What is Zinc Phosphate Coatings
Zinc phosphate coating is preffered in case of requirement of higher corrosion resistance than iron phosphate. It can be used as base for paintings (especially for thermosetting powder coating), before cold drawing / cold forming of steel and prior application of protective oil / lubrication.
This is often the method chosen when long life under corrosive conditions is required. Coating is also very good with zinc phosphate because the crystals form a porous surface which can soak up and mechanically trap the coating film. On the other hand zinc phosphate systems usually require more treatment stages, are more difficult to control and more expensive to install and operate. The zinc film is usually deposited at 200-500 milligrams per square foot. Total time required is about 4 minutes for a spray system.
For underpaint zinc phosphate coatings, coating weight varies between 2 – 6 g/m². There is no need of higher coatings weights. Coating weight of zinc phosphate layer before cold drawing / cold deformation operations of steel must be higher relatively, it varies in the range of 5 – 15 g/m². For the coating of iron / steel parts to be treated with oil or wax, coating weight has the maximum level between 15 – 35 g/m².