Process for producing hollow bodies comprising fiber-reinforced ceramic materials
Process for producing hollow bodies comprising fiber-reinforced ceramic materials, where mold cores whose shape corresponds to that of the hollow spaces are produced in a first step, at least one mold core together with a press moulding composition or formable fiber composition are introduced into a mold, where the press moulding composition comprises carbon fibers and/or carbon filaments and thermally curable carbonizable binders, in such a way that the position of the cores corresponds to the desired position of the hollow spaces to be formed in a second step, the composition is cured in a third step by heating to a temperature of from 120° C. to 280° C., to give a green body, the strengthened green body is carbonized and or graphitized in a fourth step by heating in a nonoxidizing atmosphere to a temperature of from about 750° C. to about 2400° C. to form a C/C body, wherein heating in the third and/or fourth step is at least partly effected by an electric current being passed through the pressable composition or the green body and through at least one mold core, hollow bodies produced in this way and their use for producing clutch disks or brake disks, in particular for automobiles
1. A process for producing hollow bodies comprising fiber-reinforced ceramic materials, where
mold cores whose shape corresponds to that of the hollow spaces are produced in a first step,
at least one mold core together with a press moulding composition or formable fiber composition are introduced into a mold, where the press moulding composition comprises carbon fibers and/or carbon filaments and thermally curable carbonizable binders, in such a way that the position of the cores corresponds to the desired position of the hollow spaces to be formed in a second step,
the composition is cured by heating to a temperature of from 120° C. to 280° C., if appropriate under pressure, in a third step to form a green body,
the cured green body is carbonized and/or graphitized in a fourth step by heating in a nonoxidizing atmosphere to a temperature of from about 750° C. to about 2400° C. to give a C/C body,
wherein heating in the third and/or fourth step is at least partly effected by an electric current being passed through the pressable composition or the green body and through at least one mold core.
2. The process as claimed in claim 1 , wherein, subsequent to the fourth step,
the C/C body is infiltrated with liquid metal in a fifth step, with at least partial reaction of the carbon present in the matrix of the C/C body with the metal to form carbides.
3. The process as claimed in claim 2 , wherein the liquid metal used is silicon or a silicon alloy.
4. The process as claimed in claim 1 , wherein the electrical conductivity of the press moulding composition or formable fiber composition is above 0.1 S/m.
5. The process as claimed in claim 1 , wherein the electrical conductivity of the green body is in the range from 0.1 to 50 S/m.
6. The process as claimed in claim 1 , wherein the electrical conductivity of the mold cores is in the range from 0.1 to 100 times the conductivity of the press moulding composition, the formable fiber composition or the green body.
7. An electrically conductive mold core comprising polymers for producing hollow bodies comprising fiber-reinforced composites, wherein the mold cores contain a volume fraction of at least 5% of electrically conductive fibers and/or electrically conductive particles and have an electrical conductivity of at least 0.01 S/m.
8. A mold core as claimed in claim 7 , wherein the electrically conductive fibers are selected from the group consisting of carbon fibers, graphite fibers, carbon-coated fibers, metal fibers, metal turnings and metal whiskers.
9. A mold core as claimed in claim 7 , wherein the electrically conductive particles are selected from the group consisting of carbon particles, graphite particles, carbon black, metal grains, metal powder, metal flakes and metal grit.