Plastics Engineering Blog

Tale of Two New LLDPE Film Recycling Plants

Posted on December 3, 2013 by Jan Schut

By Jan H. Schut

Postconsumer polyethylene film recycling is coming back after a 15-year hiatus with investment in new plants and new R&D. Especially interesting are new processes to clean LLDPE stretch film. Two new plants started up in 2011 with new wash processes to recycle 100% LLDPE stretch film back into film, one for pallet wrap, the other silage wrap. Wisconsin Film & Bag Inc., Shawano, WI (www.wifb.com), devoted five years to bench top R&D in-house to invent a patented hot wash process (U.S. Pat. # 8567702) for postconsumer LLDPE pallet wrap that allows WIFB to reuse the material in translucent monolayer industrial films and can liners. Soreplastic S.A., Tenneville, Belgium (www.soreplastic.com), recycles heavily contaminated LLDPE silage stretch wrap with a single large washing and recycling line making 1200 kg/hour of black film grade material. The trick, the company says, is much finer shredding.

NEW HOT WASH FOR LLDPE PALLET WRAP
Wisconsin Film & Bag’s process for LLDPE pallet wrap is designed to remove paper labels. WIFB uses hot water and surfactant to sterilize film and remove paper fiber. Typically hot water is used with PET flake to remove adhesives, but WIFB uses hot water “to get the pulping action to remove paper,” explains Robert Kulesa, vice president of operations at WIFB. “Adhesives aren’t a problem, they stay with the plastic. But if any contaminants are left after washing, they reattach to the plastic in the dryer because of the tackifiers.”
WIFB processes 90% LLDPE and 10% LDPE. The LLDPE wash line was built by Herbold Meckesheim GmbH, Meckesheim, Germany (www.herbold.com), though the idea to use hot wash for pallet wrap was WIFB’s. The line starts with a Herbold wet grinder with knives modified for LLDPE. It cuts film into large pieces, which go into Herbold’s recently designed VWE 600 prewash unit with three integrated wash sections. The first segment is float/sink to remove rocks while up-currents of water move film to the second segment, which has two conveying screws over a perforated bottom and spray nozzles to rinse sand and paper off the film. The third segment is another float/sink tank to remove fine sand and sediment. Segments can have separate water circuits for very contaminated film.
Film then goes by screw conveyor to a wet grinder, which reduces it to 1.5-2 in. flake. Next comes the proprietary hot surfactant wash (140-190 F according to the patent), followed by hydrocyclones for density separation and mechanical dryers. Because the material is sticky, WIFB releases last moisture in an agglomerator, creating crumbles that are easier to store than thin flakes. Recycled material is used in WIFB’s monolayer ECO Blend industrial films and can liners and in customers’ bags at 25%-50% recycled content.

Wisconsin Film & Bag uses patented hot surfactant washing to recycle 100% LLDPE pallet stretch wrap. It starts with Herbold’s three-part prewash and ends with an agglomerator to create manageable crumbles out of sticky flake and remove last moisture.

At least one other filmmaker puts recycled pallet wrap at high percentages into can liners and film, but using a dry cleaning process and putting the material into three-layer film. In 2008, Petoskey Plastics Inc., Petoskey, Mich., started its Greencore Recycling division with a new washing and recycling plant in Hartford City, IN (www.greencore.com). Petoskey recycles 36 million lb/year of LLDPE pallet wrap and contaminated LDPE redemption bags from MRFs. The company dry recycles the LLDPE pallet wrap, shredding it and re-pelletizing it with an extruder from Erema GmbH, Ansfelden, Austria (www.erema.at). Paper is removed with continuous melt filtration from Erema’s self-cleaning laser filter, which has some 500,000 laser-drilled holes. The wash line from Tecnofer Ecoimpianti Srl, Caneselli, Italy (www.tecnofer.bis), recycles the contaminated LDPE redemption bags. Recycled material goes into Greencore’s three-layer can liners and bags with up to 70% postconsumer content. Petoskey also dry recycles postconsumer bags and film in closed loops for customers and has done so since 1978.

NEW SHREDDING FOR 100% LLDPE SILAGE WRAP
Soreplastic’s new recycling plant for silage stretch wrap faces much higher contamination than pallet wrap. Silage film comes with up to 60% rocks and dirt. Soreplastic’s input is roughly 40 million lb/year of silage film collected from regional farm groups (which are part owners of Soreplastic). Output is 18 million-20 million lb/year of film-grade black pellets, sold for agricultural film and garbage bags. Soreplastic washes with cold water and no chemicals. Its recycling line starts with a wet shredder from Lindner ReSource GmbH, Grossbottwar, Germany (www.lindner-resource.com), with capacity for up to 15,000 lb/hour. The number and distribution of shredder knives is modified for stretch film. But the big difference is that the shredder cuts film unusually small–down to 2-4 in. pieces. Recycled stretch film is typically shredded to the size of a sheet of paper (bigger pieces reduce wear on knives).
Shredded film then goes to a Sorema wash line, starting with prewashing with a float/sink section to remove rocks and a spray wash section to screen paper out. Then the material goes to a wet grinder to reduce it to 1-1.5 in. flake—again smaller than usual. Film is typically ground into 1.5-2 in. pieces. Flake then goes to a water tank with stirrers to open up clumps of material and on to another float/sink tank for final density separation before friction washing in centrifuges. Friction washing is followed by a screw press to remove water. Soreplastic’s drying system is different from the hot air dryers typically used for HDPE film. Because of stretch film’s stickiness, Soreplastic dries flake mostly mechanically, being careful not to overheat it. Drying starts with a large double centrifuge, followed by mechanical drying.

Among several new postconsumer film recycling plants, Soreplastic in Belgium stands out for the sheer size of its Sorema recycling line with output of 1200 kg/hour from up to 60% contaminated silage stretch film. Soreplastic’s trick is unusually fine shredding.

Soreplastic isn’t the first or only company recycling LLDPE silage stretch film, but it’s believed to run the biggest single recycling line for silage film. British Polythene Industries in the U.K., a producer of LLDPE silage wrap, is the dean of agricultural film recycling with three plants recycling a total of 150 million lb/year of heavily contaminated LLDPE and LDPE agricultural film. BPI’s first plant, which started in Dumphries, Scotland, in 1995, has recycled 100% contaminated LLDPE silage wrap for 15 years. BPI’s newest plant in Rhymney, Wales, which started in 2007, recycles LLDPE silage wrap and LDPE agricultural film separately. The LLDP line starts with a drum washer from Pla.to GmbH in Goerlitz, Germany (www.plato-technology.de), to remove large contaminants. Shredding, washing, grinding and drying systems are from Tecnofer. Recycled film goes to a twin-screw extruder from MAS Maschinen-und-Anlagenbau GmbH, Pucking, Austria (www.mas-austria.com). BPI’s LDPE recycling uses a conventional dry system with manual sorting, size reduction and extrusion by an Erema TVE extruder. BPI uses recycled material in trash bags and construction films.

British Polythene Industries recycles 150 million lb/year of heavily contaminated postconsumer LLDPE silage stretch film and has since 1995. BPI uses Pla.to Technology’s giant Drum Washer to remove stones before Tecnofer washing and recycling lines.

Posted in Uncategorized | Tagged British Polythene Industries, Germany, LDPE, Linear low-density polyethylene, LLDPE, Silage, Stretch wrap | Leave a comment

New Moves for Rotating Molds

Posted on November 6, 2013 by Jan Schut

By Jan H. Schut

Two unusual new concepts for cube molds for multi-material injection molding were introduced at the Kunststoff Show (K Show) in Düsseldorf, October 16-23 this year (www.k-online.com). Both alter the normal role of cube molds to move and assemble parts by creating unusual new non-cube structures to transport molded parts for assembly. Separating part transport from the cube neatly allows secondary automation without adding cycle time providing for significantly faster production. Servo-driven rotating molds also cycled faster with more automation than ever before on the show floor, demonstrating new possibilities for durable and medical applications.

Rotating molds with two, three and four sides have been used since the 1950s to mold multi-material parts, sequentially injecting two to as many as six different materials or colors. Four-sided cubes offer much higher automation and output than two-sided rotary stack molds. Cubes are typically dedicated to in-house molding millions of parts a year of small disposables like toothpaste tube shoulders, re-closable lids and soft-touch toothbrushes. Two-sided rotary molds produce lower volumes of larger multi-material parts in the tens and hundreds of thousands for durables like tools, automotive, appliance and electronic parts.

ON TRACK FOR MORE FLEXIBILITY

One of the two new cube concepts is Flexi-Cube launched by G. B. Boucherie N.V., Izegem, Belgium (www.boucherie.com), which has a fixed cube around which light-weight mold inserts or carriers travel on a track. Parts are molded with different material shots on the stationary cube. Because the cube doesn’t turn, it doesn’t have to be square, but can be rectangular, allowing more stations to be added for molding, cooling, and other functions.

Inserts carry parts from station to station around the cube. Boucherie’s K Show announcement describes a solid track “around the cube on which holders with molded parts are traveling. These holders are moved by servo motors, allowing [them] to travel over different distances.” The patent application (U.S. Pat. Applic. # 20110117233) describes mold inserts that “serve as holders and can be lifted out of partial cavities,” pulling back from the cube just enough to travel freely around it.

Boucherie’s new Flexi-Cube technology for high-volume, multi-material injection molding has a fixed cube around which light-weight mold inserts travel on a track. The first commercial Flexi-Cube mold was installed in the U.S. last year to make soft-grip razor handles.

The first commercial Flexi-Cube mold, which took seven months to build, was installed in July 2012, in the U.S. It has 24 cavities molding three-component solid razor handles for a snap-fitting razor. There are four sets of molds on the stationary cube and five sets of inserts to move parts around the cube. The extra insert allows a fifth station on the non-operator side for robotic part removal without adding cycle time. The first parting line of the mold has two sets of cavities for the first and second shots of PP. The second parting line has cavities for contact cooling and a third shot of soft-grip TPE. Cycle time for the 10-gram razor handle is only 17 seconds. “Typically a solid razor handle like that would take 25 seconds,” says John Williams, president of Boucherie USA Inc., Knoxville, TN. Boucherie showed a two-cavity prototype in motion at K without molds.

The other unusual new cube molding concept comes from Zahoransky Formenbau GmbH, Freiburg, Germany (www.zahoransky-group.com) and combines multi-component indexing mold plates with a “TURN-stack” rotating assembly cube. The propeller-like indexing mold plates carry either two or three molds, depending on how many materials are being injected. A single-component part uses two plate molds and indexes 180 degrees with one plate always in the molding machine and the other plate transferring parts to the assembly cube. A two-component part uses three mold plates and indexes 120 degrees with two plates always in the molding machine and the third plate transferring parts to the assembly cube. The assembly cube rotates on either a vertical axis, mounted outside the machine base, or a horizontal axis, mounted off the machine platen. The cube can also do other things besides assembly like leak testing or vision inspection.

Zahoransky’s new indexing plate molds handle one- and two-component parts. Two-component parts move on three 120-degree indexing plates; one-component parts move on two 180-degree indexing plates. The two parts are then assembled on the rotating cube.

The “indexing plate/assembly cube” concept was presented January 2013 by Zahoransky managing director Michael Schmidt at the Molding 2013 conference in New Orleans, sponsored by Executive Conference Management in Dearborn Heights, MI (www.executive-conference.com). The schematic shows two-component parts made on three 120-degree-indexing plate molds and one-component parts made on two 180-degree indexing plate molds. The two parts are transferred to the cube, which indexes and assembles them. Cycle time is determined by the longest time to mold either part. Zahoransky has built a prototype to demonstrate the new technology.

FASTER CUBES, MORE AUTOMATION

Foboha GmbH in Haslach, Germany (www.advaltech.com), set a speed record at K with its patent-applied-for (U.S. Pat. Applic.# 20120328730) all-electric cube, first launched at the Fakuma Show in 2012 in Germany. Arburg GmbH, Lossburg, Germany (www.arburg.com), ran a pilot Foboha mold at K making two-component (HDPE and PP) caps for juice packs with 12 caps per side (4 x 12 + 12) on an Allrounder 720A press with 3200 kN of clamp force.

At the K Show Foboha demonstrated new automation to screw two-part drink caps together. Each cavity molds 8 tops and 8 bottoms. Tops are unscrewed automatically and screwed onto the bottoms, which remain in the mold. Assembled caps are then removed robotically.

“It molded in under six second cycles,” says Hansjoerg Keusgen, head of sales and marketing at Foboha. “That’s a record for sure for cubes.” A servo drive and servo motor allow the cube to turn as the mold opens, for cycle times at the show of 5.6 to 5.7 seconds.

Last year Zahoransky showed a 6.5-second cycle molding three-component drink caps at NPE 2012 in Orlando, FL, using a pilot total integrated manufacturing (TIM) cube with servo drive and servo motor rotation on a press from KraussMaffei Technologies GmbH in Munich, Germany (www.krauss-maffei.com). Cycles for commercial cubes have been reported as short as 7 seconds for two-component toothpaste tube shoulders.

At the K Show Foboha also demonstrated patent-applied-for new technology (U.S. Pat. Applic. # 2012/0088000) to screw two-part drink caps together automatically in the mold for the first time. The demo ran on a standard F-270 all-electric press from Ferromatik Milacron GmbH, Malterdingen, Germany (www.ferromatik.com). The molds have eight bottoms and eight tops per side (4 x 8 + 8) and inject two PPs of similar shrinkage. Caps are automatically unscrewed from the mold and screwed onto the bottoms while the bottoms are still in the mold. Assembled caps are then removed robotically. Cycle time is 10 seconds because the caps are relatively thick.

Reflecting increased interest in rotating molds for durable automotive, appliance and electronics applications, KraussMaffei showed a GX series machine for the first time with a SpinForm swivel plate. It used a two-sided mold to make a demo part with upper and lower PC/ABS blend shells, combining colored and optical grade transparent materials. Then two different polyurea coatings were flowed onto the finished surface in the mold for high gloss finished coat. Finally the parts were assembled robotically with an LED light inside. KraussMaffei introduced its ColorForm PU in-mold coating at K 2010, but says it has reengineered the RIM process since with wear-resistant pumps and more accurate metering.

Engel Austria GmbH, Schwertberg, Austria (www.engelglobal.com), demonstrated servo-driven rotating index plates, without a tiebar or conventional turntable. Engel molded three component drip chambers for blood transfusions at the show on an Engel e-victory hybrid injection molding machine. The molds index 180 degrees, making two parts, one PS and the other PP, assembling them with a filter between, and overmolding them with PP. The complex molds were built by Hack Formenbau Gmbh in Kirchheim, Germany (www.hack-formenbau.de), accommodating 14 separate moving axes driven by servo motors. “It is by far the most movement we have ever integrated into a production cell,” says Georg Steinbichler, vice president of R&D technologies at Engel.

Engel demonstrated indexing plates from Hack Formenbau, which rotate 180 degrees supported by the platen without a rotary table. The production cell uses an astonishing 14 axes of servo driven motion to mold and assemble three-component drip chambers for blood transfusions.

At the K show Zahoransky showed a TIM Light mold for the first time, which adds external assembly automation to single-component parts for lower volumes. The two-platen mold doesn’t rotate or require a tie bar support structure. “Two assembly plates enter the dual-platen mold when open, remove parts from their respective platens, and then slide back out from the mold, where they mate and assemble the parts,” explains Frank Kigyos, CEO of Zahoransky USA Inc., Sugar Grove, IL (www.zahoransky-usa.com). The system takes slightly longer cycle time than Zahoransky’s original TIM cube technology, but costs significantly less. Zahoransky also showed its TIM cube with a central rotating cube to mold and carry parts and two flat external assembly platens in 90-degree positions beside the cube. The external assembly platens included servo-slide pick-and-place units and rotated 180 degrees, providing up to four assembly functions. Outside assembly platens with servo motion can be retooled for different parts.

Ermo Group, Marcille-La-Ville, France (www.ermo-group.com), introduced a one-sided mold for two components with its in-mold assembly system (IMAS) automation. Three other makers of two- and three-component rotating molds also exhibited at K: Braunform GmbH in Bahlingen am Kaiserstuhl, Germany (www.braunform.com); Ferbe Tools AB, Gislaved, Sweden (www.ferbe.se), with “SpinStack” molds licensed from Gram; and Caco Pacific Corp., Covina, CA (www.cacopacific.com) with low inertia technology (LIT).

Posted in Uncategorized | Tagged Boucherie, ENGEL, Foboha, Injection molding, K Show, rotational molding, Zahoransky | Leave a comment

Demystifying Energy Saving Devices on Injection Molding Machines

Posted on August 31, 2013 by Jan Schut

By Jan H. Schut

Injection molding machine makers at the upcoming Kunststoff Show in Dusseldorf, Germany, in October are touting energy efficient presses that will save 30%, 50%, even 70% of energy use. But is anything really new? Energy efficient all-electric and hybrid injection molding machines have been available for nearly 30 years, and energy saving devices like servo pumps and barrel insulation have been retrofitted onto injection molding machines for almost as long.

A cynical explanation for the K Show fuss is that after years of slower business conditions, processors are newly aware of the importance of energy saving. There is also a perceived opportunity for all-electric presses in Europe, where all-electric still accounts for only 15%-20% of injection molding machine sales (see chart), while hydraulic and hybrid account for 80%-85%, based on a 2011 study for Euromap, Frankfurt-Main, Germany (www.euromap.org). In Japan roughly 80% of injection molding machine sales are all-electric vs. 20% hydraulic or hybrid, and in the U.S. sales are roughly 50/50, industry sources say.

Roughly 15%-20% of injection molding machine sales in Europe are all-electric vs. 80%-85% hydraulic or hybrid, according to data from Euromap, the European machinery association. All electric presses in the total European machine population are still only 4.5%. Source: Euromap

How do original equipment manufacturers (OEMs) calculate their energy savings percentages? Typically by comparing energy use for a new efficient machine function with old-fashioned hydraulics for the same function. An injection molding machine has seven main functions that use energy – plastification, barrel heating, platen movement, injection, clamping pressure, ejection, and barrel retraction. All seven can be made more energy efficient than conventional old-fashioned hydraulics, where a standard induction electric motor runs at constant RPM powering 1-2 hydraulic pumps, which runs even when idling.

Energy efficiency, however, isn’t just a machine function. Efficiency, which is typically measured in kilowatt-hours per kilogram (kWh/kg), is different for each molded part and depends on part weight, cycle time, machine size, and machine efficiency. The SKZ Plastic Institute in Wurzburg, Germany (www.skz.de), which researches energy saving potentials for OEMs and performs energy audits, published a study in 2011 that gives a rough idea of how much energy each machine function uses (see pie chart).

Energy consumption on an electric 100-ton injection molding machine with hydraulic injection makes 83-gram ABS storage trays with 2-mm thick walls in 16.9 second cycles and specific energy use of 0.384 kWh/kg. Source: SKZ

The SKZ tested a 100-ton mostly electric press with hydraulic injection, molding an 83-gram ABS storage tray in 16.9 second cycles and found that plastification consumed by far the most energy at 48%. Next came barrel heating at 17%, followed by clamp force at 12%, and injection force at 11%. Linear movements to open and close molds and retract the barrel for cooling used only minor amounts of energy – 4% each. So plastification and barrel heating are the big opportunities to save energy.

Uninsulated barrels waste a lot of energy, as this thermal image shows. Rex Materials’ ceramic insulated clamshells with radiant I.R. heating elements can save up to 45-50% of heat energy.

Heat is the only energy user that doesn’t involve movement, so the fixes are different. Insulating the barrel saves “an average of about 25% of heat energy,” says Bernhard Lettner, product manager for large two-platten presses at Engel Austria GmbH in St. Valentin, Austria (www.engelglobal.com). Replacing hydraulic heat with radiant I.R. heating adds cost, but saves even more. “Based on a complete retrofit of a small machine, we expect I.R. ceramics to save 45-50% of heat energy—up to twice as much as insulating blankets,” says Dean Francis, president of Windsor Kunststofftechnologie GmbH in Hanau, Germany (www.windsor-gmbh.com), which retrofits hydraulic presses for energy saving and sells all-electric presses from JSW Plastics Machinery Inc. in Japan (www.jswpmi.com). Cast in insulating ceramic, I.R. elements from Rex Materials Inc., Fowlerville, MI (www.rexmaterials.com), can convert all zones or only the feed zone.

All-electric presses like JSW’s AD110 save 20%-30% energy overall vs. energy efficient servo-hydraulics, which lose that much in conversion from electric to hydraulic and from hydraulic to mechanical energy. All-electric presses save 50% of energy over old-fashioned hydraulics.

OPTIMIZING ELECTRIC MOTOR EFFICIENCY

For both OEMs and retrofits the basic energy saving devices on injection molding machines are variable frequency drives, also known as inverters, and servo drives. Standard AC motors can be retrofitted with variable frequency drives to control motor speed, so the motor turns at exactly the RPM needed to pump the correct oil pressure for the process.

Direct electric power with a variable frequency drive and AC motor will be 50% more energy efficient than old-fashioned hydraulics and 20%-30% more energy efficient than modern servo-hydraulics for any machine function because hydraulics lose 20%-30% in two conversions. First, electric power is converted to hydraulic power; then hydraulic power is converted to mechanical power. Since plastification uses the most energy, converting plastification to electric power saves the most. It also reduces the size of remaining hydraulic pumps needed and the amount of hydraulic oil in a hybrid machine.

Servo motors controlled by servo drives do the same thing as an inverter/AC motor, but are more precise. The kW size of the variable frequency drive and servo drive has to match motor size. Large servo drives and servo motors over 50 kW to 100 kW are expensive because of the high price of copper and rare earth magnets. So a servo drive/servo motor is likely to replace positional motors for energy saving on functions like clamp opening and closing or part removal.

A direct-drive synchronous torque motor instead of an inverter/AC motor with gearbox saves energy lost in the gearbox (1.5%-2% of energy for that function). Oswald Elektromotoren GmbH in Miltenberg, Germany (www.oswald.de) offers torque motors for plastification and clamping up to 70,000 Nm. Etel S.A. in Motiers, Switzerland (www.etel.ch) makes standard torque motors up to 31,000 Nm and larger custom motors.

Electric motors lose about 8% of energy converting rotational power to linear power, typically with a conventional ball screw. Knoedler-Getriebe GmbH in Ostfildern, Germany (www.knoedler-getriebe.de), offers an alternative ZS rack and pinion electric motor, controlled by a variable frequency drive, that also converts rotation to linear movement. Knoedler’s rack and pinion motor can replace a hydraulic cylinder for plastification and injection and is offered for up to 450 ton presses.

Knoedler’s rack and pinion electric motor converts rotation to linear power and is used for energy saving for injection and plastification on all-electric presses up to 450 tons.

More savings are possible with “stop/go” movements like clamp open and close by regenerating electricity from braking. A regenerative inverter AC unit returns that energy to the grid or applies it to other movement. Regeneration can recover 10%-15% of energy for clamp movement with higher recovery for bigger molds, notes Reinhard Schiffers, head of machine technology and tests at KraussMaffei Technologies GmbH in Munich, Germany (www.krauss-maffei.com). Regenerative inverter drives are commercially available from Siemens AG in Erlangen, Germany (www.siemens.com/drives) and Bernecker + Rainer Industrie-Elektronik GmbH (B&R) in Egglesberg, Austria (www.br-automation.com) and are applicable both to hydraulic and all-electric machines and can be retrofitted. Some regenerative devices are also proprietary to OEMs, like a new mechanical fly-wheel system, which Engel will bring to K.

Siemens Simatics servo hydraulic pumps with a frequency converter and servo motor reportedly save up to 70% energy vs. conventional hydraulic pumps and are used for retrofits.

All-electric presses also have size limits because of the cost of large motors. The largest all-electric press is 3300 clamp tons vs. around 7000 tons for the largest hydraulic presses. Ube Machinery Corp. in Yamaguchi, Japan (www.ubemachinery.co.jp), and JSW have both built 3300-ton all-electric presses for automotive applications. To reach that tonnage electrically, both are believed to use four large motors in sync. Most all-electric machines are less than 350 tons. Over that size, hybrids with servo hydraulics become more cost effective.

OPTIMIZING HYDRAULIC PUMP EFFICIENCY

Another reason hydraulic injection molding is still popular in Europe is that hydraulics have roughly five times higher energy density than electric motors (kW/cu meter). Many existing molds also use hydraulics for core pulls, so on hybrid machines European OEMs typically use hydraulics for injection and for clamp force done with energy efficient servo-hydraulic pumps. The main saving from putting variable speed drives on hydraulics comes from shutting pumps down during cooling time, which can be long for large parts.

Bosch Rexroth AG in Lohr am Main, Germany (www.boschrexroth.com), combines a variable frequency drive with synchronous torque motor for hydraulics control. Siemens offers Simatics servo hydraulic pumps, launched at the K Show in 2010, with a frequency converter and servo motor for retrofits, reportedly saving up to 70% energy vs. conventional hydraulics.

More efficient drives on hydraulic pumps also allow less expensive gear-type hydraulic pumps to be used instead of variable displacement pumps, though not all OEMs agree. Negri Bossi SpA in Milan, Italy (www.negribossi.com) combines a variable frequency drive with a variable volume hydraulic pump on its Canbio VSE press, introduced in 2011, claiming oil output is more consistent. Engel also combines a servo drive/servo motor with a variable displacement pump on two-platen machines. Software optimizes servo motor setting and pivot angle on the variable displacement pump for greater efficiency, Engel says.

Better controlled hydraulics are quieter and cooler. Siemens in a 2012 publication describes retrofitting a hydraulic machine with servo motors, after which hydraulic oil ran 10 degrees C cooler (35 °C down from 45 °C), and oil cooling was “practically no longer required.” Reducing friction in oil lines, manifolds and fittings also saves energy. KraussMaffei’s GX series at K sports a new hydraulic manifold with two valves instead of one and bigger oil lines, which uses 30% less energy with lower oil temperature. And cooler oil lasts longer.

The area with genuinely new developments at K is software and control packages to monitor energy use. B&R, which supplies energy saving servo pumps for injection molding, is introducing APROL EnMon (energy monitoring) pre-installed in its PC to optimize energy use throughout the molding process. ABB Group in Zurich, Switzerland (www.abb.com) this year introduced energy monitoring capabilities in its new ACS 880 drive motors.

OEMs will show new energy optimizing software at K, too. KraussMaffei will introduce MC6 (motion control) software, which automatically optimizes screw speed and other settings for energy efficiency, then asks the operator to check the part and approve the adjustment with an Eco Button feature. Engel will introduce new “ecobalance” software to reduce peak energy consumption automatically. Instead of heating and injecting at the same time with high peak energy use, the software injects first, and then heats gradually.

Will processors get the same energy savings as OEM tests? The short answer is actual energy savings still depend on part size and cycle time, not just energy efficiency. An all-electric machine will be inefficient if it runs low throughput of small parts. Choices between all-electric and servo-hydraulics won’t be resolved soon. “All systems have usefulness,” notes Werner Knoedler, managing director of Knoedler. “The future will need more than one system.”

Posted in Uncategorized | Tagged energy efficiency, Injection molding, K Show, markets | 3 Comments

Is the S-Truder Ready for the Real World?

Posted on July 1, 2013 by Jan Schut

By Jan H. Schut

It’s hard for unusual extruders to graduate from universities into production. So a commercial trial for Germany’s “S-Truder,” developed at the University of Duisburg-Essen (www.uni-due.de),would be exciting after over ten years and four different prototypes. S stands for Schmelzetrennung, or melt separation in German, but think of it as “sieve.” The extruder uses a fairly conventional screw with a very unconventional solid/melt separation device – a sieve – which functions like the barrier section of a screw, but reportedly doesn’t cause shear. The sieve is a slightly conical sleeve with bore holes between the screw and barrel that draws melted plastic away from solid material in the melt channel, so melt doesn’t overheat.

Perforated melt separation devices have been tried before. In the 1970s, Imrich Klein and Zehev Tadmor (who wrote the early bible on extrusion, “Engineering Principles of Plasticating Extrusion”) patented an SDS Solids Draining Screw (U.S. Pat. # 3924842) for a screw-within-a-screw with holes drilled into undercuts in the channel of the outer screw, which drained melt to the inner screw. New Castle Industries, New Castle, PA, now part of NordsonXaloy (www.xaloy.com), built a few SDS screws in two sizes with up to 8-inch outer/3-inch inner screw diameters, but it remained an oddity.

In the early 1990s screw designer Robert Barr Inc. in Virginia Beach, VA (www.robertbarr.com), developed and patented a “melt bleeder” extruder (WO 2002004184) for a hollow screw with slots that bled melt off through the center of the screw. Barr called it the Barr 2000 and built two of them for testing with blow molding. The patent included another embodiment for “a cylindrical melt sleeve” with radial slots between the screw and barrel, but this was never built.

PROTOTYPE #1: THE FIRST SIEVE EXTRUDER

The first S-Truder, built in 2003 by Dirk Kaczmarek at the University of Duisburg, drew melt rapidly off the plastifying zone of the screw with a sieve. Melt had been bled off screws before but into the screw, not through a sleeve into a gap between the sleeve and barrel.

The University of Duisberg’s S-Truder is believed to use the first perforated device to drain melt off the outside of a screw, not the inside, which has advantages in cleaning and temperature control. The S-Truder is the creation of three successive doctoral students at the university under Professor Johannes Wortberg. Two students, who have since graduated, designed and built the first three prototypes, shown at K Shows in Dusseldorf, Germany, in 2004, 2007, and 2010 respectively. A third student is building the fourth prototype now. Each iteration solves some problem of the one before. The fourth and latest S-Truder, being built now, will be at the K Show in October. If it passes its tests at university, it also could be the first S-Truder to make production trials.

The target is high speed extrusion of blown film – a process where high-speed has been tried before, but with little success. High-speed extruders are typically 75-85 mm diameter with long 30-40 L/D screws that go 800 to 1500 rpm, and extrude over 2000 lb/hour of plastic – the output of an extruder twice that size. But high-speed extruder screws are optimized for one or two polymers—PP, PS, or ABS—and can’t do anything else. A high speed screw for PP, for example, would burn PE since PE’s viscosity doesn’t decrease as much with increasing shear.

The idea behind the S-Truder was to develop a high output extruder, which could process different polymers. “We wanted high-speed and flexibility,” explains Marcel Grossmann, who built the second and third prototypes during his PhD work at the university in 2007-2011. “We didn’t want a high-speed extruder that could only process one or two materials.” Grossmann now works as a project manager in development for the South African packaging company Mondi Group in Gronau, Germany (www.mondigroup.com).

The first S-Truder was built as a research project by Dirk Kaczmarek, a PhD student at the university from 2000 to 2003, who also works for Mondi as a technical account manager. The first S-Truder was shown at K 2004 by ETA Kunststofftechnologie GmbH in Troisdorf, Germany (www.eta-kunststofftechnologie.de), a builder of screws and dies. ETA is co-owned by Professor Wortberg and built the components for all the S-Truders. Kaczmarek and Wortberg published the first description of the S-Truder in a 2003 ANTEC paper on “A New High Speed Extruder with Melt Separation.”

“The sieve was a strange idea,” Kaczmarek recalls, “but we did a lot of calculations to see if it would work, and it worked.” Barrel diameter nearly doubles from 35 mm to 60 over the sleeve, which is fixed to the barrel and slightly conical, wider upstream, tapering downstream. Plastic melts underneath the sleeve and is forced out through the bore holes, which are designed so molten material leaves the screw channel without losing significant pressure.

The first S-Truder was short (16 L/D) with a 35-mm screw with five zones: a grooved feeding zone (2 L/D), a shallow-flighted metering zone (4 L/D), a tapered transition zone (3 L/D),then a long plastifying zone with the sieve sleeve (5 L/D), followed by a static mixer (2L/D). L/Ds are approximate based on a schematic drawing in a university publication.

PROTOTYPE #2: KOAX S-TRUDER

Prototype #2, the Koax-S-Truder, used two co-rotating screws – a 35-mm main screw inside a 70-mm feed screw. Perforations in the channels of the feed screw create two feed zones. The two screws allow a high feed rate combined with low plasticating temperature.

The coaxial or Koax-S-Truder was a joint development. The “Koax” part was designed and built by Kaczmarek. It has two co-rotating screws, one inside the other, a more or less standard 35-mm plasticating screw, inside a short 70-mm coaxial feed screw. The screws are separately driven by one four-motor Compact Motor Gear (CMG) drive from K&A Knoedler GmbH in Ostfildern, Germany (www.knoedler-getriebe.de). One motor drives the feed screw up to 330 rpm. The other three motors drive the main screw as slowly as possible.

The feed screw has elongated holes in the flight channels, which pass some pellets through to the main screw. Most plastic is fed via the outer feed screw, but a second feeding zone flows between the feed screw and the main screw. Both feed zones are grooved. “Using the separately driven feed screw allows higher specific throughput, no longer influenced by the bulk density or physical properties of the raw material,” explains Grossmann. “It also allows low speed plasticating for lower melt temperature.”

Grossmann combined the coaxial dual-screw feeding with the sieve sleeve into the Koax-S-Truder, which was shown by ETA at K 2007. Grossmann and Wortberg published the first description of it in a 2009 ANTEC paper called “Koax-S-Truder—A New Flexible and High Efficient Plasticating Concept.”

The coaxial S-Truder is 20 L/D with five zones; first the screw-over-screw feeding zone (4 L/D), next the transfer zone (3 L/D) on the main screw, followed by the plasticating zone with a slightly longer sieve sleeve (7 L/D), where barrel diameter again doubles to accommodate the sleeve. Last comes a low pressure homogenizing zone with a static mixer (6 L/D).

PROTOTYPE #3: HIGH-SPEED S-TRUDER

Prototype #3, the High-Speed S-Truder, uses a high-speed synchronous motor on a 35-mm screw to go up to 2000 rpm. It has a longer sleeve (9 L/D) with a sieve (6 L/D) taking melt off the screw and a new 500-hole static mixer (3 L/D) leading melt back onto the screw again.

The High-Speed S-Truder, also built by Grossmann, is shorter, simpler, and a lot faster. It was shown by ETA at K 2010 and described in an article in Kunststofftechnik magazine in Germany the same year. Instead of the 4-motor CMG drive, it uses a 75 kW high-speed synchronous motor from Oswald Motoren GmbH in Miltenberg, Germany (www.oswald.de), mounted directly onto the 35-mm screw without gear reduction.

The screw is again20 L/D, but with six zones: first a grooved, water-cooled feeding zone (4 L/D), followed by a transfer zone with deeper channels (4 L/D), then a plasticating zone with a much longer sleeve, which is partly sieve (6 L/D) and partly static mixer (3 L/D), followed by a conveying zone (3 L/D).

The High-Speed S-Truders goes six times faster and the screw-within-a-screw is gone compared to the Koax S-Truder. The sleeve over the plasticating zone has also changed dramatically. The sleeve is much longer – 9 L/D in all – with a sieve part upstream and a new static mixer with 500 smaller bore holes downstream. A blocking element on the screw builds melt pressure up under the sieve part and forces melt through the bore holes into the gap between the sleeve and barrel. This gap widens downstream as in earlier S-Truders. Melt reaches the static mixer and is redirected via the 500 holes back onto the screw again.

PROTOTYPE#4: HIGH-SPEED, ROTATING SIEVE

Prototype # 4 is being built now. It was designed using a new simulation developed at the University of Duisburg and presented at the recent SPE ANTEC. It simulates plastic flow that’s partly melted, partly solid, and was used to design a new rotating sieve sleeve.

The fourth S-Truder is being redesigned and built now by a third doctoral student at the university, Gregor Karrenberg. It uses the same high-speed synchronous Oswald motor and feed section as Prototype #3, but with improved melt homogenization. Karrenberg developed a new melt flow simulation in order to redesign the sieve. He presented the new simulation in a recent ANTEC paper in Cincinnati in April:“3D-CFD Simulation of Polymer Plastification in a Single Screw Extruder under High-Speed Conditions.”

His new math reportedly has more nuances of viscosity than previous simulations of fractional melt. Using ANSYS Fluent 14.0 software, he simulates the viscosity of material that is partly solidly packed pellets and partly melted plastic filling the melt channel of a 35-mm conventional high-speed extruder (not an S-Truder). He assumes melting of the solids bed by shear heat and heat dissipation within the bed and allows for expansion of semi-crystalline LDPE, when melting causes the crystalline structure to come apart, and for thermal expansion.

He simulates a virtual high speed extruder at 500 to 2000 rpm for LDPE with throughputs ranging from 110 kg/hr at 500 rpm to 465 kg/hr at 2000 rpm. Then he simulates the High-Speed S-Truder. The simulation showed polymer backing up outside the boreholes that didn’t get through the 500-hole static mixer. So Karrenberg redesigned a floating sieve sleeve with a flight on the outside that rotates around the screw, turned by melt flow. Karrenberg will present his S-Truder simulation in July at a conference of the Polymer Processing Society in Nuremburg. He also intends to use a newly designed dynamic mixer this time.

A high output extruder for PE for blown film or blow molding is a great idea. In fact after over a decade, Barr plans to continue work on the “melt bleeder” screw again. The practical issue both the S-Truder and Barr 2000 screws face isthat they increase melting so dramatically, that it’s hard to feed plastic and homogenize melt fast enough to keep up. It’s not easy to convert radical research ideas into production machines, but it could help that the first two engineers on the S-Truder, who built the first three prototypes, work for the same packaging firm and must itch for a test drive.

Posted in Uncategorized | Tagged Extrusion, melt, Processing Methods | 4 Comments

The New World of ‘Fractal Structuring’

Posted on June 10, 2013 by Jan Schut

By Jan H. Schut

At ANTEC 2013 in Cincinnati in April (see blog May 10, 2013), plenary speaker Han Meijer from Eindhoven Technical University in the Netherlands (www.mate.tue.nl), startled his audience with the first presentation anywhere of tooling that makes vertical plastic layers as well as horizontal ones. Called “fractal structuring,” the technology creates huge internal surfaces between dissimilar polymers inside a film or molded part. It can also combine polymers of different viscosities in precise layered structures. Seldom has such a major invention with such far reaching implications been published, not patented, leaving it open for further development.

“I looked around the room, and people’s jaws dropped,” was how ANTEC technical program chairman, Mark Spalding, a fellow at The Dow Chemical Co., describes audience reaction. Fractal tooling with vertical layers was invented by Peter Neerincx as the last chapter of his PhD thesis under Meijer, a professor of mechanical engineering and materials technology at Eindhoven TU. Meijer and Neerincx published a paper on earlier fractal tooling in Macromolecular Chemistry and Physics by Wiley-VCH Verlag GmbH in early 2013.

Neerincx, who now works in process research at Sabic Innovative Plastics BV, Bergen op Zoom in the Netherlands, (www.sabic-ip.com) was “one of those rare students who is gifted in designing and also skilled in injection molding,” Meijer recalls. “Many of our students are good at theory and modeling, but he could make things.”

Fractal structures can of course be made with two polymers in other ways as well, for example, by phase separation or chaotic advection. Phase separation blends dissimilar polymers into a matrix of one material with domains of the other. Chaotic advection blends two polymers into swirling patterns in the melt like marble cake. Both generate fractal interfaces in coextruded or coinjected plastics, but the patterns are random, whereas Neerincx’s fractal patterns are precise and repeatable.

HOW ‘FRACTAL STRUCTURING’ WORKS

Neerincx started by analyzing fluid flow patterns in static mixers, which was also the starting point for chaotic advection tooling in the 1980s. He worked with Tae Gon Kang, Sven Peelen, and Roel P. J. Denteneer, also graduate students at Eindhoven at the time, to modify a known mixing element so that it could form multiple layers. These mixing elements were known as the Dentincx and Peelincx Mixers and were reported in Macromolecular Materials and Engineering in 2011. The Dentincx Mixer is linear, the Peelincx Mixer is circular. Both form layers, slice them in the machine direction, and rotate half of the multilayer material in two successive 90-degree turns back onto itself. But at the end of the day, high numbers of layers are also made commercially by other technologies (see blog July 6, 2012).

Schematics presented at ANTEC show a developmental fractal runner that forms vertical plastic layers as well as horizontal ones for the first time. Boxes 1-10 show cross sections of the fractally patterned melt flow with vertical layer elements at numbered points in the runner.

The big breakthrough came when Meijer and Neerincx realized the potential of splitting the serpentine 90-degree rotation of the layering devices and turning the two halves of the multilayer flow on their sides. This created vertical layers in the melt for the first time ever, allowing layers to be formed perpendicular to a part surface or sandwiching vertical layers between horizontal ones.

The concept of perpendicular layers on horizontal layers isn’t totally new, however. It exists in some nanostructured film technologies and self-assembled chemical coatings and is used to create porosity, co-continuity or electrical conductivity in films for photo voltaics and batteries. Not surprisingly, Neerincx’s fractal structuring with perpendicular plastic layers also targets photo voltaics and batteries. But it has the advantage that it can potentially be done in a single environmentally friendly process vs. less controlled and environmentally hazardous coating technologies used in photo voltaics today.

SIX ‘FRACTAL’ MIXING ELEMENTS

Neerincx designed and built eight different sets of injection mold tools in the course of his PhD research over a five-year period, 2007-2012. Each tool formed one chapter of his thesis with the last chapter on the vertical fractal layers. Neerincx verified most of the tooling designs on a Ferromatic K-tec 60 two component lab injection press with a vertical and a horizontal plastification unit. Thermoplastic tests used black and white PS, PC and PP with 3% titanium dioxide for white and 3% carbon black for black.

Vertical-layer structuring was invented by Eindhoven Technical University professor Han Meijer and PhD student Peter Neerincx, who built this fractal runner out of laser-cut PMMA plates and molded black and white epoxy into a tree pattern with a trunk, branches, and leaves.

The runners for the fractal structuring, however, were built of laser-cut plates of clear polymethyl methacrylate (PMMA), stacked and bolted together and the designs verified using black and white epoxy, cured at room temperature. Fractal tooling uses six different mixing elements: flow splitting, flow addition, right flow rotation, left flow rotation, right flow rotation with flow addition, and left flow rotation with flow addition. Layer multiplication takes flow splitting, either horizontal or vertical, and flow rotation. Hierarchic designs start with layers, then take flow rotation and flow addition.

This fractal runner system was modified by enlarging the melt channels to avoid compressing and distorting vertical layer elements. The tool was cut out of 27 laser-cut PMMA plates bolted together, whereas the original fractal “tree” runner was made of only eight PMMA plates.

Neerincx’s fractal runners ranged from a stack of eight PMMA plates for a simple “tree” pattern up to 27 plates for the most complex pattern. The eight-plate fractal runner for a tree forms a trunk, two branches, and 16 leaves. It starts with a serpentine melt channel with two mixing elements that form 32 black and white layers for 16 black leaves, i.e., each mixing element multiplies the layers times four. Then branches are formed. A side layer of white is coinjected on one side and black on the other, putting half a branch onto the leaves. This half-branch-leaf structure is split, stretched, and rotated 90 degrees twice to form two branches, each with eight leaves, four on each side. The largest rotation in the hierarchy, for the tree trunk, comes last just before the pattern enters the mold. Black and white side layers are coinjected outside to form halves of the trunk. This structure is split and rotated to complete the tree. “Then a black ‘ground’ layer and white ‘sky’ layer were added on the sides, and the structure was rotated 90 degrees to make the tree stand up,” Meijer explains.

Neerincx’s most complicated fractal runner used eight mixing elements to make 130,000 black and white layers for 65,000 black leaves. It wasn’t easy to get a pattern like that into the mold without smearing. Even if the pattern didn’t disappear, vertical and horizontal layers behave differently in the runner. Horizontal layers are stretched thinner and flatter as the structure moves in the machine direction. Vertical layers are compressed, becoming shorter and fatter and curling.

Neerincx found several things helped preserve the pattern. One was to keep enlarging the height and width of the melt channel as layers and rotations were added to avoid compressing and distorting the design. Another modification that helped was to extend the pattern across the whole width of the part before the plastic entered the mold. In one complex runner system, for example, Neerincx used five modified mixers initially to create 8,000 layers. He then used eight co-injection units side by side to extend the pattern to the width of the mold. The horizontal stack of 8,000 layers was split into eight flows, each with 8,000 layers. White layers were coinjected on both sides. Then all eight square structures with a total of 64,000 horizontal black/white layers with white on both sides were cut and rotated to make a three-layer structure with 64,000 vertical layers in the middle and a white layer on the top and bottom.

After that a phenomenon known as “fountain flow” converts the three-layer structure into a five-layer one. When the layered structure reaches the front of the injection mold, the material in the middle is flowing faster than the material along the walls. This “fountain flow” effect splits the middle layer in two and creates a five-layer structure with 64,000 vertical layers on the top and bottom, separated by two white layers from 64,000 vertical layers in the middle. Fountain flow also affects injection molding of a tree pattern. First, enough polymer has to be injected into the mold to accommodate fountain flow along the walls. Then the fractal structure with the tree design can be coinjected into the center of the mold.

WHAT’S AHEAD FOR ‘FRACTAL STRUCTURING’?

Meijer and his students started fractal structuring in injection molding, but the technology is likely to be commercialized first in film. Film research continues on two fronts. Tetra Pak in Lund, Sweden, a division of Tetra Laval Holdings & Finance S.A., (www.tetrapak.com) bought rights to develop precise multi-layering for high-strength, high performance films (WO Pat. Applic. # 2012/095457) and is continuing research.

Eindhoven TU and ETH institute in Zurich are now testing three-component films with complex fractal hierarchies like these, creating huge internal surfaces that no longer resemble trees. The technology targets less expensive films for photo voltaics and batteries.

Meijer also works with Paul Smith, professor of polymer technology at the ETH institute (Eidgenoessische Technische Hochschule) in Zurich, Switzerland, (www.ethz.ch) developing three-material fractal films—two active fractal polymers and a third for support. They have built metal tooling for films with hundreds of trees, thousands of branches, and hundreds of thousands of leaves and are developing fractal films up to 12 cm wide and down to 2 microns thick. They are testing classic photovoltaic conductive organics like poly(3-hexylthyophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methylester (PCBM) blended into standard polyethylenes.

The tooling for vertical layers may be revolutionary and exciting, but it also still has to be adapted to commercial conditions. “The question,” as Meijer puts it, “is whether we can use simple geometries inside simple dies, allowing compression flows to wrinkle and crinkle huge stacks of leaflets, and then later straighten them out and unfold them during transverse stretching in the slit die.” In other words, can they create unlimited internal surfaces in plastic film in a single processing step and then orient the film without losing the internal structure?

New test methods may also be needed to measure the viscosity of fractally structured materials. Interestingly, another ANTEC paper this year addressed the issue of testing materials with internal fractal structures produced by chaotic advection, not by vertical-layer tooling. Subramanian Ramaswami, a graduate researcher, and David Zumbrunnen, professor at Clemson University, Clemson, SC, (www.clemson.edu) presented “A Device for Simultaneous In-Situ Structuring and Measurement of Rheological Properties of Polymer Blends and Composites.”

Standard viscosity tests may not be applicable to films with internal fractal structures. A rheometer developed at Clemson University and introduced at ANTEC fits into commercial rheometers and tests shear viscosity of fractally structured materials made by chaotic advection.

Their in situ structuring rheometer fits into existing commercial rheometers and has the test capabilities of the commercial rheometer, typically testing shear viscosity and viscoelastic properties. But it can perform these tests on two-polymer blends made with chaotic advection structuring. Zumbrunnen previously developed a chaotic advection device using independently rotating stir rods in a barrel to create swirling patterns in extruded or injection molded plastic. The technology is available for license from Clemson, which has sold or licensed about half a dozen chaotic advection devices.

Posted in Uncategorized | Tagged ANTEC, Fractal Structuring, Injection molding | 2 Comments

Trolling for New Technology: ANTEC 2013

Posted on May 10, 2013 by Jan Schut

By Jan H. Schut

New technologies at ANTEC 2013, the Society of Plastics Engineers (SPE) Annual Technical Conference in Cincinnati, OH, April 21-24 include the first “fractal structuring” of co-injected polymers not just into layers, but into geometric patterns of almost unlimited complexity. The technology comes from the Technical University of Eindhoven in the Netherlands (www.mate.tue.nl) and is the first 3-D structuring of any molded part. A new rheometer presented by Clemson University (www.clemson.edu) also creates and tests coex 3-D patterns for extrusion, using chaotic advection with independently turning stir rods–the only other known 3-D structuring.

Compounding news includes the first ultrasonic twin-screw extruder from the University of Akron in Ohio (www.uakron.edu), allowing comparison to ultrasonic single-screw extrusion and ultrasonic dies. South China University of Technology in Guangzhou (en.scut.edu.cn) reports a new co-rotating triple-screw extruder with vibrating middle screw, built by Guangzhou POTOP Experimental Analysis Instrument Co. Ltd. in China (www.potop-lab.com), a spin-off of the university, represented by Harden Industries Ltd., Hong Kong (www.hardenmachinery.com).

New materials include shape memory polymers with a range of temperature triggers and new biopolymer blends with polybutylene succinate (PBS), an emerging biopolyester. As five ventures around the world build plants to make bio succinic acid monomer for PBS, new PBS blends are timely (see this blog April 26, 2012). In biomaterials, soy and bone meal polymers show unusual benefits in pots and films for agriculture—as they degrade, they feed plants.

The letter and number in brackets after the title of a paper or poster indicate the day of the week and session when that paper was given, i.e. [T12] was session 12 on Tuesday, April 23. For people who didn’t attend ANTEC, all papers are available on CD from the SPE (www.4spe.org) for $200 to members and $250 to non-members. Student posters aren’t on the CD unless they were also presentations, so referenced posters not on CD are linked below.

‘STRUCTURING’ AND OTHER INJECTION MOLDING NEWS

Fractal Structuring in Polymer Processing [Plenary Speaker] by Han Meijer, professor of mechanical engineering & materials technology at Eindhoven Technical University in the Netherlands (www.mate.tue.nl). Flat tool halves with serpentine flow paths on the parting surfaces, similar to a static mixer, co-inject polymers into complex internal patterns. Patterns are made by cutting, rotating and combining horizontal and vertical stratified elements formed between the flat mold halves. The patterns are then preserved without compression in special runners into the mold. Meijer developed and verified the tooling using two colors of epoxy at room temperature before molding them with thermoplastics.

$Eindhoven Technical University "fractal structuring"$

Eindhoven Technical University’s “fractal structuring” creates serpentine flow between flat mold halves to make complex geometries like layers perpendicular to a part surface and “tree” shapes with trunks, branches, twigs and leaves–the first repeatable 3-D structures in molded parts.

Fractal structuring can make repeatable 3-D patterns for the first time, including layers perpendicular to a part surface and “tree” shapes with trunk, branches, twigs, and leaves. “Extension to multiple trees with many branches in a forest is potentially possible, but here only making of one tree with 65,000 leaves is demonstrated,” Meijer explains modestly, adding that “compression of stratified structures is to be avoided.” The technology is also being developed for coextrusion, working with ETH Zurich University in Switzerland (www.ethz.ch).

2 PC-Recu-Module for Energy Recovery with Hydraulically Driven Injection Molding Machines [W11] by Marco Lenzen, Universitaet Duisburg-Essen in Germany (www.uni-due.de). A new “2 Plates Clamping Recuperation” hydraulic module is designed and simulated with a drive, three accumulators, valves, and controls. It’s expected to recover up to 50% of the energy typically lost in hydraulic clamping. The first prototype is being built now.

Dynamic Uni-Layer Melting Model [W11] by Trevor Spika, Spiral Logic Ltd., Hong Kong, China (www.spirallogic.com.hk). Spiral Logic’s unusual new injection screw and T-Rex barrel melt without a compression zone, boasting shorter residence and cooler temperature than conventional screws. Introduced at NPE 2012, the screw is shown for the first time at ANTEC.

Spiral Logic introduced an unusual injection screw with 1:1 compression ratio at NPE 2012, but didn’t show the 14:1 screw until ANTEC. The screw was tested using a special windowed T-Rex barrel and reportedly melts faster at cooler temperatures than conventional screws.

An Investigation of Vibration-Assisted Injection Molding Manufactured Polymer Material and the Effect of Molecular Orientation on Biodegradation Activity [T12] by Qi Li, Lehigh University, Bethlehem, Pa. (www.lehigh.edu). PLA medical devices molded with more vibration-induced molecular orientation degrade more slowly in the body than ones with less orientation. Software controls vibration by opening and closing valves on the hydraulic screw.

EXTRUSION NEWS

A Device for Simultaneous In-Situ Structuring and Measurement of Rheological Properties of Polymer Blends and Composites [T20] by David Zumbrunnen, S. Ramaswami, Clemson University, Clemson, S.C. (www.clemson.edu). This rheometer creates 3-D internal patterns by chaotic advection, and then measures their properties in situ. Chaotic advection uses rotating stir rods in a barrel to blend polymers into repeatable structures for blown and cast film.

Thermal and Morphological Behavior of PLA/PBS/CSW Blends Processed by Vane Extruder [Poster #1559206] by Rong-yuan Chen, South China University of Technology, Guangzhou (en.scut.edu.cn). PLA and PBS are blended with 5% calcium sulfate whiskers on a revolutionary new vane extruder invented at the university. The vane extruder, which elongates melt, was introduced at ANTEC last year (see this blog April 2012).

3D-CFD Simulation of Polymer Plastification in a Single-Screw Extruder Under High-Speed Conditions [M8] by Gregor Karrenberg, Johannes Wortberg, University of Duisburg-Essen in Germany (www.uni-due.de). This simulation of a 35-mm screw with a transition section depth going from 6 mm to 2 mm, extruding LDPE at up to 2000 rpm, shows high-speed extrusion melts without a melting mechanism.

A Mechanism for Solid Bed Break-up in Single Screw Extruders [T27] by Gregory Campbell, Clarkson University, Potsdam, NY (www.clarkson.edu); Mark Spalding, Dow Chemical Co., Midland, MI (www.dow.com). A fresh look at solid bed melting in a conventional screw finds that screw rotation physics carries melt under the solid bed, creating flow and pressure that breaks up the bed. The authors have a new book and photos to prove it.

NEW SHAPE MEMORY MATERIALS

Tunable Shape Memory Polymers Based on Compounds of Ionomers and Fatty Acids [New Technology Forums] by Robert Weiss, Jing Dong, Ying Shi, and Rostyslav Dolog of the University of Akron (www.uakron.edu). Instead of synthesizing a new polymer for every switching temperature, this technology blends an ionic polymer and fatty acid or fatty acid salt with the desired melting point. A patent-applied-for blend of sulfonated PEEK ionomer and fatty acid salt (U.S. Pat. Applic. # 20080287582) could be the first high temperature (>300 °C) thermoplastic shape memory polymer.

Thermoplastic Elastomers with Thermally Induced Shape-Memory Effect [New Technology Forums] by Liang Xu and Krishna Venkataswamy from the GLS Thermoplastic Elastomers division of PolyOne Corp., McHenry, IL (www.glstpes.com). This patent-applied-for (WO Pat. Applic. # 2012/166782) combination of a maleated styrenic block copolymer and polycaprolactone shows “manageable” shape memory characteristics.

Injection Molding of Novel PLA/Thermoplastic Polyurethane Blends with Shape-Memory Behavior [W10] by Xin Jing, Bionates Wisconsin Institute for Discovery, University of Wisconsin, Madison, WI (wid.wisc.edu). A 70/30 blend of PLA and TPU deforms into temporary shapes at room temperature, then recovers its original shape “fairly quickly” at glass transition temperature. It’s believed to be the first PLA/TPU blend with shape memory.

ULTRASONIC TWIN- AND TRIPLE-SCREW COMPOUNDING NEWS

Preparation and Properties of Polyetherimide (PEI)/Graphite Composites with Ultrasound Assisted Extrusion [M6] by Jing Zhong, University of Akron (www.uakron.edu). A new ultrasound-assisted twin-screw extruder improves electrical conductivity of PEI/expanded graphite composites.

Continuous High Power Ultrasonic Extrusion of PEEK-CNT Nanocomposites [M4] by Todd Lewis, University of Akron (www.uakron.edu). The new ultrasonic twin-screw extruder mixes PEEK with only 1% carbon nanotubes and gets 16% higher tensile modulus and three times higher electrical conductivity.

Ultrasonic Devulcanization of Tire Rubber of Different Particle Sizes in Twin-Screw Extruder [M6; also Poster # 1657660] by Tian Liang, University of Akron (www.uakron.edu). The patent-applied-for ultrasonic twin-screw (WPO # 2012142562) devulcanizes 10- and 30-mesh rubber particles at 40 kHz, with more devulcanization and fewer gels for the smaller 30-mesh size. Revulcanized 30-mesh rubber also has higher elongation at break and tensile strength.

The University of Akron added an ultrasonic horn to the first twin-screw extruder–a 16 mm micro compounder—allowing comparison to compounded, devulcanized and decrosslinked material from ultrasonic single-screw extruders and ultrasonic dies.

Decrosslinking of Crosslinked HDPE via Ultrasonically Aided Extrusion [W7] by Keyuan Huang, University of Akron (www.uakron.edu). Decrosslinking increases with ultrasonic amplitude in both single- and twin-screw extruders, but mechanical properties of HDPE are better from the ultrasonic single-screw. This is the first reported comparison of materials from ultrasonic single- and twin-screw extruders.

Preparation and Microcellular Foaming Investigation of PLA/Talc Composites [M19] by Peng Xiang-Fang, South China University of Technology in Guangzhou (en.scut.edu.cn). A new 22 mm, 40 L/D triple-screw extruder and patent-pending foaming device are used to make this bio composite with CO₂ blowing agent. The triple-screw extruder is built by Guangzhou POTOP Experimental Analysis Instrument Co. Ltd. in China (www.potop-lab.com).

South China University triple-screw extruder

South China University of Technology reports R&D with a new co-rotating triple-screw extruder with vibration on the middle screw, built by Guangzhou POTOP, a 2009 spinoff from the university. POTOP’s lab extruders are represented by Harden Industries Ltd. in Hong Kong.

Preparation and Characterization of Poly(lactic acid)/Poly(vinyl alchohol) Blend [P2] by Peng Yu, South China University of Technology in Guangzhou (en.scut.edu.cn). POTOP’s new triple-screw extruder (www.potop-lab.com) is used to make more biopolymer blends.

PBS BLENDS AND OTHER BIO MATERIAL NEWS

Mechanical Properties and Crystallization of Talc-Filled PLA/Poly(butylene succinate) Blend Composites [T1] by Weraporn Pivsa-Art, Rajamangala University of Technology Thanyaburi, Thailand (www.eng.rmutt.ac.th). Blending up to 30 wt % PBS and up to 20% talc into PLA improves PLA’s tensile modulus, crystallinity, and impact strength.

Effect of Poly(butylene adipate-co-terephthalate) Contents on Crystallization and Mechanical Properties of Polymer Blends of PLA and Poly[(butylene succinate)-co-adipate] [T1] by Sommai Pivsa-Art, Rajamangala University of Technology Thanyaburi, Thailand (www.eng.rmutt.ac.th). Adding up to 50% PBAT to an 80/20 blend of PLA and PBSA also increases crystallization and improves properties.

The Role of Surface Interactions in Renewable Poly(butylene succinate)-Silica Nanocomposites [M21] by Margaret Sobkowicz; Poly(butylene succinate) Fumed Silica Nanocomposite: Functionality and Rheology [Poster # 1628517] by Xun Chen, University of Massachusets Lowell (www.uml.edu). Mechanical properties of PBS improve when it’s blended with fumed silica, whether the silica is surface treated or not.

Mechanical Properties of HDPE/Pennycress Press Cake Composites [M35] by Louis Reifschneider, Illinois State University, Normal, IL (www.ilstu.edu); Rogers Harry-O’Kuru, National Agricultural Utilization Research Center, Peoria, IL (www.ars.usda.gov). HDPE with 25 wt% fibers from Pennycress, a potential new oilseed crop for biodiesel, and 5% coupling agent gets 42% higher tensile modulus, 12% higher tensile strength. Impact strength drops 15%.

Blended Meat & Bone Meal Bioplastic and Polyethylene Sheets: Enhanced Moisture Resistance and Mechanical Properties [T21] by Sam Lukubira, Clemson University, Clemson, SC (www.clemson.edu). Cross-linking plasticized bone meal polymer and blending with LLDPE makes moisture-resistant film with potential for composite seed germination mats.

Sustainable Materials for Horticultural Application [T21] by Gowrishankar Srinivasan, Iowa State University, Ames, IA (www.iastate.edu). Plants grown in soy polymer/PLA pots grow better than plants grown in PP or natural fiber pots. Apparently, as soy polymer degrades, it feeds the plants, while the soy polymer/PLA blend retains moisture. The university reported this in a symposium in 2012, but ANTEC was its first public presentation.

Posted in Uncategorized | Tagged ANTEC, compounding, Injection molding, shape memory polymers | 2 Comments

Simply Brilliant

Posted on March 21, 2013 by Jan Schut

By Jan H. Schut

Imagine molding plastic with no energy cost – zero, zip, nadda, as the saying goes. Karl von Kries, CEO of startup LightManufacturing LLC (www.lightmanufacturingsystems.com) in Pismo Beach, CA, has done just that. He’s invented the world’s first solar-heated plastic molding and is launching solar-heated rotational molding commercially this month at SPE’s GPEC (www.sperecycling.org) conference in New Orleans, LA, on March 20-22. The patent-applied-for technology (U.S. Pat. Applic. # 20120104658) was first presented last November at the Association of Rotational Molders conference in Minneapolis, MN.

Don’t confuse von Kries’s approach with using solar electric power to mold, which has been done before. Penninsula Packaging (www.penpack.com) in Exeter, CA, generates about a third of its power for sheet extrusion and 14 thermoforming machines with a field of hundreds of solar panels. Instead von Kries concentrates sunlight directly onto molds to melt and mold the plastic. Cycle time is only slightly longer than conventional rotomolding, he says—25 minutes vs. 19 minutes for the same part. “We’re seeing now how much faster we can go,” he says. “If we add more Heliostats, we think we can drop cycle time a lot.”

Also at GPEC, two new environmentally friendly materials will be introduced: “hyperbranched” recycled PLA with melt strength better than, or comparable to, virgin PLA by Interfacial Solutions (www.interfacialsolutions.com), a contract R&D firm in River Falls, WI, and new developmental 25% to 50% starch-filled soft elastomers down to 55-65 Shore A from bio-plastic compounder Cereplast Inc. (www.cereplast.com), El Segundo, CA.

THE ICARUS FACTOR

LightManufacturing’s game-changing solar rotational molding machinery is built into a shipping container. It needs no building, electrical hook up, or even concrete pad. The container can be deposited on flat ground or in a customer’s parking lot (anywhere there’s enough sun) and mold parts closer to where they’re needed. It can’t run at night, and it can’t run in many parts of the country, but von Kries figures it will work on almost half of the earth’s land surface, certainly throughout the South and Southwest United States.

LightManufacturing’s solar rotomolding machine is built into a shipping container, so it needs no building, electrical hook up, or concrete pad. This isn’t solar-generated electric power.
Molds are heated directly by radiant heat from sunlight.

In the early ‘90s, von Kries worked in engineering and new product development at rotational molder Hardigg Industries Inc. in South Deerfield, MA, now part of Pelican Products Inc. (www.pelican.com), Torrance, CA. In 1994, he took a project for portable sound equipment for the military and spun it off as a separate company, called Technomad LLC (www.technomad.com) with offices in Boston, MA, of which von Kries is still CEO.

Technomad’s audio products were housed in rugged ¼ to 3/8-inch-thick, rotomolded medium density PE cases, molded by Hardigg. von Kries moved to California in 2005 and saw solar mirrors, or heliostats, heating steam turbines with reflected sunlight. He got the idea to heat rotational molds that way, too, saving a lot on energy. By 2009, he set up LightManufacturing with investors and was designing the first solar-heated roto-molding.

He started using commercially available heliostats, but the supplier went out of business. So he and his team spent two years designing their own heliostats, which he says are the lowest cost per reflected watt on the market—2,000 watts of heat for about $1,400, or $1.60 per watt. The firm’s H1 Heliostats became a separate product selling to architects and home owners for green home heating.

LightManufacturing designed H1 Heliostats

LightManufacturing designed its own H1 Heliostats out of aluminum coated reflective PET film stretched over a square frame. An array of 20 H1 Heliostats puts 40,000 watts of heat into solar rotational molds. Cycle time is 25 min. vs. 19 min. for conventional rotomolding.

H1 Heliostats are 2.3 square meter mirrors made of aluminum-coated PET film stretched over a frame. The reflective film has a threaded rod on the back that adjusts the mirror shape to focus light on a larger or smaller area to fit mold size. “If you walk around in the beams of light, which I do all the time, they feel like a strong space heater,” von Kries explains. Heliostats can stand 20 mph steady wind and gusts to 60 mph, or up to 95 mph in “safe position” sideways to the wind, LightManufacturing says. If they’re damaged, it’s relatively easy to replace the reflective film.

MOVE HEAT, NOT MOLDS

Solar molds aren’t mounted on massive articulated arms on a central rotor and moved in and out of a convection oven like conventional rotomolding. The solar rotational molding machine has two chambers, each with a molding station and a large Lexan polycarbonate window on one side to let light in. Solar-heated molds rotate on two axes, but in fixed position.

Twenty heliostats are assembled and installed in an array in front of the windows to direct sunlight first onto one mold, then onto the other, while the first mold cools. Radiant heat from sun light goes into the mold without heating the surrounding air or the framework holding the molds, so cooling is faster than with conventional molding, von Kries says. Temperature inside the molding chamber reaches only about 180 degrees F compared to 500 degrees F in a gas-fired convection oven for conventional rotational molding.

The solar machine uses standard aluminum or steel molds up to 48 in. on the diagonal, coated with black heat-absorbing material. Optional wireless thermocouples can provide real-time temperature data. Solar panels installed on top of the enclosure power motors, cooling fans and electronics.

LightManufacturing now has 10 employees and several solar rotational molding machines in beta test sites in the U.S. for over 18 months, producing parts commercially for Technomad and other customers. They have molded medium density PE and LLDPE, but haven’t yet tried PP or high heat materials like nylon. A turnkey system costs “well under” $100,000, von Kries says, including two molding stations, 20 H1 Heliostats, two photovoltaic panels, and wireless computer controls. A conventional rotational molding machine with a convection oven costs around $300,000.

Because solar rotational molding runs off-grid, it could be attractive in third world markets or for disaster relief, molding things like water tanks or sectional emergency housing without needing outside power. But von Kries argues that the competitive advantage is most compelling in a developed market with high energy costs. “Once a few companies have it, they’ll eat the competition,” he predicts.

“Rock-and-roll” type rotational machines with multiple arms could be adapted to solar heat using “a single large horizontal window,” von Kries says, “and large parts could be molded in site-assembled enclosures, instead of the shipping container approach.” Direct solar heat could also be applied to other molding processes by putting solar arrays onto factory roofs and using light pipes to bring radiant heat into the building. Thermoforming and compression molding could be adapted fairly easily to solar heat, he thinks: “Those are the next things we’re going to look at.”

NEW RECYCLED PLA, NEW SOFTER STARCH-FILLED ELASTOMERS

Interfacial Solutions’ technical director, Adam Pawloski, is introducing new post-consumer and post-industrial recycled PLA compounds at GPEC, made with the company’s reactive process for hyperbranching PLA. Interfacial introduced its patent-applied-for hyperbranching chemistry (International Pat. Applic. # WO 2010/1080760 A2) five years ago in compounds with virgin PLA to improve melt strength for durable applications and extrusion without a penalty for processability. Hyperbranching is now being used with scrap PLA to improve mechanical properties “to meet or exceed those of virgin PLA,” Pawloski says.

Hyperbranching adds lots of short chains onto linear PLA molecules, increasing melt strength without increasing viscosity and die pressure, according to tests done by the Macosko group at the University of Minnesota (research.cems.umn.edu) in Minneapolis, MN. This gives hyperbranching an advantage compared to several commercial chain extending additives for PLA like CESA-extend masterbatches from Clariant Corp. (www.clariant.com), Charlotte, NC and Joncryl ADR from BASF Group (www.basf.com) in Germany, which increase PLA’s melt strength, but also increase shear viscosity and die pressure.

Linear PLA has poor melt strength and high viscosity, making extrusion difficult. Chain extenders add a few long chains, which raise melt strength, but also raise viscosity and pressure. Hyperbranching adds short chains, improving melt strength without hurting processability.

Interfacial is commercializing several new grades of hyperbranched post-industrial recycled PLA in its “de Terra bio-based polymer” product line. For the new recycled PLA grades, Interfacial tested reclaimed PLA from eight post-industrial and one post-consumer source and reports this data as well. Post-industrial sources tested include mixed reground card stock, recycled water bottles and cups, and recycled reground gift cards. Properties of the scrap materials, especially melt flow index and impact strength, vary widely, but can be adjusted using hyperbranching to meet the needs of an application. Interfacial will make custom recycled PLA on a toll basis for customers or license its technology for companies to use in-house.

Interfacial Solutions tested “Gen I” and “Gen II” blends of recycled and reprocessed PLA with low and high initiator (INT) and low and high hyperbranching (CXL). Note how MFI decreases while molecular weight increases with more hyperbranching.

Cereplast’s chief technology officer Kelvin Okamoto is introducing softer starch-filled elastomers than the company has presented before. Its patent-applied-for (U.S. Pat. Applic. # 20090048368) starch-content elastomers were introduced at NPE 2012 last March in Orlando with two grades, Hybrid 111D with 25% starch and Hybrid 112D with 50% starch. Both elastomers, however, only go down to 85-95 Shore A in softness for injection molded applications like soft-grip handles and soft-touch automotive parts.

Base Resin	TPE1	TPE1	TPE2	TPE3	EA1
Starch Content	%	25	50	25	25	25
Density	g/cc	0.96	1.08	0.98	0.98	1.00
Melt Flow	g/10′	7.3	3.2	0.4	25.0	9.7
Tensile Strength @ Yield	MPa	4.4	5.7			4.2
Tensile Elongation	%	>450	440			245
Flex Modulus	MPa	16	51			30
Gardner Impact	J	14.2	15.9			12.1
Taber Abrasion	WI	56	144			117
Shore Hardness	A	80	93	55	65	88

Cereplast is introducing new 25% starch-filled TPEs as soft as 55-65 Shore A hardness and thinks the elastomers can be made even softer–down to 30 Shore A–still with 25% starch.

Cereplast has since developed even softer elastomers with 25% starch down to 55-65 Shore A hardness in a range of melt flow indices for injection molding and extrusion applications. These softer elastomers don’t have commercial grade names yet, but are available for testing. Cereplast’s Okamoto believes they can go even softer–down to a 30 Shore A.

Posted in Uncategorized | Tagged polylactic acid, rotational molding, Solar power, SPE GPEC, starch | 3 Comments

Plastics Engineering Blog

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The New World of ‘Fractal Structuring’

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Simply Brilliant

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