“We have sub-contracted the powder coated sheet metal panels for a commercial air conditioning unit that we produce. The panels are made of galvannealed material with a zinc-rich powder primer and a polyester top coat. This combination was chosen to meet salt spray test requirements per ASTM B117 for a minimum of 240 Hours.
Our supplier is experiencing approximately a 20% rejection rate due to visual defects. Our requirements are no blister or blemish in excess of 3mm. Or no more than 5 blemishes, less than 3mm, within 1 square inch. The part must be viewed with the unaided (eye) at 24″ in adequate lighting with 20/20 vision.
Is the problem we are experiencing more a function of the type of materials we are using? Is it more a function of the process controls of the company doing the powdercoating? Are our Quality requirements too stringent for the finish that can be attained using these materials?”
“You are doing way too much to work to obtain a 240 hour salt spray corrosion requirement. Galvanized steel, zinc rich primer, and powder top coat would be used for 2000 hours salt spray resistance. I’m afraid that in this case “more is not better”. Each process step requires stringent process controls to be done correctly. The more you do to your product the more you risk creating a reject. Statistically, all the possible problems are compounded on your product. You should consider, redesigning your process (simplification) to accommodate your corrosion requirement.”