Curing and Drying Operations: The E SOURCE Pros and …

1 Curing and Drying operations : ThePros and Cons of Infrared HeatingCuring and Drying operations : ThePros and Cons of Infrared HeatingLow thermal efficiencies are common in many types of process heat-ing equipment, making process heating a prime candidate for energy-saving improvements. In this pamphlet, we focus on opportunitieswithin Drying and Curing operations to improve energy use, productquality, and overall productivity. In many cases, infrared heating orhybrid systems that combine infrared and convection technologyoffer several advantages over convection heating alone.

2 Curing and Drying with InfraredInfrared (IR) radiation is commonly used to dry textiles andpaper products, heat metals and plastics, and dry and curepaints. For Drying and Curing operations , infrared heatingoffers several potential advantages over convection heating . IR Versus Convection heating Medium-wavelength electric IR heating is especially well-suited to the Curing and Drying of coatings, because thesewavelengths correspond well with the absorption bands forwater, which most coatings contain.

3 Additionally, since IRheating does not penetrate the surface very deeply and gener-ally only heats the outer surface, it is applicable for dryingcoated and printed products. In fact, many coatings and inksare now being specifically designed to be cured with IRheaters, by modifying the absorption characteristics of thecoatings to match the wavelengths emitted by the IR heating can also facilitate the use of water-based rather than solvent-based coatings, which reduces emissionsof volatile organic perhaps the greatest advantage of IR heating over convec-tion heating is that IR emitters can deliver heat in exactamounts directly to a specific point.

4 IR radiation is a line-of-sight technology, meaning that it only delivers heat to thesurface of an object that is in a direct line of sight from an IRemitter. Depending on the product, this can be either anadvantage or a disadvantage: Flat parts absorb energy best;complex curved parts require either more IR emitters or sup-plemental convection- heating technology. Additionally,because IR heating only heats the surface of the material, itleads to significant energy savings when Drying and curingpaints and coatings: no heat is wasted on the underlying mate-rials.

5 Table 1summarizes the comparison between IR andconvection heating . One company that switched from convection heating to IRisn t looking back. Like most of its competitors, a Chryslerautomobile assembly plant in Belvidere, Illinois, had beenusing standard gas convection ovens for its paint-dryingprocess. Chrysler switched to electric IR ovens and found thatnot only was the energy use for the Drying process reduced by50 percent but the quality of the finishes Versus Electric IR heating IR radiation is generated using one of three different tech-nologies: electric, gas catalytic, or radiant gas (and radiant gasE SOURCE Customer DirectLicensed for distribution to the customers of E SOURCE members ElectricSource: PlattsNote.)

6 IR = heat evenly, even for products with complexshapesNot sensitive to reflective properties of coatingsLower-cost energy SOURCE (when compared in dollars perunit of energy consumed)Uses less energy when only surface heating is requiredProvides well-controlled, low-intensity heatProvides highest-intensity heatIntensity can be easily adjusted for different productsIR technologyConvectionovenGasTable 1: Comparison of heating technologies for Curing and dryingInfrared heating offers several potential advantages over convection heating forcuring and Drying operations .

7 Electric infrared technology offers more flexibilitythan gas-catalytic in terms of the desired heating intensity. 2005 Platts, a Division of The McGraw Hill Companies, are mainly used for space heating rather thanprocess heating ). Electric and gas-catalytic IR technolo-gies have specific characteristics that make them more orless appropriate depending on the material and the typeof process. Gas-catalytic IR systems generally require agreater capital investment than the other two, but theyhave lower operating costs.

8 To decide which technology is right for a specificproduct or process, a number of parameters must beconsidered, including product quality, operating costs,and production rates. In processes that require fabricand paper Drying , gas-catalytic technology has a slightlysuperior heating efficiency because of the intensity ofthe radiation it emits and the amount of time theproduct spends in the oven. In general, a gas-catalytic IRsystem is a good choice for materials that require a lot ofenergy, such as some textiles, because its fuel costs arelower than those of electric IR (on a $/Btu basis).

9 Electric IR is better suited to sensitive materials thatrequire a less-intense heat or to processes that needquick response times or shorter bursts of intense radia-tion from the heating equipment. Gas-catalytic IR technology has a fixed power densitythat depends on the temperature of the fuel-oxygenreaction; it generally does not exceed 2 kilowatts persquare foot (kW/ft2 that s 22 kilowatts per squaremeter [kW/m2]). In contrast, electric IR ovens canquickly and easily vary the intensity of emitted heatwhile achieving power densities of up to 37 kW/ft2(400kW/m2) a characteristic that makes them superior forrapidly heating metals.

10 Convection OvensFor process heating operations in general, the mostcommon technology is the convection oven, which heatsand circulates the enclosed air within the oven, transfer-ring heat to the part primarily by the movement of theheat-transfer fluid (in this case, air). This technology isvery effective in many applications, such as annealing orheat-treating, where the entire part needs to be heated toand maintained at a specific temperature. For Drying and Curing operations , convection ovens arebest suited to products with complex shapes.