DESC:FIELD OF INVENTION
The present invention relates to a braking system consisting of brake shoe and brake lining riveted together for use in vehicles. Particularly, the present invention relates to a non-asbestos brake lining suitable for riveting to a brake shoe without cracks and more particularly to non-asbestos brake lining, which prevents cracks during manual riveting operations which are done on re-used brake shoes that are geometrically distorted in shape because of repeated retro fitment after every removal of service liners and also improve the durability of liners fitted on new brake shoes during vehicle manufacture.

BACKGROUND OF INVENTION
Generally brake shoe is a part of a braking system which carries a brake lining in a drum brake used on a vehicle. The brake shoe carries the brake lining, which is riveted or glued to the brake shoe. When the brake is applied, the brake shoe moves and presses the brake lining against the inside of the drum, a friction between the brake lining and the drum provides the braking effort. The brake linings are composed of a relatively soft but tough and heat-resistant material with a high coefficient of dynamic friction, which is mounted to a solid metal backing using high-temperature adhesives or rivets. The complete assembly including the brake lining and the solid metal backing is then often called a brake shoe.

Since the brake lining is the portion of the braking system which converts vehicle's kinetic energy into heat, the brake lining must be capable of surviving high temperatures without excessive wear leading to frequent replacement or out gassing which causes brake fade and a decrease in the stopping power of the brake. Conventionally, asbestos based brake linings are used as friction material for vehicles such as bus, trucks, trailers, tippers for speed control and stopping the vehicle. High dosage of the asbestos in a product gives very high strength to the matrix.

When the high strength asbestos based products are riveted during retro fitment to the brake shoes, said brake shoe can withstand riveting forces without cracks due to high strength of the matrix and the riveted shoe is able to service till end of the life of the brake lining. Due to health concerns on usage of the asbestos, non-asbestos brake linings were developed. When the asbestos is replaced with the non-asbestos materials in composition, combination of different materials are added to make a friction material to meet the requirements of frictional performance and product life cycle, said friction material includes fibers, fillers, abrasives, lubes and within each type, two or multiple materials are added to meet the functional requirement of the friction material.

Higher amount of the fibers are added to increase the strength of the friction material which also increases the cost of the product. Hence to balance cost and performance, in most non-asbestos brake lining products, materials which are good for strength improvement such as aramid fibres are not used or reduced to minimum dosage only for functioning as a process-aid, which leads to the non-asbestos brake lining product with lower strength and hence when they are retrofitted to the old brake shoes, cracks are observed due to improper surface on shoe plate or improper riveting forces which results in performance issues when cracked liners are continued in service.
Even in case of non asbestos brake lining fitted on new brake shoe as done during vehicle manufacture/assembly, rivet hole enlargements were observed on vehicles while in service especially with brake linings having low fibre content when subjected to severe duty conditions like continuous exposure to high temperature in service etc., due to low strength of such brake linings.

Known in the prior art is providing recess buttons in shoes for supporting the lining to arrest lateral movement of the lining and to prevent rivet hole enlargement which leads to liner loosening in service and risk of brake failure. The disadvantage of providing recess buttons in shoes are design of brake shoes requires the brake linings of correct dimensions to get supported at the recess, without which the problem of riveting cracks become worse due to a possibility of the lining sitting on the recess leading to crack during riveting due to gap between lining and the shoe or gap between recess and liner edge will make the recess non-functional and the problem of the liner loosening in service may persist.

Some of the prior arts are:
US6983831 discloses a brake shoe assembly comprising a brake shoe to which brake plates are assembled. The brake shoe has a key that extends outwardly from an outer radial surface of the brake shoe. The key is received in a slot formed in a backing plate of the brake plate. Pre assembled rivets are provided on the brake plates to facilitate alignment of the brake plates with the brake shoe so that the key is received in the slot. The disadvantage of the metallic backing plates are its heaviness and risk of damages during transportation and handling, the vehicle weight increases when multiple liners are used in front and rear axles leading to higher fuel consumption and in addition, cost of the product increases.

US8783428 discloses a brake shoe assembly comprising a brake shoe to which brake plates are assembled. The brake shoe and brake plates are connected by a key or tang in one to a key way or slot in the other. Pre assembled fasteners are provided on the brake plates to facilitate alignment of the brake plates with the brake shoe so that the key is received in the slot, said preassembled fasteners are threaded clinch stud bolts. The disadvantage of the brake shoe assembly are improper tightening during retro fitment leading to loosening in service, vibration induced loosening etc., and risk of brake failure.

US20140190777 discloses a brake lining for a drum brake system, comprising: a first layer that includes recycled frictional material, and is pre-formed to have varying quantities of material throughout the first layer and includes at least one uneven surface; a second layer that includes fresh frictional material that is pre-formed on top of and in combination with the pre-formed first layer to form a dual layer brake lining that has varying quantities of material throughout, with areas having greater quantities of material generating higher density regions of the dual layer brake lining slowing abrasion of lower density regions generated by areas of lesser quantities of materials, with lower density regions of the brake lining improving brake quality. The disadvantage is a profile of crest and trough is required to withstand braking force and usage of different resin in first and second layer may lead to an incompatible system.

US20070117881 discloses a friction material containing a thermosetting resin binder, reinforcing fibers, and friction modifiers are integrally formed with a pressure plate. The friction material has a first layer friction material on a side of a friction surface and a second layer friction material on a side of the pressure plate. A pre-mix containing an elastomer and a cross-linker is blended in the second layer friction material. The disadvantage of the friction material is the pressure plate support is required for making the friction material.

US20060008635 discloses a friction material comprising a first layer comprising a porous base material and at least one type of resin material, and a second layer comprising at least one type of friction modifying particle at least partially covering a top surface of the porous base material, the second layer having an average thickness of about 30-400 µm wherein the second layer has a fluid permeability lower than the first layer.

Accordingly, there exists a need for a non-asbestos brake lining, which prevents cracks during manual riveting operations which are done on re-used brake shoes.

OBJECTS OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the system and method of the present invention.

Accordingly it is the primary object of the present invention to provide a non-asbestos brake lining, which prevents liner cracks near rivet holes during manual riveting operations which are done on re-used brake shoes.
It is another object of the present invention to provide a non-asbestos brake lining, which prevents rivet hole enlargement caused by lower strength of friction material around rivet-hole.

It is another object of the present invention to provide a non-asbestos brake lining with improved durability enhanced by the prevention of rivet hole enlargement caused by lower strength of friction material around rivet hole even when fitted on a new brake shoe during vehicle assembly by Original Equipment Manufacturers.

It is another object of the present invention, wherein the non-asbestos brake lining comprising of:
Composite layer; and
Friction layer.

It is another object of the present invention, wherein the composite layer is of high strength layer positioned on a brake shoe plate through which rivets are secured to the brake shoe without back plate.

It is another object of the present invention, wherein the friction layer is positioned on top of the high strength composite layer, which is in direct contact with brake drum without back plate.

It is another object of the present invention, wherein the high strength composite layer and friction layer are integrally molded together in-situ under pre-defined temperature and pressure for a pre-defined period of time using a common binder to form a single piece brake lining.

It is another object of the present invention, wherein the single piece brake lining of required thickness is finished to the required dimension by drilling holes for riveting to the brake shoe during retro fitment or fitment to a new brake shoe.

It is another object of the present invention, wherein the friction layer surrounding the drill holes are strengthened to enable said friction layer to withstand higher riveting force without cracking during riveting.

It is another object of the present invention, wherein the high strength composite layer functions as the strength enhancing medium without affecting the friction performance of the friction layer.

It is another object of the present invention, wherein the high strength composite layer provides required higher strength to the matrix.

It is another object of the present invention, wherein the combination of the high strength composite layer and the friction layer enhances overall strength of the matrix leading to improvements in performance during braking and liner durability without premature failure.

It is another object of the present invention, wherein the high strength composite layer has cross breaking strength of approximately 50 mega Pascals [MPa].

It is another object of the present invention, wherein the friction layer has relatively lower cross breaking strength of approximately 30 mega Pascals [MPa].
It is another object of the present invention, wherein the high strength composite layer enhances the strength of the friction layer of the brake lining, which leads to the integral single piece brake lining having cross breaking strength of approximately 45 mega Pascals [MPa].

It is another object of the present invention, wherein the high strength composite layer has Rockwell hardness in the same range of 85-100 ['L' scale] as like the friction layer alone.

It is another object of the present invention, wherein density of the high strength composite layer is in the range of 2.05-2.10 [g/cc].

It is another object of the present invention, wherein the integral single piece brake lining has Rockwell hardness in the same range of 85-100 ['L' scale] as like the friction layer alone.

It is another object of the present invention, wherein density of the integral single piece brake lining is in the range of 2.00-2.05 [g/cc].

It is another object of the present invention, wherein the integral single piece brake lining has Inter laminar shear strength in the range of 15-16 [MPa] when compared with 8 [MPa] Inter laminar shear strength of the friction layer alone.

It is another object of the present invention, wherein the integral single piece brake lining has rivet holding strength in the range of 15-18 [N/mm] when compared with 12-15 [N/mm] rivet holding strength of the friction layer alone.
It is another object of the present invention, wherein the high strength composite layer is intended up to a pre defined wear mark thickness of the brake lining to ensure rivet head is within the thickness of the composite layer of high strength and materials surrounding the drill holes are covered with the composite layer of high strength.

It is another object of the present invention, wherein the high strength composite layer is intended for service up to the pre-defined wear mark limit thereby ensuring that any levelling variation in manufacturing would not lead to crack around the drill holes.

Although particular components and materials are specifically identified herein, one skilled in the art may readily substitute the components and/or materials of similar function without departing from the invention as defined in the appended objects. Therefore, the above should not be construed as limiting the invention, which is defined by the appended objects.

SUMMARY OF INVENTION
Thus according to the basic aspect of the present invention there is provided a non-asbestos brake lining comprising of:
composite layer; and
friction layer,
wherein the composite layer is of high strength layer positioned on a brake shoe plate through which rivets are secured to the brake shoe without back plate,
wherein the friction layer is positioned on top of the high strength composite layer, which is in direct contact with brake drum without back plate,
wherein the high strength composite layer and friction layer are integrally molded together in-situ under pre-defined temperature and pressure for a pre-defined period of time using a common binder to form a single piece brake lining, and
wherein the non-asbestos brake lining prevents liner cracks near rivet holes during manual riveting operations and prevents rivet hole enlargement caused by lower strength of friction material around rivet-hole.

It is another aspect of the present invention, wherein the single piece brake lining of required thickness is finished to required dimension by drilling holes for riveting to the brake shoe through holes in said brake shoe for fixing of the brake lining with rivets during retro fitment or fitment to a new brake shoe.

It is another aspect of the present invention, wherein the friction layer surrounding the drill holes upto the height of the rivet head are strengthened to enable said friction layer to withstand higher riveting force without cracking during riveting.

It is another aspect of the present invention, wherein the common binder for both the high strength composite layer and friction layer ensures bonding between said two layers during chemical cross linking that occurs during curing process which involves high temperature and high pressure for the pre-defined period of time.

BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1: illustrates assembled brake shoe with non-asbestos brake lining according to the present invention.
Figure 2: illustrates internal view of non-asbestos brake lining according to the present invention.
Figure 3: illustrates cross sectional view of a single rivet hole - exploded view of the assembled brake shoe with non-asbestos brake lining before riveting according to the present invention.
Figure 4: illustrates cross sectional view of a single rivet hole - exploded view of the assembled brake shoe with non-asbestos brake lining after riveting according to the present invention.
Figure 5: illustrates cross sectional view of the brake shoe assembly with non-asbestos brake lining of present invention after riveting according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention as discussed hereinbefore relates to a non-asbestos brake lining suitable for riveting to a brake shoe without cracks and more particularly to non-asbestos brake lining, which prevents cracks during manual riveting operations which are done on re-used brake shoes that are geometrically distorted in shape because of repeated retro fitment after every removal of service liners and also improve the durability of liners fitted on new brake shoes during vehicle manufacture. Advantageously, the non-asbestos brake lining of the present invention is suitable for any asbestos free friction layer product to improve its riveting crack behaviour and durability.

Referring to Figures 1 to 2, the non-asbestos brake lining comprises of composite layer [4]; and main friction layer [1]. The composite layer [4] is of high strength layer without back plate positioned on a brake shoe [3] plate through which rivets are secured to the brake shoe [3] as shown in Figure 1. The friction layer [1] is positioned on top of the high strength composite layer [4] without back plate, which is in direct contact with brake drum, said high strength composite layer [4] and main friction layer [1] are integrally molded together in-situ under pre-defined temperature and pressure for a pre-defined period of time using a common binder to form a single piece brake lining. The binder includes but not limited to powder binders or liquid binders.

The common binder for both the high strength composite layer [4] and main friction layer [1] ensures bonding between the two layers during chemical cross linking that occurs during curing process which involves high temperature and high pressure for the pre-defined period of time. The single piece brake lining of required thickness is finished to the required dimension by drilling holes [5] for riveting to the brake shoe [3] through holes [2] in the brake shoe [3] for fixing of the brake lining with rivets during retro fitment or fitment to a new brake shoe as shown in Figure 3. The main friction layer [1] surrounding the drill holes [5] are strengthened to enable said main friction layer [1] to withstand higher riveting force without cracking during riveting.

Referring to Figure 3, the combination of the high strength composite layer [4] and the main friction layer [1] as shown in Figure 2 enhances overall strength of the matrix leading to improvements in performance during braking and liner durability without premature failure. The high strength composite layer [4] is intended for service up to the pre-defined wear mark limit thereby ensuring that any levelling variation in manufacturing would not lead to crack around the drill holes [5]. The high strength composite layer [1] is intended up to a pre defined wear mark [6] thickness of the brake lining to ensure rivet head [7] is within the thickness of the composite layer [4] of high strength and materials surrounding the drill holes [5] are covered with the composite layer [4] of high strength before riveting [8]. Cross sectional view of a single rivet hole – exploded view of the assembled brake shoe [3] with non-asbestos brake lining after riveting [9] is illustrated in Figure 4 and cross sectional view of the brake shoe assembly with non-asbestos brake lining of present invention after riveting [9] is illustrated in Figure 5

For illustration, the high strength composite layer [4] functions as the strength enhancing medium without affecting the friction performance of the main friction layer [1]. The high strength composite layer [4] has cross breaking strength of approximately 50 mega Pascals [MPa]. The main friction layer [1] has relatively lower cross breaking strength of approximately 30 mega pascals [MPa], the high strength composite layer [4] enhances the strength of said main friction layer [1] of the brake lining, which leads to the integral single piece brake lining having cross breaking strength of approximately 45 mega pascals [MPa].

The high strength composite layer [4] has Rockwell hardness in the range of 80-100 ['L' scale]. Density of the high strength composite layer [4] is in the range of 2.05-2.10 [g/cc], said high strength composite layer [4] provides required higher strength to the matrix. The integral single piece brake lining has Inter laminar shear strength in the range of 15-16 [MPa] when compared around 10 [MPa] Inter laminar shear strength of the friction layer alone. The integral single piece brake lining has rivet holding strength in the range of 15-18 [N/mm] when compared with 12-15 [N/mm] rivet holding strength of the friction layer alone as illustrated in Table 1.

Table-1:
S.No Properties Existing Single
layered non-asbestos brake lining Twin Layered non-asbestos brake lining High strength composite layer
1 Rockwell Hardness - 'L' scale 70-100 85-100 80-100
2 Density, g/cc 1.90 - 1.95 2.00 - 2.05 2.05-2.10
3 Cross breaking strength, MPa 30-35 45-50 55-60
4 Inter laminar shear strength (at interface of two layers), MPa 9-12 15-16 -
5 Rivet holding strength,N/mm 12-15 15-18 -

The test results showing the technical effects of the present invention are annexed as Annexure-A- Summary of trials conducted with high strength composite material and confirmation on the efficacy of the improvement. The efficacy of improvement from the invention as illustrated in Annexure A is an illustrative example of the invention.

The embodiments of the invention been disclosed in detail in this specification are purely for illustrative purposes and the present invention can be embodied in many other forms or carried out in other ways, without departing from the spirit or essential characteristics thereof. It is understood that the invention is not limited thereto, but is susceptible of numerous changes and modifications as known to those skilled in the art, and all such variations or modifications lies within the scope of the present invention. The values and unit of measurement of hardness, density, cross breaking strength, interlaminar shear strength and rivet holding strength mentioned in the complete specification are only illustrative examples for understanding the invention. Therefore, the above should not be construed as limiting the invention, which is defined by the appended objects.
,CLAIMS:WE CLAIM:
1. A non-asbestos brake lining comprising of:
composite layer [4]; and
friction layer [1],
wherein the composite layer [4] is of high strength layer positioned on a brake shoe [3] plate through which rivets are secured to the brake shoe [3] without back plate,
wherein the friction layer [1] is positioned on top of the high strength composite layer [4], which is in direct contact with brake drum without back plate,
wherein the high strength composite layer [4] and friction layer [1] are integrally molded together in-situ under pre-defined temperature and pressure for a pre-defined period of time using a common binder to form a single piece brake lining, and
wherein the non-asbestos brake lining prevents liner cracks near rivet holes during manual riveting operations and prevents rivet hole enlargement caused by lower strength of friction material around rivet-hole.

2. The non-asbestos brake lining as claimed in claim 1, wherein the single piece brake lining of required thickness is finished to required dimension by drilling holes [5] for riveting to the brake shoe [3] through holes [2] in said brake shoe [3] for fixing of the brake lining with rivets during retro fitment or fitment to a new brake shoe.

3. The non-asbestos brake lining as claimed in claim 2, wherein the friction layer [1] surrounding the drill holes [5] upto the height of the rivet head are strengthened to enable said friction layer [1] to withstand higher riveting force without cracking during riveting.
4. The non- asbestos brake lining as claimed in claim 1, wherein the common binder for both the high strength composite layer [4] and friction layer [1] ensures bonding between said two layers during chemical cross linking that occurs during curing process which involves high temperature and high pressure for the pre-defined period of time.