By Jan H. Schut
At least two commercial technologies combine extrusion with injection molding to fill molds with much lower pressure than conventional injection molding. One was recently introduced by Extrude to Fill LLC, Loveland, CO (www.extrudetofill.com), which melts plastic electrically without turning the screw (see blog September 13, 2016). The other was introduced nearly 10 years ago by IB Steiner, a plastics engineering firm in Spielberg, Austria (www.exjection.com), called Exjection, which uses a sliding mold cavity.
The two technologies are completely different. Extrude to Fill has an unusual extruder that works with conventional injection molds. Exjection has an unusual mold that works with conventional injection molding machines. The results, however, are very similar. Both technologies use less expensive, smaller barrels, lower clamp tonnage, and much less energy than equivalent conventional, high-pressure injection molding for substantially lower production cost. Exjection’s moving molds cost more than conventional injection molds, but overall production costs are 20-30% less, IB Steiner says.
But savings and efficiencies aren’t why first customers choose either one. Both were commercialized to mold parts that couldn’t be molded otherwise. IB Steiner’s Exjection (U.S. Pat. # 7910044) was originally developed for the aircraft industry to mold long thin parts for commercial planes with ribs, holes and other features out of PEI and PC to meet fire codes. But the compounds were too viscous for long flow paths, and molding with multiple nozzles would have left weak weld lines.
FILLING A PARTIALLY OPEN MOLD
The solution was a long partially-enclosed mold (up to 3 meters) with all functional details like screw bosses and snap-fit hooks contained in a nearly enclosed cavity. The cavity is filled through an open slit in the top as it slides past a fixed injection nozzle in the short upper mold. The upper mold has a heated supply zone (about 130 mm), followed by the nozzle, then a cooled calibration zone (about 260 mm). The sliding cavity also splits in half length-wise for undercuts and part ejection.
“A sword-shaped bar under both the supply and calibration zones on the fixed nozzle side of the mold partially seals the otherwise open cavity to retain injection pressure. The supply zone corresponds to an extrusion die, and the calibration zone to a calibration unit,” explains Gottfried Steiner, CEO and head of engineering at IB Steiner. By the time the mold cavity moves out from under the calibration zone into open air, the exposed plastic is hard.
IB Steiner took three years to develop the concept with sister company Hybrid Composite Products GmbH, also in Spielberg (www.hcp0.com), which molded the first Exjection parts on an injection molding machine from Engel Austria GmbH, Schwertberg, Austria (www.engelglobal.com). Together with Engel they developed special software to control carriage speed to get the right pack pressure under the nozzle. Fill pressures range from 50 to 300 bar depending on melt viscosity and part thickness, but higher pressure can be used if part geometry and viscosity require it, IB Steiner says.
Engel introduced the technology at the K 2007 show in Germany running 1-meter long ABS strips with a Y-shaped cross section, 1.2 mm thin walls, and molded end caps on an Engel e-motion 200/55 Exjection machine. Arburg GmbH & Co. KG, Lossburg, Germany (www.arburg.com), showed Exjection next in 2008 during in-house Technology Days and at Fakuma on an Arburg A375V Exjection machine. The technology was written up at the time, but little has been reported since. Published patent applications, however, show impressive advances—notably two approaches to rotating mold blocks that can make either continuous long parts or high volume discrete parts, which Steiner described in an in-house presentation for customers last January.
COMMERCIAL APPLICATIONS AND NEW TECHNOLOGY
IB Steiner now has nearly two dozen licensees, some in commercial production, most still in development for a variety of applications. The first licenses were for aircraft lighting and trim parts, reportedly commercial by 2009, according to an Engel press release in 2010 after IB Steiner won an Austrian government award for Exjection technology. Aircraft parts were done for Boeing Co., Chicago, IL (www.boeing.com), and Airbus Industrie, Toulouse, France (www.airbus.com), developed with Stuekerjuergen Aerospace Composites GmbH, Rietberg-Varensell, Germany (www.stuekerjuergen.com), which has one Exjection machine, and with Hybrid Composite, which has two in operation.
Several European companies also commercialized long Exjection building products including Vossloh-Schwabe Lighting Solutions GmbH, Luedenscheid, Germany (www.vossloh-schwabe.com), a unit of Panasonic Lighting in Europe. Vossloh-Schwabe commercialized 1.5-meter LED lighting strips by 2014, simulating the sliding mold with an existing MoldFlow program for mold filling, which sequences multiple nozzles. Vossloh-Schwabe posted a video of Exjection molding on their website (www.youtube.com/watch?v=UV0w79IeGaA).
Besides giving licenses, IB Steiner also develops and patents technology jointly with customers like patent-applied-for (U.S. Pat. Applic. # 20150273747) “elongated hollow parts” for urinary catheters, under development for four years with Hollister Inc., Libertyville, IL. (www.hollister.com), a maker of medical supplies. The driver is the cost saving of replacing an injection molded connector and extruded thin-wall tube, which require assembly, with a one-piece molded catheter 40 cm long.
By 2008 IB Steiner had also gone beyond horizontal sliding molds with a new concept for “Endless Exjection,” which rotates cavities past one or two fixed injection nozzles. Steiner partnered with SaarGummi International GmbH, Bueschfeld, Germany (www.saargummi.com), a maker of automotive seals, to develop a continuous elastomeric seal carrier (U.S. Pat. 8900499), with cavities rotating on a chain like molds for corrugated pipe. Z-Werkzeugbau GmbH, Dornbirn, Austria (www.z-werkzeugbau.com), built the moving molds with 12 cavity segments. SaarGummi trials were done at Arburg’s customer center on a hydraulic two-component Arburg Allrounder 570S, molding the seal carrier at 7-8 m/min.
Arburg’s Selogica controls alternate the two injection units to create continuous flow into the “endless” part. “While the first injection unit is injecting melt, the second one is metering,” Steiner explains. “Then they switch over, and the second injection unit is injecting while the first is metering.” But SaarGummi’s elastomeric seal carrier program didn’t go ahead in the end because of a design change. SaarGummi declared bankruptcy in 2010 and was acquired by Chongqing Light Industry and Textile Holding Group in Chongquing, China in 2011, after which Exjection R&D at SaarGummi stopped.
To date Arburg and Engel have built more than 10 Exjection machines with IB Steiner since 2007, including two “Endless Exjection” machines. Steiner has three on-going development projects for Endless Exjection, all for mass production. So a decade after Exjection was introduced to mold long thin parts out of materials that couldn’t be molded otherwise, it’s under development for high-volume applications in medical, construction, and even packaging. Its advantages today are efficiency, cost saving, and better part quality for both individual and continuous parts.