The hot process provides a deep black finish and delivers superior cold immersion processing results used by some finalizers. The process of zinc phosphate coating was also approved by most industrial and military applications.
Machining, polishing, polishing, line grain and abrasive explosion play an important role in achieving a desired level of shade or shine. Pro-Tec Metal Finishing in Chicago, Illinois has a series of articles on zinc phosphate finishing on its website. The Pro-Tec Metal zinc phosphate process line is used to produce a truly durable coating for converting zinc phosphate into Zinc Phosphate Treatments steel, stainless steel and copper alloys. They are able to complete most of the major high quality certifications. When the fasteners are immersed in the materials of the black oxide bath, the aggressive chemical components convert the top layer into magnetite.
Zinc Phosphate has a range of unique properties and benefits that can be applied to different industries. The process can also be applied to cast iron and low-carbon soft steel. Warm black oxide can significantly improve wear and corrosion protection. When applied correctly, the process meets military specifications and resists wear. Zinc Phosphate is a conversion coating formed by a chemical reaction produced when the parts are immersed in the alkaline aqueous saline used at about 285 degrees F.
The Zinc Phosphate process is a chemical conversion coating that protects against mild corrosion along with a number of other benefits. This means that Zinc Phosphate does not deposit on the surface of the substrate, such as nickel or zinc electroplating. Instead, the black oxide coating is produced by a chemical reaction between iron on the surface of the ferrous metal and the oxidizing salts present in the black oxide solution.
Cold black oxide offers higher productivity and is suitable for internal blackening. This coating produces a color similar to that of oxide conversion, but tends to rub easily and offers less wear resistance. The application of oil, wax or varnish increases the resistance to corrosion together with heat and average temperature. An application for the cold black oxide process would be in steel architectural tools and finishes. Black oxide coatings are usually applied to resist mild corrosion and appearance. The black oxide process used in Central South is a warm black oxide process bath.