Main Technical Parameters of Threaded Components of Extruder

The main technical parameters of the threaded elements of the twin-screw extruder include screw diameter, screw aspect ratio, screw speed range, extruder output, maximum head pressure, etc. Unlike single-screw extruders, extruder threaded elements sometimes also show the maximum torque that each screw can withstand and the service life of the thrust bearing. The main technical parameters of the threaded elements of the twin-screw extruder are as follows:

(a) Screw diameter

The size of the screw diameter largely reflects the size of the extruder specifications and the size of the production capacity. A series of other parameters are also related to the screw diameter. For example, the rotational speed of the screw determines the circumferential speed of the screw, the shear rate of the material received in the screw groove, and the shear rate of the material received in the gap between the outer diameter of the screw and the inner wall of the tube. When the head pressure is constant, the axial thrust of the screw is basically determined, so the specifications and number of thrust bearings are also determined.

Generally, the required screw diameter depends on the designed stretch size.

(B) Center distance

The user of the extruder thread element is not necessarily known, but the center distance between the two screws in the twin-screw extruder is an important technical parameter. This is because it determines the following geometric relationships and determines the relevant design parameters:

(1) The size of the transmission system output shaft (connected to the screw) and related gears determines the effective torque that the screw can withstand.

(2) The outer diameter and root diameter of the screw determine the meshing degree of the two screws, the depth of the screw groove and the maximum theoretical extrusion volume of the twin-screw extruder.

(3) The size of the outer diameter of the thrust bearing determines how much the maximum head pressure is required.

Special attention should be paid to the mutual influence and mutual restriction between the center distance of the two screws, the outer diameter and root diameter of the screw, the depth of the screw, the maximum theoretical throughput and the maximum torque that the screw can bear. Because the development direction of meshing and twin screw extruder and the design index to be achieved are closely related.

(c) Aspect ratio

The screw elements of the extruder reflect the specifications and performance of the twin-screw extruder to a certain extent. Twin-screw extruders are mainly used to transform polymers, so sometimes several filling ports and several vents are required, and sometimes longer material residence times are required, so longer screws are required. The long cost is large, and the required constant pressure distribution can be easily set. In addition to increasing the residence time of the material at the same screw speed, it can also greatly improve the quality of the plasticization, mixing or reaction process.

(d) Screw speed range

This is a very important parameter. To a certain extent, it reflects the extrusion ability and mixing ability of the twin-screw extruder. This depends on the amount of extrusion required, the characteristics of the processed material and the work done during the extrusion process.

The mesh twin-screw extruder is mainly used for mixing, which requires high shear rate and shear stress, so high screw speed is required. In addition, at high speeds, the extrusion process is less energy intensive than at low screw speeds.

(e) Protrusion

Extruder threaded elements are generally used to weigh (starve) lobsters, so the amount of extrusion depends on the amount of feed, but has nothing to do with the screw speed. However, if the screw speed is high, the measured charge may be much more. The extrusion amount has different concepts. If there is no mounting head, it is the maximum theoretical extrusion amount.

(f) Maximum head pressure

During the extrusion process, the melt at the end of the screw is set on the screw to generate axial thrust pressure, and the pressure gradient caused by the pressure distribution along the path will also generate axial thrust on the screw. These two forces work on the thrust bearings of the drive train. The construction pressure capacity of the twin-screw extruder is relatively low, and the axial thrust is relatively small, so the number of bearings in the thrust bearing string is small. The maximum head working pressure of the twin-screw extruder is generally less than 20MPa.

The above is the main technical parameters related to the screw element of the twin-screw extruder.