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I understand the difference between single-screw extruder and twin-screw extruder

2019-03-15 16:26:09

The extruder is one of the types of plastic machinery and is the most common machinery in the modified plastics industry. It is widely used in the polymer processing industry and other production and processing fields. The extruder can be divided into a single-screw extruder and a twin-screw extruder. The working principle and application fields of the two are different, and both have advantages and disadvantages.
First of all, single-screw extruders and twin-screw extruders have many differences in plasticizing capacity, material conveying methods, and speed cleaning, as follows:
Different plasticizing ability: single screw is suitable for plasticizing extrusion of polymer, suitable for extrusion processing of granular materials; shear degradation of polymer is small, but material stays in extruder for a long time. The twin-screw has good mixing and plasticizing ability, and the material has a short residence time in the extruder, which is suitable for powder processing.
The material conveying mechanism is different: the material conveying in the single-screw extruder is drag-type flow, the solid conveying process is friction dragging, the melt conveying process is viscous dragging, the friction factor between the solid material and the metal surface and the melt material The viscosity, to a large extent, determines the transport capacity of a single screw extruder. The transfer of material in the twin-screw extruder is a positive displacement transport. As the screw rotates, the material is forced forward by the mutually meshing threads. The ability of the positive displacement transport depends on the screw edge of the screw and the other. The proximity of the screw to the screw. Maximum positive displacement delivery can be achieved with a tightly meshed counter-rotating twin-screw extruder.
Different speed fields: The speed distribution in a single-screw extruder is relatively clear and easy to describe, and the situation in a twin-screw extruder is quite complicated and difficult to describe. This is mainly due to the meshing zone in the twin-screw extruder. The complicated flow in the meshing zone makes the twin-screw extruder have many advantages such as sufficient mixing, uniform heat transfer, strong melting ability and good exhaust performance, but it is difficult to be accurate. The flow state of the meshing zone is analyzed.
Self-cleaning: The twin-screw extruder has a relatively high shear speed due to the opposite direction of the speed of the screw and the groove of the meshing zone, so that it 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. Single-screw extruders do not have this feature.
In addition to different working principles, they also have different application fields. Twin-screw extruders are widely used in physical and chemical modification of matrix resins, such as filling, reinforcement, toughening, reactive extrusion, etc. Single-screw extruders are mainly Used in the fields of pipes, plates, sheets and profiles.
Application examples of twin-screw extruder: glass fiber reinforced, fuel-resistant granulation (such as PA6, PA66, PET, PBT, PP, PC enhanced flame retardant, etc.), high filler granulation (such as PE, PP filled 75%) CaCO3), heat-sensitive material granulation (such as PVC, XLPE cable material), concentrated masterbatch (such as filling 50% toner), anti-static masterbatch, alloy, coloring, low-fill blending granulation, cable material granulation ( Such as sheathing material, insulating material), XLPE pipe material granulation (such as masterbatch for hot water crosslinking), thermosetting plastic compounding extrusion (such as phenolic resin, epoxy resin, powder coating), hot melt adhesive, PU reaction extrusion granulation (such as EVA hot melt adhesive, polyurethane), K resin, SBS devolatilization and the like.
Single screw extruder application example: suitable for PP-R pipe, PE gas pipe, PEX cross-linked pipe, aluminum-plastic composite pipe, ABS pipe, PVC pipe, HDPE silicon core pipe and various co-extruded composite pipes; suitable for PVC Extrusion of profiles and plates of PET, PS, PP, PC, etc., extrusion of various other plastics such as wire, rod, etc.; adjusting the speed of the extruder and changing the structure of the extrusion screw can be applied to the production of PVC, polyolefin And other plastic profiles.

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