DE102020122653A1 - Friction ring, wheel brake disc and method for their manufacture - Google Patents

Abstract

A friction ring (4, 5) for a wheel brake disc (1), the friction ring (4, 5) comprising a monolithically cast metal block with a friction surface (40) and a rear surface (44), with at least one hard material ( 43) is arranged, the proportion by volume of hard material (43) in the metal (42) increasing steadily from the rear surface (44) to the friction surface (40); and a wheel brake disc (1) and a method for the production thereof.

Description

The present invention relates to a friction ring according to the preamble of claim 1, as well as a wheel brake disc and a method for the production thereof.

Wheel brake discs, such as those used in rail vehicles, are known from the prior art. In the DE 44 17 813 two friction rings are centered by sliding blocks that act in a form-fitting manner in the radial direction, so that the centering of the friction rings is maintained even through heating during the braking process. So that the deformation of the friction rings due to the thermal load does not result in a conical deformation of the friction rings, cooling ribs are typically attached to the friction rings, via which the friction rings are supported on the wheel disk of the rail vehicle wheel.

From the DE 10 2007 020 891 A1 different processes for the production of a friction ring containing hard material are presented. For example, spray compacting is known, which realizes the production of a component or a semi-finished product by spraying molten metal through a nozzle. The melt droplets hit a substrate and solidify into a compact solid. The spray compacting thus makes it possible to provide a friction ring in which many melt droplets are connected to one another. The interconnected melt drops are comparable to a layered structure, as also occurs in layer casting, whereby the distribution of the hard material particles in the material can be heterogeneous or homogeneous depending on the process, but without a clear concentration distribution of the hard material particles in a given direction.

Furthermore, numerous methods are known in which a coating is applied to the surface of a provided friction ring. So reveals the EP 0 846 884 A2 a variant in which a base body is first provided by means of any casting process. In addition to many other methods, the low-pressure casting method known per se, by means of which a base body can be realized, is also disclosed here. By introducing two melts at different times, a gradient structure can be formed, with hard material particles migrating into the already solidified base body, for example through diffusion effects.

This manufacturing variant is a so-called layer casting method with which gradient structures can be realized. Theoretically, it is also possible to pour several functional layers on top of one another at different times. However, it is the case that one or more phase boundaries between metal phases, possibly also with the formation of intermetallic phases, arise between the surface of the base body that has already solidified or at least cooled down and the newly applied melt layer, with the hard material particles in the respective phases in are distributed gradually. Since the material properties can vary greatly depending on the hard material concentration, solidification temperature, application speed and application volume of the phases, very high process control is necessary for the production of friction rings with approximately the same material properties.

The invention is therefore based on the object of creating a wheel brake disc which avoids the aforementioned disadvantages of the prior art, with the aim in particular of providing a wheel brake disc with friction rings with approximately the same material properties.

The invention is based on the idea of designing a friction ring for a wheel brake disc in such a way that it is designed as a monolithically cast metal block with a friction surface and a rear surface. The metal block has a metal matrix, i.e. a metal or a metal alloy, and a hard material that is gradually distributed therein, such that the volume proportion of hard material in the metal increases steadily from the rear surface to the friction surface, so that the hard material predominantly at the point of the friction ring is provided, on which the braking friction acts.

In contrast to layer casting processes, it is a monolithic metal block, which means that thermal stresses and differences in heat conduction within the material along the cut perpendicular to the friction surface are only low.

Further advantageous embodiments of the wheel brake disc according to the invention can be found in the dependent claims.

The proportion by volume of hard material in the metal can increase discontinuously or, particularly preferably, constantly.

In particular, the metal block has no phase boundary, it is therefore uncoated and/or unlayered. However, a film such as an oil film for protection against corrosion in storage or delivery may be provided. In particular and particularly preferably, the entire friction ring can be formed from the metal block.

The friction ring can preferably have cooling ribs and/or cooling cams along the rear surface.

In an advantageous embodiment of the present invention, the density of the hard material can be at least 1 g/cm ³ higher than the density of the metal, so that the hard material in the molten metal can sink quickly, forming gradients due to the high density difference.

The metal can preferably be a light metal or a light metal alloy with a light metal as the main component. The light metal is preferably aluminum. The aluminium-based alloy is particularly preferably alloyed with silicon and/or magnesium.

The hard material particles can preferably be in the form of corundum, in particular technical corundum.

The concentration of hard material, in particular of hard material particles, in the metal can increase by at least 5% by volume, preferably by at least 10% by volume, particularly preferably by 10-18% by volume, from the rear surface to the friction surface. Typically, the thermal conductivity is reduced by hard material additives. The low concentration of hard material particles in the rear area enables better heat dissipation, which can also be reinforced by cooling fins or cooling knobs.

The concentration of hard material, in particular hard material particles, in the metal can increase from the rear surface to the friction surface by at least 50%, preferably by at least 65% by volume, particularly preferably by 70-95% by volume.

Also according to the invention is a wheel brake disc for a wheel of a rail vehicle, the wheel having a wheel web on which friction rings according to the invention are supported, which are fastened to the wheel web with connecting means.

The connecting means can advantageously be cast onto the respective friction ring, with the connecting means being particularly preferably designed as a plurality of spring elements arranged on the circumference of the friction rings, with the spring elements being arranged between the friction rings and the wheel web when the wheel brake disc is in the installed state.

However, the arrangement of spring elements is only one of several preferred design variants. In a further embodiment of the invention, the proportion of hard material in contact with the wheel web can be reduced to such an extent, for example, by sedimentation in the direction of the friction surface, that thermally induced radial disc expansion is supported by easier sliding, in particular of the screw-on area. Thus, for example, spring elements can be omitted in this embodiment variant.

1. A) Bereitstellen einer Metallschmelze;
2. B) Vermischen der Metallschmelze mit Hartstoffpartikeln;
3. C) Einbringen der Schmelze in eine Gussform zur Ausformung des Reibrings, wobei die Gussform derart ausgerichtet ist, dass die Oberfläche zur Ausformung der Reibfläche unten gegenüber den anderen Flächen bezogen auf das Schwerefeld der Erde ausgerichtet ist;
4. D) Temperaturkontrolle derart, dass das Gussmaterial in der Gussform über ein vorbestimmtes Mindestzeitintervall, insbesondere bei konstanter Temperatur, in Schmelze gehalten wird;
5. E) Erkalten der Schmelze unter Ausbildung des Reibrings, und
6. F) Montage des Reibrings mit weiteren Bauteilen zu einer Radbremsscheibe.

A method according to the invention for producing a wheel brake disc according to the invention comprises at least the following steps:

1. A) providing a molten metal;
2. B) mixing the metal melt with hard material particles;
3. C) introducing the melt into a mold for forming the friction ring, the mold being oriented such that the surface for forming the friction surface is oriented at the bottom with respect to the other surfaces with respect to the earth's gravitational field;
4. D) Temperature control such that the cast material is kept in the mold over a predetermined minimum time interval, in particular at a constant temperature, in melt;
5. E) cooling of the melt with formation of the friction ring, and
6. F) Assembly of the friction ring with other components to form a wheel brake disc.

In particular, in step E or during or after cooling, mechanical finishing can be carried out to give the final form of the friction ring that can be assembled. This can include balancing and/or abrasive machining.

In particular, the aforementioned method enables production of the friction ring with a hard material in gradual distribution in one method step without a complicated layer-casting method with multiple application that is expensive in terms of process technology.

Advantageously, the melt is introduced after step C) in a low-pressure casting process.

• 1 eine Vorderansicht einer Radbremsscheibe aus dem Stand der Technik nach bei der die Reibringe verschraubt sind und zur Zentrierung Gleitsteine eingesetzt sind;
• 2 eine Schnittdarstellung einer Radbremsscheibe aus dem Stand der Technik nach 1, bei der die Reibringe verschraubt sind und zur Zentrierung Gleitsteine eingesetzt sind;
• 3 eine perspektivische Rückansicht eines weiteren Reibringes aus dem Stand der Technik mit eingesetzten bandförmigen Federelementen;
• 4 eine schematische Ansicht eines Schnitts durch einen Reibring aus dem Stand der Technik; und
• 5 eine schematische Ansicht eines Schnitts durch einen erfindungsgemäßen Reibring.

The invention is explained in more detail below using an exemplary embodiment with the aid of the following figures. Show it:

• 1 a front view of a wheel brake disc from the prior art in which the friction rings are screwed and sliding blocks are used for centering;
• 2 a sectional view of a wheel brake disc from the prior art 1 , in which the friction rings are screwed on and sliding blocks are used for centering;
• 3 a perspective rear view of another friction ring from the prior art with inserted band-shaped spring elements;
• 4 a schematic view of a section through a friction ring from the prior art; and
• 5 a schematic view of a section through a friction ring according to the invention.

In the 1 and 2 a variant for a structure of a known wheel brake disc 1 is shown, which can preferably be used in rail vehicles. A wheel 3 of a vehicle, in particular a rail vehicle, has a wheel web 2 on which a friction ring 4 , 5 is arranged symmetrically to the axis of symmetry of the wheel web 2 . The respective friction ring 4, 5 has ribs 6, by means of which the friction ring 4.5 is supported on the wheel web 2. The friction rings 4, 5 are in the variant of 1 and 2 formed with screws, which are designed as expansion screws and by means of which the respective friction ring 4 or 5 is screwed together with a nut 8 with the wheel web 2. The respective screw has a screw head 7 which is supported on a sleeve 8 which is embedded in the friction ring 5 via a countersink. The corresponding nut 9 is also designed as a sleeve or is combined with a separate sleeve and is also embedded in a countersink in the friction ring 4 . The positive connection of the connection is generated by separate sliding blocks 10 .

As an alternative to the aforementioned specification variant of a screw connection, in 3 a perspective view of a friction ring 4, 5 with inserted spring elements 13 of a wheel brake disc 1 is shown. In this embodiment, the friction ring 4, 5 has ribs and/or cams 14, 15, 16, 17, 18, 19 on the wheel web side with different geometries, which rise in the radial direction with respect to the wheel web and essentially run in the axial direction. The ribs or cams 14, 15, 16, 17, 18, 19 are arranged in two defined, recurring patterns on the respective friction ring 4, 5. The patterns are each separated from one another by the arrangement of a spring element 13 which is only optional. The geometry of the ribs or cams 14, 15, 16, 17, 18, 19 is selected so that a deformation of the friction ring 4, 5 due to the heat introduced by the braking process in relation to the wheel 3 axial direction in terms of amount done as evenly as possible. In addition, the geometry of the ribs or cams 14, 15, 16, 17, 18, 19 is selected so that when the wheel 3 rotates, the greatest possible heat dissipation takes place by convection. The ribs or cams 14, 15, 16, 17, 18, 19 are also basically designed in such a way that they only rest on the wheel web 2 at their respective two ends 20, so that the heat input from the friction rings 4, 5 into the wheel web 2 is reduced to a minimum by the geometric design of the ribs or cams 14, 15, 16, 17, 18, 19.

A bore 30 whose axis of symmetry is in 3 shown example coincides with the axis of symmetry of the spring element 13, when the friction rings 4, 5 are in the mounted state, a screw (not shown) passes through each of them, with which the friction rings 4, 5 are fastened to the wheel web 2 and the primary screw connection of the friction rings 4, 5 to the wheel web 2 forms. Accordingly, the friction rings 4 , 5 also have a bore 31 that is coaxial with the bore 30 . The spring element 13 is connected to the cams 21, 22 via the legs 28, 29 and corresponding bores 32 with suitable connecting elements (not shown).

The spring element 13 is designed according to the invention in such a way that all relative movements that occur are in the range of the elastic deformation of the spring elements 13 in terms of absolute value. This means that the primary screw connection of the wheel brake disc 1 does not perform any relative movement in the direction parallel to the wheel web 2 , which completely prevents wear on the wheel web 2 . Other constructive details of the variant of 3 can the WO 2014/019895 A1 be removed.

Typically, the friction rings 4, 5 described above and preferably used within the scope of the present invention can be realized by various casting methods. A light metal, in particular an aluminum-based material, is used as the preferred material within the scope of the present invention, so that the preferred variant of the friction ring according to the invention is designed as a lightweight friction ring.

It can particularly preferably be an AlSiMg material, that is to say an alloy which mainly consists of aluminum. Other alloying elements are silicon and magnesium. The aluminum-based material mentioned above can be cast from pre-mixed matrix composites made of metal and hard materials Al/SiC or Al/AI203 mixture.

In the context of the present invention, a gradient-mixed material composite made of ductile base material such as aluminum and hard material particles functionally favorably distributed in a gradient structure is thereby preferably obtained. A phase boundary, as in the layer cast materials, is preferably not recognizable in the sectional image.

The difference in density, for example, between corundum (AI203) as hard material particles and aluminum is used for this purpose. This is achieved, among other things, by arranging the friction surface in the lowest area of the casting mold in relation to the earth's gravitational field.

The main advantage for the finished product as a friction ring is that the particles relevant to friction and wear are concentrated in a zone where they are needed.

The hard material added to the mixture of aluminum-based molten metal is preferably a technical corundum. This can be contained in a volume proportion of preferably more than 5%, in particular 8-15% by volume. The preferred average particle size of the hard material particles is between 10-50 μm. The particle size determination in this area can be done by static image analysis (static image analyzing) of one or more cross-sectional images

The enriched base composite can be formed into a gradient material by particle rearrangement in a low pressure casting process. Such a casting process is known per se, but not for forming the gradient structure described according to the invention. Here, a metal melt, such as aluminum, is usually pressed from below by means of a riser pipe into a casting mold placed on top of a mold cavity. This can be a mold (permanent mold). The pressure required to push up or to shift the melt can be generated by gas pressure. After the mold has been filled, the gas pressure is also maintained during solidification in order to enable refilling to compensate for the shrinkage in volume during the transition from the liquid to the solid state. Naturally, this requires solidification that is as directed as possible from top to bottom and requires the most favorable possible casting design or cross-sectional gradations.

In the friction area of the friction ring, which is at the bottom in the casting mold, the hard material particles, in particular the corundum particles, are concentrated there with an advantageous volume proportion of more than 15%, preferably 18-25%.

The corundum has a density of more than 3.75 g/cm ³ , preferably between 3.8-4.2 g/cm ³ , in particular 4.05 g/cm ³ (+/− 0.08 g/cm ³ ) on. In contrast, the base metal, e.g. an aluminum melt, has a density of less than 2.9 g/cm ³ , preferably between 2.5 and 2.85 g/cm ³ , in particular at 2.7 g/cm ³ (+/- 0 .08 g/cm ³ ).

Furthermore, a movement of the casting mold during cooling can be advantageous, for example a shaking mechanism. The movement supports the sedimentation.

As already mentioned above, the concentration of hard material particles 43 in the metal or the metal alloy 42 in the section of the friction ring 4, 5 gradually decreases from the friction surface 40 to the cooling channels 41 of the rear surface 44. this is in 5 shown. 4 In contrast, FIG. 4 shows a uniform distribution of the hard material particles 43′ between the friction surface 40′ and the corresponding rear surface 44′, as is known from the prior art.

The concentration of hard material particles can particularly preferably decrease uniformly from the friction surface of the disc to its cooling channels, for example by at least 5% by volume, preferably by at least 10% by volume, particularly preferably by 10-18% by volume.

The gradient distribution of the hard material can also be improved by temperature control in the casting process. The temperature control enables "keeping in the melt" and slow cooling, so that an improved distribution is achieved through the sinking of the hard material particles.

In addition, a brake disc that is advantageous in terms of friction can be realized by this method, which requires only little effort in each of the production steps. This reduces costs.

By using a comparatively inexpensive starting material made of aluminum or an aluminum alloy as a 'mixed system' with hard material particles, comparatively easy processing by means of casting can be achieved. At the same time, a friction ring with demonstrably good friction properties and high wear resistance is created, which can be optimally used in a wheel brake disc. Due to the creation of a virtually seamless, in particular monolithic, material without a phase interface, good thermal conductivity of the individual components of the material composite can also be achieved. The gradual development of the corundum particle concentration in the material can be more clearly defined by a low-pressure casting process in a mold that is occasionally reheated.

The gradient preferably runs as a proportion that decreases uniformly from the friction side upwards (towards the cooling side of the friction ring). Both corundum and SiC can be used as hard material particles. However, corundum has the advantage part that this hard particle material has a consistently high melting point compared to the SiC component that is also frequently used for friction purposes. In this way, a relatively uncritical temperature control of the process is achieved, in which aluminum is kept in the melt for a longer period of time, for example at least 1 hour. Furthermore, due to the tendentially smooth mold for the finish of the surfaces by machining, only a smaller volume removal is to be expected than before, which is another advantage.

Reference List

1

wheel brake disc

2

wheel dock

3

wheel

4

friction ring

5

friction ring

7

screw head

8th

sleeve

9

mother

10

sliding block

13

spring element

14

rib

15

rib

16

rib

17

pair of cams

18

rib

19

pair of cams

21

cam

22

cam

28

leg

29

leg

30

drilling

31

drilling

32

drilling

40

friction surface

41

cooling channels

42

metal and/or metal alloy

43

hard material

44

back surface

40'

friction surface

43'

hard material

44'

back surface

50

Pre-mixing (aluminum chips + hard material particles)

101

providing a melt

102

mixing of the melt

103

Insertion in mold

104

Temperature Control / Keep in Melt

105

cooling of the melt

106

Assembly of the wheel brake disc

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 4417813 [0002]
• DE 102007020891 A1 [0003]
• EP 0846884 A2 [0004]
• WO 2014/019895 A1 [0029]

Claims (11)

Friction ring (4, 5) for a wheel brake disc (1), wherein the friction ring (4, 5) comprises a monolithically cast metal block with a friction surface (40) and a rear surface (44), with at least one hard material (43 ) is arranged, characterized in that the volume proportion of hard material (43) in the metal (42) from the rear surface (44) to the friction surface (40) increases steadily. friction ring after claim 1 , characterized in that the proportion by volume of hard material (43), in particular hard material particles, in the metal (42) increases constantly. friction ring after claim 1 or 2 , characterized in that the metal block has no phase boundary, so uncoated and / or unlayered, is formed. Friction ring according to one of the preceding claims, characterized in that the friction ring (4, 5) has cooling ribs (41) and/or cooling cams along the rear surface (44). Friction ring according to one of the preceding claims, characterized in that the density of the hard material (43) is at least 1 g/cm ³ greater than the density of the metal (42). Friction ring according to one of the preceding claims, characterized in that the metal (42) is a light metal or a light metal alloy, preferably aluminum or an aluminum-based alloy with aluminum as the main component. Friction ring according to one of the preceding claims, characterized in that the aluminium-based alloy is alloyed with silicon and/or magnesium. Friction ring according to one of the preceding claims, characterized in that the hard material (43), in particular in the form of hard material particles, is in the form of corundum, in particular technical corundum. Friction ring according to one of the preceding claims, characterized in that the concentration of hard material (43), in particular in the form of hard material particles, in the metal (42) from the rear surface (44) to the friction surface (40) increases by at least 5 vol .%, Preferably by at least 10% by volume, particularly preferably by 10-18% by volume. Wheel brake disc (1) for a wheel (3) of a rail vehicle, the wheel (3) having a wheel web (2) on which friction rings (4, 5) are supported according to one of the preceding claims, which are connected to connecting means on the wheel web (2) are attached. Method for producing a wheel brake disc (1) according to one of the preceding claims, in particular by a low-pressure casting method.

Images