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Help with Delayed Blistering of Bright Tin Parts

2001

I am currently trying to understand the problems with delayed blistering, with sulphate base bright acid tin. The base metal is steel, with 2/10's to 7/10's tin plating. The process samples of the bake and quench for adhesion, pass after plating but after a few months, delayed blistering happens to the part. The parts have been reworked to ensure that the cleaning process is not a problem, due to the blistering.

The configuration of the part is 6 X 6 inches square. This part is run on a return automatic line. Parts are run anywhere from 8 to 11 amps per square foot.

Does anyone have any suggestions or information that could help us out with this problem?

Sue K
- Minneapolis, MN, USA

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Sue:

Do you see anything on the substrate surface if you peel off the blistered plating? Is the steel a free-machining alloy? I have seen plating blister after a few weeks from corrosion of the substrate by cleaning and plating liquids trapped at inclusions, especially in free-machining steel. A close look at the surfaces of the plating and substrate may also give clues to other possible problems.

Larry Hanke
Minneapolis, Minnesota
2001