FIELD OF INVENTION
This invention generally relates to novel non-asbestos friction material for a brake pad and method of preparation thereof, particularly to the non-asbestos friction material used in manufacturing brake pads for brakes of Railway vehicles.
The preferred embodiment of instant invention discloses friction material comprising chopped brass wool metal fibre and/or non-asbestos based Steel wool metal fibre formulations to be used in Brake pad. The friction material generally includes formulation of friction material includes at least one binder forming 14 – 20 % by volume; at least one fiber forming 3-6 % by volume; lubricant forming 2-6% by volume; at least one abrasive, such as a blend of magnesium oxide, Iron oxide & zinc Oxide, forming 1-5% by volume; and hot emulsion as reinforcement as well as wear resistance.
BACKGROUND/PRIOR ART
In present age of high speed automobiles and railway vehicles, role of efficient friction material to be used in braking pads has become very important. Several methods and compositions are known in the literature and with the ongoing advancements in the material science, efforts are being made to prepare better and more efficient friction materials to be used in braking pads, especially to be used in railway vehicles.
One patent US4119591 dated 10.10.1978, titled as Friction material reinforced with steel and cellulose fibers, relates to An asbestos free organic base friction material for use as a friction lining of a brake. A combination of fibers selected from a group consisting of steel, cellulose, glass mineral and rayon fibers and athermosetting resin binder are combined with cashew nut particles, elastomeric modifiers and inorganic modifiers to produce an organic base friction material having a substantial stable coefficient of friction over the normal operating range of the brake.
Another Patent US5065658A highlights several prior patents relating to non-asbestos friction material, particularly use of carbon fibers and aramid fibers in friction materials such as automotive disk brake pads, clutch facings and the like.
US patent US5428081Arelates to acrylic containing non-asbestos, frictional material composition and more particularly, to a brake lining and a brake pad which has a desirable lubricant property in a dry or humid atmosphere, and which is not affected by temperature nor wears out readily and produces little noise.
Another US Patent US 6612415B2 with Japanese priority date of 01.08.2000 relates to Friction member and method of manufacture; wherein the friction member is made up of a back plate, a non-asbestos friction material bonded to a surface of the back plate and produced by molding and curing a non-asbestos friction material composition, and a metal phosphate conversion coating formed between the back plate and the non-asbestos friction material. The friction member of said prior art comprises a back plate, a non-asbestos friction material bonded to a surface of the back plate and produced by molding and curing a composition that includes a fibrous base, a binder and a filler, and a zinc phosphate conversion coating formed between the back plate and the non-asbestos friction material; wherein the conversion coating is composed of crystals having a maximum length of 0.1 to 50 µm and an aspect ratio of 1/1 to 1/10, has a coating weight of 0.5 to 20 g/m2, and has a phosphophyllite ratio P/(P+H), based on phosphophyllite crystals (P) and hopeite crystals (H) therein, of from 0.1 to 1.
Another Chinese Patent CN1995436A of year 2006, titled as copper base particle reinforced material, discloses a reinforced friction material of copper-based particle in the friction material making domain, which comprises the following parts: 30-70% Cu, 4-11% Sn, 1-15% Al, 5-18% Fe, 2-15% Al2O3, 2-15% SiO2, 0-15% ferrochrome and 5-20% graphite.
Another Chinese prior art CN102560183A of year 2012, titled as Friction material of brake sheet for rail transit vehicle brake system, and preparation method and application of friction material,relates to an Al/Sic and Cu/Sic composite material friction pair used for railway vehicles and a manufacturing method of the Al/Sic and Cu/Sic composite material friction pair and belongs to the technical field of manufacturing of friction pairs. A friction pair in the prior art has the defects of being complex in the production technology, poor in heat conduction performance and short in service life. A network silicon carbide ceramic framework is embedded in the friction face of the friction pair, a plurality of heat dissipating ribs are arranged in the circumferential direction of the other side of the friction pair, a ventilation channel penetrating through a brake disk is formed in the middle of each heat dissipating rib, the network silicon carbide ceramic framework is embedded in the friction face of a Cu/Sic brake pad, and latticed heat dissipating fins are arranged on the other side of the Cu/Sic brake pad.
In continuation of the aforesaid efforts being made in different parts of the globe and in different time duration, the subject matter instant invention is intended to provide a further advanced friction material to be used in braking pads of railway vehicles, comprising of several efficacious structural and functional properties, particularly by involving easy industrial manufacturing methods, light in weight, high and stable in frictional coefficient, good in heat conduction performance, long in service life and suitable for the existing railway vehicles.
OBJECTS OF THE INVENTION
The prime object of the present invention is to provide non-asbestos-based friction materials for brake pads, particularly comprising reinforcement of brass wool, wherein said friction material for braking pad is characterized in many useful properties and performance characteristics including excellent reinforcing strength, increased coefficient of friction at high temperatures, excellent thermal conductive properties and increase in the life of the friction material.
Another object of the present invention is to provide certain preferred embodiments of the said non-asbestos based friction materials, which are characterized inefficient engagement on the brakingdisc and due to low wear and tear it reduces formation of dust thereof.
Another object of the present invention is to provide a non-asbestos friction material for a brake pad that is rubber base organic composite material; wherein the composition of one preferred embodiment of the said friction material, in percent (%) by volume of the friction material, is as under:
• a hot emulsion SBR forming 25-35 % by volume;
• a binder (NBR modified phenolic resin) forming 14-20% by volume;
• a fiber forming 3-6% by volume;
• a lubricant forming 2-6% by volume The lubricant includes at least one sulfide. at least one abrasive forming 1-5 % by volume; and
• a filler forming 5-20 % by volume. The filler includes a barium sulphate & zinc oxide.
Another object of the invention is to provide such a composition of the non-asbestos friction material wherein the lubricant includes at least one sulfide, and wherein one preferred lubricant selected therein is a blend of antimony tri-sulphide, Natural graphite and another metal sulphide, forming 1-5% by volume of the said material.
Another object of the present invention is to provide a novel and cost-effective method of manufacturing said non-asbestos friction material for braking pads, which includes characteristic method of mixing, comprising the step of blending the SBR with the lubricant, abrasive, and binder to form a homogeneous mixture.
Another object of the present invention is to provide a novel and cost-effective method of manufacturing said non-asbestos friction material for braking pads; wherein the homogeneity of mixture is based on the optimum volume of the mixture. Another object of the present invention is to provide a novel and cost-effective method of manufacturing said non-asbestos friction material for braking pads, wherein the mixing process comprising of two roll mills/Intermesh mixer followed by crumbling m/c to mix it into uniform granules.
Another object of the present invention is to provide a novel and cost-effective method of manufacturing said non-asbestos friction material for braking pads, wherein said method further includes pressing the homogeneous mixture & backing plate together under a pressure of 175 tons on every piece of area (comprising of 432 cm2) at a temperature of 50 ± 10°C for a process cycle of 2.5 minute.
At the outset of the description, which follows, it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment, without intending to imply any limitation on the scope of this invention. Accordingly, the description herein is to be understood as an exemplary embodiment and teaching of the invention is not intended to be taken restrictively.
SUMMARY OF THE INVENTION:
The invention disclosed hereinbelow generally relates to manufacturing of a novel composition of brass and/or steel wool reinforced friction material to be used in the braking pads, preferably in railway vehicles.
Such friction material compositions have properties of excellent friction performance in both dry & wet conditions, high abrasion resistance and very high thermal resistance. Therefore, said friction material disclosed in the instant invention increase the life of the brake pads and throughout its functional life it efficiently maintains the noise level within the acceptable limit.
Brass wool chopped in non-asbestos friction materials for brake pads, provides many useful properties and performance characteristics including excellent reinforcing strength, increased coefficient of friction at high temperatures and excellent thermal conductive properties. In addition, Brass wool provides many other qualities that increases the Life of the friction material. The friction material engages properly on the disc and due to low wear and tear it also reduces dust as well.
Steel fibres are also been used in non-asbestos friction materials for brake pads. However, steel fibers do not have many of the positive attributes like brass wool.
One aspect of the present invention provides a non-asbestos friction material for a brake pad that is rubber base organic composite material. The composition of friction material comprises, in percent (%) by volume of the friction material: a hot emulsion SBR forming 25-35 % by volume; a binder (NBR modified phenolic resin) forming 14-20% by volume; a fiber forming 3-6% by volume; and a lubricant forming 1-5% by volume.
Most preferred composition of the non-asbestos friction material for brake pad to be used in railway vehicles, and optional compositions for the same are substantially described hereinbelow:
Figure 1: Schematic representation of the braking pad, made of the non-asbestos friction material comprising of brass-wool and/or steel wool reinforcement therein.
DESCRIPTION OF THE INVENTION
Most preferred composition of the non-asbestos friction material for a brake pad comprises of the following material in percent (%) of volume:
• Fibre forming 3-6 % by volume;
• Binder forming 14-20% by volume;
• Lubricant forming 1-5% by volume, said lubricant including at least one sulphide;
• Filler forming 5-20 % by volume, said filler including at least one oxides;
• Metal fibres forming 16 -24 % by volume, said metal fiber including at least one brass wool chopped;
• Friction modifier forming 6-12% by volume, said friction modifier including at least one cashew friction dust.
• Elastomer forming 25-35 % by volume; said elastomer including at least on high styrene base SBR.
Said friction material, as disclosed in the present invention and is capable of being used in braking pad,is characterized in at least one of the following composition related specialty:
• said fiber comprises at least one polyaramid fiber & cellulose fiber;
• said binder comprises at least one NBR modified phenolic resin;
• said metal fiber comprises at least one brass wool chopped & steel wool;
• said elastomer comprises at least one high bound styrene base SBR;
• said lubricants comprises at least one metal sulphides; and
• said oxides comprises at least one magnesium oxide, namely zinc oxide & red iron oxide.
The lubricant includes at least one sulfide; wherein one preferred lubricant selected therein is a blend of antimony tri-sulphide, Natural graphite and another metal sulphide, forming 1-5% by volume of the said material.
The friction material further comprises at least one abrasive forming 3- 6 % by volume; and a filler forming 5-20 % by volume. The filler includes a barium sulphate & zinc oxide.
One preferred composition selected for the said non-asbestos friction material, to be used in the braking pad of railway vehicles, includes a binder such as NBR modified phenolic resin, forming 14 – 20 % by volume; a fiber such as aramid fiber& cellulose fiber forming 3-6 % by volume; a lubricant, such as a blend of antimony tri-sulphide, Natural graphite and another metal sulphide, forming 1-5% by volume; and at least one abrasive, such as a blend of magnesium oxide, Iron oxide & zinc Oxide, forming 3-6 % by volume.
The friction material further comprises of hot emulsion SBR as a reinforcement as well as wear resistant of about 25-30% by volume. Said elastomer comprises at least one high bound styrene base SBR.
Yet another aspect of the invention is the method of mixing, comprising the step of blending the SBR with the lubricant, abrasive, and binder to form a homogeneous mixture. The homogeneity of mixture is based on the optimum volume of the mixture. The mixing process comprising of two roll mills/Intermesh mixer followed by crumbling m/c to mix it into uniform granules.
The method further includes pressing the homogeneous mixture & backing plate together under a pressure of 175 tons on every piece of area (comprising of 432 cm2) at a temperature of 50 ± 10°C for a process cycle of 2.5 minute.
The inventive friction material is highly stable in thermal conditions.
The inventive friction material also provides excellent process capabilities, including high efficiency and low wastage, which contribute to the lower production cost.
The friction material of the present invention provides the same level of friction, pad life, noise, and other performance characteristics as in a typical non-asbestos pad. Brake pads formed of the inventive friction material pass the following vehicle application tests:
RDSO/2013/CG-01, performance test, drag test, wet performance test and noise test on inertia dynamometer.
The following examples in table of experimental sample 1, sample -2 & sample -3 provides some exemplary friction material using the present invention that have sufficient performance characteristics.

• The ingredients for the mixer of example 1 are generally prepared in standard banbury / two roll mixer for approximately 10-30 minutes & then crumbled to a crumbling m/c to make into a granular form.
• After then pressed into a press cure mould& later cured in a oven.
• The composition amount described in above table have been rounded off to the nearest for sake of simplicity.
• The friction material of sample 1 provides good level of friction characteristics & wear rate. The friction level in wet condition is lower than the desired requirement. Noise & red band observed over speed of 200 kmph at full scale dynamometer. This is particularly because of higher steel fibers.
• Some variation in sample 2 as compared to sample 1 induced. Some part of steel fiber in form chopped brass wool & increased SBR added which showing excellent friction properties & also no red band at speed of 200 kmph which indicates thermal conductivity of friction material play important role in red band formation. Apart from these characteristics the friction characteristic in wet condition is still on lower side.
• Further variation to sample 3 as compared to sample 2 to achieve the friction characteristics in wet condition some part of steel fiber replaced with CI grit induced which showing excellent performance in wet condition as well as in dry condition. The addition of brass wool chopped & increased SBR showing excellent friction characteristics, wear performance & reduced noise level.
ADVANTAGEOUS FEATURES OF THE PRESENT INVENTION
1. Excellent friction performance in both dry & wet conditions.
2. This friction material increase the life of the brake pads and the noise level is also within the acceptable limit.
Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure, are contemplated thereby, and are intended to be covered by the following claims.

WE CLAIM:
1. The composition of friction material composition for a brake pad comprises, in percent (%) by volume, a hot emulsion SBR forming 25-35 % by volume; a binder (NBR modified phenolic resin) forming 14-20% by volume; a fiber forming 3-6% by volume; and a lubricant forming 1-5% by volume.
2. Non-asbestos friction material, as claimed in claim 1, wherein the most preferred composition of the non-asbestos friction material comprises following ingredients in percent (%) of volume:
• Fibre forming 3-6 % by volume;
• Binder forming 14-20% by volume;
• Lubricant forming 1-5% by volume, said lubricant including at least one sulphide;
• Filler forming 5-20 % by volume, said filler including at least one oxides;
• Metal fibres forming 16 -24 % by volume, said metal fiber including at least one brass wool chopped;
• Friction modifier forming 6-12% by volume, said friction modifier including at least one cashew friction dust.
• Elastomer forming 25-35 % by volume; said elastomer including at least on high styrene base SBR.
3. The friction material, as claimed in claim 1 or 2, wherein one preferred composition of said friction material is selected out of following three samples:

Wherein the friction material of composition under sample-1 is characterized in the followings:-
• The ingredients for the mixer are generally prepared in standard banbury/ two-roll mixer for approximately 10-30 minutes & then crumbled to a crumbling m/c to make into a granular form;
• After then pressed into a press cure mould& later cured in a oven;
• The composition amount of said sample-1 have been rounded off to the nearest for sake of simplicity; and
• Said friction material of sample 1 provides good level of friction characteristics & wear rate, wherein the friction level in wet condition is lower than the desired requirement, noise & red band observed over speed of 200 kmph at full scale dynamometer, which is particularly because of higher steel fibers.
4. The friction material, as claimed in claims 1 to 3, wherein said fiber comprises at least one polyaramid fiber & cellulose fiber.
5. The friction material, as claimed in claims 1 to 3, wherein said binder comprises at least one NBR modified phenolic resin.
6. The friction material, as claimed in claims 1 to 3, wherein said metal fiber comprises at least one brass wool chopped & steel wool.
7. The friction material, as claimed in claims 1 to 3, wherein said elastomer comprises at least one high bound styrene base SBR.
8. The friction material, as claimed in claims 1 to 3, wherein said lubricants comprises at least one metal sulphides.
9. The friction material, as claimed in claims 1 to 3, wherein said oxides comprises at least one magnesium oxide, zinc oxide & red iron oxide.
10. Method of making the friction material, as claimed in any of claims 1-3, includes following characteristic steps/features:
• The ingredients for the mixer of example 1 are generally prepared in standard banbury/two roll mixer for approximately 10-30 minutes & then crumbled to a crumbling m/c to make into a granular form;
• After then pressed into a press cure mould& later cured in a oven;
• The composition amount described in above table have been rounded off to the nearest for sake of simplicity;
• The friction material of sample 1 provides good level of friction characteristics & wear rate. The friction level in wet condition is lower than the desired requirement. Noise & red band observed over speed of 200 kmph at full scale dynamometer. This is particularly because of higher steel fibers.
• Some variation in sample 2 as compared to sample 1 induced. Some part of steel fiber in form chopped brass wool & increased SBR added which showing excellent friction properties & also no red band at speed of 200 kmph which indicates thermal conductivity of friction material play important role in red band formation. Apart from these characteristics the friction characteristic in wet condition is still on lower side.
• Further variation to sample 3 as compared to sample 2 to achieve the friction characteristics in wet condition some part of steel fiber replaced with CI grit induced which showing excellent performance in wet condition as well as in dry condition. The addition of brass wool chopped & increased SBR showing excellent friction characteristics, wear performance & reduced noise level.