Angular contact ball bearing

Abstract

Provided is a low-cost long-life angular contact ball bearing with which it is possible to reduce the amount of heat generation and to suppress the occurrence of inclusion starting point peeling even when the surface pressure of a contact section increases. An angular contact ball bearing is provided with: an inner ring having an inner ring raceway groove having an arc-shaped cross-section on the outer peripheral surface; an outer ring having an outer ring raceway groove having an arc-shaped cross-section on the inner circumferential surface; and the plurality of balls are arranged between the inner ring raceway groove and the outer ring raceway groove in a free rolling manner. The inner ring raceway groove has a groove curvature radius ratio (Ri) of 54%-57% with respect to the ball diameter, the outer ring raceway groove has a groove curvature radius ratio (Ro) of 51%-58% with respect to the ball diameter, and in at least the inner ring and the outer ring, the alloy steel contains 0.85%-1.15% by mass of C, 0.40%-0.90% by mass of Si, 0.55%-1.20% by mass of Mn, and 1.30%-1.90% by mass of Cr, with the balance being Fe and unavoidable impurities. The steel sheet is characterized by containing 0.30% by mass or less of Mo, 0.30% by mass or less of Ni, 0.20% by mass or less of Cu, 0.025% by mass or less of S, 0.020% by mass or less of P, 15 ppm by mass or less of O, and the balance of Fe and unavoidable impurities.

Description

Technical Field

[0001] The present invention relates to an angular contact ball bearing, and more particularly to an angular contact ball bearing used for spindles of various machine tools, motors, and the like. Background Art

[0002] In recent years, the speed of the spindle of machine tools has been increasing in order to improve processing efficiency and productivity. As a result, the speed of the angular contact ball bearings used in the spindles of machine tools has also been increasing. Specifically, angular contact ball bearings are based on the ratio of dmn (the average size of the bearing inner diameter and outer diameter ≈ the pitch circle diameter of the rolling element (mm) and the rotation speed (min -1 ) is used in the high-speed rotation range of more than 800,000 to less than 2.8 million. Generally, if the angular contact ball bearing rotates at high speed, a large sliding caused by spin motion and gyroscopic motion occurs at the contact point between the ball and the raceway surface. In addition, due to the influence of centrifugal force acting on the inner ring and the ball, the internal clearance of the bearing is reduced, and the contact surface pressure between the ball and the raceway surface increases, resulting in higher heat generation. If the heat generation increases, the viscosity of the oil decreases, and the oil film breaks in the rolling contact between the ball and the raceway ring, resulting in bearing ablation, increased thermal displacement of the spindle, and deterioration of processing accuracy.

[0003] As existing technologies for reducing the heat generation of angular contact ball bearings, for example, there is known a technology in which the groove curvature radius ratio of the outer ring is set to 50.5% to 53%, the groove curvature radius ratio of the inner ring is set to 52.5% to 60% (see patent document 1), and a technology in which the groove curvature radius ratio of both the outer ring and the inner ring is set to 54% to 57% (see patent document 2).

[0004] Prior art literature

[0005] Patent Literature

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

[0007] Patent Document 2: Japanese Patent Application Publication No. 2005-240881 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, in Patent Documents 1 and 2, although low heat generation is achieved by setting the ratio of the groove curvature radius of the outer ring and the inner ring to be larger, there is a tendency for the surface pressure at the contact portion between the rolling element and the raceway surface to increase, and the stress generated near the surface of the raceway surface becomes larger. Therefore, there is a problem of reduced durability due to "inclusion-starting peeling" generated starting from inclusions inside the material.

[0010] The present invention has been made to solve such a problem, and its object is to provide an angular contact ball bearing which can reduce heat generation, can suppress the occurrence of separation starting from inclusions even when the surface pressure of the contact portion increases, and has a low cost and a long life.

[0011] Means for solving problems

[0012] In order to solve the above-mentioned problems, the present invention provides an angular contact ball bearing as described below.

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

[0014] An inner ring, wherein the inner ring has an inner ring raceway groove having an arc-shaped cross section on an outer peripheral surface;

[0015] an outer ring having an outer ring raceway groove having an arc-shaped cross section on an inner circumferential surface; and

[0016] A plurality of balls, wherein the plurality of balls are rotatably arranged between the inner ring raceway groove and the outer ring raceway groove,

[0017] The inner ring raceway groove has a groove curvature radius ratio (Ri) of 54% to 57% relative to the ball diameter, the outer ring raceway groove has a groove curvature radius ratio (Ro) of 51% to 58% relative to the ball diameter, and

[0018] At least in the inner ring and the outer ring, the C content in the alloy steel is 0.85 mass% to 1.15 mass%, Si is 0.40 mass% to 0.90 mass%, Mn is 0.55 mass% to 1.20 mass%, Cr is 1.30 mass% to 1.90 mass%, Mo is less than 0.30 mass%, Ni is less than 0.30 mass%, Cu is less than 0.20 mass%, S is less than 0.025 mass%, P is less than 0.020 mass%, O is less than 15 mass ppm, and the remainder is Fe and unavoidable impurities.

[0019] (2) The angular contact ball bearing according to any one of the above (1), wherein the ball is made of ceramic.

[0020] (3) The angular contact ball bearing according to (1) or (2) above, wherein the ratio of the ball diameter to the cross-sectional height is 0.39 to 0.65.

[0021] (4) The angular contact ball bearing according to (3) above, wherein the ratio of the ball diameter to the cross-sectional height is 0.55 to 0.65.

[0022] (5) The angular contact ball bearing according to any one of (1) to (4) above, wherein:

[0023] The angular contact ball bearing is used for a machine tool spindle having a dmn of 2.8 million or less and is preloaded.

[0024] Effects of the Invention

[0025] According to the angular contact ball bearing of the present invention, the heat generation can be reduced, and even when the surface pressure of the contact portion becomes high, the occurrence of separation from the starting point of inclusions can be suppressed, and a long life can be achieved at low cost. In particular, the angular contact ball bearing of the present invention is useful as an angular contact ball bearing for a machine tool spindle used under the condition of a dmn of 2.8 million or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a partially enlarged cross-sectional view of an angular contact ball bearing as an example of the ball bearing of the present invention.

[0027] Figure 2 is a schematic diagram for explaining spin sliding.

[0028] Figure 3 This is a schematic diagram for explaining spin sliding, and is an enlarged view showing the inner ring raceway groove of the inner ring.

[0029] Figure 4 It is a schematic diagram used to illustrate spin slip, (a) is a diagram showing the direction of centrifugal force, (b) is a diagram showing the spin amount when the inner ring groove curvature radius ratio is large, and (c) is a diagram showing the spin amount when the inner ring groove curvature radius ratio is small.

[0030] Figure 5 This is a graph showing the relationship between the inner race groove curvature radius ratio (Ri) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 1.

[0031] Figure 6 This is a graph showing the relationship between the outer race groove curvature radius ratio (Ro) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 1.

[0032] Figure 7 This is a graph showing the relationship between the inner race groove curvature radius ratio (Ri) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 2.

[0033] Figure 8 This is a graph showing the relationship between the outer race groove curvature radius ratio (Ro) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 2.

[0034] Fig. 9 This is a graph showing the relationship between the inner race groove curvature radius ratio (Ri) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 3.

[0035] Fig.10 This is a graph showing the relationship between the outer race groove curvature radius ratio (Ro) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 3.

[0036] Fig.11 This is a graph showing the relationship between the inner race groove curvature radius ratio (Ri) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 4.

[0037] Fig.12 This is a graph showing the relationship between the outer race groove curvature radius ratio (Ro) and the total spin heating amount on the inner race side and the outer race side, obtained by calculation under analysis condition 4. DETAILED DESCRIPTION

[0038] Hereinafter, an angular contact ball bearing according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0039] In addition, in this specification, "to" which shows a numerical range is used to mean that the numerical values ​​described before and after it are included as a lower limit and an upper limit.

[0040] Figure 1 An angular contact ball bearing for a spindle of a machine tool is shown as an example of the angular contact ball bearing of the present invention. The angular contact ball bearing 1 comprises: an inner ring 2 having an inner ring raceway groove 2a with an arc-shaped cross section on the outer circumferential surface; an outer ring 3 having an outer ring raceway groove 3a with an arc-shaped cross section on the inner circumferential surface; a plurality of balls 4 which are freely arranged between the inner ring raceway groove 2a and the outer ring raceway groove 3a so as to roll; and a retainer 5 which retains the plurality of balls 4 respectively. A countersunk hole 3b is formed on one axial side of the inner circumferential surface of the outer ring 3, and the balls 4 are arranged between the inner ring raceway groove 2a and the outer ring raceway groove 3a at contact angles αi, αo. It should be noted that the contact angles αi, αo are defined as the angles formed by a plane P and a line of action, the plane P being a plane perpendicular to the central axis X of the bearing, and the line of action being a line connecting each contact point where the ball 4 contacts the inner ring 2 and the outer ring 3 and the center of the ball 4. In addition, as Figure 1 As shown, the initial contact angle is αi=αo.

[0041] The balls 4 have a ratio of ball diameter to cross-sectional height, that is, diameter of ball 4 / {(outer diameter of outer ring 3 - inner diameter of inner ring 2) / 2} of 0.39 to 0.65, preferably 0.55 to 0.65.

[0042] In addition, for the inner ring rolling groove 2a and the outer ring rolling groove 3a, the groove curvature radius ratio of the inner ring rolling groove 2a to the ball diameter (Ri = curvature radius of the inner ring rolling groove / ball diameter) is set to 54% to 57%, and the groove curvature radius ratio of the outer ring rolling groove 3a to the ball diameter (Ro = curvature radius of the outer ring rolling groove / ball diameter) is set to 51% to 58%. Hereinafter, the groove curvature radius ratio Ri of the inner ring rolling groove 2a to the ball diameter is also referred to as the inner ring groove curvature radius ratio Ri, and the groove curvature radius ratio Ro of the outer ring rolling groove 3a to the ball diameter is also referred to as the outer ring groove curvature radius ratio Ro.

[0043] Hereinafter, the critical significance of the groove curvature radius ratios Ri and Ro of the above-mentioned respective rolling grooves 2a and 3a and the ball diameter will be described.

[0044] [The inner ring raceway groove curvature radius ratio (Ri) to the ball diameter is 54% to 57%, and the outer ring raceway groove curvature radius ratio (Ro) to the ball diameter is 51% to 58%]

[0045] First, for the angular contact ball bearings 1 used for high-speed rotation in machine tool spindles, such as Figure 2 As shown, if it is assumed that the ball 4 rolls purely in the outer ring raceway groove 3a of the outer ring 3, then in the contact portion (contact ellipse) between the inner ring raceway groove 2a of the inner ring 2 and the surface of the ball 4, the relative circumferential speed (indicated by the reference symbol A in the figure, which is proportional to the vertical distance from the rotation axis AX of the ball 4 to the arc of the outer peripheral surface of the ball 4) of the circumferential speed on the surface of the ball 4 caused by the rotation and the circumferential speed (indicated by the reference symbol B in the figure, which is proportional to the vertical distance from the rotation axis of the inner ring 2 to the inner ring raceway groove 2a) of the inner ring 2 caused by the revolution is expressed as spin slip. Figure 3 As shown by reference numerals D1 and D2 in the figure, the larger the contact angle αi is, the greater the circumferential speed on the inner ring raceway groove 2a of the inner ring 2 caused by the revolution. In addition, the larger the major radius of the contact ellipse formed by the contact surface between the ball 4 and the inner ring raceway groove 2a is, the greater the circumferential speed difference between the two ends of the contact ellipse (shown by Δd1 and Δd2 in the figure, Δd1>Δd2) is, and thus the relative circumferential speed C also increases. Therefore, in order to suppress spin slip, it is effective to suppress the circumferential speed on the inner ring raceway groove 2a of the inner ring 2 caused by the revolution at the contact portion between the ball 4 and the inner ring raceway groove 2a, and to reduce the major radius of the contact ellipse formed by the contact surface between the ball 4 and the inner ring raceway groove 2a. In addition, Figure 2 In the figure, reference symbol AX represents the rotation axis of the ball 4 controlled by the outer ring.

[0046] like Figure 4As shown in (a), during operation, in the angular contact ball bearing 1, due to the balance between the centrifugal force F acting on the ball 4 and the force of the preload from the inner ring 2 or the outer ring 3, the contact angle αo of the outer ring raceway groove 3a of the outer ring 3 becomes smaller, and the contact angle αi with the inner ring raceway groove 2a of the inner ring 2 becomes larger. Moreover, in the inner ring 2, if the contact angle αi between the inner ring raceway groove 2a and the ball 4 becomes larger, the amount of spin slip becomes larger and the heat generated also increases. Therefore, by increasing Ri in the inner ring 2, the contact angle αi is difficult to increase during high-speed rotation, and the length of the contact ellipse can be reduced, thereby suppressing the heat caused by spin slip. That is, as Figure 4 As shown in (b), if Ri is increased, the change in contact angle caused by the centrifugal force becomes smaller, and the spin slip amount also becomes smaller. Figure 4 As shown in (c), if Ri is reduced, the change in contact angle due to 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.

[0047] On the other hand, in the outer ring 3, when the outer ring groove curvature radius ratio Ro becomes larger, the major radius of the contact ellipse becomes smaller, which has the effect of suppressing heat generation, but it does not work in the direction in which the contact angle αo becomes smaller. Therefore, for the purpose of reducing the heat generated by spin sliding, it is not easy to obtain the effect compared with increasing the inner ring groove curvature radius ratio Ri.

[0048] Here, using the angular contact ball bearing under the following analysis condition 1, the total spin heating value on the inner ring side and the outer ring side was calculated by 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 heating value (W) corresponding to each Ri and Ro are shown in Table 1.

[0049] (Analysis Condition 1)

[0050] Bearing inner diameter: 70mm

[0051] Bearing outer diameter: 110mm

[0052] Bearing width: 20mm

[0053] Initial contact angle: 18°

[0054] Ratio of ball diameter to cross-section height: 0.595

[0055] Speed: 20,000min -1

[0056] Preload: 1,000N

[0057] [Table 1]

[0058]

[0059] Figure 5 The graph is a graph showing the relationship between the inner race groove curvature radius ratio Ri and the total spinning heat generation, Figure 6 The graph is a graph showing the relationship between the outer ring groove curvature radius ratio Ro and the total spinning heat generation. Figure 5 It can be seen from the graph that, regardless of the outer ring groove curvature radius ratio Ro, the heat generation is reduced by increasing the inner ring groove curvature radius ratio Ri, and when the inner ring groove curvature radius ratio Ri is less than 54%, the heat generation becomes extremely large. However, if the inner ring groove curvature radius ratio Ri is too large, the surface pressure between the inner ring raceway groove 2a and the ball 4 during load loading becomes high, and there is a tendency to easily generate indentations. In particular, when the inner ring groove curvature radius ratio Ri is greater than 57%, the indentation resistance is lower than that of existing products. Therefore, the inner ring groove curvature radius ratio Ri is set to 54% to 57%.

[0060] On the other hand, according to Figure 6 From the curve graph, when the outer ring groove curvature radius ratio Ro is less than 51%, the heat generation is extremely large and reaches a minimum value at around 52%. When the outer ring groove curvature radius ratio Ro is above 52%, the increase in heat generation caused by the increase in Ro is relatively gentle. Considering the deviation in the completion of Ro in manufacturing, if the area slightly larger than the minimum value of 52% is targeted, the deviation in heat generation caused by the deviation in the completion of Ri in manufacturing can also be suppressed to a smaller level. If the outer ring groove curvature radius ratio Ro is 58%, a value roughly equivalent to 51% is taken. From the perspective of the effect of reducing the spin heat generation, the outer ring groove curvature radius ratio Ro is set to 51% to 58%, which includes the minimum value of heat generation.

[0061] [Relationship between the ratio of ball diameter and cross-sectional height]

[0062] In the above analysis condition 1, when a relatively large ball diameter (large ball) is used and the ratio of the ball diameter to the cross-sectional height is 0.595, it is confirmed that the total spin heating value can be reduced by setting the inner ring groove curvature radius ratio Ri to 54% to 57% and the outer ring groove curvature radius ratio Ro to 51% to 58%. In the following, in the analysis condition 2, when a ball diameter smaller than the above is used (small ball), and the ratio of the ball diameter to the cross-sectional height is 0.437, it is also confirmed by the above Ri and Ro regulations whether the total spin heating value can be reduced. The calculation results of the total spin heating value (W) corresponding to each Ri and Ro are shown in Table 2.

[0063] (Analysis Condition 2)

[0064] Bearing inner diameter: 70mm

[0065] Bearing outer diameter: 110mm

[0066] Bearing width: 20mm

[0067] Initial contact angle: 18°

[0068] Ratio of ball diameter to cross-section height: 0.437

[0069] Speed: 20,000min -1

[0070] Preload: 1,000N

[0071] [Table 2]

[0072]

[0073] Figure 7 The graph is a graph showing the relationship between the inner race groove curvature radius ratio Ri and the total spinning heat generation, Figure 8 The graph is a graph showing the relationship between the total spin heating value 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 in analysis condition 1, the effect of reducing the total spin heating value of the inner ring side and the outer ring side was confirmed when the inner ring groove curvature radius ratio Ri was 54% to 57% and the outer ring groove curvature radius ratio Ro was 51% to 58%.

[0074] Next, for analysis conditions 3 and 4, whether the total spin heating value can be reduced was confirmed by the above-mentioned provisions of Ri and Ro. Among them, analysis condition 3 is that the bearing size is different from analysis condition 1, but the ball with a relatively large diameter (large ball) is used as in analysis condition 1, and the ratio of the ball diameter to the cross-sectional height is 0.572. Analysis condition 4 is that the bearing size is different from analysis condition 1, but the ball with a relatively large diameter (large ball) is used as in analysis condition 1, and the ratio of the ball diameter to the cross-sectional height is 0.635. Table 3 shows the calculation results of the total spin heating value (W) corresponding to Ri and Ro under analysis condition 3, and Table 4 shows the calculation results of the total spin heating value (W) corresponding to Ri and Ro under analysis condition 4.

[0075] (Analysis Condition 3)

[0076] Bearing inner diameter: 30mm

[0077] Bearing outer diameter: 55mm

[0078] Bearing width: 13mm

[0079] Initial contact angle: 18°

[0080] Ratio of ball diameter to cross-section height: 0.572

[0081] Speed: 43,000min-1

[0082] Preload: 440N

[0083] [Table 3]

[0084]

[0085] (Analysis Condition 4)

[0086] Bearing inner diameter: 110mm

[0087] Bearing outer diameter: 170mm

[0088] Bearing width: 28mm

[0089] Initial contact angle: 18°

[0090] Ratio of ball diameter to cross-section height: 0.635

[0091] Speed: 13,000min -1

[0092] Preload: 2,200N

[0093] [Table 4]

[0094]

[0095] Fig. 9 is a graph showing the relationship between the inner race groove curvature radius ratio Ri and the total spin heating value under analysis condition 3, and Fig.10 It is a graph showing the relationship between the outer ring groove curvature radius ratio Ro and the total spinning heat value under analysis condition 3, with the horizontal axis being the horizontal axis.

[0096] also, Fig.11 is a graph showing the relationship between the inner race groove curvature radius ratio Ri and the total spinning heat value under analysis condition 4, and Fig.12 It is a graph showing the relationship between the outer ring groove curvature radius ratio Ro and the total spinning heat value under analysis condition 4, with the horizontal axis being the horizontal axis.

[0097] Also in the case of analysis conditions 3 and 4, when the inner ring groove curvature radius ratio Ri was in the range of 54% to 57% and the outer ring groove curvature radius ratio Ro was in the range of 51% to 58%, the effect of reducing the total spin heat generation on the inner ring side and the outer ring side was observed.

[0098] Therefore, it can be understood that by limiting the inner ring groove curvature radius ratio Ri and the outer ring groove curvature radius ratio Ro, even if the bearing size changes, the total spin heating value can be reduced and the effect of reducing the indentation resistance can remain unchanged.

[0099] In addition, the smaller the ratio of the ball diameter to the cross-sectional height, the more beneficial it is to reduce heat generation. However, if it is too small, the effective radial clearance becomes too small due to the centrifugal expansion and thermal expansion of the inner ring when rotating at high speed, which becomes the cause of ablation. Therefore, the ratio of the ball diameter to the cross-sectional height needs to be greater than 0.39. In addition, the larger the ratio of the ball diameter to the cross-sectional height, the more beneficial it is to indentation resistance. However, if this value is greater than 0.65, the wall thickness of the raceway ring becomes too thin, resulting in manufacturing disadvantages such as heat treatment deformation and increased processing deformation, so it is not preferred. Therefore, the ratio of the ball diameter to the cross-sectional height is preferably 0.39 to 0.65. When attaching importance to indentation resistance, it is preferred to use a large ball with a ratio of the ball diameter to the cross-sectional height of 0.55 to 0.65.

[0100] In addition, the "inclusion-originated debonding" to be suppressed by the present invention refers to the following phenomenon: stress concentration generated around oxide-based inclusions and sulfide-based inclusions present inside the steel constituting the bearing component causes butterfly-shaped structural changes in the peripheral portion, and fatigue cracking generated along the interface of the changed structure becomes more severe until debonding occurs.

[0101] The butterfly-type structural change is the following phenomenon. When a large load is applied to a bearing component, stress is concentrated around oxide inclusions and sulfide inclusions existing inside the steel constituting the bearing component. In addition, the large shear stress generated by this stress concentration is repeatedly loaded on the martensitic structure of the matrix of the above-mentioned steel, thereby dislocations and dissolved carbon in the martensitic structure are moved, and the martensitic structure is gradually deformed and changed into an ultra-fine ferrite structure. In order to delay such a butterfly-type structural change, the present invention stabilizes the martensitic structure in the matrix by adding the optimal amount of Si, Mn, Cr, and Mo as alloying components in the steel. That is, the present invention stabilizes the martensitic structure, thereby making it difficult for dislocations and dissolved carbon to move in the martensitic structure, delaying the butterfly-type structural change and achieving a longer life of the bearing component.

[0102] Therefore, in the present embodiment, the inner ring 2 and the outer ring 3 are made of steel containing 0.85 mass% to 1.15 mass% of C, 0.40 mass% to 0.90 mass% of Si, 0.55 mass% to 1.20 mass% of Mn, 1.30 mass% to 1.90 mass% of Cr, 0.30 mass% or less of Mo, 0.30 mass% or less of Ni, 0.20 mass% or less of Cu, 0.025 mass% or less of S, 0.020 mass% or less of P, 15 mass ppm or less of O, and the remainder being Fe and unavoidable impurities. The reasons for limiting the elements added to the steel and their contents are described below.

[0103] [C: 0.85 mass% to 1.15 mass%]

[0104] C is an element that is dissolved in the matrix and improves hardness by quenching, so it is added to ensure the hardness required for the bearing component. If the C amount in the alloy component is less than 0.85 mass %, the hardness after quenching is insufficient, and wear resistance and rolling fatigue life are reduced. Therefore, it contains C more than 0.85 mass %. In order to obtain these wear resistance and rolling fatigue life more stably, it is preferred that the content of C is more than 0.95 mass %. On the other hand, when the content of C exceeds 1.15 mass %, the bearing component obtained becomes too hard, resulting in a reduction in grindability and a reduction in fracture toughness value. Therefore, the content of C is suppressed to below 1.15 mass %. In order to make the above-mentioned grindability more stable, it is preferred that the content of C is below 1.10 mass %.

[0105] [Si: 0.40 mass% to 0.90 mass%]

[0106] Si is dissolved in the matrix and has the effect of improving hardenability and resistance to temper softening, so it is added to ensure the hardness required by the bearing component. In addition, Si has the effect of suppressing the occurrence of inclusion-starting type peeling, which is an important purpose of the present invention. That is, Si stabilizes the martensite in the matrix structure, delays the butterfly-type structure change generated around the non-metallic inclusions, suppresses (delays) the occurrence of inclusion-starting type peeling in the bearing component, and helps to extend the life of the rolling bearing assembled with the bearing component. The life extension effect brought about by the delay of such butterfly-type structure change cannot be fully obtained when the Si content is less than 0.40 mass%. On the other hand, if the Si content exceeds 0.90 mass%, the hardness after spheroidizing annealing increases, so the turning and cold working properties are reduced. In order to suppress the hardness after spheroidizing annealing within an appropriate range and obtain stable turning and cold working properties, it is preferred to suppress the Si content to less than 0.70 mass%.

[0107] [Mn: 0.55 mass% to 1.20 mass%]

[0108] Mn has the effect of being dissolved in the matrix and improving the hardenability, so it is added to ensure the hardness required for the bearing component. In addition, Mn also has the effect of inhibiting the occurrence of inclusion-starting type peeling, which is an important purpose of the present invention, as in the case of Si mentioned above. That is, Mn also stabilizes the martensite in the matrix structure, delays the change of the butterfly-type structure generated around the non-metallic inclusions, inhibits the occurrence of inclusion-starting type peeling in the bearing component, and helps to extend the life of the rolling bearing assembled with the bearing component. In addition, Mn has the effect of easily generating retained austenite after heat treatment. Retained austenite is a relatively soft structure, which inhibits the aforementioned surface-starting type peeling, and from other viewpoints, helps to extend the life of the rolling bearing assembled with the above-mentioned bearing component. Such an effect cannot be fully obtained when the content of Mn is less than 0.55% by mass. On the other hand, if the content of Mn is higher than 1.20% by mass, the deformation resistance during hot forging increases, which reduces the hot forging property. In addition, the retained austenite in the steel constituting the bearing component gradually decomposes with the use of the rolling bearing, and the volume expands a little bit with the decomposition. Therefore, if the amount of retained austenite is excessive by increasing the content of Mn, the stability of the shape and size of the above-mentioned bearing component is reduced. Therefore, the amount of Mn in the steel constituting the bearing component is in the range of 0.55 mass% to 1.20 mass%. In addition, in order to improve the surface starting point type peeling life, it is preferred that the content of Mn is set to 0.80 mass% to 1.20 mass%.

[0109] [Cr: 1.30 mass% to 1.90 mass%]

[0110] Cr is distributed as a component dissolved in the martensite of the matrix and a component dissolved in the spheroidized carbide. Cr dissolved in the martensite of the matrix has the effect of improving hardenability and ensuring the hardness of the surface of the bearing component. In addition, Cr also has the effect of suppressing the occurrence of inclusion-starting type peeling, which is an important purpose of the present invention, as in the case of the above-mentioned Si and the above-mentioned Mn. That is, Cr also stabilizes the martensite in the matrix structure, delays the butterfly-type structure change generated around the non-metallic inclusions, suppresses the occurrence of inclusion-starting type peeling in the bearing component, and helps to extend the life of the rolling bearing assembled with the bearing component. When the Cr content is less than 1.30 mass%, such an effect cannot be fully obtained. On the other hand, if the Cr content exceeds 1.90 mass%, the hardness after spheroidizing annealing increases, so the turning and cold working properties decrease. Therefore, the amount of Cr in the steel constituting the above-mentioned bearing component is in the range of 1.30 mass% to 1.90 mass%. In order to stabilize the machinability and cold workability, the Cr content is preferably set to 1.70 mass % or less.

[0111] [Mo: 0.30 mass % or less]

[0112] Mo is dissolved in the matrix, which has the effect of improving hardenability and temper softening resistance and ensuring the hardness of the bearing component surface. In addition, Mo also has the effect of suppressing the occurrence of inclusion starting point type peeling, which is an important purpose of the present invention, as in the case of Si, Mn and Cr mentioned above.

[0113] That is, Mo also stabilizes the martensite in the matrix structure, delays the butterfly structure change generated around oxide inclusions and sulfide inclusions, suppresses the starting point peeling of the bearing component, and helps to extend the life of the rolling bearing assembled with the bearing component. However, if the Mo content exceeds 0.30% by mass, a part of the Mo forms hard carbides, which reduces the grindability. In addition, since it is an expensive element, the manufacturing cost of the rolling bearing including the above-mentioned bearing component becomes higher. Therefore, the Mo content is set to less than 0.30% by mass. It is preferred that the Mo content is set to less than 0.15% by mass. In addition, the lower limit of the Mo content is limited from the perspective of manufacturing cost, but is preferably greater than 0.01% by mass.

[0114] [Ni: 0.30 mass % or less]

[0115] Ni is an element having the effect of improving hardenability and stabilizing austenite, and further, if added in large quantities, toughness is improved. However, since it is an expensive element, the manufacturing cost of the rolling bearing including the above-mentioned bearing component becomes high. Therefore, with regard to Ni, it is not actively added, but its content is set to 0.30 mass % or less. It is preferred that the content of Ni is set to 0.18 mass % or less. In addition, the lower limit value of the content of Ni is limited from the manufacturing cost aspect, but is preferably 0.01 mass % or more.

[0116] [Cu: 0.20 mass % or less]

[0117] Cu has the effect of improving hardenability and the effect of improving grain boundary strength. However, if the content of Cu increases, hot forgeability decreases. Therefore, Cu is not actively added, but its content is set to 0.20 mass% or less. However, since there are still advantages brought by addition, it is preferred to add 0.01 mass% or more.

[0118] [S: 0.025 mass % or less]

[0119] S will form MnS and act as an inclusion, so the less S contained in the steel, the better. However, S is an element that exists in large quantities in nature. If the content of S is to be suppressed to a very small amount, the productivity of the raw materials (steel) composed of the alloy used to manufacture bearing components will decrease, and the manufacturing cost of the steel will increase, making it difficult to be widely used in industry. On the other hand, even if it contains about 0.025% by mass of S, the durability required for the bearing components can be ensured by making the content of other elements and the heat treatment method appropriate. Therefore, the upper limit of the content of S is set to 0.025% by mass.

[0120] [P: 0.020 mass % or less]

[0121] P will segregate at the crystal grain boundary, reducing the grain boundary strength and fracture toughness value, so the less the better. However, P is also an element that exists in large quantities in nature. If the content of P is to be suppressed to a very small amount, the manufacturing cost of the steel will rise. On the other hand, even if it contains about 0.020% by mass of P, by making the content of other elements and the heat treatment method appropriate, the durability required for the bearing component can be ensured. Therefore, the upper limit of the content of P is set to 0.020% by mass.

[0122] [O: 15 mass ppm or less]

[0123] O forms Al in steel 2 O 3 Oxide inclusions such as 0.04% and 0.06% O are hard and can become the starting point of peeling, which has a great adverse effect on rolling fatigue life. Therefore, the less O content, the better. However, with regard to O, if the content is extremely small, the cost of steel will increase. On the contrary, even if about 15 mass ppm of O is contained, the durability required for bearing components can be ensured by making the content of other elements and the heat treatment method appropriate. Therefore, the upper limit of the O content is set to 15 mass ppm.

[0124] Furthermore, the ball 4 may be made of the above-mentioned steel having excellent heat resistance and wear resistance, but may also be made of Si 3 N 4 (Silicon Nitride), SiC (Silicon Carbide) or Al 2 O 3 (alumina) and other ceramics. In particular, the ceramic ball 4 has a higher Young's modulus than the steel ball, so the surface pressure with the raceway groove becomes higher, the stress generated near the surface of the raceway surface becomes larger, and the inclusion starting point peeling is easy to occur. Therefore, when using a ceramic ball 4, as in the present embodiment, the angular contact ball bearing with improved durability by the materials of the inner ring and the outer ring mentioned above functions more effectively. In addition, the ceramic ball 4 is usually lighter than the steel ball, so it is not easily affected by the centrifugal force even when a large-diameter ball is used, and it also has the effect of reducing the heat generation.

[0125] As described above, in the angular contact ball bearing of the present embodiment, the groove curvature radius ratio (Ri) of the inner ring raceway groove 2a relative to the ball diameter is 54% to 57%, the groove curvature radius ratio (Ro) of the outer ring raceway groove 3a relative to the ball diameter is 51% to 58%, and at least in the inner ring 2 and the outer ring 3, the C in the alloy steel is 0.85 mass% to 1.15 mass%, Si is 0.40 mass% to 0.90 mass%, Mn is 0.55 mass% to 1.20 mass%, Cr is 1.30 mass% to 1.90 mass%, Mo is less than 0.30 mass%, Ni is less than 0.30 mass%, Cu is less than 0.20 mass%, S is less than 0.025 mass%, P is less than 0.020 mass%, O is less than 15 mass ppm, and the remainder is Fe and unavoidable impurities.

[0126] Therefore, by increasing the inner ring groove curvature radius ratio Ri, the heat generation can be reduced. Instead, even when the surface pressure at the contact portion between the rolling element and the raceway surface becomes high, by adding appropriate amounts of Si, Mn, Cr, and Mo to the alloy steel of at least the outer ring and the inner ring for production, the cost increase can be suppressed, and butterfly-type structure changes are less likely to occur around non-metallic inclusions, thereby increasing the rolling fatigue life of the bearing components and achieving improved durability.

[0127] In addition, it can achieve a longer life, long-term stable operation (maintenance-free), environmental contribution (reduced number of parts replacement, reduction of CO generated by manufacturing and disposal) 2 ).

[0128] In addition, the present invention is not limited to the above-mentioned embodiment, and appropriate modifications and improvements can be made.

[0129] For example, the lubrication method of the angular contact ball bearing of the present invention can be oil-gas lubrication or grease lubrication.

[0130] In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2022-162747) filed on October 7, 2022, and the contents are incorporated herein by reference.

[0131] Description of Reference Numerals

[0132] 1 Angular contact ball bearing

[0133] 2 Inner ring

[0134] 2a Inner ring raceway groove

[0135] 3 Outer ring

[0136] 3a Outer ring raceway groove

[0137] 4 Balls

[0138] 5 Retainer

Claims

1. An angular contact ball bearing, characterized in that: have: An inner ring, wherein the inner ring has an inner ring raceway groove having an arc-shaped cross section on an outer peripheral surface; an outer ring having an outer ring raceway groove having an arc-shaped cross section on an inner circumferential surface; and A plurality of balls, wherein the plurality of balls are rotatably arranged between the inner ring raceway groove and the outer ring raceway groove, The inner ring raceway groove has a groove curvature radius ratio (Ri) of 54% to 57% relative to the ball diameter, the outer ring raceway groove has a groove curvature radius ratio (Ro) of 51% to 58% relative to the ball diameter, and At least in the inner ring and the outer ring, the C content in the alloy steel is 0.85 mass% to 1.15 mass%, Si is 0.40 mass% to 0.90 mass%, Mn is 0.55 mass% to 1.20 mass%, Cr is 1.30 mass% to 1.90 mass%, Mo is less than 0.30 mass%, Ni is less than 0.30 mass%, Cu is less than 0.20 mass%, S is less than 0.025 mass%, P is less than 0.020 mass%, O is less than 15 mass ppm, and the remainder is Fe and unavoidable impurities.

2. The angular contact ball bearing according to claim 1, characterized in that: The material of the ball is ceramic.

3. The angular contact ball bearing according to claim 1, characterized in that: The ratio of the ball diameter to the cross-sectional height is 0.39 to 0.

65.

4. The angular contact ball bearing according to claim 3, characterized in that: The ratio of the ball diameter to the cross-sectional height is 0.55 to 0.

65.

5. The angular contact ball bearing according to any one of claims 1 to 4, characterized in that: The angular contact ball bearing is used for a machine tool spindle having a dmn of 2.8 million or less and is preloaded.

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