FIELD OF THE INVENTION
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This invention relates to carbon-carbon composite brake discs, and more particularly, to brake disc drive insert slots in carbon-carbon composite brake discs. The present invention provides an improved surface within the brake disc drive insert slots.
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OF THE INVENTION
Carbon-carbon composite brake discs used in the aerospace industry typically have metal inserts attached to them. Specifically, the metal inserts are attached to slots in the interior faces of the brake discs (rotors or stators). Those slots function to facilitate the transmission of torque to the brake discs. The metal inserts for stators serve to provide a surface that will transmit torque from the torque tube of the axle to the brake disc without crushing the face of the carbon-carbon composite material. Rotor inserts are used as the media to transmit torque form the wheel drive key interface to the brake discs. The metal inserts—typically held in place by rivets, adhesive, etc.—serve this purpose. However, they are relatively expensive additions to the brake discs. Labor is expended drilling holes for and attaching the inserts. Damage sometimes occurs to the carbon-carbon brake disc during installation or removal of rivets. Also, the inserts add significant weight to the brake assembly.
U.S. Pat. No. 5,273,140 describes a brake disc annular drive insert which comprises a generally cylindrical member with radially extending flanges at opposite axial ends thereof. The drive insert includes a generally cylindrical body having an opening at one side thereof which extends diametrically into the body and terminates at a point between the center of revolution of the body and an outer surface of the body. The opening in the body extends to an inner surface of the body to provide a generally rectangular opening for receiving a spline of a torque tube. The drive insert is typically made of steel. The flanges of the drive insert may comprise either generally annular flanges shaped complementary with the generally cylindrical body and or may be truncated at a side opposite the opening in the body.
US 2007/0175709 describes brake disc drive inserts for use in carbon-carbon composite brake discs. A rotatable brake disc annular drive insert includes a cylindrical steel body having one side of the body truncated to provide an insert opening which extends axially through the body. The insert opening extends into the body along a diameter of the body and the insert opening terminates at a radially extending surface located between the revolutional center of the body and an outer surface of the body. End flanges extend radially outwardly from the outer surface of the body to provide for axial positioning of the drive insert relative to a brake disc. The insert opening has a lining comprising carbon-carbon composite material. This low friction carbon-carbon composite material bed that is positioned between the steel insert component and the torque tube spline location provides significantly lower friction and enables significantly greater disc clamping and brake torque.
Other prior art of interest includes: US 2007/0235126 A1, entitled BONDING OF CARBON-CARBON COMPOSITES USING TITANIUM CARBIDE; US 2007/0235123 A1, entitled APPARATUS AND METHODS FOR BONDING CARBON-CARBON COMPOSITES THROUGH A REACTANT LAYER; copending application Ser. No. 11/730,373, entitled BONDING OF CARBON FIBERS TO METAL INSERTS FOR USE IN COMPOSITES; and US 2007/0193836 A1, entitled METHOD AND BRAKE DISC WITH COMPOSITE INSERT MEMBER.
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OF THE INVENTION
The present invention eliminates the need for inserts, and the drilling of rivet holes. Instead, the present invention toughens the face of the carbon-carbon composite material so that it will not crush under pressure.
In accordance with this invention, a brake disc rotor or stator is manufactured by conventional methods through the final machining process which provides slots in the interior face of the brake disc. At that point, this invention applies a paste to the areas where force is applied to the rotor slot faces or to the stator slot faces. The paste is comprised of a fine powder of a carbide-forming metal along with fine carbon powder. The metal and carbon powders are suspended in an organic binder. The disc is then placed into a furnace in a nitrogen atmosphere and heated to the ignition temperature. When the furnace reaches the ignition temperature, a combustion reaction begins that creates a molten liquid ceramic material on the slot face. The ceramic created in this way “cools” very quickly to the temperature of the carbon-carbon composite. The brake disc is then cooled to ambient temperature. The resulting brake disc has a tough, hard, abrasion-resistant ceramic surface on the portion of the brake disc slot that bears pressure. At this point, the discs are processed through additional standard processes, such as application of antioxidant.
BRIEF DESCRIPTION OF THE DRAWINGS
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The following drawings are illustrative only, and non-limiting. They illustrate possible ways in which the present invention, which toughens the face of the carbon-carbon compose material, may be implemented. However, persons skilled in the art will readily envision other ways in which the benefits of the present invention may be obtained.
FIG. 1A is a top plan view of a known type of aircraft carbon-carbon composite brake disc stator coupled with a torque tube via annular drive inserts.
FIG. 1B is an enlarged view corresponding to the circled section of FIG. 1A, but modified in accordance with the present invention.
FIG. 2A is an isometric view of a known type of aircraft carbon-carbon composite brake disc rotor.
FIG. 2B is an enlarged view corresponding to the circled section of FIG. 2A, but modified in accordance with the present invention.
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OF THE INVENTION
This invention provides a method of manufacturing a brake disc rotor or brake disc stator, wherein the rotor or stator has a tough, hard, abrasion-resistant ceramic surface on the portion of the brake disc slot that bears pressure. The method of the invention includes the following four steps.
Step (1) contemplates providing a carbon-carbon composite brake disc rotor or stator having slot slots in the interior face of said brake disc. These brake disc rotors or stators are manufactured by conventional methods through the final machining process which provides slots in the interior faces of the brake discs.
Step (2) contemplates applying a paste, comprised of a fine powder of titanium, zirconium, hafnium, and/or vanadium along with fine carbon powder suspended in an organic binder, to the areas where force will be applied to the rotor or stator slot faces. In a preferred embodiment, the fine powder is titanium powder having an average particle diameter ranging from 25 to 250 microns. In a more preferred embodiment, the average particle diameter of the titanium powder is about 45 microns. In a preferred embodiment, the carbon powder is powdered graphite and the average diameter of the graphite particles ranges from 1 to 10 microns. In a more preferred embodiment, the average particle diameter of the graphite particles is about 2 microns. In a preferred embodiment, the mole ratio of metal powder to carbon powder ranges from 3:1 to 0.5:1. In a preferred embodiment, the organic binder is a phenolic binder, an epoxy binder, or an alginate binder. In a preferred embodiment, the paste is applied to the areas where force will be applied to the rotor or stator slot faces in a thickness ranging from 30 microns to ¼ inch. In an especially preferred embodiment, the paste is a layer of titanium powder and carbon powder about 1/16 inch in thickness.
Step (3) contemplates placing the disc into a furnace having a nitrogen-containing atmosphere, and heating the disc to the ignition temperature. In a preferred embodiment, the furnace is provided with an atmosphere containing nitrogen—for instance, air or pure nitrogen gas—at a pressure ranging from 0.2 to 20 atmospheres. In a preferred embodiment, this heating step is conducted at a temperature of from 400-600° C.
Step (4) contemplates cooling the brake disc to ambient temperature. When the furnace in step (3) reaches the ignition temperature, a combustion reaction begins that creates a molten liquid ceramic material on the slot faces in the brake discs. The ceramic created in this way “cools” very quickly to the temperature of the carbon-carbon composite. This initial rapid cooling is followed by cooling the brake disc to ambient temperature, generally by the application of cooling means such as refrigerants and/or blowing air.
This invention also provides a slotted brake disc rotor or slotted brake disc stator which has a tough, hard, abrasion-resistant ceramic surface on the portion of the brake disc slot that bears pressure, said rotor or stator being manufactured by a method of described above.
Examples of the metals which may be used in this invention are titanium, zirconium, hafnium, and/or vanadium. Titanium carbide provides a ceramic with an especially high specific heat. These metal powders typically ignite at around 450° C. in a nitrogen atmosphere. Reaction between nitrogen and metal provides the low ignition temperature.
Examples of binders which may be used in this invention include phenolic binders, epoxy binders, and alginates. However, any organic binder which can provide a paste of the metal powder being used can be employed.
With reference to FIG. 1A, an aircraft carbon-carbon composite brake disc stator 10 is generally annular in shape and includes a central generally annular opening 14. A plurality of slot openings or recesses receiving therein brake disc annular drive inserts 20 is located about the periphery of opening 14. Recesses 16 of disc 10 are generally annularly shaped slots extending radially outwardly from opening 14 of disc 10. Annular drive inserts 20 couple torque tube 6 with disc 10. The torque tube is non-rotatably coupled with an axle (not shown) of an aircraft.
As illustrated in FIG. 1B, torque tube 6 includes radially extending short spines 8 which extend within the respective annular drive slots or openings 21. In accordance with the present invention, each opening 21 (slot) is lined with an area of toughened carbon-carbon composite material 19.
FIG. 2A shows an aircraft carbon-carbon composite brake disc stator that is generally annular in shape and that includes a central generally annular opening. A plurality of slot openings or recesses is located about the outer periphery of the rotor.
As illustrated in FIG. 2B, in accordance with the present invention, each opening 21 (slot) is lined with an area of toughened carbon-carbon composite material 19.
A paste is prepared from 1.0 mol of titanium powder and 0.8 mol of carbon powder in a liquid phenolic binder. This paste is applied in a layer approximately ⅛ inch thick to the faces of slot slots in a carbon-carbon composite brake disc stator. The composite disc having the paste-lined slot slots is placed in a furnace which has a pure nitrogen atmosphere at 1 atmosphere of pressure. Ignition occurs at about 410° C. The maximum combustion temperature reached is 2340° C. The resulting ceramic layer on the faces of the slot slots comprises 0.9 mol TiC and 0.1 mol TiN. This ceramic layer is a refractory material which is stable up to about 3000° C. and which has a Rockwell Hardness, A scale, of about 80 HRA.