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Why thermoformers are hot for catalytic heating.

Two years ago a South Michigan thermoformer installed the first catalytic heaters to be used in thermoforming production. The company (which prefers not to be identified for competitive reasons) replaced electric heaters used to mold bathroom products. Today, all that company's forming machines have been converted to catalytic heat, and its monthly electricity bill has dropped to about $7600 from over $30,000 with the old electric ovens, says the plant engineer.

Catalytic combustion heating-which converts natural gas to energy in a flameless catalytic reaction--isn't exactly new. It's how Coleman portable heaters have worked for years. Catalytic heaters warm transcontinental gas pipe lines and dry paint in industrial paint lines. But they had never been tried in plastic thermoforming machines. The first thermoformer to install catalytic heaters originally had considered using this type of heat to predry sheet more economically. The company hadn't thought of using it in the forming ovens, but ended up working with Vulcan Catalytic Systems Ltd. in Portsmouth, R.I., to convert an entire 8 x 12 ft oven--on condition that if the new heaters didn't work, Vulcan would remove them again. "Within six weeks of doing it, after they got their first utility bill, they ordered three more," says Vulcan president Michael Chapman.



In two years, Vulcan has converted some 31 different thermoforming processors and retrofitted exactly 50 machines. There are also three more known installations, one done by a thermoformer on its own aftervisiting a Vulcan installation, and two others done by an OEM machine builder using an imported catalytic unit. More thermoformers are converting all the time. Last fall, some 40 members of SPI's Thermoforming Institute heard a talk in Boston by technical committee chairman Thomas King on his company's catalytic conversion. King is president of Thermo-Fab Corp. in Shirley, Mass., which has run a machine with catalytic ovens for over a year. King says catalytic heat improves wall-thickness distribution on deep-draw parts, so reject rates drop.

Companies that convert say it's hard to calculate all the benefits--so many happen at once. Electricity bills drop 60-80% from previous electric heaters. Cycle time improves 20-30% because the catalytic heaters emit longer infrared waves that are more readily absorbed by plastic sheet. Uptime improves dramatically because the new heaters are virtually maintenance-free. One thermoformer needed two maintenance men before converting but only one afterward. And because catalytic heating uses infrared more efficiently and depends less on convection heating than electric i-r heaters, catalytic heat penetrates sheet more evenly. Also, because catalytic heat is a less intense heat source, it may reduce or eliminate the need to predry sheet (depending on sheet exposure to humidity).

There's also a safety advantage: catalytic elements are considerably cooler than electric elements. "When we inadvertently dropped a sheet of ABS on them, it charred, but it didn't burn," says Gordon Cross, president of Mayfield Plastics Inc. in Worcester, Mass., which converted a Comet thermoformer with 3 x 4 ft top and bottom ovens to catalytic heating.

A converted thermoformer may also qualify for hefty one-time energy rebates for switching to gas. Incentive programs are being tried by utilities on Long Island, N.Y., and in New Jersey, Pennsylvania, and Washington. They offer $100-$150 per kilowatt of electricity use avoided. Converting a 100-kw vacuum former can earn a $10,000-$15,000 rebate. Three months ago Formed Plastics Inc. in Carle Place, Long Island, spent $23,000 to convert a large vacuum former, plus another $10,000 for installation and gas piping to the machine, and got a $9300 rebate from Long Island Lighting Co. Formed Plastics, president Patrick Long says the machine costs $1.85/hr to run now vs. $6/hr in the winter and $13/hr in high-priced summer months with electric heaters. He's converting another forming machine immediately.

New England Plastics Corp. in New Bedford, Mass., installed gas just to try out catalytic heating. Now the company is converting all seven of its thermoformers. Productive Plastics Inc. in Mt. Laurel. N.T., is retrofitting a 5 x 6 ft single-station machine's oven for about $25,000 and doing an energy audit to verify energy savings.

So far, catalytic conversion heat is mostly used in heavy-gauge sheet forming like polycarbonate, ABS, PS and TPU. Vulcan has converted four roll-fed thermoformers in three companies, processing ABS, HIPS, OPS and PET. Vulcan says only one of the three experiences faster cycle times--by 20%. And many major drink cup applications are now looking at the technology.


Catalytic converter panels come in standard rectangular sizes and can even be zoned, though several thermoformers say zoning isn't necessary. A typical thermoforming oven might use four to six panels top and bottom. A large oven would add more on the periphery. Panels are made of a pad of ceramic fiber and fiberglass impregnated with a platinum alloy catalyst and contained by stainless-steel mesh in a metal frame.

Supply of natural or LP gas to the panels is controlled by servovalves once sensors have determined that panels are up to heat. Controlling gas flow is an important safety feature, since if catalyst reaction stops, gas would pass into the plant. Safety is ensured by using thermocouples or thermoswitches to shut off gas supply if the catalytic reaction slows to the point of a temperature drop. Varying gas pressure also controls the level of heat generated. Buried in the mesh are tubular electric Calrod-type elements for preheating the panels. When a thermocouple senses the pad is hot, gas "is allowed into the heater via Factory Mutual approved safety valves and reacts with the hot catalyst," Vulcan says. "After a further five minutes of reaction, the electricity is shut off."

When the gas hits the hot catalyst pad, it's converted to [CO.sub.2], a little water vapor and a lot of radiant energy. Once panels are up to proper temperature, continuous catalytic reaction keeps them hot. Pad surface temperature determines the i-r wavelength emitted. Catalytic converter panels run at 750850 F surface temperatures, emitting long (4.25 micron peak) i-r waves that are readily absorbed by plastic sheet. By contrast, electric-powered quartz or Calrod i-r elements at surface temperatures of up to 1800 F emit shorter (2.25 micron peak) i-r wavelengths, which aren't as well absorbed.

The same long (3.5 micron) i-r wavelengths can also be emitted by electric-powered ceramic i-r heater elements, but their operating cost is said to be much higher. Electric i-r elements produce waves that are just as efficiently (98%) absorbed by plastic and may also qualify for energy rebates from utility companies, according to MOR Electric Heating Associates Inc. in Comstock Park, Mich. MOR makes a brand of electric i-r heaters called Salamander, under license from a U.K. manufacturer.



A few problems surfaced with some early catalytic installations, but were relatively easily fixed. Powder-coated limit switches, for instance, overheated because the powder coating also absorbed more i-r radiation. This was solved by simply-wrapping switches in aluminum foil, which reflects i-r.

Catalytic panels can be small or relatively large. Most of Vulcan's panels are 18 x 48 in. or larger. Two large panels from Vulcan were tried out at De-Flecta Shield in Corydon, Iowa, the only processor known to have installed its own catalytic system, which is used in the forming of polycarbonate truck body parts. The catalytic panels were put in a fixed, overhead position in a heat tunnel, and a bubble of hot air built up under them, causing some sagging. De-Flecta Shield switched to panels from Infra-Red Technologies, Inc. in Kansas City, Mo., which have cross-bracing. Other thermoformers say the "pillowing" phenomenon can be corrected by leaving breathing room of 5-6 in. between the perimeter of the panels and the machine side walls to ensure an updraft to the panels. There's also a difference in optimum height of heaters off the sheet: 8-12 in. is ideal for catalytic heaters, vs. 7-8 in. for electric heaters. (CIRCLE 17)

Tank-type or zero-gravity thermoforming machines also won't readily workwith catalytic heat. It requires subjecting the whole lower heater bed to 80-100 psi pressure, which could cause the flow of gas to back up in the heater pads and quench the catalytic reaction. There is some dispute as to whether billow forming might present a similar problem. And certain contac-theating thermoformers used for light-gauge forming of candy inserts are also difficult to convert.

In places without natural-gas service like rock-bound Maine, thermoformers can hook catalytic-converter panels up to tanks of residential LP gas. But LP service can lead to problems. An industrial former in Maine started using catalytic heat in January 1992, but by February production had mysteriously slowed. It turned out that the plant's LP supplier had run low on residential-grade LP and substituted commercial grade, which contains a higher level of propylene. That coated the catalyst bed with unburned hydrocarbons, reducing the catalytic reaction. However, the effect is temporary and the heating pads will self-clean once the right mix of gas is restored. Filters can also be used for gas. Kintz Plastics Inc. in Howe's Cave, N.Y., has successfully converted three thermoformers to catalytic heat with LP gas and is converting two more.


There are at least three North American makers of catalytic converter panels: Infrared Technologies, CIS-CAN Industries Ltd. in Edmonton, Alberta (represented in the U.S. by Deidan Industries, Brooklyn, N.Y.), and Catalytic Industrial Systems in Independence, Kans. (formerly Bruerst Industries Inc.) . There are also offshore makers of similar products in Japan, Ireland and Italy, among others. (CIRCLE 13)

Two companies supply catalytic heaters and complete conversion installations. Vulcan Catalytic Systems has a partnership with Catalytic Industrial Group to supply its heaters. And American Catalytic Technologies Inc. in Old Saybrook, Conn., launched in February by David Oliver, a former representative of Vulcan, has an exclusive deal to supply Infra-Red Technologies, heaters, which are said to offer slightly different controls. (CIRCLE 14)

Two thermoforming OEMs have also already built machines with catalytic ovens. Zimco Inc. in Danbury, Conn. (see New Products section), has built two machines with catalytic heating panels from Zimcat, an Irish source. Zimco president Eduard Zimmerman (former president and owner of Drypoll Inc. in Bayside, N.Y.) says his catalytic formers are in Michigan making heavy-gauge shipping pallets and truck parts. And Thermoforming Technologies Inc. in Seabrook, N.H., has built two machines with catalytic ovens from Vulcan for automotive applications.

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Author:Schut, Jan H.
Publication:Plastics Technology
Date:Jun 1, 1993
Previous Article:Recycling update: high noon in high-density PE.
Next Article:Innovative molding cuts cost, weight of structural plastic parts.

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