Abstract:
A sealing system for sealing one end of a rotating shaft from fluids. The sealing system includes a resilient bellows element connected at each end to a thrust plate. The bellows acts like a compression spring forcing the thrust plates against respective sealing elements and thereby forming two dynamic seals around the shaft. Each of the dynamic seals alternately rotate with the shaft, depending upon the respective forces of friction acting on each.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/169,312, filed Dec. 7, 1999. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to sealing systems for rotating machines and, more specifically, to an improved sealing assembly used therein. 
   Sealing systems are often used in machine applications to provide a seal between a rotating shaft and a machine housing, wall or other stationary element of a machine. Such machine applications include, but are not limited to, fluid pumps and fluid mixing machines. The seal may be provided to prevent fluids being worked on, such as a liquid being pumped, from entering either the drive mechanism of the machine or the atmosphere. 
   These machines generally include a stationary element (such as a housing), a drive element (such as a shaft), and a driven element (such as an impeller) connected to the drive element. One way to provide a rotatable seal between the drive element and the stationary element is by providing two sealing rings and leaf springs. One ring forms a seal with a sealing face that is rigidly attached to the stationary element. The other ring forms a seal with a sealing face that is fixed to the driven part. The two sealing rings are biased against their respective sealing faces by the leaf springs. The resulting seal is actually two rotatable seals placed in series. 
   One such sealing system is shown and described in U.S. Pat. No. 3,028,163 to Heinrich. Sealing systems having only one rotatable seal are also known. All of these sealing systems are complex and thus inherently prone to failure. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a sealing system for a rotating machine having a stationary element and a drive element rotationally connected to the stationary element. The sealing system includes a plate having a bearing surface. The plate is rigidly connected to either the drive element or the stationary element. The sealing system also includes a sealing assembly having a resilient bellows secured to a thrust plate having a bearing surface. The bellows provides a force on the thrust plate forcing the bearing surface of the thrust plate against the bearing surface of the other plate to form a dynamic seal. 
   According to a further aspect of the invention, the resilient bellows comprises a collar to which the thrust plate is secured. 
   According to yet another aspect of the invention, the sealing assembly has a static sealing element disposed within a gap provided between the collar and the thrust plate. 
   According to a even further aspect of the invention, a mounting element provides the connection of the plate to either the drive element or the stationary element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a sectional side view of a portion of a rotating machine having a seal according to the invention; and 
       FIG. 2  shows a bellows seal assembly according to the invention. 
   

   DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a rotating machine  8 , such as a pump, includes a drive element or shaft  10 , and a driven element or work implement  12 , such as an impeller, propeller, or mixing bars. The implement  12  is secured to the drive shaft  10  by a bolt  13 . It should be appreciated that while, in the present embodiment, the drive element is a shaft, any suitable rotational drive element could be substituted therefor. 
   The drive shaft  10  extends through a seal chamber  14  defined by a housing  16  of the machine  8 . The housing  16  is a stationary element of the machine  8 . A bellows sealing assembly  17  is disposed on the drive shaft  10  in the seal chamber  14 . The bellows sealing assembly  17  comprises a resilient bellows  18  holding a thrust plate  20 ,  22  at each end. 
   A drive plate  24  is mounted to the drive shaft  10  by a first mounting element or drive plate mount  26 , such that the drive plate rotates with the shaft  10 . The drive plate  24  has a bearing surface  28 . 
   A bearing surface  30  at the free end of the first thrust plate  20  bears on the bearing surface  28  of the drive plate  24 . As explained below in detail, a first dynamic (rotatable) seal  32  is formed at the interface between these bearing surfaces  28 ,  30 . 
   A stationary plate  34  is mounted to the housing  16  by second mounting element or a stationary plate mount  36 . The stationary plate  34  has a bearing surface  38 . 
   A bearing surface  40  at the free end of the second thrust plate  22  bears on the bearing surface  38  of the stationary plate  34 . As explained below in detail, a second dynamic (rotatable) seal  42  is formed at the interface between these bearing surfaces  38 ,  40 . 
   It should be appreciated, that each of the aforementioned plates  20 ,  22 ,  24 ,  34 , could be substituted with other structures having bearing surfaces for sealing against. Further, in some applications, such as machines that require minimal or infrequent rotation, the mounts  26 ,  36  can be eliminated and the drive and stationary plates  24 ,  34  can be mounted by other means, for example by shrinking the plates  24 ,  34  into reverse tapers or by gluing the plates into recessed holders. 
   A seal gland  44  is disposed over the stationary plate mount  36 . The seal gland  44  is secured to the housing  16  of the seal chamber  14  by two bolts  45  and thereby closes the seal chamber  14 . 
   Referring  FIG. 2 , the bellows  18 , as the term is used herein, is a resilient tube which behaves like a compression spring. In the embodiment of  FIG. 2 , corrugations or ribs  46  provided to the bellows  18  provide a force  48  longitudinally along the axis of the drive shaft  10 . The bellows  18  imparts this force  48  on the thrust plates  20 ,  22 , biasing them outwardly against their respective plates  24 ,  34 . 
   The bellows  18  can be formed of thin wall metal or plastic tubing, which can be seamless or welded. The corrugations  46  are formed in the tubing by a known hydraulic or rolling process. Alternatively, the bellows  18  can be formed by injection molding, by the lamination of a tube to a coil spring, or by another suitable process. 
   The bellows  18  also includes inwardly turned edges at each end. The inwardly turned edges form somewhat frustoconical or tapered collars  50 ,  52  for receiving the respective thrust plates  20 ,  22  therein. The thrust plates  20 ,  22  can be statically sealed to the bellows  18  by gaskets, such as elastomeric rings or sealants, such as epoxy, disposed, for example, in respective gaps  54 ,  56 , between the thrust plates  20 ,  22  and the collars  50 ,  52 . With proper selection of the gaskets or sealants, passage of molecules as small as nitrogen (N 2 ) can be blocked. 
   During operation of the machine  8 , rotation of the drive shaft  10  causes rotation of the drive plate mount  26  and the drive plate  24 . Depending on the instant force of friction between the bearing surfaces  28 ,  30  of the first dynamic seal  32  as compared to the instant force of friction between the bearing surfaces  38 ,  40  of the second dynamic seal  42 , the bellows sealing assembly  17  will sometimes be driven by and rotate with the drive shaft  10  and at other times remain stationary. 
   The thrust plates  20 ,  22  are made of carbon, composite plastic, silicon carbide, or composite metal. Each of the members  20 ,  22 ,  24 ,  34  that have bearing surfaces  28 ,  30 ,  38 ,  40  are made of a graphite containing material, such as graphite filled carbon or silicon carbide. Relative rotation of bearing surfaces  28  and  30 ,  38  and  40  causes graphite in the members  20 ,  22 ,  24 ,  34  to form a lubricating graphite film therebetween. In this way, the respective interfaces between the drive plate  24 , the stationary plate  34 , and the thrust plates  20 ,  22  provide the dynamic seals  32 ,  42 . 
   In the embodiment shown in  FIGS. 1 and 2 , the sealing assembly  17  provides two dynamic seals  32 ,  42  and the sealing assembly  17  alternates between driven and stationary operation (as explained above). According to alternative embodiments, a single seal can be provided. 
   A single seal can be provided, as one alternative, by securing one end of the bellows  18  directly to the stationary mount  36  so that the bellows  18  becomes a permanently stationary element. In this alternative, the second thrust plate  22  and the stationary plate  34  are eliminated. 
   A single seal could also be provided, as another alternative, by securing one end of the bellows  18  directly to the drive shaft  10  so that the bellows becomes a driven element. In this alternative, the first thrust plate  20  and the drive plate  24  are eliminated. 
   The present disclosure describes several embodiments of the invention, however, the invention is not limited to these embodiments. Other variations are contemplated to be within the spirit and scope of the invention.