Detailed Explanation of Screw Thread Elements in Twin-Screw Extruder

The twin-screw extruder occupies an important position in the field of polymer processing with its excellent mixing function. Whether it is polymer blending, filling modification, fiber reinforcement or reactive extrusion, the twin-screw extruder performs outstandingly. Its efficient mixing effect is mainly due to the complex and delicate thread elements inside. So, what exactly are the thread elements in the twin-screw extruder? And what roles do they play respectively?

What are thread elements?

Thread elements are an important part of the screw of a twin-screw extruder. Through the rotation and interaction of the screws, they transport, shear, mix and plasticize the material. According to different functions, thread elements can be divided into the following categories:

1. Conveying block

The conveying block is the most basic thread element in a twin-screw extruder. Its main role is to push the material forward along the axial direction of the screw. Through their spiral design, these blocks ensure the uniform transportation of materials in the barrel and also provide a basis for subsequent mixing and shearing operations.

2. Shearing block (meshing block)

The shearing block, also known as the meshing block, is an important element for enhancing the shearing force of materials. These blocks are usually designed as a series of closely spaced disc-like elements, arranged at different angles (such as 30 degrees, 45 degrees, 60 degrees, 90 degrees, etc.). When the material flows through, a strong shearing force is generated. This high shearing force is crucial for breaking particle agglomeration, ensuring the uniform distribution of additives and enhancing the polymer mixing effect.

3. Special elements

Special elements such as TME (Twin Mixing Element) and ZME (Zigzag Mixing Element) are thread elements designed for specific processing needs. Their main role is to improve mixing efficiency, achieve specific flow characteristics or create back pressure to achieve full filling. These elements are usually used to process materials with special requirements, such as highly filled formulations or high-viscosity materials.

4. Reverse thread elements

Reverse thread elements are used to create back pressure and help the material fully fill and mix. These elements are usually set in the rear section of the screw. Through reverse design, the residence time and shearing force of the material are increased to ensure the quality and uniformity of the final product.

Main parameters of thread elements

The design parameters of thread elements directly affect their functions and performance. Here are some key parameters:

Lead: The lead is the axial distance generated when a point on the screw ridge rotates 360° along the helix. Wide-pitch elements are generally used in the feeding section and the venting section, while narrow-pitch elements are used at positions where the material needs to be compressed or filled with 100% filler.

ID/OD ratio: ID is the bottom diameter of the thread block, and OD is the outer diameter of the thread block. The ID/OD ratio limits the free volume of the extruder screw. The larger the OD/ID ratio, the larger the free volume, but the mandrel used to transmit torque is smaller.

Conclusion

The thread elements in the twin-screw extruder achieve efficient material mixing and processing through their exquisite design and configuration. Understanding the functions and roles of these elements helps optimize the extrusion process and improve product quality. I hope that through the introduction of this article, you have a deeper understanding of the thread elements of the twin-screw extruder. If you encounter problems in actual operation or have further interests, welcome to communicate and discuss at any time.