Energy-Saving Technical Transformation Solution For Injection Molding Machine Servo System

Energy-Saving Technical Transformation Solution For Injection Molding Machine Servo System

Abstract:

The injection molding industry is facing rapid development, how to effectively save energy and reduce consumption has become an urgent problem to be solved, and the electric energy waste of the quantitative pump injection molding machine, which accounts for the vast majority, is severe.
At present, the servo injection molding machine energy-saving technical transformation solution control system developed on the market according to the similar principle of the quantitative pump and the variable pump hydraulic system can be widely used in large, medium, and small sizes, various brands, and injection molding with hydraulically driven quantitative pumps or variable pumps. Machine.
Jiangsu Chunlan Machinery Manufacturing Co., Ltd. and Taizhou Shenshi Plastic Co., Ltd. selected one injection molding machine as the target equipment for transformation, and the electricity saving rate reached 66%.
It is specially designed according to the pressure and speed parameters the injection molding machine needs to control during the specific operation process. After the program is optimized, the pressure rises quickly, the control is precise, and the repeatable positioning accuracy is high.
Compared with traditional hydraulic control, it has the characteristics of energy saving, high efficiency, and low scrap rate.

The injection molding machine is the leading equipment in the plastics processing industry and is a famous “electric tiger.” Generally, the electricity consumption of injection molding machines accounts for 30-70% of the total electricity consumption of plastic enterprises (in some professional plastic enterprises, the proportion is even more than 70%).).
A Servo system is an automatic control system composed of the object’s displacement, angle, and speed and can track the arbitrary changes of the target. It is usually composed of servo drives and servo motors.
The Servo system is an extension product based on frequency conversion technology. In addition to speed and torque control, it can perform precise, fast, and stable position control.

1.  Servo motor market

It is understood that the energy-saving transformation of injection molding machines has the advantages of a high-power saving rate, good energy-saving effect, and fast investment recovery.
For example, the energy consumption of the servo motor of the injection molding machine accounts for about 70% to 80% of the total power consumption of the whole device. The original “ordinary motor + quantitative pump system” is replaced by “servo motor + gear pump (screw pump),” and the energy saving rate is Up to 40% to 85%; the cost can be recovered in 10 to 18 months, and the energy saving effect is ideal.

2. Composition of the servo control system
The servo system consists of a servo controller, servo motor, oil pump, encoder, pressure sensor, etc.

3. The development of injection molding machine transformation

While the traditional injection molding machine uses the quantitative pump drive method to bring about the massive waste of electric energy, the energy-saving transformation of the injection molding machine has also gone through three stages: (1) variable pump transformation; (2) inverter transformation; (3) servo transformation.

4. Principles of energy saving of servo system
The most significant advantage of using a servo driver is energy saving because the injection molding machine controller will give pressure and flow signals to the driver simultaneously when the system pressure is maintained. The improvement is because the servo driver drives the servo motor to run correspondingly quickly, and the servo motor can generally run to more than 2000 rpm.
Therefore, the injection molding machine implements the speed mode in other working states except for the pressure-holding state. The motor speed is very fast, which can speed up the operation cycle of the injection molding machine and improve the production capacity. Again, the pressure is stable when the system maintains pressure. The performance is very good because the drive system is an infinite loop control system. The pressure of the injection molding machine system is transmitted to the driver through the pressure sensor, and the response is quickly adjusted by the PID of the driver, thus ensuring the stability of the system pressure.

5. Overall technology of servo motor

5.1 Technical principle of hydraulic servo system

Hydraulic transmission: It uses hydraulic oil as the working medium, converts the mechanical energy of the prime mover into the pressure energy of the hydraulic oil through the power element (oil pump), then passes through the control element, and then converts the pressure energy with the help of the actuator (cylinder or oil motor). For mechanical energy, the load is driven to achieve linear or rotary motion, and the force and speed of the actuator are adjusted by remote control of the control element and adjustment of the flow.
When the outside world disturbs the above system, the actuator’s output generally deviates from the original setting value, resulting in a certain error.
Hydraulic control: Like hydraulic transmission, the system also includes power components, control components, and actuators, transmitting power through oil.
The difference is that the hydraulic control has a feedback device. The function of the feedback device is that the output of the actuator (displacement, speed, force, and other mechanical quantities) is fed back, and the input (variable or constant) is carried out. By comparison, the deviation after comparison is used to control the system so that the output of the actuator changes or remains constant with the change of the input quantity.
A hydraulic transmission system constitutes a closed-loop circuit, also called a hydraulic servo system or hydraulic servo system.

5.2 Fundamentals of the project

The traditional hydraulic power system drives the quantitative oil pump through the ordinary three-phase AC motor, runs at the rated speed, and adjusts the pressure of the system by controlling the opening size of the flow control valve and the pressure control valve to meet the pressure flow required by the supporting equipment (displacement).
Because in this system, the purpose of adjusting the pressure and displacement of the system is achieved by adjusting the pressure and flow of the valve.
Therefore, to ensure the system’s maximum flow and pressure, the system’s motor must always run at the rated speed.
Since the motor’s power consumption is only related to the system pressure, when the supporting equipment needs to run at high pressure and low speed, since the motor always runs at the rated speed, most of the power consumed by the motor is inactive power. Most of this inactive power is converted into heat energy through hydraulic oil. The pressure control valve flows back to the tank, causing the system to heat up. In many cases, especially when high pressure and large speed changes, a cooling system must be installed, resulting in increased energy consumption.
The servo system uses a specific servo motor and driver to drive the special gear oil pump directly and dynamically adjusts the speed and torque of the servo motor to provide the pressure and flow (displacement) required by the supporting equipment.
From this, it is deduced that as long as the speed and torque of the servo motor are dynamically adjusted, the pressure and flow (displacement) required by the supporting equipment can be provided.
This is the basic principle.

6. Application of Servo Motor

Taizhou Power Supply Company researched Jiangsu Chunlan Machinery Manufacturing Co., Ltd. and Taizhou Shenshi Plastic Co., Ltd. and communicated with enterprises. Jiangsu Electric Power Energy Saving Service Co., Ltd. conducted an energy-saving evaluation and analysis on the injection molding machines of the above two companies and selected one injection molding machine, respectively. As the target equipment for transformation, the servo motor (running 24 hours) is used to carry out pilot energy-saving transformation with the scheme of replacing the original motor with a servo motor.
The specific test method is: to select a modified injection molding machine and an unmodified injection molding machine to carry out the comparative monitoring of the same standard working day and the same work material production, and the monitoring equipment adopts the sy-dcs-ii mobile power monitor. , the electric energy data is saved every minute, and by processing the data obtained by monitoring, the daily electricity consumption of a modified injection molding machine and an unmodified injection molding machine is obtained, and the power saving rate is calculated.
From April 24th to 25th, 2012, Jiangsu Suyuan High-tech Co., Ltd. calculated the electricity saving rate by collecting the daily electricity consumption of a modified injection molding machine and an unmodified injection molding machine for 24 hours:
(Power consumption per unit of product before transformation – power consumption per unit product after transformation)/Power consumption per unit product before transformation = (1326.2kwh-447.2kwh)/1326.2kwh=66.3%.
It is estimated that the annual electricity saving is 111,000 kw, and the annual electricity saving income = the project’s electricity saving × p (where p is the electricity price per unit of electricity consumption, calculated at 0.68 yuan/kWh) = 11.1 × 0.68 = 75,400 yuan.
The theoretical service life of the device is 10 years.
The energy saving of the transformation has been confirmed by both parties and certified by the third party, Taizhou City Economic and Information Commission Energy Saving Office.
This pilot transformation of the injection molding machine servo motor energy saving is the first successful transformation case in the Jiangsu Electric Power Company system.
It has now negotiated with Jiangsu Chunlan Machinery Manufacturing Co., Ltd. to carry out the servo motor energy-saving transformation of the remaining 12 injection molding machines.

Conclusion:

Converting an ordinary injection molding machine into a servo injection molding machine requires a certain degree of investment. Still, this new type of injection molding machine has great advantages in saving resources, reducing costs, improving performance, and improving working conditions; as servo technology has matured, servo with the price reduction of the system and everyone’s in-depth understanding of the servo system, the development of servo injection molding machines is imperative!

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