In the field of processing polymer materials such as rubber and plastic, the internal mixer is the core equipment for achieving material mixing. It applies high temperature, high pressure, and high shear to raw rubber, plastic particles, and additives to uniformly mix different components and endow materials with specific physical and chemical properties. It is widely used in industries such as tire manufacturing, rubber product production, and plastic product processing. The following will provide a detailed introduction to the structure, working principle, classification characteristics, application scenarios, and development trends of the internal mixer.

1、 The structural composition and working principle of the internal mixer

（1） Core structure composition

The internal mixer mainly consists of seven core parts: rotor system, mixing chamber, feeding system, pressing device, unloading system, transmission system, and control system.

Rotor system: It is a key component of the internal mixer, usually including elliptical rotors, triangular rotors, and other types. The rotor surface has spiral edges, which apply shear force to the material through the gap between the edges and the mixing chamber wall during rotation, achieving material crushing, mixing, and plasticization. Different shapes of rotors are suitable for different materials and process requirements. For example, elliptical rotors have better mixing effects on rubber, while triangular rotors have higher efficiency in plastic mixing.

Mixing chamber: composed of upper and lower top plugs and chamber walls, forming a closed mixing space. There is a jacket inside the chamber wall, which can be used to introduce heating or cooling media and accurately control the mixing temperature. The top bolt applies pressure through a hydraulic cylinder to compact the material and enhance the mixing effect; The lower top bolt is used for unloading, and its sealing performance directly affects the mixing quality and material loss.

Feeding system: responsible for conveying raw rubber, carbon black, additives and other materials to the mixing room. Common feeding methods include automatic metering and manual feeding. The automatic metering and feeding system achieves precise material ratio through weighing sensors and conveying devices, improving production efficiency and product quality consistency.

Material pressing device: refers to the upper top bolt and related hydraulic system, which maintains a good filling state of the material in the mixing chamber by applying constant pressure, increases the friction between the material and the rotor, and improves the mixing effect. The pressure can be adjusted according to the material characteristics and process requirements.

Unloading system: composed of a lower top bolt, unloading door, and driving device. After mixing is completed, the lower top bolt is opened and the material is discharged to the subsequent processing equipment through the discharge door. The opening and closing speed and sealing performance of the discharge door have a significant impact on production efficiency and material residue.

Transmission system: includes components such as motors, reducers, couplings, etc., which transmit power to the rotor to rotate at a set speed. The transmission system needs to have sufficient torque and stability to meet the requirements of high load mixing operations.

Control system: Using PLC (Programmable Logic Controller) or industrial computer as the core, integrating temperature, pressure, speed and other sensors to monitor various parameters during the mixing process in real time. Operators can set process parameters through the human-computer interaction interface, and the control system automatically adjusts the equipment operation status according to the preset program to ensure stable and efficient mixing process.

（2） Working principle

The working process of the mixer is based on the principles of shear mixing and convection mixing. After the material enters the sealed mixing chamber through the feeding system, the top plug descends to apply pressure, making the material tightly contact the rotor. As the rotor rotates, the material is subjected to strong shear forces in the gap between the rotor edge and the mixing chamber wall, and is broken into smaller particles; At the same time, the spiral edges of the rotor push the material to move axially and circumferentially in the mixing chamber, achieving convective mixing of the material. Under the combined action of shear and convection, materials of different components gradually disperse uniformly and reach the ideal mixing temperature under the heating or cooling control of the mixing chamber jacket, completing the plasticization and mixing process. After mixing is completed, the lower top bolt is opened, and the material is discharged and enters the next processing step.

2、 Classification and characteristics of internal mixers

（1） Classification by number of rotors

Single rotor mixer: With only one rotor, the structure is relatively simple and the energy consumption is low, but the mixing efficiency and uniformity are slightly inferior to those of a double rotor mixer. Suitable for small businesses or experimental research scenarios with low requirements for material mixing in production tasks.

Double rotor mixer: equipped with two interlocked or tangential rotors, through the synergistic effect between the rotors, stronger shear force and mixing effect are generated, resulting in high mixing efficiency and uniform material dispersion. It is currently the most widely used type in industrial production, especially suitable for large-scale, high-quality rubber and plastic mixing operations.

（2） Classified by rotor shape

Elliptical rotor mixer: The surface of the rotor is elliptical, and the gap formed between the edges and the inner wall of the mixing chamber varies greatly, which can generate strong shear force and have good plasticizing and mixing effects on rubber. It is a commonly used equipment in the rubber processing industry.

Triangular rotor mixer: The rotor has three edges, and the material is subjected to more uniform shear and compression during the mixing process. It is suitable for mixing materials such as plastics and thermoplastic elastomers, and can effectively improve the dispersion and plasticization quality of materials.

Cylindrical rotor mixer: The rotor shape is cylindrical, with a simple structure, and the flow of materials in the mixing chamber is relatively smooth. It is suitable for processing materials that are sensitive to shear, such as certain special rubber and plastics.

3、 Application scenarios of internal mixer

（1） Rubber industry

In tire manufacturing, an internal mixer is used to mix natural rubber, synthetic rubber with additives such as carbon black, sulfur, and accelerators to produce a mixed rubber compound. By precisely controlling the mixing process, the compound can have good physical properties, such as strength, wear resistance and aging resistance, and meet the quality requirements of tire production. In addition, the internal mixer is widely used in the production of rubber products such as hoses, tapes, seals, etc., to endow the products with the required elasticity, hardness, and weather resistance.

（2） Plastic industry

In plastic product processing, the internal mixer can achieve uniform mixing of plastic particles with additives (such as flame retardants, antioxidants, and fillers), improving the processing and usability of plastics. For example, in the production of modified plastics, by thoroughly mixing the base resin with various functional additives through a mixer, engineering plastics with high strength, high toughness, flame retardancy, and other characteristics can be produced, which are widely used in fields such as automobiles, electronics, and home appliances.

（3） Other industries

In addition to the rubber and plastic industries, internal mixers can also be used in fields such as powder metallurgy and food additive mixing. In powder metallurgy, the internal mixer can achieve uniform mixing of metal powder and binder, providing high-quality billets for subsequent forming processes; In the food industry, it can be used for mixing certain special food additives to ensure even distribution of ingredients.

4、 The development trend of internal mixer

With the development of the polymer materials industry and the increasing demand for environmental protection, internal mixers are moving towards intelligence, efficiency, and greenness. In terms of intelligence, artificial intelligence algorithms and big data analysis technology are introduced to achieve equipment fault prediction, automatic optimization of process parameters, and remote monitoring, improving equipment management level; In terms of efficiency, by improving the rotor structure and mixing process, the mixing efficiency and material dispersion quality can be increased, and the production cycle can be shortened; Greening is reflected in reducing energy consumption, reducing dust emissions, and using environmentally friendly materials, such as developing new sealing materials to reduce material leakage, optimizing heating systems to reduce energy consumption. At the same time, in response to the demand for special materials and emerging processes, the internal mixer will continue to innovate, expand its application fields, and provide stronger technical support for the development of the industry.