Abstract:
The invention relates to a sectored distributor ( 112 ) for a turbomachine, including two coaxial platforms mutually connected by radial blades, the inner platform ( 130 ) being connected to an annular partition ( 138 ) for suspending an annular mounting ( 140 ) carrying elements ( 136 ) made of material subject to abrasion, this mounting sliding circumferentially on the partition and comprising a means engaging with means corresponding to the inner periphery of the partition to ensure radial restraint of the mounting on this partition.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a sectored distributor for a turbomachine such as a turbojet or a turboprop engine. 
     A turbomachine comprises turbine stages each comprising a rotor impeller and a distributor, each distributor being sectored, i.e. formed of several distributor segments arranged circumferentially end-to-end. 
     Each distributor segment comprises two coaxial annular platforms extending inside one another and connected together by substantially radial blades. The outer platform comprises means for fastening on an outer casing of the turbine. The inner platform is integral with a substantially radial annular partition which carries members made of abradable material, located radially inside the inner platform of the distributor. The members made of abradable material engage with annular lips carried by the rotor of the turbine in order to form seals of the labyrinth type. 
     In the event of substantial wear of the members made of abradable material, it is necessary to replace them with new ones during maintenance operation. With the current art, these members are fixed by brazing on the annular partition of the inner platform of the distributor. The replacing of the members made of abradable material requires a complete dismounting of the segments of the distributor, a machining of each distributor segment in order to remove the worn abradable members, and the brazing of new abradable members on the annular partition. It is then necessary to deposit an antioxidant protective coating on each distributor segment. This operation of replacing abradable members of a distributor is therefore long and expensive. 
     Moreover, the distributor segments are separated from each other with low play in the circumferential direction in order to authorise thermal dilatations of their platforms during operation. They are in addition subjected during operation to vibrations and relatively substantial dynamic stress which can result in static movements and deformations of these segments. 
     2. Description of the Related Art 
     It has already been proposed to rigidify the distributor using means for axial bearing formed on the inner platform segments of the distributor, the means for bearing of a platform sector being intended to engage with corresponding means formed on adjacent inner platform segments in order to limit the deformations of the distributor during operation. 
     With the current technique, these means for bearing comprise a very hard material called “stellite” which is deposited via a method of laser welding (“stelliting”) which is long, expensive, difficult to implement, and which risks deteriorating the distributor segments. This technology is furthermore not able to be carried out on certain distributors of which the platforms have forms that are too complex (called 3D platforms). 
     BRIEF SUMMARY OF THE INVENTION 
     This invention has in particular for purpose to provide a simple, effective and economical solution to the problems of prior art, by simplifying the replacing of the members made of abradable material of the distributor, and by suppressing the stelliting of the segments of this distributor. 
     It proposes to this effect a sectored distributor for a turbomachine, formed of segments comprising two coaxial annular platforms, respectively inner and outer, connected together by substantially radial blades, the inner platform being integral with a substantially radial annular partition carrying members made of abradable material, characterized in that the members made of abradable material are fixed on a sectored annular mounting which comprises an annular groove exiting radially towards the exterior and wherein is engage and retained in the radial direction the inner periphery of the annular partition, each mounting segment comprising at one of its circumferential ends an opening for engaging and mounting on the annular partition of one or of several distributor segments, the mounting being carried out by displacing in the circumferential direction the mounting segment on this partition, and at the other of its circumferential ends means forming a stop in the circumferential direction and engaging with the annular partition of the or of one of the distributor segments in order to ensure the restraint in one direction in the circumferential direction of the annular partition in relation to the mounting segment. 
     In a simple manner, the annular partition of the inner platform is received in means for fastening provided on the mounting of the abradable members, which can slide on this partition. Contrary to prior art, the mounting of the abradable members is mounted in a removable manner on the partition, which facilitates the replacing of worn abradable members. It is sufficient in fact to dismount the annular mounting of the partition and to carry out the aforementioned operations of machining and brazing directly on this mounting, or simply replace this mounting carrying worn abradable members with a new mounting carrying new abradable members. The remounting of the mounting on the partition is furthermore relatively simple and rapid. 
     The invention further makes it possible to simplify the manufacture of each distributor segment which is obtained from foundry, as the mounting of the abradable elements is now carried out independently of these segments. 
     The annular mounting when it extends over several distributor segments further makes it possible to rigidify the distributor segments in such a way as to limit their vibrations and their static movements during operation, while still authorising their circumferential dilatations. It is therefore no longer required to deposit via stelliting a hard material on the means for axial bearing of the distributor segments, which makes it possible to eliminate this long and expensive operation, and to suppress the risk of deterioration of the distributor segments during this delicate operation. 
     The annular mounting is sectored and each mounting segment comprises at a circumferential end an opening for engaging and mounting on the partitions of the distributor segments, the montage being carried out by displacing the mounting segment in the circumferential direction on the distributor segments by circumferential sliding. Each mounting segment comprises at its other circumferential end means forming a stop in the circumferential direction and engaging with the partition of an adjacent distributor segment in order to provide the restraining in one direction in the circumferential direction of the distributor segments in relation to the mounting segment. 
     According to another characteristic of the invention, the mounting is in the form of a rail and is made from sheet metal, which makes it possible in particular to lighten the distributor substantially in relation to prior art. 
     The mounting can have a U- or C-shaped section of which the opening is oriented radially towards the exterior, this mounting comprising two substantially radial annular wings, respectively upstream and downstream, connected together at their inner peripheries by an inner cylindrical mounting wall of the members made of abradable material. The abradable members can be fastened on the mounting by brazing or by any other suitable technique. 
     Annular deflectors made of sheet metal can furthermore be fastened, for example by brazing, on the wings of the mounting. These annular deflectors are intended to engage with corresponding members of the rotor impellers located upstream and downstream of the distributor in order to limit the passage of air in the radial direction between the distributor and these rotor impellers. 
     Each wing of the mounting can be folded at its outer periphery in order to form a substantially cylindrical outer wall extending axially towards the opposite wing, the outer walls defining between them the annular groove of passage of the annular partition of a distributor segment. 
     Each outer wall of the mounting can be folded on the side of the annular partition in order to form an annular edge extending substantially radially towards the interior, these two annular edges being substantially parallel together and to the annular partition of the mounting. In mounting position, the partition is clamped between the outer walls or between the annular edges of the mounting, and is clamped radially between the outer walls or the annular edges of the mounting on the one hand, and the inner wall of the mounting on the other hand, which makes it possible in particular to limit the vibrations of the mounting during operation. 
     The partition comprises more preferably at its inner periphery circumferential shoulders forming a stop in the radial direction, these shoulders being housed between the wings of the mounting and engaging with the outer walls or the annular edges of the mounting in order to ensure its radial restraint on the partition. 
     The number of mounting segments can be less than the number of distributor segments. Each mounting segment can extend in the circumferential direction over an angular area corresponding to several distributor segments. Each mounting segment makes it possible in this case to connect and to rigidify several distributor segments. 
     The invention also relates to a turbomachine low-pressure turbine, comprising at least one sectored distributor of the aforementioned type, as well as a turbomachine, such as a turbojet or a turboprop engine, comprising at least one distributor such as described hereinabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention shall be better understood and other details, characteristics and advantages of this invention shall appear more clearly when reading the following description provided by way of a non-restricted example and in reference to the annexed drawings, wherein: 
         FIG. 1  is a diagrammatical axial section half-view of a turbomachine low-pressure turbine, 
         FIG. 2  is a partial diagrammatical view in perspective of a distributor segment, according to art prior to the invention, 
         FIG. 3  is a diagrammatical view in perspective of the means for axial bearing between two adjacent distributor segments of prior art, 
         FIG. 4  is a partial diagrammatical view in perspective of a sectored distributor according to the invention, 
         FIG. 5  is a view on a greater scale of a portion of  FIG. 4  and shows a circumferential end of a mounting segment according to the invention, 
         FIG. 6  is a diagrammatical view in perspective of the other circumferential end of the mounting segment in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is first made to  FIG. 1  which shows a turbomachine low-pressure turbine  10  comprising four stages each comprising a distributor  12  carried by an outer casing  16  of the turbine and an impeller  18  located downstream of the distributor  12 . 
     The impellers  18  include discs  20  assembled coaxially to each other by annular flanges  22  and carrying substantially radial vanes  24 . These impellers  18  are connected to a turbine shaft (not shown) by the intermediary of a drive cone  26  fixed on annular flanges  22  of the discs. 
     Annular plates  28  for the axial retaining of the vanes  24  on the discs  20  are mounted between the discs and each include an inner radial wall  29  axially clamped between the annular flanges  22  of two adjacent discs. 
     The distributors  12  each include two annular coaxial platforms  30 ,  32 , respectively inner and outer, which delimit between them the annular stream of gas flow in the turbine and between which extend substantially radial fixed blades  14 . The outer platforms  32  of the distributors are fastened by suitable means on the outer casing  16  of the turbine. 
     The inner platform  30  of each distributor is integral with an annular partition  38  carrying annular members  36  made of abradable material, these members  36  being arranged radially inside the inner platform  30  of the distributor. In the example shown, the annular partition  38  is substantially radial and its outer periphery is connected to the inner surface of the inner platform  30  of the distributor. The abradable members  36  are fixed on the inner periphery of the annular partition  38 . 
     The abradable members  36  are arranged radially outside and across from outer annular lips  41  carried by the plates  28 . The lips  41  are intended to engage by friction with the members  36  in such a way as to form labyrinth-type seals and to limit the passage of air in the axial direction through these seals. 
     The distributors  12  of the turbine are sectored and are each formed of several segments arranged circumferentially end-to-end around the longitudinal axis of the turbine. 
       FIG. 2  shows a portion of a distributor segment  12  according to the art prior to this invention. This distributor segment  12  comprises an inner platform segment  30  and an outer platform segment (not visible) connected together by seven blades  14 . The inner platform segment  30  is integral with a partition segment  38  carrying abradable members  36 . The platform sector  30  and the partition segment  38  are formed of a single piece of foundry. 
     In the current technique, the abradable members  36  are fixed by brazing on the inner periphery of the partition segment  38 . Annular deflectors  42  made of sheet metal are furthermore fastened by brazing on the inner periphery of the partition segment  38 , upstream and downstream of the abradable members  36 . These deflectors engage via a baffle effect with the corresponding means of the impellers  18  located upstream and downstream of the distributor in order to limit the passage of gas in the radial direction between the distributor and these impellers. 
     The replacing of the abradable members  36  is in this case a long and expensive operation, as has been seen hereinabove. 
     The longitudinal edges  44 ,  44 ′ of the inner platform segment  30  of each distributor segment  12  have forms that are complementary with the corresponding longitudinal edges of the inner platform segments of the adjacent distributor segments, in such a way that the longitudinal edges are embedded circumferentially into one another during the mounting of this distributor ( FIG. 3 ). 
     In the current technique, the longitudinal edges  44 ,  44 ′ of the inner platform segments  30  are machined in Z in order to define means  46  of axial bearing between the distributor segments  12 . The axial bearing of an inner platform segment  30  on an adjacent inner platform segment makes it possible to limit the static movements and the vibrations of the distributor segments  12  during operation of the turbine. 
     The means for bearing  46  comprise a hard material called “stellite” deposited by a method that is long, expensive, and very difficult to implement, such has also been described hereinabove. 
     Moreover, the longitudinal edges  44 ,  44 ′ of the platform sector  30  and the radial edges of the partition segment  38  comprise straight slots  48  for housing the tabs providing a seal between the distributor segments. These slots  48  are obtained during an operation of machining that is relatively long and delicate, the radial slot formed on each radial edge of the partition segment  38  extending at its radially inner end to the immediate vicinity of the abradable members  36 . 
     The invention makes it possible to overcome at least partially the problems indicated hereinabove thanks to an annular mounting  140  which is fastened in a removable manner on the annular partition  138  of the distributor and which carries the members made of abradable material  136 . 
     In the embodiment shown in  FIGS. 4 to 6 , the annular mounting  140  is in the form of a rail and is sectored, the mounting segments  140  being arranged end-to-end. The mounting segments  140  are made of sheet metal, for example from stamped sheet. 
     According to a characteristic of the invention, the number of mounting segments  140  is less than the number of distributor segments  112 . By way of example, the number of distributor segments  112  is eighteen and the number of mounting segments is six, in such a way that each mounting segment  140  extends over an angular area corresponding to three consecutive distributor segments. In this case, each mounting segment connects three consecutive distributor segments of which the circumferential ends can be devoid of stellite. 
     Alternatively, each mounting segment can rigidify two or four consecutive distributor segments  140 , and even more. 
     The longitudinal edges  144 ,  144 ′ of the inner platform segments of each distributor can be conformed in Z, as in prior art, in order to conserve the axial bearing surfaces, or be of a straight section in order to suppress these axial bearing surfaces. 
     The annular mounting  140  according to the invention comprises an annular groove  150  exiting radially towards the exterior and wherein is engaged and retained in the radial direction the inner periphery of the radial partition  138 . The mounting  140  is mounted and dismounted from the inner periphery of the partition  138  simply and rapidly, such as shall be described in more detail in what follows, which makes it possible to facilitate the replacing of the abradable members  136  when they are worn. 
     In the example shown, the mounting  140  has a U- or C-shaped section of which the opening exists radially towards the exterior. The mounting  140  comprises two substantially radial annular wings  152 , respectively upstream and downstream. These wings  152  are substantially parallel together and connected together at their inner peripheries by a substantially cylindrical inner annual wall  151 . Members  136  made of an abradable material are fastened, for example by brazing, on the inner surface of this inner cylindrical wall  151 , and annular deflectors  142  made of sheet metal are also fastened by brazing on the wings  152 . 
     Each wing  152  is folded at its outer periphery in such a way as to form a substantially cylindrical outer annular wall  154  extending axially towards the other wing. These outer cylindrical walls  154  are themselves folded at their axial ends located next to the opening of the groove  150  in order to form annular edges  156  extending substantially radially towards the interior, in the groove  150  of the mounting. The inner periphery of each annular edge  156  is at a radial distance from the inner wall  151 , the radial dimension of the edges  156  being for example substantially equal to half of that of the wings  152 . 
     These edges  156  are substantially parallel together and to the partition  138 . They define here the opening of the groove  150  of the mounting  140 . The axial distance between the faces across from the annular edges  156  is less than the thickness of the partition  138  in such a way that, in mounting position, the partition is maintained axially clamped between the edges  156  of the mounting  140 . 
     The partition  138  of the distributor  112  has in the example shown an inverted T section and comprises at its inner periphery circumferential shoulders  158  intended to be housed in the groove  150  of the mounting, and to engage by bearing with the annular edges  156  and the inner wall  151  of the mounting in order to immobilise in the radial and axial direction the mounting  140  on the partition  138 . 
     The width if the shoulders  158  in the axial direction is determined in such a way that the inner peripheral edges of the annular edges  156  are bearing radially towards the interior on the outer annular surfaces of these shoulders. The thickness of the shoulders  158  in the radial direction is determined in such a way that these shoulders are inserted with a radial clamping between the outer surface of the inner wall  151  and the inner peripheral edges of the edges  156 . 
     The shoulders  158  can have an angular area equal to or less than that of the distributor segment. The distributor segment  112  can include of each side of the partition segment  138  several shoulders  158  at a circumferential distance from one another. 
     Each mounting segment  140  comprises an open circumferential end ( FIG. 5 ) for the engagement and the mounting on a given number of distributor segments (three in the example shown), and an opposite circumferential end which is closed ( FIG. 6 ) in order to retain the mounting segment in one direction in the circumferential direction on the distributor segments. 
     In the example shown in  FIG. 6 , the circumferential end of the mounting segment was closed via fixation, for example by brazing or welding, of a plate  160  on this circumferential end. This plate  160  forms a means of retaining on the distributor segments  112  in the circumferential direction. The plate  160  bears circumferentially in one direction on the partition segment  138  of the distributor segment  112  adjacent to this plate ( FIG. 6 ). This plate  160  is blocked circumferentially in the opposite direction by bearing on the partition segment  138  of another distributor segment whereon is mounted an adjacent mounting segment. 
     In  FIGS. 4 to 6 , it can be seen that the slots  148  formed on the radial edges of the partition segment  138  are shorter than those of prior art and are therefore faster to carry out. 
     The annular mounting  140  is fastened on the distributor segments  112  in the following manner. Three distributor segments  112  are arranged end-to-end. A mounting segment  140  is arranged next to one of the distributor segments  112  in such a way that its open circumferential end is aligned in the circumferential direction with the shoulders  158  of the partition segment  138  of this distributor segment. The mounting segment  140  is then displaced in the circumferential direction in relation to the distributor segments  112  in such a way that the shoulders  158  of the distributor segments penetrate into the groove  150  of the mounting segment, being inserted between the inner peripheral edges of the annular edges  156  of the mounting segment and the inner cylindrical wall  151  of the mounting segment, and that the partition segments  138  are engaged between the annular edges  156  of the mounting segment. This results in a slight axial separation of the annular edges  156 . The mounting segment  140  is displaced by circumferential sliding on the partition segments  138  until its plate  160  bears on one of the distributor segments  112 . These operations are repeated for each mounting segment (in the number of six in the example described) then all of the distributor segments whereon are fastened the mounting segments are arranged flat and end-to-end in such a way as to form the distributor. A suitable tool is then used to grasp the entire distributor and mount it directly on the casing of the turbine. The aforementioned operations are carried out in the opposite order in order to dismount the distributor, and pour the replacing of the mounting  140  or of a mounting segment according to the invention.