I. Air spraying
(1) atomization principle
Air spraying generally takes 0.3Mpa-0.6Mpa compressed air working pressure, high flow rate to the air nozzle of the gun, so that a local vacuum is formed around the nozzle, the paint is sucked into the vacuum space by the compressed air, the paint atomized into tiny droplets, coated on the surface of the coated parts to form a continuous coating film.
(2) features and Applications
The main features of air spraying are simple structure, convenient operation, easy color change, and the ability to adjust the size of the fan surface with the geometry of the painted workpiece, and good atomization effect. However, the paint mist of air spraying is easy to rebound and scatter, polluting the operating environment, and the utilization rate of paint is only 15%-30%. Air spraying paint and compressed air mixing contact, the air source must be installed dust, oil and water filtering device, clean compressed air, to ensure the quality of the coating film.
The working pressure of air spraying air source is low, and it is difficult to atomize high viscosity paint, and it is generally suitable for decorative low viscosity paint spraying.
In today's painting industry, the most used is air spray gun, especially for products with high coating film quality requirements, such as high-class cars, high-end furniture, etc., are used air spraying or air electrostatic spraying.
Classification of air spraying
1.According to the way of supplying material
1) air siphon spray gun
Air siphon spray gun is widely used in painting. The lower part of the gun with the paint cup, compressed air in the gun nozzle at high speed flow through, around the local vacuum, the paint cup paint into the nozzle and atomized into paint droplets.
The capacity of the paint cup is usually 600mL-1000mL, which is selected according to the amount of spraying, and the gun is connected to the compressed air for spraying. The gun nozzle should not be vertical up or down, so that the paint will not leak out from the ventilation hole of the paint cup.
2) gravity spray gun
Gravity spray gun is small workpiece and filler paint, it is attached to the upper part of the paint cup, by the weight of the paint down to the gun. According to the position of the paint cup relative to the axis of the gun, divided into central and side type. In spraying, the central type allows the gun to be tilted in a restricted position; the side type can be positioned differently while the paint cup remains vertical. Gravity guns generally have a small paint cup capacity of 400-600 mL. Gravity gun color change, cleaning is convenient, less material consumption, suitable for frequent color change of the spraying process and spraying fast curing two-component coatings.
3) pressure spray gun
The pressure type gun delivers the paint to the gun by pressure. The gun itself does not come with a paint cup, the gun is light weight and can be sprayed at any position and angle. Suitable for workpiece gap type, continuous spraying or coating line use, spraying efficiency, good quality coating film.
II. High pressure airless spraying
(1), atomization principle
High-pressure airless spraying is a kind of atomization of paint using compressed air as power, not directly with compressed air, it uses booster pump to pressurize the paint to 10Mpa-25Mpa, high-pressure paint through the nozzle of the small spray hole high-speed spray atomization dispersion into very fine droplets, while the atomized paint particles pushed to the surface of the coated workpiece. The paint is increased to very high pressure, and the sprayed paint does not carry compressed air.
(2), Features and Applications
High pressure airless spraying can use high viscosity paint, large area spraying rate up to 4m2/min-7m2/min, high production efficiency. Spraying of paint without compressed air mixing, paint mist rebound scattering phenomenon less than air spraying, reduce the consumption of paint, improve environmental pollution.
High-pressure airless spraying of paint volume and paint mist fineness is not soft enough, the coating thickness is not easy to control. Fine decorative coating film spraying is not as detailed as air spraying.
Generally suitable for single species of higher viscosity paint and simple shape, large surface area of the workpiece mass production. Widely used in shipbuilding, container, steel structure parts, building internal and external walls, large pipelines and other industries.