the reactant gas to infiltrate the porous structure and also forces removal of the cracked reactant gas by products from the porous structure in all of these variants of the cvi cvd process carbon deposition is continued until a preset density is achieved for the friction material application following the densification process a final heat treatment may be performed to set the thermal mechanical and frictional properties desired for the composite a preform is manufactured totally from segments in which the continuous fibers are oriented parallel to the segment arc bisector these segments are referred to as radial segments and are depicted in fig1 needling is carried out with a conventional annular needling machine individual fabric segments are placed one at a time onto a rotating closed cell polymeric foam ring having the inside diameter and outside diameter of the annular shape of the preform being manufactured the segments are laid end to end and needled together following a helical lay up pattern to a desired weight and dimension as the preform grows in thickness it is lowered to maintain the same needle penetration depth from layer to layer the resultant preform is composed of many layers of segments that are mechanically bonded together during the needling process the foam ring is removed at the end of the performing process the resulting preform is depicted schematically in fig2 a preform was manufactured from alternating layers of 45 degree fiber oriented segments and u2212 45 degree fiber oriented segments an oxidized polyacrylonitrile fiber sold under the trade name panox by sgl was used for both the continuous fiber and the staple fiber the fabric was a duplex fabric composed of a carded needle punched staple web which had been needled to a layer of.