Abstract:
A rotor disc for a vacuum pump, in particular a turbo molecular pump, having an inner ring. The inner ring is connected to a plurality of blade elements extending radially outward. The inner ring has at least one expansion joint. For assembly, the inner ring can be surrounded by a retaining ring and arranged on a hollow cylindrical carrier element as applicable.

Description:
BACKGROUND 
       [0001]    1. Field of the Disclosure 
         [0002]    The disclosure relates to a rotor disc for a vacuum pump, in particular a turbomolecular pump, as well as to a rotor comprising such rotor discs. 
         [0003]    2. Discussion of the Background Art Vacuum pumps, such as in particular turbomolecular vacuum pumps, have a rotor shaft supported in a pump housing. The rotor shaft which is driven in particular by an electric motor carries a rotor surrounded by a stator arranged in the pump housing. In particular turbomolecular pumps comprise a plurality of rotor discs. The individual rotor discs comprise a plurality of rotor blades. Stator discs of the stator surrounding the rotor are respectively arranged between adjacent rotor discs, the stator discs also having stator blades. 
         [0004]    It is known to produce the rotor of a turbomolecular pump as a single piece. In this regard, the individual rotor discs are manufactured from a solid block, in particular by milling. This is an extremely tedious and expensive method. With such rotors, the stator discs are most often of a two-part design so that they can be inserted between two adjacent rotor discs from outside. 
         [0005]    It is further known from DE 10 2007 048 703 to assemble a rotor for a turbomolecular pump from individual rotor discs. In this case, the individual rotor discs are connected with each other via reinforcement rings, each disc having in particular a plane of rotor vanes. The reinforcement rings respectively surround an inner ring of the rotor disc. A rotor of a vacuum pump built from a plurality of rotor discs is manufactured using mechanical joining methods. For this purpose, the inner ring of the rotor disc is oversized with respect to the reinforcement ring. Joining is performed by heating or cooling the components to be joined and by subsequent pressing. This is disadvantageous in that the joining process introduces tensions into the inner ring or the hub of the rotor disc. Further tensions occur due to the great centrifugal forces, as well as to the different thermal expansions of the rotor disc and the reinforcement ring during operation. 
         [0006]    It is an object of the present disclosure to provide a rotor disc and a rotor having a plurality of rotors discs, wherein the occurrence of tensions is reduced, in particular at the inner ring of the rotor disc. 
       SUMMARY 
       [0007]    The present rotor disc for a vacuum pump and in particular for a turbomolecular pump comprises a preferably substantially cylindrical inner ring. The same is connected and in particular integrally formed with radially outward extending blade elements. According to the disclosure the inner ring has at least one expansion joint or a slot. Providing such an expansion joint is advantageous in that thermal expansions can be compensated thereby. Due to the slot being provided, the occurrence of tangential tensions is reduced or possibly even avoided altogether. By providing an expansion joint according to the present disclosure, the occurrence of tangential tensions is at least significantly reduced in particular in the outer region of the inner ring, i.e. in particular at the transitions between the inner ring and the blade elements. Thereby, it is preferably possible to operate a rotor built from such rotor discs at higher rotational speeds. 
         [0008]    The expansion joint or the slot preferably extends in parallel with the blades over the entire width of the inner ring. Thus, the inner ring of the rotor disc is entirely slotted. It is particularly preferred that the slot or the expansion joint is slanted. In particular the slant is such that any damage to the blade elements by the slot is avoided. In a particularly preferred embodiment the expansion joint or the slot is thus arranged slanted and in particular has the same inclination as the blade. When the inclination of the blade changes, the relevant aspect is the inclination of the blade in the region of the blade base, i.e. in the transition region of the connection of the blade elements with the inner ring. 
         [0009]    In a preferred development of the rotor disc of the present disclosure it is also possible to provide a plurality of expansion joints or a plurality of slots. Preferably, the expansion joints are regularly distributed over the circumference of the inner ring. Here, the individual inner ring segments may possibly carry only one blade element so that an inner ring is provided that is assembled from a plurality of inner ring segments. The individual inner ring segments may be connected with each other by connecting elements. For example, connecting elements made of an elastomer may be provided in the slots or the expansion joints. Moreover, it is possible to connect the individual inner ring segments while assembling them into a rotor. Due to the segmentation of the inner ring, the tendency to an unbalance caused by a one-sided expansion is reduced or suppressed. Further, providing a plurality of a plurality of expansion joints regularly distributed over the circumference is advantageous in that the tensions are compensated better and the deformation of individual segments is respectively less than the deformation of a whole ring segment having only one slot. 
         [0010]    In a further particularly preferred embodiment of the rotor disc according to the present disclosure the blade elements are tapered in the region of the blade base, i.e. in the transition region between the blade elements and the inner ring. The taper is formed in particular by recesses provided both in the upper and the lower side. These recesses are preferably formed to be mirror-symmetric so as to avoid unbalances. Thus, the recesses are mirror-symmetric with respect to a centre line of the blade elements or to a central plane of the blades. Providing a tapering of the blade elements in the region of the blade base has positive effects on possibly occurring vibrations of the blade elements. This is advantageous in particular in the mounted state. 
         [0011]    The disclosure further refers to a rotor for a vacuum pump, in particular a turbomolecular pump. The rotor has a plurality of rotor discs arranged in the longitudinal direction of the rotor or in the longitudinal direction of a rotor shaft, the discs preferably being designed as described above. 
         [0012]    Preferably, the at least one inner ring is surrounded by a retaining ring for fixation. In particular the retaining ring is a reinforcement ring preferably made of fiber-reinforced plastic material such as CFC. Preferably the retaining rings are designed and arranged at least in part such that a respective retaining ring surrounds two adjacent inner rings of the rotor discs. In this regard, the retaining ring at least partly surrounds two adjacent inner rings in the longitudinal direction. In a preferred embodiment an inner ring is thus fixed in particular by two retaining rings. The retaining rings each project in part over the inner ring. In particular a part of the inner ring is not surrounded by a retaining ring in the longitudinal direction, the blade elements in this region of the inner ring being connected, in particular integrally formed with the inner ring. 
         [0013]    In the preferred development of the rotor disc in which the blade elements are tapered at the blade base, providing the retaining ring may effect damping. Depending on the operating state, the blade elements are possibly caused to vibrate. These vibrations may be reduced by the retaining ring. In this embodiment the retaining ring thus has the additional function of a damper. 
         [0014]    It is particularly preferred that the retaining ring covers the recesses forming the taper. Thus, a part of the retaining ring contacts the upper or the lower side of the blade elements. A good damping of vibrations of the blade elements may thereby be achieved. In this embodiment it is particularly preferred that the retaining rings contain fiber-reinforced plastics, it being particularly preferred to design the retaining rings as CFC tubes. 
         [0015]    In another preferred embodiment of the disclosure in which the inner rings are of a multi-part design, a tensioning element is preferably provided inside the inner ring. The tensioning element presses the individual inner ring segments against the retaining ring so that a defined position of the inner ring segments is guaranteed. 
         [0016]    It is possible that the inner rings for a self-supporting structure in connection with the retaining rings and possibly with the tensioning elements. It is preferred to additionally provide a supporting element inside the inner rings. The supporting element may be the rotor shaft itself or an element to be connected with the rotor shaft. Such an element to be connected with the rotor shaft is preferably designed as a hollow cylinder so that the rotor shaft protrudes at least in part into the hollow cylinder, in which case the hollow cylinder carries the inner rings. 
         [0017]    In a preferred development the supporting element which is designed in particular as a hollow cylinder comprises a preferably annular retaining protrusion directed radially outward. Due to this also step-shaped retaining protrusion in particular the position of a—seen in the longitudinal direction—outer inner ring and/or a—seen in the longitudinal direction—outer retaining ring is defined. 
         [0018]    Further, the in particular hollow cylindrical supporting element may have an opening in the longitudinal direction which is closed at least in part by cover element. The cover element may also serve to fix an outer inner ring and/or an outer retaining ring. The cover element may have a step-shaped, radially outward directed protrusion. The cover element specifically serves for a positionally accurate fixation of the inner rings and the retaining rings on the supporting element. 
         [0019]    For the assembly of an inner ring having an expansion joint it is possible to slightly compress the same and to insert the ring into the retaining ring so that the inner rings are fixed in the retaining ring by their inherent tension. With multi-part inner rings, the individual inner ring segments are pressed against an inner side of the retaining rings by means of a tensioning element. 
         [0020]    The following is a detailed explanation of the disclosure with reference to preferred embodiments and to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the Figures: 
           [0022]      FIG. 1  shows a schematic top plan view of a rotor disc, 
           [0023]      FIG. 2  is a schematic sectional view of the rotor disc illustrated in  FIG. 1  in the direction of the arrows II-II in  FIG. 1 , 
           [0024]      FIG. 3  is a schematic sectional view of a rotor having a plurality of the rotor discs illustrated in  FIGS. 1 and 2 , 
           [0025]      FIG. 4  is a schematic sectional view of a further preferred embodiment of a rotor having a plurality of inner ring segments, and 
           [0026]      FIG. 5  is an enlarged sectional view of a detail of another preferred embodiment of a rotor constructed according to the disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    A rotor disc  10  of the present disclosure comprises an inner ring  12  having a plurality of blade elements  16  arranged on the outer side  14  thereof in a manner regularly distributed over the circumference. The blade elements  16  are connected with the inner ring  12  in particular integrally. In sectional view ( FIG. 2 ), the inner ring  12  has two substantially cylindrical ring elements  18 , the blade elements  16  being respectively connected with the ring element  12  between the two ring elements  18 . 
         [0028]    In a first preferred embodiment of a rotor ( FIG. 3 ) a plurality of the rotor discs illustrated in  FIGS. 1 and 2  is arranged in the longitudinal direction  20  on a supporting element  22 . In the embodiment illustrated the supporting element  22  is hollow cylindrical so that the same can be plugged and fixed on a rotor shaft not illustrated herein. 
         [0029]    A its lower end in  FIG. 3  the supporting element  22  has a stepped retaining protrusion  24  with a step  26 . Seen in the longitudinal direction  22 , five rotor discs  10  are arranged in the longitudinal direction on an outer side  28  of the supporting element in the embodiment illustrated. The rotor discs  10  each have slot or an expansion joint  30  ( FIG. 1 ). In the mounted state, the inner rings  12  of the rotor discs  10  are surrounded by retaining or reinforcement rings  32 . For assembly, the inner rings  10  having a slot  30  are compressed and set into the retaining rings  32  which are designed as closed rings. Each retaining ring  32  surrounds two ring elements  18  of two adjacent inner rings  12  with the exception of the two outer inner rings  12 . The lower retaining ring in  FIG. 3  surrounds both the ring element  18  of the lower inner ring  12  and the step  26  of the retaining protrusion  24  of the supporting element  22 . 
         [0030]    The possible pre-assembled rotor discs  10 , together with the retaining rings  32 , may be plugged onto the supporting elements  22  from above in  FIG. 3 . In this case, stator discs arranged between the rotor discs  10  may be designed as closed rings and are arranged between the latter already during assembly of the rotor discs. It is also possible that the stator discs are two-part stator discs, for example, which are inserted between two adjacent rotor discs  10  from outside after the rotor is fully assembled. 
         [0031]    The upper rotor disc  10  in  FIG. 3  is connected with a cover element  34  via an upper retaining ring. For this purpose the cover element  34  has a retaining projection  36  which in the embodiment illustrated also has a step  38 . 
         [0032]    The upper retaining ring  32  thus contacts the ring element  18  of the upper inner ring  12  and the step  38  of the retaining projection  36  of the cover element  34 . The cover  34  is set into an opening  40  of the hollow cylindrical supporting element  22 . In the embodiment illustrated the cover  34  has a bore  42 . Through the same the rotor may be fixed, e.g. by a screw, to a front end of a rotor shaft inserted into the supporting element  22 . 
         [0033]    In operation only the forces of one rotor disc act on the upper retaining ring  32  in  FIG. 3  and the lower retaining ring in  FIG. 3 . It may therefore possibly be suitable to give these retaining rings another design in order to avoid in particular a tilting of the rotor discs  10  caused by the tensions and loads occurring. This could, for example, be effected by reducing, in particular halving the width of the upper retaining ring  32  and the lower retaining ring  32 . 
         [0034]    In the further preferred embodiment of the rotor according to the present disclosure illustrated in  FIG. 4  similar or identical components are identified by the same reference numerals. 
         [0035]    This embodiment has the essential difference that the rotor discs not only have one slot  30 , but a plurality of slots so that individual rotor segments or inner ring segments are provided. In the assembled form the individual rotor segments  42  again form a rotor disc which corresponds in function to the rotor disc  10 . In order to guarantee a secure arrangement of the inner ring segments of the rotor disc segments  42 , a recess is provided in the inner side of the inner ring segments  44 , in which recess a tensioning element  46  is arranged. The tensioning element is in particular annular in shape. For the rest, the assembly and the arrangement of the individual elements corresponds to the embodiment described with reference to  FIG. 3 . 
         [0036]    In the further embodiment illustrated in  FIG. 5  similar or identical components are identified by the same reference numerals. The essential difference of this embodiment is in the design of the rotor discs. Again, these have an inner ring  12  connected with the blade elements  16 . Instead of the inner ring  12 , an inner ring may be provided that corresponds to the design of the inner ring  44  ( FIG. 4 ). In the region of a blade base  48 , i.e. in the transition region between the inner ring  12  and the blade element  16 , a taper is provided. In the embodiment illustrated the same is formed on each blade element  16  by two opposite recesses  50 . The recesses  50  are formed as circumferential annular trough-shaped recesses. The recesses  50  are designed to be mirror-symmetric to a centre line  52  of the blade element  16 . 
         [0037]    The radial width of the retaining rings  32 , which in particular are CFC tubes, is selected such that the retaining rings  32  fully cover the recesses  50 . In particular, the retaining rings  32  contact an upper side  54  and a lower side  56  of the blade elements. This contact preferably extends over several millimeters. Due to the contact of the retaining rings  32  on the upper side  54  and the lower side  56  of the blade elements  16 , the retaining rings  32  additionally act as damping elements. 
         [0038]    The assembly of the embodiment illustrated in  FIG. 5  corresponds to the assembly described with respect to  FIG. 3 .