Unveiling the Manufacturing Process of Carbon Fiber Yarn: Key Processes and Quality Control from Raw Silk to Finished Products

Carbon fiber yarn is produced through a series of complex processes. Quality control is carried out at each stage to ensure the high - quality production of carbon fiber yarn. The following are the key processes and quality control measures from raw silk to finished products:

Key Manufacturing Processes

1. Raw Material Preparation: Usually, polyacrylonitrile (PAN) - based precursors, pitch - based precursors, or rayon - based precursors are used. PAN - based precursors are the most common due to their high carbon yield and good mechanical properties. The raw silk should have uniform quality, with consistent linear density, strength, and elongation to ensure stable production and product quality.

2. Spinning: The raw material is dissolved in a suitable solvent to form a spinning solution. This solution is then extruded through spinnerets to form filaments. In the case of PAN - based precursors, wet spinning or dry - jet wet spinning methods are often employed. The spinning process needs to precisely control parameters such as the concentration of the spinning solution, the extrusion rate, and the take - up speed to ensure the uniform diameter and structure of the filaments.

3. Stabilization: The as - spun filaments are heated in an oxidizing atmosphere to convert the linear polymer chains into a thermally stable ladder - like structure. This process is crucial as it determines the thermal stability and subsequent carbonization behavior of the fibers. The stabilization temperature, heating rate, and residence time are carefully controlled. Typically, the temperature range is from 200 to 300°C, and the heating rate is slow to ensure uniform oxidation throughout the filament.

4. Carbonization: The stabilized fibers are heated to a high temperature, usually between 1000 and 2000°C, in an inert atmosphere such as nitrogen or argon. At this stage, the non - carbon elements in the fibers are removed, and the carbon atoms are rearranged to form a graphite - like structure, resulting in a significant increase in the carbon content of the fibers. The heating rate, final temperature, and holding time in the carbonization process affect the graphitization degree and mechanical properties of the carbon fibers.

5. Surface Treatment: To improve the adhesion between the carbon fiber and the matrix material in subsequent composite applications, the surface of the carbon fiber is often treated. Common surface treatment methods include oxidation treatment (such as air oxidation, electrochemical oxidation, or plasma treatment) and sizing treatment. Oxidation treatment introduces polar functional groups on the fiber surface, while sizing treatment coats the fiber with a thin layer of sizing agent to protect the fiber and enhance its wettability by the matrix resin.

6. Winding and Packaging: The treated carbon fiber yarn is wound onto bobbins or spools for easy storage and transportation. The winding process should ensure that the yarn is wound evenly and without tangles to prevent damage to the fibers. The finished carbon fiber yarn is then packaged in suitable packaging materials to protect it from moisture, dust, and mechanical damage.

Quality Control Measures

1. Raw Material Inspection: The quality of the raw silk is strictly inspected before production. This includes testing the physical and chemical properties of the raw material, such as its molecular weight distribution, viscosity, and moisture content. Any batch of raw material that does not meet the specified standards is rejected to avoid affecting the quality of the final product.

2. In - Process Monitoring: During each production process, key process parameters are continuously monitored and controlled. For example, in the spinning process, the temperature, pressure, and flow rate of the spinning solution are monitored in real - time. In the stabilization and carbonization processes, the temperature and atmosphere are precisely controlled to ensure the consistency of the fiber structure and properties. Regular sampling and testing are also carried out to check the intermediate product quality.

3. Final Product Testing: After the carbon fiber yarn is produced, a series of comprehensive tests are conducted to evaluate its quality. This includes testing the mechanical properties such as tensile strength, modulus of elasticity, and elongation at break. The diameter and cross - sectional shape of the fibers are measured to ensure dimensional accuracy. The surface morphology and chemical composition of the fibers are also analyzed to check the effectiveness of the surface treatment. Only the carbon fiber yarn that meets all the quality standards is considered qualified for shipment and use in various applications.