The Powder Coating Process begins with applying powder to the substrate. There are many types of equipment that take part in this process, each doing a specific task.
The main types of powder coating equipment include:
– Powder coating ovens (used for preheating and baking) – Powder curing ovens (used for curing, post heating, and baking) – Powder sprayers
Powder coating ovens
Powder coating ovens are used to preheat the powder so that it will melt and stick when cured. It’s a large, heated metal enclosure with a door on the front. Inside the oven there is a conveyor belt or track where parts sit for a certain amount of time, which is determined by the type of powder coating being applied. A sensor on the gun will determine when the powder has melted and stick to the parts. Then t he oven door opens and t he conveyor belt or t rack moves the part through the curing unit where it cures inside for a certain period of time until it reaches a temperature where it will not be damaged if cooled quickly.
If a fast cure is needed, the oven can be fitted with multiple burners at different temperatures to vary the curing time from 3 seconds to 60 seconds.
Powder coating ovens are typically controlled by programmable logic controllers ( PLC ) or touch screen interface panels that set the oven time according to the material being coated and recommendations from the powder manufacturer.
Powder curing ovens
Powder curing ovens are used to cure/bake powder that has already been applied. They come in a variety of different shapes and sizes, but typically have an enclosed chamber with a door where parts can be placed inside before being baked. Inside, there may be a conveyor belt or track that the parts sit on for a certain amount of time which is determined by the powder used and the formula written on the can. When finished baking, heaters in the oven open a door on top and allow air to cool down inside before opening completely.
The term “powder sprayer” is a generic term for an airless gun and hopper assembly used in the powder coating process. Powder sprayers apply pre-mixed, electrostatic dry powder paint to a part or assembly in the same way an airless paint sprayer applies a coating of liquid.
A high pressure producer gas (usually nitrogen) pushes a stream of powder from the gun towards the cathode(negative electrode) charge collector where it sticks and builds up on the part being painted. Powder guns come in different styles including cup, bell or siphon. Pretreating the part before spraying is important for adhesion of the final powder coatings.
Importance of pretreatment :
-Method to ensure good coating adhesion on metal substrates (create a consistent surface) -Provide corrosion protection (coating can be acidic) -Makes sure that there is no oil on the surface (protects against rusting)
-Improve performance of powder coatings by providing a consistent base for proper adhesion, mechanical properties and appearance. -Make surfaces easier to clean and more resistant to abrasion.
Coatings applied with a powder spray gun must be dry when they leave the gun (no more than 1-3% moisture for alkyd and polyester resins, 0.5-1% for epoxy) to ensure that powder spray will not clog in the airless gun or hopper assembly during spraying.