FIELD OF INVENTION
The present invention relates to a template for inspection of complete root profile of steam turbine blades with technological allowance and a method for the same. More particularly, the invention relates to a process and a template for performing quality inspection of complete root profile of steam turbine blades with technological allowance in a single setting after machining on the manual/CNC machine to guarantee improvements in inspection in single setting and therefore greatly prolonging service life of the blade.
BACKGROUND OF INVENTION
A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft.
Running through the center of the steam turbine is a sturdy axle called the rotor, which is what transfers power from the turbine to an electricity generator called turbogenerator. The blades are the most important part of a turbine. Their design is crucial in capturing as much energy from the steam as possible and converting it into rotational energy by spinning the rotor round. All turbines have a set of rotating blades attached to the rotor and spin it around as steam hits them. The blades and the rotor are completely enclosed in a very sturdy, alloy steel casing.

Each set of blades is called a stage and works by either impulse or reaction, and a typical turbine can have a mixture of impulse and reaction stages, all mounted on the same rotor axle and all turning the generator at the same time. Often the impulse stages come first and extract energy from the steam when it's at high pressure; the reaction stages come later and remove extra energy from the steam when it's expanded to a bigger volume and lower pressure using longer, bigger blades. In practice, there are usually a number of stages of blades, each one helping to extract energy from the steam before it's exhausted.
Presently many LMW (Leningrad Metal Works, Russia) make sets operating at different power stations in India have completed more than their service life of 25 years or on the verge of ending their service life. With Renovation and Modernization (R&M) of older in-service thermal sets, large populations of whom have completed more than 25 years or are on verge of end of their service life, being considered a more cost effective way of augmenting power generation capacity than installing new, their technology dates back to early 1950's thereby providing admirable scope of improving the efficiency and increasing the output by R&M of these sets.
While the inspection of advance design steam turbine blades is carried on a 3D-coordinate measuring machine, these tenon blades cannot be quality inspected at root profile (which includes blade root width, neck width, root slot and T slot, see figure 2) because of its dimensionally complex and intricate T-slot at root with technological allowance.

As per prior art, since there was no established technology to inspect the blade root dimensions with technological allowance in a single setting and therefore, a need exists template for inspection of complete root profile of steam turbine blades with technological allowance.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a template for inspection of complete root profile of steam turbine blades with technological allowance which is capable of eliminating the disadvantages of prior art.
Another object of the invention is to propose a template for inspection of complete root profile of steam turbine blades with technological allowance which is capable of inspecting complete root profile of steam-turbine blades with technological allowance.
A further object of the invention is to propose a template for inspection of complete root profile of steam turbine blades with technological allowance which is able to bring a process improvement and minimize process related errors and thus reduce reworking and overall cycle time.

A template (T) for inspection of complete root profile (5) of steam turbine blades (B) with technological allowance (6) and a method thereof comprising a blade matching template (T) for performing quality inspection of blade root profile (5) in single setting by snugly passing the blade root (5) in matching template setup for physical examination or passing passive light waves from one side of the blade root-template setup once the complete root (5) is inside the template (T) and visually detecting any light waves emanating from the gap in matching surfaces of blade viz. blade root width (54), root slot (53), T-slot (52) and neck width (51) and corresponding stepped positions (54’, 53’, 52’, 51’) in template for any indication of improper blade dimensions.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:
Figure 1 shows schematic diagram of an advance class steam turbine blade B’
with integrated shroud 2’ root 5’ and airfoil 1’;

Figure 2 shows schematic diagram of an tenon blade, in accordance with the
present invention;
Figure 3 shows schematic diagram of a tenon blade with technological allowance
in accordance with the present invention;
Figure 4 shows schematic diagram of the detailed assembly of developed template
as well as counter template;
Figure 5 shows schematic diagram of the detailed assembly of developed template
with tenon blade root profile having technological allowance.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Before describing in detail, template (T) for inspection of complete root (5) profile of steam turbine blades with technological allowance (6) of tenon blades in accordance with the present invention, it should be observed that the present invention resides primarily in a novel and non-obvious combination of hardware elements and method steps. Accordingly, these elements and steps have been represented by conventional elements and steps in the drawings, showing only those specific details that are pertinent to the present invention so as not to obscure the disclosure with

details that will be readily apparent to those skilled in the art having the benefit of the description herein.
Typically, as shown in figure 1, an advance technology based steam turbine blade B’ consists of three parts viz. a shroud 5` forming the top part of the blade B’, the airfoil or profile part 1` at the center of the blade B` so that the steam can smoothly glide over the airfoil part 1` and cause the turbine to rotate, a root 5` at the base of the blade B` to fix the blade with turbine rotor and to restrict the blade movement when subjected to large centrifugal forces during turbine functioning.
However, while referring to figure 2 in detail, LMW technology blades (referred herein this application as tenon blades) do not have an integral shroud. Instead, these blades used tenon and mortise form of blade (B) in which, either, a tenon (3) is provided over the tip (2) of the blade B through fabrication instead of shroud and a mortise ring is circumscribed over plurality of individual tenon (3) to form complete blading stage, or, the ring is fitted over the blade B and the tenon (3) is then riveted with multiple blows or welded.
With practices in manufacturing of complex components getting advance with the advent of corresponding advances in machines, tools, quality inspection methods etc. it is required that all manufacturing process be standardized and all redundant processes be eliminated to the extent possible to produce a component with minimum cost and quality denominators.

All Turbine blades essentially consist of a root (5) that fixes in the turbine shaft, an airfoil (1) portion over the root (5) on which the steam glides, and a tenon (3) part at the top. The blade design varies in physical aspects such as shape, sizes etc. depending upon the temperature and pressure applications they would be operating in. A typical steam turbine blade experience enormous dynamic stresses while it operates and functions at temperature and pressure levels that can easily reach upto 700 degree Celsius and above 250 bar pressure respectively.
To sustain these operative hostility, steam turbine blade is often nominated as the most precise and critical component of Steam turbine system. Given the aggressive operating parameters in which a steam turbine works, the turbine blades fitted in the machining grooves of the turbine rotor are required to be quality inspected to ensure that these manufactured blades adhere to precise dimensions. Highly accurate CNC machines are used are therefore used to achieve such preciseness in machining of blades.
Earlier, these tenon blades (B) were manufactured in conventional method on manual machines where plurality of steps was followed to machine the complete blade and correspondingly it was required that each blade was quality checked by a number of templates for all its major dimensions at each step of manufacturing. At present, to meet the need of supplying spare blades, these blades are manufactured on currently used advanced CNC multi-axis machines.

As seen in figure 2, while the inspection of advance design steam turbine blades is carried on a 3D-coordinate measuring machine, these tenon blades (B) cannot be quality inspected at root profile (5) because of its dimensionally complex and intricate design segments such as blade root width (54), neck width (51), root slot (53) and T slot (52) at root profile (5) that may or may not accompany technological allowance (6). A technological allowance is initially provided in a blade in order to enable the multi axis manufacturing machine to first machine the aerofoil (1), root (5) and shroud (2’) profiles. After abovementioned manufacturing operations, the technological allowances (6) are being milled off from axis (7) to get the final blade dimensions.
However, the blade root profile (5) cannot be checked on 3-D CMM after machining on multi-axis machine with technological allowance (6) because of T-slot (52) and other intricate dimensions at root (5). As the blade root (5) dimension is critical for the blade to be rigidly secured in the rotor through its root (5), a blade quality inspection template (T) is developed.
The blade root (5) is checked in a single setting, while the blade is free from any clamping or even in condition when the blade is secured in a manufacturing setup on multi axis machine (not shown), by first holding the blade rigidly in a setup in such a way that the root (5) of the blade (B) along with or without technological allowance (6) is free for performing quality inspection as well as there is provided enough space for operator hand movement during the inspection. The root (5) of the blade (B) is then snugly passed through the matching template (T) steadily in such a way that any

obstruction in the passage of template (T) through blade root (5) or vice versa is noticed without any damage to the blade (B) or the template (T). This ensures that the complete dimension of the blade root width (54), root slot (53), T-slot (52) and neck width (51) are secured at their respective matching grooved or stepped positions (54’, 53’, 52’, 51’) in the template (T) while the root technological allowance (6) is accommodated in template space (6’). To allow easy entry and exit of the blade root (5) in the template (T), a radius (55) is provide in the template (T).
Once the complete root (5) is inside the template (T), passive light waves are passed from one side of the setup to visually detect any light waves emanating from the gap in matching surfaces of template (T) and blade (B) displays an indication of improper blade dimensions. For the quality inspection chamfer (56) is provided at the root (5) to prevent from any harm during manual operation.
The template (T) is developed using Manganese Chromium Tungsten Tool Steel while the template tolerances are provided in such a way that it does not exceeds the maximum and minimum tolerances of the blade.
A counter template (CT) is also manufactured as per the blade (B) drawing in order to check dimensional calibration of the developed template (T) in case the actual blade (B) is not available and therefore this counter template (CT) validates the template (T) for its suitability to perform the quality inspection operation for the blade root.

The foregoing has outlined rather broadly features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

WE CLAIM
1. A template (T) for inspection of complete root profile of steam turbine blades with
technological allowance, the said template consisting of:
- matching grooved or stepped positions (54’, 53’, 52’, 51’);
- template space (6’) below stepped positions (54’, 53’, 52’, 51’) for accommodating root technological allowance (6);
- radius (55) for allowing easy entry and exit of the blade root (5) in the template (T); wherein
- the template (T) is calibrated for its dimension by a counter template (T) manufactured as per blade (B) profile and dimension.
2. A method for performing quality inspection of blade root profile in single setting
through the template as claimed in claim 1 comprising of the steps of:
- holding the tenon blade (B) rigidly in a setup in such a way that the root (5) of the blade along with technological allowance (6) is free for performing quality inspection;
- ensuring that there is provided enough space for hand movement during the inspection;
- passing snugly the root (5) of the blade (B) through the matching template (T) steadily in such a way that any obstruction in the passage of template

through blade root or vice versa is noticed without any damage to the blade or the template; wherein - passive light waves are passed from one side of the blade root-template assembled setup once the complete root is inside the template, for detecting visually if any light waves emanating from the gap in matching surfaces of template for any indication of improper blade dimensions.
3. The template as claimed in claim 1 is made of Manganese Chromium Tungsten Tool Steel while the template tolerances are provided in such a way that it does not exceed the maximum and minimum tolerances of the blade.