Powder Coating Troubleshooting Guide

Overcoming the Obstacles of the Electrostatic Process:

• Blast powder into the recesses
• Increase the powder flow rate
• Maximize the gun to part distance
• Use slotted tip to concentrate the spray

Trying to overcome the process leads to excess film thickness and powder usage and may cause a non-uniform build.

Using the Electrostatic Process:

• Finesse the powder into recesses
• Decrease powder gun flow rates
• Reduce the gun’s microamps (µA) to 20
• Maintain gun to part distance of ~ 8-10"
• Use slotted tip to concentrate spray
• Approach recess at an obtuse angle

These methods may result in a slower application time.

Spraying in the Faraday Cage:
Spraying at the recesses of a part at an obtuse angle can help to apply the coating properly.

• It reduces air turbulence
• Allows deeper penetration
• Minimizes early back ionization
• Utilizes more lines of force

A: Lines of Force
The corona generated charge field and lines of force tend to create Faraday cage difficulties.

B: Particle Space Charge
Lowering the voltage and allowing space charge created by powder cloud to develop near the recess will help with penetration.

Causes of Impact Fusion:

• Plugged or worn pump sleeves
• Scratched or burred venturis
• Crimped, worn, or cracked hoses
• Deflectors and gun nozzles
• Powder pathway diameter change
• Heat present on powder pathway
• Excessively high gun pressures
• Low glass transition temperature powder
• Powder particle size to fine
• Moisture in the air supply
  
  

Typically 2-3 Air Controls per Gun:

1. Powder Regulator (also called Flow or Main) controls the amount of powder being sprayed and the velocity and throw of the powder.
2. Atomizer Regulator (also called diffuser or Sub) controls the density and size of the powder cloud as well as insuring steady output.
3. Swirl Regulator (also called TIP) delivers air directly to the gun tip which can shape the cloud and prevent powder build up at the electrode and deflector.

Fluidization pressure on a feed hopper can also noticeably affect the amount of powder being sprayed.

Excessive gun pressures will have a dramatic NEGATIVE impact on spray quality and efficiency.

Too much powder/flow pressure can:

• Cause excessive wear of equipment
• Create impact fusion problems
• Cause gun spitting and puffing
• Increase film thickness uniformity
• Decrease first pass transfer efficiency
• Increase amount of reclaim or overspray
• Reduce electrostatic attraction:
  • Large particles can bounce off
  • Particles traveling too fast for wrap
  • Less time in corona field charge
  • More particles to share charge
  • Increased friction generates high static (positive) charge and reduces the effectiveness of the corona (negative) charge