Powder coating is a process by which a surface is sealed, using dry- or liquid-bedded powders that are baked in an oven until the powder formulation reaches its melting point and fuses into a smooth, moisture-proof film. Correctly formulated and applied, powder coatings are resistant to rust, abrasion, peeling and checking. Powder compositions vary, based on the purpose of the object being covered. For example, indoor appliances---like refrigerators and washing machines---receive a different kind and thickness of powder coating than outdoor items---like fence panels used in corrals and stock pens.
Testing Powder Coatings
The American Society for Testing and Materials has established procedures by which manufacturers of powder-coated goods can identify the durability and quality of their products. Powder-coated items undergo specifically-formulated ASTM tests that reflect how well they will perform in their intended applications.
ASTM B117--Testing for Corrosion Resistance in Salt Spray Environments
Marine hardware, dock parts and marine engineering equipment are all at risk of failure from undetected corrosion, creating safety hazards, as well as serviceability concerns. ASTM B117 tests items in a simulated weather cabinet, using warm temperatures and a five percent saline spray to detect resistance of powder-coated surfaces to infiltration and corrosion.
ASTM D2794--Testing Impact Resistance
ASTM set minimum standards for a powder-coated surface's ability to resist chipping or cracking. Using a standard tool called the Gardner Impact Tester, a small diameter object is fired at the surface, with impact force calibrated to 26 inch/pounds. Another standard test tool, 3M Y-9239 tape, is applied over the impact site and then removed. The coating passes the test if the tape fails to lift any coating fragments.
ASTM D522--Bend Testing
Powder coated panels undergo bend tests, where they are stressed over a 1/4-inch mandrel. 3M Y-9239 tape is applied to and removed from bend sites in panels, to test whether crazing or chipping caused loss of coating at the bend site.
ASTM D523--Gloss Testing
Coatings are tested for uniform surface shine, using a standard reflectivity testing tool, the Gardner 60-Degree Meter. Powder-coated panels have to test within five percent of preset requirements for a given powder-coat composition.
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