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Paint and Coatings Industry Standards
D7378 Standard Practice for Measurement of Thickness of Applied Coating Powders to Predict Cured Thickness
Many physical and appearance properties of the finished coating are affected by the film thickness. Film thickness can affect the color, gloss, surface profile, adhesion, flexibility, impact resistance and hardness of the coating. The fit of pieces assembled after coating can be affected when film thickness is not within tolerance. Therefore coatings must be applied within certain minimum and maximum film thickness specifications to optimize their intended use.
All procedures involve taking measurements of applied coating powders in the pre-cured, pre-gelled state to help insure correct cured film thickness. This enables the application system to be set up and fine-tuned prior to the curing process. In turn, this will reduce the amount of scrap and over-spray. Accurate predictions help avoid stripping and re-coating which can cause problems with adhesion and coating integrity.
Measurements of cured powder coating thickness can be made using different methods depending upon the substrate. Non-destructive measurements over metal substrates can be made with magnetic and eddy current coating thickness gages (see Practice D7091). Non-destructive measurements over non-metal substrates can be made with ultrasonic coating thickness gages (see Test Method D6132). Destructive measurements over rigid substrates can be made with cross-sectioning instruments (see Practices D4138).
