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Brittle brake washer after zinc plating

April 23, 2008

Good morning,
We got a large trouble on simple "screw" made by CVB in Italy. We have screw posidrive 2 with a brake washer like "GROVER" washer and then a normal washer...after manufacturing this device = screw + brake washer+ standard washer is plated with Zinc...and then the device is baken to avoid hydrogen inside which make the spring steel brittle. We got a lot of brake washer broken....what is the possible reason. Can we guaranty a nice screw if we take all precaustion with plating and thermal treatment?
regards,

Combette Marc
celduc - France

Hi, Combette. The first requirement is that the baking must be done immediately after plating. Is that the case?

Regards,

Ted Mooney, P.E.
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey
April 24, 2008

You should read ASTM B850-98, which prescribes baking cycled as determined by the hardness (tensile strength) of the substrate plated. ASTM B849-02 sets forth requirements prior to plating. Keep in mind that ASTM B850-98 says that baking can reduce the risk of hydrogen embrittlement but can not eliminate it. If you need a hydrogen-embrittlement-free process, look at mechanical plating or painting with a zinc-rich paint such as Magni, Doerken, Dacromet (Dacral in France) or Geomet.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.

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April 28, 2008

adv.

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