Patent Abstract:
A bearing cage, including: a body fabricated of phenolic material and having an outer circumferential surface and an inner circumferential surface; and a coating of molybdenum disulfide or polytetrafluoroethylene adhered to the outer circumferential surface or the inner circumferential surface. A method of manufacturing a bearing cage, including: fabricating a body from phenolic material, the body including an outer circumferential surface and an inner circumferential surface connecting first and second sides; and adhering a coating of molybdenum disulfide or polytetrafluoroethylene to the inner or outer circumferential surface.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/904,808, filed Nov. 15, 2013, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a bearing cage with an inner or outer circumferential surface with a self-lubricating coating of molybdenum disulfide or polytetrafluoroethylene. The present disclosure relates to a method of manufacturing a bearing cage with an inner or outer circumferential surface with a self-lubricating coating of molybdenum disulfide or polytetrafluoroethylene. The present disclosure relates to a bearing assembly including a bearing cage with a self-lubricating coating of molybdenum disulfide or polytetrafluoroethylene. 
     BACKGROUND 
     It is known to use spindle bearings with phenolic cages for high-speed applications such as machine tools. Such spindle bearings typically have inner and outer rings, the phenolic bearing cage radially located between the inner and outer rings, and a plurality of roller elements retained by the bearing ring. In a radially outwardly guided configuration, an outer circumferential surface of the bearing cage (the land guiding surface) is engaged with and guided by an inner circumferential surface of the outer ring (land surface). Oil from bearing grease or similar lubricant forms a lubricant film between the land guiding surface and the land surface. In a radially inwardly guided configuration, an inner circumferential surface of the bearing cage (the land guiding surface) is engaged with and guided by an outer circumferential surface of the inner ring (land surface). 
     Oil from the bearing grease or similar lubricant forms a lubricant film between the land guiding surface and the land surface. Lubrication of the land guiding surface is critical for operation of the bearing. However, at start up, the lubricant film is not yet fully formed between the land surface and the land guiding surface and base oil has only starting to migrate to the land guiding surface. Known spindle bearings do not provide a desired level of lubrication of the land guiding surface at start up. 
     EP 0 695 884 B1 discloses a greased rolling bearing element with a solid lubricating coating. The description of EP 0 695 884 B1 mentions GB 826 091 A, which described cages with metallic bodies and a plastic coating of polyamide or poly tetrafluorethylene containing about 3% of MoS 2  or graphite. 
     The description of EP 0 695 884 B1 mentions U.S. Pat. No. 3,500,525, JP-A-62 141 314 and JP-A-3 255 223, all of which disclose a coating of MoS 2  for a bearing cage. However, all these references relate to bearings for use in (high) vacuum and/or at elevated temperatures (250° C. or more). Grease lubrication cannot be used in (high) vacuum and/or at elevated temperatures. 
     EP 0 695 884 B1 discloses use of a coating of MoS 2  and poly tetrafluorethylene over a steel bearing cage. 
     SUMMARY 
     According to aspects illustrated herein, there is provided a bearing cage, including: a body fabricated of phenolic material and having an outer circumferential surface and an inner circumferential surface; and a coating of molybdenum disulfide or polytetrafluoroethylene adhered to the outer circumferential surface or the inner circumferential surface. 
     According to aspects illustrated herein, there is provided a bearing assembly including: an inner ring including a first outer circumferential surface; an outer ring including a first inner circumferential surface; a bearing cage fabricated of phenolic material and including first and second sides, a second outer circumferential surface connecting the first and second sides, a second inner circumferential surface connecting the first and second sides, and a coating of molybdenum disulfide or polytetrafluoroethylene adhered to the second outer circumferential surface or to the second inner circumferential surface; and a plurality of rolling elements retained by the bearing cage. The second outer circumferential surface is engaged with the first inner circumferential surface to guide the bearing cage. The second inner circumferential surface is engaged with the first outer circumferential surface to guide the bearing cage. 
     According to aspects illustrated herein, there is provided a method of manufacturing a bearing cage, including: fabricating a body from phenolic material, the body including an outer circumferential surface and an inner circumferential surface connecting first and second sides; and adhering a coating of molybdenum disulfide or polytetrafluoroethylene to the inner or outer circumferential surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: 
         FIG. 1A  is a perspective view of a cylindrical coordinate system demonstrating spatial terminology used in the present application; 
         FIG. 1B  is a perspective view of an object in the cylindrical coordinate system of  FIG. 1A  demonstrating spatial terminology used in the present application; 
         FIG. 2  is a perspective view of a bearing cage with a self-lubricating coating on an outer circumference; 
         FIG. 3  a schematic cross-sectional view generally along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a schematic cross-sectional view of a bearing cage with a coating on an inner circumferential surface; and, 
         FIG. 5  is a partial cut-away view of a bearing assembly including a bearing cage with a self-lubricating coating on an outer circumference. 
     
    
    
     DETAILED DESCRIPTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
     Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure. 
       FIG. 1A  is a perspective view of cylindrical coordinate system  80  demonstrating spatial terminology used in the present application. The present disclosure is at least partially described within the context of a cylindrical coordinate system. System  80  has a longitudinal axis  81 , used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis  81 , radius  82  (which is orthogonal to axis  81 ), and circumference  83 , respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects  84 ,  85 , and  86  are used. Surface  87  of object  84  forms an axial plane. That is, axis  81  forms a line along the surface. Surface  88  of object  85  forms a radial plane. That is, radius  82  forms a line along the surface. Surface  89  of object  86  forms a circumferential plane. That is, circumference  83  forms a line along the surface. As a further example, axial movement or disposition is parallel to axis  81 , radial movement or disposition is parallel to radius  82 , and circumferential movement or disposition is parallel to circumference  83 . Rotation is with respect to axis  81 . 
     The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis  81 , radius  82 , or circumference  83 , respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes. 
       FIG. 1B  is a perspective view of object  90  in cylindrical coordinate system  80  of  FIG. 1A  demonstrating spatial terminology used in the present application. Cylindrical object  90  is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention in any manner. Object  90  includes axial surface  91 , radial surface  92 , and circumferential surface  93 . Surface  91  is part of an axial plane, surface  92  is part of a radial plane, and surface  93  is a circumferential surface. 
       FIG. 2  is a perspective view of bearing cage  100  with a self-lubricating coating on an outer circumference. 
       FIG. 3  a cross-sectional view generally along line  3 - 3  in  FIG. 2 . The following should be viewed in light of  FIGS. 2 and 3 . Cage  100  includes axis of rotation AR and body  102  fabricated of phenolic material and having outer circumferential surface  104  and inner circumferential surface  106 . Body  102  can be fabricated of any phenolic material known in the art. Cage  100  includes coating  108  of molybdenum disulfide or polytetrafluoroethylene adhered to outer circumferential surface  104 . That is, surface  104  is at least partially covered with coating  108 . In an example embodiment, the coating is molybdenum disulfide. In an example embodiment, the coating is polytetrafluoroethylene. In an example embodiment, cage  100  includes grease GR. Grease GR is generally located proximate surface  106 . The thickness of coating  108  in  FIGS. 2 and 3  has been exaggerated for purposes of illustration. 
     In an example embodiment, at least a portion of the coating forms a continuous ring, in circumferential direction CD, encircling surface  104 . In an example embodiment, an entirety, that is, all of the coating is continuous in circumferential direction CD on surface  104 . Body  102  includes sides  110  and  112 . Outer circumferential surface  104  and inner circumferential surfaces  106  connect sides  110  and  112 . That is, sides  110  and  112  bound the outer circumferential surface and the inner circumferential surface in axial direction AD. In an example embodiment, at least a portion of coating  108  is continuous from side  110  to side  112 , that is, between side  110  and  112 . In an example embodiment, an entirety, that is, all, of coating  108  is continuous from side  110  to side  112 , that is, between side  110  and  112 . Stated otherwise, surface  104  is completely covered with coating  108 . 
       FIG. 4  is a schematic cross-sectional view of bearing cage  200  with a coating on an inner circumferential surface. Cage  200  includes axis of rotation AR and body  202  fabricated of phenolic material and with outer circumferential surface  204  and inner circumferential surface  206 . Body  202  can be fabricated of any phenolic material known in the art. Cage  200  includes coating  208  of molybdenum disulfide or polytetrafluoroethylene adhered to inner circumferential surface  206 . That is, surface  206  is at least partially covered with coating  208 . In an example embodiment, the coating is molybdenum disulfide. In an example embodiment, the coating is polytetrafluoroethylene. In an example embodiment, cage  200  includes grease GR. Grease GR is generally located proximate surface  204 . The thickness of coating  208  has been exaggerated for purposes of illustration. 
     In an example embodiment, at least a portion of the coating forms a continuous ring in circumferential direction CD encircling surface  206 . In an example embodiment, an entirety, that is, all of the coating is continuous in circumferential direction CD on surface  206 . Body  202  includes sides  210  and  212 . Outer circumferential surface  204  and inner circumferential surfaces  206  connect sides  210  and  212 . That is, sides  210  and  212  bound the outer circumferential surface and the inner circumferential surface in axial direction AD. In an example embodiment, at least a portion of coating  208  is continuous from side  210  to side  212 , that is, between side  210  and  212 . In an example embodiment, an entirety, that is, all, of coating  208  is continuous from side  210  to side  212 , that is, between side  210  and  212 . Stated otherwise, surface  206  is completely covered with coating  608 . 
       FIG. 5  is a partial cut-away view of bearing assembly  300  including bearing cage  100  with a self-lubricating coating on an outer circumference. The following should be viewed in light of  FIGS. 2 ,  3  and  5 . Assembly  300  includes axis of rotation AR, bearing cage  100 , outer ring  302 , inner ring  304 , and at least one rolling element  306 . Ring  302  includes inner circumferential surface  308 , also referred to as land surface  308 . Outer circumferential surface  104  engages surface  308 . 
     Advantageously, bearings  100  and  200  addresses the problems noted above regarding the lack of lubrication on the surface of a bearing cage during start-up. Specifically, coatings  108  and  208  provide effective friction reduction prior to the build up of oil on surfaces  104  and  206 , respectively. There are no teachings, suggestions, or motivations in the prior art to use coating  108  on a phenolic bearing cage or that the use of coating  108  on a phenolic bearing cage would be successful. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Technology Classification (CPC): 5