What Is Shear Heat Release?

01 Introduction

An extruder is one of the most common pieces of equipment for material processing. Whether it is a single-screw extruder or a twin-screw extruder, the melting and plasticizing of materials are achieved through barrel heating and the shearing and plasticizing action of the screw. Those familiar with the extrusion process may know that the real-time monitored melt temperature inside the extruder is usually slightly higher than the set barrel temperature. This is because the shearing action of the rotating screw generates heat, a phenomenon known as shear heat release.

02 Principle of Shear Heat Release

Shear heat release refers to the frictional heat generated when materials undergo relative motion under the shearing action of the screw during the extrusion process. This heat originates from the conversion of the screw's mechanical energy into the internal energy of the material. The intensity of shear heat release is closely related to the screw design, material properties, and process conditions.

03 Manifestations of Shear Heat Release in Different Screw Sections

Feeding Section: Since the screw channels are relatively deep and the material is not yet compacted, frictional heat is minimal, and external heaters provide most of the heat.

Compression Section: As the screw channel depth gradually decreases, the material is pushed against the barrel wall, increasing shear force and generating more shear heat. The heat in this section primarily comes from shear action.

Metering Section: By this stage, the material is fully melted, and the screw channels are shallower, leading to significant shear heat generation. In some cases, cooling      devices are required to control the temperature.

04 Factors Affecting Shear Heat Release and Control Methods

(1) Factors Affecting Shear Heat Release

Screw Design: Parameters such as the length-to-diameter ratio, compression ratio, and screw channel depth influence the generation of shear heat. For example, a larger      length-to-diameter ratio and shallower screw channels increase shear heat.

Material Properties: The thermal sensitivity and melt viscosity of the material also impact shear heat. Heat-sensitive materials (such as PVC) are more prone to degradation due to shear heat.

Process Conditions: Higher screw rotation speeds generate more shear heat, and the barrel temperature settings also affect the contribution of shear heat.

(2) How to Reduce the Impact of Shear Heat Release

Optimizing Screw Design: Adjusting the screw channel depth and compression ratio can help reduce shear heat generation.

Controlling Screw Speed: Lowering the screw speed can decrease shear heat.

Cooling Devices: Installing cooling devices in the metering section helps regulate the temperature.

05 How to Make Rational Use of Shear Heat Release

Shear heat release is an essential heat source in the extrusion process, particularly in the compression and metering sections, where its heat contribution may exceed that of external heaters. Therefore, effectively controlling shear heat is crucial for ensuring uniform material plasticization and maintaining product quality.

Proper utilization of shear heat release can significantly improve extrusion efficiency and product quality. By optimizing screw design, controlling screw speed, implementing segmented temperature control, and adjusting process parameters based on material characteristics, it is possible to reduce energy consumption while ensuring uniform plasticization and performance optimization.

In certain applications, shear heat release can be leveraged to promote chemical reactions or modify materials. For example, in the preparation of high-thermal-conductivity polymer-based composites, controlling shear heat release can reduce interfacial thermal resistance between the filler and the matrix, thereby significantly improving the thermal conductivity of the material. This approach not only enhances material performance but also reduces the need for additional heating.

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