Claims:WE CLAIM:
1. A setup for milling operation of root and shroud of steam turbine blades comprising of a blade to be machined placed between blade root and blade shroud resting on front pad, wherein said blade root is connected to the root locator, which is secured to horizontal milling machine, wherein said root locator block and front pads are height adjustable.

2. A setup for milling operation of root and shroud of steam turbine blades as claimed in claim 1, wherein axis of the blade and setup are disposed in parallel to each other.

3. A setup for milling operation of root and shroud of steam turbine blades as claimed in claim 1 or 2, wherein the blade root and blade shroud are secured to the front pad.

4. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims, wherein said pad is common for both said root and shroud.

5. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the axis of the blade is aligned horizontally and the central axis of the blade is aligned with machine fixture axis for root and shroud milling of blade.

6. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the base pad rests on angle block of horizontal milling center in which the transverse positions of the blade are set by means of the angle block and base pad.

7. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the front pad forms a block having substantially L-section, which comprises a shorter part and longer part.

8. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the shorter part is provided with plurality of nut and bolt and the longer part is having multitude of holes for fastening with the horizontal milling center.

9. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the root locator constitutes a cuboidal block with a slot for movement of bolt therethrough.

10. A setup for milling operation of root and shroud of steam turbine blades as claimed in any of the preceding claims wherein the cuboidal block may be provided with a cut at each corner thereof.
, Description:A setup for milling operation of root and shroud of steam turbine blades
FIELD OF INVENTION
[001] The present invention relates generally to a setup for milling operation of root and shroud of steam turbine blades, more particularly, to a setup for standardizing and reducing root and shroud milling complexity of steam turbine blades of supercritical design.

BACKGROUND OF INVENTION

[002] The steam flow path of a steam turbine is formed by a stationary cylinder and a rotor. A large number of stationery vanes are attached to the cylinder in a circumferential array and extend inward into the steam flow path. Similarly, a large number of rotating blades are attached to the rotor in a circumferential array and extend outward into the steam flow path. The stationary vanes and rotating blades are arranged in alternating rows so that a row of vanes and the immediately downstream row of blades form a stage. The vanes serve to direct the flow of steam so that it enters the downstream row of blades at the correct angle. The blade airfoils extract energy from the steam, thereby developing the power necessary to drive the rotor and the load attached thereto.

[003] Blade manufacturing firms around the globe are engaged in manufacturing of turbine blades for steam and gas turbines of various ratings ranging from a few megawatts to 1000-1200 MW. These blades vary in physical aspects viz. shape, sizes etc. depending upon the input steam parameters. Steam turbine blade is a very precise and critical component of steam turbine system. Each stage of steam turbine blades which are fitted into the turbine rotor is required to be very precise dimension wise.

[004] Root and shroud milling of steam turbine blades is carried out by using two adjacent planes in the blade root and shroud as well as the root slot to completely define the position of the blade in the fixture on a horizontal milling machine and the same is carried out by using fixed pads at root and shroud to clamp the blade horizontally in such a way that blade central axis remains parallel to the machine fixture. For carrying out the operation, the position of the blade in the machine fixture is completely defined by root locator with the help of root slot.

[005] At present root and shroud milling is carried out by using fixed pads at root and shroud to clamp the blade horizontally in such a way that blade central axis remains parallel to the machine fixture.

[006] For carrying out the operation the position of the blade in the machine fixture is completely defined by root locator with the help of root slot. The fixture is presently designed for root and shroud milling of steam turbine blades having total height less than 460mm.

[007] Root and shroud milling of blades having total height greater than 460 mm is not possible in the current setup.

[008] The primary drawback of the existing system is its limit to accommodate bigger size work-piece of steam turbine blade. The length of the work piece is accommodated through adjustment in gap between fixture arms. The known setup allows adjustment that can accommodate maximum blade length upto 460mm.

[009] Another drawback of the existing system is the mechanism of positioning of blade on the machine through its root locator. In the currently available system, the major portion of root to be machined used to lie inside the fixture body thereby posing difficulty in approach of cutting tool for milling operation.

[0010] However, with the advancement of blade designs with respect to varied turbine ratings, it is required to manufacture a wide range of blades having total length greater than 460mm. The difficulty in machining such blades is that the root portion of the blades protrudes out from the fixture setup and thus, locking the position of blade in longitudinal direction through root locator is not possible.

[0011] Hence, it is required to design a novel setup for root and shroud milling of such blades, wherein the root locator system has been modified so that the root portion of the blade is completely outside the fixture body, thereby providing clear approach for cutting tools for milling.

[0012] According to the present invention, the foregoing and other disadvantages, shortcomings, inefficiencies and problems are overcome by introducing a newly devised setup for root and shroud milling of large size steam turbine blades.

OBJECTS OF THE INVENTION

[0013] An object of the present invention is to provide a setup for root and shroud milling of steam or gas turbine blades having total height greater than 460mm on CNC horizontal machining center.

[0014] Another object of the present invention is to provide a locating mechanism for steam turbine blades having higher value of total height.

[0015] Still another object of the present invention is to shorten the setting time required for RS milling of steam turbine blades.

[0016] Yet another object of the present invention is to improve the productivity of RS milling of steam turbine blades.

[0017] Further object of the present invention is to improve the quality of steam turbine blades by eliminating rework and rejection.

SUMMARY OF THE INVENTION

[0018] According to this invention, there is provided a setup for milling operation of root and shroud of steam turbine blades comprising of a blade to be machined placed between blade root and blade shroud resting on front pad, wherein said blade root is connected to the root locator, which is secured to horizontal milling machine, wherein said root locator block and front pads are height adjustable.

[0019] The axis of the blade and setup are disposed in parallel to each other.

[0020] The blade root and blade shroud are secured to the front pad.

[0021] Said pad is common for both said root and shroud.

[0022] The axis of the blade is aligned horizontally and the central axis of the blade is aligned with machine fixture axis for root and shroud milling of blade.

[0023] The base pad rests on angle block of horizontal milling center in which the transverse positions of the blade are set by means of the angle block and base pad.

[0024] The front pad forms a block having substantially L-section, which comprises a shorter part and longer part.

[0025] The shorter part is provided with plurality of nut and bolt and the longer part is having multitude of holes for fastening with the horizontal milling center.

[0026] The root locator constitutes a cuboidal block with a slot for movement of bolt therethrough.

[0027] The cuboidal block may be provided with a cut at each corner thereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0028] Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
Fig. 1 shows: Setup for root and shroud milling of steam turbine blades.
Fig. 2 shows: Principle of operation of root and shroud milling.
Fig. 3 shows: Detailed view of arrangement of pads in root and shroud milling fixture.
Fig. 4 shows: Root locator with height adjustable front pads.
Fig.5 shows: Height adjustable front pad at shroud.
Fig. 6 shows: Height adjustable pad (Root and Shroud).
Fig. 7 shows: Height adjustable front pad (Root and Shroud).
Fig. 8 shows: Root locator with provision of height adjustment along the slot.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

[0029] The present invention makes a disclosure regarding setup for root and shroud milling of large size steam turbine blades. The fixture for root and shroud milling works on the principle that the blade axis (X1, Y1) and fixture axis (X2, Y2) must be disposed in parallel to each other for carrying out the root and shroud milling as best seen in figure 2.

[0030] The fixer of the present invention includes a root locator block (1) and front pad (2), height of both of which is adjustable. The front pad (2) is common for both said root and shroud of blade.

[0031] For root and shroud milling of a blade, the axis of the blade is aligned horizontally. Also the central axis of the blade is aligned with machine fixture axis.

[0032] The above alignment is controlled by the height of the pads (2) on which the blade root (3) and shroud (4) rests. As height of the front root pads (2) is adjustable, therefore it is not needed to change the pads frequently for every blade for which pads of different heights are required. Further, the transverse positions (both horizontal and vertical) of the blade are set with the help of angle block (5) and base pads (2) on the fixture.

[0033] However, longitudinal position (along the length of the blade) of the blade is locked by means of the root locating block (1). It locks the position of the blade in fixture as well as provides support against any lateral movement of blade during root and shroud milling operation thus avoiding size variation, which inturn prevents rework/rejection.

[0034] This root locator (1) also provides adequate space for cutter movement for machining of root face of the blade with varying total height of steam turbine blades.

[0035] The root locator (1) of invention positions the blade in such a manner by which the entire root portion of the blade protrudes outwards giving the milling cutter ample space to perform the machining as shown in figure 4. Also it can be adjusted in length for different types of blades together with provision of height adjustment through bolts (P1) at root end. Further, there is provision of height adjustment through bolts (P2) at shroud end.

[0036] Thus the setup of the invention comprising of a blade (D) to be machined placed between blade root (3) and blade shroud (4). Said root and shroud rest on pad (2) and also secured to the front pad (2) by means of fasteners as shown, wherein said blade root (3) is connected to root locator (1).

[0037] The base pad (2) rests on angle block (5) of horizontal milling machine (H). The root locator (1) is fastened to the horizontal milling machine (H) on the side of the blade root (3).

[0038] The invented front pads at root and shroud (2, Figure 7) are also having provision of adjustment in height to accommodate variation in blade sizes (figure 4 & 5) wherein figure 4 and 5 illustrates provision of height adjustment through bolts at root and shroud end (P1 & P2) respectively. A locking nut (N) is also provided to lock the position of adjustable bolts (B) at required heights as in the figure 6.

[0039] Now reference may be made to figure. 7 wherein the front pad (2) forms a block having substantially L-section. The block comprises a shorter part (2A) and longer part (2B), wherein the shorter part (2A) is provided with a plurality of nut and bolt (N and B) and the longer part (2B) is having multitude of holes (L) for fastening with the horizontal milling center (H).

[0040] Referring to figure. 8, the root locator (1) constitutes a cuboidal block with a slot (S) for movement of bolt therethrough, in which there may be provision of a cut (C) at each corner thereof.

[0041] The invented fixture facilitates not only machining of blades with greater length through positioning of root locator (1, Figure 8) outside fixture body but also enables adjustment in transverse direction for any shape and size of blade, thereby eliminating the need of separate root locators for different types of blade.

[0042] The present invention can be used with any blade irrespective of its height& tang height size in order to standardize the root and shroud milling of bar type steam turbine blades (TX, 3DS & F) on CNC horizontal machining center.

[0043] Advantageous Features:-

- Root and shroud milling of large size steam turbine blades having total height greater than 460mm.
- Shortens the setting time required for RS milling of steam turbine blades.
- Improves the productivity of RS milling of steam turbine blades.
- Improves the quality of steam turbine blades by eliminating rework and rejection.

[0044] It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-