US1970549A - Process of electroplating bronze - Google Patents

Description

Patented Aug. 21, 1934 UNITED STATES PATENT OFFICE 1,970,549 PROCESS or ELECTROPLATING BRONZE tion of Ohio No Drawing. Application August 14, 1933 Serial No. 685,146

27 Claims.

The invention relates to a new process for producing ele'ctrodeposited coatings upon a base metal either polished or unpolished.

The application is a continuation in part of our application, Serial No. 569,852, filed October 19, 1931, and some features of this invention are disclosed but not claimed in our application, Serial No. 569,853, filed October 19, 1931.

The primary object of the invention is to obtain a process for producing a coating adapted for use as an intermediate between a relatively rough polished or unpolished base metal and a highly lustrous finish metal such as chromium.

Another object is to obtain a process for electrodepositing a coating composition at a rapid rate and at low cost while still obtaining desirable properties of an undercoating.

A further object is to produce an electrodeposit which can be built up to a considerable thickness without blistering or becoming roughened.

Another object is to obtain a process which can be successfully carried out under commercial operating conditions over a wide range of conditions such as bath composition, temperature, current density, etc.

An important object of the invention is to produce a coating adapted to be easily buffed to a high polish.

Another object is to obtain a metal or composition that may be electrodeposited over itself in successive layers.

Another object is to obtain a coating that is not only highly resistant to corrosion in itself but has that property of being electrodeposited to or buffed to a dense surface that closes up porosity within the electrodeposited coating.

One of the chief objects of the invention is to obtain a process for plating bronze which may be maintained in commercial operation for long periods of time with a minimum amount of regulation.

Another object is to provide a means for accurately regulating the composition of a bronze plating bath and the operating conditions whereby consistently good electrodeposits of bronze may be commercially obtained over long periods of time.

These and other minor objects are obtained by the novel process hereinafter more fully described.

Our improved process is designed to give an electrodeposited coating of a mixture or alloy comprising the two metals copper and tin.

55 The process comprises the electrolyzing of a so- (Cl. 204-2) i lution containing a soluble copper compound and a soluble tin compound while maintaining the alkalinity thereof between certain pH values and maintaining a certain amount of free cyanide. The composition of the bath is varied widely under different conditions, depending upon the requirement of the particular work under treatment. -We have found it most desirable to use for the soluble copper compound copper cyanide from 10 to 90 grams per liter and for the soluble tin compound an alkali stannate such as sodium stannate from 10 to 90 grams per liter. It is to be understood however that under some conditipns it is possible to use other copper compounds such, for example, as other cyanide compounds containing copper. It is also permissible to use other soluble tin compounds such as other soluble metal stannates.

For continuous operation it is desirable to use anodes which will be sufficiently corroded during the electrolysis to maintain in the electrolyte the same proportions of tin and copper; preferably the anodes comprising both copper and tin. A suitable electrolyte may be made up by mixing the following ingredients within the ranges given:

Copper cyanide Sodium stannate Sodium hydroxide. N a0 Sodium cyanide (free). Sodium cyanide (total) 10 to grams per liter. 10 to 90 grams per liter. 0 to 30 grains per liter.

0 to 60 grams per liter. 15 to 195 grams per liter.

Copper cyanide 40 Sodium stannate 20 grams per liter Sodium cyanide (total)--- 65 grams per liter Sodium hydroxide 7 grams per liter The above formula will produce a bath having a free cyanide content of approximately 20 grams per liter and a pH of 13.0. s

The bath gives good electrodeposits at current densities from 1 to 80 amperes per square foot and it is possible to carry the current density much higher but with increasingly lower efficiency. A density of 320 amperes per square foot has 110 grams per liter been used but this results in an abnormally high evolution of hydrogen and requires some means for inhibiting the hydrogen at the cathode in order to obtain commercial satisfaction.

The recommended temperature of operation of the bath is between 15 and 70 0., preferably 60 C.

The anodes used are preferably of a mixture or alloy of copper and tin suitably heat treated, but anodes of pure copper and tin may be used in lieu thereof. I

It is a noteworthy fact that the alloy anodes show a very uniform corrosion and an entire absence of polarization in contradistinction to the opposite properties in many other electroplating processes.

This bath when operated at our preferred temperature and current density will produce an electrodeposit having a tin content of 13 to 16 percent. We have discovered however that unless the free cyanide and pH are controlled or maintained, erratic results will be obtained.- In fact either or both might become so low that the bath would become inoperative due to anode polarization and the depletion of the bath as well as changing the tin content of the deposit to a point where it will not serve the purpose intended.

It is therefore an important feature of this invention to control the alkalinity and free cyanide content of the bath within such limits as to maintain the bath in commercial operation.

For the best commercial values we find it desirable to maintain the alkalinity of the bath between pH 12.9 and 18.1. Under some conditions, however, satisfactory results may be obtained with an alkalinity within the range from pH 12.8 .to 13.5. We have also found it possible to obtain actual deposits when the alkalinity has been within the range from pH 11.7 to 13.8.

We have found that for the best commercial results it is desirable to maintain the free cyanide content of the bath within the range of 15 grams per liter to 25 grams per liter, although satisfactory results are often obtained within the range of 10 to 45 grams per liter.

We have also discovered that the following factors influence the composition of the electrodeposit:

Increasing the temperature and free cyanide content or lowering the pH increases the percent of tin.

With the preferred free cyanide and pH the maximum tin content together with the maximum bufling properties is obtained at approximately 30 amperes per square foot current density.

As stated above, the preferred process gives a bronze electrodeposit having 13 to 16% tin. If it is desired to obtain an electrodeposit with less tin, the preferred process should be modifled to raise one or more of the factors, pH, free cyanide, and current density. For a deposit with a greater proportion of tin, the preferred process is modified by lowering one or more of the same factors.

The anode used is preferably an alloy of copper and tin in the approximate proportions of the electrodeposit obtained by the process, although it may vary as much as 10% or more, and still be operable providing the current density, temperature, pH and free cyanide are properly adjusted. The anode is heat treated to obtain maximum softness by casting in a metal mold, cooling in the mold, heating to 1000 F.

for fifteen minutes and quenching in water. Other heat treatments for obtaining the alloy in a soft condition may sometimes be substituted.

For maintaining the bath in condition for commercial operation it is desirable to frequently check the amount of alkalinity and free cyanide in the solution and to add the necessary amount of alkali cyanide and/or alkali hydroxide to bring the pH value and the free cyanide value within the preferred limits heretofore set forth. The copper and tin contents need not ordinarily be changed provided the anodes are of the approximate composition of the electrodeposit, but it falls within the purview of our invention to regulate the amount of the tin compound and/or copper compound by adding (or subtracting) the original reagents or their equivalents as heretofore described.

Our process may be used for electroplating directly on iron and its alloys including steel. It may also be used for plating on other metals whether they be the base metal or only a coating over another base metal. Examples of such metals are copper, nickel, tin, cobalt, silver, as well as combinations of these metals such as nickel and cobalt, copper and zinc, cadmium and silver and copper and nickel. The above metals can also be electrodeposited over the alloy formed by our process.

Qne of the principal uses of our process is in obtaining a coating upon an unusually rough surface which can readily be buffed to obtain a high luster, thereby permitting an overcoating of a bright metal such as chromium.

The alloy resulting from our process has the following outstanding properties:

(a) A high spreading property.

(b) Easy bufiing.

(c) A low loss of metal upon buifing.

(d) High corrosion resistance.

(e) An improved surface for superimposing another coating.

(1) Allows other metals to be electroplated thereon in a smooth lustrous condition.

(9) Does not peel even in thick deposits.

(It) Can be superimposed over itself.

Our process has the following advantageous properties:

1. High rate of deposition.

2. A greatly improved ability to be electrodeposited to a greater thickness without becoming blistered or rough.

3. Ease of control.

4. A greater ability to produce a suitable coating over wide ranges of solution composition.

5. A greater ability to produce a suitable coating over wide ranges of current density.

6. A greater ability to produce a suitable coating over a wide range of temperature.

7. More deposit per unit of power input.

8. The ability to control the composition of the plated coating by varying the following: Current density, temperature, and composition of solution. v v

The electroplated coating may advantageously be used as an undercoat in the production of bright metal finishes. For example in chromium plating an automobile radiator shell in order to obtain both resistance to corrosion and high luster, it is common practice in the prior art to take the steel shell as it comes from the dies and subject it to a series of polishing operations to remove die marks, cuts, slight metal distortions, pits and other surface defects in the metal as otherwise these blemishes would show 150 in the final finish. With our process, we are enabled to eliminate the polishing of the base metal and electrodeposit our metal or alloy directly on the unpolished metal. We plate a sufliciently thick coating of alloy so that it can be buffed without cutting through and because of the high spreading property of the alloy, the surface defects are completely obliterated leaving a highly buffed smooth surface for the final finish. Several types of finishes may then be superposed on the bronze. For example, bright chromium may be directly superposed or a nickel layer may be deposited, then bufied and finally covered with chromium.

While our process for electrodepositingbronze makes it possible in many instances to eliminate the polishing of the foundation metal, it is sometimes desirable to mechanically eliminate some of the major surface defects even though the surface is not given a highly polished finish. We have found that if the work is mechanically polished with an abrasive as coarse as to 120,'our bronze plating process with its subsequent buffing will provide a highly lustrous smooth finish. It is of course understood that our process can be used also with a polished foundation metal wherever desired.

While our process is capable of considerable modification, it is preferable to maintain the variable factors within such limits as to obtain a coating being within 3 to 35 percent tin, the balance being copper.

A desirable composition. for automobile radiator shells is:

Copper 1 Tin 1 15% What we claim as our invention is:

1. The process of electrodepositing a copper tin coating comprising electrolyzing a solution containing a soluble tin compound and a soluble copper compound-and maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8.

2. The process of electrodepositing a copper tin coating comprising electrolyzing a solution containing a soluble tin compound and a soluble copper compound and maintaining free cyanide in an amount not to exceed 60 grams per liter.

3. The process of electrodepositing a copper tin coating comprising electrolyzing a solution containing a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8 and maintaining free cyanide in an amount not to exceed 60 grams per liter.

4. The process of electrodepositing a copper tin coating comprising passing a current from an anode comprising copper and tin to a cathode in an electrolyte containing a soluble copper compound and a soluble tin compound, maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8 and maintaining free cyanide in an amount not to exceed 60 grams per liter.

5. The process of electrodepositing a copper tin coating comprising passing a current at a current density of from 1 to 80 amperes per square foot from an anode comprising copper and tin to a cathode in an electrolyte containing a soluble copper compound and a soluble tin compound, maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8 and maintaining free cyanide in an amount not to exceed 60 grams per liter.

6. The process as set forth in claim 3 where the copper compound is a cyanide of copper in an amount from 10 to grams per liter.

7. The process as set forth in claim 3 where the tin compound is an alkali stannate in an amount from 10 to 90 grams per liter.

8. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 12.8 to 13.5 and maintaining free cyanide.

9. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 12.9 to 13.1 and maintaining free cyanide.

10. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 12.8 to 13.5 and maintaining free cyanide between 10 and 45 grams per liter.

'11. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 12.9 to 13.1 and maintaining free cyanide between 15 and 25 grams per liter.

12. The process of producing a metal finish which consists in electrodepositing on an unpolished surface of the base metal an alloy of copper and tin, bufling the surface of said alloy to obtain a highly polished mirror finishj'and electrodepositing a bright metal thereover.

13. The process of producing a metal finish which comprises electrodepositing on an unpolished surface of the base metal a thick coating of a metal composition comprising from 3 to 35% tin and the balance copper, bufling said metal to remove the surface imperfections in the original base metal and obtain a bright finish, and electrodepositing a bright metal finish.

14. The process of electroplating which comprises the electrolysis of an electrolyte comprising soluble stannate, soluble copper, excess cyanide and alkali at current densities from 10 to 320 amperes per square foot with anodes comprising copper and tin.

15. The process of electroplating which comprises the electrolysis of an electrolyte comprising copper cyanide, soluble stannate, free cyanide and alkali at current densities from 10 to 320 amperes per square foot with anodes comprising copper and tin.

16. The process of electroplating which comprises the electrolysis of an electrolyte comprising copper cyanide, alkali stannate, alkali cyanide and caustic alkali at current densities from 10 to 320 amperes per square foot with anodes comprising copper and tin.

17. The process of electroplating which comprises the electrolysis of an electrolyte comprising at current densities from 10 to 320 amperes per Grams per liter Copper cyanide 10 to 90 Sodium stannate 10 to 90 sodium hydroxide Mo 30 Sodium cyanide (free) Oto 60 Sodium cyanide (total) 15 to 195 20. An electrolyte for electrodepositing a copper-tin coating comprising:

Grams per liter Copper cyanide 40 Sodium stannate 20 Sodium cyanide (total) 65 Sodium hydroxide 7 21. An electrolyte for electrodepositing a copper-tin coating comprising a. soluble stannate, a soluble copper compound, an alkali and free cyanide.

22. An electrolyte for electrodepositing a copper-tin coating comprising a soluble stannate, a soluble copper compound and free cyanide.

23. An electrolyte for electrodepositing a cop- I per-tin coating comprising a soluble stannate and copper cyanide.

24. An electrolyte for electrodepositing a copper-tin coating comprising a soluble stannate, copper cyanide and free cyanide.

25. An electrolyte for electrodepositing a copper-tin coating comprising a soluble stannate, copper cyanide, free cyanide and alkali.

26. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8 and using an anode comprising copper and tin.

27. The process of electrodepositing a coppertin coating which comprises electrolyzing a solution comprising a soluble tin compound and a soluble copper compound, maintaining the alkalinity of said solution within the range from pH 11.7 to 13.8 and using a heat treated anode comprising copper and tin.

HARRISON M. BATTEN. CARL J. WELCOME.