Extruders are one of the types of plastic machinery that originated in the 18th century. Extruders can be divided into right-angle and angled heads according to the direction of the material flow in the head and the angle of the screw centerline. The screw extruder relies on the pressure and shear force generated by the rotation of the screw, which allows the material to be fully plasticized and uniformly mixed and molded through the mouth die. Plastic extruders can be basically classified as twin-screw extruders, single-screw extruders, and, less commonly, multi-screw extruders and screwless extruders. This article will briefly introduce the extrusion process and the types of extruders.
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What is the extrusion molding process?
What are the types of extruders?
The extrusion molding process is the most diverse, versatile, productive, adaptable, versatile, and production-intensive molding process in the polymer processing field. Extrusion is the process by which a polymer melt (or viscous fluid) is extruded by an extruder screw through a shaped die, resulting in a continuous profile with a constant cross-sectional shape.
The extrusion molding process is suitable for all polymer materials. It can mold almost all thermoplastics and can be used for thermosetting plastics, but is limited to a few thermosetting plastics such as phenolic. Extruded plastic products include pipes, sheets, rods, sheets, films, monofilaments, cable cladding, various profiles, and compounds of plastics with other materials. Currently, about 50% of thermoplastic products are formed by extrusion. In addition, the extrusion process is also commonly used in plastic coloring, mixing, plasticizing, granulation and plastic blending modification, etc. Based on extrusion, with blowing and stretching technology, it is also developed into extrusion blow molding and extrusion center molding to manufacture hollow blow molding and biaxially stretched film and other products. It can be seen that extrusion is the most important method in polymer molding.
There are two types of extrusion equipment: screw extruders and plunger extruders, the former for continuous extrusion and the latter for intermittent extrusion, which is mainly used for molding of high viscosity materials, such as PTFE and UHMWPE. Screw extruders can be divided into single-screw extruders and multi-screw extruders. The single-screw extruder is the most basic extruder in production. Twin-screw extruders are the fastest growing among multi-screw extruders in recent years, and their applications are becoming more and more widespread. At present, in the processing of PVC plastic doors and windows profiles, twin-screw extruder has become the main production equipment, single-screw extruder will be gradually eliminated. However, in the extrusion of other polymers, single-screw extruders still dominate.
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