Abstract:
A retainer assembly for a seal encircling a shaft to prevent migration along the shaft, has at least two rings that encircle the shaft. A first ring is fastened to the wall and encircles the shaft to form an annular recess surrounding the periphery of the seal. A second ring encircles the shaft with outside and inside diameters allowing at least a portion of the second ring to fit into the annular recess between the first ring and the seal. A plurality of fasteners attach to the first ring and are external to the second ring. Each fastener engages a peripheral portion of the second ring to press the second ring toward the wall. In a preferred embodiment, the retainer has inner, middle, and outer rings that allow retaining of two seal sections.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a regular application filed under 35 U.S.C. §111(a) claiming priority, under 35 U.S.C. §119(e)(1), of provisional application Ser. No. 61/491,677, previously filed May 31, 2011, under 35 U.S.C. §111(b). 
     
    
     BACKGROUND 
       [0002]    Pumps and other types of processing devices often have rotating shafts that penetrate the device housing to an internal space that contains fluids or particles undergoing processing. Such devices frequently employ seals that surround the shafts to prevent the fluids or particles from migrating during use from the internal space along the shaft to outside the housing. These seals, being subjected to constant rubbing during use, deteriorate over time, and require replacing. Large shafts used because of high torque requirements, have seals and retainers for them that are large and expensive, and difficult to replace properly. 
         [0003]    The seals and their retainers are attached to the housing itself. Such shafts have bearings that usually are external to the device housing. Thus, these large shafts and the bearings that support them are difficult if not impossible to remove in order to replace a seamless or unitary seal and housing. To simplify replacement, the seals and their retainers usually have a segmented or multi-part structure that allows disassembly and assembly on the shaft. 
         [0004]    In some scenarios, especially with large shafts, lip seals in a back-to-back arrangement provide an improved sealing function. This requires that the retainer for these seals accommodate a large cross-section width, i.e. axial length, for the seals. Since the retainers are made of steel, a typical retainer design for large shaft seals has very large and heavy components, which creates issues for seal installation and replacement. Access to the seals and their retainers may be in a crowded space as well, further complicating seal replacement. 
         [0005]      FIGS. 1 ,  2 A, and  2 B show the prior state of the art for multi-part seals.  FIG. 1  is a front elevation view of a processor  10  having a wall  11  through which passes a shaft  26  for providing torque to an internal mechanism. A seal assembly  30  surrounds shaft  26  to prevent the migration of material into and from the internal space generally indicated at  19  in  FIGS. 2A and 2B . 
         [0006]      FIGS. 2A and 2B  are cross sections each showing one minor variation of the configuration of a conventional seal assembly  30  encircling the shaft  26 . These two configurations provide different axial positions for a seal unit  15  comprising seals  15   a  and  15   b.    
         [0007]    A mounting ring  27  permanently attached to wall  11  and with an axial dimension greater than that of wall  11 , forms a periphery for the opening through which shaft  26  passes. Ring  27  has an inside diameter somewhat larger than the shaft  26  diameter, as  FIGS. 2A and 2B  show. Ring  27  strengthens and stiffens wall  11  in the vicinity of shaft  26 . 
         [0008]    Seal assembly  30  includes a seal  15  comprising flexible ring-type seal elements  15   a  and  15   b , an inner retainer element  13 , and an outer retainer element  12 . Each of seal elements  15   a  and  15   b , inner retainer element  13 , and outer retainer element  12 , have two or more segments to allow assembly to and disassembly from shaft  26 , of the parts of seal assembly  30  necessary to replace seals  15   a  and  15   b . An extension spring  15   c  presses the lip of seal element  15   a  or  15   b  against shaft  26  to insure good contact between them. The seal elements  15   a  and  15   b  are preferably similar and are intended to be installed with a small axial spacing between them, as  FIGS. 2A and 2B  show. 
         [0009]    Retainer elements  12  and  13  serve to hold the individual seals  15   a  and  15   b  in place encircling shaft  26  and to prevent leakage around seals  15   a  and  15   b  to and from internal space  19 . Each retainer ring  12  and  13  comprises two half circle segments. Cap screws  23  pass through holes at the end of one segment into threaded holes in the end of the other segment to hold the two outer retainer element  12  segments together to encircle shaft  26 . Cap screws  29  pass through holes at the end of one segment of retainer  13  into threaded holes in the end of the other segment to hold the two inner retainer element  13  segments together to encircle shaft  26 . (By the term “cap screw” is meant a fastener for machine parts, threaded at one end of its shank and held by threads tapped in a hole into which the cap screw is screwed. The end of the shank opposite the threads has a head with a feature such a hex shape or a square socket for applying torque to the shank.) 
         [0010]    When replacing seals  15   a  and  15   b , it is possible that removing only outer retainer element  12  will be necessary if seals  15   a  and  15   b  can be easily removed from their recess, and their recess does not require cleaning. 
         [0011]    In configurations of both  FIGS. 2A and 2B , inner retainer element  13  is fastened to the mounting ring  27  of processor  10  with cap screws  17 , and the outer retainer element  12  is fastened to inner retainer element  13  with threaded rod fasteners  9 . Retainer element  13  has an annular flange  22  and retainer element  12  also has an annular radial flange  23 , both flanges  22  and  23  extending toward shaft  26 . In an operating installation, retainer element flanges  22  and  23  retain seals  15   a  and  15   b  on the inside and the outside respectively in the desired axial position on shaft  26 . 
         [0012]    Inner retainer element  13  maintains the position of annular seals  16 , allowing seals  16  to prevent migration of material along inner retainer element  13 . A Zerk fitting  18  allows filling the space between and adjacent to seals  15   a  and  15   b  with grease after assembly is complete. 
         [0013]      FIG. 2A  shows a first orientation of retainer element  13  with the flange  22  adjacent to mounting ring  27 .  FIG. 2B  shows a second, reversed orientation of retainer element  13  with the flange  22  spaced from mounting ring  27 . In the  FIG. 2B  configuration, a spacer ring  14  comprising two half circle segments held in place by means not shown, space retainer elements  12  and  13  to place flanges  22  and  23  at the appropriate axial spacing to accommodate seals  15   a  and  15   b . Thus, by orienting element  13  one way or the other, the seal assembly  30  can position seals  15   a  and  15   b  at two different axial positions on shaft  26  relative to housing wall  11 . 
         [0014]    The various components for this conventional seal assembly  30  are quite heavy for at least two reasons. In the first place, shaft  26  may have a diameter for large processors  10  of nearly 20 in., meaning that retainer elements  12  and  13  must have even larger maximum diameters. Secondly, the seal assemblies  30  must also be quite large in the axial dimension to accommodate the holes into which the tangential cap screws  23  and  29  thread. The retainer elements  12  and  13  may therefore weigh several tens of pounds. 
         [0015]    The weight of the seal assembly  30  components becomes an issue during the periodic replacement of seals  15   a  and  15   b  that normal wear and deterioration requires. The working space for replacing seals  15   a  and  15   b  is often cramped. Yet when reattaching the retainer elements  13  and  12 , they must be positioned so that the cap screws  17  and fasteners  9  precisely align with their respective holes. This is difficult with a heavy retainer element  13  while working in a cramped space. This situation makes replacement of seals  15   a  and  15   b  time-consuming and difficult. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0016]    A seal retainer assembly cooperates with a seal to prevent migration of material along a rotatable shaft passing through a wall. The seal encircles the shaft adjacent to the wall and has a surface facing away from the wall. The retainer assembly supports the shape and maintains the location of the seal to prevent this migration. 
         [0017]    The retainer assembly has a number of individual parts designed to simplify disassembly and reassembly. An inner ring of the assembly is fastened to the wall and encircles the shaft to form an annular recess surrounding the periphery of the seal. A middle ring encircles the shaft, and has outside and inside diameters allowing the middle ring to fit into the annular recess between the inner ring and the seal. 
         [0018]    An outer ring encircles the shaft, and has a flange projecting toward the shaft and contacting the surface of the seal facing away from the wall to retain the seal. The outer ring has a plurality of holes, each one in alignment with a hole in the middle ring. 
         [0019]    A plurality of first fasteners attaching the outer ring to the middle ring. A plurality of second fasteners attached to the inner ring and engage a peripheral portion of the middle ring to press the middle ring toward the wall. When assembled, the middle ring encircles the outer periphery of the seal, and the outer ring&#39;s flange presses against the side of the seal facing away from the wall. Normally, the fasteners will comprise cap screws and threaded holes into which the cap screws fit. 
         [0020]    The second fasteners preferably comprise cap screws in the threaded holes having engagement elements extending radially inwards past the inner edge of the inner ring, and engaging the outer periphery of the middle ring. For example, the engagement elements may comprise washers through which the cap screws pass. 
         [0021]    One advantage of this design is that the rings comprise at least two circular arc sections having ends that contact another section in a self-aligning manner at interface points. Each interface point has an alignment feature such as a tongue and groove interface between adjacent section ends. 
         [0022]    Ideally the ends of the middle ring sections are angularly displaced with respect to the ends of the outer ring sections. This arrangement allows the middle and outer rings to mutually maintain each other in the desired circular configuration. 
         [0023]    Preferably, the seal comprises two similar seal elements to be installed with axial spacing between them, and middle ring has a flange projecting radially into the space between the seal elements. 
         [0024]    A further embodiment of this invention comprises a retainer assembly having two rings. 
         [0025]    A first ring is fastened to the wall and encircles the shaft to form an annular recess surrounding the periphery of the seal. A second ring encircles the shaft and has outside and inside diameters allowing at least a portion of the second ring to fit into the annular recess between the first ring and the seal. A plurality of fasteners attached to the first ring and external to the second ring, each engage a peripheral portion of the second ring to press the second ring toward the wall. 
         [0026]    Preferably, the fasteners comprise cap screws. More preferably, the cap screw have washers on their shanks adjacent the heads thereof. The washers extend to overlap the second ring&#39;s periphery, to press the second ring toward the wall as the cap screws are tightened. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]      FIGS. 1 ,  2 A and  2 B show the structure of prior art seal retainers. 
           [0028]      FIGS. 3-8  show a version of an improved seal retainer structure  31 . 
           [0029]    For improved seal assembly  31 : 
           [0030]      FIG. 3  shows a front elevation view of seal retainer structure  31 . 
           [0031]      FIGS. 3A and 7  show a cross section at a first point of the periphery of seal retainer structure  31 . 
           [0032]      FIG. 3B  shows a cross section at a second point of the periphery of seal retainer structure  31 . 
           [0033]      FIG. 3C  is a cross section of the entire seal retainer structure. 
           [0034]      FIG. 4  is a plan view of an inner retainer ring  33 . 
           [0035]      FIG. 4A  is a section view of ring  33 . 
           [0036]      FIG. 5  is a plan view of a middle ring  37 . 
           [0037]      FIG. 5A  is a section view of ring  37 . 
           [0038]      FIG. 6  is a plan view of an outer retainer ring  32 . 
           [0039]      FIG. 6A  is a section view of ring  32 . 
           [0040]      FIGS. 7-8  show alternate versions of the mating surfaces of the ring  32  sections. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0041]      FIG. 3  shows a wall  11  of a housing having a shaft  26 . The housing encloses an industrial process of the type for which migration of materials such as gasses, liquids, or particles along shaft  26  should not occur, precisely as with the embodiments shown in  FIGS. 1 ,  2 A and  2 B. 
         [0042]    To prevent such migration of materials along shaft  26 , wall  11  has a seal retainer assembly  31  that is completely compatible with seals  15   a  and  15   b  now in use, and that has added advantages. Individual elements of assembly  31  are lighter than for the conventional assembly  30 . Reassembly is easier because holes of a heavy outer ring  12  need not be simultaneously aligned with a number of individual fasteners  9 . In addition, assembly  31  provides better stability for seals  15   a  and  15   b.    
         [0043]    Assembly  31  includes three major elements: an inner retainer ring  33 , a middle spacer ring  37 , and an outer retainer ring  32 . Each of these three rings  33 ,  37 , and  32  comprises at least two individual ring segments that mate to create a continuous ring  33 ,  37 , or  32  after assembly is complete. Seal retainer assembly  31  holds conventional seals  15   a  and  15   b  in place with effectiveness and functionality equivalent to or better than the seal assembly  30  structure. 
         [0044]      FIG. 3  and the cross section views of  FIG. 3B  show how cap screws  39  attach inner ring  33  to mounting ring  27 . Cap screws  39  pass through washers  38  and holes  39   a , see  FIGS. 4 and 7  to attach ring  33  to ring  27 . In general, inner ring  33  need not be removed when replacing seals  15   a  and  15   b .  FIG. 3C  shows the entire retainer assembly in cross section, to provide a helpful perspective of the assembly&#39;s overall shape. 
         [0045]      FIGS. 3B and 6  show two passages  42  in outer ring  32  for injecting grease into a grease space formed by seal elements  15   a  and  15   b  and shaft  26 . Middle ring  37  has two troughs  42   a  that align with passages  42  to provide a route allowing grease to flow to the grease space. Outer ring  32  must be angularly positioned with middle ring  37  to align passages  42  with troughs  42   a.    
         [0046]    In one preferred embodiment, inner ring  33  comprises two semicircular segments  33   a  and  33   b  fastened to each other with cap screws  45 .  FIG. 4  shows tangentially oriented cap screws  45  that fasten two inner ring half segments  33   a  and  33   b  to each other to form inner ring  33 . Dowels  48  shown in the detail of  FIG. 4  assist in accurately aligning segments  33   a  and  33   b  to each other. Ring  33  may also comprise three or more segments held together with screws  45  and aligned with dowels  48 . 
         [0047]    Ring  33  has an interior flange  44 , shown best in  FIGS. 3A ,  3 B,  4 , and  4 A, for axially aligning and retaining seal  15   a . The outwardly facing surface of flange  44  defines an inner surface of an annular recess that receives ring  37  and seal  15   a .  FIG. 3B  shows how inner ring  33  attaches to mounting ring  27  with cap screws  39  that pass through holes  39   a  and when tightened, press washers  38  against ring  33  to clamp same in place. 
         [0048]    The substantial amount of clearance space between individual cap screws  39  and holes  39   a  allows the installer to accurately center ring  33  with respect to shaft  26 . Once inner ring  33  is centered and cap screws  39  tightened, there normally will be no reason to remove and then later realign inner ring  33 . Accurate centering of inner ring  33  assures accurate centering of the entire assembly  31  and rings  15   a  and  15   b  with respect to shaft  26 . Three temporary shims placed between the inner edge of flange  44  and shaft  26  may aid in centering ring  33 . Sealant, O-rings, or other types of gasket material between inner ring  33  and mounting ring  27  prevents migration of material through this area. 
         [0049]    The middle retaining ring element  37  comprises two or more segments  37   a ,  37   b  shown assembled in the front projection view by  FIG. 5 . Cap screws  55  bolt segments  37   a ,  37   b  together to form element  37 , with dowels  58  providing for accurate alignment of the segments  37   a ,  37   b  ends. The outer diameter of ring element  37  should fit snugly into the annular recess of ring element  33 . The inner diameter of ring element  37  should accommodate the outer diameter of seal element  15   a.    
         [0050]    Ring element  37  has a number of holes  34   b  threaded to receive cap screws  34 . While ring element  37  is shown with only two segments  37   a ,  37   b  are show in  FIG. 5 , other numbers, such as four or six segments are also possible, each having alignment features  46  with the two adjoining segments. 
         [0051]      FIG. 5  and the inset therein shows at the end of each segment  37   a ,  37   b , an alignment feature comprising a dowel  58  that fits into holes of the segment  37   a ,  37   b  ends. Other types of interface structures are also possible. For example,  FIG. 8  shows the interface as simple overlapping projections at  46   a . The interfacing surfaces of segments  37   a  and  37   b  need not align with the axis of shaft  26 , but may lie transverse to that axis in an overlapping relationship. A further benefit of the tongue and groove structure for interface features  46  is more effective resistance to migration of lubricating grease forced into the cavity between the seals  15   a  and  15   b  and ring  37  than a simple butt interface furnishes. 
         [0052]    Middle ring element  37  is held in place by a number of cap screws  35  that fit into threaded holes  35   b  ( FIG. 4 ) angularly distributed around inner ring  33 .  FIG. 4  shows eight holes  35   b  at angular intervals of 45°. Each cap screw  35  passes through an engagement element preferably comprising a washer  36  that extends radially inwards past the inner edge of inner ring  33  to engage ring  37 . When cap screws  35  are tight, washers  36  press against the outer periphery of the middle ring  37  outwardly facing surface. 
         [0053]    Ring  37  should have a peripheral thickness provided in  FIG. 5  by a peripheral recess  41  that projects slightly past the outer face of inner ring  33  to allow washers  36  to engage ring  41  and force ring  37  against flange  44 . A thicker ring  37  may have an annular projection that aligns with the outer face of inner ring  33  allowing washers  36  to engage and press on ring  37 , forcing ring  37  toward wall  11 . 
         [0054]    Importantly, ring  37  has an inwardly extending annular flange  52  best seen in  FIGS. 3A and 5A . Flange  52  serves to retain the outer edge of seal element  15   a  and the inner edge of seal element  15   b , to help maintain seal elements  15   a  and  15   b  in the desired shape and axial position. 
         [0055]    The outer ring element  32  that  FIGS. 3A ,  3 B,  6 , and  6 A show, preferably comprises two or more similar segments  32   a ,  32   b , each in the general shape of a circular arc. Segments  32   a  and  32   b  have a number of equally-spaced holes  34   a  that are countersunk to receive cap screws  34  by which outer ring segments  32   a ,  32   b  attach to segments  37   a  and  37   b  of middle ring element  37 . An exterior and inwardly directed flange  42  on ring element  32  provides axial alignment and retention for seal  15   b .  FIGS. 3A and 7  show how flange  42  of outer ring  32  provides axial alignment and retention for the outer edge of seal element  15   b.    
         [0056]    Each segment  32   a ,  32   b  has on each end thereof, an attachment feature comprising a pair of cap screws  57  and an alignment feature comprising dowels  60 . The detail view of  FIG. 6  shows these features in more detail, which may be similar to the attachment and alignment features for middle ring element  37 . These dowels  60  fit into holes on the ends of adjacent segment  32   a  or  32   b  to assist the ends thereof into alignment. 
         [0057]    Other types of alignment features are possible. In  FIG. 7 , the alignment features on outer ring segments  32   a ,  32   b  comprise a tongue and groove  56  interface but other types of interface shapes are also possible, such as the mating projections  46   a  in  FIG. 8 . Rings  33  and  37  may also use such alignment features. If ring elements  33 ,  37 , or  32  comprise more than two segments, each segment should have alignment features that interface with the two adjoining segments. 
         [0058]      FIGS. 3A and 7  show means for fastening ring elements  33 ,  37 , and  32  to each other and to mounting ring  27 . Cap screws  34  directly bolt outer ring  32  to middle ring  37 . This can be done before placing the elements of outer ring  32  and middle ring  37  in the position adjacent to inner ring  32 , which simplifies the assembly process. Attachment elements comprising for example cap screws  35  thread into holes near the inner periphery of inner ring  33  to press washers  36  against peripheral segments  37   a ,  37   b  of middle ring  37  within ring  33  and against flange  44 . Middle ring  37  can assume any angular position with respect to inner ring  33 , again simplifying assembly. 
         [0059]    The alignment interfaces  56  of outer ring  32  should be angularly displaced with respect to the alignment interfaces  46  of middle ring  37 . In this way, ring segments  32   a ,  32   b  and  37   a ,  37   b  can be connected to each other to mutually maintain the circular shape of the other. 
         [0060]      FIGS. 3B and 6  show two passages  42  in outer ring  32  for injecting grease into a grease space formed by seal elements  15   a  and  15   b  and shaft  26 . Middle ring  37  has two troughs  42   a  that align with passages  42  to provide a route allowing grease to flow to the grease space. Outer ring  32  must be angularly positioned with middle ring  37  to align passages  42  with troughs  42   a.    
         [0061]    Assembly of seal assembly  31  involves first assembling inner ring  33  by atttaching the two inner ring halves  33   a  and  33   b  to each other using cap screws  45 , see  FIG. 4 . A cap screw  45  passes though an individual hole at one end of each ring half  33   a  and  33   b , into a threaded hole at the end of the other ring half  33   a  or  33   b.    
         [0062]    As previously explained, cap screws  39  attach inner ring  33  to housing  11  typically more or less permanently and with accuracy that assures precise centering of the entire assembly  31  on shaft  26 . When replacing seal  15 , rings  32  and  37  are detached and the old seal  15  is removed. Then first seal element  15   a  is assembled on shaft  26  by gluing or otherwise attaching ends of seal strip material to each other, and spring  15   c  is installed. Seal  15   a  is then pushed into the position shown in  FIGS. 3A and 3B . Using cap screws  55  and dowels  58 , middle ring segments  37   a ,  37   b  are bolted to each other around shaft  26  and slid against seal element  15   a  within the annular recess of inner ring  33 . Flange  52  should be spaced away from the flange  44  on ring  33 . The larger annular space between ring  33  and seal section  15  compared to the prior art, simplifies reassembly. 
         [0063]    Next, seal element  15   b  is assembled around shaft  26  and a spring element  15   c  installed as shown in  FIGS. 3A and 3B . Seal element  15   c  is then slipped along shaft  26  to press against flange  52 . Ring  32  is then assembled on shaft  26  using cap screws  57  and dowels  60  and shifted into position, to match the configuration in  FIGS. 6 and 6A  with holes  34   b  aligned with holes  34   a  in ring  37 . Cap screws  34  are then inserted into holes  42   b  and tightened to hold outer ring  32  against middle ring  37 . It may well be than none of the cap screws  34  and  35  should be tightened until all engage their individual threaded holes. 
         [0064]    The relatively small and light segments  37   a ,  37   b  and  32   a ,  32   b  are quite easy to maneuver and position for installation, even in cramped spaces. Further, the machining cost and difficulty is likely reduced since the layered thin rings  37  and  32  replace the relatively larger blocks of steel of the conventional designs in  FIGS. 1 ,  2 A and  2 B. 
         [0065]    When seals  15   a  and  15   b  replacement is necessary, it is relatively easy to detach and disassemble rings  32  and  37 , and remove them from shaft  26 . After new seals  15   a  and  15   b  have been mounted on shaft  26 , the relatively small and light segments  32   a ,  32   b  and  37   a ,  37   b  are easy to quickly and easily reinstall. 
         [0066]    In some installations, only a single seal element  15   a  need be retained. In such a case, outer ring  32  is unnecessary. Flange  52  then serves to retain the outer edge of inner seal element  15   a . In that case, flange  52  might extend closer to shaft  26 .