A single screw extruder is a kind of extruder, which has the characteristics of simple structure, low price, and easy operation. This article will introduce the single screw extruder from both the structure and the conveyor theory of the single screw extruder.
The following is the list of contents
Structural characteristics of single screw extruder
single screw extruder extrusion process and the function of each section of the screw
The single-screw extruder is composed of several parts, such as a transmission system, extrusion system, heating and cooling system, and control system. Among them, the extrusion system is the key part of extrusion molding, which plays an important role in the quality and output of extrusion molding. The extrusion system mainly includes several parts such as a feeding device, barrel, screw, head, and mouth die. The basic structure and role of the extruder are discussed below only for the extrusion system.
From polymer physics, we know that there are three physical states of polymers, namely, glass state, high elasticity state, and viscous flow state, and under certain conditions, these three physical states will change each other. After the solid plastic is fed into the barrel from the hopper, it advances toward the head with the rotation of the screw, and in this process, the physical state of the plastic is constantly changing. According to the process of changing the three physical states of plastic in the extruder and the working requirements of each part of the screw, the screw of the extruder is usually divided into three sections: charging section (solids conveying area), compression section (melting area) and homogenization section (melt conveying area). Non-engaging extruders are very different from engaging extruders and are closer to the single-screw extruders, which are fundamentally different from each other.
Feeding section
The plastic enters the barrel of the extruder from the hopper and moves forward under the rotation of the screw due to the friction between the inner wall of the barrel and the surface of the screw. In this section, the function of the screw is mainly to compact the plastic to provide forward transport power, the material still exists in a solid-state, although due to the strong frictional heat, near the end of the barrel wall contact with the plastic has approached or reached the viscous flow temperature, the surface of the solid particles began to sticky, but the melting has not yet begun. This area is called the hysteresis zone, which refers to the end of the solid conveying area to the initial start of the molten one for the viscous flow state.
Homogenization section
The material entering the homogenization section from the melting section is a viscous fluid that has been completely melted. The viscous fluid conveyed to the front is further mixed and plasticized by the resistance of the head die, and part of it is extruded from the head die with a fixed pressure.
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