Electrostatic powder spraying is a highly efficient and environmentally friendly surface finishing process. In actual production, however, defects often appear due to improper pretreatment, unstable spraying parameters, equipment issues, or environmental conditions. The following are the most common problems and their systematic solutions.
1. Contamination in the coating
Causes:
Contamination may come from the curing oven, spray booth, conveyor chain, powder itself, pretreatment residue, or water quality.
Solutions:
Clean the inner walls of the curing oven regularly, especially the conveyor chain area and the gaps in air ducts.
Blow out the spray booth with compressed air before starting each day, then clean it with a damp cloth and vacuum.
Remove sludge from pretreatment tanks in time and control the concentration of the phosphating solution.
Use purified water for the final two rinsing stages and install an inlet filter.
Store powder properly in sealed containers to prevent moisture absorption and clumping.
2. Craters and pinholes
Causes:
Poor degreasing, incomplete rinsing, oil or water in compressed air, damp powder, or oil falling from hanging fixtures can all cause craters or pinholes.
Solutions:
Strengthen pretreatment by using alkaline chemical degreasing with emulsifiers to remove mineral oil, followed by deionized water in the final rinse.
Install an oil-water separator in the compressed air line and drain it regularly.
Store powder in a dry environment with humidity at or below 50% RH. If the powder absorbs moisture, it can be dried at low temperature, typically 50–60°C for 2–4 hours.
Clean conveyor chains regularly to prevent oil contamination from being blown onto the workpiece.
3. Orange peel / poor leveling
Causes:
Poor powder leveling, insufficient curing temperature or time, excessive spraying voltage, and coarse particles can all lead to orange peel.
Improvements:
Choose powder with better leveling properties and optimize the curing curve by slightly increasing temperature or extending curing time.
Control the electrostatic voltage in the range of 50–90 kV, depending on the powder type and the performance of the powder coating gun.
Keep the atomizing air pressure stable so the powder particle distribution remains uniform, with 10–90 μm particles accounting for at least 90%.
4. Poor adhesion
Root causes:
Incomplete pretreatment, residual oil or oxide film, poor phosphating quality, or insufficient curing can weaken adhesion.
Measures:
For steel parts, use a medium-temperature zinc-calcium phosphating solution, controlling the coating weight at 1.5–2 g/m².
Apply a surface conditioner before phosphating to refine the crystal structure.
Follow curing temperature and time requirements strictly; for example, epoxy powder may require 180–200°C for 15–25 minutes.
For thicker workpieces, increase curing temperature appropriately to ensure full crosslinking.
5. Low powder deposition rate / uneven spraying
Causes:
Insufficient voltage, poor grounding, uneven powder fluidization, excessive air pressure, or clogging in the spray gun may reduce efficiency.
Solutions:
Repair or replace the high voltage electrostatic sprayer generator to ensure stable output, ideally around 60 kV.
Check the grounding of the workpiece and remove insulating layers from hanging fixtures.
Replace the micro-porous plate in the powder supply hopper and adjust the air pressure so the powder remains in a fluidized "boiling" state.
Use PTFE parts inside the powder coating gun to reduce clogging.
Keep conveying air volume at about 3 L/s to avoid blowing powder away.
6. Uneven coating thickness
Causes:
Unstable line speed, uneven gun movement, electrostatic shielding, and powder clumping can all create thickness variation.
Countermeasures:
Keep the distance between the powder coating gun and the workpiece at 15–30 cm and move the gun at a constant speed.
For complex shapes, use a conductive primer or a fan-shaped gun pattern to improve coverage.
Dry or air out clumped powder before use, and limit the proportion of recycled powder to no more than 30%.
7. Particles or rough surface
Sources:
Dust, fibers, fixture debris, aluminum chips, accumulated powder inside equipment, and impurities in the powder can all affect surface quality.
Prevention:
Cover the workpiece with cotton cloth after pretreatment to prevent dust contamination.
Operators should wear synthetic fiber clothing and rubber gloves.
Clean the powder coating gun, powder delivery lines, and the inner walls of the curing oven regularly.
After aluminum extrusion, blow out all chips from internal cavities thoroughly. Replace adhesive labels at the ends with small clips whenever possible.
8. Color variation
Causes:
Uneven pigment dispersion in the powder, unstable curing temperature, and inconsistent film thickness may all cause color differences.
Control methods:
Use high-quality powder with consistent L, a, and b values.
Stabilize conveyor speed and oven temperature.
Ensure uniform spraying and avoid local overbuild or underbuild.
Key Prevention Tips
1. Give full attention to pretreatment
Pretreatment may account for about 25% of total cost, but it determines more than 80% of coating quality. It should never be simplified just to save money.
2. Maintain the equipment regularly
Inspect the high-voltage system, powder feeding unit, and compressed air purification equipment on a regular basis.
3. Control the spraying environment
Keep the powder coating workshop under positive pressure and clean conditions, with a temperature of 20–30°C and humidity at or below 60% RH.
4. Manage powder properly
Store powder in sealed containers, avoid high temperature and high humidity, and never use expired or clumped powder.
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For further information on specific process parameters or equipment selection, please contact Jiangsu Tianwang Solar Technology Co., Ltd via email: fgd@twgdmall.com
