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-----Discolouration of passivated components in storage.
We are plating MS components in a fully automatic barrel acid zinc plating plant. We are facing a peculiar problem, the fully passivated components after through rinsing and drying are packed in polythene bags and these bags are packed in paper boxes. we have observed that 6 to 8% of the components are either discoloured or faded or darkened. This phenomenon is observed only occasionally and not on regular basis. We are not able to overcome this problem. can anybody comment on this?
Ramesh KhareCMPPVTLTD. - Mumbai
2000
2000
I expect that the discoloration is a sign that your chromate conversion coating is being degraded. This could be a result of corrosive elements.
One other possibility is that the parts are being exposed to high temperatures (220F or higher). If hexavalent chrome is exposed to high temperature, it begins to dehydrate, fade, and lose its effectiveness. Is it possible that the parts that went bad saw higher temperatures? Does this occur more in the summer?
Tim Neveau
Rochester Hills, Michigan
Occasional problems are hard to correlate with a specific causes !
Suggestions: Check the Iron level in your chloride zinc bath. Are you tumbling long enough in the chromate (passivation ) tank to expose parts uniformly to chemistry? Check the dissolved salt in the water that touches your parts last. I would try a 96 hr. blue bright chromate and see if that helps.
Could water be splashed on the parts at the barrel to dryer basket dump station, This water often get contaminated accidentally?
Good Luck !
Let me know what you find
Danny Tynes
used electroplating equipment
- Birmingham, Alabama
2000
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