(1) Static voltage
The voltage level affects the charging rate and adhesion rate of the remaining material, and the electrostatic effect increases with the increase of the voltage, but above 100,000 volts, the coating adhesion rate no longer increases significantly with the increase of the voltage (see Figure 2_2_14). Therefore, the voltage is generally below 100,000 volts, 80,000 to 90,000 volts for fixed Spray Guns, and 60,000 volts for portable Spray Guns, that is, the voltage has been determined according to the type of Spray Gun.
(2) The distance between the Spray Gun and the workpiece
When the voltage is determined, the electric field strength is inversely proportional to the distance between the poles, and when the distance between the Spray Gun and the workpiece is too short, spark discharge will occur. The relationship between breakdown voltage and electrode distance is shown in Figure 2_2_15. If the distance is too far, the paint mist adhesion rate will be reduced. Therefore, the electrostatic spraying distance is generally between 250 and 350mm. Take a low value for small workpieces and a high value for large workpieces. Modern electrostatic Spray Guns have close-range anti-breakdown automatic safety protection facilities, and spark discharge will not be generated during operation.
(3) Arrangement of electrostatic Spray Gun
Contrasting cup type electrostatic Spray Gun, the spray pattern is circular, so multiple Spray Guns are used to spray to make the thickness of the coating film uniform. The distance height is determined by 1.5 times of the spray width, generally around 800mm.
(4) hanger
The hanger should avoid swinging back and forth, so as not to cause the spraying distance to be high or near or far away. This will not only cause uneven thickness of the coating film and affect the flatness, but also bring unsafety. To avoid affecting the adhesion rate of the paint mist on the workpiece, the hook should regularly remove the attached paint to ensure that the workpiece has a good grounding path to prevent electric shock when unloading the workpiece.
(5) Cup diameter
The diameter of the rotary cup is large, the paint mist is fine, the spray pattern is wide but the hollow is also large. Generally, according to the shape and width of the workpiece, Spray Guns with different caliber rotary cups are used in combination to make the film thickness uniform.
(6) Discharge volume
When the amount of spraying is large, some coating liquids cannot be charged at the muzzle, and the electrostatic effect cannot be effectively exerted. From this point of view, electrostatic spraying also needs to increase the total paint output by setting multiple Spray Guns, but in order to High production efficiency, the ejection volume should be under the premise of ensuring the electrostatic effect, the bigger the better.
(7) The characteristic requirements of the coating
The resistance of the coating is generally above 100Ma·cm. The coating with high resistance has a poor charging rate during electrostatic spraying. Therefore, the coating used for electrostatic spraying needs to use polar solvents such as dipropylcetone to improve the conductivity of the coating. Make the coating impedance reach 5~50Ma·cm, the coating with better conductivity, the charge disappears too fast, and the static voltage cannot go up. For example, water-based paint and metal 1 moonlight paint, the paint container needs to be well insulated from the ground before electrostatic spraying can be carried out.
The viscosity of the coating affects the atomization performance, generally around 20s. If you want to increase the solid content of the coating, you can heat the coating to 40°C. At this time, the viscosity of the coating at room temperature is allowed to be as high as 30~40s.
