Double-screw extruder is divided into parallel double-screw and conical double-screw. Compared with single screw, it mainly increases the plasticization of materials, reduces the formulation cost, makes the raw and auxiliary materials disperse more evenly, and improves the production efficiency and physical properties of the product, making it more beautiful.
The differences between double-screw extruder and single-screw extruder are mainly reflected in the following two aspects.
1. Material transmission mode
In a single screw extruder, the friction resistance is in the solid conveying section and the viscosity resistance is in the melt conveying section. The transport behavior is determined by the friction characteristics of solid materials and the viscosity of molten materials. If the friction property of some materials is poor, it will be more difficult to feed the materials into the single screw extruder if the feeding problem is not solved. In double-screw extruders, especially in intermeshing double-screw extruders, the conveying of materials is a positive displacement drive to a certain extent, and the degree of positive displacement depends on the spiral edges of one screw and another screw. Relative proximity of threaded grooves. The screw geometry of closely engaged counter rotating extruders can achieve high positive displacement conveying characteristics.
2. Velocity field of material
At present, the velocity distribution of materials in single screw extruders has been described clearly, while that in double-screw extruders is more complex and difficult to describe. Many researchers only analyzed the velocity field of materials without considering the material flow in the meshing area, but these analysis results are very different from the actual situation. Because the mixing characteristics and overall behavior of double-screw extruder mainly depend on the leakage flow in the meshing area, the flow in the meshing area is very complex. The complex flow patterns of materials in double-screw extruders show the incomparable advantages of single screw extruders, such as full mixing, good heat transfer, large melting capacity, strong exhaust capacity, good material temperature control, and so on.
