The Difference between Conical Twin Screw Extruder And Parallel Twin Screw Extruder

According to whether the axis lines of the twin screws are parallel or not, they can be divided into two types of extruders: those with parallel axis lines and those with intersecting axis lines.

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.

Parallel and conical twin-screw extruders have the same characteristics: they have a conveying mechanism that forces plastic forward, good mixing and plasticizing capabilities and dehydration capabilities, and they have basically the same adaptability to materials and plastic product molding processes.

The differences between parallel and conical twin-screw extruders:

1. Diameter: The diameter of parallel twin screws is the same, while the diameter of the small end of the conical twin screw is different from the diameter of the big end.

2. Concentric distance: The center distance of the parallel twin-screw is the same, while the two axes of the conical twin-screw are at an angle, and the size of the center distance changes along the axis.

3. L/D ratio: The L/D of parallel twin screws refers to the ratio of the effective part length of the screw to the outer circle of the screw;

The L/D of a conical twin screw refers to the ratio of the effective part length of the screw to the average of the big end diameter and the small end diameter.

From the above, we can clearly see that the most significant difference between parallel and conical twin-screw extruders is the different geometric shapes of the screw barrel, which leads to many differences in structure and performance. Although the characteristics of the two are different , but have their own advantages.

The parallel twin-screw extruder is limited by the small center distance between the two screws. In the transmission gearbox, the space given to the radial bearings and thrust bearings that support the two output shafts and the related transmission gears is very limited, resulting in a small output torque and poor load resistance of the parallel twin-screw extruder. However, the plasticity of the aspect ratio is the advantage of the parallel twin screw. It can increase and decrease the aspect ratio according to the differences in molding conditions to adapt to the requirements of the plastic processing technology. Thus the application range of parallel twin-screw extruders can be expanded, but this is difficult to achieve with conical twin-screw extruders.

The two conical screws of the conical twin-screw extruder are arranged horizontally, and the two axes are installed into the barrel at an angle. The center distance between the two axes gradually increases from the small end to the large end, so that the two output shafts of the transmission gear box have a larger center distance. The gears and gear shafts in these transmission systems, as well as the radial bearings and thrust bearings supporting these gear shafts, leave a large installation space, which can accommodate larger-sized radial bearings and thrust bearings. Each transmission shaft has a shaft diameter sufficient to transmit torque, so large working torque and large load-bearing capacity are major features of the conical twin-screw extruder.

For users, the purchase of twin-screw extruders is very important. Different types of twin-screw extruders have different performance and application situations. Therefore, it is necessary to understand the performance and application situations of various twin-screw extruders.

For example, the intermeshing co-rotating twin-screw extruder, due to its high speed, large shear rate and combined screw, is widely used in the modification of polymers that are not easily decomposed by thermal decomposition---Blending, filling, fiber reinforcement and reactive extrusion of materials.

For example, the meshing counter-rotating twin-screw extruder has good mixing and plasticizing functions, and its biggest feature is the direct molding and processing of PVC powder. If the geometric structure of the screw is changed, it can also be used for the molding of other materials, but its strength is still the molding of PVC.

According to the size of the plastic cross-section, the extrusion amount is determined, and then the specifications of the twin-screw extruder are selected based on the extrusion amount. Under the condition that the plastic processing and molding process conditions are basically the same, the conical twin-screw extruder can adapt to larger machine head pressure, and the parallel twin-screw extruder can adapt to smaller machine head pressure.

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