Electrostatic powder coating: what it is and how it works
Your powder covers the outside of a part, but the corners are thin. In such a case, adding more powder may not fix the problem. Electrical attraction works differently on open surfaces and deep recesses. Once you see why, it is easier to understand what to adjust.
What is electrostatic powder coating
Electrostatic powder coating uses an electrical charge to help the dry powder stick to the grounded component. Grounded means the part is connected to the earth.
Compressed air carries the powder through the spray gun, where it picks up the charge. The charged powder is pulled towards the part and stays on the surface.
The part then goes into a separate oven. With thermoset powders, the heat melts the powder so it flows, then hardens it into the finished coating.
An electrostatic powder coating machine controls two connected functions: powder delivery and electrical charging. When something goes wrong, check both.
How does the gun charge the powder?
A corona powder coating gun has a high-voltage electrode near its tip. The electrode charges the air around it. That charged air passes its charge to the powder particles.
The nozzle has a different job. It shapes the powder cloud. A nozzle change affects where the powder goes. The electrical settings affect how well the powder is charged. Know which one you are adjusting.
What do kV and µA tell you?
Most controllers show two readings.
- Kilovolts (kV): the gun’s voltage.
- Microamps (µA): the electrical current used for charging.
Many controllers let you change the voltage and limit the current. Limiting the current can stop too much charging, which can harm how the powder sticks and how the finish looks.
Maximum voltage is not the best setting for every job. Red Line describes controlled, variable output up to 100 kV. Its troubleshooting guidance says to lower the voltage when corner and crevice coverage is poor.
Check grounding before adding more powder
Grounding connects the part to earth. A poor connection through the part, jig or hanger can stop powder sticking well.
If your coating is too thin, check these connections as well as the charging and powder-flow settings. Red Line lists weak grounding and poor contact on the hanger as possible causes of thin film. More powder will not fix these problems.
Why are corners harder to coat?
The electric field around a part can keep charged powder out of deep channels and inside corners. This is called the Faraday cage effect. Open surfaces may look fine while recessed areas stay thin.
Red Line’s guidance is to check grounding and lower the charging voltage. Follow the equipment instructions and check the coating after each change.
Where does tribo charging fit in?
A tribo powder coating gun charges particles through frictional contact with its internal surfaces. A corona gun charges the air with a high-voltage electrode instead.
Before you choose tribo charging, check that your powder suits it. Powders do not all respond in the same way. Ask your powder supplier and your equipment maker.
How do you know the changes worked?
Do not judge by looks alone. Measure the film thickness against your coating specification. Suitable instruments can measure the cured coating or the powder before curing.
Also check powder delivery. Too much air speed can blow powder off the part. Too little flow or spray time can leave the coating too thin.
Use these checks to find the cause of uneven results. Work out whether the problem is charging, grounding or delivery. Then check the result of each change.