The structure of the commonly used Spray Gun is composed of three parts: the gun head, the adjusting part and the gun body. The gun head is composed of air cap, nozzle, needle valve, etc. (see Figure 1). Air caps, nozzles , and needle valves are kits, which cannot be combined at will and should be replaced as a whole.
Figure 1 Cutaway section of an air Spray Gun and a schematic cutaway view of a Spray Gun nozzle 1—airfoil or horn; 2—angular converging nozzle opening; 3—side orifice; 4—annular hole around the fluid nozzle
①Gun tip paint nozzles are easily worn by the sprayed paint, and are generally made of alloy. The larger the caliber of the nozzle, the more paint is sprayed. If the air pressure is not enough, the atomized particles will become thicker and the quality of the paint film will deteriorate. The diameter of commonly used nozzles is 0.8-1.6mm, which is suitable for nitro paint, synthetic resin paint, etc.
The diameter of 0.5-0.8mm is only suitable for low-viscosity paints such as colorants that are easy to atomize. Topcoat, 1.0~1.6mm, primer, intermediate paint and other paints with slightly thicker atomized particles and higher viscosity, 2.0~2.5mm. Coarse and viscous coatings such as plastisol and anti-sound coatings, 3.0~5.0mm. Use a round nozzle with a diameter of 0.5mm when spraying the repair paint . For spraying small areas, the nozzle diameter is 1-1.5 mm; for large areas, 2.5-3 mm; for various patterns and characters, 0.2-1.2 mm.
② The air cap of the adjustment device of the Spray Gun has a central hole, a side hole, and an auxiliary air hole. The central hole is used to atomize the paint, the side holes are used to change the shape of the paint mist pattern (see Figure 2), and the auxiliary air holes make the paint mist particles finer, the particle size distribution is more uniform , and the spray width is wider.
Figure 2 Function of the air hole on the side of the air cap
There are two types of air caps: less porous and porous (see Figure 3). The less-hole type has a center hole and a . The center hole and the paint nozzle are in the same circle, and the gap between them is 0.15~0.30mm. The compressed air sprayed through this gap forms a negative pressure area at the front end of the paint nozzle, so that the paint is sprayed and atomized, and forms a circular shape. The spray pattern, the compressed air sprayed from the corner holes on both sides will flatten the circular spray pattern, forming an elliptical spray pattern.
Figure 3 Air cap type 1—center hole; 2—auxiliary air hole; 3—side air hole
There are a number of symmetrically arranged auxiliary air holes around the corner holes of the porous air cap. The compressed air ejected from these holes balances the air volume and pressure ejected from the air assists in adjusting the size of the spray pattern and keeps it stable, and promotes paint spraying. The atomization is finer and evenly distributed , and it is not easy to accumulate paint around the paint nozzle. The number of air holes in the porous air cap is 5, 7, 9 , 11, 13, 15 and so on.
a. Air volume adjustment device The air pipeline in front of the Spray Gun is equipped with a pressure reducing valve to adjust the appropriate spraying air pressure. Rotate the air adjustment bolt at the lower part of the Spray Gun handle to adjust the sprayed air volume and pressure.
b. Adjusting device for the amount of paint spraying The paint spraying amount can be adjusted by rotating the bolt at the end of the gun needle. When the trigger is pulled , the gun needle moves backwards, the larger the moving distance, the more paint will be sprayed, and the smaller the moving distance, the less paint will be sprayed.
c. Spray pattern adjustment device, the air . Close the side air hole, the spray pattern will be circular; open the side air hole, the spray pattern will become oval. As the air volume in the side air holes increases, the spray pattern changes from round to oval to flat.
③ In addition to supporting the gun head and adjusting device, the gun body is also equipped with a trigger and various seals .
④The inner wall of the operating nozzle of the Spray Gun is needle-shaped, which forms a needle valve with the gun needle. When the trigger is pulled to move the needle back, the nozzle opens and the paint sprays out. When the nozzle and the gun needle are closed, they should be closely matched so that the paint does not leak. When using the Spray Gun, squeeze the trigger with your hand to open the channel of compressed air first, and then open the channel of the paint nozzle. The compressed air is piped to the spray head, and the paint flows out from the nozzle, blowing the paint onto the workpiece. When the trigger is released, the small hole of the paint nozzle is closed by the thimble, and the compressed air passage is also blocked. The Spray Gun trigger should be turned on when the Spray Gun is moving, and the Spray Gun trigger should also be turned off when the Spray Gun is moving, so as to avoid excessive paint accumulation and sagging on the surface of the workpiece.
After spraying, the excess recyclable paint should be poured back into the original paint bucket, and then the Spray Gun should be cleaned, and no residual paint in the Spray Gun is allowed. When cleaning the Spray Gun, pour the corresponding thinner of the paint into the paint can. Pull the trigger, the solvent is sprayed out from the nozzle of the Spray Gun, so that the paint pipeline can be cleaned. Then shut off the compressed air, remove the Spray Gun, and wipe it clean with solvent. Clean the air cap, nozzle, and gun body carefully with a brush with solvent . When the air hole is blocked, it needs to be dredged with a cork needle.
