The powder coating
process
The powder coating process involves
three basic steps.
(1)Part preparation or the Pretreatment
(2)The powder application
(3)Curing
Part Preparation Processes & Equipment
Removal of oil, soil, lubrication greases, metal oxides, welding scales 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 soil to be removed and the performance requirement of the finished product
Curing Prosses
When a thermoset 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 curing process, called crosslinking, requires a certain degree of 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) in 10 minutes. The curing schedule could vary according to the manufacturer's specifications.
The application of energy to the product to be cured can be accomplished by convection cure ovens or infrared cure ovens.
Powder Application Processes
The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or Corona gun. The gun imparts a positive electric charge on the powder, which is then sprayed towards the object, which is Earthed. The object is then heated, and the powder melts into a uniform film and is then cooled to form a hard coating. It is also common to heat the metal first and spray the powder onto the hot substrate. Preheating can help to achieve a more uniform finish but can also create other problems, such as runs caused by excess powder.
The powder can also be applied using specifically adapted electrostatic discs, and the alternative charging system called tribo guns.
How does powder coating compare to liquid paints?
The powder is a harder and more resilient coating. Powder does not have VOC emissions.The powder cannot be site applied but is a factory controlled process. Powder has more textured finishes available that liquid pain.