FIELD OF THE INVENTION:
[001] The present invention relates to development of means for checking frequency of low pressure (LP) rotor blades in vertical position. The blades are responsible for extracting energy from the high temperature, high pressure steam produced by the boiler. The turbine rotating blades are commonly mounted on the discs by means of ‘fir-tree’ roots in horizontal position in prior art. Natural Frequency Testing is usually done on Turbine free standing blades every time when new blades are manufactured or when the blades are removed and refitted during over hauling period after long operation.

[002] More particularly, the present invention relates to a fixture which has been developed to hold the LP Rotor Blades in Vertical Position to check the natural frequency of the blades before mounting it upon rotor.

BACKGROUND OF THE INVENTION:
[003] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[004] Since the inception of steam turbine, steam turbines have been the major source of power generation worldwide. Steam turbine blades are the heart of turbine as they are responsible to convert the gliding steam energy into the rotary motion of the turbine. However, in the process, the blades experience the most severe dynamic operating conditions throughout their life span. To accommodate the low pressure steam of higher specific volume, low pressure turbine (LPT) blades are largest in size. These large size blades are most vulnerable for failure in severe dynamic loading. Due to the severe operating conditions these blades are periodically inspected for crack detection during power plant shut down and maintenance.

[005] Any rotating component exhibits a natural frequency of motion at which it offers minimum resistance to forces. The geometry, material properties and fixity conditions dictate the natural frequency of any component. Important components like Turbine Blades particularly the blades of larger lengths, such as the LPT blades, are so designed that the natural frequencies are away from the prevailing excitation frequencies during normal operating ranges of the machine. This is done for increasing the fatigue life of the component to avoid dangerous resonance conditions. The natural frequency which is dependent on root contact, increases with the fixity of the blade attains a constant value. For the purpose of testing, the fixity condition is simulated in the stationary root by fixing specially wedges in the slot at the root of the blade on the disc.

[006] Blades are important component of steam turbine and its failure is a common problem. A frequent cause of turbo machinery blade failure is excessive resonant response. The most common excitation source is the non-uniform flow field generated by inlet distortion, wakes and/or pressure disturbances from adjacent blade rows. A rotating turbine blade has larger bending stiffness than a stationary blade because rotation leads to stiffening effect due to the centrifugal force. The stiffening effect further depends on the rotational speed. Thus, in such structures natural frequency is a function of rotational speed and they are presented in the form of Campbell diagram.

[007] Natural Frequency of blades cannot be measured in rotating condition of rotor. Hence the natural frequency of blades is required to be checked in free standing condition using proper clamping in vertical position so as to mimic the gravitation force of the blade on the rotor in vertical position.

[008] Thus there exists a need of method and means for clamping of LP rotor blades on a vertical clamping fixture acting as a single unit which mimics the gravitation force of blade on rotor.

[009] In view of the above, the Present invention introduces a root holding fixture for LP rotor blades in free-standing vertical position mimicking the position of blades in actual LP rotor.

OBJECTS OF THE INVENTION:
[0010] An object of the present invention is to provide a fixture for checking natural frequency of low pressure rotor blades in vertical position.

[0011] Another object of the present invention is to provide a fixture for checking natural frequency of low pressure rotor blades in vertical position, which minimizes the gravitational forces of LP rotor blades on fixture that helps in achieving better frequency compared to clamping in horizontal position.

[0012] Yet another object of the present invention is to provide a fixture for checking natural frequency of low pressure rotor blades in vertical position, which gives rise to good quality blades with required natural frequency so as to minimize resonance between two consecutive blades.

[0013] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:
[0014] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0015] According to this invention, there is provided a fixture for clamping LP rotor blades in free standing vertical position inside a rectangular pit with suitable isolation in the foundation to isolate from any external shock/vibration / handling of hydraulic forces applied on the system for accurate determination of frequency. The whole fixture is to be mounted inside pit (below shop floor level) on inflated air bags in order to isolate from the external vibrations and material. The aforesaid fixture comprises of the following key elements:

[0016] Base Block (11) which rests on four Plates (24) in resting condition and gets lifted up with the help of inflated air bags (22) which are also placed above four plates (23). Hydraulic cylinders (15) are assembled with the base block (11) with the help of locking plates (17) and ‘O’ Rings (13) so as to prevent misalignment. A top Plate (8) is mounted above the base block (11) by using a plurality of fasteners/studs (5 & 7). Tapered slot is provided on the Top Plate (8) for Control Segment of different forms (1, 18, 19, 20 & 21) of blade profile and for its movement along the tapered surface, the control segment (1, 18, 19, 20 & 21) is guided by Key (4). At one point of time one form of control segment (1/18/ 19/20 /21) can be used for a particular form of blade profile. The blade is clamped vertically in control segment (two parts) such that it is pushed from bottom by hydraulic cylinders in such a manner that control segment moves in upward direction along the taper and firmly holds the blade. After clamping of blade, the whole system works as single unit against the external vibrations. The complete system ensures that, blade remains in vertical position while clamped and maintains repeatability in respect to perfection of contact with control segment and also verticality of its axis.

[0017] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0018] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0019] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
[0020] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-

Figure 1 illustrates: a fixture for checking natural frequency of low pressure rotor blades in vertical position in accordance with the present invention.
Figure 1A illustrates: Horizontal clamping fixture for frequency checking according to the prior art.
Figure 2 illustrates: Base Block, according to the present invention.
Figure 3 illustrates: Top Plate, in accordance with the present invention.
Figure 4 illustrates: Clamping of fir-tree root blade in vertical position, in accordance with the present invention.
Figure 5 illustrates: Control Segment of the present invention.

[0021] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
[0022] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0023] Although embodiments for the present subject matter have been described in language specific to package features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/device of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

[0024] The instant invention makes a disclosure regarding a technology pertaining to a fixture for checking natural frequency of low pressure rotor blades in vertical position.

[0025] Now reference may be made to figure 1, wherein the proposed fixture comprises of different components lying in the rectilinear pit below shop floor level. Above the pit there are multiple Plates above which the fixture is mounted under different conditions. Base Block (11) which rests on four Plates (24) on resting condition and gets lifted up with the help of inflated air bags (22) which are also placed above four plates (23). The pressure inside the air bags and the elevation of the same can be observed with the help of pneumatic scheme with which the air bags are connected. Similarly, the pressure with which hydraulic cylinder (15) will push the control segment (1, 18, 19, 20 & 21) can also be observed with the help of hydraulic scheme with which the hydraulic cylinders (15) are connected. The space for these connections and hydraulic cylinders (15) is provided in Base Block (11). Locking Plates (17) are also fixed on Base Block (11) with the help of plurality of fasteners. These locking plates (17) restrict the radial movement of hydraulic cylinders (15) so as to ensure the uniform stroke. Top Plate (08) is mounted above base block (11) using plurality of fasteners/studs (5 & 7). Control segment is guided along the tapered surface of Top Plate with the help of Key (04) and keyways on both ends. Control segment (1, 18, 19, 20 & 21) is divided in two halves, on one half , Support arm (10) is attached which push the other half of control segment (1, 18, 19, 20 & 21) along with the attached half to ensure the uniform movement along the tapered surface.

[0026] After assembling the whole system, the fixture is raised with the help of inflated air bags (22) up to certain height then blades are clamped on fixture using hydraulic cylinders (15) and power pack in vertical position.

[0027] Material required to manufacture components of fixture is the same as that of rotor without restricting scope of the invention to the same. Thus, other materials readily apparent to a person skilled in the art are understood to be within purview of the invention. To reduce vibrational effects of external sources the fixture is to be mounted equi-spaced on lifting bags. Then blades are clamped on fixture using hydraulic cylinders and powerpack in vertical position, and natural frequency of LP blades are measured.

[0028] Frequency is measured using stethoscope mounted on LP blade with the help of a means for vibration measurement. Blades are made to vibrate using manual hammering and then frequency is measured. If frequency lies between the normal range, blades are accepted for further assembly with LP rotor.

Advantages of invention over prior art:
- During clamping of root of Fir-tree blades in horizontal position as in Figure 1A, natural frequency is distorted due to weight component of long fir tree blades in cantilever position. Hence clamping in vertical position in present invention minimizes the gravitational forces of LP rotor blades on fixture which helps in achieving better frequency.

- In horizontal clamping , root of blade is in contact at three faces of control segment whereas in vertical clamping only face is in contact of control segment during frequency checking which mimics the actual working condition of rotor blades is fitted in rotor.

- Economic significance is huge in present invention since better natural frequency achieved with vertical clamping results in lesser fatigue in LP rotor blades during operation. Lesser fatigue amounts to lesser wear and tear and thus lesser maintenance.

Working of Invention:
[0029] After assembling the whole system, the fixture is raised with the help of inflated air bags (22) upto certain height then blades are clamped on fixture using hydraulic cylinders and powerpack (15) in vertical position. The blade is clamped vertically in control segment (two parts)(1) such that it is pushed from bottom by hydraulic cylinders in such a manner that control segment moves in upward direction along the taper and firmly holds the blade (Figure-4). After clamping of blade the whole system works as single unit against the external vibrations. Complete system ensures that blade remains in vertical position while clamped and maintains repeatability in respect to perfection of contact with control segment and also verticality of its axis. Frequency is measured using stethoscope mounted on LP blade using means for vibration measurement. Blades are made to vibrate using manual hammering and then frequency is measured. If frequency lies between the normal range blades are accepted for further assembly with LP rotor.

[0030] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other cast structures for carrying out the same purposes of the present subject matter.

[0031] It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.

[0032] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0034] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0035] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0037] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0038] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims:WE CLAIM

1. A fixture for checking natural frequency of low pressure rotor blades in vertical position comprises a base Block (11) supported on multiple Plates (24) in resting condition and gets lifted up by inflated air bags (22) which are placed above multitude of plates (23), wherein a plurality of Hydraulic cylinders (15) are assembled with the base block (11) and a top Plate (8) is mounted above the base block (11), in which a tapered slot is provided on the Top Plate (8) for Control Segment of different forms (1, 18, 19, 20 & 21) for blade profile.

2. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claim 1, wherein the Hydraulic cylinders (15) are assembled with the base block (11) with the help of locking plates (17) and ‘O’ Rings (13) so as to prevent misalignment.

3. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claim 1 or 2, wherein the top Plate (8) is mounted above the base block (11) by a plurality of fasteners/studs (5 & 7).

4. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claims 1-3, wherein for movement along the tapered surface, the control segment (1, 18, 19, 20 & 21) is guided by Key (4) and keyways on both ends, in which at one point of time one form of control segment (1/18/ 19/20 /21) is used for a particular form of blade profile.

5. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claims 1-4, wherein the blade is clamped vertically in control segment (two parts) (1, 18, 19, 20 & 21) that it is pushed from bottom by hydraulic cylinders that control segment moves in upward direction along the taper and firmly holds the blade.

6. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claims 1-5, wherein Control segment (1, 18, 19, 20 & 21) is divided in two halves, on one half, Support arm (10) is attached which push the other half of control segment (1, 18, 19, 20 & 21) along with the attached half to ensure the uniform movement along the tapered surface.

7. The fixture for checking natural frequency of low pressure rotor blades in vertical position as claimed in claims 1-6, wherein the Locking Plates (17) are fixed on Base Block (11) with the help of plurality of fasteners and restrict the radial movement of hydraulic cylinders (15) so as to ensure the uniform stroke.
, Description:A FIXTURE FOR CHECKING NATURAL FREQUENCY OF LOW PRESSURE ROTOR BLADES IN VERTICAL POSITION