According to the working principle of spray guns, they can be divided into three categories:
① At the same time, the coating gravity and front vacuum suction gravity are used;
② The suction type of front-end vacuum suction is only used;
③ The coating pump delivers the coating to the pressure type at the front end of the nozzle.
In addition, according to the use of different types of coating, it can also be divided into primer spray gun, finish spray gun and miniature spray gun.
According to the different ways of coating supply, coating nozzle size, air usage amount and spray pattern, they can be divided into three types: suction type, gravity feed spray gun and pressure type.
Suction spray gun: the principle is to use high-speed air flow and make the spray gun partially vacuum, thus generating suction to suck the coating from the pot to the spray nozzle for atomization and spraying, mainly for a large area of spraying, the advantage is that the coating atomization is better, which can meet the thickness and glossiness requirements of the coating film.
The coating tank of the suction type spray gun is located in the lower part of the spray gun. The coating nozzle generally protrudes forward more slightly compared with the central hole of the air cap. Compressed air is ejected from the central hole of the air cap, namely around the coating nozzle, forming a negative pressure at the front end of the coating nozzle,
The coating is sucked out of the coating tank and atomize. The spray rate of the spray gun is obviously affected by the viscosity and density of the coating, and is closely related to the diameter of the coating nozzle. The suction spray gun is suitable for general discontinuous spraying operation.
Gravity feed spray gun: use gravity to lead the coating from the upper pot to the lower nozzle, and then spray it with the wind. The previous design is for small area repair, and now it has developed to full-scale spraying. The advantage is that the coating can be saved in small area repair.
The coating tank of the gravity feed spray gun is located at the upper part of the spray gun. The coating is ejected from the coating nozzle by its own gravity and the negative pressure formed at the front end of the coating nozzle and mixed with air for atomization. The basic structure of the spray gun is the same as that of the suction spray gun, but under the same spraying conditions, the spraying amount of the coating is larger than that of the suction spray gun.
The gravity feed spray gun is used in the spraying operation with less coating consumption and frequent color change. When there is a large amount of coating, a high-level coating tank can be set up to connect the spray gun with the hose. In this case, the spraying amount of the coating can be adjusted by changing the height of the coating tank.
Pressure spray gun: the pressure spray gun supplies coating from another coating booster tank (or coating pump), which can supply coating to several spray guns at the same time by increasing the pressure of the booster tank. The coating nozzle of the spray gun is located in the same plane with the central hole of the air cap, or is slightly concave compared with the central hole of the air cap, so there is no need to form negative pressure at the front end of the coating nozzle. The pressure spray gun is suitable for the continuous spraying with a large amount of coating.
Internal mixing spray gun: there are two air supply systems in the body of the internal mixed spray gun, i.e. the compressed air system used for mixing and atomizing the coating and the compressed air system for pressurizing coating in the coating container. The coating supply mode is the pressure type. The center hole of the air cap is long olive shaped, so the spray pattern is elliptical. The spray gun has no side air holes and auxiliary air holes and cannot adjust the spray pattern arbitrarily. The spray pattern is determined by the shape of the center hole of the air cap. To change the width of the spray pattern, the air cap must be replaced. Therefore, the internal mixing spray gun has no spray pattern adjustment mechanism, and the other adjustment mechanism is similar to the external mixing type spray gun.