The coating method in which the paint passes through the shower head of the paint spraying machine to form a uniform paint curtain and pours on the surface of the object to be coated sent by the conveyor belt is called flow coating. Since the paint forms a curtain shape during shower coating, shower coating is also called "curtain coating", and the paint spraying machine is also called "curtain coating machine", and the shower head of the paint shower is also called "paint curtain head" and "Injection head".
Curve coating is widely used in the coating of wood products, especially suitable for the coating of hand-made furniture board parts (plane boards, plywood, medium density fiberboard, etc.).
The principle of flow coating is shown in Figure 22. The paint is sent to the shower head (1) by the Circulating Chiller (5), and what flows out is a uniform paint curtain (2), which is sprayed on the coated workpiece (3) sent by the conveyor belt. Then enter the drying tunnel to dry and form a film. The excess paint flows into the paint tank (4), and after being filtered and defoamed, it is sent to the shower head (1) by the circulation pump for recycling.
Whether the paint liquid can be made into a uniform paint curtain in the flow coating depends on the shower head. The shower head has various forms such as inclined plate type, bottom seam type, overflow type, and inclined plate overflow type. The paint spraying machine is composed of a shower head, a paint conveying pump through the volume, a filter defoaming volume, a constant temperature paint storage tank for heating and cooling the paint, and a transmission volume. According to its function, the painting machine can be divided into plane painting machine, square material painting machine and edge painting machine.
1) High paint efficiency and high paint utilization. The workpiece conveying speed of the bottom seam spraying machine is as high as 40~120 m/min, which is very suitable for mass coating of plates and flat parts. Its paint consumption can save 30%-40% compared with spraying.
2) The plant material in the leaching is recycled, and it is easy to entrain impurities and air. When forming a film, it becomes bubbles and particles, which impairs the decorative quality. Therefore, filtration and defoaming of coatings for flow coating are very important. To obtain a uniform coating, the first thing to do is to ensure the uniformity and continuity of the Circulating Chiller. Avoid the phenomenon that the shower head is not smooth, even clogged or the paint curtain is swayed by the wind. It is necessary to maintain the stability of the paint conveyed by the Circulating Chiller, the speed of the conveyor belt and the uniformity of the viscosity of the conveyed material, etc. The viscosity of the coating is mainly affected by the ambient temperature, and it is necessary to control the temperature change of the coating environment and limit the wind speed of the environment. In addition, the flow of paint needs to be controlled. If there is too much paint on the workpiece per unit time, it will not only cause the paint film to be too thick, but also cause the paint to overflow from the painted surface and flow on the edge to form a thick edge. The flow of the material removal is also restricted by the speed of the workpiece transmission.
3) Various coatings can be sprayed. The pigments in the flow coating should not be easy to sink and float, and have good leveling, defoaming and anti-oxidation properties. Oil-based enamel and synthetic resin paint can be applied by flow coating. It is also suitable for curtain coating for baking coatings with slow initial oxidation rate. It can also be used for high-viscosity coatings after taking measures such as workpiece preheating. If the front and rear shower heads and metering strip paint supply pipelines are designed in the shower coating machine, double-group paint can be shower coated.
4) The curtain coating method is not suitable for painting art paints, including wrinkle paints, hammer paints, etc., and the coating of paints formulated with more metallic pigments. It is not easy to obtain a thin and uniform coating by flow coating. During the flow coating, the solvent volatilizes a lot, resulting in an increase in the viscosity of the material. It needs to be adjusted by adding solvent at any time. Curve coating is not suitable for the coating of three-dimensional and complex-shaped workpieces, nor can it coat the vertical surface of the workpiece. It is also not suitable for coatings with many varieties and small batches, because it will lead to frequent paint changes and shower head cleaning. and paint pipelines.
