EP3362648B1 - Method for producing a base part of a turbine blade - Google Patents

Description

The invention relates to a method for producing a base body of a turbine blade, comprising at least the successive steps, providing the base body, which successively comprises a blade root, a blade platform and an airfoil along a virtual longitudinal axis, detecting a value of a parameter of the base body representing a vibration characteristic Comparing the detected value with a predetermined target interval and if the detected value is outside the target interval, reducing the mass of the main body. Furthermore, the invention relates to a blade ring for a rotor of an axial flow turbine.

It is known to provide turbine blades with a protective layer so that they have an increased lifetime when operating in a gas turbine. As a protective layer, a MCrAlY type anticorrosion layer is often applied to the turbine blade produced by a casting process. The application of the protective layer takes place in the region of that surface which is exposed during operation to the hot gas of the gas turbine. This area includes both the airfoil and the platform of the turbine blade on which the airfoil forms. In addition to the anticorrosion layer, a heat-insulating layer can also be applied in the abovementioned area in order to minimize the heat input from the hot gas into the base material of the turbine blade. The application of the layers thereby alters the vibration behavior of the turbine blade.

Furthermore, it is known that turbine blades are exposed to vibrational excitation during operation of the gas turbine. The vibration excitation occurs due to the rotation of the rotor to which the turbine blades are attached. Another contribution to the vibration excitation experienced by the blades of the turbine blades through the impinging hot gas. Since the blades of the turbine blades - seen in the flow direction of the hot gas - rotate behind a ring of turbine vanes, they are excited by cyclically impinging hot gas to vibrate. Therefore, it is necessary that each turbine blade has a sufficiently high natural frequency, so that both the rotor speed and the hot gas originating vibration excitation with the respective excitation frequencies does not lead to an unduly high vibration of the airfoil. Accordingly, in the prior art, the turbine blades are designed such that their natural frequency deviates from the excitation frequencies of the stationary gas turbine. During the development of the turbine blade, care is also taken to ensure that the finished turbine blade as a whole satisfies the requirements for natural resonance, also with regard to the expected rotor speeds.

In the manufacturing process of the turbine blade is therefore intended to check each turbine blade on their vibration characteristics. In this test, the turbine blade is clamped at the foot and excited by mechanical impulse to vibrate. Then the vibration response of the turbine blade and in particular its blade is detected. If the vibration response of the turbine blade does not meet the predetermined frequency values at natural frequency, this is to be rejected or manipulated by suitable measures such that it meets the requirements of the natural frequency and thus is suitable for operation. To turbine blades, which are not provided solely for use in the gas turbine due to their vibration property, the supply still supply, is for example from the EP 1 985 803 A1 known to introduce a recess in the tip of the airfoil, whereby the mass of the turbine blade at her free, swingable end can be reduced. By reducing the mass of the turbine blade, the vibration characteristic is positively influenced. Its natural frequency can be shifted to higher values by removing the mass.

Besides that is from the EP 0 537 922 A1 known to insert a tubular damper in the blade platform of a turbine blade. This can slightly push out under centrifugal force and thus come to rest on a platform of a neighboring bucket to dampen blade-to-bucket vibrations during operation.

The object of the invention is to provide a method for producing basic bodies of turbine blades, the natural frequencies of which correspond to the requirements for use within a stationary gas turbine. Another object is to provide a blade ring, the blades are particularly robust against induced by the hot gas vibrational excitation.

The object related to the method is achieved by a method according to the features of claim 1, wherein advantageous embodiments are reflected in the subclaims. The related to the blade ring task is solved by the features of claim 6.

The invention is based on the recognition that the introduction of the recesses for setting the natural frequency need not be made solely on the blade. In particular, the measure for influencing the vibration properties of the turbine blades or of their cast base body can also take place on the blade root or on the so-called platform underside. The platform underside is that side of the platform of a turbine blade or the base body, which faces the hot gas side of the platform and thus faces the blade root. As measures, the introduction of recesses or the reduction of a Dimension be provided below the setpoint. Of course, both measures could be combined.

The advantages of both measures are that they neither change the structure-mechanical integrity of the airfoil nor worsen their aerodynamics. This makes it possible to achieve the predetermined life and performance of the blade body or the turbine blade ultimately resulting therefrom.

Thus, the invention proposes that the blade root body on the blade root and / or on the underside of the platform has a region whose shape and / or dimensions are selected so that they have no structural mechanical functions. Due to this property and the dimensions originally provided, the base body comprises at least one region which is regarded as a sacrificial region in order to modify the vibration properties of the base body by reducing the mass there, without the functional properties changing as well. To reduce the mass, for example, a recess can be made in a planar side of the blade root. Another example is the reduction in the width of a ridge provided on the platform underside of the turbine bucket.

Preferably, the areas are located where the measures described above can be carried out without significantly deteriorating the structural mechanical integrity of the base body required for the relevant mechanical load occurring during operation. Thus, those moments of inertia and that rigidity of the turbine blade are changed, which in any case does not limit the life of the turbine blade. This leaves the predetermined service life of the turbine blade unaffected.

Preferably, the area in question or lie the respective areas outside of those areas of the body, which are overflowed by a hot gas. Thus, the method can also be applied after the coating of turbine blades with an erosion and / or thermal barrier coating.

Preferably, the method according to the invention is applied in a rather late phase of the manufacturing process of the turbine blades. This means that the base body usually produced in the casting process has already been brought to the specified size before the value of the parameter representing a vibration characteristic is detected. This ensures that the vibration measurement is carried out on the almost finished turbine blade and thus further manufacturing steps, which can also change the vibration characteristics of the main body or the turbine blade, are at least largely avoided.

More preferably, the method can also be carried out before coating the base body, if it can be predicted by what (average) value the detected value of the parameter changes due to the then subsequently applied coating. Then already in an earlier stage of the manufacturing process, the aforementioned measures can be carried out to select those basic body whose vibration characteristics and values could not be transferred into the associated target intervals despite the implementation of the inventive measures. Hereby expenses for waste can be avoided at an early stage.

Conveniently, only some of the turbine blades of a blade ring, or even all made according to the aforementioned method.

In this application, conceptually becomes between a turbine blade and a main body of a turbine blade distinguished. In this case, a turbine blade is understood to mean that which is finished and provided for being able to be attached to a rotor of a turbine without further processing. In contrast, the basic body of a turbine blade is understood to mean a turbine blade blank which is still in the middle of the manufacturing process, at the end of which the finished turbine blade is located. Thus, the invention relates only to some of the manufacturing steps required overall for manufacturing a ready-to-use turbine blade, wherein the method steps mentioned here can also represent the very last production steps for producing the ready-to-use turbine blade.

The invention will be explained with reference to a drawing, wherein identical reference numerals describe the same acting components.

• FIG 1 ein Ablaufdiagramm mit den unterschiedlichen Herstellungsschritten eines erfindungsgemäßen Verfahren zum Herstellen eines Grundkörpers einer Turbinenlaufschaufel,
• FIG 2 ein Ablaufdiagramm mit weiteren Herstellungsschritten und
• FIG 3 eine perspektivische Ansicht auf eine Unterseite eines Grundkörpers einer Turbinenlaufschaufel.

Show it:

• FIG. 1 1 is a flowchart with the different production steps of a method according to the invention for producing a base body of a turbine blade,
• FIG. 2 a flowchart with further manufacturing steps and
• FIG. 3 a perspective view of an underside of a main body of a turbine blade.

The inventive method 10 is in FIG. 1 shown. The method 10 for producing a basic body 30 (FIG. Fig. 3 ) of a turbine blade comprises in a first step 12 the provision of the main body 30 of the turbine blade. The main body 30 comprises along a virtual Longitudinal axis 31 successively a blade root 32, a platform 34 and an airfoil 36th

The contour of the blade root 32 is fir-tree-shaped when viewed perpendicularly on its planar end face 38 and merges via a so-called blade neck 40 into an underside 42 of the platform 34. Opposite the underside 42, the platform has a hot gas side 44, at which the airfoil 36 connects monolithically. This is drop-shaped and aerodynamically curved to form a pressure side 46 and a suction side 48.

The blade root 32 extends over a length L between the two axially opposite planar end faces 38.

In a second production step 14, a size of at least one parameter of the base body 30 is detected, wherein at least one of the parameters represents a vibration property of the base body. Usually, the natural frequencies and the vibration modes are detected by the usual methods.

In a third production step 16, the detected value (s) is compared with an (associated) target interval. If the detected values lie outside the associated target interval, vibration-changing measures are carried out according to the invention on the blade root 32 and / or on the underside 42 of the platform as the fourth production step. These can be the introduction of one or more recesses 50 and / or the reduction of the previous dimensions such as length, width or height of certain features arranged there. For example, the length L of the blade root 32 can be shortened by a few hundredths of a millimeter to a level which is below the otherwise prescribed setpoint for the length L. The reduction of the mass of the main body 30 takes place in the region 49, which were provided in particular for it. This changes the weight and possibly the contact surface of the turbine blade under centrifugal force, which has a favorable effect on the vibration property of the turbine blade.

If in doubt, the second, third and fourth steps 14, 16, 18 are repeatedly executed as a series in order to check the suitability of the main body 30. Only when the investigated turbine blades meet the requirements with regard to the vibration characteristic is it passed on to the further production process.

The base body 30 or the turbine blade may also be one which is or should be provided with a protective layer. The protective layer is preferably a corrosion protection layer of the MCrAlY type. Alternatively, it is also possible to provide a two-layer or multi-layer protective layer comprising, as a bondcoat, a layer of the MCrAlY type on which a ceramic thermal barrier coating (TBC) has been applied further out. By applying the protective layer, in particular a corrosion protection layer, the mass of the base body is further increased. The change in the natural frequency associated with the increase in mass can be compensated for by inserting recesses 50 on the blade root 32 or on the underside of the platform 34. It is provided that so many and such deep recesses are introduced until the turbine blade meets the requirements of the natural frequency. It may be that despite the application of the method according to the invention, the natural frequency can not be strongly influenced enough that it meets the requirements. In this case, the body is not suitable for commercial use.

The coating of the main body 30 can be carried out before the first execution of the second production step 14 or after the last time the fourth production step 18 is carried out.

By means of the end face arranged in the blade root 32 recess 50 is a frequency shift of the natural frequency. The shape of the recesses 50 is arbitrary.

Fig. 2 shows a second flowchart for another embodiment of a manufacturing process. According to the further exemplary embodiment, the manufacturing method comprises the previously mentioned steps 12, 14, 16, 18, supplemented by production steps 13 and 19 to be carried out partially therebetween. On the one hand, the production step 13 in which the main body 30 is made to size as far as possible was supplemented. In other words: in this production step, the dimensions of the main body 30 that are subject to the greasing tolerances are brought to the planned nominal values, which in turn can also be subject to tolerances.

In the manufacturing step 19, a hitherto uncoated base body 30 can be provided with an erosion and / or thermal barrier coating.

Overall, the invention thus proposes a method for producing turbine blades or their basic bodies 30, whose frequency characteristic can be adapted particularly easily to the required boundary conditions. For this purpose, it is provided that the introduction of recesses 50 into the blade root 32 and / or by reducing a dimension below the corresponding desired value, if the base body 30 has insufficient vibration properties. As a result, a method is specified with which the vibration characteristic of the turbine blade can be set particularly easily and variably. This can reduce the reject rate in the manufacture of turbine blades.

Claims (4)

1. Method (10, 20) for producing a base body (30) or a turbine rotor blade (40), comprising at least the successive steps of

   a) providing the base body (30), which comprises, following one another along a longitudinal axis (31), a blade root (32), a blade platform (34) and a blade airfoil (36),

   b) sensing a value of at least one parameter of the base body (30), at least one of the parameters representing a vibrational property of the base body (30),

   c) comparing the sensed value with a predetermined target interval,

   d) if the sensed value lies outside the target interval, reducing the mass of the base body (30),

   characterized
   in that the reduction of the mass takes place at the blade root (32) and/or on the blade platform (34) by introducing at least one recess (50) and/or by reducing a dimension below the corresponding target value.
2. Method (10, 20) according to Claim 1,
   in which the region (49) concerned or the regions (49) concerned lies or lie outside those regions of the base body (30) that can be flowed over by a hot gas.
3. Method (10, 20) according to Claim 1 or 2,
   in which, before carrying out step b), at least most of the dimensions of the base body (30) are brought to their target size.
4. Rotor turbine ring for a rotor of an axially flowed-through turbine,
   with a number of turbine rotor blades, the base bodies (30) of which are produced by a method according to one of Claims 1 to 3.

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