Temperature regulation of PVC conveyor belt vulcanizing machines is a crucial link to ensure vulcanization quality and production efficiency. The following is an in-depth analysis from aspects such as the core principles, key components, control strategies, and common problem handling of temperature regulation:
First, the core principle of temperature regulation
The vulcanization process of PVC conveyor belts is essentially a cross-linking reaction, and the temperature directly affects the activation energy of the molecular chain and the cross-linking density. The vulcanization temperature is usually controlled between 150 and 180℃, and it needs to be adjusted according to the PVC formula (such as the type of plasticizer and the activity of the vulcanizing agent). For instance, when using peroxide vulcanizing agents, the temperature should be precisely controlled at 160-170℃. If it is too high, it will lead to premature decomposition; if it is too low, the crosslinking will be insufficient.
The temperature regulation needs to meet the following requirements:
Heating rate: Rapidly heat up to the target temperature (usually completed within 10-15 minutes), reducing the impact of thermal history on material properties.
Temperature uniformity: The temperature difference on the surface of the vulcanized plate should be controlled within ±3℃ to avoid local over-vulcanization or under-vulcanization.
Stability: The temperature fluctuation during the vulcanization process does not exceed ±1℃, ensuring the consistency of the crosslinking reaction.
Second, key components and temperature control implementation
Heating element
Electric heating tube/heating rod: It directly heats the vulcanizing plate through resistance heating. The power density should be selected according to the size of the vulcanizing machine (usually 1-2W/cm²).
Heat transfer oil/steam circulation system: Suitable for large-scale vulcanizing machines, it is indirectly heated by heat medium, with better temperature uniformity, but the response speed is relatively slow.
Temperature sensor
Thermocouple (Type K/Type J) : Wide measurement range (-200℃ to 1300℃), short response time (<1 second), often used for monitoring the surface temperature of vulcanized plates.
Infrared thermometer: Non-contact measurement, suitable for dynamic monitoring, but the emissivity needs to be calibrated to avoid errors.
Control actuator
Solid state relay (SSR) : It regulates the power of the electric heating tube through a PWM signal to achieve stepless temperature regulation, with a long service life and no noise.
Proportional control valve: Used in steam/heat transfer oil systems, it controls the flow of heat medium by adjusting the valve opening.
Third, the control strategy for temperature regulation
PID control algorithm
Proportion (P) : Quick response to temperature deviation, but prone to overshoot.
Integral (I) : Eliminates steady-state errors, but may cause oscillations.
Differential (D) : Predict the trend of temperature change and suppress overshoot.
Optimization method: The PID parameters are determined through the Ziegler-Nichols method or the self-tuning algorithm. For example, for a certain vulcanizing machine, when P=15%, I=300 seconds, and D=60 seconds, the temperature fluctuation can be controlled within ±0.5℃.
Segmented temperature control strategy
Preheating stage: Heat at full power to 90% of the target temperature (for example, 90% of 150℃ is 135℃), shortening the heating time.
Constant temperature stage: Switch to PID control and maintain the target temperature within ±1℃.
Cooling stage: Natural cooling or forced ventilation is adopted to prevent the material from deforming due to sudden cooling.
Temperature compensation technology
Ambient temperature compensation: When the ambient temperature is below 10℃, the heating power is automatically increased by 5-10%.
Load compensation: Dynamically adjust the target temperature according to the thickness of the vulcanized belt (such as 2mm vs 5mm) to compensate for the difference in heat conduction.
Fourth, Common Problems and Solutions
Temperature overshoot
Reason: The PID parameters are unreasonable or the inertia of the heating element is large.
Solution: Reduce the P value (for example, from 20% to 15%) and increase the D value (for example, from 30 seconds to 60 seconds).
Poor temperature uniformity
Reason: Uneven thickness of the vulcanized plate or unreasonable distribution of heating elements.
Solution: Optimize the structure of the vulcanized plate (such as using honeycomb-shaped flow channels), or control the power of the heating elements in zones.
Sensor failure
Performance: Abnormal temperature display or control failure.
Solution: Regularly calibrate the sensors (once every three months) and adopt a redundant design (switching between primary and backup sensors).
Vulcanization quality defect
Oversulfurization: The surface becomes brittle and the strength decreases.
Sulfur deficiency: Poor adhesion and prone to delamination.
Solution: Determine the optimal vulcanization temperature through DSC (Differential Scanning Calorimetry) and optimize the process parameters.
Fifth, future trends in temperature regulation
Intelligent predictive control: By integrating machine learning algorithms, it predicts the temperature change trend based on historical data and adjusts control parameters in advance.
Wireless sensor network: Multi-node temperature monitoring is achieved by using LoRa or ZigBee technology, reducing wiring costs.
Energy optimization: By dynamically adjusting the heating power through a fuzzy control algorithm, energy consumption is reduced by 10-15%.
Summary
The temperature regulation of the PVC conveyor belt vulcanizing machine needs to comprehensively consider the material properties, equipment structure and control algorithm. By optimizing the PID parameters, adopting the segmented temperature control strategy and temperature compensation technology, the vulcanization quality and production efficiency can be significantly improved. Meanwhile, the heating elements and sensors need to be maintained regularly to prevent temperature control failure due to equipment aging. In the future, intelligence and energy conservation will become the main development directions of temperature regulation technology.