Plastic extruders can be divided into single-screw extruders, twin-screw extruders, and multi-screw extruders according to their number of screws. At present, the single-screw extruder is the most widely used and suitable for extrusion processing of general materials. The twin-screw extruder has less heat due to friction, more uniform shearing of the material, greater conveying capacity of the screw, relatively stable extrusion volume, long stay of the material in the barrel, and even mixing.

Conical twin-screw extruder has features such as forced extrusion, high quality, wide adaptability, long life, low shear rate, non-decomposable materials, good mixing and plasticizing properties, direct powder molding, etc., automatic temperature control, vacuum row Gas and other devices. Applicable to the production of pipes, plates, special-shaped materials and other products.

Single-screw extruders occupies an important position as plastic granulation machinery or molding processing machinery. In recent years, the single-screw extruder has made great progress. At present, the large pelletizing single-screw extruders produced in Germany have a screw diameter of 700 mm and a production volume of 36 t/h.

The main sign of the development of single-screw extruders is the development of its key part, the screw. In recent years, a large number of theoretical and experimental researches on screw have been carried out. Up to now, there have been nearly 100 types of screws, and there are commonly used separation type, shear type, barrier type, shunt type, and wavy type.

From the standpoint of single-screw development, although single-screw extruders have been relatively complete in recent years, with the continuous development of polymer materials and plastic products, more innovative new types of screws and special single-screw extruders will emerge. In general, single-screw extruders are moving toward high speed, high efficiency, and specialization.

Twin-screw extruder has good feeding characteristics and is suitable for powder processing. It has better mixing, venting, reaction and self-cleaning functions than single-screw extruder. It is characterized by poor thermal stability of plastics and blends. When it is expected, it shows its superiority. In recent years, foreign twin-screw extruders have made great progress. Various types of twin-screw extruders have been serialized and commercialized, and there are also many manufacturers. They are roughly classified as follows:

(1) According to the relative positions of the two axes, there are parallel and conical points;

(2) According to the two screw engagement procedures, there is a meshing type and a non-meshing type;

(3) According to the direction of rotation of the two screws, there are points in the same direction and in different directions. In the opposite direction, there are points inward and outward.

(4) According to the screw rotation speed, there are points of high speed and low speed;

(5) According to the structure of the screw and the barrel, there are integral and combination points.