1 - Acta Technica Corviniensis

Figure 3. Materials evolutionThe properties and price of carbon fibers alsoencompass a broad territory. With the pricedecreasing of the higher filament numbered (higherthan 24K), carbon tows produced for commercialusage, the greater volume and the wider industrialusage came to prominence and this tendency,expectedly, will continue.The Carbon Fiber is made mostly (approx; 95 %) from asynthetic fiber well known in the textile industry,namely PAN (Polyacrylonitrile), and it is so calledprecursor fiber (Figure 4), whereas the raw material ofthe remaining 5 % is either tar or regenerated fibers.ACTA TECHNICA CORVINIENSIS – Bulletin of Engineeringfrom the fiber, while its chemical structure changes.The OPAN fiber (approximate with 62% of carboncontent) formed after oxidation, becomes a textilematerial having excellent heat, flame and fire resistantproperties, which after various textile industryoperations (Stretch ‐ Breaking, Carding, Spinning,Weaving, Knitting, or in Tow / Staple fiber form usingnon‐woven methods) may be further processed.Products’ made from OPAN do not melt, have a highLOI value (40‐60), its heat resistance is above (300 ⁰C),and because of this, they are mainly used in areaswhere heat, fire resistance, heat insulation (weldingblankets, protective clothing, etc.) is required. Duringthe oxidation process, a crust forms on the surface ofthe OPAN fiber, and because of this, its loop tenacity islow (8‐15% of the tensile strength), thusly the fiber isbrittle. By increasing of the temperature andprocessing time, the density of OPAN fiber (ρ=1.35‐1.42g/cm³) can also be increased, and with this, heatresistance of the material can be augmented, but thefiber will be more rigid. Although OPAN and carbonfibers are both black, their other properties arebasically different (Figure 6.).Figure 4. Manufacturing processof carbon fibers (PAN‐based)The PAN precursor based oxidized fiber (OPAN),carbon and graphite fiber production process is welldepicted in Figure 5.Figure 6. Properties of OPAN and carbon fibersOPAN products processed by textile industry methodsand then carbonized can be used in a variety of uniqueapplications.In the hydrogen driven electrical transformer, thecarbon membrane allows the protons to pass throughwhile by separating the electrons, electric current isgenerated.In the case of sodium‐sulphur electrical energy storing,the sulphur is stored in the carbonized OPANmembrane sponge.In the C‐C composite technology, the thick felt madefrom OPAN is carbonized at high temperature and theC is diffused into the material. From the thuslycreated, compact structured CandC compositematerial, high temperature 1000 ⁰C bearing, aircraftand racing car brake discs and brake pads are made.In the manufacturing of carbon fiber, by leading thepre‐tensioned fibers exiting from the oxidation oveninto high temperature (800‐1500 ⁰C) nitrogen gasblanketed ovens, the structure of the carbon fiber isformed (Figure 7).Figure 5. The oxidation, carbonizationand graphitisation processThe OPAN fiber is produced by oxidizing themoderately stretched PAN fiber at 220‐250 ⁰C. In theprocess of the oxidation, taking several hours, most ofthe burnable gases and toxic materials are exhausted54Figure 7. Structure of carbon fiber2012. Fascicule 3 [July–September]