Historical Articles

January, 1953 issue of Plating

 

Question Box—readers’ questions of general interest

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Q. 148. Our company is planning an installation of a line of equipment for the bright dipping of an assembly of aluminum and brass, the aluminum finish being major consideration. Is there any preferred treatment cycle for such an item?

A. The conventional nitric-phosphoric bright dip for aluminum has been found to be satisfactory, yielding a bright aluminum finish with not too severe an etched brass surface. However, immersion deposits of copper have been found to occur in the rinse after the aluminum bright dip with a resultant finish on the aluminum from a dark smut to a copper color. A follow up dip in a regular brass bright dip or a simple nitric solution was found to remove the copper film. The design of a layout for your assembly will depend upon the amount of copper in your first rinse.—A. KORBELAK.

Q. 149. In the construction of replaceable rack contacts stainless steel is a desirable material because of the ease of stripping at the end of a shift. 18-8 stainless is not springy enough. What stainless alloys have good spring properties?

A. SAE 420 has good corrosion resistance, has desirable properties of hardness and springiness. SAE 440B though generally used for gages and instruments also may be of value because of good spring properties.— H. J. EHRINGER.

Q. 150. We have recently had to use British aluminum stock and find our nitric-phosphoric acid bright dip yields a less bright and uniform finish than we had been getting on American aluminum. Any information you can give us on the bright dipping of British aluminum will be appreciated.

A. Assuming you control your bright dip carefully (you must, you know) there are two reasons why this occurs:

1. The stock may contain greater amounts of impurities, Cu, Si and possibly traces of Fe.

2. The type of finishing operation may be different and consequently the physical structure may be such as not to bright dip well.
First, check your bright dip against aluminum stock you know to be good. If the bright dip itself is satisfactory it is suggested that very little can be done except to (a) specify to your supplier the type of aluminum you want, or (b) determine whether any proprietary bright dip bath may be sufficiently better to justify its use.—ANON.