In the traditional die-casting machine, pressure is generated by an asynchronous motor – vane pump unit with two stages: one stage low pressure-high flow and one stage high pressure-low flow.

Up to 40 bar, both stages go in-line: when this threshold is exceeded, the high flow/low pressure is diverted directly and regularly to discharge (=Drain). Pressure control is achieved by means of shut-off valves which discharge the hydraulic fluid once the set pressure has been reached. When the machine is switched on but at standstill, i.e. during workpiece cooling time and mould lubrication cycles, but also during tooling phases, both flows are generated, not utilised and sent to drain. As a result, the motor draws current from the line continuously throughout the entire moulding cycle.

The solution of applying an inverter to the motor power supply, which reduces its speed when no line pressure is needed, results in modest energy savings, in the region of 25% on average. However, without any positive effect on the general operation of the machine; the hydraulic circuit remains the standard one. The Green Line machine is equipped with a driver-controlled, variable-speed servomotor connected to an internal gear pump with constant displacement. The closed-loop controlled system produces the oil pressure only at the times and in the quantity actually needed and nothing is wasted. The control driver allows the speed and pressure to be adjusted according to the instantaneous requirements of the current production process, with very high energy savings.