I am working on a project to find a corrosion resistant coating system for steel. The product is a refrigerator cabinet. The requirement for the product is that the steel cabinet of the refrigerator, which is made from sheet steel, needs to pass a 500-hour salt spray exposure test without any corrosion. Could you tell me if it is possible to get a coating system that will pass this test? How should I prepare the steel and what coating system should I use? D.G.
Not only is it possible, but it’s done commercially all the time. You must clean the steel to remove contaminants such as oily soils and corrosion products. Next, pretreat the cleaned steel surface with an iron phosphate. Although zinc phosphates provide better corrosion protection than iron phosphates, with the following organic coating system applied over an iron phosphate you will be able to pass the 500-hour salt spray requirement:
• After pretreatment apply an epoxy primer.
• The epoxy primer can be topcoated with either a thermosetting acrylic or polyurethane enamel. Both the acrylic and polyurethane enamels will provide the abrasion and mar resistance required for a refrigerator finish.