LABORATORY EXTRUDERS | MACHINERY Getting it right at small scale
The need to boost output has focused development on large extruders – but many principles and process conditions are first proven using specialist laboratory extruders
Laboratory-scale extrusion is a critical factor in testing out formulations and processing conditions before scaling up to full production. It is also a useful tool for study – whether in an industrial or academic context. Conextru of Austria has developed a special lab-sized extruder for a university department – in- cluding software, screw design, pressure sensors and a special valve for screw testing. The C30 30 extruder has a 7kW motor and is mounted on a frame with height-adjustable wheels. The screw has a maximum speed of 200rpm and is driven by a Zambello gearbox. At the same time, the 29.4D barrel is nitrided and has four heating/ cooling zones. Two screws were supplied with the system: one with a mixing tip, the other with a dynamic mixing tip. The machine was also supplied with a special adapter for independent measurement of melt temperature. It also includes a PLC with interface to read out data for further use, says Conextru. The barrel is adapted with four 0.5in melt-pressure holes, to accommodate pressure sensors. In all, five melt pressure measurements are made – four in the barrel and one in the adapter. The software and analytical capability allows
data to be logged at regular intervals – which is adjustable from 1 to 10 seconds. “The data we want to log is everything we see on the screen – such as the measured and set barrel and head temperature of each zone, the pressure of each sensor, rpm, melt temperature and power,” said Josef Dobrowsky, managing director of Conextru. Logged data can be saved onto a USB stick. Melt pump control or software to keep melt pressure constant it possible to set an extruder pressure with automatic (software) modulation of the screw rotational velocity? The main purpose of the special extruder is to
allow screw design to be analysed – by measuring the pressure curve over the screw’s length. “Results were seen to be different to theory,” said Dobrowsky. The system can also be used for a range of other
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applications including: screw melting and mixing analytics; recording an output curve – thanks to the special pressure valve; recording output at differ- ent pressure levels and studying the influence of pressure on output; recording viscosity data, thanks to the special die nozzle; and teaching extruder behaviour.
Peek performance Collin Lab & Pilot Solutions, which supplies a range of lab-scale extrusion machinery, says that its systems have been used to make highly specialised pipe – from high temperature materials such as Peek and polyetherimide (PEI). Pipes made from these types of material are typically used in order to reduce weight, or to solve difficult mechanical or chemical requirements. PEI pipes, for instance, have high-quality internal and external surfaces – with high transparency and precise stability of diameter and wall thickness. The Collin equipment used to make these pipes – which have a diameter of up to 25mm and wall thickness of 0.5mm – has a two-step vacuum dry cali- bration at its core. Each calibration unit can sepa- rately be oil-tempered (up to 250°C). This allows pipes to be made with very low residual stress. Precise line control allows the wall thickness to
March 2021 | PIPE & PROFILE EXTRUSION 29
Main image: Conextru has supplied a special lab extrusion line, with ancillaries, to a university department
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