Powder coating is a type of coating that is applied as a free-flowing, dry powder. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a “skin”. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, and automobile and bicycle parts. Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using different methods.
Powder coating was first discovered in 1967 in Australia. They are generally used to coat metal surfaces such as iron and aluminum. To achieve the maximum adhesion before painting; oil, dirt, lubrication greases, metal oxides, welding scale etc. should be removed. This can be done by a variety of chemical and mechanical methods. The selection of the method depends on the size and the material of the part to be coated, the type of impurities to be removed and the performance requirement of the finished product.
Chemical pre-treatments involve the use of phosphates or chromates in submersion or spray application. These often occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final phosphating or chromating of the substrate. The pre-treatment process both cleans and improves bonding of the powder to the metal. Recent additional processes have been developed that avoid the use of chromates, as these can be toxic to the environment. Titanium zirconium and silanes offer similar performance against corrosion and adhesion of the powder.
Source(s): Wiki, HERE