Abstract:
A mechanical seal  10  provides a fluid tight seal between relatively rotatable elements such as a drive shaft and a housing. The seal includes first and second seal faces ( 13, 11 ) and transmission means ( 27 ) which engage said second seal face and extend axially therefrom in a direction away from said first seal face. Biasing means ( 28 ) bias the transmission means, and thereby the second seal face, towards the first seal face. Drive means ( 29 ) engage the transmission means and are for mounting in driving engagement with the second element. The drive means include at least one radially extending engagement portion ( 30 ) which extends into an axially enclosed opening ( 31 ) in the transmission means.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to mechanical seals, more particularly to the drive and coupling arrangements within mechanical seals.  
       BACKGROUND TO THE INVENTION  
       [0002]     A mechanical seal comprises a “floating” component which is mounted axially movably around the rotary shaft of, for example, a pump and a “static” component which is axially fixed, typically being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more spring members. In use, one of the floating and static components rotates; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component.  
         [0003]     Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary, the seal is referred to as a stationary seal.  
         [0004]     If the sliding seal between the rotary and stationary components are assembled and pre-set prior to despatch from the mechanical seal manufacturing premises, the industry terminology for this is “cartridge seal”. If the rotary and stationary components are despatched individually (unassembled) from the mechanical seal manufacturing premises, the industry terminology for this is “component seal”.  
         [0005]     Mechanical seals are used in all types of industries to seal a variety of different process media and operating conditions. The general industry term which defines the area adjacent to the process media is “inboard”. The industry term which defines the area adjacent to the atmospheric side is “outboard”.  
         [0006]     Like most industries, the mechanical seal industry is highly competitive. As a result, mechanical seal manufacturers constantly seek methods of improving competitive advantage. Pressed and formed components are one way in which mechanical seal manufacturers can reduce the manufacturing cost of said component.  
         [0007]     Unfortunately pressed components can compromise the technical aspects of a single component or a combination of components working relative to each other. One such example of this is the drive mechanism between two components working relative to each other. As pressed components are manufactured from a given thickness of material, the cross-sectional area of the drive mechanism is traditionally thereby limited to a multiplication of said thickness.  
         [0008]     Pressed components are typically manufactured from sheet material, typically steel or stainless steel with a material thickness of 0.2 mm to 2.5 mm. Most mechanical seal components are pressed using 1,2 mm to 1.7 mm thick material. Pressed components offer the advantage that, in most cases, subsequent machining operations are not necessary. This therefore reduces the manufacturing cost considerably.  
       STATEMENTS OF THE INVENTION  
       [0009]     According to the present invention there is provided a mechanical seal for providing a fluid-tight seal between relatively rotatable elements, the seal comprising first and second seal faces for mounting in fixed rotational relationship with respective first and second relatively rotatable elements, transmission means engaging said second seal face and extending axially therefrom in a direction away from said first seal face, means for biasing said transmission means, and thereby said second seal face, towards said first seal face, and drive means engaging said transmission means and for mounting in driving engagement with said second element, said drive means including at least one radially extending engagement portion which extends into an axially enclosed opening in said transmission means.  
         [0010]     Preferably the drive means includes at least two radially extending engagement portions and said transmission means includes at least two corresponding enclosed openings within which said engagement portions locate.  
         [0011]     Preferably the arrangement is such that rotational drive is transmitted from said drive means to said transmission means over a cross-sectional engagement area which is larger than the sum of the respective material thicknesses of said drive means and said transmission means.  
         [0012]     Preferably a mechanical seal of the invention includes two engagement portions the seal being assembled by locating at least one engagement portion of said drive means in an enclosed opening of said transmission means, thereafter pivoting said drive means relative to the transmission means such that the outermost radial part of a second engagement portion on the drives means is an interference fit with the innermost radial part of the transmission means adjacent to that enclosed opening for accommodating the second engagement portion. More preferably the axial end of the second enclosed slot of the transmission means terminates within close proximity of the axial end of said transmission means to provide a thin section web which elastically deforms when presented to the interference fit of the engagement portion of said drive means.  
         [0013]     Preferably a seal in accordance with the present invention has drive means and transmissions means are made of one or more thin material.  
         [0014]     Alternatively the drive means may be made from relatively thin material and said engagement portions provided by a machined lug. Furthermore the transmission means may be made from relatively thick material.  
         [0015]     A mechanical seal in accordance with the present invention may be in the form of a single component mechanical seal, a single cartridge mechanical seal or another form of mechanical seal.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings are as follows:— 
         [0017]      FIG. 1  is a cross-sectional view of a prior art single component mechanical seal;  
         [0018]      FIG. 2  is a isometric view showing the staking operation conducted after the assembly of two components of the seal of  FIG. 1 ;  
         [0019]      FIG. 2   b  is an enlarged partial cross-section of the arrangement shown in  FIG. 2 ;  
         [0020]      FIG. 2   c  is an enlarged isometric view of part of the arrangement of  FIG. 2 ;  
         [0021]      FIG. 3  is a cross-sectional view part of a single rotary mechanical seal of the invention;  
         [0022]      FIG. 3   b  is a partial cross-sectional view of the entire mechanical seal of  FIG. 3 ;  
         [0023]      FIG. 4  shows cross-sectional and plan view of two of the components of the seal of  FIG. 3 ;  
         [0024]      FIG. 5  is an isometric view of the components shown in  FIG. 4 ;  
         [0025]      FIG. 6  is an exploded isometric view of the components of  FIG. 5 ;  
         [0026]      FIG. 7  shows further cross-sectional and plan views of the components of  FIG. 4 ;  
         [0027]      FIG. 8  shows cross-sectional and plan views of alternative components similar to those shown in  FIG. 4 ; and  
         [0028]      FIG. 9  is a partial cross-sectional view of a single cartridge seal of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The invention will now be described, by way of examples only, with reference to the accompanying drawings.  
         [0030]     The prior art single component mechanical seal partially shown in  FIGS. 1 and 2  includes a rotary holder  1 , a drive plate  2  and rubber bellows  4 . The rotation of the drive shaft  5  is transmitted to seal face  6  through rubber bellows  4 , drive plate  2  and rotary holder  1 . Rotary holder  1  includes circumferentially spaced apart slots  7  within which upstanding lugs  8  of rotary holder locate.  
         [0031]     In order to keep rotary holder  1  and drive plate  2  from disconnecting, the entrance corners of slots  7  are staked, as indicated at  3 . The staking operation is typically conducted using a hammer and a sharp implements such as a chisel. This staking operation is a manual process and, as a result, the results are somewhat variable, the variation ranging from a particularly deep-staked impression to no staking at all due to a manual error.  
         [0032]     The staking operation creates a sharp raised surface in rotary holder  1 . This surface can damage other components such as the rubber bellows  4 . Furthermore, the sharp surface can result in injury to personnel.  
         [0033]     Referring to  FIG. 3  of the accompanying drawing, a rotary mechanical seal  9  of the invention includes a rotary and axially floating seal face  11  which is biased by spring  28  towards a static stationary seal face  12 . The rotary seal face  11  is allowed to slide on the static seal face  12  and the interface between the rotary seal face  11  and stationary seal face  12  forms sealing area  13 . This seal area  13  is the primary seal that prevents the process medium  14  from escaping from the process chamber  15 .  
         [0034]     In addition to the sliding seal face, the process medium  14  is sealed by a rotary elastomeric member  16  in contact with the shaft  17  and rotary seal face  11 . This is the first secondary sealing area. The second secondary sealing area is formed between the stationary seal face  12  and the stationary gland plate assembly  21  by means of elastomeric member  22 . The third secondary sealing area is formed between the gland plate assembly  21  and the process chamber  15  by means of gasket  25 .  
         [0035]     The three secondary sealing areas and the primary sliding sealing interface prevent the process media  14  from escaping from the process chamber  15 .  
         [0036]     The static seal face  12  is prevented from rotating by radial squeeze between the elastomeric member  22  and the gland plate assembly  21 . An additional or alternative anti-rotation device can be incorporated if it is considered desirable.  
         [0037]     The rotary sealing assembly  26  includes a rotary holder  27  which is a pressed metal device and which transmits the axial force spring  28  to the seal face  11 .  
         [0038]     A drive ring  29  is fitted to the radially outward portion of elastomeric member  16 . This drive ring  29  radially compresses elastomeric member  16  to form a seal to the shaft  17 .  
         [0039]     The rotational movement of shaft  17  is transmitted through the elastomeric member  16  to drive ring  29 . Drive ring  29  in turn transmits the rotational movement to the rotary holder  27  by means of drive lugs  30  circumferentially spaced apart around drive ring  29 . At least one of these drive lugs  30  engages in a axially enclosed slot  31  in rotary holder  27 . Other drive lugs  30  may engage in either axially enclosed slots or axially open slots such as those shown in the prior art seal of  FIGS. 1 and 2 .  
         [0040]     The rotary holder  27  transmits the rotation movement to the seal face  11  by means of drive lugs  30  which extend into and engage in slots  33  located in the seal face  11 .  
         [0041]     In alternative embodiments the drive mechanism may be varied from that described above. For example an alternative drive mechanism may include a pin in the slot arrangement.  
         [0042]     Referring to  FIG. 4  of the accompanying drawings, the rotary holder  27  and drive plate  29  ae shown in their working position. The drive plate  29  is axially captured in rotary holder  27  because at least one drive lug  30  of drive plate  29  is located in a corresponding enclosed slot  31  of the holder  27 . Accordingly drive plate  29  cannot become decoupled from rotary holder  27 . This is of particular advantage in certain applications such as those creating reduced pressure or vacuum conditions in the process chamber  15 . Furthermore, during installation of the seal, the rotary seal assembly  26  is often pushed, pulled and rotated as it is fitted to the shaft  17 . If the driver in  29  is not axially retained relative to the rotary holder  27 , the rotary assembly  26  can fall apart.  
         [0043]     Referring to  FIG. 5  of the accompanying drawings, it can be seen or appreciated that, while four drive lugs  35  engage in open slots  31  in the rotary holder, two drive lugs  30  engage in enclosed slots  31 . It will be appreciated that any number and combination of open slots  36  and closed slots  31  can be incorporated in a rotary holder  27 .  
         [0044]     Referring to  FIG. 6  of the accompany drawings, it is seen more clearly that the drive plate  29  includes a plurality of lugs  37  which have a radially outwardly extending portion of which subsequently return in an axial direction. These lugs  37  correspond to slots  38  in the rotary holder  27 . The axial return  39  of each lug  37  coincides with the radial position of a corresponding slot  38  in the rotary holder  27 .  
         [0045]     Referring to  FIG. 7  of the accompanying drawings, the drive plate  29  includes two drive lugs  40  and  41  which extend radially outwardly over a restricted circumferential extent.  
         [0046]     During assembly of the rotary holder  27  and drive plate  29 , the drive lug  41  is located in an enclosed slot  42  with the result that the drive ring  29  is then radially off-centre to the rotary holder  27 . The drive ring  29  is then pivoted about the area of engagement of the drive lug  41  and enclosed slot  42 , until the second drive lug  40  locates in the second enclosed slot  43 .  
         [0047]     The driver ring  29  is slightly radially larger than the corresponding inner surface  44  of the rotary holder  27  in that area adjacent to the second enclosed slot  43 . This results in a radial interference during the above mentioned pivoting movement, thereby allowing the drive ring  29  to click into position as a result of the web  45  of enclosed slot  43  elastically deforming radially to accommodate the interference. This deformation is not permanent and the web  45  returns to its original conformation once the lug  40  has located into slot  43 .  
         [0048]     Referring to  FIG. 8  of the accompanying drawings, there is illustrated a partial enlarged cross-sectional view of a rotary holder  27  and drive plate  29 . The drive cross-sectional area  50  is considerably increased when compared to the cross-sectional area  51  of the prior art arrangement illustrated if  FIG. 2   b . This increase in cross-sectional drive helps to prevent the drive plate  52  (see  FIG. 2   c ) wearing the rotary holder  54  at  53 . This reduction or elimination of wear results from the same rotational force, derived from the drive torque, being spread over a larger cross-sectional area  50  ( FIG. 8 ) compared to that of the  FIG. 2   c  arrangement, even though the same thickness of pressed material is employed in both arrangements. Accordingly, the invention helps to improve mechanical seal life.  
         [0049]     Referring to  FIG. 9  of the accompanying drawings, there is illustrated a single cartridge mechanical seal  60  in accordance with the invention. The rotary assembly  61  is identical to that described above. The seal shown in  FIG. 9  includes a sleeve  62  which connects the rotary assembly  61  with a clamp ring  63 . Clamp ring  63  contains at least one screw  64  for connecting the rotating parts of the cartridge mechanical seal  60  to the shaft  65 .  
         [0050]     It should be appreciated that the present invention may be applied to both rotary and stationary seals whether of single, double or triple seal type and whether designed in a cartridge or component seal format.  
         [0051]     The invention may be used with metallic components as well as non-metallic components such as plastic. Furthermore some types of equipment rotate the housing and have a stationary shaft. The invention can be applied to such an arrangement.