Powder is a dry coating. Instead of being dissolved or suspended in a liquid medium, such as solvent or water, powder is applied in a granular form. This material is finer than ground pepper but coarser than flour, and is applied directly to the surface to be coated.
The powder is created by blending the various components (binders, resins, pigments, fillers and additives) and processing them through an extruder into a continuous mass. This homo-genous mass is cooled and broken into small chips, which are then ground into the powder. Each powder particle contains within it the necessary components for reforming into the finished coating. After the powder is applied to the part, typically using an electrostatic spray process, the part passes through an oven and cures, melting into a smooth film on the surface of the part.
There are two distinct types of powder, Thermo set and Thermoplastic . The Thermo set powders are reactive, which means that under cure conditions there is a chemical "crosslinking", so that, once cured, the coating will not remelt. Epoxies, acrylics, and most hybrids are examples of Thermo set powders, making up over 90% of the current powder market.
Thermoplastic powders do not "crosslink" when cured, but simply melt and flow over the surface of the part. The film hardens on cooling, but if it is reheated it will remelt. Vinyl’s, nylons and fluorocarbons are examples of thermoplastic powders.
Enamel powder is a specialized formulation used in applications that previously used liquid porcelain enamel. It utilizes glass in its formulation and is cured, or fired, at a very high heat. The result is a finish that is particularly resistant to heat, scratching and harsh chemicals, and is typically used in appliances, such as washers, dryers, ovens and ranges.
The application process involves applying a charge to the dry powder particles and spraying them onto a grounded substrate. The substrate, or part, is typically grounded through the conveyor or hanger holding the part. The powder, once attracted to the part, is then held on the surface until it is melted and cured into a smooth coating film in the bake oven. The spray process takes place inside a booth designed to contain the over sprayed powder and makes it possible to collect the overspray and ultimately reclaim it for reuse.
The powder is fed pneumatically out of the powder container, or hopper, into the powder applicator, or gun. As the powder exits the gun, a low amperage, high voltage charge is applied to the powder particles, causing them to be attracted to the grounded work piece. This attraction may even cause the powder to "wrap" around the piece, coating the back side.
The over sprayed powder, suspended in the air contained inside the powder booth, is then passed through a separation process that permits the powder particles to be retrieved from the air. The clean air is fed back to the work environment, eliminating the need for air make-up. The reclaimed powder is mixed with a proportionate amount of fresh, virgin powder for reuse achieving consistent results and up to 98% material utilization.
