In the production of PVC pipe manufacturing equipment, PVC is a thermally sensitive material. Even with the addition of heat stabilizers, its decomposition temperature can be raised, and the stabilization time can be extended to avoid degradation. Therefore, it is crucial to strictly control the molding temperature of PVC. The extrusion temperature must be determined based on several factors such as formulation, extruder characteristics, die structure, screw speed, position of temperature measurement points, instrument error, and depth of measurement. Here are the key details:
(1) Temperature Control: Temperature plays a vital role in determining the quality of plasticization and the final product. If the temperature is too low, the plasticization process will be inadequate, leading to poor surface finish and mechanical properties of the pipe. After the split, visible weld lines may appear or the weld strength may be weak. On the other hand, if the temperature is too high, due to PVC's poor thermal stability, decomposition can occur, resulting in discoloration, scorching, and even operational failure.
(2) Screw Cooling: Since RPVC melt has high viscosity and poor fluidity, it is essential to cool the screw to prevent overheating caused by friction. Overheating can lead to material decomposition or roughening of the pipe's inner wall. Proper cooling ensures better plasticization and a smoother inner surface, improving the overall quality of the pipe. The screw temperature is typically maintained between 80°C and 100°C. If the temperature is too low, back pressure increases, output decreases, and in severe cases, the material may not be extruded, potentially damaging the screw bearings. To maintain this, the cooling water outlet temperature should not be lower than 70°C to 80°C. This is usually achieved by using a copper tube inside the screw for water cooling.
(3) Sizing Pressure and Vacuum: Once the tube blank exits the die, it is still at a high temperature. To achieve a smooth surface, correct dimensions, and proper geometry, the tube must be sized and cooled immediately after exiting the die.
(4) Screw Speed: The screw speed directly affects the quality and output of the pipe. Adjustments are made based on the extruder and pipe specifications. Generally, larger machines produce smaller pipes at slower speeds, while smaller machines produce larger pipes at higher speeds. For example, a single-screw extruder with a diameter of 45mm typically operates at 20–40 rpm, while a 90mm single-screw extruder runs at 10–20 rpm. Twin-screw extruders usually operate at 15–30 rpm. Although increasing the screw speed can boost output, excessive speed without adjusting the material or screw design can lead to poor plasticization, rough walls, and reduced pipe strength.
(5) Traction Rate: The traction rate directly impacts the production process and the wall thickness of the pipe. An unstable traction rate can cause fluctuations in the pipe’s diameter. The traction speed should be closely matched to the extrusion speed. In normal operation, the traction rate should be slightly faster than the extrusion line speed, typically by 1% to 10%. A slower traction rate results in a thicker wall, while a faster rate leads to a thinner wall. This can also increase longitudinal shrinkage and internal stress, affecting the pipe's size, pass rate, and performance. To adjust the traction rate during production, one simple method is to place the extruded pipe on the traction track without clamping it, then observe the difference between the track speed and the pipe's speed. If the traction rate is too slow, it should be increased until the wall thickness meets the required standards.
Qingdao Huarunde Plastic Machinery Co., Ltd.
Email: @qq.com
Pine Commercial Plywood
Pine Commercial Plywood,Linyi Pine Lvl Plywood,Radiata Pine Commercial Plywood,Pine Plywood Decoration Plywood
Shandong Yami Import and Export Co., Ltd. , https://www.yamiwood.com