Process for producing shaped bodies of carbon fiber reinforced carbon and shaped body produced by the process

Abstract

A process is provided for producing shaped bodies including carbon fiber reinforced carbon in which the fibers are present in the form of bundles having a defined length, width and thickness. The defined configuration of the fibers in the bundles allows a targeted configuration of the reinforcing fibers in the carbon matrix and thus a structure of the reinforcement which matches the stress of shaped bodies including carbon fiber reinforced carbon, for example brake disks. A shaped body produced according to the invention is also provided.

1 . A process for producing shaped bodies having a carbon matrix reinforced with carbon fiber bundles, the process comprising the following steps:
 producing or providing bundles of parallel carbon fibers held together by a dimensionally stable cured, carbonizable binder, with the bundles having a specifically set, defined uniform length, width and thickness;   producing a molding composition by mixing the fiber bundles, a carbonizable matrix former and optional auxiliaries;   producing a green body being close to a final shape by pressing the molding composition in a mold being close to the final shape at elevated temperature with curing of the carbonizable matrix former, and subsequent demolding;   carbonizing the green body to form a carbonized shaped body;   mechanically re-working the carbonized shaped body, if necessary; and   densifying the carbonized shaped body by deposition of a carbon matrix in a chemical vapor infiltration (CVI) process.   
   
   
       2 . The process according to  claim 1 , which further comprises:
 carbonizing the binder in the fiber bundles produced or provided in the step of producing or providing bundles of parallel carbon fibers; and   re-impregnating the fiber bundles with a carbonizable matrix former in a mechanically generated fluidized bed before the step of producing the molding composition.   
   
   
       3 . The process according to  claim 1 , wherein the production of the fiber bundles includes the following steps:
 impregnating at least one roving, including a plurality of parallel carbon fiber filaments, with a carbonizable binder to yield a prepreg;   pressing at least one impregnated roving or a plurality of parallel impregnated rovings to form a laminate sheet including parallel filaments (UD laminate) and having a defined thickness, combined with curing of the binder by heat treatment to yield a dimensionally stable laminate sheet of defined thickness; and   cutting the (UD) laminate sheet, which may have been separated into individual bands, to yield segments of fiber bundles of defined width and length.   
   
   
       4 . The process according to  claim 1 , which further comprises setting a thickness of the fiber bundles to a value in a range of from 0.15 to 0.4 mm, setting a length of the fiber bundles to a value in a range of from 6 to 15 mm, and setting a width of the fiber bundles to a value in a range of from 0.5 to 3.5 mm. 
   
   
       5 . The process according to  claim 4 , which further comprises setting the width of the fiber bundles at 1 mm. 
   
   
       6 . The process according to  claim 1 , wherein the carbonizable matrix former is a phenolic resin. 
   
   
       7 . The process according to  claim 1 , wherein a proportion by mass of the fiber bundles in the molding composition is from 70 to 80%. 
   
   
       8 . The process according to  claim 1 , wherein the molding composition contains not more than 10% by mass of the auxiliaries. 
   
   
       9 . The process according to  claim 8 , which further comprises providing at least one of the following auxiliaries:
 tribological auxiliaries such as silicon carbide,   oxidation-inhibiting auxiliaries, such as zirconium carbide, tantalum carbide or tantalum boride.   
   
   
       10 . The process according to  claim 1 , which further comprises introducing the molding composition into the mold through a charging grate causing the fiber bundles to assume an alignment determined by the charging grate. 
   
   
       11 . The process according to  claim 1 , which further comprises producing the green body with a mold being close to the final shape at a pressure in a range of from 1.5 to 5 N/mm 2  and a temperature of from 120 to 200° C. in a hot molding press. 
   
   
       12 . The process according to  claim 1 , wherein the carbonized shaped body is re-impregnated with a carbonizable matrix former and then carbonized again before the chemical vapor infiltration (CVI) process. 
   
   
       13 . The process according to  claim 12 , which further comprises using a resin or pitch as the carbonizable matrix former for the re-impregnation of the carbonized shaped body. 
   
   
       14 . The process according to  claim 1 , which further comprises using methane as a carbon donor in the chemical vapor infiltration (CVI) process. 
   
   
       15 . The process according to  claim 1 , wherein the shaped body is a brake disk. 
   
   
       16 . The process according to  claim 15 , which further comprises introducing the molding composition into the mold through a charging grate containing a plurality of concentric rings causing the fiber bundles to assume a tangential alignment. 
   
   
       17 . A shaped body, comprising:
 carbon reinforced with carbon fiber bundles and a carbon matrix including a pyrolysis residue of a carbonizable matrix former and carbon deposited by chemical vapor infiltration (CVI);   said carbon fiber bundles having specifically set, defined uniform dimensions, with a thickness of said bundles being set to a value in a range of from 0.15 to 0.4 mm, a length of said bundles being set to a value in a range of from 6 to 15 mm, and a width of said bundles being set to a value in a range of from 0.5 to 3.5 mm, and said carbon fiber bundles having carbon fibers aligned parallel to one another.   
   
   
       18 . The shaped body according to  claim 17 , wherein said width of said fiber bundles is 1 mm. 
   
   
       19 . The shaped body according to  claim 17 , wherein said fiber bundles have a random orientation. 
   
   
       20 . The shaped body according to  claim 17 , wherein said fiber bundles are aligned according to a loading direction of the shaped body. 
   
   
       21 . The shaped body according to  claim 17 , wherein the shaped body is a brake disk in which said fiber bundles are disposed tangentially.