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Problems and solutions during powder coating spraying

(1) Low powder loading rate
Reasons: incorrect electrostatic high voltage, excessive powder conveying speed causing rebound, poor powder particle size distribution, and poor profile grounding.
Solution: Adjust the optimal value of the electrostatic voltage, adjust the powder supply air pressure and atomization air pressure appropriately, adjust the powder particle size distribution, and adjust the electrostatic system parameters.

(2) Insufficient spray penetration into cavities and gaps

Reasons :too fast powder supply speed causing powder rebound, incorrect type of nozzle used to produce electrostatic shielding, and poor profile grounding.

Solution: Adjust the electrostatic voltage to an appropriate level, reduce the powder supply air pressure so that the powder feeding speed is appropriate, adjust the nozzle, use a manual spray gun to replenish powder, measure the grounding resistance, and adjust the electrostatic system parameters.
(3) Poor fluidization in the powder bin
Reasons : the powder is too fine or moist, the fluidizing air pressure is insufficient, and the fluidizing air contains oil and water.
Solution: Use a screen to conduct particle size analysis, adjust the particle size distribution of the powder, cool or dry the powder, stir up the powder, increase the fluidization air pressure, and filter the compressed air.
(4) Uneven coating thickness
Reasons: uneven powder spraying speed, excessive powder delivery, incorrect distance between the spray gun and the profile, inconsistency between the speed of the suspension chain and the lifting speed of the spray gun, changes in electrostatic high voltage, moisture in the powder, and electrostatic shielding caused by the profile design structure.
Solution: Adjust the powder supply air pressure to achieve uniform spraying speed, adjust system parameters, cool or dry the powder, and stir up the powder.
(5) Cavities and pinholes appear in the coating
Reasons: residual grease or corrosion pits on the surface of the profile, powder supply gas and atomization gas containing oil, chain lubricating oil or thermal circulation air containing oil, excessive water content in the powder, and powder precipitation and agglomeration.
Solution: Check the pretreatment, degreasing must be complete, use filter paper to check the oil content of the compressed air, filter the compressed air, replace with essential oils that do not contain silicone oil, cool or dry, and stir to disperse the powder.

(6) The coating has bulges
The reasons include: there is dust on the surface of the profile, the powder contains unground metal components, too much powder accumulates at the nozzle of the spray gun, and the powder is too thick.
Solution: Blow clean the surface of the profile with compressed air, clean and replace the powder in time.
(7) There are bubbles in the coating
Reasons: the surface of the profile contains moisture, the compressed air contains moisture, and the coating is too thick.
Solution: Pre-treat the drying oven to dry the profile, filter the compressed air, and reduce the amount of powder supply.
(8) Flow marks appear in the coating
Reasons: preheating temperature rises too fast, curing temperature is too high, the coating is uneven before baking and curing, and the coating is too thick.
Solution: Adjust the curing process parameters, spray powder evenly, and reduce the coating film thickness.
(9) Poor leveling and orange peel phenomenon
Reasons: the curing preheating temperature rises too slowly, the powder particles are too small and unevenly distributed, and the coating is too thick or too thin.
Solution: Record the curing temperature change curve, adjust the curing process parameters, and use other particle size distribution
powder. Adjust the powder spraying process parameters.

(10) The coating has poor physical and chemical properties such as corrosion resistance, impact resistance and adhesion.
Reasons: the curing preheating temperature is too high or too low, the preheating time is too long or too short, the profile is not degreased cleanly, and there is residual grease. The conversion is not good, the profile pretreatment drying temperature is too high, the conversion film loses too much crystal water, and the powder quality is problematic.
Solution: Adjust the curing process parameters, adjust the pretreatment degreasing, conversion, and drying processes, and replace the powder.
(11)The coating turns yellow
Reasons: the curing and baking temperature is too high, the time interval between powder spraying and curing is too long, the profile is not degreased cleanly, and the powder itself turns yellow.
Solution: lower the curing oven temperature, cure as soon as possible after powder spraying, improve degreasing ability, and replace the powder.

In short, in electrostatic powder spraying production, each process parameter must be correctly grasped and adjusted according to the actual production situation. Quality problems that arise during production must be analyzed and resolved in a timely manner. By strengthening production process control, high-quality products can be obtained.