US2442195A - Cleaning and electroplating process - Google Patents

Description

Patented May 25, 1948 2,442,195 CLEANING AND ELECTROPLATING PROCESS James T. Clenny, Swampscott, General Electric Company,

New York Mass., assignor to a corporation of Nollrawing. Application July 31, 1945, Serial No. 608,089

The present invention relates to the surface treatment of metal articles with the object of removing adherent surface contaminations, including inorganic material such as rust and scale, and also organic material such as grease and oil. The cleaned surface, by a step in the same process, is prepared by the electrolytic deposition of a metal which will facilitate the subsequent application by casting or otherwise of an unlike metal and thereby cause it to make a firm union with the cleaned and coated surface.

'My invention is applicable in particular to cleaning of metal castings, rolled plate, or forgings, and the subsequent application thereto of an unlike metal, for example Babbitt metal, to pro ducecomposite articles. My invention is particularly applicable to the manufacture of bearings.

'I-Ieretofore metal objects which were coated with oil or grease, and also with rust or other oxides. have been subjected to a succession of independent stripping operations in order to remove such undesired surface contaminations. The cleaning operations in some cases were followered by an electrolytic treatment for depositing a coating metal. Commonly the cleaning operations included pickling in an aqueous solution of a strong acid which is not desirable and is not suitable for carrying out a plating operation.

In accordance with my invention I have provided a procedure comprising the combination of a plurality of electrolytic steps carried out successively in a single fused electrolyte in which the metal object to be cleaned functions alter nately as anode and cathode, As a consequence, the treatment of the metal is simplified, short ened in time and made more efficient.

For example, in the course of manufacture of ferrous bearings for rotating machinery, it is required to remove adherent rust, scale and grease, and it is desirable also that the cleaned metal surface next should be coated with a nonferrous metal which both protects the cleaned surface of the ferrous metal from reoxidation and prompts alloyage with a non-ferrous metal.

These objects of my invention are attained by a combination of chemical and electrochemical operations carried out in sequence in a fused alkali electrolyte which may consist of a strong alkali, preferably caustic soda, having dissolved therein a suitable copper compound which is especially adaptable to the manufacture or bearings, for example one to ten per cent of copper oxide (CuO). However, oxides and metallic salts of other oxidation-resisting non-ferrous metals 'may be used. In general, metals of the group 1 Claim. (Cl. 204-34) consisting of copper, nickel and silver can be used in a similar manner for various applications as protective coatings on metal surfaces.

The castings are immersed in such alkali bath which may be heated to a temperature in the range of 400 to 500 C. The articles to be treated are connected to an electric circuit charged with direct current at a potential of about three to six volts, the polarity of the castings first bein made positive. The negative cooperating electrode may be constituted by the container for the electrolyte or by a suitably spaced electrode which is connected to the negative terminal of the circuit. Theresulting passage ofcurrent causes oxidation and removal of the grease and'other organic matter from the surface of themetal article. The anodic treatment is continued for only a short time. About one minute is satis-- factory, the length of time not being critical. The current value may be about to 200 amperes per square foot of surface.

The polarity thereupon being cleaned becoming the cathode. The cathodic treatment is continued at approximately the same current density until adherent scale and rust are removed. In general, about seven minutes is satisfactory.

The third step is carried out by reducing the voltage, and thereby the current, to approximately one-tenth of the original density and by charging the casting again to positive potential, that is, reversing the polarity. By this step the spongy, loosely adherent copper which was deposited as an unavoidable incident during the previous step is caused to g0 into solution.

Finally, the metal article is charged negatively, that is, becomes cathodic for the electrolytic action occurring in the fused bath. During the fourth step, which is continued for about ten minutes, copper is deposited as a homogeneous, adherent layer on the ferrous metal object by electrolytic action, the current still being maintained at about 25 amperes per square foot.

The ferrous metal object, upon the completion of the copper coating step, is removed from the fused bath and immersed in water. The water dissolves the adherent coating of electrolyte. The surface of the ferrous metal article upon removal from the fused bath is copper-colored and retains this color after its immersion in water. The indications are that the copper coating becomes alloyed with the surface of the ferrous metal article.

the surface of the copper- As the final step, coated metal article is coated with a suitable is reversed, the article flux, for example, a flux containing zinc and ammonium chlorides. The followin flux is il- Upon removal from the flux bath, the article is then coated with tin, eitherby being preferably immersed in a bath of molten tin or having the molten tin way.

applied in any otherconvenient tin; or 4 copper,

or no-s'egreg'ating of alloying constituents.

What- I claim as new and desire to secure by Letters Patent 01" the United States is:

The process of cleaning and copperplating the current through said bath the articleto the following series of electrolytic and article to subject of alloys of copper, antimony and tin in the fol-5' JAMES T. CLENNY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date. 1,004,673 Monnot Oct. 3, 191-1 1,417,896 Fletcher May 30, 1922 1,600,355 Otis et al Sept. 21,1926 1,795,512 Schmidt eta! Mar 10; 193 1 1,909,149 Hitner- May 16; 1933- 2,042,800- Pike June 2, 1936 2,134,457 Tainton Oct, 25;,1938 2,311,139 Tainton Feb.,16-,19,43; 2,327,676 Spence '24, 19.413 2,366,477 Bayley Jan..v2,- 1.945 2,395,694 Spence et al Feb. '26; 1946 FOREIGN PATENTS Number Country Date.

Great Britain, V Mar. 13,1935