Coatings are important for decorative and protective reasons. Decorative coatings allow for color-matching where appearance is important. Protective coatings are important to prevent corrosion where salt spray, moist air, ultraviolet light, heat, chemicals and other corrosive conditions exist.
There are two main coating methods: wet and power. Wet coating, most basically defined, is a liquid paint applied to a surface, also called a substrate. It has a long history in the fan and other industries. Liquid paint consists of three components: pigment which provides the color, a binder, the actual protective film forming component and a reducer or solvent to liquefy the content, allowing the paint to be spread, rushed or rolled onto the substrate. Immediately after application, the reducer will start to flash off or evaporate, leaving the pigment and binder on the substrate. This process may take up to two weeks and in some instances longer to totally cure the coating. Many reducers contain volatile organic compounds or VOCs that are known to cause cancer and damage the environment. Wet coating may require multiple coats to bring the dry film thickness to the vendor’s specifications, which is measured in mils (thousands of an inch).
Power coating is a dry-finished process that uses finally ground electrostatically charged particles of color and resins that are spread onto a metal or alloy surface. The coated component is electrically grounded so that the charged power particles adhere to the metal part and are held there until melted or fused into a smooth coating in the curing oven. A single powder coat provides two to three mils of thickness, providing fast and uniform coverage.
For additional protection in harsh environments, a two-coat process can be applied. Extremely effective two-coat power applications utilize a zinc-rich base coat of one and half to two mils of thickness. The zinc-rich base coat protects the substrate by creating a chemical reaction that keeps the substrate in a neutral state when it is exposed to a harsh environment. Then a top coat is applied over the base coat, adding two to three mils more in thickness, providing the finished color and additional protective properties.