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16 POWDER COATING, November 2016 Once the two coatings are applied, they are merged together on the MDF part during the curing phase. The infrared (IR) heat that's applied melts the layers together and hardens them to the sub- strate for a smooth, tough finish. Cur- ing ovens can range from standard IR to gas catalytic. The key is to ensure that the coating material is cured properly for a consistent quality finish. When coating with powder, the pow- der is fused or cured into a continuous film by heat or radiant energy provided by the oven. This is achieved by main cure attributes such as temperature, which refers to the coated product's sur- face temperature; dwell time, which refers to the amount of time the coated part is held at cure temperature; and cure time, which is defined as the oven cycle time. The effects of over or under curing diminish the physical properties such as gloss, color, adhesion, and chemical resistance. For this reason, choosing the right oven is important. Comparing the available curing methods Understanding the different types of curing technologies and the benefits of each is the first step in determining the right type of curing technology for the application. There are a few basic types of powder curing systems, including gas fired convection, gas catalytic, and elec- tric IR technology. Gas catalytic oven Photo 3 Photo 2 A gas fired convection oven transfers heat to the powder coated part by circu- lating air around the part. Of this tech- nology, there is direct and indirect fired. With a direct system, the burner flame directly heats the circulated air. With an indirect system, the flame is exposed to an air stream inside a heat exchanger. An advantage to gas convection is the low cost of gas and low capital initial in- vestment cost. Disadvantages are that it's a slower process, larger floor space is required, and there are cleanliness issues due to airflow. Another big disadvan- tage is that the heat is not transferred di- rectly to the part being cured, but in- stead it's circulated around the part. Gas catalytic ovens, as shown in Photo 3, are natural gas or propane fired cat- alytic IR heaters that emit heat through flameless technology, which produces a Electric short-wave infrared oven Photo 4