Abstract:
A pin joint for eccentric screw pumps. The special design of the inner joint head of the pin joint, with its bores for the flushing liquid and the length of the joint pin, makes it possible also to carry out cleaning using the CIP method.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an open pin joint and a method for operating this pin joint for eccentric screw pumps in the hygiene sector. The joint has an inner and an outer joint head, wherein each joint head comprises at least one diametrical bore, which is penetrated by a pin which is provided at both ends with a cap in each case. The inner spherical joint head has a convex bore course in the region of the pin. 
       BACKGROUND OF THE INVENTION 
       [0002]    A pin joint for an eccentric screw pump emerges from DE 10 2006 058 166 A1. The pin joint is surrounded by a collar in order to keep the lubricant in the region of the joint. When the lubricant is replaced, the interior of the joints can also comprise a central lubricant channel per joint in order to remove the lubricant. Since the joint does not have to be completely cleaned for the replacement of lubricant, this design of the joint may be sufficient. 
         [0003]    DE 101 16 641 A1 discloses a pin joint with a part of a drive shaft and a part of a coupling rod. An end region of the drive shaft is provided with a coaxial plug-in socket. The coupling pin of the coupling rod projects into this plug-in socket. For the cleaning of the interior of the plug-in socket, the wall of the latter comprises two diametrical flushing bores. 
         [0004]    The problem of the present invention is to design a pin joint which can also be used for the hygiene sector, wherein attention is focused in particular on the difficult, but necessary cleaning of the bore of the inner joint head which accommodates a joint pin. 
       SUMMARY OF THE INVENTION 
       [0005]    The inventive technical solution to the problem is achieved by the features of the invention. 
         [0006]    According to a first embodiment of the pin joint according to the invention, a spherical joint head comprises at its end face at least two channels which are disposed eccentrically with respect to the longitudinal axis. 
         [0007]    In a preferred embodiment of the pin joint, the channels are inclined at an angle of 10° to 30° outwards from the longitudinal axis of the drive shaft in the direction of the outer side of the pin joint. The cleaning liquid thus flows in the paraxial region of the drive shaft into the inner joint head and flows radially offset to the inlet at the inner side of the inner joint head. The cleaning of the joint or joints accordingly takes place radially from the longitudinal axis of the jointed shaft from the inner joint head to the outer joint head. 
         [0008]    In order that the flushing liquid passes into every region of the gap between the pin and the inner and outer joint head, the pin extends in its length by at least 5% of the cap diameter beyond the external diameter of the outer joint heads. The effect of lengthening the pin is that the pin can move radially in the joint and a relative motion component thus results in the joint gaps, which leads to circulation of the cleaning liquid. The cross-section of the pin/pins is reduced compared to the cross-section of the bores. 
         [0009]    For the further improvement of the flow of the cleaning liquid, the channels for the cleaning liquid are disposed in such a way that they each emerge in the case of the inner joint head in the region of the pin, in which region its bore diverges from the longitudinal axis of the jointed shaft radially in the direction of the respective outer joint head. 
         [0010]    The cleaning of the open pin joint according to the invention takes place during the rotation of the joint or joints, wherein the flushing liquid exerts a radially acting pressure on the flushing liquid on account of the eccentric wobbling motion of the joint. The wobbling motion causes a constant reduction and increase in the cylindrical annular space between the pin and the bore of the inner joint head. Each joint head connection thus represents its own pump for the flushing liquid. Since the flushing liquid is introduced eccentrically into the joint, where the gap between the joint head and the pin is at its smallest, the quantity of flushing liquid corresponding to the pin joint according to the invention is much greater per unit of time. The flushing liquid is displaced from the inner region into the outer region of the pin joint. 
         [0011]    The invention is explained below with the aid of diagrammatic drawings. 
         [0012]    In the figures: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows an eccentric screw pump with two open pin joints. 
           [0014]      FIG. 2  shows a detail with a pin joint with parallel flushing liquid bores. 
           [0015]      FIG. 3  shows a detail with a pin joint with flushing liquid bores disposed inclined. 
           [0016]      FIG. 4  shows a plan view of the pressure flange of the eccentric screw pump. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  shows an eccentric screw pump  36  with a stator  38  in which a rotor  40  is located. Rotor  40  moves eccentrically in stator  38  and, for this purpose, is connected via a jointed shaft  42  to an intermediate shaft  44 , and the latter to drive shaft  46  of a drive (not represented). A pressure flange  48  sits on one end of the stator, said pressure flange being clamped with pump housing  52  by means of screws  50 . Suction port  54  sits on the upper side of pump housing  52 , via which suction port the medium to be conveyed enters into pump housing  52 . 
         [0018]    Suction port  54  is located in the immediate vicinity of sealing housing  56  and seal  58 , which can be embodied as a slip-ring seal. Suction port  54  is disposed tangential to or on pump housing  52 . Seal  58  sits on intermediate shaft  44 , which is rigidly connected to drive shaft  46 . Jointed shaft  42  is connected non-rotatably by joints, here pin joints  34 , both to intermediate shaft  42  and also to rotor  40 . 
         [0019]    A variant of a pin joint  34  is represented in  FIG. 2 . The example shows an inner joint head  10  and an outer joint head  12 . Both joint heads  10 ,  12  are provided with bores  14 ,  15 ,  16 , through which a pin  18  extends. The pin is constituted cylindrical between its caps  20 ,  22 . Bore  15 , on the other hand, is rounded inwardly in a convex manner in the region of the pin, so that the course of the bore diverges from inside outwards, i.e. widens. This widening of bore  15  gives pin  15  the necessary freedom of movement with respect to inner joint head  10 . When pin joint  34  rotates, inner joint head  10  performs a wobbling motion which arises due to eccentrically rotating rotor  40 , which transmits this motion via the jointed shaft to the two pin joints  34 . 
         [0020]    Two channels  26 ,  28  begin at end face  24  of inner joint head  10 , said channels extending into diametrical bore  15 . Flushing liquid passes through these bores from the pump housing in a targeted manner into bore  15  and here removes residues of the conveyed medium. Since the bores do not run centrally along longitudinal axis  30  of intermediate shaft  44 , but at an angle A of 10° to 30°, this radially directed flow assists removal from or cleaning of bore  15 . On account of the wobbling motion of joint head  10 , the radially widening inner faces of bore  15  push the flushing liquid out of the internal region of joint head  10 . The channels in head end  60  of the joint head emerge, at a distance from longitudinal axis  30 , in the region of bore  15  in the already diverging surface region. 
         [0021]    A further possibility for cleaning a pin joint with flushing liquid is represented in  FIG. 3 . Here too, joint head  10  comprises a diametrically running bore  15  and, in this example of embodiment too, bore  15  widens from longitudinal axis  30  radially in the direction towards outer joint head  12 . Bores  26 ,  28  run parallel to longitudinal axis  30  of joint head  10  and intermediate shaft  44 . Channels  26 ,  28  emerge inside bore  15  in the joint head  10  in the region of bore  15  which widens radially in the direction towards outer joint head  12 . The circulation of the flushing liquid in the region of diametrical bore  15  is achieved by the motion of pin  18 . Pin  18  comprises two caps  20 ,  22  which, depending on the position of pin joint  34 , lie adjacent to the respective upper side of pin joint  34 . As a result of the relative motion of pin  18  along its longitudinal axis, the gaps in bores  14 ,  16  are also flushed. Cap  20  is part of a screw which is part of pin  18 . 
         [0022]    A plan view of pressure flange  48  of the eccentric screw pump  36  is reproduced in  FIG. 4 . Tangentially disposed suction port  54  in the pump housing can also be seen from this view. As a result of this tangential arrangement of the suction port, the flushing liquid acquires, upon the entry into the pump housing, also referred to as the pump inlet housing, a swirling flow component and therefore, already in the inlet region, flushes the inner side of the pump housing up to outlet  62  along a self-generating helical flow. 
       LIST OF REFERENCE NUMBERS 
       [0023]      10  joint head 
         [0024]      12  joint head 
         [0025]      14  bore 
         [0026]      15  bore 
         [0027]      16  bore 
         [0028]      18  pin 
         [0029]      20  cap 
         [0030]      22  cap 
         [0031]      24  end face 
         [0032]      26  channel 
         [0033]      28  channel 
         [0034]      30  longitudinal axis 
         [0035]      34  pin joint 
         [0036]      36  eccentric screw pump 
         [0037]      38  stator 
         [0038]      40  rotor 
         [0039]      42  jointed shaft 
         [0040]      44  intermediate shaft 
         [0041]      46  drive shaft 
         [0042]      48  pressure flange 
         [0043]      50  screws 
         [0044]      52  pump housing 
         [0045]      54  suction port 
         [0046]      56  sealing housing 
         [0047]      58  seal 
         [0048]      62  outlet 
         [0049]      64  axis