Abstract:
An improved friction material includes inorganic fibers formed from a melt of volcanic black rock and additives. The black rock comprises silica oxide, magnesium oxide, potassium permanganate, aluminum oxide, iron oxide, silicon dioxide, titanium dioxide, sodium oxide, and boron. The additives include potassium permanganate and boron. As a result of their composition, the fibers are temperature resistant and lightweight, yet strong. The fibers exhibit a melting point between 1500 degrees centigrade and 1650 degrees centigrade, a working range of −130 degrees centigrade to 700 degrees centigrade, a density of 1.8 g/cc, a surface density between 160 g/m 2  and 350 g/m 2 , and a tensile strength between 500 lbf/in 2  and 1800 lbf/in 2 . The friction material is made from layers of the inorganic fibers and a bonding material and has a working temperature between 250 degrees centigrade and 650 degrees centigrade, with a melting point of approximately 1200 degrees centigrade.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to friction material and in particular to a friction material made from volcanic black rock and used in brake and clutch systems and similar applications. 
     Known vehicles require means for reducing linear velocity and momentum and means for reducing angular velocity and momentum of rotating members carrying the vehicles. Mechanical friction brakes are commonly used for such purposes and known brakes are suitable for typical vehicles operated at moderate speeds and loads in flat terrain. Such friction brakes work by converting kinetic energy into heat energy, and the greater the speed or mass of the moving vehicle, the greater the amount of heat generated to slow or stop the vehicle. The friction is generally created by forcing a friction material against a rotating surface. When vehicles are operated at high speeds with frequent braking, with heavy cargo creating greater linear momentum, or on long down hill stretches of road, the friction material may overheat and either fail or fade. Such loss of braking creates a severe risk of accidents. Although disk brakes have greatly improved braking performance over older drum brakes, there remains a need to further improve friction material used in vehicle brakes for both commercial and racing applications. 
     Many applications also require coupling and decoupling rotating members initially rotating at different angular speeds. The different angular speeds of the rotating members generally must first be synchronized before final coupling is achieved, and in the case of a manual transmission vehicle, motion is initiated from a stop by briefly slipping a clutch before fully engaging. In known vehicles, the clutch couples an engine flywheel to a transmission input shaft. Commonly, a clutch pressure plate is rotationally fixed to the flywheel and a clutch disk(s) with friction material on two opposite sides is sandwiched between the pressure plate and the flywheel. The clutch disk includes an inside spline which engages the transmission input shaft. The pressure plate includes an axially moving plate and spring(s) which push the plate against the clutch disk. The amount of torque transmittable through the clutch is proportional to the force applied on the plate by the springs, and in some instances, by weights and effects of centrifugal force. When the vehicle makes a standing start, the clutch slippage creates heat which may damage the friction material and result in continuous clutch slippage while driving. Because of the clutch slippage issue, clutches in high performance applications remain a weak link between the engine and transmission and a need remains for an improved friction material. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an improved friction material which includes inorganic fibers. The inorganic fibers are formed from a melt of volcanic black rock and additives. The black rock is comprised of silica oxide, magnesium oxide, potassium permanganate, aluminum oxide, iron oxide, silicon dioxide, titanium dioxide, sodium oxide, and boron. The additives include potassium permanganate and boron. As a result of their composition, the fibers are temperature resistant and lightweight, yet strong. The fibers exhibit a melting point between 1500 degrees centigrade and 1650 degrees centigrade, a working range of −130 degrees centigrade to 700 degrees centigrade, a density of 1.8 g/cc, a surface density between 160 g/m 2  and 350 g/m 2 , and a tensile strength between 500 lbf/in 2  and 1800 lbf/in 2 . The friction material is made from layers of the inorganic fibers and a bonding material and has a working temperature between 250 degrees centigrade and 650 degrees centigrade, with a melting point of approximately 1200 degrees centigrade. 
     In accordance with one aspect of the invention, there is provided a low cost friction material made from a raw mixture of low cost volcanic black rock and additives. The raw mixture is comprised of approximately 55 to 60 percent by weight silica oxide, approximately eight to ten percent by weight magnesium oxide, approximately five to ten percent by weight potassium permanganate, less than approximately fifteen percent by weight aluminum oxide, approximately two to five percent by weight iron oxide, less than approximately two percent by weight silicon dioxide, less than approximately five percent by weight titanium dioxide, less than approximately two percent by weight sodium oxide, less than approximately two percent by weight boron, and approximately one to five percent by weight rayon. More preferably, the raw mixture is comprised of approximately 55 percent by weight silica oxide, approximately nine percent by weight magnesium oxide, approximately 8.4 percent by weight potassium permanganate, approximately 13.2 percent by weight aluminum oxide, approximately 3.5 percent by weight iron oxide, approximately 0.85 percent by weight silicon dioxide, approximately 3.5 percent by weight titanium dioxide, approximately 0.8 percent by weight sodium oxide, approximately two percent by weight boron, and approximately four percent by weight rayon. 
     In accordance with another aspect of the invention, there is provided a low cost friction material made from a raw mixture of low cost volcanic black rock and additives. The raw mixture consists essentially of approximately 55 to 60 percent by weight silica oxide, approximately eight to ten percent by weight magnesium oxide, approximately five to ten percent by weight potassium permanganate, less than approximately fifteen percent by weight aluminum oxide, approximately two to five percent by weight iron oxide, and approximately one to five percent by weight rayon. 
     In accordance with yet another aspect of the invention, there is provided a low cost friction material made from a raw mixture of low cost volcanic black rock and an additive. The additive is comprised of includes about 26 to 33 percent by weight potassium permanganate, about 39 to 45 percent by weight iron oxide, about 22 to 31 percent by weight whitestone and about three percent by weight boron. The potassium permanganate is provided as a fuel source for melting the raw materials  26  and the iron oxide is provided to modify the black rock  74 . 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is a side view of a disk brake assembly including brake pads having friction material according to the present invention. 
         FIG. 1B  is a front view of the disk brake assembly including brake pads having friction material according to the present invention. 
         FIG. 1C  is a top view of the disk brake assembly including brake pads having friction material according to the present invention. 
         FIG. 2A  is a side view of a brake pad including a friction material according to the present invention. 
         FIG. 2B  is a front view of the brake pad including a friction material according to the present invention. 
         FIG. 2C  is a top view of the brake pad including a friction material according to the present invention. 
         FIG. 3  is a side view of an engine, flywheel and clutch assembly, and transmission including a clutch disk having the friction material according to the present invention. 
         FIG. 4  is a cross-sectional view of the clutch assembly taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5A  is a side view of the clutch disk including the friction material according to the present invention. 
         FIG. 5B  is a front view of the clutch disk including the friction material according to the present invention. 
         FIG. 6  is a schematic diagram exemplifying a method for manufacturing inorganic fibers used in the construction of the friction material according to the present invention. 
         FIG. 7A  depicts a first step in the manufacture of the friction material according to the present invention. 
         FIG. 7B  depicts a second step in the manufacture of the friction material according to the present invention. 
         FIG. 7C  depicts a third step in the manufacture of the friction material according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A side view of a disk brake assembly  10  including brake pads  18  having friction material  20  according to the present invention is shown in  FIG. 1A , a front view of the disk brake assembly  10  is shown in  FIG. 1B , and a top view of the disk brake assembly  10  is shown in  FIG. 1C . The disk brake assembly  10  includes a caliper  12  residing over a portion of a disk  14  and hat  16 . The disk  14  and hat  16  are often separate pieces in high performance and racing brake assemblies, but are commonly a single piece in production cars. Two brake pads  18  reside inside the caliper  10  and are pushed together by pistons  11  to tightly sandwich the disk  14 . The resulting drag between the brake pads  18  and the disk  14  converts kinetic energy in a moving vehicle into heat to slow the vehicle. 
     A side view of the brake pad  18  including a friction material  20  according to the present invention is shown in  FIG. 2A , a front view of the brake pad  18  is shown in  FIG. 2B , and a top view of the brake pad  18  is shown in  FIG. 2C . The friction material  20  may be bonded, riveted, or otherwise attached to a backing plate  22 . The backing plate is  22  is generally steel and is shaped to slide towards and away from the disk  14  inside the caliper  12 . The friction material  20  according to the present invention is formed from inorganic fibers as described below. 
     While common vehicle brakes utilize disks  14  made from cast iron, many racing applications use disks made from ceramic composites (including carbon, KEVLAR® fiber, and silica), and the like. Such ceramic brakes include the Brembo Ceramic Brake Systems made by Brembo in Italy. Disks made from ceramic composites materials are much lighter than conventional cast iron disks. This light weight has major advantages of reducing unsprung weight, reducing angular momentum, and reducing gyroscopic effects. The friction material according to the present invention may be used to replace carbon fiber materials presently used and provide advantages such as lower cost and improved strength and durability. Carbon fiber materials are known to loose strength over time, the brake disks including the friction material according to the present invention provide better retention of the original mechanical properties. Such disks are described in U.S. Pat. No. 6,767,602, U.S. Pat. No. 7,370,738, and US Patent Application Publication No. 2002/0153213, which are incorporated herein by reference. 
     A side view of an engine  30 , flywheel  40 , clutch assembly  42 , and transmission  46  is shown in  FIG. 3 . The engine  30  includes an engine block  32 , head(s)  34 , and oil pan  36 . The flywheel  40  is bolted to an engine crankshaft  48  (only partially shown) and the clutch assembly  42  is bolted to the flywheel  40 . A bell housing  38  (shown in a cross-sectional view) is bolted to the engine block  32 , and a transmission  46  is bolted to the bell housing  38 . A transmission input shaft  44  extends from the transmission  46  into the clutch assembly  42 . 
     A cross-sectional view of the clutch assembly  42  taken along line  4 - 4  of  FIG. 3  is shown in  FIG. 4 . The clutch assembly  42  includes an axially moving plate  52  pushed towards the flywheel  40  by springs  54 . A clutch disk  56  is sandwiched between the axially moving plate  53  and the flywheel  40 . The clutch disk  56  rides on the input shaft  44  and engages spline  60  (see  FIG. 4B ) to rotationally couple the clutch disk  56  to the input shaft  44 . Friction between the two opposite faces of the clutch disk  56  and the faces flywheel  40  and the axially moving plate  53  couples the clutch disk to the engine and thereby couples the transmission  46  to the engine  30 . Levers (not shown) residing inside a pressure plate assembly are generally actuated by a throwout bearing to lift the moving plate  52  away from the clutch disk  56  to disengage the clutch assembly  42 . 
     A side view of the clutch disk  56  including the friction material  50   a  and  50   b  according to the present invention attached to opposite sides of a center plate  51 , is shown in  FIG. 5A  and a front view of the clutch disk is shown in  FIG. 5B . The friction material  50   a  and  50   b  is approximately the same diameter as the center plate  51  and attached to the center plate  51  by bonding, rivets, and the like. The friction material  50   a  and  50   b  and center plate  51  are sandwiched between hub halves  58   a  and  58   b . The hub halves  58   a  and  58   b  have an inside spline  60  for axially slideably engaging cooperating spline on the input shaft  44 . A known lever mechanism (or a diaphragm replacing both lever arms and the springs  54 ) not shown, engages the axially moving plate  53  to pull the axially moving plate  53  away from the clutch disk  56  to disengage the transmission  46  from the engine  30 . 
     While the friction material  50   a  and  50   b  are shown as continuous washer shapes, the friction material may be broken into segments, or the clutch disk may have “paddles” with friction material on each paddle. Further, the friction materials  50   a  and  50   b  may be different friction materials, with one friction material made from inorganic fibers according to the present invention, and the other made from a different material to provide a dual friction clutch disk. 
     During partial engagement, the friction material  50   a  and  50   b  slips between the flywheel  40  and the axially moving plate  53 . In particular, when the vehicle makes a standing start, the clutch slippage creates heat which may damage the friction material and result in continuous clutch slippage while driving. The friction material according to the present invention provides a strong, light, thermally stable allowing consistent performance in high performance applications. The inorganic fibers in the friction material provide a great benefit in heat dissipation and recover mechanical properties very quickly. The presence of the inorganic fibers according to the present invention in the friction material allows heat to dissipate quickly and, for example, the coefficient of friction of the friction material to be maintained. 
     A system  70  for manufacturing the inorganic fibers is shown in  FIG. 6 . As shown, the system  70  includes a furnace  78 . The furnace  78  is preferably a cupola furnace and includes a chamber  82  formed by a sidewall  80 . The chamber  82  is dimensioned to receive the raw materials needed to manufacture the inorganic fibers. Specifically, the raw materials include black rock  74  and an additive  76 . As indicated, the black rock  74  and additive  76  are provided to the chamber  82  in the form of crushed solids. Once they are received in the chamber  82 , they are liquefied therein to form a melt  83 . 
     Downstream of the furnace  78 , the system  70  includes an extruding device  84 . The extruding device  84  may be integral with the furnace  78  or it may be connected directly to the furnace  78  for receiving the melt  83 . Alternatively, the melt  83  may be delivered to the extruding device  84  via a carrier such as a ladle or the like. In either case, the extruding device  84  includes a pump or other means to force the melt  83  though an aperture, or several apertures, to form a plurality of inorganic fibers  86 . Preferably, the apertures of the extruding device  84  are formed by a stationary platinum nozzle that can withstand the high temperatures of the melt  83 . 
     As shown in  FIG. 6 , the system  70  further includes a cooling device  88  which is positioned downstream of the extruding device  84 . Similar to the extruding device  84 , the cooling device  88  may be integral with the furnace  78  or it may be connected thereto. As shown, the cooling device  88  is positioned to receive the plurality of fibers  86  from the extruding device  84 . Further, a sizing station  92  is positioned downstream of the cooling device  88  to receive the plurality of cooled fibers  90  therefrom. The sizing station  92  includes a sizing agent which can be applied to the plurality of cooled fibers  90  to form a plurality of fibers  94 . 
     In more detail, the black rock  74  of the present invention is preferably of the type of volcanic black rock that is commonly found in Oregon, Washington and other locations. Such black rock  74  typically contains about 55 to 60 percent by weight silica oxide, about 18 percent by weight magnesium oxide, about fifteen percent by weight potassium permanganate, about twelve percent by weight aluminum oxide, about two percent by weight iron oxide, about one percent by weight silicon dioxide, about two percent by weight titanium dioxide, and about one percent by weight sodium oxide. Unless treated or mixed with other materials, the black rock  74  typically has a melting point of over twelve hundred degrees centigrade (1200 degree C.). Before it is introduced to the chamber  82  of the furnace  78 , the black rock  74  is preferably graded to individual pieces having diameters “d” of about four to eight inches. Preferably, the individual pieces of black rock  74  all have approximately the same diameter “d”. 
     As further shown in  FIG. 6 , the additive  76  is provided in the form of crushed solids. The additive  76  preferably has a melting point of about 900 degrees centigrade and includes about 26 to 33 percent by weight potassium permanganate, about 39 to 45 percent by weight iron oxide, about 22 to 31 percent by weight whitestone and about three percent by weight boron. The potassium permanganate is provided as a fuel source for melting the raw materials  26  and the iron oxide is provided to modify the black rock  74 . The boron and whitestone are provided to reduce the melting point and facilitate processing of the mixture of the raw materials. Whitestone contains about 58 percent by weight calcium oxide, about 41 percent by weight magnesium oxide, less than about one percent by weight silicon oxide, and less than about one percent by weight iron oxide, 
     As a batch process, a desired amount of black rock  74  and additive  76  are delivered to the furnace  78 . Preferably, the raw material provided to the chamber  82  consists essentially of 60 to 90 percent by weight black rock  74  and 10 to 40 percent by weight additive  76 . In certain preferred embodiments, the raw material consists essentially of 87 to 88 percent by weight black rock  74  and 12 to 13 percent by weight additive  76 . Volumetrically, the raw material is preferably about one hundred parts of black rock  74  and about fourteen parts of additive  76 . 
     Because volcanic black rock is a natural product formed by a range of components, it is preferred that the additives are selected and the manufacturing process is controlled so that the raw material is preferably comprised of approximately 55 to 60 percent by weight silica oxide, approximately eight to ten percent by weight magnesium oxide, approximately five to ten percent by weight potassium permanganate, less than approximately fifteen percent by weight aluminum oxide, approximately two to five percent by weight iron oxide, less than approximately two percent by weight silicon dioxide, less than approximately five percent by weight titanium dioxide, less than approximately two percent by weight sodium oxide, less than approximately two percent by weight boron, and approximately one to five percent by weight rayon. More preferably, the raw material is comprised of approximately 55 percent by weight silica oxide, approximately nine percent by weight magnesium oxide, approximately 8.4 percent by weight potassium permanganate, approximately 13.2 percent by weight aluminum oxide, approximately 3.5 percent by weight iron oxide, approximately 0.85 percent by weight silicon dioxide, approximately 3.5 percent by weight titanium dioxide, approximately 0.8 percent by weight sodium oxide, approximately two percent by weight boron, and approximately four percent by weight rayon. 
     When deposited in the chamber  82  of the furnace  78 , the mixture of raw materials is heated to a temperature in the range of approximately 955 degree C. to 1270 degrees centigrade, and preferably to between 1200 degrees centigrade and 1270 degrees centigrade. Regardless of the specific temperature attained, the mixture of raw materials is heated sufficiently to reduce the raw materials to liquefy to the melt  83  having a viscosity proper for processing. When the raw material is heated, the potassium permanganate is burned as a fuel and facilitates liquefying the other raw materials. 
     After the melt  83  is properly formed, it is delivered to the extruding device  84 . The extruding device  84  extrudes the melt  83  into a plurality of hot fibers  86  by forcing the melt  83  through nozzles. The resulting fibers  86  have diameters up to fourteen microns and preferably in a range between seven and twelve microns. In order to prevent deformation of the fibers  86 , they are delivered to the cooling device  88  to be cooled and hardened to a soft solid state. During the cooling process, the cooling device  88  first cools the plurality of fibers  86  to about 800 degrees centigrade and maintains that temperature for about 30 minutes. Then it cools the plurality of fibers  86  to about 355 degrees centigrade and maintains that temperature for about 30 minutes. As a result, the plurality of fibers  86  reaches a substantially soft solid state that facilitates further processing. 
     After the fibers are extruded from the melt, they are sized or coated with a rayon sizing agent. Preferably, the resulting fibers have a diameter in a range of seven to fourteen microns and more preferably seven to twelve microns and is approximately 95 to 99 percent by weight inorganic filaments and approximately one to five percent by weight rayon, and more preferably approximately 98 percent by weight inorganic filaments and approximately four percent by weight rayon. 
     Steps in the manufacture of the friction material according to the present invention are depicted in  FIGS. 7A-7C . The friction material is preferably formed in a multiple layer process to allow certain gases to escape and allows a better curing process of each layer. In  FIG. 7A  a first layer  102   a  of the friction material comprising a mixture of the inorganic fibers according to the present invention at least between 0.5 and one inches long, and resin, is laid in a lay-up plate  100 . The first layer  102   a  is set under of about 400 Pounds per Square Inch (PSI) and cured at between 275 degrees centigrade and 350 degrees centigrade in an autoclave. 
     In  FIG. 7B  a second layer  102   b  of the friction material comprising a mixture of the inorganic fibers between 0.5 and one inches long and an organic binding agent (phenolic) is laid in the lay-up plate  100  on top of the first layer  102   a . The second layer  102   b  is also set under of about 400 PSI and cured at between 275 degrees centigrade and 350 degrees centigrade in an autoclave. 
     In  FIG. 7C  a third layer  102   c  of the friction material comprising a mixture of the inorganic fibers at least between 0.5 and one inches long and resin (an organic binding agent, for example, phenolic) is laid in the lay-up plate  100  on top of the second layer  102   b  and an optional plate  104  may be laid over the third layer  102   c . The third layer  102   c  and plate  104  are set under of about 250 PSI and cured at about 300 degrees centigrade in an autoclave. The plate  104  may be a backing plate  22  for a brake pad  18  (see  FIGS. 2A-2C ). The thickness of the third layer  102   c  may vary depending on the application (e.g., brake pads, clutch disks, or disk brake rotors). 
     The thickness of each layer  102   a - 102   c  depends on the application and purpose. Each layer  102   a - 102   c  increases the thermal insulation properties of the friction material, so that in a brake pad application, the heat generated by braking will not transfer to the brake calipers pistons and therefore into the brake fluid. Forming the friction material from layers using the multiple layer process with each layer at the most approximately ⅜ inches thick is preferable, and allows certain gases to escape and allows a better curing process. 
     Because of the high temperatures experienced by friction material, phenolics and other high temp systems, including newly developed sugar based resins are preferred bonding materials. Following laying up the three layers  102   a ,  102   b ,  102   c , and optionally the plate  104 , the friction material is cured at about 300 degrees centigrade and about 250 PSI. The curing is preferably performed in an autoclave. The resulting friction material has a working temperature between 250 degrees centigrade and 650 degrees centigrade, with a melting point of approximately 1200 degrees centigrade. The curing step stabilizes the friction material similar to a heat treat. 
     While friction material used in vehicle brakes and clutches was described above and applications of the friction material according to the present invention, any application of the friction material according to the present invention is intended to come within the scope of the present invention. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.