The polar paint material is dissolved into a hydrosol, moved and deposited on the surface of the conductive metal workpiece under the action of the electric field force, and cured into a film after high temperature baking. According to the polarity of the sol, electrophoresis coating can be divided into anodic electrophoresis and cathodic electrophoresis. At present, anodic electrophoresis has been gradually replaced by cathodic electrophoresis, mainly because the anodic electrophoresis takes the workpiece as the anode, and the anodic dissolution in the initial stage of electrodeposition greatly affects Corrosion resistance of the film. The electrophoretic coating has the characteristics of high material utilization, good film thickness consistency, strong water resistance and salt spray resistance. It is especially suitable for the coating of anti-corrosion primers for parts with complex shapes, but because it must be high-baked, cross-linked and cured, Limiting the application on thick-walled workpieces.
Air spraying is a traditional spraying method for coating production lines. It relies on air to "blow" the paint into atomization to form paint mist. According to the air atomization situation of the spray gun, air spraying usually includes high-pressure air atomization spraying, medium-pressure high-flow air spraying, low-pressure high-flow air spraying, and high-pressure air atomization spraying. The atomization effect of high-pressure air atomization spraying is better than the other two atomization methods. The spraying construction of highly decorative workpieces is currently a relatively environmentally friendly air spraying method. Medium-pressure spraying has the characteristics of good paint mist atomization, and has been applied to the coating of some highly decorative workpieces.
The high-pressure airless spraying line originated from the coating of the shipbuilding industry. It has the advantages of high paint transfer efficiency, one-time film thickness, and high production efficiency. However, the atomization is not perfect, and it is not suitable for high decorative occasions. The bottom and middle coating construction for protective light decorative flat-shaped occasions. The principle of high-pressure airless spraying is different from that of air spraying. The atomization of paint does not rely on air, but on the pressure of the paint itself, so it is called high-pressure airless spraying. The principle of paint atomization is that the paint is added to a high pressure of 0.4-0.6Mpa. When the high-pressure paint reaches the nozzle, it passes through a very small hole, and the pressure is released instantly to achieve the purpose of atomizing the paint.
Air-assisted airless spraying in the coating production line is a new technology that combines the advantages of air and airless spraying. The application of this technology has been fully verified so far. Its principle is: use a plunger pump with a lower pressure ratio to pressurize the paint, the paint atomization is not perfect, and the two channels of low pressure air in the air cap are combined to assist the secondary atomization, so that the paint is atomized better. It also prevents the shortcomings of the first two methods.
The electrostatic liquid spraying of the coating production line is based on the atomization of the liquid paint to make the paint mist electrostatically, and the workpiece is grounded. The charged paint mist particles are mainly absorbed to the surface of the workpiece by the action of the electrostatic field, and the electrostatic paint mist particles fly in the air. It takes longer to fly in the air than ordinary air spraying, high-pressure spraying and other atomization methods. Therefore, the paint must have good electrical conductivity, and the solvent balance volatilization speed is slower than that of ordinary solvent-based coatings.