pVc compounding | machinery feature
improve your vinyl mixing
pVc compounding uses various types of equipment. Traditionally, raw materials are first pre-mixed in a high-intensity mixer and cooled, and the resulting powdered dry-blend is sent to a kneading extruder or twin-screw extruder (TSE). conical and parallel counter- rotating TSEs are primarily used for direct extrusion into parts such as pipes or profiles, while co-rotating TSEs can be used for direct extrusion or for compounding into pellets. Kneading extruders have also traditionally been used for compounding pVc, and advances in these technologies now offer even more options.
Kneader news B&P Process Equipment’s TriVolution Tri-Kneader is the most recent major development in pVc compound- ing technology. The Tri-Kneader, a reciprocating single- screw with mixing flights that interact with stationary pins on the barrel wall, has more pin/flight interactions per revolution than traditional kneaders, which increases mixing. “The combination of multiple strokes per revolution and having a constant clearance result in efficient mixing that emulates the high dispersion obtained in a twin-screw,” explains michael lazorchak, global product manager for mixing systems at B&p. in addition, the Tri-Kneader’s l/d ratio, with configurations available from 8:1 to 20:1, is much
www.compoundingworld.com
producing pVc compounds presents some special challenges. Jennifer Markarianlooks at a variety of
solutions based on kneaders and twin-screw extruders
shorter than that of twin-screw extruders. This is claimed to make the machine more efficient because a greater percentage of the mechanical energy goes into the compounding process. The Tri-Kneader is also designed to run at lower screw speeds, which reduces wear and improves energy-efficiency. in tests using a rigid pVc formulation run in the B&p
processing lab, the TriVolution achieved a higher throughput at 80 rpm than a TSE at 500 rpm. The TriVolution maintained a constant, low temperature over a broad throughput range, up to nearly 300 kg/hr, while the legacy co-kneaders and a TSE were limited in throughput and demonstrated temperature increases (Figure 1). lazorchak says that the TriVolution excels in
January 2012 | compounding world 43
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