Powder coating is an advanced method of applying a decorative and protective finish to a wide range of materials and products. The powder used for the process is a mixture of finely ground particles of pigment and resin, which is sprayed via a gun onto a surface to be coated. At the spray gun, the powder is charged by ion bombardment in an electric field. Charged powder is propelled towards the grounded parts by air supplied to the guns. The charged powder particles adhere to the electrically grounded part surfaces forming a layer of powder which is then heated and fused into a smooth coating in a curing oven. The result is a uniform, durable, high-quality, and attractive finish.
Infrared (IR) preheat utilize radiant energy to cure the powder coating on the part. IR ovens can efficiently cure powder coatings in as little as 30 seconds in some applications. The high heat rates possible in an IR oven allow the surface to be heated without heating the entire substrate. This provides for a rapid heat-up as well as a rapid cool-down. Thus, total processing time can be significantly reduced.
There is "free heat" in an IR oven produced by convection heat emanating from the product being cured and the IR emitters. This "free heat" is normally captured within the oven enclosure and can aid in heating the hidden areas of the parts providing a more even cure.
Iron phosphate pretreatment. Phosphate coatings are used to promote the bonding of powder coatings to a metallic substrate and impede the spread of any corrosion under the powder coating. These coatings can only be produced on properly cleaned surfaces. When the clean metal comes in contact with the slightly acidic phosphatizing solution, pickling occurs. This results in a reduction of the acid concentration where the liquid contacts the metal surface. Iron is dissolved, hydrogen is evolved, and the phosphate coating is deposited.
One example of a pretreatment system may involve three stages to clean both steel and aluminum surfaces:
Stage I - has a dual cleaner/phosphatizer heated to 140°F and sprayed at 15 to 25 psi. This stage removes soils and applies the phosphate coating.
Stage II - is a continuous overflowing, fresh water rinse and removes any excess cleaners.
Stage III - is a final seal rinse. Sealers are used to increase rust resistance without using environmentally harmful materials such as hexavalent chrome sealers.