Phosphating
A phosphate layer is chemically generated by immersing the workpieces into a heated and acidic zinc, manganese, zinc-calcium or tri-cation phosphate solution. A chemical reaction occurs through the pickling attack of the metal surfaces with the substrate. This is followed by hydrogen-formation and a shift in pH value on the metal surface. Low solubility phosphates are formed, uniformly distributed across the metal surface as permanently anchored crystallites.
Properties of a phosphate coating:
- Light to dark grey manganese, zinc or zinc/calcium phosphate coating consisting of secondary and tertiary manganese, zinc or zinc/calcium phosphates.
- Tightly fixed on the base material.
- Fine to coarse crystalline appearance.
- Coating-forming layer (3–20 µm), has to be taken into account for fitting pieces.
- Corrosion protection oils and varnishes can be absorbed very well due to the presence of many capillaries in the coating, resulting in a very high corrosion protection.
- Phosphate coatings are electrically non-conductive, i. e. the insulation resistance is high.
- The phosphate coating can be applied as a corrosion protection or adhesion base for subsequent coating treatments, or varnishes or for improvement of sliding properties to reduce the sliding friction (non-cutting deformation).
- Damaged coatings will hardly be tunnelled by rust.
