Phosphating is a chemical process which converts a metallic surface to a non metallic surface by chemically bonding a phosphate coating to the metal.
This gives the surface an excellent keying effect for subsequent coatings such as paint for decoration, (typically used in with Electrophoretic paints / E Coat) as a bonding agent for rubber seals, or with oils for corrosion protection
A major advantage is that the coating is relatively thin so no clearance problems will be encountered with threaded products.
Manganese phosphate is frequently used as an anti galling coating used on engine bolt screws, machined gears etc
Manganese Phosphating
Manganese phosphate coatings are the heaviest of all phosphate conversion coatings, with coating weights of 30 - 40g/m2.
They have a coarse, heavy crystalline structure which enables them to retain a larger quantity of lubricant and rust-inhibiting oil than any of the other phosphate coatings. This feature makes them useful for preventing galling of moving parts.
When applied to bearing components, the ability to maintain a continuous film of lubricant between the contacting surfaces results in improved wear resistance, as well as providing a corrosion resistant finish.
Zinc Phosphating
Heavy zinc phosphate coatings are crystalline, with coating weights ranging from 10 - 30g/m2. They are mainly used as binders for lubricants and rust-preventative waxes and oils, and can also be used as undercoat for Delta Seal, Xylan and other organic finishes.
Another important use of zinc phosphate coatings is to facilitate cold-forming operations such as extrusions, deep-drawing and wire and tube-drawing. This application of zinc phosphate coatings arises from their ability to absorb and hold lubricants such as stearates under severe conditions of heat and pressure, thereby eliminating scoring and galling, reducing tool wear, and permitting cold-forming operations which would be impossible with conventional lubricants.
