Abstract:
A seal system including a sleeve configured to receive a rotatable shaft therein and a dynamic race configured to be rotatably coupled to the shaft. The seal system further includes a biasing element configured to urge the dynamic race into engagement with a static race to form a primary seal, and a shroud configured to be rotatably coupled to the sleeve and positioned radially outside the biasing element. The seal system also includes a sealing element configured to be positioned radially inside the biasing element and to sealingly engage the sleeve to provide a secondary seal to generally block fluid bypassing the primary seal.

Description:
[0001]    The present invention is directed to a seal assembly for use with a rotatable component, and, more particularly, to a seal assembly including a shroud. 
       BACKGROUND 
       [0002]    Seal assemblies are often utilized to journal the ends of a rotating shaft in a sealed manner. Such seal assemblies may be used in fluids processing technologies, such as wastewater treatment, food processing, materials handling and the like in which a rotatable shaft is utilized to carry cutters, spacers, baffles, diverters, agitators, mixers, pumping elements, etc. In many applications, it is desired to isolate the material being processed. However, the material being processed can be under high pressure and can be trapped in or otherwise interfere with proper operation and sealing of the seal assemblies. 
       SUMMARY 
       [0003]    In one embodiment the present invention is an improved, robust seal assembly. More particularly, in one embodiment the present invention is a seal system including a sleeve configured to receive a rotatable shaft therein and a dynamic race configured to be rotatably coupled to the shaft. The seal system further includes a biasing element configured to urge the dynamic race into engagement with a static race to form a primary seal, and a shroud configured to be rotatably coupled to the sleeve and positioned radially outside the biasing element. The seal system also includes a sealing element configured to be positioned radially inside the biasing element and to sealingly engage the sleeve to provide a secondary seal to generally block fluid bypassing the primary seal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0004]      FIG. 1  is a front view of a grinder assembly in which the seal assembly may be utilized; 
           [0005]      FIG. 2  is a side view of the grinder assembly of  FIG. 1 ; 
           [0006]      FIG. 3  is a side cross section of the lower part of the grinder assembly of  FIG. 1 ; 
           [0007]      FIG. 4  is a front cross section of the lower part of the grinder assembly of  FIG. 1 ; 
           [0008]      FIG. 5  is a detail view of area indicated in  FIG. 3 ; 
           [0009]      FIG. 6  is a perspective view of the seal assembly shown in  FIG. 5 ; and 
           [0010]      FIG. 7  is an exploded view of the seal assembly of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIGS. 1-4  illustrate a grinder assembly/comminutor  10  in which a seal assembly disclosed herein may be utilized. However, it should be understood that the seal assembly can be used in any of a wide variety of systems or components in which it is desired to seal and/or journal a rotating shaft, such as such as wastewater treatment systems, food processing equipment, materials handling systems and the like which can carry any of a variety of elements (if any) on the shafts such as cutters, spacers, baffles, diverters, agitators, mixing elements, screens, augers, pumping elements or the like. For example, besides being used in a grinder assembly the seal assembly can be used to journal a shaft carrying a cylindrical screen which is configured to screen or divert solids suspended in a liquid stream; to journal a shaft of a progressing cavity pump; to journal a shaft of an auger, etc. 
         [0012]    The grinder assembly  10  shown in  FIGS. 1-4  includes a pair of parallel rotatable shafts  12  (shown as shafts  12   a ,  12   b  in  FIG. 4 ), each shaft  12  carrying a plurality of generally disc-shaped cutter teeth  14  thereon. The teeth  14  of one shaft  12  are spaced and sized to intermesh with the teeth  14  of the other shaft  12  such that, during rotation of the shafts  12 , the teeth  14  create shearing forces to grind, shear, comminute or macerate solids suspended in a fluid flow. A series of spacers  16  may be located on each shaft  12  such that a  16  spacer is positioned between adjacent teeth  14  on each shaft  12  to maintain alignment of the teeth  14  and potentially to aid in processing of the suspended solids. 
         [0013]    The grinder assembly  10  includes a motor  34  ( FIGS. 1 and 2 ) which drives the drive shaft  12   a  ( FIG. 4 ) which carries a drive gear  31  thereon. The drive gear  31  meshes with a driven gear  33  of the driven shaft  12   b  such that rotation of the drive shaft  12   a  causes corresponding counter-rotation of the driven shaft  12   b . In the illustrated embodiment, the drive shaft  12   a  and driven shaft  12   b  are driven in opposite directions (i.e., in counter-rotation) towards each other relative to the upstream side of the grinder assembly  10 . However, the shafts  12   a ,  12   b  can be geared to be driven in the same direction (i.e., at differing speeds) or counter-rotated away from each other (relative to the upstream side), if desired. 
         [0014]    As best shown in  FIG. 1 , the grinder assembly  10  includes a frame  18  having an inlet port  20  and an outlet port  22  through which fluid carrying the suspended solids (such as wastewater) flows. The frame  18  defines base openings  24  and top opening  26  ( FIGS. 3 and 4 ), each of which receives an end casing  28  therein. Each end casing  28  has a pair of bores  30 , each of which receives a seal assembly  32  therein in a sealed manner. Each shaft  12  is journaled in a seal assembly  32  at each end thereof, resulting in a total of four seal assemblies  32  for the illustrated grinder assembly  10 , as shown in  FIG. 4 . However, in certain cases and for certain devices, only selected ones of the shafts  12 , or only a selected end of a shaft  12 , may be journaled in a seal assembly  32 . 
         [0015]    As best shown in  FIGS. 5-7 , each seal assembly  32  includes a generally cylindrical sleeve  36  which receives the distal end of the rotating shaft  12  therein. The sleeve may include a lip  38  at an axial end thereof, although in some cases the sleeve  36  may lack the lip  38 . The sleeve  36  may be rotationally coupled to the associated shaft  12  due to a frictional fit or by mechanical couplings or the like. For example, in the illustrated embodiment the shaft  12  includes an axially-extending keyway  40  ( FIG. 5 ) that is aligned with an axially-extending slot  42  of the sleeve  36  (see  FIG. 7 ). A key  44  ( FIG. 5 ) is received in the keyway  40  and the slot  42  to rotationally couple the shaft  12  to the sleeve  36 . 
         [0016]    The seal assembly  32  includes a shroud  46  positioned at or adjacent to end of the sleeve  36  and coaxial with the sleeve  36 . In the illustrated embodiment the shroud  46  is a separate piece from the sleeve  36 , although the sleeve  36  and shroud  46  may be a unitary, one-piece item if desired. The shroud  46  may be positioned adjacent to the lip  38  such that the lip  38  can help to maintain the desired axial positioning of the shroud  46 . The shroud  46  may be rotationally coupled to the sleeve  36  by a shrink/interference fit or by various mechanical coupling arrangements. The shroud  46  includes a generally radially-extending portion  48  engaging the sleeve  36  and a generally axially-extending portion  50  extending away from the lip  38 /generally radially-extending portion  48 . If desired, the sleeve  36  may include an area of increased thickness/stiffness where the shroud  46  engages the sleeve  36  (i.e. below the lip  38 ), to ensure the sleeve  36  retains its shape due to any forces applied thereto, such as forces applied by the shroud  46  in the case of an interference fit. 
         [0017]    A biasing element  52 , such as a spring, is positioned adjacent to, and radially inwardly of, the shroud  46  and captured therein. The biasing element  52  is placed in compression when the seal assembly  32  is assembled and operatively engages a generally annular dynamic race  54  and urges the dynamic race  54  into contact with a generally annular static race  56 . In this manner, the rotatable dynamic race  54  is urged into contact with the generally non-rotating static race  56  to form a primary seal of the seal assembly  32  at the facial contact between the races  54 ,  56 . 
         [0018]    A sealing element  58  is positioned radially inwardly of the biasing element  52  and engages the sleeve  36  such that a radial plane extends through both the sealing element  58  and the biasing element  52 . The sealing element  58  is also configured and positioned such that at least part of the sealing element  58  is positioned axially between the biasing element  52  and the dynamic race  54 . In this manner, the sealing element  58  help to prevent the flow of fluid (including wastewater and/or surrounding environmental fluids such as air) which might otherwise pass though a radial gap  60  between the sleeve  36  and the static  56  and/or dynamic race  54 , thereby forming a secondary seal of the seal assembly  32  along edge  62 . The secondary seal  62  generally blocks the flow of any fluid bypassing or attempting to bypass the primary seal. The sealing element  58  is arranged such that higher pressure fluids (i.e., on the radially outer surface thereof) press the sealing element  58  tighter against the sleeve  36 . Thus, higher pressures actually increase the scaling at the secondary seal  62 . 
         [0019]    In the illustrated embodiment, the sealing element  58  takes the form of a bellows including a middle, generally radially-extending portion  64 , and first  66  and second  68  generally axially-extending portions positioned on opposite sides of the middle portion  64 . The first portion  66  engages, and forms a seal  62  with, the sleeve  36 . The middle  64  and second  68  portions wrap around the dynamic race  54  and are positioned adjacent to, and engage, the axially inner surface and radially outer surface of the dynamic race  54 , respectively. However, the sealing element  58  can take any of a wide variety of shapes and configurations beyond the bellows shown in  FIG. 5 , such as a simple gasket or washer which sealingly engages the sleeve  36   
         [0020]    In the illustrated embodiment, the sealing element  58  includes a stiffening component  70  positioned on the radially outer surface thereof, and a protective element  72  positioned between the first axially-extending portion  66  and the stiffening component  70 . This stiffening component  70  and/or protective element  72  may be made of relatively stiff materials, such as metals or the like, whereas the portions  64 ,  66 ,  68  may be made of a more compliant, resilient material, such as a fluoroelastomer, rubber, synthetic rubber, or the like. The stiffening component  70  and/or protective element  72  thereby protect the softer components  64 ,  66 ,  68  from wear and tear, extending the life of the sealing element  58 . The stiffening component  70  can also serve to swage the sealing element  58  about the dynamic race  54  to aid in forming a seal between those components. 
         [0021]    A seal insert/retaining component  74  is loosely mounted on the sleeve  36  and receives the static race  56  therein. The seal insert  74  may be fixed to the end casing  28  which is in turn fixed in the base opening  24  (or top opening  26 ) of the frame  18  by a frictional attachment or by other mechanical means. An O-ring or the like  76  is positioned between the seal insert  74  and the end casing  28  to aid in sealing the seal assembly  32 . An O-ring  78  or the like is also positioned between the radially outer surface of the static race  56  and the radially inner surface of the seal insert  74  to maintain a seal between those components. Finally, an O-ring  80  or the like may be positioned in a groove  81  in the shaft  12 , and be positioned between the shaft  12  and the sleeve  36 , to further aid in sealing the end of the shaft  12 . 
         [0022]    Both the seal insert  74  and static race  56  are rotationally isolated from the shaft  12 /sleeve  36  (that is, the seal insert  74  and static race  56  generally do not rotate with the shaft  12 /sleeve  36 ). In contrast, since the shroud  46 /sleeve  36  are rotationally coupled to the shaft  12 , they carry the biasing element  52 , sealing element  58  and dynamic race  54  with them such that those components are all rotatably coupled with the shaft  12 . 
         [0023]    The shroud  46  protects and shields the biasing element  52  to prevent fibrous materials from wrapping around the biasing element  52 , which would otherwise interfere with proper operation of the seal assembly  32 . Accordingly, the shroud  46  may extend axially at least the entire axial length of the biasing element  52 , and may extend axially along part of the dynamic race  54 , as shown in the illustrated embodiment. In addition, the shroud  46  may be positioned relatively close to the wall of the bore  30 /end casing  38  such that the gap G between the radially outer surface of shroud  46  and the bore  30  wall/end casing  38  is quite small, equal to or less than at least about 6/1000 of an inch in one case. The shroud  46 , or at least its radially outer surface, may be made of a relatively smooth material and have a surface roughness less than at least about 100 Ra, or more particularly less than about 75 Ra. The shroud  46  can be made of a variety of materials, such as metal, including stainless steel, which may be finished or otherwise treated to provide the desired finish/smoothness. The shroud  46  should have a thickness sufficient to withstand the rigorous operating conditions to avoid wear and deformation. In some cases, such as in the case of a dual-shafted grinder, it has been found that the shroud should have a thickness (in the radial direction) of at least about 90/1000 inch. 
         [0024]    The positioning of the shroud  46  relative to the biasing element  52  and the relatively close clearance between the shroud  46  and the bore  30 /end casing  28  prevents fibers and other materials from passing through the gap G, thereby protecting the biasing element  52 . In particular, it has been found that fibrous materials, particularly those typically found in wastewater treatment and other similar applications, are typically prevented from passing through the gap G if the gap has a size of 6/1000 of an inch or less. In addition, the smooth finish of the shroud  46 , and the fact that the shroud  46  is positively driven by the sleeve  36 /shaft  12 , inhibits any fibrous or other materials from binding on the outer surface of the shroud  46 , thereby ensuring that the gap G remains unclogged, allowing free rotation of the shroud  46 . The shroud  46  can be used in combination with various seal assemblies, including seal assemblies with a more conventional dynamic race that do not form the secondary seal as described above. 
         [0025]    In the illustrated embodiment, the biasing element  52  takes the form of a coil spring, but could include other biasing means, such as resilient bodies, volute springs, washer springs, leaf springs, gas springs, etc. One advantage of the coil spring, and certain other biasing elements, is that the coil spring has gaps between the coils which allow fluid to pass from a first or inner radial side to an outer or second radial side thereof to allow pressure equalization of the seal  32 . A biasing element which does not allow pressure equalization thereacross can lead to pressure build up on one side or the other, which can compromise the seal  32  and/or lead to seal failure. In addition, the generally axially-extending portion  50  of the shroud  46  may be spaced away from, and not form a seal with, the radially inner components (such as the sealing element  58  and dynamic race  54 ) to further enable pressure equalization thereacross and not seal the spring  52  in a chamber. 
         [0026]    In the illustrated embodiment, a bearing  82  is mounted about the sleeve  36  and positioned adjacent to the seal insert  74 . The bearing  82  is designed to be slid on the sleeve  36  after the seal assembly  32  is mounted on the shaft  12 . However, after being mounted on the shaft  12  or sleeve  36 , the bearing  82  and the seal assembly  32  remain separate and are not directly attached to one another. Thus, the seal assembly  32  and bearing  82  are entirely separate structures that are never pre-assembled or joined together prior to insertion or mounting. The bearing  82  may include an inner race  84  which is positioned adjacent to and/or engaging the sleeve  36 , and an outer race  86  which is positioned adjacent to and/or engaging the bore  30  wall/end casing  28 . 
         [0027]    A spacer  88  may be mounted on the sleeve  36  and engage the inner  84  and/or outer  86  race of the bearing  82 . A bolt  90  may be threaded through the spacer  88  and into the end of the shaft  12  to retain the spacer  88 , bearing  82  and seal assembly  32  in place on the end of the shaft  12 . However, it should be understood that various other mechanisms may be utilized to retain the seal assembly  32 /bearing  82  onto the sleeve  36 /shaft  12 , such as a snap ring received in a groove of the shaft  12 , etc. The seal assemblies  32  at the top end of the shafts  12  ( FIGS. 3 and 4 ) may be mounted in a similar manner with adjustments as appropriate. For example, the spacer  88  may have a different configuration, and a snap ring may be used in place of the bolt  90 , etc. 
         [0028]    A retainer ring  92  ( FIG. 5 ) may be mounted on the sleeve  36 , positioned axially between the bearing  82  and the seal insert  74 . When the bearing  82  is fully mounted onto the sleeve  36 , the bearing  82  engages the retainer ring  92  so that the retainer ring  92  maintains the bearing  82  in the proper axial position. During assembly or disassembly (i.e., when the bearing  82  is removed from the sleeve  36 ), the seal assembly  32 , and more particularly the seal insert  74 , shifts downwardly and engages the retainer ring  92  as biased by the spring  52 . In this manner, the retainer ring  92  prevents the seal assembly  32  from being entirely pushed off of the sleeve  36 . Thus, the retainer ring  92  serves the dual purpose of retaining the bearing  82  in place during operation, and retaining the seal assembly  32  in place (i.e., on the sleeve  36 ) during assembly/disassembly operations. 
         [0029]    When the seal assembly  32  is utilized at the end of the shafts  12  of the grinder unit  40 , a labyrinth seal  94  may be mounted on the end casing  28  adjacent to the seal assembly  32 , and axially inwardly thereof, to aid in protecting and sealing the seal assemblies  32 . In some cases, the bore  30  in the casing  28  may be a stepped bore having a smaller diameter portion  30   a  ( FIG. 5 ) receiving the shroud  46 , biasing element  52 , sealing element  58  and dynamic race  54 , and a larger diameter portion  30   b  receiving the static race  56  and seal insert  74 . In this case, a spacer  96  may be positioned in the larger diameter portion  30   b  axially inwardly of the seal insert  74  to maintain proper positioning for the seal insert  74 . In some cases the bore  30  may be a smooth, constant diameter bore in which case the spacer  96  may not be utilized, and in some cases the labyrinth seal  94  may not be utilized. 
         [0030]      FIG. 6  illustrates the seal assembly  32  in an assembled condition. The seal assembly  32  can be mounted onto a shaft  12 , either during production or in the field, to provide the advantages described herein. 
         [0031]    Having described the invention in detail and by reference to the various embodiments, it should be understood that modifications and variations thereof are possible without departing from the scope of the invention.