Plastics Engineering - May 2014 - 13

Efficient TSEs
Although various types of blenders and compounding
extruders are used (depending on the type of polymer,
additives, and output), co-rotating, intermeshing twin-screw
extruders (TsEs) are widely used because of their dispersive
mixing characteristics and the ability to dose additives
downstream of the feed-zone into the melted polymer.
These TsEs are also known for their modular, segmented
screw design that allows the design to be optimized for a formulation by changing, for example, the types of mixing
elements or locations of downstream feeding or venting
ports.
in the past decade, advances in shaft design and metallurgy have resulted in step changes in the output possible
with co-rotating, intermeshing, segmented TsEs. leistritz's
asymmetric splined shaft design, developed in 2004, enabled
an increased free volume with an outer/inner diameter
(OD/iD) ratio of 1.66, up from the traditional standard of 1.55.
subsequent improvements in metals used for the shaft
allowed manufacturers to also increase the torque possible
with a given shaft size, boosting specific torque up to 15
nm/cm3.
At the K 2013 trade fair, leistritz displayed its ZsE 50 XX
concept extruder, which reportedly allows specific torque of
20 nm/cm3 for even higher throughputs in torque-limited
processes. The higher torque is enabled by the smartXX
screw, which is a one-piece, solid screw rather than a modular, segmented screw. leistritz expects that the production
extruder will be built in 2015.

coperion launched its high-torque ZsK Mc18 series, with
a specific torque of 18 nm/cm3, at K 2010 and, at the most
recent K show, introduced several improved features. The
ZsK Mc18 "smart" is designed to be more easily accessible
for cleaning; its screw shaft axes are low, and ancillary
units can be mounted by a swivel arm and operated from
floor level, rather than from a raised platform, to improve
operator safety. "This design was driven by customer
requests for easier accessibility and improved ergonomics,"
explains Peter von Hoffmann, general manager for the
compounding business unit at coperion. "Eliminating stairs
makes the operator's job easier and reduces injury risk."
customers are also increasingly looking for manufacturing equipment that is easier to keep clean on the outside as
well as the inside. "in medical-grade compounding and also
in markets such as automotive, compounding facilities are
more frequently being audited by customers. The production facility is now also a showroom, and companies want
to show that their equipment is clean and in good condition,"
says von Hoffmann. compounding plants can be dusty
places, but designs such as the ZsK Mc18 smart, in which the
electrical and water supply systems are integrated into the
base frame of the machine, make the exterior easy to clean.
The "smart" design can also improve feeding; locating
the feeder directly above the extruder throat minimizes
the length of the drop into the extruder, which can minimize
the amount of air added to low bulk-density fillers and
thus improve feeding efficiency. The design is available for
the ZsK Mc18 series (with screw diameters of 18, 26, and 32
mm) and for the ZsK MEgAvolume Plus series (screw

The Coperion ZSK Mc18 "smart"
features an easy-to-clean exterior
(photo courtesy of Coperion).

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