Powerful twin-screw extruder offered by new supplier.

Powerful Twin-Screw Extruder Offered By New Supplier

A corotating, intermeshing twinscrew compounding extruder is the first product offering of a new company, Delaware Extruder Corp. in Milford, Del. (see PT, Sept. '90, p. 14 for an initial report). It's said to offer high torque, a novel cooling system, and custom screw elements to handle a range of engineering resins. The machine was originally developed for Plastic Materials Co., Inc. of Milford, a color and engineering thermoplastics compounder and parent company of Delaware Extruder, and represents the first of a line of twin-screw compounding machines being brought to market. The two companies, which share facilities, plan to use the first production-scale unit for testing new materials.

HIGH TORQUE, LOW SPEED

The unit, called DEC 92, is a 92-mm machine said to provide up to 50,000 lb of thrust at 200 rpm, delivering up to 150 hp per screw. The key to the extruder's high torque capacity lies in the design of the gearbox, according to v.p. Waino Kangas, who designed the machine.

The gearbox configuration is claimed to maximize the torque to each shaft. The output shafts are in contact with two larger gears above and below. Energy from each larger gear is counterbalanced by the other and is directed inward, toward the gears turning each shaft. The opposing gears reduce the defection that occurs when using a single, unopposed gear, thus delivering higher torque to each shaft. In addition, an external oil pumping and cooling system maintains proper oil temperature and pressure, and oil-pressure interlock protection is provided.

FLEXIBLE BARREL DESIGN

A segmented barrel allows feed ports and venting sections to be placed in any configuration. Barrel segments are provided in two standard lengths: 3.6 L/D, which can be used for feeding, venting, or additives, and 6 L/D. A patent-pending design on the cooling system is said to offer maximum flexibility of temperature control. Coolant is run through holes drilled through and connected between each barrel section and flange. The configuration allows all of the quadrants surrounding the screws to be cooled either together or selectively by capping off various sections of the flow path. The system also allows the passages to be cleaned easily, says Kangas, because plugs can be removed to permit cleanout of mineral deposits. He adds that the capacity for controlled cooling make the machine suitable for reactive compounding applications.

Unlike many high-torque twin screws that use multiple-key shafts, the DEC 92 uses a single, 12-mm-wide key to hold screw elements and kneading blocks in place. Although Kangas admits that the single-key design may sacrifice a minimal amount of torque, he points out that the configuration makes screw elements easier to remove for reworking and repair.

Bi-lobal kneading blocks were chosen to provide maximum throughput. Kangas claims that additional mixing can be achieved by adjusting the combination of screw elements and kneading blocks. Standard kneading blocks are of 90-mm length and 18-mm lobe width; others are available. Screw elements can also be customized, and are available in lengths of 30 to 234 mm and pitches from 60 to 156 mm. The die is of a quick-release, swing-away type.

A single control panel includes tachometer, individual barrel temperature controllers with heat and cool programs, and individual ampere gauges for each heater element. Temperature controls are programmable for gradual heating and cooling.

Price of the DEC 92, which is supplied as a turnkey system, is about $610,000 and includes motor, drive system, die, control panel, machine base and mezzanine. All parts are stocked by Delaware Extruder, ensuring quick availability. In the future, Kangas expects to complement the DEC 92 with a smaller, lab-sized twin-screw unit of about 60 mm diam., as well as a larger unit, and is investigating the use of three-lobe mixing sections. (CIRCLE 4)

PHOTO : The DEC 92, a 92-mm corotating intermeshing twin-screw extruder, is the first product of a brand-new firm, Delaware Extruder Corp. Features include a powerful gearbox delivering 50,000 lb of thrust and a unique cooling system.