Phosphating Plant PT Line

The most commonly applied paint pretreatment for developing good bonding qualities between paint and the steel sheet is zinc phosphate. In addition to the excellent effect that a phosphate coating has on paint adhesion, it also aids to decrease, often dramatically, the tendency for paint disbondment during subsequent atmospheric exposure in a corrosive environment.

Phosphate coatings can be applied to the steel sheet while it is in coil form by either the steel manufacturer or a coil coater (manufacturer of prepainted sheet), or it can be applied to the cut sheet or fabricated article by the end-use manufacturer.

The usual phosphate process involves several steps, both if the coating is applied on a coil line or by the part manufacturer. If there are oils present on the surface of the steel, the first step is the removal of the oil by degreasing. This might involve cleaning with the use of an aqueous, alkaline cleaning solution or by other forms of degreasing with the use of solvents. Preferably, if the phosphating is done on a coil processing line, the next step involves the use of a Typically, the final rinse contains chromates for enhanced corrosion protection.