Issue link: https://www.e-digitaleditions.com/i/727416
30 POWDER COATING, September 2016 I ndustrial customers are often faced with the challenge of heating differ- ent size parts in a common convec- tion batch oven or continuous oven. While the larger and heavier parts take more time to absorb the heat, the smaller and thinner gauge parts take a shorter time for heating and curing. However, the batch process cycle time (or line speed for a continuous oven) is typically the same for both part types, which may result in the under- or over- curing of parts. This condition can also lower productivity since operators are unable to do any further processing while the parts are being heated. Another challenge faced by industrial customers is the aging convection heat- ing system. Many of the convection heating systems currently being used are close to the end of their lifetime and are ready to be retired and replaced. How- ever, they are still in operation at many facilities because of various reasons, such as a lack of capital to replace the ovens, lack of awareness of newly avail- able technologies, familiarity with the older equipment along with an unwill- ingness to make a change, and so on 1 . This article will explore two possible so- lutions that can help increase the pro- ductivity of industrial plants in the sce- narios described above. In the first op- tion, the batch or continuous oven is fit- ted with infrared (IR) emitters inside the oven that are turned on as needed to boost heat to the parts. In the second option, a totally separate IR oven is used as a second batch oven in order to aug- ment the existing convection oven. Case studies will be presented and ana- lyzed in an effort to examine the advan- tages and disadvantages of each of these options. Option I: Combination IR- convection oven (IR booster) In the past couple of years, there have been great successes with IR being in- stalled inside the convection heat zone in both batch as well as continuous ovens. This application not only elimi- nates any need for additional floor space, but also takes advantage of the added energy (BTUs) coming off the IR heaters to the overall heat balance of the convection process. There are two major advantages to using this type of application: • Heat large geometrically complex parts to provide a reduction in both cycle time and energy • Batch small and large parts together without under- or over-curing any of the parts inside the convection oven Case 1: Heating large geometric parts. Several industrial customers use straight convection to preheat and cure heavy parts of various shapes. In many instances, these large convection ovens (usually gas-fired) must be turned on a few hours prior to operation to allow the oven to completely heat up before production can begin. Once the oven is at the setpoint temperature (usually be- tween 400°F and 500°F), the part is then placed in the oven to soak. De- pending on the desired preheat temper- ature, the parts are left in the oven for 1 to 2 hours to make sure the entire part has reached temperature. Independent testing was performed with a convection oven to determine the energy savings through this ap- proach. During testing, the benefits of using electric IR inside a convection oven were examined in detail. The tests employed a standard 300 kilowatt (kW) electric convection oven that was retrofitted with approximately 127 kW (ten 12.735 kW heaters) of electric IR. The part used for the test was a single 350-pound part, as shown in Figure 1. Two tests were performed to examine the amount of energy and time it took the part to reach a temperature of 350°F in 300 kW of electric convection only compared to a combined 300 kW of IR (130 kW) and electric convection (170 kW). The results show that the 300 kW combination IR-convection oven used only 131.5 kWh (kilowatt hour) to get the part temperature to 350°F while the Marek W. Urban, Ph.D. Clemson University IR Curing ShopTalk Infrared Equipment Division of IHEA This column is provided to you by members of the Infrared Equipment Division (IRED) of the Industrial Heating Equipment Association (IHEA). The group includes infrared (IR) curing equipment suppliers from throughout North America. We publish the column three times a year to give you the latest information about IR curing techniques and equipment. Contact information is at the end of the column. Most IR man- ufacturers offer testing for free or for a fee. Any IRED member can assist you in finding solutions to curing problems and best practices for finishing of coatings. This issue's column was submitted by IRED members Scott Bishop, Alabama Power Co., Birmingham, Ala., and Baskar Vairamohan, Electric Power Research Institute (EPRI), Knoxville, Tenn. Designing effective and efficient curing processes with infrared to meet convection oven challenges