Angular contact ball bearing

Abstract

To provide an angular ball bearing which can make sufficiently compatible both high-speed rotation performance and a load capacity while being the same as a prior art in fundamental dimensions of an inside diameter, an outside diameter and a width of the bearing.SOLUTION: An angular ball bearing has a plurality of balls 3 interposed between raceway surfaces 1a, 2a of an inner ring 1 and an outer ring 2, and the balls 3 are held in pockets Pt which are formed in a plurality of points of a cylindrical cage 4 in a circumferential direction. Then, a ratio of an inter-ball distance Pd which is obtained by subtracting a diameter Da of the ball 3 from a distance PC between centers of the adjacent balls 3, 3 with respect to a dimension Da of the ball 3 is equal or larger than 0.16, and equal to or smaller than 0.35. Also, a ratio of an inner-ring groove curvature radius Ri which is obtained by dividing a diameter Di of a groove 1g of the raceway surface 1a of the inner ring 1 by the diameter Da of the ball 3 with respect to an outer-ring groove curvature radius Ro which is obtained by dividing a diameter Do of a groove 2g of the raceway surface 2a of the outer ring 2 by the diameter Da of the ball 3 is equal to or larger than 0.97, and equal to or smaller than 0.99.SELECTED DRAWING: Figure 2C

Description

[Technical field]

[0001] The present invention relates to an angular ball bearing for use in, for example, the main spindle of a machine tool. [Background technology]

[0002] In recent years, machine tools are being required to further improve their performance to meet the diverse needs of various industries. For example, typical requirements include higher rigidity for machining difficult-to-cut materials, process consolidation and integration for highly efficient machining, 5-axis machining for machining complex shapes, and miniaturization for space saving. In particular, there is a strong demand for one-chuck full machining that satisfies all of these requirements. This one-chuck full machining is a machining process in which a single machine tool is responsible for everything from heavy cutting at low and medium speeds of the spindle to finish cutting at high speeds, and the rolling bearings used in the spindles of these machine tools are required to achieve a higher level of both high-speed rotation performance and load capacity, which are in a contradictory relationship.

[0003] In addition, in one-chuck full machining, the feed speed of the spindle and table is increased to improve productivity. In addition, the shape of the workpiece is becoming more complex, so unexpected collisions between the tool attached to the tip of the spindle and the workpiece are more likely to occur, and impact loads may be applied to the bearings. If the load at the time of this collision exceeds the allowable limit of the bearing, an indentation occurs, hindering the smooth and highly accurate rotation of the spindle. Therefore, in order to prevent and reduce the occurrence of indentations, the bearings for the spindle are also required to have improved resistance to collisions. For example, it is possible to increase the load capacity by increasing the inner and outer diameters of the bearings, but this requires the structure including the spindle around the bearing to be enlarged, which increases the production cost of the spindle and complicates the structure. Therefore, the bearings for the spindle are required to have a higher load capacity while maintaining the basic dimensions of the inner diameter, outer diameter, and width the same as conventional products.

[0004] Specifically, it is conceivable to adopt balls with a larger diameter than those in conventional high-speed bearings such as those shown in Bearing A in Figure 3, but in that case, the bearing would be more likely to generate heat due to the increased contact area with the raceway surface and the increased centrifugal force caused by the increased weight of the balls, which would be disadvantageous for high-speed rotation. In particular, under conditions of high-speed rotation and high load, the inner ring, which has a higher contact pressure than the outer ring and is therefore disadvantageous in terms of heat dissipation, will generate more heat. Also, to increase the load capacity, it is better to have more balls, but the more balls there are, the shorter the distance between the balls (the heat source) will be, which will worsen heat dissipation and further increase heat generation.

[0005] Furthermore, as the diameter of the ball increases, the thickness of the outer ring decreases accordingly, which results in a larger difference in deformation on the outer surface of the outer ring between the contact position and non-contact position of the ball on the outer ring raceway surface under high load, resulting in increased vibration and reduced machining accuracy.

[0006] Therefore, conventionally, attempts have been made to achieve both high-speed rotation performance and load capacity by using a bearing that combines a cooling technology such as that described in Patent Document 1 with a vibration suppression technology such as that described in Patent Document 2. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-062617 A [Patent Document 2] JP 2020-148220 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, such conventional bearings required significant modifications and complication to the structure of the spindle of the machine tool in which they were used, and were unable to fully satisfy both high-speed rotational performance and load capacity while maintaining the same basic dimensions as conventional products.

[0009] SUMMARY OF THE PRESENTINVENTION An object of the present invention is to provide an angular contact ball bearing which has the same basic dimensions of inner diameter, outer diameter and width as conventional bearings, yet which satisfies both high speed rotational performance and load capacity. [Means for solving the problem]

[0010] The angular contact ball bearing of the present invention comprises an inner ring, an outer ring, a plurality of balls interposed between the raceway surfaces of the inner ring and the outer ring, and a cylindrical cage which holds the balls in pockets provided at a plurality of locations in the circumferential direction, wherein a ratio of the inter-ball distance, calculated by subtracting the diameter of the balls from the distance between the centers of adjacent balls, to the diameter of the balls is 0.16 or more and 0.35 or less, and a ratio of an inner ring groove curvature, calculated by dividing the diameter of the groove in the raceway surface of the inner ring by the diameter of the balls, to an outer ring groove curvature, calculated by dividing the diameter of the groove in the raceway surface of the outer ring by the diameter of the balls, is 0.97 or more and 0.99 or less.

[0011] In order to suppress heat generation in the bearing during high-speed rotation, it is necessary to set the inner ring groove curvature to 0.97 to 0.99 of the outer ring groove curvature, suppressing the contact pressure of the inner ring, which is more likely to have a higher contact pressure, to approximately the same as that of the outer ring, while ensuring heat dissipation by setting the inter-ball distance to 0.16 or more times the diameter of the ball. On the other hand, in order to ensure load capacity with a large number of balls, the inter-ball distance must be 0.35 or less times the diameter of the ball. The angular contact ball bearing of the present invention satisfies this condition, and therefore, while the basic dimensions of the bearing's inner diameter, outer diameter, and width are the same as those of conventional products, heat generation during high-speed rotation is suppressed and load capacity is ensured, thereby achieving a sufficient balance between high-speed rotation performance and load capacity.

[0012] In a preferred configuration of the angular ball bearing of the present invention, the ratio of the outer ring minimum thickness, which is the smallest value of the thickness of the outer ring from the raceway surface to the outer peripheral surface, to the diameter of the ball is 0.39 or more and 0.63 or less, and the ratio of the diameter of the ball to the bearing cross-sectional height, which is the outer diameter of the outer ring minus the inner diameter of the inner ring divided by 2, is 0.44 or more and 0.56 or less.

[0013] In order to keep deformation of the outer peripheral surface of the outer ring within a range that does not affect machining by machine tools, it is preferable that the minimum thickness of the outer ring be 0.39 or more times the diameter of the balls and that the diameter of the balls be 0.56 or less times the cross-sectional height of the bearing, while in order to ensure load capacity with larger diameter balls, it is preferable that the minimum thickness of the outer ring be 0.63 or less times the diameter of the balls and that the diameter of the balls be 0.44 or more times the cross-sectional height of the bearing. The above-mentioned preferred configuration satisfies these conditions, thereby suppressing vibrations caused by deformation of the outer peripheral surface of the outer ring during high-speed rotation and ensuring even greater load capacity.

[0014] In the angular contact ball bearing of the present invention, the cage may be an outer ring guide cage that is guided by the inner peripheral surface of the outer ring. In this case, a portion of the lubricant (lubricating oil or grease) in the bearing passes through the guide surface of the cage that is guided by the inner peripheral surface of the outer ring, so that excessive wear on this guide surface can be prevented. Therefore, the bearing can be operated at a higher speed.

[0015] In the angular contact ball bearing of the present invention, the cage may be a rolling element guide cage that is guided by the rolling elements, which are balls. In this case, the radial space between the inner circumferential surface of the outer ring and the cage can be expanded, and the lubricant can be efficiently held in the expanded space.

[0016] In the angular contact ball bearing of the present invention, the balls are preferably made of ceramics.

[0017] Furthermore, the angular contact ball bearing of the present invention is suitable for use in the main spindle of a machine tool. Effect of the Invention

[0018] In the angular contact ball bearing of the present invention, the ratio of the inter-ball distance, calculated by subtracting the diameter of the ball from the distance between the centers of adjacent balls, to the diameter of the ball is 0.16 or more and 0.35 or less, and the ratio of the inner ring groove curvature, calculated by dividing the diameter of the groove in the raceway surface of the inner ring by the diameter of the ball, to the outer ring groove curvature, calculated by dividing the diameter of the groove in the raceway surface of the outer ring by the diameter of the ball, is 0.97 or more and 0.99 or less.Therefore, while the basic dimensions of the inner diameter, outer diameter and width of the bearing are the same as those of conventional products, heat generation during high-speed rotation is suppressed and load capacity is secured, thereby enabling a sufficient balance between high-speed rotation performance and load capacity. [Brief description of the drawings]

[0019] [Figure 1] 1 is a vertical sectional view of an angular ball bearing according to a first embodiment of the present invention. [Figure 2A] FIG. 2 is a vertical cross-sectional view of an inner ring of the angular contact ball bearing. [Figure 2B] FIG. 2 is a vertical cross-sectional view of the outer ring of the angular contact ball bearing. [Figure 2C] FIG. 2 is a cross-sectional view of the angular contact ball bearing. [Figure 2D] FIG. 2D is a partially enlarged view of FIG. 2C. [Diagram 3] 4 is a diagram showing a comparative example between the angular contact ball bearing and a conventional angular contact ball bearing. FIG. [Figure 4] FIG. 4 is a vertical sectional view of an angular contact ball bearing according to a second embodiment of the present invention. [Diagram 5] FIG. 2 is a vertical cross-sectional view showing an outline of a high-speed rotation test machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an angular ball bearing according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, this angular ball bearing includes an inner ring 1, an outer ring 2, a plurality of balls 3 interposed between the raceway surfaces 1a, 2a of the inner ring 1 and the outer ring 2, and a cylindrical cage 4 that holds the balls 3 in pockets Pt provided at a plurality of locations in the circumferential direction. The balls 3 are preferably made of ceramics, but may be steel balls. This angular ball bearing is used in air-oil lubrication, in which lubricating oil is supplied to the bearing space together with compressed air, for example, and the lubricating oil is spread over the inner circumferential surface 4a of the cage 4 and the inner circumferential surface 2c of the outer ring 2 by the centrifugal force generated by the rotation of the inner ring, and is temporarily held therein. The lubricating oil on the inner circumferential surface 4a of the cage 4 and the inner circumferential surface 2c of the outer ring 2 adheres to the surfaces of the balls 3 and is carried to the raceway surface 1a of the inner ring 1 and the pockets Pt of the cage 4, enabling the bearing to rotate smoothly for a long period of time.

[0021] The cage 4 is an outer ring guide cage that is guided by the inner peripheral surface 2c of the outer ring 2 (in the case of FIG. 1, the inner peripheral surface 2c on the left side in the axial direction). In an outer ring guide cage, part of the lubricating oil in the bearing passes along a guide surface of the cage 4 that is guided by the inner peripheral surface 2c of the outer ring 2 (in the case of FIG. 1, the outer peripheral surface 4b of the cage 4 on the left side in the axial direction), so that excessive wear on this guide surface can be prevented. Therefore, the bearing can be operated at a higher speed.

[0022] The cage 4 is made of a resin material such as an aliphatic polyamide resin (nylon) reinforced with glass fiber, carbon fiber, etc., an aromatic polyamide resin, a polyether ether ketone resin (abbreviated as PEEK material), a polyphenyl sulfide resin (abbreviated as PPS material), or a phenol resin. The cage 4 has a rectangular cross section cut along a plane including the axis L, and pockets Pt for holding the balls 3 are formed at multiple locations in the circumferential direction of the axial center. The diameter of the inner peripheral surface 4a of the cage 4 is set to be smaller than the pitch circle diameter PCD of the balls 3. On the other hand, the diameter of the outer peripheral surface 4b of the cage 4 is set to be larger than the pitch circle diameter PCD and smaller than the diameter of the inner peripheral surface 2c of the outer ring 2 (the inner peripheral surface 2c on the left side in the axial direction in the case of FIG. 1).

[0023] Here, as shown in Fig. 2C, the ratio Pd / Da of the inter-ball distance Pd, which is the distance Pc between the centers of adjacent balls 3 minus the diameter Da of the ball 3, to the diameter Da of the ball 3 (Fig. 1) is 0.16 to 0.35, and preferably 0.18 to 0.25. Note that, as shown in Fig. 2D, which is an enlarged view of the bold rectangle in Fig. 2C, Pc = 2 × (PCD / 2) × sin α, where α is the angle obtained by dividing 360 degrees by the number of balls and then dividing it by 2.

[0024] Furthermore, the ratio Ri / Ro (=Di / Do) of the inner ring groove curvature Ri (=Di / Da) obtained by dividing the diameter Di of the groove 1g of the raceway surface 1a of the inner ring 1 shown in FIG. 2A by the diameter Da of the ball 3 to the outer ring groove curvature Ro (=Do / Da) obtained by dividing the diameter Do of the groove 2g of the raceway surface 2a of the outer ring 2 shown in FIG. 2B by the diameter Da of the ball 3 (FIG. 1) is 0.97 or more and 0.99 or less, and preferably, in addition to this, the inner ring groove curvature Ri is 1.04 or more and 1.08 or less, and the outer ring groove curvature Ro is 1.06 or more and 1.10 or less.

[0025] Furthermore, as shown in FIG. 1, the minimum thickness To of the outer ring 2 from the raceway surface 2a to the outer peripheral surface 2b with respect to the diameter Da of the ball 3 is min To min / Da is 0.39 or more and 0.63 or less, and preferably 0.46 or more and 0.57 or less. Furthermore, the ratio Da / H of the diameter Da of the ball 3 to the bearing cross-sectional height H, which is calculated by subtracting the inner diameter of the inner ring 1 from the outer diameter of the outer ring 2 and dividing the result by 2, is 0.44 or more and 0.56 or less, and preferably 0.48 or more and 0.52 or less.

[0026] FIG. 3 is a diagram showing comparative examples of the angular contact ball bearings of this embodiment (bearings B, C, and D) and conventional angular contact ball bearings (bearings A and E). Conventional bearing A is, for example, an angular contact ball bearing with a designation of "7014" size and small diameter balls for high speed rotation. Specifically, the diameter of the balls in bearing A is approximately 8.731 mm (11 / 32 inches), and the number of balls is 25. Conventional bearing E is, for example, an angular contact ball bearing with a designation number of "7014" and a large diameter ball specification. Specifically, the diameter of the balls in bearing E is about 11.906 mm (15 / 32 inches), and the number of balls is 21.

[0027] In contrast, the angular contact ball bearing of this embodiment (bearings B, C, D) has, for example, an angular contact ball bearing designation size "7014", and has a ratio Pd / Da of the inter-ball distance Pd to the diameter Da of ball 3 of 0.16 or more and 0.35 or less, a ratio Ri / Ro of the inner ring groove curvature Ri to the outer ring groove curvature Ro of 0.97 or more and 0.99 or less, a ratio Tomin / Da of the outer ring minimum thickness Tomin to the diameter Da of ball 3 of 0.39 or more and 0.63 or less, and a ratio Da / H of the diameter Da of ball 3 to the bearing cross-sectional height H of 0.44 or more and 0.56 or less.

[0028] Evaluation tests were conducted on the bearings with the designation number "7014" and the bearings with the designation number "7020" with similar specifications, to obtain the results shown in Table 1 below. The evaluation test was conducted using a spindle with four rows of angular contact ball bearings Bg arranged in a back-to-back arrangement, with ceramic balls in each bearing Bg, and with air-oil lubrication using VG32 (ISO viscosity) lubricant. In Table 1, the high-speed performance was evaluated under the first condition of a preload of 1400N after assembly, a rotational speed of 18000rpm, and continuous rotation for 100 hours, the vibration during high-speed rotation was evaluated under the second condition of a preload of 600N after assembly, and a rotational speed of 0 to 22000rpm, and the load capacity was evaluated under the first and second conditions. The evaluation criteria in Table 1 are as follows. The dmn value is the value obtained by multiplying the pitch circle diameter PCD (mm) of the balls 3 by the rotational speed (rpm).

[0029] <High speed> ◎: When the outer ring temperature rise during rotation is 20℃ or less, it is evaluated as having excellent high speed performance. ○: When the temperature rise of the outer ring during rotation exceeds 20°C and is below 25°C, it is evaluated as having no problem with high speed performance. △: When the temperature rise of the outer ring during rotation exceeds 25°C, it is evaluated as having a problem with high speed performance. <Vibration during high speed rotation> ◎: Vibrations during high-speed rotation with a dmn value of 2 million or less are at a level that will not affect the machining accuracy of the machining center in which the bearing is intended to be used. ○: Vibration during high-speed rotation with a dmn value of 1.6 million or less is at a level that does not affect the machining accuracy of the machining center in which the bearing is intended to be used. △: Vibration during rotation in the low to medium speed range with a dmn value of 1.4 million or less is at a level that does not affect the machining accuracy of the machining center in which the bearing is intended to be used. <Load capacity> *Calculated value based on the internal specifications of the bearing ◎: The value calculated from the internal specifications is at a level that is sufficient to withstand heavy cutting in a single row on the machining center in which the bearing is intended to be used, and is evaluated as having excellent load capacity. ○: The value calculated from the internal specifications is at a level that can be withstood in a single row for heavy cutting in a machining center in which the bearing is intended to be used, and is evaluated as having no problem with the load capacity. △: The value determined from the internal specifications is at the level required for two rows in parallel to withstand heavy cutting in a machining center in which the bearing is intended to be used.

[0030] [Table 1]

[0031] It is clear from Table 1 that with the angular contact ball bearing of this embodiment, while the basic dimensions of the bearing's inner diameter, outer diameter, and width are the same as those of conventional products, heat generation during high-speed rotation is suppressed while load capacity is ensured, thereby fully achieving both high-speed rotation performance and load capacity, and furthermore, bearing vibration during high-speed rotation is suppressed while even greater load capacity is ensured.

[0032] Next, an angular ball bearing according to a second embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 4, this angular ball bearing employs a rolling element guided cage guided by balls 3 as the cage 4A, but the other configuration is the same as that of the angular ball bearing of the first embodiment. According to the angular ball bearing of the second embodiment, the radial space between the inner peripheral surface 2c of the outer ring 2 and the cage 4A is expanded, and lubricating oil can be efficiently held in the expanded space.

[0033] The angular contact ball bearing of the present invention is not limited to use with air-oil lubrication, and may be used with oil mist lubrication or grease lubrication. In addition, in the angular contact ball bearing of the present invention, a seal (not shown) that does not contact the outer peripheral surface 1b of the inner ring 1 may be provided at both axial ends or one axial end of the inner peripheral surface 2c of the outer ring 2. For example, a seal mounting groove may be formed in the inner peripheral surface 2c of the outer ring 2, and the base end of the seal on the outer diameter side may be attached to this seal mounting groove. In this case, the grease inside the bearing can be more reliably retained when used with grease lubrication.

[0034] Although the embodiment of the present invention has been described above, the disclosed embodiment is illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0035] 1...inner ring, 1a...raceway of inner ring, 1g...groove in raceway of inner ring, 2 outer ring, 2a...raceway of outer ring, 2b...outer peripheral surface of outer ring, 2c...inner peripheral surface of outer ring, 2g...groove in raceway of outer ring, 3...ball, 4,4A...retainer, 4a...inner peripheral surface of retainer, 4b...outer peripheral surface of retainer, Da...diameter of ball, Di...diameter of groove in raceway of inner ring, Do...diameter of groove in raceway of outer ring, H...cross-sectional height of bearing, Pc...distance between ball centres, Pd...distance between balls, Pt...pocket in retainer, Ri...curvature of inner ring groove, Ro...curvature of outer ring groove, Tomin...minimum thickness of outer ring

Claims

1. An angular contact ball bearing having an inner ring, an outer ring, a number of balls interposed between the raceway surfaces of the inner ring and the outer ring, and a cylindrical cage that holds the balls in pockets provided at a number of locations in the circumferential direction, a ratio of a ball-to-ball distance, calculated by subtracting the diameter of the ball from the center distance between the adjacent balls, to the diameter of the ball is 0.16 or more and 0.35 or less; An angular contact ball bearing used in a main spindle of a machine tool, wherein a ratio of an outer ring groove curvature, obtained by dividing the diameter of the groove in the raceway surface of the outer ring by the diameter of the ball, to an inner ring groove curvature, obtained by dividing the diameter of the groove in the raceway surface of the inner ring by the diameter of the ball, is 0.97 or greater and 0.99 or less.

2. 2. The angular contact ball bearing according to claim 1, a ratio of an outer ring minimum wall thickness, which is a minimum value of a wall thickness of the outer ring from the raceway surface to an outer peripheral surface, to a diameter of the ball is 0.39 or greater and 0.63 or less, An angular contact ball bearing, wherein the ratio of the diameter of the ball to a bearing cross-sectional height, calculated by subtracting the outer diameter of the outer ring from the inner diameter of the inner ring and dividing the result by 2, is 0.44 or more and 0.56 or less.

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

4. 3. The angular contact ball bearing according to claim 1, The angular contact ball bearing has a cage that is a rolling element guide cage that is guided by the rolling elements, which are balls.

5. 5. The angular contact ball bearing according to claim 1, The angular contact ball bearing, wherein the balls are made of ceramics.

Images