Letter 18020

CLARIFICATION FOR HARDNESS CHECK ON PLATED PARTS [Canada] 

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I have a Door cam steel part (matl: MS 459(SAE J404 4230)for which the drawing says as follows,

1) Heat treatment: Thru Harden oil quench and temper to Rockwell C 43-49

2) Finish: Zinc coat per Chrysler standard PS-4220 Code 30 .Part must be properly baked per Chrysler standard PS-9500 tp prevent Hydrogen Embrittlement.

I am a Quality Engineer approving the part heat treated and finished by a supplier. My doubt is apart from Coating thickness check, salt spray test,is there a test stipulated for Zinc plating hardness check( I think Vickers-iam not sure) Is plating hardness one of the criteria for quality check. I am having a difference of opinion with the supplier who claims that he has not come across anyone asking for plating hardness check. Would u be kind enough to clarify on this issue.

Thank you, Regards,

PRABHAKAR SHANMUGAM
FineStamping Inc - CANADA

Prabhakar,

Hardness check is essential.You can do that with vickers or Knoops.

Venkat Raja   plating supervisor Walkerton, Ontario, Canada

You have the answer in your question. Hardness requirement is for the heat treated steel. Zinc plate has a hardness but it is so low and the plate is so thin compared to the steel that it will barely be detected by the Rockwell C apparatus. If there was a specification for the zinc hardness (which I also have never heard of), it would have to be clearly indicated which method to use and the reading would have to be taken from a cross section of the plate parallel to the surface to avoid influence from the steel. This is known as microhardness and is only specified for hard coatings not zinc plating.

Guillermo Marrufo
Monterrey, NL, Mexico

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