Thin bearing and computed tomography apparatus having this type of thin bearing

Abstract

The present invention relates in particular to a thin bearing (1, 1') for a computed tomography apparatus, comprising at least one inner ring (2, 2a, 2b), at least one outer ring (3, 3a, 3b), and a plurality of spherical rolling elements (4), wherein the inner diameter (D i ) of at least one inner ring (2, 2a, 2b) exceeds 700 mm, at least one outer ring (3, 3a, 3b) and at least one inner ring (2, 2a, 2b) are made of a non-hardened metal substrate (6) having a hardness of less than 58 HRC, at least one outer ring (3, 3a, 3b) and at least one inner ring (2, 2a, 2b) each form at least one raceway region (7a, 7b, 7c, 7d) in contact with the rolling elements (4), the substrate (6) is laser hardened in at least one raceway region (7a, 7b, 7c, 7d), and the raceway region (7a, 7b, 7c, 7d) has a hardness of at least 58 HRC.

Description

Technical Field

[0001] The present invention relates to a thin bearing having at least one outer ring, at least one inner ring and a plurality of spherical rolling elements, and in particular to a thin bearing having an inner diameter of the at least one inner ring exceeding 700 mm for use in a computed tomography apparatus.

Background Art

[0002] Patent Document 1 describes a thin bearing and a method for manufacturing a raceway ring from a wire-shaped material for a thin bearing. The wire is wound, bent, and the free ends are welded together. The resulting solid ring is then annealed and finally cold-rolled and hardened if necessary.

[0003] i A thin bearing is a rolling bearing in which the inner diameter D of the inner ring is large with respect to the distance A between the inner diameter and the outer diameter of the bearing (in sectional view). In particular, the ratio A / D i is 1:30 to 1:150.

[0004] Patent Document 2 describes a wire race bearing having two support rings arranged concentrically, having guide wires in recesses facing each other, and in which rolling elements roll on a track related thereto. The wire race bearing is configured as a four-point ball bearing and is used as a rotary joint in a computed tomography method.

[0005] Patent Document 3 discloses the configuration of a bearing for medical equipment such as a computed tomography apparatus. The bearing configuration has an integral inner ring and an integral outer ring, each having a hollow cylindrical basic outer shape.

[0006] Patent Document 4 describes a computed tomography apparatus and a method for arranging a raceway ring of a rolling bearing. In this document, it is described that a computed tomography apparatus usually has a fixed part and a rotating part, and the rotating part has an X-ray radiation source and an X-ray detector that interacts with the radiation source. The rotating part can have a mass of, for example, about 600 to 900 kg and can rotate at a speed of about 60 to 240 revolutions per minute. A very accurate, smooth and quiet operation of the rotational movement is essential. The rotational movement of the rotating part can be driven by direct drive or by a drive belt that interacts with a pulley of the rotating part. Using a rolling bearing, the rotating part can be pivoted relative to the fixed part. The rolling bearing has a plurality of rolling elements and a number of raceways for rolling the rolling elements.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] To generate high-quality images, high operating accuracy, extremely smooth movement, no play, and high tilt rigidity are essential. So far, for this purpose, raceway rings made of high-purity, and therefore expensive, steel grades that are usually fully hardened have been used. Stress and strain in the raceway rings frequently occur during the hardening process.

[0009] Accordingly, an object of the present invention is to provide a suitable thin bearing that brings about cost reduction in production and reduction of thermal deformation in the hardening process.

Means for Solving the Problems

[0010] This object is achieved by a thin bearing comprising at least one inner ring, at least one outer ring, and a plurality of spherical rolling elements, wherein the inner diameter D of at least one inner ring i exceeds 700 mm, at least one outer ring and at least one inner ring are made of a non-hardened metal substrate having a hardness of less than 58 HRC, at least one outer ring and at least one inner ring each form at least one raceway region in contact with the rolling elements, the substrate is laser hardened in at least one raceway region, and the raceway region has a hardness of at least 58 HRC.

[0011] Since the laser hardening of at least one inner ring and at least one outer ring is only carried out locally, the distortion of the raceway rings is minimized. The inexpensive non-hardened metal substrate is in contact with the rolling elements and is hardened only in the region where the raceway of the rolling elements is formed. Thereby, the manufacturing cost of the thin bearing can be significantly reduced.

[0012] However, it has been proven effective to quench the metal substrate to a hardness of 250 + 100 HV before laser hardening in order to improve the microstructure.

[0013] The metal substrate is preferably made of steel having 0.38 to 0.56 wt% C, 0.3 to 1.2 wt% Mn, 0.9 to 1.2 wt% Cr, 0.15 to 0.30 wt% Mo, the balance being iron and unavoidable impurities or other elements such as Si, Al, P, S, Pb in a proportion of less than 0.5 wt%. This is inexpensive, can be laser hardened, and can be used for the thin bearing according to the present invention. In particular, steels of grade 1.7228 (50CrMo4) or 1.7225 (42CrMo4) have been proven effective.

[0014] It is preferable that there are an outer ring and an inner ring, each being separately arranged, and having two annular and mutually parallel track regions running annularly. The two track regions are preferably separated from each other by an annular groove. The groove functions as a lubricant container and prevents the heat-affected zones of the two track regions from overlapping.

[0015] Alternatively, it has been proven effective to have two outer rings and / or two inner rings, each having an annular track region. The two outer rings and / or two inner rings can have local recesses in the regions where their tracks are adjacent to each other.

[0016] The free surface of at least one track region forming a track for rolling elements can be machined and / or forged. The free surface of at least one track region forming a track for rolling elements is particularly honed.

[0017] It is preferable that at least one track region has different thicknesses when viewed in a cross-section passing through at least one outer ring or at least one inner ring. Preferably, the penetration depth of laser hardening in the base material is maximum in the region of the progression of the contact angle.

[0018] A computed tomography apparatus comprising at least one thin bearing according to the present invention has been demonstrated with respect to the achievable high operating accuracy, extremely smooth operation, lack of play, and high tilting rigidity of the thin bearing.

[0019] Figures 1 to 4 illustrate a thin bearing according to the present invention by way of example.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 shows a cross-section of a first thin bearing 1 having an outer ring 3 and an inner ring 2. Further, a plurality of spherical rolling elements 4 are present. The inner diameter D of the inner ring 2 i exceeds 1 m. The outer ring 3 and the inner ring 2 are made of a non-hardened metal base material 6 having a hardness of less than 58 HRC (see FIG. 2). The outer ring 3 and the inner ring 2 each form at least one raceway region 7a, 7b, 7c, 7d in contact with the rolling element 4. The base material 6 is laser hardened in the raceway regions 7a, 7b, 7c, 7d, and the raceway regions 7a, 7b, 7c, 7d have a hardness of at least 58 HRC. The distance A between the inner diameter D i and the outer diameter of the thin bearing 1 (in cross-sectional view) is recorded, and the A / D i ratio is in the range of 1:30 to 1:150. The outer ring 3 and the inner ring 2 are each arranged separately from each other and have two raceway regions 7a, 7b, 7c, 7d that run annularly and parallel to each other, and these raceway regions are separated from each other by annular grooves 9a, 9b.

[0022] FIG. 2 is an enlarged detailed view of the first thin bearing 1 according to FIG. 1 in the cross-sectional area (see the region surrounded by the broken line in FIG. 1). The contact angle 5 is indicated by a broken line in FIG. 2. The hardening depth of the base material 6 is maximum in the regions of the raceway regions 7a, 7b, 7c, 7d that intersect the contact angle 5. In any case, the free surface 8 of the raceway regions 7a, 7b, 7c, 7d forms the raceway of the rolling element 4.

[0023] FIG. 3 shows a cross-section of a second thin bearing 1' having two outer rings 3a, 3b and two inner rings 2a, 2b. Further, a plurality of spherical rolling elements 4 are present. The inner diameter D of the inner rings 2a, 2b iIt is larger than 700 mm. The outer rings 3a, 3b and the inner rings 2a, 2b are made of a non-hardened metal substrate 6 with a hardness of less than 58 HRC (see Fig. 4). The outer rings 3a, 3b and the inner rings 2a, 2b each form a raceway region 7a, 7b, 7c, 7d that contacts the rolling elements 4. The substrate 6 is laser hardened in the raceway regions 7a, 7b, 7c, 7d, and the raceway regions 7a, 7b, 7c, 7d have a hardness of at least 58 HRC. The inner diameter D of the thin bearing 1' (in cross-sectional view) i The distance A between the outer diameter is recorded, and A / D i The ratio is in the range of 1:30 to 1:150. The outer rings 3a, 3b and the inner rings 2a, 2b each have an annular raceway region 7a, 7b, 7c, 7d.

[0024] Fig. 4 shows an enlarged detailed view of the second thin bearing 1' according to Fig. 3 in the cross-sectional area (see the region surrounded by the dashed line in Fig. 3). The contact angle 5 is shown by the dashed line in Fig. 4. The hardening depth of the substrate 6 is maximum in the region of the raceway regions 7a, 7b, 7c, 7d that intersect the contact angle 5. In any case, the free surface 8 of the raceway regions 7a, 7b, 7c, 7d forms the raceway of the rolling elements 4.

Explanation of symbols

[0025] 1, 1' Thin bearings 2, 2a, 2b Inner rings 3, 3a, 3b Outer rings 4 Rolling elements 5 Contact angle 6 Substrate 7a, 7b, 7c, 7d Raceway regions 8 Free surface of the raceway region or the raceway 9a, 9b Annular grooves A Distance D i Inner diameter

Claims

1. A thin bearing (1, 1') comprising at least one inner ring (2, 2a, 2b), at least one outer ring (3, 3a, 3b), and a plurality of spherical rolling elements (4), wherein the inner diameter (D ｉ ) of the at least one inner ring (2, 2a, 2b) exceeds 700 mm, the at least one outer ring (3, 3a, 3b) and the at least one inner ring (2, 2a, 2b) are made of a non-hardened metal substrate (6) having a hardness of less than 58 HRC, the at least one outer ring (3, 3a, 3b) and the at least one inner ring (2, 2a, 2b) each form at least one raceway region (7a, 7b, 7c, 7d) in contact with the rolling elements (4), the substrate (6) is laser hardened in the at least one raceway region (7a, 7b, 7c, 7d), and the raceway region (7a, 7b, 7c, 7d) has a hardness of at least 58 HRC.

2. The thin bearing (1, 1') according to claim 1, wherein the metal substrate (6) is made of steel having 0.38 to 0.56% by weight of C, 0.3 to 1.2% by weight of Mn, 0.9 to 1.2% by weight of Cr, 0.15 to 0.30% by weight of Mo, the balance being iron and unavoidable impurities or other elements such as Si, Al, P, S, Pb in a proportion of less than 0.5% by weight.

3. The thin bearing (1) according to claim 1 or 2, wherein there are an outer ring (3) and an inner ring (2), each being separately arranged from each other and having two raceway regions (7a, 7b; 7c, 7d) that run annularly and parallel to each other.

4. The thin bearing (1) according to claim 3, wherein the two raceway regions (7a, 7b; 7c, 7d) are separated from each other by annular grooves (9a, 9b).

5. The thin bearing (1') according to claim 1 or 2, wherein there are two outer rings (3a, 3b) and / or two inner rings (2a, 2b), each having an annular raceway region (7a, 7b, 7c, 7d).

6. The thin bearing (1, 1') according to any one of claims 1 to 5, wherein the free surface (8) of the at least one raceway region (7a, 7b, 7c, 7d) forming the raceway of the rolling elements (4) is machined and / or forged.

7. The thin bearing (1, 1') according to claim 6, wherein the free surface (8) of the at least one raceway region (7a, 7b, 7c, 7d) forming the raceway of the rolling elements (4) is honed.

8. The thin bearing (1, 1') according to any one of claims 1 to 7, wherein the at least one raceway region (7a, 7b, 7c, 7d) has different thicknesses when viewed in a cross-section passing through the at least one outer ring (3, 3a, 3b) or the at least one inner ring (2, 2a, 2b).

9. A computed tomography apparatus comprising at least one thin bearing (1, 1') according to any one of claims 1 to 8.

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