Uneven Coating: Causes & Solutions

Uneven powder coating can lead to both visual and functional defects. Common causes include powder grain size, contamination, or incorrect workpiece temperatures.

🚩 Overview of Causes

• Too coarse particle distribution: Larger particles charge less effectively and result in inconsistent adhesion. GEMA recommends consulting the powder manufacturer.
• Contaminated system: Foreign powder, dirty lines, or uncleaned guns cause uneven application. Different powders should never be mixed.
• Incorrect output setting: Coating is too thick or too thin – visible through fluctuations in powder flow.
• Wet or overheated workpiece: Moist or hot substrates interfere with electrostatic attraction. Check drying and temperature levels.
• Build-up on nozzle: Powder residue (“teardrops”) disrupts uniform distribution. Regular maintenance is essential.

🛠️ Effective Solutions

• Check powder quality: Ensure uniform particle distribution. Contact the supplier if inconsistencies are found.
• Thorough cleaning: Clean feed lines, sieves, and guns regularly. Never mix different powder types.
• Adjust output settings: Set powder flow and storage for consistent buildup. Ideal: 4–5 Nm³/h air volume.
• Control temperature & humidity: Ensure dry and temperature-stabilized workpieces before coating.
• Nozzle maintenance: Regularly remove residue – especially if teardrop formation occurs.

✅ Process Benefits

• Uniform layer quality without visual defects
• Reduced material consumption with optimized output
• Stable and repeatable results with consistent process quality

🔗 More Technical Guidance

For deeper insights on uneven coating, output control, and cleaning, see the GEMA “Uneven Coating” section under Tips & Tricks.