energy management | Drives
Figure 1: VSD technology realises energy savings at all points in the moulding cycle except injection, where full power is needed, in this two-motor fi xed displacement Engel 1,000 tonne application. Only 35% of the total saving is achieved during cooling and holding
Source: CCS T echnology
sequences through the moulding cycle,” he says. Figure 1 shows actual energy consumption data taken from a 1,000 tonne Engel moulding machine converted from a two-motor fi xed pump system to SyncroSpeed VSD, demonstrating that savings are made throughout the entire moulding cycle and not only during the extended cooling and holding periods.
Variable benefi ts Until recently, conventional wisdom said VSDs would only deliver an energy saving for machines with fi xed delivery hydraulic systems. However, Pratt says that is no longer the case. “We have been doing this for quite a while and until maybe two years ago I was warning not to expect too much in energy savings from systems with variable volume pumps. But to our surprise we have found we can get more of a saving than we thought,” he says. “We know that a variable volume pump will adjust its
volume to demand. So if you want 85% of full demand a variable volume system will adjust its swash position so that you get 85% volume of oil. However, we have found by trial and error that a variable volume pump works more ineffi ciently when it is at 85% volume and running at full speed that when it is at full volume and running at 85% of full speed,” says Pratt. “The effi ciency can drop signifi cantly due to the positioning of the swash plate; we are talking in terms of 10 to 15%, in some cases more. We have developed some control features that push the pump to a better operating point,” he says. Pratt says one customer using a number of Husky
1,150 tonne machines powered by triple variable volume pump systems driven by 200hp motors has realised energy savings of between 22% and 30%, depending on
26 INJECTION WORLD | September 2012
the particular part in production. These savings – dem- onstrated in Figure 2 – have been achieved through a combination of regulating the motor speed together with some additional optimisation made possible through the SyncroSpeed controller, he says. CCS Technology’s SyncroSpeed system comprises a VSD, which controls the frequency and voltage delivered to the drive to regulate its speed, and a controller. The controller is the key to successful operation of the system. Integrating with the injection machine control, the control unit detects any change in the moulding pro- cess and then automatically determines and adjusts the motor speed to deliver the required volume of oil. While the principle of matching motor speed to oil demand is simple, the practice is not so straightfor- ward, he says, and involves a detailed understanding not only of the hydraulic system components but also the moulding process itself. The controller has to be able to cope with all combinations of injection, plasticising, clamp, ejector and core movements, must detect the savings opportunities, and then make every feasible energy reduction at each step of the moulding cycle. While retrofi tting VSDs will provide an energy saving
on any fi xed or variable volume moulding machine, the hardware is not inexpensive so careful analysis of the likely return on investment is required. Pratt says every machine and application is unique. However, due to the cost of the controllers, return on investment is typically too long for machines with installed motors of less than 37kW capacity – around 300 tonnes. As the SyncroSpeed technology realises the greater
proportion of its savings during periods of low demand, such as during part cooling, injection holding period, and other active states where set-point speeds are less than
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