Turbine blade with inclined blade airfoil and method for manufacturing same

Abstract

The invention relates to a turbine blade (1), which has a blade root (14), an adjoining neck (24), an adjoining blade platform (27), and a blade airfoil (30), wherein: the blade root has depressions (21, 22) between projections (11, 12, 13), which blade root has a cooling air inlet channel (54) in the interior, which cooling air inlet channel extends in the radial direction in the region of the blade root (14) the the respective distances between the maxima of two opposite projections (11, 12, 13) of the blade root (14); and the cooling air inlet channel (54) are of different lengths, the distance being as follows: a perpendicular at the maximum of the respective two opposite projections (11, 12, 13) intersects an inner boundary (46) of the cooling air inlet channel (54), and the distance (51, 52) results from said intersection point up to the maximum of the respective projection (11, 12, 13).

Description

TURBINE BLADE WITH INCLINED BLADE AIRFOIL AND METHOD FOR MANUFACTURING SAMEThe invention relates to a turbine blade with an inclined blade airfoil, to a method for manufacturing, and to a rotor.Due to requirements of the operators of power plants, inter alia, turbine blades and guide vanes are constantly being modernized and adapted to new operating conditions. While it is easier to modify some design features such as coating thickness and / or material, cooling patterns, fillet radius, etc., there are some parts and / or features whose modification would require more extensive redesigns. Typical examples of this are blade hooks and blade roots. Here, there are interfaces to other turbine design features, such as turbine blade carriers or rotor construction. Modifications to these parts require modifications to the adjacent turbine components that are not to be replaced.This is expensive and time-consuming.A blade root in the form of a fir tree root is known from EP 3 059 394 B1. The latter has a plurality of projections and depressions.There are also turbine feet with only one projection: DE 197 05 323 A1.The projections can also be designed to be hammer-shaped, as known from EP 2 918 783 A1.It is therefore an object of the invention to solve the above-stated problem.The object is achieved by a turbine blade as claimed in claim 2, by a method as claimed in claim 1, and by a rotor as claimed in claim 7.The dependent claims set forth further advantageous measures which can be combined with one another as desired in order to achieve further advantages.In the figures:figure 1 shows a blade according to the prior art,figure 2, 3 show a blade according to the invention,figure 4 shows a rotor according to the invention.The description and the figures represent only exemplary embodiments of the invention.It has been found that the creep life responds very sensitively to the thermal and mechanical load. The mechanical load is caused by the centrifugal forces. Moreover, gas pressure and temperature stress have an effect on the creep life.Therefore, the blade airfoil should be balanced in order to avoid additional force components that influence the creep life.The displacement and tilting of the turbine blade can take place during the machining process.Otherwise, this would mean high costs to perform the modification during the casting process if an existing casting tool is to be used.Figure 1 schematically illustrates a turbine blade 1‘ according to the prior art.The turbine blade 1‘ has a blade root 4‘ which presently comprises in particular a so-called fir tree root 14‘.A neck 24 adjoins the fir tree root 14‘.Formed on the end of the neck 24 is a blade platform 27 from which a blade airfoil 30 extends.The blade root 4‘, or the fir tree root 14‘, has, in particular, a plurality of projections 11‘, 12‘, 13‘ on both sides, between which corresponding depressions 21‘, 22‘ are formed on both sides in each case.The shape of the fir tree root 14‘ (hammer head) as well as the number of projections (only one) and accordingly the number of recesses (none) can vary.The blade root 4‘ furthermore has a distal end 7‘.An old axis of symmetry 33 is defined as a line of symmetry with respect to the blade root 14‘.Often, the distal end 7‘ of the blade root 4‘ is at least partially flat, such that the axis of symmetry 33 is also perpendicular to the flat distal end 7‘.After casting, the blade root 4‘ deliberately has an oversize which has to be machined.In the process, the old axis of symmetry 33 is to be inclined according to the invention.Typically, ceramic or removable cores are used in the casting of cooled or hollow turbine blades. The core exit is important to define the form of the blade airfoil as delivered. The core exit is located in the region of the blade root, the latter being exposed to very high centrifugal forces. During casting, this core outlet is the location of the fixed core bearing in order to prevent a large core displacement. Any large core displacement in the blade root region has an effect on the wall thicknesses, which would have a negative effect on the service life of the blade root.In order to avoid wall thickness deviations in the blade root region, the tilt center should be located very close to the most highly stressed region with the smallest wall thickness.With this type of definition of the tilt point, the blade root stresses are not negatively influenced, in particular not in the thinnest region at the lowermost peak of the blade root.Since the blade root 4‘ has an oversize, it can be machined in such a way that the axis of symmetry 33 according to the prior art (fig. 1) is inclined by an angle 42 of 1.2°-1.8°, in particular 1.5°, and a new line of symmetry 40 forms the axis of symmetry of the machined fir tree root 14‘, that is to say of the fir tree root 14 (fig. 2).Preferably, the tilt point 44 or common point of the old axis of symmetry 33 and of the new axis of symmetry 40 lies at the level of the lowermost depression 21, that is to say preferably at the level of the shortest spacing from opposite depressions 21 of the fir tree root 14, as viewed in the radial direction of the turbine blade 1, as illustrated in figure 2, or at the level of the lowermost depression or the single peak.As a result of this machining, spacings 51, 52 of the projections 11 (left and right) or the spacings of the projections 12 (left and right) from a cooling air inlet duct 54 are of different lengths (fig. 3).The cooling air inlet duct 54 ran parallel to the old axis of symmetry 33. The spacings 51, 52 are determined in such a way that a perpendicular runs on the maximum of a projection 11, 12, here only projections 12 shown as an example, and the respective length between the maximum of the respective projection 12 and the boundary 46 of the cooling air inlet duct 54 is the spacing 51, 52.Instead of a boundary 46, the old line of symmetry can also be used.Correspondingly, the other spacing is determined on the other side of the same projection 12, wherein - as can be seen in figure 3 - the two perpendiculars or straight lines do not extend parallel to one another.The spacing 52 is 4% to 15%, in particular 4% to 10%, longer than the spacing 51.The relative difference of such spacings would correspondingly also result for the other projections 11, 13.This then also has the consequence that, in the installed state of such turbine blades 1, for a rotor 100, there is a shoulder 53 between two adjacent blade platforms 27. This is shown in figure 4.In figure 4, two directly adjacent turbine blades 1 are installed schematically by way of their schematically illustrated blade roots 4 in a disk 90, conjointly forming the rotor 100.To be seen is a shoulder 53 between two blade platforms 27 adjacent in the circumferential direction 91, which shoulder is not provided by a general tolerance of machined turbine blades which are installed conjointly.AdvantagesLower operating risk of blades stressed at creep speed.Possibility of a minor modification of machining for retrofitted motors if the creep life is critical.No change of casting tool.Controlled balancing of cooled blades if the displacement between blade airfoil and blade root is not possible.The approach can be used for future compressor blades when they are cooled.The warm-up play of the blade changes as a result of the change in the boundary conditions and as a result of the imbalance situation of the blade, which has an effect on the frictional behavior of the blade.The frictional behavior of the blade is improved.The disk load is positively influenced by this balancing method.

Claims

 1. A methodfor machining a turbine blade (1‘)which has a blade root (14‘),wherein the blade root (14‘) has depressions (21‘, 22‘) between projections (11‘, 12‘, 13‘),an adjacent neck (24),an adjacent blade platform (27),and an adjoining blade airfoil (30),wherein the blade root (14‘) has an oversizewhich has to be machined for the installation of a turbine blade (1),wherein an old axis of symmetry (33) is established inthat the latter represents a line of symmetry of the blade root (14‘) in the non-machined state,wherein the machining takes place in such a way thata new axis of symmetry (40),which represents a line of symmetry of the fir tree root (14) in the machined state,is tilted in relation to the axis of symmetry (33) of the non-machined blade root (4‘)between 1.2° and 1.8°,wherein a tilt point (44) of the new axis of symmetry (40) in relation to the old axis of symmetry (33) lies in the lower region of the turbine root (14),in particular lies at the level of the lowermost depressions (21) of the two lowermost teeth (11, 12).  2. A turbine blade (1),which has a blade root (14),wherein the blade root (14) has depressions (21, 22) between projections (11, 12, 13),which has, in the interior, a cooling air inlet duct (54) that runs in the radial direction in the region of the blade root (14),wherein the respective spacings between the maxima of two opposite projections (11, 12, 13) of the turbine root (14) and the cooling air inlet duct (54) differ from 4% to 15%,in particular from 4% to 10%,wherein the spacing is defined as follows:a perpendicular in the maximum of the respective two opposite projections (11, 12, 13) intersects an inner boundary (46) of the cooling air inlet duct (54), andthe spacing (51, 52) results from this intersection point up to the maximum of the respective projection (11, 12, 13)and hasan adjacent neck (24),an adjacent blade platform (27),and an adjoining blade airfoil (30).  3. The method or the turbine blade as claimed in claim 1 or 2, having only one projection.  4. The method or the turbine blade as claimed in claim 1 or 2, having a plurality of projections (11, 12, 13).  5. The method or the turbine blade as claimed in claim 1, 2, 3 or 4,having a fir tree root as the blade root.  6. The method or the turbine blade as claimed in claim 1, 2, 3 or 4,having a hammer head root as the blade root.  7. A rotor (100),having a disk (90) in which the turbine blades (1) as claimed in one or more of claims 1 to 6 are installed,wherein a shoulder (53) is present in the circumferential direction (91) between two blade platforms (27) directly adjoining one another,which shoulder manifestly exceeds the usual machining tolerances. 

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