3 traditional injection molding machine drive system
The drive system of the traditional injection molding machine is usually composed of PQ controller + quantitative pump + induction motor. The block diagram of the structure is shown in Figure 2:
Figure 2 Traditional injection molding machine drive system architecture
When the traditional injection molding machine system enters the pressure keeping, the motor still drives the oil pump at full speed at high speed. Since the system is now in a pressure-holding state, there is no need to supply oil to the system. Therefore, the oil pumped by the oil pump returns to the fuel tank through the safety valve. The waste of electric energy is generated and the wasted electric energy is also converted into heat, which can increase the oil temperature of the fuel tank and reduce the life of the seal ring. In short, with the traditional injection molding machine driving method, the longer the pressure holding and cooling time, the more energy the system consumes.
4 three improved drive methods
4.1 Variable pump drive
The traditional injection molding machine driving method introduced above leads to increased power waste. The industry has introduced a variable-pump-driven injection molding machine. The system is usually composed of PQ controller + variable pump + induction motor, as shown in Figure 3:
Figure 3 Variable Pump Drive System Architecture
The biggest advantage of switching to a variable pump is that, although the system is under high pressure, although the motor runs at high speed, the variable pump will adjust its displacement according to the pressure of the system. That is, when the system pressure reaches the set value, the variable pump will switch to small. The displacement thus reduces the output flow of the pump during pressure keeping to reduce the output torque of the motor to achieve a reduction in motor power output, ultimately achieving energy savings.
In short, the advantages of this program: there are certain energy-saving effects, disadvantages: the PQ controller is required, and the motor is still in high-speed operation, so energy saving is not optimal.
4.2 Inverter drive
Driven in the above way, since the motor is still running at high speed, the energy saving in this way is not very good, so the industry has also studied to drive with a frequency converter, which is usually driven by PQ controller + inverter + inverter motor + metering pump Part of the composition, as shown in Figure 4:
Figure 4 Inverter drive system architecture
The biggest advantage of using the inverter to drive the motor is that when the system is under pressure, the injection molding machine controller will give a proportional flow signal to the inverter to tell the inverter that it is going to perform low speed operation. At this time, the inverter drives the motor at a low level. The speed operation makes the energy saving effect, but since the frequency converter has acceleration and deceleration time when starting and stopping, the operation cycle of the injection molding machine is slower than that without the frequency converter, so the holding time is short and the working time is short. The product is not suitable for inverters. Only injection molding machines with a large holding time and long tonnage can be considered to be driven by inverters. It is the easiest to use energy-saving retrofits with inverters, and basically does not change the mechanical structure of the injection molding machine itself. It is only necessary to add a frequency converter to the three-phase input of the electrode. At present, the special inverter of Delta FG injection molding machine has a successful case in the injection molding machine industry.
In short: the advantage of this scheme is that the transformation is simple and has better energy-saving effect; the disadvantage is that when the production capacity is rushed, the utility power needs to be cut back, and the PQ controller is still needed.
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