Industrial Process Heating

Infrared Created a Better Learning Environment

Why did the Norfolk Technical Vocational Center (NTVC) choose electric infrared heating for its auto body shop? The many advantages of IR combined to convince instructor Jerry Wellings that it was the right choice for his new down-draft paint booth. Not only does IR provide a superior finish but also it dries waterborne paint much faster than gas. Furthermore, the system is easy and inexpensive to both operate and maintain.

Assistance

After Virginia Power recommended that the NTVC modify its spray booth to incorporate infrared curing, Wellings contacted RDM Enterprises, Inc., of Greenville, South Carolina, a company that designs and sells down-draft spray booths with infrared curing.

Solution

RDM installed 18 medium wave, quartz tube IR emitters. These emitters are located around and above a car to provide full-car IR heat coverage. Each emitter has a stainless reflector, housing, cover, and on/off switch. During paint spraying, the emitter cover is closed to seal out paint over spray. The on/off switch is activated by opening the cover. Emitters can be left closed – and off – if not needed, as when only part of a car, such as a fender, is to be painted. Each emitter draws a maximum of 2000 watts. The control system chosen for IR heating of this spray booth is simple, cheap, and requires that the operator select only the “intensity” and time of heating. An SCR controller varies the voltage supplied to the emitters based upon the intensity setting selected. This varies the emitters’ tube temperatures and thus the heat radiated. Wellings’ extensive knowledge of painting enables him to correctly choose time and intensity settings for various size and color vehicles. Automatic con-controller systems are available that use IR pyrometers to measure the vehicle surface temperature and automatically control each emitter’s power output.

Benefits

Before the auto body shop started using IR heating, only one car could be painted each day. A freshly painted car had to be left in the spray booth with its filtered air supply and exhaust system for four to five hours, until the paint was dry “to touch.” Now the entire process can be accomplished in as little as an hour and a half. Wellings comments on the increased speed and productivity resulting from his new system: “With my IR heaters, I can now paint, bake, and roll out a car during each of my two-hour-and-forty-minute classes.” The following additional comments by Wellings underscore more benefits of the IR curing system.

Quality: From my experience, gas heating had a real problem with “solvent pop.” A gas heated booth is just a hot box. With it, the paint must dry from the outside, in. If the drying is too fast, a dry skin forms on the outside of the paint. As the inside of the paint dries, the solvents fight to come out. As they do, they break the dry, top crust, leaving little craters in the paint that we call, “solvent pop.” IR heating penetrates the paint, heating up the paint all the way through and also heating the metal underneath the paint. This helps drive the solvents out. IR heating is really a better and faster way to dry a paint job.

Reliability: IR heating is very reliable. I was looking for long, trouble free operation. I’m a firm believer in buying good stuff only once. You can buy a good tool one time, or you can buy a cheap tool five times.

Efficiency: If I want to paint only part of a car, I only open the emitter covers located near that part. There is no need to operate all the emitters.

Safety: IR heating is safe. To change an emitter, I need only to throw one switch and lock it out. There is never any fear of a gas explosion.

Cleanness: IR heating is totally clean. With gas heating, I would expect to have to change my intake air filters at least once a year for school shop use. A commercial shop would be much more often. We’ve had this spray booth system over two years and the filters are still good.

Quiet: Another thing I like is the quietness of IR curing. Once we stop spraying paint, we can turn off the air supply blower fans, and only the exhaust fan continues running. I can now teach a class next to the booth while a car is being dried.

Ease of maintenance: There is no concern for corrosion of gas burners when not in use, or the need for adjustment after periods of school vacation. With electric infrared medium wave emitters, I can immediately see if an emitter has failed, and it is quick and easy to change. There is almost no maintenance of this IR system.

Low cost: IR heating doesn’t cost much. The maximum IR heating cycle I use is 40 minutes. I seldom set the intensity setting for the emitters above 80%. Even if they were set at maximum intensity, 18 emitters would draw only 36 kW. For 40 minutes usage, that’s 23 kWh, which only costs less than a dollar and a half at six cents per kWh. That’s cheap to dry a car’s paint job.

Mac McColm, president of RDM Enterprises, adds another benefit to the list: IR’s compatibility with any paint formulation and method of application, whether it be waterborne, high solids, urethane, or powder coating. McColm agrees that medium wave electric IR is an excellent choice for Norfolk Technical Center. He explains, “First, they are in the business of training people for the local job market, and that responsibility requires that their training be on the leading edge of technology. Second, in terms of initial cost, operational cost, and efficiency, IR is the only technology that allows them the best use of funds.”

For More Information

Contact Mark Gentry at (336) 679-4020 or mgentry@advancedenergy.org.