Application Methods For Powder Coating

Applying powder is reasonably simple and, providing you have access to the following equipment, is something that most practical people can lea. You will need: a powder gun, a supply of clean dry compressed air, an electrical supply and the powder for spraying.

Powder is sucked from the container, which can be the manufacture's box or a hopper, depending on the type of equipment, via a powerful pump. In order to get a constant smooth flow two methods are used: vibration and fluidisation. Vibration helps to keep the powder level towards the suction tube; fluidisation enables the powder to flow through the pump easily.

The powder is sucked vertically from the container to the pump where it is passed along the powder tube; this can vary in length but is usually around three meters. The powder will then enter the gun body. The manual gun is shaped for ease of handling and comfort and will usually allow the powder to enter at the bottom of the handle. On automatic equipment the powder will usually enter from the rear as the gun body will be straight.

There are many types and variations of application equipment to suite specialised methods of application but the main two main types of gun in common use are Tribo charge and Corona charge. Both rely on the powder getting an electrical charge that in tu enables the materiel to attract to the surface of the object to be coated.

Tribo charge relies on the powder passing along the pipe and through specialised plastics in the gun body in order to create friction. The surfaces of the powder attract opposite polarity charges that in tu attract each other, even after separation. This method is, however, limited to certain types of powders.

Corona charge relies on an electrical charge at very high voltage (up to 100kv) to be released into the powder cloud at the point it is released from the gun. The charge is relayed to the gun via a low voltage (10-12v) cable and then the voltage is multiplied in the gun handle to the very high voltage required. This is then discharged into the powder cloud at the point of exit. The Decorative powder coatings on this type of equipment will also pick up a certain amount of tribo charge along its route, so will enable this type of equipment to be the preferred choice for most coaters.

The fully charged powder will now exit the gun in a fine dust cloud and will be attracted to anything that is able to accept a charge from a distance of around 100 - 300 mm; this then remains as a powder on the surface of the component until cured. The curing process will be discussed in further articles.