The powder coating process involves three basic steps:
1. Part preparation or the pre-treatment
2. The powder application
3. Curing
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.
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
In many high end applications, the part is electrocoated following the pretreatment process, and subsequent to the powder coating application. This has been particularly useful in automotive and other applications requiring high end performance characteristics
Advantages of Powder Coating Process.
There are several advantages of powder coating over conventional liquid coatings:
1.Powder coatings emit zero or near zero volatile organic compounds (VOC).
2.Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging.
3.Powder coating overspray can be recycled and thus it is possible to achieve nearly 100% use of the coating.
4.Powder coating production lines produce less hazardous waste than conventional liquid coatings.
5.Capital equipment and operating costs for a powder line are generally less than for conventional liquid lines.
5.Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items.
6.A wide range of specialty effects is easily accomplished which would be impossible to achieve with other coating processes.
Methylene Chloride is generally effective at removing powder coating, however most other organic solvents (Acetone, thinners, etc.) are completely ineffective. Most recently the suspected human carcinogen Methylene Chloride is being replaced by Benzyl alcohol with great success. Powder coating can also be removed with abrasive blasting. 98% sulfuric acid commercial grade also removes powder coating film.[citation needed] Certain low grade powder coats can be removed with steel wool, though this might be a more labor- intensive process than desired.
