Angular contact ball bearing

Abstract

The present application relates to an angular contact ball bearing including a plurality of balls (3) interposed between raceway surfaces (1a, 2a) of an inner ring (1) and an outer ring (2), the balls (3) being held in pockets (Pt) at a plurality of positions in the circumferential direction of a retainer (4) in the shape of a cylinder. Also, the ratio of the inter-ball distance (Pd) obtained by subtracting the diameter (Da) of the ball (3) from the distance (Pc) between the centers of adjacent balls (3, 3) with respect to the diameter (Da) of the ball (3) is 0.16 or more and 0.35 or less. Furthermore, the ratio of the inner ring groove curvature (Ri) obtained by dividing the diameter (Di) of the groove (1g) of the raceway surface (1a) of the inner ring (1) by the diameter (Da) of the ball (3) with respect to the ratio of the outer ring groove curvature (Ro) obtained by dividing the diameter (Do) of the groove (2g) of the raceway surface (2a) of the outer ring (2) by the diameter (Da) of the ball (3) is 0.97 or more and 0.99 or less.

Description

[0001] Related applications

[0002] This invention claims priority to Japanese Patent Application No. 2021-041252, filed on March 15, 2021, the entire contents of which are incorporated herein by reference and form part of this application. Technical Field

[0003] The present invention relates to an angular contact ball bearing, for example, for a machine tool spindle. Background Technology

[0004] In recent years, machine tools have demanded further performance improvements to meet the diverse needs of various industries. Representative requirements include: increased rigidity for machining difficult-to-cut materials; integration and compositing of machining steps for high efficiency; five-axis machining of complex shapes; and miniaturization for space saving. In particular, the demand for complete machining in a single setup is extremely strong. This single-setup machining involves machining from heavy cutting in the low-to-medium speed range of the spindle to finishing cutting in the high-speed range, all performed by a single machine tool. For the rolling bearings used in the spindle of this machine tool, there is a need to balance the seemingly contradictory high-speed rotational performance and load capacity at a higher level.

[0005] Furthermore, in a single-setup machining process, the feed rates of the spindle and table are increased to improve productivity. In addition, due to the increasing complexity of the workpiece shape, unexpected collisions between the tool mounted at the front end of the spindle and the workpiece are more likely to occur, potentially placing impact loads on the bearings. If the load during this collision exceeds the bearing's tolerance limit, indentation will occur, hindering the smooth and high-precision rotation of the spindle. Therefore, to prevent and mitigate indentation, the spindle bearings are required to have enhanced impact resistance. For example, increasing the bearing's inner and outer diameters could increase load capacity, but this would necessitate a larger structure around the bearing, including the spindle, leading to increased spindle production costs and structural complexity. Therefore, spindle bearings are required to maintain the same basic dimensions of inner diameter, outer diameter, and width as previous products while possessing a higher load capacity.

[0006] Specifically, consider using a ratio Figure 3Bearing A, as shown in the conventional high-speed bearing, uses larger diameter balls. However, in this case, the increased contact area with the raceway and the increased centrifugal force due to the increased ball weight make the bearing more prone to overheating, which is detrimental to high-speed rotation. In particular, under high-speed rotation and high load conditions, the inner ring, which has a higher contact surface pressure and poorer heat dissipation compared to the outer ring, will generate more intense heat. Furthermore, while more balls are generally better for increasing load capacity, more balls mean shorter distances between them, which are heat sources, resulting in poorer heat dissipation and further increasing heat generation.

[0007] In addition, if the diameter of the ball increases, the wall thickness of the outer ring will correspondingly decrease. Therefore, under high load, the difference in deformation between the contact and non-contact positions of the balls in the outer ring track surface may increase, resulting in increased vibration and reduced machining accuracy.

[0008] Therefore, in the past, attempts have been made to achieve a balance between high-speed rotation performance and load capacity by combining the cooling technology described in Patent Document 1 with the vibration suppression technology described in Patent Document 2 in the form of bearings.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2014-062617

[0012] Patent Document 2: Japanese Patent Application Publication No. 2020-148220 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, in this type of bearing, the construction of the applicable machine tool spindle must be significantly changed or complicated, which cannot fully meet the requirements of high-speed rotation performance and load capacity under the same basic dimensions as previous products.

[0015] The purpose of this invention is to provide an angular contact ball bearing whose basic dimensions of inner diameter, outer diameter, and width are the same as those of previous products, but which can fully balance high-speed rotation performance and load capacity.

[0016] Technical means to solve the problem

[0017] The angular contact ball bearing of the present invention comprises: an inner ring, an outer ring, a plurality of balls sandwiched between the raceways of the inner and outer rings, and a retainer that is cylindrical in shape and holds the balls with pockets provided at a plurality of positions in the circumferential direction; the ratio of the distance between adjacent balls (the distance between the centers of the balls minus the diameter of the balls) to the diameter of the balls is 0.16 to 0.35; and the ratio of the inner ring groove curvature (the diameter of the groove on the raceway of the inner ring divided by the diameter of the balls) to the outer ring groove curvature (the diameter of the groove on the raceway of the outer ring divided by the diameter of the balls) is 0.97 to 0.99.

[0018] To suppress bearing heat generation during high-speed rotation, the inner ring groove curvature must be set to 0.97 to 0.99 of the outer ring groove curvature. This ensures that the contact surface pressure of the inner ring, which is more prone to increasing, is equal to that of the outer ring. Simultaneously, the ball spacing must be set to 0.16 or more of the ball diameter to ensure heat dissipation. Furthermore, to ensure load capacity through multiple balls, the ball spacing must be 0.35 or less of the ball diameter. Since the angular contact ball bearing of this invention meets these conditions, its basic dimensions of inner diameter, outer diameter, and width are the same as conventional products. It effectively suppresses heat generation during high-speed rotation and ensures load capacity, thus balancing high-speed rotation performance and load capacity.

[0019] In a preferred configuration of the angular contact ball bearing of the present invention, the ratio of the minimum wall thickness of the outer ring (from the raceway surface to the outer circumferential surface) to the diameter of the ball is 0.39 to 0.63, and the ratio of the diameter of the ball to the bearing profile height obtained by subtracting the inner diameter of the inner ring from the outer diameter of the outer ring and dividing by 2 is 0.44 to 0.56.

[0020] To keep the deformation of the outer ring's outer circumferential surface within a range that does not affect machine tool processing, it is preferable to set the minimum wall thickness of the outer ring to 0.39 or more of the ball diameter and the ball diameter to 0.56 or less of the bearing profile height. On the other hand, to ensure load capacity while utilizing large-diameter balls, it is preferable to set the minimum wall thickness of the outer ring to 0.63 or less of the ball diameter and the ball diameter to 0.44 or more of the bearing profile height. Since this preferred configuration satisfies these conditions, vibrations caused by deformation of the outer ring's outer circumferential surface during high-speed rotation can be suppressed, and load capacity can be further ensured.

[0021] In the angular contact ball bearing of the present invention, the retainer may also be an outer ring guide retainer guided by the inner circumferential surface of the outer ring. In this case, since a portion of the lubricant (lubricating oil or grease) within the bearing passes through the guide surface in the retainer guided by the inner circumferential surface of the outer ring, excessive wear on this guide surface can be prevented. Thus, further high-speed operation of the bearing can be achieved.

[0022] In the angular contact ball bearing of the present invention, the retainer may also be a rolling element guided retainer guided by the balls as rolling elements. In this case, the radial space between the inner circumferential surface of the outer ring and the retainer can be increased, and the lubricant can be efficiently retained in this increased space.

[0023] Furthermore, in the angular contact ball bearing of the present invention, the balls are preferably made of ceramic.

[0024] Furthermore, the angular contact ball bearing of the present invention is suitable for machine tool spindles.

[0025] This invention comprises any combination of at least two of the components disclosed in the claims and / or the description and / or drawings. In particular, any combination of two or more of the claims is also included in this invention. Attached Figure Description

[0026] The invention should be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description only and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. In the drawings, the same reference numerals in a plurality of figures denote the same part.

[0027] Figure 1 This is a longitudinal cross-sectional view of the angular contact ball bearing according to the first embodiment of the present invention.

[0028] Figure 2A This is a longitudinal section view of the inner ring of the same angular contact ball bearing.

[0029] Figure 2B This is a longitudinal section view of the outer ring of the same angular contact ball bearing.

[0030] Figure 2C This is a cross-sectional view of the same angular contact ball bearing.

[0031] Figure 2D for Figure 2C A magnified view of a portion of the image.

[0032] Figure 3 This diagram illustrates a comparison between the same angular contact ball bearing and conventional angular contact ball bearings.

[0033] Figure 4This is a longitudinal cross-sectional view showing the angular contact ball bearing according to the second embodiment of the present invention.

[0034] Figure 5 A rough longitudinal sectional view of a high-speed rotating testing machine. Detailed Implementation

[0035] Hereinafter, the angular contact ball bearing of the first embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 As shown, the angular contact ball bearing includes: an inner ring 1, an outer ring 2, a plurality of balls 3 sandwiched between the raceways 1a and 2a of the inner ring 1 and the outer ring 2, and a retainer 4, which is cylindrical in shape and holds the balls 3 through pockets Pt located at multiple positions in the circumferential direction. The balls 3 are preferably made of ceramic, but can also be steel balls. This angular contact ball bearing is used in a bearing space under oil-air lubrication, for example, by supplying lubricating oil together with compressed air. The lubricating oil is distributed throughout and temporarily held on the inner circumferential surface 4a of the retainer 4 and the inner circumferential surface 2c of the outer ring 2 by the centrifugal force generated by the rotation of the inner ring. The lubricating oil on the inner circumferential surface 4a of the retainer 4 and the inner circumferential surface 2c of the outer ring 2 adheres to the surface of the balls 3 and is transported to the raceway 1a of the inner ring 1 and the pockets Pt of the retainer 4, allowing the bearing to rotate smoothly for an extended period.

[0036] The retainer 4 is affected by the inner circumferential surface 2c of the outer ring 2. Figure 1 In the case of an outer ring guide retainer, the inner circumferential surface 2c on the left side of the axial direction is guided by the outer ring 2. In the outer ring guide retainer, a portion of the lubricating oil within the bearing will be guided by the inner circumferential surface 2c of the outer ring 2 in the retainer 4. Figure 1 In this case, the outer peripheral surface 4b) of the retainer 4 on the left side in the axial direction passes through, thus preventing excessive wear on this guide surface. This allows for further high-speed operation of the bearing.

[0037] The retainer 4 is formed of resin materials such as aliphatic polyamide resin (nylon), aromatic polyamide resin, polyetheretherketone resin (PEEK material), polyphenylene sulfide resin (PPS material), and phenolic resin reinforced with glass fiber, carbon fiber, etc. Furthermore, the retainer 4 has a rectangular cross-section including the plane cut from the axis L, and the retaining holes Pt of the ball 3 are formed at multiple positions in the circumferential direction at the center of the axial direction. The diameter of the inner circumferential surface 4a of the retainer 4 is set to be smaller than the pitch circle diameter PCD of the ball 3. On the other hand, the diameter of the outer circumferential surface 4b of the retainer 4 is set to be larger than the pitch circle diameter PCD and larger than the inner circumferential surface 2c of the outer ring 2. Figure 1 In the case where the diameter of the inner circumferential surface 2c on the left side of the axial direction is smaller.

[0038] Here, as Figure 2CAs shown, the distance between the balls, Pd, obtained by subtracting the diameter Da of the ball 3 from the distance Pc between the centers of adjacent balls 3, is the distance between the balls relative to the diameter Da of the ball 3. Figure 1 The Pd / Da ratio is 0.16 to 0.35, preferably 0.18 to 0.25. Additionally, if... Figure 2C The enlarged view within the thick rectangle is... Figure 2D As shown, Pc = 2 × (PCD / 2) × sinα, where α is the angle obtained by dividing 360 degrees by the number of balls and then further dividing by 2.

[0039] In addition, Figure 2A The inner groove curvature Ri (=Di / Da) obtained by dividing the diameter Di of the groove 1g of the inner ring 1 track surface 1a by the diameter Da of the ball 3 is relative to the... Figure 2B The diameter Do of the groove 2g of the track surface 2a of the outer ring 2 shown is divided by the diameter Da of the ball 3. Figure 1 The ratio of the outer groove curvature Ro (=Do / Da) to Ri / Ro (=Di / Do) is preferably 0.97 or more and 0.99 or less. In addition, the inner groove curvature Ri is preferably 1.04 or more and 1.08 or less, and the outer groove curvature Ro is preferably 1.06 or more and 1.10 or less.

[0040] Furthermore, such as Figure 1 As shown, the minimum wall thickness Tomin of the outer ring 2, which is the minimum wall thickness from the track surface 2a to the outer peripheral surface 2b, is in the ratio Tomin / Da to the diameter Da of the ball 3. This ratio is 0.39 to 0.63, and preferably 0.46 to 0.57. Furthermore, the ratio Da / H to the bearing section height H obtained by subtracting the inner diameter of the inner ring 1 from the outer diameter of the outer ring 2 and then dividing by 2 is 0.44 to 0.56, and preferably 0.48 to 0.52.

[0041] Figure 3 This diagram illustrates a comparison between the angular contact ball bearings (bearings B, C, and D) of this embodiment and conventional angular contact ball bearings (bearings A and E). Conventional bearing A is, for example, an angular contact ball bearing with the nominal designation "7014," and is a small-diameter ball bearing for high-speed rotation. Specifically, bearing A has balls with a diameter of approximately 8.731 mm (1 1 / 32 inches) and a number of 25 balls.

[0042] The previous bearing E was, for example, a nominal size of angular contact ball bearing with the designation "7014", and it featured large-diameter balls. Specifically, bearing E has balls with a diameter of approximately 11.906 mm (15 / 32 inches) and a number of 21 balls.

[0043] In contrast, the angular contact ball bearings (bearings B, C, and D) of this embodiment are, for example, the size of an angular contact ball bearing with the nominal designation "7014". The ratio of the ball spacing Pd to the diameter Da of the ball 3, Pd / Da, is 0.16 to 0.35. At the same time, the ratio of the inner ring groove curvature Ri to the outer ring groove curvature Ro, Ri / Ro, is 0.97 to 0.99. Furthermore, the ratio of the minimum outer ring wall thickness Tomin to the diameter Da of the ball 3, Tomin / Da, is 0.39 to 0.63. And the ratio of the diameter Da of the ball 3 to the bearing section height H, Da / H, is 0.44 to 0.56.

[0044] For bearings with nominal designations "7014" and "7020" bearings with similarly defined conditions, evaluation tests were conducted on high-speed performance, vibration during high-speed rotation, and load capacity. The results are shown in Table 1 below. Figure 5 As shown, this evaluation test used a spindle composed of four rows of back-to-back angular contact ball bearings Bg, with ceramic balls in each bearing Bg, and was performed using oil-air lubrication with VG32 (ISO viscosity) lubricating oil. In Table 1, the evaluation of high-speed performance was conducted under the first condition of a preload of 1400 N after assembly, a rotational speed of 18000 rpm, and continuous rotation for 100 hours. The evaluation of vibration during high-speed rotation was conducted under the second condition of a preload of 600 N after assembly and a rotational speed of 0–22000 rpm. The evaluation of load capacity was conducted under both the first and second conditions. The evaluation criteria in Table 1 are as follows. Furthermore, the dmn value is the value obtained by multiplying the pitch circle diameter PCD (mm) of the ball 3 by the rotational speed (rpm).

[0045] <High Speed>

[0046] ◎: When the temperature of the outer ring rises below 20°C during rotation, it is rated as having excellent high-speed performance.

[0047] ○: The outer ring temperature rises above 20°C during rotation, but below 25°C, the high-speed performance is considered to be without problems.

[0048] △: If the temperature of the outer ring rises above 25°C during rotation, it is considered that there is a problem with high-speed performance.

[0049] <Vibration during high-speed rotation>

[0050] ◎: Vibrations during high-speed rotation with a dmn value below 2 million will not affect the machining accuracy of a machining center that uses the same bearing.

[0051] ○: Vibrations during high-speed rotation with a dmn value below 1.6 million are at a level that will not affect the machining accuracy of a machining center assuming the same bearing is used.

[0052] △: Vibration during rotation in the low to medium speed range with a dmn value below 1.4 million will not affect the machining accuracy of a machining center using the same bearing.

[0053] <Load Capacity> * Calculated values ​​from various elements inside the bearing

[0054] ◎: The values ​​obtained from each internal element are considered to have excellent load capacity, which is sufficient to withstand the load of a single row in heavy cutting operations using a machining center with the same bearings.

[0055] ○: The values ​​obtained from each internal element, under the assumption of using a combined machining center with the same bearing, can be evaluated as having no problem with the load capacity, as they can be borne by a single row.

[0056] △: The value obtained from each internal element is the level that must be borne by two columns in parallel during heavy cutting machining, assuming the use of a machining center with the same bearing.

[0057] [Table 1]

[0058]

[0059] As shown in Table 1, the basic dimensions of the angular contact ball bearing according to this embodiment are the same as those of conventional products in terms of inner diameter, outer diameter, and width. However, it can suppress heat generation during high-speed rotation while ensuring load capacity, thus fully balancing high-speed rotation performance and load capacity. In addition, it can suppress bearing vibration during high-speed rotation and further ensure load capacity.

[0060] Next, the angular contact ball bearing of the second embodiment of the present invention will be described with reference to the accompanying drawings. Figure 4 As shown, in this angular contact ball bearing, a rolling element guide retainer guided by the balls 3 is used as the retainer 4A, while the other configurations are the same as those in the angular contact ball bearing of the first embodiment. According to the angular contact ball bearing of the second embodiment, the radial space between the inner circumferential surface 2c of the outer ring 2 and the retainer 4A can be expanded, thereby allowing the lubricating oil to be efficiently retained in the expanded space.

[0061] Furthermore, the angular contact ball bearing of the present invention is not limited to use under oil-air lubrication, but can also be used under oil mist lubrication or grease lubrication. Additionally, in the angular contact ball bearing of the present invention, a bearing oil seal (not shown) that is not in contact with the outer peripheral surface 1b of the inner ring 1 may be provided at either end or at one end of the inner peripheral surface 2c of the outer ring 2 in the axial direction. For example, a bearing oil seal mounting groove may be formed on the inner peripheral surface 2c of the outer ring 2, and the base end of the bearing oil seal on the outer diameter side may be mounted in the bearing oil seal mounting groove. In this case, when used under grease lubrication, the grease inside the bearing can be retained more reliably.

[0062] While preferred embodiments have been described above with reference to the accompanying drawings, various modifications and alterations within the obvious scope will readily occur to those skilled in the art upon reading this specification. Therefore, the aforementioned modifications and alterations are to be construed as falling within the scope of the invention as defined by the appended claims.

[0063] Symbol Explanation

[0064] 1…Inner ring, 1a…Inner ring raceway, 1g…Inner ring raceway groove, 2…Outer ring, 2a…Outer ring raceway, 2b…Outer ring outer circumferential surface, 2c…Outer ring inner circumferential surface, 2g…Outer ring raceway groove, 3…Ball, 4, 4A…Retainer, 4a…Retainer inner circumferential surface, 4b…Retainer outer circumferential surface, Da…Ball diameter, Di…Diameter of the raceway groove of the inner ring, Do…Diameter of the raceway groove of the outer ring, H…Bearing profile height, Pc…Distance between the centers of the balls, Pd…Distance between balls, Pt…Retainer pocket, Ri…Inner ring groove curvature, Ro…Outer ring groove curvature, Tomin…Minimum outer ring wall thickness.

Claims

1. An angular contact ball bearing, comprising: Inner circle; Outer ring; Multiple balls, said multiple balls being sandwiched between the track surfaces of the inner and outer rings; and A retainer, the retainer being cylindrical in shape and holding the ball with pockets located at multiple positions in the circumferential direction; The ratio of the distance between adjacent balls to the diameter of the balls, obtained by subtracting the diameter of the balls from the distance between their centers, is more than 0.16 and less than 0.

35. The ratio of the inner ring groove curvature (obtained by dividing the diameter of the inner ring's track surface groove by the diameter of the ball) to the outer ring groove curvature (obtained by dividing the diameter of the outer ring's track surface groove by the diameter of the ball) is between 0.97 and 0.

99. This angular contact ball bearing is used for machine tool spindles.

2. The angular contact ball bearing according to claim 1, wherein, The ratio of the minimum wall thickness of the outer ring (from the track surface to the outer circumference surface) to the diameter of the ball is 0.39 or more and 0.63 or less. The ratio of the diameter of the ball to the bearing profile height obtained by subtracting the inner diameter of the inner ring from the outer diameter of the outer ring and then dividing by 2 is between 0.44 and 0.

56.

3. The angular contact ball bearing according to claim 1 or 2, wherein, The retainer is an outer ring guide retainer guided by the inner circumferential surface of the outer ring.

4. The angular contact ball bearing according to claim 1 or 2, wherein, The retainer is a rolling element guided retainer guided by the balls, which are rolling elements.

5. The angular contact ball bearing according to claim 1 or 2, wherein, The ball bearing is made of ceramic.

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