By Jan H. Schut
Here is a look at three unusual integrations of extruder barrel heaters with hot air removal to save substantially on energy. All were designed as retrofits, but are also used on new extruders, and two have been adapted for injection molding. WEMA GmbH, Luedenscheid, Germany (www.wema.de), a maker of heating elements for extruders, and Insul-Vest Inc., Tulsa, OK (www.insul-vest.com), a maker of insulation blankets for extruders, separately patented ceramic heaters with very controlled hot air retention and removal.
All three heat/cool systems claim big energy savings on barrel heat ranging from 30% to 70%. WEMA’s technology uses thermally conductive ceramic over resistance heater bands covered with an enclosed cooling hood with fans and vent flaps. Insul-Vest’s technology, licensed to and built by Rex Materials Group Inc., Howell, MI (www.rexmaterials.com), uses thermally insulating ceramic over radiant heaters and cools by sucking air through a narrow gap between the heaters and the barrel. WEMA and Davis-Standard LLC, Pawcatuck, CT (www.davis-standard.com), both have patent-applied-for shrouds that fit over each of their existing resistance heaters to control the release of hot air.
WEMA INTRODUCES HEAT/COOL HEATERS IN THE U.S.
WEMA’s patented heat/cool bands (DE 19855357C2) were first introduced in the U.S. at NPE 2015 (www.npe.org), though they were commercialized in Europe back in 2001. They are standard on many extruder brands including Kuhne GmbH, Sankt Augustin, Germany (www.kuhne-group.com), Windmoeller & Hoelscher KG, Lengerich, Germany (www.wuh-lengerich.de), and Rollepaal BV, Dedemsvaart, the Netherlands (www.rollepaal.com. They’re also used on twin-screw extruders and injection molding machines.
WEMA developed the technology in the late 1990s working with Robert Michels, at the time a PhD candidate at the University of Duisburg-Essen, Germany (www.uni-due.de/kkm/index_en.shtml), and now head of project management at ETA Kunststofftechnologie GmbH, Troisdorf, Germany (www.eta-gmbh.de), which builds specialty screws, barrels, and dies. WEMA and Michels developed fins made of special aluminum oxide ceramic with high thermal conductivity of 16-28 W/mK comparable to stainless steel vs. 2-3 W/mK for standard ceramic.
The conductive ceramic is made into “stones” with concave and convex ends that can easily be adapted to different barrel diameters and zone lengths. WEMA’s KH214 bands come 48 and 63 mm wide. Ceramic fins increase cooling surface area 2.5 times vs. a smooth ceramic heater band. For applications requiring more intense cooling, KH214 heat/cool bands can be sequenced with WEMA’s KE300 aluminum cooling fins, also developed with ETA’s Michels.
KH214 heat/cool bands are also combined with WEMA’s patent-applied-for shroud (Pat. Applic. # 202009005822), introduced in 2008. The shroud controls release of hot air with its Ecowema system of vent flaps that open when fans are on and seal closed when fans are off. Each temperature zone on the extruder requires its own heat control and cooling shroud. KH214 heaters with Ecowema shrouds save up to 40% on barrel heating energy.
REX MATERIALS’ LATEST ENERGY-SAVING ‘TCS’ HEATERS
Insul-Vest’s patented ceramic heater technology (WO 2001032396) was also invented 15 years ago, then licensed to Rex, which commercialized the technology eight years ago as its TCS (thermal control solution) heaters. Rex’s TCS heaters use thermally insulating ceramic and radiant heater elements, which Rex claims heat the barrel 55% faster than conventional heater bands, which have to heat the surrounding ceramic band before heating the barrel.
Cooling is also faster because TCS heaters aren’t in direct contact with the barrel. Instead there is a 3/8 inch gap between the radiant heaters and the barrel. When cooling is needed, high speed (3000 rpm) axial fans suck hot air out of this space and pull in ambient air. The hot exhaust air can then be directed where needed to dry or preheat plastic pellets, heat the plant in winter, or keep it cool in summer by venting hot air outside. TCS heaters save up to 70% on energy for barrel heating, Rex says.
TCS heaters are distributed by Milacron ServTek in Cincinnati, OH (www.milacron.com), and sold primarily to retrofit single screw extruders for energy saving. Each temperature zone requires its own heaters and suction fans. One or two fans are used depending on the level of cooling needed. A variation for injection molding treats the whole barrel as a single zone and is used for rapid barrel cooling before product changeovers. Insul-Vest recently applied for a patent on the next generation of its energy saving heater technology.
DAVIS-STANDARD’S FIRST COMMERCIAL ‘EEACEH’ COOLING SHROUDS
Davis-Standard also introduced a patent-applied-for heater/cooler system (U.S. Pat. Applic. # 20120090819) in 2011 called energy-efficient, air-cooled, electrically heated (EEACEH). The insulated cover prevents radiant heat loss and uses a conventional air cooling fan with a valve system. Valves open with air flow when the cooling fan is on and close with gravity when the air flow stops. The cover is designed to retrofit Davis-Standard extruder barrels with cast aluminum heaters built after 2000 and even reuses the bottom plate of the barrel cover.
Each temperature zone on the barrel requires a separate shroud. EEACEH shrouds have been field tested and are now commercial. Davis-Standard recently booked a large order for 27 extruders with the energy saving shrouds for barrel sizes from 1.5 to 5 inches in diameter. Shrouds are available for up to 6-inch diameter extruders. The technology is “most effective for cast film and extrusion coating where higher temperatures are used,” says Davis Standard’s Vice President of Technology John Christiano. The shrouds save 30% to 50% on energy for barrel heating compared to conventional air-cooled heaters.