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Temperature Control Methods for Extruders at Home and Abroad

Time：

2021-08-18

The temperature‑control process of an extruder begins by preheating each zone of the barrel to the processing temperature required for the specific compound before normal extrusion commences. Throughout the extrusion cycle, cold material entering the die from the feed port removes heat from the barrel, while shear between the screw and the polymer generates substantial mechanical friction, converting kinetic energy into thermal energy. Consequently, the barrel temperature continuously oscillates between heating and cooling. To maintain a relatively constant temperature, the control system employs auxiliary heating and cooling circuits to mitigate these fluctuations.

Temperature control technology encompasses two main aspects: temperature measurement and temperature regulation. Temperature measurement primarily comprises two methods: contact-based measurement and non-contact measurement. Based on the control objective, temperature regulation can be categorized into two types: dynamic temperature tracking and constant‑value temperature control. Dynamic temperature tracking aims to make the controlled object’s temperature follow a pre‑defined profile. Constant‑value temperature control, on the other hand, seeks to maintain the controlled object’s temperature at a specified setpoint, with the requirement that the temperature deviation—i.e., the steady‑state error—remains within an allowable tolerance. Temperature control in extruders is a typical example of constant‑value temperature regulation.

The temperature‑control process of an extruder begins by preheating each zone of the barrel to the processing temperature required for the specific compound before normal extrusion commences. During the extrusion cycle, cold material entering the die from the feed port removes heat from the barrel, while shear between the screw and the polymer generates substantial mechanical friction, converting kinetic energy into heat. Consequently, the barrel temperature continuously oscillates between heating and cooling. To maintain a relatively stable temperature, the control system employs auxiliary heating and cooling mechanisms to mitigate these fluctuations.

During temperature control in an extruder, the efficiency of external heat exchange varies across different production environments, introducing unpredictability. Consequently, achieving high‑precision temperature control in industrial settings is challenging, and tailored control strategies are often required to attain optimal performance in diverse application contexts.

In China, extruder temperature control systems typically employ a control scheme consisting of a temperature controller, contactors, and electric heaters. Early extruder temperature control systems utilized on–off temperature controllers, which simply switched the relay on and off. The device’s switch is used to turn the electric heating coil on and off, thereby controlling the screw temperature. However, this approach yields suboptimal temperature control: it exhibits significant overshoot, long response times, and a substantial steady-state error—up to +10°C.

Subsequently, three‑position control instruments gradually replaced two‑position controllers, improving temperature‑control accuracy to ±5°C. With advances in instrumentation, temperature‑control systems employing time‑proportional controllers emerged; by applying proportional regulation as the temperature approached the setpoint, overshoot and undershoot were mitigated to a certain extent, enabling temperature‑control accuracy of ±3°C.

However, in recent years, the rapid advancement of computer technology has enabled several control strategies based on modern control theory and artificial intelligence to be implemented in practical applications. Among these, microcomputer‑based control approaches are typically categorized into three types: classical control schemes, designs grounded in modern control theory, and intelligent control schemes.