Powder Coating Experience

Blue Powder Coated Sculpture

Blue Powder Coated Sculpture

I recently had an aluminum ribbon sculpture finished with blue powder coating for a couple living in Vancouver. Actually, my customer was a gallery in San Diego, who was working with an Art Consultant in Vancouver who was working with the client. You can get many levels of people between an artist and the artwork’s final destination.

The gallery sent me a design and I said I could do it in 1/4″ aluminum, with a few small design/engineering changes. It was to be 48″ tall x 24″ x 24″.  After about 3 months of back-and-forth, including discussions of powder coating colors, we finally booked the order January 20th, just after we shipped the 10′ aluminum sculpture to Phoenix. We were pretty tired by then, but exultant. We usually give a 12-16 week lead time and that seemed feasible at the time, given our back log. 12 weeks would be May 20th – that seemed do-able.

I finally get the project started in mid-April, I use two 60″ x 4″ ribbons for the two long pieces and two 50″ x 4″  ribbons for the two short pieces. I shape the pieces on my 48″ pexto roller and weld them up with my Lincoln Power Mig 300, with the Cobra push-pull gun. I make a frame of 2×4’s to let me stand up the pieces and arrange them, as I tweak their shapes with the roller. It’s a 3-D puzzle, my favorite. I anneal a piece of aluminum to 750 degrees with the soot-on-soot-off technique, shape it into a squared-off dome for the center part and weld that together (to hide the bolts that connect the sculpture to the base). I locate a granite base maker and order a black granite base, 15″ x 15″ x 1.25″.  It takes about 20 hours to lay it out, shape and weld then a few days more for the base and another day to clean it up for the powder coating finisher. Time flies – suddenly it’s late May.

We contact Cast Coatings, in Galien, MI. Rob is the manager there, but didn’t remember my wife visiting him to get the paint chip. We negotiate a price, $200, which seems high but we are behind schedule and need to get it done. He explains that 5 lbs of paint costs $75 and he will have to get that from Atlanta and that takes a few days. I say that I need a cosmetic powder coating and it will probably have to go through the process twice. So my wife brings it over. Now we get to the part about what they didn’t tell us.

Powder Coating: More to Know

  1. They are super-busy, mainly do white and black, usually 1000+ pieces at a time, usually smaller pieces, often truckloads, so a $200 order is very small for them. (But their ovens are large, so they can handle large pieces.) Onesies are unusual for them.
  2. They won’t be able to schedule it until the next time the line stops, which will be in about 7 days + the time to get the paint = 10 days.
  3. They have to chromate dip it first, then let it dry.
  4. I should have had it sand-blasted first. My typical flapwheel finish, which looks great on clear-coated or transparent-colored aluminum, isn’t good enough for high gloss powder coating, which makes every surface flaw instantly visible.
  5. It’s hard to strip off the powdercoating and do the sand-blasting after the first coat. You have to do it before. (But they didn’t tell me before.)
  6. Repairing small holes with epoxy prior to powder-coating isn’t a good idea. If they haven’t fully cured, or if the ratio was a little off, there can be some out-gassing during the bake cycle.
  7. Prior to doing a second coat, they have to scuff it up with a 3M scotch-brite pad.

All in all, it took a month to get the blue powder coating on. It looked fine, or good enough anyway. Some tooling marks are expected, even desirable, with hand-made artwork.

Powder Coating: Discussion

Powder coating has a certain cachet. People think powder coating makes their artwork more valuable. It sounds so industrial. But what is powder coating exactly? I worked at Cook Paint & Varnish back in the 80’s, just when powder coatings were coming on the market. You take the two parts of epoxy and mix them together into a rigid, brittle thin film. Then you break these up with a roller mill into manageable sized pieces then put them into a large ball mill where they are ground very fine. Now this fine coating is applied with an electrostatically charged spray gun, positive on the gun and negative on the metal. So when you spray it, there is very little overspray – this is the chief advantage of powder coating. Next, the coated material is melted onto the substrate in a 450-500 degree oven. So it is a thermoplastic coating – it doesn’t really bond to the metal, like a true epoxy coating. It just melts on. It is hard and brittle and chips easily. It is removable with acetone and other solvents. That’s why they don’t use it for cars. It would come off with gasoline or brake fluid and it would scratch and chip easily. Since it doesn’t bond to the metal, water and oxygen can work their way through tiny pores. Our powder-coated patio furniture is definitely rusting. It is hard to touch up with paint, though you can spray paint over it easily.

Would I do powder coating again? I would work hard to talk the client out of it. It takes too long. Too many trips back and forth. If they need an opaque coating and the sculpture is made of steel, better to get a 2-part polyurethane automotive coating with a 2-part epoxy primer undercoat. It will last longer and look better. Also easier to do touch-ups and repairs.

The check took 2 weeks to arrive – more delays. We never ship without getting paid first. Otherwise, we find that some people never pay and some wait 180 days. We can’t afford to play bank for anyone. We finally shipped out the box on the 7th of July. I need to find a way to get this work done faster.

I really enjoyed this project and love the look of the metal ribbons.  On reflection, the 1/4″ aluminum was not as rigid as I would have liked – okay for inside but not for outside. the wind would whip the ribbons around and clang them together.  3/16″ steel might have been the way to go, or 3/8″ aluminum. Not sure if I will be able to roll those in my Pexto. I know I can’t do 1/4″ steel unless I get it to red-hot first. But then it’s very hard to handle. The great thing about aluminum is that once it’s annealed it’s full soft, even when cold. I will have to try shaping some thicker aluminum. I might be able to do 1/2″! But how to get the full soft 1/2″ rigid again after shaping? I hear I can re-heat it, then do a fast water cool-down to get the hardness back. Maybe I should just send it out to be shaped. There are companies around the country that can shape steel up to 2″ thick. That may be the best solution.

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