nuts & bolts

maintenance & restoration Powder Coating 101 Cooking Your Paint for Color M I KE NOR TON, E A A 6 3 7 2 1 1

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eing involved with street rods and seeing the technique used frequently for frames, wheels, and miscellaneous items, powder coating had always fascinated me. I decided to explore the process to see how I could apply it to my aviation hobby, but first I needed to answer a few questions. Powder coating, often called “dry painting,” uses electrostatically charged dry particles of pigment and resin that are sprayed onto an item and then heated in an oven, permanently fusing them to the surface. This creates strong, colorful finishes that are more durable than liquid paints and that resist corrosion, scratching, wear, and fading. When the product is heated in a curing oven, the particles are fused into a smooth coating resulting in a uniform, exceptionally durable, high-quality, and attractive finish. The powder is relatively inexpensive and comes in virtually any color or finish. I started with small 8-ounce bottles that cost $6.99 each. The process is simple and can easily be accomplished by an amateur at home. To start with, the item to be coated should be conductive, able to withstand the 400-degree curing temperature, and be clean. Sand blasting or glass bead blasting the items is ideal, but not necessary. A wipe down with a solvent like acetone or lacquer thinner is done just before the powder is applied. You will need a powder coating kit or gun of some type. These are available from multiple sources including Harbor Freight, Sears, and The Eastwood Company. Prices will vary from $69 to $250 for hobbyist type kits. The guns all are very similar, and the kit prices will vary depending on what and how many accessories come with the kit. You will also need an oven of some type to bake (cure) the coated items in. Each kit will caution you not to use your kitchen oven, as the fumes given off while curing are toxic. I rescued an ugly harvest gold stove someone discarded during a kitchen remodel and installed it in my garage. It works great for curing coated items as well as for heat forming Plexiglas and Lexan for windows and landing light lenses. A small toaster oven could also be used as long as it can be set to 300-500 degrees. This would 100

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obviously limit the size of item you could cure but would be a good starting place.

How Is It Done? The first step is to make sure the gun is set up correctly. Follow the manufacturer’s directions. My kit requires only 10-15 psi of airflow, so any compressor should be able to handle that. The kit also included a moisture collector for the air input, as the powder will not flow well if damp. To fill the gun with powder, use a clean sheet of paper to funnel the powder into the cup. Fill the cup up with approximately 1 inch of your powder to ensure the bottle has room to sufficiently mix the powder with air. You should always keep the powder containers tightly closed when not being used to help minimize any moisture pickup. After connecting the air supply to the gun and attaching the grounding clip to the part you are coating, it is a good idea to check the pattern of the gun and make needed adjustments. The manufacturer’s guide that comes with the equipment should describe the process in detail. Just make sure you have an even spray of powder sufficient to cover the parts. Before coating, the part must be clean. The finished product will look much better if you spend a little extra time here. I have coated and cured items with only a little sand blasting to knock off rust or dirt, but the final product ends up a little rougher than I like. The powder will stick better to a rough surface, but the final product is slicker on a smoother surface. The parts must be free of oil, dirt, and rust prior to powder coating. Although not completely necessary, a picky builder looking for a highquality, flawless finish will bake the cleaned part in the oven to boil off any undetected oils and other contaminants. The part would then need to cool before proceeding to the next step. I have had to redo parts when I was unaware something was lurking in the pores that surfaced only during the curing stage. I stripped the old and ugly chipped paint

Valve covers show before, and the elegance of after.

from a yoke removed from my Swift as a test item. After chemically stripping it and washing it with water and then a little sanding, I coated it with glossy black powder and cured it. The results were awful. Either the chemical stripper or the water bubbled up through the powder during curing and ruined the finish. I had to strip all of the newly applied powder off the yoke. The powder is a little more difficult to remove than paint, but the same procedure will get it off even though it might require two applications of stripper. After thoroughly cleaning the yoke again, I baked it in the oven for 20 minutes at 400 degrees to boil off any water or stripper hiding in the pores of the metal. After it cooled I recoated it, and this time the results were great. It turned out glossy and glass smooth. The next item I wanted to try was a valve cover for the Continental O-300D engine in my Swift. I didn’t want to test one from my current engine (I’m not that stupid), so I scrounged around at the airport shop hangar (while the mechanic was in Oshkosh) and looked for the most disgusting Continental valve cover I could find. The photo above is what I found and is a good example of an item that should be baked prior to coating. Although only slightly porous, there will be oil spots that could affect your final results. After cleaning I baked the valve cover for 20 minutes at 400 degrees prior to coating. Then the clean sand-blasted part was hung up and grounded with a wire that attaches to a power supply, which puts out high voltage from the kit control box. Even though it is a high-voltage source, the current is low so you don’t have to worry about electrocuting yourself. The gun has a powder cup that doubles as a mixing chamber. The low-pressure air whips up the powder

into a mist that is lightly blown out the nozzle. The negatively charged powder is attracted to the positively charged part that is attached to the power supply with the grounding wire. Most guns will have a foot switch for the high voltage and a trigger for the airflow. Move the gun in slightly different angles to ensure all areas of the part are covered. Be sure to coat deeper crevices and inside corners first to prevent uneven coating. The coated surface will have a dull opaque coating of powder. Make sure all areas of the part are coated evenly. Powder can sometimes be difficult to apply in deep recessed areas or into corners. The powder will stick quite aggressively to the item. Any excess powder just falls to the floor and can be swept up when finished. Moving the item from wherever you had it hanging to the oven will not disturb the powder, but bumping it into something will. After you have coated the item with powder to your satisfaction, transfer it to the oven, which has been preheated to 400 degrees. The item must be able to hang inside the oven without the powdered surfaces touching anything. You can coat anything that will fit in your oven. The item needs to cure in the oven for 15 minutes and then be removed to cool. My manual recommends turning the oven off and cracking the door to allow the parts to slowly cool. The resulting finish will be glossier if allowed to cool slowly. The item will be ready to use approximately one hour after cooling. For the valve cover I tried the new single stage chromelike finish. The powder goes on looking like a medium gray powder, but as it cures it turns to a shiny silver finish, almost like chrome. I was quite impressed with the final finish of the valve cover. Next time I will do some additional sanding after the sand blasting to smooth out the finish. This first time I just want-

EAA Sport Aviation

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ed to see how well the powder would hide any imperfections without doing a lot of prep work. After seeing the final results, I should have either sanded the surface down a little smoother or put another coating of powder on, but it came out well for only being sand blasted. To go along with my valve cover project, I also had 36 valve cover screws that I wanted to coat the heads of. I drilled 36 holes into a thin piece of sheet metal and screwed in all of the screws. This allowed me to hook the electrode up to the sheet metal and coat them all at once. The screws were smooth before coating and turned out very slick. They look almost like real chrome-plated screws. Since the powder will coat around corners, be sure to mask all areas you do not want coated. I masked off the entire back of the metal sheet above to protect the screw threads from becoming coated. For holes where you do not want any coating, you can stuff them with just about anything that can tolerate the 400 degrees for 15-20 minutes. There are high-temperature plugs and tape made to withstand the curing process. Larger or significantly thicker items may require additional time for a complete cure. During the cure process the powder gradually melts, changing from a dull flat finish to a smooth gloss finish. If items are left in the oven too long, the coating may become rough and will need to be removed and redone. Once the curing is complete, allow the item to cool down gradually by turning the oven off and opening the door slightly. Always cure the powder in a well-ventilated area and wear an activated charcoal respirator while applying or curing to protect against breathing unpleasant fumes or the fine powder. When the items are cool to the touch they can be removed from the oven. I could not be happier with the results I am getting. After you complete two or three batches of items you start looking for other items to coat. The most difficult thing is getting an oven big enough to cure the items you want to powder coat. It is inexpensive, easy to do, and anyone should be able to do it at home.