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  Carbon-carbon friction material with improved wear lifeThe Patent Description & Claims data below is from USPTO Patent Application 20080090064. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]This invention relates generally to carbon-carbon composite materials and methods of production thereof. More specifically, the present invention relates to a method for improving the wear performance of carbon-carbon composite materials by densifying a carbon preform and subsequently infiltrating it with a ceramic additive. BACKGROUND OF THE INVENTION [0002]Carbon-carbon composites are essential materials in a variety of high-technology applications requiring durability at very high temperatures. For decades, these composites have been used in the disk brakes of jet fighters and large passenger airliners due to their excellent friction performance, low weight, and resistance to thermal shock. Additional applications include disk brakes of land transportation means such as tanks, special vehicles, rapid transit trains and racing cars, high-temperature structures such as gas jet-engine parts, rocket nozzles of launch vehicles, re-entry surfaces of space shuttles, walls of fusion reactors and other high-temperature industrial equipment. [0003]Carbon-carbon-carbon composites generally comprise a carbon fiber substrate (fiber component) embedded in a carbon matrix (filler component). Although both consist of carbon, the behavior of the material essentially depends on the state of the carbon of the respective component. Crystalline carbon, i.e. graphite, consists of closely joined hexagonal crystals which are arranged inn layers and which are held together primarily by Van der Waals forces. In addition to its defined forms, graphite and diamond, carbon can assume a large number of intermediate states in a quasi-crystalline form, from an amorphous, vitreous carbon to a highly crystalline graphite. [0004]Threads, bands and fabrics are typically used as the fiber component. The highest strength is achieved by a straight orientation of the fibers. For most technical applications, two-dimensional (2-D) fabrics are used. If high strength is required in all three directions it is possible to use fabrics that are woven in three directions of space, i.e. 3-D fabrics. [0005]The method of manufacturing carbon-carbon composites can be basically divided into a process of producing a preform using a carbon-based fiber or fabric, and a process of densifying the preform to meet application criteria. The method also typically includes an oxidation-resistance treatment to impart durability on the finished product. [0006]A continuous need exists to improve the friction and wear performance of aircraft brake friction materials manufactured with carbon-carbon composites without a substantial increase in manufacturing costs which reduce industrial applicability. SUMMARY OF THE INVENTION [0007]In view of the above, it is one of the objects of the present invention to provide an improved method for manufacturing a carbon-carbon composite material which provides lower wear rates (longer life) without significantly increasing manufacturing costs. The method of the present invention comprises a step of carbonizing a nonwoven carbon preform and subjecting it to densification. Densification may be achieved by chemical vapor deposition/chemical vapor infiltration (referred to for convenience herein by the acronym "CVD") and/or liquid resin/pitch impregnation procedures. A key feature of the inventive method is a specific sequence of processing steps, including densification of the nonwoven material followed by infiltration of the material with a liquid resin/pitch carbon followed by infiltration of a ceramic additive. After drying and heat-treating, the nonwoven material is subjected to a second cycle of carbon densification with either CVD or liquid resin prior to further processing. The sequence of densification with CVD and/or liquid resin/pitch carbons and infiltration of the additive results in the optimum pore-size distribution that controls and improves distribution and final particle size in the additive, which in turn results in lower wear rates while maintaining good friction properties. [0008]It is another object of the present invention to provide an improved carbon-carbon composite material article which exhibits the strength and thermal requirements necessary in aircraft brake applications, while at the same time providing lower wear rates and good friction properties. The inventive material comprises a carbonized nonwoven preform which is subjected to densification using either liquid resin infiltration or chemical vapor deposition/infiltration of carbon and is subsequently infiltrated with a solution comprising a ceramic additive. The specific sequence of carbon densification followed by infiltration with liquid resin carbon provides the desired pore-size distribution that will enable infiltration of a ceramic additive and prevent the agglomeration of the additive and the formation of large particles and will result in lower wear rates with good friction properties. [0009]One embodiment of the present invention is a method for manufacturing a carbon-carbon composite material article. This method comprising sequentially: providing a nonwoven material (e.g., a preform); carbonizing the nonwoven material; subjecting the nonwoven material to chemical vapor deposition/infiltration (CVD) and/or liquid resin/pitch densification, e.g. to a density of at least 1.5 gm/cc; carbonizing the nonwoven material; infiltrating the nonwoven material with a ceramic additive in suspension; drying the nonwoven material; and subjecting the nonwoven material to another CVD or liquid resin/pitch densification procedure--e.g. to RTM processing using high viscosity pitch resin--and to a heat treatment, before or after this second densification procedure, to set the ceramic additive. In said RTM processing, the pitch may be stabilized and then carbonized or charred. The step of adding a ceramic additive may include infiltrating the nonwoven material with a ceramic additive solution, such as a solution of silica suspended in water. This invention also contemplates carbon-carbon composite articles manufactured by the above-described method. [0010]A specific embodiment of the above method includes subjecting a carbonized nonwoven preform sequentially to CVD processing, then to rapid densification using a resin transfer molding (RTM) process with a high viscosity pitch resin, then to infiltration with a solution of silica suspended in water, then to CVD processing. [0011]In another embodiment, this invention provides a method for manufacturing a carbon-carbon composite preform. This method involves the sequential steps of: providing a nonwoven preform; carbonizing the preform; subjecting the preform to a first chemical vapor deposition procedure; subjecting the preform to a resin transfer molding process with a high viscosity resin/pitch; stabilizing the resin/pitch; carbonizing or charring the resin/pitch; infiltrating the preform with a solution of silica suspended in water; drying the preform; subjecting the preform to a second chemical vapor deposition procedure; and heat treating the preform. [0012]Carbon-carbon composite preforms manufactured by the above process are also provided by the present invention. In such preforms, it is preferable that the weight-% of silicon carbide in the preform is less than 2%, and that all silicon carbide particles have an average diameter of less than 1 micron. An example of such a preform is a carbonized nonwoven preform, wherein the preform has been subjected to a first chemical vapor deposition procedure prior to the step of densification, to rapid densification using a high viscosity pitch resin in a resin transfer molding process, to subsequent infiltration with silica suspended in water, and to a second chemical vapor deposition procedure subsequent to infiltration with the silica suspended in water. BRIEF DESCRIPTION OF THE DRAWINGS [0013]The present invention will become more fully understood from the detailed description given herein and from the accompanying drawings. The drawings are not to scale, and are given by way of illustration only. Accordingly, the drawings should not be construed as limiting of the present invention. [0014]FIG. 1 is a flowchart illustration of general manufacturing process steps that can be applied to manufacture a carbon-carbon composite material in accordance with the present invention. [0015]FIG. 2 is a flowchart illustration of a preferred embodiment of the method for manufacturing a carbon-carbon composite material in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION [0016]The present invention is directed to an improved carbon-carbon composite material. The present invention is also directed to an improved method for manufacturing a carbon-carbon composite material wherein at least one of the densification steps with carbon involves rapid infiltration with a liquid resin/pitch carbon followed by infiltration with a ceramic additive which results in lower wear rates with good friction properties. [0017]A composite is a material created from a fiber (or reinforcement) and an appropriate matrix material in order to maximize specific performance properties. The individual constituents do not dissolve or merge completely but retain their identities as they act in concert. In composites, the matrix material acts to hold the fibers together and protect them, and to transfer the load to the fibers in the fabricated composite part. The reinforcing fiber imparts strength and other required properties to the composite. Among composites, carbon-carbon composites are used in a variety of applications and consist of a composite of carbon fiber in a carbon matrix. [0018]Carbon fibers are reinforcing fibers known for their lightweight, high strength, and high stiffness properties. They are generally produced by pyrolysis of an organic precursor fiber in an inert atmosphere at high temperatures. These fibers may be produced from several different types of precursor fibers, such as polyacrylonitrile (PAN), rayon, and petroleum pitch. The carbon fibers are produced by the controlled burning off of the oxygen, nitrogen, and other non-carbon parts of the precursor fiber, leaving only carbon in the fiber. During the burning off (carbonization/graphitization) steps, the fibers are run through a furnace to produce carbon or graphite fibers. The carbon or graphite fibers are produced at furnace temperatures of 1000-3000.degree. C. [0019]A carbon preform is a fibrous reinforcement pre-shaped to the approximate contour and thickness desired in the finished part. Processing carbon-carbon composite preforms consists of building up of the carbon matrix around the carbon fibers. There are two common ways to create the matrix: through chemical vapor deposition/infiltration and through impregnation with a resin/pitch. Chemical vapor deposition/infiltration begins with a preform in the desired shape of the part, usually formed from multiple layers of woven carbon fabric. The preform is heated in a furnace pressurized with an organic gas, such as methane, acetylene, or benzene. Under high heat and relatively low pressure, the gas decomposes and deposits a layer of carbon onto the carbon fibers. The gas must diffuse through the entire preform to make a uniform matrix, so the process is very slow, often requiring several weeks and several processing cycles to make a single part. Continue reading... Full patent description for Carbon-carbon friction material with improved wear life Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Carbon-carbon friction material with improved wear life patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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