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Historical Articles
September, 1952 issue of Plating
Question Box
Readers’ questions of general interest
Q. 143. Our company is interested in a quick means of production testing the thickness of sulfuric anodic coatings on aluminum alloys. Do you hare any information providing a relationship between salt spray resistance and dielectric strength of anodic coatings?
A. The salt spray resistance of anodic coatings is not a measure of the thickness of the coatings, a thin dense coating may give better resistance than a thick porous coating. A number of methods have been employed for the determination of the thickness of anodic coatings, stripping of the coating is most widely used. Both stripping and microscopic methods are described in the Proceedings, American Society Testing Mats. 37, 261 (1937) and ibid, 40, 959 (1940). A voltage breakdown method is given in the same publication, 40, 978 (1940). The use of an electronic heat-frequency oscillator is described in the A. S. T. M. Bulletin for October, 1947, page 47. The Filmeter as this instrument is called should give rapid production results.— D. G. FOULKE.
Q. 144. For some time we have had a problem of masking gears off so that we may copper plate them approximately 0.002 inch. So far everything we use will either break down under our various operations; caustic, copper strike, etc., or if it held up we have a terrible time trying to remove same after plating. Any information you may furnish will be greatly appreciated
A. In order to hold the plating lie to the place desired, obviously, a material of good adhesive qualities is required. Just as obviously such a material is hard to remove, so that a trick must be employed to do a good stop-off job in this case. One successful method is as follows: First, place a piece of pressure sensitive electroplating tape not quite to the edge to be held. Without using any primer, dip in or paint with a plastisol rack coating to the point where protection is desired. The mechanics of this procedure can be easily worked out, particularly if the complete tooth is to be stopped off.
In some cases it is the practice not to machine to size those areas to be hardened. The whole part is then copper plated, followed by machining to size at which time the copper and some steel is removed. It is assumed that the high melting point waxes have been tried and found unsuitable in this case.—Lous DONROE
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