The screw cooling mode of the PVC plastic pipe production line is divided into external circulation and internal circulation. The screw oil cooling belongs to the outer circulation. The oil temperature can ensure the plasticization of the materials in contact with the screw, and the plasticization inside and outside the material is even and sufficient. In order to prevent coking and carbonization of cooling oil and block the oil passage, the oil temperature is generally not higher than 100 °C. For the internal circulation screw system, it belongs to the water cooling system, and the temperature cannot be controlled. The water sealed inside the screw during the screw operation generally keeps boiling state for a long time. The temperature and pressure of the heated steam are high, so the screw coating is easy to change color. After a long time, the sealing effect is poor, the water vapor is leaked under the action of high pressure, and the internal circulation cooling effect is lost or weakened.
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