The present invention relates to the field of gas turbine technology. It refers to a blade for a gas turbine and a method for producing such a blade by a casting technique.
Blades of gas turbines, which are fastened either as rotor blades on the rotor or fastened as stator blades on the casing which encloses the rotor, are subjected to impingement by hot gas which comes from the combustor and are exposed to thermal loads in the process. These blades, in the course of improving the thermal efficiency, are increasingly exposed to circumferential flow at still higher turbine inlet temperatures. It is not to be ignored, therefore, that these blades have to be cooled internally and/or externally by a cooling medium, especially cooling air, being introduced preferably via the blade root into the hollow interior of the blade airfoil, cooling the blade internally there via convectively applied cooling methods or selectively by means of impingement cooling, and then being blown out into the hot gas flow, in order to carry out a so-called film cooling there if necessary on the external side of the blade. The cooling medium flows through the interior of the blade mostly in a plurality of cooling passages which are connected in a serpentine-like manner and extend through the blade airfoil in the radial direction.
When producing such a blade by a casting technique, a casting core, which forms and keeps the internal hollow cavity of the blade with the cooling passages free and further details during the casting of the blades, has to be created. For producing the casting core, use is made of a core mold assembled from two halves which during demolding of the finished casting core are drawn apart in a specified direction (see U.S. Pat. No. 5,716,192, for example). Contingent upon the direction in which the two mold halves have to be drawn apart, limitations ensue in the design of the casting core and therefore in the design of the cavity of the subsequent blade. These limitations play a role particularly in the case of complex shapes of the cavity, as are described in WO-A1-03/042503, for example. In order to create the cavity of the blade there, which cavity consists of various cooling circuits and a multiplicity of pins and turbulators, a plurality of casting cores are produced and combined with each other, which leads to a very costly production process.
In a first aspect, the present disclosure is directed to a blade for a gas turbine. The blade includes a leading edge and a trailing edge, and an interior cavity, which is delimited by internal surfaces, for guiding cooling air therethrough. To improve the transfer of heat between the wall of the blade and the cooling air, a multiplicity of members, which are formed on the wall to improve cooling. The members are arranged in a distributed manner in the region of the trailing edge and project from the internal surfaces into the cavity. The members extend into the cavity in a direction which can be freely selected within an angular range.
In a second aspect, the present disclosure is directed to method for producing the above blade. The method includes, in a first step, providing a core mold for forming a casting core which keeps the cavity of the blade free. The method also includes, in a second step, producing the casting core by means of the core mold, in a third step, removing the casting core from the core mold and, in a fourth step, casting the blade by the casting core. The core mold which is provided in the first step comprises two mold halves, which during demolding are drawn apart in a first direction. At least one mold insert, which is provided for forming the members, is arranged in the mold halves in the trailing edge region. In the third step, after the parting of the mold halves in the first direction, the at least one mold insert is withdrawn from the formed casting core in a second direction which differs from the first direction.
The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawing. All elements which are not essential for the direct understanding of the invention have been omitted. Like elements are provided with the same designations in the various figures. In the drawings:
The invention should provide a remedy here. It is therefore an object of the invention to propose a blade which is improved with regard to internal cooling, overcoming certain limitations created by the casting core, and which at the same time can be produced with little additional cost. It is furthermore an object of the invention to disclose a method for producing such a blade.
The object is achieved by means of the entirety of the features of the independent claims. It is a feature of the invention that the turbulators or pins which are formed on the wall in the region of the trailing edge for improving the heat transfer between the wall of the blade and the cooling air extend into the cavity in a direction which can be freely selected within an angular range.
With regard to the cooling, it is particularly advantageous if, according to one development of the invention, the turbulators or pins extend into the cavity in a direction which is essentially perpendicular to the associated internal surface.
The method according to the invention for producing the blade by a casting technique, in which, in a first step, a core mold is provided for forming a casting core which keeps the cavity of the blade free, in a second step, the casting core is produced by means of the core mold, in a third step, the casting core is removed from the core mold, and in a fourth step, the blade is cast by means of the casting core. The core mold, which is provided in the first step, comprises two mold halves which during demolding are drawn apart in a first direction, wherein at least one mold insert, which is provided for forming the turbulators or pins, is arranged in the mold halves in the trailing edge region, and in the third step, after the parting of the mold halves in the first direction, the at least one mold insert is withdrawn from the formed casting core in a second direction which differs from the first direction.
In one development of the method according to the invention, the second direction is perpendicular to the internal surface which is associated with the turbulators or pins.
According to another development of the method, a plurality of mold inserts are arranged in the mold halves and during demolding of the formed casting core are withdrawn in different directions which differ from the first direction.
For forming the cavity 16 and the details and elements which are arranged therein, a casting core 21 (
According to the invention, additional elements 18 in the cavity, which can be formed as (round) pins or (rib-like) turbulators and improve the transfer of heat between the cooling air which flows in the cavity 16 and the wall 15, are now arranged or formed in the trailing edge region of the blade 10. The direction in which the elements 18 project from the wall 15 into the cavity 16 should now be able to be selected within an angular range independently of the demolding direction of
In order to be able to realize the elements 18 from
In order to be able to create such differently oriented elements 18 in a simple manner and without the risk of damage within the production process for the casting core 21, however, according to
During the production of the casting core 21 with a core mold configuration according to
Number | Date | Country | Kind |
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00898/08 | Jun 2008 | CH | national |
This application is a divisional of U.S. application Ser. No. 12/961.659, filed on Dec. 7, 2010, which is a continuation of Int. App. No. PCT/EP2009/056150, filed on May 20, 2009, which claims priority to Swiss App. No. 00898/08, filed on Jun. 12, 2008 the entire contents of which are incorporated by reference herein.
Number | Date | Country | |
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Parent | 12961659 | Dec 2010 | US |
Child | 14075555 | US |
Number | Date | Country | |
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Parent | PCT/EP2009/056150 | May 2009 | US |
Child | 12961659 | US |