Raised Lumps

Potential Cause

Clogging of the powder feed hoses, caused by agglomerates building up in spray equipment.  These are periodically freed by delivery air.

Solution

Change hose diameter, shorten hose.  Optimise the air pressure settings.  Check in-line filters and moisture traps

Potential Cause

Electrical earth.  Powder builds up on the gun tip and periodically spurts onto the coating.  This may be particularly noticeable in dry-blended metallic effect coatings. 

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.

Potential Cause

Powder falls off booth ceiling onto work below

Solution

Adjust/increase frequency of booth cleaning intervals

Potential Cause

Powder falls off workpiece onto work below

Solution

Test electrical earth, check diameter of hoses.

Potential Cause

Powder moist

Solution

Use dry powder, check air filter and moisture traps in compressed air system

Potential Cause

Powder agglomerating in the box.

Solution

Agglomeration can occur under inappropriate storage conditions.  If possible, manually break up the powder coating lumps.

Potential Cause

Spray gun settings.  A defective gun, or certain gun types may cause a rash of lumps caused by build-up in the gun.

Solution

Often, increasing kV to the gun tip can correct this.

Potential Cause

Worn venturi or pump.

Solution

Replace worn parts

Potential Cause

Powder too fine

Solution

Decrease amount of reclaim to hopper.  Optimise virgin powder plus reclaim ratio.  Contact HMG.

Potential Cause

Film thickness of the coating is below the recommended DFT.

Solution

Ensure DFT is above the recommended minimum.

Potential Cause

Single- and multi-headed inclusions caused by contamination from the reclaim system:

• Compromised reclaim system sieve;
• Dirt of grit being collected in the spray booth from jigs, flight bars and conveyor system;

Solution

Check the recovery and reclaim system, particularly ensuring the sieve is in place and not ripped.

Potential Cause

Multi-headed inclusions which under the microscope are revealed as fibres.

Solution

The source of fibre contamination is often clothing or a poor choice of cleaning cloth.  Operators in the spray area should wear suitable protective clothing and gloves.  A lint-free cloth is preferable.

Potential Cause

Single- and multi-headed inclusions caused by air movement in the plant.

Solution

The spray booth extraction system will drag contaminants from the local environment into the booth.  Restrict the air movement in the spray area, ensuring that outer doors are closed to prevent dirt and grit being drawn onto the work or reclaim system.

Potential Cause

Deposits of dust and powder on cured film, often these can be felt on the surface as slightly raised bumps.

Solution

Ensure cooling zone is dust free and is protected from cross draughts.

Potential Cause

Single- and multi-headed inclusions originating from dirty parts entering booth.

Solution

Check that the quality of the cleaning system is sufficient to remove all dirt from the parts.  Check for weld spatter and other burrs on the substrate surface.

Potential Cause

Contamination in virgin powder.

Solution

Contact us to discuss.