Metal finishing Q&As since 1989

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Chemical Spot Check for Fastener Surface Coating Determination

I am a test engineer at a US Truck OEM. I have had the opportunity to run some torque-tension testing, recently, the results of which did not correlate with historical data collected for the same nut/bolt combination. As a check, our fastener engineer sent samples of the same nut/bolt out to be tested for confirmation. The independent testing matched the questionable results. Our fastener engineer has requested that we check the tested samples to verify that the finish conforms to specifications. Can anyone help point me in the direction of methods that can be used to check for Zinc and Cadmium surface coatings (i.e. some sort of chemical spot check).

David Fernandes
- Allentown, Pennsylvania, USA
2003

I don't think a chemical spot check is what your fastener engineer had in mind. Large OEMs have requirements for coating type (zinc, cadmium), subsequent layers (chromate coating, sealers, lubricants, etc.), coefficient of friction (min and max), etc. All of these need to be verified in order to perform a thorough analysis of root cause. Your fastener vendor should be capable of performing these tests, as well as a number of A2LA certified independent labs.

Toby Padfield
- Michigan
2003