1. Poor powder coating

For example, in summer or rainy weather, the air humidity is too high, causing the powder to become damp. Metal powder itself has poor electrical charge, and the charge is carried away. The electrostatic adsorption is too poor, which not only reduces the powder loading rate, but also causes powder to fall off and form lumps if the suspension chain vibrates. Therefore, air conditioning needs to be added to the powder room for dehumidification. In addition, if the powder after opening the box is not used up, it needs to be resealed to prevent moisture.

2. Powder acne

This kind of drawback can be found before curing after spraying, and the powder layer after spraying has acne like defects. After curing, it presents prominent powder acne with a large amount of metallic effect pigments inside. This situation is usually caused by some metal effect pigments not dispersing properly, such as poor powder atomization, powder moisture agglomeration, and accumulation of metal effect pigments on the gun head. Specific reasons need to be identified for elimination. When spraying metal powder, it is best to have a blowing device on the spray gun to remove the accumulation of metal effect pigments at the nozzle.

3. Bubbling

This phenomenon often occurs in areas with thick coating. The powder coating rate of metal powder is relatively low, and there is more powder falling. When spraying certain shapes of workpieces, the fallen powder will form powder accumulation in some parts of the workpiece, and the thickness can reach several times that of normal spraying. Excessive coating causes poor degassing and foaming. This can be solved by strictly controlling the powder output, improving the suspension method of the workpiece, and enhancing the degassing performance of the powder.

4. Dark spots

5. Aluminum powder corrosion

This situation often occurs after being left for a period of time, resulting in point like or patchy discoloration.

Aluminum powder, as a metallic effect pigment, has the advantages of bright white color and light weight, but its corrosion resistance is poor. Aluminum is a amphoteric metal with active chemical properties and is easily corroded by acid, alkali, and salt. Aluminum is particularly sensitive to corrosion in alkaline media. The aluminum powder used in powder coatings is generally coated to reduce the corrosion of external chemicals on it. For powder coatings, it is necessary to select aluminum powder with appropriate corrosion resistance level according to the requirements. The current metal pre-treatment oil removal process generally uses alkali, and some of the alkali solution in the front tank will be carried to the back tank, leaving some alkali residue on the metal workpiece after a long time. Alkali solution generally does not evaporate when heated, but instead condenses, which poses a risk of corrosion and discoloration of aluminum powder in the future. It is necessary to regularly check the pH value in the washing tank to prevent excessive alkalinity.