Traditionally, coating equipment only has protective and decorative properties of coating materials, usually these properties are unidirectional. Therefore, the surface treatment of metal before coating must be through oil removal, rust removal, phosphating (oxidation) to ensure the basic performance of the product.
The quality of surface treatment before coating (also known as pretreatment process) is an important link that directly affects the service life and decoration effect of coating. The purpose of coating pretreatment is to remove oil, rust and other foreign matters on the surface of the substrate, provide a clean surface suitable for coating, and significantly improve the adhesion and corrosion resistance of the coating.
The methods of oil removal can be divided into physical mechanical method and physical chemical method. The former includes wipe method, combustion method and jet method. The main methods of degreasing before automobile coating are physical and chemical methods, including alkali degreasing, emulsion degreasing and solvent degreasing. Alkaline degreasing is mainly through saponification to remove oil. When the unsaponifiable mineral oil is removed, the surfactant can help emulsification and degreasing. This method is widely used, with good degreasing effect and economy. Emulsion degreasing method is a kind of mixture composed of one or several surfactants in organic solvent or weak three detergents. When Lou uses this kind of emulsion to dip or spray on the object to be cleaned, the oil will be micronized by solvent soaking, and the oil will be removed by surfactant emulsifying and dispersing the oil particles in the cleaning solution. There are two methods of solvent degreasing: impregnation and trichloroethylene cleaning. Impregnation is a method of immersing the cleaned matter in organic solvent and then stirring or manually washing to degrease it. The commonly used solvents are gasoline, xylene, acetone, etc. Trichloroethylene cleaning method is also called dry cleaning method. Trichloroethylene is usually heated, and trichloroethylene vapor is used to degrease the cleaned products.
Precautions for plastic paint spraying:
1. After spraying plastic paint, dust must be removed before the next operation.
2. Plastic paint mainly plays the role of covering, do not spray too thick, otherwise the paint will be too dark and too deep.
3. Mix evenly. The aluminum powder and other plastic particles in the plastic paint are easy to precipitate at the bottom of the paint tank, so the plastic paint needs to be thoroughly stirred before spraying than the general natural color paint.
4. The matching diluent and corresponding dilution ratio must be selected according to the instructions, and the viscometer shall be used correctly to master the required viscosity, so as to ensure that the paint color meets the requirements.
5. Use of spray gun. When spraying plastic paint, even film thickness is very important. The nozzle shall aim at the spraying surface at a vertical angle, and the distance between the two shall be kept between 5-20cm. The spray gun shall be moved in a straight line at a constant speed to avoid moving the spray gun in an arc-shaped way. 50% overlap area is required for each back and forth spraying, so that a fixed color can be obtained. When it is necessary to adjust the paint output of the spray gun, the trigger of the spray gun can be turned to the end, and the moving speed of the spray gun can be used to increase or reduce the thickness and dryness of the paint film.