The extrusion molding process is the molding processing method in the field of polymer processing with the largest variety, the most change, the high productivity, the adaptability, the wide application, and the largest proportion of the output. This paper is based on the practice and summary of the field technicians. It introduces the heating and cooling dual output function of the Yudian intelligent regulator AI-526 to achieve precise control of the cable extruder.
1. Principle of cable extrusion The plastic insulation and sheath of wire and cable are carried out by continuous extrusion. The extrusion equipment is generally a single-screw extruder. Before extrusion, the plastic should be inspected beforehand for moisture or other debris, and then the plastic is preheated and added to the hopper. During the extrusion process, the plastic loaded into the hopper enters the barrel by gravity or feeding screw, and under the action of the rotating screw, the material is continuously pushed forward, and gradually moves from the preheating section to the homogenization section; meanwhile, plastic It is agitated and squeezed by the screw, and is transformed into a viscous flow state by the external heat of the barrel and the shear friction between the plastic and the device, forming a continuous and uniform flow in the groove. Under the action of the temperature specified by the process, the plastic changes from a solid state to a molten plastic object, and then pushes or stirs the screw to push the completely plasticized plastic into the machine head; the flow to the machine head passes through the core The annular gap between the sleeve and the sleeve is extruded from the sleeve and extruded around the conductor or core to form a continuous dense insulating or sheathing layer which is then cooled and solidified to form a wire and cable product.
Figure 1 Principle process of cable extrusion
2, Yudian AI-526 thermostat specific application 2.1 customer introduction and requirements: Dongguan Weidalong Machinery Co., Ltd. is a well-known old-fashioned enterprise in the wire and cable industry, engaged in professional wire and cable equipment design and manufacturing services for nearly 25 years, is the local line One of the leading companies in cable equipment.
The temperature part of the cable extruder is mainly composed of two parts: the barrel and the head. Each part is composed of 3-7 temperature zones, and the temperature setting value of each temperature zone can be different. This makes the extruder The control is more complicated than the average machine. The difference between the temperature values ​​set by the process requirements, the screw rotation and the heat generated by the material friction will cause interference to the control effect. The direct effect is that the temperature is difficult to control accurately, and the temperature fluctuations of each hot zone are more Large, easy to make temperature overshoot or insufficient temperature, resulting in the final product is not qualified, can not meet the acceptance criteria. The OMRON E5EZ type thermostat used by the customer has a general control effect. The customer wants to further improve the temperature control accuracy and stability of the equipment, and decided to use the Yudian AI-526 thermostat instead.
2.2 Implementation plan and application analysis: According to the customer's requirements, the model of the U-power meter selected for the customer is AI-526EGL1S (V8.28). The instrument model has the following instrument functions: 0.25-level accuracy, dual PID, heating and cooling Output, support for dual communication protocols. Based on the function of this instrument, the PLC is designed for the customer to use the instrument. The specific process is as follows: when the system starts, it enters the heating state, and the temperature sensor (thermocouple or thermal resistance) detects the temperature analog signal and sends it to the instrument. Taking the temperature, the measured measured value is compared with the temperature set value to obtain a deviation. According to the AI ​​artificial intelligence PID adjustment algorithm built in AI-526, the corresponding control amount is obtained to control the solid state relay, thereby adjusting the heating power of the electric heater. . When the temperature reaches the set value, the heating is stopped. At this time, the PLC obtains the signal by means of 485 communication, and uses the signal to control the operating state of the system. Due to the shearing of the screw rotation, the excess heat generated by the friction is generated. In order to avoid the temperature being too high, the plastic is decomposed, scorched or shaped. When the temperature is too high, the cooling function of the AI-526 thermostat is activated, and the cooling end is output. The signal controls the air cooling system to start, causing the temperature to drop to the set value. Through the coordinated control of the heating and cooling dual output, a closed-loop measurement and control of the temperature analog quantity is formed to achieve the desired temperature of the customer. In the whole system, for example, the logic control of the switching quantity, the sequence control, and the collection of other analog signals such as pressure and flow are given to the PLC to complete.
Figure 2 Overall structure of the extruder control system
2.3 After the implementation of the effect scheme, the on-site technicians made the self-tuning before using the meter for the first time, but the actual control effect was overshoot 5 °C, which did not reach the customer's expected temperature, because the temperature of the cable extruder was different. The distance between the zones is very close, which is easy to cause mutual interference, so the parameters of the first self-tuning are not well controlled. By fine-tuning the PID parameters, the P value is increased, and the I value is increased (each adjustment value is 5%-10%). After fine tuning a few times, the temperature is finally stably controlled at a deviation of about 1 °C, and the control effect expected by the customer is smoothly achieved.
The five sets of PID parameters that the customer finally adjusted are as follows (for reference only):
3. Summary Using the AI-526 temperature controller of Yudian to replace the Omron E5EZ thermostat, the accuracy and stability of the temperature control of the cable extruder equipment are further improved, and the whole system is safe, reliable and stable. The actual use of the customer, Yudian's AI-526 temperature controller is easy to operate, full-featured, cost-effective and practical compared to the original instrument is more competitive.
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Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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