Working principle of injection molding machine:

The electric motor drives the oil pump to suck oil from the oil tank and pressurize the output. The pressure, flow rate, and direction of the oil are controlled by various control valves to ensure that the working mechanism moves in the required direction with a certain force (or torque) and speed. Thus achieving the various processes of injection molding.

Energy consumption location:

The oil pump speed of the quantitative pump injection molding machine cannot be adjusted, and excess oil is discharged into the oil tank through overflow.

Traditional quantitative pump injection molding machines usually use valves to adjust the load flow rate and pressure when needed. At this time, the input power does not change much, and a large amount of energy is lost in the form of pressure difference on the valve, resulting in overflow.

The SAJ frequency converter can automatically adjust the speed of the oil pump and the fuel supply of the oil pump according to the current working status of the injection molding machine, such as mold locking, injection molding, glue melting, mold opening, top needle and other stages, as well as the pressure and speed setting requirements, so that the actual fuel supply of the oil pump can be consistent with the actual load flow of the injection molding machine at any working stage. This minimizes the energy consumption of the motor throughout the entire load range, completely eliminates overflow phenomena, and ensures smooth and accurate operation of the motor.

According to the process of injection molding machine, draw the relationship between system oil pressure P and time t as shown in the following figure:

As shown in the figure, the oil pressure required for the mold closing and demolding, as well as the mold opening system, is relatively low and the time is short; The oil pressure required for injection, pressure maintenance, and cooling systems is relatively high and takes a long time, usually 40% to 60% of one working cycle. The length of time is related to the workpiece being processed; The interval period is shorter, which is also related to the processing of the workpiece, and sometimes the interval period can be omitted. The above figure is only a simple approximation. In fact, if the injected screw is driven by an oil motor, the system oil pressure during injection will be higher. The weight of workpieces processed by injection molding machines ranges from tens of grams to tens of thousands of grams, with the largest injection molding machine weighing up to 92000 grams. Therefore, injection molding machines can be classified into medium, small, and large types, with different cycle times for processing small workpieces weighing tens of grams and large workpieces weighing several kilograms; It means that for the same injection molding machine, the required pressure and time in each stage of the process flow also vary depending on the raw materials used to process the workpiece. The setting of these process parameters is determined by on-site technicians based on empirical data and experimental results.

From the above figure, it can be seen that in a cycle workflow, changes in load cause significant changes in system pressure, but the oil pump still operates at 50Hz with a constant oil supply. Excess hydraulic oil flows back to the oil tank through the relief valve, doing useless work and wasting electrical energy. Perform variable frequency speed regulation on the oil pump to transform the quantitative pump into a variable displacement pump. When the required pressure of the system is high, the oil pump motor operates at 50Hz, and when the required pressure is low, the frequency converter operates at a reduced frequency. The shaft power output by the motor is proportional to the product of the outlet pressure and flow rate of the oil pump. When the motor speed of the oil pump decreases, the output shaft power decreases, which can achieve effective energy saving. Generally, the energy saving rate is between 20% and 50%.

By using the SAJ-8000Y frequency converter, the injection molding machine oil pump motor can achieve soft start, improve the power factor COS ￠ of the motor, and dynamically adjust the output power of the injection molding machine motor to achieve energy-saving goals.

1. Before renovation

The power consumption of injection molding machines is closely related to various working conditions such as motor performance, molds, and raw materials. Based on our renovation experience, the load rate is around 60%, which means that the actual power consumption of the commercial power operation is 55% of the power of the oil pump motor. Before the renovation, the hourly power consumption of the oil pump motor was:

45KW X 55%=24.75 degrees per hour

The electricity bill is priced at 0.85 yuan/kWh, and the usage time is based on 30 days per month and 20 hours per day. Therefore, the monthly electricity bill for the injection molding machine oil pump motor is approximately:

24.75 degrees/hour X 30 days X 20 hours X ¥ 0.85 yuan/degree=¥ 12622.5 yuan/month

2. After renovation

The energy-saving rate of the modified injection molding machine is calculated at an average of 30%, and the monthly recycling benefit is ¥ 12622.5 X 30%=¥ 3786/month. The annual recycling benefit is ¥ 3786/month X December=¥ 45432

The above is only an example, and the specific data is subject to the actual test data of your company's test machine.

In general, all investments of your company can be recovered through electricity cost savings within 6-10 months.