How to Prepare Your Metal Work for Powder Coating
A viewer, Mike, asked how to prepare when you are going to have your metal creations powder coated. What do you have to think about?
Kevin shows his sculpture Prickly Passion, an art commission for a patron in New York. It's based on the purple cactus Opuntia macrocentra. He shows some spatter he missed when doing his finish grinding. He checked all the cactus pads, operating a grinder with a gloved hand while he ran his other, bare hand across the pads, grinding as needed. Well, he missed one.
Also, you don't want to create a closed vessel. When you are creating a piece made of connected closed vessels, look for ways to vent from one enclosed section to another - Kevin shows he he vented this sculpture from cactus pad to cactus pad. If you flipped the sculpture over, you'd see an 1/8" hole in the bottom pad through the base, so all of the closed vessels are vented. Otherwise, when it went into the oven and is heated, the hot air inside of the piece will get hot enough to vent, or blow out. If you have any imperfection anywhere in your welds - a cracked weld, some porosity, whatever - it'll blow out. Now you have a hole.
After he is done fabricating, Kevin likes to take his sculptures to a sandblaster and have them sandblasted. Then he brings them back to the studio and inspects all the welds, joints, seams, etc. looking for any cracks, welds, porosity - anything that's going to cause a problem later.
Another tip: always try to have holes somewhere in your metal work so the powder coater can hang it - metal work is usually sandblasted and powder coated upside down hanging on a big rack. A hole gives them a way to hold the piece, whether it's the mounting holes like in this sculpture, or a place underneath the piece where you can cut some holes to run a chain through it. That can also vent the metal work.
Next, Kevin shows some scratches on a sound sculpture he is fabricating. You can see the scratches from when he ground off the dross after cutting the piece of metal with a plasma cutter. There also are some other gouges in the metal where the piece slid across the workbench. Sandblasting the artwork might mute the scratches, but all of those grrrrr marks and gouges will show up through the powder coat.
Kevin shows another section of metal where he ground the whole piece with the same 40 grit that he used to make those gouges, but he went over it all so that the surface was the same. You can grind it with 40, 60, 80 grit, but grind all of the metal. If he was going to powder coat that artwork (he's not; it's going to be oxidized) - he'd come in with the 40 grit, buzz it with some 80 grit, then maybe some 100 grit, but get it all the same texture.
Mike also asked about what you need to know when you get to the powder coater. Do they have any code words? What will they ask? What should I know?
First, is it an indoor or an outdoor piece? There are two different types of powder coating.
Also, what do you want under the powder coat? Do you want to prime it? On his fountains, Kevin likes to prime them, powder coat them, bake them, clear coat them, and bake them again, trying to seal it the best he can. If your metal work is going to be indoors, though, you might just want to powder coat it.
As far as finishes, there's matte, which is sort of dull. There's semi-gloss or satin, and there are gloss, or shiny, finishes. So when you are picking out your color, the gloss level is something else to think about.
As for multiple colors, some powder coating companies don't want to spray more than one color, but it can be done. The piece can be taped off to spray one color then another, then baked. Or you can let the colors blend, as he did with his sculpture FireStick ( http://www.kevincaron.com/art_detail/firestick.html ), which has four colors. Talk to your powder coater and see what they will do for you.
If you want to keep your piece plain metal and clear-coat it, make sure your finish is perfect, and tell the powder coating company not to sandblast it first. They'll just wipe it down with acetone to get any oils from hands or gloves off of it, they spray it. Any imperfection will show up like a sore thumb.
Kevin is ready to go back to work, but you can take one moment to enjoy his burst of amnesia ....
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