Process for Carbon-Carbon Composite Fabrication.
Patent, Filed 16 Apr 86, patented 17 May 88,
DEPARTMENT OF THE AIR FORCE WASHINGTON DC
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A fabrication process is disclosed that achieves a higher density carbon-carbon article, than the prior art processes by maintaining a vertical temperature gradient in a reservoir of pitch e.g. 550 C. at the bottom to 250 C. at the top into which a carbon fiber preform is immersed. The use of the vertical temperature gradient results in a reservior of hot fluid pitch around the upper end of the preform during pitch impregnation of the preform. This permits the fluid pitch to drain down by gravity into the interstices of the carbon fiber and the hardening pitch below. The next step of the process involves gradually increasing the pitch-hardening temperature from bottom to top to harden the pitch from bottom to top. Thereafter, the impregnated preform is carbonized at high temperature. This method takes advantage of the thermal conductivity of the carbon fibers and does not require extremely high pressures. In fact, a high pressure would be a detriment since it results in closed pores. The process of the present disclosure depends on the development of large, connected pores that can be more easily filled. This manner results in the production of suitable carbonized billets in a fraction of the time currently required and using much less energy.
- Laminates and Composite Materials