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machinery feature | Lab compounders


would be best processed on a co- or counter-rotating extruder when scaled up to full production.  www.leistritz.com


Randcastle says that compounding with a single rotor or single screw featuring its spiral-fl uted extensional mixer (SFEM) technology delivers high levels of product mixing for smaller volumes of material. The company offers the SFEM technology on its expanded line of micro-batch mixers, and the mixing elements can be scaled up for use on its single-screw extruder.


Randcastle’s batch mixer uses the company’s SFEM technol- ogy to deliver very high levels of mixing


American Leistritz Extruder. The Nano-16 can process batch sizes of 50 g or smaller, and the polymer compounding industry is starting to take notice of the model for high-value formulation developments. The unit integrates a twin-screw extruder with a unique micro-plunger feeder that simulates a continu- ous extrusion process for batch samples from 20 g to 100 g. The 16 mm diameter screw has the lowest free volume available for a twin-screw extruder, claims the company.


The micro-feeder plunger delivers material to the


feed barrel for precision feeding at extremely low rates, and it can meter materials in virtually any form, including powders, micro-pellets, pastes, slurries, and granules.


At the other end of the lab scale, Leistritz’s ZSE 27 Maxx has 28.3 mm diameter screws with a high-volume 1.66 OD/ID confi guration. The company reports that


Steer’s new OMicron 10 model can process high-end


polymers in


batch sizes as small as 15 g


customers are achieving throughputs of more than 300 kg/h with the machine which bridges the gap between lab and production models. For example, Innovative Polymer Compounds (IPC) of Ireland is using a ZSE 27 Maxx for the production of compounds for medical applications in its Class 100,000 clean room, as reported in last month’s Compounding World. The processing units of the ZSE 27 Maxx are interchangeable with the company’s Micro 27 GL/GG modular twin-screw extruder which can operate in both co-rotation and counter-rotation modes. The operating mode is selected using a switch in the gearbox. Leistritz says that this is a unique feature that allows users to decide whether a formulation


42 COMPOUNDING WORLD | December 2012


“Initially one would think that it impossible to get material elongation using one shaft until there is the realization that there are two forces at work on the material; pressure fl ow and drag fl ow,” says Randcas- tle’s president Keith Luker.


Rather than designing screw fl ights that wrap


around the screw in a helical manner, Randcastle instead splits a certain section of the rotor into two design halves. Each half of the rotor at that section features a melt channel with drag fl ows similar in depth, pitch and length, but designed to move material in a direction exactly opposite to the melt channel design on the other half. Grooves at each end of this special section allow


pressure fl ow and drag fl ow forces to create elongation and mixing. Material washes over the geometry in the section, creating fl ow that is dominantly elongational, says Luker.


A paper delivered at the SPE Antec 2011 conference


by Dow Chemical and Randcastle showed that the use of SFEM elements can deliver better mixing than a twin-screw. Luker says that the SFEM elements mixed eight times better than the twin-screw, and 1,000 times better than a conventional single-screw extruder.  www.randcastle.com


www.compoundingworld.com





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