Twin-screw extruders are the most common machinery in t […]
Twin-screw extruders are the most common machinery in the modified plastics industry. They are widely used in the polymer processing industry and other production and processing fields. There are many types of twin-screw extruders, which can be divided into two categories: intermeshing and non-intermeshing. Intermeshing twin-screw extruders can be divided into two categories: co-rotating and counter-rotating.
1. The difference in working principle between co-rotating twin-screw extruder and single-screw extruder
The structure and function of the co-rotating twin-screw extruder are very similar to the single-screw extruder, but there are big differences in the working principle. Mainly manifested in the following aspects:
1) Forced delivery. The meshing co-rotating twin screws, the two screws move in opposite directions at the meshing position, one screw must pull the material into the meshing gap, while the other screw pushes the material out of the gap, resulting in the material from a screw groove Turning to another screw groove, the material is forced to be conveyed in the direction of the machine head in the shape of "∞" along the screw.
2) Homogenization and mixing. The co-rotating twin-screw has a small gap at the meshing point, and the speed of the screw edge and the screw groove are opposite, and the relative speed is high. Therefore, the meshing zone has a high shear speed and a large shear force. The mixing effect is much better than that of a single Screw extruder and counter-rotating twin screw extruder.
3) Self-cleaning. Co-rotating twin-screw extruder, due to the opposite direction of the speed of the screw edge and the screw groove in the meshing zone, the relative speed is high, so it has a fairly high shear speed, which can scrape off any accumulated material adhering to the screw. Good self-cleaning effect, so that the residence time of the material is very short, and it is not easy to cause local degradation and deterioration.
4) Plasticization of materials. The size of the screw gap has a great influence on the plasticization quality of the material. The smaller the gap, the greater the shearing force, but the amount of material passing through decreases; the larger the gap, the amount of material passing increases, but the shearing force decreases.
5) Compression of materials. The co-rotating twin-screw extruder has many more ways to compress materials, and the overall effect is good.
6) Feeding method. The co-rotating twin-screw extruder requires uniform and quantitative feeding, and adopts the metering and starvation feeding method.
7) Exhaust. Because it is hungry feeding, a large-lead screw conveying element can be used to make the screw groove in an under-filled state and in a zero pressure state, so that an exhaust section can be set.
2. Application of twin screw extruder
The twin-screw extruder can be divided into counter-rotating twin-screw and co-rotating twin-screw according to the rotation direction of the two screws.
The intermeshing co-rotating twin-screw extruder is widely used in the physical and chemical modification of matrix resin, such as filling, strengthening, toughening, reactive extrusion, etc.