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Question: soaking work in Tripass passivate BEFORE zinc plating?

One of the platers in the plant I work for has recently started soaking work in Tripass PK3 passivate for several minutes before running it through the plating tank (which is cyanide zinc, but he does rinse the work beforehand).

While the work does appear to come out OK in the end, I personally expect that there will be an overall loss of plating quality, whether the adhesion to the steel is affected, or the durability of the zinc is affected.

But I am also open to the possibility that there could be no effect, or even some improvement.

Thoughts please, anyone?

Thanks in advance.

David Chord
Plating shop employee - Lower Hutt, New Zealand
July 27, 2008

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July 28, 2008

Hi, David. I think you need to ask him why he does that. What past defect does he think he is addressing, and what evidence does he have that the cure works? There are an infinite number of ways to complicate a plating cycle through steps that don't seem to have a point, and the rule is that every one of them is a bad idea unless you have evidence that it isn't. In addition to that, when you use a proprietary for a purpose for which it wasn't intended, you constantly stand at risk that the supplier may reformulate it without warning in ways that improve its intended function but are deleterious to that non-intended use.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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By soaking the raw steel (I assume steel) parts in an acidic solution which contains other corrosive materials, you are dissolving some of the steel increasing the iron in the process solution. This will shorten the life of the process bath. This can also lead to chrome contamination of the zinc tank with hexavalent chromium!

I can only presume that the worker has found this to be effective in overcoming some problem. I would guess that the problem is an acid pickle that in ineffective on a certain condition.

Gene Packman
process supplier - Great Neck, New York
July 29, 2008