Casing ring

A jacket ring for the low-pressure-turbine region of a gas turbine, having a plurality of lined-up segments which are arranged between a moving blade ring with a shroud band and the casing of the gas turbine, which carry a run-in lining and which hold guide blades in a positive-locking manner, wherein each segment comprises a hot-gas-side seal carrier and a casing-side securing element, the seal carrier and the securing element are at the greatest possible distance from one another and only have common contact points which are as small as possible, and the securing element is axially supported directly on the casing of the gas turbine.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a jacket ring for the axial-flow low-pressure-turbine region and/or power-turbine.

In low-pressure turbines and power turbines of gas turbines for aircraft, land vehicles and watercraft and also for stationary use, segmented jacket rings (Outer Air Seals, OAS) are arranged above the moving blades and have the following tasks:screening of the casing of the gas turbine from the high gas temperatures,providing a run-in lining for the sealing tips at the moving-blade shroud band, andoften also securing the upstream guide-blade stage in the casing by positive locking.

According to the prior art, at least the last two tasks are assumed by one component, i.e. by the respective jacket ring segment. To fulfill the first task, it is often necessary to arrange additional heat insulation material between the jacket ring and the gas turbine casing enclosing said jacket ring from outside, which increases the costs, the weight and the effort involved during assembly.

Due to the high heat transfer from the run-in lining, usually a honeycomb structure, into the jacket ring segments, which of course also fulfill the guide-blade securing function, the segments become very hot with the following adverse effects:heating of the guide-blade fastening elements on the casing and of the casing itself by direct, heat-conducting contact,drop in the strength and in the wear resistance of the heated parts,dimensional changes and relative movements in the region in which the guide blades are secured, and thus wear and the requirement for large clearances particularly in the axial direction.

The combination of the two last-mentioned effects has in some cases led to the guide-blade securing function failing as a result of plastic deformations and thus to one or more guide blades being released during operation, thus resulting in considerable damage to or destruction of the turbine region affected.

Such a conventional design of the jacket rings has been disclosed, for example, by DE-C-27 45 130. Here, the jacket rings are designated by “covers (10)” or by “jacket ring covers (10)” and the run-in linings by “sealing surfaces (11)”. The casing (13) of the gas turbine has fastening elements (cylinders14) which carry both the guide blades (1) and the jacket rings (covers10). The radially outer, upstream ends of the guide blades (1) enclose widened portions (beads22) of the fastening elements in a claw-like manner, and the downstream ends of the jacket rings do this in the same way. The radially outer, downstream ends of the guide blades (1) bear radially from inside against the fastening elements (cylinders14) and are secured in a positive-locking manner by the claw-like, upstream ends of the jacket rings. Due to the construction, therefore, the thermal and mechanical problems already described exist here too.

Against this background, an object of the invention is to design a segmented jacket ring having a sealing carrier function and a guide-blade securing function in such a way that, by thermal relief of the guide-blade fastening points and of the turbine casing, the mechanical loading capacity is increased and thus wear and plastic deformations are greatly reduced or avoided. At the same time, in particular the guide-blade securing function is to be fulfilled with the greatest reliability.

This object is achieved by a plurality of segments which are lined up in the circumferential direction and are arranged radially outside a moving blade ring with a shroud band and inside the casing of the gas turbine, which carry a run-in lining for at least one sealing tip of the shroud band and which hold guide blades in a positive-locking manner at their radially outer downstream end, said guide blades being arranged upstream of the moving blade ring. Each segment (2) comprises a hot-gas-side seal carrier (3), provided with the run-in lining (6), and a casing-side securing element (7) supporting at least one upstream guide blade (15) and extending axially to an extent comparable with the seal carrier (3), in that the seal carrier (3) and the securing element (7) are at a distance from one another over regions of their surfaces which are as large as possible and only have common, heat-conducting contact points (Cl, C2) which are as small as possible, and in that the securing element (7) is axially supported directly on the casing (17) of the gas turbine via a stop part (10).

According to the invention, the seal carrier function on the one hand and the guide-blade securing function on the other hand are in each case fulfilled by a separate component, so that each segment of the jacket ring comprises a seal carrier and a securing element. The seal carrier and the securing element touch one another, but are not firmly connected to one another. The seal carrier and the securing element are designed in relation to one another in such a way that they are at a distance from one another over regions of their surfaces which are as large as possible and only have common, heat-conducting contact points which are as small as possible. The seal carrier more or less absorbs the local temperature of the hot gas during operation, whereas the securing element remains at a markedly lower temperature due to the screening effect of the seal carrier with minimized heat conduction. As a result, the casing-side guide-blade fastening elements also remain markedly cooler during operation and can be loaded mechanically to a considerably higher degree. The temperature reduction continues right into the turbine casing, in the course of which the screening effect of the shell-like securing element also comes to bear. Additional heat-insulation measures or materials are thus as a rule no longer necessary. Owing to the fact that the securing element is axially supported directly on the casing, the guide-blade securing function continues to be reliably fulfilled within the entire operating range irrespective of thermal expansions of the following guide blades.

DETAILED DESCRIPTION OF THE DRAWINGS

The turbine region which can be seen from the FIGURE is the low-pressure-turbine region or power-turbine region, the latter in the case of a shaft-power gas turbine. In the case of triple-shaft powerplants, this region could also be the intermediate-pressure turbine region. Here, the direction of flow is to run from left to right, the casing-side passage boundary rising in a divergent manner from the bottom left to the top right. The longitudinal center axis/rotation axis of the gas turbine would run horizontally and below the region of the FIGURE; the hub region likewise lies too deep in order to be covered by the illustration.

The moving blade ring11to be sealed has a shroud band12with two sealing tips13,14, which interact with a run-in lining6, here stepped in diameter, of honeycomb structure. Guide blades15,16can be seen upstream and downstream of the moving blade ring11and are arranged statically in the casing17of the turbine as individual parts or as segments composed of a plurality of blades. The radially outer, downstream end of the guide blade15—or of the guide blade segment—lies in a slot18which is open radially inward and runs all round the casing17. The radially outer, upstream end of the guide blade16—or of the guide blade segment—engages in a slot19which is open axially toward the rear and runs all round the casing17. The guide blade15also has a comparable, upstream suspension (on the left outside the illustration). It can be imagined that the guide blade15, without further securing measures in the casing, and in the hub region, could escape from the slot18by radial movement inward in a pivoting manner about its upstream suspension (see region around item19). This is where the retaining and securing function of the jacket ring1comes in, which ring extends axially from the guide blade15up to the guide blade16and in the circumferential direction round the casing17. The prior art is to design jacket rings in a segmented manner; however, a special feature of the present invention is to subdivide the segments2into further components having defined functions. Here, a seal carrier3is arranged on the hot-gas side and holds the run-in lining6as part of the Outer Air Seal (OAS). There is a securing element7here on the casing side, this securing element7, in its primary function, securing the guide blade15so as to prevent it from escaping from the slot18. Here, the seal carrier3, in addition to the run-in lining6, comprises a shell-like carrier part4and a stop part5which is hook-like in axial section. Since a plurality of such seal carriers3are positioned adjacent to one another over the turbine circumference, there may be additional sealing elements, such as tongues, straps, etc., on these seal carriers3. However, these are not shown. The seal carrier3is movable axially within certain limits, the foremost position with effective stop part5being shown here. Since the inner contours of the run-in lining6which are effective from the sealing point of view are in each case cylindrical and sufficiently long axially, the axial position is not critical. The securing element7comprises a securing part8, which is C-shaped in axial section and engages under the slot18containing the guide blade end, a shell-like screening part9and stop part10which is hook-like in axial section. The elements3and7, which are at the greatest possible distance from one another, have defined contact points C1, C2, the extent of which is minimized with regard to low heat conduction, e.g. by periodic interruptions in the circumferential direction, but which are necessary for the mutual support. It would be conceivable to apply local ceramic coatings at C1and C2in order to reduce wear and heat conduction further. The securing element7acts thermally as an additional radiation shield between the hot seal carrier3and the casing17. As a result, additional thermal insulating materials may be dispensed with in this region. It can also be seen that the hot carrier part4, according to the invention, does not bear directly against the fastening elements of the casing17in the region of the slots18and19. These mechanically critical regions are therefore likewise thermally relieved. In this connection, it is possible, for thermal reasons, to produce only the part4from a cobalt alloy; the parts5,6,8,9and10may be made of nickel alloys, which are more favorable from the point of view of production and wear, or even of steels. Brazing is exclusively envisaged for fixed connections within the parts3and7using suitable high-temperature brazing filler metals. However, the seal carrier3and/or the securing element7may also be produced in each case integrally as a turned part from a forged ring or as a casting. On account of the segmented type of construction of the jacket ring1, the parts3and7themselves constitute segments, which are in each case lined up in a relatively large number over the casing circumference. In this case, it may be appropriate to offset the joint gaps of the parts7in the circumferential direction relative to those of the parts3.

The invention does not presuppose that a guide blade ring follows downstream of the jacket ring, as illustrated in the FIGURE. A casing liner, for example, may also form the constructional and fluidic continuation of the jacket ring with supporting and stop function for the latter.