What Is Conical Twin Screw Extruder

Whether the axis lines of the twin screws of the extruder are parallel or not can be divided into two types: the axis lines are parallel and the axis lines intersect. The one with parallel axis lines is a parallel twin-screw extruder, and the one with intersecting axis lines is a conical twin-screw extruder. The conical twin-screw extruder is a model developed on the basis of a fully meshed parallel outward counter-rotating twin-screw extruder.

The main characteristics of the conical twin-screw extruder are: the groove depth of the screw is no longer a constant value but decreases along the extrusion direction with the decrease of the screw diameter; the ratio of the diameter of the large end of the screw to the diameter of the small end is greater than. This structural form is called a double cone because its groove depth has a constant ratio to its diameter and it has two cone angles. The screw with this structural form has a deeper groove depth than the ordinary type. The free volume of the screw increases, resulting in a larger feeding amount. At the same time, the residence time of the material increases, and the extrusion output will also be greatly improved.

Compared with the parallel meshing counter-rotating twin-screw extruder, the structural characteristics of the conical twin-screw determine that in addition to the closed screw cavity, forced material transportation, narrow material residence time distribution, good self-cleaning, and suitable for powder processing In addition to common advantages, it also has the following unique advantages:

(1) The feeding section has a large diameter, a large screw channel volume, and a large feeding amount;

(2) The screw surface areas in the feeding section and compression section are relatively large, which is conducive to the shearing and heating of the material;

(3) The screw has high strength and system stiffness, and can be configured with a relatively large torque distributor and gearbox, making the transmission system safe and reliable;

(4) The screw diameter of the extrusion section is small and the surface area is relatively small, which can effectively prevent decomposition caused by excessive melt temperature caused by excess shear heat. The risk of thermal damage is small, and it is suitable for processing materials with poor thermal stability.

In view of this, the conical twin screw extruder is particularly suitable for processing temperature-sensitive, shear-sensitive and fluffy materials. It has now become the main model for extrusion molding of RPVC dry mixed powder materials. It is very suitable for directly extruding powder materials into plastic products with different cross-sections such as pipes, plates, sheets, and special profiles.