14 characterized by said bath having a pH of 10 to 14.

16. The process of claim 14 characterized by said bath having a conductivity between 0.10 and 0.40 mho.

17. The process of claim 14 characterized by said electrolytic surface treatment being carried out for up to about 5 minutes.

18. The process of claim 14 characterized by said bath having a pH of 10 to 14, and by said bath having a conductivity between 0.10 and 0.40 mho.

19. The process of claim 14 characterized by immersing a second metal article into said bath, said two articles forming the two electrodes of said bath.

References Cited by the Examiner UNITED STATES PATENTS 2,325,957 8/43 Krogel 204141 2,615,840 10/52 Chapman 204-145 2,685,564 8/54 Emmett et al 204-145 2,915,444 12/59 Meyer 204-145 2,973,307 2/61 Hahn 204-145 3,025,225 3/62 Snyder et al. 204145 FOREIGN PATENTS 167,907 6/56 Australia.

JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner.

Claims

1. A PROCESS FOR ELECTROLYTIC SURFACE TREATMENT OF METALS WHEREIN DEGREASING, PICKLING AND POLISHING OF THE METAL SURFACES ARE SIMULTANEOUSLY CARRIED OUT IN A SINGLE ALKALINE BATH, SAID PROCESS COMPRISING IMMERSING A METAL ARTICLE AND AN ELECTRODE IN SAID BATH AND PASSING AN ALTERNATING CURRENT BETWEEN THE ARTICLE AND SAID ELECTRODE, SAID ALTERNATING CURRENT BEING USED AT BETWEEN 5 AND 30 VOLTS AND AT A CURRENT DENSITY OF SUBSTANTIALLY 20-200 AMPERES PER DM.2, SAID BATH CONSISTING ESSENTIALLY OF (A) AN ALKALINE DEGREASING AGENT SELECTED FROM THE GROUP CONSISTING OF CAUSTIC SODA, SODIUM ORTHOSILICATE AND SODIUM METASILICATE, SAID DEGREASING AGENT BEING IN AMOUNTS BETWEEN 20 AND 200 G./L.; (B) AN ALKALINE CYANIDE AS AN ALKALINE PICKLING AGENT, SAID PICKLING AGENT BEING IN AMOUNTS BETWEEN 25 AND 250 G./L.; (C) A TENSIO-ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF AN ALKALINE SALT OF A FATTY SECONDARY SULFONATED ALCOHOL, AN ALCOYLARYL-SULFONATE AND SODIUM SULFORICINATE, SAID TENSIO-ACTIVE AGENT BEING IN AMOUNTS BETWEEN 0.5 AND 20 G./L.; AND (D) A CHELATING AGENT SELECTED FROM THE GROUP CONSISTING OF POLYPHOSPHATES, A SODIUM SALT OF ETHYLENE DIAMINOTETRACETIC ACID, TERTIARY AMINO-ALCOHOLS, AND POLYACIDS-ALCOHOLS, SAID CHELATING AGENT BEING IN AMOUNTS BETWEEN 5 AND 100 G./L.