The main content of car surface treatment before painting
Source: China coating network
Metal surface treatment before painting mainly includes oil removal, rust removal, phosphating (oxide).
Oil removal method is divided into two categories, physical and mechanical and physical and chemical methods, the former has a wipe method, burning method and spray method. Oil removal method is mainly used in automobile coating before physical and chemical methods, including alkali degreasing method, emulsion degreasing and solvent degreasing method. Alkali degreasing method mainly through saponification and remove oil and grease. When clearing cannot saponification of mineral oil, rely on the role of surface active agent, help emulsifying degreasing, this method is widely applied, the degreasing effect is better, and more economic. Emulsion degreasing method is in the organic solvent to join one or several kinds of surfactants, or add a mixture composed of weak three kind cleaner. Lou using this emulsion dipping or spraying in the cleaning, solvent saturated fat make fat particles, and surfactant oil emulsion particles dispersed in the cleaning fluid, so as to remove grease. Solvent degreasing method usually has two kinds: impregnation method and trichloroethylene cleaning method. Impregnation method is to be washed into organic solvent, classics agitate or artificial flush degreasing method. Commonly used solvents is gasoline, xylene, acetone, etc. Trichloroethylene cleaning method is also called dry cleaning method, heat the trichloroethylene, usually with cross-linked with steam, to be for degreasing cleaning.
Cleaning is to remove the metal surface generated oxide, hydroxide was removed. Cleaning method, usually according to the color of rust, generate and procedure to choose. Cleaning method can divide two categories, physical cleaning and chemical cleaning. Physical cleaning has two kinds of manual cleaning and mechanical cleaning. Pickling method commonly used chemical cleaning. Manual derusting usually play rust using shovel knife, scraper, hammer, steel wire brush and emery cloth such as tools, so the labor intensity, work efficiency is low, the quality is not stable, labor protection is poor, not suitable for application in automotive manufacturing. But in the automobile maintenance industry is still one of the most simple methods. Mechanical cleaning tools have hands of commonly used type electric wheel, electric brush brush wheel, pneumatic and pneumatic derusting with needle beam into the wheel, the current mechanical descaling with sandblasting derusting method and blasting derusting method. Chemical cleaning of commonly used is the pickling method, namely the metal immersed in acid solution, make the surface of metal oxide and hydroxide through chemical reaction, dissolved in acid solution, so as to remove the rust.
Phosphating is after some chemical treatment of metal surface, the metal surface was born in a layer of insoluble, phosphating method of double salt protective film. Phosphating on automobile industry, covering parts are widely used in bridge, panels, etc. As the surface treatment before, can increase the coating adhesion and corrosion resistance. Commonly used type phosphating film with zinc phosphate and phosphoric acid manganese type two kinds big. Zinc phosphate coating is compact and thin, smooth, has certain corrosion resistance, can absorb a certain amount of deformation, but the bath stability and maintenance more complex enough. While manganese phosphate type has the characteristics of the bath stability and convenient maintenance.
Metallic paint spraying the matters needing attention
(1) after spraying metallic paint, must remove dust before the next operation.
(2) metallic paint mainly cover effect, do not spray is too thick, or paint color will be too dark too deep.
(3) to stir evenly. Aluminum metal particles, such as easy to precipitation in metallic paint paint in the tank bottom, so the metallic paint than the general grey paint need more thoroughly mixing before spraying.
(4) must choose according to the paint manufacturers specification matching thinner, and the corresponding dilution ratio, and the correct use of viscosity meter, to master the required viscosity, meets the requirements to ensure that the paint color.
The correct use of gun
Figure 5 the correct use of spray gun
(5) the use of the gun. When spraying metallic paint, uniform film thickness is very important. Nozzle should be vertical spray Angle on the surface, the distance between them should be kept between 5 ~ 20 cm (figure 5), a straight line at a constant speed mobile spray gun, avoid moving in the form of arc spray gun. Each reciprocating spray need 50% overlap, such can get fixed color. Need to adjust the amount of the paint spray gun, spray gun trigger buttons can be exactly, spray gun moving speed to increase or reduce the thickness of paint film and drying.
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