1. Powder spraying process
When spraying powder coatings with high-voltage electrostatics, the same as solvent-based coatings, high-voltage static electricity should be applied between the electrostatic Spray Gun and the workpiece. The Spray Gun is connected to the negative electrode of the electrostatic field, and the workpiece is connected to the ground. The difference is that the powder coating is in Under the action of purified compressed air, the powder feeder enters the electrostatic powder Spray Gun through the powder delivery pipe. A metal ring or pole needle with a sharp edge at the front end is installed on the Spray Gun head as an electrode. When the electrode is connected to high-voltage static electricity, corona discharge will be generated at the tip of the electrode, and dense negative charges will be generated near the electrode. When the powder coating is sprayed from the head of the electrostatic powder Spray Gun, it will capture the charge and be negatively charged, and fly to the workpiece under the action of airflow and electric field and adsorb on its surface. During the powder spraying process, the paint powder is subjected to the action of gravity, air thrust and electrostatic field attraction, and under the action of air thrust and electrostatic field attraction, it overcomes its own gravity and is adsorbed to the surface of the workpiece.
2. Adsorption process
The adsorption process of powder coating on the workpiece surface can be roughly divided into three stages, as shown in Figure 6-1. The first stage [as shown in Figure 6-1(a)] The negatively charged paint powder flies along the electric force line in the electrostatic field to the workpiece as the positive electrode of the electrostatic field and is evenly adsorbed on its surface; the second stage [as shown in Figure 6-1 (b)] Since the electrostatic attraction of the workpiece as the positive electrode of the electrostatic field to the powder is greater than the electrostatic repulsion between the negatively charged powder, the powder will continue to be adsorbed to the surface of the workpiece and densely piled up to form a certain thickness. Coating; in the third stage [as shown in Figure 6-1(c)], as the thickness of the coating formed by accumulation increases, the amount of negative charges it carries also increases, and the electrostatic repulsion to the subsequent flying powder is also positive. Increase, when the attraction of the positive electrode of the workpiece to the flying powder is equal to the repelling force of the powder coating to the powder, the powder that continues to fly will no longer be absorbed by the workpiece but will scatter in other directions. After the adsorption process is completed, The coating thickness formed by powder coating is no longer increased.
3. Curing process
In order to make the powder coating loosely accumulated on the surface of the workpiece form a uniform and continuous coating film, it is usually cured by heating or a combination of infrared radiation and ultraviolet radiation (uV). Among them, the infrared radiation can make the coating powder melt and keep the molten state to complete the leveling of the coating film, while the ultraviolet radiation can make the coating film solidify. Sometimes a thermal curing process is used after ultraviolet radiation to further cure the coating film. The curing process of infrared-ultraviolet radiation (uv) is shown in Figure 6-2.
