Coverage – a coating will not perform if there is not complete coverage of all functional areas of a component. DECC ensures coverage two ways: visual inspection and a measurement of the coating’s thickness. Visually, the substrate must not be visible thru the coating. Thickness is measured using a Fischerscope or a beta backscatter depending on the substrate. The thickness must be at a minimum of what is required per the coating’s product data sheet.
Cure – we talked about the importance of cure and full film properties in a previous blog post. If a coating is not fully cured, it will not exhibit all of its intended performance characteristics. To check if a coating is properly cured, we will wipe the coated surface a designated number of times with a solvent, such as MEK. Once complete, there should be no transfer of the coating to the wipe.
Cross Hatch – we also talked about the need for a quality surface prep method in a previous post, which is essential for proper coating adhesion. If the coating doesn’t stick to the substrate, it will fail. To check for proper adhesion, we perform a cross hatch test. This entails basically cutting the coating in a pattern or grid per the applicable coating specification. Once all the cuts are made, a piece of tape is placed over the top of the cross hatch and then slowly peeled off. If the coating has been applied correctly, there should be little to no coating on the tape.
If we have done our job correctly, the coating should pass the above three tests. And if it does, it should display the performance characteristics for which it was designed. However, as we like to say, each application is different and each environment a component operates in is unique…the best way to verify performance is to test a part after it is coated.
The Importance of Fixture Design
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Common Surface Prep Types
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Full Film Properties & Cure
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