D-LFT in-line compounding & molding: new equipment provides easier entry.
Engel Canada is now offering injection presses outfitted with special add-ons for the Pushtrusion D-LFT process, and MGS Mfg. Group has introduced those add-ons as portable retrofit kits for existing presses. Pushtrusion combines molten resin with continuous glass or other fibers, cuts the fibers to a predetermined length, and feeds the mix to the primary screw of an injection press.
Pushtrusion was developed in 2000 by Ronald Hawley, president of Woodshed Technologies, Winona, Minn. The process technology, patents, and related know-how were acquired from Woodshed in 2005 by PlastiComp, which is headed by Steve Bowen, another pioneer in long-fiber technology.
PlastiComp previously supplied a complete add-on system for Pushtrusion but now it supplies the proprietary "heart" of the Pushtrusion system to both Engel and MGS. The result is said to be lower total cost.
Engel offers Pushtrusion technology fully integrated (including controls) into an injection press. MGS supplies a portable add-on unit based on its Universal Multi-Shot (UMS) series of add-on injection units. Engel says it is ready to supply Pushtrusion technology on a 300-ton press but has not yet sold one. MGS says it can deliver the add-on systems for up to a 10-b shot in as little as six weeks. MGS has built one add-on unit for use on a 750-ton press from Krauss-Maffei.
In addition, PlastiComp has built six Pushtrusion systems using its own injection unit design. One has been sold and two others are located at PlastiComp (on a 300-ton Milacron press) and MGS.
Pushtrusion units can be scaled up or down for a wide range of injection press sizes.
How it works
The Pushtrusion system starts with an extra reciprocating-screw unit mounted above the main injection unit. That injector plasticates the unfilled resin and feeds it to a proprietary cylindrical chamber called an entrainment die. This is the critical point where the molten polymer wets out continuous fibers as they enter the chamber from a spool or creel. As the melt is injected into the chamber, it enters an L-shaped channel. It makes a right-angle turn where it encounters the fiber strand. The high-pressure melt stream encapsulates the fiber and drags it toward a cutter at the end of the entrainment die. The cutter chops the fibers encased in molten resin to a programmed length. The hot material then drops down into the throat of the main injection unit.
"The add-on injection unit is the power source of the Pushtrusion process. The high-pressure flow of the resin 'pushes' the melt and fiber through the die at speeds from 200 to 1000 ft/min," says Eric Lee, Pushtrusion product manager for PlastiComp. This eliminates the need for mechanical pullers or belts to pull the fiber through a wet-out die. This keeps the Pushtrusion system simple and compact.
The Pushtrusion system operates on a signal from the primary machine. When the primary injection screw requires material, it signals the add-on unit to deliver a shot of plasticated resin to the entrainment die. The signal also turns on the cutter, which reportedly senses the speed of the moving fiber strands and adjusts itself to maintain a preset fiber cut length. The primary injection unit requires a modified screw that adds no further plasticating work to the melt--which would break up the fibers--but serves only to gently meter and inject the melt.
Lee notes that for very large parts an add-on extruder can be used for initial plastication in place of a reciprocating screw. Since the extruder would run continuously, the system would require an accumulator to store melt with cut fibers above the throat of the injection press.
The Pushtrusion system reportedly can provide fiber loadings up to 60% by weight and control fiber content to (+ or -) 2%. It also can cut the fiber to lengths within a similar tolerance. Fiber lengths can be set from less than 0.125 in. up to 2.5 in. The Pushtrusion part of the process can be shut down, and the press can run in a conventional manner, if needed, Lee notes.
"The cost of materials to the molder is greatly reduced if the molder purchases the raw materials--resin, fiber and additives--and produces the compounded product itself," says Lee. Raw-material costs can be 20% to 30% less than buying precompounded pellets, he says. Compounding also allows the molder to create exactly the formulation required for the specific job. PlastiComp offers formulation guidance.
The Pushtrusion process can process amorphous materials, which have historically been difficult for long-fiber molding due to their tendency toward higher viscosity than crystalline resins, adds Lee. Besides injection, Pushtrusion may be adapted to compression molding, profile extrusion, and filament winding.
One of the first licensees of Pushtrusion technology is another company started by Ron Hawley, Composite Products, Inc. (CPI), Winona, Minn. CPI uses (and offers for license) a different D-LFT process, called CPI Advantage. It uses a pair of extruders--one to melt the resin and another to combine the melt with precut glass and then extrude a "log" which can be robotically transferred to an injection cylinder or compression mold. CPI took a Pushtrusion license last year. Hawley says the Pushtrusion equipment has the advantage of being smaller and portable. It is suitable for smaller parts than CPI Advantage, and because it uses continuous rather than chopped glass, it can produce longer fiber lengths.
Lee says that not all applications are suited to direct in-line compounding--for example, short runs with frequent resin or reinforcement changes. For that reason, PlastiComp also offers pre-compounded pellets in its Complet line.
NEED TO KNOW MORE?
For more information, enter PT Direct code at www.ptonline.com.
Composite Products, Inc., Winona, Minn. (800) 239-2881 * PT Direct: 624RH
Engel Canada Inc., Guelph, Ont. (519) 836 0220 * PT Direct: 819LR
MGS Mfg. Group, Germantown, Wis. (262) 255-5790 * PT Direct: 822NF
PlastiComp LLC, Winona, Minn., (507) 454-4334 * PT Direct: 671BH
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|Title Annotation:||INJECTION MOLDING: Close-Up|
|Date:||Dec 1, 2006|
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