Powder coating is not like traditional, liquid paint, it does not dry it has to be heated in an oven to cure this process takes 10-15 minutes dependent on the powder type and to achieve the correct properties it must follow the correct curing process.
Curing of Liquid coatings involves either a chemical reaction which releases volatile organic components or the driving off of solvents by heat.
Powder coating is made up of particles of resin and pigment ground together. The curing process enables the synthetic polymer chains within powder coating to bond with each other. This is known as cross linking.
It is the reason why the finished coating is so hard wearing.
During this process, the dry powder coating first melts, then bonds together, forming a uniform, durable outer shell.
Therefore, the curing process is critical in the application of powder coatings.
Proper curing of powder coating requires a combination of temperature and timing.
To cure a powder coating, you must bake it, and any coated component must reach its optimum curing temperature during this bake.
The cure schedule is based on the part metal temperature (PMT) of the specific component, and you should only time the curing process once this temperature has been reached.
This will then ensure that the surface hardens sufficiently.
The more resilient the powder coating is at higher temperatures, the faster this curing time will be.
However, if you start timing the curing before PMT is reached, then this will give you an under-cured finish.
To understand the PMT of the surface you are coating, you must take its temperature first, usually with an infrared gun or laser.
The powder coating will begin to melt before the ideal cure temperature is reached, but you should only time the curing process from when the optimum product temperature is reached.
An under-cured finish will be brittle, and have poor resistance to UV light and chemicals.
Another error in the powder coating process is over curing.
Over curing occurs when you bake the coated product for too long, or at too high a temperature for the specified curing schedule.
Generally, powder coatings will have some built-in bake stability, so that they can handle being baked a little longer than specified.
However, over baking for too long results in brittle finishing, and can also leave a burnt discolouration to the finish.
Over curing can be a risk where the products to be coated is of varying thicknesses. Here, the thinner areas will cure before the thick ones.
A good powder coating Applicator should be able to allow for these kinds of discrepancies.
Cure ovens designed for powder bring up part temperature rapidly, to allow for the proper length of time for a 100% cure of the film coating.
This will provide a tough and impact resistant finish.
For more information about our diverse, technically outstanding powder coating range, please contact us.