Patent Publication Number: US-11022180-B2

Title: Holding device for application of a sealing element on a shaft

Description:
This application is a national phase of International Application No. PCT/SE2016/051175 filed Nov. 28, 2016 and published in the English language, which claims priority to Swedish Patent Application No. 1551628-9 filed Dec. 11, 2015, which are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention relates to a holding device for application of a sealing element on a shaft according to the preamble of claim  1 . 
     The holding device can be comprised in a mechanical sealing device which may be arranged in a hydrodynamic machine such as a pump. In this case, the mechanical sealing may have the task to seal a space between a rotatable shaft and a housing. Such a mechanical sealing device may comprise a non-rotatable sealing element which is attached in the housing and a rotatable sealing element which is attached on the rotatable shaft. The sealing elements comprise sealing surfaces having a high degree of evenness such that they also at mutual rotation provide a very reliable sealing. Pumps provided with mechanical sealing devices may be used to transport foodstuffs and medicines. However, there are high hygienic requirements on components that come in contact with foodstuffs and medicines. Consequently, it is important that such components are easy to clean and that they do not comprise unevennesses or recesses where foodstuffs and medicines can get stuck. 
     SE 531 210 shows a mechanical sealing device for a pump where a sealing element is attached on a rotatable shaft by means of an annular body. The annular body is attached on the shaft by means of a radially inwardly projecting portion which is received in a correspondingly shaped recess in the shaft surface. Thus, the annular body and the sealing element obtain a reliable attachment on the shaft. However, such an attachment is not suitable to use in case the pump should transport foodstuffs. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a holding device by which it is possible to attach a sealing element on a shaft in a relative simple and reliable manner without cutting of the surface of the shaft. 
     This object is achieved with the holding device according to claim  1 . By providing the annular body with an inclined inner surface in relation to the shaft, it requires a relatively small force by the displacement mechanism to displace the clamping element in an axial direction to a position where it is clamped on the shaft. The clamping element is designed as a segment of a ring and the segment comprises an inner surface having a corresponding curved form as an outer surface of the shaft. Thus, the clamping element may be adapted to the inner surface of the annular body and the shaft surface in an optimal manner. Consequently, a relatively large contact area is also obtained between the clamping element and the shaft. The pressure force transmitted from the clamping element to the shaft may thus be distributed over the entire contact area which reduces the risk for stress concentrations and deformations of said surfaces. The annular body and the sealing element which is connected to the annular body will thus rotate with the shaft as a unit. Since the annular body is attached on the shaft with a clamping force, no recesses or other cuttings are required in the shaft surface for attaching the sealing element on the shaft. Thus, the shafts may have a completely even surface which is easy to clean. Advantageously, the holding device can thus be used in the food industry and the pharmaceutical industry where the hygiene requirements are high. 
     According to an embodiment of the invention, the clamping element comprises an outer surface having a corresponding shape as the inner surface of the annular body. Thus, a relatively large contact area is obtained between the annular body and the clamping element. The pressure force which is transmitted from the annular body to the clamping element is thus distributed over the entire contact area which reduces the risk for stress concentrations and deformations of said surfaces. 
     According to an embodiment of the invention, the holding device comprises a plurality of attachment devices which are arranged at constant intervals around the shaft. The holding device may thus comprise two or several clamping elements in the form of segments of a ring which are symmetrically arranged around the shaft. Thus, the pressure forces from the respective clamping elements may be distributed in an optimally manner on the shaft. However, the attachment devices may be arranged asymmetrically around the shaft. 
     According to an embodiment of the invention, the displacement device comprises a screw element having an extension in an axial direction, wherein the screw element comprises a threaded portion to be engaged with a threaded portion of the clamping element and a head portion which is rotatably arranged in the annular body. In this case, the head portion of the screw element may be turned by means of a suitable tool. The turning motion of the screw element results in that its threaded portion displaces the clamping element in an axial direction in relation to the annular body. Thus, the clamping element may in a simple manner and reliable manner be displaced to a position where it is pressed with a relatively great force against the shaft. However, it is possible to design the displacement device, which displaces the clamping element, in other ways. 
     According to an embodiment of the invention, the annular body comprises a radially inwardly directed portion. Such a radially inwardly directed portion may have many functions. The radially inwardly directed portion may comprise at least one through hole for application of the head portion of the screw element. Such a through hole has a somewhat elongated shape in a radial direction such that the screw element can be displaced radially inwardly together with the clamping element in connection with the application of the annular body on the shaft. 
     Alternatively or in combination, the radially inwardly directed portion may comprise at least one through hole for application of a spring element which is adapted to act with an axially directed force on the sealing element. The task of the spring element is to press the sealing surface of the sealing element against a sealing surface of another sealing element. 
     Alternatively or in combination, the radially inwardly directed portion may comprise at least one through hole for application of an elongated axially directed locking element of the connection mechanism which connects the annular body with the sealing element. Such a connection mechanism allows a certain axial mobility of the sealing element in relation to the annular body at the same time as it prevents rotation between the sealing element and the annular body such that they rotate as a unit. 
     According to an embodiment of the invention, the annular body comprises, at a first end, a first sealing element which provides a sealing between a surface of the annular body and a radially outer surface of the sealing members and, at a second end, a second sealing member which provides a sealing between a surface of the annular body and the shaft surface. The sealing members prevent thus leakage at the ends of the annular body at the same time as they prevent penetration of possible impurities. 
     According to an embodiment of the invention, the holding device comprises a mechanical sealing device where said sealing element comprises a sealing surface which is adapted to abut sealingly against a sealing surface of a further sealing element in a radial plane through the shaft. Advantageously, the holding device may thus be comprised in a mechanical sealing device. Advantageously, the mechanical sealing device may be arranged in a space between the shaft and a connecting component which are rotatably arranged in relation to each other. The connecting component may be a housing of a hydrodynamic machine in the form of a pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, a preferred embodiment of the invention is described as an example with reference to the drawings on which: 
         FIG. 1  shows an elongated cross sectional view of a mechanical sealing device which comprises a holding device according to the present the invention, 
         FIG. 2  shows a front view of the clamping element in a separated state and 
         FIG. 3  shows a cross sectional view in the plane A-A in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
       FIG. 1  shows a mechanical sealing device comprising a first part  1  and a second part  2 . In the shown embodiment, the mechanical sealing device in comprised in a pump. The mechanical sealing device may also be used in other applications comprising a rotatable shaft which extends through a passage in a housing or the like, for example, a mixer or a stirrer. In the shown embodiment, the first part  1  is stationary while the second part  2  rotates around a rotation axis x. It is to be noted that the first part  1  can be rotatable and the second part  2  can be stationary or substantially stationary. It is also possible to let the first part  1  and the second part  2  rotate at different rotation speeds. 
     The first part  1  comprises a first annular sealing element  11 . The first sealing element  11  is attached in a housing  12  by means of a first holding device  13 . The first the holding device  13  may be connected to the housing  12  by means of a thread engagement. A schematically shown first connection mechanism  14  connects the sealing element  11  and the holding device  13  in a manner such that rotation of the first the sealing element  11  in relation to the holding device  13  is prevented. A sealing member in the form of an O-ring  15  is arranged around the first the sealing element  11  in order to prevent leakage between the first the sealing element  11  and the first the holding device  13 . The first sealing element  11  comprises a first plane sealing surface  11   a.    
     The second part  2  comprises a second sealing element  21 . The second sealing element  21  comprises a second plane sealing surface  21   a  which is adapted to abut against the first sealing surface  11   a  in a radial plane in relation to the rotation axis x. The sealing surfaces  11   a ,  21   a  have each a very high degree of evenness such that they abut sealingly against each other also when the sealing surfaces  11   a ,  21   a  are rotated in relation to each other. The second part  2  comprises a second holding device  22  which is adapted to attach the second sealing element  21  on a rotatable shaft  23  which is rotatably arranged around the rotation axis x. The second holding device  22  comprises an annular body  24  which is arranged around the shaft  23 . A second connection mechanism  24   e ,  25 , which only is shown in  FIG. 3 , connects the annular body  24  with the second sealing element  21  in a manner such that the second sealing element  21  is axially displaceable along the rotation axis x in relation to the rotatable shaft  23 , but it is fixedly connected to the rotatable shaft  23  in a periphery direction. The annular body  24  and the second sealing element  21  thus rotates as a unit. 
     The second holding device  22  comprises at least one but preferably a plurality of attachment devices which each comprises a clamping device  26  and a screw element  27 . The attachment devices are in this case arranged in different positioner at regular intervals around the shaft  23 . The clamping elements  26  are arranged in a periphery space between an inner surface  24   a  of the annular body  24  and a surface  23   a  of the shaft  23 . Each of the clamping elements  26  comprises an inner surface  26   a  having a corresponding shape as the shaft surface  23   a . Each one of the clamping elements  26  comprises an outer surface  26   b  having a corresponding shape as inner surface of the annular body  24   a . The outer surface  26   b  of the clamping elements  26  and an inner surface of the annular body  24   a  are provided with an inclination in an axial direction in relation to the shaft  23 . Each one of the clamping elements  26  comprises a thread through hole  26   c . A threaded portion  27   a  of a screw element  27  is arranged in the through hole  26   c . The screw element  27  comprises, at an end, a head portion  27   b  with a gripping recess in order to enable turning of the screw element  27  by a tool. The head portion  27   b  of the screw element  27  is arranged in a through hole  24   c  of a radially inwardly protruding part  24   b  of the annular body  24 . The through hole  24   c  has a certain radial extension such that the screw element  27  has a corresponding mobility in a radial direction. 
     A first sealing member  28  is adapted to seal between a surface of a first end of the annular body  24  and an outer surface  11   b  of the second sealing element  11 . A second sealing member  29  is adapted to seal between a surface of a second end of the annular body  24  and the shaft surface  23   a . The second holding device  22  comprises at least one but preferably a plurality of spring elements  30  which may be arranged at regular intervals around the shaft  23 . The tensioning elements  30  comprise spring members which in a mounted state supply a spring force on the second sealing element  21  such that it is pressured against the first sealing element  11  which results in that the sealing surfaces  11   a ,  21   a  are kept together with a predetermined force. 
       FIG. 2  shows a front view of a clamping element  26 . The clamping element  26  is designed as a segment of a ring. The clamping element  26  has an inner surface  26   a  with a curvature in a radial plane. Advantageously, the shaft surface  23   a  has a corresponding curvature. The clamping element  26  has an outer surface  26   b  with a curvature in a radial plane. Advantageously, the inner surface  24   a  of the annular body  24  has a corresponding curvature. It is here also apparent that the head portion  27   b  of the screw element is provided with a gripping recess for a tool. 
       FIG. 3  shows a cross sectional view in plane A-A in  FIG. 1 . In this embodiment, the inwardly directed portion  24   b  of the annular body comprises three through holes  24   c  for receiving of a respective head portion  27   b  of a screw element  27 . The screw elements  27  and the clamping elements  26  are here arranged at constant intervals around the periphery of the shaft  23 . The inwardly directed portion  24   b  comprises three through holes  24   d  for receiving of a through spring element  30  which exerts an axial pressure force on the second sealing element  21 . The holes  24   d  and the spring elements  30  are arranged with constant intervals around the periphery of the shaft  23 . The inwardly directed portion  24   b  comprises two through holes  24   e  for receiving of a respective elongated axial locking element  25  which is attached on the second sealing element  21 . When the locking elements  25  are applied in the through holes  24   e , mutual rotation between the second sealing element  21  and the annular body  24  is prevented. However, a certain axial mobility is allowed between the second sealing element  21  and the annular body  24 . The number of holes  24   c, d, e  and its sharing can obviously be varied. 
     At mounting of the mechanical sealing device, the second holding device  22  is initially applied on the shaft  23 . The second holding device  22  comprises the annular body  24 , the clamping elements  26 , the screw element  27 , the sealing members  28 ,  29  and the spring element  30 . The holding device  22  is displaced to a predetermined axial position on the shaft  23 . By means of a screw tool, the respective screw elements  27  are in proper order given a turning motion such that the respective clamping elements  27  are displaced in a direction to the right in  FIG. 1 . The downwardly inclined inner surface  26   a  of the annular body  26  thus presses the respective clamping elements  26  and screw elements  27  radially inwardly in direction towards the shaft  23 . Consequently, the inner surface  26   b  of the respective clamping elements is pressured with a successively increasing pressure force against the periphery surface  23   a  of the shaft. The screw motion of the screw element  27  is stopped when a predetermined pressure force is achieved. The through holes  24   c  may be dimensioned such that the screw element  27  reaches a radially inwardly surface of the hole  24   c  as the predetermined pressure force is achieved. When all clamping elements  26  have been applied with a predetermined clamping force against the periphery surface  23   a  of the shaft, the holding device  22  has a very stable attachment on the shaft  23 . The holding device  22  and the shaft  23  can now rotate as a unit. 
     Thereafter, the second sealing element  21  is applied on the shaft  23  and displaced in an axial direction to engagement with the annular body  24  at the same time as the locking element  25  is moved through the through holes  24   e . A rotation locking is thus provided of the second sealing element  21  in relation to the holding device  22  and the shaft  23 . The first part  1  of the mechanical sealing device is applied on the shaft  23  and displaced in an axial direction towards the second part  2 . The first part  1  is displaced to an axial position in which the spring element  30  provides a predetermined force which pressures the sealing surfaces  11   a ,  21   a  of the sealing elements  11 ,  21  against each other. Finally, the first the holding device  13  is attached in the housing  12 . 
     The invention is not restricted to the embodiments shown but may be varied and modified within the scope of the following claims.