Abstract:
Seal assemblies and methods for forming them are described. Aspects of the seal assemblies include a seal ring made of a relative soft material supported by a specially configured backing ring made of a much higher modulus material, such as ferrous and non-ferrous metal or engineered plastic. The seal assemblies may optionally include a retaining ring to prevent slippage relative to the environment or housing in which they are placed and to prevent shuttling. The seal assemblies may also optionally include an energizer to alter the force generating by a sealing lip on the seal ring.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a regular utility application of provisional application Ser. No. 61/012,179, filed Dec. 7, 2007, which bears the same title. The contents of the provisional application are expressly incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     Seal assemblies are generally discussed herein for sealing a first environment or chamber from a second environment or chamber of a machinery or equipment with particular discussions extended to shaft seals in which a seal is retained within a housing on a shaft and a constant pressure is exerted by the seal on the shaft to maintain a dynamic seal between the shaft and the seal. Seal assemblies for use in static services are also discussed. 
     Seal assemblies for rotating, reciprocating, and face seal applications are well known in the art and are taught by, for example, U.S. Pat. Nos. 4,805,943; 4,830,344; 5,134,244; 5,265,890; 5,979,904; 5,984,316; 5,992,856; 6,050,572; 6,161,838; 6,264,205; and 6,641,141, the contents of each of which are expressly incorporated herein by reference. 
     Prior art polytetrafluoroethylene (PTFE) based seals are preferred by some because they provide flexibility, low-friction, and self-lubrication when used in sealing arrangements with a moving shaft, such as a rotating or reciprocating shaft. However, PTFE material used in making seals has a natural tendency to cold-flow and creep, especially in high temperature, pressure, and surface velocity applications, which are common in the oil and gas industry and other applications. Thus, operating life of PTFE-based seals is shorter than preferred when placed in these applications and conditions. 
     PolyEtherEtherKetone (PEEK) material, on the other hand, is better suited for high pressure, temperature and velocity applications. However, PEEK material is rigid and generally is not applicable or workable as a primary contact seal against moveable shafts, such as rotary or reciprocating shafts. 
     It has been found that when a relatively softer polymer seal is supported by a more temperature resistant and higher modulus polymer jacket or housing (such as PEEK or other materials as further discussed below), the sealing characteristics and operating life of the overall seal against a moveable surface is substantially improved while its propensity for distortion, cold-flow and creep is minimized. 
     SUMMARY 
     Aspects of the present invention comprises a seal assembly comprising a rigid backing ring made of a first material having an axially extending flange; a seal ring positioned next to the backing ring and in mechanical engagement with the backing ring, said seal ring comprising a lip extending radially for dynamic contact with a moveable shaft; and a retaining ring positioned next to the seal ring and in mechanical engagement with the seal ring; wherein a spring is positioned in a holding bore, which is defined, at least in part, by the seal ring and the retaining ring. 
     Optionally, the seal assembly comprises an outside flange and an inside flange separated from one another by a center channel section. 
     In one aspect of the present invention, the seal assembly comprises a seal ring made from a PTFE material, a polymer material, or a PTFE composite with other performance enhancing additives. 
     In one aspect of the present invention, the seal assembly comprises a backing and support ring made from a PEEK or PEEK composite or other high temperature resistant and high modulus polymer materials, a metal, or other high performance engineering plastic material having suitable properties for the application. 
     In another aspect of the present invention, a seal assembly is provided for sealing engagement with a shaft comprises a seal ring comprising an outside flange, an inside flange, and a center channel section; a canted-coil spring or O-ring, cantilever vee spring or other types of seal energizer positioned between the inside flange and the outside flange; a backing ring in adjacent contact with the center channel section and having a flange extending co-axially with the inside flange of the seal ring; and wherein the inside flange further comprises a seal lip comprising an arcuate section overlapping an end edge of the flange of the backing ring. Seal energizers of the type that further assist a lip seal in exerting a positive force against a sealing surface are preferred, but energizers are not always required. For example, in certain applications, the resiliency of the seal is adequate for sealing against the shaft without an energizer. 
     The present invention is further directed to a method for preventing or minimizing seal distortion of a relatively pliable seal in high pressure applications. The method comprises the steps of creating a backing ring having an axially extending flange; mounting a seal ring comprising an axially extending flange and mechanically coupling the two axially extending flanges together: placing a canted-coil spring or other energizer device in a hold bore such that a spring force generated by the energizer or the canted-coil spring is directed against the axially extending flange of the seal ring; and mounting the combination backing ring, seal ring, and canted coil-spring in a sealing environment such that the axially extending flange of the seal ring is directed towards a high pressure region of the sealing environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional side view of a seal assembly mounted on a moveable shaft inside a seal cavity. 
         FIG. 2  is a cross-sectional side view of a seal assembly comprising a tandem seal set mounted on a moveable shaft. 
         FIG. 3  is a cross-sectional side view of a seal assembly provided in accordance with another aspect of the present invention, which may be used in a rotary or a static application. 
         FIG. 4  is a cross-sectional side view of a seal assembly provided in accordance with another aspect of the present invention, which may be used in a rotary or a reciprocating application. 
         FIG. 5  is a cross-sectional side view of a seal assembly provided in accordance with yet another aspect of the present invention, which may be used in a static or a reciprocating application. 
         FIG. 6  is a cross-sectional side view of a seal assembly provided in accordance with still another aspect of the present invention, which may be used in a rotary or a static application. 
         FIG. 7  is a cross-sectional side view of a seal assembly provided in accordance with still another aspect of the present invention, which may be used in a reciprocating or a static application. 
         FIG. 8  is a cross-sectional view of another alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of seal assemblies provided in accordance with aspects of the present invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. The description sets forth the features and the steps for constructing and using the seal assemblies of the present invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and structures may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. As denoted elsewhere herein, like element numbers are intended to indicate like or similar elements or features. 
     With reference now to  FIG. 1 , there is shown a cross-sectional side view of a seal assembly  10  mounted in a gland, stuffing box, or sealing cavity  12  of a rotating, oscillating, or static equipment, such as a pump, compressor, turbine, gear box, or engine. The seal assembly  10  is mounted to a gland or equipment housing  14  and is preferably stationarily positioned relative to the gland  14 . The seal assembly is generally circular in nature and comprises an inside diameter  16  in dynamic sealing communication with a shaft  20  and an outside diameter  18  in static communication with an internal bore  22  of the gland  14 . Known interference requirements between the seal and the shaft and between the seal and the gland  14  may be used to implement the preferred seal assembly. 
     In the embodiment shown, the seal assembly  10  is formed of at least four distinct components, namely an externally facing backing ring  24 , a seal ring  26 , an inner retaining ring  28 , and a energizer  30 , which may be a resilient member, a canted-coil spring, cantilever vee spring, or an O-ring (not shown) of suitable resilient characteristics to provide a biasing force, as further discussed below. In the specific embodiment shown, the energizer  30  is a canted coil spring. In the preferred assembly, the seal ring  26  comprises an outside flange  32 , a center channel section  34 , and an inside flange  36  and is made from a polymer material, which in one embodiment is a PTFE material. Other polymer and PTFE-based composite materials may be used as sealing components of the assembly. The inside flange  36  extends axially internally from the center channel section  34  and terminates in a generally linear lip  38 . The lip  38  is in dynamic contact with the shaft  20 , in a cross-sectional view, along a straight line. In a less preferred embodiment, the lip  38  makes a single point contact with the shaft. Exemplary O-rings or energizers are disclosed in U.S. Pat. Nos. 4,893,795; 4,974,821; 5,108,078; 5,139,276; and 7,175,441, the contents of each of which are expressly incorporated herein by reference. 
     In one exemplary embodiment, the inside flange  26  further incorporates a plurality of spaced-apart notches or recesses  40  formed along an external surface for mating with corresponding bumps or projections  42  formed on the backing ring  24 . The engagement between the two secure the seal ring  26  to the backing ring  24  in fixed orientation. In the embodiment shown, the backing ring  24  is made from a PEEK or a PEEK composite material. Its rigid characteristic allows the backing and support ring to resist pressure force from a higher pressure region  44  that would tend to push the seal ring  26  outwardly to a lower pressure region  46 . Thus, the backing and support ring acts to resist distortion, cold flow or creep of the seal ring. In an alternative embodiment, the backing ring  24  may be made from a suitably stiff strong material such as stainless steel, ferrous or non-ferrous metals, or engineering plastics. 
     The inner retaining ring  28  is configured to mate with the outside flange  32  of the seal ring  26 . In one exemplary embodiment, a snap fit arrangement is provided to engage the two, which when assembled, create a holding bore  48  for capturing the energizer, such as a canted-coil spring or O-ring  30 . Tire spring or O-ring (not shown)  30  may be a radial or axial canted coil spring and the surfaces of the inner retaining ring  28  and the seal ring  26  define the holding bore  48 . The holding bore therefore has a contour that is defined, at least in part, by the inner retaining ring and the seal ring, which may be altered to create different holding space for the energizer  30 . Using the physical contour of the holding bore to modify the spring deflection will in turn allow the radial force acting on the sealing lip  38  to be adjusted upwardly or downwardly. 
     In one exemplary embodiment, the inner retaining ring  28  is made from a PEEK material or a metal material, such as stainless steel or any other ferrous or non-ferrous metal or engineering plastic meeting the application requirements (such as high modulus). The outer diameter is sized as an interference fit  61  to accommodate tolerance variations. The groove inboard of the outer diameter  62  allows adequate flexibility to ensure that the ring locks the seal assembly to the fixed housing. 
     The seal assembly  10  is compression fitted into the internal bore  22  of the gland  14 . In the embodiment shown, this is accomplished by providing an external area along the outside flange  32  designed to be compressed by the relative diameter of the internal bore  22 . 
       FIG. 2  is a cross-sectional side view of an alternative seal assembly  50  provided in accordance with aspects of the present invention. In one exemplary embodiment, the alternative seal assembly  50  comprises two seat assemblies mounted in-line  51   a ,  51   b , each comprising a backing ring  52 , a seal ring  54 , an inner retaining ring  56 , and an energizer  58 , such as a canted-coil spring, which may be an axially canted coil spring or a radially canted coil spring. 
     The two in-line seal assemblies are configured for high pressure applications. As is well known in the art, baring leakage, pressure passing through the inner seal assembly  51   a  is reduced by the sealing engagement between the sealing lip  57  and the shaft  20 . Thus, the outer seal assembly  51   b  should experience less pressure from the stuffing box or seal cavity than the inner seal assembly  51   a , provided there is no leakage. In-line seals of this configuration also have the advantage of redundancy. Additionally, the first seal protects the second seal from debris and potential damage thus permitting the second seal to provide longer useful life should the first seal begin to fail. 
     In the embodiment shown, the inner seal  51   a  is separated by the outer seal  51   b  by a divider plate  68 , which provides a back support for supporting the backing ring  52  of the inner seal assembly  51   a . It is also preferable to have varying outer diameters between the inner and outer seals to facilitate assembly. 
     In one exemplary embodiment, the seal ring  54  and the backing ring  52  are engaged to one another in fixed orientation by a detent engagement  60  near the outside flange of the seal ring. Alternatively, the seal ring  54  and the backing ring  52  may engage one another using both a bump/notch engagement, as discussed above with reference to  FIG. 1 , and a detent engagement. 
     In one exemplary embodiment, the inner retaining ring  56  is made from a PEEK material or a metal material, such as stainless steel or any other ferrous or non-ferrous metal or engineering plastic meeting the application requirements (such as high modulus). The outer diameter is sized with an interference fit  63  to accommodate tolerance variations. The groove  64  inboard of the outer diameter allows adequate flexibility to ensure that the ring locks the seal assembly to the fixed housing. In certain embodiments, if the supporting backing ring  52  is made from a PEEK material, it can be fiber-filled to enhance its mechanical properties and preferably has additives to lower its friction coefficient. 
       FIG. 3  is a cross-sectional view of an exemplary seal assembly  70  provided in accordance with another aspect of the present invention, which may be used for a high pressure rotary or static applications. The current assembly embodies a ring and has an outside diameter  72  and an inside diameter  74  sized to fit over a shaft  76 , which is shown schematically with a centerline ℄. The seal ring  80  has a generally C-shape cross-section that includes a first flange  82 , a center channel section  84 , and a second flange  84  defining a holding bore  86  therebetween. The contour or shape of the holding bore may be modified or adjusted to vary the manner in which an energizer is retained therein. For example, the center race section may be arcuate in shape or may incorporate a flat strip or multiple flat strips and the sections near the lips  92  incorporate bumps or protrusions. 
     The seal ring  80  is preferably made from a resilient material, such as PTFE, and has a contact length  90  formed at an end of the first and second flanges  82 ,  86  for forming a line contact with a surface to seal against, such as a housing, gland, shaft, or stuffing box. Internally, the seal ring  80  incorporates a pair of retaining lips  92  for capturing an energizer (not shown), which may be a canted coil spring, an O-ring, or other devices configured to create a biasing force on the two flanges  82 ,  86 . 
     The backing ring  78  is preferably made from a high modulus material, such as PEEK, PEEK composite or metallic material, or an engineered plastic. In one preferred embodiment, the backing ring  78  incorporates a corresponding mating C-shape cross-section to support the seal ring along multiple sides. In particular, the backing ring  78  has a first flange  94  for supporting the first flange  82  of the seal ring, a second flange  96  for supporting the second flange  86  of the seal ring, and a center channel section  98  for supporting the center channel section of the seal ring. The multi-sided support helps the seal ring  80  to resist radial, and/or axial distortion or creep due to the differential between a high pressure region  44  and a low pressure region  46 . In one particular embodiment, the second flange  96  and optionally the outside flange  94  incorporate a radiussed section  100  to form a line contact  102  along an end portion of the respective flange. However, the line contact  102  of the backing support is preferably slightly larger in diameter than the seal ring so that only the seal ring makes contact with the shaft or other housing structure. Most preferably, the seal ring has a longer contact line than the contact line on the backing ring. The backing ring  78  and the seal ring  80  may engage one another by one or more detents  104 . 
     Thus, aspects of the present invention include a seal assembly comprising a seal ring having multiple external side walls supported by a backing ring made of a material having substantially higher modulus properties. In one particular embodiment, the backing ring supports the seal ring along a first flange, a center channel section, and a second flange of the seal ring to minimize distortion. The multi-sided support preferably reduces or minimizes deflection of the seal ring along the radial and/or axial direction. Although the backing ring has a generally rectangular center channel section, it may be contoured or have distinct lines or notches. 
       FIG. 4  shows a seal assembly  106  having a similar construction as the outside seal assembly  51   b  of  FIG. 2 . Thus, the present invention includes a locking ring  107 , a seal ring  109 , a backing ring  111 , and an optional energizer (not shown), which may be a canted coil spring, an O-ring, or other bias generating devices for biasing the inside flange of the seal ring. However, in the present embodiment, the outer flange  108  and the inner flange  110  of the seal ring are substantially longer than the corresponding sections of the seal ring of  FIG. 2 . In one embodiment, the flanges are about 30% to about 150% longer than corresponding overall lengths of the seal ring of  FIG. 2 . The relatively longer lengths create a corresponding larger holding bore  48  to retain an energizer in a different configuration, such as a radial canted coil spring versus an axial canted coil spring. The longer length further allows a relatively longer inside backing flange section  112  to support the inside lip  114  to thereby limit distortion of the contact length  116  due to pressure differentials between a high pressure environment and a lower environment. Although the inside backing flange section  112  has a contact line  118 , it preferably does not contact the shaft. 
     Referring now to  FIG. 5 , a cross-sectional side view of an alternative seal assembly  120  provided in accordance with another aspect of the present invention is shown. The present seal assembly is somewhat similar to the seal assembly  70  of  FIG. 3  in that it incorporates a backing ring  122  and a seal ring  124  without a retaining ring. The ring is also formed orthogonally so that the inner diameter  74  and the outer diameter  72  differ from that of  FIG. 3 . Thus, an aspect of the present invention is a seal assembly comprising a backing ring made of a first modulus property for supporting a seal ring made of a second modulus property along multiple sides, which include an outer flange side, a central channel side, and an interior flange side, and wherein the first modulus property is higher than the second modulus, property. In one particular embodiment, the seal ring is made from a PTFE material and the backing ring is made from a PEEK material, steel material, or a composite. 
     As with the seal assembly  70  of  FIG. 3 , the present seal assembly incorporates a contact length  126  for a line contact with a shaft, shown schematically with a centerline ℄. The backing ring  122  similarly has a contact length  128  that in one embodiment is configured to contact the shaft. The length of the respective contact lengths  126  and  128  is formed by a radiused section  130  on each of the inside flanges. In one embodiment, a center notch or indentation  132  is formed by creating another radiused section  134  on the inside flange. Optionally, the outer flange is provided with a similar center indentation. 
     As shown, a secondary backing ring  136  is incorporated to further support the seal assembly  120  and in particular the seal ring  124  and the first backing ring  122 . The secondary backing ring  136  is formed with an interior arcuate race  138  for mating engagement with a corresponding outer arcuate race  140  of the first backing ring  122 . In one particular embodiment, the secondary backing ring  136  is made with a material having a high modulus property, such as PEEK, suitably stiff strong material such as stainless steel, ferrous or non-ferrous metals, or engineering plastics. The secondary backing ring may be a loose piece held by the housing or potentially bonded to the first backing ring or alternatively a mechanical engagement may be used, such as one or more detents. In one embodiment, the seal assembly is made from a seal ring of a first material, a first backing ring of a second material, and a secondary backing ring of a third material. In a particular embodiment, the first material is PTFE or PTFE composition, the second material is PEEK or PEEK composition, and the third material is either a ferrous or a non-ferrous metal. Alternatively, the third material is made from an engineering plastic material. Exemplary engineering plastics include Ultem® (PEI) amorphous polyetherimide polyethersulfone (PES), semi-crystalline polyphenylsulfide (PPS), semi-crystalline polyphthalamide (PPA), among others. Fibers Filler additives may be added to the third material to enhance their properties. The third material for the outer backing ring can also be made from a PEEK material, or PEEK composite material. 
     Thus, an aspect of the present invention is understood to include a seal assembly comprising a seal ring made of a first material, a first backing ring made of a second material, and a second backing ring made of a third material, and wherein the first backing ring incorporates a cavity comprising multiple sides for supporting the seal ring along multiple sides. In one particular embodiment, the multiple sides include an outer flange, a center channel section, and an inner flange. In another particular embodiment, the seal ring includes a holding bore sized to accommodate an energizer, which in particular embodiments may include a canted coil spring or an O-ring. 
       FIG. 6  is a cross-sectional side view a seal assembly  142  provided in accordance with another embodiment of the present invention. The present seal assembly is similar to the seal assembly of  FIG. 5  with the exception of the orientation of the overall ring of the seal assembly. In the present embodiment, the ring inside diameter  144  is formed about the two inside lips  92  of the seal ring  148  and the outside diameter is formed about the exterior surface  149  of the secondary backing ring  150 . A primary backing ring  152  is incorporated between the seal ring and the secondary backing ring. 
     Thus, aspects of the present invention is understood to include a seal ring having an inside retaining lip that defines an inside diameter, a first backing ring made of a high modulus material mechanically engaged to the seal ring, and a second backing ring made of a high modulus material surrounding, at least in part, the first backing ring, and wherein an exterior wall surface of the second backing ring define an outside diameter. In one embodiment, the materials of the first backing ring and of the second backing ring are different. In one particular embodiment, the first backing ring  152  is made from a PEEK or PEEK composite material with friction reducing additives and the second backing ring is made from a conventional engineered plastic. In the present embodiment, static sealing may be formed about the inside and outside contact lines  90  and dynamic sealing about the radial surface  93  of the two lips  92 . 
       FIG. 7  is a cross-sectional side view a seal assembly  154  provided in accordance with yet another embodiment of the present invention. The present seal assembly is similar to the seal assembly  70  of  FIG. 3  with the exception of the orientation of the overall ring of the seal assembly. In the present embodiment, the ring inside diameter  156  is formed about both the seal ring  158  and the backing ring  160  and the outside diameter  162  is formed also about both rings. 
       FIG. 8  is a cross-sectional side view of a seal assembly  164  provided in accordance with another embodiment of the present invention. The present seal assembly is similar to the seal assembly  106  of  FIG. 4  with the exception of the inclusion of a secondary backing ring  166 , which has an arcuate inner race  168  for mating with a corresponding arcuate outer race  170  of the primary backing ring  172 . Thus, the present seal assembly  164  is understood to include a locking ring  174  mechanically connected to a seal ring  176 , which is mechanically connected to a primary backing ring  172  made of a first material and a secondary backing ring  166  made of a second material. In particular embodiments, mechanical connection between the various pieces can be by way of detents, interference fit, or combinations thereof. 
     The present alternative embodiment is further understood to include a seal assembly for isolating a high pressure region  44  of an equipment, such as a pump, a compressor, or a turbine as non-limiting examples, from a low pressure region  46  by forming a seal around a shaft (shown schematically with a centerline ℄) along its inside diameter  156  and supporting the seal from distortion with a backing ring, which supports the seal along at least an inner flange  110  of the seal and the central channel section  98  of the seal. In one preferred embodiment, a locking ring is provided, which has a projection  178  that extends into a holding bore of the seal and defines, at least in part, a geometry of the holding bore for accommodating an energizer, which may be a canted coil spring or an O-ring. In a further aspect of the present invention, a secondary backing ring  166  is provided with an arcuate inner race for mating with a corresponding arcuate race of the backing ring. 
     Although limited embodiments of seal assemblies and their components have been specifically described and illustrated herein, many modifications and variations will be apparent to those skilled in the art. For example, a different combination of pliable seal ring plastic material and rigid plastic housing structure may be used instead of PTFE and PEEK. Furthermore, it is understood and contemplated that features specifically discussed for one seal embodiment may be adopted for inclusion with another seal embodiment, provided the functions are compatible. The present invention further includes methods for forming the seal assemblies as described. Accordingly, it is to be understood that the seal assemblies and their components constructed according to principles of this invention may be embodied other than as specifically described herein. The invention is also defined in the following claims.