Hydraulic equipment and discharge volume and pressure adjustment The centrifugal pump produces an average hydraulic pressure of up to 140 bar, which is particularly suitable for injection molding. In all other phases of the cycle, the requirements are significantly lower, except in the specific case where fast plasticizing is required (eg PET injection-blow one-shot injection molding machines).
In order to reduce energy consumption, variable displacement pumps and pressure accumulators can be used during the discharge peak period. The fixed displacement pump moves the same amount of oil each time it rotates. Therefore, the pump selection depends on the amount of oil that needs to be moved in a specific time. Three-phase motor speed is generally 1440 rpm, usually requires the installation of dual pumps. Only in the plasticization process (up to 100% power) can the utilization of the oil pump be maximized. During the pause, the machine does not need energy, and even if it is needed, it is power loss.
All injection molding machines use proportional servo valves of different quality levels. Two or more proportional valves are installed on the injection press to precisely control the following aspects:
Open mold speed (two-stage), closed mold speed (two-stage), closed-mold safety, injection (3-10 grades), feeding (3-5 grades), suction and top rod (two-stage).
Molding pressure, mold closing pressure, mold safety, mechanical fixture (barrel or toggle), injection (filling stage once, 3-10 times in subsequent stages), suction and back pressure (grades 3 - 5)
Screw rotation speed (3 - 5 levels).
The proximity of the carriage (the speed at which the mechanical nozzle closes on the mould to fix the injection pad on the mould half) and the movement speed of the jack (top table speed) can also be adjusted. The auxiliary motor sends the amplified signal (output signal) to the valve through a weak input signal, causing the servo valve to perform the adjustment function. In the servo valve, the weak input electrical signal is converted into a hydraulic output signal, which is modified in the form of a pressure drop according to the required discharge requirements. The valve must make rapid, repeatable, and low hysteresis output response to tension or general instructions. In fact, the purpose of the current study is to improve the frequency response, enabling dialogues between power equipment (hydraulic edges) running at a frequency of several kilohertz (kHz) and electronic devices. Since the effective discharge depends on the degree of polymerization (DP) on the valve, the oil temperature in the hydraulic line must be maintained in the 45-55°C range (usually a closed-loop regulation system), depending on the viscosity of the fluid and the transition ports. It depends on the geometry. There is no proper adjustment system in the valve, the temperature rise will cause the viscosity of the solution to drop; if it is equipped with the equalization open threshold value, the discharge quantity can be increased. Increasing the output of the drive system means that the injection speed will increase. Precise control of high-tech servo transmission valves virtually eliminates hysteresis and enhances the repeatability of all functions.
