When deciding between convection and infrared heat processing equipment, it is important to consider the benefits of infrared.

When making a decision about what type of heat processing equipment is needed for a particular application, you may want to evaluate both convection and infrared heat processing equipment. Within reason, hot air (convection) is hot air. When thinking about infrared heating, remember that there are several different types of infrared heaters (and both electrically powered and gas fueled). Electric emitters include:

  • Short-wave, high-intensity emitters such as Type T3 quartz lamps and tungsten filament lamps.

  • Medium wavelength, medium-intensity emitters such as coil or wire filaments in unsealed quartz or silicon tubes or panels; metal ribbon emitters; and ceramic emitters.

  • Long-wavelength heaters, which are available but not included in this discussion due to their low intensity.

With those types in mind, consider the 10 benefits that electric infrared heaters can provide for your process heating application.

Tip 1: Take Cost into Account

The components used in the construction of an electric infrared heat process system are likely to be comparable to or slightly more expensive than those used in the construction of convection ovens and dryers. However, an infrared system likely will be smaller than a convection system, resulting in lower overall material and fabrication costs. The smaller footprint also will save floor space, which may offset any higher component costs.

In most parts of the country, when comparing the cost of a kilowatt hour and the cubic feet per hour of gas, gas is less expensive than electricity. The cost advantage of gas may be neutralized by managing the electricity being used. For instance, a convection oven is on and fired up for a whole shift; during the same shift, an electric infrared heating system might be on for only a fraction of the time.

Tip 2: Regard Response

The ability of electric infrared heaters to heat up and cool down rapidly is paramount to any discussion about convection vs. infrared processing systems. Being electric, they can be turned off and on quickly like a light bulb. Infrared heaters take only seconds to reach full power. The electromagnetic waves become thermal energy that radiates to the product very quickly. The ability of electric infrared to heat a product is limited only by the product’s ability to absorb infrared energy. (Some materials are better able to absorb infrared than others, and because infrared is a line-of-sight technology, the product must be able to “see” the infrared energy.)

Gas convection systems, conversely, need time to heat up and to cool down. To heat a given substrate to temperature using convection, the oven must reach its operational temperature, and the substrate must be subjected to that heated environment for the time needed for it to reach its optimal temperature. The convection oven may take many minutes to reach its operational temperature.

Tip 3: Appreciate Control and Configuration Flexibility

Electric infrared heating offers the user a high degree of control flexibility. As noted previously, electric infrared heaters can be turned off and on in a short time. In addition, electric infrared heaters can be programmed to provide heatup and cool down cycles that suit products sensitive to overheating. Infrared emitters can deliver heat at low rates similar to a convection oven -- or heat that is more than 20 times greater. Heating rates greater than 80 kW/m2 are seldom necessary although electric infrared can produce more.

Electric infrared ovens can have multiple zones, each with a different heat profile. Independently controlled heating, drying and curing zones can be incorporated into a single oven.

Tip 4: Obtain High Speeds

Due to the higher heating rates and the high degree of control available with electric infrared process heating, most products can be heated faster than in a convection oven. Thus, it is possible to decrease the dwell in the oven and increase the throughput.

Tip 5: Enjoy Increased Efficiency

The use of electric infrared may enable some manufacturers to make better use of their production facilities by delivering per-product processing costs that are comparable to, or lower than, those of a gas convection oven. Electric infrared will deliver a higher amount of input energy to the product than a gas convection oven. An electric infrared oven does not require a long startup time as might be required with a convection system. When infrared is the heat source, heat is delivered directly to the product and not into a carrier medium such as air. Infrared radiation can be directed to precisely heat only select areas of an assembly without overheating other areas that may be heat sensitive.

Tip 6: Take Advantage of Compact Footprint and Low Weight

Electric infrared ovens tend to be more compact in size because electric infrared emitters deliver more heat to the product in less space than convection ovens. Production floor space can be better utilized.

Because heat delivered by infrared emitters is not dependent on convection (airflow), infrared ovens usually require much less insulation and bulky frames. Also, because there are no moving parts, there are no motors and motor supports for the heating components. Some manufacturers will hang infrared panels from the ceiling to save floor space.

Tip 7: Consider Reliability

Electric infrared process heating systems tend to be reliable. With no moving parts or motors, they are, in most cases, modular. The ability to quickly heat up and coon down is important. For instance, in the time it takes a gas system to reach full temperature, an infrared system can be cooled enough to be worked on for maintenance.

Tip 8: Remember Product Quality

Electric infrared energy emissions can be controlled, directionally directed, and temperature controlled more accurately than is possible in a convection oven. For instance, infrared systems effectively heat materials such as coatings and paints that must be dried or cured. Infrared energy will penetrate the coating and warm the substrate material, flashing off the solvents quickly to eliminate bubbles and blistering. Infrared heating does not require convection currents to heat the product being manufactured; consequently, the uncured finish is not disturb by airflow -- an effect found in convection ovens that can cause unpredictable or unacceptable finishes at times. Airborne particles are not deposited on the surface because the air turbulence in the oven can be limited to that of the products’ movement through it.

Tip 9: Enjoy Versatility

An infrared oven or dryer’s operating parameters are versatile because of most systems have short setup times, easy control of temperature and controllable speed. Consequently, many different products with different heat profiles and desired results can be run on the same manufacturing line.

Increases in line speeds that increase production rates usually are attainable by adding infrared modules. The length of most convection ovens is set to heat products for a particular time based on line speed through the oven or dryer. Many operations that have convection dryers add infrared to the input or output side to increase speed and production.

Tip 10: Contemplate Environmental Impact

In today’s markets, manufacturers are increasingly required to adhere to regulations that limit the amount of emissions of solvents allowed to be freed into the atmosphere. Many manufacturers are replacing solvent-based coatings, adhesives and paint with water-based systems to comply with these air quality standards. Usually, it takes longer to dry or cure water-based chemistries than to flash off solvents. Fortunately, electric and gas infrared heating can increase the rate of heating coated surfaces. Production efficiencies lost in the switch to water-based materials can be recovered.

Also, infrared heat processing systems will generate less heat into a surrounding air-conditioned work area, less noise emissions, and fewer noxious odors than convection systems. While it makes sense to consider both infrared and convection systems, be sure to understand what advantages infrared heating can offer your process and company.

This article originally was published with the title "10 Tips: Infrared Illuminated" in the September 2009 issue of Process Heating.