FORM 2
THE PATENT ACT  1970
(39 OF 1970)
AND
THE PATENTS RULES  2003

COMPLETE SPECIFICATION
(See Section 10; rule 13)

A method of measurement of width of tapered groove at the root of the
blades in a Steam turbine

TRIVENI TURBINE LTD
an indian company 
of 12A  Peenya Industrial Area 
Banglore-560058.

The following specification particularly describes the present invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to the field of measurement of width of tapered groove at the root of the blades. Particularly  the present invention relates to measurement of width of tapered groove at the root of the blades precisely for quality purposes either to accept /reject the blades or to perform rework on defective blades.

BACKGROUND OF THE INVENTION:
Figure 1 illustrates an isometric view of conventional T-root blade.

Figure 2 illustrates an isometric view of newly developed blade with tapered groove at the root of the blade.

Figure 3(a) illustrates an isometric view of conventional T-root blades assembled on to a disc of a rotor.

Figure 3(b) illustrates an isometric view of newly developed blades of figure 2 assembled on to a disc of a rotor.

It can be inferred from figure 1  figure 2  figure 3(a) and figure 3(b) that the mating edges M of the conventional T-root blade with the rotor disc are right angled whereas the mating edges M of the newly developed blades are tapered. The tapered edges of the root of the newly developed blades facilitate in providing more contact surface area with the rotor disc and thereby reduce peak stresses and average stresses. The reduction in peak stresses and average stresses enhances the reliability of the blades.

Figure 4 illustrates a schematic diagram of newly developed blade of figure 2.

As per assembly standards  the width W of the tapered groove at the root of the newly developed blade should be within the range of 5.94mm to 5.98mm inclusive of the limits. During machining operation  there is a possibility of machining the width W of the tapered groove at the root of the blade below 5.94mm due to wear and tear of the tool or there is a possibility of machining the width W of the tapered groove at the root of the blade above 5.98mm due to misalignment of tool axis and spindle axis.

Typically  the cases of misalignment of tool axis and spindle axis are nominal but the cases of wear and tear of the tool are frequent.

The measurement of the width W of the tapered groove at the root of the newly developed blade is very difficult and is being done by CMM (Coordinate Measuring Machine) after the manufacturing of the blades. The measurement of the width W of the newly developed blades with CMM is time consuming and labour intensive.

Therefore  there is felt a need for development of a new method for measurement of width of tapered groove at the root of the blades to overcome the drawbacks of the prior art.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a simple and easy method for measurement of width of the tapered groove at the root of the blades.

Another object of the present invention is to provide a method that can measure the width of the tapered groove at the root of the blades during the machining of the blades itself.

One more object of the present invention is to provide a less time consuming method for measurement of width of the tapered groove at the root of the blades.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an isometric view of conventional T-root blade;

Figure 2 illustrates an isometric view of newly developed blade with tapered groove at the root of the blade;

Figure 3(a) illustrates an isometric view of conventional T-root blades assembled on to a disc of a rotor;

Figure 3(b) illustrates an isometric view of newly developed blades of figure 2 assembled on to a disc of a rotor;

Figure 4 illustrates a schematic diagram of newly developed blade of figure 2;

Figure 5(a) and 5(b) illustrates a pictorial representation of measurement of width of the tapered groove at the root of the newly developed blades in accordance with the present invention; and

Figure 6 illustrates a schematic diagram of measurement of width of the tapered groove at the root of the newly developed blades.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Figure 5(a) and 5(b) illustrates a pictorial representation of measurement of width of the tapered groove at the root of the newly developed blades in accordance with the present invention.

Figure 6 illustrates a schematic diagram of measurement of width of the tapered groove at the root of the newly developed blades.

In accordance with the present invention  there is provided a method of measuring width W of the tapered groove at the root of newly developed blades comprising a ball 12 and a washer 14.

The tapered edges T of the tapered groove of newly developed blades make an angle 60 degrees with the horizontal and are generally indicated by a reference numeral a1. The tapered edges T at the intersection with the base B of the tapered groove are filleted having a radius of 0.8mm and is generally indicated by a reference numeral R.

Typically  the ball 12 diameter is of 10.49mm for the tapered groove width W in the range of 5.94mm to 5.98mm and is generally indicated by a reference numeral D1.

Typically  the ball 12 is made of steel.

Typically  the inner diameter of the washer 14 is of 10.70mm for the ball diameter of 10.49mm.

Typically  the diameter of the ball 12 and the washer 14 varies depending on the width W of the tapered groove of the newly developed blades.

The method of measuring the width W of the tapered groove at the root of the newly developed blades is as follows:

The newly developed blade is placed on Magnetic V-Block MB. The ball 12 is placed in the tapered groove of the blade such that tapered edges T of the tapered groove tangentially touch the ball 12. The ball 12 is held in position by means of the washer 14 placed on the root of the blade encompassing the ball 12 as shown in figure 5(a).

At mean width W of 5.96mm (i.e.  mean width =(5.94+5.98)/2  average of allowable minimum and maximum widths) of the tapered groove of the newly developed blades  a gap of 0.083mm exists between the ball 12 and the base B of the tapered groove and is indicated by a reference numeral D2.

At mean width W of 5.96mm (i.e.  mean width=(5.94+5.98)/2  average of allowable minimum and maximum widths) of the tapered groove of the newly developed blades  the height of the ball 12 above tapered groove is 7.07mm and is indicated by a reference numeral H1.

The height H1 of the ball 12 above the tapered groove is calculated in three steps:
1) Touching the height gauge on root of the blade as shown in figure 5(b) and making the reading H11 in the dial gauge to zero.
2) Touching the height gauge on the top of the ball 12 as shown in figure 5(a) and noting the reading H21 in the dial gauge.
3) The subtraction of the readings H21-H11 gives the height H1 of the ball 12 above the tapered groove.
The height H1 of the ball 12 above the tapered groove varies depending on the width W of the tapered groove of the newly developed blade. The width W of 5.94mm of the tapered groove corresponds to a height H1 of 7.10mm. The width W of 5.98mm of the tapered groove corresponds to a height H1 of 7.04mm.

In the case  When the width W of the tapered groove of the newly developed blade is greater than 5.98mm  then the height H1 of the ball 12 above the tapered groove will be less than 7.04mm and the work piece gets rejected.

In the case  When the width W of the tapered groove of the newly developed blade is less than 5.94mm  then the height H1 of the ball 12 above the tapered groove will be greater than 7.10mm and rework needs to be done on work piece. To perform rework on the work piece  the distance that needs to be traversed to the left of the tool is to be calculated.

The distance that needs to be traversed to the left of the tool is calculated by forming a triangle between the tangential point of contact of the ball 12 and top of the ball 12 as shown in figure 6. The line drawn joining the tangential point of contact of the ball 12 and top of the ball 12 makes an angle 30 degrees with the vertical and is indicated by a reference numeral a2.
The distance that needs to be traversed to the left of the tool (TL) =
[tan30*(H1 (At width of the tapered groove below 5.94) – H1 (At mean width 5.96 of the tapered groove)]

The above mentioned formula (TL) calculates the corresponding increase in the width of the tapered groove that needs to be machined in relation to increase in the height of the ball 12.

Although the invention has been described herein above with reference to the embodiments of the invention  the invention is not limited to the embodiments described herein above. It is to be understood that modifications and variations of the embodiments can be made without departing from the spirit and scope of the invention.
We claim:
1) A method of measurement of width of tapered groove at the root of the blades in a steam turbine  said method comprising the steps of:
a) placing of a ball in said tapered groove making a tangential contact with tapered edges of said groove leaving a gap therein at the bottom of said ball and base of said groove;
b) restricting the movement of said ball in said groove by placing a washer on the root of said blade encompassing said ball;
c) calculating the height of the ball above said tapered groove at mean width(average of allowable minimum and maximum widths) of said tapered groove by means of touching the dial gauge at two positions 1) At the top of said ball 2) At the root of said blade and subtracting the readings in the dial gauge from each other;
d) calculating the height of the ball above said tapered groove at width less than the allowable minimum width of said tapered groove by means of touching the dial gauge at two positions 1) At the top of said ball 2) At the root of said blade and subtracting the readings in the dial gauge from each other; and
e) calculating the increase in the width of said tapered groove that needs to be machined corresponding to increase in the height of the ball by means of subtracting the height of the ball at mean width from height of the ball at width less than the allowable minimum width and multiplying said increase in the height of the ball with tan a2 degrees.

2) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the value of said a2 is 30 degrees.

3) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the width of said tapered groove of the blade should be within the range of 5.94mm to 5.98mm inclusive of the limits.

4) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the diameter of said ball is of 10.49mm.

5) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1 or 4  wherein the diameter of said ball varies depending on the width of said tapered groove of the blade.

6) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the tapered edges of said tapered groove of the blade makes an angle 60 degrees with the horizontal.

7) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1 or 2  wherein the value of said a2 varies depending on the angle the tapered edges of said tapered groove of the blade makes with the horizontal.

8) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein said ball is made of steel.

9) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the inner diameter of said washer is of 10.70mm.

10) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 1  wherein the inner diameter of said washer varies depending on the width of said tapered groove of the blade.

11) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 2  wherein the width of said tapered groove of the blade is greater than 5.98mm  the blade will get rejected.

12) A method of measurement of width of tapered groove at the root of the blades in a steam turbine as claimed in claim 2  wherein the width of said tapered groove of the blade is less than 5.94mm  rework will be done on the blade.

Dated this 27th day of September  2012 (for Triveni Turbine Ltd)


Dr.Sunil Jajit GM-IPR