Bearing Liner

1. Field of the Invention

This invention relates generally to low friction liners for reducing the friction between wearing surfaces, and more specifically to bearing liners for use between bearing balls and bearing races.

2. Description of the Prior Art

Bearing liners have been disposed between bearings and bearing races to reduce the friction forces created by their wearing surfaces. One of the most recent advances in the bearing liner art is the disclosure by Peter H. Turner in U.S. Pat. No. 3,594,049, of a backing member coated on one side with a layer of adhesive and coated on the opposite side with an intimate mixture of adhesive and small particles of a low friction material. The adhesive layer provides a means for bonding the backing member to one of the wearing surfaces, and the low friction layer provides a means for permanently lubricating the wearing surfaces. In U.S. Pat. No. 3,594,049, the backing member is disclosed in one embodiment to comprise a woven sheet formed from dacron or nylon strands. Such a bearing liner provides a significant advance over the prior art especially with respect to its reduced thickness and the considerably increased duration of its useful life.

The present invention includes a backing member having an adhesive layer on one side thereof and an intimate mixture of an adhesive and a low friction material on the opposite side thereof. The backing member can be an unwoven material impregnated with randomly disposed compressed fibers such as vegetable fibers to provide the bearing liners with stress-strain characteristics which are substantially linear regardless of the compressive stress imposed upon the backing member. The deflection of the improved liners in response to a particular value of compression is accordingly minimized. This characteristic is particularly advantageous in improving the accuracy of movement of the bearings within the bearing liners.

The surfaces of the backing member can be calendered or smoothed to harden the backing member and to enable the layer including the low friction material to be fabricated with a substantially constant thickness. A low friction layer with a substantially constant thickness will have a longer useful life since there will be no thin spots to wear through and end prematurely the life of the liner.

The backing member also can comprise a laminate including layers of fiber-impregnated material wherein the fibers in each layer are aligned substantially perpendicular to those in adjacent layers. The resulting bearing liners have a modulus of elasticity which is similar to that of metals. The improved liners have characteristics including high tensile strength and compressive rigidity to extend their useful life and improve the accuracy of movement of the bearing balls within their races.

FIG. 1 is a side elevational view partially in section of a shaft supported by a bearing ball and a bearing race with a bearing liner disposed between the ball and the race;

FIG. 2 is a side elevational view in cross section of one embodiment of the bearing liner;

FIG. 3 is a perspective view of a further embodiment of the bearing liner; and

FIG. 4 illustrates curves representing bearing liner compression versus bearing liner deflection for the bearing liners of the prior art and the improved bearing liners.

Referring to the drawings and in particular to FIG. 1 thereof, reference numeral 11 designates a rotatable shaft on which is mounted a bearing ball 13 having an outer or wearing surface 15. A bearing race 17 having an inner or wearing surface 19 can be centered upon the ball 13 to provide support for the shaft 11. A bearing liner 21 is preferably disposed between the wearing surface 19 of the race 17 and the wearing surface 15 of the ball 13. Thus disposed the bearing liner 21 can provide a means for permanently lubricating the bearing 13 and the race 17 so that there is less resistance to relative movement therebetween and a reduction in the deterioration of the wearing surfaces 15 and 19.

A cross-section view of one embodiment of the bearing liner 21 is shown in FIG. 2. The reference numeral 23 designates a backing such as paper having first and second opppositely facing major surfaces 25 and 27, respectively. An adhesive layer 29 can be disposed upon the first major surface 25 of the backing 23, and a low friction layer 31 can be disposed upon the second major surface 27. The low friction layer 31 is partially defined by a wearing surface 33.

In the preferred embodiment the backing 23 is adhered to the wearing surface 19 of the race 17 by the adhesive layer 29. Thus disposed the liner 21 has a fixed relationship with the bearing race 17, and the wearing surface 33 of the low friction layer 31 slidably engages the wearing surface 15 of the ball 13. It can be appreciated by those skilled in the art that the bearing liner 21 may be adhered to the ball 13 in which case the wearing surface 33 would be in contact with the wearing surface 19.

The adhesive comprising the adhesive layer 29 can be any of those adhesives disclosed by Peter H. Turner in U.S. Pat. No. 3,594,049 and assigned of record to the assignee of record of the present application. One such adhesive is Rabond R-84015 produced by Raybestos-Manhattan of Bridgeport, Connecticut.

The low friction layer 31 can comprise a similar adhesive filled with a 5-micron polytetrafluoroethylene powder manufactured by DuPont. The adhesive and the powder can be intimately mixed in the proportions disclosed in U.S. Pat. No. 3,594,049; however, lower ratios of powder to adhesive are preferred since the compressed fibers in the backing have a tendency to absorb some of the adhesive from the wear coating mixture. For example, the low friction powder may have a range of approximately twenty percent (20%) to thirty-five percent (35%) by weight with the remainder being adhesive. In the preferred embodiment the low friction layer contains twenty percent (20%) by weight of polytetrafluoroethylene powder. The low friction layer may have a thickness of approximately 0.003 inch beyond the peaks of the backing layer 23. Preferably this dimension is no greater than approximately 0.0035 inch.

The backing 23 can comprise a fibrous material such as paper having fibers such as those shown generally at 35. In one of the embodiments the fibers 35 are chopped and randomly disposed within the backing 23. The fibers 35 are preferably compressed since a minimum porosity is desirable to augment the adhesion of the adhesive and low friction layers 29 and 31, respectively, to the backing 23. It should be understood that the randomly disposed fibers 35 can comprise any fiber although the compressed vegetable fibers commonly available in the form of paper are particularly advantageous and economically desirable. Calendered paper and rice paper contain fibers which are some of the most compressed and therefore provide excellent deflection characteristics.

Since the backing 23 is a fibrous material, the particles of powder can be retained between the fibers to provide a mechanical bond between the fibers and the particles of low friction material. This is particularly desirable since the particles are quite small. A chemical bond also can be produced between the adhesive and the particles of low friction material. Furthermore, by compressing the backing 23, the thickness of the backing is maintained substantially constant so that the thickness of the layer 31 of the adhesive and the low friction material will be substantially constant. This will insure that there will be no thin spots in the low friction layer to wear prematurely and end the useful life of the liner 21.

The layer 31 has all of the advantages disclosed in U.S. Pat. No. 3,594,049. For example, it has a long life. This results in part from the thin dimensions of the layer 31 and in part from the combination of the mechanical and chemical bonding of the particles of low friction material. It also results in part from the small size of the particles of low friction material. All of these advantages tend to prevent the low friction material from forming into a continuous smear on the exposed surface of the layer 31.

A further embodiment of the backing 23 is shown in FIG. 3. In this backing a plurality of layers such as layers 37, 39, and 41, are adhered to each other to form a laminate. Each of the layers 37, 39, and 41 includes fibers 43, 45, and 47, respectively, oriented in a single direction so that the tensile strength of the layer is increased in that direction. In the preferred embodiment each layer, such as the layer 39, is disposed with respect to the layers on either side thereof, such as the layers 37 and 41, so that its fibers are substantially normal to the fibers in the adjacent layers. It follows that the direction of orientation of the fibers 43 and 47 in the layers 37 and 41, respectively, may be substantially parallel. The laminate shown in FIG. 3 provides the backing 23 with increased tensile strength and substantially uniform stress properties. This increased strength can be advantageous in those applications wherein a higher degree of liner reinforcement is desirable.

It is apparent that the bearing liners 21 will be subjected to compressive forces as the shaft 11 and the ball 13 rotate. It can be appreciated that any deflection of the bearing liners in response to these compressive forces will increase the wear on the engaging surfaces and reduce the accuracy of the shaft rotation. Bearing liners including woven materials, such as dacron, as disclosed in U.S. Pat. No. 3,594,049, have represented a significant advance over the prior art. As satisfactory as the bearing liners disclosed in U.S. Pat. No. 3,594,049 have been found to be, it is always desirable to provide bearing liners with enhanced characteristics such as enhanced deflection characteristics.

The stress-strain curve shown in FIG. 4 and designated by the reference numeral 49 is characteristic for the bearing liners disclosed in U.S. Pat. No. 3,594,049. For comparison, a stress-strain curve 51 characteristic of the improved liners 21 is also shown in FIG. 4. The curve 51 has a yield point 53 beyond which the liner will deflect with progressively decreased increments in load. It will be noted that the deflection is substantially linear in the regions of compressive force below the yield point 53, where the effects of the bearing liner 21 are most significant. It is apparent also that, for a given compressive force, the deflection is less in the liners 21 comprising the compressed fiber backing 23 then in the liners comprising the backings of the prior art. In fact, the backing 23 provides the liner 21 with a modulus of elasticity which is similar to that for metals in that the stress-strain curve 51 is substantially linear for values of compression less than that at the yield point 53.

It can be seen that the bearing liners 21 including the improved backing 23 have particularly advantageous properties for reducing the coefficient of friction between the wearing surface 15 and 19 without significantly reducing the compressive strength of the material supporting the ball 13. Thus, the bearing liner 21 provides a means for permanently lubricating the ball 13 without sacrificing the accuracy of movement and stability of the shaft 11. This accuracy of movement can have particular significance in systems which incorporate servomechanisms for amplifying mechanical movement. It is apparent that, in these systems, even a slight deflection of the shaft 11 can be amplified to ultimately produce a substantial error in movement. Thus, the low deflection characteristics of the backing 23 significantly decrease the error associated with these systems. Furthermore, the resulting bearing liners 21 also have increased rigidity and improved wear life characteristics.

While the present invention has been shown and described in what are conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein.