| 1. Precursor Preparation | Acrylonitrile-based polymer, commonly PAN, converted into precursor dope and wet- or dry-spun filaments | Polymerization and spinning conditions vary according to polymer composition, solvent system, spinneret design, and target filament count | Polymerization vessels, dope tanks, metering pumps, spinnerets, coagulation baths, washing units, and drawing rolls | Polymer molecular weight, solution viscosity, spinning speed, draw ratio, filament linear density, and impurity level | Continuous PAN precursor tow with controlled filament count and orientation | Filament uniformity, tensile strength, elongation, denier, surface defects, and residual solvent | Stable metering, precise tension control, effective solvent recovery, and compatibility with the intended tow size |
| 2. Precursor Washing and Drying | Freshly spun PAN precursor containing residual solvent, water, and processing additives | Multiple washing and drying zones; exact temperature and residence time depend on solvent chemistry and line speed | Counter-current washing units, squeeze rolls, drying ovens, air knives, and tension-control systems | Residual solvent, moisture content, tow spread, drying temperature, line tension, and residence time | Clean, dry, and dimensionally stable precursor tow | Residual solvent, moisture uniformity, filament bonding, fuzz generation, and tow-width consistency | Low-tension conveying, uniform drying across the tow width, and closed-loop solvent or water management |
| 3. Stabilization or Oxidation | Dry PAN precursor tow | Typically approximately 200–300 °C in an oxidizing atmosphere; the tow is heated gradually to prevent runaway exothermic reactions | Multi-zone stabilization ovens, air-circulation systems, tow guides, exhaust treatment, and temperature-control systems | Temperature profile, oxygen availability, residence time, tow tension, oven uniformity, and exotherm control | Infusible, thermally stabilized PAN fiber with a ladder-like molecular structure | Stabilization index, density, shrinkage, color uniformity, tensile retention, and cross-sectional consistency | Independent zone control, reliable exhaust handling, even airflow, fire protection, and accurate tension regulation |
| 4. Low-Temperature Carbonization | Stabilized PAN fiber | Usually about 800–1,000 °C in an inert atmosphere such as nitrogen | Inert-atmosphere carbonization furnaces, gas-sealing systems, high-temperature rolls, cooling sections, and off-gas treatment | Furnace temperature, nitrogen flow and purity, residence time, line tension, furnace pressure, and off-gas composition | Carbon fiber with increased carbon content and reduced non-carbon elements | Tensile strength, modulus, density, electrical resistivity, tow integrity, and surface cleanliness | Uniform heat distribution, controlled oxygen exclusion, low tow breakage, efficient inert-gas use, and safe off-gas handling |
| 5. High-Temperature Carbonization | Partially carbonized fiber | Commonly approximately 1,200–1,600 °C under inert conditions, depending on the required fiber grade | High-temperature furnaces, graphite or ceramic hot zones, inert-gas systems, tension stands, and cooling chambers | Peak temperature, temperature uniformity, gas purity, tow tension, residence time, and furnace atmosphere | High-strength carbon fiber with a more developed turbostratic carbon structure | Strength, modulus, density, filament breaks, fuzz level, electrical resistance, and batch consistency | Stable high-temperature operation, low contamination, precise tension control, heat recovery, and maintainable hot-zone components |
| 6. Graphitization, When Required | Carbonized fiber intended for high-modulus or specialized grades | Approximately 2,000–3,000 °C in an inert atmosphere; not required for every carbon-fiber product | Graphitization furnace, graphite hot zone, inert-gas purification, high-temperature power supply, and cooling system | Maximum temperature, residence time, fiber tension, gas purity, electrical power stability, and hot-zone condition | Higher-modulus carbon fiber with increased graphitic ordering | Modulus, tensile strength, density, electrical conductivity, structural uniformity, and surface condition | High-temperature capability, power efficiency, hot-zone service life, precise tow handling, and contamination control |
| 7. Electrochemical or Controlled Surface Treatment | Carbonized or graphitized fiber | Aqueous electrochemical treatment is commonly used; current density, bath chemistry, and treatment time are product-specific | Electrochemical cells, electrolyte circulation, anodes and cathodes, washing units, conductivity meters, and drying sections | Surface-treatment intensity, bath concentration, pH, conductivity, temperature, residence time, and tow tension | Fiber surface with improved compatibility and interfacial bonding with a selected resin system | Surface oxygen functionality, wettability, interfacial shear strength, tensile retention, and treatment uniformity | Uniform treatment across the tow, accurate bath control, low fiber damage, wastewater management, and resin-specific compatibility |
| 8. Washing and Drying After Treatment | Surface-treated carbon fiber containing residual electrolyte and moisture | Controlled rinsing followed by drying at a temperature that avoids fiber damage and excessive finish degradation | Rinsing tanks, dewatering rolls, dryers, conductivity sensors, wastewater-treatment equipment, and tension controls | Rinse-water conductivity, residual ions, moisture, drying temperature, tow spread, and line tension | Clean, dry, surface-treated carbon fiber ready for sizing | Residual ionic contamination, moisture, surface energy, filament cohesion, and mechanical-property retention | Efficient water use, stable rinse quality, closed-loop monitoring, and minimal tow abrasion |
| 9. Sizing Application | Carbon fiber and a resin-compatible sizing formulation, often aqueous or solvent-based | Application concentration and drying conditions are matched to the target matrix resin and end use | Immersion or kiss-coater, sizing bath, metering rolls, drying oven, circulation system, and concentration-control equipment | Sizing add-on level, bath concentration, viscosity, temperature, pickup uniformity, and drying profile | Carbon fiber with improved handling, filament protection, and matrix-resin compatibility | Sizing percentage, uniformity, fuzz, tensile strength, interfacial performance, and resin wet-out | Accurate low-add-on application, formulation flexibility, clean bath circulation, and repeatable drying |
| 10. Spreading, Winding, and Packaging | Finished sized carbon-fiber tow | Controlled winding tension and package density; packaging format depends on tow size and customer process requirements | Tow spreaders, tension controllers, traversing winders, package-build systems, weighing equipment, and protective packaging stations | Winding tension, package width, winding speed, package density, tow alignment, and splice frequency | Commercial packages such as continuous tow, bobbins, or larger industrial packages | Package geometry, net weight, tow continuity, fuzz, winding defects, labeling, and traceability | Low-tension handling, accurate package formation, automated inspection, barcode traceability, and flexible packaging formats |
| 11. Final Inspection and Release | Packaged carbon-fiber product | Testing follows internal specifications and applicable customer or international methods | Universal testing machines, density and electrical-resistance instruments, microscopy, sizing-analysis equipment, and laboratory data systems | Tensile strength, tensile modulus, elongation, density, sizing content, electrical resistance, and visual quality | Released product with a documented certificate of analysis and production traceability | Lot-to-lot consistency, statistical process control, defect rate, test repeatability, and customer-specification compliance | Integrated laboratory information systems, calibrated instruments, sampling discipline, and complete batch genealogy |