Abstract:
The invention relates to a closing assembly for closing the gap remaining between the first and the last blade of a blade ring that is inserted in a peripheral groove of a turbo machinery, said assembly consisting of at least two lateral parts, at least one of which can be hooked onto a projection that forms an undercut in said peripheral groove and at least one securing element, which secures the parts from coming detached from the peripheral groove. To provide a particularly reliable closing assembly, the securing element is configured as a pin, joining the parts of the closing assembly in a non-positive fit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2006/070226, filed Dec. 27, 2006 and claims the benefit thereof. The International Application claims the benefits of European application No. 06000025.4 filed Jan. 2, 2006, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a locking sub-assembly for closing the remaining gap between the first and the last blade of a blade ring which are inserted in a circumferential groove of a turbomachine, which sub-assembly comprises at least two side pieces, of which at least one can be interlocked with a projection, which forms an undercut, of the circumferential groove, and at least one locking element which secures the pieces against disengaging from the circumferential groove. 
       BACKGROUND OF THE INVENTION 
       [0003]    Locking sub-assemblies of such generic type for example originate from EP 1 457 642 A2 and US 2002/0127105 A1. The two locking sub-assemblies essentially comprise two side pieces which are inserted in the remaining gap between the first and the last blade of a blade ring. Since each side piece interlocks in each case with a projection, which forms the undercut, of the circumferential groove, and as a result the two side pieces can be introduced into the gap, the two side pieces together, as seen in the axial direction, are narrower than the gap which is to be filled and closed. After installation of the two side pieces, a gap remains between these in turn which has to be filled with an intermediate piece. The intermediate piece secures the two side pieces against an axial displacement, which disengages the respective interlocking, and consequently against a disengaging from the circumferential groove. In order to secure the intermediate piece itself against disengaging, this is equipped in each case with two lip-like members which by plastic deforming are bent in each case into a pocket which is provided on each side piece. Consequently, the intermediate piece is interlocked with each side piece in a positive locking manner, as a result of which the two side pieces are also retained in the circumferential groove. US 2002/0127105A1, moreover, proposes that the intermediate piece is interlocked with the first and the last blade of the blade ring via a dovetail, whereas according to EP 1 457 642 A1 each side piece of the locking sub-assembly is interlocked with the first and the last blade of the blade ring. Consequently, a gap formation and gap enlargement between adjacent rotor blades and the locking sub-assembly in the circumferential direction is essentially prevented. 
         [0004]    In the case of the known locking sub-assembly, however, it is disadvantageous that for removing the locking sub-assembly this has to be at least partially expensively destroyed in the region of the positive lock. Moreover, it is to be noted that the locking sub-assembly has to withstand the thermal and mechanical loads which occur, especially the centrifugal force which occurs during operation, if it is installed in the rotor of a turbomachine. 
         [0005]    In addition, a blade root locking arrangement with a split nut which is formed from two elements, is known from laid-open specification DE 29 34 298. The two elements in this case are interlockable in each case with one of the projections of the circumferential groove. By screwing in of a grub screw, the two elements are held at a distance and therefore interlocked. 
         [0006]    Furthermore, a multi-piece locking sub-assembly, in which the pieces can be inserted simultaneously into the remaining gap, is known from GB 659 592. In this case, a screw is provided in the center intermediate piece which is conically formed in cross section. The screw which is supported on the groove base can raise the intermediate piece in the direction of the groove opening. On account of side faces which are arranged on the side pieces and inclined in a manner corresponding to the intermediate piece, these side faces can be securely interlocked in each case with the circumferential groove as a result of the raising of the intermediate piece. 
         [0007]    Furthermore, a rotor lock for rotors of thermal turbomachines, which comprises locking halves, is known from DE 103 10 431 A1. The two locking halves in the installed state are interconnected by means of a dovetail fastening. In this case, the elements of the dovetail fastening are formed on the two halves in such a way that the dovetail fastening is created as a result of a displacement of the two halves towards each other, which is oriented in the circumferential direction. As a result of this, it is necessary that for closing the gap which exists between the first and the last blade of a blade ring by means of the rotor lock, a residual gap remains, as seen in the circumferential direction. Therefore, despite the use of the rotor lock of DE 103 10 431 A1, a further residual gap remains between the inserted rotor blades, which, however, can be distributed along the circumference of the circumferential groove. 
       SUMMARY OF INVENTION 
       [0008]    Consequently, the object of the invention is the creation of a locking sub-assembly for complete closing of the remaining gap between the first and the last blade of a blade ring which are inserted in a circumferential groove of a turbomachine, which object can be simply and inexpensively achieved and which still reliably and durably withstands the high mechanical stresses. 
         [0009]    For achieving the object, according to the invention a generic-type locking sub-assembly is disclosed, which is configured according to the features of the claims. 
         [0010]    According to the invention, the pieces are inserted one after the other into the circumferential groove and then releasably interconnected by means of a pin-like locking element. Previously, in the case of the prior art, the locking element, which was formed as an intermediate element, was retained in a positive locking manner between the side pieces, so that the locking sub-assembly as a whole was secured against disengaging from the circumferential groove. The invention is now based on the knowledge that contrary to the current conception a releasable connection of the pieces of the locking sub-assembly reliably achieves the object. Furthermore, the locking sub-assembly can be disengaged from the circumferential groove, without being damaged, by the inserted locking element also being removed by a suitable tool. Furthermore, all the pieces which have already been used once can be used again, which saves production costs. For example, the releasable connection can be produced by means of a locking screw. 
         [0011]    Moreover, with the invention a first development is firstly also disclosed, in which only the side piece which is inserted first into the circumferential groove, for example the front side piece, is interlockable with a projection of the circumferential groove. The rear side piece of the locking sub-assembly, as the second inserted piece, serves for covering the remaining opening of the gap after inserting the first side piece. In addition, the second side piece prevents a displacement of the first side piece, which would release its interlocking. The centrifugal force loading which acts upon the two side pieces of the locking sub-assembly is altogether absorbed by the projection which is interlocked with the first side piece. Consequently, the first side piece which is interlocked with the projection prevents disengaging of the locking sub-assembly as a whole from the circumferential groove. 
         [0012]    In order to prevent an axially-oriented gap formation between two abutting pieces due to a clearance formation or due to the locking element pressing the pieces apart, these pieces are interlocked in a positive locking manner via a dovetail guide. The dovetail guide, therefore, enables an interlocking of two abutting pieces of the locking sub-assembly, which ensures a releasable and, depending upon requirement, an especially reliable non-positive connection of the pieces of the locking sub-assembly by means of the locking element. An undesirable disengaging of the locking element as a result of pieces which grip round the locking element moving away from each other, is therefore safely avoided. 
         [0013]    Advantageous developments of the inventions are disclosed in the dependent patent claims. 
         [0014]    The dovetail guide in this case is preferably arranged on the pieces of the locking sub-assembly in such a way that during the radial inserting of the last piece the elements of the dovetail guide intermesh. During the insertion process of the last piece, this is interlocked together with the already inserted piece, or with the already inserted pieces. This has the advantage that the locking sub-assembly can completely fill up, i.e. without clearance, the gap of the circumferential groove which is to be filled, as seen in the circumferential direction. Displacing of the rotor blades which are inserted in the circumferential groove, both after installation of the locking sub-assembly and during operation of the turbomachine, can be safely avoided in this way. 
         [0015]    Within the scope of a second development of the invention, the locking sub-assembly comprises an intermediate piece, which can be inserted between the two side pieces which are now interlockable in each case with the circumferential groove. Since each side piece is interlockable in each case with an encompassing projection on a side wall of the circumferential groove, which projects in the axial direction, and the two side pieces are inserted one after the other into the circumferential groove, a farther gap remains between these which is filled by the subsequently inserted intermediate piece. The filling of the further gap prevents the displacement of the side pieces in the axial direction, so that their secure interlocking remains ensured. The locking element is arranged so that both the two side pieces and the intermediate piece, which lies between them, of the locking sub-assembly are releasably interconnected. The individual pieces of the locking sub-assembly, and this sub-assembly as a whole, are then secured against disengaging from the circumferential groove. 
         [0016]    An especially favorable securing against disengaging from the circumferential groove is provided if the locking sub-assembly comprises a further pin-like locking element, wherein each side piece is secured with the intermediate piece in each case by means of one of the two pin-like locking elements. Therefore, each locking element interconnects only two of the three pieces of the locking sub-assembly, as a result of which the mechanical load of each locking element, compared with the development with only one locking element, is lower. 
         [0017]    In an especially advantageous development of the invention, the two abutting side pieces abut, or each side piece abuts, upon the intermediate piece in a contact plane, wherein the locking element extends, or the locking elements extend, longitudinally within the contact plane. The locking element is accordingly arranged in halves in the contact plane and releasably interconnects in each case two abutting pieces. 
         [0018]    Alternatively to the last-mentioned development, the locking element, or the locking elements, can extend transversely through the contact plane, through one of the two contact planes, or through the two contact planes. 
         [0019]    A releasable locking sub-assembly can be especially advantageously achieved by a non-positive locking connection. The centrifugal force load which acts upon the two non-positive locking interconnected side pieces of the locking sub-assembly is altogether absorbed by the projection, or the projections, which is, or are, interlocked with the side piece, or the side pieces. 
         [0020]    An especially simply releasable locking sub-assembly can be disclosed by a further development in which the locking element is a locking screw. The locking screw interconnects at least two pieces of the locking element in a non-positive locking manner. At least one threaded section is provided for the locking screw in each piece of the locking sub-assembly. The aligning threaded sections accommodate a common locking screw for the non-positive locking connecting of the pieces, if applicable, so that the locking screw extends transversely through the contact plane on which the two pieces abut. Alternatively to this, the thread can be divided over its whole height into two thread halves, wherein each half of the thread is arranged on one of the pieces of the locking sub-assembly. By this it is to be understood that each thread flight of the thread is divided into two halves, wherein one half is provided on a first of two pieces which abut in a contact plane, and the other half of each thread flight is arranged on the second of the two abutting pieces. Although the halves are referred to as such, these do not have to be identical in size. 
         [0021]    By the use of a locking screw, a particularly reliable and re-releasable and, if applicable, non-positive locking connection of the pieces of the locking sub-assembly is provided, which, even with a centrifugal load acting upon the locking sub-assembly, safely prevents disengaging of the pieces of the locking sub-assembly from the circumferential groove. Moreover, the locking screw, on account of the friction forces of this screw which are increased as a result of the centrifugal force, is secured against loosening. 
         [0022]    In particular, the provision of the dovetail guide safely prevents the two thread halves from moving away from each other, as a result of which the loosening of the locking screw, which is gripped by them, is reliably avoided. 
         [0023]    In order to maintain a particularly aerodynamic surface of the locking sub-assembly, which closes off the opening of the gap in an approximately flush manner, the locking screw is formed as a grub screw so that the end which is required for screwing-in and unscrewing does not require additional space for a rotating tool. 
         [0024]    The development in which each piece can abut against a side wall which is formed by a projection, which forms the undercut, of the circumferential groove, is particularly advantageous. As a result of this, the whole locking sub-assembly is prevented from being able to twist as a unit inside the circumferential groove if the gap between the first and the last blade of the blade ring becomes larger in the circumferential direction for unforeseeable, reasons. Even for this case, a locking sub-assembly which is particularly reliable and secured against disengaging from the circumferential groove, is disclosed by the proposed development. 
         [0025]    In order to disclose a locking sub-assembly which is particularly reliable and secured against disengaging from the circumferential groove, the locking element can additionally be mechanically secured against loosening, for example by means of peening. 
         [0026]    The locking sub-assembly is customarily provided for closing the gap of a circumferential groove, which is arranged in a rotor of a turbomachine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]    The further explanation of the invention follows, with reference to the exemplary embodiments which are represented in the drawing. 
           [0028]    In detail, in the drawing 
           [0029]      FIG. 1  shows a circumferential groove in cross-sectional view with a locking sub-assembly which comprises two side pieces and a locking element, 
           [0030]      FIG. 2  shows the locking sub-assembly according to  FIG. 1  in a plan view, 
           [0031]      FIG. 3  shows a second development of the locking sub-assembly with a locking element which passes obliquely through the three pieces of the locking sub-assembly, 
           [0032]      FIG. 4  shows a third variant of the invention with a locking sub-assembly which comprises three pieces and two locking elements, 
           [0033]      FIG. 5  shows the plan view according to  FIG. 4  and 
           [0034]      FIG. 6  shows the plan view according to  FIG. 4  in a further embodiment variant. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0035]      FIG. 2 ,  FIG. 5  and  FIG. 6  show in each case a detail of a plan view of a circumferential groove  10 , in which rotor blades  12   a ,  12   b  of an axial compressor of a gas turbine are inserted. Instead of the compressor, the invention could also be applied in a steam turbine or in a turbine unit of the gas turbine. 
         [0036]    The endlessly encompassing circumferential groove  10  is provided on an external surface  11  of the rotor of the compressor. The circumferential groove  10  could also be provided on an annular inner casing of the compressor, in which stator blades are fastened. The circumferential groove  10 , as seen in the axial direction of the rotor, has a front side wall  16  and a rear side wall  18  upon which projections  20 ,  22 , which extend in the circumferential direction and extend in the axial direction, are arranged in each case and respectively form a front and a rear undercut  24 ,  26  ( FIG. 1 ,  FIG. 3  and  FIG. 4 ). 
         [0037]    Rotor blades  12   a ,  12   b , which have inverted T-shaped blade roots which are constructed to correspond to the undercuts  24 ,  26 , are inserted in the circumferential groove  10 . For installation, the rotor blades  12   a ,  12   b  are inserted into the circumferential groove  10  and then rotated enough, for example by 45° or 60°, until the inverted T-shaped blade roots fit behind the projections  20 ,  22 . 
         [0038]    The gap, which remains between the first rotor blade  12   a  and the last rotor blade  12   b , of the circumferential groove which is otherwise completely fitted with blades  12  of a blade ring and, if applicable, intermediate pieces which are arranged between them, has to be closed by means of a special device, which is referred to as locking sub-assembly  33 , blade lock or even rotor lock. 
         [0039]    The first development of the invention, which is shown in  FIG. 1  and  FIG. 2 , is essentially characterized in that the locking sub-assembly only comprises a front side piece  30  and a rear side piece  32 , wherein only the front side piece  30  is interlocked with the projection  20  of the circumferential groove  10 . The front side piece  30 , as seen in cross section, is C-shaped in form ( FIG. 1 ), and has an outer arm  50  and an inner arm  52  which are interconnected via a bridge  54  which extends in the radial direction. The inner arm  52  engages in the undercut  24  which is formed by the projection  20 . Subsequently, the arm  52  abuts against the projection  20  and prevents falling out from the circumferential groove  10 . The rear side piece  32  closes the opening of the gap  28  after the front side piece  30  has been inserted into the gap  28  of the circumferential groove  10 . The first development of the invention is especially characterized in that the rear side piece  32 , as seen in cross section, is simply L-shaped and not C-shaped like the front side piece  30 . The rear side piece  32  does not engage in the undercut  26  and is not interlocked with the projection  22 . 
         [0040]    The front side piece  30 , as shown in  FIG. 2 , is interlocked with the rear side piece  32  in a positive locking manner via a dovetail guide  46 . The dovetail guide  46  comprises two elements, these being a recess with undercuts, and an extension which is formed correspondingly to it and which can fit behind the undercuts of the recess. One each of the elements is provided on one of the pieces which is interlockable with the dovetail guide. Both the recess with the undercuts and the extension, as seen in cross section, that is to say perpendicular to the guide direction, have in this case a contour in the form of a dovetail. 
         [0041]    The dovetail guide  46  of the locking sub-assembly  33  is oriented so that during the radial inserting of the rear side piece  32  into the circumferential groove  10  this is interlocked with the front side piece  30  which is already inserted. The dovetail guide  46  prevents a possible gap formation between the two side pieces  30 ,  32 . 
         [0042]    The front side piece  30  and the rear side piece  32  abut in a contact plane  48 . A hole  62  which has a female thread  61 , in which the locking element  36 , which is formed as a locking screw  64 , is screwed, is provided in the contact plane  48 . The female thread  61  is arranged in halves in the front side piece  30  and in the rear side piece  32 . In halves means that one half of each thread flight of the female thread  61  is formed on the front side piece  30 , and the other half of each thread flight is formed on the rear side piece  32 . 
         [0043]    By the screwing-in of a locking screw  64 , which for example is formed as a grub screw, into the female thread  61 , the two side pieces  30 ,  32  are interconnected in a way in which they can be released again. The grub screw can be tensioned in the tapering female thread  61 , forming a particularly tight frictional lock. By means of the axial gap formation between the two pieces  30 ,  32 , which is prevented by the dovetail guide  46 , the locking screw  64  is reliably screwed into the female thread  61 , although this is formed by two separate pieces  30 ,  32 . 
         [0044]    The assembled locking sub-assembly  33  is retained as a whole in the circumferential groove  10  via the interlocking of the front side piece  30  with the projection  20  and therefore is secured against disengaging from the circumferential groove  10 . 
         [0045]    The rear side piece  32  is securely retained in the circumferential groove, despite a faulty interlocking with the projection  22 , since the centrifugal forces which act upon the rear side piece  32  are transmitted by means of the locking screw  64  onto the front side piece  30 , so that the rear side piece  32  is indirectly also supported by the projection  20  which serves as an abutment for the interlocked inner arm  52 . 
         [0046]    Although the centrifugal forces which act upon the locking screw  64  and upon the two side pieces  30 ,  32  prevent a self-acting loosening of the locking screw  64 , this can additionally be secured once more against unscrewing by means of peening, as a result of which a locking sub-assembly  33 , which is particularly secured against disengaging from the circumferential groove  10 , is disclosed. 
         [0047]      FIG. 3  shows a second development of the invention, in which the locking sub-assembly comprises three pieces  130 ,  131 ,  132  which are inserted into the gap  28 . The two lateral side pieces  130 ,  131 , which are C-shaped in cross section, are individually inserted one after the other into the circumferential groove  10  and axially displaced so that their inner arms  52  are interlocked in each case with the projections  20  or  22  by each arm  52  engaging in each case in one of the undercuts  24 ,  26 . After that, the gap which remains between these two side pieces  130 ,  131  is filled by the inserting of an intermediate piece  132 , which secures the two side pieces  130 ,  131  against axial displacement and prevents loosening of the interlock. The intermediate piece  132  has a width B, extending in the axial direction, which corresponds at least to the dimension a by which the projection  20  or  22  penetrates into the circumferential groove  10  in the axial direction. 
         [0048]    The pieces  130  and  132  abut in a contact plane  148 , and the pieces  131  and  132  abut in a contact plane  149 . A hole  162  extends obliquely through the contact planes  148  and  149 . In order to interconnect the pieces  130 ,  131 , and  132  in a non-positive locking manner, a pin-like locking element  136  is provided, which can be inserted into the hole  162 . The hole  162  extends along an axis  140  which obliquely penetrates the contact faces  148 ,  149  and penetrates the three pieces  130 ,  132 ,  131  in alignment. A female thread  161  is provided inside the hole  162 , into which the locking element  136 , which is formed as a locking screw  164 , can be screwed. Consequently, the three pieces  130 ,  131 ,  132 , which have in each case a threaded section, are releasably interconnected, as a result of which the intermediate piece  132  and also the locking sub-assembly  133  as a whole are secured against disengaging from the circumferential groove. It is even possible that only the intermediate piece  132  features the female thread  161  and that the locking screw  164  is supported on the groove base of the circumferential groove  10  in order to secure the locking sub-assembly  133  as a whole. Furthermore, instead of a support on the groove base of the circumferential groove, a locking screw  164 , which is provided with a screw head, can clamp the side pieces  130 ,  132  together in a non-positively locking manner. 
         [0049]    Likewise, the pieces  130 ,  131 ,  132  of the locking sub-assembly  133  can be interlocked by a dovetail guide according to the first development. 
         [0050]    Alternatively to the development which is shown in  FIG. 3 , the three pieces  130 ,  132 ,  131  could also be secured by means of two locking elements which are axially offset to each other. For this case, the locking element  136  would only interconnect the side piece  131  with the intermediate piece  132  in a non-positively locking manner, and a further locking element, which is not shown and also extends obliquely, would only interconnect the two pieces  130  and  132  in a non-positively locking manner. In addition, in the second development a dovetail guide can also interconnect the pieces  130 ,  132 , and  131 ,  132 . 
         [0051]      FIG. 4  shows a third development of the invention in a cross-sectional representation, and  FIG. 5  shows this third development in a plan view. The side pieces  230 ,  231 , which can be inserted one after the other into the circumferential groove  10 , are interlocked in each case with one of the projections  20  or  22 . The two side pieces  230 ,  231  are essentially C-shaped in form, as seen in cross section, and have in each case an outer arm  250 , which partially closes the gap  28  partially on the outside, and an inner arm  252 , which is interlocked with the projections  20 ,  22 . The inner arms  250  are interconnected with the outer arms  252  in each case by means of a bridge  254 . 
         [0052]    An intermediate piece  232  is provided between the two side pieces  230 ,  231 , which secures the two side pieces  230 ,  231  against axial displacement and therefore against loosening of the interlock. The intermediate piece  232  has a width B, extending in the axial direction, which corresponds at least to the dimension a by which each projection  20  or  22  penetrates into the circumferential groove  10  in the axial direction. 
         [0053]    If this condition is not fulfilled, then the side piece  130  or  131 , which is to be inserted into the groove as the second side piece, cannot be inserted. 
         [0054]      FIG. 5  shows the plan view of the third development of the invention according to  FIG. 4 . The intermediate piece  232  abuts against the front side piece  230  in a contact face  248 , and is interlocked with this via a first dovetail guide  246 . For this purpose, a dovetail-shaped extension is formed on the intermediate piece  232 , and the corresponding recess which is associated with it is formed on the front side piece  230 . In a similar manner, the rear side piece  231  is interlocked with the intermediate piece  232 , wherein these abut in a contact face  249 . In the case of the second dovetail guide  247 , or dovetail toothing, the dovetail-shaped extension is provided on the rear side piece  231 , and the recess which is formed correspondingly to it is provided on the intermediate piece  232 . In this case, the second dovetail guide  247 , as seen in the circumferential direction, can be constructed narrower than the first dovetail guide  246  in order to enable an axial sliding of the narrower dovetail-shaped extension in the larger recess during installation of the side piece  231  or  230  which is inserted as the second side piece, and in this way to achieve a maximization of the centrifugal force-stressed cross sections of the bridges  254 . 
         [0055]    In a similar way to the first development according to  FIG. 1  and  FIG. 2 , a pin-like locking element  236 , which is formed as a locking screw  264 , is provided in each case in the contact faces  248 ,  249 . At least one hole  262  is provided in each contact plane  248 ,  249  for accommodating the locking element  236 . Each hole  262  is provided with a female thread  263  which are arranged in each case in halves in two pieces  230 ,  231 , and  231 ,  232 . The pin-like locking element  236 , which is formed as a locking screw  264 , can be screwed in each case into this female thread  263  for the non-positive and/or positive connecting of the pieces  230 ,  231 ,  232  of the locking sub-assembly  233 . Although each female thread  263  is arranged in each case in halves in two pieces  230 ,  232 , and  231 ,  232 , a threaded connection which is reliable and secured against loosening is possible, since by means of the respective dovetail guide  246 ,  247  the two pieces  230 ,  232 , or  231 ,  232  which form each female thread  263  cannot be axially moved apart. 
         [0056]      FIG. 6  shows the plan view of a variant of the third development. In this case, the dovetail guide  247  is formed between the pieces  232  and  231  the other way round in relation to  FIG. 5 . The two dovetail-shaped extensions are arranged on the intermediate piece  232 , and each side piece  230 ,  231  has a recess in the corresponding contact faces  248 ,  249  for accommodating the respective extension. 
         [0057]    If in the exceptional case the blades  12  of the blade ring wander so that a gap occurs between the locking sub-assembly  33 ,  133 ,  233  and a directly adjacent blade  12   a  or  12   b , the locking sub-assembly as a whole could possibly disengage from the circumferential groove  10  by rotating. This can be prevented by the bridges  54 ,  254  of each side piece  30 ,  32 ,  130 ,  131 ,  230 ,  231  abutting against the side walls  58  of the projections  20 ,  22  like a flange, as  FIG. 4  exemplarily shows it. 
         [0058]    Instead of a locking screw  64 ,  164 ,  264 , a pin-like bolt, which is secured against loosening by means of a press fit, could also be inserted into the hole  62 ,  162 ,  262 . For removing the locking sub-assembly, this bolt would have to be simply drilled out. 
         [0059]    Furthermore, a locking screw  64 ,  164 ,  264 , which is provided with a screw head, could be screwed into each locking sub-assembly  33 , wherein the screw head, which is recessed in one or more of the pieces  30 ,  32 ,  130 ,  131 ,  132 ,  230 ,  231 ,  232 , abuts against this with pretensioning in a non-positively locking manner. 
         [0060]    In all, by the locking sub-assembly a device for closing the remaining gap between the first and the last blades of a blade ring which are inserted in a circumferential groove, can be disclosed, which can be easily installed and disassembled. Since the installation of the locking sub-assembly does not necessitate plastic deformation of the components, but proposes the non-positive locking connection of the components, these can be loosened and disassembled by means of working steps carried out in reverse. All the components of the locking sub-assembly can be used again. Moreover, the simple type of construction enables a relatively favorable manufacturing cost.