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Powder Coating Defects and Causes – Troubleshooting Guide

detecting powder coating defects and causes in black fence

Recognise powder coating defects and causes to minimise damage

Coating failures happen. When they do, it is important to trace the cause of the problem as quickly as possible and to remedy it. Powder coating problems can be caused by issues with pre-treatment, powder supply, powder application, curing, or equipment. By looking at the issue you have, you can trace the problem back to a likely cause. In this guide we look at some of the most common powder coating defects and causes and how to solve these powder coating problems.

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The most common powder coating defects and causes – solving the problems

We have divided the top powder coating problems into powder application problems and coating properties problems. Below you will find a description of the problem, its possible causes, and how to solve it.

Powder coating application problems

Powder coating defects and causes related to application are the easier issues to solve. Very often problems arise here simply because equipment is on the wrong setting or has not been properly cleaned. Below are a few of the most common powder coating application problems. Different application methods will be more likely to experience different issues.

Powder Coating Application ProblemCausesSolutions
Inadequate/low film build and coverage

  1. Powder delivery rate is too high
  2. The part is not sufficiently grounded
  3. Voltage is too low at charging electrode
  4. Powder composition
  5. Incorrect spray method for powder

  1. Reduce powder delivery rate until particles charge sufficiently.
  2. Check ground contact areas and clear of any buildup, grease, or insulating material.
  3. Check if the high voltage source is actually on. If yes, check for powder build up and clean. If still not working, it may be a broken electrode.
  4. If the powder is too fine it may not take charge. Check particle size.
  5. Some powders work better for tribo charging than others. Check with manufacturer.

The powder feed is surging or spitting

  1. Insufficient air pressure or volume
  2. Hoses blocked, kinked, flattened or too long
  3. Incorrect feeder hopper fluidising

  1. Check air supply – there needs to be sufficient volume to maintain air pressure.
  2. Check and clean hoses, powder pumps and guns, check air supply for moisture, and coating area for humidity.
  3. Adjust fluidisation air pressure. Check porous fluidising membrane for clogging or defects.

Back ionisation – powder layers are repelled from the part

  1. Voltage too high
  2. Gun too close to the part
  3. Poor grounding
  4. Heavy powder build up

  1. Turn down the voltage
  2. Move the gun farther away from the part
  3. Check and clean ground contacts
  4. Check for gun proximity and whether the air setting is too high

The powder will not penetrate a Faraday cage (holes, grooves, channels, recesses etc)

  1. Powder delivery too low, poor ground, voltage too high, poor gun placement and spray pattern, powder delivery velocity too high

  1. Check your equipment and settings!

Powder coating properties problems

Issues with appearance and film formation can reveal issues with equipment, powders and techniques. Employing a host of quality control tests will help to analyse the powder coating problem.

Powder Coating DefectsCauses Solutions
The cured film has poor adhesion

  1. Unsatisfactory cleaning or pre-treatment
  2. Possible change to substrate
  3. Under curing

  1. Check cleaning conditions and chemical for cleaning, rinse, and pre-treatment stages
  2. Contact the substrate suppliers to check if any alterations have been made
  3. Modify cure conditions through increasing oven termperature and dwell time

Pinholes form in the surface of the coating

  1. Coating is contaminated by an incompatible powder
  2. Pinholes produced from outgassing
  3. Unsatisfactory rinse stages
  4. Vapours in the curing oven

  1. Make sure to clean equipment when changing from one powder to the next
  2. Determine metal porosity and adjust processing accordingly. Ensure no moisture is on part. Reduce film thickness. Note oven temperatures to check for excessive temperature issues.
  3. Check rinse stage conditions to ensure no chemical residues are drying on the surface of the substrate
  4. Vapours can be produced by masking products in an oven. Monitor ovens and maintain air exchange procedures

Gloss levels do not match the standard

  1. Under cured films will vary in their gloss levels
  2. Pinholes will reduce gloss

  1. Modify cure conditions through oven temperature and dwell time
  2. See ‘pinholes’, above

Too much orange peel

  1. Film thickness may be too thick or thin

  1. Increase or decrease film thickness accordingly

Poor corrosion resistance

  1. Unsatisfactory cleaning and/or pretreatment

  1. Check the cleaning, rinse, and pre-treatment chemicals and conditions

Low flexibility and impact resistance

  1. A change has been made to the substrate without a corresponding change in the process
  2. Film thickness may be too thick
  3. Under curing

  1. Contact suppliers to ensure no changes to the substrate have been made
  2. Reduce film thickness
  3. Modify cure conditions

The film has poor hardness

  1. Under curing

  1. Modify cure conditions with oven temperature and dwell time

Coating colour drifts from the standard

  1. Oven air is not exchanged enough to eliminate combustion by-products
  2. Oven temperature is too high
  3. Coating formulation may not have sufficient pigment opacity
  4. Film thickness may be too thick or thin

  1. Adjust the air exchange rate to reduce the concentration of by-products. With light colors the oven volume must be exchanged several times more often than with dark colors to minimize discoloration and haze.
  2. Reduce oven temperature. Know oven profile and set temperature and dwell to match cure schedule. Find hot spots in the oven. If an infrared oven is used vary the energy density and the line speed.
  3. Increase coating thickness to provide coverage.
  4. The pigment opacity dictates the required thickness for proper color. Adjust for proper coverage. This is most predominant in metallic finishes.