Comparing twin screw extrusion versus single screw extrusion is an important exercise for
most decision-makers who want to invest in extrusion technology. In the checklist below,
based on our long term experience in providing twin screw extruders for a wide range of
applications, here is a checklist of the main processing advantages of the Clextral twin
screw extrusion technology.
Co-rotating twin screw extruders versus single screw extruders show :
Remarkable mixing capability, due to the interpenetration of the screws and the broad
diversity of specialized screw designs (such as reverse screw elements, kneading blocks,
gear mixing elements, etc.) which allow the extent of shearing/mixing to be precisely
adjusted; hence leading to control the degree of mixing in regards to mixing intensity and
mixing quality (dispersive versus distributive). Conversely, mixing capability of single screw
extruders is very limited, and any flow restrictions to enhance mixing through special screw
designs lead to depress the extruder throughput.
High level of process flexibility, due to throughput and screw speed independency, and
capability to handle multiple processing functions in series (such as melting, mixing,
cooking, venting, cooling, etc.) in one single extruder. Conversely, with single screw
extruders throughput and screw speed are dependent, and screw designs with multiple
processing functions in series are restricted.
Better control of process parameters, that are: narrower residence time distribution, lower
dispersion of shear rates and strain, higher convective heat transfer, accurate control of
temperature profile; hence leading to much better control of shear-time-temperature histories
in the extruder, to much wider range of mechanical energy inputs, and so to more
consistency in regards to material conversion and product quality.
Higher process productivity, due to positive pumping action of the screws, ability to handle
wider varieties of raw materials and mix formulations including complex recipes, screw
speed-aided compensation of screw wear (with single screw extruders process performances
invariably decrease when screw wear increases), lower downtime.
Higher economical opportunities and business potential than single screw extruders, owing
to higher process flexibility and productivity, to produce wider range of end products, to
convert materials and handle product quality more consistently, to compensate the effect of
screw wear through screw speed adjustment.