Abstract:
A retainer ( 30 ) for maintaining a relative angular spacing of a plurality of rolling elements includes a body ( 34 ) having an annular portion ( 38 ) and a plurality of engaging portions ( 42 ). Each of the engaging portions is configured to engage at least one of the plurality of rolling elements. The body is made of a sintered powdered metal infiltrated with bronze.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to co-pending U.S. Provisional Patent Application No. 61/870,375 filed on Aug. 27, 2013, the entire content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to retainers, and more particularly to methods of manufacturing retainers. 
       BACKGROUND OF THE INVENTION 
       [0003]    A retainer, also commonly referred to as a cage, is a common component in bearings, constant-velocity joints, and other types of rotary couplings that include a plurality of rolling elements. A retainer typically includes pockets that constrain the rolling elements to maintain a desired angular spacing between the rolling elements. 
         [0004]    Conventional retainers are made from a variety of materials in order to suit a particular application and production volume. For example, when production volume is high, retainers are typically made of steel or polymers. When production volume is low, retainers are typically made of brass or bronze. Additionally, brass and bronze offer superior tribological (i.e., lubrication and wear) characteristics compared to steel. 
         [0005]    Conventional retainers are made by a variety of manufacturing processes in order to suit a particular production volume. For high-volume manufacturing, retainers can be manufactured by a stamping process for steels or by an injection molding process for polymers. These processes can produce parts quickly and relatively inexpensively, but they require large initial tooling investments. As such, these processes are riot suitable for low-volume manufacturing. For low-volume manufacturing, retainers can be machined from a solid block casting or rolled forging. Although machining requires less tooling investment, it can be time consuming and expensive. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides, in one aspect, a retainer for maintaining a relative angular spacing of a plurality of rolling elements. The retainer includes a body having an annular portion and a plurality of engaging portions. Each of the engaging portions is configured to engage at least one of the rolling elements. The body is made of a sintered powdered metal infiltrated with bronze. 
         [0007]    The invention provides, in another aspect, a bearing, assembly including an inner raceway, an outer raceway, and a plurality of rolling elements. The rolling elements are disposed between the inner raceway and the outer raceway. The bearing assembly also includes a retainer for maintaining a relative angular spacing of the rolling elements. The retainer is made of a sintered powdered metal infiltrated with bronze. 
         [0008]    The invention provides, in another aspect, a method of manufacturing a retainer for maintaining a relative angular spacing of a plurality of rolling elements. The method includes forming a body of the retainer from powdered metal using an additive manufacturing process. 
         [0009]    Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a cutaway view of a typical ball bearing including a retainer that can be manufactured by a method in accordance with the invention. 
           [0011]      FIG. 2  is a perspective view of a typical tapered roller bearing including a retainer that can be manufactured by a method in accordance with the invention. 
           [0012]      FIG. 3  is a cutaway view of a typical cylindrical roller bearing including a retainer that can be manufactured by a method in accordance with the invention. 
           [0013]      FIG. 4  is a cutaway view of a typical spherical roller bearing including a retainer that can be manufactured by a method in accordance with the invention. 
           [0014]      FIG. 5  is an exploded view of a typical constant velocity joint including a retainer that can be manufactured by a method in accordance with the invention. 
           [0015]      FIG. 6  is a perspective view of a retainer in accordance with an embodiment of the invention. 
           [0016]      FIG. 7  is a perspective view of a retainer in accordance with another embodiment of the invention. 
           [0017]      FIG. 8  is a perspective view of a portion of a retainer in accordance with another embodiment of the invention. 
           [0018]      FIG. 9  is a perspective view of a portion of a retainer in accordance with another embodiment of the invention. 
       
    
    
       [0019]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION 
       [0020]      FIGS. 1-5  illustrate a variety of exemplary antifriction hearings  10 , each of which includes an inner raceway  14 , an outer raceway  18  (not shown in  FIG. 2 ), a plurality of rolling elements  22  arranged and positioned between the raceways  14 ,  18 , and a retainer  26 . The retainer  26  maintains separation of the rolling elements  22  and guides the rolling elements  22  for uniform rotation with respect to the inner and outer raceways  14 ,  18 . 
         [0021]      FIG. 6  illustrates a retainer or cage  30  according to an embodiment of the invention. The retainer  30  of  FIG. 6  may be assembled, for example, as pail of a double-row spherical roller bearing. The retainer  30  includes a body  34  having an annular portion  38  and a plurality of engaging portions  42  extending axially from the annular portion  38 . Adjacent engaging portions  42  define pockets  46  that can receive a complement of rolling elements (not shown). 
         [0022]      FIG. 7  illustrates a retainer  30   a  according to another embodiment of the invention. The retainer  30   a  is similar to the retainer  30  of  FIG. 6 , and like components are given like reference numerals with the letter “a.” The retainer  30   a  of  FIG. 7  may be assembled, for example, as part of a spherical or cylindrical roller bearing. The retainer  30   a  includes a body  34   a  having two, axially-spaced rings  50 ,  54  interconnected by a plurality of engaging portions  42   a.  Adjacent engaging portions  42   a  define pockets  46   a  that can receive a complement of rolling elements (not shown). 
         [0023]    A method of manufacturing any of the retainers  26 ,  30 ,  30   a  illustrated in  FIGS. 1-7 , as well as other retainers not illustrated or described herein, in accordance with the invention is described below. 
         [0024]    The body  34 ,  34   a  of the retainer  30 ,  30   a  is formed from powdered metal by an additive manufacturing process, and more specifically by a three-dimensional (3D) printing process. Unlike subtractive manufacturing processes (e.g., machining) that remove material in order to form a finished part, additive manufacturing processes progressively add material to form a finished part. 
         [0025]    To produce the retainer  30 ,  30   a,  a slicing algorithm first divides a 3D computer or CAD model of the retainer  30 ,  30   a  into numerous thin slices or layers along a central axis of the retainer  30 ,  30   a.  layer data from the slicing, algorithm is then sent to and interpreted by a 3D printing apparatus (not shown) which, as described in further detail below, can sequentially construct the retainer  30 ,  30   a  layer by layer to produce a complete part. 
         [0026]    The 3D printing apparatus can include a powder bed, a spreader, and a printing head. It should be understood that the 3D printing apparatus can be configured in any manner and can include any number and variety of other components and features. Each layer of the retainer  30 ,  30   a  begins with a thin distribution of powdered metal spread over a surface of the powder bed by the spreader. In some embodiments the powdered metal can be iron. In other embodiments, the powdered metal can be mild or low carbon steels. Mild steels have a carbon content between about 0.3% and about 0.6%, while low carbon steels have a carbon content of about 0.3% or less. In still other embodiments, the powdered metal can be mild steel having a carbon content of about 0.15% or less. In yet other embodiments, the powdered metal can be stainless steel, such as 316 stainless steel or 420 stainless steel. Alternatively, the powdered metal can be any other metal or metal alloy. 
         [0027]    The printing head then selectively joins particles of the powdered metal that make up a particular layer of the retainer  30 ,  30   a.  In some embodiments, the printing head dispenses a binder material or adhesive to join the powder particles. In other embodiments, the printing head includes a laser that melts or sinters targeted areas to join the powder particles. Once the powdered metal particles are joined to form a cohesive layer, the powder bed is lowered and the spreader applies the next powder layer on top of the partially-constructed retainer  30 ,  30   a.  This layer-by-layer process repeats until the retainer  30 ,  30   a  is completely formed within a surrounding area of unbound metal powder. 
         [0028]    Next, for embodiments where the powder particles are joined by binder or adhesive, the retainer  30 ,  30   a  can be heated to an elevated temperature for a predetermined time period in order to cure the binder or adhesive and strengthen the retainer  30 ,  30   a.  Once the retainer  30 ,  30   a  has cured, the surrounding unbound powder is removed from the retainer  30 ,  30   a  using vibration, vacuum, high velocity air, or any other suitable method. Alternatively, the surrounding unbound powder can be removed before the curing process. 
         [0029]    The retainer  30 ,  30   a  is then heated in a sintering process for additional strengthening. During sintering, the retainer  30 ,  30   a  is heated in a furnace and held at a temperature less than a melting temperature of the powdered metal for a predetermined time period (e.g., 12-36 hours). The sintering process can burn off any binder or adhesive, and accelerates molecular diffusion to bond the powdered metal together. In other embodiments, such as those where the powder particles are joined by laser sintering, the curing and/or sintering processes can be omitted. 
         [0030]    The sintered retainer  30 ,  30   a  is generally a porous structure having, a density between about 50% and about 70% of a theoretical density of the powdered metal material (i.e., the density of the metal in wrought form). Depending on the desired application, the retainer  30 ,  30   a  can be used as a finished part in this state, or may undergo additional machining, treatment, or polishing. In other embodiments, the porous retainer  30 ,  30   a  can be infiltrated with another material, such as a lower inciting temperature metal, to increase the density of the retainer  30 ,  30   a  and provide it with desirable properties. More specifically, it has been found that infiltration of the porous retainer  30 ,  30   a  with bronze or copper increases the density and strength, reduces porosity, and provides superior tribological characteristics (i.e., reduces wear and/or friction experienced by the retainer and/or rolling elements during operation). 
         [0031]    The infiltration process can constitute a separate heating process or can be performed concurrently or sequentially with the sintering process. A predetermined quantity of infiltrant (e.g., bronze powder) is deposited over the retainer  30 ,  30   a,  then heated to a temperature above the melting point of the infiltrant. Gravity, capillary action, and/or pressure draws the melted infiltrant into the porous retainer  30 ,  30   a  until the infiltrated retainer  30 ,  30   a  has a porosity less than or equal to about 30%. In some embodiments the infiltrated retainer  30 ,  30   a  has a porosity less than or equal to about 20%. In other embodiments the infiltrated retainer  30 ,  30   a  has a porosity less than or equal to about 10%. In still other embodiments, the infiltrated retainer  30 ,  30   a  has a porosity less than or equal to about 5%. 
         [0032]    The infiltrated retainer  30 ,  30   a  possesses both the strength benefits of the base metal (e.g., mild steel, stainless steel, etc.) and the tribological benefits of the infiltrant, thereby eliminating the compromise required when selecting conventional retainer materials. For example, a retainer manufactured from mild steel powder infiltrated with bronze in accordance with the method described above has superior strength compared to a conventional brass or bronze retainer and superior tribological characteristics compared to a conventional steel retainer. 
         [0033]    The use of additive manufacturing processes such as 3D printing has many advantages in the manufacturing of retainers. For example, the process requires no tooling, thus small and medium production volumes can be made cost effectively. For high production volumes, a conventional powder metal compaction and sintering process can be used to create a porous powder metal retainer, which can then be infiltrated in the manner described above. 
         [0034]      FIG. 8  illustrates a retainer  30   b  according to another embodiment of the invention. The retainer  30   b  is similar to the retainer  30  of  FIG. 6 , and like components are given like reference numerals with the letter “b.” The retainer  30   b  includes an annular portion  38   b  and a plurality of engaging portions  42   b  that define pockets  46   b  for receiving a plurality of rolling elements (not shown). Each of the engaging portions  42   b  includes dimples  58  that can retain lubricant, reduce an overall weight of the retainer  30   b,  and reduce a contact area between the engaging portions  42   b  and the rolling elements. 
         [0035]      FIG. 9  illustrates a retainer  30   c  according to another embodiment of the invention. The retainer  30   c  is similar to the retainer  30  of  FIG. 6 , and like components are given like reference numerals with the letter “c.” The retainer  30   c  includes an annular portion  38   c  and a plurality of engaging portions  42   c  that define pockets  46   c  for receiving a plurality of rolling elements (not shown). Each of the engaging portions  42   c  includes a recessed area or channel  62  that can retain lubricant, reduce an overall weight of the retainer  30   c,  and reduce a contact area between the engaging portions  42   c  and the rolling elements. In addition, the annular portion  38   c  is substantially hollow to reduce an overall weight of the retainer  30   c.    
         [0036]    The retainers  30   b,    30   c  of  FIGS. 8 and 9  incorporate features and geometries that are easily producible with the 3D printing process described above, but otherwise cost prohibitive or not possible with traditional manufacturing methods. 
         [0037]    In some embodiments, any of the retainers  30 ,  30   a,    30   b,    30   c  described herein may undergo one or more finishing processes to improve the surface finish, dimensional accuracy, corrosion resistance, wear resistance, hardness, or appearance of the engaging portions  42 ,  42   a,    42   b,    42   c.  Such finishing processes may be particularly advantageous in high performance and high precision bearing applications. The engaging portions  42 ,  42   a ,  42   b,    42   c  can be finished by machining, mass finishing (e.g., tumble: or vibratory finishing), superfinishing, polishing, or any other finishing process. 
         [0038]    Various features of the invention are set forth in the following claims.