Abstract:
A rotary piston pump with at least two double- or multi-lobe rotary pistons rotating in opposite directions, the drive shafts whereof include seals, wherein the seals are constituted as slip ring seals or lip seals or stuffing-box seals, which in each case are disposed on the shaft shoulder belonging to the respective rotary piston, and one slip ring per seal is provided with a locking device, which includes a large number of fixing positions. The seals are pushed onto a tubular shoulder of the rotary piston, the rotary piston is introduced into the pump housing, the securing element is connected to the slip ring seal in a form-fit manner by rotation of the rotary piston and the shaft shoulder is then rigidly connected to the drive shaft.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rotary piston pump with at least two double- or multi-lobe rotary pistons rotating in opposite directions, the drive shafts whereof comprise seals. 
     BACKGROUND OF THE INVENTION 
     A rotary piston pump emerges from German Publication 198 06 657, which comprises two drive shafts for the rotation of the rotors. Both drive shafts are provided at their end in the pump space with screw connections, by means of which the rotors are fixed to the drive shafts. Both drive shafts are produced in one piece and remain in the pump housing during the assembly or dismantling of the rotors. In order that the assembly work is facilitated, one of the drive shafts is connected to the drive by means of a coupling and can thus rotate freely with respect to the other drive shaft in the uncoupled state. 
     Patent specification U.S. Pat. No. 6,283,740 B3 discloses a rotary piston pump with an improved seal, which is mounted between the rotor and the external diameter of the shaft. An adapter is provided for the drive shaft, with which the drive shaft can easily be coupled to a large number of drive mechanisms. The adapter can be replaced by an alternative adapter in order to match alternative drives. 
     Patent application US 20080038138 A1 discloses a rotary piston pump with a pump body, with a drive unit and with an external housing, wherein the housing is provided with an insert. The insert comprises a housing made of a plastic material and is provided with an inlet opening and an outlet opening. The housing comprises openings through which the rotors can be driven in a rotary manner, so that the rotors engage in one another and thus pump a fluid from the inlet opening to the outlet opening. 
     SUMMARY OF THE INVENTION 
     The problem of the present invention compared with the prior art consists in making available a rotary piston pump, wherein the fitting and removal of the rotary pistons and the slip ring seal is optimized. 
     This problem is solved with regard to the mechanical design of the rotary piston pump with at least two double- or multi-lobe rotary pistons rotating in opposite directions, the drive shafts whereof comprise seals, characterized in that the seals are disposed in each case on a shaft shoulder belonging to the respective rotary piston, wherein each seal is provided with a locking device, which comprises a large number of fixing positions on the housing of the seal. 
     With regard to the problem to be solved with the invention in terms of the fitting and synchronisation of the rotary pistons, reference is made to the features of the method claim. 
     Advantageous possible embodiments of the invention are to be found in the dependent claims. 
     A rotary piston pump with at least two double- or multi-lobe rotary pistons rotating in opposite directions is disclosed, the drive shafts whereof each comprise a seal. The seals are disposed in each case on a shaft shoulder belonging to the respective rotary piston. These shaft shoulders are drilled and/or moulded hollow and are connected fixedly to the respective rotary piston. The seals, which are fitted on the shaft shoulders, are provided with a locking device, wherein each locking device comprises a large number of fixing positions on the housing of the seal. 
     The locking device according to the invention is a ring, which is connected to the housing of the seal. Furthermore, the locking device comprises a plurality of axial grooves running parallel to the rotary piston axis. These axial grooves extend over the whole periphery of the annular locking device and are disposed at a uniform distance from one another on the annular locking device. It is also possible for the axial grooves to cover only a partial region of the periphery of the annular locking device. A configuration is preferably selected, in which a partial region of 45 degrees is covered twice. By means of this configuration, it is possible for a securing element to engage in each case in one of the two 45 degree regions and to engage here in each case in an axial groove. The axial grooves are chamfered, so that the securing elements can lock home in an ideal manner. Furthermore, more rapid and more reliable locking-home of the securing elements in the axial grooves is enabled by the chamfering. 
     In a preferred embodiment, the axial grooves are not introduced completely into the locking device, but comprise a web which is intended to space a securing element apart from the seal itself. The rear end face of the locking device forms an axial stop, which creates an active mating with the rear side of the pump housing. As a result of the interaction of the locking device and the rear side of the pump housing, the slip ring seal is subjected to a desired pretensioning. 
     Furthermore, it is possible to leave the internal diameter of the slip ring seal open, so that the slip ring seal lies freely on the shaft shoulder. In a supplementary embodiment, a lip seal or a second slip ring seal is disposed in the internal diameter of the slip ring seal. 
     It is clear to the person skilled in the art that there are many possible ways of producing the locking device and/or of fitting it on the slip ring seal. The locking device can be a ring which is fitted on the slip ring seal. In a further embodiment, the locking device, during production of the seal, is at the same time milled out from the seal housing. 
     At least one securing element is assigned to the axial grooves, wherein the securing element engages in one or more axial grooves. The securing element comprises at least two pins and/or bolts, which engage in the axial grooves. In a preferred embodiment, the securing element comprises an annular element extending around the seal, approximately over 180°. Furthermore, the securing element is connected fixedly and/or in a non-rotatable manner to a part of the housing of the seal. 
     The seal can be a lip seal, a stuffing-box seal or preferably a slip ring seal. The housing, the seal constituted as a slip ring seal, is connected torsionally stiff to a slip ring of the slip ring seal. 
     Via a tubular shaft shoulder, each rotary piston is connected by means of a clamping device to its respective drive shaft. 
     Furthermore, a method for fitting seals in rotary piston pumps is disclosed. Here, the seal is fitted on a tubular shaft shoulder of the rotary piston. The rotary pistons are then introduced into the pump housing. By rotation of the respective rotary piston, the securing element becomes connected in a form-fit manner to the seal, wherein pins and/or bolts engage in a locking device. The tubular shaft shoulder is then connected in a non-rotatable manner to the respective drive shaft. Each rotary piston is thus connected in a friction-locked manner and detachably to the drive shaft by means of its tubular shaft shoulder. 
     A defined formation of components arises as a result of the previously described arrangement of the seals on the respective shaft shoulder of the rotary pistons. This component formation guarantees that the rotary pistons are always fitted with the correct distance from the housing rear wall of the pump chamber. In the past, this distance was always ensured by measurement and adjustment during the fitting of the rotary pistons. This earlier method required enormous skill on the part of the technician and meant that the rotary pistons had to be repeatedly fitted and removed during assembly. 
     Examples of embodiment of the invention and its advantages are explained in greater detail below with the aid of the appended figures. The size ratios of the individual elements with respect to one another in the figures do not always correspond to the actual size ratios, since some forms are represented simplified and other forms magnified compared with other elements for the sake of better clarity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an overall view of a rotary piston pump having first and second rotary pistons. 
         FIG. 2A  shows a partial view of a first slip ring seal with the first rotary piston and a first clamping device, and  FIG. 2B  shows a partial view of a second slip ring seal with the second rotary piston and a second clamping device. 
         FIG. 3  shows the first slip ring seal with first axial grooves. 
         FIGS. 4 and 5  show possible embodiments of the first securing elements and the first accommodation housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Rotary piston pump  10 , as represented in  FIG. 1 , essentially comprises a machine stand  12  to which a motor  14  for the drive of first and second rotary pistons  16 ,  18  is fixed. The first and second rotary pistons  16 ,  18  extend along respective first and second rotary piston axes  66 ,  68 , and are connected for example, as emerges here from the prior art, to first and second drive shafts  20 ,  22  and rotate in the represented formation simultaneously and in opposite directions about the axes of first and second drive shafts  20 ,  22 . During rotation of the first and second rotary pistons  16 ,  18 , the first and second rotary pistons  16 ,  18  make contact with pump housing  24  and thus form constantly recurring pump chambers  26 , which suck in the product to be pumped and eject it on the opposite side of the pump. The application of seals, which seal off the surroundings with respect to the pump space, cannot be seen, but is necessary. 
       FIG. 2A  shows a part of the first rotary piston  16  with a first tubular shaft shoulder  28 . First accommodation housing  30  for first slip ring seal  32  follows on from first rotary piston  16  on the left. First slip ring seal  32  comprises first housing  38 , two first slip rings  34 ,  36  and the respective O-rings, which seal off the interior space of first slip ring seal  32  from first accommodation housing  30  of first slip ring seal  32 . First housing  38  of first slip ring seal  32 , which can also be first housing  38  of a lip seal or stuffing-box seal, extends beyond the actual sealing region in the opposite direction to first rotary piston  16 . This extended region of first housing  38  forms first locking device  40 , which comprises a large number of fixing positions or first axial grooves  42  (see  FIG. 3 ). The part of first housing  38  of first slip ring seal  32  that is located outside first rotary piston  16  is connected in a torsionally stiff manner by means of a first pin or bolt  44  to left-hand first slip ring  34 .  FIG. 2B  shows a part of the second rotary piston  18  with a second tubular shaft shoulder  28 ′. Second accommodation housing  30 ′ for second slip ring seal  32 ′ follows on from second rotary piston  18  on the left. Second slip ring seal  32 ′ comprises second housing  38 ′, two second slip rings  34 ′,  36 ′ and the respective O-rings, which seal off the interior space of second slip ring seal  32 ′ from second accommodation housing  30 ′ of second slip ring seal  32 ′. Second housing  38 ′ of second slip ring seal  32 ′, which can also be second housing  38 ′ of a lip seal or stuffing-box seal, extends beyond the actual sealing region in the opposite direction to second rotary piston  18 . This extended region of second housing  38 ′ forms second locking device  40 ′, which comprises a large number of fixing positions or second axial grooves  42 ′. The part of second housing  38 ′ of second slip ring seal  32 ′ that is located outside second rotary piston  18  is connected in a torsionally stiff manner by means of a second pin or bolt  44 ′ to left-hand second slip ring  34 ′. 
     Referring to  FIG. 2A , located in first accommodation housing  30  for first slip ring seal  32  at the outermost end is a first recess  46 , in which first securing element  48  engages. First securing element  48  extends radially beyond first recess  46  into first axial grooves  42  in first housing  38  of first slip ring seal  32 . It can also be seen here how first securing element  48  engages in first locking device  40 . The connection between first accommodation housing  30  and the pump housing (not represented) takes place by means of screws. Referring to  FIG. 2B , located in second accommodation housing  30 ′ for second slip ring seal  32 ′ at the outermost end is a second recess  46 ′, in which second securing element  48 ′ engages. Second securing element  48 ′ extends radially beyond second recess  46 ′ into second axial grooves  42 ′ in second housing  38 ′ of second slip ring seal  32 ′. It can also be seen here how second securing element  48  engages in second locking device  40 ′. The connection between second accommodation housing  30 ′ and the pump housing (not represented) takes place by means of screws. 
     Referring to  FIG. 2A , first shoulder  28  is fixedly connected to first rotary piston  16  and accommodates a first clamping device  50  at its side adjacent to first slip ring seal  30 . First clamping device  50  also connects first rotary piston  16  to first drive shaft  20 . First clamping device  50  operates mechanically by means of components with conical faces and, when screws are operated, leads to a reduction of the internal cross-section of the annular components engaging into one another. Referring to  FIG. 2B , second shoulder  28 ′ is fixedly connected to second rotary piston  18  and accommodates a second clamping device  50 ′ at its side adjacent to second slip ring seal  30 ′. Second clamping device  50 ′ also connects second rotary piston  18  to second drive shaft  22 . Second clamping device  50 ′ operates mechanically by means of components with conical faces and, when screws are operated, leads to a reduction of the internal cross-section of the annular components engaging into one another. 
     The invention does not relate to the internal components of first and second seals/slip ring seals  32 ,  32 ′ or possible seal variants according to the invention, but to their parts visible to the exterior. In particular, it concerns first and second locking devices  40 ,  40 ′. First locking device  40  is represented in  FIG. 3 , which comprises a first outer ring  54 , which is fitted laterally to first slip ring seal  32 . This first outer ring  54  comprises axial grooves, which are disposed at identical distances from one another and which have a free open end in order that the securing element (not represented) can engage with its pins/bolts into first axial grooves  42  when the first rotary piston  16  is introduced into the pump housing. This engagement brings about the immobilization of first slip ring  34  and thus ensures the desired sealing of the pump chamber. Although first housing  38  of first slip ring seal  32  is described for the function of first slip ring seal  32  in this example of embodiment, first housing  38  can also accommodate in its interior a seal in the form of a stuffing-box seal or a lip seal. In these examples of embodiment, the securing element secures the overall sealing package and seals off the first tubular shaft shoulder  28  and the pump chamber. 
     The two  FIGS. 4 and 5  show different embodiments of first securing element  48 . This first securing element  48  can be seen from  FIG. 4  as an annular element  56 , which sits in first accommodation housing  30  of the first slip ring seal  32 . Annular element  56  comprises first pins or bolts  44 , which engaged in the housing of the first slip ring seal  32 . This engagement leads to the immobilization of the first slip ring  34 . The components of the first accommodation housing  30  are connected to one another via the holes in shoulders  60 . In a further embodiment, it is possible to press first pins or bolts  44  into holes (not represented) of first accommodation housing  30  provided for the purpose. 
     The function of the embodiment of first securing element  48  represented in  FIG. 5  is identical to that in  FIG. 4 . The difference lies solely in the design of the elements that lead to the immobilization of the first slip ring  34 . Block-shaped elements  64  are represented here, wherein it can also be wedges or identically acting embodiments. The first securing element  48  has here the shape of a semicircular clasp  62 , which by its spring force also provides for a more secure hold to the first accommodation housing  30 . 
     The invention has been described by reference to a preferred embodiment. It is however conceivable for the person skilled in the art that modifications or changes to the invention can be made without departing from the scope of protection of the following claims.