Abstract:
Radial shaft seal designs are provided in which the use of PTFE and other flouro-elastomers are utilized for the unique chemical and heat resistance properties. Additional retaining rings and/or elastomer sealing rings are provided to improve the bore retention force of the seal within the seal housing.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to seals for rotary shafts, and more particularly, to an improved radial lip seal for sealing around a rotatable shaft.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     Radial lip seals are used to prevent fluids such as liquids or gases from leaking along a rotatable shaft from a region filled with this fluid in an apparatus in which the shaft is mounted to a region without this fluid. Such radial lip seals typically include a circular or annular seal ring or body which is sealably fit within a seal bore formed within a seal housing surrounding the rotatable shaft. A sealing lip extends radially inward from the seal body to slidably contact against the rotatable shaft and provide a leak-tight seal therewith. Known lip seal technology and in particular, radial seal technology, commonly uses elastomer rubbers. However, these elastomer seals have a somewhat limited temperature and velocity range in which they can operate as radial lip seals. Elastomer rubber radial lip seals also have a limited shelf life and have uses that are limited to a somewhat narrow range of compatible fluids and gases.  
         [0003]     Accordingly, polytetraflouroethylene (PTFE) and other flouro-elastomer materials have found a wide use in sealing and other applications due to their unique chemical and heat resistant properties. Seals constructed entirely out of PTFE or other flouro-elastomer materials have limited working temperature range due to loss of bore retention force. In particular, as the seals are heated up and subsequently cooled, the seals can expand and shrink to a size smaller than its original size, thus causing the seal to lose its retention capability.  
         [0004]     Accordingly, the present invention provides structural retaining rings assembled into or onto the PTFE or other flouro-elastomer seal such that the seal component is being squeezed between the two retaining rings with one or both of the retaining rings being made of metal, or alternatively, plastic. The retaining rings provide the seals with structural rigidity and bore retention in a wide temperature range.  
         [0005]     According to yet another aspect of the present disclosure, a PTFE or other flouro-elastomer shaft seal is provided with a rubber elastomer sealing ring which provides a sealing engagement between the interior surface of the bore and the seal housing and the outermost surface of the PTFE or other flouro-elastomer seal body.  
         [0006]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a schematic cross-sectional side view of a radial lip seal constructed according to the principles of the present invention, as shown surrounding a shaft;  
         [0009]      FIG. 2  is a cross-sectional view of a radial shaft seal according to the principles of the present invention;  
         [0010]      FIG. 3  is a cross-sectional view of an alternative radial shaft seal according to the principles of the present invention;  
         [0011]      FIG. 4  is a cross-sectional view of a second alternative radial shaft seal according to the principles of the present invention;  
         [0012]      FIG. 5  is a cross-sectional view of a third alternative radial shaft seal according to the principles of the present invention;  
         [0013]      FIG. 6  is a cross-sectional view of an elastomer seal ring utilized in combination with the seal shown in  FIG. 5 ; and  
         [0014]      FIG. 7  is a cross0sectional view of a fourth alternative radial shaft seal according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0016]     With reference to  FIGS. 1 and 2 , a radial shaft seal  10  is shown received in a bore  12  of a seal housing  14  and engaging a rotating shaft  18 . With reference to  FIG. 2 , the radial shaft seal  10  includes an annular body  20  preferably formed of PTFE or other flouro-elastomeric material. An outer retaining ring  22  is disposed radially outward of a portion  20   a  of the annular body  20 . An inner retaining ring  24  is disposed radially inward of the portion  20   a  of the annular body  20  so as to fix the portion  20   a  of annular body  20  between the outer retaining ring  22  and inner retaining ring  24 . The outer retaining ring  22  is provided with a cylindrical body portion  22   a  and radially inwardly extending flange portion  22   b  which extends over an end of the portion  20   a  of annular body  20 . The inner retaining ring  24  abuts against the radially inwardly extending flange portion  22   b  of outer retaining ring  22 . The inner retaining ring  24  includes a cylindrical body portion  24   a  and a radially inwardly extending flange portion  24   b  that is disposed adjacent to a radially inwardly extending sealing lip  26  which extends from the annular body  20 .  
         [0017]     The outer retaining ring  22  and inner retaining ring  24  are formed from metal or plastic materials which can be either snap-inserted into the prepared seating places within the annular body  20 , or alternatively, the annular body can be formed (plastically, or otherwise) around the inner and outer retaining rings  24 ,  22  during the manufacturing process. The annular body  20  is preferably provided with beads  28  extending from a radially outermost surface thereof for improving the sealing/retention within the housing bore  12 . Preferably, the material used for making the retaining rings  22 ,  24  (metal, plastic, or other suitable material) provides structural rigidity and bore retention in a wide temperature range.  
         [0018]     According to an alternative embodiment of the radial shaft seal  10 ′ as shown in  FIG. 3 , the outer retaining ring  22 ′ is shown to merely include a cylindrical ring portion recessed in the outermost surface of the annular body  20 ′ while the inner retaining ring  24 ′ is further provided with a radially outwardly extending flange portion  24   b ′ that extends along an end face of the annular body  20 ′. It should be understood that other variations of the shapes and configurations of the inner and outer retaining rings  24 ,  22  can also be utilized without departing from the spirit and scope of the present disclosure.  
         [0019]     With reference to  FIG. 4 , a still further alternative embodiment of the radial shaft seal  50  is provided. The radial shaft seal  50  includes an annular body portion  52  having an embedded retaining ring  54  received therein. The retaining ring  54  includes a cylindrical inner ring portion  54   a  with a radially outwardly extending flange portion  54   b  that terminates in a cylindrical outer ring portion  54   c . The retaining ring  54  is preferably made of metal or other plastic material that provides sufficient structural rigidity and bore retention characteristics along a wide temperature range. The annular body  52  is provided with a plurality of beads  56  on an outermost surface thereof for providing sealing/retention of the seal within the bore  12  of a seal housing  14 . In the event of expansion and contraction of the PTFE or other flouro-elastomer due to temperature variations, the retaining ring  54  is also press-fit within the recessed bore  12  of the seal housing  14  and maintains retention of the radial shaft seal  50  therein. The annular body  52  includes a radially inwardly extending sealing lip  58  that engages the shaft  18 .  
         [0020]     With reference to  FIG. 5 , an alternative shaft seal design  70  is shown including a continuous annular body portion  72  preferably formed of PTFE or other flouro-elastomer material. A sealing lip  74  extends radially inward from the body portion  72  and engages a rotating shaft  18 . The outermost surface  76  of the body portion  72  includes a first annular recess  78  which further includes a recessed groove portion  80  disposed in a bottom portion thereof. An elastomeric sealing ring  82  is disposed in the annular recess  78  and bridges the recessed groove portion  80 . The radial shaft seal  70  is inserted into a recessed bore  12  of a seal housing  14  with the elastomeric ring  82  providing a sealing engagement between the interior surface of the bore  12  and exterior surface  76  of shaft seal body portion  72 . When the seal  70  is heated up during use, the expansion and contraction thereof is accommodated by the outermost surface  76  being smaller than the interior diameter of the recessed bore  12  provided in the seal housing  14 . Thus, expansion of the body portion  72  can be accommodated without the body portion  72  being subjected to compression forces that would normally occur if the body portion  72  were in a tight fit with the recessed bore  12 . Furthermore, the recessed groove portion  80  provides an extra space which may allow for the elastomeric ring  82  to deform into while being compressed between the PTFE component and the bore  12 . The elastomeric sealing ring  82  is disclosed as including axially spaced bulb portions  82   a ,  82   b  and an intermediate portion  82   c  connected to the larger bulb portions  82   a ,  82   b . It should be understood, however, that other configurations of the elastomeric seal could also be utilized including a D-shaped cross-section elastomeric ring seal  82 ′, as illustrated in  FIG. 6 . The elastomeric sealing ring  82 ,  82 ′ preferably provides retention and sealing between the annular body  72  and the interior surface of recessed bore  12  while not being as susceptible to expansion and contraction due to temperature variations.  
         [0021]     With reference to  FIG. 7 , an alternative shaft seal  100  is shown including an annular body portion  102  made from PTFE or other flouro-elastomer. A seal lip  104  extends radially inwardly from the annular body portion  102 . The annular body portion  102  includes a discontinuous outermost surface  106  having an annular recess  108  for receiving an elastomeric ring  110 . The discontinuous outermost surface includes axially extending and circumferentially spaced slots  112  creating discontinuities in the outermost surface  106 . The discontinuities of the outermost surface  106  prevent plastic deformations in the PTFE or other flouro-elastomer material. The outermost surface  106  can tightly engage the inner surface of the bore  12  to assist the elastomer ring in providing seal retention, however, during expansion of the seal material, the discontinuities accommodate such expansion without imparting plastic deformation.  
         [0022]     With the design according to the principles of the present invention, the radial shaft seal is designed to utilize PTFE and other flouro-elastomer materials which have unique chemical and heat resistant properties that provide good sealing characteristics, while the problem of providing sufficient bore retention forces is overcome by the use of metal, or alternatively, plastic components which provide the seals with structural rigidity and bore retention and a wide temperature range ( FIGS. 2-4 ). An added advantage of the current design is that the structural components are not exposed to the environment and, therefore, can be made from cheaper grades of materials or with less expensive finish coatings. Yet another advantage is that the static sealing between the bore and a seal outside diameter can rely either on the PTFE or other flouro-elastomer material, or on the structural retaining rings, or both, reducing needs for extra sealing elements, such as molded rubber elements or assembled elastomeric gaskets/O-rings. Yet another advantage is that no sealing is required between retaining rings and the PTFE element, thus improving overall sealing reliability. The use of PTFE or other flouro-elastomer materials is further accomplished by a specially designed annular recess in the outermost surface for receiving an elastomeric ring therein, and/or by providing a discontinuous outermost surface of the seal.  
         [0023]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.