01 October 2007
Cold extrusion is an important part of the recycling process and the Department for Business and Enterprise sponsored research includes trials with different processes, feed plastics, additives and final products.Dr Patel said his team had already started with cold and warm extrusion and quickly realised that cold extrusion was “more suited” to recycled plastic.He said: “Our process now is to granulate the recycled materials to a consistent size, mix in binders as appropriate to basically, glue the particulates back together, and cold extrude it into sheets or blocks.“The extrusion process is the critical stage, so we are monitoring many parameters relating to this.”The most important parameter is torque in the extruder drive. This indicates the force required to process the material and hence both the power requirements of the drive and the viscosity of the plastic.It is measured using a digital TorqSense torque sensor, which uses Surface Acoustic Wave techniques to provide a non-contact method of monitoring continuous rotary torque, allowing accurate modelling of the instantaneous load changes. TorqSense is manufactured by Bicester based Sensor Technology.It is in effect a frequency dependent strain gauge operating at ultrasound frequency and consists of a transducer mounted on the mixer’s rotating shaft to monitor variations in its resonance frequency as the torsional load varies.An RF (radio frequency) link is used for wireless transmission of signals to an adjacent couple so that rotation is unhindered.Currently the project is sending its recycled plastic off to be made into acoustic baffles for use in new buildings.However, the best examples of the recycled plastic are indistinguishable from virgin plastic so could be used in more demanding applications.
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