Curing of Powder Coated Parts

produce the chemical reaction. The powder material will melt when exposed to heat, flow into a level film, then begin to chemically crosslink before ultimately reaching full cure. Various methods can be used to supply the energy needed for cure.

Convection ovens use a heat source, usually natural gas, fan and distribution duct to circulate air inside the oven and heat the part. As the part reaches peak temperature it will conduct heat into the coating and cause the powder to cure.

Infrared (IR) ovens, using either gas or electricity as their energy source, emit radiation in the IR wavelength band. This radiated energy is absorbed by the powder and substrate immediately below the powder without heating the entire part to cure temperature. This allows a relatively rapid heat rise, causing the powder to flow and cure when exposed for a sufficient time. Parts can be cured in less time in an IR oven but the shape and density of the part can affect curing uniformity.

Combination ovens generally use IR in the first zone to melt the powder quickly. The following convection zone can then use relatively higher airflows without disturbing the powder. These higher flows permit faster heat transfer and a shorter cure time.

A variety of radiation curing technologies are available, including near-infrared, UV and electron beam. These processes have the potential to open up new applications for powder coating of heat-sensitive substrates such as wood, plastic parts and assembled components with heat-sensitive details.

UV curing requires specially formulated powders that can be cured by exposure to ultraviolet light. The powder first needs to be exposed to enough heat so it is molten when exposed to UV energy; the initial heat source is typically infrared but convection heating can also be used. The coating is then exposed to a UV lamp. A photoinitiator in the coating material absorbs the UV energy and converts the molten film to a solid cured finish in a matter of seconds.

Near-infrared curing also uses specially formulated powders coupled with high-energy light sources and high-focusing reflector systems to complete the powder coating and curing process within several seconds. Heat-sensitive assembled parts such as internal gaskets, hydraulic cylinders, and air bag canisters can benefit from this technology.

Induction ovens are normally used to pre-heat parts before powder coating to help accelerate film build. Induction ovens are often used in fusion-bonded epoxy coating applications such as concrete rebar and coating of pipe used for gas transmission. Such systems operate at high line speeds, and film builds of >10 mils are common.