How to pretreat test pieces before phosphating?

Pretreatment before phosphating

Generally, phosphating treatment requires that the surface of the workpiece should be a clean metal surface (except for two-in-one, three-in-one, and four-in-one) . The workpiece must be pre-treated to remove grease, rust, scale and surface adjustment before phosphating. In particular, phosphating for primer before painting also requires surface adjustment to make the metal surface have a certain degree of "activity" in order to obtain a uniform, fine, and dense phosphating film to meet the requirements of improving the adhesion and corrosion resistance of the paint film. . Therefore, phosphating pretreatment is the basis for obtaining high-quality phosphating film.

1 Degreasing

The purpose of degreasing is to remove grease and oil on the surface of the workpiece. Including mechanical method and chemical method. Mechanical methods mainly include: manual brushing, sand blasting, flame burning, etc. The main chemical methods are: solvent cleaning, acidic cleaning agent cleaning, strong alkali cleaning, and low alkaline cleaning agent cleaning. The following describes the chemical grease removal process.

1.1 Solvent cleaning

Solvent method is used to remove grease, usually using non-flammable halogenated hydrocarbon vapor method or emulsification method. The most common ones use trichloroethane, trichlorethylene, and perchlorethylene steam to remove grease. Steam degreasing has fast speed, high efficiency, clean and thorough degreasing, and is very effective in removing all kinds of oil and grease. Adding a certain amount of emulsion to chlorinated hydrocarbons has a good effect whether it is soaked or sprayed. Since chlorinated halogens have certain toxicity and high vaporization temperature, and due to the emergence of new water-based low-alkaline cleaning agents, solvent steam and emulsion degreasing methods are now rarely used.