When a 23 year old plastic bottle blow moulding machine was failing to deliver its proper output, Northern Ireland’s PrimePac faced a dilemma. The machine uses a hydraulic motor to run an extruder on a blow moulder. Because it had spent its life running 24 hours a day, five days a week, its motor was operating inefficiently and suffered poor speed holding properties.
Previously it took 10 seconds to create a bottle. In recent years this had extended to 12 seconds. The extruder was also creating long tails of excess plastic that needed to be trimmed and recycled in a very energy intensive process.
PrimePac was quoted £30,000 to refurbish the machine. This work would have kept it running but with the same technology and still using the same amount of energy. This was a critical factor as the site’s 600 kVA electrical capacity was at its limit. Therefore, plans to introduce an additional all-electric injection moulding machine to produce a new type of medicine bottle would require an investment of over £250,000 in upgrading the electrical supply
Energy assessment reveals opportunities
To find an alternative, PrimePac asked its energy and automation partner, Advantage Control, an ABB authorised value provider, to carry out an energy assessment of the existing machine.
Over a week, its energy use was measured against an existing all-electric model. This proved that when making bottles of the same size and weight the old machine consumed significantly more energy. Its power use was also erratic and consumption was high due to the hydraulic pack requiring extra torque on start up.
Furthermore, the old blow molding machine’s speed regulation was causing issues that resulted in a poorly formed bottle.
It was decided that a package comprising ABB’s synchronous reluctance motor (SynRM) and an ACS880 drive would not only reduce electricity use, improve speed holding and the quality and consistency of the finished product but would also free electrical capacity that could be used to power the new injection molding machine.
Following the installation, logged data revealed a 60 percent energy saving. Even with the modifications that were required to the machine, the £7,400 purchase of the 55kW, IE4 SynRM package is expected to payback in under 12 months.
Speed regulation critical to success
The ABB industrial drive features direct torque control (DTC) that has provided a real step forward in terms of the actual speed holding on the drive. It is now much more accurate, leading to a consistent length and weight of plastic through the extruder and into the mold. This means less wastage – no more long tails - as there is no product overspill.
Previously, only 63 percent of extrusions actually became bottles. This was due to the erratic and sporadic movement of the machine. Following installation of the SynRM package, 96 percent of extrusions turn into bottles. The missing four percent is purely due to when the machine is ramping down.
Because there is less waste, the 18.5kW granulator used to recycle the waste is used less often. This has saved around five percent of the energy on its own.
Other benefits include a significant reduction in noise and vibration, and operators can now hear what their colleagues are saying while standing alongside the motor.
Clifford Craig, engineering manager at PrimePac, says: “We couldn’t install a new electric machine because we didn’t have the available power. But with the 60 percent energy saving we achieved on the old blow moulder we have been able to install another new all-electric injection moulding machine. This is beyond our wildest ambitions. We have managed to massively increase our production, just by installing one SynRM package from ABB.”