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Metal finishing Q&As since 1989

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Problems regarding discoloration/tarnish of brass components

We are component manufacturers for Automobiles, Defence and agricultural industries. Recently we started having problems with one of our brass tubular sleeves(25 mm OD x 35 mm length). They were being returned due to discoloration/tarnish. Is there a cost/time effective way to solve this problem. Currently our final operation is to ball burnish these parts after a quick acid dip (dil H2SO4). Please advise.

Thanks

Praj Amin
Component Manufacturer - Bombay, Maharashtra, India
2004

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Dear Praj,

If you can think of having chemical dip as a final treatment, tarnishing may be avoided, by using an additive 1,2,3 Benzotriazole(BTZ) [on eBay or Amazon (adv.)] in your chemical dip, the concentration may be 1%.

Just try out, Good Luck.

Keshava Prasad M
- Bangalore
2004

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Ref a book-technica przeciwkorozyina-warszawa-1973(russian trans)-page105. brass may have what they call seasonal cracking, that may be seen if the metal is stessed or if there is ammonium (NH3) in the air. A high percentage of chlorides, sulfur, or ammonium in soil would increase rate of corrosion.

Khair Shishani
aircraft maintenance - Al Ain, UAE
2004

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Dear Mr. Praj Amin

The problem seems to be due to dezincification. Use of 1, 2, 3-benzotriazole (as suggested by Mr. Keshava) as corrosion inhibitor (CI) is generally recommended. However there are several new and effective CI available. The usage condition (i.e. temperature, duration and concentration of CI etc.) is more important in all cases.

D. JAMAL
- Pune, India
2004