In the early 1970s, Interrad Corporation introduced powder coatings in the United States. It all began at a New Jersey company that manufactured air conditioning mufflers for the automotive industry. Due to space limitations the company selected a unique oven: the oven used air, pressurized by a blower, in order to move heated air through “jet pipes” containing several openings through which air speed increased due to a venturi effect. This created what is called a “rapid heat transfer”. The air moving at higher speed induced the coating materials to cure more quickly, because the mass of the product didn’t need to be brought up to curing temperatures. Instead, the curing was done at the product surface.
This technological innovation eventually led to the successful use of different types of Infra-Red (“IR”) curing systems that focused on surface curing. There are many varieties of IR curing methods or equipment. They can be electric, gas or even ceramic. They are particularly popular for their ability to cure the surface of an individual part, rather than requiring the heating of the whole product. Some IR systems are limited to “Line of Sight”, which means that the area must be able to be “seen” directly by the curing components. However, the need for a system that can gel the powder in line before it cures, as well as cure the powder in a short period of time (especially in quick color change systems) have led to the development of systems that are in popular use today.
When powder is applied to an individual part, most of the powder adheres to the part electrostatically. But some powder forms additional deposits due to gravity, especially on horizontal surfaces. This gravity-deposited powder does not adhere to the part with the electrostatic molecular adhesion. As a consequence, it will blow away the first time it is exposed to air velocity. In a quick color change system, this effect can be very damaging, since the blown off powder can create deposits on the next part that comes through — one that may be a different color — thereby damaging its surface. The introduction of IR equipment at the entrance of the oven provided a crucial benefit in this regard, because it gelled the powder before it was able to enter the high velocity curing area.
With time, even this concept was improved upon. The combined use of IR and high velocity hot air started to show amazing results. Many job shops discovered that such a combination of systems not only helped with the color change, but also enabled them to do both thin and thick parts on the same line. This was made possible because the curing became focused on surface curing rather than on heating the whole product. (For further reference, please see our article “Power Coating’s Westside Story”).
Cure powder coatings with gas-fired infrared burners
As mentioned above, there are many methods of curing powder coatings. One method that has been in existence for many years but today is gaining greater acceptance is the use of Infrared (IR) heat to cure the powder coating. Gas infrared is best suited for curing products with mixed metal thicknesses in shorter time cycles. The additional efficiency of the infrared radiation within the oven interior shows the glow that the Infrared radiation is emitting to bathe the product with energy.
The radiant burner provides both medium wavelength infrared curing and curing with convection heat assisted by air circulation. This combination provides excellent paint and powder curing. It enables a reduction in cure time, faster curing time on multiple metal thicknesses, and a reduction in operating costs, since the product is further cured with hot convection air. Wire mesh, re-bars and many other products are now efficiently being cured in just this way.