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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
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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