Friction brake body and method for producing same

Abstract

The invention relates to a friction brake body (1) for a wheel brake (8) of a motor vehicle, having a base body (5) which is manufactured from grey cast iron. The base body (5) has at least one friction contact surface (2, 3) with a wear protection layer (6, 7), and the wear protection layer (6, 7) has a stainless steel matrix with hard material particles. According to the invention, the wear protection layer (6, 7) has a plurality of agglomerates (13) of hard material particles (12), and the agglomerates (13) are infiltrated by the stainless steel matrix.

Description

[0001] Description

[0002] title

[0003] The invention relates to a friction brake body for a wheel brake of a motor vehicle, comprising a base body made of grey cast iron, wherein the base body has at least one friction contact surface with a wear protection layer, and wherein the wear protection layer has a stainless steel matrix with hard material particles.

[0004] Furthermore, the invention relates to a method for producing such a friction brake body.

[0005] State of the art

[0006] Friction brake bodies of the type mentioned above are already known from the prior art. Classic motor vehicle braking systems utilize wheel brakes, which have a brake disc that is non-rotatably connected to the wheel and can be clamped between two brake shoes of a body-mounted brake caliper to generate a braking torque. The brake shoes each interact with a friction contact surface of the brake disc. During clamping, friction occurs between the brake shoes and the brake disc, leading to wear and heat. To ensure high temperature resistance, it is common practice to manufacture the base body of such a brake disc from gray cast iron.

[0007] To improve the wear behavior of the gray cast iron base body, it is also known to provide the respective friction contact surface with a wear-resistant coating, particularly applied by laser deposition welding, which ensures a long service life of the friction brake body. It is known to provide a metal matrix containing hard material particles as a wear-resistant coating to form a contact surface that exhibits high material strength and surface hardness, while simultaneously offering high load-bearing capacity.

[0008] Corresponding friction brake bodies are already known, for example, from the published patent applications EP3 034 902 A1, DE10 2019 207 291 A1 or DE 10 2021 104 237 A1.

[0009] EP 4 146 428 A1 also discloses a friction brake body with a wear-protection layer applied by laser deposition welding, comprising a stainless steel matrix and embedded hard material particles. The resulting metal-ceramic composite material is given a particularly high degree of hardness and wear resistance by the hard material particles. Furthermore, published patent application DE 10 2019 208 411 A1 discloses a wear-protection layer for a friction brake body with an intermediate layer made of austenitic or partially austenitic chromium-nickel steel, wherein the wear-protection layer is reinforced with up to 70 vol% carbide particles.

[0010] Disclosure of the invention

[0011] The friction brake body according to the invention with the features of claim 1 has the advantage of ensuring a favorable bond between the stainless steel matrix material and the hard material particles. This ensures that during braking, i.e., when the wear protection layer is subjected to stress, hard material particles cannot be dissolved from the matrix phase and enter the wear disc and brake pad as an abrasive. Furthermore, the inventive design significantly increases the crack resistance of the wear protection layer. This is achieved according to the invention by the wear protection layer comprising a plurality of agglomerates of hard material particles, and by the agglomerates being infiltrated by the stainless steel matrix.Instead of individual hard material particles introduced into the stainless steel matrix, the invention provides for agglomerates of hard material particles, i.e., clusters of firmly bonded hard material particles, to be integrated into the wear-resistant layer, with these clusters being infiltrated by the material of the stainless steel matrix. The agglomeration of several hard material particles creates free spaces between the adjacent hard material particles and a certain porosity of the agglomerates. When applying the wear-resistant layer or when producing it on the friction brake body, in particular by means of laser deposition welding, the molten material of the stainless steel matrix also penetrates these free spaces and into any cavity located within the agglomerate, thereby ensuring a particularly strong bond between the stainless steel matrix and the agglomerates.The hard material particles incorporated into the wear protection layer as agglomerates thus ensure particularly high load-bearing capacity and a particularly low risk of cracking.

[0012] According to a preferred development of the invention, the average particle size of the hard material particles is less than 10 pm, in particular less than 5 pm.

[0013] Particularly preferably, the average particle size of the hard material particles is between 1 pm and 3 pm.

[0014] According to an advantageous development of the invention, the agglomerates themselves, i.e., without taking into account any infiltrated metal matrix, have an average porosity of at least 20%, in particular of at least 40%. This ensures that the agglomerates are advantageously infiltrated into the stainless steel matrix during production.

[0015] The agglomerates of hard material particles preferably have an average size of 20 to 100 pm, particularly preferably of 30 to 60 pm.

[0016] Furthermore, it is preferred that the wear protection layer has an average porosity of less than 2%. This makes the wear protection layer itself relatively dense, resulting in a reduced risk of corrosion.

[0017] Furthermore, it is preferably provided that the agglomerated hard material particles comprise at least one of the materials titanium carbide, titanium nitride, titanium carbonitride, molybdenum carbide, niobium carbide, and / or tungsten carbide. This results in advantageous hardness and resilience of the wear-resistant layer.

[0018] As a particularly preferred embodiment, the agglomerated hard material particles consist of titanium carbide or a mixture of titanium carbonitride and molybdenum carbide.

[0019] In this case, the molybdenum carbide particularly preferably has a weight fraction of a maximum of 10% of the mixture of titanium carbonitride and molybdenum carbide.

[0020] According to a preferred embodiment of the invention, a metallic intermediate layer is formed between the wear-resistant layer and the base body. This intermediate layer serves, in particular, as a bonding layer, ensuring a secure bond between the wear-resistant layer and the gray cast iron of the base body.

[0021] Furthermore, it is preferably provided that the wear-resistant layer is a wear-resistant layer applied by laser deposition welding. Laser deposition welding heats and melts the stainless steel matrix, so that when applied to the base body, it advantageously penetrates or infiltrates the additionally added agglomerated hard material particles, thereby achieving the aforementioned advantages.

[0022] The method according to the invention with the features of claim 12 is characterized in that the hard material particles are introduced into the wear-resistant layer as agglomerates of hard material particles, particularly during laser deposition welding of the wear-resistant layer. This results in the advantages already mentioned above.

[0023] Preferably, the wear-resistant layer is applied to the base body by laser deposition welding, with the agglomerated hard material particles being added to the stainless steel matrix, particularly during the laser deposition welding process. According to a preferred embodiment of the invention, the agglomerates are produced in advance in a separate process in which the hard material particles are agglomerated and sintered.

[0024] Preferably, the agglomerates are produced in such a way that the agglomerates have an average porosity of higher than 20%, particularly preferably higher than 40%, after sintering and before introduction into the metal matrix.

[0025] Preferably, the agglomerates are produced in such a way that after sintering, the agglomerates do not contain any additional iron-based materials that can act as binding agents in the agglomerates.

[0026] Furthermore, it is preferably provided that the agglomerates of the hard material particles are made from at least one of the following ceramic materials: titanium carbide, titanium nitride, titanium carbonitride, molybdenum carbide, niobium carbide, and / or tungsten carbide. Particularly preferably, the agglomerates are made from titanium carbide or from a mixture of titanium carbonitride and molybdenum carbide, with molybdenum carbide then being added to the mixture in a weight proportion of up to 10%.

[0027] Preferably, the pores of the agglomerates are infiltrated by the molten metal of the stainless steel matrix material in such a way that the wear protection layer has an average porosity of less than 2% after coating.

[0028] Furthermore, it is preferably provided that a metallic intermediate layer is applied to the grey cast iron base body before the wear protection layer.

[0029] The invention will be explained in more detail below with reference to the drawings.

[0030] Figure 1 shows a friction brake body in a perspective view,

[0031] Figure 2 shows a wheel brake with the friction brake body in a simplified

[0032] Sectional view, and Figure 3 an agglomerate of hard material particles.

[0033] Figure 1 shows a simplified perspective view of an advantageous friction brake body 1 for a motor vehicle (not shown in detail here). The friction brake body 1 is designed as a brake disc and has a friction contact surface 2 or 3 on each of its end faces, each of which serves to interact with a brake pad of a wheel brake. In the center, the brake disc 1 has a carrier cup 4 for fastening the brake disc to a wheel bearing or a wheel of the motor vehicle. The carrier cup 4 can be made of a different material than that in the friction brake body 1 and can be made of aluminum, for example. The carrier cup 4 advantageously has a plurality of holes for screw connections for fastening to, for example, the wheel bearing.

[0034] The friction contact surfaces 2, 3 are subject to wear during operation, which means that the brake disc must be replaced regularly.

[0035] The friction brake body 1 comprises a base body 5 made of gray cast iron, on whose end faces the friction contact surfaces 2, 3 are arranged. To enable increased braking performance and ensure greater wear resistance, the friction brake body 1 or the base body 5 has a wear protection layer 6 or 7 on each of the friction contact surfaces 2, 3.

[0036] Figure 2 shows an example of a wheel brake 8 of a motor vehicle in a simplified sectional view. The wheel brake 8 has a brake caliper 9 on which two movably mounted brake shoes 10, 11 are arranged, between which the brake disc with the friction contact surfaces 2, 3 is arranged. When the brake shoes 10, 11 are moved toward each other, the brake disc is clamped between them, and the resulting friction generates a braking torque.

[0037] Air ducts can be formed between the two friction contact surfaces 2, 3, as shown in the figures, so that the friction contact surfaces 2, 3 are ultimately located on two friction rings, which are held apart from each other by radially extending webs. The centrifugal force generated during driving even leads to an air flow between the friction rings from the inside to the outside, so that the friction brake body 1 is actively cooled. Optionally, ventilation holes can also be provided axially through the friction brake body 1 to improve air flow and cooling.

[0038] Advantageously, the respective wear protection layer 6, 7 is or will be applied to the gray cast iron body 5 by laser deposition welding and has a stainless steel matrix with agglomerated hard material particles, wherein the average particle size of the hard material particles is less than 10 pm. Preferably, the average particle size is less than 5 pm, particularly preferably it is between 1 and 3 pm. The hard material particle agglomerates in the wear protection layer are infiltrated by the molten stainless steel matrix material during laser deposition welding, so that the wear protection layer 6, 7 has an average porosity of less than 2% after coating by laser deposition welding. Due to the infiltration of the agglomerates by the matrix melt into the agglomerates, a strong bond is formed between the agglomerates and the matrix material.Furthermore, thanks to the infiltration of matrix melt, the agglomerates after coating no longer consist only of brittle hard material particles, but of a metal-ceramic composite material with significantly increased fracture toughness, whereby the wear protection layer offers improved crack resistance compared to conventional solutions.

[0039] Such an agglomerate is shown as an example in Figure 3. Individual hard material particles 12 are combined to form several larger agglomerates 13, which in this case are at least substantially spherical. The agglomerates preferably have an average size of 20 to 100 μm, particularly preferably 30 to 60 μm.

[0040] Thanks to the increased crack resistance, cracks in the braking process are

[0041] Stress occurs later on the braking surfaces compared to conventional friction brake bodies. Furthermore, cracks on the friction contact surface 2, 3 propagate significantly more slowly toward the gray cast iron base body 5.

[0042] The agglomerated hard material particles preferably comprise at least one of the following ceramic materials: titanium carbide, titanium nitride, titanium carbonitride, molybdenum carbide, niobium carbide, and / or tungsten carbide. The hard material particles are particularly preferably made of titanium carbide or a mixture of titanium carbonitride and molybdenum carbide, with the molybdenum carbide accounting for a maximum of 10 percent by weight in the mixture.

[0043] Optionally, a metallic intermediate layer 14 is arranged between the base body 5 and the respective wear-resistant layer 6, 7 to further increase the layer adhesion and crack resistance of the layer system comprising the wear-resistant layer 6, 7, the intermediate layer 14, and the base body 5. The agglomerates 13 are used in the laser deposition welding process as filler material for production. The agglomerates 13 used in the coating process have an average porosity of more than 20%, particularly preferably more than 40%. The agglomerates 13 used as filler material preferably do not contain any additional iron-based materials that could act as binding agents in the agglomerates.During the laser deposition welding process, the pores of the agglomerates are infiltrated by the molten metal of the stainless steel matrix material due to the capillary action, so that the wear protection layer 6,7 then has the above-mentioned average porosity of less than 2% after coating.

Claims

Claims 1. Friction brake body (1) for a wheel brake (8) of a motor vehicle, with a base body (5) which is made of grey cast iron, wherein the base body (5) has at least one friction contact surface (2, 3) with a wear protection layer (6, 7), and wherein the wear protection layer (6, 7) has a stainless steel matrix with hard material particles, characterized in that the wear protection layer (6, 7) has a plurality of agglomerates (13) of hard material particles (12), and that the agglomerates (13) are infiltrated by the stainless steel matrix.

2. Friction brake body according to claim 1, characterized in that the average particle size of the hard material particles (12) is less than 10 pm, in particular less than 5 pm.

3. Friction brake body according to one of the preceding claims, characterized in that the average particle size of the hard material particles (12) is between 1 and 3 pm.

4. Friction brake body according to one of the preceding claims, characterized in that the agglomerates (13) themselves have an average porosity of at least 20%, in particular of at least 40%.

5. Friction brake body according to one of the preceding claims, characterized in that the agglomerates (13) have an average size of 20 to 100 pm, in particular of 30 to 60 pm.

6. Friction brake body according to one of the preceding claims, characterized in that the respective wear protection layer (6, 7) has an average porosity of less than 2%.

7. Friction brake body according to one of the preceding claims, characterized in that the agglomerated hard material particles (12) comprise at least one of the materials titanium carbide, titanium nitride, titanium carbonitride, molybdenum carbide, niobium carbide and / or tungsten carbide.

8. Friction brake body according to one of the preceding claims, characterized in that the agglomerated hard material particles (12) consist of titanium carbide or of a mixture of titanium carbonitride and molybdenum carbide.

9. Friction brake body according to claim 8, characterized in that the molybdenum carbide in the mixture has a maximum weight proportion of 10%.

10. Friction brake body according to one of the preceding claims, characterized in that a metallic intermediate layer (14) is formed between the respective wear protection layer (6, 7) and the base body (5).

11. Friction brake body according to one of the preceding claims, characterized in that the respective wear protection layer (6, 7) is a wear protection layer (6, 7) applied by laser deposition welding.

12. Method for producing a friction brake body (1) for a wheel brake (8) of a motor vehicle, in particular a friction brake body according to one of claims 1 to 11, with a base body (5) which is made of grey cast iron, wherein the base body (5) has at least one friction contact surface (2, 3) to which a wear protection layer (6, 7) is applied, which has a stainless steel matrix with hard material particles (12), characterized in that the hard material particles (12) are introduced into the wear protection layer (6, 7) as agglomerates (13) of hard material particles (12).

13. Method according to claim 11, that the wear protection layer (6,7) by Laser deposition welding is applied to the base body (5), whereby in particular during laser deposition welding, the agglomerated hard material particles (12) are added to the stainless steel matrix.

14. Method according to one of the preceding claims, characterized in that the agglomerates (13) are produced beforehand in a separate process in which the hard material particles are agglomerated and sintered, in particular such that the agglomerates (13) have an average porosity of greater than 20%, in particular greater than 40%, after sintering.

15. Method according to one of the preceding claims, characterized in that a metallic intermediate layer (14) is applied to the gray cast iron base body (5) before the wear-resistant layer (6, 7).

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