Abstract:
A core die is provided. The core die includes a first half and a second half where a cavity is formed between the two. Pins are arranged on the halves and the pins are replaceable. By virtue of the modular inner structure of a core die, the core die may be matched to the desired changes of the core, by small changes, more quickly and more easily than would be the case if the core die had only one part or if the pins were a fixed component of the core die halves.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 01018784.0 EP filed Oct. 18, 2010, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to a core die with replaceable pins and to a process for producing a core. 
       BACKGROUND OF INVENTION 
       [0003]    When producing a ceramic casting mold, use is made of core dies for the production of a ceramic core which emboss the core on certain inner structures, e.g. a continuous connection of outer walls or two inner walls. 
         [0004]    These inner struts also represent a flow resistance and, in the case of hollow components which are produced by means of such a core, also influence the flow of the cooling air and the transfer of heat into the cooling air. 
         [0005]    When producing a core for a turbine blade or vane, a plurality of development iterations are often needed so as to produce the core in such a manner that it corresponds to the required tolerances (e.g. the mass flow of cooling air). To date, this has been done either by reworking the core die completely and therefore expensively, or by producing a new and more expensive core die in each case. This is expensive and complex at the same time. 
       SUMMARY OF INVENTION 
       [0006]    It is therefore an object of the invention to solve the aforementioned problem. 
         [0007]    The object is achieved by a core die as claimed in the claims and by a process as claimed in claims. 
         [0008]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to obtain further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIGS. 1 ,  2  schematically show a core die, 
           [0010]      FIG. 3  shows a gas turbine, 
           [0011]      FIG. 4  shows a turbine blade or vane, 
           [0012]      FIG. 5  shows a list of superalloys. 
       
    
    
       [0013]    The figures and the exemplary embodiment represent only exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0014]      FIG. 1  schematically shows a core die  1 . 
         [0015]    The core die  1  has at least two halves, here an upper half  3  and a lower half  4 , between which a cavity  2  is formed. 
         [0016]    Pins  5  are present between the halves  3 ,  4  of the core die  1  and here are preferably formed in two parts as pin parts  8 ,  11 . 
         [0017]    However, they can also be formed as single-part pins  9  ( FIG. 2 ). 
         [0018]    The core die halves  3 ,  4  have protuberances  13 ,  13 ′, to which the upper pin part  8  and the lower pin part  11  or the pin  9  ( FIG. 2 ) are preferably fastened. This can be effected by mechanical interlocking, soldering or welding. The pin parts  8 ,  11  are arranged directly opposite in pairs and preferably make contact with one another. 
         [0019]    The same fastening is employed for the single-part pin  9  ( FIG. 2 ). 
         [0020]    The shape and size of these pins  8  ( FIG. 1 ),  9  ( FIG. 2 ) here also determine the flow of a cooling medium (the mass flow of cooling air) through a hollow cast turbine component, in particular through a turbine blade or vane  120 ,  130  ( FIG. 4 ) as an example for a cast component, which is preferably produced from nickel-based or cobalt-based superalloys, very preferably from an alloy shown in  FIG. 5 . 
         [0021]    To produce a core for a casting mold, a ceramic material in the form of a viscous mass or another material is pressed into the cavity  2  around the pins  5  ( FIG. 1 ),  9  ( FIG. 2 ), and the core thereby provided is later fired to sinter the ceramic particles and used to represent cooling channels during casting of the hollow cast turbine component  120 ,  130 . 
         [0022]    If it becomes apparent that the flow of the cooling medium through the cast component cast around the core does not correspond to the technical specifications (e.g. it is excessive or other geometrical deviations arise), the pins  5 ,  8  ( FIG. 1 ),  9  ( FIG. 2 ) are replaced by other pins with a different shape and/or size. The pins  5 ,  9  can similarly be changed if other specifications are not met. 
         [0023]    In this case, the lower pin part  11  ( FIG. 1 ) and the upper pin part  8  ( FIG. 1 ) or the entire pin  9  ( FIG. 2 ) are detached from the core die halves  3 ,  4 , in particular from the protuberances  13 ,  13 ′, and pins with a modified cross section, in particular with a smaller cross section if the flow is too small or with a larger cross section if the flow is too great, are applied. 
         [0024]    The core die halves  3 ,  4  can thus be reused, with the replaceable pin parts  8 ,  11  ( FIGS. 1) and 9  ( FIG. 2 ) being produced quickly, easily and inexpensively. 
         [0025]    Then, a new core is produced in turn with a changed core die with a changed diameter of the pins  5 ,  8 ,  11  ( FIG. 1 ),  9  ( FIG. 2 ), such that a new cast component with this core, which is used for casting, then corresponds to the specification, or if appropriate the pins  5 ,  8 ,  11 ,  9  are changed once again in a further iteration, until the desired tolerance is achieved. 
         [0026]    The advantage consists in the fact that the required process development iterations for matching the requested mass flow of cooling air can be carried out by a very small and easily executable change in the core die by means of the replaceable pins  5 ,  8 ,  11 ,  9 . 
         [0027]    At the end of the iteration(s), the result is a core die which is suitable for series production and allows the cast components which meet the desired specifications to be cast. 
         [0028]    Furthermore, during production the pins can be replaced quickly, easily and inexpensively in the case of wear by a ceramic mass. 
         [0029]      FIG. 3  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0030]    In the interior, the gas turbine  100  has a rotor  103  with a shaft  101  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0031]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
         [0032]    The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  form the turbine  108 . 
         [0033]    Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  formed from rotor blades  120 . 
         [0034]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by means of a turbine disk  133 . 
         [0035]    A generator (not shown) is coupled to the rotor  103 . 
         [0036]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
         [0037]    While the gas turbine  100  is operating, the components which are exposed to the hot working medium  113  are subject to thermal stresses. The guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. 
         [0038]    To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant. 
         [0039]    Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0040]    By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . 
         [0041]    Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0042]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon, scandium (Sc) and/or at least one rare earth element, or hafnium). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0043]    It is also possible for a thermal barrier coating to be present on the MCrAlX, consisting for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0044]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0045]    The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor  103  and is fixed to a securing ring  140  of the stator  143 . 
         [0046]      FIG. 4  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0047]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0048]    The blade or vane  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade or vane platform  403  and a main blade or vane part  406  and a blade or vane tip  415 . 
         [0049]    As a guide vane  130 , the vane  130  may have a further platfoi (not shown) at its vane tip  415 . 
         [0050]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
         [0051]    The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0052]    The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
         [0053]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
         [0054]    Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0055]    The blade or vane  120 ,  130  may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0056]    Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. 
         [0057]    Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. 
         [0058]    In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component. 
         [0059]    Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). 
         [0060]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0061]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0062]    The density is preferably 95% of the theoretical density. 
         [0063]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0064]    The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0065]    It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0066]    The thermal barrier coating covers the entire MCrAlX layer. 
         [0067]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0068]    Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0069]    Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
         [0070]    The blade or vane  120 ,  130  may be hollow or solid in form. If the blade or vane  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines).