Method of making carbon fibers and resin-impregnated carbon fibers

A method of making carbon fibre, comprising passing a multifilament commercial heavy tow of fibres formed of an acrylonitrile polymer or copolymer through an initial heating stage at a temperature in the range of from 100.degree. to 160.degree. C whilst holding it under sufficient tension to remove crimp and to stretch the fibres by up to 75%;

• passing the thus heated and stretched multifilament heavy tow through a pre-heat zone maintained at a temperature at least 100.degree. C below the critical temperature of the fibres;
• passing the thus pre-heated multifilament heavy tow through an oxygenation zone comprising at least two stages, a first stage in which the multifilament heavy tow is contacted with an oxygenation medium selected from the group consisting of oxygen and oxygen-containing gases, gradually heated up to a first temperature in the range of from 220.degree. to 250.degree. C, at which the fibres are able to take up oxygen without degradation and maintained at that temperature, and a second stage in which the partly oxygenated multifilament heavy tow of fibres is further heated in the presence of an oxygenation medium to a second higher temperature, in the range of from 260.degree. to 300.degree. C, and is maintained at that second temperature, the multifilament heavy tow of fibres passing straight through each stage of the oxygenation zone without a change in direction within either of such stages, the fibres being held under sufficient uniform tension within the oxygenation zone to stretch the fibres by at least 50% during heating and oxygenation;
• and thereafter passing the multifilament tow of oxygenated fibres through a carbonizing zone comprising at least one stage in which the multifilament heavy tow of fibres is heated to a third elevated temperature in the range of from 1050.degree. to 1600.degree. C under non-oxidizing conditions to yield a fibre with a mean Young's modulus of at least 25 .times. 10.sup.6 p.s.i. and a mean tensile strength of at least 250,000 p.s.i.