The powder coating is adsorbed on the workpiece by corona discharge. The process is as follows: the powder coating is fed into the spray gun by the compressed air gas from the powder supply system, and the high voltage generated by the high-voltage electrostatic generator is added at the front end of the spray gun. Due to the corona discharge, dense charges are generated near it. When the powder is sprayed from the gun nozzle, charged coating particles are formed, which are attracted to the workpiece with opposite polarity by the electrostatic force, As the powder sprayed increases, the charge accumulates more. When it reaches a certain thickness, due to electrostatic repulsion, it will not continue to absorb, so that the whole workpiece can obtain a certain thickness of powder coating, and then the powder is melted, leveled and solidified through heat, that is, a hard film is formed on the surface of the workpiece.

Process flow of electrostatic spraying:

1. Pretreatment:

Purpose: Remove the oil stain, dust and rust on the surface of the workpiece, and generate a "phosphating layer" on the surface of the workpiece that is corrosion resistant and can increase the adhesion of the spraying coating.

Main process steps: large shot blasting machine is selected, and steel sand shot blasting is used for cleaning. Not only is the surface of the workpiece free of oil, rust and dust after treatment, but also a uniform and rough gray phosphating film that is not easy to rust is generated on the silver white shiny surface after shot blasting treatment, which can both prevent rust and increase the adhesion of the plastic spraying layer

2. Electrostatic spraying

Purpose: Spray the powder coating evenly on the surface of the workpiece. Special workpiece (including the position where electrostatic shielding is easy to occur) should be sprayed by high-performance electrostatic spraying machine.

Process steps:

Build a plastic spraying room in the plastic spraying workshop. It is required to use transparent daylighting boards on the roof and wall of the plastic spraying room to avoid absorption of powder. Four powder recovery machines are placed at the four corners of the plastic spraying room to recover excess powder and avoid powder floating. Then use the electrostatic adsorption principle to evenly spray a layer of powder coating on the surface of the workpiece;

The fallen powder is recovered through the recovery system and can be reused after sieving

3. High temperature curing

Purpose: Heat the powder coating on the surface of the workpiece to the specified temperature and hold it for a corresponding time to melt, level and solidify it, so as to obtain the desired surface effect of the workpiece.

Process steps: push the sprayed workpiece into the curing oven (electric oven), heat it to the preset temperature (generally 185 ℃), and keep it warm for a corresponding time (15 minutes); Open the furnace and take it out for cooling to get the finished product.

Plastic spraying is also known as electrostatic powder spraying. It uses an electrostatic generator to charge the plastic powder, adsorb it on the surface of the iron plate, and then bake it at 180-220 ℃ to make the powder melt and adhere to the metal surface. The paint film presents a flat or matte effect. Spray powder mainly includes acrylic powder, polyester powder, etc.

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