Five Key Considerations in PVC Pipe Production

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with over 30 years of experience in plastic pipe extrusion equipment, as well as new environmental protection and new materials equipment. Since its establishment, Fangli has developed based on user demands. Through continuous improvement, independent R&D in core technologies, and the digestion and absorption of advanced technologies, we have developed PVC pipe extrusion lines, PP-R pipe extrusion lines, and PE water supply/gas pipe extrusion lines. These products have been recommended by the Chinese Ministry of Construction as replacements for imported products. We have been awarded the title of “First-Class Brand in Zhejiang Province.”

During the production process, it is important to note that PVC is a heat-sensitive material. Even with the addition of heat stabilizers, it is only possible to increase its decomposition temperature and extend the stabilization time without decomposition. This necessitates strict control of the PVC molding temperature. This is particularly critical for RPVC, as its processing temperature is very close to its decomposition temperature, often leading to decomposition due to improper temperature control. Therefore, the extrusion temperature must be determined based on the formulation, extruder characteristics, die structure, screw speed, temperature measurement point location, thermometer accuracy, and depth of the temperature sensor.

I. Temperature control is a critical factor in the extrusion process. Key control parameters include barrel temperature, die head temperature, and die temperature. If the temperature is too low, poor plasticization will occur, resulting in a dull pipe appearance, inferior mechanical properties, and failure to meet product quality requirements. If the temperature is too high, material decomposition and product discoloration may occur.

II. As screw speed increases, the extrusion output also increases, thereby enhancing productivity. However, excessively high screw speeds can lead to inadequate plasticization, causing a rough inner wall and reduced strength. To address this, the head pressure must be adjusted to achieve optimal output and quality. Screw temperature control affects material conveying speed, plasticization, and melt quality. The extrusion process requires cooling water for the screw; reducing the screw temperature helps improve plasticization quality. The recommended temperature range for the screw when cooled with water is approximately 50–70°C.

III. In extrusion operations, adjusting the haul-off speed is crucial. After the material is extruded, melted, and plasticized, it is continuously drawn through the die head into the sizing device, cooling unit, and haul-off equipment. The haul-off speed must be synchronized with the extrusion speed. In general production, the haul-off speed should be 1% to 10% faster than the extrusion speed of the pipe.

IV. Compressed air is used to inflate the pipe, maintaining its roundness. The air pressure must be sufficient: if it is too low, the pipe will not be round; if it is too high, the mandrel may cool excessively, leading to cracking and roughness on the inner wall of the pipe, thereby reducing quality. Additionally, the pressure must remain stable—pressure fluctuations can easily cause cracks in the pipe.

V. Different sizing and cooling methods are employed for extruding different plastic products. Cooling media may include air, water, or other liquids, and their temperatures must be carefully controlled. Temperature regulation directly affects production efficiency and the internal stress of the product.

For further information, please feel free to contact Ningbo Fangli Technology Co., Ltd. We welcome detailed inquiries and will provide professional technical guidance or equipment procurement recommendations.