Plastic and nonmetallic article shaping or treating: processes – Carbonizing to form article – Controlling varying temperature or plural heating steps
Patent
1999-03-25
2000-10-10
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Carbonizing to form article
Controlling varying temperature or plural heating steps
4234472, 4234478, C01B 3102
Patent
active
061298689
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to the rapid fabrication of high density carbon-carbon composites or preforms used for friction materials and thermal management systems for automotive and aerospace applications.
BACKGROUND OF THE INVENTION
One way to improve the production efficiency of carbon-carbon composite materials is the development of processes which take advantage of the benefits of pitch matrix precursors. The main advantages of pitch matrices reside in their high carbon content (90% and more), relatively short process steps, as well as specific material properties resulting from their high graphitizability, which provide high thermal conductivity, density and good friction and wear performance.
It is highly desirable to provide rapidly a preform or composite with high density (1.2 g/cm.sup.3 and above) prior to densification by conventional precursor carbon methods: carbon vapor deposition or densification ("CVD") and also called carbon vapor infiltration ("CVI"), pitch or resin and their combinations.
SUMMARY OF THE INVENTION
The present invention provides solutions to the above by providing a method of producing rapidly a carbon-carbon composite made from a green preform comprising carbon fibers and at least one pitch, comprising the steps of: C., then increasing the temperature at a lesser rate up to approximately 520.degree. C.; 450-520.degree. C. for a period of time; C.-1,000.degree. C. followed by a soak; and
We have disclosed a thermomechanical pressing ("TMP") method for obtaining rapidly a carbon/carbon composite material using any carbon fiber including polyacrylonitrile ("PAN") based carbon fibers and industrial coal-tar or petroleum pitches (including synthetic derivatives) having a melting point m.p.=80-350.degree. C. Generally, a green preform may be prepared from mixtures of chopped carbon fibers and pitch, for example a mixture prepared from 1 part by weight of carbon fibers chopped to the length of Lf=10-50 mm and 1-3 parts by weight of pitch. The resulting mixture is pressed to impart a cylindrical shape to the green preform. The green preform is charged into a metallic mold where it is heated, pressurized, stabilized, and cooled.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in detail below with reference to the drawings in which:
FIG. 1 is a graph of the thermal decomposition of coal tar petroleum pitches and mixtures;
FIG. 2 is a graph of the thermal decomposition of pitches and low temperature carbon fiber mixtures;
FIG. 3 is a graph of the thermal decomposition of pitches and high temperature carbon fiber mixtures; and
FIG. 4 is a graph of the temperature/pressure/time profile used during the TMP process.
DETAILED DESCRIPTION OF THE INVENTION
Among processes for improving the production efficiency of pitch-based carbon-carbon composite materials, we think it expedient, with regard to the requirements for friction materials, to use thermal stabilization methods in combination with a forced mechanical contraction or pressing of the material during pyrolysis. The method developed is referred to as thermomechanical pressing ("TMP").
A pitch matrix and PAN fiber reinforcement were chosen for the TMP process. At present, commercially produced coal tar pitches have softening points Ts=65-75.degree. C. and Ts=135-140.degree. C. and toluene insolubles (.alpha.-fraction) content of 20-25 wt. % and 45-54 wt. %, respectively, for medium and high-temperature pitches.
Medium pitches enable the preparation of high-quality "green" bodies with a low coke yield. High-temperature pitches have a higher coke residue of about 55-60%, but their use presents difficulties because at temperatures of 120-280.degree. C. they do not wet carbon substrates thus preventing the use of conventional methods to press "green" bodies.
Therefore, it is of interest to determine if an industrial petroleum pitch with Ts=140.degree. C. can be used in TMP processes. Such pitches have coke residue somewhat lower than a high-temperature coal tar pitch, but considerably higher than a
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Demin Aleksandr Viktorovich
Kostikov Valery Ivanovich
Kulakov Innokentii Victorovich
Penkov Igor Alexandrovich
Allied-Signal Inc.
Palguta Larry J.
Tentoni Leo B.
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