Powder coating is a type of coating that is applied as a free-flowing, dry powder. The difference between a 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.” It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals.
The Advantages of Powder Coating
Powder coatings are friendly to the environment because emit zero or near zero volatile organic compounds (VOC), Powder coating overspray can be recycled and thus it is possible to achieve nearly 100% use of the coating and production lines produce less hazardous waste than conventional liquid coatings. It can produce much thicker coatings than conventional liquid coatings without running or sagging. Is resistant to scratching, fading, chipping than other finishes. The Capital equipment and operating costs for a powder line are generally less than for conventional liquid lines. Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items. A wide range of specialty effects is easily accomplished which would be impossible to achieve with other coating processes.
The powder coating process
The powder coating process involves three basic steps:
- Part preparation or the Pre-treatment
- The powder application
Part Preparation Processes & Equipment
Removal of oil, soil, lubrication greases, metal oxides, welding scales etc. is essential prior to the powder coating process. It 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 powder coated, the type of soil to be removed and the performance requirement of the finished product.
Powder Application Processes
The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun. The gun imparts a positive electric charge on the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the work piece 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 cross linking, requires a certain degree of 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) in 10 minutes. The curing schedule could vary according to the manufacturer’s specifications.
Reference – Wikipedia