GMNA GM9079P PDF

This standard provides three versions of a test for rapidly evaluating the integrity of zinc phosphate coatings on steel.

The test is commonly referred to as the "Ferrotest". It was initially developed by the Polymers Department of GM Research Laboratories for verification of the quality of newly phosphated automobile body sheet metal, while the car parts remain on the phosphate-to-paint production line. Successful use for this purpose led to adaptation of the test principles to verification of the quality of newly phosphated small parts (such as bolts, nuts and clips), as parts are dumped from the processing barrel. Control of quality at this point in the production cycle permits necessary corrections to be made in the phosphating system before large quantities of defective parts are produced. Another adaptation of the test has been found useful for verifying the quality of the phosphate portion of the phosphate and oil type finishes on small parts, where the recipient of the parts is located at some distance from the phosphating operation. (For further discussion of the Ferrotest, see the Journal of Paint Technology, 41, No. 531, pp. 259 to 265, 1969.)