When a thermoset powder is exposed to elevated temperature, it will
begin to melt. As the material begins to melt, it will flow out and then
chemically react to form a higher molecular weight polymer in a network- like structure.
This cure 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 that the material was designed for. The application of energy to the product to be cured can be
accomplished by convection cure ovens or infrared cure ovens.
A convection oven uses a heat source, most commonly a gas burner,
and a fan to heat the interior of an insulated enclosure. Different powder
materials require different cure temperatures, commonly in a range
between 350 °F and 400 °F (177 - 204 °C). The part is heated by the
hot air in the oven and it in turn conducts heat into the coating.
The coating must be held at temperature for a predetermined length of
time to reach full cure. So the cure cycle is so many minutes at so
many degrees of temperature. The time it takes to bring the metal up
to temperature must be added to the cure time requirement to determine the full cycle time in the oven.
Convection cure time may be as short as 10 minutes or as long as 30
minutes, depending on the mass of the substrate and the cure requirements of the powder.
The generally accepted standard for curing is 20 minutes @ 400 deg F.
Convection curing is dependable and flexible. The oven can be adjusted along a full range of temperature requirements and the line speed can be adjusted for the time requirement.
The part can be exposed for a longer period of time than what is
called for, usually with no change in color, gloss or performance in the
Energy consumption is related to the load of product, the amount of insulation and the volume of exhaust. Typically, a gas-fired oven is very efficient and cost effective.
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June 18, 2012