Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
  • F16D69/00—Friction linings; Attachment thereof; Selection of coacting friction substances or surfaces
  • F16D69/02—Composition of linings ; Methods of manufacturing
  • F16D69/025—Compositions based on an organic binder
  • F16D69/026—Compositions based on an organic binder containing fibres
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
  • F16D69/00—Friction linings; Attachment thereof; Selection of coacting friction substances or surfaces
  • F16D69/02—Composition of linings ; Methods of manufacturing
  • F16D69/027—Compositions based on metals or inorganic oxides
  • F16D69/028—Compositions based on metals or inorganic oxides containing fibres
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
  • F16D2200/00—Materials; Production methods therefor
  • F16D2200/006—Materials; Production methods therefor containing fibres or particles
  • F16D2200/0069—Materials; Production methods therefor containing fibres or particles being characterised by their size
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
  • F16D2200/00—Materials; Production methods therefor
  • F16D2200/0082—Production methods therefor
  • F16D2200/0095—Mixing an aqueous slurry of fibres with a binder, e.g. papermaking process

Definitions

• This invention relates to friction materials and particularly, though not exclusively, to friction materials usable for brake and clutch surfaces.
• Conventional friction materials consist normally of cotton or asbestos fibres impregnated with a resin and made up into a variety of forms such as segments, cones, discs, rollers and so forth, which forms may be rigid or flexible.
• Cotton is used largely for light duties involving relatively low temperatures at the friction interface, whereas asbestos is used for heavier duties and consequent higher temperatures. As interface temperature increases, however, the friction coefficient falls, leading to brake fade.”
• a proportion of the asbestos may be liberated from the friction material as the latter wears and can produce a significant atmospheric pollution problem, for example in the case of automobiles used in towns.
• a friction material comprising a synthetic metal oxide fibre and a binder.
• Synthetic inorganic fibres can be produced with controlled physical properties, which is an advantage in making friction materials with reproducible properties.
• single metal oxides, double metal oxides or mixtures of oxides include thoria; urania; rare earth oxides; yttria; titania; chromia; magnesia; zinc oxide; calcia; double oxides of alkaline earth oxides and alumina, zirconia or chromia, for example BaO/6Al O BaO/ZrO CaO/Cr O MgO/Al o MgO/Cr O SrO/ZrO and other double oxides, for example Al- O
• polycrystalline alumina, alumina/silica or zirconia fibres prepared for example as disclosed in our co-pending United Kingdom Patent Applications Nos. 36,693/72; l2,088/72; 4,369/7l and 29,909/70, as fibres thus prepared have a high coefficient of friction, are hard and have other desirable properties as hereinafter described.
• alumina or zirconia fibres are formed by fibrising a composition having a viscosity of greater than I poise comprising an aqueous solution of a metal compound for example an oxychloride, basic acetate, basic formate or nitrate of aluminium and/or zirconium, and a minor proportion of a water-soluble organic polymer especially polyethylene oxide, polyvinyl alcohol (and, when alumina/silica fibres are requires, a water-soluble organic silicon compound such as polysiloxane), drying the fibre formed and heating to decompose the metal compound to oxide and to decompose the polymer. Heating in the presence of steam is often preferred.
• a metal compound for example an oxychloride, basic acetate, basic formate or nitrate of aluminium and/or zirconium
• a water-soluble organic polymer especially polyethylene oxide, polyvinyl alcohol (and, when alumina/silica fibres are requires, a water-soluble organic silicon compound such as polysi
• Fibrising is preferably carried out by a blowing process which comprises extruding the fibrising composition through one or more apertures into at least one converging gas stream having a component of high velocity in the direction of travel of extruded composition.
• the dimensions and shape of the said aperture may vary widely. We prefer to use an aperture having at least one dimension larger than 5 microns and smaller than 500 microns.
• the gas stream is preferably air, more preferably air at ambient temperature. It is convenient to employ two streams of gas which converge at or near the point where the composition is extruded from the aperture; preferably the angle between the converging gas streams is from 30 to 60.
• At least part of the water in the composition is removed by the gas stream, and the rate of removal may conveniently be controlled by mixing the gas with the water vapour, for example air at a relative humidity of greater than percent may be used.
• the velocity of the air stream may be varied over wide limits, but we prefer to use velocities in the region of 200 to l,500 feet per second.
• the pressure employed to extrude the composition through the apertures will depend on the viscosity of the composition and on the desired rate of extrusion. We find that pressures from 16 to pounds per square inch absolute are convenient for compositions having viscosities up to about 100 poise.
• the average diameter and diameter distribution of the fibres is important; fine fibre diameters and relatively narrow diameter distributions are preferred.
• An average fibre diameter from 0.5 to 10 microns is especially preferred; a diameter distribution which ensures that the fibres contain not greater than 30 percent by weight of fibres of greater diameter than 5 microns, or not greater than 20 percent by number of fibres of greater than 5 microns is also especially preferred.
• Alumina or zirconia fibres available under the Trade Mark of Saffil are especially useful as such fibres have these properties.
• a stabiliser for example in the case of zirconia fibres a minor proportion, for example I to 10 percent of one or more of alkaline oxides, yttria, rare earth oxides, alumina, thoria or hafnia, and in the case of alumina fibres a minor proportion of siltea.
• the amount of shot in the fibres should be as low as possible; shot content less than 5 percent by weight is preferred.
• Alumina fibres are especially useful in preferred embodiments of the invention.
• Alumina exists in a number of phase forms and transformation of one to the other depends upon the temperature to which the alumina is subjected; while not wishing to be restricted to any particular theory it is believed that this property of alumina gives an advantage over many other inorganic fibres used in friction material.
• the friction materials according to the invention are subjected to a temperature which depends upon the degree of friction produced at a braking interface. At a temperature greater than about 700C non-crystalline alumina is converted, at least partially, to a transitional alumina (for example "eta" alumina). At higher temperatures, for example greater than 950C, alpha" alumina is formed.
• transitional and alpha aluminas consist of small crystallites, for example of the order of 100 Angstroms, which, although hard and friction-generating, are not gritty so that they do not accelerate the wear of the braking counter-surface.
• the hardness of alpha alumina is greater than that of transitional alumina which is in turn harder than non-crystalline alumina. It is believed therefore that as the friction temperature increases the coefficient of friction between the braking surface increases. Thus a braking action involving friction materials according to the invention is less subject to fading.
• the temperatures at which the non-crystalline alumina is converted to a transitional alumina or a transitional alumina is converted to alpha alumina may be varied within useful limits by suitable modification of the composition of the alumina fibres and/or the methods used to make them. Methods used to modify the composition of alumina fibres are disclosed in the patent applications hereinbefore referred to. Thus a desirable degree of control over the effect of temperature on coefficient of friction may be achieved by a suitable modification of the alumina fibre composition or the use of suitable blends of alumina fibre.
• the binder used in the friction material according to the invention is preferably an organic binder, for example a thermosetting resin or a natural or synthetic rubber.
• the most preferred binder is one based on a phemoi-formaldehyde resin. Combinations of binders may also be used.
• the friction materials according to the invention may comprise further materials to achieve any particular desired combination of properties.
• lubricants for example litharge, graphite or molybdenum disulphide; fillers, either inert or friction-augmenting, for example ground barytes, perlite, corundum, borax or clays; metals such as zinc, copper, brass, lead or iron, conveniently in the form of wires, turnings or powders for example as scavengers may be incorporated as desired.
• the relative proportions of metal oxide fibre, binder and other ingredients of the friction material are chosen as normally in the art to give the properties required for the duty to be performed.
• the binder is present in the range to 35 percent by weight of the total, the metal oxide fibre in the range 40 to 85 percent by weight of the total and other ingredients from 0.1 to 25 percent by weight of the total.
• the friction materials according to the invention are prepared by any convenient process known in the art.
• the fibre is incorporated into the binder and the mixture shaped into the desired end form for example by dry processing, sheeter processing or processes suitable for the incorporation of woven fibre into the binder.
• Wet board processing is especially preferred for loose fibre; in this process the weighed ingredients except the binder are dispersed for example by adding to a beater or hydrapulper with a quantity of water.
• the wet mixed pulp is then further diluted and felted for example by feeding to a paper-making machine to be formed into a blanket of suitable thickness.
• This felted product is then saturated in a liquid binder, for example a solution of a phenolic resin in an evaporable solvent, shaped and solidified usually by drying.
• the beating stage may be omitted.
• the friction materials according to the invention may be fabricated or formed into any shape suitable for the application in which it is to be used. Thus they may be formed into segments or discs for use as brake linings or clutch facings.
• EXAMPLE I 30 grams of Saffil alumina fibre blanket (ex lCl Ltd.) was shredded into approximately I cm pieces, added to about 250 ml of water and dispersed by means ofa high speed laboratory stirrer. The dispersed fibres were separated off, dried and mixed with l0 grams of a heatsetting liquid phenolic resin (R674l ex BXL) dissolved in 100 ml of acetone. The acetone was removed by applying vacuum. The dry mix was then slightly moistened with water and compressed into a small block in a hydraulic press at 4,500 pounds line pressure. The compressed block was dried at C and cured at l30C for several hours (e.g., over night).
• Saffil alumina fibre blanket ex lCl Ltd.
• Friction/wear tests were carried out on the block using the rubber wear tests defined by BS.903 Part A9 (Method A) and ASTM D394.47 (Method A) using a Croydon abrasion tester. Abrasive paper (600C grade) was used on the disc and a force of 3.6 kg (approximately equal to 1.8 kg/cm) was used to hold the sample against the disc.
• a friction material comprising from 40 to 85 percent by weight of a synthetic inorganic polycrystalline refractory metal oxide fibre having an average fibre diameter of from 0.5 to lO microns having a shot content of less than 5 percent by weight,
• a friction material as claimed in claim 1 wherein the fibre is a polycrystalline alumina fibre.
• a friction material as claimed in claim 5 wherein the water-soluble organic polymer is polyethylene oxide, polyvinyl-alcohol or polyvinylpyrrolidone.
• a friction material as claimed in claim 3 wherein fibrising is effected by extruding the composition through one or more apertures into at least one converging gas stream having a component of high velocity in the direction of travel of the extruded composition.
• a friction material as claimed in claim 8 wherein the gas is air at a relative humidity of greater than percent.
• zirconia fibre is stabilised with a minor proportion of an alkaline earth oxide, yttria, a rare earth oxide, alumina, thoria or hafnia or mixtures thereof.
• a friction material as claimed in claim 1 comprising a lubricant selected from litharge, graphite or molybdenum disulphide.
• a process as claimed in claim 18 wherein the friction material is prepared by wet board processing, comprising the steps of dispersing the fibre, felting the dispersed fibres, saturating the felted fibres in a liquid binder, shaping and solidifying.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Braking Arrangements (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10413659

Family Applications (1)

Country Status (12)

Cited By (17)

Families Citing this family (11)

Citations (11)

• 1972
  • 1972-08-30 GB GB4018972A patent/GB1445975A/en not_active Expired
• 1973
  • 1973-08-15 AU AU59253/73A patent/AU5925373A/en not_active Expired
  • 1973-08-22 BE BE134846A patent/BE803916A/xx unknown
  • 1973-08-22 NL NL7311560A patent/NL7311560A/xx unknown
  • 1973-08-24 US US391515A patent/US3891595A/en not_active Expired - Lifetime
  • 1973-08-28 LU LU68322A patent/LU68322A1/xx unknown
  • 1973-08-28 BR BR6624/73A patent/BR7306624D0/pt unknown
  • 1973-08-29 FR FR7331237A patent/FR2197960B3/fr not_active Expired
  • 1973-08-29 CH CH1240373A patent/CH576595A5/xx not_active IP Right Cessation
  • 1973-08-29 IT IT28328/73A patent/IT998492B/it active
  • 1973-08-30 DE DE19732343822 patent/DE2343822A1/de active Pending
  • 1973-08-30 JP JP48096785A patent/JPS4985439A/ja active Pending

Patent Citations (11)

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