What is Orange Peel in Electrostatic Powder Coating? How to Solve?

What is Orange Peel in Electrostatic Powder Coating?  

Orange peel is a surface defect where the cured coating film has an uneven, wavy, or bumpy texture, similar to the skin of an orange. It is a common leveling defect in electrostatic powder coating application

Causes of Orange Peel and Their Solutions

Solving orange peel requires a systematic troubleshooting approach, focusing on four main areas: the powder, process parameters, equipment, and environment.

Cause 1: Issues with the Powder Coating Itself

1. Poor Powder Quality/Formulation: Low-quality raw materials (resins, hardeners, leveling agents) or an improper formulation can lead to high melt viscosity and poor leveling.

2. Powder is Damp or Deteriorated: Moisture absorption reduces powder fluidity and affects its electrostatic charge, leading to uneven application and poor leveling.

3. Unfavorable Particle Size Distribution: Powder that is too coarse or has too high proportion of fine particles can adversely affect l eveling.

Solutions: Select High-Quality Powder, Store Powder Properly, Control Particle Size:

Cause 2: Environment and Pre-treatment Issues

1. High Humidity in the Spray Environment: High humidity can cause powder to absorb moisture and lead to condensation on the workpiece.
   

2. Unclean Compressed Air: Oil or moisture in the compressed air can contaminate the powder, affecting its flow.

3. Poor Pre-treatment: Oily, rusty, or unevenly phosphated surfaces prevent proper powder adhesion and leveling.

4. Poor Grounding: Inadequate electrical grounding of the workpiece affects electrostatic deposition, causing uneven powder application.

Solutions:  1)Control Ambient Humidity in the spray area below 60-70%. 2)Purify and Dry Compressed Air, 3) Improve Pre-treatment to produce a clean, dry, and uniform surface. 4) Check and Ensire Good Grounding; 

Cause 3: Equipment & Incorrect Process Parameters

This is the most common and easily adjustable cause.

1. Film Thickness Too High: An excessively thick coating cannot flow out completely during melting. Trapped air or volatiles cannot escape easily, leading to orange peel.

2. Incorrect Curing Temperature/Time:

   1)Temperature Too High / Time Too Long: The powder gels and cures too quickly, not allowing enough time for leveling.

   2)Temperature Too Low / Time Too Short: The powder does not fully melt and flow, resulting in a consistently high viscosity.

3. Excessive Electrostatic Voltage: Too high a voltage intensifies the "Faraday cage effect," making it difficult for powder to reach recessed areas and causing a buildup on edges, leading to an uneven coating.

4. Clogged or Worn Spray Gun: Uneven powder delivery results in an inconsistent film thickness, which becomes visible as orange peel after leveling.

Solutions:

• Control Film Thickness: Maintain the coating thickness within the specified range (typically 60-100μm). Avoid applying too much in one pass; use several thin coats instead.

• Optimize the Curing Profile: Strictly follow the curing conditions (temperature and time) provided by the powder supplier. The key is to ensure the workpiece itself reaches the required temperature and holds it for the correct duration. 

• Adjust Electrostatic Parameters: Reduce the voltage and powder output to achieve a uniform and even deposition of powder on the workpiece surface.

• Perform Regular Gun Maintenance: Regularly clean the spray gun nozzle, injector sleeves. hose and connectors where powder conveying. Check for wear and tear to ensure consistent powder flow and charging.

As we can see, the powder coating equipment acts an essencial role to create a uniform coating film. COLO professional powder coating gun is ideal to control film thickness as it offers a great flexibility to precisely adjust all process parameters(voltage, current, powder output, dosing air) by digital, and it is easy to penetrate deep corners by overcoming faraday-cage effect.