October 30, 2006 at 4:30 am #30309tncMember
Just thought I would share this info I found while researching about problems with grounds.
What is “grounding”?
The term “grounding” is the most misunderstood issue in powder coating. Grounding will be the least of your coating problems. Yet, grounding will be blamed for paint chipping and light coverage or no coverage in corners and tight areas. Because powder is charged with high-voltage of 80 kv or more, a very low resistance to ground is not necessary. A typical voltmeter powered by a 9 volt battery is useless in measuring the thoroughness of ground for electrostatic coating. This test should be done using a megaohmeter. But its usefulness will be limited. It is the amount of surface area being coated that will determine the toleration of paint build-up on the hanger before the hanger must be cleaned. The larger the surface area for charged powder to collect, the greater the energy level on the surface will become. It is the level of electrical energy that develops on the surface of the part being coated that will determine how poor grounding condition of the hanger or conveyer before it must be cleaned. If we attempt to coat a part with a small surface area using a hanger with a heavy paint build-up, the part will not accept charged powder. Taking an identical hanger with the same heavy paint build-up and try coating a part with a much larger surface area part and you will coat with no problem! Under test conditions, a refrigerator liner, which has an extremely large surface area, was hung with an insulated hanger. The liner using the insulated hanger was then placed on a conveyer for normal coating production. As the liner pasted through the spray booth, the liner surface became an electrical capacitor, which produced several very long electrical arcs that jumped from the refrigerator liner to the spray booth wall. The arcing that took place indicated that at the moment of each arc, the liner had discharged the excessive amount of electrons that had accumulated on its surface and that the liner had returned to a neutral condition ready to accept more charged powder. After the test, the coating thickness on the liner tested was compared to that of normal liners coated with clean hangers. With a digital measuring equipment, little difference if any was found. Under no condition should electrostatic coating continue if sparking exist! If you are told that your spray gun coverage will improve by cleaning the hangers or conveyer, reconsider. First try using a long grounding wire to those parts in question. If you truly see a definite improvement in coverage using a grounding wire, then clean the hangers and conveyer line as you would for normal maintenance. Don’t be surprised if you see little or no improvement in coverage. Cleaning of the hangers and conveyer system will only reduce the sparking or arcing condition, which in turn will improve the safety conditions for electrostatic coating.
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