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Rockwell test after phosphate coating

July 30, 2011

Hello everyone,

My name is Jim Gallo and I perform incoming inspection on components supplied from outside vendors.

Can the hardness of the base material be tested after Phosphate coating?
Typical requirement is 4140 material hardened to 35-40 RC then Phosphate coated.
Parts are received complete from suppliers so pre-coated testing (by us) is not an option.
Readings from a standard Wilson Hardness Tester give varying results, sometimes the range exceeds 25 pts. on the same part.

Any comments will be greatly appreciated.

Jim

Jim Gallo
Quality control - Mechanicsville Virginia, USA

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August 2, 2011

Depending on the type of phosphate, your true values might vary a couple of points. It is totally impossible for it to vary by 25 points.
Check your method for the hardness testing and check readings of your equipment with a certified hardness block in the range that you need to be testing.
You can always sand or scotch brite the phosphate coating off to get a true reading of the base metal.
I would get a hardened scrap part and do a lot of testing on it. Your readings should be within ± 1 . If it exceeds 2, your tester or the operator has a problem.

James Watts
- Navarre, Florida

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Dear Jim Gallo,
To avoid this type of problem,
ask your supplier to send few samples without phosphating, so you can check the hardness on this parts.
Normally, Hardness is specified for the base material, not for the phosphating coating.

Kannan Boopathi
- Salem,Tamil Nadu, India
August 8, 2011

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August 12, 2011

In this case the end user requires 100% inspection of finished parts so any testing before plating or test sampling is not an option. If the answer is hardness should only vary a couple of points then there must be a heat treat issue as our testing procedure is being performed properly.
Does anyone else have any comments?
Thanks
Jim

Jim Gallo
- Mechanicsville Virginia