Abstract:
The invention relates to a stator casing for eccentric worm pumps comprising an elastic lining, the cylindrical stator casing having a surface on the inner side, along the longitudinal axis whereof grooves are incorporated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending International patent application PCT/DE2007/000845 filed on May 10, 2007 which designates the United States and claims priority from German patent application 10 2006 021 897.3 filed on May 11, 2006, the content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a stator for an eccentric worm pump which consists of a stator casing and an elastic lining disposed movably in the stator casing. 
       BACKGROUND OF THE INVENTION 
       [0003]    A stator whose stator casing and lining are configured in a spiral shape is deduced in this regard from DE 198 21 065 A1. Both parts are screwed together, whereby any twisting during operation of the pump should be avoided. It is also deduced from this document that stator combinations in which the stator casing has projecting strips on its inner side which engage in grooves on the surface of the lining, prevent any twisting of both components. 
         [0004]    FIG. 4 of DE 1553127 A1 discloses a polygonal lining which is surrounded by a likewise polygonal-shaped stator casing. In this example, the lining is not vulcanised-in but a withdrawal device is required to remove it from the pump casing. 
         [0005]    A configuration to improve the adhesive effect of the lining with the stator casing can be deduced from DE 29 07 392 A1. For this purpose, the basically round inner surface of the stator casing has a plurality of groove-shaped indentations in which the elastic material of the lining is vulcanised. No axial mobility of the lining is thereby provided. 
         [0006]    However, these exemplary embodiments neglect the fact that the pressure produced in the pump during pumping presses the lining very firmly against the stator casing which can then only be moved, removed or exchanged subsequently and during operation of the pump with a very expenditure of force and in most cases not without mechanical aids. 
         [0007]    It is therefore the object of the invention to configure the stator casing such that adhesion of the lining is counteracted. 
       SUMMARY OF THE INVENTION 
       [0008]    This object is achieved with the features of claim  1 . Further embodiments of the invention are deduced from the features of the dependent claims. 
         [0009]    Depending on the pressure ratios, products and materials with which an eccentric worm pump is operated, loads are produced on the lining. These loads can naturally result in exchange or correction of the position of the lining earlier or later. In addition, the axial mobility of the stator lining in the stator casing can be necessary for optimum adjustment of the stator dimensions. With the structure of the conventional stator combinations, exchanging the lining or positional compensation is only possible with great difficulty since the stator lining abuts very tightly against the inner surface of the stator casing. Even when the lining abuts against the stator casing free from binders, the forces of attraction or suction produced or caused require high opposing forces to remove the lining from the stator casing or to keep it movable in relation to said casing. According to the invention, the required opposing forces are almost eliminated by reducing the adhesive forces, for which grooves are inserted in the surface of the inner side of the stator casing. Thus, the stator lining also retains its axial mobility during pumping operation. 
         [0010]    In a preferred embodiment, the grooves run on the inner surface of the stator casing parallel to its longitudinal axis. The adhesive effect is uniformly cancelled out thereby or with the spiral arrangement of the grooves. 
         [0011]    According to a further embodiment, the cross-section of the grooves is adapted to different elastic materials for the stator lining. Thus, when using highly elastic material and V-shaped grooves, the release process can take place more efficiently than with angular-shaped or swallowtail-shaped grooves. This groove shape is in turn better suited for low-elasticity material since the depth of penetration can be kept small here. 
         [0012]    It has been shown that depth and width ratios in the range of 1:1 to 2:1 are very well suited to safeguard the stator insert from twisting during operation of the pump and on the other hand, to positively support the separation process. Should the lining not become detached from the stator casing, the stator alone could be inserted between an end plate and a pressure medium storage device. The subsequent introduction of the pressure means (gas, liquid) into the grooves would initiate and accelerate the release process. 
         [0013]    A further exemplary embodiment of the invention relates to the polygonal cross-sectional shape of the stator casing and the lining. Depending on which conveying cross-section is required by the eccentric worm pump and what friction is produced by the rotor in the stator, compensation must take place between the force produced in the area of the grooves and the area of the edges between the polygonal casing surfaces, in order to avoid undesirable wear of the lining. The polygonal configuration of the stator casing serves here as optimal fixing of the stator lining. A uniform distribution of the loading takes place above an edge number of 8 edges upwards. 
         [0014]    Special numbers of grooves and groove shapes are possible depending on the pump capacity and delivery pressure. With all groove shapes, care should be taken to ensure that all the radii of the grooves do not fall below a radius of 0.2 mm so that deformation and re-formation of the lining material is not impeded. 
         [0015]    Special products which are pumped at specific temperature influence the stator lining differently in the partial areas. Thus, according to a further embodiment according to the invention, it can be advantageous if at least every other polygonal surface has grooves or if at least one groove is inserted in the polygonal surfaces. The different pressure regions of the stator casing can also be configured differently. Thus, for example, the number of grooves can be increased or their width or depth increased, in areas of higher delivery or counter-pressure values. 
         [0016]    To simplify mounting and dismounting of the stator linings, the stator casing can have a continuous slit over the entire length which allows a slight widening. The slit can be covered and reduced by a closure strip during operation of the pump. In the operating state, the stator casing is therefore under a pre-stress which is released on removing the closure strip and thus expands the diameter of the stator casing. 
         [0017]    According to a further exemplary embodiment, the longitudinal dimension of the lining after manufacture is greater than in the built-in state of the lining in the eccentric worm pump when ready for operation. 
         [0018]    According to another exemplary embodiment, the closure strip has a conduit system with which a fluid can be pressed between the stator casing and the lining. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Examples of the invention can be seen from the following drawings. In the figures: 
           [0020]      FIG. 1  shows a stator casing for an eccentric worm pump. 
           [0021]      FIG. 2  shows a stator casing for an eccentric worm pump. 
           [0022]      FIG. 3  shows a stator casing for an eccentric worm pump. 
           [0023]      FIG. 4  shows a lining for a stator casing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  shows a stator casing  10  having a smooth cylindrical surface as is usual in the hitherto known prior art. The inner surface of the stator casing is configured to be polygonal-shaped. Twelve surfaces  12  flat both in their length and in their width are arranged around the inner circumference of the stator casing. Two surfaces are continuously delimited by an interposed edge  14  or are interconnected by an edge  14 . In this exemplary embodiment, each surface  12  has three grooves  16 . The grooves run parallel to one another along the longitudinal axis of the stator casing  10 . The distance of the grooves  16  from one another is same on each and with respect to each surface  12 ,  12 ′,  12 ″,  12 ′″ etc. A longitudinal slit  36  whose width is dependent, inter alia, on the diameter and the elasticity of the lining  18 , divides the stator casing on one side. 
         [0025]    A closure strip  20  makes a positive connection with these two ends  22 ,  24  and thus ensures that the stator casing does not expand during operation of the pump. In order that the desired anti-adhesion properties remain uniform over the entire inner circumference which is ensured by the inserted grooves  16 , the strip can also be provided with a groove. In order that the plane profile of the inner surfaces  12 ,  12 ′,  12 ″ is retained, the ends  22 ,  24  are outwardly curved, whereby the closure strip forms a tight fit in the outer region and is integrated internally in the surface profile. 
         [0026]      FIG. 2  shows a stator casing having fundamentally the same structure as in  FIG. 1 . As a result of its naturally smaller diameter compared with  FIG. 1 , here only 10 polygonally arranged surfaces  12  form the inner surface of the stator casing. In accordance with the smaller capacity required with smaller pumps and counter-pressure depending on the pump head, a double groove arrangement per polygonal surface is provided for this size. As a result of the reduction in the material thickness in the area of the edges, the region is reinforced with ribs  26 . The rib width corresponds to the spacing of the grooves  16 . Both the ribs  26  and also the platform  28  are provided as a centring aid and as protection from twisting.  FIG. 2  shows the stator casing without closure strip with opened longitudinal slit  36 . 
         [0027]    The stator casing  10  according to  FIG. 3  is configured as polygonal-shaped on its inner and outer side. The inner surfaces  12  and outer surfaces  30  are arranged to be coincident. All the inner surfaces  12  each have three grooves  16  at the same distances from one another. If the strength of the closure strip is selected to be smaller than that of the stator casing, the closure strip at the same time fulfils the function of a safeguard against excess pressure. 
         [0028]      FIG. 4  shows a lining  18  of the stator casing  10 . A cavity  32  with a multiple thread in which the rotor of the pump revolves, extends through the interior of the lining. The outer surface of the lining is polygonal-shaped and has for this purpose a plurality of outer surfaces  34  arranged parallel to one another. The length of the lining in the dismantled state is always larger than that of the stator casing. As a result, on insertion into the stator casing or into the eccentric worm pump, the stator lining is axially compressed and acquires the necessary nominal dimensions for the pump cavity. The outside diameter of the stator lining accordingly has an undersize in the dismantled state.