The structure and main components of a single-screw extruder are introduced below: The single-screw extruder is the most widely used, versatile type in the extruder product family. Its defining feature is that its plasticizing system consists of a single screw paired with a barrel. With its broad range of applications, a single-screw extruder can handle the extrusion of various thermoplastic materials; by simply changing the screw’s design, it can readily adapt to produce molded products from different raw materials.

The structural components of a single-screw extruder primarily include the drive system, plasticizing system, feeding system, heating and cooling system, and electrical control system.

(1) Main components of the compression molding system

The extruder’s plasticizing system is a key component of the extrusion equipment. Its function is to feed the raw material into the system, where it undergoes compression and heating, transitioning from a solid state to a plasticized, molten state. The material is then uniformly extruded at equal flow rates and pressures through the die plate (also known as the porous plate) at the front end of the barrel, entering the mold for shaping the final product.

　(2) Main components of the transmission system

The drive system of a single-screw extruder primarily consists of an electric motor, a gear reducer, a V‑belt drive, or a coupling, among other components. Its main function is to rotate the screw within the specified speed range; in accordance with process requirements, it ensures that the screw rotates uniformly and smoothly under torque, thereby achieving plastic melting and plasticization as well as the conveyance of the molten material out of the barrel.

In the drive system, the component that supports the screw’s rotation and bears the axial load during operation is a frequently failing part in extrusion production. The primary causes of failure are hard foreign objects—such as metal fragments—being mixed into the raw material, which can jam the screw within the barrel, or insufficient heating of the feedstock during extrusion, leading to damage of the rolling bearings at the support shaft.

　(3) Heating and Cooling System

When a single-screw extruder initiates production, heating the barrel supplies thermal energy to the plastic inside, enabling it to plasticize under the action of the screw. Barrel cooling, on the other hand, is used to regulate the temperature rise caused by compression and friction as the plastic moves through the barrel, keeping the barrel temperature within the process‑controlled range and ensuring smooth extrusion operation.

(4) Screen-changing device

In the extrusion and plasticization system of a single-screw extruder, a die plate and a filter screen are typically installed on the barrel at the screw’s front end. Depending on the product requirements, filter screens and die plates of different mesh counts can be interchanged; for certain products, extrusion molding may even be carried out without a die plate or filter screen. Nowadays, when using filter screens in extrusion, screening‑change devices are already available. When a screen change is needed, a hydraulic cylinder drives a sliding plate, which moves to swap the old and new screens into position. During this process, some molten material is extruded through the gap between the sliding plates and cools and solidifies within that gap, forming a thin layer approximately 0.1 mm thick that serves as a sealing barrier.

(5) Control System

In single-screw extrusion equipment, the control system is primarily used to regulate process parameters such as screw speed, heating temperatures at various zones, and melt pressure during the extrusion process. Currently, most extruders employ instrument‑based control; PLC‑based programmable control systems are also beginning to be adopted. Compared with instrument‑based control, PLC‑based systems are better suited for automating and digitally controlling the extrusion process.

X. Structure and Main Components of a Single-Screw Extruder