Self-aligning roller bearing

Abstract

To provide a self-aligning roller bearing that improves wear resistance and suppresses grease degradation. [Solution] When the shortest radial distance of the cage between the rolling surface of each spherical roller and the circumferential side surface of each column is H1, and the shortest radial distance of the cage between the opposing surface and the end face when each spherical roller is furthest from the surface on the inner surface of each pocket that faces the end face of each spherical roller, H2 satisfies H1 ≥ H2. At least one of the outer ring, inner ring, and spherical roller is made of alloy steel for rolling parts with a carbon content C of 0.4 to 0.7 by weight, carburized and quenched to an additional carbon content of 0.35 to 1.0 by weight on the surface and a solid solution carbon content of 0.75 to 1.1 by weight on the surface, with a core hardness of HRC 40 to 64. A DLC coating is provided on the rolling surface of the spherical roller 30, and the DLC coating is mainly made of tungsten carbide or silicon carbide and carbon, with a film thickness of 1 to 2 μm.

Description

Technical Field

[0001] The present invention relates to a self-aligning spherical roller bearing.

Background Art

[0002] A self-aligning spherical roller bearing, which is one of rolling bearings, has self-aligning properties because the center of curvature of the outer ring raceway surface coincides with the bearing center, and can also be used when inclination occurs between the outer ring and the inner ring due to machining of the housing or deflection of the shaft due to load. For this reason, self-aligning spherical roller bearings are widely used as bearings for various industrial machines such as wind turbines, paper-making machines, steel rolling mills, and construction machinery.

[0003] Particularly, in the wind turbine 100 shown in FIG. 8, the rotational driving force of the main shaft 102 that rotates by the wind force received by the blade 101 is amplified by the speed increaser 103 and converted into electrical energy by the generator 104 to generate electricity. At that time, since large radial loads and axial loads are applied to the bearing that supports the main shaft 102, a self-aligning spherical roller bearing 105 that can simultaneously bear both loads is used.

[0004] In the self-aligning spherical roller bearing described in Patent Document 1, the outer peripheral surface of the roller has a DLC coating with a multilayer structure having a film thickness of 2.0 μm or more, and the film hardness of each layer is made such that the layer on the outer layer side becomes higher step by step, and the film hardness on the outermost layer side is increased to further improve the wear resistance. At the same time, the innermost layer in contact with the base material is made relatively soft to obtain high adhesion with the base material, so that it is excellent in peel resistance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, in the main shaft bearings of wind turbines, the rotation is usually at a low speed of 10 to 20 min-1, making it difficult to form a sufficient oil film. Furthermore, rapid changes in wind size and direction can easily cause oil film breakdown on the raceway surface, especially on the axial load side (right side in Figure 8), leading to peeling and wear. In the self-aligning roller bearing described in Patent Document 1, a DLC coating is provided on the outer surface of the rollers to improve wear resistance and peel resistance. However, further improvements are needed to further enhance wear resistance under the above-mentioned conditions. In addition, a central flange is provided in the center of the outer surface of the inner ring to improve the guidance accuracy of the rollers. However, wear particles are generated by sliding, which can easily contaminate the grease, and there is room for improvement in suppressing grease degradation.

[0007] This invention has been made in view of the aforementioned problems, and its objective is to provide a self-aligning roller bearing that can improve wear resistance and suppress grease deterioration even in harsh environments. [Means for solving the problem]

[0008] Therefore, the above objective of the present invention is achieved by the following configuration [1] relating to a self-aligning roller bearing. [1] A self-aligning roller bearing comprising: an outer ring having a concave spherical outer ring raceway on its inner circumferential surface; an inner ring having a pair of inner ring raceway surfaces facing the outer ring raceway on its outer circumferential surface; a plurality of spherical rollers arranged in two rows between the outer ring raceway and the inner ring raceway surfaces so as to be rotatable, each having a rolling surface that rolls on the inner ring raceway and the outer ring raceway; a plurality of columnar portions spaced apart in the circumferential direction and extending in the axial direction; an annular rim portion connecting the plurality of columnar portions; and a cage having pockets between adjacent columnar portions capable of rotatably holding each of the plurality of spherical rollers, The retainer is a roller guide type, and the opposing end faces of the two rows of spherical rollers are each supported only by the rim portion. When the central axis of the cage coincides with the central axis of the self-aligning roller bearing, and each spherical roller is positioned at the circumferential center of adjacent columnar portions in the circumferential direction, the shortest radial distance of the cage between the rolling surface of each spherical roller and the circumferential side surface of each columnar portion is H1, and when each spherical roller is furthest from the surface on the inner surface of each pocket that is opposite to the end face of each spherical roller, the shortest radial distance of the cage between the opposing surface and the end face is H2, then H1 ≥ H2 satisfies, At least one of the outer ring, the inner ring, and the spherical roller, Mn: 0.2~1.7% by weight, Si: 0.2~1.2% by weight, Cr:0.2~1.7wt%, Mo: 0.1~0.3% by weight, Ni: Two or more types in 0.1-1.0% by weight, C: 0.4~0.7% by weight, A rolling component alloy steel consisting of the remainder Fe is carburized and quenched to an additional carbon content of 0.35 to 1.0% by weight on the surface and a solid solution carbon content of 0.75 to 1.1% by weight on the surface, resulting in a core hardness of HRC40 to 64. A self-aligning roller bearing is provided on the rolling surface of the spherical roller, wherein the DLC coating portion is mainly composed of at least one of tungsten carbide or silicon carbide and carbon, and has a film thickness of 1 to 2 μm. [Effects of the Invention]

[0009] According to the self-aligning roller bearing of the present invention, wear resistance can be improved even in harsh environments, and the deterioration of the grease can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view of a self-aligning roller bearing according to the first embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional perspective view of the self-aligning roller bearing shown in Figure 1. [Figure 3] Figure 3 shows a view of a part of the retainer from the inner circumference. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a part of the cage. [Figure 5] FIG. 5 is a schematic cross-sectional view exaggerating the size of the gap between the spherical roller and the inner surface of the pocket. [Figure 6] FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 5. [Figure 7] FIG. 7 is a diagram schematically showing the positional relationship of each point arranged on each of these surfaces in order to obtain the radial distance of the cage between the circumferential side surface of the column portion and the rolling surface of the spherical roller. [Figure 8] FIG. 8 is a cross-sectional view showing the structure inside a nacelle of a general wind turbine in which a self-aligning roller bearing is incorporated as a main shaft support bearing.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, a self-aligning roller bearing according to an embodiment of the present invention will be described in detail based on the drawings. As shown in FIGS. 1 and 2, the self-aligning roller bearing 1 of the present embodiment includes an outer ring 10, an inner ring 20, and a plurality of spherical rollers 30 (hereinafter sometimes simply referred to as [rollers]) that are divided into two rows across the axial center line CL and are rotatably arranged between the outer ring 10 and the inner ring 20, and a pair of cages 40 each having a pocket 43 capable of rotatably holding each of the plurality of spherical rollers 30.

[0012] The axial centers C2 of the rollers 30 arranged in two rows are inclined with respect to the central axis (central axes of the outer ring 10 and the inner ring 20) C1 of the self-aligning roller bearing 1. Specifically, in FIG. 1, the axial center C2 of the rollers 30 arranged on the right side is inclined so as to go radially inward as going to the right, and the axial center C2 of the rollers 30 arranged on the left side is inclined so as to go radially inward as going to the left.

[0013] The outer ring 10 is formed with a concave spherical outer ring raceway surface 11 having a single center over the entire width in the inner circumferential surface.

[0014] The inner ring 20 has a pair of concave spherical inner ring raceway surfaces 21, 21 facing the outer ring raceway surface 11, with the axial (left-right direction in Figures 1 and 2) center side being convex, and a nearly flat top surface 22 is formed in the axial center between the two raceway surfaces 21, 21. Furthermore, outward-facing flange-shaped flange portions 23 are formed on the outer circumferential surfaces of both ends of the inner ring, preventing each spherical roller 30 from falling out in the axial direction outward from the space between the inner circumferential surface of the outer ring 10 and the outer circumferential surface of the inner ring 20.

[0015] Each spherical roller 30 is provided in two rows, with multiple rollers in each row, between the outer ring raceway surface 11 and the inner ring raceway surfaces 21, allowing for free movement. The outer surface of the roller 30 has a spherical shape with a larger diameter in the center, forming the outer ring raceway surface 11, the inner and outer ring raceway surfaces 21, and the rolling surface 51 relative to 21. The self-aligning roller bearing 1 has a positive internal clearance, and during use, a load acts on the inner ring 20 downwards in Figures 1 and 2 due to the weight of the rotating shaft fixed inside the inner ring 20. Therefore, the lower side of Figures 1 and 2 is the load area, and the upper side is the unloaded area.

[0016] As shown in Figures 3 and 4, the pair of retainers 40 are independent of each other and are assembled to be rotatable relative to each other. The retainer 40 comprises an annular rim portion 41 positioned approximately in the axial center, and a plurality of column portions 42 extending axially from the axial end of the rim portion 41, spaced apart in the circumferential direction. Thus, each column portion 42 has its base end connected to multiple equally spaced points in the circumferential direction on the axial side surface of the rim portion 41, and its tip is a free end not connected to any other part. A U-shaped pocket 43 is formed by the circumferential side surfaces 42a of each column portion 42 adjacent to each other in the circumferential direction and the axial side surface 41a of the rim portion 41. The spherical roller 30 is rotatably held in the pocket 43.

[0017] Furthermore, the radius of curvature of the generatrix shape of the circumferential side surface 42a of each column portion 42 is slightly larger than the radius of curvature of the generatrix shape of the rolling surface of each spherical roller 30. The axial side surface of the rim portion 41 is formed parallel to the end surface 32 of each spherical roller 30, with each surface facing the other with a small gap between them.

[0018] Furthermore, the circumferential side surface 42a of the tip of each column 42 has a snapping portion 42b, where the distance between opposing circumferential side surfaces 42a is smaller than the maximum diameter of the spherical roller 30, thereby preventing the spherical roller 30 from coming loose in the axial direction. In addition, the circumferential side surface 42a of each column 42 is formed spherically along the generatrix shape of the spherical roller 30 in the portion of the spherical roller 30 that is closer to the tip than the axial middle portion of the spherical roller 30, excluding the snapping portion 42b at the tip, and is formed to partially embrace the spherical roller 30. Note that in Figure 4, the pocket gap between the circumferential side surface 42a of the column portion 42 and the spherical roller 30 is exaggerated, so the distance between opposing snap portions 42b appears to be larger than the maximum diameter of the spherical roller 30. However, in reality, the distance between opposing snap portions 42b is smaller than the maximum diameter of the spherical roller 30.

[0019] Furthermore, a curved relief groove 44 is formed at the joint between the base end of each column 42 and the rim 41, thereby reducing stress concentration at the joint.

[0020] <Regarding the guide for the retainer> In this embodiment, the pair of cages 40 have a gap between the rim portion 41 and the top surface 22 of the inner ring 20, and are configured without a guide ring. That is, the cage 40 is a roller guide type, and the axial side surface 41a of the rim portion 41 is in close proximity to the end face 32 of the spherical roller 30. As a result, the opposing end faces 32 of the two rows of spherical rollers 30 are each supported only by the rim portion 41, and sliding between the guide ring and the end face 32 of the spherical roller 30 and sliding between the guide ring and the cage 40 does not occur, thereby reducing the generation of wear particles, suppressing grease deterioration, and increasing the amount of grease in the bearing space.

[0021] Furthermore, by omitting the guide ring, the axial dimension of the spherical roller 30 can be increased, thereby increasing the load capacity. Also, the increased contact area between the spherical roller 30 and the raceway surface reduces the contact pressure on the spherical roller 30, making it easier for an oil film to form. In addition, by optimizing the cage shape design without the guide ring, the maximum stress of the cage 40 does not increase compared to conventional products, and the thickness of the column section can be reduced. By reducing the thickness of this column section 42, the number of rollers and the roller diameter can be increased, further reducing the contact pressure on the spherical roller 30. The dimensions of the spherical roller 30 can be set to 1.0 × D to 2.0 × D, where D is the maximum diameter of the roller.

[0022] <Relationship between the retainer and spherical rollers: Regarding H1 and H2> Furthermore, in this embodiment, when the central axis O of both cages 40 coincides with the central axis C1 of the self-aligning roller bearing 1, the relationship between the inner surface of each pocket 43 and the rolling surface 31 or end surface 32 of each spherical roller 30 is restricted as follows. First, when each spherical roller 30 is located at the center (neutral position) of adjacent columnar portions 42 in the circumferential direction, H1 is defined as the shortest radial distance (vertical direction in Figures 5 and 6) between the rolling surface 31 of each spherical roller 30 and the circumferential side surface 42a of each columnar portion 42. Also, when each spherical roller 30 is located furthest from the axial side surface 41a of the rim portion 41 (located furthest outward in relation to the axial direction of each spherical roller 30), H2 is defined as the shortest radial distance between the axial side surface 41a of the rim portion 41 and the end surface 32 of each spherical roller 30.

[0023] In Figures 5 and 6, distance H1 is shown as the distance between the radially outer portion of the circumferential side surface 42a of each column 42 and the rolling surface 31 of each spherical roller 30. However, if the distance between the radially inner portion of the circumferential side surface 42a and the rolling surface 31 of each spherical roller 30 is shorter, this distance will be taken as H1. In short, H1 is the distance at which the radial distance between the circumferential side surface 42a of each column 42 and the rolling surface 31 of each spherical roller 30 is shortest. In contrast, distance H2 does not change with radial position because the end face 32 of each spherical roller 30 and the axial side surface 41a of the rim 41 are parallel.

[0024] As described above, given the defined distances H1 and H2, if both retainers 40 are capable of moving from a state where one spherical roller 30 is in contact with the end face 32 or rolling surface 31 of the spherical roller 30 located symmetrically with respect to the central axis O of both retainers 40 (located 180 degrees apart in the circumferential direction) to a state where it is in contact with the end face 32 or rolling surface 31 of the other spherical roller 30, the maximum movement distance for each can be expressed as follows. That is, when each spherical roller 30 is in a neutral position with respect to the circumferential direction, the maximum distance that both retainers 40 can move radially is the distance until the rolling surface 31 of each spherical roller 30 located symmetrically in contact with the circumferential side surface 42a of each column 42. In this case, the radial movement distance of both retainers 40 is 2H1. Furthermore, the maximum distance that both retainers 40 can move radially until the end faces 32 of the spherical rollers 30 located symmetrically with respect to the axial side surface 41a of the rim portion 41 are in contact is reached when each spherical roller 30 is located at its furthest position from the axial side surface 41a of the rim portion 41. In this case, the radially movable distance of both retainers 40 is 2H2. In this embodiment, H1 and H2, expressed in this way, are restricted to satisfying H1 ≥ H2.

[0025] H2, one of H1 and H2, can be calculated using the formula H2 = d / sinα, where d is the axial gap between the end face 32 of each spherical roller 30 and the axial side 41a of the rim 41, and α is the contact angle of the self-aligning roller bearing 1, when each spherical roller 30 is furthest from the axial side 41a of the rim 41. However, it is assumed that the end face 32 of each spherical roller 30 and the direction of the contact angle α (the direction parallel to the line of action L of the contact angle α, the direction pointing to the lower left in Figure 5 and the lower side in Figure 6) are parallel to each other. Therefore, the axial side 41a of the rim 41 and the direction of the contact angle α are parallel to each other. Note that if the above conditions are not met, such as when the end face 32 of each spherical roller 30 and the direction of the contact angle α are not parallel, the above formula cannot be applied to obtain an accurate value. Therefore, in this case, H2 should be determined for each specification of the self-aligning roller bearing.

[0026] Furthermore, H1 is also determined by considering the radius of curvature and contact angle α of the circumferential side surface 42a of each spherical roller 30 and each columnar portion 42. For example, H1 can be determined by the following approximate formula. First, when each spherical roller 30 is in the neutral position, let h be the distance in the direction of the contact angle α between the circumferential side surface 42a of each columnar portion 42 and the rolling surface of each spherical roller 30 in a virtual plane χ that is parallel to the plane that includes the central axis O of the cage 40 and is in the direction in which the cage 40 moves radially (up and down direction in Figure 6). In this case, the radial distance H1 between each surface of the cage 40 is approximated by h / cosα (H1 ≈ h / cosα). This point will be explained with reference to Figure 7, considering the relationship between the spherical roller 30 located in the right column of Figure 5 and on the right side of Figure 6, and the circumferential side surface 42a of the columnar portion 42 that faces the rolling surface of this spherical roller 30. Note that the lengths of H1 and h shown in Figures 5 and 6 have been exaggerated for illustrative purposes. Accordingly, in Figure 5, the relative positions of points P, Q, and q, which will be described below, are shown as being further apart than their actual relative positions. Also, since Figure 6 is a cross-sectional view of VI-VI in Figure 5, h appears to be longer than H1, but in reality, H1 is longer than h.

[0027] Figure 7 is a view from the same direction as Figure 5, schematically showing the relationship between each distance H1 and h. Points P, Q, and q shown in Figures 5 and 7 are located within the virtual plane χ. Point P is located on the circumferential side surface 42a of the column 42 and represents an arbitrary point that contacts the rolling surface of the spherical roller 30 when the cage 40 is moved radially and in the direction of the contact angle α. Point Q is the point where the rolling surface of the spherical roller 30 intersects with a virtual line M passing through point P and parallel to the direction of the contact angle α. That is, it is the point on the rolling surface of the spherical roller 30 that point P contacts when the cage 40 is moved in the direction of the contact angle α. Point q is the point where the rolling surface of the spherical roller 30 intersects with a virtual line N passing through point P and parallel to the radial direction of the cage 40. In other words, when the retainer 40 is moved radially, point P is a point on the rolling surface of the spherical roller 30 that contacts it.

[0028] If we draw a perpendicular line from point q to the imaginary line M, and let the intersection point be r, and let i be the distance between this intersection point r and point P in the direction of the contact angle α, then the distance j from point P to point q is expressed as i / cosα. This distance j corresponds to the radial distance H1 shown in Figures 5 and 6 (j=H1). Therefore, this distance H1 is expressed as i / cosα. Although exaggerated in Figures 5 to 7, in reality the radius of curvature of the spherical roller 30 in the direction of the axial direction of the spherical roller 30 is large between the rolling surface of the spherical roller 30 and the circumferential side surface 42a of the column 42. For this reason, distance i can be approximated as the distance from point P to point Q, i.e., the distance h in the direction of the contact angle α (i≒h). From the above, the radial distance H1 is approximated as h / cosα (H1≒h / cosα).

[0029] Furthermore, as mentioned above, H1 is represented by h because this h can be determined relatively easily from the size of the gap between the side surface of the column 42 and the rolling surface of the spherical roller 30 (the difference in the radii of curvature of both sides), compared to directly determining H1. Also, the approximation formula described above is just one example of a formula for determining H1 and is applicable when the conditions described above are met (or when the conditions are close to these). Therefore, depending on the conditions, the approximation formula may not be applicable. For this reason, H1 is determined by design for each specification of the self-aligning roller bearing 1.

[0030] In the case of the self-aligning roller bearing 1 of this embodiment, configured as described above, when the cage 40 is displaced radially, the axial side surface 41a of the rim portion 41 and the end face 32 of each spherical roller 30 will always come into contact with each other, among the inner surfaces of the pockets 43 of both cages 40. That is, as previously stated, the radial distance that can be moved between the rolling surfaces of each spherical roller 30, which are located symmetrically to each other, and the circumferential side surface 42a of each column portion 42 is 2H1. Also, the radial distance that can be moved between the end face 32 of each spherical roller 30, which are located symmetrically to each other, and the axial side surface 41a of the rim portion 41 is 2H2. In this embodiment, since H1 ≥ H2, when both cages 40 move radially and the inner surfaces of each pocket 43 come into contact with each spherical roller 30, at least the axial side surface 41a of the rim portion 41 and the end face 32 of each spherical roller 30 will come into contact. Therefore, the radial position of both cages 40 is restricted by the engagement between the axial side surface 41a of the rim portion 41 and the end face 32 of each spherical roller 30. In this embodiment, firstly, since the cage 40 is used as a roller guide, the dynamic torque of the self-aligning roller bearing 1 and the amount of heat generated during operation can be reduced compared to cases where an outer ring guide or an inner ring guide is used. Furthermore, by not providing a guide ring, there is no sliding surface between the heads of the spherical rollers 30 and the inner or outer diameter surface of the cage 40, which reduces the amount of wear particles generated between the sliding surfaces and suppresses the deterioration of the grease.

[0031] Furthermore, as described above, the structure restricts the radial position of the cage 40 by the engagement between the end face 32 of each spherical roller 30 and the axial side surface 41a of the rim portion 41. Therefore, even if both cages 40 are displaced radially due to their own weight, the distance between the end face 32 of the spherical roller 30 in the unloaded area and the axial side surface 41a of the rim portion 41 is shortened, effectively suppressing the occurrence of skew in the spherical roller 30 in the unloaded area. In other words, the movement of the spherical roller 30 in the unloaded area is mainly restricted by the cage 40 (in the case of a self-aligning roller bearing 1 having a positive internal clearance, as in this embodiment, the movement of the spherical roller 30 in the unloaded area is restricted almost entirely by the cage 40). Specifically, the spherical roller 30 in the unloaded area revolves by being pushed by the column portions 42 of both cages 40. In contrast, the spherical rollers 30 in the loaded zone are constrained by the outer ring 1 and the inner ring 20, and therefore revolve through rolling contact between the rolling surface of each spherical roller 30 and the outer ring raceway surface 11 and the inner ring raceway surface 21. Consequently, the spherical rollers 30 in the unloaded zone are more affected by both cages 40 than those in the loaded zone, making them more prone to skew.

[0032] Furthermore, in this embodiment, as described above, due to the weight of the rotating shaft fitted inside the inner ring 20, the lower side of the self-aligning roller bearing becomes the load zone, and the upper side becomes the unloaded zone. Consequently, both cages 40 are displaced downward by their own weight, and the end faces 32 of the spherical rollers 30 in the unloaded zone and the axial side surface 41a of the rim portion 41 come into contact or close proximity before skew tends to occur in each spherical roller 30. Therefore, if skew tends to occur in each spherical roller 30 in the unloaded zone, the end faces 32 of each spherical roller 30 come into contact with the axial side surface 41a of the rim portion 41 before the skew becomes large, effectively suppressing the occurrence of skew.

[0033] On the other hand, the downward displacement of both cages 40 causes the end faces 32 of the spherical rollers 30 located in the lower load zone of the self-aligning roller bearing 1 to separate from the axial side surface 41a of the rim portion 41. As a result, the end faces 32 of the spherical rollers 30 located in the load zone and the axial side surface 41a of the rim portion 41 become less likely to come into contact. During operation, the spherical rollers 30 located in the load zone make rolling contact with the inner surface of the pocket 43 that holds each spherical roller 30. Therefore, it is preferable that the end faces 32 of each spherical roller 30 and the axial side surface 41a of the rim portion 41 become less likely to come into contact, as this reduces the contact area between each spherical roller 30 and both cages 40, thereby preventing increased wear of both cages 40 due to rolling contact with each spherical roller 30. Furthermore, as mentioned above, the spherical rollers 30 in the load zone are less prone to skew, so it is not necessary to actively bring the end faces 32 of the spherical rollers 30 in the load zone into contact with the axial side surface 41a of the rim portion 41 in order to prevent this skew.

[0034] In this way, if skew is less likely to occur on each spherical roller 30, the heat generation and vibration caused by skew can be suppressed.

[0035] <Regarding the composition of bearing components> Furthermore, in this embodiment, at least one of the outer ring 10, inner ring 20, and spherical roller 30 is made of alloy steel for rolling parts having a carbon content (base carbon) of 0.4 to 0.7% by weight, and (a) the amount of carburization or carbonitriding of the surface is 0.35 to 1.0% by weight, and (b) the amount of solid dissolved carbon or the sum of solid dissolved carbon and solid dissolved nitrogen on the surface is 0.75 to 1.1% by weight, thereby (c) the hardness of the core is HRC40 to 64.

[0036] It is known that carbon diffuses between iron atoms during heat treatment, resulting in solid solution strengthening. In this case, the carbon dissolved in the austenite at the material surface is composed of carbon originally present in the material (base carbon) and additional carbon that penetrates from the surface due to carburizing. Generally, when additional carbon is used in combination, the diffusion length is shorter compared to when only base carbon is used, resulting in more uniform diffusion and solid solution. That is, if the amount of carburizing is less than 0.35 wt%, diffusion is insufficient and solid solution strengthening is not achieved sufficiently. On the other hand, if it is more than 1.0 wt%, the amount of retained austenite increases, which actually reduces the surface strength. When the amount of carburizing is between 0.35 and 1.0 wt%, C atoms diffuse uniformly into the Fe atoms, resulting in solid solution strengthening with less stress concentration (martensitic transformation with less stress concentration), and a longer rolling fatigue life L10.

[0037] Furthermore, the amount of carbon dissolved in the surface, which is the amount of carbon added to the surface and the amount of carbon initially contained in the alloy steel for rolling parts, is also related to the rolling fatigue life L10. In other words, if the amount of carbon dissolved in the surface is less than 0.75% by weight, the strength of the surface layer will be insufficient, and if it is more than 1.45% by weight, there will be a lot of retained austenite on the surface after heat treatment, which will actually decrease the strength of the surface layer. As a result, the rolling fatigue life L10 will be lower compared to conventional carburized steel bearings, and the carburizing time will be unnecessarily prolonged.

[0038] In this embodiment, an alloy steel for rolling parts is used, and (a) the surface is carburized or carbonitrided by 0.35 to 1.0% by weight. Compared to the method of quenching an alloy steel that contains carbon from the beginning, the solid solution of C (or N) in the austenite becomes more uniform, resulting in uniform solid solution strengthening of the surface layer after quenching. As a result, there are fewer sources of stress concentration, and resistance to rolling fatigue is provided. (b) By setting the amount of solid-solution carbon in the surface or the sum of the amount of solid-solution carbon and solid-solution nitrogen to 0.75 to 1.1% by weight, a rolling bearing with high surface hardness is obtained while ensuring that retained austenite is appropriate and that the high toughness of retained austenite helps to mitigate strain accumulation.

[0039] Furthermore, among the components of alloy steel for rolling parts, Mn, Si, Ni, Mo, and Cr all contribute to improved hardenability. In particular, Mn readily forms retained austenite, Si increases the strength of the matrix structure, Cr provides wear resistance, Mo provides toughness, and Ni provides impact resistance.

[0040] Each of the numerical limitations for the composition of alloy steel for rolling parts has the following critical significance. The carbon content in alloy steel for rolling components serves as base carbon. If it is less than 0.4 wt%, the carburizing time required to achieve the desired hardness increases, and the diffusion length of dissolved carbon in the austenite lengthens. As a result, the state of carbon in the austenite becomes non-uniform, creating stress concentration points and reducing the rolling fatigue life L10. On the other hand, if it is greater than 0.7 wt%, the amount of dissolved carbon in the austenite becomes excessive, resulting in increased residual austenite after quenching and a decrease in surface hardness. 0.4 to 0.7 wt% is the appropriate value for the core hardness to approach the surface hardness, and as will be explained later, it is also within the range where the rolling fatigue life L10 is longer than that of conventional carburized steel bearings, and the carburizing time can be shortened. In particular, 0.45 to 0.70 wt% is the optimal value.

[0041] Manganese (Mn) is present in amounts of 0.2% by weight or more, serving as a component that improves hardenability and as a deoxidizing agent during melting and refining. However, if the amount exceeds 1.7% by weight, the amount of retained austenite increases, reducing the machinability and hot workability of the steel.

[0042] A silicon (Si) content of 0.2% by weight or more contributes to improved hardenability and deoxidation. However, if the Si content exceeds 1.2% by weight, the surface decarburizes during heat treatment, and ferrite increases in the core, reducing press formability, cold forgeability, and mechanical properties. When the Si content is within the appropriate range of 0.2 to 1.2% by weight, the crush value also improves, and it contributes to an improvement in rolling fatigue life L10.

[0043] Chromium (Cr), at a concentration of 0.2% by weight or more, is significant as an ingredient that improves hardenability, carburization, wear resistance, and mechanical properties. However, if the Cr content exceeds 1.7% by weight, excessive carburization occurs, increasing the amount of retained austenite and granular carbides, making the carburized and quenched layer brittle.

[0044] Molybdenum (Mo) at a concentration of 0.1% by weight or more enhances hardenability and imparts toughness. However, if the Mo content exceeds 0.3% by weight, it leads to excessive carburization, increasing the amount of retained austenite in the carburized layer. Furthermore, to achieve further improvements in hardenability, it is more economical to use C, Si, Mn, or Cr instead.

[0045] Nickel (Ni), at a concentration of 0.1% by weight or more, improves hardenability and enhances impact resistance by homogenizing the hardened structure. However, from the perspective of improving hardenability, increasing the Ni content to 1.0% by weight or more is uneconomical; it is more economical to use C, Si, Mn, or Cr instead.

[0046] In this embodiment, it is necessary to effectively include two or more of manganese, silicon, chromium, molybdenum, and nickel in order to bring the rolling fatigue life L10 to the same level as that of conventional carburized steel bearings.

[0047] Incidentally, as mentioned above, the main shaft bearings of wind turbines rotate at a low speed of 10 to 20 min-1, making it difficult for a sufficient oil film to form. In this case, foreign matter and wear particles that have entered the lubricating oil can become trapped on the raceway surface, potentially degrading the surface properties and leading to wear and delamination.

[0048] The inventors continued their research to obtain bearings with a long rolling fatigue life even under the aforementioned foreign matter contamination conditions, and as a result, they found that the amount of retained austenite affects the length of the bearing life. Specifically, they found that bearings with an extremely long lifespan were found when the amount of retained austenite was in the range of 25 to 45 volume percent. This can be understood as follows.

[0049] Under conditions of foreign matter contamination, surface cracks that form at the edges of indentations caused by the foreign matter often spread, eventually leading to fatigue failure. If the retained austenite content is 25 volume percent or more, even if an indentation is formed, the edges of the indentation are rounded as the rolling elements roll over it, resulting in reduced stress concentration and suppression of edge loading. On the other hand, if the retained austenite content exceeds 45 volume percent, it has a counterproductive effect on L10 because retained austenite is not inherently strong.

[0050] The amount of retained austenite is closely related to the amount of dissolved carbon (or dissolved carbon and nitrogen). The amount of dissolved carbon or the sum of dissolved carbon and dissolved nitrogen (hereinafter collectively referred to as "equivalent dissolved carbon") required to achieve an optimal amount of retained austenite of 25-45 volume% for L10 is 0.85-1.1% by weight.

[0051] Furthermore, the two or more elements and their amounts contained in the alloy steel for the rolling components used in the self-aligning roller bearing 1 also affect the amount of retained austenite. (γ R The relationship between ) and the Ms point is shown by equation (1) proposed by D.P. Koistinen. γ R =e a(Ms-Tq) (vol%)……(1) a = -1.1 × 10 -2 Tq = Quenching oil temperature (°C)

[0052] Furthermore, the influence of the elements and amounts added to the alloy steel on the Ms point can be shown, for example, by equation (2). Ms(℃)=538-317×(%C)-33×(%Mn)-28×(%Cr) -17×(%Ni)-11×(%Si+%Mo+%W)……(2) % represents weight percentage

[0053] From equations (1) and (2), suitable additive elements and their amounts are as follows: for Mn-Cr systems, Mn 1.2-1.7 wt% and Cr 0.2-0.6 wt%; for Mn-Cr-Ni systems, Mn 1.0-1.5 wt%, Cr 0.3-0.6 wt% and Ni 0.5-10 wt%; for Mn-Cr-Si systems, Mn 0.5-1.0 wt%, Cr 0.3-0.6 wt% and Si 0.8-1.2 wt%; and for Mn-Si systems, Mn 1.2-1.7 wt% and Si 0.8-1.2 wt%.

[0054] Under the above-mentioned preferred additive element amount conditions and preferred solid solution equivalent carbon amount conditions, an appropriate amount of retained austenite (γ R ) γ is approximately the median of 25-45 volume% R A self-aligning roller bearing 1 is provided that yields a large quantity of material, and in particular precipitates a large amount of fine carbides and nitrides, thereby providing a long lifespan even under foreign matter contamination, as well as improved wear resistance and seizure resistance.

[0055] <DLC coating on rolling surfaces> Furthermore, a DLC coating portion 33 is provided on the rolling surface 31 of the spherical roller 30 (see Figure 4). The DLC coating portion 33 is mainly composed of at least one of tungsten carbide (WC) or silicon carbide (SiC) and carbon (C), with a film thickness of 1 to 2 μm.

[0056] This reduces the frictional force when the outer ring raceway surface 11 of the outer ring 10 and the inner ring raceway surface 21 of the inner ring 20 come into contact with the spherical roller 30, thereby preventing contact between the steel materials and thus preventing peeling and wear.

[0057] While a thicker DLC coating 33 extends the wear life, if it is thicker than 2 μm, residual stress within the DLC coating 33 increases, making the coating more prone to peeling. Since the DLC coating 33 is harder than the raceway surface 5 of the inner ring 3 and the raceway surface 9 of the outer ring 7, there is a greater concern about peeling than wear. Therefore, by limiting the film thickness of the DLC coating 33 to 1-2 μm, peeling of the DLC coating 33 can be prevented, and the effect of the DLC coating 33 can be sustained.

[0058] In this embodiment, for example, the outer ring 10 and inner ring 20 are made of the aforementioned alloy steel for rolling parts that has been carburized and hardened, and the spherical rollers 30 on which the DLC coating portion 33 is formed are made of high-carbon chromium steel or the like as the base material.

[0059] As described above, the self-aligning roller bearing 1 of this embodiment can improve wear resistance and suppress grease deterioration even in harsh environments.

[0060] It should be noted that the present invention is not limited to the embodiments described above, and can be modified or improved as appropriate.

[0061] In this embodiment, the cage 40 for holding one row of spherical rollers 30 and the cage 40 for holding the other row of spherical rollers 30 are made independent of each other, allowing for relative rotation. Therefore, even if there is a difference in the orbital speed of the spherical rollers 30 in the two rows, the cages 40 holding the spherical rollers 30 in both rows rotate independently. That is, in the self-aligning roller bearing 1, one row of spherical rollers 30 is often operated with a larger load supported by the other row. In this case, a difference in the orbital speed of the spherical rollers 30 in the two rows occurs. In this embodiment, in such cases, since the cages 40 holding the spherical rollers 30 in both rows rotate independently, the spherical rollers 30 in the row with a faster orbital speed do not drag the spherical rollers 30 in the row with a slower orbital speed, nor do the spherical rollers 30 in the row with a slower orbital speed apply braking to the orbital motion of the spherical rollers 30 in the row with a faster orbital speed. As a result, dynamic torque and heat generated during operation can be kept low.

[0062] On the other hand, the retainer 40 of the present invention is not limited to that of this embodiment, and an integrated type may be used. That is, in an integrated type retainer, the multiple columnar portions 42, which are divided into two rows, extend axially from both axial sides of the annular rim portion 41, spaced apart in the circumferential direction. In addition, each pocket 43 of the retainer 40 is formed so as to be offset by half a pitch in the circumferential direction between each row of rollers, and the rollers 30 of each row are arranged alternately (staggered) in the circumferential direction with respect to the rim portion 41.

[0063] In this case, if there is a difference in the orbital speed of the spherical rollers 30 in the two rows, there is concern that the difference between the orbital speed of the spherical rollers 30 in the faster row and the orbital speed of the spherical rollers 30 in the slower row may affect the rotation of the retainer 40. However, if an integrated retainer 40 is used and there is a difference in the orbital speed of the spherical rollers 30 in the two rows, as mentioned above, if the pocket gap is designed to absorb the difference in the orbital speed of each spherical roller 30 within a range of approximately 0.4 to 2% of the maximum diameter of each spherical roller 30, the effect of this difference in orbital speed on the rotation of the retainer 4f can be reduced.

[0064] Furthermore, the present invention is not limited to the embodiments described above, and can be modified, improved, etc., as appropriate.

[0065] As described above, the following matters are disclosed in this specification: (1) A self-aligning roller bearing comprising: an outer ring having a concave spherical outer ring raceway on its inner circumferential surface; an inner ring having a pair of inner ring raceway surfaces facing the outer ring raceway on its outer circumferential surface; a plurality of spherical rollers arranged in two rows between the outer ring raceway and the inner ring raceway surfaces so as to be rotatable, each having a rolling surface that rolls on the inner ring raceway and the outer ring raceway; a plurality of columnar portions spaced apart in the circumferential direction and extending in the axial direction; an annular rim portion connecting the plurality of columnar portions; and a cage having pockets between adjacent columnar portions capable of rotatably holding each of the plurality of spherical rollers, The retainer is a roller guide type, and the opposing end faces of the two rows of spherical rollers are each supported only by the rim portion. When the central axis of the cage coincides with the central axis of the self-aligning roller bearing, and each spherical roller is positioned at the circumferential center of adjacent columnar portions in the circumferential direction, the shortest radial distance of the cage between the rolling surface of each spherical roller and the circumferential side surface of each columnar portion is H1, and when each spherical roller is furthest from the surface on the inner surface of each pocket that is opposite to the end face of each spherical roller, the shortest radial distance of the cage between the opposing surface and the end face is H2, then H1 ≥ H2 satisfies, At least one of the outer ring, the inner ring, and the spherical roller, Mn: 0.2~1.7% by weight, Si: 0.2~1.2% by weight, Cr:0.2~1.7wt%, Mo: 0.1~0.3% by weight, Ni: Two or more types in 0.1-1.0% by weight, C: 0.4~0.7% by weight, A rolling component alloy steel consisting of the remainder Fe is carburized and quenched to an additional carbon content of 0.35 to 1.0% by weight on the surface and a solid solution carbon content of 0.75 to 1.1% by weight on the surface, resulting in a core hardness of HRC40 to 64. A self-aligning roller bearing is provided on the rolling surface of the spherical roller, wherein the DLC coating portion is mainly composed of at least one of tungsten carbide or silicon carbide and carbon, and has a film thickness of 1 to 2 μm. This configuration allows for improved wear resistance and suppression of grease degradation, even in harsh environments.

[0066] (2) A self-aligning roller bearing as described in [1], for supporting the main shaft of a wind turbine. With this configuration, the self-aligning roller bearing of the present invention can be suitably used for supporting the main shaft of a wind turbine. [Explanation of Symbols]

[0067] 1 Self-aligning roller bearing 10 Outer ring 11 Outer ring raceway 20 Inner circle 21 Inner ring raceway surface 30 spherical rollers 31 Rolling surface 33 DLC coating part 40 Retainer 42 Pillar part 42 43 pockets

Claims

1. A self-aligning roller bearing comprising: an outer ring having a concave spherical outer ring raceway on its inner circumferential surface; an inner ring having a pair of inner ring raceway surfaces facing the outer ring raceway on its outer circumferential surface; a plurality of spherical rollers arranged in two rows between the outer ring raceway and the inner ring raceway surfaces so as to be rotatable, each having a rolling surface that rolls on the inner ring raceway and the outer ring raceway; a plurality of columnar portions spaced apart in the circumferential direction and extending in the axial direction; an annular rim portion connecting the plurality of columnar portions; and a cage having pockets between adjacent columnar portions capable of rotatably holding each of the plurality of spherical rollers; The aforementioned retainer is a roller guide type, and the opposing end faces of the two rows of spherical rollers are each supported only by the rim portion. When the central axis of the cage coincides with the central axis of the self-aligning roller bearing, and each spherical roller is positioned at the circumferential center of adjacent columnar portions in the circumferential direction, the shortest radial distance of the cage between the rolling surface of each spherical roller and the circumferential side surface of each columnar portion is H1, and when each spherical roller is furthest from the surface on the inner surface of each pocket that is opposite to the end face of each spherical roller, the shortest radial distance of the cage between the opposing surface and the end face is H2, then H1 ≥ H2 satisfies, At least one of the outer ring, the inner ring, and the spherical roller, Mn: 0.2 to 1.7% by weight, Si: 0.2 to 1.2% by weight, Cr: 0.2 to 1.7% by weight, Mo: 0.1 to 0.3% by weight, Ni: Two or more types in a weight of 0.1 to 1.0%, and C: 0.4 to 0.7% by weight, A rolling component alloy steel consisting of the remainder Fe is carburized and quenched to an additional carbon content of 0.35 to 1.0% by weight on the surface and a solid solution carbon content of 0.75 to 1.1% by weight on the surface, resulting in a core hardness of HRC 40 to 64. A self-aligning roller bearing is provided on the rolling surface of the spherical roller, wherein the DLC coating portion is mainly composed of tungsten carbide or silicon carbide and carbon, and has a film thickness of 1 to 2 μm.

2. A self-aligning roller bearing according to claim 1, for use in supporting the main shaft of a wind turbine.

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