How does the conical screw barrel adapt to extrusion materials of different viscosities and hardnesses?

In many industries such as plastic processing, food manufacturing, chemicals and pharmaceuticals, extruders are indispensable production equipment, and one of their core components is the conical screw (conical screw barrel). This cleverly designed structure not only improves extrusion efficiency, but also greatly enhances the machine's adaptability to a variety of materials, especially when processing materials of different viscosities and hardnesses, showing excellent performance.
1. Structural characteristics of conical screws
As the name suggests, the diameter of the conical screw gradually changes along the axial direction, usually gradually decreasing from the large diameter in the feed zone to the small diameter in the discharge zone. This design not only optimizes the material conveying path, but also adapts to the processing needs of different materials by changing the gap between the screw and the barrel and the shear force distribution.
Variable diameter design: The large-diameter feed zone facilitates the initial crushing and pre-plasticization of large or high-viscosity materials, reducing the risk of blockage; the small-diameter discharge zone strengthens the shear and mixing effects, and promotes the homogenization and melting of the material.
Helix angle and depth: The reasonable design of helix angle and groove depth is crucial to control the residence time and shear degree of materials in the screw. Deeper grooves and smaller helix angles are suitable for high-viscosity materials, increasing shear force and residence time to promote melting; conversely, they are suitable for low-viscosity or high-fluidity materials.
2. Adapt to materials with different viscosities
High-viscosity materials: For high-viscosity materials, such as rubber, certain thermosetting plastics, etc., conical screws increase the initial crushing area and pre-plasticization space of the material by increasing the diameter of the feed zone and adopting a deep groove design, while slowing down the material forward speed and extending the shear and melting time. In addition, adjusting the screw speed and temperature settings can also effectively promote the melting and flow of materials.
Low-viscosity materials: For low-viscosity or high-fluidity materials, such as some thermoplastics, certain food raw materials, etc., conical screws reduce shear force and residence time by reducing the diameter of the feed zone, adopting a shallow groove design, and increasing the helix angle to prevent overheating and degradation of the material or excessive shearing. At the same time, maintain an appropriate screw speed and temperature to ensure that the material maintains stable fluidity and good product quality during the extrusion process.
3. Adapt to materials of different hardness
The hardness of the material directly affects its crushing and melting difficulty during the extrusion process. The conical screw copes with materials of different hardness by adjusting the compression ratio and shear strength of each section.
High hardness materials: For high hardness materials, such as certain reinforced plastics, hard rubber, etc., the conical screw adopts a stronger shearing and crushing action in the feeding area, and improves the crushing efficiency of the material by reducing the gap, increasing the spiral depth and adopting a steeper spiral angle. At the same time, the shear strength is gradually reduced in the subsequent stages to ensure that the material will not be damaged by excessive shearing during the melting process.
Low hardness materials: For low hardness materials, such as soft plastics, certain food colloids, etc., the conical screw pays more attention to protecting the integrity of the material, and reduces the mechanical damage of the material during the extrusion process by reducing the shear strength, maintaining a larger gap and adopting a gentler spiral angle. In addition, reasonable temperature control is also the key to ensure the smooth extrusion of low hardness materials.