Patent Application
20200269365
Priority is claimed to German Patent Application No. DE 10 2019 202 673.7, filed on Feb. 27, 2019, the entire disclosure of which is hereby incorporated by reference herein.
The present invention relates to a method for machining or testing a blade for a turbomachine.
A turbomachine is functionally organized into the compressor, combustion chamber, and turbine In the case of an aircraft engine, intake air is compressed in the compressor and combusted in the downstream combustion chamber with kerosene mixed in. The resulting hot gas, a mixture of combustion gas and air, flows through the downstream turbine and is expanded in the process. As a rule, each of the turbine and the compressor has a multi-stage structure, where a respective stage includes a nozzle ring and a rotor blade ring. Each blade ring is constructed from a plurality of circumferentially consecutive blades that, depending on the application, have the compressor gas or the heating gas flowing around them.
In production, such blades can be machined in various ways; for example, material can be removed by machining with a geometrically defined or undefined cutting edge. On the other hand, because the blades are subjected to high loads during operation, a thorough testing of the blades may also be of interest. A vibration load, by means of which, for example, durability tests can be carried out or simulations can be compared, can have be of particular significance here. In both machining and testing, holding the blade reliably in the machining or testing apparatus can be a challenge.
In an embodiment, the present invention provides a method that machines or tests a blade for a turbomachine. The method includes: clamping the blade in a clamp such that a point contact or a line contact forms between the blade and the clamp as clamping partners. One of the clamping partners has a lower strength than the other clamping partner and plasticizes in the region of the point contact or the line contact.
Embodiments of the present invention will be described in even greater detail below based on the exemplary figures. The present invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the present invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:
The present invention addresses the technical problem of specifying an advantageous method for machining or testing a blade.
An advantageous innovation according to the present invention includes holding the blade with a clamping device, which is designed in such a way that a point or line contact is formed between the blade and the clamping device. In this case, one of the two clamping partners, that is to say the blade or the clamping device, is provided at least locally with a lower strength than the other clamping partner, and plasticizes in the region of the point or line contact. The clamping device is locally very limited, thereby or therefore, however, pressed against the blade with a high contact pressure.
An alternative approach includes, for example, to clamp a large area of the blade or a blade root with a complementarily shaped clamping device, for example a Christmas-tree-shaped blade root between metal blocks with complementary grooves. This results in comparatively large contact zones and, depending on the tolerance position, inhomogeneous surface pressures as well, particularly including locally low surface pressures. As a result, harmful adhesive sliding transitions may occur, which may result in damage to the blade and/or the clamping device, for example.
This can be prevented by the point or surface contact according to the invention between the blade and clamping device. The contact zones, which are better defined in comparison, can also, for example, be depicted better in simulations, which can be of interest specifically in material testing. With regard to vibration analyses, a linear behavior can result (for instance with respect to natural frequency, amplitude and attenuation) as a result of the point or line contact, for example over a wide excitation region, which can simplify the test implementation and evaluation.
Preferred embodiments of include method or use aspects in the representation of the features; in any case, the disclosure is implicitly to be read with regard to all claim categories.
The term “point or line contact” is to be understood herein as a technical term (not as an infinitesimally small point or a thin line in the mathematical sense). In the technical sense, this is a Hertzian contact, that is to say the smallest possible point or line contact surface, which results when the clamping device and the blade are pressed against one another under Hertzian pressure. For illustration, a corresponding point diameter or a line width can be, for example, at least 1/100 mm or 1/10 mm, wherein a possible upper limit can be, for example, at most 1 mm.
The “line contact” can be subdivided into a plurality of non-contiguous line contact regions. These may, for example, be arranged on opposite sides of the blade in such a way that the blade is reliably held therebetween, see in detail below. The same applies to the “point contact”, which can correspondingly be subdivided into a plurality of separate point contact regions between which the blade is then enclosed by different sides. The clamping jaws of the clamping device can be produced conventionally For example, it can be cut out of a metal block in a spark-erosive manner. In general, the blade, in particular a turbine blade, can also be made, for example, of nickel-based alloys; the clamping device (the clamping jaws) can also be made of a nickel-based alloy, which can then, for example, have a lower strength (is malleable).
Generally, the blade includes a blade body and a base or foot piece. This can be a blade root with a tooth or a tooth structure (in particular a Christmas-tree geometry) for insertion into a disk, but equally a disk piece together with blade body can also be cut out of a disk (blisk) formed integrally with blade bodies and clamped for test purposes, see in detail below. In principle, the blade can also be a guide blade, that is to say it can serve as a base, for example an inner or outer cover band section. Especially with regard to testing and vibration loading, however, the application can particularly be directed at a rotor blade.
In a preferred embodiment, the clamping device is the clamping partner with the lower strength; that is, it plasticizes the clamping device in the region of the point or line contact. In general, the strength comparison of the clamping partners relates to the contact region, i.e. the material properties of the blade and clamping device are considered where they are pressed against one another. In the case of the clamping device, for example, the strength of the clamping jaws between which the blade is clamped is used as a basis. In the case of the blade, for example, the strength of the blade body or of the blade root is used as a basis.
In a preferred embodiment, a line contact is formed between the blade and the clamping device. Preferably, the blade is clamped in such a way that a homogeneous surface pressure is present over the entire line contact. The clamping partner with the lower strength, that is to say, for example, the clamping device (its clamping jaws), thus plasticizes along the entire line contact, thus homogenizing the surface pressure. In figurative terms, any irregularities of the contact pressure along the line, which could result, for example, from slight uneven spots or misfits, are “eaten up” by the plastic deformation; the elastic component, which is constant along the line, remains. As a result, even the smallest tolerances or misfits can be compensated for, and the blade is optimally clamped. During the machining or in particular testing of the blade, no further placement occurs, and the blade is reliably held.
In a preferred embodiment, the clamping device is pressed with a normal force against the blade in the region of the point or line contact. This is considered locally in each case in the contact region; therefore, in the individual line contact or point contact regions, the contact force is in each case perpendicular to the respective surface region. By avoiding tangential components, the risk of exceeding the adhesive boundary can be prevented.
In a preferred embodiment, the blade is held in the clamping device in a kinematically defined manner, ignoring any tangential forces as well. The latter means that even if there were tangential forces (which is not preferred), these are disregarded. If only the normal forces between the blade and clamping device are considered, the blade is “kinematically defined” if firstly it cannot move and secondly the holder is not overdefined either. The latter means that there are no more contact regions than necessary in order to keep the blade immobile.
A preferred embodiment relates to a blade with a blade body and a blade root having a tooth or tooth structure. Viewed axially, the tooth or teeth can protrude in the circumferential direction. Such a blade root can be inserted axially into a complementarily shaped blade root receptacle in the disk. The blade root with two teeth can, for example, have a dovetail shape, with a plurality of radially offset teeth being referred to as a Christmas-tree geometry. Generally, within the scope of this disclosure, the terms “axial,” “radial,” and “circumferential,” as well as the associated directions, refer to the axis of rotation about which the blades rotate during operation (and which typically coincides with the longitudinal axis of the turbomachine).
In a preferred embodiment, the blade is clamped to the blade root. In this case, a region of the point or line contact is preferably arranged on a flank of the tooth pointing radially inward, and another region on a flank of the tooth pointing radially outward. Depending on the flank, the contact force is preferably perpendicular to the respective region, see above.
The blade root preferably has, circumferentially opposite, an additional tooth, which can form a dovetail profile with the tooth or can be part of a Christmas-tree structure. In a preferred embodiment, the blade root is then also clamped on the additional tooth, specifically again both on a radially inward pointing and on a radially outward pointing flank. On each of the flanks, the contact force is preferably perpendicular to the respective contact region, see above.
As already mentioned, the blade can alternatively also be separated from a blisk (blade integrated disk). It is then preferably held on the separated disk piece. In this case, the clamping device can, on the one hand, have the lower strength (see above); however, on the other hand, the blade can also be the clamping partner with the lower strength. In the case of the separated disk piece, the formation of a point contact or of point contact regions can in particular also be preferred.
In principle, a compressor blade can also be machined or tested in a manner described in the present case; the method is preferably used in a turbine blade.
In a preferred embodiment, the blade held in the clamping device is tested, namely subjected to a vibration load. In this connection, an advantage of the point or line contact can result, for example, such that the damping of the structure is significantly lower (no adhesive sliding transitions). Consequently, with conventional vibration exciters, higher loads can be introduced (which opens up a test regime which has hitherto not been accessible) or the same vibration input can be achieved with less excitation power. An advantage can also result, for example, in that, on account of the avoidance of the adhesive sliding transitions, an unintentional heat input can be prevented. Such a phenomenon could otherwise lead to pronounced fretting in the contact zones, as a result of which the blade and/or the clamping device can be damaged.
The invention also relates to the use of a blade and/or a clamping device in a method disclosed herein, that is to say in particular for holding the blade over a point or line contact.
The invention will be explained in more detail below with reference to an exemplary embodiment, a distinction still not being made in detail between the different claim categories.
For checking or certification of the blades 20, they are subjected to different vibration loads. For such testing purposes,
Each clamping device 40, specifically clamping jaws 40.1-40.4, has a convex contour; they are each pressed with a normal force 47.1-47.4. While, like the blade root 21, clamping jaws 40.1-40.4 are made of a nickel-based alloy, they have a lower strength. The normal force 47.1-47.4 is set so high that the clamping jaws 40.1-40.4 plasticize in each case in the region of the point or line contact 41. Reference is expressly made to the introduction of the description with regard to the advantages.
While embodiments of the invention have been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
Compressor 1a
Combustion chamber 1b
Turbine 1c
Clamping jaw 30.1
Clamping jaw 30.2
Contact surface 31.1
Contact surface 31.2 p0 Clamping device 40
Clamping jaws 40.1-40.4
Regions thereof 41.1-41.4
Flanks thereof 45.1, 45.2
Flanks thereof 46.1, 46.2
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 202 673.7 | Feb 2019 | DE | national |
