Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation is a lubricant or a surface friction...
Reexamination Certificate
1998-12-17
2001-07-03
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation is a lubricant or a surface friction...
C442S136000, C442S140000, C442S148000, C442S179000, C428S293400, C523S149000, C523S157000
Reexamination Certificate
active
06255234
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to low friction, wear resistant materials and is particularly directed to a carbon-carbon composite material, and method of preparation therefor, which is characterized by an ultra low coefficient of friction over a wide temperature range, including high temperature regimes.
BACKGROUND OF THE INVENTION
Materials that exhibit low friction are needed in a variety of applications such as bearings, seals and the like. Composites of nickel oxide and calcium fluoride or zinc oxide, stannous oxide and calcium fluoride are currently under investigation for use in low friction applications. These materials have friction coefficients of approximately 0.6 and service lives of only 500 hours. There is therefore a need to develop materials that exhibit the characteristics of a low coefficient or friction, low wear, and high temperature operating capabilities. Conventional materials such as those comprised of carbon generally have good tribological properties at low temperatures, but tend to become easily graphitized and lose their low coefficient of friction at higher temperatures.
Carbon/carbon composites in which a carbon matrix is reinforced with carbon fiber is one form of these conventional carbon materials. The initial use of these materials was in providing thermal barriers in aerospace vehicles. Such applications are based on the very high temperature capability, i.e., at temperatures up to 5400° F. (3000° C.), of these carbon/carbon composites. At the present time, the major use of carbon/carbon composites is in aircraft brakes with approximately 85% of total carbon carbon/composite production targeted toward this market sector. Previously known properties of carbon/carbon composites which make them an ideal candidate for aircraft brakes are: (1) high coefficient of friction (in the range of 0.4-0.5); (2) high temperature capability; and (3) low weight.
The present inventors have developed a novel use and application for modified carbon/carbon composite materials, which makes use of heretofore unknown characteristics of a specialized class of carbon-carbon materials in applications requiring very low friction and very high wear resistance. These characteristics, coupled with the high temperature capability of the carbon/carbon composite, make this material particularly adapted for use in applications such as bearings, seals and virtually any component or element which engages another body in a frictional manner.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a material which affords excellent high temperature lubrication and high wear resistance to sliding surfaces.
It is another object of the present invention to provide a carbon/carbon composite material which exhibits exceptional slipperiness particularly at elevated temperatures making the material particularly adapted for use in seals, bearings, shafts, flexible joints, and in virtually any component which engages and slides or rotates in contact with another component or body.
It is another object of the present invention to provide a material having a lubricating surface with high integrity and which exhibits low friction and wear, good chemical and dimensional stability, and high temperature operating capability.
In one embodiment, this invention contemplates a method for forming a low friction component for use at high temperatures comprising the steps of impregnating a sheet-like carbon fiber reinforcement material with a phenolic resin or pitch; forming a laminated panel with sheets of the impregnated carbon fiber reinforcement material; forming the laminated panel into a component such as a seal, a bearing, a shaft, a flexible joint, or the like; heating the component in an inert atmosphere at an elevated temperature to carbonize the component by converting the phenolic resin or pitch to carbon, wherein the carbonized component is porous and of low density; densifying the carbonized component by depositing carbon in the pores of the component; and heating the densified carbonized component in an inert atmosphere for graphitizing and removing impurities from the component, wherein the component has a coefficient of friction in the range of 0.022 to 0.11, preferably 0.04 to 0.1, and is capable of operating at temperatures greater than 930° F. (500° C.).
The present invention therefore provides a carbon/carbon composite component adapted for high operating temperature use in a frictional operation wherein said component engages and moves relative to a body, wherein said component has a coefficient of friction in a range of about 0.022 to about 0.11 within an operating temperature range of 70° F. to 1000° F.; and wherein said component comprises a pyrolyzed composite of a carbon fiber reinforced densified carbon matrix, having a final fiber volume of from about 30 volume percent to about 70 volume percent, a matrix resin char content of 0 to about 20 volume percent, a matrix carbon black filler content of 0 to about 10 volume percent, a matrix pyrolitic carbon content of from about 5 to about 20 volume percent, and a final density of from about 1.6 to about 2.0 g/cc; wherein said composite contains a controlled amount of at least one of boron and an inorganic boron compound in a range of about 0.1 to about 10 volume percent
In one embodiment, the component may be formed by:
impregnating a carbon fiber reinforcement material with a pre-impregnating mixture containing amounts of resin or pitch, boron or inorganic boron compound, and carbon black, sufficient to provide their respective final component contents;
shaping laminated sheets of the carbon fiber reinforcement material into a component precursor before or after said impregnating;
curing the component precursor;
heating the component precursor in an inert atmosphere or vacuum at an elevated temperature to form a carbonized component by converting the resin or pitch to carbon, wherein the carbonized component is porous and has low density;
pyrolyzing the component in an inert atmosphere or vacuum at a temperature of about 1800° F. (980° C.) to about 5000° F. (2760° C.); and,
densifying the low density component by depositing pyrolytic carbon in the pores of the component before or after said pyrolyzing.
REFERENCES:
patent: 4339021 (1982-07-01), Kosuda et al.
patent: 4874564 (1989-10-01), Sudani et al.
patent: 5037699 (1991-08-01), Ichikawa et al.
patent: 5667310 (1997-09-01), Oyagi et al.
patent: 5744075 (1998-04-01), Klett et al.
patent: 5895716 (1999-04-01), Fiala et al.
Busch Donald E.
Erdemir Ali
Fenske George R.
Lee Sam
Pruett Gary J.
Cole Elizabeth M.
Hitco Carbon Composites, Inc.
Renner Kenner Greive Bobak Taylor & Weber
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