Powder coating can withstand impact and the application releases no volatile organic compounds, making powder coating more durable and less harmful to the environment than paint. Until recently, however, paint has had the clear advantage in looks. That is changing, as the finish options for powder coating now include clear coats and flake finishes that are drawing the two technologies to par for appearance.
To learn more about the process of powder coating, I visited Tommy and Julie Graves of Tommy Graves Customs of Jeffersonville Vermont and watched them powder coat a set of chrome handlebars. The Graves use powder coating extensively in their custom motorcycle business, including on their award winning bike, Smackdown. The Graves can powder coat any part of a motorcycle or car, as long as its metal.
Powder coating on the Community High School of Vermont Harley Time project bike.Powder coating is a free-flowing, dry powder that is applied using an electrostatic process. The positively charged powder adheres to a negatively charged metal and heat fuses the two together. The finish bonds with the metal, integrating the color coat with the substrate.
As in painting, quality powder coating begins with proper surface preparation. “Like everything in life, a good foundation brings good results,” said Julie.
The cleaning and surface prep step is the longest of the process. They clean the part meticulously, removing all grease and dirt. The part is then media blasted to remove rust, chrome or old finishes. The media blasting creates a rough surface that enables the powder to adhere better.
“The smoother your surface, the tougher it’s going to be to stick to the surface,” Tommy said.
To remove all particulates, they wipe the part and blast it with compressed air. Tommy and Julie thread copper wire through the piece and hang it on a wire rack. A non-toxic spray cleaner removes any remaining grease.
Tommy and Julie wear latex gloves throughout the process to prevent transferring oil from their hands to the part. “We’re talking about microscopic levels here,” said Tommy. “Even a small amount can create a bubble that would ruin the piece.”
The next step is pre-heating, or “bake-out”, which thoroughly dries the piece and brings it to a good temperature for applying the powder.
After completing bake-out and cooling, the part is ready for the powder application. Tommy electrically grounds the part, giving it a strong negative charge.
An electrostatic gun called a corona gun, propels the powder with compressed air. The powder -- which has the consistency of powdered sugar – flows past the tip of the gun, getting a positive electric charge. The negatively grounded part attracts the positively charged powder, sticking the two together.
“If you don’t have a good ground it’s horrible. The powder just comes out and goes to the floor,” Tommy said.
The application is odorless, since there are no solvents required to bind the coating to the surface. Overspray floats harmlessly to the floor where it is swept up. Large-scale powder coating operations frequently collect and recycle the overspray.
The part is placed into an oven to cure. The type of powder determines the oven temperature and the density of the part determines the time in the oven.
The heat liquefies the powder and spreads it, forming a uniform film over the piece.
The high heat cures the powder coating. “You can’t say drying,” said Tommy. “Powder coat goes on dry and is always dry. It creates a plastic like coating over your part. It’s what makes it so durable.”
Tommy and Julie frequently check the temperature of the part during heating using an infrared temperature gauge. “When you’re powder coating parts, it’s not just spraying the powder and sticking it in the oven. You have to monitor that temperature.” Tommy said. “If you don’t have your part at the correct temperature at a steady state, you’re not going to get the performance value from the powder.”
Their oven is one of the largest in Vermont at eight feet tall, four feet wide and four feet deep. They can easily handle up to three motorcycle frames or large car parts like bumpers.
The part is fully cured when they remove it from the oven: no additional time is required before handling or installation. A builder can bolt on the part as soon as it has cooled sufficiently to touch it.
The durability of powder coating makes it ideal for wheels, frames and tanks. The advent of powder coating clear coats, metal flake, and custom colors make powder coating a viable option for refurbishing a bike or doing a custom project. Visit Tommy and Julie yourself to learn how they can create a durable, custom finish for your project.
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Update 3-9-2012: Unfortunately, Tommy Graves Customs closed their doors during the winter 2012.