THIN RING BEARING AND COMPUTER TOMOGRAPH WITH SUCH A THIN RING BEARING

Description

[0001] The invention relates to a thin-section bearing comprising at least one outer ring, at least one inner ring and a plurality of spherical rolling elements, wherein the at least one inner ring is designed with an inner diameter greater than 700 mm, in particular for use in a computed tomography scanner.

[0002] DE 102009056038 A1 describes a thin-section bearing and a method for manufacturing a bearing ring from wire-shaped material for a thin-section bearing.

[0003] Thin-section bearings are rolling bearings that have a large inner diameter Di of the inner ring relative to the distance A between the inner and outer diameters of the bearing (viewed in cross-section). In particular, the ratio A / Di is typically between 1:30 and 1:150.

[0004] DE 10 2017 222 208 B3 discloses a computed tomography device and a method for arranging a bearing ring of a rolling bearing. The rolling bearing is designed as a three-point ball bearing and comprises a bearing ring with a groove profile, a first wire ring, and a second wire ring. Such computed tomography devices typically have a stationary part and a rotating part, the rotating part comprising an X-ray source and an X-ray detector that interacts with the source. The rotating part can have a mass of approximately 600 to 900 kg and rotate at a speed of approximately 60 to 240 revolutions per minute. A rolling bearing can be used for the rotational support of the rotating part relative to the stationary part.

[0005] High running accuracy, extremely smooth running, zero backlash, and high tilting stiffness are essential for producing high-quality images. Currently, bearing rings made of high-purity, and therefore expensive, steel grades are used for this purpose.

[0006] US Patent 2020 O 166 080 A1 describes a bearing component comprising a metallic base body and a coating applied to it by weld overlay. The base body is made of unalloyed steel or cast iron, while the coating is made of alloy steel.

[0007] DE 10 2009 018 822 A1 describes a rolling bearing comprising an inner race and an outer race made of hard metal, which are each connected to a support ring on their side facing away from the rolling elements via a brazing alloy layer.

[0008] DE 10 2010 006 423 A1 discloses a rolling bearing with bearing rings having a metallic base body bonded, soldered or screwed to ceramic running surfaces.

[0009] DE 103 33 542 B2 describes a rotary bearing arrangement of a large bearing, in particular for a tomography device. A contour is embossed into a first and / or a second component of the rotary bearing arrangement, onto which one or more high-strength layers are welded and which are machined to form a rotationally symmetrical running surface for rolling elements.

[0010] The object of the invention is to provide a suitable thin-section bearing that results in significant cost savings in its manufacture.

[0011] The problem is solved by a thin-section bearing according to claim 1. The thin-section bearing comprises at least one outer ring, at least one inner ring, and a plurality of spherical rolling elements, wherein the at least one inner ring has an inner diameter greater than 700 mm. The inner diameter of the at least one inner ring has a ratio of A / D i = 1:30 to 1:150 relative to a distance A between the inner diameter and an outer diameter of the thin-section bearing, viewed in a cross-section in the axial direction of the thin-section bearing. The at least one inner ring and the at least one outer ring are formed from an unhardened metallic base material with a hardness of less than 60 HRC, wherein the at least one inner ring and the at least one outer ring each form a raceway bearing surface.The base material is at least partially covered in the area of ​​the raceway receiving surfaces with a functional layer with a functional layer thickness in the range of 0.5 to 3 mm, wherein the functional layer is formed from a metallic functional layer material with a hardness of at least 60 HRC.

[0012] According to the invention, the thickness of the functional layer is designed differently in the cross-section in a direction perpendicular to the raceway receiving surface, such that the functional layer does not completely cover the raceway receiving surface and the thickness of the functional layer decreases towards its edge regions in the direction perpendicular to the raceway receiving surface.

[0013] Thus, only the functional layer needs to be formed using a high-quality, very pure, and roll-resistant functional layer material of high hardness. Since the functional layer material can be applied separately and in a thin layer, the material-related manufacturing costs for the bearing rings are significantly reduced. The thickness of the functional layer is selected according to the minimum required hardening depth on each ring to ensure a functional and durable component. The base material onto which the functional layer is applied no longer needs to have the same high level of purity. Furthermore, stresses and distortion can be minimized without having to subject the entire bearing ring to heat treatment.

[0014] The metallic base material is preferably steel. In particular, the metallic base material is selected from bearing steel, heat-treatable steel, or case-hardening steel. For example, a weldable heat-treatable steel with a carbon content of less than 0.3 wt.% is used. Alternatively, aluminum can also be used as the metallic base material.

[0015] The metallic functional layer material is preferably a steel with a proportion of 0 to 10 wt.% Mo, 0 to 19 wt.% W, 0 to 5 wt.% V, 3.5 to 5 wt.% Cr, 0 to 11 wt.% Co, 0.75 to 1.2 wt.% C, balance iron and unavoidable impurities or other elements, such as Mn, Si, Cu, Ni, P, S, with a proportion of less than 0.5 wt.%.

[0016] In particular, steel grade 1.3344 (X 130 WMoCrV 6-5-4-3) is used. High-speed powder metallurgy steels of high hardness are preferred.

[0017] Alternatively, the metallic functional layer material is preferably a hard metal based on tungsten carbide in a nickel binder matrix, also known on the market under the name "Cermadur"

[0018] Particularly preferred is a combination of a metallic base material in the form of heat-treated steel with a carbon content of less than 0.3 wt.% with a functional coating material made of steel grade 1.3344.

[0019] The functional layer is applied to the base material, primarily by laser cladding. This results in a wavy structure in the transition zone between the base material and the functional layer, which is visible in the micrograph and can be influenced by the laser cladding process parameters. The resulting heat-affected zone extends into the base material, with the waviness covering an area corresponding to the measured distance Z between the mean of the wave peaks and the mean of the wave troughs, where this distance Z is at least 50 µm. This ensures a particularly close and pore-free bond between the base material and the functional layer. The waviness and extent of the heat-affected zone depend on the cladding parameters, such as power, cladding speed, and cladding width.

[0020] A free surface of the functional layer, which forms the raceway for the rolling elements, is preferably machined and / or burnished. This adapts the flatness and surface roughness of the free surface of the functional layer, and thus of the raceways, to the requirements of the application of the rolling bearing components. In particular, the free surface of the functional layer is ground and honed.

[0021] The at least one outer ring and / or at least one inner ring can be heat-treated to optimize stress on the ring and increase the hardness of the functional coating material. In particular, heat treatment is carried out in a temperature range of 400°C to less than 600°C for 1 to 2 hours. Subsequently, the at least one outer ring and / or at least one inner ring is cooled to room temperature. In the case of a particularly preferred combination of a metallic base material in the form of heat-treatable steel with a carbon content of less than 0.3 wt.% with a functional coating material made of steel grade 1.3344, this heat treatment is preferably carried out in a temperature range of 500°C to less than 600°C.

[0022] The raceway bearing surfaces are preferably coated with the functional layer only in the contact area with the rolling elements. This saves on functional layer material and further reduces the cost of a bearing ring.

[0023] Furthermore, the functional layer thickness varies across the cross-section of a raceway surface, which further reduces costs.

[0024] It is preferred if two outer rings and / or two inner rings are present. This considerably simplifies the installation of the thin-section bearing at the installation site.

[0025] The thin-section bearing is preferably designed with a square or predominantly square cross-section. The thin-section bearing is preferably designed as a deep groove ball bearing, a four-point contact bearing, or an angular contact ball bearing.

[0026] A computed tomography scanner comprising at least one thin-section bearing according to the invention has proven successful. With regard to a possible embodiment of a computed tomography scanner, reference is made to the aforementioned DE 10 2017 222 208 B3.

[0027] The Figures 1 to 3 They are intended to illustrate a thin-section bearing according to the invention by way of example. This shows: Figure 1 shows a section through a thin-section bearing, Figure 2 shows an enlarged section from Figure 1 , and Figure 3 shows a micrograph of a section through the functional layer and the adjacent base material.

[0028] Figure 1Figure 1 shows a section through a thin-section bearing 1 with a split outer ring 2a, 2b, a split inner ring 3a, 3b, and rolling elements 4. The inner diameter Di of the split inner ring 3a, 3b is greater than 1 m. The distance A between the inner diameter Di and the outer diameter of the split outer ring 2a, 2b is only 30 mm, resulting in an A / Di ratio of at least 1:34. The cross-section of the thin-section bearing 1 (see the area marked with a dotted line) is in Figure 2 Shown enlarged.

[0029] Figure 2 shows this enlarged section from Figure 1 . Same reference symbols as in Figure 1The following are identical components. The split outer ring 2a, 2b, made of a base material 6 and featuring raceway support surfaces 5, is visible. The split inner ring 3a, 3b, also made of a base material 6 and featuring raceway support surfaces 5, is also visible. Functional layers 7, made of a functional layer material, are applied to each of the raceway support surfaces 5. The functional layer 7 is applied with varying thicknesses across the cross-section of each raceway support surface 5. Furthermore, the functional layer 7 does not completely cover the respective raceway support surface 5. This allows for savings in functional layer material and reduces the cost of the thin-section bearing 1.

[0030] Figure 3Figure 1 shows a micrograph of a section through the functional layer 7 and the adjacent base material 6 of the inner ring 3a. The functional layer 7 is formed on the base material 6 by laser cladding. In the transition zone 12, where the base material 6 is fused with the functional layer 7, a wavy structure is present. The distance Z between the mean of the wave crests and the mean of the wave troughs (see dashed lines) is at least 50 µm. The free surface 8 of the functional layer 7, which faces away from the base material 6, has been post-processed by grinding and honing. For the sake of simplicity, the free surface 8 of the functional layer 7 is shown flat here, although it has a curvature in the thin-section bearing 1 to accommodate the rolling elements 4 in the form of balls. Reference symbol list

[0031] 1 Thin section bearing 2a, 2b Outer ring 3a, 3b Inner ring 4 Rolling elements 5 Raceway bearing surface 6 Base material 7 Functional layer 8 Free surface of the functional layer 12 Transition area A Distance D i Inner diameter

Claims

1. A thin-ring bearing (1) comprising at least one outer ring (2a, 2b), at least one inner ring (3a, 3b) and a plurality of spherical rolling elements (4), wherein the at least one inner ring (3a, 3b) is designed to have an inner diameter (Di) that is greater than 700 mm, wherein the inner diameter (Di) of the at least one inner ring (3a, 3b), in relation to a distance A between the inner diameter (Di) and an outer diameter of the thin-ring bearing (1), as viewed in a cross-section in the axial direction of the thin-ring bearing (1), has a ratio of A / Di = 1:30 to 1:150, wherein the at least one inner ring (3a, 3b) and the at least one outer ring (2a, 2b) are formed from an unhardened metallic base material (6) with a hardness of less than 60 HRC, and wherein the at least one inner ring (3a, 3b) and the at least one outer ring (2a, 2b) each form a raceway receiving surface (5), wherein the base material (6) in the region of the raceway receiving surfaces (5) is at least partially covered with a functional layer (7) with a functional layer thickness in the range of 0.5 to 3 mm, wherein the functional layer (7) is formed from a metallic functional layer material with a hardness of at least 60 HRC, and wherein the functional layer thickness of the functional layer (7) varies in cross-section in a direction perpendicular to the raceway receiving surface (5), such that the functional layer (7) does not completely cover the raceway receiving surface (5) and the functional layer thickness of the functional layer (7) decreases in the direction perpendicular to the raceway receiving surface (5) towards its edge regions.

2. The thin-ring bearing (1) according to claim 1, wherein the metallic base material (6) is formed from steel.

3. The thin-ring bearing (1) according to claim 1 or claim 2, wherein the metallic functional layer material is made of steel of grade 1.3344 (X 130 WMoCrV 6-5-4-3) or of a hard metal based on tungsten carbide in a nickel binder matrix.

4. The thin-ring bearing (1) according to any one of claims 1 to 3, wherein the functional layer (7) is applied to the base material (6) by laser cladding, whereby a wavy transition area is formed between the base material (6) and the functional layer (7) in cross-section.

5. The thin-ring bearing (1) according to any one of claims 1 to 4, wherein a free surface (6) of the functional layer (7), which forms a raceway for the rolling elements (4), is finish-machined and / or burnished.

6. The thin-ring bearing (1) according to any one of claims 1 to 5, wherein the at least one outer ring (2a, 2b) and / or at least one inner ring (3a, 3b) is heat-treated.

7. The thin-ring bearing (1) according to any one of claims 1 to 6, wherein the raceway receiving surfaces (5) are only covered with the functional layer (7) in a contact region with the rolling elements (4).

8. The thin-ring bearing (1) according to any one of claims 1 to 7, wherein two outer rings (2a, 2b) and / or two inner rings (3a, 3b) are provided.

9. A computed tomography unit comprising at least one thin-ring bearing (1) according to any one of claims 1 to 8.