Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-03-02
2003-09-09
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S153000, C524S015000
Reexamination Certificate
active
06617375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to non-asbestos friction materials which are particularly well suited for use as brake linings in drum brakes because they undergo little wear during high-speed braking and have an excellent heat resistance, a stable braking performance and good strength.
2. Prior Art
Drum brake friction materials used for braking in automobiles, large trucks, railroad cars and various industrial equipment are required to have a number of performance features. These features include not only an excellent braking effectiveness (i.e., a high friction coefficient), but also a high heat resistance, minimal noise generation, and good strength to prevent cracks from forming when the friction material is bolted or riveted to the brake shoe.
Unlike in disk brakes, the brake shoe and brake lining in drum brakes are situated at the interior of the drum, making it difficult for heat generated during braking to dissipate to the exterior. As a result, the brake shoe and the friction material at the surface of the brake lining are scorched by heat, which greatly reduces braking effectiveness and tends to lead to brake fade. Accordingly, there is a strong desire for better heat resistance.
Moreover, the development of extensive highway networks and the increased use of long-distance transportation in recent years have brought about a sharp rise in the frequency of high-speed braking, greatly increasing both the amount of wear by the brake linings and, owing to the thermal history, the frequency of cracking at the surface of the lining against which the brake drum rubs.
Various attempts have been made to resolve these problems in frictional materials for drum brakes. Such efforts have included adding a large amount of graphite as a lubricant to reduce noise (in which case the amount of binder also increases), enhancing heat resistance by adding cashew dust that discharges little tar when heated, and including a higher proportion of binder to improve the strength of the friction material.
However, none of these approaches has succeeded in providing friction materials for drum brakes with all the desired performance features. Indeed, the prospects for developing in particular a friction material for drum brakes endowed with low wear during high-speed braking, stable brake effectiveness, and excellent heat resistance have been regarded as very poor.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to provide a high-quality non-asbestos friction material having low wear during high-speed braking, excellent heat resistance, stable braking effectiveness and good strength.
The inventor has found that, in non-asbestos friction materials, incorporating high-tar cashew dust and lowering the amount of binder and graphite are effective ways for achieving reduced wear during high-speed braking, improved heat resistance and other desirable aims.
That is, in non-asbestos friction materials obtained by molding and curing a composition comprising a fibrous base, a filler and a binder, the incorporation of a high-tar cashew dust as at least part of the filler results in the formation by the high-tar cashew dust of a thin, uniform organic film on the friction surface, thereby reducing the amount of friction material wear during high-speed braking and stabilizing braking effectiveness. Also, by having the total amount V
1
of binder present in the friction material composition and the amount V
2
of graphite present as part of the filler (both amounts being expressed in volume percent based on the overall composition) be such that the product V
1
×V
2
is from 10 to 100 inclusive and the sum V
1
+V
2
is from 10 to 30 inclusive, the level of organic components can be held much lower than in the prior art. This makes it possible to achieve a high-quality non-asbestos friction material having a greatly improved heat resistance and, together with this, an excellent performance during high-speed braking.
The inventor has also found that, in non-asbestos friction materials comprising a molded and cured composition that includes a fibrous base, a filler and a binder, when the filler is at least partially composed of 1 to 35 vol % of high-tar cashew dust and less than 5 vol % of graphite and when the binder is present in a total amount of at most 30 vol %, based on the overall composition, these components work together to lower the amount of wear. As a result, in spite of the presence of much lower amounts of graphite and binder than in prior-art non-asbestos friction materials, or rather because of the presence of graphite and binder in such small amounts, the friction material has a vastly improved heat resistance. Hence, there can be obtained a high-quality non-asbestos friction material having low wear during high-speed braking, excellent heat resistance, stable braking effectiveness and sufficient strength to prevent crack formation when the friction material is bolted or otherwise mounted on a brake shoe.
Therefore, according to a first aspect, the invention provides a non-asbestos friction material obtained by molding and curing a composition comprising a fibrous base, a filler and a binder; wherein the binder is present in a total amount V
1
and the filler includes in part graphite present in an amount V
2
, each expressed in volume percent of the overall composition, such that the product V
1
×V
2
is from 10 to 100 inclusive and the sum V
1
+V
2
is from 10 to 30 inclusive.
According to a second aspect, the invention provides a non-asbestos friction material obtained by molding and curing a composition comprising a fibrous base, a filler and a binder; wherein the filler is at least partially composed of 1 to 35 vol % of high-tar cashew dust and less than 5 vol % of graphite, based on the overall composition, and the binder is present in a total amount of at most 30 vol %.
DETAILED DESCRIPTION OF THE INVENTION
The non-asbestos friction material of the invention is made by molding and curing a non-asbestos friction material composition composed primarily of a fibrous base, a filler and a binder. According to a first embodiment of the invention, the friction material includes the binder in a total amount V
1
and includes as part of the filler graphite in an amount V
2
(both amounts being expressed in percent by volume of the overall composition), such that the product V
1
×V
2
is from 10 to 100 inclusive and the sum V
1
+V
2
is from 10 to 30 inclusive (that is, 10≦V
1
×V
2
≦100 and 10≦V
1
+V
2
≦30). By satisfying these conditions, the inventive material has a vastly improved performance during high-speed braking.
The product V
1
×V
2
is in a range of preferably 15 to 100, more preferably 20 to 90, and most preferably 20 to 80. The sum V
1
+V
2
, which represents the combined amount of binder and graphite, is in a range of preferably 10 to 27, more preferably 15 to 25, and most preferably 17 to 28.
If the total amount of binder V
1
and the amount of graphite V
2
(both in volume percent) are such that the product V
1
×V
2
and the sum V
1
+V
2
do not fall within the above ranges, the amount of organic components in the friction material becomes too large, lowering the heat resistance and compromising the performance during high-speed braking.
The binder may be any known binder commonly used in friction materials. Illustrative examples include phenolic resins, various rubber-modified phenolic resins such as high-ortho phenolic resins modified with acrylonitrile-butadiene rubber (NBR), NBR-modified phenolic resins and acrylic rubber-modified phenolic resins, and also melamine resins, epoxy resins, NBR, nitrile rubber and acrylic rubber. Any one or combinations of two or more of these may be used. The binder is included in a total amount V
1
which is up to 30 vol %, preferably up to 27 vol %, more preferably up to 25 vol %, even more preferably up to 23 vol %, and most preferably up to 20 vol %, based on the overall amount of the frictio
Kobayashi Mitsuru
Sawamura Shinya
Birch & Stewart Kolasch & Birch, LLP
Buttner David J.
Nisshinbo Industries Inc.
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