Nondestructive Test for Adhesion

Question:

Is there a nondestructive test for adhesion of powder coating to a substrate? Will this test data provide actual numbers rather than pass/fail? What is the best and most accurate way to determine film thickness? L.B.

Answer:

I know of one company that makes a nondestructive adhesion test kit. This device uses an adhesive button that you apply to the coated surface. The kit then provides a micrometer-type tester that pulls on the button. If the coating is within tolerance, the adhesive on the test button will fail before the coating gives way. The micrometer will provide a numerical value of the test. The only problem is the test button stays on the part after testing. They say this is useful to prove that the coating adhesion test was performed successfully. However, the test button can be a problem on high appearance products (like refrigerators), where the buyer may object to a paper button on the front of the appliance.

As far as what film thickness tester is the most accurate, I would recommend the standard electronic testers that provide a digital numerical readout. Pretty much all of these devices have accuracy that can be traced back to the U.S. Bureau of Standards. Select the device that best fits your product, such as hand-held, desktop, etc. There is a complete list of suppliers at www.pfonline.com. Go to the Suppliers page and click on “Thickness Testing,” then “Testing Equipment, thickness of coating.” Suppliers can also be found in the 2000 Products Finishing Directory and Technology Guide under the same category.