Anniversary of Coperion’s high-performance ZSK extruder series

60 years of ZSK twin screw extruders
Anniversary of Coperion’s high-performance ZSK extruder series
Stuttgart, September 2017 – The ZSK twin screw extruder, the “forefather” of all twin screw
extruders, celebrates its 60th anniversary this year. Werner & Pfleiderer, known nowadays as
Coperion GmbH, delivered the first co-rotating, closely intermeshing ZSK twin screw extruder in
1957 – exactly 60 years ago. Since then, the ZSK extruders have undergone a transformation
that was inconceivable 60 years ago – from what would now be considered relatively simplistic
co-kneaders with a throughput rate of 170 kg/h to sophisticated, high-performance processing
machines for a variety of applications in the plastic, chemical, food and pharmaceutical
industries. They are manufactured with screw diameter sizes ranging from 18 to 420 mm and
achieve throughput rates from 200 g to 125 t/h for polyolefins.

Four years from the first prototype to serial production
In 1953, Werner & Pfleiderer acquired an exclusive license from Bayer in Leverkusen,
Germany. The work was started by Rudolf Erdmenger and Walter Meskat at the IG plant in
Wolfen in 1943. In 1945 Rudolf Erdmenger continued the work as part of the “High-Viscosity
Technology” group and developed the fully self-wiping profile for co-rotating intermeshing
screws. This was the inception of the ZSK twin screw extruder, which remains functional over a
wide range of viscosities or frictional properties of the processed material. The prototype of this
machine invented by Erdmenger was still equipped with vertically arranged screws, unlike the
ZSK twin screw 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 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
reliable 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.

A bright future
There is no end in sight for the ZSK success story. The developers at Coperion already have
their sights set on the machines of tomorrow – with an even wider spectrum of applications for
new tasks in a vast range of industrial sectors. Energy efficiency, the conservation of resources
and the integration of ZSK high-performance extruders into companies’ digital environments are
the current hot topics that are shaping the future of the ZSK. Frank Lechner, Head of Process
Technology at Coperion, states: “Current examples of our innovative strength are the
changeover from batch processes to continuous processes, which are increasingly in demand
by customers in the chemical and pharmaceutical industries in particular. We have already been
able to achieve impressive results with our ZSK extruders when producing products such as
sealants or cleaning agents. In many processes, we are also able to increase the throughput
rates and the product quality many times over with our latest development, the recently
introduced involute screw elements, thus contributing to more efficient use of the systems and
resources. We are also equipped for the future requirements of the ‘Circular Economy’ as far as
both extruder technology and our decades of processing know-how are concerned.”
Coperion  is the international market and technology leader in compounding and
extrusion systems, feeding and weighing technology, bulk materials handling systems and services.
Coperion designs, develops, manufactures and maintains systems, machines and components for the
plastics, chemicals, pharmaceutical, food and minerals industries. Within its four divisions –
Compounding & Extrusion, Equipment & Systems, Materials Handling and Service – Coperion has 2,500
employees and nearly 30 sales and service companies worldwide.

A modern, high-performance extruder from the ZSK Mc18 series with a specific torque of 18
Nm/cm³ and a Do/Di ratio of 1.55 for preparing products with high torque requirements, such as
engineering plastics

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
Image: Coperion, Stuttgart