FIELD OF INVENTION
The present invention generally relates to a guide blade carrier assembly
adapted in gas turbines. More particularly, the invention relates to a method for
correcting an increased taper diameter of a guide blade carrier in a gas turbine
to achieve the desired radial and axial clearance between the rotor and stator
blade rings. The invention further relates to a ring-type fixing device to
implement the inventive method.
BACKGROUND OF INVENTION
A gas turbine uses atmospheric air as the working fluid which is drawn inside the
turbine and compressed by a compressor. Fuel is added and burnt in the
combustion chamber to heat the air to match the desired turbine inlet
temperature. A guide blade carrier assembly of the compressor secures the
stationary blade rings, in position and transmits the reaction forces generated
due to flow and pressure of the compressed gas to an outer casing. The inner
and outer rings of the stationary blade carry the blades.
As shown in figure-1 the compressor guide blade carrier assembly (1,2,3)
consists of three stationary blade carriers (I,II,III). The first guide blade carrier
(I) is firmly mounted in position between compressor bearing housing (6) and a
center casing (4) and forms a part of the outer casing. The second and third
guide blade carrier II and III are suspended in the center casing (4) so as to
allow for thermal expansion.
Proper concentric position of the guide blade carriers (I,II,III) relative to a
centerline of the turbine shaft is ensured in a horizontal direction by disposing at
least two vertically opposed bolts each guided in a first pair of eccentric bushes,
and in a vertical direction by two horizontally opposed bolts, similarly guided in a
second pair of eccentric bushes. The bolts take up the torque including the
generated forces due to weight, and allow adjustment of the alignment of the
stator blade carriers (II, III) without disturbing the casing. The axial position is
fixed by providing a ring around the guide blade carrier (I) and configurating a
peripheral groove in the casing. The annular spaces between the compressor
guide blade carriers (I,II,III) allow blowing-off of sufficient quantities of air to
ensure a stable operation of the compressor at low speeds, particularly during
start-up and shut-down.
According to the known methodology of constructing a guide blade carrier
assembly in a gas turbine, the first compressor guide blade carrier (I) is rigidly
installed between the intake casing (4) and a turbine casing (5) and forms a part
of the outer casing (4,6). The remaining two stator blade carriers (II, III) which
are in a higher temperature region are suspended in the outer casing to allow a
free thermal expansion. The circumferential slots are cut in the first guide blade
carrier (I) in which stationary blade rings are inserted. The stationary blade ring
is made up of three parts, inner ring (9a), an outer ring (9b) and a plurality of
guide blades (9). All the stator guide blades (9) are held in place in the radial
and circumferential directions by inserting dovetails into correspondingly
configured grooves of the outer rings (9b). The outer rings (9b) are inserted into
circumferential grooves arranged in the guide blade carrier (I) and locked in the
axial direction.
The inner rings (9a) join the blades (9) on the inner periphery and support the
inner rings (seal trips) for shaft sealing.
The technical requirements for configuration of known guide blade carriers, as
shown in figure-2, are to:
> Firmly hold the stator blade rings, which consists of an inner ring (9a), an
outer ring (9b) and the guide blades (9) in its circumferential cut slots
> Maintain a radial clearances (A) between the rotor moving blades (8) with its
internal diameter of guide blade carrier (I)
> Maintain an axial clearances (B, C) between the rotor discs (7) with the inner
rings (9a) of stator blade rings.
> Maintain a radial clearances between the inner rings (9a) of stator blade rings
with the rotor discs (7).
> Provide boroscopic holes for internal inspection of the rotor blades (8).
It is known that a guide blade carrier assemble has to maintain a stage-wise
radial clearance "A" between the rotor moving blades (8) and internal diameter
of the guide blade carrier (I) as shown in Fig.-2. If due to any reason this radial
clearance (A) is increased then working fluid i.e. air will leak through the annular
space between the rotor blades (8) and internal of the guide blade carrier (I). If
this happens the actual compression in that particular stage will be less than the
required compression rate. This phenomenon leads to deterioration in the
performance of the compressor.
A guide blade carrier is generally formed from a nodular cast iron grade metal in
rough condition. During shop manufacturing of the guide blade carrier, the rough
carrier is machined to a required shape and size. The finished guide blade carrier
(I) is assembled with rotor discs (7) and stator blade rings (9,9a,9b) and radial
and axial clearances (A,B,C) are maintained and recorded. But in a situation of
over machining of the internal diameter of the guide blade carrier (OMID-I), for
example, a taper along the turbine shaft axis, the radial clearance 'A' increases in
different stages. This increased internal diameter, if any, needs to be corrected
to the required value if the guide blade carrier (I) is to be retained. Accordingly
there exists a need to eliminate the disadvantages of over machined internal
diameter of guide blade carrier (OMID-I).
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method for correcting an
increased taper diameter of a guide blade carrier in a gas turbine to achieve the
required radial clearances, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a ring-type fixing device for
implementing the method for correcting an increased taper diameter of a guide
blade carrier in a gas turbine.
SUMMARY OF THE INVENTION
Accordingly, in a first aspect of the invention, there is provided a method for
correcting an increased taper diameter developed during machining of a guide
blade carrier, the correction of the over-sized diameter enabling achievement of
a desired radial clearance between the stator and rotor blade rings in a gas
turbine, the method comprising the steps of enlarging the over-sized diameter of
the guide blade carrier through further machining to generate pockets on the
surface of the carrier to accommodate a ring-type fixing device; individual
cylindrical rings in rolled condition are inserted into the slots of the guide blade
carrier and their colour contacts are checked; after the adequate colour contact,
location of the holes are transferred from the rings to the guide blade carrier
body; a matching threading is done in the guide blade carrier body Counter sunk
screws are tightened and the rings are locked with respect to the guide blade
carrier body; after full tightening of the screws the remaining portion of the
empty holes over screw heads are slowly weld filled and sufficient time is allowed
to cool down the weldment; a final machine cut is applied on the extra material
of cylindrical rings to achieve the required taper profiles; the roller is placed in
position and the radial clearances (A) in all the over-size positions are checked to
ensure achievement of the desired radial clearance; and final assembly of the
guide blade carrier.
According to a second aspect of the invention, a ring-type fixing device is
proposed consisting of a plurality of conical rings firmly attachable including
corresponding configured countershank screws within a plurality of pockets
developed through enlargement by further machining the oversized internal
diameter of the guide blade carrier. The pockets after insertion and tightening
through the rings and the countershank screws are weld-filled and allowed to
cool down to produce a rigid radial clearance of a desired dimension.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a longitudinal sectional diagram of a known gas turbine
Figure 2 - shows a schematic diagram of a compressor guide carrier assembly
Figure 3 - shows an interior view of a guide blade carrier
Figure 4 - shows a guide blade carrier in which the over-machined internal
diameter has been further increased according to the invention
Figure 5(a)- shows a ring-type fixing device to implement the inventive method
Figure 5(b)- shows an in-position configuration of the device features according
to the invention
Figure 6 - shows a countershank screw of the fixing device according to the
invention
Figure 7 - shows a guide blade carrier body fixed with the device
incorporating the correction parameter.

DETAIL DESCRIPTION OF THE INVENTION
Figure-4 exhibits a schematic view of the over-sized internal diameter of the
guide blade carrier developed during shop-machining, which have now been
further enlarged by machining according to the invention to accommodate the
device for correcting the over-sized internal diameter of the guide blade carrier.
As shown in fig-5(a), the cylindrical rings (10) each has a plurality of pre
machined holes (11) all around their circumferences for locking those with the
guide blade carrier body (I) by means of corresponding number of counter sunk
screws (12).
Figure-5(b) shows the positioning of the screws (12) on the cylindrical rings (10),
where a parting plane is created between two rings by providing a parting plate
(13) during the assembly, which is removed after the assembly of the guide
blade carrier (I).
Figure-6 shows a countershank screw adapted in the device.
Figure-7 shows the assembly of the device in the guide blade carrier.
After configurating the pockets on the Guide blade carrier (I) to accommodate
the cylindrical rings (10), and the Counter sunk screws (12), the following steps
are carried out:
- individual cylindrical rings (10) in rolled condition are inserted into the slots of
the guide blade carrier (1) and their colour contacts are checked;
- after the adequate colour contact, location of the holes (11) are transferred
from the rings (10) to the guide blade carrier body (1);
- a matching threading is done in the guide blade carrier body (1);
- Counter sunk screws (12) are tightened and the rings (10) are locked with
respect to the guide blade carrier body (1);
- after full tightening of the screws (12) the remaining portion of the empty
holes (11) over screw heads (12) are slowly weld filled (14) and sufficient
time is allowed to cool down the weldment;
- a final machine cut is applied on the extra material of cylindrical rings (10) to
achieve the required taper profiles;
- the roller is placed in position and the radial clearances (A) in all over-size
positions are checked to ensure achievement of the desired radial clearance;
and
- final assembly of the guide blade carrier (1).
FIELD APPLICATION
Assembly was successfully completed in manufacturing shop and gas turbine.

WE CLAIM
1. A method for correcting an increased taper diameter developed during
machining of a guide blade carrier, the correction of the over-sized diameter
enabling achievement of a desired radial clearance between the stator and
rotor blade rings in a gas turbine, the method comprising the steps of:
- enlarging the over-sized diameter of the guide blade carrier through further
machining to generate pockets on the surface of the carrier to accommodate
a ring-type fixing device;
- inserting individual cylindrical rings (10) in rolled condition into the slots of
the guide blade carrier (1) and checking their colour contacts;
- transferring location of the holes (11) after achieving a complete colour
contact, from the rings (10) to the guide blade carrier body (1);
- configurating a matching threading is done in the guide blade carrier body
(1);
- tightening the Counter sunk screws (12) and locking the rings (10) with
respect to the guide blade carrier body (1);
- slowly weld filling with a filler (14) after full tightening of the screws (12) the
remaining portion of the empty holes (11) over screw heads (12) and
allowing and sufficient time to cool down the weldment;
- applying a final machine cut on the extra material of cylindrical rings (10) to
achieve the required taper profiles;
- checking the radial clearances (A) in all over-size positions to ensure
achievement of the desired radial clearance; and
- carrying-out the final assembly of the guide blade carrier (1).

A method for correcting an increased taper diameter developed during machining
of a guide blade carrier, the correction of the over-sized diameter enabling
achievement of a desired radial clearance between the stator and rotor blade
rings in a gas turbine, the method comprising the steps of enlarging the over-
sized diameter of the guide blade carrier through further machining to generate
pockets on the surface of the carrier to accommodate a ring-type fixing device;
inserting individual cylindrical rings (10) in rolled condition into the slots of the
guide blade carrier (1) and checking their colour contacts; transferring location of
the holes (11) after achieving a complete colour contact, from the rings (10) to
the guide blade carrier body (1); configurating a matching threading is done in
the guide blade carrier body (1); tightening the Counter sunk screws (12) and
locking the rings (10) with respect to the guide blade carrier body (1); slowly
weld filling with a filler (14) after full tightening of the screws (12) the remaining
portion of the empty holes (11) over screw heads (12) and allowing and
sufficient time to cool down the weldment; applying a final machine cut on the
extra material of cylindrical rings (10) to achieve the required taper profiles;
checking the radial clearances (A) in all over-size positions to ensure
achievement of the desired radial clearance; and carrying-out the final assembly
of the guide blade carrier (1).