Powder coating

Orange Peel Phenomenon:

Orange peel is a common surface defect after powder coating spraying, where the surface exhibits a bumpy, orange peel-like texture, giving an uneven appearance. The causes of orange peel include:

• Curing Issues: If the curing process is too fast or the curing temperature is too low, the fluidity of the melted coating will be restricted, preventing the surface from leveling uniformly.

• Spraying Operation Issues: Problems such as inconsistent powder flow, large distance between the spray gun and workpiece, or electrostatic shielding during spraying can lead to orange peel.

• Powder Defects: If the powder has poor dispersion, with uneven mixing of pigments, resins, and additives, or if the powder particles are too coarse, the melting and leveling process can be hindered, resulting in orange peel.

To learn more about minimizing defects during spraying, see Top 5 Common Powder Coating Defects and How to Avoid Them.

Exposed Substrate:

Exposed substrate occurs when the powder coating is too thin in certain areas, exposing the underlying material. This defect is usually caused by:

• Insufficient Spraying Time: If the spraying time is too short due to fast conveyor speeds, the powder cannot fully cover the surface, leading to exposed substrate.

• Low Powder Flow or Air Pressure: Inadequate powder flow or low air pressure can result in insufficient powder coverage.

• Low Electrostatic Voltage: A low voltage on the electrostatic generator may cause insufficient powder charge, resulting in uneven powder coverage and exposed areas.

For more on how voltage affects powder coating quality, see Powder Coating vs. Liquid Paint: Pros & Cons.

Particle Issues:

Particles on the surface of the powder coating are a common cause of rework during spraying. Particle-related issues usually stem from:

• Poor Surface Preparation: If the workpiece surface is not thoroughly cleaned and has dust, grease, or other particles, they will adhere to the coating.

• Environmental Contamination: Dust and other particles in the spraying environment can contaminate the workpiece surface, affecting coating quality.

• Recycled Powder Contamination: Recycled powder may contain particles, and if the powder separator does not properly filter the powder box, particles may be sprayed along with the powder.

Cratering Phenomenon:

Cratering refers to the formation of small holes in the coating surface, which is typically caused by oil contamination, air pollution, and improper spraying techniques:

• Oil Contamination: If the workpiece surface is contaminated with oil, either due to incomplete degreasing or contamination from gloves and transport boxes, it can cause cratering during spraying.

• Compressed Air Contamination: Oil contamination in compressed air or the evaporation of lubricants from the conveyor chain can lead to cratering.

For a deeper understanding of common defects in the powder coating process, refer to Powder Coating Pinhole Problems: Causes and Solutions.

Poor Mechanical Properties:

Powder coating with poor mechanical properties is characterized by weak adhesion, poor flexibility, and low impact resistance. The causes of these issues include:

• Improper Curing Conditions: Short curing times or low temperatures during curing can prevent the coating from fully curing, leading to poor mechanical performance.

• Poor Quality of Powder Coating: Low-quality resins, curing agents, and pigments can negatively affect the mechanical properties of the coating.

• Inadequate Surface Preparation: Contaminants such as oil or dust on the workpiece surface can weaken the adhesion and mechanical properties of the powder coating.

Loss of Gloss and Discoloration:

Loss of gloss and discoloration commonly occur during high-temperature curing, with the main reasons being:

• Excessive Curing Time or Temperature: If the curing time is too long or the temperature is too high, pigments that cannot withstand high temperatures may cause discoloration or yellowing of the powder coating.

• Inconsistent Gloss Levels: Differences in gloss levels between batches of powder coating or mixing different gloss levels of powders can lead to uneven gloss on the final product.

Pinhole Phenomenon:

Pinholes are small holes in the coating surface, usually caused by:

• High Electrostatic Voltage or Spray Gun Proximity: High electrostatic voltage or a spray gun positioned too close to the workpiece may result in the coating being penetrated, causing pinholes.

• Rough Phosphating Layers: Rough phosphating layers or incomplete coverage of rough surfaces can also lead to pinhole formation.