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topic 18164

Hot tin dip yellows when heated



I'm a Quality Manager for metal stamping company. We produce an automotive part made from CDA194 that is hot tin dipped (97.5 % pure) and hot air leveled to 100-350 micro inches before stamping. The finished stamping is heated through three different process (molding, epoxy cure etc.)with the highest temperature at 300 degree F for twenty minutes. The product has been made for years but material from a single plater has turned yellow at the heating process.

Lab tests suggest that 1) The plating is oxidizing and turning yellow - normal for tin. 2)The copper is migrating through the plating. 3) The plating was not properly cleaned and should have had an aqueous wash and rinse as part of the process. Could you review the hot dip tin process and suggest what you feel could be the cause of the yellowing.

Thanks for your help.

Thomas Coles
- Attleboro, Massachusetts


Any of the above are possibilities, especially point 1, but since the problem seems related to one plater I would also suggest investigating if he may be using a bright acid tin instead of a matte tin. I am not a hands-on guy on this particular problem, but I would take a wild guess that this yellowing may be organic brighteners decomposing under heat, and that point 3 will not prove adequate to remove them.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"

February 12, 2009

I have received some material that supplier confirms has passed Hot Tin dip process which's made surface finished to be white slough around there. I have little experience in this process and it's hard to explain by wording, but please let me know your e-mail to send picture to review.
It's deviated from the previous parts I got, that's the reason of this problem. May someone drop your advise about white slough from Hot Tin dipped process, Please?

Ariya Sirisomboon
supplier quality engineer - Chonburi, Thailand   


Ed. note: email the photos to, Ariya

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