GB2314892A

GB2314892A - Bearing cage assembly and method of making same

Info

Publication number: GB2314892A
Application number: GB9713261A
Authority: GB
Inventors: Stephen M Mondak; Anthony Storey
Original assignee: Torrington Co
Current assignee: Timken US LLC
Priority date: 1996-07-01
Filing date: 1997-06-20
Publication date: 1998-01-14
Also published as: GB9713261D0; DE19726825A1

Abstract

Rolling elements are introduced into open pockets 18 of a cage member 12. An end cap 14 is positioned against the cage member such that the open ends of the pockets are blocked, capturing the rolling elements. The end cap is secured to the cage member by thread-forming screws 16 that form a thread in the cage member by displacing material without cutting. The cage member and end cap may be machined out of heavy wall bronze or brass tubing, or formed by casting or stamping.

Description

2314892 BEARING CAGE ASSEMBLY AND METHOD OF MAKING SAME This invention

relates generally to rolling element bearings and more particularly to a multi-piece cage assembly for rolling element bearings.

In conventional large roller bearings, the rollers are typically retained by a two-piece bearing cage that is machined out of large diameter, heavy wall, non-ferrous tubing. After the rollers are loaded into pockets of a cage member, an end cap is hot-riveted over the pockets to contain the rollers as an assembly. Other forming methods such as casting or stamping may be used to make similar cage members or end caps of riveted bearing cages.

is In applications involving high vibration or acceleration loads, relative motion may occur between the cage member and the end cap, causing the rivet to loosen and ultimately break.

Another problem is the difficulty of drilling deep holes through the cage member without the drill "wandering" into the roller pockets. The size of bearing cages that may be manufactured is limited by this difficulty of drilling the axial length of a bearing cage.

According to one aspect of the present invention there is provided a method of making a cage assembly for a rolling element bearing, the method comprising providing a cage member with pockets for receiving rolling elements, the pockets being open to an axial end of the cage member, introducing rolling elements into the pockets through the open axial ends of the pockets, positioning an end cap against the cage member such that the open ends of the pockets are blocked by the end cap, capturing the rolling elements, and securing the end cap to the cage member by thread-f orming screws that form a thread in the cage member by displacing material without cutting the material.

According to a second aspect of the present invention there is provided a cage assembly for use with a rolling element bearing, the cage assembly comprising a cage member with pockets for receiving rolling elements, the pockets being open to an axial end of the cage member, rolling elements within 10 the pockets, an end cap positioned against the cage member such that the open ends of the pockets are blocked by the end cap, capturing the rolling elements, and thread-forming screws threaded into the cage member such that a thread is formed in the cage member without cutting the cage member and such that 15 a clamping force secures the end cap and cage member together. 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 the accompanying drawings, in 20 which:- Fig. 1 is an exploded cross-sectional view of a bearing cage assembly; Fig. 2 is an end view of a portion of the cage member of Fig. l., with a roller indicated in phantom; and Fig. 3 is an enlarged view of thread-forming screw of the bearing cage assembly of Fig. 1.

Referring to the drawing, Figure 1 illustrates elements of bearing cage assembly 10 prior to assembly, specifically, a cage member 12, end cap 14 and thread-forming screws 16.

The cage member 12 and end cap 14 may be machined out of heavy wall non-ferrous tubing such as bronze or brass.

Alternatively, other forming methods including casting or stamping operations and other materials may be used, depending on the application.

The cage member 12 is an annular ring with pockets 18 bored parallel to an axis 20 of the cage member 12 along a concentric circle 22. In the embodiment shown, the pockets 18 are regularly spaced about the circumference of the cage member 12 and have a cylindrical configuration with conical recesses 24. The pockets 18 are open at one axial end to allow rollers 26 to be inserted during assembly. The rollers 26 extend radially outwardly and radially inwardly from the cage member 12 to engage bearing raceways, not shown.

Material between adjacent pockets 18 forms crossbars 28 with curved surfaces 30 that restrain radially outward and radially inward movement of the rollers 26.

The end cap 14 is a flat ring that is positioned against the cage member 12 such that the open ends of the pockets 18 are blocked, capturing the rolling elements. The end cap 14 has countersunk clearance holes 32 aligned with pilot holes 34 for receiving thread-forming screws 16. An annular groove 36 at the perimeter of the end cap 14 co-operates with mating annular ridge 38 formed by a recess in the open end of the cage member 12 to maintain concentricity of the end cap 14 and cage member 12.

In the embodiment shown, the thread-forming screws 16 each have a tapered end portion 42 with rounded lobes 44 extending above the thread profile for displacing material of cage member 12 to form internal threads without cutting. This method of rolling the internal thread does not remove material and results in improved thread finish, improved grain flow and improved thread rood strength over that obtained by conventional machine screws in pre-tapped holes or by tapping screws with cutting surfaces. Further advancement of the thread-forming screws 16 increases the internal thread to full size without producing chips.

The bearing cage assembly 10 offers better resistance to loosening of fasteners due to vibration than conventional riveted cages due to the self-locking zero clearance mating thread formed by thread-forming screws 16. Apparently, the interference fit of the thread-forming screws 16 causes adjacent material of the cage member 12 to be compressed and biassed against the screws so there are no gaps between the mating threads. As a result, the thread-forming screws 16 provide higher resistance to backout torque and permit higher tensile loads than conventional self-tapping screws.

The bearing cage assembly 10 offers greater predictably and control of the clamping force between mating parts of the cage member 12 and end cap 14 than conventional riveted cages because the thread-forming screws 16 are torqued to predetermined guidelines at assembly. The clamping force provides a frictional force between the cage member 12 and end cap 14 that resists relative motion therebetween that would contribute to fastener loosening and ultimately to bearing failure in some applications. In addition, the flathead configuration and mating countersunk surface in the end cap 14 also resist relative motion.

Preferably, the thread-forming screws 16 each have a square socket 46 or other engagement means allowing convenient torquing of the screws during assembly. The amount of desired torque depends on the material of the cage member 12, the surface finish/material of thread-forming screws 16, the size number and placement of the screws, as well as several other factors and can be determined by pragmatic testing of sample cage assemblies assembled with varying torque specifications.

Unlike conventional bearing cage assemblies, the present construction does not limit the axial length of the bearing cages that can be manufactured. The pilot holes 34 can be relatively shallow and are not required to penetrate the full axial length of the cage member 12. As a result, the drilling of the pilot holes 34 is much easier to control without the drill "wandering" into the bearing pockets 18, and the bearing assembly 10 can be utilised in larger bearings where it would be impractical or impossible to use a conventional riveted bearing cage.

The present invention is not limited to radial cylindrical bearings as illustrated in the embodiment of Figures 1 to 3 but is applicable to the multi-piece bearing cages in other types of bearings, for example: window style cages for radial spherical roller bearings, various thrust bearings using two-piece machined cages and end rings, machined cages of multi-piece construction for large ball bearings and machined cages of multi-piece construction for radial tapered roller bearings. Suitable thread-forming screws are available commercially from Parker-Kalon, a Black & Decker company, as well as other sources.

From the above description, it should be apparent that the present construction provides an improved multi-piece bearing cage assembly suitable for applications involving high vibration or acceleration loads. In addition, the present construction has increased versatility and allows larger bearing cages to be manufactured than practical using conventional riveted construction.

7

Claims

CLAIMS:

1. A method of making a cage assembly for a rolling element bearing, the method comprising providing a cage member with pockets for receiving rolling elements, the pockets being open to an axial end of the cage member, introducing rolling elements into the pockets through the open axial ends of the pockets, positioning an end cap against the cage member such that the open ends of the pockets are blocked by the end cap, capturing the rolling elements, and securing the end cap to the cage member by thread-forming screws that form a thread in the cage member by displacing material without cutting the material.

2. A method according to Claim 1, wherein the step of securing the end cap to the cage member includes applying a predetermined torque to the thread forming screws to control the amount of clanping force biassing the end cap and cage member together.

3. A method according to Clain 1 or 2, wherein the rolling elements are rollers and the cage member is formed by machining the pockets by boring recesses parallel to the axis of the cage member.

4. A method according to Claim 1, 2 or 3, wherein the cage member is formed with pilot holes for thread-forming screws and wherein the thread-forming screws reform the pilot holes into a zero-clearance mating thread during the step of securing the end cap to the cage member.

5. A method according to any one of the preceding claims, wherein the thread-forming screws include lobes protruding 8 - from a starting taper of a male thread for displacing material of the cage member and making the material more dense to form mating threads in the cage member.

6. A method according to any one of the preceding claims, wherein the cage member and end cap are made of metal.

7. A method of making a cage assembly, substantially as hereinbefore described, with reference to the accompanying 10 drawing.

8. A cage assembly for a rolling element bearing when made according to any preceding claim.

9. A cage assembly for use with a rolling element bearing, the cage assembly comprising a cage member with pockets for receiving rolling elements, the pockets being open to an axial end of the cage member, rolling elements within the pockets, an end cap positioned against the cage member such that the open ends of the pockets are blocked by the end cap, capturing the rolling elements, and thread-forming screws threaded into the cage member such that a thread is f ormed in the cage member without cutting the cage member and such that a clamping force secures the end cap and cage member together.

10. A cage assembly according to Claim 9, wherein the thread forming screws are thread-rolling screws that form an interference fit with respect to the cage member.

11. A cage assembly according to Claim 9 or 10, wherein the thread-forming screws have a starting taper with rounded lobes for displacing material of the cage member during assembly.

12. A cage assembly for use with a rolling element bearing, substantially as hereinbef ore described, with reference to the accompanying drawing.