extruder of today. Werner & Pfleiderer undertook an
additional four years of development work in order
to make the first machines fit for production.
Throughput increased by a factor of 35
Today, the ZSK twin screw extruder is distinguished
by a performance level considered revolutionary at
the time of its market launch and for a long time
afterwards. For a machine of the same shaft center
distance, the throughput rate today is 35 times
higher than it was 60 years ago. At the same time,
today’s compounding machines handle a considerably
higher number of processing tasks. The length of the
process section is a main factor enabling this. Today,
the process section can be extended up to 80 D (D =
screw diameter) from an original figure of 6 D. While
the first ZSKs featured a specific torque Md/a³ of 3.7
Nm/cm³, today’s ZSK high-performance extruders
boast torques of 18 Nm/cm³ on the ZSK Mc18 and
11.3 Nm/cm³ on the ZSK Mv PLUS. Together with
a significant increase in speed from 150 min-1 to
1,200 min-1 or 1,800 min-1 – which some experts
initially viewed with skepticism – the current ZSK
•
range can achieve incredibly high throughput rates.
Continuous development of the technology
The levels of performance and flexibility currently
achieved by the ZSK twin screw extruder are the
result of intensive, continuous development work
by the engineers at Werner & Pfleiderer – as it was
back then – and Coperion today. These developments
include the following examples:
• The transition to a process section with modular
barrel sections and screw elements facilitates
the versatility needed to fulfill a wide range of
processing tasks while remaining cost-effective.
• The type of connection between the screw shaft
and the screw elements is vital in determining
the maximum transferable torque. Over the
years, development has progressed from the
simple taper and keyway to the spline shaft, and
then to an involute toothing optimized with the
ZSK Mv PLUS twin screw extruder with a screw
diameter of 54 mm, in hygienic design, designed
especially for the strict requirements of
food production applications.
aid of the FEM and produced in a special cold
hammering process for increased robustness.
This type of connection is capable of transmitting
extremely high torque.
Improved materials and production methods
have made it possible to gradually increase the
screws’ ratio of outer diameter Do to inside
diameter Di from an original value of 1.22 to a
current value of 1.55 (on the ZSK Mc18 and the
ZSK MEGAcompounder) and 1.80 (on the ZSK
Mv PLUS), which has led to a significant increase
in the free volume in the process section.
• Numerous developments with the aim of pushing
back the boundaries of process feasibility enabled
the torque available today to be used to the
fullest. These include the new Feed Enhancement
Technology (FET) for considerably improved
feeding of fillers with a low bulk density and the
ZS-EG side devolatilization unit for more efficient
and r eliable devolatilization.
• Today, various materials and coatings are
available for areas of the screws and barrels which
come into contact with products to ensure
both a prolonged service life and a high
purity of product.
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TUBE NEWS October 2017
13