Phosphating

Phosphate coatings are predominately applied to ferrous metals. However, it is also used on Zinc and Aluminium for some specific applications. These coatings on its own are insufficiently protective for treated metal surfaces but excellent as pretreatment before painting, powder coating, impregnation with enamels, lacquers, oils and waxes. The coating is thin and adherent to the substrate metal whilst being porous and insulating. Consequently, the coating permits “keying” or mechanical interlocking of applied paint film whilst the electrical inertness of coating localize corrosion beneath adjacent unbroken painted areas of the base metal surface. Phosphate coatings may be produced by immersion, brush or spray, since surface conversion depends only on contact between substrate and phosphating solution. These coatings are also used in cold forming operations such as drawing, stamping and cold extraction operations.

 

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