Application of micro energy vector frequency converter in energy saving of variable displacement pump injection molding machine

Plastic products processing industry is the light industry in recent years, one of the fastest growing industries, with the increase in the number of plastic enterprises, reduce production costs, improve product competitiveness has become a common concern of many plastic products factory issues. In processing costs, electricity accounts for a large proportion, and a large number of injection molding machine is the most power-consuming equipment, therefore, many plastics companies quantitative pump injection molding machine a lot of energy-saving technological transformation to save energy and improve the business Competitiveness, but for variable-displacement pump injection molding machine many companies, including many professional energy-saving companies are helpless, so for the existence of a large number of variable-volume injection molding machine on the market how to save energy has become the focus of many plastic companies, Shenzhen Micro Technology Co., Ltd. Through the in-depth study of the variable displacement pump plastic injection molding machine, the energy saving retrofit of the variable displacement pump plastic injection machine has been successfully implemented with the latest vector control frequency conversion technology and the energy saving effect of 10-20% has been achieved.

At present, most of the transformation of the injection molding machine belongs to the hydraulic transmission injection molding machine, hydraulic power transmission system driven by the motor to provide the pump, the hydraulic pump for the vane pump, the fuel supply and pump speed is proportional to when the pump motor to 50HZ Constant speed operation, the fuel pump is unchanged, so called quantitative pump. The system diagram is as follows:

The general process of injection molding machine has the following links in the production process: clamping, injection plastic, melt adhesive, packing, cooling, mold. Injection molding machine in different processes require different flow and pressure, to be dependent on the flow valve and pressure valve to adjust the flow and pressure required for different processes, when the required flow is small, the pump fuel supply is greater than the amount of oil required for the implementation of components , Excess hydraulic oil in high pressure state all through the overflow valve backflow, a lot of energy consumed by the temperature rise of oil. This not only exacerbated the wear and tear of various valves, but also caused the oil temperature is too high, but also in order to reduce the oil temperature, often require additional cooling water cycle, resulting in further waste of energy. Therefore, the general quantitative pump injection molding machine transformation with the inverter to control the pump motor speed to regulate the flow, pump the oil within the specified time, just to meet the needs of the various aspects of the movement, the overflow can be controlled at a minimum, thus saving Energy.

At present, variable-displacement pump injection molding machines use variable-displacement pumps as driving components, which are typical volumetric speed-regulating systems, which have obvious energy-saving effects compared with injection-molding machines with variable displacement pumps. In Figure 2, the piston pump system is a load sensing variable proportional, proportional relief valves , proportional control valve, the pressure valve feedback, the feedback flow valves and other components.

A1: Cylinder rodless piston area F: Working load P1: Working pressure Q1: Working flow

â–³ P: Proportional pressure control valve across the pressure difference Pb: Pump pressure Qb: Pump flow n: Motor speed

working principle

(1) When the system is in flow control state, the pump pressure Pb is greater than the working pressure P1 and less than the pressure set by the press, and the proportional relief valve will be reliably closed. When the load changes, there is a corresponding fluctuation in the pressure difference ΔP between Pb and P1, and the working flow Q1 is changed. The above changes through the flow, pressure feedback valve to the variable displacement pump piston. Piston then promote plunger pump swashplate and change the pump displacement, and ultimately stabilize the pump output flow Qb. From this it can be seen that the system realizes the pressure adaptive control, basically without overflow loss, but in order to control the working flow Q1, the throttling valve still has some throttling loss.

(2) When the system is under the pressure control state, the displacement of the variable displacement piston pump is very small. Only a small amount of hydraulic oil flows through the proportional relief valve to ensure a certain system pressure. By changing the proportional relief valve input signal, you can get the corresponding pump output pressure. Compared with the traditional quantitative injection molding machine, the control method to a certain extent, reduce the overflow loss.

3, Variable pump energy-saving injection molding machine principle

We can see from the above description, variable displacement pump injection molding machine compared with the quantitative injection molding machine, reducing a large number of overflow losses, making the pump motor load lighter, the current decreases, in a light load condition. Variable displacement pump injection molding machine is from the hydraulic components point of view, excavation of energy-saving oil on the road space to improve the work of the oil system efficiency. However, due to the limitation of its control method, the system can not completely eliminate the throttling and overflow losses.
1) Variable displacement pump The injection molding machine still has a waste of space. The oil coming out of the oil pump still has to go through the adjustment of the proportional control valve and the proportional relief valve, and there is still some power loss on the valve.

2) The motor speed of the pump still can not be adjusted. Although the load of the pump is much lighter than that of the dosing pump, it is obvious that the energy consumption of the pump is more than that of adjusting the speed of the pump. Especially when the system is under pressure control, the system needs a lot of pressure but the flow rate is very small, but the speed of the pump motor can not be adjusted. If the output flow of the pump, the output pressure, displacement, speed, respectively, expressed as Q, P, Vb, n, the pump output power N is expressed as:

N = Q * P = Vb * n * P

Injection molding machine through the mechanical device to adjust the displacement of the pump Vb, apparently adjustable linear range is limited, can not achieve zero-displacement output. And in any case, the motor is running at full speed, there is a lot of unnecessary energy loss.

3) start the pump motor is still star delta start, lower power factor.

4, micro-energy company system

Micro-energy company is the vector frequency technology used in injection molding machine motor drive, through the speed control and pressure PID closed-loop control functions to complete the precise control of the injection molding machine. Proportional speed control valve will be man-made on the oil flow will be adjusted to the maximum and maintain or remove, while cutting off flow, pressure feedback valve on the variable displacement pump piston control. Variable vector PID control to maintain a constant pressure, pressure automatically to achieve adaptive control, so that the system from the source to eliminate throttling in the oil and overflow energy loss, so that the injection molding machine to obtain the best energy-saving effect. The system is as follows:

working principle:

When the pump flow Qb close to or reach the set value of the press, the oil system into the flow control state, the inverter output frequency proportional to the press set flow. In this process, the pump flow Qb = Vb × n is always consistent with the needs of the work loop, without proportional valve speed control, and no excess flow overflow, can fundamentally eliminate throttling and overflow energy loss.

When the pump is under pressure, as shown below:

Inverter control system is equipped with an intelligent conversion card, the inverter will monitor this pressure change in real time through the pressure sensor and compare with the pressure setting value of the press. When the difference between them is very small, the inverter's intelligent conversion card will promptly switch the inverter to the pressure control state. , Start PID control and keep the system pressure constant by PID function. At this point, the inverter output frequency will be proportional to the pressure difference. Due to the small difference, the inverter output frequency and motor speed will be rapidly reduced, the pump only to maintain a small flow output to make up for a variety of leakage in the oil loss.

Micro-WIN-PSS-IV inverter is open-loop vector mode, starting torque, 0.5HZ can reach 150% of the rated torque; dynamic response, step torque response time is less than 200MS; steady speed accuracy of 0.5% . Through the inverter's closed loop vector speed control function, the frequency conversion injection molding machine's pump speed n can realize the linear adjustment range from 0 to the rated speed, especially in the stand-by and no-action condition of the press (such as cooling stage), motor and pump speed Can be reduced to 0, the basic loss of energy consumption. It is noteworthy that the volumetric efficiency of the pump at low speed will decline, which to a certain extent, will affect the energy-saving effect. In this regard, we will improve this by raising the frequency converter's low-frequency gain. Moreover, the actual production is less than 20% of the flow is very small, so the pump speed is not too low.

5, cost and maintenance analysis

From the company's plastics plant in Dongguan some of the variable pump plastic machine energy-saving examples of the case, the 120 tons of clamping force of horizontal variable-frequency plastic molding machine for energy-saving transformation is still 20% of the saving rate. Thus, variable frequency injection molding machine saving rate is higher than the variable displacement pump injection molding machine, and maintenance analysis is as follows:

6, concluding remarks

Micro Technology Co., Ltd. of Shenzhen City in many years of practical application has accumulated many valuable experience in the development of a variety of energy-saving applications in the injection molding machine inverter program, this time to develop a variable-frequency pump injection molding machine frequency energy-saving inverter, will Will lead the new trend of plastic machine energy-saving transformation.

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