Angular contact ball bearing

Abstract

An angular contact ball bearing has: an inner ring having a cross-sectional circular-arc-shaped inner ring raceway groove on an outer peripheral surface; an outer ring having a cross-sectional circular-arc-shaped outer ring raceway groove on an inner peripheral surface; and a plurality of balls disposed freely rolling between the inner ring raceway groove and the outer ring raceway groove. A ratio (Ri) of a groove curvature radius of the inner ring raceway groove to a ball diameter is 54 to 58%, a ratio (Ro) of a groove curvature radius of the outer ring raceway groove to the ball diameter is 51 to 58%, and Ri-Ro is 0% or more, and at least the inner ring raceway groove has a maximum surface pressure of 4.7 to 6.0 GPa when a sum of permanent deformations of the ball and the inner ring raceway groove at a center of a contact portion of the ball and the inner ring raceway groove is one ten-thousandth of the ball diameter. Thus, an angular contact ball bearing capable of reducing a heat generation amount and suppressing damage caused by an external impact load at a standstill is provided.

Description

TECHNICAL FIELD

[0001] The present application relates to angular contact ball bearings, and particularly to ball bearings for main shafts for various machine tools, motors, and the like. BACKGROUND

[0002] In recent years, in order to improve machining efficiency and productivity, machine tool main shafts have been increasingly operated at higher speeds, and in conjunction therewith, the rotational speed of angular contact ball bearings used in the machine tool main shafts has also been increasing. Generally, when an angular contact ball bearing is rotated at high speed, a large amount of sliding due to spin motion and gyro motion occurs at the contact points between the balls and the raceway surfaces, and in addition, due to the effects of centrifugal forces acting on the inner ring and the balls, the internal clearance of the bearing decreases, and the contact surface pressure between the balls and the raceway surfaces increases, as a result of which the amount of heat generation becomes high. If the amount of heat generation increases, the viscosity of the oil decreases, and oil film breakdown occurs at the rolling contact portions between the balls and the raceway rings, which can cause problems such as seizure of the bearing, large thermal displacement of the main shaft, and deterioration of machining accuracy.

[0003] As a prior art for reducing the amount of heat generation in an angular contact ball bearing, for example, there is known a technique in which the groove curvature radius ratio of the outer ring is set to 50.5 to 53%, and the groove curvature radius ratio of the inner ring is set to 52.5 to 60% (see Patent Document 1), and a technique in which the groove curvature radius ratios of the outer ring and the inner ring are both set to 54 to 57% (see Patent Document 2).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: International Publication No. 2000 / 37813

[0007] Patent Document 2: Japanese Patent Application Publication No. 2005-240881 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, in Patent Documents 1 and 2, low heat generation is achieved by setting the groove curvature radius ratio of the outer ring and the inner ring to be large, but there is a tendency for the surface pressure of the contact portion of the rolling element with the raceway surface to become high. In the case where the bearing is viewed from the axial side, the contact portion of the rolling element with the raceway surface of the inner ring and the contact portion of the rolling element with the raceway surface of the outer ring each become the contact of the outer peripheral portion of the rolling element arc with the outer peripheral portion of the inner ring raceway surface arc and the contact of the outer peripheral portion of the rolling element arc with the inner peripheral portion of the outer ring raceway surface arc, and thus there is a tendency for the contact surface pressure of the raceway surface of the inner ring to become particularly high. Therefore, when an external impact load at rest is applied to the angular contact ball bearing, a dent is easily generated in the raceway surface of the inner ring. The external impact load here is not a machining load applied during normal cutting, but is a collision load generated due to accidental interference of the main shaft (a member including a tool) with a workpiece, a jig, or a member constituting a machine tool in a machining chamber, a loosening load during tool replacement, an accidental collision during an assembly process of the main shaft, or a load caused by vibration or impact applied to the bearing during transportation of the bearing, and is a large load that is ten times or more larger than a machining load during operation. Therefore, if operation is performed in a state where a dent is generated in the raceway surface due to the external impact load, there is a possibility that vibration is generated to reduce the quality of a machined surface of a workpiece, or peeling or the like is generated starting from the dent of the raceway surface.

[0010] The present application has been achieved in order to solve such a problem, and has an object to provide an angular contact ball bearing capable of reducing the amount of heat generation and suppressing damage caused by an external impact load at rest.

[0011] Technical means for solving the problem

[0012] In order to solve the above problem, the present application provides an angular contact ball bearing as shown below.

[0013] (1) An angular contact ball bearing characterized by comprising:

[0014] an inner ring having an inner ring raceway groove of a cross-sectional circular arc shape on an outer peripheral surface;

[0015] an outer ring having an outer ring raceway groove of a cross-sectional circular arc shape on an inner peripheral surface; and

[0016] a plurality of rolling elements disposed freely rollable between the inner ring raceway groove and the outer ring raceway groove, wherein

[0017] a ratio (Ri) of a groove curvature radius of the inner ring raceway groove to a rolling element diameter is 54 to 58%, a ratio (Ro) of a groove curvature radius of the outer ring raceway groove to the rolling element diameter is 51 to 58%, and Ri - Ro ≥ 0%, and

[0018] At least the maximum surface pressure of the inner ring raceway groove when the sum of the permanent deformation of the ball and the inner ring raceway groove at the center of the contact portion of the ball and the inner ring raceway groove is one ten-thousandth of the diameter of the ball is 4.7 to 6.0 GPa.

[0019] (2) The angular contact ball bearing according to (1), wherein

[0020] Ri - Ro ≥ 1%.

[0021] (3) The angular contact ball bearing according to (1) or (2), wherein

[0022] At least the inner ring raceway groove is formed with a surface hardened layer by machining.

[0023] (4) The angular contact ball bearing according to (1) or (2), wherein

[0024] In the inner ring raceway groove and the outer ring raceway groove, only the inner ring raceway groove is formed with a surface hardened layer by machining.

[0025] (5) The angular contact ball bearing according to any one of (1) to (4), wherein

[0026] The ball is made of ceramic.

[0027] (6) The angular contact ball bearing according to any one of (1) to (5), wherein

[0028] The value of the ball diameter / cross-sectional height is 0.39 to 0.65.

[0029] (7) The angular contact ball bearing according to (6), wherein

[0030] The value of the ball diameter / cross-sectional height is 0.55 to 0.65.

[0031] (8) The angular contact ball bearing according to any one of (1) to (7), wherein

[0032] The angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is applied with a pre-load.

[0033] (9) The angular contact ball bearing according to any one of (1) to (8), wherein

[0034] At least one of the inner ring and the outer ring is made of steel containing 0.2 to 1.2 mass% of C, 0.7 to 1.5 mass% of Si, 0.5 to 1.5 mass% of Mo, 0.5 to 2.0 mass% of Cr, a remainder of Fe and inevitable impurity elements, and

[0035] The angular contact ball bearing has a surface carbon concentration of 0.8 to 1.3 mass% and a surface nitrogen concentration of 0.2 to 0.8 mass%.

[0036] Inventive Effects

[0037] The angular contact ball bearing according to the present application can reduce the amount of heat generation and can suppress damage caused by external impact load at the time of standstill. In particular, the angular contact ball bearing according to the present application is useful as an angular contact ball bearing for a machine tool spindle used in high-speed rotation of 80 million rpm or more. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a partial enlarged sectional view of an angular contact ball bearing as an example of the ball bearing according to the present application.

[0039] Figure 2 is a schematic view for explaining spin sliding.

[0040] Figure 3 is a schematic view for explaining spin sliding, which is a view in which an inner ring raceway groove of an inner ring is enlarged.

[0041] Figure 4 is a schematic view for explaining spin sliding, (a) is a view showing a direction of centrifugal force action, (b) is a view showing spin amount in a case where a curvature radius ratio of an inner ring groove is large, and (c) is a view showing spin amount in a case where the curvature radius ratio of the inner ring groove is small.

[0042] Figure 5 is a graph showing a relationship between a curvature radius ratio (Ri) of an inner ring groove and a total spin heat generation amount of inner ring side and outer ring side in the case of analysis condition 1, which is obtained by calculation.

[0043] Figure 6 is a graph showing a relationship between a curvature radius ratio (Ro) of an outer ring groove and a total spin heat generation amount of inner ring side and outer ring side in the case of analysis condition 1, which is obtained by calculation.

[0044] Figure 7 is a graph showing a relationship between Ri-Ro and a ratio between an inner ring surface pressure and an outer ring surface pressure in the case of analysis condition 1, which is obtained by a calculated value.

[0045] Figure 8 is a graph showing a relationship between a curvature radius ratio (Ri) of an inner ring groove and a total spin heat generation amount of inner ring side and outer ring side in the case of analysis condition 2, which is obtained by calculation.

[0046] Figure 9is a graph in which the relationship between the outer ring groove curvature radius ratio (Ro) and the total spin heat generation of the inner ring side and the outer ring side is calculated and obtained in the case of analysis condition 2.

[0047] Figure 10 is a graph in which the relationship between the inner ring groove curvature radius ratio (Ri) and the total spin heat generation of the inner ring side and the outer ring side is calculated and obtained in the case of analysis condition 3.

[0048] Figure 11 is a graph in which the relationship between the outer ring groove curvature radius ratio (Ro) and the total spin heat generation of the inner ring side and the outer ring side is calculated and obtained in the case of analysis condition 3.

[0049] Figure 12 is a graph in which the relationship between the inner ring groove curvature radius ratio (Ri) and the total spin heat generation of the inner ring side and the outer ring side is calculated and obtained in the case of analysis condition 4.

[0050] Figure 13 is a graph in which the relationship between the outer ring groove curvature radius ratio (Ro) and the total spin heat generation of the inner ring side and the outer ring side is calculated and obtained in the case of analysis condition 4.

[0051] [Explanation of symbols]

[0052] 1 angular contact ball bearing

[0053] 2 inner ring

[0054] 2a inner ring raceway groove

[0055] 3 outer ring

[0056] 3a outer ring raceway groove

[0057] 4 ball

[0058] 5 retainer

[0059] 10 surface hardened layer DETAILED DESCRIPTION

[0060] Hereinafter, an angular contact ball bearing according to one embodiment of the present application will be described in detail with reference to the accompanying drawings.

[0061] Further, in the present specification, "〜" indicating a numerical range is used in the meaning that the numerical values recited before and after it are included as lower limit values and upper limit values.

[0062] As an example of the angular contact ball bearing of the present application, Figure 1An angular contact ball bearing used in a main shaft of a machine tool is shown. The angular contact ball bearing 1 is provided with an inner ring 2 having inner ring raceway grooves 2a of a cross-sectional circular arc shape on an outer peripheral surface, an outer ring 3 having outer ring raceway grooves 3a of a cross-sectional circular arc shape on an inner peripheral surface, a plurality of balls 4 which are disposed so as to roll freely between the inner ring raceway grooves 2a and the outer ring raceway grooves 3a, and a cage 5 which holds the plurality of balls 4. A counterbore 3b is formed on the inner peripheral surface of the outer ring 3 on the axial one side, and the balls 4 are disposed between the inner ring raceway grooves 2a and the outer ring raceway grooves 3a at contact angles ai, ao. Note that the contact angles ai, ao are defined as the angles formed by a plane P which is perpendicular to a bearing center axis X and a line of action which connects each contact point at which the ball 4 contacts the inner ring 2 and the outer ring 3, respectively, and the center of the ball 4.

[0063] For the balls 4, balls having a ball diameter / cross-sectional height ratio, that is, a diameter of the ball 4 / {(outer diameter of the outer ring 3 - inner diameter of the inner ring 2) / 2} of 0.39 to 0.65 times, preferably 0.55 to 0.65 times are used.

[0064] Further, of the inner ring raceway grooves 2a and the outer ring raceway grooves 3a, the ratio of the groove curvature radius of the inner ring raceway grooves 2a to the ball diameter (Ri = curvature radius of inner ring raceway grooves / ball diameter) is 54 to 58%, the ratio of the groove curvature radius of the outer ring raceway grooves 3a to the ball diameter (Ro = curvature radius of outer ring raceway grooves / ball diameter) is 51 to 58%, and Ri - Ro is set to be ≥ 0%, preferably Ri - Ro is set to be ≥ 1%. Hereinafter, the ratio of the groove curvature radius of the inner ring raceway grooves 2a to the ball diameter Ri is also referred to as the inner ring groove curvature radius ratio Ri, and the ratio of the groove curvature radius of the outer ring raceway grooves 3a to the ball diameter Ro is also referred to as the outer ring groove curvature radius ratio Ro.

[0065] Further, in the present embodiment, in the inner ring raceway grooves 2a, a surface hardening layer 10 is formed by a mechanical machining, that is, a roll polishing process, and the inner ring raceway grooves 2a are provided so that the maximum surface pressure of the inner ring raceway grooves 2a is 4.7 to 6.0 GPa when the sum of the permanent deformation of the ball 4 and the inner ring raceway grooves 2a at the center of the contact portion of the ball 4 and the inner ring raceway grooves 2a is one ten-thousandth of the ball diameter. On the other hand, the outer ring raceway grooves 3a are not subjected to the roll polishing process, and the surface hardening layer is not formed.

[0066] Further, the inner ring raceway grooves 2a of the inner ring 2 which are formed by cutting machining are subjected to a heat treatment and a finish machining, and then subjected to a roll polishing process. Furthermore, if necessary, a precision machining can be performed after the roll polishing process.

[0067] The following describes the groove curvature radius ratios Ri, Ro, the maximum surface pressure of the inner ring raceway groove 2a when the sum of the permanent deformations of the above-mentioned ball 4 and inner ring raceway groove 2a becomes one ten-thousandth of the ball diameter, and the respective critical meanings of the ball diameter.

[0068] [The ratio of the groove curvature radius of the inner ring raceway groove to the ball diameter (Ri) is 54 to 58%, and the ratio of the groove curvature radius of the outer ring raceway groove to the ball diameter (Ro) is 51 to 58%]

[0069] First, in the angular contact ball bearing 1 for high-speed rotation use of a machine tool spindle, as shown in Figure 2 , if it is assumed that the ball 4 is purely rolling in the outer ring raceway groove 3a of the outer ring 3, then in the contact portion (contact ellipse) of the inner ring raceway groove 2a of the inner ring 2 and the surface of the ball 4, the relative circumferential velocity (symbol C of the figure) of the circumferential velocity on the surface of the ball 4 caused by the rotation (indicated by symbol A of the figure, proportional to the perpendicular distance from the rotation axis AX of the ball 4 to the circular arc of the outer peripheral surface of the ball 4) and the circumferential velocity on the inner ring raceway groove 2a of the inner ring 2 caused by the revolution (indicated by symbol B of the figure, proportional to the perpendicular distance from the rotation axis of the inner ring 2 to the inner ring raceway groove 2a) appears in the manner of spin sliding. As shown by symbol Di and symbol D2 in Figure 3 , the greater the contact angle ai, the greater the circumferential velocity on the inner ring raceway groove 2a of the inner ring 2 caused by the revolution, and in addition, the greater the long radius of the contact ellipse formed by the contact surface of the ball 4 and the inner ring raceway groove 2a, the greater the circumferential velocity difference (indicated by Adi, Ad2 of the figure, Adi > Ad2) at both ends of the contact ellipse, and thus the relative circumferential velocity C also becomes greater. Therefore, in order to suppress spin sliding, it is effective to suppress the circumferential velocity on the inner ring raceway groove 2a of the inner ring 2 caused by the revolution and to reduce the long radius of the contact ellipse formed by the contact surface of the ball 4 and the inner ring raceway groove 2a at the contact portion of the ball 4 and the inner ring raceway groove 2a. In addition, in Figure 2 , reference sign AX indicates the rotation axis of the ball 4 controlled by the outer ring.

[0070] As shown in (a) of Figure 4 , during operation, in the angular contact ball bearing 1, the contact angle ao of the ball 4 and the outer ring raceway groove 3a of the outer ring 3 becomes smaller and the contact angle ai of the ball 4 and the inner ring raceway groove 2a of the inner ring 2 becomes greater due to the balance of the centrifugal force F acting on the ball 4 and the force from the pre-load of the inner ring 2 or the outer ring 3. And in the inner ring 2, if the contact angle ai of the inner ring raceway groove 2a and the ball 4 becomes greater, the amount of spin sliding becomes greater and the amount of heat generation also becomes greater. Therefore, by increasing Ri in the inner ring 2, the contact angle ai is difficult to become greater in high-speed rotation and the contact ellipse length can be reduced, and thus the heat generation caused by spin sliding can be suppressed. That is, as shown in Figure 4As shown in (b) of FIG. 6, if Ri is increased, the contact angle change caused by the centrifugal force becomes smaller, and the spin slip amount also becomes smaller. In contrast, as shown in (c) of FIG. 6, if Ri is decreased, the contact angle change caused by the centrifugal force F becomes larger, and the spin slip amount also becomes larger. Therefore, it is considered that, in order to suppress the spin slip amount, it is preferable to increase Ri. Figure 4

[0071] On the other hand, in the outer ring 3, if the outer ring groove curvature radius ratio Ro is increased, the major radius of the contact ellipse becomes smaller, and has an effect of suppressing heat generation, but since there is no force acting in a direction in which the contact angle a0 is made smaller, it is difficult to be more effective than increasing the inner ring groove curvature radius ratio Ri for the purpose of reducing the heat generation amount due to spin slip.

[0072] Here, using an angular contact ball bearing with the following analysis condition 1, the total spin heat generation amount on the inner ring side and the outer ring side was calculated while changing the inner ring groove curvature radius ratio Ri and the outer ring groove curvature radius ratio Ro. The calculation results of the total spin heat generation amount (W) corresponding to each Ri and Ro are shown in Table 1.

[0073] (Analysis Condition 1)

[0074] Bearing inner diameter: 70 mm

[0075] Bearing outer diameter: 110 mm

[0076] Bearing width: 20 mm

[0077] Initial contact angle: 18°

[0078] Ball diameter / cross-sectional height ratio: 0.595

[0079] Rotation speed: 20000 min -1

[0080] Preload: 1000 N

[0081] [Table 1]

[0082]

[0083] Figure 5 is a graph showing the relationship with the total spin heat generation amount with the inner ring groove curvature radius ratio Ri as the horizontal axis, Figure 6 is a graph showing the relationship with the total spin heat generation amount with the outer ring groove curvature radius ratio Ro as the horizontal axis. First, from Figure 5 ​As shown in the chart, regardless of the outer ring groove radius of curvature ratio Ro, increasing the inner ring groove radius of curvature ratio Ri reduces heat generation, with the heat generation becoming extremely high when Ri is less than 54%. However, if the inner ring groove radius of curvature ratio Ri is too large, the surface pressure between the inner ring raceway groove 2a and the ball 4 increases under load, making it prone to indentation. In particular, when the inner ring groove radius of curvature ratio Ri is greater than 58%, even if indentation resistance is improved due to surface hardening, the indentation resistance will still be lower than that of existing products. Furthermore, to improve the degree of surface hardening, more stringent processing conditions are required, but this reduces productivity, thus limiting the product's performance. Therefore, the inner ring groove radius of curvature ratio Ri is set to 54-58%.

[0084] On the other hand, according to Figure 6 The chart shows that the heat generation is extremely high when the outer groove radius of curvature ratio Ro is less than 51%, reaching a minimum around 52%. When the outer groove radius of curvature ratio Ro is above 52%, the increase in heat generation with increasing Ro is relatively slow. Considering the deviation in the manufacturing result of Ro, if the target area is slightly larger than the minimum value of 52%, the deviation in heat generation caused by the deviation in the manufacturing result of Ri can be suppressed to a smaller extent. If the outer groove radius of curvature ratio Ro is 58%, a value roughly equivalent to 51% is obtained. From the perspective of reducing spin heat generation, the outer groove radius of curvature ratio Ro is set to 51-58%, which includes the minimum heat generation value.

[0085] [In the inner ring raceway surface, the maximum surface pressure is 4.7–6.0 GPa when the sum of the permanent deformation of the ball at the center of the contact area between the ball and the inner ring raceway groove and the inner ring raceway groove is one ten-thousandth of the ball diameter.]

[0086] As described above, by setting the inner ring groove radius of curvature Ri to 54–58% and the outer ring groove radius of curvature Ro to 51–58%, the spin heat generation during rotation can be reduced. However, it is believed that when an external impact load is applied while the ring is stationary, the contact surface pressure increases, raising the likelihood of indentation. Therefore, a surface-hardened layer 10 with applied surface residual stress is formed at least in the inner ring raceway groove 2a of the inner ring 2, thereby further preventing indentation.

[0087] To form the surface hardened layer 10, the raceway groove is subjected to a roll polishing treatment. The roll polishing treatment is to move a ball (indenter) of ceramic or super-hard alloy, which is held by hydraulic pressure, along the axial section of the inner ring raceway groove 2a while rolling in contact with the inner ring raceway groove 2a. The surface is hardened by this roll polishing treatment, but at this time, the maximum surface pressure at which the sum of the permanent deformation of the ball 4 and the inner ring raceway groove 2a at the center of the contact portion of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter is selected to be 4.7 to 6.0 GPa in a manner that the indenter diameter, the pressing force, and the like of the polishing tool are selected.

[0088] In addition, as a limit that does not hinder smooth rotation of the bearing, the sum of the permanent deformation of the ball 4 and the inner ring raceway groove 2a at the center of the contact portion of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter.

[0089] If it is a ball bearing to which no residual compressive stress is applied to the surface layer of the raceway surface, the maximum surface pressure at which the sum of the permanent deformation of the ball and the raceway groove at the center of the contact portion of the ball and the raceway groove is one ten-thousandth of the ball diameter is 4.2 GPa (according to JIS B1519), and thus by applying a residual compressive stress, an effect that a dent is not easily generated for an external impact load at rest can be obtained.

[0090] Note that according to the applicant's investigation, a surface pressure of about 4 GPa or more is applied to bearings that are returned from the market as collision damage. In the case where a residual compressive stress is applied to the surface layer of the raceway surface and the maximum surface pressure at which the sum of the permanent deformation of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter is 4.7 GPa, a case where a dent is generated at a surface pressure of about 4 GPa or more and less than 4.7 GPa in the past to become a defective product is not recognized as a defective condition. Thus, there is no need to perform the trouble of bearing replacement.

[0091] In addition, in the inner ring raceway groove 2a, the maximum surface pressure at which the sum of the permanent deformation of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter is set to be 4.7 to 6.0 GPa, which is set in consideration of processing conditions that do not reduce productivity.

[0092] In addition, the surface hardened layer is not limited to the inner ring raceway groove 2a of the inner ring 2, and can be applied to the outer ring raceway groove 3a of the outer ring 3.

[0093] Note that the technology of the patent document 1 to form a hard film of 0.05 to 8 μm in thickness on the raceway surface is a technology to improve wear resistance and reduce the coefficient of friction by coating a hardened layer on a raceway ring after machining by chemical treatment. On the other hand, the surface processing layer 10 of the present embodiment is hardened by machining to improve dent resistance.

[0094] [Ri-Ro≥0%]

[0095] The inner ring groove curvature radius ratio Ri and the outer ring groove curvature radius ratio Ro are set in the above range, but by making the inner ring groove curvature radius ratio Ri equal to or greater than the outer ring groove curvature radius ratio Ro, the surface pressure rise when a load is applied is suppressed to be lower in the outer ring 3 than in the inner ring 2. On the other hand, since the surface-hardened layer 10 is formed in the inner ring raceway groove 2a, if an external impact load is received at rest, it is possible to prevent the bearing from being damaged by a dent being produced in the outer ring 3 before a dent is produced in the inner ring 2, and in this case, by setting the maximum surface pressure when the sum of the permanent set of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter in the inner ring raceway groove 2a in the above range, it is possible to sufficiently obtain the effect of improving the dent resistance.

[0096] Figure 7 This is a graph showing the relationship between the difference between Ri and Ro and the magnitude of the outer ring surface pressure and the inner ring surface pressure in the bearing specifications under the analysis condition 1, and shows the relationship between the difference between Ri and Ro and the magnitude of the outer ring surface pressure and the inner ring surface pressure when a load is applied to the bearing. That is, the region where the inner ring surface pressure / outer ring surface pressure > 1 indicates that the inner ring surface pressure is high, the region where the inner ring surface pressure / outer ring surface pressure < 1 indicates that the outer ring surface pressure is high, and in the case where the inner ring surface pressure / outer ring surface pressure = 1, the inner ring surface pressure and the outer ring surface pressure are equal. For example, in the case of a general bearing in which the inner ring raceway groove 2a and the outer ring raceway groove 3a are not subjected to surface-hardening treatment, the maximum surface pressure of the inner ring raceway surface and the outer ring raceway surface is 4.2 GPa when the sum of the permanent set of the ball and the raceway groove at the center of the contact portion of the ball and the raceway groove is one ten-thousandth of the ball diameter, which is defined in JIS B 1519, and therefore means that in the region where the inner ring surface pressure / outer ring surface pressure > 1, a dent is produced in the inner ring raceway surface first, in the region where the inner ring surface pressure / outer ring surface pressure < 1, a dent is produced in the outer ring raceway surface first, and in the region where the inner ring surface pressure / outer ring surface pressure = 1, a dent is produced in the inner ring raceway surface and the outer ring raceway surface at the same time.

[0097] The inner ring raceway groove 2a of the inner ring 2 is subjected to surface-hardening treatment to form the surface-hardened layer 10, the maximum surface pressure when the sum of the permanent set of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter is set to 4.7 to 6.0 GPa, and in the case where the outer ring raceway groove of the outer ring is not subjected to surface-hardening treatment, the ratio of the inner ring surface pressure to the outer ring surface pressure at which a dent is produced in the inner ring raceway surface first compared to the outer ring raceway surface is Figure 71.120 ≤ inner ring surface pressure / outer ring surface pressure ≤ 1.429. Note that the lower limit value 1.120 and the upper limit value 1.429 of the ratio of the inner ring surface pressure to the outer ring surface pressure at which the inner ring raceway surface first generates a dent compared to the outer ring raceway surface are the ratio of the surface pressure of the inner ring raceway surface on which the surface hardening treatment is performed to the surface pressure of the outer ring raceway surface on which the surface hardening treatment is not performed, and thus are respectively calculated as 4.7 ÷ 4.2 = 1.120, 6.0 ÷ 4.2 = 1.429.

[0098] As a result of this Figure 7 As a result, in the bearing in which the surface hardening treatment is performed on the inner ring raceway groove, when Ri - Ro ≥ 0%, the inner ring surface pressure / outer ring surface pressure ≥ 1.120, and thus a dent is not first generated on the outer ring, and the surface hardening effect on the inner ring can be sufficiently obtained. In addition, it is known that even if the surface hardening treatment is not performed on the outer ring raceway groove 3a of the outer ring 3, a dent resistance equal to or higher than that of the inner ring 2 on which the surface hardening treatment is performed on the inner ring raceway groove 2a can be obtained. Therefore, in the present embodiment, the surface hardening treatment does not need to be performed on the outer ring raceway groove 3a, and a manufacturing advantage can be obtained.

[0099] In addition, according to the results of Figure 7 As a result, in the range where Ri is 54 to 58% and Ro is 51 to 58%, the inner ring surface pressure / outer ring surface pressure at Ri - Ro = 0% is in the range of 1.120 ≤ inner ring surface pressure / outer ring surface pressure ≤ 1.124, and at Ri - Ro = 1%, 1.151 ≤ inner ring surface pressure / outer ring surface pressure ≤ 1.191. That is, the value of the inner ring surface pressure / outer ring surface pressure at Ri - Ro = 1% is larger than that at Ri - Ro = 0% and the range is large, and thus the inner ring surface pressure tends to be higher than the outer ring surface pressure, and becomes a condition in which a dent is easily first generated on the inner ring and a dent is not easily first generated on the outer ring, and thus the effect of the surface hardening treatment is more easily obtained. Therefore, it is preferable that Ri - Ro ≥ 1% be provided.

[0100] [Relationship between ball diameter / cross-sectional height ratio]

[0101] In the above-described analysis condition 1, a ball having a larger ball diameter (large ball) was used, and it was confirmed that in the case where the ball diameter / cross-sectional height ratio was 0.595, by setting the inner ring groove curvature radius ratio Ri to 54 to 58% and the outer ring groove curvature radius ratio Ro to 51 to 58%, the total spin heat generation could be reduced. In the following analysis condition 2, a ball having a smaller ball diameter (small ball) than the above-described ball was used, and in the case where the ball diameter / cross-sectional height ratio was 0.437, it was also confirmed whether the total spin heat generation could be reduced according to the above-described Ri and Ro. The calculation results of the total spin heat generation (W) corresponding to each Ri and Ro are shown in Table 2.

[0102] (Analysis Condition 2)

[0103] Bearing inner diameter: 70 mm

[0104] Bearing outer diameter: 110 mm

[0105] Bearing width: 20 mm

[0106] Contact angle: 18°

[0107] Ball diameter / cross-sectional height ratio: 0.437

[0108] Rotation speed: 20,000 min -1

[0109] Preload: 1,000 N

[0110] [Table 2]

[0111]

[0112] Figure 8 is a graph showing the relationship with the total spin heat generation with the inner ring groove curvature radius ratio Ri as the horizontal axis, Figure 9 is a graph showing the relationship with the total spin heat generation of the inner ring side and the outer ring side with the outer ring groove curvature radius ratio Ro as the horizontal axis. In this case, as with Analysis Condition 1, in the range where the inner ring groove curvature radius ratio Ri is 54 to 58% and the outer ring groove curvature radius ratio Ro is 51 to 58%, the effect of reducing the total spin heat generation of the inner ring side and the outer ring side was confirmed.

[0113] Next, in Analysis Condition 3 in which the bearing size was different from Analysis Condition 1 but the same ball (large ball) as in Analysis Condition 1 was used, the ball diameter / cross-sectional height ratio was 0.572, and in Analysis Condition 4 in which the ball diameter / cross-sectional height ratio was 0.635, whether or not the total spin heat generation could be reduced was also confirmed in accordance with the above-mentioned Ri, Ro. In Analysis Condition 3, the calculation results of the total spin heat generation (W) corresponding to each Ri, Ro are shown in Table 3, and in the case of Analysis Condition 4, the calculation results of the total spin heat generation (W) corresponding to each Ri, Ro are shown in Table 4.

[0114] (Analysis Condition 3)

[0115] Bearing inner diameter: 30 mm

[0116] Bearing outer diameter: 55 mm

[0117] Bearing width: 13 mm

[0118] Contact angle: 18°

[0119] Ball diameter / cross-sectional height ratio: 0.572

[0120] Rotation speed: 43000 min -1

[0121] Preload: 440 N

[0122] [Table 3]

[0123]

[0124] (Analysis condition 4)

[0125] Bearing inner diameter: 110 mm

[0126] Bearing outer diameter: 170 mm

[0127] Bearing width: 28 mm

[0128] Contact angle: 18°

[0129] Ball diameter / cross-sectional height ratio: 0.635

[0130] Rotation speed: 13000 min -1

[0131] Preload: 2200 N

[0132] [Table 4]

[0133]

[0134] Figure 10 is a graph showing the relationship with the total spin heat generation with the inner ring groove curvature radius ratio Ri as the horizontal axis in the case of analysis condition 3, Figure 11 is a graph showing the relationship with the total spin heat generation with the outer ring groove curvature radius ratio Ro as the horizontal axis in the case of analysis condition 3.

[0135] In addition, Figure 12 is a graph showing the relationship with the total spin heat generation with the inner ring groove curvature radius ratio Ri as the horizontal axis in the case of analysis condition 4, Figure 13 is a graph showing the relationship with the total spin heat generation with the outer ring groove curvature radius ratio Ro as the horizontal axis in the case of analysis condition 4.

[0136] In the case of analysis conditions 3 and 4, it was also confirmed that the effect of reducing the total spin heat generation on the inner ring side and the outer ring side was obtained in the range where the inner ring groove curvature radius ratio Ri was 54 to 58% and the outer ring groove curvature radius ratio Ro was 51 to 58%.

[0137] Therefore, it is understood that by defining the inner ring groove curvature radius ratio Ri and the outer ring groove curvature radius ratio Ro, even if the bearing size varies, the total spin heat generation can be reduced, and the effect of reducing the indentation resistance does not change.

[0138] In addition, the smaller the ratio of the ball diameter to the cross-sectional height, the more advantageous it is for heat reduction, but if the ratio of the ball diameter to the cross-sectional height is too small, when running at high speed in a rotating state, the effective radial clearance becomes too small due to the effects of centrifugal expansion and thermal expansion of the inner ring, which becomes a cause of seizure. Therefore, the ratio of the ball diameter to the cross-sectional height needs to be 0.39 or more. In addition, the larger the ratio of the ball diameter to the cross-sectional height, the more advantageous it is for indentation resistance, but if the value is greater than 0.65, the wall thickness of the raceway ring becomes too thin, resulting in manufacturing disadvantages such as large heat treatment distortion, machining distortion, etc., and therefore is not preferred. Therefore, the ratio of the ball diameter to the cross-sectional height is preferably 0.39 to 0.65 times, and in the case of emphasizing indentation resistance, it is more preferable to use large balls with a ratio of the ball diameter to the cross-sectional height of 0.55 to 0.65.

[0139] In addition, the inner ring 2 and the outer ring 3 are generally composed of a bearing steel such as SUJ2 (high-carbon chromium bearing steel) or the like. This SUJ2 or the like is used at a relatively low temperature because the hardness of the SUJ2 or the like significantly decreases at high temperatures, and the life is shortened. Therefore, in the case of requiring higher speed rotation, the contact pressure at the contact surface where the balls 4 and the inner ring 2 and the outer ring 3 contact each other, the sliding of the balls 4 increases and heat is generated, and locally becomes high temperature. Therefore, the inner ring 2 and the outer ring 3 are preferably composed of a material that is excellent in heat resistance and wear resistance.

[0140] Therefore, a material that forms secondary hardening precipitated eutectic carbide is preferred, such as high speed steel, semi-high speed steel, martensitic stainless steel, and SKD, SKH, M50, SUS440C, etc. can be cited. In addition, a material obtained by increasing the tempering temperature of a general bearing steel (SUJ2) to 240 to 330°C can also be used, and a hard coating treatment is performed thereon. In this case, although the hardness of the base material itself decreases, since the hardness of the raceway ring surface can be hardened by the hard coating, a performance equivalent to the case of using the metal material described above can be obtained.

[0141] In addition, a material that improves temper resistance using a constituent element composition (a material based on high-carbon chromium steel) is preferable, and as an example, SHX material can be cited. In this case, at least one of the inner ring 2 and the outer ring 3 is made of a steel material containing 0.2 to 1.2 mass% of C, 0.7 to 1.5 mass% of Si, 0.5 to 1.5 mass% of Mo, 0.5 to 2.0 mass% of Cr, and the remainder being Fe and inevitable impurity elements, and after nitrocarburizing treatment, quenching and tempering treatment is performed, thereby making the surface carbon concentration 0.8 to 1.3 mass%, and making the surface nitrogen concentration 0.2 to 0.8 mass%. Here, the critical meaning of the effective range of each of the above constituent elements is described.

[0142] (1) Si: 0.7 to 1.5 mass%

[0143] Si is an element that has an effect on temper softening resistance, has an effect of improving high-temperature strength, and delaying the decomposition of retained austenite that effectively prevents indentation initiation type peeling in a high-temperature environment. If the Si content is less than 0.7 mass%, the high-temperature strength is insufficient, and indentation initiation type peeling occurs, so the lower limit value of Si is set to 0.7 mass%. On the other hand, if the Si content exceeds 1.5 mass%, the mechanical strength decreases, and carburizing is hindered, so the upper limit value of Si is set to 1.5 mass%.

[0144] (2) Mo: 0.5 to 1.5 mass%

[0145] Mo, like Si, is an element that has an effect on temper softening resistance, and has an effect of improving high-temperature strength. In addition, Mo functions as a carbide forming element that forms fine carbides on the surface after nitrocarburizing. If the Mo content is less than 0.5 mass%, the high-temperature strength is insufficient, and the amount of carbides precipitated on the surface is insufficient, so the lower limit value of Mo is set to 0.5 mass%. On the other hand, if the Mo content exceeds 1.5 mass%, large carbides are formed at the stage of the raw material, leading to the detachment of carbides and reducing the rolling fatigue life of the bearing, so the upper limit value of Mo is set to 1.5 mass%.

[0146] (3) Cr: 0.5 to 2.0 mass%

[0147] Cr is an additive element that has the same effect as Mo. If the Cr content is less than 0.5 mass%, the high-temperature strength is insufficient, and the amount of carbides precipitated on the surface is insufficient, so the lower limit value of Cr is set to 0.5 mass%. On the other hand, if the Cr content exceeds 2.0 mass%, large carbides are formed at the stage of the raw material, leading to the detachment of carbides and reducing the rolling fatigue life of the bearing, so the upper limit value of Cr is set to 2.0 mass%.

[0148] (4) C: 0.2 to 1.2 mass%

[0149] As described above, if the amount of retained austenite is too much, the retained austenite decomposes and the shape changes with time, and the dimensional stability of the bearing is impaired. On the other hand, the presence of retained austenite on the raceway ring surface is effective in preventing the initiation-type peeling. Therefore, on the basis of the presence of retained austenite on the surface, it is preferable to limit the amount of retained austenite in the entire bearing, and thus it is necessary to suppress the amount of retained austenite in the bearing core. From such a viewpoint, it is preferable to set the amount of retained austenite in the steel to 5 vol% or less on average including the surface and the core, and thus it is necessary to make the carbon concentration on which the retained austenite depends 1.2 mass% or less, and thus the upper limit value of the carbon concentration is set to 1.2 mass%. On the other hand, if the carbon concentration is less than 0.2 mass%, a long time is required to obtain the desired carburizing depth in the nitrocarburizing treatment, and the overall cost rises, and thus the lower limit value of the carbon concentration is set to 0.2 mass%.

[0150] (5) Surface carbon concentration: 0.8 to 1.3 mass%

[0151] By adding carbon to the surface through the nitrocarburizing treatment, the martensite structure that becomes the matrix is solid solution strengthened, and a large amount of retained austenite that effectively prevents the initiation-type peeling can be formed in the extreme surface layer portion. If the surface carbon concentration is less than 0.8 mass%, the surface hardness is insufficient, and the rolling fatigue life and the wear resistance are reduced, and thus the lower limit value of the surface carbon concentration is set to 0.8 mass%. On the other hand, if the surface carbon concentration exceeds 1.3 mass%, large carbides are precipitated at the time of the nitrocarburizing treatment, and the rolling fatigue life is reduced, and thus the upper limit value of the surface carbon concentration is set to 1.3 mass%.

[0152] (6) Surface N concentration: 0.2 to 0.8 mass%

[0153] When nitrogen is added to the surface through the nitrocarburizing treatment, the temper resistance is increased, the high-temperature strength is increased, the wear resistance is improved, and a large amount of retained austenite that effectively prevents the initiation-type peeling can be present in the extreme surface layer portion. If the surface nitrogen concentration is less than 0.2 mass%, the high-temperature strength is reduced, and the wear resistance is reduced, and thus the lower limit value of the surface nitrogen concentration is set to 0.2 mass%. On the other hand, if the surface nitrogen concentration exceeds 0.8 mass%, the grinding finish at the time of bearing manufacture becomes difficult, and the productivity of the bearing is reduced due to the difficulty in grinding, and thus the upper limit value of the surface nitrogen concentration is set to 0.8 mass%.

[0154] (7) Other component elements

[0155] The remaining portion is Fe and unavoidable impurities, but as other component elements, a trace amount of Ti is preferably added. This is because, if Ti is added, fine titanium carbide (TiC), nitride carbide (Ti(C+N)) is precipitated and dispersed in the matrix, and wear resistance and seizure resistance are improved. At this time, the Ti content is preferably 0.1 to 0.3 mass%. If the Ti content is less than 0.1 mass%, the precipitation effect of the carbide cannot be obtained, and therefore the lower limit of the Ti content is set to 0.1 mass%. On the other hand, if the Ti content exceeds 0.3 mass%, it is easy to form a large precipitate, which becomes a defect, and sometimes the rolling fatigue life is reduced, and therefore the upper limit of the Ti content is set to 0.3 mass%. In addition, if the size of the titanium precipitate (TiC, Ti(C+N)) is 0.1 μm or less, it is helpful to improve the wear resistance and seizure resistance.

[0156] In addition, it is preferable not to include unavoidable impurity elements such as S, P, H, O, and the like as much as possible. In particular, if the content of oxygen (O) exceeds 12 ppm, it is easy to form oxide inclusions, which become defects, and sometimes the rolling fatigue life is reduced, and therefore it is preferable that the oxygen content be less than 12 ppm.

[0157] Furthermore, the ball 4 can be steel that is excellent in heat resistance and wear resistance, but can also be composed of ceramics such as Si3N4 (silicon nitride), SiC (silicon carbide), or Al2O3 (alumina). In particular, the Young's modulus of the ceramic ball 4 is higher than that of a steel ball, and therefore the surface pressure with the raceway groove is high, and it is easy to generate a dent, and therefore the angular contact ball bearing in which the dent resistance is improved as in the present embodiment is more effectively used.

[0158] As described above, the angular contact ball bearing of the present embodiment is configured such that the ratio (Ri) of the groove curvature radius of the inner ring raceway groove 2a to the ball diameter is 54 to 58%, the ratio (Ro) of the groove curvature radius of the outer ring raceway groove 3a to the ball diameter is 51 to 58%, Ri - Ro ≥ 0%, and the maximum surface pressure when the sum of the permanent deformation of the ball 4 and the inner ring raceway groove 2a is one ten-thousandth of the ball diameter at the central portion of the contact of the ball 4 with the inner ring raceway groove 2a is 4.7 to 6.0 GPa at least for the inner ring raceway groove 2a. Thereby, the heat generation is suppressed, and the dent resistance is excellent, and therefore it is suitable for use in high-speed rotation, use in applications in which an excessive load is applied in a stationary state, and in particular, use in a machine tool spindle of dmn 80 million or more, and is useful as an angular contact ball bearing to which a preload is applied.

[0159] In addition, the above structure can enjoy the manufacturing advantage as long as the surface hardening layer is formed only in the inner ring raceway groove 2a among the inner ring raceway groove 2a and the outer ring raceway groove 3a by machining.

[0160] Note that the present application is not limited to the above-described embodiments, and can be appropriately modified, improved, or the like.

[0161] For example, the lubrication method of the angular contact ball bearing of the present application can be oil gas lubrication or grease lubrication.

[0162] Note that the present application is based on Japanese Patent Application (Japanese Patent Application No. 2020-162504) filed on September 28, 2020, the content of which is incorporated herein by reference.

Claims

1. An angular contact ball bearing, characterized by, Possessing: an inner ring having an inner ring raceway groove of a cross-sectional circular arc shape on an outer peripheral surface; an outer ring having an outer ring raceway groove of a cross-sectional circular arc shape on an inner peripheral surface; and a plurality of balls disposed freely rollable between the inner ring raceway groove and the outer ring raceway groove, a ratio Ri of a groove curvature radius of the inner ring raceway groove to a ball diameter is 54 to 58%, a ratio Ro of a groove curvature radius of the outer ring raceway groove to the ball diameter is 51 to 58%, and Ri - Ro ≥ 0%, and a surface-hardened layer is formed by subjecting the inner ring raceway groove to a surface-hardening treatment, and when a sum of permanent deformations of the ball and the inner ring raceway groove at a contact portion center of the ball and the inner ring raceway groove is one ten-thousandth of the ball diameter, at least a maximum surface pressure of the inner ring raceway groove is 4.7 to 6.0 GPa.

2. The angular contact ball bearing according to claim 1, wherein Ri - Ro ≥ 1%.

3. The angular contact ball bearing according to claim 1 or 2, wherein at least the inner ring raceway groove is formed with the surface-hardened layer by machining.

4. The angular contact ball bearing according to claim 1 or 2, wherein only the inner ring raceway groove is formed with the surface-hardened layer by machining among the inner ring raceway groove and the outer ring raceway groove.

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

6. The angular contact ball bearing according to claim 1 or 2, wherein a value of a ball diameter / cross-sectional height is 0.39 to 0.

65.

7. The angular contact ball bearing according to claim 6, wherein the value of the ball diameter / cross-sectional height is 0.55 to 0.

65.

8. The angular contact ball bearing according to claim 1 or 2, wherein the angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is applied with a pre-press.

9. The angular contact ball bearing according to claim 5, wherein the angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is applied with a pre-press.

10. The angular contact ball bearing according to claim 6, wherein the angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is applied with a pre-press.

11. The angular contact ball bearing according to claim 7, wherein the angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is applied with a pre-press.

12. The angular contact ball bearing according to claim 1 or 2, wherein at least one of the inner ring and the outer ring is made of steel containing 0.2 to 1.2 mass% of C, 0.7 to 1.5 mass% of Si, 0.5 to 1.5 mass% of Mo, 0.5 to 2.0 mass% of Cr, a remainder of Fe, and inevitable impurity elements, and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The angular contact ball bearing has a surface carbon concentration of 0.8 to 1.3 mass% and a surface nitrogen concentration of 0.2 to 0.8 mass%.

13. The angular contact ball bearing according to claim 5, wherein The angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is preloaded.

14. The angular contact ball bearing according to claim 6, wherein The angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is preloaded.

15. The angular contact ball bearing according to claim 7, wherein The angular contact ball bearing is used for a machine tool spindle of dmn 80 million or more, and the angular contact ball bearing is preloaded.

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