Casting apparatus for manufacturing a turbine blade of a gas turbine and turbine blade
The invention relates to a casting apparatus for producing a turbine blade of a gas turbine according to the preamble of claim 1. Furthermore, the invention relates to a turbine blade according to the preamble of claim 6.
Casting devices, also called casting devices, for producing a turbine blade of a gas turbine are known from the prior art for the longest time. As is known, for example, from US Pat. No. 5,465,780, a casting device comprises a plurality of grape-like mold shells for the simultaneous pouring of a plurality of turbine blades. Each mold shell is hollow, wherein the cavity is the negative mold of the produced
Representing turbine blade. Since turbine blades, in particular the blades of front turbine stages, usually have to be cooled, these are also hollow. During operation, a cooling medium, usually cooling air, can be carried through the cavities of the turbine blade so that the turbine blades have a particularly long service life and do not undergo thermal damage prematurely due to the flow of hot gas past them. The supply of cooling air takes place via arranged in the blade root openings, which are in flow communication with the cavity or the cavities of the rotor blade. For this reason, the mold shell for producing such a turbine blade generally comprises one or more casting cores, which are arranged in the cavity of the casting apparatus.
The casting cores, after their removal in the cast turbine blade, leave the cavities through which the coolant flows during operation of the gas turbine. Furthermore, it is known that the casting device has at least one inlet channel, usually called feeder, through which the casting material can be fed into the cavity of the shell mold during casting of the rotor blade. Consequently, the inlet channel opens with its inlet opening in that surface which limits the cavity of the mold shell.
It has been found in turbine blades, that the walls of the arranged in the blade root portions of the cooling channels in operation tend to cracking and crack growth. These cracks can affect the service life of the turbine bucket and shorten it if necessary.
The object of the invention is therefore to provide a
A turbine blade having an increased life and providing a casting apparatus for making such a turbine blade.
The object directed to the casting apparatus is achieved with a casting apparatus designed according to the features of patent claim 1. The task relating to the turbine blade is achieved with a turbine blade formed according to claim 5.
The invention is based on the finding that crack formation during the solidification of the melt in the walls of the cooling channels in the blade-root-side region of the turbine blade is production-related. In the prior art, turbine blades are poured by standing as standard, with the cavity in the mold shell being formed such that the negative mold of the blade of the turbine blade is formed at the bottom and above that the platform and the blade root. The terms "top" and "bottom" refer to the
Horizontal plane. The feed for the molten casting material is usually also on top, since it has been found to be advantageous that turbine blades are produced in falling casting, in which the location of the last solidification of the casting material is above and thus at the more massive blade root. In known from the prior art casting devices of the inlet channel extends transversely to the longitudinal axis of the turbine blade and thus approximately parallel to the horizontal plane to indicate a low in the casting device. As a result of this transverse feed of the molten casting material, after it leaves the inlet opening, it flows into the cavity of the shell mold and subsequently falls to the bottom of the shell mold, where the negative of the blade tip is formed.
Continued feeding of molten cast material completely fills the cavities for the airfoil, platform, and blade root of the turbine blade with liquid, hot
Casting material on. Since the blade root is usually hammer-shaped or fir tree-symmetrical, and the cooling channels are usually positioned centrally in the blade root, situations always occurred in the conventional casting devices in which the liquid casting material flowing into the cavity of the shell mold impinged transversely on the casting cores positioned in front of the inlet opening , In detail, the molten casting material hit the foot area of the centered casting core. As a result, the casting cores heated more at the point of impact of the hot casting material than in other areas. These hotter core areas are also referred to as hot spots. The other areas of the casting cores, on the other hand, were not so extremely heated up.
During the cooling of the casting material and the consequent solidification occurred in those areas of the casting material, which adjoined the locally hotter areas of the casting cores, a delayed solidification of the casting material, compared with cooler areas of the casting cores. Due to the delayed solidification of the casting material in the corresponding areas, disturbances in the microstructure of the solidified material occurred, which favored crack formation and crack growth during operation. On the basis of this knowledge, the invention proposes that the inflow of hot liquid casting material into the cavity of the shell mold during casting of the turbine blade now has to be such that it does not directly occur on casting cores.
According to the invention, the casting material now flows freely and undisturbed into the cavity and impinges on the shell bottom, which forms the blade tip. Since in most cases the inlet is arranged on the front side in the center of the blade root, it is necessary for the casting cores to be arranged eccentrically with respect to the longitudinal axis of the blade root. This leads to a casting apparatus in which that part of the cavity in which an imaginary extension of the inlet channel protrudes is free of casting cores, at least on the inlet opening side.
With a casting device according to the invention, it is thus avoided that during the filling of the flowing hot casting material into the cavity of the shell mold it occurs transversely on casting cores and hot casting core areas, so-called hot spots, thereby arise. By avoiding hot casting core areas, a locally retarded solidification of the casting material no longer occurs during cooling. The solidification of the casting material is so uniform overall, so that impurities in the structure of the turbine blade material can be avoided. By avoiding the impurities crack formation and
Crack growth in the material of turbine blades, which surrounds the blade root side sections of cooling ducts, effectively avoided during operation. This reduces waste and prolongs the life of turbine blades.
Since the casting cores are generally rod-shaped at least in the section of the blade root, their eccentric placement in the shell mold results in the openings of cooling channels in the blade root of the turbine blade also being arranged eccentrically relative to the generally symmetrical outer contour of the blade root. The symmetry is in this case related to the fir tree-shaped or hammer-shaped contour of the blade root in cross-section.
The surface of the mold shell has a contour for the blade root of the turbine blade which is mirror-inverted along a blade root center. The contour is fir tree-shaped or hammer-shaped. Furthermore, the inlet channel is centered and one of the casting cores is eccentric at least in the region of the inlet opening, both centered on a blade root center, which by definition is located centrally between the lateral corrugated surfaces or contours of the blade root. Due to the eccentric arrangement of the casting cores and the compact blade root to be held, it is necessary that the cross-sectional area of the previous casting core is divided into two casting cores.
By dividing the previous, centrally placed cooling channels in two parallel eccentrically positioned cooling channels required for the cooling air cross-sectional area can be further maintained, however, where the previous
Cross-sectional area then distributed to the respective two cooling channels, which then each have a half of the previous cross-sectional area. Consequently, a prior art cooling channel input is split into two cooling channel inputs in a turbine blade according to the invention.
This has the consequence that in a turbine blade two openings at the bottom, but on both sides of the blade root center are arranged, wherein the openings
Represent supply openings of coolant for the turbine blade. Each aperture thus forms one end of a cooling passage of the turbine blade.
Advantageous embodiments of the casting apparatus and the
Turbine blade are specified in the subclaims. Preferably, the inlet channel opens into that part of the surface of the cavity of the mold shell, which forms the negative of the end face of the blade root of the turbine blade. This makes it possible to form a sufficiently large inlet channel. At the same time, a falling cast of turbine blades with a blade root arranged at the top makes it possible to cast turbine blades, whose largest-volume area, namely the blade root, finally solidifies. Possibly. Shrinkage of the casting material occurring during solidification can be compensated by the inflow of molten casting material from the casting area. In addition, so that a compact casting device can be specified.
Preferably, in a casting apparatus, that part of the cavity in which an imaginary extension of the inlet channel protrudes is completely free of casting cores. Thus, not only zulauföffnungsseitig the cavity of the shell mold is free of casting cores, but also that portion of the cavity free of casting cores, which is opposite to the inlet opening.
Depending on the configuration of the turbine blade of the casting apparatus and the process parameters set during the casting of the turbine blade, it is sufficient that not all casting cores are arranged eccentrically, but only those which are arranged particularly close to the inlet opening. In other words, the casting cores furthest away from the inlet opening, the sections of which are arranged in the rotor blade area of the turbine blade, can also lie in the imaginary extension of the inlet channel in the event that the casting material flowing into the cavity does not reach them.
The further explanation of the invention will now be described with reference to the embodiment shown in the drawing. Advantageous embodiments result from the advantageous combination of features of the devices described below. Show it:
1 shows a perspective view of a casting apparatus with therein according to the invention arranged casting cores and
2 shows a perspective view of a turbine blade according to the invention for a gas turbine.
1 shows a perspective, schematic representation of part of a casting apparatus 10 for producing a turbine blade of a gas turbine. The casting apparatus 10 comprises at least one mold shell 12 with a cavity 14.
The cavity 14 is bounded by a surface 16, which is the negative mold of the turbine blade to be produced. In the cavity 14 a total of six casting cores 18 are arranged. The casting cores 18 are always arranged in pairs. In total there are three pairs of cores.
Of course, a larger or a smaller number of casting core (pair) s in the shell 12 may be present. Furthermore, an inlet channel 20 is provided in the mold shell 12 for the filling of the liquid casting material. Its inlet opening 22 opens in the surface 16, which limits the cavity 14. The cavity 14 is formed in the mold shell 12 such that the negative mold of the airfoil tip of the turbine blade is located at the bottom. The overlying portion of the surface forms the negative of the airfoil blade. Again, above that, the part of the surface is contoured so that the negative mold of the platform of the turbine blade is formed. Following this, and thus arranged at the top opposite the horizontal plane, the remaining part of the surface 16 forms the contour of the blade root.
The inlet channel 20 opens with its inlet opening 22 in that part of the surface which predetermines an end face of the blade root. The inlet channel 20 has a straight longitudinal extension immediately upstream of the inlet opening 22 in the illustrated casting device. The longitudinal extent of the inlet channel 20 extends approximately parallel or slightly inclined relative to the horizontal plane.
The casting cores 18 are not completely shown in FIG. In FIG. 1, only those sections of the casting cores 18 are shown which are arranged in the uppermost part of the cavity 14, which predetermines the negative shape of the blade root. The shape, contour and type of the casting cores 18 in the platform-side region or in the blade-side region is not of further interest to the invention and can therefore be arbitrarily, for example meander-shaped, rectilinear or even slightly curved. The respective cooling channels can also be partially recombined.
Each casting pair of cores 18 are spaced from one another. The existing between them distance A is so large that hot, liquid casting material when filling the cavity 14 does not strike the casting cores 18 directly. As it were, the hot casting material fed into the cavity 14 flows between two directly adjacent casting cores 18. So it should be avoided as possible the contact between inflowing liquid casting material and Gusskernoberfläche in the foot area. As a result, casting core areas are avoided with locally elevated temperature. The locally increased core temperature was the cause of prior art cracking phenomena on the walls of cooling passages of turbine blades.
The imaginary extension of the longitudinal extent of the inlet channel 20 thus extends into the free area between the two casting cores 18 of a casting core pair. According to the embodiment of FIG 1, the imaginary extension of the inlet channel is completely free of casting cores 18. Alternatively, it is possible that only that part of the imaginary extension is free of casting cores 18, which is formed zulauföffnungsseitig. With reference to the embodiment in FIG. 1, this means that, for example, the casting core pair shown on the left or the casting core pair shown on the left can each also be replaced by a single casting core, whose sections arranged in the blade root are in the imaginary extension of FIG
Inlet channel 20 are positioned. However, this presupposes that the range of the inflowing hot cast material is not so far that the inflow jet can hit it.
FIG. 2 shows, in a perspective view, a turbine blade 30, which was produced by the casting device according to FIG. The turbine blade 30 has a blade root 32 contoured in the manner of a fir tree in longitudinal section, on which a platform 34 is arranged. The platform 34 is adjoined by an aerodynamically curved airfoil 36 which terminates at a freestanding airfoil tip 38. The turbine blade 30 thus extends along a longitudinal axis 40 from the blade root 32 to
Blade tip 38 out. The longitudinal axis 40 is arranged such that it runs centrally or symmetrically to the contour of the fir tree-shaped blade root 32. The blade root 32 has on its side facing away from the blade 36, transversely to the longitudinal axis 40 extending surface, also called bottom 42, a plurality of openings 44, which remain when the casting cores 18 have been removed from the cast turbine blade 30. The openings 44 are arranged on both sides of the blade root center, which is defined in cross-section by the longitudinal axis 40 and also lies centrally between the lateral, corrugated surfaces of the blade root. They lie in two rows, each with three openings 44. The openings 44 serve to introduce a coolant into the interior of the turbine blade 30.
Each opening 44 forms one end of a cooling channel of the turbine blade 30. Its course in the interior of the turbine blade 30 is of no importance to the invention.
By the invention, a non-uniform local overheating of the casting cores 18 in the vicinity of the inlet during filling of the cavity 14 is prevented. At the same time, a better filling can take place since casting cores 18 no longer block the inlet opening 22. A collision of inflowing hot casting material with casting cores 18 is prevented by the use of the invention. In addition, the solidification can be further improved by the unobstructed flow of hot casting material (food) from the feeds, which reduces remaining residual stress or residual stress and avoids the formation of cracks.
In summary, the invention relates to a casting apparatus 10 for producing a turbine blade 30 of a gas turbine, in which the shell mold 12, its inlet and the casting cores 18 disposed therein are aligned with each other such that a casting material flowing into the cavity 14 of the shell mold 12 does not impinge on casting cores 18 directly. This makes so-called hotter areas
(Hot spots) avoided on casting cores 18, which have so far adversely affected the solidification of the cast material. In particular in the area of the blade root 32 of the turbine blade 30 to be produced, improved solidification of the cast material can thus be achieved, which reduces interference in the structure of the solidified cast material. Due to the reduction or avoidance of the disturbances cracking and crack growth in the area of the blade root side cooling channel sections is avoided, which increases the life of the turbine blade 30.