Publish Time: 2022-11-08 Origin: Site
In the plastic extrusion molding line, the plastic extruder is usually called the main machine, and the plastic extrusion machine of the following equipment is called the auxiliary machine. After more than 100 years of development, plastic extruders have been derived from the original single screw, twin screw, multi-screw and even screw models.
What is the function and principle of plastic extruder?
What is the production process of plastic extruder?
What are the characteristic dimensions of a plastic extruder?
The function of plastic extruder is to convert the solid plastic into a uniform melt by heat, pressure and shear, and feed the melt to the next process. During the production of the melt, additives such as color masterbatches are mixed, resins are blended and reground. The finished melt must be homogeneous in concentration and temperature. The pressure must be high enough to extrude the viscous polymer. The plastic extruder completes all the above processes through a barrel with a screw and a screw. Plastic pellets enter the barrel through a hopper at one end of the barrel and are then conveyed by a screw to the other end of the barrel. To have sufficient pressure, the thread depth of the auger decreases as the distance from the hopper increases. External heating and internal heat due to friction between the plastic and the screw soften and melt the plastic.
Different polymers and different applications often have different requirements for plastic extruder design. Many options include outlet ports, multiple feed ports, special mixing devices along the screw, cooling and heating of the melt or no external heat source (adiabatic extruder), the relative size of the gap between the screw and barrel varies, and the number of screws, and so on. For example, a twin-screw plastic extruder can mix the melt more thoroughly than a single-screw plastic extruder. In tandem extrusion, the melt extruded by the first extruder is fed to the second extruder as raw material, which is commonly used to produce extruded polyethylene foam.
The characteristic dimensions of a plastic extruder are the diameter (D) of the screw and the ratio (L/D) of the length (L) to the diameter (D) of the screw. plastic extruders usually consist of at least three sections. The first section, near the feed hopper, is the feed section. Its function is to allow material to enter the extruder at a relatively constant rate. Generally, this section is maintained at a relatively low temperature to prevent clogging of the feed channel. The second part is the compression section, where the melt is formed and the pressure is increased. The transition from the feed section to the compression section can be abrupt or smooth (gentle). The last part metering section, next to the extruder outlet. Its main function is to ensure that the material flowing out of the extruder is uniform. In this part, the material should have sufficient residence time to ensure uniformity of composition and temperature.
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