The cleanliness of metal surface seriously affects the bonding force of spraying coating. The removal of residual or adsorbed water, oil and other foreign matter on the surface of workpiece is not clean, which often results in pinholes, nodules, peeling or poor bonding.

After phosphating treatment of iron and steel parts, chemical oxidation or anodization treatment of aluminium alloy parts, chemical oxidation treatment of magnesium alloy parts, etc., should be sprayed in no more than 24 hours in time. Iron and steel parts after sandblasting and shot blasting treatment must also be sprayed in six hours. This technological measure is proved to be a good way to improve the adhesion between coating layer and substrate and enhance its corrosion resistance.

The incomplete separation of oil and water in the compressed air used for spraying inevitably affects the quality of the coating and produces various defects due to the excessive water and oil in the compressed air. Therefore, the motor painting line insists on regularly cleaning and replacing the filters in the oil-water separation facilities to keep the compressed air clean, which is beneficial to improve the performance of the painting spray layer.

The effect of temperature and humidity on the quality of spray coating is very obvious. Attention should be paid to keeping the temperature in the spray painting construction site in the range of 10-30 C, and the relative humidity should not exceed 80%. The construction site must be kept clean, clean and orderly.

Excessive temperature, high relative humidity, whitening and orange peel appearance of the coating layer, while too low temperature, the paint layer is easy to flow, which has a negative impact on the quality of the coating on the metal surface.

Air spraying is commonly used in metal surface painting operation. Attention should be paid to keeping the distance between the spray gun and the sprayed surface in the range of 200-300 mm, and the compressed air pressure should be controlled in the range of 2-4 kg/c, so as to effectively guarantee the quality of spray painting.