In the field of modern industrial manufacturing, sheet metal coating is a crucial link. It can not only give sheet metal products a beautiful appearance, but also provide good protective performance and extend its service life. The following is a detailed introduction to the sheet metal coating process and related precautions.
Sheet metal coating is mainly divided into 6
1. Surface pretreatment
Degreasing: sheet metal parts in the processing and storage process, the surface is often contaminated with oil. Degreasing is the use of chemical degreasing agents or alkaline cleaning agents to remove these oil stains. Common degreasing methods include soaking method, spray method and ultrasonic degreasing method. Soaking method is to soak sheet metal parts in degreasing agent solution for a certain time, so that the oil is fully dissolved; The spray method is to clean the surface by spraying degreaser under high pressure; Ultrasonic degreasing enhances degreasing effect by using ultrasonic cavitation, and can effectively remove oil stains on complex sheet metal parts.
Rust removal: If there is rust on the surface of the sheet metal, remove the rust. Physical rust removal methods include manual grinding, mechanical grinding and sandblasting. Manual grinding is suitable for small areas of rust removal, using sandpaper or file and other tools; Mechanical sanding is more efficient, and an electric or pneumatic sander can be used. Sandblasting is the use of high-speed sand flow impact sheet metal surface, remove rust and oxide. Chemical rust removal is the use of rust remover and rust chemical reaction, to achieve the purpose of rust removal.
Phosphating or passivation: Phosphating is the formation of a phosphating film on the surface of the sheet metal, which can improve the adhesion of the coating. Passivation treatment is to form a dense oxide film on the surface of the metal, which plays a role in anti-corrosion.
2. Primer coating
Select primer: Select the appropriate primer according to the material of the sheet metal, the use environment, and the requirements of the subsequent coating. For example, for steel sheet metal parts, the commonly used primers are epoxy primer, alkyd primer, and so on. Epoxy primer has good adhesion and anti-corrosion properties. Alkyd primer price is relatively low, convenient construction.
Coating method: The main coating methods of the primer are brush coating, spray and dip coating. Brush coating is suitable for sheet metal parts with small area and complex shape, but the efficiency is low; Spraying is the most commonly used method, which can be divided into air spraying, airless spraying and electrostatic spraying. Air spraying atomizes the paint to the sheet metal surface through compressed air to obtain a uniform coating; Airless spraying efficiency is higher, suitable for large area coating; Electrostatic spraying uses the principle of electrostatic adsorption to make the paint mist uniformly attached to the sheet metal parts, which can reduce the paint mist flying and improve the utilization rate of the paint. Dip coating is to dip sheet metal parts into the primer, then remove and drain, suitable for batch parts with regular shapes.
3. Putty construction
Scraping putty: If the surface of the sheet metal has defects such as dents and holes, you need to scrape putty to fill them. Putty is generally composed of resin, filler, curing agent, etc. When scraping putty, pay attention to the thickness of putty, generally should not be too thick, so as not to affect the quality of the coating. Usually divided into multiple scraping, each scraping to wait for the putty dry curing before the next scraping.
Polish putty: After the putty is dry, it needs to be polished to make the surface smooth and smooth. Sanding can be done using sandpaper or a sander, from coarse sandpaper to fine sandpaper, until the putty surface is smooth and smooth, and the surrounding sheet metal surface transition is uniform.
4. Intermediate paint coating
The role of the intermediate paint: the intermediate paint mainly plays the role of increasing the thickness of the coating and improving the shielding performance of the coating. It can fill the tiny pores between the primer and the top paint and improve the overall quality of the coating.
The coating method is similar to the primer, and the appropriate coating method can be selected according to the actual situation.
5. Finish coating
Select the top coat: The main role of the top coat is to provide a beautiful appearance and good weather resistance, chemical resistance and other properties. Common topcoats are acrylic topcoats, polyurethane topcoats and so on. Acrylic paint has high gloss and good color retention. Polyurethane topcoats have excellent wear and chemical resistance.
Coating method: The same as the primer coating method, but when painting the top paint, pay special attention to environmental conditions, such as temperature, humidity, ventilation, etc. Generally, the ambient temperature is required to be 5-35 ° C and the relative humidity is not higher than 85% to ensure the coating quality of the top paint.
6. Drying and curing
Drying: The coated sheet metal needs to be dried to make the solvent in the paint volatilize and the resin solidify. Drying can use hot air drying, infrared drying and other ways. Hot air drying is to heat sheet metal parts through hot air circulation; Infrared drying is the use of infrared radiation heat, high heating efficiency, can quickly cure the paint.
Curing: For some special coatings, such as two-component coatings, a certain curing time and curing conditions are also required to ensure that the coating is fully cured to achieve the best performance.
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