WO2012172099A1

WO2012172099A1 - Cast turbine blade

Info

Publication number: WO2012172099A1
Application number: PCT/EP2012/061535
Authority: WO
Inventors: Lars Engl; Thomas Duda; Brian Kenneth Wardle
Original assignee: Alstom Technology Ltd.; Brandl, Herbert
Priority date: 2011-06-17
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: CH705187A1

Abstract

A cast turbine blade is described, with a blade leaf which is defined by a pressure-side blade leaf wall and a suction-side blade leaf wall that are connected to one another at least along a leading edge of the blade leaf assignable to the turbine blade and define at least one cavity that, as a result of the blade being manufactured by casting, is open in the tip region of the turbine blade. A method for producing a cast turbine blade is also described. The invention is distinguished in that, in the region of the turbine blade tip, at least one blade leaf wall has a structure that faces the cavity and that locally increases a blade leaf wall thickness assignable to the blade leaf wall.

Description

Cast turbine blade

Technical area

The invention relates to a cast turbine blade, with an airfoil, which is bounded by a pressure and suction side airfoil wall, which are at least along one of the turbine blade assignable blade leading edge connected to each other and limit at least one cavity on both sides, which opens open in the region of the turbine blade tip due to casting production , Furthermore, the invention relates to a casting method for producing a related turbine blade in which a casting core is used to form a cavity within the turbine blade, which projects beyond the shape of the turbine blade in the direction of the turbine blade tip and in which after cooling and separation of the turbine blade from the casting core Turbine blade is obtained.

State of the art

Turbine blades, which are designed both as running and as vanes, which are used in modern, efficient gas or steam turbine plants, are produced by means of a casting process using so-called casting cores, which during the casting process as shaping placeholder for within the forming turbine blade serve cavities located. Such casting cores, which generally consist of ceramic materials, have to be positioned exactly within the casting mold during the entire casting process in order to take into account the requirements of high dimensional accuracy for the formation of turbine blade walls of the smallest possible thickness. In particular, the production of high-performance turbine blades for use in gas turbine stages, in which the blades are exposed to very high thermal and mechanical loads, requires a maximum of precise casting core position. nierung within the mold, especially since the airfoil wall thickness for purposes of active cooling may be only a few millimeters thick.

The attachment of the casting core within the mold requires, at least in a few places Fixierverstrebungen between the casting core and the mold, through which, however, the forming turbine blade giesstechnisch-related openings learns that it must be partially or completely closed during reworking.

In WO 00/19065 A1 a gas turbine blade is described, the blade tip is frontally limited by a cover plate also produced in the casting process, are introduced in the casting manufacturing through openings for purposes of fixing the casting core. Furthermore, cylindrical bearing pins are inserted into one or more of these casting-related through openings in this turbine blade, which is also referred to as being closed-cast, and whose foot regions projecting beyond the opposite side of the cover plate are each tied up.

Another possibility for fixing the casting core within a casting mold for producing a turbine blade, in particular a turbine blade, consists in the technical production of a turbine blade with an open blade tip. The blade tip area of a turbine blade configured in this way, here set forth as a turbine blade, is shown schematically in FIG. The blade tip is bounded laterally by a pressure-side blade blade wall 1 and a suction side airfoil wall 2. Both blade walls 1, 2 are integrally connected via the blade leading edge 3 and the blade trailing edge 4 and define innwandig a cavity 5, which in the illustrated embodiment by three partitions 6, ^' ^"is divided. the intermediate walls 6, 6, ^6' and ^6" 6 respectively connect the inner wall on the pressure and suction blade leaf wall 1, 2 and divide the cavity 5 in each case separated by a coolant can flow cooling channel sections. Due to the open design of the blade tip, the casting core required for producing the turbine blade (not shown) can protrude beyond the blade tip and be fixed correspondingly relative to the casting mold for carrying out the casting process. Compared to the casting technology of a casting turbine closed turbine blade, the casting process costs considerably simplified. Nevertheless, a post-processing step is required in order to close the open blade tip structure by means of a suitably designed cover plate, in order ultimately to prevent or at least reduce coolant loss through the open blade tip structure. For fitting and connecting a cover plate to the open-form turbine blade tip, a cover sheet fitted to the inner contour of the cavity delimited by the blade walls is usually used and welded or soldered to the inner walls of the blade walls. In order to ensure a sufficiently stable joining connection between the cover sheet and the inner sides of the blade walls in the blade tip area, it is necessary, inter alia, to form the inner wall contours stepped in the blade tip area so that the cover plate comes to rest on a shoulder surrounding the inner wall side of the blade leaf walls , Also, for reasons of improved brushing of the blade tips on stationary turbine components as well as for a controlled cooling air outlet, the cover plate is lowered relative to the end face end turbine blade walls. In the figurative sense, this consideration applies, at best with certain restrictions, also for turbine vanes.

In this context, reference is made to FIGS. 3 a, b, which show a cross section through the sectional axis AA of the turbine blade in the blade tip region which can be seen in FIG. FIG. 3a shows the blade tip region immediately after completion of the casting process. In this case, the pressure-side blade-blade wall 1 and the suction-side blade-blade wall 2 bound the cavity 5 enclosed by the turbine blade on both sides, which is divided into individual partial volumes by an inner connecting wall 6 ^' . In the manufacturing step illustrated in FIG. 3a, the blade-blade walls 1, 2 each have a thickness a in the blade-blade tip area. In order to seal the open design of the blade tip by means of a suitably designed cover plate 7, the inner sides the airfoil walls 1, 2 made thinner by means of a material removal to form a support surface 8. Such a cross-sectional profile is illustrated in FIG. 3b. Both the pressure-side and suction-side airfoil wall 1, 2 now each have a vane wall thickness b on the front side, which is reduced by the wall dimension c relative to the original wall thickness a. The supporting surface 8 resulting from the material removal process, for example by way of a milling, grinding or abrasive process, measures a shoulder width c which is dimensioned sufficiently large in order, in conjunction with a welding or soldering connection, to securely seat the cover plate 7 within the blade tip. For carrying out the material removal explained above for producing a support surface 8, two conditions must be met. On the one hand, it is the paragraph width c greater than or equal to a minimum required paragraph width c _me , to choose that it is important not to fall short to ensure sufficient robustness for the joint connection. On the other hand, it is not the wall thickness b to reduce below a critical Mindestwanddickenmass b _mi n, especially when falling below the critical wall thickness b _me , the structurally given

Shovel stability can no longer be guaranteed.

For the choice of wall thickness of the pressure and suction side airfoil walls in the turbine blade tip area to be produced by means of the casting process, it is necessary to make the wall thickness a at least large enough to meet the following requirement: a> b _me , + c _min . The above requirement is readily met for turbine blades with thicker blade wall thickness.

However, high-performance gas turbine blades must be designed for the most efficient possible cooling, which requires the most thin-walled design of the airfoil walls, in order to avoid large temperature differences between the hot air exposed blade airfoil outer sides and the Kühlmittelbeaufschlagten airfoil inner sides. On the other hand, if large temperature differences occur between the two blade surfaces, this leads to high thermal stresses and, as a result, to a short service life of the individual turbine blades. Therefore, it is a stated design goal in the design of high performance turbine blades to make the airfoil walls as thin as possible embody. However, this leads to a conflict in connection with the above-described requirements for a robust implementation and connection of a cover plate to a turbine blade openly formed in the blade tip region. Due to the cooling-related optimization of a thin-walled turbine blade, neither the requirement b> bmin nor c> c _me can be met.

Presentation of the invention

The invention is based on the object, a cast turbine blade, which may in principle be both a blade and a vane, with an airfoil, which is bounded by a pressure and suction side airfoil wall, which are at least along one of the turbine blade assignable blade leading edge connected together and define at least one cavity on both sides with one another, which opens openly in the region of the turbine blade tip in such a way that a secure and robust joint between turbine blade tip and a cover plate is possible despite reduced blade leaf wall thickness, without the minimum requirements with respect to a minimum width c _m in for Supporting surface and the airfoil wall thickness bmin to fall below.

If, in the following, a turbine blade is mentioned, then both a blade and also a guide blade are to be subsumed, regardless of whether such guide blades reach the same scope of application as the blade.

Furthermore, it is necessary to provide a method with which the production of a turbine blade explained above is possible.

The solution of the problem underlying the invention is specified in claim 1. The subject matter of claim 9 is a method according to the invention for producing a turbine blade of this type. The inventive concept in advantageous Pursuant to forming features are the subject of the dependent claims and the description in particular with reference to the illustrated embodiments.

According to the solution, a cast turbine blade with the features of the preamble of claim 1 is characterized in that at least one airfoil wall in the area of the turbine blade tip has a locally increasing structure facing the cavity, which can be assigned to an airfoil wall thickness.

The solution-cast cast turbine blade initially represents a semi-finished product, in which the condition is created that despite reduced airfoil wall thickness in the vast airfoil area, the upwardly open turbine blade tip can be safely and reliably equipped with a cover plate. The solution according to the invention provided on the turbine blade tip the blade wall thickness locally increasing structure has a blade wall thickness in the region of the turbine blade tip, which is greater than the minimum required blade wall thickness b _m in plus the minimum width c _m in, which provides a stable support of the cavity closing cover plate , In a particularly advantageous manner, the airfoil wall in the turbine blade tip region is formed completely circumferentially with an enlarged wall thickness relative to the remaining airfoil wall, ie both the suction and pressure side airfoil walls and also the areas of the airfoil leading and trailing edges have wall thickenings in the region of the turbine blade tip. However, in the simplest case, the solution according to the measure can also be provided only locally limited to a blade wall.

The structure according to the invention, which locally increases the blade wall thickness, in the blade tip region is preferably designed such that the cavity bounded on both sides by the pressure and suction sides has a contour narrowing in the direction of the turbine blade tip. Also limits a corresponding bottle neck-like contour both the inside in the turbine blade cavity also on the sides of the Schaufelvorder- and trailing edge.

As part of a reworking by means of controlled material removal at the turbine blade tip end-ended, the blade airfoil thickness locally locally increasing structure is partially removed to form a support surface, which is preferably oriented flat and orthogonal to the airfoil wall. The material removal process is preferably carried out by means of erosion technology.

The removal of material takes place in the direction of the blade airfoil extension in a uniform measure, so that the support surface forming by the material removal on the airfoil inner walls spans a storage plane on which the cover plate can be brought to rest.

The cover plate is supported laterally on the support surfaces worked out by the material removal process, and preferably also, if present, on the end faces of the turbine blade tip in the direction of the turbine blade tip of the intermediate walls provided in the interior of the turbine blade. As already mentioned above, for the realization of the solution according to the invention, it is not absolutely necessary to provide the abovementioned support surface in a completely circumferential manner inside the turbine blade.

For a durable, durable attachment of the cover plate in the turbine blade tip region, the cover plate lying on the support surface described above is connected to the turbine blade inner wall newly formed by the material removal in the turbine blade tip region by means of soldering or welding connection.

The manufacturing method underlying the solution-cast cast turbine blade is based on the use of a casting core to form at least one cavity within the turbine blade, which projects beyond the shape of the turbine blade in the direction of the turbine blade tip and obtained after cooling and separation of the turbine blade from the casting core a turbine blade is, which has an airfoil, which is bounded by a pressure and suction side airfoil, the at least longest one of the turbine blade assignable blade leading edge are interconnected and the at least one cavity bound each other on both sides, the open ends in the region of the turbine blade tip due to casting production , Such a turbine blade is in comparison to the turbine blade tip region largely closed formed turbine blades with a lower procedural effort and thus conditionally cheaper to produce. In order on the one hand to meet the requirements for a turbine blade blade wall to be formed as thinly as possible, but in addition to meet the existing high structural rigidity requirements, the turbine blade according to the solution is cast with at least one airfoil wall, which provides a structure in the region of the turbine blade tip which forms one of the airfoil wall at the turbine blade tip having an assignable blade wall thickness that is greater than an airfoil wall thickness in an airfoil wall area spaced from the turbine blade tip. Such a cast turbine blade, which is in the form of a semi-finished product, is reworked after cooling and separation from the casting core in such a way that the structure locally enlarging the airfoil wall thickness is partly removed from the side of the turbine blade tip. The material removal process takes place innwandig on the turbine blade tip thereby, so that a step structure is formed with a flat and orthogonal to the blade wall wall oriented surface portion, which is surmounted by the thickness-reduced blade wall in the direction of the turbine blade tip. The forming surface portion serves as a support surface for the support of a cover that covers the at least one cavity within the turbine blade at least partially in the direction of the turbine blade tip or seals accordingly. For this purpose, the cover with appropriate soldering and welding technology with the cover element surrounding the circular airfoil inner wall is preferably completely encircling.

Brief description of the invention The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawing. Show it:

1 a - e sequence diagram representation for illustrating the production of a turbine blade according to the invention,

2 is a perspective view of an open turbine blade tip according to the prior art,

3a, b are longitudinal sectional views of a turbine blade tip according to

State of the art as well

Fig. 4 is a longitudinal sectional view through a turbine blade tip with

Blade trailing edge.

Ways to carry out the invention, industrial usability

FIGS. 1 a - e correspond to sectional images through a turbine blade tip along one of the sectional planes AA indicated in FIG. FIG. 1 a illustrates the embodiment of a turbine blade with an open turbine blade tip in the manner of a known casting method. To form the inner cavity 5 located between the blade blade walls 1, 2, a casting core 9 is introduced during the casting process, the consistent position of which is effected throughout the casting process by appropriate fixation within the casting mold (not shown) in the region of the core region 9 ^' protruding beyond the turbine blade tip , According to the situation illustrated in FIG. 1 a, the casting core 9 is formed with a constant thickness, so that during the casting process the blade-blade walls 1, 2 result with a blade-face wall a that is also constant.

In order to avoid the problems arising in particular in the production of state-of-the-art turbine blades, which has already been explained above with reference to FIGS. 3 a, b, it is proposed according to the solution to use a casting core 10 during the casting process which can be seen from the illustration. 1 b can be seen according to FIG. The novel casting core 10 has a bottle-neck-like taper in the region of the turbine blade tip, as a result of which the blade blade walls 1, 2 each receive a structure 1 1 locally enlarging the blade blade wall thickness a during the casting process in the area of the turbine blade tip. The structural wall thickness a 'of the structure 1 1 locally increasing the airfoil wall thickness is larger than the airfoil wall a, which otherwise has the airfoil blade spaced from the turbine blade airfoil tip.

In particular, for the choice of the increased structural wall thickness a ^' : a ^' >a> b _m in +

Cmin

In the sequence image representation according to FIG. 1 c, the casting core 10 is removed from the cooled turbine blade whose blade blade walls 1, 2 delimit a bottle neck-like cavity 5 in the turbine blade tip region.

By means of a material removal process, the structures 1 1 locally enlarging the blade wall thickness are removed in the manner illustrated in FIG. 1 d. Here, on the one hand, the wall thickness of the airfoil wall in the turbine blade tip region is thinned out so that the airfoil wall formed there does not fall below a minimum wall thickness of b _m in which satisfies the structural strength requirements for the operation of a turbine blade. In addition, by means of the material removal process within a measured by the turbine blade tip t removal depth t a support surface 8 whose minimum extent orthogonal to the airfoil wall 1, 2 c _m in corresponds, in which a firm joining a cover with the support surface is ensured.

In FIG. 1 e, a cover plate 7 is applied to the support surfaces 8, which are located inwardly between two blade walls 1, 2, whereby the cavity 5 flushed with cooling air is covered in the direction of the turbine blade tip. The cover plate 7 is typically soldered or welded to the inner wall portions of the blade blades 1, 2, respectively. The cover plate 7 can Purpose of a targeted coolant discharge from the cavity 5 may be provided with a correspondingly sized opening 7 ^' or more openings.

FIG. 4 shows a longitudinal section through a turbine blade in the region of the turbine blade tip along a section BB, which can be seen from FIG. The illustrated in Figure 4 embodiment illustrates the provision of the blade wall thickness locally increasing structure 1 1 also innately along the turbine blade trailing edge 4, so that the not illustrated in Figure 4 cover plate 7 is also stably supported on sides of the trailing edge. The structure which preferably extends completely along the inner wall contour of the blade tip and enlarges the blade wall thickness forms a cover plane E which is uniform for the cover plate and which preferably coincides with the end faces 6s of any partition walls 6 provided in the interior of the turbine blade. In this way, the cover plate 7 stores not only on the lateral support surfaces 8, but is also supported by the inner partitions 6 frontally.

LIST OF REFERENCE NUMBERS

1 pressure side airfoil wall

2 suction side airfoil wall

3 blade leading edge

4 blade trailing edge

5 cavity

6, 6 ', 6 "internal partitions

6s front of the partition

7 cover plate

8 support surface

9 casting core

9 'End side over the open end of the turbine blade protruding casting core

10 casting core

1 1 the blade blade wall thickness locally increasing structure

E support plane for the cover plate

Claims

claims

1 . Turbine blade, which is produced by a casting process, with a

An airfoil, which is delimited by a pressure and suction side airfoil wall (1, 2), which are at least along one of the turbine blade assignable blade leading edge (3) connected to each other and at least one cavity (5) bound each other on both sides, the casting in the region of the turbine blade tip due to open opens, characterized in that at least one airfoil wall in the region of the turbine blade tip has a cavity (5) facing, one of the airfoil wall wettable airfoil wall thickness locally locally increasing structure (1 1).

2. Turbine blade according to claim 1, characterized in that the turbine blade is a blade or a vane.

3. turbine blade according to claims 1 and 2, characterized in that the blade blade wall thickness locally locally increasing structure (1 1) facing the turbine blade tip flat and orthogonal to the blade wall wall oriented surface portion (8).

4. turbine blade according to one of claims 1 to 3, characterized in that the blade blade wall thickness locally locally increasing structure (1 1) facing away from the turbine blade tip, the cavity (5) in the direction of the turbine blade tip on one side bottle neck narrowing contour.

5. turbine blade according to one of claims 1 to 4, characterized in that the airfoil wall overhanging the airfoil wall thickness locally locally increasing structure (1 1) in the direction of the turbine blade tip, and that the airfoil wall ends on one end side of the turbine blade tip.

6. turbine blade according to one of claims 1 to 5, characterized in that the blade blade wall thickness locally increasing structure (1 1) is made in one piece with the blade wall during a casting process.

7. turbine blade according to one of claims 1 to 6, characterized in that the pressure and suction side airfoil wall (1, 2) have a common cross-sectional plane in which the space bounded by two blade walls cavity (5) due to the provision of each one of the airfoil wall thickness locally enlarging structure (1 1) on both the pressure and on the suction side airfoil wall (1, 2) is locally bottle-like tapered.

8. turbine blade according to claim 7, characterized in that the blade blade wall thickness locally locally increasing structure (1 1) both on the pressure and suction side airfoil wall (1, 2) each have a planar and orthogonal to the respective airfoil wall oriented surface portion (8) both lying in a common plane (E).

9. turbine blade according to one of claims 1 to 8, characterized in that the at least one blade wall thickness locally enlarging structure (1 1) with at least one cavity (5) at least partially in the direction of the turbine blade tip covering cover element (7) is joined ,

10. turbine blade according to 8 and 9, characterized in that the at least one cover member (7) respectively to the surface portion (8) of the blade blade wall thickness locally locally increasing structure (1 1) of the pressure and suction side airfoil wall (1, 2) to form a Welding or solder joint is joined.

1 1. Method for producing a turbine blade by means of a casting process, in which a cavity (5) is formed inside the turbine shell schaufei a casting core (10) is used, which projects beyond the shape of the turbine blade in the direction of the turbine blade tip and in which after cooling and separation of the turbine blade from the casting core (1 0) is obtained a turbine blade having an airfoil, which of a pressure and Suction-side airfoil wall (1, 2) is limited, which are at least along one of the turbine blade assignable blade leading edge (3) connected to each other and the at least one cavity (5) bound each other on both sides, which open in the region of the turbine blade tip casting production, characterized in that at least one airfoil wall (1, 2) is cast in the turbine blade tip region having a structure (11) having a blade wall thickness assignable to the airfoil wall at the turbine blade tip that is greater than a blade wall thickness in a blade wall region spaced from the turbine blade tip, and by means of a material removal method on the cooled turbine blade separated from the casting core (10) from the side of the turbine blade tip, the structure locally enlarging the blade blade wall thickness is partly removed.

12. The method of claim 1 1, characterized in that the removal of material takes place such that spaced from the turbine blade tip a flat and orthogonal to the blade wall (1, 2) oriented surface portion (8) is generated by the airfoil wall (1, 2) in Towards the turbine blade tip is projected.

13. The method of claim 1 1 or 12, characterized in that on the partially ablated structure (1 1) a cover (7) is joined, by which the at least one cavity (5) at least partially covered or sealed in the direction of the turbine blade tip becomes.

14. The method according to any one of claims 1 1 to 13, characterized in that the removal of material takes place such that the airfoil wall, which extends over the structure (1 1) in the direction of the turbine blade tip has at least one blade wall thickness having a minimum wall thickness (b _me ,) does not fall below, which satisfies the structural strength requirements that can be detected on the turbine blade.

15. The method according to any one of claims 12 to 14, characterized in that the removal of material takes place in such a way that the planar and orthogonal oriented to the airfoil wall surface portion (8) at least a minimum extension (c _me ,) orthogonal to the airfoil wall provides that a firm joining a cover element (7) ensures with the joining surface.