In the PVC extrusion process, equipment factors have a significant impact on the burnt problem. As a professional extruder manufacturer, Yongte Plastic Machinery will analyze the relationship between equipment factors and PVC burnt problems for you from the aspects of key components of the extruder and temperature control.
Extruder screw and PVC burnt problem
The screw structure affects plasticization and paste risks: The screw is the core component of the extruder, and its structure plays a key role in the plasticization effect of the material. The gradual screw is suitable for PVC processing. The depth of the screw groove changes gradually. The material is slowly compressed and plasticized in the screw to reduce the risk of overheating and decomposition. If the screw structure is not designed reasonably, such as the screw groove is too shallow, the material stays in the screw for a short time, and the plasticization is not sufficient, it is easy to cause local pressure and temperature rise, and increase the possibility of paste; the screw groove is too deep, the material is not subject to sufficient shear force, and the plasticization is poor, which may also cause paste problems.
Screw wear and paste association: After long-term use, the screw will wear due to material friction. After the screw is worn, the thread gap becomes larger, the material is not transported stably in the screw, and local material accumulation is prone to occur. The accumulated materials are affected by the shear force and friction of the screw, generating too much heat. When the heat cannot be dissipated in time and the temperature exceeds the decomposition temperature of PVC, the paste phenomenon will occur. In addition, the plasticizing ability of the worn screw on the material decreases, which indirectly increases the risk of paste.
Extruder barrel and PVC burnt problems
The condition of the inner wall of the barrel affects the material flow and paste: The smoothness and integrity of the inner wall of the barrel are crucial to the flow of materials. If the inner wall of the barrel has a rough surface or pits due to wear and corrosion, the material is prone to stagnation when flowing in the barrel. The retained material stays at high temperature for a long time and gradually decomposes, which in turn causes paste. Moreover, the rough inner wall increases the friction between the material and the barrel, causing the local temperature of the material to rise, further increasing the risk of paste.
The impact of the barrel heating and cooling system on the paste: The heating and cooling systems of the barrel need to work together to accurately control the material temperature. Failure of the heating system, such as damage to the heating element or failure of the temperature control instrument, may cause the local temperature of the barrel to be too high, causing the PVC material to quickly decompose into paste. If the cooling system cannot take away the excess heat in time, the material will continue to be heated at high temperature, which will also cause paste. For example, if the cooling water pipe is blocked, the cooling medium cannot circulate normally, and the material temperature is out of control, which will eventually lead to paste problems.
Temperature control equipment and PVC burnt problems
Accuracy of temperature monitoring equipment such as thermocouples: Temperature monitoring equipment such as thermocouples is used to monitor the temperature of various parts of the extruder in real time. If these devices are inaccurate, there is a deviation between the displayed temperature and the actual temperature. The operator adjusts the process parameters based on the wrong temperature data, which may cause the actual temperature of the material to be too high without noticing. For example, if the thermocouple measurement value is lower than the actual temperature, the operator does not reduce the heating temperature accordingly, and the material continues to be heated at high temperature, it is very likely to cause paste.
Stability of temperature control system and paste: Advanced temperature control systems, such as PID control algorithms, can effectively stabilize the temperature. However, if the temperature control system fails, such as control algorithm errors, signal transmission interference, etc., it will cause excessive temperature fluctuations. When the temperature fluctuates greatly, the material temperature may be too high or too low during the extrusion process. The unstable temperature environment may cause the PVC material to overheat and decompose locally, leading to paste problems.
