New multiscrew compounds, reactors.

Several new developments in multiscrew machines for compounding, reacting and devolatilizing have come to light recently, some of them at the recent SPE ANTEC in Montreal. Reported here are new twinscrew models and some enhancements, a "convertible" pelletizer in development, deep-flight twin-screw reactors, and a novel 10-screw reactor/devolatilizer.

TWIN-SCREW

COMPOUNDING NEWS

Werner & Pfleiderer Corp., Ramsey, N.J., is developing a number of new features for its line of Super Compounders. One is a side-venting device to be offered as an alternative option to the top vent. Another is a new family of distributive mixing elements called ZME, which are designed to have full self-wiping capability. Unlike existing TME elements, the new ZME elements' teeth are pitched, so that the teeth wipe not only the root of the element, but also the entire barrel portion as well. TME elements are self-wiping at the root only, and rely on the velocity profile to push the material through the barrel and eliminate stagnation.

A third development, expected to become available in the next 12 months, is a water-ring pelletizer that can be converted to an underwater pelletizer "on the-fly." (W&P already offers a water-ring pelletizer that can be converted to an underwater pelletizer with minimum modification; changeover usually takes about 1 hr.) The automated conversion system was briefly described at the SPE Polyolefins VII RETEC in Houston this February. This new system will allow start-up of a compounding line in water-ring pelletizing mode and subsequently switching to underwater mode, while a time throughput is brought up to production speed.

Teledyne Readco, York, Pa., has designed its first corotating, intermeshing extruder for compounding. The company has a 3 1/2-in. machine with 75-hp drive in its lab for tests. Standard barrel-segment L/D is 4:1. The barrel is oval shaped and circulates fluids for heating and cooling.

And starting in January, Toshiba Machine Co. America, Elk Grove Village, Ill., will be permitted to sell its line of twin-screw compounding extruders in the U.S., following the expiration of a three-year trade sanction. Toshiba offers a line of corotating, intermeshing twin-screw extruders, as well as a newer line of TED counterrotating, intermeshing extruders. The TED line is available in 75-, 95-, and 135-mm sizes (see PT, Feb. 88, p.13).

Features of the TED machine include nitrided screws and barrel, circulating-oil barrel- and screw-temperature control (together with heater bands on the barrel), movable barrel mount to ease screw removal, forced lubrication with temperature-controlled oil, head section that opens on hinges for easy maintenance, split gearbox to facilitate thrust-bearing maintenance, and thrust-bearing protection against abnormally high pressure.

MULTISCREW REACTORS

Two new machines, one with two screws and one with 10, are aimed at continuous reacting and devolatilization. Both were unveiled at ANTEC.

Berstorff Corp., Charlotte, N.C., introduced a ZER series of twin screws from 45 to 310 mm diam., all with deeper flights to provide longer residence time, as is required for some reactions. For an idea of how ZEA models compare with Berstorff's other machines, a 130-mm, 48:1 L/D unit would have a total flight volume 3.3 times that of a ZE machine and 67% larger than a ZEA model of similar size.

ZER units are designed for melt-fed, low-viscosity applications requiring relatively low torque and shear. The barrels are said to incorporate new and unique venting provisions to permit very high-vacuum devolatilization.

Berstorff also presented a paper at the conference on an unusual 10-screw continuous, vertical reactor of a planetary-screw type. This system, which is said to be in advanced stages of development, reportedly can handle a wide range of very low to very high viscosities and eliminate problems presented by incorporating vent ports in the barrels of other extruders. It's also said to be highly energy efficient, and residence times of up to 30 min are reportedly possible.

Various designs of the machine have been developed. Earlier versions have 10 intermeshing screws around the periphery of a barrel, with the large empty space in the center used as a devolatilization zone. The thin 0.3 mm) film of material on the screw is readily degassed as it passes through this zone on each screw rotation. To make sure the outer barrel wall is thoroughly wiped, the entire collection of screws revolves around the central axis. A later design of this machine has a smooth drum in the center instead of an open space. This drum is also wiped by the screws.

And at the bottom end of this vertical machine, the planetary screws can intermesh with the feed end of a single discharge screw.