Iron phosphate coatings have been in used more than 5 decades because they improve paint adhesion and reduce rust on metal. There are two types of iron phosphate coatings used by industry today.
Degreasing and Coating iron phosphate is done in two steps. Degreasing and Coating metal parts is done simultaneously in the first step, hence the name and then the parts are rinsed in the second step. Direct iron phosphating requires multiple steps degreasing, rinse, iron phosphate stage and often followed by DI water rinse.
Iron phosphate products are formulated with different formulations and work under different operating parameters. There are two types of iron phosphate catalysts, non-metal-accelerated and metal-accelerated. Non-metal-accelerated iron phosphate coatings produce higher coating weights, resulting in better paint adhesion and corrosion resistance. This type of coating usually has a matt-grey-to-brown colour whereas metal-accelerated iron phosphate has an iridescent-to-purple-to-blue colour.
Prior to painting steel parts, iron phosphate coating is applied by either spray or immersion. Metal corrosion prevention is very important to the general market place. It’s in everyone’s interest that a properly pretreated and painted metal item should last for many years without rusting. Iron phosphating is an important first step to achieve high quality paint field performance.