Everything About Powder Coating Process and Equipment

Powder coating is a process that coats an object's surface by applying a dry powder on it using various techniques. Then it is heated in an oven up to its melting point, and the powder forms a uniform layer of paint on the surface.

This layer or film has many advantages when compared to conventional painting techniques. The film is less susceptible to cracks, peels, scratches, UV rays, and rust as compared to liquid coating.

The equipment needed for this process consists of an assembly that involves spraying of electrostatically charged powder on a pre-heated grounded substrate. It come in two types, electrostatic coating equipment, and Fluidized bed. In the former one, the powder particles are charged and accelerated to the grounded part with the help of a gun.

This reduces wastage and overspray. The guns that are used are of two types:

• Tribo charging guns: Friction between the gun barrel and the powder generates the electrostatic charge.
• Corona charging guns: Electrostatic charge is generated by electric power supply.

Fluidized bed is a container that is filled with powder, and has an air chamber at the bottom. The substrate is pre-heated and suspended in this bed. The powder sticks to the surface of the substrate.

There are basically three steps involved in this process, which are discussed here.

Step #1: Preparation of the Substrate
This is an essential step of powder coating that will affect the finishing of the paint. The part that is to be coated, should be prepared well to get the best coating. It is necessary to remove any traces of oil, lubrication greases, oxide remains, or any other stain on the surface of the part to be coated.

To clean the surface, either the abrasive blasting technique or chemical treatment is used. The type of the cleaning technique depends on the type of stain to be cleaned, the size, and the material of the substrate. Phosphates and chromates are the chemicals that are usually used for chemical cleaning of the part.

The techniques used for preparation of different types of surfaces vary, and are provided below:

• Sandblasting: Wood, Plastic, and Glass
• Silicon Carbide Grit: Non-Metallic Material
• Cast Steel Shot: Steel parts (angles, beams, etc.)

Thus, the aim of the preparation step is to clean the surface of the substrate, and make it ready for powder coating so that the coat adheres well to it.

Step #2: Applying the Powder
In this step, the powder is applied to the surface of the part. The powder consists of finely ground particles of pigments and resin. These particles are electrostatically charged and sprayed on the surface.

Before this, the part is electrically grounded (0 voltage) so that the positively charged particles sprayed on its surface, adhere to it until the coating process is completed. Different types of guns are used for this purpose. A positive charge is imparted on the particles by the gun, and then they are ejected on the surface.

This is a conventional method of spraying the powder on the part. Another method is called the Fluidized bed technique. In this method, the part is heated and then dipped in powder-filled bed. The powder adheres to the part, and melts on the hot surface to form a coat.

Step #3: Curing
It is necessary so that the powder sticks to the substrate permanently. In this step, the part to be coated is kept in an oven, and the powder is allowed to melt to form a uniform layer on the surface. It can be infrared cure or a convection cure oven.

Particular temperatures are set for the powder to melt to form a coat on the surface. Usually, this temparature is around 200 degree Celsius, and the duration for which it needs to be heated is about 10 minutes.

With the use of appropriate equipment, we get a durable finishing, and the bond of the paint is stronger as compared to conventional painting. The main advantage of powder coating is that there is no need of a solvent, and the coat is resistant to chemicals. This process is becoming increasingly popular as it is also environment friendly.