Streaking in powder coating: identifying and eliminating causes
Streaking is a common problem in powder coating that can impair the aesthetics and quality of the coated surface. This phenomenon manifests itself in visible lines or streaks on the surface, which are particularly noticeable with large-area or uniform colour applications. Below, we explain the most common causes and provide practical solutions based on GEMA recommendations.
1. Uneven powder application
Uneven powder application caused by incorrect spray gun guidance or insufficient overlap of the spray patterns can lead to streaking.
Solution: Ensure that the gun is guided evenly with sufficient overlap of the spray patterns. Training and regular checks of the application technique can help to minimise this problem.
2. Unsuitable powder quality
Variations in powder quality, such as different particle sizes or poor flowability, can lead to uneven powder flow and thus to streaking.
Solution: Use high-quality powder with consistent particle size and good flowability. Store the powder under suitable conditions to prevent moisture absorption.
3. Inadequate fluidisation
Insufficient fluidisation of the powder in the container can lead to uneven powder flow and streaking.
Solution: Ensure that the fluidisation pressure is set correctly and that the fluidisation plates are clean and in good working order. Regular maintenance of the powder container is essential.
4. Dirty or worn gun components
Contaminated or worn gun components, such as nozzles or electrodes, can impair powder flow and cause streaking.
Solution: Clean and check the gun components regularly. Replace worn parts to ensure an even powder flow.
5. Electrostatic charge
Uneven electrostatic charge on the powder can cause uneven attraction of the powder to the surface, resulting in streaks.
Solution: Check the high voltage settings and ensure that the workpieces are correctly earthed. If necessary, use the PCC mode (Precise Charge Control) on GEMA OptiStar control units for more precise control of the powder charge.
By observing these points and regularly maintaining your equipment, you can increase the efficiency of your powder coating processes and avoid quality problems.
