GB2339246A

GB2339246A - Polymeric roller cage and method of making same

Info

Publication number: GB2339246A
Application number: GB9915761A
Authority: GB
Inventors: Robert Duane Richtmeyer
Original assignee: Torrington Co
Current assignee: Timken US LLC
Priority date: 1998-07-07
Filing date: 1999-07-07
Publication date: 2000-01-19
Also published as: DE19930370A1; GB9915761D0; JP2000055058A

Description

2339246 POLYMERIC ROLLER CAGE AND METHOD OF MAKING SAME This invention

relates generally to roller thrust bearings and more particularly to polymeric roller cages and to a method of making such cages, particularly from high temperature tolerant polymeric materials.

The requirement for roller thrust bearings which can run longer and faster under low oil flow conditions has increased the temperature demands on the bearings to the extent that commonly used polymers for making roller cages cannot meet the service requirements. Although some of the newer engineered polymers can withstand the higher operating temperatures encountered in such service, it is difficult or impossible to mould cages using those polymers in existing moulds. The softer and more elastic polymers used for normal-service thrust bearings would tolerate the forming tool removal through the restricted opening between the retention features of the pocket; however, because the high-temperature tolerant polymers are much more hard and brittle, the retention features of roller pockets are frequently damaged or broken completely during removal of the pocket forming tools of existing moulds.

According to one aspect of the present invention, there is provided a polymeric roller cage for a roller thrust bearing, comprising a flat annular body having a circular inner bore about an axis, a plurality of hollow radially- orientated roller pockets, each said roller pocket comprising an elongated cavity with straight sidewalls in a direction parallel to the axis of said annular body, at least three pairs of roller retention tabs disposed on each pocket, at least one pair of said tabs on one face of said body and at least two pairs of said tabs radially spaced on an opposite face of said annular body and radially offset from said at least one pair on said one face of said annular body.

2 According to a second aspect of the present invention, there is provided a method of making a roller cage from a polymer for a roller thrust bearing, comprising the following steps:

providing a mould having one or more flat annular cavities and appropriate injection gates and risers, said cavities being defined by a mould body and bottom and top cover members; providing a plurality of radiallyarrayed core pin pairs for each flat annular cavity, said core pin pairs comprising core pin members on said bottom cover and complementary opposed core pin members on said top cover, each core pin member consisting of an elongated ridge having alternating profiled axially -proj ec ting portions and flat axially-receding portions, said core pin members extending axially into the flat annular cavity to interengage, such that the profiled projecting portions and flat receding portions of one member of said core pin pair contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair when the mould is closed; closing said mould by axially clamping said cover members against said mould body; - injecting a polymeric material into the cavities within said mould, and unclamping and axially removing said bottom and top covers, and removing said polymeric roller cage from the mould.

According to a third aspect of the present invention, there is provided a method of making a polymeric roller cage for a roller thrust bearing, comprising the following steps:

providing a mould having one or more flat annular cavities and appropriate injection gates and risers, said cavities being defined by a mould body and at least a top cover member; - 3 providing a plurality of radially arrayed axially reciprocatable core pin pairs within said top cover member and an oppositely disposed surface of said mould body for each flat annular cavity, said core pin pairs comprising complementary opposed core pin members, each core pin member consisting of a flat plate having alternating profiled projecting portions and flat receding portions, said core pin members being oppositely axially reciprocatable to interengage within said flat annular cavity, such that the profiled projecting portions and flat receding portions of one member of said core pin pair contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair; reciprocating said core pin members to interengaging positions within said one or more flat annular cavity; injecting a polymeric material into said mould; reciprocating said core pin members out of interengaging positions; and opening said mould and ejecting said polymeric roller cage.

According to a fourth aspect of the present invention, there is provided a mould for making a polymeric roller cage for a roller thrust bearing, comprising:

a mould body with injection gates and risers, bottom and top covers, and one or more flat annular cavities; a plurality of radially- arrayed core pin pairs for each flat annular cavity, each said core pin pair comprising a core pin member on said bottom cover and a complementary opposed core pin member on said top cover, each core pin member consisting of an elongated ridge having alternating profiled axially-proj ecting portions and flat axially-receding portions, said core pin members extending axially into the flat annular cavity to interengage, such that the profiled projecting portions and flat receding portions of one member of said core pin pair - 4 contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair when said bottom and top cover members are installed on said mould body; means for clamping said cover members on said mould body to close the mould; and means for ejecting said polymeric roller cage from the mould.

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 which:

is Figure 1 is a fragmentary plan view of a known thrust bearing roller cage made with the current mould design; Figure 2 is a view, partly in cross-section, of a roller pocket of the known roller cage taken in the direction of arrows 2 - 2 in Figure 1; Figure 3 is a perspective view, partly in cross-section, of the cage of Figures 1 and 2; Figures 4a and 4b are views of two common pocket forming tools and the pockets formed by them, each showing half of the tool and pocket; Figure 5 is a plan view of a roller cage made according to the present method; Figure 6 is a perspective view, partly in section, of one of the roller pockets of Figure 5 with a roller added; Figure 7 is a sectional view, taken on line 7 - 7 of Figure 5, to illustrate a preferred roller pocket form; - 5 Figure 8 is a view taken along line 8 - 8 of Figure 5; Figure 9 is a schematic illustration of one member of a core pin pair used for the form shown in Figure 8; Figure 10 is an illustration of the opposing member of the core pin member in Figure 9 used to make the f orm in Figure 7; Figures 11a, llb, 12a, and 12b show another embodiment of the two complementary core pin members and cross-sections of the complementary forms of the cage pocket portions produced by the core pin pair; and Figures 13 and 14 illustrate the core pins which are used to form a cage with radially shorter retention tabs.

As used throughout the description, the terms radial, axial, top, and bottom denote directions with respect to the radius and axis of a flat annular thrust bearing cage, as shown in Figures 1 - 8. The prior art has many different designs of roller cages for roller thrust bearings. One such design is schematically illustrated in Figs. 1 - 4 in which a roller cage 15 has a flat annular body 20 with a plurality of elongated radially orientated pockets 25. In each of the plurality of pockets 25 a roller 30 is retained. The width of the pockets 25 at top and bottom surfaces of the cage body 20 is less than the diameter of the rollers 30. Thus, although the rollers 30 fit loosely within the pockets 25 of the cage 20, they must be forced into them, and this requires a level of elasticity for the cage edges if that force is not to damage the cage pocket edges.

The pocket forming tools (halves) 35a, 35b, shown in Fig.4, have a diameter or maximum dimension larger than that of the rollers 30.They are used as a core about which a polymer is injected within a mould to form a roller pocket within a cage. The pockets 25a, 25b and the tools 35a, 35b for forming them may have a circular or polygonal cross section of virtually any form as long as the roller fits loosely therein and cannot fall out. It is clear that, once the polymer has been moulded around the tool and cured, the tool must be removed by pulling in the direction of the arrow. This method of removal is possible with softer polymers of the prior art, but it is very difficult, if not impossible, to use with hightemperature tolerant polymers as are now required for more demanding applications. This results in excessive losses during manufacturing due to breakage of the retention features during removal of the cages from the forming tools and moulds.

Figs. 5 - 8 schematically illustrate a roller cage 50 made by the present method. it consists of an annular cage body 60 with a plurality of radially arrayed elongated pockets 70. In this case, the roller 30 is retained by retention tabs 75 and 80 which are alternately positioned on top and bottom surfaces of the cage body 60. Figs. 7 and 8 show cross-sectional views of the cage body 60 at lines 7 - 7 and 8 - 8 of Fig 5, and reveal the straight-walled sidewalls of the pockets 70. These straight sidewalls, which are straight in a direction parallel to the axis of the cage body 60, and the alternating retention tabs 75, 80 at the top and bottom surfaces of the cage body, permit bi-directional axial withdrawal of the opposed core pins used in forming the roller pockets 70 and the tabs without exerting any deforming force on the tabs. This feature viewed in conjunction with Figs. 9 and 10, shows the functional design of the roller pockets 70 and the core pin members 90 and 100 of a single core pin pair used to form them. Core pin 90 consists of a ridge defined by a profiled axially projecting portion 77 radially flanked by two flat axially receding portions 79. Core pin 100 consists of two profiled axially projecting portions 95 radially flanking a flat axially receding portion 85. Note that the core pin members 90, 100 are shown with very thick flat axially receding portions 79, 85. This is exaggerated to illustrate and describe the shapes of the complementary core pin members used to form the pockets 70 of the invention. By this means they can be described as ridges with alternately projecting and receding portions.

An alternative embodiment of the core pin pair 190, is shown in Figs. 11a, 11b, 12a, and 12b. When interengaged within a mould cavity, this core pin pair produces moulded cavities with cross sections as in Fig.

llb and 12a. The rounded contours between the sidewalls and the retention tabs 180, 175 reduce the notch effect created by intersecting planar surfaces and may be more resistant to mechanical damage. However, core pins with such rounded contours are more difficult to fabricate than those with intersecting planar surfaces and are therefore more costly to produce.

in any embodiment, it may be desired to decrease the radial extent of the retention tabs to increase the ease of installation of the rollers in the pockets. This is accomplished by providing core pins of the type shown in Figures 13 and 14, in which the contoured axially projecting portions 277, 295 of core pins 290 and 300 engage with flat axially receding portions 285, 279, respectively when the mould is closed.

In their simplest form, the core pins are directly fixed to bottom and top covers of a mould and are inserted and removed from the mould cavity in an axial direction along with the top and bottom covers. Note that top and bottom may actually be right and left depending on the design of the moulding equipment. The parallel sides of - 8 the core pin members permit easy axial extraction of the pins from the moulded cages and vice versa. In more complex and costly moulds because of the parallel sides of the projecting portions the core pin members may be axially reciprocatable through the top and bottom mould covers to reach an interengaged position within the mould cavity and to thereby define the roller cavities in the moulded roller cage.

Depending upon the polymeric moulding material chosen, some curing provision may be included in the present method. This may include heating or cooling of the mould while maintaining the formed cages within the mould.

Claims

1. A polymeric roller cage for a roller thrust bearing, comprising a flat annular body having a circular inner bore about an axis, a plurality of hollow radially- orientated roller pockets, each said roller pocket comprising an elongated cavity with straight sidewalls in a direction parallel to the axis of said annular body, at least three pairs of roller retention tabs disposed on each pocket, at least one pair of said tabs on one face of said body and at least two pairs of said tabs radially spaced on an opposite face of said annular body and radially offset from said at least one pair on said one face of said annular body.

2. A method of making a roller cage from a polymer for a roller thrust bearing, comprising the following steps:

providing a mould having one or more flat annular cavities and appropriate injection gates and risers, said cavities being defined by a mould body and bottom and top cover members; providing a plurality of radiallyarrayed core pin pairs for each flat annular cavity, said core pin pairs comprising core pin members on said bottom cover and complementary opposed core pin members on said top cover, each core pin member consisting of an elongated ridge having alternating profiled axially-proj ecting portions and flat axially-receding portions, said core pin members extending axially into the flat annular cavity to interengage, such that the profiled projecting portions and flat receding portions of one member of said core pin pair contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair when the mould is closed; - 10 closing said mould by axially clamping said cover members against said mould body; injecting a polymeric material into the cavities within said mould, and unclamping and axially removing said bottom and top covers, and removing said polymeric roller cage from the mould.

3. A method according to claim 2, wherein the mould body is provided with the bottom cover member fixed thereto.

4. A method according to claim 2 or 3, wherein the core pin members on the top cover member are provided with a single profiled projecting portion between two flat receding portions, and the core pin members on the bottom cover member are provided with a single flat receding portion between two profiled projecting portions.

5. A method of making a polymeric roller cage for a roller thrust bearing, comprising the following steps:

providing a mould having one or more flat annular cavities and appropriate injection gates and risers, said cavities being defined by a mould body and at least a top cover member; providing a plurality of radially arrayed axially reciprocatable core pin pairs within said top cover member and an oppositely disposed surface of said mould body for each flat annular cavity, said core pin pairs comprising complementary opposed core pin members, each core pin member consisting of a flat plate having alternating profiled projecting portions and flat receding portions, said core pin members being oppositely axially reciprocatable to interengage within said flat annular cavity, such that the profiled projecting portions and flat receding portions of one member of said core pin pair contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair; reciprocating said core pin members to interengaging positions within said one or more flat annular cavity; injecting a polymeric material into said mould; reciprocating said core pin members out of interengaging positions; and opening said mould and ejecting said polymeric roller cage.

6. A method according to claim 2, 3, 4 or 5, wherein the polymeric material is cured.

7. A mould for making a polymeric roller cage for a roller thrust bearing, comprising:

a mould body with injection gates and risers, bottom and top covers, and one or more flat annular cavities; a plurality of radially- arrayed core pin pairs for each flat annular cavity, each said core pin pair comprising a core pin member on said bottom cover and a complementary opposed core pin member on said top cover, each core pin member consisting of an elongated ridge having alternating profiled axially-proj ecting portions and flat axially-receding portions, said core pin members extending axially into the flat annular cavity to interengage, such that the profiled projecting portions and flat receding portions of one member of said core pin pair contact the complementary flat receding portions and profiled projecting portions, respectively, of the other member of said core pin pair when said bottom and top cover members are installed on said mould body; means for clamping said cover members on said mould body to close the mould; and means for ejecting said polymeric roller cage from the mould.

8. A mould according to claim 6, and comprising means for curing a polymeric material as required.

9. A roller cage according to claim 1, a method according to any one of claims 2 to 6, or a mould according to claim 7 or 8, wherein said polymeric material is a high temperature-tolerant polymer.

10. A roller cage, substantially as hereinbefore described with reference to the accompanying drawings.

11. A method of making a roller cage, substantially as hereinbefore described with reference to the accompanying drawings.

12. A mould for making a roller cage, substantially as hereinbefore described with reference to the accompanying drawings.