(1) phenomenon
During the spraying process, the paint mist splashes or falls on the surface to be coated or the coating film (in the form of virtual mist), which affects the gloss and decorative , as shown in Figure 9_19. If it falls on the paint mist of different colors, it is called paint mist pollution. If the paint is scattered in a dusty form and reaches the surface to be coated, it is called dry spraying.
(2) Reason
① Improper adjustment of the Spray Gun, poor atomization, vibration of the Spray Gun, etc.
②The spraying operation is not correct. Such as the Spray Gun is too far away from the surface to be sprayed, not perpendicular to the surface to be coated, the Spray Gun moves too fast, the spraying pressure is too high and the air volume is too large, etc.
③The viscosity of the paint is too high or the thinner used evaporates too fast. (Related instrument: Viscosity Cup)
④The distance between the painted part and the one being sprayed is too close, or the spraying sequence is improper when spraying a large area.
⑤ The airflow in the spray booth is disordered, the wind speed is too low (less than 0.3m/1s), and the temperature is too high.
⑥ The paint mist scattered in the air in the spraying room cannot be eliminated.
⑦ Surfaces not to be painted are not covered.
(3) Preventive measures
①Adjust the Spray Gun to a good state.
②Use a high-quality diluent to thin it to the correct viscosity. In a dry and hot environment, you should add or use a slow-drying diluent. (Related instrument: viscometer)
③ master the use of good spraying technology.
④Arrange the spraying sequence reasonably, and try to avoid the pollution of the sprayed area and the area to be sprayed by the dispersion of paint mist.
⑤ Sufficient distance should be kept between the painted parts to prevent splashing. Taking the car body as an example, the spacing should not be less than 1.5m.
⑥The airflow in the painting room should have a certain direction (generally from top to bottom); the wind speed in the case of manual painting should be in the range of (0.35~0.5m/s).
⑦ Do a good job in the daily maintenance and cleaning of the spray booth.
⑧The surface that does not need to be painted should be covered, especially in the occasion of spraying different color paint and repairing spraying.
(4) Remedy
① Primer: Let it dry and then remove the rough surface with a full Grinder.
②Finish paint: The dry-sprayed coarse film of the final paint layer can be removed by sanding with fine sandpaper, and the gloss can be reproduced by polishing. If it is a single layer of silver powder paint, it needs to be polished and resprayed. (Related instrument: gloss meter)
