Patent Publication Number: US-2015059184-A1

Title: Methods of Fabricating a High Pressure Bushing and Supporting a Shaft

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to bearings, and more particularly to bushings for high-pressure applications. 
     Plain bearings or bushings are well known and include a generally annular body with an inner circumferential surface for supporting a sliding and/or rotational movement of a cylindrical body, such as a shaft or piston, along a central axis. These bushings are typically installed within an annular groove or gland that retains the body with respect to the axis. In certain applications, the bushing can be installed within a gland by sliding the body axially into an open end of the gland, and then “closing” the gland with an adjacent structural member (e.g., retainer ring in a bearing block). 
     In other applications, the bushing must be installed within a “closed” gland that is spaced from the axial ends of a solid bore. In such cases, the bushing must be deflectable, at least to a certain extent, to enable the outside diameter of the body to inwardly deflect or contract for axial displacement of the body through the bore, and then expand outwardly when positioned within the gland. The bushings in such applications are typically formed of a polymeric material to enable such radial contraction and expansion. However, in high pressure applications, such polymeric bushings may lack the necessary material strength and thereby fail under loading. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention is a method of fabricating a bushing for supporting a shaft within a housing, the housing having an inner circumferential surface and the shaft having an outer circumferential surface. The method comprises the steps of: determining a size of a section of the housing inner circumferential surface and a size of a section of the shaft outer circumferential surface; fabricating a generally tubular body having an outer circumferential surface sized to fit within the housing inner surface section and an inner circumferential surface sized to receive at least a portion of the shaft; and separating the tubular body into a plurality of generally arcuate tube segments. 
     In another aspect, the present invention is a method of supporting a cylindrical body within a housing, the method comprising the steps of: forming an annular groove in an inner circumferential surface of the housing; providing a plurality of generally arcuate tube segments; and installing the tube segments within the annular groove such that the tube segments are aligned circumferentially about the central axis so as to form a generally tubular body configured to slidably support the cylindrical body. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, which are diagrammatic, embodiments that are presently preferred. It should be understood, however, that the present invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is perspective view of a presently preferred construction of a multi-piece bushing, shown in an assembled state; 
         FIG. 2  is a perspective view of the multi-piece bushing of  FIG. 1 , shown in an exploded or “unassembled” view; 
         FIG. 3  is a perspective view of the multi-piece bushing shown installed in a housing; 
         FIG. 4  is an axial cross-sectional view of a presently preferred housing; 
         FIG. 5  is an enlarged, broken-way view of an axial cross-section of  FIG. 3 ; 
         FIG. 6  is a perspective view of an alternative construction of a multi-piece bushing; 
         FIG. 7  is a side view of the multi-piece bushing of  FIG. 1 ; 
         FIG. 8  is an enlarged view of section  8  of  FIG. 7 ; 
         FIGS. 9A-9C , collectively  FIG. 9 , are each a broken-away, perspective view of an alternative interface of a first and second tube segment of the multi-piece bushing; 
         FIG. 10  is a side view of a solid bushing used to fabricate the multi-piece bushing, shown marked for cutting; 
         FIG. 11  is a side view of the bushing of  FIG. 10  after the cutting process; 
         FIG. 12  is an axial cross-sectional view of a housing and a first tube segment of the bushing, viewed in a downward direction and depicting a first step in an installation process; 
         FIG. 13  is a perspective view of the housing with the first segment installed; 
         FIG. 14  is an axial cross-sectional view of the housing, the first tube segment and a second tube segment of the bushing, viewed in a downward direction and depicting a second step in the installation process; 
         FIG. 15  is a perspective view of the housing with the first and second segments installed; 
         FIG. 16  is an axial cross-sectional view of the housing, the first and second tube segments and a third tube segment of the bushing, viewed in a downward direction and depicting the beginning of a third step in the installation process; 
         FIG. 17  is an axial cross-sectional view of the housing and the first, second and third tube segments, depicting the completion of the installation process; 
         FIG. 18  is an axial cross-sectional view of the housing and bushing after installation; and 
         FIG. 19  is an axial cross-sectional view of the housing and installed bushing, showing the insertion of a movable cylindrical body supported by the bushing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “upper” and “upward” designate directions in the drawings to which reference is made. The words “inner”, “inwardly” and “outer”, “outwardly” refer to directions toward and away from, respectively, a designated centerline or a geometric center of an element being described, the particular meaning being readily apparent from the context of the description. The terminology includes the words specifically mentioned above, derivatives thereof, and words of similar import. 
     Referring now to the drawings in detail, wherein like numbers are used to indicate like elements throughout, there is shown in  FIGS. 1-19  a multi-piece bushing  10  for supporting a movable cylindrical body  12  ( FIG. 19 ) within a housing  14  having an axis A C . The body  12  has an outer circumferential surface  12   a  with an outside diameter OD S  ( FIG. 19 ) and is rotatable about, and/or linearly displaceable along, the axis A C . The cylindrical body  12  may be any type of movable body requiring support, such as a rotary shaft, a linearly displaceable piston, etc. The housing  14  has an inner surface  16  extending circumferentially about the axis A C  and an annular groove  18  or “gland” formed in the surface  16  so as to extend radially outwardly from a remainder of the surface  16  and circumferentially about the axis A C . The bushing  10  basically comprises a plurality of generally arcuate tube segments  20  disposeable within the groove  18  and alignable circumferentially about the housing axis A C  so as to form a generally tubular body  11  configured to slidably support the cylindrical body  12 . 
     Preferably, each tube segment  20  is formed of a generally rigid metallic material, such as for example, low carbon steel, so that the bushing  10  is capable of supporting relatively higher loads or pressures than a similarly sized bushing formed of a polymeric material. By forming the bushing  10  of a plurality of tube segments  20 , the metallic bushing  10  is capable of being installed within existing “closed” glands, particularly those in which a solid metallic bushing is incapable of deflecting to the extent necessary for installation. Although depicted as relatively thin-walled tube segments  20 , each segment  20 , and the resultant bushing  10  formed thereby, may have any appropriate thickness as required by the specific application of the bushing  10 . 
     More specifically, each tube segment  20  has inner and outer circumferential surface sections  22 ,  24  respectively, two opposing radial ends  26  and two opposing axial ends or sides  28 . Each one the tube segments  20  has an axial width W AS  between the two axial ends/sides  28  and a radial thickness t R  between the inner and outer surface sections  22 ,  24 , as indicated in  FIG. 5 . The inner circumferential surface sections  22  of all of the plurality of tube segments  20  collectively form a generally continuous inner circumferential bearing surface  23  defining a bushing bore  25  when the segments  20  are disposed within the housing groove  18 . 
     The bearing surface  23  is configured to slidably support the cylindrical body  12 , so as to reduce friction when the body  12  linearly displaces or/and angularly displaces about the central axis A C . Additionally or alternatively, the tube segments  20  may be sized to provide a bushing inside diameter ID B  ( FIG. 7 ) with a magnitude relative to the magnitude of the cylindrical body outside diameter OD C  ( FIG. 19 ) such that bearing surface  23  seals against the body outer circumferential surface  12   a.  Further, when the bushing  10  is installed in the groove  18 , each segment radial end  26  is located generally adjacent to one of the radial ends  26  of one of the other tube segments  20  and each segment axial end  28  is generally axially aligned with one of the two axial ends  28  of each one of the other tube segments  20 , as best shown in  FIGS. 3 and 18 . 
     That is, the tube segments  20  are spaced about the central axis A C  with the radial end  26  of each segment  20  generally abutting the end  26  of an adjacent segment  20  and the axial ends  28  on each side of all the segments  20  are generally aligned with each other to form one of two generally continuous axial side ends or edges. Although the radial ends  26  of the segments  20  are each located relatively closely proximal to the end  26  of the adjacent segment  20 , there is preferably a radial clearance between at least some of the segment radial ends  26  to facilitate installation within the groove  18 . In one preferred application, the total radial clearance between all the pairs of adjacent radial ends  26  of the tube segments  20  is about fifty-one thousands of an inch (0.051″), which results from three wire EDM cuts to a solid bushing in a preferred fabrication method, as discussed below. However, the actual radial clearance between any particular pair of segment radial ends  26  may be substantially lesser, such as when the radial ends  26  of two segments  20  are contacting each other. 
     Preferably, the bushing  10  is formed of three pieces, such that the plurality of tube segments  20  includes a first segment  21 A, a second segment  21 B and a third segment  21 C. However, the bushing  10  may include only two tube segments  20  or four or more segments  20  (no alternatives shown). As best shown in  FIG. 2 , each one of the first and second segments  21 A,  21 B preferably has a first radial end  27   a  adjacent to a first end  27   a  of the other one of the first and second segments  21 A,  21 B and an opposing, second radial end  27   b  with an angled end surface  30  facing generally “inwardly” or toward the central axis A C . The third tubular segment  21 C preferably has an angled end surface  32  on each one of first and second radial ends  27   a,    27   b,  with each of the two angled end surfaces  32  of the third segment  21 C facing generally “outwardly” or away from the central axis A C . 
     As described in greater detail below, the first and second tube segments  21 A,  21 B are first installed within the housing groove  18  and then the third tubular segment  21 C is installed in the groove  18  by positioning the segment  21 C between the other two segments  21 A,  21 B and then displacing the third segment  21 C generally radially outwardly. The two outwardly angled end surfaces  32  of the third segment  21 C slide against the two inwardly-angled end surfaces  30  of the first and second segments  21 A,  21 B until each of the third segment end surfaces  32  are generally juxtaposed with a separate one of the angled end surfaces  30  of the first and second tube segments  21 A,  21 B. 
     Preferably, the inwardly-facing angled radial end surface  30  of each one of the first and second tube segments  21 A,  21 B extends generally obliquely between the two axial ends  28  of the segment  21 A,  21 B, as best shown in  FIGS. 1 and 2 . That is, the two angled end surfaces  30  are both angled so as to face generally radially inwardly toward the axis A C  and lay in a plane extending between the axial ends  28  that is skewed with respect to the central axis A C , as opposed to being within a generally radial plane that includes or is parallel to the central axis A C , as depicted in  FIG. 6 . Further, each one of the two outwardly-facing angled radial end surfaces  32  of the third tube segment  21 C preferably extends generally obliquely between the two axial ends  28  of the third segment  21 C. One of the two angled end surfaces  32  of the third tube segment  21 C is oriented so as to generally mate with the angled radial end surface  30  of the first tube segment  21 A and the other one of the two angled end surfaces  32  of the third tube segment  21 C is oriented so as to generally mate with the angled radial end surface  30  of the second tube segment  21 B. The obliquely-extending interfaces between the radial end surfaces  30 ,  32  of the three segments  21 A,  21 B and  21 C reduces the potential for uneven wear on a linearly displacing cylindrical body  12  (e.g., a piston) as could be caused by a substantially axially-extending interface between the tube segments  20 . 
     As depicted in  FIG. 9 , the first radial end  27   a  of at least one of the first and second tube segments  21 A,  21 B preferably has a projection  34  and the first radial end  27   a  of at least the other one of the tube segments  21 B,  21 A has a recess  36 . The recess(es)  36  is/are configured to receive the projection(s)  34  so as to interlock the first and second tube segments  21 A,  21 B, which is particularly beneficial when installing the bushing  10  in the manner as described below. The projection  34  may extend from only one of the first radial ends  27   a  and be formed with generally wedge-shaped radial cross-sections ( FIG. 9A ), generally ball-shaped radial cross-sections ( FIG. 9C ) or in any other appropriate manner, with a mating recess  36  formed in a complementary fashion in the other first radial end  27   a.  Alternatively, the first radial ends  27   a  of both the first and second tube segments  21 A,  21 B may be formed with both a projection  34  and a recess  36 , such as for example, an interlocking “S”-shaped interface as depicted in  FIG. 7B . As a further alternative, the two mating ends  27   a,    27   b  of the first and second tube segments  21 A,  21 B may be formed to generally abut without interlocking. 
     Referring to  FIGS. 10 and 11 , the bushing  10  is preferably formed by first fabricating a solid, generally tubular body or bushing  40  of a metallic material, as shown in  FIG. 10  with markings  41  to indicate intended separation zones/planes. The tubular body/bushing  40  has an outer circumferential surface  40   a  sized to fit within the housing annular groove  18  and an inner circumferential surface  40   b  sized to receive at least a portion of the shaft  12 . More specifically, the solid bushing  40  is formed having an inside diameter ID B  with a selected value approximately or generally equal to the measured value of the shaft outside diameter OD S  and an outside diameter OD B  with a selected value generally/approximately equal to the measured value of the inside diameter ID G  of the housing groove  18  (described in further detail below). Then, the solid bushing  40  is separated into the plurality of tube segments  20  by any appropriate means, such for example, cutting with a wire EDM (“electrical discharge machine”), a saw, a torch, a water jet or a laser device, so as to form the tube segments  20 , as indicated in  FIG. 11 . 
     The separating or cutting process is conducted so as to form the first and second ends  27   a,    27   b  of each tube segment  20  with the radial end surfaces  30 ,  32 , projection(s)  34  and recess(es)  36  as described above. 
     It must be noted that the solid bushing  40  may either be fabricated to fit an existing housing groove  18  or an existing (i.e., “prefabricated”) solid bushing  40  may be selected, and the groove  18  formed (e.g., machined) in the housing  14  to accommodate the tube segments  20  cut from the selected solid bushing  40 . Specifically, the size of a section (e.g., the groove  18 ) of the housing inner circumferential surface  16  and the size of the shaft outer circumferential surface  12   a  may first be determined, for example by measuring the inside diameter ID G  of the housing groove  18  and the outside diameter OD S  of the shaft outer surface  12   a.  Then, the solid bushing  40  may be fabricated as discussed above to fit within the groove  18  and receive at least a section of the shaft  12 . 
     Alternatively, the solid bushing  40  may be selected from existing prefabricated or manufactured stock, such as for example, a bushing intended for a different application, having an inside diameter ID B  appropriately sized to receive the shaft  12 . Then, the groove  18  is formed within the housing inner circumferential surface  16  by a machining process, such as boring, to the required dimensions to accommodate the tube segments  20  cut from the solid body/bushing  40 . 
     Referring to  FIGS. 3 ,  4 ,  5  and  18 , the bushing  10  in combination with the housing  14  forms a support assembly  15  for a movable cylindrical body or shaft  12  ( FIG. 19 ). Although depicted as a generally circular cylinder with an axial length that is not substantially greater than axial length/width of the bushing  10 , the housing  14  may be any appropriate body or assembly for at least partially containing the cylindrical body  12 , such as for example, a pump body, a cylinder of a piston device, a pillow block for a bearing, etc, and may have any appropriate size or shape. As discussed above, the housing  14  has an inner surface  16  extending circumferentially about the axis A c , which defines a bore  17  for receiving at least a portion of the cylindrical body or shaft  12 , and opposing axial ends  14   a,    14   b.  The annular groove or gland  18  extends radially outwardly from a remainder of the housing inner surface  16  and circumferentially about the axis A C , and has opposing axial ends  18   a,    18   b.    
     Preferably, the groove  18  is spaced from the two axial ends  14   a,    14   b  of the housing  14  by a first axial distance d 1  between the housing first end  14   a  and the groove first axial end  18   a  and a second axial distance d 2  between the housing second end  14   b  and the groove second end  18   b,  each distance d 1 , d 2  being greater than zero such that the groove  18  is not “open ended”. The spacing distances d 1 , d 2  may be generally equal, such that the groove  18  is generally centrally located within the housing  14 , or may be substantially different, such that the groove  18  is located more proximal to one of the two axial ends  14   a  or  14   b  than to the other end  14   a,    14   b.  Further, the groove  18  may be formed in the housing  14  by any appropriate means, such as for example, machining the groove  18  into a finished housing  14 , casting or forging the groove  18  during casting/forging of the housing  14 , etc. 
     As best shown in  FIG. 4 , the groove  18  includes an inner circumferential surface  50 , which is spaced radially outwardly from the housing inner surface  16  and has an inside diameter ID G , and two facing shoulder surfaces  52 A,  52 B. The shoulder surfaces  52 A,  52 B are spaced axially apart and extend generally radially between the groove inner surface  50  and the housing inner surface  16 . As such, the housing groove/gland  18  has an axial width W AG  defined as the axial or perpendicular distance between the shoulder surfaces  52 A,  52 A (i.e., and thus between the two axial ends  18   a,    18   b ) and a radial depth d R  defined as the radial distance between the housing inner surface  16  and the groove inner surface  50 . In one presently preferred application, the housing  14  is oriented with the central axis A c  extending generally vertically, such that the two shoulder surfaces  52 A,  52 B extend generally horizontally, one shoulder surface  52 A facing generally upwardly and providing a support surface, as discussed below. 
     Further, the housing groove  18  is sized to receive the bushing tube segments  20  with a slight axial clearance and with each of the segments  20  projecting radially inwardly with respect to the housing inner surface  16  and into the bore  17 . That is, the axial width W AS  of each tube segment  20  is lesser than the groove axial width W AG , such that all of the tube segments  20  fit within the groove  18  with clearance, as best shown in  FIG. 5 . Also, the radial thickness t R  of each tube segment  20  is greater than the groove radial depth d R  such that the bearing surface  23  is spaced radially inwardly from the housing surface  16 . Thus, the cylindrical body or shaft  12  only contacts the bearing surface  23  and not the housing inner surface  16 . Furthermore, the inside diameter ID G  of the housing groove  18  is sized slightly larger than the outside diameter OD B  of the assembled bushing body  11  to receive all the bushing segments  20  with minimal radial clearance. 
     Referring now to  FIGS. 12-19 , in the preferred application described above with a substantially vertically-extending central axis A c , the plurality of bushing tube segments  20  are installed within the groove  18  in the following manner The first tube segment  21 A is first inserted into the groove  18  and positioned such that one axial end  28  of the first segment  21 A is disposed on the groove support surface  52 A, and the segment outer surface  24  contacts the groove inner surface  50 , as shown in  FIGS. 12 and 13 . Next, the second tube segment  21 B is inserted into the groove  18  such that one axial end  28  is disposed on the groove support surface  54 , the segment outer surface  24  is disposed on the groove inner surface  50 , and the first radial end  27   a  of the second segment  21 B is adjacent to, and preferably abutting, the first radial end  27   a  of the first segment  21 A, as depicted in  FIGS. 14 and 15 . If present, the projection(s) and recess(es) of the first and second tubular segments  21 A,  21 B are engaged to interlock. Then, as shown in  FIGS. 16 and 17 , the third tube segment  21 C is inserted into the housing groove  18  such that one axial end  28  of the third segment  21 C is disposed on the groove support surface  52  and each third segment angled end surface  32  is juxtaposed with a separate one of the angled end surfaces  30  of the first and second segments  21 A,  21 B. 
     More specifically, the third tube segment  21 C is positioned generally between the first and second segments  21 A,  21 B and is then displaced generally radially outwardly, as indicated in  FIG. 16 . The two outwardly angled end surfaces  32  of the third segment  21 C slide against the two inwardly-angled end surfaces  30  of the first and second segments  21 A,  21 B until the mating surfaces are juxtaposed and the third segment outer surface  24  is disposed against the groove inner surface  50 , as shown in  FIGS. 17 and 18 . Thereafter, the cylindrical body  12  (shaft, piston, etc.) is displaced generally vertically along the axis A C  to first enter one end of the housing bore  17  and then extend through the bushing bore  25 , such that the cylindrical body  12  prevents radially-inward displacement of the tube segments  20  and thereby retains the segments  20  within the housing groove  18  and forms as shaft assembly  13 , as shown in  FIG. 19 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as generally defined in the appended claims.