Chemical solution to prepare parts for an application of organic deposition, liquid or powder paint. Different phosphating ranges are available and a brief summary follows.
The Process
Phosphating is a chemical conversion process which consists of transforming the surface of certain metals (steel, cast iron, zinc, aluminium, titanium) in stable and insoluble metal phosphate. This layer is inked in the metal and gives it different characteristics. The properties of the phosphate coatings are improved by:
- The use of anti-corrosive paint
- The use of anti-corrosive varnish
- The use of oil, MoS2 lubricant or graphite resistant to storage corrosion
- The use of chromic or alkaline passivation
The Main Uses
⇒ Preparation for organic coatings
In this case, the types of phosphates used are generally microcrystalline based on zinc or zinc aluminium, the thicknesses being less than 5μ. Because of the fineness of the crystals, these coats are characterised by their excellent adhesion to the substrate: the temporary resistance to corrosion is enhanced by the use of chromic finish, which also improves paint adhesion and resistance to mechanical stress. This preparation can be carried out in jet coating tunnels in the following phases:
- Alkaline or acid degreasing with surfactant
- Rinsing
- Phosphating
- Rinsing
- Chromic or similar passivation
- Rinsing + Rinsing with demineralised water
This process is more commonly known as 7-stage coating.
This preparation is also carried out in a “Drop Section” wet tank and enables hollow bodies to be coated as well as the use of a more elaborated Tri-Cation Zinc Manganese or Nickel phosphating bath currently used after the cataphoresis operations.
⇒ Anticorrosion treatment by deep phosphating
The most common coats for this application are the zinc or zinc and iron phosphates with a mineral oil finish. The corrosion resistance may be 48 hours to 96 hours BS in thick coats (8/20μ) combined with chromic or similar finish.
⇒ Improved friction without lubrication by Manganese phosphating
This phosphating is applied to all steels whose content of additive element Ni+, Cr +, Mo + is less than 5% (not including the carbon). This process enables the coefficient of friction to be reduced, the running-in conditions to be improved, binding to be prevented and the operating noise to be attenuated.
⇒ Application of cold deformation
