Metal finishing Q&As since 1989

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Discoloration on Nickel Parts after washing

2000

We are a large-volume manufacturer of terminals with nickel-plated parts.

A client is having trouble with discoloration of parts during washing. Their washing cycle involves an acid washing step with a solution containing phosphoric acid, an alkali washing step, and a step with a rust inhibitor. Each step has a rinse after it, and it is all concluded with a hot air drying process carried out at 185 degrees F.

An EDX of the discolored parts shows the presence of phosphorus in addition to nickel. The discoloration is usually a black or a dark tan/sepia color. The shape of the discolored spots suggests that they form while the droplets of solution are drying.

Is there anything that the client can do to alleviate this situation?

Mark Matsuno
- Cincinnati, Ohio

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Much better rinsing is required. This could be more rinse tanks, better water, more water or longer duration in the rinse cycle. Warmer rinse water will even help. James Watts
- Navarre, Florida
2000