Historical Articles

October, 1953 issue of Plating

 

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Question Box—readers’ questions of general interest

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Q. 168. We are attempting to improve the appearance of a certain line of steel hinges (which are copper plated, sulfided, wire brushed, and lacquered) by ball burnishing the copper plate. Can you give us a satisfactory method for removing the film of burnishing compound so that the sulfide coating will have good adhesion?

A. In all probability, a soap film has been left on the copper after the ball-burnishing operation. This may be due to incomplete rinsing after burnishing, or due to the use of soap or a burnishing compound with insufficient detergent action. Either a suitable burnishing compound should be used and the work rinsed well after the tumbling operation, or else the work should be cleaned with a mild alkali soap cleaner after burnishing. At this point the work should be cleaned free of water breaks before any coloring operation is attempted.

Improper cleaning or the presence of oil or soap residues will produce a nonuniform job in the sulfide coloring treatment.

When a sulfide treatment is used on copper, the solution should be very dilute, approximately 1/8 to 1/4 oz polysulfide per gallon, and the bath preferably operated at room temperature. The more dilute solutions produce a black coating which forms more slowly but gives a finer, harder and more adherent deposit. If the coating is formed in too concentrated a solution, the coating tends to be spongy, soft, and somewhat flaky. Some operators add a small amount of ammonia to the sulfide bath, although in most cases this is not necessary.—A. S. KOHLER.

Q. 169. Stainless steel is a material which is easily available now in our country and we are therefore anxious to have your advice on the use of stainless steel tanks for plating solutions of chromium, nickel, silver, zinc, gold, lead and platinum group metals.

A. Unlined tanks for plating solutions are not generally recommended. Stainless steel tanks have been used for silver, gold, zinc (cyanide) and other plating solutions. However, it is advisable to use lined tanks wherever possible and by that is meant an insulating lining. Of course, it is still common practice to use lead lined steel for chromium plating solutions even though the lining is conductive. It is suggested that stainless is satisfactory in any oxidizing type solution, such as nitric acid, but that it should not be used for solutions containing halides. If you are to use unlined tanks stainless is not needed for zinc, tin or cadmium cyanide solutions because steel is less expensive and perfectly satisfactory.—D. GARDNER FOULKE.

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