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Compounding.

Most of the focus at K next month is on new high-speed, high-torque twin-screw machines, a concept introduced at the last K show by Krupp Werner & Pfleiderer (U.S. office in Ramsey, N.J.). At least two novelties will also be on display: One is a new way to process continuous glass roving and attain longer glass lengths in finished pellets. A second process coextrudes strands for pelletizing sticky or otherwise difficult materials.

Novel processes to debut

KWP will demonstrate what's believed to be a unique method for introducing continuous glass roving into the compounding process on the new ZSK 50 Megacompounder. Roving is fed into the top of the extruder half-way down the barrel instead of the usual method of screw-feeding chopped fibers into the side of the extruder. The patented feeding device preheats and impregnates the rovings with a low-viscosity polymer to aid dispersion. Although the continuous strands break up in the extruder, a new, patented screw element is said to minimize breakage, so that longer glass ends up in the pellet. KWP says the glass comes out around 2.5 mm long, about the same as the pellets themselves. Total cost is slightly higher than using chopped glass, but product quality is reportedly better.

Leistritz will demonstrate an unusual new "coextruded-strand" pelletizing process, which coats strands with a cap layer before pelletizing them. This makes it possible to pelletize sticky materials, resins with poor melt strength (by coating them with a stiffer material), or water-soluble materials that would dissolve in the cooling bath. A ZSE-27 mm twin screw will devolatilize and pump the primary melt into a new multi-strand die, while a Micro-18 mm twin-screw feeds the same die and coats the strands with a thin outer layer. The process was developed at American Leistritz Extruder Corp.'s Edison, N.J., lab and isn't yet commercial.

More 'muscle' machines

The latest in high-speed, high-torque machines on display will include a new size from KWP, the 50-mm ZSK 50 Megacompounder, capable of 1200 rpm.

New from Leistritz are "HP" (high-performance) versions of ZSE 50-, 60-, and 100-mm twin screws.

Farrel Corp., Ansonia, Conn., will show not only a high-speed, high-torque model FTX-80-H, but also a vented version of its Model CP-1000V continuous-mixer system.

New lab versions of 1200-rpm, high-torque compounders will also be shown by three firms. KWP will bring its ZSK25WLE (World Lab Extruder), while Berstorff (U.S. office in Florence, Ky.) will show its ZE25 Ultra Glide machine. The latter has a motorized "traveling gearbox," which can pull the entire screw rapidly out the back end of the barrel to permit visual inspection of what's happening inside the extruder. And Leistritz will show its ZSE 27 lab machine for the first time.

Pelletizer improvements

In pelletizers, KWP has come up with new features for automating start-up and minimizing wear in underwater models. The latter improvement involves a redesigned knife-rotor bearing that maintains optimal pressure of the knife against the die plate independent of cutter speed, throughput, and resin processed. First developed for very large models used by polyolefin producers, these features will be incorporated in all the company's UG models.
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Author:Schut, Jan H.
Publication:Plastics Technology
Date:Sep 1, 1998
Words:524
Previous Article:Materials.
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