Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2002-02-20
2003-12-02
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S308000, C051S309000, C051S298000, C106S036000, C188S017000, C188S012000, C188S073100, C188S25100R, C188S25100R
Reexamination Certificate
active
06656240
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-asbestos friction material which generates little squeal or other undesirable noise and has a good wear resistance.
2. Prior Art
Conventional friction materials contain large amounts of organic fillers such as cashew dust and rubber dust to satisfy performance requirements concerning noise and wear. Abrasives are also included for improving braking effectiveness, but are generally kept to an absolute minimum to avoid adversely impacting the noise performance.
However, this general rule does not apply to certain friction materials used in combination with rotors, drums and the like made of aluminum alloy reinforced with a suitable hard material. Namely, a non-asbestos friction material for such use having added thereto 0.1 to 30 vol % of a hard inorganic substance having a Mohs hardness of at least 6 is disclosed in JP-A 6-228539.
Yet, in the case of iron-based rotors and drums in predominant use today, the incorporation of hard inorganic substances in friction materials exacerbates brake noise characteristics and thus poses a practical problem.
Moreover, where the ease of rust removal is an important concern, the friction material should contain a large amount of abrasive, which undesirably aggravates the brake noise characteristics and attack of the mating surface in friction, resulting in brake squeal and brake judder.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a non-asbestos friction material that generates little squeal and other undesirable brake noise, has a good wear resistance, and in particular is highly suitable for use in combination with a rotor or drum having a mating surface that comes into contact with the friction material and is made of a material selected from among cast iron, cast steel and stainless steel.
The inventor has found that adjusting the ratio between the total amount of organic substances and the total amount of abrasive within the friction material is effective for minimizing attack to the mating surface and holding down the generation of squeal and other undesirable sounds. The use of a combination of two or more abrasives of different Mohs hardnesses is particularly effective.
A non-asbestos friction material is generally obtained by molding and curing a composition comprising a fibrous base other than asbestos, a binder, an organic filler and an inorganic filler. A high-performance non-asbestos friction material is obtained by further incorporating in the composition an abrasive composed of one or more inorganic substance selected from among inorganic substances having a Mohs hardness of at least 4.5 and inorganic substances having a Mohs hardness of less than 4.5 and containing at least 50 wt % of a component having a Mohs hardness of at least 4.5, by adjusting the volumetric ratio of the total amount of organic substances (which is the combined amount of organic fibers within the fibrous base, binder, and organic filler) to the total amount of abrasive (i.e., total organics/total abrasive) within a range of 1.5:1 to 3.5:1, and preferably by using a mixture of two or more abrasive substances having different Mohs hardnesses as the abrasive. The non-asbestos friction material exhibits high performance because the respective components act effectively. When used in combination with a rotor or drum having a mating surface that comes into contact with the friction material and is made of a material selected from among cast iron, cast steel and stainless steel, this non-asbestos friction material minimizes the generation of low-frequency noise during braking and the generation of brake squeal. The non-asbestos friction material is also characterized by little attack to the mating surface and excellent wear resistance. The present invention is predicated on the above finding.
Accordingly, the invention provides a non-asbestos friction material made by molding and curing a composition comprising a fibrous base other than asbestos, a binder, an organic filler and an inorganic filler. The composition includes also an abrasive composed of one or more inorganic substance selected from among inorganic substances having a Mohs hardness of at least 4.5 and inorganic substances having a Mohs hardness of less than 4.5 and containing at least 50 wt % of a component having a Mohs hardness of at least 4.5. A total amount of organic substances and a total amount of abrasive are in a volumetric ratio (total organics/total abrasive) of 1.5/1 to 3.5/1.
Preferably, the abrasive is a mixture of two or more abrasive substances of different Mohs hardnesses selected from the group consisting of zirconium oxide, zirconium silicate, triiron tetraoxide, magnetite, vermiculite, mica, stannic oxide, magnesium oxide (magnesia), iron sulfide, pyrite, ferric oxide (red iron oxide), chromium oxide, manganese oxide, titanium oxide, zinc carbonate, calcium oxide, calcium silicate, magnesium sulfide, calcium tungstate (scheelite), tungsten oxide, nickel oxide, rock wool, titanium carbide, silicon carbide, silicon dioxide (silica), aluminum oxide, glass fibers, alumina ceramic fibers, alumina-silica ceramic fibers, mullite, alumina-silica-zirconia ceramic fibers, tungsten carbide and silicon nitride. It is advantageous for up to 50 wt % of the abrasive to be an inorganic substance having a Mohs hardness of at least 6.5. The non-asbestos friction material is typically used in combination with a rotor or drum having a mating surface that comes into contact with the friction material and is made of a material selected from among cast iron, cast steel and stainless steel.
DETAILED DESCRIPTION OF THE INVENTION
The friction material composition used to form the non-asbestos friction material of the invention includes a fibrous base other than asbestos, a binder, an organic filler, and an inorganic filler.
Exemplary fibrous bases include inorganic fibers other than asbestos, organic fibers and metal fibers that are commonly employed in friction materials. Suitable organic fibers include nylon, polyester, rayon, phenolic fibers and aramid fibers. Suitable inorganic fibers include potassium titanate whiskers, rock wool, wollastonite, sepiolite, attapulgite and glass fibers. Suitable metal fibers include iron, copper, brass, bronze and aluminum fibers. These fibrous bases may be used singly or as combinations of two or more thereof.
The fibrous base is used in the form of short fibers or a powder and is included in an amount of preferably 1 to 50 vol %, and most preferably 3 to 30 vol %, based on the overall friction material composition.
The binder may be any known binder commonly used in friction materials. Illustrative examples include phenolic resins, melamine resins, epoxy resins, various types of modified phenolic resins (e.g., silicone-modified phenolic resins, acrylic-modified phenolic resins, epoxy-modified phenolic resins, oil-modified phenolic resins, alkylbenzene-modified phenolic resins, cashew-modified phenolic resins), and acrylonitrile-butadiene rubber. Any one or combinations of two or more of these may be used.
The binder is included in an amount of preferably 5 to 30 vol %, and most preferably 10 to 25 vol %, based on the overall friction material composition.
Illustrative examples of the organic filler include cashew dust, rubber powders of various types (e.g., rubber dust, melamine dust), and tire powder. Any one or combination of two or more thereof may be used.
The organic filler is included in an amount of preferably 5 to 25 vol %, and most preferably 10 to 20 vol %, based on the overall frictional material composition.
The inorganic filler is typically a substance which has a Mohs hardness of less than 4.5 and is not among the abrasives to be described later. Illustrative examples include molybdenum disulfide, antimony trisulfide, calcium carbonate, barium sulfate, magnesium sulfate, graphite, calcium hydroxide, slaked lime, calcium fluoride, talc, iron sulfide, zinc sulfide and metal powder. Any one or combination of two or more thereof m
Birch & Stewart Kolasch & Birch, LLP
Marcheschi Michael
Nisshinbo Industries Inc.
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