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Pits on parts

We apply a copper topcoat on some of our parts before heat treat processes, and black oxide treat the same parts later. We periodically have two pits, which appear to look like hot spots or burns where the metal rack contacts the part. We use current while plating copper and copper strip. The parts while plating copper and copper strip, are hanging on a hook rack and rocks on a rocker, not a tight contact point. We do not use any current on the black oxide line. Is it possible that the pits are coming from the black oxide process. The shop platers and myself believe the pits are more related from the copper process.

Need some information and help.

Marion Lee Baker
Bell Helicopter / Textron - Hurst, Texas

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You seem to know what the answer is to the problem already.

From what you have said it is hard to say where the problem lies. Can you check the parts in between stages. Also I assume the parts are steel - are they etched with current at any stage e.g.,anodic sulfuric etch before copper. If they are this may be the step where the burning occurrs due to the high current.

If I was to trouble shoot this I would first base it on the assumption that is current related and look at the current at each step. Then look at the parts before and after the highest current step. You also know the answer which is to improve your jigging (cost!). Just use the argument that each part is worth $xxx and the proper jigging will cost $x. You could even work out a pay back on the amount of scrap reduced.

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England