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Systematic design and function of screw configurations for traditional and new applications in
extrusion. Dr.-Ing. Bernhard van Lengerich. Senior Technology Officer, Gen. Mills, Minneapolis, MN,
USA.
The screw geometry of twin screw extruders affects all unit operations
that occur either simultaneous or subsequent inside the extruder barrel. Extruder operation with an optimum
screw configuration, i.e. crossectional and longitudinal geometry, enables the manufacturer to achieve
desired product attributes at maximum capacities. However, a systematic design of new screw
configurations can increase substantially the potential of extrusion for new applications. In the past, the
discussions and research about the optimum screw configurations on extruder processing and product
quality for even conventional applications have been controversial and inconclusive, mainly because of
inconsistent screw element geometry definitions by their manufacturers and the large variety of different
screw elements available today. This presentation will cover some basic principles of crossectional and
longitudinal screw design and its impact on conventional and nontraditional applications such as, for
example the processing of expanded products, doughs, cookies and ice cream. Furthermore, the design,
function and usage of individual screw elements as well as the systematic design of simple and complex
screw configurations and their impact on time-temperature-shear-history inside the extruder barrel will be
discussed.
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