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Differences between Twin Screw Extruders and Single Screw Extruders
Plastic extruders can be divided into single-screw extruders, twin-screw extruders and multi-screw extruders according to the number of screw. At present, single screw extruder is widely used and suitable for extrusion processing of general materials. Twin-screw extruder has less heat generated by friction, more uniform shear of materials, larger screw conveying capacity, more stable extrusion volume, long residence time of materials in the barrel, and even mixing.
Conical twin-screw extruder has the characteristics of forced extrusion, high quality, wide adaptability, long life, low shear rate, difficult material decomposition, good mixing and plasticizing performance, powder direct forming, temperature self-control, vacuum exhaust and so on. It is suitable for the production of pipes, plates, profiles and other products.
Single screw extruder plays an important role in both plasticizing and granulating machine and forming and processing machine. In recent years, single screw extruder has made great progress. At present, the single screw extruder produced in Germany has a diameter of 700 mm and a output of 36 t/h.
The main sign of the development of single screw extruder is the development of its key parts - screw. In recent years, a large number of theoretical and experimental studies have been carried out on screw. Up to now, there are nearly 100 kinds of screw, such as separation type, shear type, barrier type, diversion type and wavy type.
From the point of view of single screw development, although the single screw extruder has been relatively perfect in recent years, with the continuous development of polymer materials and plastic products, more characteristic new screw extruders and special single screw extruders will emerge. Generally speaking, single screw extruders are developing in the direction of high speed, specialization.
Twin-screw extruder has good feeding characteristics and is suitable for powder processing. It has better mixing, exhaust, reaction and self-cleaning functions than single-screw extruder. It is characterized by its superiority in processing plastics and blends with poor thermal stability. Overseas twin-screw extruders have developed greatly in recent years. Various types of twin-screw extruders have been serialized and commercialized. There are many manufacturers producing twin-screw extruders, which can be roughly classified as follows:
(1) According to the relative position of two axes, there are parallel and conical.
(2) According to the meshing procedure of two screw, there are meshing type and non-meshing type.
(3) According to the rotation direction of the two screw, there are homo-directional and hetero-directional, and in hetero-directional, there are inward and outward.
(4) According to the rotating speed of the screw, there are high speed and low speed.
Dismantling of Screw Shafts