Zinc Phosphating of steel components gives increased corrosion resistance (with dewatering oil), lubricity or as a substrate for further coating. It serves as a conversion coating where the components are immersed in a hot dilute solution of phosphoric acid and phosphate salts which chemically react with the surface, forming a layer of insoluble crystalline phosphates. For greater corrosion resistance, a specially formulated dewatering oil is applied after the phosphating process, it is widely used in the oil and gas industry where parts are subject to harsh environmental conditions giving months of corrosion resistance, and lower friction/anti galling properties when the components are finally used. Zinc phosphate also is also a very good substrate for paint or powder coatings due to its properties.
Components are cleaned and de-greased to remove any contamination. If required components can be shot blasted which etches the surface to give a very good phosphate finish.
The components are then lowered into the phosphate tank until a uniform phosphate coating is achieved, and then rinsed thoroughly with water.
Some components are oiled with a de-watering oil which further inhibits corrosion and others go on for further coatings.