Field of the invention:-
The present invention relates to the design & development of Universal
Root locator which can be used with any blade irrespective of its tang
height size in order to standardize the root and shroud milling of bar type
steam turbine blades on CNC horizontal machining center.
Background of the invention:-
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 has to be very precise dimension wise.
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.
The fixture which is used to carry out root and shroud milling is a
specially designed one. 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. For carrying out the operation, the position of the blade in the
machine fixture is 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 tang height greater than 9mm. But with the
technological advancement of blade designs, manufacturing is being
taken up for wide range of blades including those having tang heights
less than 9mm also . Root and shroud milling of such blades having tang
height less than 9mm is not possible in the existing setup.

Object of the invention:-
The object of the present invention is to develop a Universal Root locator
to standardize the root and shroud milling of bar type steam turbine
blades having tang height of any value on CNC horizontal machining
centre.
Another object of the invention is to develop a Universal Root locator to
standardize the root and shroud milling of bar type steam turbine blades
which shorten the setting time required for Root and shroud milling of
steam turbine blades.
A further object of the present invention is to develop a Universal Root
locator to standardize the root and shroud milling of bar type steam
turbine blades which improves the quality of the steam turbine blades
during milling operation by eliminating rework and rejection as well as
improving the productivity.
Brief description of the accompanying drawings:-
Figure 1 shows a 3d model of the fixture in the machine explaining the
entire Root and shroud milling setup.
Figure 2 shows a 3d model of the invention, the universal root locator.
Figure 3 shows the top, bottom and side view of the invention.

Figure 4 shows the application of invention through positioning of blade
on the universal root locator.
Figure 5 shows applicability of root locator on both types of blade
geometries.
Detailed description of a preferred embodiment of the invention:-
The fixture used for root and shroud milling of steam turbine blades has
two sides. One is used for carrying out root and shroud milling of steam
turbine blades while the other is used for carrying out centering of blanks
which is not a part of the present invention.
For root and shroud milling of a blade, the degrees of freedom of the
blade movements need to be arrested. The axis of the blade should lie
horizontally while keeping the root slot of the blade in perfectly vertical
position. The transverse positions (both horizontal and vertical) of the
blade are set with the help of angle and base pads on the fixture. The
variation in geometries of different types of blade is compensated by
varying the height as well as angles of these pads. However, longitudinal
position (along the length of the blade) of the blade is locked with the
help of the Root Locating Block. 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 results in rework/rejection.

The root locator should also provide adequate space for cutter movement
for machining of root face of the blade which, is a problem for blades
having low tang heights as the exiting setup has a limitation of up to 9
mm tan height. The developed universal root locator positions the blade
in such a manner by which the entire root portion of the blade is
protruding outwards giving the milling cutter ample space for performing
the machining work.

We claim:-
1. A universal root locator to standardize the root and shroud milling of
bar type steam turbine blades comprising:
a block (1) milled in a symmetrical stepped form having a top surface (3)
formed by vertical side faces (9, 10), the block (1) having plurality of
holes (13) on each side for fixing with a fixture;
a locator pad (2) welded on the inner wall of the block (1) near the top
surface for locating the root portion of a turbine blade (5) such that when
the blade blank (5) is located in the machine during milling , the groove
of the blade root butt with the surface (4) of the locator pad (2) at
reference position (11) whereas the surface (3) of the block (1) butt with
the shank of blade blank (5) at reference position (12) such that the
arrangement provides a tang height (6) that gives a sufficient spaces (7)
further movement for removing the technical allowance (8) of the blank
which is the material at the root of the blade blank to be milled.
2) The universal root locator as claimed in claim 1 where the block (1) is
so symmetrically shaped that it can hold and locate the left hand and
right hand geometric blades by placing the block (1) accordingly with
faces (9) or (10) of the block (1) on top (as shown in fig. 5).

3) The device as claimed in claim 1 where all the parts are made of alloy
steel material and subsequently hardened.