Abstract:
An idler roller assembly is comprised of a polymeric tubular body and an end cap fitted within a cavity of the tubular body at each end of the tubular body. An inner circumferential surface of the tubular body defining the cavity is configured with a plurality of recesses to define first, second and third cavity portions, with the third cavity portion being adjacent to each end of the tubular body. The first and third cavity portions have an inner diameter that is greater than an inner diameter of the cavity, and the second cavity portion has an inner diameter greater than the inner diameter of the first and third cavity portions. An end cap configured to house a bearing race to support each end of the tubular body on a shaft is configured with a first end, a second end and an outer cylindrical wall therebetween. The outer cylindrical wall is stepped to provide first, second and third outer cylindrical surface portions sized to fit closely within the first, second and third cavity portions of the tubular body. The outer cylindrical wall is radially tapered between the first and second outer cylindrical surface portions to facilitate insertion of the end cap within the cavity of the tubular body.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an idler roller assembly for a belt conveyor system. In particular, the present invention relates to a polymeric idler roller with snap-fit end caps for housing shaft-mounted bearings on which the idler roller assembly rotates. 
   Belt conveyor systems for transporting bulk materials, such as sand, gravel, and the like, utilize idler roller assemblies rotatably mounted on an elongate frame to support a motor-driven endless conveyor belt at various locations along the length of the frame. Typically, idler roller assemblies generally have comprised metal cylindrical tubes sealed at each end by a metal cap that is welded to the metal tube. Housed within each metal cap are bearings which are supported on a shaft. The shafts of one or more idler roller assemblies are mounted to support the conveyor belt in a desired configuration as the belt travels along the frame. Metal idler roller assemblies are durable, but they are noisy and add considerable weight to a belt conveyor system. Also, some bulk materials are prone to adhering to metal idler rollers, which can cause belt alignment problems, corrosion of the metal roller and increased wear of the conveyor belt. 
   Idler roller assemblies are also known in which the cylindrical tube and end caps are formed from a polymer. Assembly of such roller assemblies is time consuming, involving the use of adhesives to secure the end caps to the tube. Also, separate molds are required to produce idler roller assemblies having different lengths. There is a continuing need for improved idler roller assemblies formed from polymeric materials that are quick and easy to manufacture with varying lengths. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a polymeric idler roller assembly comprising a polymeric tubular body and a polymeric end cap. The polymeric tubular body has a cylindrical wall, a first end and a second end. The cylindrical wall defines an outer cylindrical surface and an inner cylindrical surface. The inner cylindrical surface defines a cavity having a first inner diameter and is configured to define a plurality of recesses in the cavity adjacent to each of the first and second ends of the tubular body. First and second recesses of the plurality of recesses have an inner diameter that is greater than the first inner diameter. A third recess of the plurality of recesses is located between the first and second recesses and has an inner diameter that is greater than the inner diameter of the first and second recesses. A polymeric end cap is positioned within the cavity of the tubular body adjacent to each of the first and second ends of the tubular body. Each end cap comprises an outer cylindrical wall, and inner cylindrical wall, a first end, a second end and an end wall connected between the outer and inner cylindrical walls at the second end of the end cap. The outer cylindrical wall of the end cap comprises first, second and third outer surface portions with first, second and third outer diameters, respectively, that approximate the respective inner diameters of the first second and third recesses of the tubular body. The first, second and third outer surface portions are positioned within the first, second and third recesses of the tubular body to secure the end cap to the tubular body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an idler roller assembly of the present invention. 
       FIG. 2  is a side view of a tube of the idler roller assembly of  FIG. 1  with one end portion of the tube shown in longitudinal cross-section. 
       FIG. 3  is a longitudinal cross-sectional view of an end cap of the idler roller assembly of  FIG. 1 . 
       FIG. 3A  is a perspective view of the end cap from an outer end of the end cap. 
       FIG. 3B  is a perspective view of the end cap from and inner end of the end cap. 
       FIG. 4  is a partial cross-sectional side view of the tube and end cap of the idler roller assembly with the end cap mounted to the tube. 
       FIG. 5  is a partial cross-sectional view of an assembled idler roller assembly of the present invention. 
   

   DETAILED DESCRIPTION 
   An embodiment of the idler roller assembly  10  of the present invention is shown generally in  FIG. 1 . In this embodiment, idler roller assembly  10  generally comprises a tubular body  12  having ends  14  and  16 , an end cap  18  mounted within tubular body  12  flush with ends  14  and  16 , and a shaft  20  which extends through openings in each end cap  18  for mounting to a support frame on a belt conveyor system. Shaft  20  carries the tubular body  12  and end cap  18  on a set of bearings (not shown) mounted within end cap  18  and covered by a dust cover  22 , as will be more fully described herein. 
     FIG. 2  shows a side view of tubular body  12  with a portion adjacent end  16  shown in cross-section. Tubular body  12  comprises an outer surface  24  and an inner surface  26  which together define a cylindrical wall  28  that extends from end  14  to end  16 . In one embodiment, wall  28  has a thickness of about 0.5 inches to about 1.0 inches. Inner surface  26  defines a cavity  30  that is exposed at ends  14  and  16 . Tubular body  12  is formed from a suitable polymer, such as high density polyethylene (HDPE), in an extrusion process. As such, tubular body  12  has a length from end  14  to end  16  which may be varied according to the particular application for a given belt conveyor system. In one embodiment, HDPE is extruded to define a tubular body  12  having a length of X feet. Subsequently, tubular body  12  is cut to the desired length for the given application. One such application is a troughing idler system for supporting a conveyor belt, in which case tubular body  12  may have a length of about 13.0 inches. Another such application is a return idler system, in which case tubular body  12  may have a length of about 18.0 inches to about 72.0 inches. An exemplary outer diameter of tubular body  12  is about 5.0 inches to about 6.0 inches. 
   Once tubular body  12  is formed at the desired length, the inner surface  26  is machined adjacent to ends  14  and  16  to define steps in wall  28 . As shown in  FIG. 2 , in one embodiment, the machined steps define a first cavity portion  30 A immediately adjacent end  16 , a second cavity portion  30 B immediately adjacent cavity portion  30 A, and a third cavity portion  30 C immediately adjacent cavity portion  30 B. Tubular body  12  is similarly machined adjacent end  14 . The corresponding inner surfaces  26 A,  26 B,  26 C of cavity portions  30 A,  30 B,  30 C, respectively, are generally cylindrical and coaxial with inner surface  26  of tubular body  12 . The inner diameter of cavity portions  30 A and  30 C are generally equal in size, while the inner diameter of cavity portion  30 B is greater than cavity portions  30 A and  30 C. The inner diameter of cavity portion  30 C is greater than the inner diameter of cavity  30 . As such, cavity portion  30 C defines a radial shoulder  32  which faces end  16 , and cavity portion  30 B defines facing radial shoulders  34  and  36 . In one exemplary embodiment, cavity portion  30 A has an inner diameter of about 4.000 inches, cavity portion  30 B has an inner diameter of about 4.120 inches, and cavity portion  30 C has an inner diameter of about 4.000 inches. Further, in one exemplary embodiment cavity portion  30 A has a width of about 0.369 inches, cavity portion  30 B has a width of about 0.500 inches, and cavity portion  30 C has a width of about 0.432 inches. Cavity portions  30 A,  30 B and  30 C define a docking site for coupling end cap  18  to tubular body  12 , as will be more fully described herein. 
     FIGS. 3 ,  3 A and  3 B show end cap  18  in longitudinal cross-section and end perspective views of opposite ends of end cap  18 , respectively. End cap  18  generally comprises a composite cylindrical body having an outer cylindrical wall  40 , an inner cylindrical wall  42  radially spaced from and generally coaxial with the outer cylindrical wall  40 , a first end  44 , a second end  46  and an end wall  48  which extends between the inner cylindrical wall  42  and the outer cylindrical wall  40  adjacent to the second end  46 . The outer cylindrical wall  40  includes an outer surface  50  and an inner surface  52 . Likewise, the inner cylindrical wall  42  includes an outer surface  54  and an inner surface  56 . Integrally connected to the inner cylindrical wall  42  at the first end  44  is a radial wall  58  which extends radially inward from the inner cylindrical wall  42  and defines an opening  60  at the first end  44  of end cap  18 . Radial wall  58  comprises an outer surface  62 , which faces toward second end  46  and an inner surface  64  which faces toward first end  44 . 
   Integrally connected to and between the outer cylindrical wall  40 , inner cylindrical wall  42 , end wall  48  and radial wall  58  are a plurality of radially spaced ribs  66 . Ribs  66  include a first planar portion  66 A, which extends between and is integrally formed with the inner surface  50  of the outer cylindrical wall  40  and the outer surface  56  of the inner cylindrical wall  42 , and a second planar portion  66 B which is integrally formed with the inner surface  64  of radial wall  58 . The first planar portion  66 A further is integrated into the end wall  48  ( FIG. 3 ). The second planar portion  66 B extends rearward of first end  44  and has a radially tapered outer edge  68  and a radially tapered inner edge  69 . Outer edges  68  and  69  converge toward one another. Ribs  66  provide structural support to the respective walls  40 ,  42 ,  48  and  58  of end cap  18 . In one embodiment, end cap  18  comprises eight generally equally radially spaced ribs  66 . In an alternate embodiment, end cap  18  comprises twelve generally equally radially spaced ribs  66 . In one embodiment, end cap  18  is formed by molding a suitable polymer, such as HDPE, using known molding techniques. In one exemplary embodiment walls  40 ,  42 ,  48  and  58  and ribs  66  have a wall thickness of about 0.125 inches to about 0.187 inches. The relatively thin wall and rib structure of end cap  18  makes end cap  18  relatively light in weight and yet imparts radial structural integrity adequate to support the tubular body  12 . 
   As shown in  FIGS. 3 and 3A , the outer surface  50  of outer wall  40  is configured with various tapers. Immediately adjacent to first end  44  of end cap  18 , there is a radially tapered surface portion  70 , which has a gradually increasing outer diameter relative to the outer diameter of first end  44 . The outer diameter of first end  44  is selected to be smaller than the inner diameter of cavity portion  30 A of tubular body  12 , but greater than the inner diameter of cavity  30  of tubular body  12 . Immediately adjacent to surface portion  70  is a first cylindrical surface portion  72  of outer surface  50 , which has a relatively constant outer diameter. In general, the outer diameter of the first cylindrical surface portion  72  is selected to approximate the inner diameter of cavity portion  30 C of tubular body  12 . 
   Immediately adjacent to surface portion  72  is a ramped surface portion  74 , which has a gradually increasing outer diameter relative to surface portion  72 . Immediately adjacent to ramped surface portion  74  is a second cylindrical surface portion  76 , which has a relatively constant outer diameter that is greater than that of the first cylindrical surface portion  72 . In general, the outer diameter of the second cylindrical surface portion  76  is selected to approximate the inner diameter of cavity portion  30 B of tubular body  12 . Immediately adjacent to the second cylindrical surface portion  76  is a third cylindrical surface portion  78 , which has a relatively constant outer diameter that is smaller than the outer diameter of the second cylindrical surface portion  76 . In general, the outer diameter of the third cylindrical surface portion  78  is selected to approximate the inner diameter of cavity portion  30 A of tubular body  12 . Outer surface  50  transitions from the second cylindrical surface portion  76  to the third cylindrical surface portion  78  via a transverse surface that defines a radial shoulder  80 . In one exemplary embodiment, the outer diameter of the first cylindrical surface portion  72  and the third cylindrical surface portion  78  is about 4.020 inches and the outer diameter of the second cylindrical surface portion  76  is about 4.140 inches. Further, in one exemplary embodiment, the combined width of surface portions  70  and  72  are selected to generally equal the width of cavity portion  30 C of tubular body  12 ; the combined width of surface portions  74  and  76  are selected to be generally equal to the width of cavity portion  30 B; and the width of surface portion  78  is selected to be generally equal to the width of cavity portion  30 A. 
     FIG. 4  shows a partial cross-sectional view of end  16  of tubular body  12  with end cap  18  fitted within cavity  30 . End cap  18  is installed within cavity  30  by inserting end  44  within cavity  30 A. The radially tapered outer surface portion  70  facilitates this initial insertion step. Sufficient axial force is exerted on end  46  of end cap  18  to move end  44  of end cap  18  toward cavity  30 C. As end  44  of end cap  18  enters cavity  30 A, the first cylindrical surface portion  72  of end cap  18  functions to guide the travel of end cap  18  along the inner surface  26 A of cavity portion  30 A until the ramped surface portion  74  engages the inner surface  26 A of cavity portion  30 A. Under sufficient axial force, plastic deformation of tubular body  12  and end cap  18  allows movement of the second cylindrical surface portion  76  through cavity  30 A and into cavity  30 B. As the second cylindrical surface portion  76  begins to enter cavity  30 B, the first cylindrical surface portion  72  is in engagement with the inner surface  26 C of cavity portion  30 C, which functions to keep end cap  18  coaxially aligned throughout the installation of end cap  18 . When end  44  of end cap  18  contacts radial shoulder  32  in cavity portion  30 C, the radial shoulder  80  of end cap  18  axially engages radial shoulder  36  of cavity  30 B thereby locking end cap  18  within cavity  30  with end  46  of end cap  18  in a generally common plane flush with end  16  of tubular body  12 . Thus the axial locking mechanism of the present invention is stabilized by opposing cylindrical surfaces (i.e., first and third cylindrical surface portions  72  and  78 ) on either side of the captured second cylindrical surface portion  76 . 
   As shown in  FIG. 5 , once end cap  18  is secured within tubular body  12 , final assembly of idler roller assembly  10  involves fitting a bearing race  82  within the inner cylindrical wall  42  and against radial wall  58  of end cap  18 . A shaft  20  is fitted within each bearing race  82  in a conventional manner. Each bearing race  82  is then covered with a suitable dust cover  22  which is secured relative to shaft  20  with a retaining clip that seats within in a groove formed in the shaft outer surface a manner known in the art. One such dust cover is made by Superior Industries under the brand name SPINGUARD®. In one embodiment, dust cover  22  has an outer surface that is configured to lie in the same general plane as end  16  of tubular body  12  and end  46  of end cap  18 . The resulting construction of tubular body  12 , end cap  18  and dust cover  22  defines a flat end surface of idler roller assembly  10  which aids in eliminating a build-up of transported material coming in contact with idler roller assembly  10 . Further, the internal mounting of end cap  18  so as to be flush with each end of tubular body  12  ensures that no radial impact forces from objects being transported on a conveyor belt will be able to act on an exposed portion of an end cap. All such forces are absorbed via the composite idler roller assembly. Thus damage to idler roller end caps and bearings is minimized. 
   The idler roller assembly of the present invention is easy to manufacture and assemble without the use of adhesives to secure the end cap to the tubular body. The method of extruding the tubular body and machining the inner circumferential surface of the tubular body adjacent each end of the tubular body to define a docking site for end caps conveniently allows the idler roller assembly to be constructed at different lengths without the need for separate molds. The configuration of the outer wall of the end cap allows the end cap to be supported and guided relative to the inner cylindrical surface of the tubular body throughout the installation of the end cap. The elevated central portion of the end cap outer wall serves to secure the end cap within a corresponding cavity of the tubular body, with adjacent flanking surface portions of the end cap outer wall supporting end cap  18  relative to tubular body  12 . The completely internal mounting of end cap  18  flush with each end of tubular body  12  protects the end cap and bearings from radial forces and aids in minimizing and preventing material build-up on the end of the idler roller assembly. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.