There are many factors affecting electrostatic powder coating, such as equipment factors and operating factors. However, the main factors are powder conductivity, powder particle size, spray voltage, spray distance (between gun and workpiece), and supply pressure.
1. Powder Conductivity: The volume of powder particles must be moderate, the volume resistance is too large, the powder charge is not easy to release, the surface of the workpiece is too concentrated, and the repulsive force is too large to obtain a thick film. The volume resistance is too small, the charged powder is easy to release the charge, and the attached powder is easy to fall off. Therefore, the volume resistance of the powder is generally in the range of 1010 to 1014 Ω·cm.
2, powder particle size: particle size affects powder flow, coating, and the gun blockage and film thickness. The particle size is too small, the charge amount is small, the electrostatic attraction is small, the paint particles are easily collapsed, and the powder rate is low. The particle size is too large, self-important, the charge is large, the repulsive force between the paint particles is also large, and the powder rate is lowered.
3, spraying voltage: spraying voltage is proportional to electrostatic attraction, generally low voltage, with the increase of voltage, the powder charge increases, the amount of adhesion increases, but reaches the saturation value, will produce electrostatic repulsion, play the opposite role, due to the voltage too High, the powder will break down. The general voltage is controlled at 60-80KV.
4, spraying distance (gun and workpiece): the size of the spraying distance affects the electric field strength. Generally, the spraying distance is controlled at 200-300mm, and the powder deposition efficiency is the best. When the distance is too small, it is easy to generate sparks, which causes the powder to penetrate and affect the quality. When the distance is too large, the powder deposition efficiency is too low, and the recycled powder is increased, so that the powder is more likely to be contaminated.
5. Gas supply pressure: When spraying, try to keep the air pressure and powder conveying air volume at the minimum required amount. The gas supply pressure is large and the powder kinetic energy is increased, which may cause the powder to rebound on the surface of the workpiece, so that the powder deposition rate decreases. The gas supply pressure includes the powder supply pressure, the atomization pressure, and the fluidization pressure, which all affect the spraying efficiency and the coating quality. Spray gun classification: two corona spray guns and friction guns
The friction gun can better overcome the Faraday shielding effect, the powder coating effect is good, and the powdering rate is high. The corona gun does not overcome the Faraday shielding effect.