Issue link: https://www.e-digitaleditions.com/i/1063364
24 POWDER COATING, December 2018 POWDER COATINGS TROUBLESHOOTING GUIDE Troubleshooting the powder-coated finish Problem: Color deviations Cause Solution Film thickness varies greatly Assure constant film thickness Differing substrates and substrate colors Use substrates of same type for (steel, aluminum, brass, glass) comparisons Differing surfaces and reflections (polished, blasted, chromated) Use surfaces of same type for comparisons Film thickness too thin (poor coverage) Apply higher film thickness (same as samples) Color deviations due to curing technique or Use suitable powder coatings control oven atmosphere (for example, direct-fired gas oven; use outside air supply for burner oven, infrared oven); use of room air for burner Overcuring of powder coating (especially with organic pigments) Observe curing parameters of powder manufacturer Differing curing parameters with same parts Observe powder manufacturer's curing parameters Differing curing parameters with greatly varying Observe curing parameters of powder manufacturers parts (different wall thickness) and adjust to wall thickness Several powder manufacturers-suppliers Use powder coatings from the same manufacturer or check compatibility Varying film thickness with overcoating Assure even film thickness Bleeding of first coat with overcoating Check suitability of first coat when overcoating Uneven pretreatment of parts Assure more even pretreatment of parts Metamerism, color deviations with differing Judge workpieces in daylight, not direct sunlight; light sources use daylight cabinet Rough texture too pronounced Assure appropriate film thickness; use suitable powder coating Problem: Cloud formation Cause Solution Gun distance from part too great or small Test distance Uneven powder transport Introduce sufficient virgin powder; test for deviations in air pressure Manual touch-up Precoat if possible Uneven charging Test application Uneven grounding of parts Test grounding Strongly varying film thickness (especially with matte finishes) Optimize film thickness by adjusting air pressure Separation of matte finish powders in reclaim Assure consistent powder quality; adhere to the system; uneven parts of virgin and reclaim powder recommended percentage of virgin and reclaim powder Problem: Insufficient coverage Cause Solution Film thickness too low Assure appropriate minimum film thickness, especially with critical colors (for example, red, orange, yellow) Film thickness varies greatly from part to part Optimize system parameters; lower powder output Differing materials and material colors (steel, aluminum, brass, glass) Use same materials for comparison Differing surfaces and reflections (polished, blasted, chromated) Use same surfaces for comparison Mechanical treatment shows through (for example, polishing) Assure minimum film thickness is reached Source: Published with the kind permission of TIGER Drylac USA, Ontario, Calif.