JP7674865B2 - Angular contact ball bearing - Google Patents

Description

This invention relates to angular ball bearings used, for example, in the main spindles of machine tools.

In recent years, machine tools have been required to further improve their performance to meet the diverse needs of various industries. Typical requirements include, for example, high rigidity for machining difficult-to-cut materials, process consolidation and integration for highly efficient machining, 5-axis machining for machining complex shapes, and miniaturization to save space. 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 type of machining in which a single machine tool is responsible for everything from heavy cutting at low and medium speeds to finish cutting at high speeds, and the rolling bearings used in the spindles of these machine tools are required to achieve a high level of compatibility between high-speed rotational performance and load capacity, which are mutually exclusive.

In addition, in one-chuck full machining, the feed speed of the spindle and table is increased to improve productivity. In addition, as the shape of the workpiece becomes more complex, unexpected collisions between the tool attached to the tip of the spindle and the workpiece are 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, indentations will occur, hindering the smooth and highly accurate rotation of the spindle. Therefore, in order to prevent and reduce the occurrence of indentations, it is necessary to strengthen the resistance to collisions in the spindle bearings. 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, it is required that the spindle bearings have a higher load capacity while maintaining the basic dimensions of the inner diameter, outer diameter, and width the same as conventional products.

Specifically, it is possible to adopt balls with a larger diameter than those used in conventional high-speed bearings such as bearing A in Figure 3, but in that case, the increased contact area with the raceway surface and the increased centrifugal force caused by the increased weight of the balls would make the bearing more susceptible to heat generation, 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, would generate more heat. Also, to increase the load capacity, it is better to have a larger number of balls, but the more balls there are, the shorter the distance between the balls (the heat source) becomes, which would worsen heat dissipation and further increase heat generation.

In addition, as the diameter of the ball increases, the thickness of the outer ring decreases accordingly, which increases the difference in deformation on the outer peripheral 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, which can increase vibration and reduce machining accuracy.

Therefore, conventional bearings combine the cooling technology described in Patent Document 1 with the vibration suppression technology described in Patent Document 2 in an attempt to achieve both high-speed rotation performance and load capacity.

JP 2014-062617 A JP 2020-148220 A

However, such bearings using conventional technology required significant changes and complexity 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.

The objective of this invention is to provide an angular contact ball bearing that has the same basic dimensions of inner diameter, outer diameter, and width as conventional bearings, but can fully achieve both high-speed rotational performance and load capacity.

The angular ball bearing of the present invention has 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, and the ratio of the distance between the balls, calculated by subtracting the diameter of the balls from the distance between the centers of the adjacent balls, to the diameter of the balls 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 on the raceway surface of the inner ring by the diameter of the balls, to the outer ring groove curvature, calculated by dividing the diameter of the groove on the raceway surface of the outer ring by the diameter of the balls, is 0.97 or more and 0.99 or less.

To suppress heat generation in the bearing during high-speed rotation, the inner ring groove curvature must be set 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 the same level as the contact pressure of the outer ring, while ensuring heat dissipation by setting the distance between the balls to 0.16 or more times the diameter of the balls. On the other hand, to ensure load capacity with a large number of balls, the distance between the balls must be 0.35 or less times the diameter of the balls. The angular contact ball bearing of the present invention satisfies this condition, and therefore suppresses heat generation during high-speed rotation and ensures load capacity, even though the basic dimensions of the bearing's inner diameter, outer diameter, and width are the same as those of conventional products, thereby achieving a sufficient balance between high-speed rotation performance and load capacity.

In a preferred configuration of the angular ball bearing of the present invention, the ratio of the minimum outer ring thickness, which is the minimum thickness of the outer ring from the raceway surface to the outer peripheral 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 cross-sectional height, calculated by subtracting the inner diameter of the inner ring from the outer diameter of the outer ring and dividing the result by 2, is 0.44 to 0.56.

To keep deformation on 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 ball and that the diameter of the ball be 0.56 or less times the cross-sectional height of the bearing. On the other hand, to ensure load capacity with large diameter balls, it is preferable that the minimum thickness of the outer ring be 0.63 or less times the diameter of the ball and that the diameter of the ball be 0.44 or more times the cross-sectional height of the bearing. The above-mentioned preferred configuration satisfies this condition, so vibrations caused by deformation on the outer peripheral surface of the outer ring during high-speed rotation are suppressed and load capacity is further ensured.

In the angular contact ball bearing of the present invention, the retainer may be an outer ring guide retainer that is guided by the inner peripheral surface of the outer ring. In this case, part of the lubricant (lubricating oil or grease) in the bearing passes through the guide surface of the retainer that is guided by the inner peripheral surface of the outer ring, which can prevent excessive wear on this guide surface. This allows the bearing to run at even higher speeds.

In the angular ball bearing of the present invention, the retainer may be a rolling element guided retainer that is guided by the rolling elements, which are the balls. In this case, the radial space between the inner peripheral surface of the outer ring and the retainer is expanded, and the lubricant can be efficiently retained in the expanded space.

In addition, in the angular contact ball bearing of the present invention, it is preferable that the balls are made of ceramics.

Furthermore, the angular contact ball bearing of the present invention is suitable for use in the main shaft of a machine tool.

In the angular contact ball bearing of the present invention, the ratio of the ball-to-ball distance, calculated by subtracting the ball diameter from the distance between the centers of adjacent balls, to the ball diameter 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 on 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 on 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 ensured, and high-speed rotation performance and load capacity can be fully achieved at the same time.

1 is a longitudinal sectional view of an angular ball bearing according to a first embodiment of the present invention; FIG. 2 is a vertical cross-sectional view of an inner ring of the angular contact ball bearing. FIG. 2 is a vertical cross-sectional view of the outer ring of the angular contact ball bearing. FIG. 2 is a cross-sectional view of the angular contact ball bearing. FIG. 2D is a partially enlarged view of FIG. 2C. 4 is a diagram showing a comparative example between the angular contact ball bearing and a conventional angular contact ball bearing. FIG. FIG. 4 is a longitudinal sectional view of an angular ball bearing according to a second embodiment of the present invention. FIG. 2 is a vertical cross-sectional view showing an outline of a high-speed rotation test machine.

The angular ball bearing according to the first embodiment of the present invention will be described below 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 retainer 4 that retains 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 to the inner circumferential surface 4a of the retainer 4 and the inner circumferential surface 2c of the outer ring 2 by the centrifugal force caused by the rotation of the inner ring, and is temporarily retained. 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 surface 1a of the inner ring 1 and the pockets Pt of the retainer 4, allowing the bearing to rotate smoothly for a long period of time.

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 over the 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 excessive wear on this guide surface can be prevented. This allows the bearing to run at even higher speeds.

The cage 4 is made of resin materials such as aliphatic polyamide resin (nylon), aromatic polyamide resin, polyether ether ketone resin (abbreviated as PEEK material), polyphenyl sulfide resin (abbreviated as PPS material), and phenolic resin reinforced with glass fiber, carbon fiber, etc. 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).

As shown in Fig. 2C, the ratio Pd/Da of the inter-ball distance Pd, calculated by subtracting the diameter Da of the ball 3 from the distance Pc between the centers of adjacent balls 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 x (PCD/2) x sin α, where α is the angle obtained by dividing 360 degrees by the number of balls and then dividing it by 2.

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.

1, the ratio To _min /Da of the outer ring minimum thickness To _min , which is the minimum value of the thickness of the outer ring 2 from the raceway surface 2a to the outer peripheral surface 2b, to the diameter Da of the ball 3 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 obtained 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.

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 number of "7014" and a small-diameter ball specification for high-speed rotation. Specifically, the diameter of the balls in bearing A is about 8.731 mm (11/32 inches), and the number of balls is 25.
The conventional bearing E is, for example, an angular contact ball bearing with a bearing number of "7014" and a large diameter ball specification. Specifically, the diameter of the balls in the bearing E is about 11.906 mm (15/32 inches), and the number of balls is 21.

In contrast, the angular ball bearings of this embodiment (bearings B, C, D), for example, have a designation number of "7014" and have a ratio Pd/Da of the ball-to-ball distance Pd to the ball 3 diameter Da 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 ball 3 diameter Da of 0.39 or more and 0.63 or less, and a ratio Da/H of the ball 3 diameter Da to the bearing cross-sectional height H of 0.44 or more and 0.56 or less.

These bearings with the designation number "7014" and the bearing with the designation number "7020" with similar specifications were subjected to evaluation tests for high speed performance, vibration during high speed rotation, and load capacity, and the results shown in Table 1 were obtained. This evaluation test was performed using a spindle with four rows of angular contact ball bearings Bg arranged in a back-to-back arrangement as shown in Figure 5, with ceramic balls in each bearing Bg, and air-oil lubrication using lubricating oil of VG32 (ISO viscosity). In Table 1, the high speed performance was evaluated under the first condition of a preload of 1400N after assembly, a rotation speed of 18000 rpm, and 100 hours of continuous rotation, the vibration during high speed rotation was evaluated under the second condition of a preload of 600N after assembly, and a rotation speed of 0 to 22000 rpm, 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 pitch circle diameter PCD (mm) of the ball 3 multiplied by the rotational speed (rpm).

<High speed>
⊚: When the temperature rise of the outer ring during rotation is 20°C or less, it is evaluated as excellent in high speed performance.
◯: When the temperature rise of the outer ring during rotation exceeds 20° C. and is 25° C. or less, it is evaluated as having no problem with high speed performance.
Δ: When the temperature rise of the outer ring during rotation exceeds 25° C., it is evaluated that there is 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 does 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.
Δ: Vibrations during rotation in the low to medium speed range with a dmn value of 1.4 million or less are 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> * Value calculated from the bearing's internal specifications ◎: 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 a level that would be required for two rows in parallel to withstand heavy cutting in a machining center in which the bearing is intended to be used.

From Table 1, it is clear 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 and load capacity is ensured, thereby achieving a sufficient balance between high-speed rotation performance and load capacity, and further suppressing bearing vibration during high-speed rotation while ensuring even greater load capacity.

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 uses a rolling element guided retainer guided by balls 3 as the retainer 4A, but the rest of the configuration is the same as the angular ball bearing according to the first embodiment. With the angular ball bearing according to the second embodiment, the radial space between the inner peripheral surface 2c of the outer ring 2 and the retainer 4A is expanded, and lubricating oil can be efficiently retained in the expanded space.

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 on 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.

The above describes the mode for carrying out the present invention based on the embodiment, but the embodiment disclosed herein is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1...inner ring, 1a...raceway of inner ring, 1g...groove on 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 on 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...groove on raceway of inner ring, Do...groove on raceway of outer ring, H...bearing cross-sectional height, Pc...distance between ball centers, Pd...distance between balls, Pt...pocket on retainer, Ri...curvature of inner ring groove, Ro...curvature of outer ring groove, Tomin...minimum thickness of outer ring

Claims (5)

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

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