Application

Spray Characteristics

Depending on the choice of nozzle, the powder coating spray pattern will be different.  However all powder coating spray clouds should be an even, soft stream of powder, free from surges and spitting.

Surging

The powder flow is non-continuous and uneven, surging or spitting during application.

  • Potential Cause

    Spray environment gun settings are not optimized.

  • Solution

    High humidity has a detrimental effect on application.  Adjust environmental conditions for best application.  Check hoses, pumps and guns for blockages. Make sure air supply is sufficient for good air volume.

  • Potential Cause

    The powder flow is not continuous

  • Solution

    Refer to the 'Fluidisation' and 'Supply Problems' pages.  Sustain sufficient powder levels.

  • Potential Cause

    Metallic Effects: spurting occurs when either metallic particles build up on gun nozzles.

  • Solution

    Gun nozzles should be regularly monitored and cleaned where necessary.  Higher than normal air pressures may be needed in the fluidised bed as metallics may have a higher gravity than solid colours.

Wrapping

Poor Wrapping.  With one sided gun positioning only minimal film thickness can be achieved on opposite side

  • Potential Cause

    Spray equipment settings are not optimal, in particular:

    • Powder delivery too high, causing poor charging;
    • Air flow is too high, causing the powder to be blown past the part;
    • Air flow is too flow, causing the powder to be pulled away by extraction system before reaching the part;
    • Gun voltage is too low.

  • Solution

    Reduce the powder delivery and review airflow.  If airflow is too high, consider increasing the distance from gun to part.

    Increase the kV at the gun tip.

  • Potential Cause

    Insufficient electrical earth

  • Solution

    Use clean hooks. Check contact areas to ensure there is no build-up of cured coating, grease or other insulating material that impedes ground continuity.  Test electrical earth quality, resistance should be below 1.0 megaohms and ideally below 0.5 megaohms.

  • Potential Cause

    Poor positioning of the parts

  • Solution

    Adjust hanging configuration

  • Potential Cause

    Too many 'fines' in the powder

  • Solution

    Increase the virgin powder to reclaim ratio.

Poor penetration

The powder will not penetrate into a box (a Faraday cage); this is particularly obvious at the corners.

  • Potential Cause

    Spray equipment settings are not optimal, in particular:

    • Powder delivery rate is too low;
    • Air velocity is too high;
    • Voltage is too high;
    • Poor spray pattern and gun placement.

  • Solution

    Adjust the spray gun settings.  Review the choice of gun nozzle, a flat pattern rather than a conical deflector can be useful for coating hard to reach zones of a part.

  • Potential Cause

    The part does not have an adequate electrical earth for powder penetration and film build.

  • Solution

    Check contact areas between parts and jigging hooks and ensure there is no build-up of cured powder coating, or any other insulating material.  Jigs should not be too thin and the earth connection to ground should be secure and tested.  Ideally resistance should be less than 0.5 megaohm, but should certainly be less than 1.0 megaohm.

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