Q: I’m a finishing engineer at a fabrication shop and have a question regarding powder coating application. What will I notice if my grounding starts to fade?
A: This is something that creeps up in a finishing system: You can be running good parts for days, and then you notice something isn’t right. First thought may be, “Is the powder bad?” Before you start switching boxes of powder in an effort to fix the problem, however, you should examine your hangers and racks for a good ground.
If the ground to earth is fading or inconsistent, you will begin noticing a few things. Your booth will appear cloudier, and more powder will accumulate on the interior walls and floor of the powder booth. You may see powder drifting out of the booth openings. As for your parts, you will probably observe lower film build and less penetration into corners.
Powder coatings are deposited on conductive parts with an electrostatic process. The powder/air mixture is pneumatically propelled from the fluidized hopper by a venturi process and conveyed through the hoses to the gun. A negative electric charge is generated by a corona and discharged at the exit of the gun, creating an electrostatic field. The powder passes through this field and picks up this negative charge. The negatively charged particles seek the nearest ground, which should be your parts.
Continuity to ground can be tested. Checking for ground to earth requires a megohmmeter that not only measures resistance but also provides up to 500 VDC, which helps define resistance more accurately. Adequate grounding requires 1 megohm or less resistance. Megohmmeters can be purchased online.
If you suspect poor continuity, the first places to inspect are hooks and hangers. Are the hooks coated and devoid of good, clean contact points? Hooks should be cleaned regularly and/or replaced to ensure good contact with the ground.
Well-grounded parts will have excellent continuity to the hooks/hangers, which need to be connected to a secure ground to earth. This requires good contact from the parts to clean (uncoated) contact points on the hooks. The hooks/hangers should be in contact with a conductive rod buried in the earth. Ideally, this grounding rod should be 0.75 in. in diameter and 8-10 ft long. You can find UL-listed, copper-plated grounding rods online or at your local hardware store.
The grounding rod should be buried, leaving about 6 in. of rod above ground for attaching ground wire(s). Getting the rod buried is a task in and of itself, and there are a couple of methods you could use. Drill a suitably sized hole in the concrete, then pound the length of the rod into the earth with a sledgehammer while standing on a ladder. Not a fun endeavor. Alternately, you can invest in a ground rod rotary bit and drill the hole using a hammer drill. My frugal self has done the sledgehammer routine. Trust me, it’s a workout.