Roller bearing and manufacturing method for pin-type cages

Abstract

A roller bearing includes an outer ring defining an outer raceway, an inner ring defining an inner raceway, and a plurality of rolling elements (122). The rolling elements (122) provide a rolling interface between the inner raceway and the outer raceway. A cage of the bearing assembly extends between the inner ring and the outer ring, the cage having a plurality of pins. Each one of the plurality of pins extends into a corresponding opening (136) formed through the center of one of the plurality of rolling elements, the plurality of pins being spaced to separate the plurality of rolling elements from one another. The opening (136) in each of the plurality of rolling elements (122) is formed to include, along an axial lengthwise span thereof, a first end contact region (136A) for the pin, a central enlarged portion (136B), and a second end contact region (136A) for the pin.

Description

ROLLER BEARING AND MANUFACTURING METHOD FOR PIN-TYPE CAGESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 586,917, filed on September 29, 2023, the entire contents of which are incorporated by reference herein.BACKGROUND

[0002] Roller bearings are provided with a plurality of rollers (or “rolling elements”) dispersed about a rotational axis of the roller bearing. Many such roller bearings utilize a cage (or “retainer”) to maintain roller-to-roller spacing. Among the various types of cages, there are pin-type cages such as those depicted in U.S. Patent No. 9,127,719 or Japanese Patent Application Publication No. 2003-269467. The pin-type cage comprises two annular plates or rings with pins extending between the two plates. The rollers comprise respective holes into which the pins of the cage are inserted. The pin-to-hole contact provides the forces that guide the rollers and support the weight of the cage structure and the unloaded rollers.SUMMARY

[0003] The friction and wear generated by the contact between the cage pin and the roller hole may damage the contact surfaces and reduce rotational speed of the unloaded rollers. As the bearing turns, the unloaded rollers lose rotational speed and then regain rotational speed as they become loaded. During the acceleration, the traction forces and slippage damage the rolling contact surfaces. Increased accuracy and reduced roughness of the pin and hole reduce the frictional losses which slow the rollers. The long, slender shape and high hardness of the hole make the process of hole finishing difficult and expensive. This invention reduces the difficulty and expense of this process while improving the performance of the bearing.

[0004] Aspects of the invention may be applied in large tapered roller bearings and cylindrical roller bearings used in, among other applications, metal rolling mills that commonly apply pin-type cage to prevent roller-to-roller contact.

[0005] In one aspect, the invention provides a roller bearing comprising an outer ring defining an outer raceway, an inner ring defining an inner raceway, and a plurality of rolling elements. The rolling elements provide a rolling interface between the inner raceway and the outer raceway such that the outer ring is rotatable relative to the inner ring about a rotational axis. A cage of the bearing assembly extends around the inner ring at a location between the inner ring and the outer ring, the cage having a plurality of pins. Each one of the plurality of pins extends into a corresponding opening formed through the center of one of the plurality of rolling elements, the plurality of pins being spaced to separate the plurality of rolling elements from one another. The opening in each of the plurality of rolling elements is formed to include, along an axial lengthwise span thereof, a first end contact region for the pin, a central enlarged portion, and a second end contact region for the pin.

[0006] In another aspect, the invention provides a method of manufacturing rolling elements for a roller bearing having a plurality of rolling elements retained by a pin-type cage. A rolling element is provided with an outer cylindrical rolling surface, a first axial end, and a second axial end. A central hole is formed through the rolling element, between the first and second axial ends, the central hole including along an axial lengthwise span thereof, a central zone and end zones flanking the central zone. A finished surface of the central zone is created in a step of soft machining prior to heat treat hardening. A finished surface of the end zones is created in a discrete step of hard machining following the heat treat hardening.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 A is a perspective view of a roller bearing including a pin-type cage according to the prior art.

[0008] FIG. IB is a perspective view of one set of rollers and the pin-type cage removed from the roller bearing of FIG. 1A.

[0009] FIG. 2 is a cross-section taken along line 2 — 2 of FIG. 1 through one of the rollers of the prior art roller bearing.

[0010] FIG. 3 is a cross-section taken through a roller according to one embodiment of the present disclosure.

[0011] FIG. 4 is a cross-section taken through a roller according to another embodiment of the present disclosure.DETAILED DESCRIPTION

[0012] Before any embodiments are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0013] With reference to FIGS. 1A and IB, a roller bearing 10 includes an inner race 14, an outer race 18, and a plurality of rolling elements (or “rollers” 22) situated between the inner and outer races 14, 18. The rollers 22 provide rolling support about a central axis A between the inner and outer races 14, 18. As shown in FIG. 1A, the roller bearing 10 can include multiple inner races 14, multiple outer races 18, and multiple sets of rollers 22 along the axial direction. However, the invention is not limited to the particular configuration of FIG. 1A, and features described below can be incorporated into any number of various bearing configurations. As shown in FIGS. 1 A and 1 B, the roller bearing 10 includes a pin-type cage 26 to maintain roller- to-roller spacing. As known in the art, the pin-type cage 26 includes two end plates or flange rings 28 spaced apart axially to span the set of rollers 22 and aligned with one another. The flange rings 28 are connected to each other by pins 32 that extend through corresponding holes 36 in the respective rollers 22. The roller holes 36, which are described in particular detail below, are through holes provided axially, along a roller axis Al (FIG. 2), through the center of each of the rollers 22.

[0014] Referring to FIG. 2, one of the rollers 22 of the roller bearing 10 is isolated and shown in cross-section. As is conventional, the roller 22 is drilled to form the hole 36 as a cylindrical opening in an unhardened condition of the metal of the roller 22. The original cylindrical opening is not shown. The roller 22 is then hardened (via heat treatment). The originally-cylindrical surface of the hole 36 is distorted by the hardening process. For example, the shape of the hole 36 may distort into a barrel shape as illustrated by the solid line 40. In otherconstructions, the shape of the hole 36 may distort into the opposite shape in which the central portion has a smaller diameter than the end portions. The aim of the prior art is to provide the hole 36 with a cylindrical surface after hardening (i.e., surface 44 in FIG. 2), and this is accomplished by grinding or honing to remove a large amount of stock 48 from the distorted bore shape of the hole 36. In other words, the metal is removed so that the hole 36 is defined by the surface 44 rather than the original surface 40 that was created pre-hardening and then deformed. Although the depiction of the distortion is exaggerated in the drawing, the machining of the hole 36 post-hardening, in order to obtain the finished cylindrical surface 44, is carried out on the entirety or nearly the entirety of the length of the roller 22.

[0015] FIG. 3 illustrates a roller 122 and manufacturing method embodying aspects of the present disclosure as an improvement to the roller structure and manufacturing method of FIG. 2 described above. The roller 122 is compatible with the roller bearing 10 or others having a pintype cage. The roller 122 is drilled to form a hole 136 as a cylindrical opening in an unhardened condition of the metal. Similar to the above description of FIG. 2, the roller 122 of FIG. 3 is hardened via heat treatment, and the hardened roller hole 136 has a non-cylindrical shape due to heat treat distortions as illustrated by the solid line 140. The original cylindrical opening is not shown. The finishing process such as grinding removes a small amount of stock 148 providing a division of the hole 136 into cylindrical end regions or zones 136A, at each end of the opening 136, and a larger center portion or zone 136B towards the middle length of the opening 136. In particular, the machining of the hole 136 after heat treating can be limited to the end zones 136A. The small stock removal and shorter length of the finished sections (end zones 136A) substantially reduce the time to produce an accurate contact surface(s) for the cylindrical pin 32 of the cage 26. The center zone 136B can define a non-contact region where the cylindrical pin 32 does not make contact with the hole 136. The center zone 136B can provide a reservoir of lubricant for the pin-to-hole contact that occurs within the end zones 136A. Within the opening 136 of the roller 122, two separate geometry zones (i.e., the end zones 136A having one geometry and the center zone 136B having a different geometry) are created in at least two discrete steps: soft machining and hard machining.

[0016] FIG. 4, illustrates a roller 222 and manufacturing method embodying aspects of another embodiment of the present disclosure. Similar to the roller 122 of FIG. 3, the roller 222has two separate geometry zones (i.e., ends 236A and center 236B) created in at least two discrete steps: soft machining and hard machining. However, the first step machines the hole 236 in the unhardened state to a non-cylindrical shape, rather than a cylindrical one. For example, the opening 236 can have two cylindrical end zones 236A along with a slightly enlarged curved center zone 236B (e.g., concave or barrel-shaped, like the shape of the unfinished hole of the roller 122 after heat treating distortion shown in FIG. 3). The machining of the different zones 236A, 236B having different diameters prior to hardening can be accomplished by boring in which the roller 222 is rotated (e.g., on a lathe) and a cutting tool is manipulated inside the roller 222. The second step removes exclusively end zone stock 248 in the hardened state that produces the cylindrical end zones 236A.

[0017] For both FIG. 3 and FIG. 4, the resulting final shape is the two spaced-apart, cylindrical end zones along with a relieved, curvilinear center zone therebetween. The original soft-machined surface (now shape-distorted by heat treating) remains in the center section. In the end zones 136A, 236A, the original shape is altered by the hard-machining - i.e., stock removal after heat treating. In some constructions, the maximum diameter of the center zone 136B, 236B is more than 1% greater (e.g., about 2% greater) in diameter than the end zones 136A, 236A (finished dimensions). The center zone 136B, 236B may have a substantially circular form (i.e., constant radius Rl) in a radial cross-section plane. The center zone 136B, 236B may extend 40% or more (e.g., about 50%) of the axial lengthwise span of the opening 136, 236 (i.e., the length of the roller 122, 222). As such, the two end zones 136A, 236A combine to make up less than 60% of the axial lengthwise span of the opening 136, 236. In other constructions (e.g., due to variance in heat treat distortion), the center zone 136B, 236B may extend 10% or more of the axial lengthwise span of the opening 136, 236, corresponding to the two end zones 136A, 236A combining to make up less than 90% of the axial lengthwise span of the opening 136, 236. Each end zone 136A, 236A can have a surface roughness Ra of less than 0.3 pm for good frictional level. The center zone 136B, 236B may have a substantially higher surface roughness measure Ra than the end zones 136A, 236A. The center zone 136B, 236B can have a surface roughness Ra less than 3 pm for resistance to fatigue cracking. There are many alternative soft machining options for shape: combinations of radii, straight, and tapered surfaces can be used to provide the two distinct types of finished zones 136A and 136B or 236A, 236B within the respective roller 122, 222.

[0018] It should be noted that a bearing may be constructed with rollers of various geometries, at least some of which conform to the features of the preceding embodiments. In some constructions, a bearing may include rollers that vary in final geometry due to the variance in distortion that occurs during heat treatment. While a bearing may include a plurality of rollers that fall within the scope of the present disclosure, the same bearing may include one or more additional rollers that do not fall within the scope of the present disclosure. Such rollers may not individually enjoy all the benefits provided by the present disclosure. In some constructions, a majority of the rollers within a bearing may conform to aspects of the above described embodiments. In other constructions, all of the rollers within a bearing may conform to aspects of the above described embodiments.

[0019] Although some aspects have been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects as described. Various features and advantages of the invention are set forth in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A roller bearing comprising: an outer ring defining an outer raceway; an inner ring defining an inner raceway; a plurality of rolling elements providing a rolling interface between the inner raceway and the outer raceway such that the outer ring is rotatable relative to the inner ring about a rotational axis; and a cage extending around the inner ring at a location between the inner ring and the outer ring, the cage having a plurality of pins, wherein each one of the plurality of pins extends into a corresponding opening formed through the center of one of the plurality of rolling elements, the plurality of pins being spaced to separate the plurality of rolling elements from one another, wherein the opening in each of the plurality of rolling elements is formed to include, along an axial lengthwise span thereof, a first end contact region for the pin, a central enlarged portion, and a second end contact region for the pin.

2. The roller bearing of claim 1, wherein, in each of the plurality of rolling elements, the central enlarged portion makes up at least 10% of the axial lengthwise span.

3. The roller bearing of claim 1, wherein, in each of the plurality of rolling elements, the central enlarged portion makes up at least 40% of the axial lengthwise span.

4. The roller bearing of claim 1, wherein, in each of the plurality of rolling elements, the central enlarged portion has a maximum diameter greater than a diameter of the first and second end regions by more than 0.5% and less than 5%.

5. The roller bearing of claim 1, wherein, in each of the plurality of rolling elements, the central enlarged portion has a constant radius in a section plane containing a roller axis that extends along the center of the opening.

6. The roller bearing of claim 1, wherein, in each of the plurality of rolling elements, the first and second end contact regions have a roughness less than 0.3 gm Ra, and the central enlarged portion has a roughness greater than 0.3 pm Ra.

7. The roller bearing of claim 1, wherein the plurality of rolling elements having the central enlarged portion and the first and second end contact regions make up less than all of the rolling elements of the roller bearing.

8. The roller bearing of claim 1, wherein the plurality of rolling elements having the central enlarged portion and the first and second end contact regions make up all of the rolling elements of the roller bearing.

9. The roller bearing of claim 1, wherein the plurality of rolling elements , the roller bearing further comprising an additional plurality of rolling elements providing a rolling interface between the inner raceway and the outer raceway, the additional plurality of rolling elements each having an opening that receives a corresponding one of an additional plurality of pins of the cage, wherein each of the opening of each of the additional plurality of rolling elements has a cylindrical shape along an entire axial lengthwise span thereof.

10. A method of manufacturing rolling elements for a roller bearing having a plurality of rolling elements retained by a pin-type cage, the method comprising: providing a rolling element with an outer cylindrical rolling surface, a first axial end, and a second axial end; and forming a central hole through the rolling element, between the first and second axial ends, wherein the central hole includes along an axial lengthwise span thereof, a central zone and end zones flanking the central zone, wherein a finished surface of the central zone is created in a step of soft machining prior to heat treat hardening, and a finished surface of the end zones is created in a discrete step of hard machining following the heat treat hardening.

11. A method of manufacturing a roller bearing including a pin-type cage and a set of rolling elements distributed in a circumferential array, wherein at least some of the set of rolling elements are manufactured by the method of claim 10.

12. The method of claim 10, further comprising finishing only the end zones to a roughness less than 0.3 pm Ra.

13. A method of manufacturing a roller bearing including a pin-type cage and a set of rolling elements distributed in a circumferential array, wherein at least some of the set of rolling elements are manufactured by the method of claim 12.

14. The method of claim 10, wherein the step of hard machining the finished surface of the end zones includes machining to a diameter less than a maximum diameter of the finished surface of the central zone.

15. A method of manufacturing a roller bearing including a pin-type cage and a set of rolling elements distributed in a circumferential array, wherein at least some of the set of rolling elements are manufactured by the method of claim 14.

16. The method of claim 10, wherein the hard machining following the heat treat hardening to create the finished surface of the end zones includes machining less than 90% of the axial lengthwise span of the central hole.

17. A method of manufacturing a roller bearing including a pin-type cage and a set of rolling elements distributed in a circumferential array, wherein at least some of the set of rolling elements are manufactured by the method of claim 16.

18. The method of claim 16, wherein the hard machining following the heat treat hardening to create the finished surface of the end zones includes machining less than 60% of the axial lengthwise span of the central hole.

19. A method of manufacturing a roller bearing including a pin-type cage and a set of rolling elements distributed in a circumferential array, wherein at least some of the set of rolling elements are manufactured by the method of claim 18.

20. The method of claim 10, wherein the step of soft machining to create the finished surface of the central zone includes machining the central zone with a non-cylindrical barrel shape.

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