Substrate shows through and/or the powder coating has a poor grainy flow. Dry Film Thickness (DFT) measurement shows that the coating is below the recommended film thickness.
Spray guns settings are not optimised:
Review settings and discuss with your spray gun supplier.
The electrical earth is not sufficient
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.
The powder coating may contain excessive concentrations of small size particles (‘fines’); this is usually accompanied with poor fluidisation.
Sustain a constant ratio of virgin powder and reclaimed powder. Reduce the reclaim : virgin powder ratio; if the problem persists, the virgin powder may contain excessive fines for the spray system. Contact us.
The powder coating or the local air conditions may contain too much moisture (humidity). Moisture acts as an anti-static agent
Monitor and control the local humidity in the spray booth and air supply. Should the powder coating have excess humidity in the bag, this can be conveniently fixed by opening the bag and leaving it open to the atmosphere for a few hours. Protect the powder from possible contamination during this period.
The spray equipment may be a Tribostatic system and powder is not suitable.
Should the equipment be Tribo, check with us that the coating is suitable for Tribostatic application. Ensure the tribo tube is not coated with powder particles limiting the creation of friction. In certain circumstances is is possible to enhance the tribo-charging of the coating by addition of an additive to the fluidising container
The powder coating, which should electrostatically adhere to the substrate, falls off. In more extreme cases, the powder coating does not apply to the edges of a part, or may not adhere at all.
There is a poor electrical earth causing first-pass charged powder coating particles to limit further deposition onto the part.
Check contact areas to ensure there is no build-up of cured powder coating, grease or any other insulating material which would impede electrical earthing. In particular, check that jigs are thick enough for the job and that the contact of the jig with the part and the jig with the hanging rail is free from any coating build-up.
Excessive moisture:
Moisture, usually from humidity air acts as an antistatic agent
Control the humidity in the booth and the air supply. Store powder in a controlled (cool and dry) environment. Powder may be dried using a fluidised bed in a controlled (warm & dry) environment, although usually just leaving the bag open in a dry environment will acclimatise the powder. In exceptional circumstances, additives can be used – these are best applied in a fluidised bed.
The spray gun is tribostatic and the powder may not be suitable for tribostatic application
Some powders have the ability to charge by friction (tribostatic) others do not. Contact us. Ensure tribo tube is not coated with powder particles limiting the creation of friction. In certain circumstances is is possible to enhance the tribo-charging of the coating by addition of an additive to the fluidising container
The powder coating is a metallic effect and the metallic flakes are adversely affecting the charging process. This is particularly noticeable in blended ‘chrome’ effect coatings.
Reduce the powder delivery rate to lower the metallic flake content in the spray gun. This problem is particularly noticeable in blended metallic effects; we can offer a bonding service which solves the issue.
High voltage creating a strong magnetic field
Reduce voltage to the electrical field to eliminate electrostatic rejection
A gun too close to a part will create a strong magnetic field.
Increase the distance between the gun and part.
Coating surface is orange peeled and/or hazy. DFT measurement shows that the coating has been applied above the recommended film thickness.
Spray guns settings are not optimised:
Review settings and discuss with your spray gun supplier.
Coating time too long
Lower the coating time, or reduce the amount of passes when spraying.
Too much pre-heat (if used)
Reduce temperature of pre-heat cycle
We can make any powder coating colour or finish to order so get in touch to discuss your requirements.