The process of spraying paint from the Spray Gun to forming a coating film includes three steps: paint atomization, paint mist flying to the workpiece, and paint film formation in the workpiece. Improper handling of each step will affect the effect of spraying. There are many subjective and objective factors that affect each step, so when problems arise, the reasons should be found from both subjective and objective aspects.
Only when the paint is atomized and dispersed into fine particles can a uniform and thin coating be formed, so the atomization effect is an important factor affecting the spraying effect. A satisfactory spray shape should be symmetrical, evenly distributed, with clear edges, and only a small amount of paint mist particles exist outside the edge of the spray shape.
The main factors affecting the effect of coating atmosphere are as follows.
(1) Viscosity of the coating The high viscosity indicates that the coating particles have a strong cohesive force and are not easy to separate from each other. Therefore, it is necessary to overcome the interaction force between the particles by adding diluent or heating to make it easier to atomize.
(2) The pressure of atomizing air
Air spraying relies on the negative pressure generated by the compressed air sprayed from the air cap to disperse the paint, so the pressure of the atomizing air is not enough, which is often an important reason why the air spraying fails to achieve a good atomization effect. On the premise that the coating achieves a satisfactory atomization effect, the lowest air atomization pressure should be selected. In order to make the air nozzle operate effectively, the compressed air source must provide sufficient air supply. The atomizing air pressure should be equal to the hydraulic pressure of the paint.
(3) Fan-shaped spray width
There is a side nozzle on the air cap to adjust the width of the spray pattern of the paint. If the width of the fan-shaped spray pattern formed is not enough, it means that the degree of dispersion of the paint is not enough. At this time, the degree of dispersion of the paint should be increased by adjusting the width of the spray pattern to obtain a better effect. Atomization effect.
(4) Flow rate of paint
If the spraying speed of the paint from the nozzle is too high, or the pressure of the paint is too high, the flow rate of the paint will be too large and it will not be atomized well. Therefore, it is necessary to adjust the paint flow by adjusting the caliber of the paint nozzle and the paint hydraulic pressure. The principle of adjusting the appropriate paint hydraulic pressure is to use the lowest hydraulic pressure as much as possible on the premise of meeting the paint flow requirements required by the Spray Gun. When using air spraying, the atomization air pressure and hydraulic pressure are kept equal, and when high-pressure airless spraying is used, the lowest hydraulic pressure for satisfactory atomization of the paint is used. The principle that should be followed when adjusting the air pressure and hydraulic pressure is: the pressure is appropriate when the spray pattern is adjusted, and the lowest pressure should be selected as far as possible under the condition that good atomization can be achieved.