A blank area in the powder coat, which extends all the way to the substrate (diameter up to 2mm).
Insufficient pre-treatment (eg oil and grease residues).
Test pre-treatment and ensure parts coming out of the system are clean. Run a white cloth over the surface, it should not be stained. If necessary contact pre-treatment supplier.
Rust on parts
Assure clean surface, apply recommended pre-treatment
Incompatibility with powder coatings from other manufacturers, particularly for acrylic coatings.
Cleaning of coating and application equipment, contact powder coating supplier
Surrounding air contaminated, especially from silicone oils. Surprisingly, deodorants can cause this problem too.
Balance air flows in plant, avoid cross drafts. Discuss with operators whether they've changed deodorants.
Work piece moist/wet
Increase drying time/temperature in dry-off oven
Liquid and powder paint in same plant
Definitely avoid – reconfigure plant
Base part was cleaned with highly volatile solvents such as MEK or Cellulose (Standard) Thinners.
Solvent rags quickly become saturated in oils that spread further surface oil rather than removing it. Replace rags more frequently or consider another method of cleaning.
Very small craters, usually not extending down to the surface.
Coating is contaminated by an incompatible powder
Clean application equipment when changing from one powder to the next.
Pinholes produced from out-gassing
Adjust dry off oven temperature to ensure no moisture is on the part. Check powder for oil or moisture introduced in reclaim, from the air supply or the virgin powder. A thick film may cause out-gassing. Reduce the film thickness to enable the gas to escape through the surface during cure. Polyurethane powder coatings may emit a blocking agent. Excessively high cure temperatures may make lower polymeric components within the coating volatile. Note oven temperatures if pinholes form.
Zinc substrate, including hot dip galvanising or zinc metal spray, releasing gases trapped during the galvanising process.
Zinc substrates are notorious. Use a powder coating specifically formulated for zinc substrates; use a zinc sealer primer coat; preheat zinc above curing cycle temperature; add a ‘degassing modifier’
Unsatisfactory rinse stages
Chemical from cleaning and pretreatment stages may be dried onto the surface, evaporating at higher cure temperatures. Assess conditions of rinse stages.
Pinholes produced from contaminating emissions in the curing oven.
Masking products are often plasticized to make the product soft and flexible. Plasticizers can emit volatiles that may reduce the coating’s hardness and produce pinholes. Monitor ovens and maintain appropriate air exchange.