Powder Coating Process: Powder Coating Equipment

Powder coating is a process that coats a surface by applying a dry powder on the object to be coated, using various techniques. After applying the powder on the surface, 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 formed on the surface has many advantages when compared to conventional painting. The film is less susceptible to cracks, peels, scratches, UV rays and rust as compared to liquid coating. Before we learn more about the process, let's have a look at the necessary equipment.

Equipment Required for Powder Coating

Powder coating equipment is an assembly that involves spraying of electrostatically charged powder on a pre-heated grounded substrate. The equipment come in two types, electrostatic coating equipment and Fluidized bed. In electrostatic coating, the powder particles are charged and accelerated to the grounded part with the help of a gun. This type of equipment reduces wastage and overspray. The guns 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 powder bed. This powder sticks to the surface of the substrate.

What is Powder Coating

As discussed earlier, powder coating is a process of applying dry powdered paint to a surface. There are basically three steps involved in the process. These steps are discussed below.

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 powder coated, should be prepared well, so that we 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 powder 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. Preparation of the part is multistage process that involves various steps. The techniques used for preparation of different types of surfaces vary. These are given below:

• Sandblasting: Wood, Plastic, 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 the surface ready for powder coating, so that the coat adheres well to the surface.

Step #2: Applying the Powder
In this step, the powder is applied to the surface of the part. The powder used for powder coating consists of finely ground particles of pigments and resin. These particles are electrostatically charged and sprayed on the surface. Before spraying the powder, the part is electrically grounded (0 voltage) so that the positively charged particles sprayed on its surface, adhere to the surface until the powder coating process is completed. Different types of guns are used to spray the powder on the surface. A positive charge is imparted on the particles by the gun and then they are ejected on the surface to be painted. This is a conventional method of spraying the powder on the part. Another method used for powder coating 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
The powder coating process does not end with spraying the powder on the part. Curing is necessary, so that the powder sticks to the substrate permanently. Curing is the step where the part to be coated is kept in an oven and the powder is allowed to melt and to form a uniform layer on the surface. The oven used for curing can be infrared cure oven or convection cure oven. The part is kept in an oven set at a temperature required for the powder to melt and to react chemically in order to form a proper coat. Usually, the temperature required for the powder to cure is around 200 degree Celsius and the duration for which it needs to be heated, is about 10 minutes.

With the use of appropriate powder coating 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.