Powder coating is a coating that is applied as a free-flowing, dry powder. The difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form.
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.
The powder coating process
The powder coating process involves three basic steps:
Removal of oil, soil, lubrication greases, metal oxides, welding scales etc. is essential prior to the powder coating process. We use chemical pre-treatments which involves the use of phosphates or chromates in submersion applications. These occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final chromating of the substrate. The pre-treatment process both cleans and improves bonding of the powder to the metal.
The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or corona gun. The gun imparts a negative electric charge to the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpiece by the powerful electrostatic charge.
When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200°C (390°F) for atleast 10 minutes in an oven.