Infrared ovens are used to bake, cure, bond, burn-off, preheat, thermal-form, cook, fuse, shrink, laminate and dry a wide variety of materials. But, how can you know whether an infrared oven is right for your application? The answer lies in testing. Visiting an oven manufacturer's testing laboratory will allow you to see your product under many different heating scenarios and help you to make the best choice.
If you are considering using an infrared oven, you may have a few questions. Here are seven common questions and answers about infrared ovens.
1.Do infrared ovens work better in a vacuum with little or no air?
Air is virtually transparent to infrared radiation, and infrared is neither absorbed nor scattered by air. However, water vapor, carbon dioxide and other greenhouse gases do absorb infrared radiation. If the distance between the emitter and the absorber of infrared energy is a few feet or less, the ener-gy absorbed by the gas will be negligible.
2. Are infrared ovens only effective in heating flat surfaces?
Flat surfaces are ideally suited to infrared radiation. They can be heated rapidly and effectively in an infrared oven. However, more complex, three-dimensional shapes also can be heated effectively in infrared ovens. Parts can be rotated so that all sides are evenly exposed to radia-tion as they pass through the oven. Also, the oven can be zoned to vary heating rates, allowing sufficient cure times to heat internal regions of a part.
The oven's design also can incorporate air (convection) heating into many infrared systems to provide a convective assist to the infrared energy. In cases where the process requires water dry-off, for example, effective drying can be achieved by using an air impingement oven as a stand-alone unit or in conjunction with infrared.
3. Is short-wave infrared color sensitive?
Less than 5% of the infrared from a 4,000°F (2,204°C) short-wave emitter falls into the visible spectrum. At 3,600°F (1,982°C), the percentage drops to less than 3%. The difference in product temperature from a black to a white object in an infrared oven should be no greater than 10 to 15°F. As a general statement, medium and long waves are less sensitive to color.
4. Is infrared radiation harmful to the oven operator?
There is no immediate danger associated with the use of infrared, compared with ultraviolet radiation or microwave radiation. However, as a precaution, one should avoid prolonged viewing of high intensity infrared emitters at distances less than 15'. Reflectors and shields used to improve the efficiency of the oven also make them safer.
5. Are infrared ovens more expensive than convection ovens?
Often costs for infrared ovens are comparable to convection ovens, and they can be less expensive. In general, the overall size of the infrared oven will be smaller than a comparable convection oven, resulting in savings in materials and fabrication costs.
Individual components of an infrared oven may be more expensive than those of a convection oven. For example, electric infrared emitters may cost more than a gas burner. Another factor to consider is the ability to control infrared, which results in more efficient use of electric or gas.
6. Are infrared ovens more costly to operate than convection ovens?
Infrared ovens are more efficient than convection ovens in delivering energy to the product. According to "Technology Guidebook for Electric Infrared Process Heating" published by the Electric Power Research Institute (EPRI), Center for Materials Fabrication (CMF) and the Infrared Equipment Association (IREA), electric infrared ovens are, on average, three times more efficient than gas convection ovens. Actual costs will be determined by the cost of gas vs. kilowatt-hour -- that is, the cost of energy delivered to the product for a given oven.
Some infrared ovens' emitters provide a nearly instant response with virtually no warmup time required. These ovens can be turned on shortly before the process begins and off during production stoppages, which may reduce operating costs
7. Do infrared ovens require more maintenance than convection ovens?
Both infrared and convection ovens require regular preventative maintenance. Maintenance of infrared ovens includes examination of emitters and replacement of any that have failed. In addition, regular cleaning of reflectors in electric infrared ovens will help maintain efficiency.
Gas convection ovens require periodic maintenance to check and clean the burner, clean the oven, check the flue for proper draft, and clean the flue. Convection ovens may tend to be more forgiving than infrared ovens when routine maintenance is ignored. There may, however, be a compromise of product quality and safety. One must keep in mind that the advantages of infrared rely on the system operating as designed. Buildups in burner orifices, failed emitters or dirty reflectors will have an adverse effect on the operation of the oven.
So, if you are considering an infrared oven, keep the following benefits in mind. Infrared ovens allow you to save time by increasing production line speed and enjoy fast emitter response. Most infrared oven designs reduce the overall size of the curing system, and electrically powered designs have less need for stacks or venting because no byproducts of combustion are created. Infrared ovens can be zoned to process various parts, and their repeatable results ensure continuity of quality.
This article was provided by the engineering staff at Fostoria Industries Inc., Fostoria, Ohio, a manufacturer of infrared heaters, ovens and dryers. For more information from Fostoria Industries, call (419) 435-9201; or visit www.fostoriaprocessequipment.com