I. The Development History of Extruders

Since the advent of the first extruder, extrusion technology has advanced rapidly—evolving from the initial plunger‑type design to more sophisticated screw‑type systems, from manual operation to fully automated control, and from single‑product processing to diversified product lines—resulting in the gradual maturation of extrusion molding technology. Today, extrusion molding boasts high production efficiency, ease of manufacturing, and continuous production capabilities. It holds a very important position in the plastic molding and processing industry.

Over the past half-century and more, China’s plastics industry has undergone a development trajectory from scratch to maturity, growing steadily from small-scale beginnings to substantial scale, particularly during the rapid expansion of the past two decades since the reform and opening-up. A comprehensive industrial system has been preliminarily established, with output now ranking among the highest and leading global trends. The plastics machinery industry is the sector that provides technological equipment to the plastics industry. Strong market demand has driven the growth of the plastics machinery industry, and extrusion molding technology has advanced significantly.

II. Classification and Composition of Extruders

1. Classification of Extruders

Plastic extruders are classified according to the number of screws into single-screw, twin-screw, and multi-screw extruders. At present, single-screw extruders are widely used and suitable for the extrusion processing of common materials. Whether employed as plasticizing and pelletizing equipment or as molding machinery, single-screw extruders occupy a pivotal position. The primary hallmark of its development lies in its key components. — The evolution of screws. To date, nearly a hundred types of screws have been developed and standardized. Common configurations include the separating type, shear type, barrier type,分流 (diverting) type, and corrugated type. Looking at the development of single-screw extruders, although they have become quite sophisticated in recent years, overall they are trending toward higher speeds and greater specialization.

2. Components of a Screw Extruder

A plastic extruder primarily consists of a main machine, auxiliary equipment for the extrusion unit, and a control system.

( 1) (1) The main body of an extruder consists of the extrusion system, the drive system, and the heating–cooling system. The extrusion system includes the screw, barrel, hopper, die head, and mold. Plastics are plasticized into a uniform melt within the extrusion system and, under the pressure generated during this process, are continuously forced through the die head by the screw. The drive system serves to rotate the screw, supplying the torque and rotational speed required for extrusion. It typically comprises an electric motor, a reducer, and bearings. Heating and cooling are essential conditions for carrying out the plastic extrusion process.

( 2) The auxiliary equipment of an extrusion line typically includes a pay-off reel, a straightening unit, a traction device, a cooling system, a preheating unit, a take-up reel, a meter counter, and a spark tester. Depending on the specific application of the extrusion line, the auxiliary equipment employed may vary.

( 3) The extruder’s control system comprises a heating system, a cooling system, and a process‑parameter measurement system, and is primarily composed of electrical components, instrumentation, and actuators. Its main functions are to control and regulate the drive motors of the main and auxiliary machines, delivering rotational speeds and power that meet process requirements while ensuring coordinated operation between the two; to monitor and adjust the temperature, pressure, and flow rate of the plastic within the extruder; and to enable either manual or automatic control of the entire unit.