Manufacture of carbon/carbon composites by hot pressing
A mixture of carbon-containing fibers, such as mesophase or isotropic pitch fibers, and a suitable matrix material, such as a milled pitch, is compressed while resistively heating the mixture to form a carbonized composite material having a density of about 1.5 g/cm 3 , or higher. The composite material is formed in under ten minutes. This is a significantly shorter time than for conventional processes, which typically take several days and achieve a lower density material. Consequently, carbon/carbon composite materials having final densities of about 1.6-1.8 g/cm 3 , or higher are readily achieved with one or two infiltration cycles using a pitch or other carbonaceous material to fill voids in the composite and rebaking.
1 .- 21 . (Canceled)
22 . An apparatus for forming a compressed composite material comprising:
a vessel which defines a cavity for receiving composite material to be treated;
a means for applying pressure which applies a pressure of at least 35 kg/cm 2 to the material in the cavity;
a source of electric current which applies a current to the material, the current flowing through the material to resistively heat the material;
a temperature detector which detects the temperature of the material; and
a control system which controls the pressure applying means and source of electrical current such that the mixture is sequentially heated at a first temperature and pressed at a first pressure for a first period of time, and heated at a second temperature higher than the first temperature and at a second pressure higher than the first pressure for a second period of time.
23 . (Canceled)
24 . The apparatus of claim 22 , wherein the means for applying pressure comprises a first piston positioned to engage the material within the vessel.
25 . The apparatus of claim 24 , wherein the means for applying pressure comprises a second piston positioned opposite the first piston.
26 . The apparatus of claim 22 , wherein the source of electric current operative engages the material through the means for applying pressure.
27 . The apparatus of claim 22 , further comprising insulation positioned around the vessel.
28 . The apparatus of claim 22 , further comprising a pressure sensor operatively attached to the pressure applying means and the control system to indicate the presence of the first pressure and the second pressure within the vessel.
29 . The apparatus of claim 28 , wherein the pressure sensor is a displacement sensor relaying the displacement of the pressure applying means to the control system.
30 . An apparatus for forming a compressed composite material comprising:
a holding area shaped to receive the material;
a first pressure element positioned to engage the material to apply pressure to the material in a first direction; and
a source of electric current operatively engaging the first pressure element to apply a current to the material through the first pressure element to resistively heat the material.
31 . The apparatus of claim 30 , further including a second pressure element positioned to engage the material to apply pressure to the material in a second direction.
32 . The apparatus of claim 31 , wherein the first pressure element is positioned opposite the second pressure element.
33 . The apparatus of claim 31 , wherein the source of electric current operatively engages the second pressure element to apply a current to the material through the second pressure element to resistively heat the material.
34 . The apparatus of claim 30 , further comprising a control system operatively connected to the holding area, the first pressure element, and the source of electric current to regulate the pressure and the electrical current in the material.
35 . The apparatus of claim 34 , wherein the control system controls the source of electric current and the first pressure element to sequentially heat the material at a first temperature and press the material to a first pressure for a first period of time and heat the material at a second temperature higher than the first temperature and press the material at a second pressure higher than the first pressure for a second period of time.
36 . The apparatus of claim 34 , further comprising a temperature monitoring device operatively connected to the material and the control system to relay the temperature of the material to the control system.
37 . The apparatus of claim 34 , further comprising a pressure monitoring device operatively connected to the material and the control system to relay the pressure of the material to the control system.
38 . The apparatus of claim 30 , wherein the holding area includes sides and each side is substantially shaped as a parallelogram.
39 . An apparatus for forming a compressed composite material comprising:
a holding area shaped to receive the material;
a first pressure element positioned to engage the material to apply pressure to the material in a first direction;
a second pressure element positioned opposite the first pressure element to engage the material to apply pressure to the material in a second direction;
a source of electric current operatively engaging the first and second pressure elements to apply a current to the material through the first and second pressure elements to heat the material; and
a control system operatively connected to the first pressure element, the second pressure element, and the source of electric current to regulate the pressure and electrical current in the material.
40 . The apparatus of claim 39 , wherein the control system controls the source of electric current and the first and second pressure elements to sequentially heat the material at a first temperature and press the material to a first pressure for a first period of time and heat the material at a second temperature higher than the first temperature and press the material at a second pressure higher than the first pressure for a second period of time.
41 . The apparatus of claim 40 , further comprising:
a temperature monitoring device operatively connected to the material and the control system to relay the temperature of the material to the control system; and
a pressure monitoring device operatively connected to the material and the control system to relay the pressure of the material to the control system.
42 . The apparatus of claim 41 , further including insulation positioned around the holding area.