Description
Introduction:
Powder coating is an advanced technology for various applications of paints on metal objects. Powder coating gives a more attractive finish, superior corrosion resistance and protection, better mechanical properties and is more economical than conventional liquid paints.
Powder coating is carried on various consumer and industrial products. It gives a protective coating to the articles and also it improves their aesthetic appearance.
Powder Coating Process
The powder coating process involves three basic steps:
1. The Pre-treatment
2. The Powder Application
3. Curing or Baking
1. The Pretreatment -
Removal of oil, dirt, lubrication greases, metal oxides, welding scale 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 impurities to be removed and the performance requirement of the finished product.
2. The Powder Application -
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 to 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.
There are a wide variety of spray nozzles available for use in electrostatic coating. The type of nozzle used will depend on the shape of the work piece to be painted and the consistency of the paint. The object is then heated, and the powder melts into a uniform film, and is then cooled to form a hard coating.
3. Curing Process -
When a thermo set 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 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 10 minutes. The curing schedule could vary according to the manufacturer's specifications.
The advantages of using Powder Coating -
a. Powder coatings emit near zero volatile organic compounds (VOC).
b. Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging.
c. Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items.
d. The wide range of specialty effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes.
e. Most importantly it offers long durability and corrosion resistance.
