[China Aluminum Network] First, the shrink hole
Defect features: surface similar to pores, pinholes, crater defects.
Powder coating reasons and preventive measures: 1, leveling agent, defoamer dosage is not enough. 2, leveling agent, defoamer mixing uneven. 3. Contamination between powder coatings with poor compatibility during the manufacturing process. 4. In the manufacturing process, compressed air contains oil and water.
Spraying process causes and corresponding preventive measures: 1, degreasing is not clean. 2, the workpiece surface is not smooth. 3. Insufficient drying after surface treatment. 4. When the powder type is changed, the cleaning is not complete. 5, spraying with compressed air oil containing water or chain off the oil pollution. 6, powder moisture or shop air tide.
Second, the material
Defect feature: particle on the surface of the coating
Powder coating causes and prevention measures: 1, raw material quality is not good, the resin contains gel particles. 2. Pigments, fillers or additives contain mechanical impurities. 3. The self-cleaning effect of the extruder is not good, and some of the gelled particles that are not melted are brought into the extruder. 4, dust and other mechanical impurities in the environment into the powder coating.
Spraying process reasons and the corresponding preventive measures: 1, the workpiece surface burr, or rough surface, there are micro pits. 2. Impurities such as chromium residue in the surface treatment solution still adhere to the surface of the workpiece. 3. The surrounding environment of the spray booth is not clean, some dust and particles in the air are carried into the powder coating or spray booth, or charged impurities are adsorbed on the workpiece due to electrostatic induction. 4. The coating is too thin to hide the tiny non-melting particles on the coating. 5. Recycled paint is too coarse without mesh or screen. 6. The particles of the solidified powder coating on the conveyor chain hanger drop into the coating.
Third, the film thickness is too bad
Defect feature: film thickness of the same workpiece exceeds the scope of the contract.
Spraying process reasons and the corresponding preventive measures: 1, the number of air spray guns arranged in the way. 2, gun powder and air pressure. 3, the operating speed of the conveyor chain. 4, the suspension and arrangement of the workpiece. 5. The proportion of recycled powder is improper or mixed.
Fourth, not on the powder
Defect feature: The ratio of the amount of powder attached to the surface of the workpiece to the amount of powder sprayed is less than 60%.
Reasons for powder coating and preventive measures: 1. For the corona discharge system, we should choose the type of filler with good electrostatic properties, or add special additives such as electroactive agent to improve the static performance of the coating; 2. For frictional charge The system should be added with frictional charge aids in the formula; 3, high mass fraction of pigments and fillers, leading to high density, coarse particles, so that gravity is greater than the electrostatic adsorption force; 4, or the particle size is too small, less charged, electrostatic adsorption is small .
Spraying process reasons and the corresponding preventive measures: 1, corona spray gun voltage is too low or too high; workpiece resistance is too large (poor grounding or racks are not cleaned); 2, excessive spraying amount; 3, air pressure is too large.
V. Loss of light yellowing
Defect feature: 60° gloss lower limit exceeded
Powder coating reasons and preventive measures: 1, the interference between different resin types of powder coatings. 2. Powder coatings formulated with two different reactive resins also tend to interfere with each other.
Spray process reasons and the corresponding preventive measures: 1, dusting system cleaning is not complete. 2, the curing temperature is too high, the time is too long, exceeding the heat-resistant temperature of the paint.
Sixth, color difference
Defect feature: The color difference between the coating and the standard swatch is out of specification.
Reasons for powder coating and preventive measures: The heat resistance of the raw materials selected in formula design, such as pigments, matting curing agents, etc., is not satisfactory. There is a gap between the bake curing of the coating plant and the bake curing conditions when the powder manufacturing plant is toning. A certain gap.
Spraying process reasons and corresponding preventive measures: 1, uneven film thickness. 2, furnace temperature is uneven. 3. When workpieces with a large difference in thickness are hung in the same solidification furnace, the thickness of the workpiece material is thicker than that of the thin ones, resulting in a color difference. 4, dusting system cleaning is not clean.
Seventh, the physical performance is not qualified
Powder coating causes and prevention measures: In the formula design, the matching of the resin and the curing agent is unreasonable, for example, the reactivity of the resin is selected or the type and amount of the curing agent are unreasonably selected, and the mass fraction or volume fraction of the filler is too large.
Spraying process reasons and corresponding preventive measures: 1, did not meet the coating required curing temperature. 2, can not reach the required curing time of the paint. 3, the workpiece surface treatment is not good. 4, the film thickness is too thick. 5, the test temperature is too low. 6, curing temperature is too high, baking time is too long.
Eight, chemical resistance failed
Reasons for powder coating and preventive measures: In the formula design, the matching of the resin and the curing agent system, the chemical stability of the pigment and the filler, and the mass fraction factor in the formulation are not suitable.
Spraying process reasons and corresponding preventive measures: 1, the surface treatment quality is not good. 2, curing is not complete. 3, film thickness is not uniform.
Nine, poor hiding power
Powder Coating Causes and Preventive Measures: The paint formulation has insufficient amount of pigment to cover, so that the coating film does not have enough hiding power.
Spraying process causes and corresponding preventive measures: The coating thickness is too thin.
(Note: 1, physical properties refer to the indentation hardness, impact resistance, adhesion and cupping test values. 2, chemical resistance refers to resistance to hydrochloric acid, solvent resistance, mortar resistance, salt spray corrosion resistance, heat and humidity Sex, boiling water resistance and artificial accelerated weatherability.)
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