Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT International Application No. PCT/EP2014/059431, filed May 8, 2014, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2013 208 511.7, filed May 8, 2013 and German Patent Application No. 10 2014 006 568.5, filed May 7, 2014, the entire disclosures of which are herein expressly incorporated by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    The invention relates to a pump arrangement, in particular magnetic clutch pump arrangement. 
         [0003]    The pump arrangement has an interior space formed by a pump casing, a containment can which has a central longitudinal axis and which hermetically seals off a chamber surrounded by said containment can with respect to the interior space formed by the pump casing, an impeller shaft which can be driven in rotation about an axis of rotation, an impeller which is arranged on one end of the impeller shaft, having an inner rotor arranged on the other end of the impeller shaft, and an outer rotor which is arranged on a drive shaft and which interacts with the inner rotor. The containment can has a base with at least one bead which projects into the chamber. The invention also relates to a method for producing a containment can of a pump arrangement. 
         [0004]    In the case of such pumps, the rotating magnetic field induces eddy currents in the metallic containment can situated between inner rotor and outer rotor. Said statically positioned containment can, together with the casing cover and the pump casing itself, forms the pressure-bearing pump part, whereby the inner rotor, which is situated within said enclosure, is in constant contact with the delivery medium. To reduce the eddy currents and the associated continuous heating of the medium to the point of evaporation, use is firstly normally made of metallic containment can materials with high electrical resistance. Particularly expensive nickel-based alloys (Hastelloy) have become established for this purpose. Secondly, the heat losses are dissipated by way of a cooling flow. Said flow, which is branched off as a bypass from the main delivery flow, is, owing to the pressure distribution in the chamber, transported over the outer diameter of the inner rotor, in a radially inward direction between inner rotor and containment can base to the impeller shaft, and back to the main hydraulic system via a hollow bore in said impeller shaft. Owing to the rotation of the inner rotor and the resulting formation of vortices in the bypass flow of the delivery medium, an excessive pressure gradient arises between the inner rotor outer diameter and the inlet, situated coaxially with respect to the axis of rotation, of the hollow bore of the impeller shaft. The cooling flow rate and thus the heat dissipation are restricted. Integration of a geometry, which has the effect of impeding or breaking up vortices in the delivery medium, on the static containment can base can prevent or limit this, whereby the inertial rotor chamber temperature remains at a corresponding level below the vapor pressure curve of the delivery medium. 
         [0005]    German patent document no. DE 91 00 515 U1 has disclosed a magnetic coupling pump in which it is intended to reduce the formation of swirl phenomena in the delivery medium by way of a bead provided in the base of the containment can. The pressure loading-optimized geometry or shape of the base without beads results from the expandability or deformability of the convex-ellipsoidal base under load. This is however impeded owing to the centrally provided beads, which thus have a stiffening action. This results in increased stresses in the containment can material of the bead region. In relation to convex-ellipsoidal shapes without beads, and using the same wall thicknesses or starting material thicknesses, the disclosed bead contour achieves a compressive strength of only approximately 40%. In this way, an equal compressive strength can be attained only through the use of more material, with an associated increase in costs. 
         [0006]    It is the object of the invention to provide a pump arrangement in which the formation of vortices in the delivery medium within the containment can is further reduced, without reducing the stability of the containment can. 
         [0007]    The object of the invention is achieved in that the at least one bead is arranged with a radial spacing to the central longitudinal axis of the containment can, wherein the ratio of inner radius of the containment can to spacing of bead outer edge and central longitudinal axis of the containment can lies in a range from 1.3 to 1.6. 
         [0008]    The ratio of inner radius of the containment can to spacing of bead outer edge and central longitudinal axis of the containment can preferably lies in a range from 1.38 to 1.57. 
         [0009]    The spacing of the bead inner edge to the central longitudinal axis of the containment can is advantageously 1/7*containment can inner radius Y , wherein Y preferably lies in a range from approximately 1.14 to 1.17. 
         [0010]    Through such a specification of the ratio of inner radius of the containment can to radius of the bead outer edge, or of the spacing of the bead inner edge to the central longitudinal axis, the axial expandability or deformability of the containment can base is maintained, whereby the pressure-withstanding capability is maintained to a degree of 90 to 95% in relation to a containment can base of the same wall thickness without beads. 
         [0011]    In a preferred implementation of the invention, for a high compressive strength of the preferably deep-drawn or cast containment can, the base thereof is formed by a substantially spherical—segment-shaped spherical cap region and by a rim region which forms the transition region between main body and spherical cap region. 
         [0012]    According to the invention, for an optimum spacing between inner rotor and the bead base, the bead base runs in a plane which is situated substantially parallel to the plane in which the transition from the spherical cap region to the rim region is situated. The imaginary planes lie substantially perpendicular to a central longitudinal axis of the containment can. 
         [0013]    Here, in a particular refinement, it is provided that the inner wall of the containment can in the region of the bead base lies substantially in the same plane as the transition from the spherical cap region to the rim region. 
         [0014]    In an alternative refinement, the bead base is formed so as to run parallel to the spherical cap region. 
         [0015]    A good mode of operation with regard to the reduction of vortex formation is achieved if, in the region of the bead base, the maximum spacing of the inner wall of the containment can to the face side, facing toward the base of the containment can, of the inner rotor is approximately 20 mm. 
         [0016]    It is preferable if, in the region of the bead base, the maximum spacing of the inner wall of the containment can to the face side of the inner rotor is approximately 10 mm, in order to further reduce vortex formation. 
         [0017]    Since the mechanical stresses are at their greatest at the transition from the spherical cap region to the bead region, and sharp-edged transitions are the most effective for preventing the formation of vortices, it is provided according to the invention that the transitions between the spherical cap region and the bead walls have greater radii than the transitions from the bead walls to the respective bead base. At the same time, it is possible for the pressure acting outwardly in the chamber enclosed by the containment can to be accommodated in a particularly effective, that is to say low-stress manner. 
         [0018]    If the at least one bead extends in a radial direction to a point close to the rim region, or extends as far as the latter, the vortices that arise in the chamber enclosed by the containment can (said vortices being most pronounced at the inner rotor in a region with the greatest circumferential speed, that is to say close to the outer diameter of the rotating inner rotor) are effectively reduced. 
         [0019]    A method according to the invention provides that the containment can is produced by way of a deep-drawing process or by way of a casting process, wherein at least one bead is produced in the base, which bead is arranged with a radial spacing to the central longitudinal axis of the containment can. 
         [0020]    Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  shows a longitudinal section through a magnetic clutch pump arrangement having a containment can according to an embodiment of the invention, which has beads in its base, 
           [0022]      FIG. 2  shows the longitudinal section through the containment can in  FIG. 1  in an enlarged illustration, 
           [0023]      FIG. 3  is a three-dimensional illustration of the containment can in  FIG. 1 , 
           [0024]      FIG. 4  shows the longitudinal section through the containment can according to a different embodiment of the invention, 
           [0025]      FIG. 5  is a three-dimensional illustration of the containment can according to a further embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a pump arrangement  1  in the form of a magnetic clutch pump arrangement. The pump arrangement  1  has a multi-part pump casing  2  of a centrifugal pump, which pump casing comprises a hydraulics casing  3  in the form of a spiral casing, a casing cover  4 , a bearing carrier cage  5 , a bearing carrier  6  and a bearing cover  7 . 
         [0027]    The hydraulics casing  3  has an inlet opening  8  for the intake of a delivery medium and has an outlet opening  9  for the discharge of the delivery medium. The casing cover  4  is arranged on that side of the hydraulics casing  3  which is situated opposite the inlet opening  8 . The bearing carrier cage  5  is fastened to that side of the casing cover  4  which is opposite from the hydraulics casing  3 . The bearing carrier  6  is mounted on that side of the bearing carrier cage  5  which is situated opposite the casing cover  4 . The bearing cover  7  in turn is fastened to that side of the bearing carrier  6  which is opposite from the bearing carrier cage  5 . 
         [0028]    A containment can  10 , preferably produced by deep drawing or by casting, is fastened to that side of the casing cover  4  which is opposite from the hydraulics casing  3 , and said containment can extends at least partially through an interior space  11  delimited by the pump casing  2 , in particular by the casing cover  4 , by the bearing carrier cage  5  and by the bearing carrier  6 . The containment can  10  hermetically seals off a chamber  12 , which is enclosed by said containment can, with respect to the interior space  11 . 
         [0029]    An impeller shaft  13  which is rotatable about an axis of rotation A extends from a flow chamber  14 , which is delimited by the hydraulics casing  3  and by the casing cover  4 , into the chamber  12  through an opening  15  provided in the casing cover  4 . 
         [0030]    An impeller  16  is fastened to a shaft end, situated within the flow chamber  14 , of the impeller shaft  13 , and an inner rotor  17  arranged within the chamber  12  is arranged on the opposite shaft end, which has two shaft sections  13   a ,  13   b  with increasing diameters in each case. The inner rotor  17  is equipped with multiple magnets  18  which are arranged on that side of the inner rotor  17  which faces toward the containment can  10 . 
         [0031]    Between the impeller  16  and the inner rotor  17  there is arranged a bearing arrangement  19  which is operatively connected to the impeller shaft  13 , which can be driven in rotation about the axis of rotation A. 
         [0032]    A drive motor, preferably an electric motor, which is not illustrated drives a drive shaft  20 . The drive shaft  20 , which can be driven rotatably about the axis of rotation A, is arranged substantially coaxially with the impeller shaft  13 . The drive shaft  20  extends through the bearing cover  7  and through the bearing carrier  6  and is mounted in two ball bearings  21 ,  22  which are accommodated in the bearing carrier  6 . On the free end of the drive shaft  20  there is arranged an outer rotor  24 , which bears multiple magnets  23 . The magnets  23  are arranged on that side of the outer rotor  24  which faces toward the containment can  10 . The outer rotor  24  extends at least partially over the containment can  10  and interacts with the inner rotor  17  such that the rotating outer rotor  24 , by way of magnetic forces, sets the inner rotor  17  and thus likewise the impeller shaft  13  and the impeller  16  in rotation. 
         [0033]    The containment can  10 , illustrated on an enlarged scale in  FIGS. 2 and 3 , has a substantially cylindrical main body  25  with a central longitudinal axis B arranged substantially coaxially with respect to the axis of rotation A as per  FIG. 1 . The main body  25  is open on one side, and is closed by way of a domed base  28  on the side situated opposite the open side. On the open side, there is arranged a ring-like attachment flange  27  which is formed integrally with the main body  25  or which is connected to the latter by welding or other suitable fastening means or devices, for example screws, rivets or the like. 
         [0034]    The attachment flange  27  has multiple bores  28  which extend parallel to the central longitudinal axis B and through which screws (not shown) can be passed and screwed into corresponding threaded bores in the casing cover  4  as per  FIG. 1 . 
         [0035]    The base  26  is formed by a substantially spherical—segment-shaped spherical cap region  29  and an outer rim region  30  which forms the transition region between main body  25  and spherical cap region  29 . In the spherical cap region  29  there are provided multiple beads  31  which project into the chamber  12  and which have a bead base  32  and a bead wall  33 . The beads  31  have a bead inner edge  31   a , arranged close to the central longitudinal axis B, and a bead inner edge  31   b , arranged remote from the central longitudinal axis B. The chamber  12  has the greatest axial extent close to the central longitudinal axis B, wherein the ratio of inner radius r is  of the containment can  10  to spacing A Sa  of bead outer edge  31   b  and central longitudinal axis B of the containment can  10  lies in a range from 1.3 to 1.6, and preferably in a range from 1.38 to 1.57. 
         [0036]    The spacing A Si  of the bead inner edge  31   a  to the central longitudinal axis B of the containment can  10  is defined by the formula 1/7*containment can inner radius Y , wherein Y preferably lies in a range from approximately 1.14 to 1.17. 
         [0037]    The containment can  10  is produced by deep drawing or by casting, wherein at least one bead  31  is produced in the base  26 , which bead is arranged with a radial spacing to the central longitudinal axis B of the containment can  10 . In the case of a containment can  10  produced by deep drawing, the beads  31  are stamped into the base  26  during the deep drawing process. 
         [0038]    The beads  31 , which are arranged with a radial spacing to the central longitudinal axis B of the containment can  10 , extend in a radial direction to a point close to the rim region  30 , or even extend as far as the latter. 
         [0039]    As can be seen from  FIG. 2 , the bead base  32  runs in a plane which is situated substantially parallel to the plane which corresponds to the transition from the spherical cap region  29  to the rim region  30 . In particular, the inner wall  34  of the containment can  10  in the region of the bead base  32  lies substantially in the same imaginary plane, perpendicular to the central longitudinal axis B, as the transition from the spherical cap region  29  to the rim region  30 . Alternatively, as shown in  FIG. 4 , the bead base  32  of the containment can  10  may be formed so as to run parallel to the spherical cap region  29 . Here, a part of the bead base  32  extends as far as a plane which runs perpendicular to the central longitudinal axis B and which lies in the rim region  30 . As illustrated in  FIG. 1 , in the region of the bead base  32 , the maximum spacing X of the inner wall  34  of the containment can  10  to a face side  35 , facing toward the base  26  of the containment can  10 , of the inner rotor  17  is approximately 20 mm. It is preferably the case that, in the region of the bead base  32 , the maximum spacing X of the inner wall  34  of the containment can  10  to the face side  35  of the inner rotor  17  is approximately 10 mm. 
         [0040]    The transitions between the spherical cap region  29  and the bead walls  33  have greater radii than the transitions from the bead walls  33  to the respective bead base  32 . 
         [0041]    The beads  31  illustrated in  FIGS. 1 to 4  have a substantially stadium-shaped geometry. Alternatively, said beads may have any other desired geometry. The beads  31  may for example be of prism-shaped, cuboidal or spherical form or may be formed from similar truncated geometries or combinations thereof or may, as shown in  FIG. 5 , have a bead base  32  which is domed in the direction of the inner rotor. 
         [0042]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
       LIST OF REFERENCE DESIGNATIONS 
       [0000]    
       
           1  Pump arrangement 
           2  Casing 
           3  Hydraulics casing 
           4  Casing cover 
           5  Bearing carrier cage 
           6  Bearing carrier 
           7  Bearing cover 
           8  Inlet opening 
           9  Outlet opening 
           10  Containment can 
           11  Interior space 
           12  Chamber 
           13  Impeller shaft 
           13   a  Shaft section 
           13   b  Shaft section 
           14  Flow chamber 
           15  Opening 
           16  Impeller 
           17  Inner rotor 
           18  Magnet 
           19  Bearing arrangement 
           20  Drive shaft 
           21  Ball bearing 
           22  Ball bearing 
           23  Magnet 
           24  Outer rotor 
           25  Main body 
           26  Base 
           27  Attachment flange 
           28  Bore 
           29  Spherical cap region 
           30  Rim region 
           31  Bead 
           31   a  Bead inner edge 
           31   b  Bead outer edge 
           32  Bead base 
           33  Bead wall 
           34  Inner wall 
           35  Face side of the inner rotor 
         A Axis of rotation 
         B Central longitudinal axis 
         r is  Inner radius r is  of containment can 
         A Sa  Spacing between bead outer edge and central longitudinal axis 
         A Si  Spacing between bead inner edge and central longitudinal axis

Technology Category: 2