Cold extrusion is playing a greater part in recycling of waste plastic. Engineers at Bradford University in the UK have built a pilot plant and are running trials with different processes, feed plastics, additives, and final products.

Leader of the project, Dr Raj Patel explains: “We started out comparing cold extrusion and warm extrusion, in which the material is heated prior to processing, and quickly realised that cold extrusion was more suited to recycled plastic. Our process is to granulate the recycled materials to a consistent size, mix in binders to 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.”

Torque in the extruder drive indicates the viscosity of the plastic. It is measured using a digital TorqSense torque sensor, which uses Surface Acoustic Waves to provide a non-contact method of monitoring rotary torque, allowing modelling of the load.

“With research work, there is an inordinate amount of dismantling and reassembling equipment,” says Patel. “TorqSense being non-contact does not need to be dismantled. It is also naturally robust, important in the laboratory and critical since it is likely to be used on the full scale plants that we will ultimately develop.”

Sensor Technology Ltd is based in Upper Heyford, Biscester, Oxfordshire, UK. www.sensors.co.uk