Abstract:
A rotor for a turbomachine, having at least two bladed stages, the discs of which are detachably connected to one another, in which rotor, in order to avoid notch locations in the highly stressed discs, a first disc, at least at one side face, has a first flange which is connected to or restrained with a second flange of an adjacent disc by bolts.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rotor for a turbomachine, having at least two bladed stages, the discs of which are detachably connected to one another. 
     BACKGROUND INFORMATION 
     Rotors of turbomachines generally have a plurality of stages, which are provided with blades and the discs of which are connected to one another in different ways, e.g. by welding or detachably by bolting. Only stages which are detachably connected to one another are considered in this case. 
     In a known rotor, the discs have cylindrical or conical shells which extend essentially in the axial direction and on whose end sections in each case flanges in the shape of a disc ring are provided, to which adjacent discs are connected by screws, studs or the like. If an intermediate-stage seal is not integrated in the shells, it is in each case clamped in place between the flanges. Such a type of connection can only be used in the case of components having a relatively low circumferential velocity, such as, for example, slow-speed low-pressure turbines, since the centrifugal forces which occur in the case of discs designed for high circumferential velocities produce excessive circumferential stresses in the flanged connection. The bores in the flanges constitute notch locations causing local stress increases and greatly restrict the cyclical service life of the component. 
     German Published Patent Application No. 196 27 386 discloses a connecting arrangement for two turbine rotor discs which each have disc connecting arms with through-bores into which specially designed threaded bolts for connecting the rotor discs are inserted. The fact that radial expansion of the flanged connection occurs as a result of centrifugal-force effect proves to be disadvantageous especially at high circumferential velocities. 
     U.S. Pat. No. 5,388,963 discloses a rotor for compressors of gas turbines, in which rotor adjacent discs are detachably connected by flanges, a first flange having slots and a second flange having holes for receiving connecting bolts, and a separate clamp with opposite tongues, which can be bent, being used in order to prevent turning of the connecting bolt during assembly and dismantling. 
     German Published Patent Application No. 2 104 172 discloses a turbine rotor and a method of producing it, in which adjacent discs are clamped together via inwardly directed flanges having aligned bolt bores through which a bolt is passed in each case. A problem in this case is that the bolt bores in the flange constitute notch locations causing local stress increases and restrict the cyclical service life of the rotor. 
     U.S. Pat. No. 5,350,278 discloses an arrangement of spaced apart rotor discs which are detachably bolted to one another via flanges provided on spacers, an annular space along a disc pair for structural support being defined by the spacers. For the bolting, bores, which constitute notch locations, are provided in the flanges. 
     In high-speed low-pressure turbines, additional discs extending radially inwards have been provided, for example, at the intermediate-stage seals. 
     This is intended to limit the radial expansion in such a way that the circumferential stresses produced as a result of the centrifugal -force effects are kept at a low level and the requisite cyclical service life is achieved. However, the additional discs lead to considerable weight disadvantages and problems during assembly. 
     In a further known turbine, the disc has bores through which it is connected by bolting to adjacent discs which have cylindrical or conical shells with flanges. The disc body limits the radial expansion of the connecting point as a result of centrifugal-force effect. A problem, however, is that the bores in the highly loaded disc body constitute notch locations, which limit the service life. 
     U.S. Pat. No. 4,844,694 discloses a connection of rotor elements of a gas turbine in which the disc lying at the connecting point has a bore for inserting a bolt, the bores in the highly loaded disc body constituting notch points, which limit the service life. The last mentioned disadvantage also exists in the bolt connection disclosed by U.S. Pat. No. 5,052,891 between rotor elements of a gas turbine, in which bolt connection a bore for the same is provided in the disc lying at the connecting point. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a rotor for a turbomachine of the generic type described at the beginning, in which rotor the discs are detachably connected to one another without extreme stress increases occurring due to notch locations in the disc. 
     The advantage of such a refinement consists in the fact that the radial expansion of the flanged connection by the disc body is limited, but the disc itself has no bores or notch locations which cause the local stress increases, which are partly extremely high. 
     The first flange preferably extends radially inwards at an axial distance from the side face of the first disc while forming an intermediate space. 
     The first flange is designed as a disc ring which has apertures along its inner end edge or circumferential edge. 
     The apertures are open towards the inside, so that the centrifugal force produced by the bolts can be absorbed by the marginal surface of the apertures. 
     Furthermore, it is advantageous that the apertures are arranged equidistantly along the circumferential edge. 
     To reduce the notch effect, in each case a bore, an elongated hole or a further aperture may be provided between the apertures. 
     It is highly preferable for a flange section of an intermediate-stage seal to be clamped in place in each case between the first and second flanges, the flange section of the intermediate-stage seal preferably having bores which are in alignment with the apertures of the first flange and fix the bolts in the radial direction during assembly. 
     Furthermore, it is expedient that the bolts, at their ends facing the first disc, have a transverse portion which extends at right angles to their longitudinal axis and with which they are supported on the inner side face of the first flange. The bolts are preferably T-head bolts. 
     The distance of the first flange from the side face of the first disc is preferably as small as possible, but greater than the thickness of the transverse portion of the bolt in order to avoid a pressure point at the highly loaded, first disc. 
     The flange of an adjacent disc, at its radially inner end, has a supporting portion which extends substantially in the axial direction and on which the transverse portion of the bolts is supported in order thus to provide anti-rotation locking of the bolts. 
     In a preferred refinement, the first disc has a first flange at both side faces, so that, in this way, the discs of rotors having more than two stages can also be detachably connected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows, in longitudinal section, a view of an exemplary embodiment of the rotor according to the present invention, this view having no hatching for the sake of clarity, 
     FIG. 2 shows a truncated cross-sectional view along line II—II from FIG. 1, and 
     FIG. 3 shows, in longitudinal section, a truncated view of a further exemplary embodiment of the rotor according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a longitudinal section of an exemplary embodiment of the rotor according to the present invention for a turbomachine, this rotor having three stages. The stages are each provided with a blade  1 ,  2  and  3  and with a first disc  4  and two adjacent discs  5 , 6 . The first disk  4  has a flange  9  and  10  respectively at each of its two side faces  7 , B. The flanges  9 ,  10  extend at an axial distance A from their inner side faces  11 ,  12  to the side faces  7 ,  8 . In this way, there is an intermediate space Z, which is open towards the inside in the radial direction, between the first disc  4  and the flanges  9 ,  10 . The distance A is to be kept as small as possible in order to limit the radial expansion of the flanges  9 ,  10  or the flanged connection by the body of the disc  4 . 
     For the detachable connection of adjacent discs  5 ,  6 , a transverse portion  13  of a (screw) bolt  14  engages in the intermediate space Z and is supported in each case on the inner side face, such as  12  for example, of the flange  10  after the restraining/bolting. 
     The discs  5 ,  6  adjacent to the center, first disc  4  each have cylindrical shells  16  which extend substantially in the axial direction and may also be of conical design. At their ends remote from the discs  5 ,  6 , the shells  16  each have a second flange  17 , which in each case is firmly restrained with the flanges  9 ,  10  of the first disc  4  by (screw) bolts  14  or the like. A supporting portion  18  running essentially in the axial direction in each case adjoins the second flanges  17  of the discs  5 ,  6 , on which supporting portion  18  the transverse portions  13  of the bolts  14  can be supported, as a result of which rotation of the bolts  14  is prevented. This ensures that no pressure points occur at the highly loaded, first discs  4  during the fitting or tightening of the (screw) bolts  14 . 
     In each case an intermediate-stage seal  19  is clamped in place and detachably fastened with its flange section  20  between the flanges  9 ,  10  of the first disc  4  and the flanges  17  of the two adjacent discs  5 ,  6 . Alternatively, the intermediate-stage seals  19  may also be arranged integrally on the discs  5 ,  6  or their shells  16 . 
     FIG. 2 shows a cutaway and truncated crosssectional view along line II—II from FIG. 1, in the top partial cutaway portion of which the flange  9  is shown in a plan view. The flange  9  is designed as a disc ring, on the inner end face or circumferential edge  21  of which slot-like apertures  15  which are open towards the inside in the radial direction are provided. Inserted into one aperture  15  is a (screw) bolt  14 , the transverse portion  13  of which is shown by a broken line. After fitting, this transverse portion  13  is supported on the inner side face  11  of the flange  9 . In addition, in order to prevent the (screw) bolt  14  from rotating during the assembly,. its transverse portion  13  is supported on the supporting portion  18  of the shell  16  of the adjacent disc  5 . Provided in each case between the apertures  15  is a relief bore  22 , which reduces the notching factor as a result of the aperture  15 . Alternatively, the bores  22  may also be designed as elongated holes, further apertures or the like. 
     Shown in the bottom partial cutaway portion from FIG. 2 is the flange section  20  of the intermediate stage seal  19 , this flange section  20  being designed in the shape of a disc ring and having bores  23 . The bores  23  are in alignment with the apertures  15  in the flanges  9 ,  10  of the first disc  4  as are corresponding bores  24  in the second flanges  17  of the discs  5 ,  6  adjacent to the first disc  4 . As can be seen in FIG. 2, the bores  23  in the flange section  20  of the intermediate-stage seal  19  are open radially towards the inside, their degree of opening being less than their diameter, in order thus to ensure radial fixing of the (screw) bolts  14  during the assembly. Alternatively, the bores  23  may also be designed as closed bores. 
     If a rotor has more than three stages, every second stage is provided with a first disc  4  having at least one flange  9  or  10 . 
     FIG. 3 shows a further exemplary embodiment of the rotor according to the invention, in which the radius R at the transition between the inner side face  8  of the first disc  4  and the flange  10  or its inner side face  12  is increased for strength reasons. Since the distance A between the side face  8  of the first disc  4  and the inner side face  12  of the flange  10  is consequently larger, the (screw) bolt  14  has a shear ring or collar  25 , which rests on an outer side face  26  of the flange  10  and prevents an axial displacement of the (screw) bolt  14 , so that the transverse portions  13  are not pressed against the first disc  4  during the assembly and do not lose their anti-rotation locking.