one. Injection Molding Machine Overview For half a century, plastic has become one of the major materials for industry, agriculture and civilian use. Injection molding machine is a special plastic molding machine. It uses plastic thermoplastic, after appropriate heating and melting, high pressure quickly into the mold cavity, after a certain period of pressure, cooling, and become a variety of profiles and plastic products. The promotion and application of frequency converters on injection molding machines can save energy, improve productivity and product quality, reduce oil pollution and noise pollution, and extend machine life. Therefore, it will be gradually used.
Injection molding machine is the main equipment for molding various kinds of plastics (such as polyethylene, polypropylene). Its working principle is: through multi-stage heating of plastic particles in a twin-screw injection molding machine, the material will be pressurized after melting and stirring. Into the mold cavity, complete the molding process.
two. The status quo of the production process of the quantitative pump injection molding machine The injection molding machine and the extruder are the main production equipment of the plastics industry, and also the main power-consuming equipment. It is known as “electric tiger†and its power consumption accounts for 80 of the production power of the enterprise. %about. Injection molding machine consumes a lot of power, on the one hand, it causes a huge waste of electrical energy in the whole society, on the other hand, it causes the production cost of the enterprise to remain high, and the product lacks competitive advantage, which seriously affects the economic benefits of the enterprise.
The process of injection molding machine is generally divided into several stages such as clamping, injection, melting, pressure keeping, cooling, and mold opening. Each stage needs different working pressure and flow. For an oil pump motor, the injection molding process is in a changing load state. In the hydraulic system of the dosing pump, the oil pump motor always provides a constant flow at a constant speed, and the excess hydraulic oil flows back through the relief valve. This process is called high-pressure throttling. According to statistics, the energy loss caused by high-pressure throttling is as high as 25-50%. At the same time, due to the long-term cyclic flow of hydraulic pressure, and the violent friction of hydraulic parts and mechanical parts, the oil temperature is too high, the noise is too loud, and the mechanical life is shortened.
In the complete process of the injection molding machine process, various types of injection molding machines, its process is the same, roughly five process processes (see Figure 1).
Figure 1 injection molding machine production process flow chart from Figure 1 that the injection molding machine in the different processes and pressure in the process and time is so distributed:
(1) Mold feeding process: low pressure and short time.
(2) Molding process: The two molds are connected until they are completely closed. The pressure is slightly higher and the time is not long.
(3) Pressure maintaining process: Feed the mold cavity until it is formed and cured. High pressure, long time, about 40-60% of a product's manufacturing time.
(4) Demoulding process: forming, opening the mold, demoulding, and removing the workpiece. The pressure is slightly higher and the time is not long.
(5) The process of removing the mold: The workpiece is taken out, the mold is back in place, and after the auxiliary work is performed, it is to be processed again. The pressure is low and the time is short.
For the same injection molding machine, the pressure (P) and time (t) are different for different plastic parts. Due to the complexity of the workpiece molds, the use of different plastics, the total amount of a workpiece, the presence of inserts and so on. The specific parameter settings are generally determined by engineers and technicians after testing.
three. Energy-saving principle and feasibility analysis of injection molding machine 1. Theoretical output of pump: pt=p*Qt=p*v*n (1)
Theoretical torque of oil pump: Tt=1/2π×p×V (2)
P is the pressure, Qt is the flow rate, V is the displacement of the oil pump, and n is the rotation speed of the oil pump. Substituting (2) into the formula (1) yields:
Pt=2π×Tt×n (3)
If the energy loss from the mechanical energy to the hydraulic energy conversion process is neglected, it can be approximated that the output power of the oil pump is equal to the product of the motor output torque and the motor rotation speed. Therefore, it can be seen that when the system requires low flow, the power required by the system is actually very low. However, the actual situation is that since the motor is always running at the power frequency of 50 Hz, it cannot reduce the speed according to the actual demand, thereby reducing the flow. Therefore, excess hydraulic oil can only flow back to the tank through the proportional flow valve, causing wasted energy.
2. The frequency conversion and energy saving operation of the oil pump can be seen from the process of the P=f(t) process of the injection molding machine in Fig. 1. In different time periods, the main oil pump pressure is changed, and the fluctuation is large, which has energy saving. The possibilities are great. According to statistics, the energy-saving rate of injection molding machines can generally reach 25%-50%. It is well known that when the injection molding machine is not using a frequency converter, the main pump motor always operates at a constant speed, which is an extremely uneconomical operation mode.
The energy-saving controller of the injection molding machine will control the current signal of the proportional flow valve (0-1A) according to the proportion of the flow rate set in each production stage to obtain a proportional 0-1 meter to open the proportional opening of the solenoid valve. To provide the pressure needed for the system. Excess flow overflows through the overflow valve. Connect the proportional flow signal to the power-saving controller of the injection molding machine as the drive command to control the rotation speed of the hydraulic drive motor. The oil pump only replenish the consumed part of the oil circuit. The oil pump motor runs the corresponding speed according to the proportional command and outputs the corresponding flow. To provide the pressure needed for the system. That is, how much you need to provide, at the source so that it does not produce waste. Therefore, the frequency conversion energy-saving system has obvious power-saving effect in the entire production process of the injection molding machine, so that it can save energy and save energy and bring considerable economic benefits to the user.
4. Current status of Hefei Xingtong Rubber & Plastic Co., Ltd. Through the understanding and research of Hefei Xingtong Rubber & Plastic Co., Ltd., your company has 2800T, 2000T, 1450T, 1200T, 800T, 500T, 360T, 250T, 80T computer injection molding machine series. The total motor power is about 1000 kilowatts. According to the energy saving rate of about 30% of the theoretical value, if all machines are operated at full load, the overall energy saving space is about 200 to 300 kWh per hour, and the economic benefits are considerable.
In order to verify the energy-saving space of the injection molding machine, it is recommended that your company can use an 80T injection molding machine to calculate the average power consumption per hour at full load in the power frequency state through the method of measuring the power meter, and then convert this device to frequency conversion. Energy-saving transformation, and then measure the power consumption under the frequency conversion energy-saving state, through the comparison of data, your company can see the transformation of the energy-saving space, the effect is significant and then gradually implement the energy-saving transformation of other equipment.