Rotary Tube Furnace Applications in Activation and Carbonization of High-Performance Carbon Fibers

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Rotary Tube Furnace Applications in Activation and Carbonization of High-Performance Carbon Fibers

High-performance carbon fibers, renowned for their exceptional properties such as high strength, high modulus, and lightweight, have become crucial materials in fields like aerospace, new energy, and high-end equipment manufacturing. In their production process, carbonization and activation are the core steps that determine the final performance of the fibers. The rotary tube furnace, with its advantages of uniform temperature distribution, consistent material heating, and strong continuous production capacity, has emerged as the key equipment for these steps. This article systematically analyzes the working principles, technical advantages, and application prospects of rotary tube furnaces in the carbonization and activation processes of high-performance carbon fibers.

1. Process Fundamentals: The Core Role of Carbonization and Activation in Carbon Fiber Production
In the full-scale production of high-performance carbon fibers (from precursor spinning to final surface treatment), carbonization and activation are the critical steps that enable the transformation from "organic fibers to inorganic high-performance fibers". These two processes are functionally complementary and closely connected in terms of process logic.

1.1 Carbonization Process: Building the Basic Structural Framework of Carbon Fibers
Carbonization is a pyrolysis process where pretreated precursors (such as PAN-based or pitch-based precursors) are heated in an inert atmosphere (typically nitrogen or argon) within a temperature range of 400-1200°C. Its core objective is to gradually remove non-carbon elements (e.g., H, O, N, which are released as gases like H₂O, CO₂, and NH₃) from the precursors, thereby enriching carbon elements and forming a graphite-like microcrystalline structure—the structural foundation that endows carbon fibers with high strength and high modulus.

During this process, the linear molecular chains of the precursors undergo cyclization, dehydrogenation, and cross-linking reactions, eventually transforming into carbonized fibers with a carbon content exceeding 90%. If the temperature is further increased to 1500-3000°C (a process known as "graphitization"), the arrangement of microcrystals can be further optimized to enhance the fiber modulus. However, the heating rate must be strictly controlled to avoid structural defects.

1.2 Activation Process: Endowing Carbon Fibers with High Specific Surface Area and Functionality
The activation process is usually carried out after carbonization. Its purpose is to create a porous structure on the surface of carbonized fibers through physical or chemical means, increasing their specific surface area (from 1-10 m²/g after carbonization to 500-2000 m²/g) to meet the requirements of applications such as adsorption, catalysis, and energy storage.

Based on the type of activation medium, activation can be divided into physical activation (e.g., using CO₂ or H₂O vapor) and chemical activation (e.g., using reagents like KOH or H₃PO₄). Among these, physical activation is more suitable for the functional modification of high-performance carbon fibers due to its environmentally friendly process and high product purity. The rotary tube furnace, with its characteristics of "continuous introduction of activation medium + uniform heating", has become the preferred equipment for physical activation.

2. Equipment Characteristics of Rotary Tube Furnaces: Core Advantages Adapted to Carbon Fiber Processes
Compared with traditional box furnaces and pusher furnaces, rotary tube furnaces exhibit irreplaceable advantages in the carbonization and activation processes of carbon fibers, and their design principles are highly compatible with process requirements.

2.1 Temperature Uniformity: Ensuring Consistency in Fiber Performance
High-performance carbon fibers are extremely sensitive to temperature—local temperature fluctuations exceeding ±5°C can lead to uneven arrangement of microcrystals inside the fibers, thereby causing differences in strength. Rotary tube furnaces achieve temperature uniformity through the following designs:
Heating Method: Multi-stage resistance heating or induction heating is adopted, with each heating zone controlled independently. The axial temperature deviation of the furnace tube can be controlled within ±2°C;
Furnace Tube Rotation: The furnace tube rotates slowly at a speed of 5-20 r/min, driving the fiber materials (or fiber bundles) to continuously tumble, avoiding local overheating or insufficient heating;
Insulation Structure: The furnace lining is made of high-purity alumina or zirconium-containing ceramic fibers, which reduces heat loss and prevents fiber contamination caused by coking on the furnace wall.

2.2 Atmosphere Control: Meeting Inert/Activation Environment Requirements
Carbonization requires a strictly inert atmosphere (oxygen content < 100 ppm to avoid fiber oxidation), while activation demands precise control of the concentration and flow rate of the activation medium. Rotary tube furnaces achieve precise atmosphere control through "sealing + airflow design":
Sealing System: Both ends of the furnace tube adopt double-end mechanical seals or magnetic fluid seals, with an air leakage rate < 0.1%/h, ensuring no leakage of inert gas or activation medium;
Airflow Distribution: The activation medium (e.g., CO₂) is uniformly introduced through a porous distributor at one end of the furnace tube, making full contact with the rotating fibers to avoid local over-activation;
Exhaust Gas Treatment: The other end of the furnace tube is connected to an exhaust gas cooling and absorption device, which treats harmful substances such as tar and NH₃ generated during carbonization and recovers unreacted activation medium.

2.3 Continuous Production: Improving Process Efficiency and Stability
The industrial production of high-performance carbon fibers needs to balance "high quality" and "high productivity", and the continuous production characteristics of rotary tube furnaces perfectly meet this demand:
Feeding/Discharging Design: One end of the furnace tube continuously feeds precursors or carbonized fibers through a screw feeder, and the other end continuously discharges products through a sealed discharge port, realizing the full-process continuity of "feeding - heating - reaction - discharging". The daily output of a single device can reach several hundred kilograms;
Process Controllability: By adjusting the furnace tube rotation speed, feeding rate, and temperature curve, the residence time of fibers in the furnace can be precisely controlled (usually 30-60 minutes for carbonization and 60-120 minutes for activation), avoiding performance fluctuations in batch production.

3. Conclusion and Outlook
With its advantages of uniform temperature, controllable atmosphere, and continuous production, the rotary tube furnace has become the core equipment for the carbonization and activation processes of high-performance carbon fibers. The precise control of its process parameters (such as heating rate and activation medium concentration) directly determines the mechanical properties and functional characteristics of the fibers. Technological innovations targeting issues such as furnace tube wear and high energy consumption will further promote its application in the production of high-end carbon fibers.

In the future, as the demand for high-performance carbon fibers in aerospace, new energy, and other fields continues to grow, rotary tube furnaces will develop towards "higher temperature control accuracy (within ±1°C), better atmosphere tightness (air leakage rate < 0.05%/h), and more intelligent automatic control (realizing parameter adaptive adjustment by combining AI algorithms)", providing key equipment support for the high-quality development of the carbon fiber industry.

Zhengzhou Protech Technology Co.,LTD is a professional manufacturer specializing in tube furnaces, muffle furnaces, atmosphere furnaces, and vacuum furnaces. We are committed to providing targeted solutions to meet your diverse heating equipment needs.
For customized heating solutions tailored to your specific requirements, feel free to get in touch with us:
WhatsApp: +86 17719806024
Email: info@lab-furnace.com

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Rotary Tube Furnace Applications in Activation and Carbonization of High-Performance Carbon Fibers

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