Friction lining for drum brake

Abstract

The invention relates to a friction lining mixture for producing a brake lining for a drum brake, comprising at least 15% by weight of metal fibres, preferably steel fibres, in particular steel wool, at least 7% by weight of glass fibres, in the form of glass fibre bundles, at least 4% by weight of a resin, and at least 2% by weight of friction particles, preferably having a Mohs hardness equal to or greater than 9, as well as friction linings and drum brake linings produced thereby and methods for producing drum brake linings.

Description

Technical Field

[0001] The present invention relates to a friction lining mixture which is particularly suitable for drum brakes and a friction lining produced therefrom. The invention also comprises a method for producing such a friction lining and the use of such a friction lining. Background Art

[0002] A drum brake is a closed, cylindrical structure. Its most important components are the cylindrical brake drum, the brake caliper, and the wheel cylinder. During braking, the wheel cylinder presses against the fixed brake caliper, which in turn presses the caliper against the brake drum, thereby slowing the vehicle.

[0003] The brake caliper primarily serves as a carrier for the friction material or friction lining. Due to the cylindrical shape of the brake drum, the brake caliper (the lining carrier plate with the friction lining) presses against the brake drum from the inside. The lining carrier plate, and in particular the friction lining, must have a shape that is as ideal as possible for contact with the inner wall of the brake drum—that is, it must adopt the shape of the inner wall of the brake drum. Therefore, the friction lining or friction material used for drum brakes must have the necessary flowability to achieve the desired sickle shape during the forming process (when the friction material / friction lining mixture is pressed).

[0004] Although the friction characteristics of drum brake linings generally lag behind those of disc brake linings, drum brakes also offer some advantages over disc brakes: for example, encapsulated brakes to prevent contaminants, reduced release of brake dust into the environment and desirable durability.

[0005] Various friction linings are known in the prior art, which can be used as disc and / or drum brake linings for passenger cars and trucks and as clutch linings.

[0006] DE-OS 2 023 227 describes the use of glass fibers in brake caliper linings having a curved braking surface.

[0007] DE 10 2021 204 132 A1 relates to a drum brake for a motor vehicle, in which the brake lining contains steel wool.

[0008] The subject of EP 0 050 377 B1 is an asbestos-free friction material comprising aramid fibers, steel fibers, and mineral fibers. Besides various other materials, glass fibers can also be used as the mineral fibers. The resulting elasticity of the friction lining can be adjusted by varying the binder used.

[0009] EP 2 270 353 A2 discloses a friction lining mixture for brake and clutch linings. The friction lining mixture may contain several components, in particular resin, steel wool, a small proportion of glass fibers, and a small amount of friction particles, with metallic tin added to enhance performance. Application areas include brake and clutch linings.

[0010] The above-mentioned documents constitute only a small part of the prior art in the field of friction lining mixtures and friction linings for disc and drum brake linings and for clutch linings.

[0011] Basically, it is certain that the friction linings for disk brakes and drum brakes have different compositions. Both friction linings contain steel wool or steel fibers and / or metal fibers, such as copper fibers or zinc fibers, for reinforcement (increasing the internal strength of the friction lining).

[0012] Disc brake friction linings (also called disc brake linings) typically contain 20 to 30% by weight of steel fibers for reinforcement and no more than about 5% by weight of resin. Glass fiber bundles are not usually used as a friction lining component in mass-produced disc brake linings.

[0013] Friction linings for drum brakes typically contain 5-10% by weight of glass fiber strands for reinforcement, and significantly more resin (approximately 10-15% by weight). There are also brake linings for drum brakes that contain steel wool to improve the friction properties. However, in these cases, these friction linings also contain flake graphite and / or layered silicates (e.g., vermiculite) and an increased amount of resin to ensure the flowability of the friction lining material, thereby giving the resulting friction lining the sickle shape required for drum brake linings.

[0014] The flowability of the friction material can be significantly influenced by different binder resin types, varying binder resin contents, and by using solid materials that are smooth and have good sliding properties. Examples of these materials include glass fiber bundles, layered silicates, and flake graphite. However, the use of layered silicates and flake graphite can lead to manufacturing difficulties and long pressing times. Summary of the Invention

[0015] Against this background, the present invention is based on the object of providing a friction material / friction lining (or a brake lining consisting of a lining carrier plate and a friction lining) for a drum brake that exhibits significantly improved friction properties (e.g., friction values) while exhibiting sufficiently improved flow properties so that the resulting friction lining assumes a stable, crack-free, elongated sickle shape and thus also lies flat and tightly against the brake drum over the entire surface. To ensure the simplest possible production of such a drum brake lining, the friction lining should preferably be able to be pressed directly onto the lining carrier plate without adhesive or intermediate layers. The friction lining is preferably attached to the lining carrier plate by the friction material itself.

[0016] This object and its various sub-aspects are achieved by a friction lining mixture and a friction lining for a drum brake produced therefrom according to claim 1. Preferred embodiments of the invention are specified in the dependent claims.

[0017] The present invention therefore relates to a friction lining mixture which is characterized by a special combination of metal fibers, glass fiber bundles, resin and friction particles.

[0018] The friction lining mixture preferably comprises at least 15% by weight of metal fibers, in particular steel fibers, which are preferably in the form of steel wool; at least 7% by weight of glass fibers, which are added to the friction lining mixture in the form of glass fiber bundles; at least 4% by weight of binding resin and at least 2% by weight of friction particles.

[0019] Particularly preferably, the friction lining mixture comprises the following components:

[0020] 15-20% by weight of metal fibers, preferably steel fibers, especially steel wool,

[0021] 7-10% by weight of glass fibers in the form of glass fiber bundles,

[0022] 4-9 wt% of a binder resin, and

[0023] 2-10% by weight of friction particles.

[0024] A further preferred embodiment of the invention relates to a friction lining mixture which, in addition to the aforementioned components, contains heavy metal sulfides from the fourth or fifth main group of the periodic table, such as tin, antimony and bismuth sulfides, in a content of greater than or equal to 2% by weight.

[0025] Furthermore, the friction lining mixture according to the invention is preferably substantially free of phyllosilicates and flake graphite or contains less than 2% by weight of such materials.

[0026] The % by weight used in this application relate to the weight of the finished friction lining mixture.

[0027] The friction particles used according to the present invention preferably have a Mohs hardness of greater than or equal to 9. Examples include SiC (Mohs hardness 9.5-9.75), Al2O3 (Mohs hardness 9), B4C (Mohs hardness 9.3), and various Si3N4 variants with a Mohs hardness of 9. These particles preferably have a particle size with a diameter d50 of 3-150 μm. The particle size can be determined using an analyzer, such as those from CILAS (France) or Anton Paar (Germany).

[0028] Steel, stainless steel, copper, brass, or bronze fibers are preferably used as metal fibers. These fibers are preferably designed as very short fibers of 0.1 to 0.3 mm or as medium-length fibers of 0.3 to 0.5 mm, for example in the form of shavings or as longer fibers or threads with a length exceeding 0.5 mm. The metal fibers preferably have a diameter of between 0.05 and 0.2 mm. Copper wool or brass shavings can be used as metal fibers, for example.

[0029] While friction linings typically use individual glass fibers with varying orientations to increase strength or reinforcement, the present invention uses glass fiber bundles. Here, multiple individual short glass fibers with the same orientation are combined into bundles. Glass fiber bundles improve flowability in the friction lining mixture according to the present invention. Fibers made of quartz glass, borosilicate glass, aluminum silicate glass, magnesium aluminum silicate glass, and / or calcium aluminum silicate glass are preferably used for this purpose. The glass fibers preferably have a length of 1 to 5 mm. A length of 3 mm is particularly preferred. The fibers preferably have a diameter of 0.5 to 50 μm. Glass fiber bundles are produced, for example, from a glass melt by extruding it through spinnerets, for example, made of tungsten. The number of nozzles determines the bundle thickness or width. The nozzles are arranged in a row, resulting in a smooth sheet. The width of the glass fiber bundle is, for example, 0.25 to 2 mm. The bundle is then cut into lengths of, for example, 3 mm. The bundles can also be treated with a slurry that further reduces their tendency to disintegrate. The slurry used depends on the manufacturer and consists of a coating and / or adhesive.

[0030] The resin used according to the present invention can be based on natural resins or synthetic resins. Phenolic resins are preferably used. Organic synthetic resins can also be used, such as resins based on cresols, alkyls, CSNLs, epoxies, nitrile rubber, resorcinol, aryls, styrene-butadiene rubber, and CR. Inorganic synthetic resins can also be used, such as resins based on boron, phosphorus, silicon, and chromium.

[0031] Heavy metal sulfides are preferably present in the friction lining mixture at 2 to 10% by weight. These sulfides act as high-temperature lubricants and reduce thermal wear. They also contribute to good disc crack prevention. Furthermore, they smooth friction values and are an effective means of preventing pressure and speed decay.

[0032] As additional ingredients, the friction lining mixture may preferably contain 15-30% by weight of coke and graphite. Coke stabilizes the properties of the friction lining. Graphite contributes to lubrication and reduces wear. Ground graphite and / or electrode graphite can be used for this purpose.

[0033] Preferably, the friction lining mixture may also contain 1-10% by weight of natural rubber or synthetic rubber, thereby achieving improved damping or noise minimization and improved flexibility of the friction lining.

[0034] Furthermore, the friction lining mixture may preferably contain 10-40% by weight of minerals. Cost-effective fillers such as chalk, barite, magnesium oxide, shale powder, and kaolin are preferably used. These fillers assist friction and reduce wear.

[0035] It is particularly advantageous that the friction lining mixture according to the invention can be pressed directly onto the lining carrier plate, thereby forming a sufficiently stable connection between the friction lining and the lining carrier plate. According to the invention, the use of adhesives or intermediate layers applied to the lining carrier plate can be dispensed with. Separate mechanical fixing aids to the lining carrier plate, such as screws, bolts, or rivets, are also unnecessary for a sufficiently stable connection between the friction lining and the lining carrier plate.

[0036] A friction lining made from the friction material according to the present invention has a friction coefficient μ with respect to sliding friction of at least 0.3, in particular 0.4 to 0.5. The coefficient of friction μ is also known as the friction value or friction number. The determination of the friction value is described, for example, in Wikipedia under the keyword "friction coefficient" in the section on calculation of friction.

[0037] As described above, according to the invention, the friction material can be pressed directly onto the lining carrier plate at increased pressure and temperature without adhesive and intermediate layers, and thus a friction lining or brake lining / brake caliper for a drum brake can be obtained directly.

[0038] To further increase the stability of curved drum brake linings, the carrier plate / lining carrier plate can have one or more projections and / or recesses that receive friction material or extend into the friction material layer and are thus suitable for absorbing tangential forces transmitted by the friction lining during driving. In this case, the projections of the carrier plate, which is curved according to the radius of the brake drum, extend into the friction material / friction lining until a predetermined wear limit is exceeded.

[0039] A preferred embodiment of the carrier plate according to the invention is one in which the carrier plate has a plurality of surface recesses, which are arranged in a grid-like manner on the carrier plate (on the side facing the friction lining). Furthermore, an embodiment of the lining carrier plate is preferred in which the carrier plate has a plurality of projections designed as pins, and in particular an embodiment in which the carrier plate has a plurality of rows of pins, wherein the pins are arranged in a plurality or all of the existing surface recesses.

[0040] The present invention also provides a method for producing a drum brake lining according to the present invention, which comprises a lining carrier plate having a curved surface and a friction lining arranged thereon. For this purpose, a lining carrier plate (having a surface curved to a radius corresponding to the brake drum, so that the friction lining subsequently lies in close contact with the brake drum) and a flowable friction lining mixture according to the present invention are provided. A flowable friction lining mixture means that, under the manufacturing conditions of the friction lining, i.e., the temperatures used and the pressures applied, the friction lining mixture is flowable and can be arranged or adhered to the surface of the carrier plate in accordance with a predetermined shape. Furthermore, after the mold is filled with the friction lining mixture, it is distributed in the mold without any special measures. After the mold is filled with the friction lining mixture, the carrier plate is pressed directly onto the friction lining mixture in the mold while increasing the temperature and pressure. Preferably, a temperature of 140-180°C and a pressure of 30-60 N / mm² are used for a period of 2-5 minutes. 2 The friction lining is then hardened.

[0041] According to the invention, it can be provided that the friction lining formed in this way is further processed after being removed from the mold by means of conventional methods, such as machining (for example grinding).

[0042] Finally, the invention comprises the use of the friction lining mixture according to the invention and the friction linings obtained therefrom for producing drum brake linings.

[0043] In summary, it can be determined that the friction material according to the present invention is different not only from the materials used in disc brake linings, but also from the materials used in drum brake linings.

[0044] For example, or in contrast to the prior art, there are no layered silicates or flake graphite, nor are there any resin quantities, which are unusually high for disc brake linings but considerably lower for drum brake linings. Conventional drum brake linings also do not use heavy metal sulfides or friction particles with a Mohs hardness greater than or equal to 9. Finally, the quantitative combination of glass fiber strands and metal fibers, particularly steel wool, according to the invention is not found in prior art brake linings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1Examples of glass fiber bundles that can be used according to the present invention are shown.

[0046] Figure 2 An example of a metal fiber in the form of steel wool which can be used according to the invention is shown.

Claims

1. A friction lining mixture for producing a brake lining for a drum brake, comprising: at least 15% by weight of metal fibers, preferably steel fibers, especially steel wool, at least 7% by weight of glass fibers, in the form of glass fiber bundles, at least 4% by weight of resin, and At least 2% by weight of friction particles, preferably having a Mohs hardness of 9 or greater.

2. The friction lining mixture according to claim 1, comprising: 15-20% by weight of metal fibers, 7-10% by weight of glass fiber bundles, 4-9% by weight of resin, and 2-10% by weight of friction particles.

3. The friction lining mixture according to claim 1 or 2, characterized in that The friction lining mixture additionally comprises sulfides of tin, antimony and bismuth, preferably equal to or greater than 2% by weight.

4. The friction lining mixture according to any one of claims 1 to 3, characterized in that The friction particles are composed of Al2O3, SiC, B4C or Si3N4 or a mixture thereof.

5. The friction lining mixture according to any one of claims 1 to 4, characterized in that The friction lining mixture does not comprise phyllosilicates and flake graphite.

6. The friction lining mixture according to any one of claims 1 to 5, characterized in that The metal fibers are configured as steel wool.

7. A friction lining for a drum brake, produced from the friction lining mixture according to any one of claims 1 to 6.

8. The friction lining according to claim 7, characterized in that The friction lining has a coefficient of friction μ of at least 0.3, in particular 0.4 to 0.

5.

9. A drum brake lining comprising a lining carrier plate having a curved surface, on which a friction lining according to claim 7 or 8 is arranged.

10. The drum brake lining according to claim 9, characterized in that The friction material is pressed directly onto the lining carrier plate for fastening, and neither adhesive nor intermediate layer is arranged between the carrier plate and the friction material.

11. The drum brake lining according to claim 9 or 10, characterized in that The friction material is fixed to the lining carrier plate without separate mechanical fixing aids and without the use of screws, bolts or rivets.

12. A drum brake lining according to any one of claims 9 to 11, characterized in that The lining carrier plate has elevations and / or recesses, wherein the recesses are filled with the friction lining and the elevations extend into the friction lining until below a wear limit.

13. The drum brake lining according to claim 12, characterized in that The recesses are of planar design and are arranged in a grid-like manner on the surface of the lining carrier plate.

14. The drum brake lining according to claim 12 or 13, characterized in that The projections are designed as pins and are preferably arranged in a plurality of rows, in particular in a flat recess.

15. A method for manufacturing a drum brake lining according to any one of claims 9 to 14, comprising the steps of: - providing a lining carrier plate having a curved surface, - provide friction lining mixture, - filling the friction lining mixture into a mold, wherein no separate measures are taken for distributing the friction lining mixture in the mold during and after filling the friction lining mixture, - pressing the lining carrier plate onto the friction lining mixture located in the mold at elevated temperature and elevated pressure, and - Hardening of the friction lining obtained.

16. The method according to claim 15, characterized in that During and after filling the friction lining mixture into the mold, no separate measures are taken to distribute the friction lining mixture in the mold.

17. Use of a friction lining mixture according to any one of claims 1 to 6 for producing a friction lining according to any one of claims 7 or 8.

18. Use of a friction lining according to claim 7 or 8 for producing a drum brake lining according to any one of claims 9 to 14.

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