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Mechanical Principles of Plastic Pipe Extrusion Line

Time：

2017-05-10

Water or an appropriate liquid is added to the raw powder, and continuous mixing is carried out. The thoroughly mixed material is then extruded through a porous die or metal screen under high extrusion pressure. Typically, the material is loaded into a cylindrical vessel, and a screw mechanism forces it through the die. With the adoption of variable-frequency drive technology, extrusion pressure can be precisely controlled, allowing selection of an optimal linear extrusion speed. Principle of single-screw extruders: A single screw is generally divided into three sections along its effective length, with each section’s length determined by the screw diameter, pitch, and flight depth; these sections are usually allocated in roughly equal thirds. Starting from the first thread immediately after the feed zone is the conveying section, where the material must remain un‑plasticized while being preheated and compacted under pressure.

Water or an appropriate liquid is added to the raw powder, and continuous stirring is carried out. The stirred mixture is then extruded through a porous die or metal mesh under high extrusion pressure.

　　Typically, the material is loaded into a cylindrical container and then extruded using a screw. With the adoption of variable-frequency technology, pressure can be precisely controlled, enabling the selection of an appropriate linear extrusion speed.

　　Principle of a single-screw extruder

　　A single-screw extruder is typically divided into three sections along its effective length. The lengths of these three sections are determined based on the screw diameter, pitch, and flight depth, and are generally allocated in equal thirds.

　　The section of the screw immediately following the feed port is referred to as the conveying zone: here, the material must not undergo plasticization but rather be preheated and compacted under pressure. Early extrusion theory held that the material in this region was a loose mass; however, subsequent research has demonstrated that it actually forms a solid plug—meaning that, once subjected to compressive forces, the material behaves like a solid plug. Consequently, its sole function is to ensure efficient material conveyance.

　　The second section is called the compression zone, where the screw channel volume gradually decreases while the temperature is maintained to achieve the desired degree of material plasticization. Compression occurs here, transitioning from the conveying section; at this point, the compression ratio reaches 3:1—this is the screw’s compression ratio. Some machines may vary, but once the material has been fully plasticized, it moves into the third section.

　　The third section is the metering zone, where the material is maintained at the plasticizing temperature and, like a metering pump, precisely and quantitatively conveys the molten polymer to the die. At this stage, the temperature must not fall below the plasticizing temperature; it is typically set slightly higher.

Extruder Operating Procedures:

In plastic extrusion production lines, each type of product has its own operational characteristics; only by gaining a thorough understanding of these can the machine’s full potential be realized. Extruders are one such category, and mastering their key operating principles ensures proper and efficient use. The operation of a screw extruder encompasses a series of steps—installation, adjustment, trial runs, routine operation, maintenance, and repair—and shares common features with other machinery, particularly in the drive motor and the speed‑reduction and gear‑changing mechanisms. However, the extrusion system—the heart of the screw extruder—possesses unique characteristics that must be carefully considered during operation.

　　The installation, adjustment, and commissioning of the machine are typically specified in the extruder’s operating manual. Below is a brief overview of the key operational procedures, as well as maintenance and upkeep guidelines for the extruder:

　　Operators should be thoroughly familiar with the structural features of the extruder they are operating, accurately understand the screw’s design characteristics, the control‑instrumentation parameters for heating and cooling, the die configuration, and the assembly details, so as to properly set the extrusion process conditions and operate the machine correctly.