The main advantages and benefits of retrofitting injection molding machines with frequency converters are energy saving, which can be summarized in the following three aspects. The following details how to achieve these three aspects of energy saving after retrofitting with a frequency converter.
1. Speed regulation and energy saving
According to the process requirements of the injection molding machine, the switching signals of the main pressure valve, low pressure valve, first pressure valve, and second pressure valve are converted and applied to the input terminal of the frequency converter as the frequency command signal of the frequency converter. The frequency converter samples it in real time and processes it through the CPU, so that the output frequency changes linearly with the analog signal of the proportional valve. In processes that require lower pressure and flow, the motor speed is reduced, thereby reducing the output power of the motor. During cooling and semi-finished product loading, the motor can be stopped, so that the energy loss of the motor is minimized throughout the entire load range.
2. Improve power factor and save energy
Reactive power not only increases line losses and equipment heating, but more importantly, it reduces the active power of the power grid due to the decrease in the power factor. From the formula S²=P²+Q², Q=S*SINφ, P=S*COSφ, where: S - apparent power, Q - reactive power, P - active power, COSφ - power factor, it can be seen that the larger the COSφ, the larger the active power P. The COSφ value of a typical quantitative injection molding machine is between 0.6 and 0.8, but after using a variable frequency drive (VFD), due to the compensation effect of the filter capacitor within the VFD, COSφ≈1, thereby reducing reactive power loss and increasing the active power of the power grid.
3 Soft Starter
Because the original motor uses direct start or Y/Δ start, the starting current is equal to (3-7) times the rated current. This causes a severe impact on the electromechanical equipment and the power grid, and also increases the grid capacity requirements. The large current and vibration generated during startup are extremely detrimental to the service life of the equipment. However, by using a frequency converter energy-saving device, the soft-start function of the frequency converter allows the starting current to start from zero, and the maximum value is limited to the acceleration current limit level set by the frequency converter, generally not exceeding 1.7 times the rated current. This reduces the impact on the power grid and the grid capacity requirements, and extends the service life of the equipment and molds.
