You could be the most experienced operator, spraying the most expensive powder – but if the part’s not properly grounded for powder coating, you won’t get far.
Here are three signs that something is wrong with your ground.
Poor transfer efficiency
Imagine you’re spraying ten pounds of powder. If, when you’re done spraying, the part is ten pounds heavier, you’ve achieved 100% transfer efficiency. This never happens, of course – a more realistic scenario would involve powder falling off of corners and welds, or struggling to penetrate recesses, all of which are signs of less-than-perfect grounding. A little bit of powder on the floor is unavoidable. Too much might be the sign of a serious grounding problem.
Difficulty building film thickness
Each pass of the spray gun adds a layer of powder to the part, and each layer of powder acts as an insulator. Eventually, grounded parts become so insulated that they can no longer accept powder. This is totally normal. You’ve simply reached maximum film thickness for that coat. Poorly-grounded parts, however, will stop accepting powder much sooner than you’d like them to. If, after a single pass, your transfer efficiency declines dramatically, it’s unlikely that you’ll be able to achieve the film thickness you need. It’s time to check your grounding.
If the powder appears to be dancing over the part’s surface as you’re spraying, it means there’s too much charge on the part. This phenomenon is known as back ionization, or starbursting. The powder’s movement will leave behind some strange patterns after curing. A well-grounded part gives the charge somewhere to go (namely, into the ground), preventing back ionization.
Similarly, if the charge is unevenly distributed across the part’s surface, the powder will follow suit. This could cause orange peel.
Thankfully, grounding parts for powder coating isn’t hard. Here’s how to do it right.