Manganese phosphate coating is the treatment of irons or steels with a dilute solution of phosphoric acid and selected proprietary chemicals which produces a crystalline, oil absorptive coating with excellent wear resistance.
During the continuous immersion process grain refiners are incorporated into the sequence prior to tansfer into the manganese phosphate solution. The grain refiners influence the deposition of small crystals and control the finish on a microscopic level. Coating weights can be up to 40g/m2 and the coatings are used to enable the break in of new parts such as pinions, gears, camshafts and bearings.
The crystalline structure on the component surface retains a large quantity of lubricant and rust inhibiting oil thereby reducing galling in moving parts. In addition when used for bearings the coatings enable a continuous film of lubricant which improves wear resistance.
Zinc Phosphate Coating
Zinc phosphate coatings are formed by the immersion of components into a proprietary zinc coating solution. The coating that forms is typically 10 - 30 g/m2. Principally the coating is used as a binder for oils, rust-preventative waxes and an undercoat for bonded lubricant coatings.
A common proprietary bonded lubricant used by Wallwork Newcastle Ltd is Molykote which imparts a permanent, dry and maintenance-tree lubricating film with a low coefficient of friction and corrosion inhibition.
Wallwork Newcastle Ltd operates a fully automatic phosphate coating line. The components are processed on racks and each stage of the operation is closely controlled by a PLC driven cycle enabling immersion times to be varied depending on depth of coating required. Quality control is maintained by regular process auditing of bath chemistries. In addition crystal size and density can be measured via coating weight tests and also by scanning electron microscopy.