I. Introduction With the rapid development of the variety and quantity of plastic products, people are increasingly demanding the geometric accuracy and intrinsic performance uniformity of extruded products. The main way to improve the geometric accuracy of extruded products is to overcome various fluctuations in the extrusion process through machinery, processes and advanced control measures. To achieve precise extrusion molding, on the one hand, it can meet the requirements of some products that have stringent requirements on the assembly size and shape as well as the molding process conditions, and it is also the basis for high-speed extrusion molding. II: System Principle and Design The control system of the plastic extruder includes a heating system, a cooling system, and a process parameter measurement system, which is mainly composed of a touch screen, a PLC, a frequency converter, and a sensor. Its main functions are: controlling and adjusting the drive motor of main and auxiliary engines, outputting the speed and power that meet the technological requirements, and enabling the main and auxiliary machines to work in coordination; detecting and regulating the temperature, pressure, and flow rate of the plastic in the extruder; Control or automatic control of the entire unit. The system hardware structure is shown in Figure 1, as follows: The temperature and pressure of the system are all controlled by PID closed loop. When PID is adjusted, the proportional adjustment reflects the deviation of the system. As long as there is a deviation, the proportional mediation will have a control effect to reduce the deviation. Derivative adjustment produces a control action based on the trend of deviation, which can improve the dynamic response of the system. Integral adjustment generates the control action according to the variation of the deviation integral, and has a lag effect on the control of the system, which can eliminate the static error. Increasing the integral time constant can improve the static accuracy, but the integral action is too strong, especially if the system deviation is large, the system will have a large overshoot and even cause oscillation. Three: weinview human-computer screen design The system uses weinview MT8100I man-machine, the man-machine using 400Mhz RISC CPU, high-quality widescreen design, using LED backlight module, built-in power isolation protector, to ensure stability in a complex environment; that plug and plug USB2. 0 The MiniUSB download line of the interface and PC provides high-speed download and data storage, with up to 48MB of event recording and data storage space. The inlet and outlet pressure parameters can be corrected in time according to the process requirements. The screen is as shown in the figure below. Temperature values ​​in various zones can be displayed and adjusted in real time. Since the temperature in each zone and the pressure at the inlet and outlet are adjusted by the PID closed-loop adjustment, you need to freely set the PID parameters, as shown in the figure below. Because under different process conditions, the required pressure is not the same, so the pressure limit also needs to make appropriate adjustments with different process requirements, as shown in the figure below Four: Data Save and Event Login The data is saved using periodic sampling, or triggered sampling data can be saved. The data source is the VW storage area in the PLC, as shown in the following figure. The use of event registration components can promptly view the display of alarm information. The settings are as follows V: Conclusion: This system adopts the application of weinview MT8100I touch screen and PLC control system in the extruder of plastic industry. The system uses PID closed-loop regulation to control the melt pump, screw operation and temperature control of each zone, and achieves precise control effect by adjusting PID parameters. . And can save the pressure change trend throughout the process, and access to historical alarm information. The system achieves more energy-saving, more accurate, more stable, and more convenient operation control requirements, greatly improving the traditional control mode of the past.
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Precision extrusion molding can eliminate the follow-up processing means, to better meet the needs of product applications, while achieving the purpose of reducing material costs and improving product quality. This technology has been widely used in chemical fiber, film, profiles, pipe, sheet, cable, composite extrusion, granulation and other production lines.
1. The power supply enters the 3-phase 4-wire 380V and the melt pump motor 3-phase 0-380V;
2, pump heater single phase 0-220V;
3, inlet and outlet pressure detection signal 0-10V or 4-20mA;
4, the temperature sensor before the pump, pump, pump temperature signal using thermocouple temperature sensor;
5. Single-phase 220V heater before pump and after pump.
6, extruder control signal is 0-10V. Extruder inverter control signal is 0-10V.
7. The motor power line should be connected according to the instructions. Before starting the machine, check the insulation of the motor and correct the positive and negative rotation of the motor.
In Fig. 2, Tm is the set temperature of a certain section of the barrel or head, +ΔT1, +ΔT2, which are the first and second temperature interval values. The temperature measured by the thermocouple is denoted by T. The control strategy is as follows:
(1) When T<Tm-â–³T2, the heater is heated at full power in order to increase the heating rate.
(2) When Tm-△T2<T<Tm-△T1, PID control is used. (3) When Tm-△T1<T<Tm+ΔT1, adaptive PID control is used.
1: touch screen screen design requirements The main screen needs to display the current inlet and outlet pressures, temperature values ​​and currents in each zone, speed, flow, etc., as shown in the figure below.