The extrusion system, transmission system, and heating and cooling system of the twin-screw extruder are functionally consistent with the single-screw extruder, but the specific structure is specifically designed based on the actual situation of the twin-screw extruder.
According to the relative position of the two screws, the twin screw extruder can be divided into intermeshing type and non-engaging type. Intermeshing twin screw
According to the degree of meshing, it can be divided into partial meshing and full meshing. As shown in Figure 3-11. Center distance of full-mesh twin screw
A = r + R, where r is the radius of the root of the screw and R is the radius of the top of the screw. Center distance of partially meshing twin screw A ＞ r
+ R. Non-meshing twin screw center distance A ≥ 2 R.
According to the different conditions of screw ribs and screw pitches, the screw grooves in the meshing area can be open or closed. So-called openness
The material can pass at a certain position; closed means that the material cannot pass. Open and closed conditions are divided into longitudinal openings or closures, horizontal openings or closures according to the helical grooves and across the grooves.
Working principle of twin screw extruder
The twin-screw extruder, like the single-screw extruder, undertakes the work of conveying, plasticizing, mixing and mixing polymers.
There are many differences from the single screw in the working principle.
The principle of conveying materials by a twin screw extruder is not only different from a single screw extruder, but also not completely equivalent to plugs or teeth.
Positive displacement transmission of wheel pump. The so-called positive displacement conveying refers to a conveying method in which a moving external surface replaces part of the liquid in the system. The conveying mechanism of the twin screw is related to whether it is engaged or not, whether it is open and horizontally and to what extent, and the direction of rotation of the screw.
Non-meshing twin-screw extruder cannot form a closed or semi-closed chamber due to the two screws, and there is no positive displacement conveying bar
The conveying mechanism is similar to the single screw extruder. The friction factor of the material and the barrel, the screw, and the viscous force of the material are the main factors controlling the conveying volume.