TECHNICAL FIELD

The present invention relates to a gas turbine combustion chamber with reversible fastening device for thermoinsulating tiles.

BACKGROUND ART

As known, inspection, maintenance or repair operations involving bodies connected to each other by means of threaded coupling may have critical aspects under specific conditions, especially when the space available for operators is narrow. For example, if the screw breaks, often extracting the stump is difficult or even impossible and requires a hole to be made and new thread to restore the nut screw.

A case in which problems are particularly frequent associated with a threaded element breaking and being replaced is the one of gas turbine combustion chambers in energy production power plants.

A combustion chamber generally comprises a casing, for example toroidal or cylindrical in shape, covered internally by thermoinsulating tiles. The tiles are normally connected to the wall of the casing with screw fastening devices. The nut screw is carried out in a through hole directly in the wall of the casing and the screw is inserted (or extracted for disassembly) from the inside .

Although the screws are made of special alloys that are resistant to hot temperatures, over time they become fragile due to exposure to repeated thermal cycles involving considerable temperature variations. The screws may therefore break with given easiness when the tiles are to be removed due to regular maintenance or for replacing a damaged element.

In case of breaking, the broken part of the leg remains inside its seat in the casing of the combustion chamber. Often, this possibility forces the broken part to be removed by means of drilling and successive new thread and/or replacing any heli-coils present. The operations to be carried out are delicate, complex and in any event invasive and may cause further damage to the casing of the combustion chamber also when performed by highly qualified personnel.

Furthermore, even if the operations are carried out workmanlike and without inducing further damage, the fact is to be considered that often the dimensions of combustion chambers allow a single operator alone to operate from the inside. Restoration operations are therefore particularly lengthy, in addition to being laborious.

Screws breaking, which is a relatively frequent phenomenon during the disassembly of the tiles, therefore has a negative impact on the duration of the maintenance intervention times and requires prolonged machine downtimes, with a significant increase in costs.

DISCLOSURE OF INVENTION

It is therefore the object of the present invention to provide a gas turbine combustion chamber that allows the limitations described to be overcome.

According to the present invention, a gas turbine combustion chamber is provided as defined in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention shall now be described with reference to the accompanying drawings, which illustrate several non-limiting embodiment examples thereof, in which:

- figure 1 is a cross section of a combustion chamber of a gas turbine;

- figure 2 is a side view of a reversible fastening device in accordance with one embodiment of the present invention;

- figure 3 is a plan view from above of the reversible fastening device in figure 2;

- figure 4 is an exploded front view of the reversible fastening device in figure 2, sectioned along the path plane IV- IV in figure 3;

- figure 5 is an exploded side view of the reversible fastening device in figure 2, sectioned along the path plane V-V in figure 3 in a first configuration;

- figure 6 is a plan view from above, with parts removed for clarity, of the reversible fastening device in figure 2 ;

- figure 7 is a side view of the reversible fastening device in figure 2, sectioned along the path plane V-V in figure 3 in a second configuration;

- figure 8 is a plan view from above of a reversible fastening device in accordance with a different embodiment of the present invention;

- figure 9 is a front view of the reversible fastening device in figure 8, sectioned along the path plane IX-IX in figure 8;

- figure 10 is a side view of the reversible fastening device in figure 8, sectioned along the path plane X-X in figure 8;

- figure 11 is a plan view from above, with parts removed for clarity, of the reversible fastening device in figure 8; and

figure 12 is a perspective view of a fastening device in accordance with a further embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described below with particular reference to fastening the thermoinsulating tiles to the inner wall of the casing of a combustion chamber of a gas turbine. However, the invention may also be advantageously applied in other backgrounds, in particular when there is a need to connect two bodies to each other with a threaded coupling that is easy to restore when broken.

With reference to figure 1, a combustion chamber 1 of a gas turbine (not wholly shown) comprises a toroidal casing 2 extending about an axis A and having a first radially outer shell 3 defined by a doughnut-shaped wall, and a second radially inner shell 4 defined by a substantially truncated cone-shaped wall. The combustion chamber 1 is provided with a thermoinsulating covering which covers inner faces 3a, 4a of the first shell 3 and of the second shell 4, respectively, and comprises a plurality of thermoinsulating tiles 7. In one embodiment, the thermoinsulating tiles 7 are arranged in adjacent groups along circumferences about axis A of the combustion chamber 1.

The thermoinsulating tiles 7 are mounted on circumferential guides (not shown) by means of connecting elements 8. The connecting elements 8 are shaped so as to couple to retaining portions of respective thermoinsulating tiles 7 and are connected to casing 2 by means of fastening devices 10 through respective through holes 11 obtained in the first shell 3 and in the second shell 4 (see also figure 2) .

With reference to figures 3 to 7, the fastening device

10 in one embodiment of the invention comprises a bushing 12 and a supporting body 13. Bushing 12 is threaded internally and externally and is removably coupled to the supporting body 13. In one embodiment, the coupling between bushing 12 and the supporting body 13 is a bayonet connection .

In particular, the inner thread 12a (figures 4, 5 and 7) allows a screw 30 (figure 2) to be introduced to lock a respective thermoinsulating tile 7.

The outer thread 12b (figures 4, 5, and 7) is opposite to the inner thread 12a and allows the coupling of bushing 12 with an extraction tool 35 with corresponding thread (shown in figure 7, e.g. in the shape of a socket spanner) .

In detail (figures 4 and 5) , bushing 12 extends along an axis B, is substantially cylindrical in shape and is provided at one end with locking tabs 14 which radially extend with respect to axis B. In one embodiment, the locking tabs 14 are substantially circular or elliptical in shape .

The supporting body 13 is substantially cup-shaped and comprises an annular member 15 and a cover 16 defining together a locking seat 18 shaped to receive and axially lock bushing 12.

The annular member 15 extends about an axis, which coincides with axis B when the bushing is coupled to the supporting body 13. An edge 15a of the annular member 15 is intended in use to be coupled to an outer face 3b of the first shell 3 or to an outer face 4b of the second shell 4 of casing 2. The annular member 15 further comprises an inner baffle 20 which extends perpendicular to axis B and has an opening 21 for access to the locking seat 18. The profile of opening 21 is complementary to the profile of the end of bushing 12, to allow the insertion and extraction in axial direction.

The inner baffle 20 delimits the locking seat 18 on one side and in particular has recesses 22 which define a locking position for bushing 12. In greater detail, the recesses 22 have a complementary profile with respect to the locking tabs 14, so that the rotation of bushing 12 is prevented once the bushing is put in traction by means of a screw, as explained later.

In one embodiment, cover 16 is arranged to close the annular member 15 and has a cavity which delimits the locking seat 18 one an opposite side to the side delimited by the inner baffle 20 of the annular member 15. As shown in figure 6, the portion of the locking seat 18 which is inside cover 16 has just as many lobes 18a as there are locking tabs 14 of bushing 12. The lobes 18a are shaped so as to allow a rotation of bushing 12 inside the locking seat 18 between an insertion and extraction position, in which the locking tabs 14 are aligned with opening 21 and the bushing is axially sliding, and a locking position (indicated with a broken line in figure 6), in which the locking tabs 14 are retained in a dead portion of the locking seat 18 and prevent the extraction of bushing 12. The locking position corresponds to the position in which the recesses 22 are arranged of the inner baffle 20 of the annular member 15. In one embodiment, the lobes 18a are shaped so as to prevent rotations of bushing 12 past the insertion and extraction position and the locking position. Furthermore, the portions of the locking seat 18 corresponding to the locking position are delimited by the inner baffle 20, by cover 16 and by the walls of the lobes 18a, and are dead. Furthermore, the dead portion of each lobe 18a is arranged so as to promote the insertion and extraction of bushing 12. In other words, bushing 12 is internally threaded (inner thread 12a, figures 4, 5 and 7) so that screwing a screw 30 (figure 2) inside bushing 12 causes bushing 12 to rotate from the insertion and extraction position to the locking position (that is toward the dead portion of each lobe 18a) , and unscrewing screw 30 causes bushing 12 to rotate from the locking position to the insertion and extraction position (that is from the dead portions of the lobes 18a toward the access opening 21 to the locking seat 18) . Vice versa, the outer thread 12b, which is opposite to the inner thread 12a, allows the extraction tool 35 to be tightened on bushing 12 and, by again acting in the tightening direction, a torque to be exerted to rotate bushing 12 from the locking position toward the insertion and extraction position. In particular, once the coupling is tightened on the outer thread 12b, the extraction tool 35 may advantageously be used to force the separation of bushing 12 from the supporting body 13 both in axial direction, and with a rotation toward the insertion and extraction position. The high temperatures in the combustion chamber 1 indeed promote the oxidization of the materials of bushing 12 and of the supporting body 13, which may join together. Separating bushing 12 from the supporting body 13 may be difficult in the absence of a simple and at the same time solid connection between bushing 12 and the extraction tool 35, to the point of making the removal of the parts to be replaced almost impossible.

A hole 25 on the bottom of cover 16 allows the inlet of cooling air from the outside. Furthermore, holes 26 passing through the annular member 15 and cover 16 allow the supporting body 13 to be fastened to casing 2 of the combustion chamber 1 by means of screws 27, as shown in figure 2.

More precisely, the supporting body 13 is fastened to the outer face of the wall that defines one from the first shell 3 and the second shell 4 (for the sake of convenience, reference will be made hereinafter to the first shell 3, shown in figure 2), in position corresponding to one of the through holes 11. In addition to or in replacement of screw fastening the supporting body 13 as shown in figure 2, edge 15a of the annular member 15 may be welded to casing 2 of the combustion chamber 1.

Practically, the supporting body 13 may be arranged so that bushing 12 is accessible from the side of the fastening surface (that is of the inner surface of casing 2) opposite to the side where the locking seat 18 is. Furthermore, the releasable coupling between bushing 12 and the supporting body 13 allows bushing 12 to be quickly and simply replaced when required, for example when screw 30 breaks .

Bushing 12 may be easily introduced into the locking seat 18 in insertion and extraction position. As a result of how the inner thread of bushing 12 is made, tightening screw 30 tends to bring bushing 12 toward the locking position, thus avoiding accidental release. As a further tightening effect of screw 30 and of the action of the body that is fastened against the inner surface of casing 2 (that is of one of the connecting elements 8, in the embodiment described) , bushing 12 is put in traction and the locking tabs 14 are received in the recesses 22 of the inner baffle 20, thus preventing further rotations.

When screw 30 is unscrewed, the locking tabs 14 are no longer tightened in the recesses 22 and bushing 12 may rotate toward the insertion and extraction position. Bushing 12 is equally free to rotate when screw 30 breaks.

At this point, the bushing may be easily extracted and replaced.

The operation for restoring an unserviceable threaded seat is therefore highly simplified due to the fastening device 10, and does not require any radical interventions (drilling and new thread) on the wall. In the case of combustion chambers, restoring the original conditions by replacing bushing 12 may be easily done by a single operator and also when little space is available.

Furthermore, the supporting body is advantageously outside casing 2 of the combustion chamber 1 and therefore is exposed to moderate thermal stresses.

Figures 8 to 11 show a different embodiment of the invention. In this case, the fastening device 100 comprises a bushing 112 and a supporting body 113.

Bushing 112 is threaded internally and externally and is removably bayonet-connected to the supporting body 113. Bushing 112 extends along an axis B' , is substantially cylindrical in shape and is provided at one end with locking tabs 114 which radially extend with respect to axis B' . An inner thread 112a of bushing 112 is opposite to an outer thread 112b.

The supporting body 113 is cup-shaped and defines a locking seat 118 adapted to receive bushing 112.

The locking seat 118 is delimited on one side by a bottom wall of the supporting body 113 and, on the opposite side, by a plate, in particular a disk 116 accommodated in the supporting body 113. In greater detail, the supporting body 113 has an inner annual projection on which disk 116 rests, so as to remain separate from the bottom wall of the supporting body 113. Radial pins 116a accommodated in seats 119 of the supporting body 113 prevent the rotation of disk 116. Disk 116 has an opening 121 which conforms with the profile of the end of bushing 112 provided with tabs 114, to allow access to the locking seat 118.

As shown in figure 9, the portion of the locking seat 118 defined in the bottom wall of the supporting body 113 has just as many lobes 118a as there are locking tabs 114 of bushing 112. The lobes 118a are shaped so as to allow a rotation of bushing 112 inside the locking seat 118 between an insertion and extraction position, in which the locking tabs 114 are aligned with opening 121 and the bushing is axially sliding, and a locking position, in which the locking tabs 114 are retained in a dead portion of the locking seat 118 and prevent the extraction of bushing 112.

A pack of Belleville washers 130 is accommodated in the cavity of the supporting body 113, about bushing 112, in abutment against disk 116. The Belleville washers 130 allow the tension to be decreased on the fastening screw 130 and the thermal expansions of the combustion chamber to be compensated.

Through holes 126 allow the supporting body 113 to be fastened to casing 2 of the combustion chamber 1 by means of screws 127.

In one embodiment, shown in figure 12, a bushing 212 provided with locking tabs 214 stands out from bushing 12 in figures 2-7 for having longitudinal guides 212a on the outer surface (for example, two diametrically opposing), in place of the outer thread. The longitudinal guides 212a may be defined by respective grooves which extend from an edge of bushing 212 opposite to the locking tabs 214 toward the latter, and allow the sliding coupling with respective inner teeth 235a of an extraction tool 235 (e.g. in the shape of a socket spanner) . In one embodiment, the longitudinal guides 212a have respective retaining seats 212b of sufficient axial dimension to receive a respective tooth 235a of the extraction tool 235. The retaining seats 212b extend laterally to the longitudinal guides 212a and the teeth 235a may be introduced by means of rotation, after the extraction tool 235 has been inserted up to the end of the longitudinal guides 212a. Furthermore, the retaining seats 212b are shaped so that once engaged, the axial sliding of the teeth 235a is prevented, to allow traction to be exerted on bushing 212. Advantageously, the retaining seats 212b are arranged with respect to the longitudinal guides 212a so as to be engaged by the teeth 235a when the extraction tool 235 is rotated to bring bushing 212 from the locking position to the insertion and extraction position.

Finally, it is apparent that modifications and variants may be made to the combustion chamber herein described without departing from the scope of the present invention, as defined in the appended claims.

For example, locking the bushing inside the seat could be done with other means than those described. In particular, different locking members could be used in place of the tabs described, such as pins or flange portions. Furthermore, the locking members could differ in number, e.g. three or four. In this case, the locking seat may advantageously comprise just as many lobes, each of which allows and limits the rotation of the bushing to an arc defined between the insertion and extraction position and the locking position.