Controlling rinse water purity to prevent corrosion failure
Sound cleaning is the foundation for high performance and adhesion of powder coatings on parts. This article tells you why cleaning is so important in corrosion control, stressing rinse water quality in the prevention of coating failures in the field. The article explains why monitoring total dissolved solids (TDS) leads to quality rinsing and includes troubleshooting tactics to control TDS.
Powder coatings vary in inherent corrosion resistance based on binder type, filler content, and crosslink density. However, nothing does more to ensure corrosion performance than sound metal cleaning and conversion coating. Organic coatings act as a semi-permeable membrane, allowing moisture to migrate through the polymer film as a result of osmotic pressure. When mechanical adhesion of a powder coating to the substrate is impaired, moisture readily permeates the coating film and causes it to swell, thus creating a corrosion site and lifting the coating film away from the substrate. Coatings with high levels of inert extenders or low crosslink density will be more permeable and thus more susceptible to corrosion. As a side note, coatings heated above the glass-transition temperature (Tg) will be more permeable as the increased molecular motion will allow moisture to pass through the film more easily.