Drives | energy management
Hydraulic moulding machines need not be huge energy
consumers. Retrofi t variable speed drives are
delivering savings for users of older fi xed and more modern variable volume pump systems
The drive for energy savings
Operating hydraulic moulding machinery does not have to be a drain on your energy bills, as the latest genera- tion of servo pump driven equipment quite clearly shows. Operating a hydraulic machine at optimum effi ciency is essentially simple – run the hydraulic pump motor only when and at a speed required to meet the oil volume demand for each individual stage of the moulding process. New servo pump moulding machines do this to great effect, offering energy effi ciency levels not far short of the all-electric benchmark. But few moulders can afford to replace their entire machine park and for them an alternative may be to upgrade. Conversion to variable speed drives (VSDs) has long
been shown to deliver signifi cant energy savings in fi xed delivery hydraulic system applications. More recently, VSD technology has also been shown to offer signifi cant savings in variable volume hydraulic system applica- tions, says Fred Pratt, business development manager at UK-based CCS Technology, which has fi tted several hundred of its SyncroSpeed packaged VSD systems to moulding machines across North America, Europe and Asia over the past decade. Pratt says conversion of a fi xed delivery hydraulic
system to its VSD technology will yield a reduction in direct motor energy consumption of between 25% and
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55%, while the reduced load on the oil cooling system can add a further saving of 5% or more. The reasoning behind the savings is simple to
explain, he says. A conventional fi xed volume single pump hydraulic system is powered by a motor running at a constant speed, with the system designed to deliver a continuous volume of oil suffi cient to power the moulding machine at peak performance. The result is that for almost all of the machine cycle the pump is producing more oil volume and pressure than is required at that moment and this excess is “dumped” back into the oil tank via the pressure relief valve, in the process wasting signifi cant amounts of energy. Dual pump fi xed displacement systems provide some additional fl exibility to optimise energy use, but even here the end result is a compromise. “There’s always an over-production of oil. The larger pump may be rated at two thirds of the oil volume and the smaller one at one third, but if the requirement is for 50% then the small pump isn’t big enough and the big one is too big,” says Pratt. “Pumping more oil than is needed is waste that has
to be paid for. By regulating the speed of the motor, the supply of hydraulic oil from the pumps is precisely metered to match the true demand of the machine as it
September 2012 | INJECTION WORLD 25
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