Brake disc for a disc brake

Description

[0001] The present invention relates to a brake disc having the features of the preamble of claim 1.

[0002] Brake discs have the function of acting as friction partners in a disc brake system, interacting with a brake pad. A disc brake system comprises a brake disc (also called a rotor) and at least one brake pad, which is pressed against the brake disc to generate friction.

[0003] Frictional forces are typically transferred to a hub as braking torque. A large portion of the resulting heat is absorbed by the brake disc and must be dissipated. The use of a brake disc results in significant thermal and mechanical stresses.

[0004] Brake discs for disc brakes are usually made of steel or cast iron. WO2012157680 (A1), for example, describes a martensitic stainless steel for a brake disc for a bicycle.

[0005] German patent DE102014015474 A1 (Daimler) discloses a brake disc made of a gray cast iron substrate with surface enrichment of the gray cast iron substrate with chromium or molybdenum. According to this document, an adhesive layer for the friction lining is applied to the gray cast iron substrate, which adhesive layer can contain 20 to 60 wt.% molybdenum.

[0006] DE3930402 A1 (Honda) describes a friction material for a brake pad that can contain 5 to 20% molybdenum disulfide by weight. DE69714587 T2 (FREINRAIL) relates to the production of friction linings that interact with discs in braking systems, particularly railway braking systems. For this purpose, a powder mixture is sintered and forged. The powder mixture can contain 10% molybdenum by weight.

[0007] The D4 - DE10354655 A1 (Bosch) describes a process for manufacturing a composite component, in particular a brake disc, by pressing the ceramic powder, sintering it to form a ceramic preform and subsequently infiltrating it with a molten metal.

[0008] The aim is to increase the thermal and / or mechanical load-bearing capacity of brake discs.

[0009] The object of the present invention is to provide an improved brake disc.

[0010] The problem is solved by a brake disc having the features of claim 1. Preferred embodiments are set out in the dependent claims.

[0011] According to the invention, the brake disc has a circumferential friction section, which is made entirely of a metallic material with a molybdenum content of ≥ (greater than or equal to) 50 wt.% (weight percent). The brake disc for a disc brake comprises the friction section, a mounting section for attaching the brake disc to a hub or the like, and a support section for transmitting forces between the friction section and the mounting section. Typically, a brake disc has significant material voids. "Significant" here means that, in particular, more than 10% of the surface is not filled with material.

[0012] The material with a molybdenum content of ≥ 50 wt.% is preferably metallic. The material with a molybdenum content of ≥ 50 wt.% can, for example, be a molybdenum-based alloy, a composite material containing molybdenum (such as copper-infiltrated molybdenum), a composite material consisting of different layers (such as a laminate or a composite with sprayed coatings), or even pure molybdenum. In other words, molybdenum or a molybdenum-based material is proposed for at least some sections of a brake disc. In the case of an alloy, the mixture of molybdenum with alloying elements exists at the atomic level, while in composite materials and material combinations, the mixture of molybdenum with at least one other material exists at the macroscopic level.

[0013] Preferably, the material has a molybdenum content of ≥ 80 wt.%, more preferably ≥ 90 wt.%, and particularly preferably ≥ 95 wt.%. In other words, the material preferably consists predominantly of molybdenum. Due to the commercial availability of semi-finished products made of molybdenum or a molybdenum-based alloy, a production from pure molybdenum or a molybdenum-based alloy can be particularly economical.

[0014] The material is typically and preferably produced using powder metallurgy. Powder metallurgy production involves preparing and compacting metal powders followed by sintering. A material produced using powder metallurgy exhibits a sintered microstructure, which is recognizable as such to a person skilled in the art from micrographs. Characteristics of a sintered microstructure, particularly that of a molybdenum-based alloy, include a finer and more uniform grain structure compared to a cast microstructure. The material is generally chemically very homogeneous.

[0015] Furthermore, the powder metallurgy route is particularly economical for refractory metals. This is partly because sintering occurs significantly below the melting temperature.

[0016] Materials with a molybdenum content of ≥ 50 wt.% are generally used because of their high-temperature properties and / or corrosion resistance and / or special thermophysical properties.

[0017] The applicant has surprisingly discovered that molybdenum or molybdenum-based materials have very advantageous properties for use in a brake disc.

[0018] The following properties, among others, have proven particularly interesting and are listed in tabular form below, along with their associated advantages over steel or aluminum as reference materials. The table compares material properties of pure molybdenum with those of a martensitic stainless steel, with values ​​given at room temperature (RT). Where applicable, the steel with the material number 1.4021, a typical representative of steels used for brake discs, especially bicycle brake discs, was used for direct comparison. Properties of molybdenum / molybdenum-based materials Advantages of molybdenum compared to reference material high wear resistance longer service life and / or lower permissible material thickness high thermal conductivity (thermal conductivity of molybdenum: 142 W / mK) Improved heat dissipation (thermal conductivity 1.4021: 30 W / mK) low specific heat capacity (heat capacity of molybdenum 0.25 J / (g K) Faster temperature assumption, particularly advantageous in wet operation (heat capacity 1.4021: 0.46 J / g K) Low thermal expansion of Mo (5.3*10 -6< K -1< ) Reduced deformation of the brake disc (steel: 10.5*10 -6< K -1< ) high modulus of elasticity (modulus of elasticity molybdenum: 320 GPa) Higher stiffness than steel (E-modulus 1.4021: 215 GPa)

[0019] In investigations conducted by the applicant, molybdenum-based brake discs proved particularly advantageous during initial braking (short braking pulse) and in wet conditions. The applicant attributes this to the comparatively low specific heat capacity [J / gK] of molybdenum: even a short braking pulse causes the brake disc to heat up quickly and dry rapidly before the high thermal conductivity of molybdenum ensures effective heat dissipation.

[0020] The low thermal expansion of molybdenum leads to smaller deformations and / or lower thermally induced stresses.

[0021] Molybdenum brake discs have also been found to exhibit favorable friction characteristics, with a substantially constant coefficient of friction across a wide temperature range. This results in less change in braking performance with temperature compared to steel.

[0022] Furthermore, the high strength and high modulus of elasticity of molybdenum allow for a particularly thin-walled design of the brake disc.

[0023] A brake disc can typically be divided into the following categories with regard to its spatial areas and the associated primary functions: a friction section which, during a braking process, is in friction pairing with a friction partner, a (usually) centrally located mounting section for attaching the brake disc to a hub or the like, and an intermediate support section for transmitting the forces between the friction section and the mounting section.

[0024] The friction zone refers to the geometric area on the brake disc where braking force is applied during operation. Typically, the friction zone is located on the outer circumference of the brake disc. Braking force is generated through friction by pressing brake pads against the rotating brake disc. Specifically, the friction zone is circumferential, meaning it forms a continuous ring around the disc.

[0025] It is intended that the brake disc has a circumferential friction section which consists at least partially of a material with a molybdenum content of ≥ 50 wt.%.

[0026] The circumferential friction section is a region of the brake disc whose radial extent can be defined and which is intended for contact with at least one friction partner (typically a brake pad). According to this variant, only that section of the brake disc which is in friction with a friction partner during a braking process is made of the material with a molybdenum content of ≥ 50 wt.%.

[0027] It can also be provided that the material with a molybdenum content of ≥ 50 wt.% is arranged in the friction section in the form of inserts.

[0028] The circumferential friction section can be materially bonded to the rest of the brake disc or exist as a ring that is mechanically and / or materially connected to a support section of the brake disc.

[0029] The material with a molybdenum content of ≥ 50 wt.% does not necessarily have to form an outer surface of the circumferential friction section.

[0030] Preferably, however, the material with a molybdenum content of ≥ 50 wt.% forms the outer surface of the circumferential friction section. This also includes variants made from the molybdenum-containing material with a coating. A coating made from a different material for this application is typically a few µm thick (especially < 20 µm thick).

[0031] In particular, the circumferential friction section consists entirely of the material with a molybdenum content of ≥ 50 wt.%, apart from any coating.

[0032] As already stated, the material with a molybdenum content of ≥ 50 wt.%, which here forms the circumferential friction section, preferably has a molybdenum content of ≥ 80 wt.%, more preferably ≥ 90 wt.%, and particularly preferably ≥ 95 wt.%.

[0033] The circumferential friction section can be designed as a separate component that can be connected to the support section. For example, it is conceivable to manufacture only the circumferential friction section from a material with a molybdenum content of ≥ 50 wt.% and to connect it to a cost-effective and / or lightweight support section, for example made of steel or aluminum.

[0034] In one variant, the entire brake disc is made of a material with a molybdenum content of ≥ 50 wt.%. This is the simplest solution from a manufacturing perspective. In this further development, it is also preferably provided that the material has a molybdenum content of ≥ 80 wt.%, more preferably ≥ 90 wt.%, and particularly preferably ≥ 95 wt.%. In other words, it is preferably provided that the brake disc is made of molybdenum or a molybdenum-based alloy.

[0035] Preferably, the entire brake disc is manufactured in one piece, meaning that there is preferably no material separation between the aforementioned sections. This allows for particularly simple manufacturing, for example by cutting or stamping. Laser cutting and waterjet cutting, for instance, have proven effective for cutting molybdenum-based alloys. This manufacturing process utilizes a semi-finished product, particularly sheet metal, as the starting material. The semi-finished product is preferably manufactured by forming, especially by rolling, a blank produced using powder metallurgy.

[0036] Another option is representation via pressing and sintering (engl. pressand-sinter,p / s). This eliminates the step of manufacturing a semi-finished product. Instead, in the pressing and sintering process, the final shape of the component is created during pressing and then sintered. Using a brake disc as an example, it can be produced near its final shape through uniaxial pressing and sintering. Machining and / or calibration may follow.

[0037] It may be provided that the material forming at least part of the brake disc has a molybdenum content of ≥ 50 wt.% and is designed as a composite material or as a material composite.

[0038] In a composite material, a matrix is ​​present as the first phase, into which a second phase (for example, copper) is embedded. The matrix can preferably consist of molybdenum, which is infiltrated by a second metal.

[0039] A composite material typically consists of discrete layers of different materials. An example of a composite material is a laminate made of layers of molybdenum and copper. Of course, hybrid forms can also exist. Furthermore, the literature does not always clearly distinguish between composite materials and material composites.

[0040] By forming the material as a composite material or as a material composite, the favorable properties of molybdenum can be advantageously combined with the properties of other materials.

[0041] Of particular note is the possibility of increased heat dissipation through combination with copper (thermal conductivity at room temperature: 398 W / mK) or aluminum (thermal conductivity at room temperature: 234 W / mK).

[0042] The composite material can, for example, be formed by a porous molybdenum body impregnated with another material, typically copper.

[0043] The composite material can also be formed by a layered composite of molybdenum and other materials. An example of this type of composite material is a laminate made of molybdenum and copper layers.

[0044] For brake discs, a composite material containing aluminum would be particularly interesting due to aluminum's low density and high thermal conductivity. Aluminum would then preferably form a layer in the core of the composite, while molybdenum would form outer layers.

[0045] It may be provided that the material forming at least part of the brake disc is formed as a sprayed layer with a molybdenum content of ≥ 50 wt.%.

[0046] For example, it is conceivable that molybdenum is applied as a sprayed coating to a carrier body. The carrier body can be made of steel or aluminum, for instance. The sprayed coating of molybdenum or a mixture containing molybdenum can preferably be formed in the area of ​​the brake disc that is intended for contact with a friction partner. The sprayed coating can be formed, for example, by flame spraying or cold gas spraying.

[0047] In a further training course, a friction layer and / or a carrier body made of a different material is applied as a spray layer to molybdenum, for example on a molybdenum sheet.

[0048] It has proven particularly advantageous if the material, with a molybdenum content of ≥ 50 wt.%, is formed from a molybdenum alloy with a molybdenum content of ≥ 99.93 wt.%, a boron content of ≥ 3 ppmw (wt. ppm), and a carbon content of ≥ 3 ppmw. Preferably, the total carbon and boron content is in the range between ≥ 15 ppmw and ≤ 50 ppmw. Particularly well-balanced mechanical properties have been achieved with this composition.

[0049] This micro-doped molybdenum alloy is characterized by exceptional ductility and damage tolerance and is readily weldable. The previously mentioned description of pressing and sintering (p / s) is particularly relevant for this molybdenum alloy, as it already exhibits excellent strength and ductility values ​​in the pressed-sintered state (i.e., without further forming).

[0050] Unless otherwise stated, where values ​​do not add up to 100%, the difference is due to normal impurities.

[0051] For all further training concerning the molybdenum-based material, it applies that the brake disc can consist partially or completely of the material in question.

[0052] Preferably, the brake disc is designed for a motorized or non-motorized vehicle, in particular for a two- or three-wheeler. Further preferably, the brake disc is designed as a brake disc for a two-wheeler, in particular for a bicycle.

[0053] The advantageous properties of molybdenum-based materials are particularly evident in bicycle brake discs. The trend towards e-bikes (electrically powered or at least electrically assisted bicycles) has led to a demand for robust brake discs, as the moving masses and speeds are greater than in purely muscle-powered bicycles. These factors also apply, for example, to cargo bikes and bicycle trailers.

[0054] Furthermore, optimal braking behavior for disc brakes, including braking pauses to allow the brake discs to cool down, is not always guaranteed. In this context, the brake discs according to the invention are particularly advantageous due to their increased thermal load capacity and favorable braking characteristics.

[0055] For the purposes of this registration, cargo bikes, e-bikes (bicycles with electric motor assistance, even without pedaling) and pedelecs (bicycles with electric motor assistance when pedaling) are specifically considered bicycles, even if they may have more than two wheels and / or are not considered bicycles according to a road traffic regulation.

[0056] Brake discs for two-wheelers, especially bicycles, are often made of sheet metal, while brake discs for passenger cars or trucks are usually made of cast material.

[0057] Sheet metal brake discs are a suitable material for two-wheeled vehicles, especially bicycles, as they can be produced cost-effectively from strip material by cutting or stamping. Sheet metal discs can also be used for mopeds and lighter tricycles. Typical dimensions for bicycle brake discs include diameters typically between 140 mm and 180 mm, while diameters of 203 mm and above are common for downhill bikes.

[0058] The material thickness is typically at least 1.5 mm to 2.5 mm. Conventional brake discs with a thickness below 1.5 mm lack sufficient stiffness. Here, the use of molybdenum can be advantageous compared to steel due to its high modulus of elasticity.

[0059] Material thicknesses exceeding 2.5 mm are uncommon due to the high mass. However, low brake disc weight is less important in downhill racing. Here, 2.5 mm thick brake discs are frequently used, as they are particularly robust.

[0060] Brake discs are often drilled and / or have cutouts. These holes and / or cutouts serve to improve cooling and reduce weight.

[0061] Furthermore, brake discs typically have a mounting section through which the generated braking torque can be transmitted to a hub. This mounting section can be implemented, for example, as a polygonal recess or via screw holes. Mounting components may also be provided for attaching the brake disc to the hub.

[0062] Protection is also sought for a disc brake with a brake disc according to the invention. A disc brake essentially consists of a brake disc, a brake caliper, and brake pads. The brake caliper serves to receive and position the brake pads against the brake disc. Actuation can be hydraulic or mechanical. The brake disc and the brake pads are the friction partners in the disc brake system.

[0063] Protection is also sought for the use of a brake disc according to the invention in a disc brake, in particular in a disc brake of a two-wheeler, especially a bicycle.

[0064] A disc brake is also disclosed, in which at least one of the friction partners consists, at least partially, of a material with a molybdenum content of ≥ 50 wt.%. This implies the possibility that only the brake pads could consist of a material with a molybdenum content of ≥ 50 wt.%. Several of the advantages of molybdenum, particularly its wear resistance, are also beneficial for use in a brake pad.

[0065] In another variant, a brake pad is proposed that can also contain less than 50 wt.% molybdenum. Even at lower molybdenum contents, for example ≥ 10 wt.%, preferably ≥ 20 wt.%, and more preferably ≥ 30 wt.%, the molybdenum ensures good wear resistance.

[0066] In an arrangement with a brake pad containing molybdenum, the brake disc could be made of conventional materials, for example steel.

[0067] Protection is also sought for a process for manufacturing a brake disc. The process comprises the following steps: Providing a powder mixture with a molybdenum content of ≥ 50 wt.% and i) pressing and sintering the powder mixture into a sintered piece, forming the sintered piece into a semi-finished product and separating the brake disc or ii) pressing the powder mixture near the final shape and subsequent sintering and optional machining to produce the brake disc.

[0068] In the first variant (i), a semi-finished product is first manufactured via a powder metallurgy route. To manufacture a brake disc, a sintered block would typically be rolled into a sheet, and brake discs would then be cut from this sheet. If necessary, the brake disc can be further processed, for example, by grinding.

[0069] According to variant (ii), the brake disc is manufactured near-net-shape using a powder metallurgy process. The production of a semi-finished product is therefore eliminated.

[0070] Both variants offer the advantages described for the powder metallurgy route. The first variant (i) is advantageous in terms of flexibility, for example regarding dimensions. Its mechanical properties are also generally more favorable than those of p / s material.

[0071] The manufacturing process for a brake pad is also revealed. The process includes the following steps: Providing a powder mixture with a molybdenum content of ≥ 10 wt.%. Pressing and sintering the powder mixture to form the brake pad.

[0072] The powder mixture preferably contains ≥ 20 wt.% molybdenum, more preferably ≥ 30 wt.% molybdenum, particularly ≥ 40 wt.% and further ≥ 50 wt.% molybdenum. In addition to molybdenum, the powder mixture contains organic and / or inorganic friction agents. Graphite is typically included. The molybdenum ensures good wear resistance. EXPERIMENTAL RESULTS

[0073] The following summarizes test results on brake discs according to the invention from measurements on a friction test bench.

[0074] In the test setup, geometrically identical brake discs made of steel and molybdenum were subjected to different braking forces, and the braking effects were compared. For this purpose, the brake discs were mounted flat onto a steel support body, which was driven by an instrumented milling spindle.

[0075] A 160 mm diameter SRAM "Centerline" steel brake disc was used as a reference. A geometrically identical brake disc made of molybdenum sheet material was used as the molybdenum brake disc. The material thickness was 1.8 mm in both cases.

[0076] The brake discs were subjected to a normal force of 500 N (Newtons) on one side via a brake pad. Organically bonded brake pads "Elixir XX Organic Compound" from SRAM were used for the tests.

[0077] The resulting braking torque was measured using a torque sensor on the milling spindle. The braking power was varied across the rotational speed. During the tests, the brake discs were subjected to a normal force of 500 N on one side at speeds ranging from 240 rpm (revolutions per minute) to 1000 rpm. A single braking cycle lasted 10 seconds, including a five-second steady-state phase of constant braking force.

[0078] Each test series comprised 100 braking cycles. In total, over 1000 braking cycles were performed on the respective steel and molybdenum brake discs.

[0079] It was found that molybdenum brake discs exhibit significantly less variation in braking torque under the same normal forces. In other words, the braking torques generated by molybdenum brake discs fall within a much narrower range than those generated by steel brake discs. For the user, this translates into a more consistent and smoother braking effect. This low variation was observed both within a single braking event and when considering the average of the steady-state braking force across multiple braking cycles. The steady-state braking force of a braking event is defined as a phase of constant braking force, as explained in more detail in the figure description.

[0080] The low variation means that, for a given braking force, molybdenum brake discs result in a braking torque within a narrow range, which fluctuates only slightly even during braking. The braking effect within a single braking action is therefore particularly consistent.

[0081] The low variation in mean braking torques when considered over several braking cycles means a predictable and repeatable braking effect.

[0082] Furthermore, it was found that the molybdenum brake discs tend to deliver higher braking torques at high braking loads (tests at 1000 rpm) and consequently high temperatures than when cold. This property can counteract brake fade (reduced braking performance during continuous braking).

[0083] In addition to the tests on the friction test bench, practical tests were carried out with molybdenum brake discs on bicycles (mountain bikes). During the test rides, approximately 5000 meters of descent were completed.

[0084] The test drivers' subjective experiences with steel brake discs as a reference were recorded in a comparison matrix. The following findings were made: criterion Molybdenum brake disc vs. steel brake disc comparison Braking effect during continuous braking (high brake disc temperature) better Braking performance in wet conditions better Fading (decrease in braking effectiveness during continuous braking) better (less) Squeak better (less) Wear (visual assessment) better (less)

[0085] After the test drives, no wear was detected on the molybdenum brake discs. However, wear was observed on the steel discs.

[0086] Further advantages and expediencies of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures.

[0087] The figures show: Fig. 1: A brake disc in an exemplary embodiment. Fig. 2a, 2b: Schematic cross-sections of further exemplary embodiments. Fig. 3: An exemplary embodiment of a composite brake disc. Fig. 4: A schematic representation of a disc brake. Fig. 5: A schematic representation of a brake pad. Fig. 6: A vehicle with a disc brake. Fig. 7a, 7: A diagram of individual braking processes. Fig. 8: A diagram of a series of 100 braking tests. Fig. 9: A diagram of a series of 500 braking tests.

[0088] Figure 1Figure 1 shows a perspective view of a brake disc 1 in an exemplary embodiment. A typical brake disc for disc brakes on bicycles is depicted. These types of brake discs are characterized by a thin-walled design. The material thickness – s – is typically between 1.5 mm and 2.5 mm. The diameter – D – is usually between 140 mm and 210 mm. The brake disc 1 has a circumferential friction section 2, which is in friction contact during braking. The friction section 2 often has holes 21 for improved heat dissipation. A brake disc 1 typically has distinct material cutouts.

[0089] The brake disc 1 can be connected to a hub or the like for transmitting a braking torque via a mounting section 4. Here, the mounting section 4 is designed as a 6-hole mount.

[0090] Between fastening section 4 and friction section 2 lies a support section 3. Often the support section 3 is not filled with material, but has distinct material recesses 31, so that the support section 3 essentially consists of arms 32.

[0091] The dimensions of the arms 32 follow mechanical requirements. The thermal management of the brake disc 1 can also influence the design of the support section 3.

[0092] Friction section 2, support section 3, and mounting section 4 are not materially separated here. Rather, in the present embodiment, the brake disc 1 is made in one piece from a material with a molybdenum content of ≥ 50 wt.%. It can be manufactured, in particular, by laser cutting of sheet metal.

[0093] As an alternative to the one-piece design, friction section 2, support section 3 and fastening section 4 can be manufactured separately and connected to each other.

[0094] Figures 2a and 2b The figures schematically and exemplarily show cross-sections of possible further embodiments of a material with a molybdenum content of ≥ 50 wt.%, from which the brake disc 1 according to the invention consists at least section by section. The cross-sections can, for example, be a section along a section plane - S - from Figure 1 be taken from it.

[0095] Figure 2a shows a composite material consisting of a framework of molybdenum ("Mo") and a second material ("X"), with which second material the molybdenum framework is infiltrated.

[0096] Using copper as a second material, particularly high thermal conductivity can be achieved while maintaining good mechanical properties. One example is a composite material containing up to 30% copper by weight. This composite combines the high thermal conductivity of copper with the low thermal expansion of molybdenum.

[0097] Using aluminium as an example of a second material, high thermal conductivity can be achieved with very good mechanical properties and low weight.

[0098] Figure 2b Figure 1 schematically shows another alternative embodiment of a material for a brake disc 1 according to the invention. Here, the material with a molybdenum content of ≥ 50 wt.% is present as a composite material of layers of molybdenum with at least one second material ("X"). For example, it can be provided that the layers forming a surface of a brake disc 1 consist of molybdenum with a copper core laminated to it.

[0099] Using aluminium as an example of a second material, high thermal conductivity can be achieved with very good mechanical properties and low weight.

[0100] Of course, multiple layers and / or other material combinations are possible. In particular, it is also conceivable to coat a substrate material, such as steel, with molybdenum. Specifically, molybdenum can be applied as a thermal spray coating or via cold gas spraying (also known as...). cold gas spray, CGS ) be formed as a cold gas spray layer.

[0101] Figures 2a and 2b These examples illustrate, only partially and by way of example, possible forms of the molybdenum-based material.

[0102] It is conceivable to make the entire brake disc 1 from molybdenum-based composite materials or from material composites containing molybdenum. However, it may be more economical to make only the friction section 2 from a molybdenum-based composite material or material composite.

[0103] In the simplest case, of course, the molybdenum-based material consists of pure molybdenum or a molybdenum alloy.

[0104] Figure 3 Figure 1 shows a brake disc 1 in a further embodiment. In this embodiment, the circumferential friction section 2 is designed as a separate component, which is connected to the support section 3. Not shown here, but also conceivable, is a materially separate design and subsequent connection of the support section 3 and the mounting section 4.

[0105] The circumferential friction section 2 is preferably made of a molybdenum-based material. The support section 3 and the fastening section 4 can, for example, be made of steel.

[0106] The connection between friction section 2 and support section 3 is achieved here using rivets as the fastener. Alternatively or additionally, other connections or joining techniques such as positive locking, welding, soldering, gluing, etc. are also conceivable.

[0107] The design shown here, with a separately executed friction section 2, is particularly interesting when the friction section 2 is made of, for example, a molybdenum-based composite material or material composite. In such a case, support section 3 and fastening section 4 can then be designed primarily with regard to mechanical criteria, while the friction section 2 can be designed primarily with regard to its friction properties and / or thermal management. In other words, this design allows for the decoupling of the design criteria of friction section 2, support section 3, and fastening section 4.

[0108] The design also makes it particularly easy to implement different material thicknesses on friction section 2, support section 3 and fastening section 4.

[0109] Of course, it is also conceivable to make a brake disc 1 entirely from a molybdenum-based material according to the design principle shown here.

[0110] Figure 4 Figure 1 schematically shows a disc brake 5 for a bicycle. The disc brake 5 comprises a brake disc 1, a brake caliper 6, and brake pads 7.

[0111] When the disc brake 5 is actuated, the brake pads 7 are pressed against the brake disc 1 and generate a braking effect through friction.

[0112] Figure 5 Figure 7 schematically shows a brake pad 7. Here, brake pad 7 refers to the actual friction lining, which is fixed to a carrier plate.

[0113] For brake discs 1 made of a material with a molybdenum content of ≥ 50 wt.%, conventional, commercially available brake pads 7 can be used.

[0114] According to another aspect of the disclosure, brake pads 7 may be made of a material with a molybdenum content of ≥ 10 wt.%. Preferably, the material has a molybdenum content of ≥ 20 wt.%, more preferably ≥ 30 wt.%, and particularly preferably ≥ 40 wt.% and further ≥ 50 wt.%. The advantages of molybdenum are also beneficial for use in a brake pad, especially the increase in wear resistance.

[0115] In such an arrangement, the brake disc could be made of a conventional material, for example, steel.

[0116] Of course, in the case of brake pads 7 made of a molybdenum-based material, the brake disc 1 can also be made of a molybdenum-based material. Figure 6Figure 1 schematically shows a vehicle, in this example a bicycle, which is equipped with disc brakes 5 with brake discs 1 according to the invention. The brake discs 1 according to the invention are particularly suitable for two-wheeled vehicles, especially bicycles.

[0117] Figures 7a and 7b The diagrams show individual braking processes according to the test setup described above.

[0118] A single braking process consists of a phase of approximately 2.5 seconds for building up braking force, followed by a steady-state phase of constant braking force of around five seconds. After approximately 7.5 seconds, the braking force is reduced again. For a subsequent discussion of steady-state braking behavior, only the steady-state period between 2.5 and 7.5 seconds of a single braking process will be considered, and values ​​from this period will be used for averaging.

[0119] Figure 7aThis shows the curve of the braking torque in [Nm] (Newton meters) on the ordinate over time in seconds [s] for a braking process on a steel brake disc ("St"). Figure 7b The graph shows a braking process on a molybdenum brake disc ("Mo"). Comparing the two curves, it is evident that the fluctuation of the braking torque is greater for the steel brake disc than for the molybdenum brake disc. In one example test, the braking torque of the molybdenum brake disc varied by approximately 0.3 Nm around a mean value of 11.6 Nm in steady-state conditions. For the steel disc, in a comparable data range, the braking torque varied by approximately 0.5 Nm around a mean value of 12.6 Nm. In practice, this translates to smoother braking behavior during a braking process with the molybdenum brake disc.

[0120] The average braking torque on steel is slightly higher than on molybdenum. One reason for this could be that the brake pads used are optimized for use with steel.

[0121] Figure 8 This diagram shows a representation of the mean braking torque values ​​from previously discussed steady-state ranges of individual braking operations. The diagram plots the mean braking torque values ​​in Nm on the ordinate for the molybdenum brake disc ("Mo" - bold line) and the steel brake disc ("St" - thin dashed line) against the number - n - of braking cycles on the abscissa. A number - n - is dimensionless, i.e., [-]. One hundred braking cycles were performed, with the plotting representing the chronological order of the individual braking operations.

[0122] A striking feature is the significant variation in stationary braking torques on the steel brake disc compared to a smooth curve with low variation on the molybdenum brake disc. In practice, this translates to particularly consistent and repeatable braking performance with the molybdenum brake disc.

[0123] Furthermore, a somewhat faster increase in the average braking torque can be observed with molybdenum, reaching a plateau after approximately three to five braking cycles, whereas with steel, a plateau was only reached after about 20 braking cycles. Without committing to a specific physical theory, the faster increase with molybdenum could be attributed to its lower heat capacity and thus faster heating. In practice, this means a rapid attainment of operating temperature with essentially constant friction behavior.

[0124] Figure 9This graph shows a summary of five test series, each consisting of 100 braking cycles. The average braking torques from the steady-state phases of each braking operation are again depicted. The braking torques in Nm are plotted on the ordinate, with the number – n – of braking cycles on the abscissa. The results are plotted in chronological order. The results of the test series were then combined to create the graph.

[0125] It can be seen that the molybdenum brake disc ("Mo" - bold line) exhibits a very consistently reproducible braking torque over the course of 500 braking cycles. The deviations within each of the five test series are smaller than those of the steel brake disc ("St" - thin line). Furthermore, the variation in braking torque between test series is lower for molybdenum than for steel.

Claims

1. Brake disc for a disc brake, wherein the brake disc (1) has a circumferential friction section (2) which friction section (2) is formed entirely from a metallic material with a molybdenum content of ≥ 50 wt.%.

2. Brake disc according to claim 1, wherein the brake disc (1) is formed entirely from the material with a molybdenum content of ≥ 50 wt.%.

3. Brake disc according to one of the preceding claims, wherein the material with a molybdenum content of ≥ 50 wt.% is formed from a molybdenum alloy with a molybdenum content of ≥ 99.93 wt.%, a boron content of ≥ 3 ppmw and a carbon content of ≥ 3 ppmw.

4. Brake disc according to one of the preceding claims, wherein the brake disc (1) is manufactured by powder metallurgy.

5. Brake disc according to claim 4 , wherein the brake disc (1) is manufactured by pressing and sintering.

6. Use of a brake disc (1) according to one of the preceding claims on a bicycle.

7. Disc brake comprising at least one brake caliper (6), at least one brake pad (7) and a brake disc (1) according to one of the preceding claims.

8. Disc brake (5) comprising at least one brake caliper (6), a brake disc (1) according to one of the preceding claims and a brake pad (7), wherein the brake pad (7) consists at least in sections of a material with a molybdenum content of ≥ 10 wt.%.

9. Method for manufacturing a brake disc (1) according to one of the preceding claims, comprising the steps: - providing a powder mixture with a molybdenum content of ≥ 50 wt.% and i) pressing and sintering the powder mixture to form a sintered compact, forming the sintered compact into a semi-finished product and cutting out the brake disc (1), or ii) pressing the powder mixture to a near net shape and then sintering and optionally machining to produce the brake disc (1).