Infrared heat processing is still more of an art today than an exact science. Experience is the key ingredient to successfully conceive and manufacture industrial heating systems to solve a specific set of customer requirements. That said, many urban myths remain concerning the use of infrared heating, drying and curing for industrial processes.
First on this list is the requirement of “direct line of sight”. Too many people think direct line of sight is a must for every infrared heating process; that is the infrared source must see every/all portions of a product substrate in order to properly heat a product or dry and/or cure a coating on it. They think you can essentially only process flat products.
That assertion is just NOT true. While it is helpful to have a good line of sight, in fact, there are many factors that come into play in properly conceiving and sizing an infrared system that influence this theoretical requirement. These factors include: product dimensions including substrate wall thicknesses, substrate material(s), process line speeds, and how the individual parts present themselves to the heating system and part racking scenarios (eg, are the parts single file, do multiple parts block one another from the line of sight of the heaters, etc.). Also, infrared heaters do not just emit energy straight or on a 90 deg angle with respect to the front of a heater or heater face. The energy is distributed on a range of angles from the heat source even at 45 and 30 deg angles.
For the more difficult applications where a multitude of parts are processed through large work openings, where dimensionally complicated parts are processed, and/or racking methods are such that they block or significantly reduce the line of sight of the parts, a number of methods can be employed that make the use of infrared a major benefit for heat processing.
For example, given a lack of good “line of sight”, great heating, drying and curing can still take place with:
- Infrared heating as a boost to quickly raise the temperature of coated product in front of or in the first zone of an existing hot air convection oven.
- Enough heated dwell to allow the heat/dry/cure process to take advantage of product substrate conductivity.
- The introduction of (non purposely heated) recirculated air movement to assist in the drying and curing in the hidden or recessed area(s) of parts.
- The introduction of true convection (purposely heating air) to help finish the drying and curing of coatings on products either following or right in the infrared oven section.
- Product rotation through the heated oven chamber.
- Multiple temperature control zones vertically, horizontally and in the direction of the conveyor or machine travel
Properly employing the above infrared oven design techniques will allow you and your company to meet process requirements in a cost effective, energy efficient, reduced footprint way that will result in successful equipment installations.
Another myth worth mentioning is that infrared heating must be an electric energy source. Again that is just NOT true. Actually any source that generates or gives off heat is considered infrared, including your body. While some sources of infrared are better than others in terms of longevity, ease of maintenance, warmup or heatup and cooldown times, and energy efficiency with many process tradeoffs, there are a wide variety of both electric and gas infrared heaters.
Based on the misconceptions with regard to the use of infrared heat processing, it is highly recommended that you find an experienced company that manufactures a broad range of electric and gas infrared emitter types that it can bring to bear (such as ours) to is contract to conceive and build your infrared industrial heating systems for your process improvements and new projects, no matter how small or large they may be.
Background: David Weisman, L.L.C. designs and manufactures gas & electric infrared heater/control packages, and infrared, hot air/convection & combinations ovens and spray booths for a broad range of industrial heating, drying and curing applications for individual metal, plastic, wood products and and paper, film, foil, textile, continuous webs, wire and cable extruded rubber products. Conveyorized and batch ovens and turn-key systems. Automated or batch processes.