The powder coating process involves three key steps:
- Preparation of the surface to be coated
- Application of the coating material
- Heated curing of the applied coating material
Rather than relying on a liquid that is applied while wet and then dries, powder coating involves the application of a powdery substance made up of small, dry particles- the powder in powder coating. This is followed by a curing process where the coating material melts and forms a seamless, solid covering over the surface being coated. Once it cools, the powder coated finish is uniform in appearance and very durable.
Most coaters start with a manual “batch” type system that enables the operator to coat and cure multiple parts at once. This is simpler than the automated processes used in many large-scale coating facilities. A batch system includes some type of prep equipment to get the surface ready to coat, a powder gun and spray enclosure with powered exhaust, and a powder curing oven, along with racks and metal hooks that are used to hold the parts while they are being coated.
Preparing the surface is fairly simple. It needs to be free of dirt, grease, oil, rust and other contaminants. This can be achieved by blasting the surface with abrasives and/or using a chemical cleaning agent. Once the surface is clean, it may be chemically primed or coated as-is.
Although other application methods are sometimes used, the most popular powder coating technique involves the use of a powder “gun.” The gun is used to impart an electrostatic charge to the powder particles, and it uses compressed air to transfer them onto the object being coated—much like a spray gun propels wet paint. This process is generally more efficient and easier to perform than traditional wet spraying because the powder is attracted to the surface being covered and the coating material tends to even itself out as it melts during the curing process. The material that does not adhere to the surface is usually trapped by filters mounted in the exhaust system of the spray enclosure. The overspray can either be discarded (in “spray-to-waste” type systems) or collected and saved for re-use (in more expensive “reclamation” type systems).
Curing is done in an industrial oven designed for powder coating use. The most popular “walk in” sized ovens use LP or natural gas fuel. Smaller ovens sometimes use electric heating elements. There are also models that use infrared panels or gas catalytic infrared heating. Almost all powder coatings cure at a temperature of 325° to 425° Fahrenheit.
Unlike conventional solvent-based wet painting techniques, the powder coating process does not require the use of coating materials containing harmful chemicals, so it is environmentally friendly and currently in great demand.