Lumps in cured film. Lumps are raised areas typically >2mm diameter.
Clogging of the powder feed hoses, caused by agglomerates building up in spray equipment. These are periodically freed by delivery air.
Change hose diameter, shorten hose. Optimise the air pressure settings. Check in-line filters and moisture traps
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.
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.
Powder falls off booth ceiling onto work below
Adjust/increase frequency of booth cleaning intervals
Powder falls off workpiece onto work below
Test electrical earth, check diameter of hoses.
Use dry powder, check air filter and moisture traps in compressed air system
Powder agglomerating in the box.
Agglomeration can occur under inappropriate storage conditions. If possible, manually break up the powder coating lumps.
Spray gun settings. A defective gun, or certain gun types may cause a rash of lumps caused by build-up in the gun.
Often, increasing kV to the gun tip can correct this.
Worn venturi or pump.
Replace worn parts
Powder too fine
Decrease amount of reclaim to hopper. Optimise virgin powder plus reclaim ratio. Contact HMG.
Small pinpoint raised peaks in the coating surface, often referred to as 'bits' or 'seeds'. The particles are often so fine that sieving does not remove them. Under the microscope, these inclusions may be the same colour as the coating, or a different colour.
Film thickness of the coating is below the recommended DFT.
Ensure DFT is above the recommended minimum.
Single- and multi-headed inclusions caused by contamination from the reclaim system:
Check the recovery and reclaim system, particularly ensuring the sieve is in place and not ripped.
Multi-headed inclusions which under the microscope are revealed as fibres.
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.
Single- and multi-headed inclusions caused by air movement in the plant.
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.
Deposits of dust and powder on cured film, often these can be felt on the surface as slightly raised bumps.
Ensure cooling zone is dust free and is protected from cross draughts.
Single- and multi-headed inclusions originating from dirty parts entering booth.
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.
Contamination in virgin powder.
Contact us to discuss.