Plastic recycler is soft on the environment
April 2007

A 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 Softstart UK range of automation equipment.

Axion Polymers in Salford, Manchester use both fixed and mobile equipment to 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 is often continuous.”

The first stage in the process is shredding the infeed materials using a rotating drum. 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 30kW 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 to 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 go through a wet 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. This is configured like a rotating auger and 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.
Axion were so pleased with the performance of their fixed machine that they also have developed a mobile version, which would open up new markets to them.
“The mobile machine is virtually identical to the fixed one,” says Lamy. “The main difference is that we use an infeed conveyor rather than a compactor. When we realised that this would need an inverter to control the feed rate I suggested a Hitachi Unit and Axion were only too happy to agree.”