Roller bearing cage and method of forming same

Abstract: A flat strip of metal is formed to provide a depressed centre relief portion (40) between two edge portions. Depressions (48) are formed in the two edge portions (32, 34) and centre slots (38) are pierced across the centre relief portion such that roller receiving slots (38) are formed with slot end depressions (48) at both ends of the roller receiving slots. The partially formed bearing cage is then formed into a circular hoop such that the edge portions form rings at the axial ends of the circular hoop.

Description: This invention relates generally to a method of forming a roller bearing cage and, more particularly, to a roller bearing cage of "sigma" configuration. Roller bearings commonly employ separators, retainers or cages to maintain separation and alignment of the rollers. Although the terms are frequently used interchangeably, the term "cage" is often used to describe a device that retains the rollers both radially and axially. Thus, a roller bearing cage prevents rollers from moving axially or radially out of the cage, allowing the cage and rollers to be handled as a bearing subassembly. One particular type of roller bearing cage is known as a sigma cage. Referring firstly to Figure 1, which is an isometric view illustrating a known roller bearing sigma cage, a typical sigma cage 10 has annular end rims 12 and 14, axially spaced apart along a common axis, joined together by crossbars 16 to form slots 18 for receiving rollers, not shown. The crossbars 16 have a central portion 20 offset radially inwardly from laterally outward portions 22 and 24 such that, when viewed in longitudinal section, the end rims 12 and 14 and crossbars 16 resemble the Greek letter "sigma". The end rims 12 and 14 extend radially as end flanges 26 and 28, respectively. The end flanges 26 and 28 provide stop surfaces which assist the slots 18 to ensure that axial movement of the rollers is restricted. Edge surfaces on the central portion 20 prevent radially inward movement of the rollers and edge surfaces of the laterally outward portions 22 and 24 prevent radially outward movement of the rollers US-A-5 255 985 discloses a method of forming roller bearing cage in accordance with the preamble of claim 1. In some applications, a significant axial offset is required between the roller pockets (slots) and the end flanges of the cage. Such offset materially affects the axial containment of the rollers because the end flanges no longer provide stop surfaces proximate to the slots. As a result, roller loss can occur during handling of the cage before installation or upon installation of the bearing in the housing. According to the present invention, there is provided a method for forming a roller bearing cage, the method comprising the steps of forming a flat strip of metal such that a centre relief portion is offset with respect to two edge portions that lie within a plane, piercing centre slots across the centre relief portion to form crossbars and roller receiving slots such that a partially formed bearing cage is formed, forming the partially formed bearing cage into a circular hoop, having an axis such that the edge portions form rings at axial ends of the circular hoop, and forming abutment surfaces at the ends of each roller receiving slot such that rollers located within the respective roller receiving slots are retained in the axial direction by engagement with said abutment surfaces; characterised that, in order to form said abutment surfaces, slot end depressions are formed in the material of said two edge portions, whereby the edges of said slot end depressions form said abutment surfaces for the rollers. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to Figures 2 to 5 of the accompanying drawings, in which:- Figure 2 is an isometric view illustrating an embodiment of the present roller bearing cage; Figure 3 is a sectional view of two roller bearing cages of Fig. 2, as indicated by reference line 3-3, as installed in an elongate bearing housing having a cross drilled lubrication hole; Figure 4 is a diagram illustrating outlines of multiple punches that may be used to pierce slots of the bearing cage of Figure 2; and Figure 5 is a sectional view of a roller bearing cage illustrating a second embodiment of the present roller bearing cage. Referring now to Figures 2 to 5 of the drawings, Figure 2 illustrates a preferred embodiment of roller bearing cage 30 of the present invention having end rims 32 and 34, axially spaced apart along a common axis, joined together by crossbars 36 to form slots 38 for receiving rollers, not shown. The crossbars 36 have a central portion 40 offset radially inwardly from laterally outward portions 42 and 44. The cage 30 is considered a sigma cage because the end rims 32 and 34 and crossbars 36 suggest the Greek letter "sigma" when the cage is viewed in longitudinal section. Unlike the roller bearing cage of Figure 1, the roller bearing cage 30 has depressed slot ends designed to abut end surfaces of bearing rollers received within the slots 38. Abutment surfaces 46 are formed by periodic depressions 48, one at each end of the roller receiving slots 38, to prevent escape of the bearing rollers, especially in the absence of close proximity bearing cage flanges. Specifically, axial movement of the bearing rollers in both axial directions is limited by engagement of the abutment surfaces 46 by the bearing rollers. In the particular embodiment shown, the abutment surfaces 46 have a curved profile, curved with a circular arc or otherwise, along a transverse section of the bearing cage 30. The depressions 48 are dimple-like recesses having a substantially angular longitudinal section and a substantially conical configuration. However, the depressions 48 may be of various shapes, depending on the shape of tooling used to form the recesses, as described below. The end rims 32 and 34 are annular and comprise axially extending side portions 50 and flange side portions 52 extending radially inwardly at the axially outward ends of the axially extending side portions 50. The depressions 48 are formed within the axially extending side portions 50 at locations between crossbars 36. The abutment surfaces 46 are radially offset rim portions forming ends of the slots 38. The end rims 32 and 34 and crossbars 36 are formed from a single sheet of steel or other metal and have substantially the same thickness. As illustrated in Figure 2, the central portions 40 of the crossbars 36 and abutment surfaces 46 are offset radially inwardly relative to the laterally outward portions 42 and 44 of the crossbars 36. However, the configuration may provide an inverted sigma bearing cage, as illustrated in Figure 5, in which central portions 76 and abutment portions 78 are offset radially outwardly. Similarly, flange portions 80 may extend radially outwardly rather than radially inwardly or may be omitted. Figure 3 illustrates an example requiring a significant offset of the roller receiving slots from the bearing flanges. Two roller bearing cages 30, shown in longitudinal section, are installed in an elongate bearing housing 54 having a cross drilled lubrication hole 56. The depressions 48 of the end rims 32 and 34 allow two roller cage bearings to maintain proper axial location of rollers 58 and 60 without roller interference to the breakout location of the lubrication hole 56 on a load bearing shaft 62. End washers 64 and 66 mounted on the bearing housing 54 engage outward flanges of the two roller bearing cages 30 to limit remote end axial movement of the cages. Adjacent end flanges of the roller bearing cages 30 overlie the lubrication hole 56 and abut each other to limit inward axial movement of the cages. The central portions 40 of the crossbars 36 separate the rollers 58 and 60 circumferentially and co-operate with outward portions 42 (Figure 2) to contain the rollers during handling and installation. The preferred method of manufacturing the roller bearing cage 30 is by flat blank, wrap, and weld, using multislide techniques. Flat coil stock of uniform section is pressed to form a depressed centre relief portion between two edge portions. Pairs of slot end relief openings are pierced in the edge portions, and forming punches are seated against the laterally outward edges of the slot end relief openings, thereby forming the angled slot end depressions 48. Centre slots are then pierced across the centre relief portion and between each pair of slot end relief openings to provide the remaining perimeter of the slots 38 such that the depressions 48 are at the ends of the slots 38. Strip edge gutting and flange forming may be used to trim and shape edges of the resulting cage blank. The cage blank is cut to a predetermined length by a block cut from the formed strip. The completed blank is wrapped to a 360 degree circular hoop and welded such that the edge portions form rings at the axial ends of the resulting cage. Figure 4 illustrates outlines and relative positions of multiple punches that may be used to pierce the slots 38 according to the method just described. Heavier outlines 68 and 72 represent the shape of tooling used to pierce one pair of slot end relief openings in the edge portions of the flat strip. Light outline 70 represents the shape of tooling used to pierce the centre slots across the slot end relief openings. As shown by the positions illustrated, the opening pierced by the centre slot punch blends with the slot end relief openings, even if a slight misalignment of the punches occurs. The separate cutting of the slot end relief openings avoids distortion to the slot that might occur during pressing to form depressions 48. Overlapping of the punches results in circumferentially extending trapezoidal shaped tabs 74 (also in Figure 2) which extend into the roller receiving slots and assist in controlling radially outward movement of the rollers. The depressions 48 may also be formed by pressing a "dimple" or recess in the edge portions of the metal strip without piercing of slot end relief openings. The full perimeter of the slots 38 would then be pierced such that a portion of the dimple remains, thereby providing the depressions 48. That method ensures a square profile (in longitudinal section) abutment surface 46 which gives maximum contact with the ends of the rollers; however, tool maintenance with that method may be more difficult. Other variations in the method of manufacturing the cage 30 or the inverted sigma bearing cage are envisaged. The depressions 48 may be formed either before or after piercing of the centre slots. The depressions 48 and slots 38 may also be formed and pierced simultaneously or may be accomplished by a single tool. Strip edge gutting, flanging and welding steps may be added or omitted, as desired. Joining ends of the circular hoop may be by other means than welding or may be omitted. From the above description, it will be apparent that a solution is provided to the end containment problem in conventional sigma bearing cages which results in roller loss during handling and upon bearing installation, especially when a significant offset is required between the rollers and the end flanges. Axial emergence of the bearing rollers is prevented by roller contact with the depressed slot end to maintain proper location of the rollers.

Claims: A method for forming a roller bearing cage (30), the method comprising the steps of forming a flat strip of metal such that a centre relief portion (40) is offset with respect to two edge portions that lie within a plane, piercing centre slots (38) across the centre relief portion to form crossbars (36) and roller receiving slots such that a partially formed bearing cage is formed, forming the partially formed bearing cage into a circular hoop having an axis such that the edge portions form rings (32,34) at axial ends of the circular hoop, and forming abutment surfaces (46) at the ends of each roller receiving slot (38) such that rollers (58, 60) located within the respective roller receiving slots are retained in the axial direction by engagement with said abutment surfaces (46); characterised that, in order to form said abutment surfaces, slot end depressions (48) are formed in the material of said two edge portions (50), whereby the edges of said slot end depressions (48) form said abutment surfaces (46) for the rollers (48, 60). A method according to claim 1, wherein the step of forming the depressions (48) in the two edge portions occurs before the step of piercing the centre slots (38) across the centre relief portion. A method according to claim 1, wherein the step of forming the centre portion relief (40) occurs after the step of piercing the centre slots (38). A method according to claim 1, 2 or 3, further comprising the step of forming a flange in each edge portion and extending perpendicular to the plane of the edge portions. A method according to any one of the preceding claims, further comprising the step of cutting the partially formed bearing cage to a predetermined length before the step of forming the circular hoop. A method according to any one of the preceding claims, further comprising the step of joining ends of the circular hoop to form a closed bearing cage (30) with continuous end rims (32, 34). A method according to any one of the preceding claims, wherein the forming of the partially formed bearing cage into a circular hoop results in the depressed centre portion (40) and slot end depressions (48) extending radially inwardly. A method according to any one of claims 1 to 6, wherein the centre relief portion (40) and the depressions (48) are both offset radially outwardly with respect to the side portions (42, 44). A method according to any one of the preceding claims, wherein the steps of piercing the pairs of slot end relief openings and piercing the centre slots (38) results in at least one tab (74) extending circumferentially into the roller receiving slots. A method according to any one of the preceding claims, wherein the end rims (32, 34) and crossbars (40) have substantially the same thickness. A method according to any one of the preceding claims comprising forming a radially extending flange portion (80) at the axially outward ends of each edge portion (32, 34).

Inventors: ALLING RICHARD L, ALLING, RICHARD L.
Applicants: TORRINGTON CO, THE TORRINGTON COMPANY
Application year: 1995
Main classification: F16C33
IPC codes: F16C33