FAQ

The main disadvantages of powder coatings include color fading, yellowing, particles, bubbles, orange peel, and poor coating efficiency. Let’s explore these six issues and find out how they occur and what specific solutions are available.

1. Color fading

1.1 Causes:

1.1.1 Uneven coating thickness;

1.1.2 Uneven temperature distribution in the curing oven;

1.1.3 Simultaneous production of workpieces with varying materials, thicknesses, shapes, and sizes;

1.1.4 Changing paint colors; and improper cleaning of the powder supply system, spray gun, powder chamber, and powder coating recovery system.

1.1.5 Color fading caused by uneven powder pigment distribution.

1.2 Solutions:

1.2.1. Ensure uniform coating thickness;

1.2.2. Ensure uniform oven temperature distribution;

1.2.3. Workpieces should be classified according to their material, thickness, shape, and size, and then different baking times should be set for baking and curing to minimize color variation in the film;

1.2.4. When changing paint, clean the parts and stagger the paint as much as possible to produce different colors.

1.2.5. Improve powder quality to ensure L, A, and B values ​​are consistent and positive and negative.

2. Yellowing

2.1 Causes:

2.1.1. The pigment in the powder coating itself is not heat-resistant or the resin material is prone to yellowing at high temperatures;

2.1.2. Poor workpiece pre-treatment quality, resulting in residue;

2.1.3. Curing time is too long or the curing temperature is too high, the local temperature is too high, or the paint is too close to the heating pipe;

2.1.4. Two different colors or properties of powder are mixed together.

2.2 Solutions:

2.2.1. Select high-quality powder coating.

2.2.2. Clean thoroughly after pre-treatment and remove debris before coating.

2.2.3. Select an appropriate curing temperature and time for this situation. Increase hot air circulation in the curing oven and ensure an appropriate distance between the workpiece and the heat source.

2.2.4. When changing powder, thoroughly clean the powder feed barrel, recovery system, powder feed hose, spray gun, spray chamber, and other equipment.

3. Particles

3.1 Causes:

3.1.1. Impurities in the curing oven.

3.1.2. Mainly dust, clothing fibers, equipment abrasive particles, and scale in the powder spraying system. Excessive powder additives, uneven pigment dispersion, or excessively high temperatures during powder preparation may cause some powder to crosslink and solidify.

3.1.3. Powder coating clumps due to moisture, resulting in poor atomization when sprayed. Before spraying the profile, there were particles and debris on the surface; too much recycled powder was added without screening; the coating was sprayed too thinly, and the substrate was difficult to cover with minor defects.

3.2 Solutions:

3.2.1. The solution is to thoroughly clean the interior of the curing oven with a damp cloth and a vacuum cleaner, focusing on the gaps between the hanging chains and the air ducts.

3.2.2. The solution is to use compressed air to purge the powder spraying system before starting work each day, and thoroughly clean the powder spraying equipment and the spray booth with a damp cloth and a vacuum cleaner.

3.2.3. Improve powder quality.

3.2.4. Improve warehouse conditions, avoid using expired plastic powder, and modify coating equipment.

3.2.5. Clean thoroughly before spraying to reduce burrs on the profile.

3.2.6. The recycled powder added is appropriate and should be screened.

3.2.7. Appropriately increase coating thickness.

4. Bubbles

4.1 Causes

1. Shrinkage caused by residual surfactants due to incomplete pre-treatment degreasing or post-degreasing washing.

2. Excessive oil and water content in the compressed air.

3. Excessive moisture content in the powder coating itself or substandard raw materials with excessive volatiles.

4. Oil stains from hanging chains that fall into the powder spray booth or drying oven can contaminate the powder coating, the booth, and the drying tunnel.

5. Shrinkage caused by mixing powders.

6. The spray gun is too close to the workpiece, causing electrical shock and perforation.

4.2 Solutions

4.2.1. Control the concentration in the degreasing tank to reduce the amount of oil on the cross-section and enhance the cleaning effect.

4.2.2. Add an oil-water separator to achieve dry compressed air.

4.2.3. Select high-quality powder coatings or improve powder storage and transportation conditions, add a dehumidifier, and ensure timely use of recycled powder.

4.2.4. Clean the chain promptly to prevent oil leaks.

4.2.5. Thoroughly clean the dust removal system when changing powder.

4.2.6. Use an appropriate distance (preferably 150-300mm) for powder spraying.

5. Severe Orange Peel

5.1 Causes:

5.1.1. The workpiece surface is too rough, making it difficult for the coating to flow smoothly.

5.1.2. The powder is too coarse or has poor flatness.

5.1.3. Electrostatic shielding, resulting in uneven coating thickness.

5.1.4. The curing temperature is too low, resulting in inadequate curing.

5.1.5 The coating is too thin or too thick. If it is too thin, it will appear wrinkled, while if it is too thick, it will appear mottled and have an orange peel appearance.

5.2 Solutions:

5.2.1. Use sandpaper or other methods to refine the surface and apply an appropriate thickness of coating.

5.2.2. Use high-quality powder coating.

5.2.3. Control the powder output and spraying time to ensure an appropriate thickness (60-90μm).

5.2.4. Improve the spray gun, minimizing the electrostatic shielding area or using a friction spray gun.

5.2.5. Increase the curing temperature and extend the leveling time. The melt leveling area should be 110-135 minutes, and the heating rate should be slow, with a holding time of 8-10 minutes.

6. Poor Powder Transfer Rate

6.1 Causes:

6.1.1 The voltage is set too low during spraying.

6.1.2 The workpiece is not properly grounded.

6.1.3 The high-voltage generator resistance is too low, resulting in excessive output current.

6.1.4 The spray pressure is too high.

6.1.5 The hook is insulated and has poor conductivity.

6.1.6 The spray gun is too far from the workpiece.

6.1.7 The performance of this powder is very poor.

6.2 Solutions:

6.2.1 Adjust the voltage to an appropriate value of 60-90 kV.

6.2.2 Install a ground wire to ensure good grounding.

6.2.3 Increase the resistance appropriately.

6.2.4 Reduce the powder supply pressure appropriately.

6.2.5 Clean the hook regularly to ensure good conductivity.

6.2.6 Adjust the spray gun distance appropriately.

6.2.7 Use high-quality powder coating.

7. Summary

The above explains the causes and solutions for powder coating shortcomings. We hope this helps. Standard International Group (HK) Limited was founded in 2003. Over the years, Standard Group has established long-term strategic cooperative relationships with many well-known industrial chemical manufacturers, such as Sherwin-Williams, LANXESS, Evonik, Covestro, Elementis, and others, ensuring that customers receive consistent, high-quality services. If you have any questions, please feel free to contact us!