Apart from above protective coatings thermal blackened finish, Zinc phosphate coating and natural finish are also provided to the fasteners as per customer requirement with a thin layer of rust preventive oil.
Thermal blackening is done by quenching parts to be thermal blackened into water soluble oil mixture from suitable temperature and protect it with rust preventive oil.
Zinc phosphate coating is a chemical conversion coating given on steel surface to retain rust preventive oil and to provide good corrosion resistance. The coating will be about 10-20 gm per square meter and will look grey to black. It will provide a temporary protection of about 48 hours of salt spray life.