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The most important production process in the production of plastic profiles is the control of temperature parameters. The temperature control accuracy of the extruder directly determines the product quality and mechanical properties. At the same time, the barrel temperature has a direct and obvious influence on the plasticization and mixing of raw materials. If the temperature is not high enough, the raw materials will not be able to be integrated into plasticization or even extrusion molding is difficult; if the temperature is too high, tiny bubbles will be generated on the surface of the product and even lead to the decomposition and scorching of the raw materials; temperature fluctuations will cause the melt flow rate to fluctuate, resulting in the size of the product. Variety. Therefore, achieving precise temperature control of plastic extruders has become a key factor in determining the quality and output of plastic products.
The main process parameters that affect extrusion molding are temperature, pressure and extrusion rate. Among them, temperature control plays a decisive role and is an important aspect of the extrusion process. If the temperature changes during the extrusion process, the melt pressure of the extruder, the plasticization degree of the raw materials, and the residual stress of the product will all change to a certain extent, which will reduce the stability of the control system and make it difficult to ensure the quality and output of plastic products. In the extrusion temperature setting, it is not only necessary to determine a temperature level, but also to control the temperature in stages according to the specific extrusion process.
The material is plasticized in the barrel, and the heater is further heated and melted to reach a certain viscous flow temperature, otherwise the smooth progress of the extrusion process cannot be guaranteed. Excessive barrel temperature or relatively high temperature for a long time will lead to aggravation of plastic decomposition, resulting in discoloration and foaming of plastic products, which seriously affects product quality.
According to the control requirements of the plastic extruder, the system is divided into the upper computer PC and the lower computer PLC. The lower computer is controlled by PLC and mainly completes the functions of extruder data acquisition, command input and output, and program control.
The temperature control system of the plastic extruder mainly adopts multi-stage and multi-zone continuous control. In order to ensure the accuracy of temperature control, a reliable programmable logic control system is used as the low-level control. Its working process is that the thermocouple sensor detects the current temperature of the barrel and the machine head, converts it into electricity and transmits it to the PLC main controller, and the digital quantity template integrated on the PLC converts the electricity into a digital quantity that can be recognized by the PLC. The PLC processes the temperature digital quantity and the set temperature value through the BP-PID control algorithm, and outputs the obtained control quantity to the PLC digital quantity template. The digital quantity output realizes the signal level of 0 or 1 to control the solid state relay SSR on and off. , to realize the control of heating coil and cooling fan, so as to control the temperature of extruder barrel and head.