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.
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.
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.
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
Seal assembly 30 includes a seal 15 comprising flexible ring-type seal elements 15a and 15b, an inner retainer element 13, and an outer retainer element 12. Each of seal elements 15a and 15b, 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 15a and 15b. An extension spring 15c presses the lip of seal element 15a or 15b against shaft 26 to insure good contact between them. The seal elements 15a and 15b are preferably similar and are intended to be installed with a small axial spacing between them, as
Retainer elements 12 and 13 serve to hold the individual seals 15a and 15b in place encircling shaft 26 and to prevent leakage around seals 15a and 15b 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.)
When replacing seals 15a and 15b, it is possible that removing only outer retainer element 12 will be necessary if seals 15a and 15b can be easily removed from their recess, and their recess does not require cleaning.
In configurations of both
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 15a and 15b with grease after assembly is complete.
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.
The weight of the seal assembly 30 components becomes an issue during the periodic replacement of seals 15a and 15b that normal wear and deterioration requires. The working space for replacing seals 15a and 15b 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 15a and 15b time-consuming and difficult.
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.
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.
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.
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'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.
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.
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.
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.
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.
A further embodiment of this invention comprises a retainer assembly having two rings.
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.
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's periphery, to press the second ring toward the wall as the cap screws are tightened.
For improved seal assembly 31:
To prevent such migration of materials along shaft 26, wall 11 has a seal retainer assembly 31 that is completely compatible with seals 15a and 15b 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 15a and 15b.
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 15a and 15b in place with effectiveness and functionality equivalent to or better than the seal assembly 30 structure.
In one preferred embodiment, inner ring 33 comprises two semicircular segments 33a and 33b fastened to each other with cap screws 45.
Ring 33 has an interior flange 44, shown best in
The substantial amount of clearance space between individual cap screws 39 and holes 39a 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 15a and 15b 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.
The middle retaining ring element 37 comprises two or more segments 37a, 37b shown assembled in the front projection view by
Ring element 37 has a number of holes 34b threaded to receive cap screws 34. While ring element 37 is shown with only two segments 37a, 37b are show in
Middle ring element 37 is held in place by a number of cap screws 35 that fit into threaded holes 35b (
Ring 37 should have a peripheral thickness provided in
Importantly, ring 37 has an inwardly extending annular flange 52 best seen in
The outer ring element 32 that
Each segment 32a, 32b 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
Other types of alignment features are possible. In
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 32a, 32b and 37a, 37b can be connected to each other to mutually maintain the circular shape of the other.
Assembly of seal assembly 31 involves first assembling inner ring 33 by atttaching the two inner ring halves 33a and 33b to each other using cap screws 45, see
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 15a is assembled on shaft 26 by gluing or otherwise attaching ends of seal strip material to each other, and spring 15c is installed. Seal 15a is then pushed into the position shown in
Next, seal element 15b is assembled around shaft 26 and a spring element 15c installed as shown in
The relatively small and light segments 37a, 37b and 32a, 32b 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
When seals 15a and 15b replacement is necessary, it is relatively easy to detach and disassemble rings 32 and 37, and remove them from shaft 26. After new seals 15a and 15b have been mounted on shaft 26, the relatively small and light segments 32a, 32b and 37a, 37b are easy to quickly and easily reinstall.
In some installations, only a single seal element 15a 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 15a. In that case, flange 52 might extend closer to shaft 26.
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).
Number | Date | Country | |
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61491677 | May 2011 | US |