There are 3 steps to the powder coating process: pre-treatment, powder application and finally, curing. These processes can vary slightly depending upon the material being coated and the type of powder coating being applied, however the principles remain the same.
To ensure proper application and a perfectly smooth finish, it is vital that the material is cleansed of all dirt, oil, grease, rust etc. This can be done through a variety of methods, usually dependent on what the material is. Chemical treatments are most often used, involving the use of phosphates or chromates that cleanse the material and also aid the process of bonding the powder. Another method that can be used is abrasive blasting; this prepares the material and can also be used to create a texture on the surface of the material.
Powder coatings are most often applied to metals using an electrostatic spray gun. The gun applies a positive charge to the particles, which are then attracted to the grounded material. A variety of different nozzles can be used depending on the shape of the object being coated. Once the powder has been sprayed on, the object is then heated to allow the powder to melt and form a uniform film, which then cools to a hard finish. Other methods of powder coating include Fluidised Bed Coating, which involves pre-heating the material to be coated and then submerging it into a powder filled bed. The powder sticks to the material and then melts. This method is most useful when a thicker layer of coating is required.
Once the item has been powder coated using either of the above methods, it then needs to be cured. This is important to achieve the durable, hardwearing finish that powder coating is known for. With the application of heat of a period of time, the chemicals within the powder coating react to form long molecular chains. This is called crosslinking and creates a dense network-like structure within the material that is very resistant to breakdown. Curing times and temperatures can vary slightly, but generally powders are cured at 200°C for around 10 minutes.