PLASTIC RECYCLER IS SOFT ON THE ENVIRONMENT
April 2007

A groundbreaking plastic recycling company is making full use of soft starts on all the major axes of its processing equipment, along with inverters, PLCs and HMIs, all from the Silverteam range of automation equipment.

Axion Polymers in Salford, Manchester, reduce damage to the environment by preparing discarded plastic for reuse. Its control systems were designed and built by Sean Lamy of integrator 3-Ohms Ltd.

“Parts of the process are very demanding,” he says, “so we had to design-in a level of sophistication and robustness to guarantee reliable operation – which often runs on a 24x7 continuous cycle.”

The first stage in the process is shredding the infeed materials using a single-shaft shredder with a rotating drum-cutter. This represents a large mass, which would draw a lot of power at start up and feed voltage spikes into the supply. It is also in the nature of this axis to jam.

“We have a main drive motor of 60kW and therefore fitted a soft start with a current monitor. If the current rises to 250 percent, the soft start reverses the motors to clear the obstruction then goes back into forward drive to resume shredding,” Explains Lamy.

Another soft start is used on the outfeed screw conveyor, and a third is fitted to the motor on the power pack of the hydraulic compactor which feeds the shredder.

After shredding, the plastic goes through a novel separation stage to classify different type of plastic. These are melted, extruded and granulated to form new plastic stock for sale to moulders, extruders and manufacturers.

A final soft start is fitted to the 110kW drive motor of the granulator, which incorporates a heavy, precision engineered cutting rotor. This rotating cutter needs a phenomenal but controlled starting torque – provided through the soft start – for when it is starting under partial or
full load.

An Hitachi EH150 PLC is used to control the whole system, including control of the hydraulics and collection of throughput data for productivity analysis.

“The EH150 accepts both analogue and digital inputs, using the former to monitor the current to the
250 percent threshold. Despite being a fairly complex machine we were able to achieve a very neat control architecture based on a single PLC.”

An HMI provides the operator with clear, concise information on machine status. This includes
operation information, production information, diagnostics for easy fault finding and e-stop activities.