What are the four areas of the screw barrel
Plastic extrusion, also known as plasticizing extrusion, is a continuous high-volume manufacturing process in which thermoplastic materials (in powder, pellet, or pellet form) are uniformly melted and then extruded from a forming die by pressure.
In screw extrusion, the pressure comes from the rotation of the screw against the barrel wall. As the plastic melt passes through the die, it acquires the die hole shape and exits the extruder. The extruded product is called an extrudate, and a typical extruder consists of four zones:
1. Feed zone. In this area, the flight depth is constant. The distance between the large diameter at the top of the thread and the small diameter of the screw at the bottom of the thread is the thread depth.
2. Transition or compression zone. The flight depth in this area began to decrease. In effect, the thermoplastic material is compressed and begins to plasticize.
3. Mixed zone. In this area, the flight depth again remains the same. To ensure complete melting and homogeneous mixing of the material, special mixing elements can be used.
4. Metering area. The flight depth of this region is smaller than that of the blended region but remains the same. Furthermore, the pressure pushes the melt through the forming die in this area.
On the other hand, the melting of the polymer mixture is caused by three main factors:
1. Spread heat. Heat transfer is the energy transferred from the extruder motor to the extruder shaft. In addition, polymer melting is affected by screw profile and residence time.
2. Friction. This is brought about by the internal friction of the powder, screw profile, screw speed, and feed rate.
3. Extruder barrel. Three or more independent temperature controllers are used to maintain the temperature of the barrel.
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