Apparatus and method for sealing gas turbine blade roots

A sealing apparatus and method for delivering a sealing material to gaps between gas turbine blade roots and the corresponding grooves of a rotor disc are disclosed. The sealing apparatus comprises a tank for housing a pressurized sealing material, a delivery tube for delivering the sealing material from the tank to the rotor disc, a control valve for controlling the flow of the sealing material, a sealing fixture for distributing the sealing material to the gaps between the blade roots and the corresponding grooves, an O-ring seal for effecting a tight seal between the sealing fixture and the rotor disc, and jack screws for maintaining the sealing fixture securely in place.

FIELD OF THE INVENTION 
The present invention relates generally to gas turbines, and more 
particularly to an apparatus and method for sealing the gaps between gas 
turbine blade roots and the corresponding grooves of a rotor disc. 
BACKGROUND OF THE INVENTION 
Gas turbines comprise a casing for housing a compressor section, combustion 
section and turbine section. The compressor section comprises an inlet end 
and an outlet end. The combustion section comprises an inlet end and a 
combustor transition. The combustor transition is proximate the discharge 
end of the combustion section and comprises a wall that defines a flow 
channel that directs the working fluid into the turbine inlet end. 
A supply of air is compressed in the compressor section and directed into 
the combustion section. The compressed air enters the combustion inlet and 
is mixed with fuel. The air/fuel mixture is then combusted to produce high 
temperature and high pressure gas. This gas is then ejected past the 
combustor transition and injected into the turbine section to run the 
turbine. 
Gas is forced through the blades of a gas turbine to run the turbine and 
produce electricity by causing the rotor to drive a generator. The blades 
of a turbine, as well as the blades in the compressor section of a 
turbine, typically comprise an airfoil, a platform, a shank and a root 
that fits into a complementary-shaped groove formed in the periphery of a 
rotor disc, which itself is located on the periphery of the rotor. 
The airfoil portion of the blade is the distal portion of the blade that 
translates the axial flow of the gas to rotor rotation. Moving radially 
inward, the platform is the portion of the blade that rests on the outer 
surface of the rotor disc. The shank is the portion that extends down into 
the rotor disc from the platform and usually has a narrower cross-section 
than that of the platform. The root is the bottom portion of the blade 
that has a jagged or dovetail shape so as to fit securely within the 
groove of the rotor disc, which has a correspondingly complementary shape 
to that of the blade root. 
During the operation of a gas turbine, the working gas can leak through 
gaps between the turbine blade roots and the corresponding grooves of a 
rotor disc. This yields a reduction in working gas to turn the turbine 
blades, thereby reducing the efficiency of the turbine section. Likewise, 
air in the compressor section of a gas turbine can leak through these same 
gaps. Thus, not all of the air entering the compressor is compressed, 
resulting in a decrease in efficiency of the compressor section. Leakage 
occurring in the compressor section of the turbine section reduces the 
efficiency of the gas turbine. 
To prevent any leakage between the turbine blade roots and the 
corresponding grooves of a rotor disc, those skilled in the art have 
utilized several methods to seal this space. A common technique, during 
turbine assembly, is to affix a sealing device to the blade root and then 
mount the blade in the corresponding groove of the rotor disc. One such 
sealing method, disclosed in U.S. Pat. No. 5,558,500, is to affix an 
elastomeric seal made of silicone rubber to a portion of a blade root and 
then mount the blade root in the groove of a compressor rotor disc. This 
technique, as well as other prior art techniques, however, require sealing 
the gaps prior to mounting the turbine blades onto a rotor disc. 
Therefore, to seal the gaps between turbine blade roots and corresponding 
grooves on a rotor disc of a working gas turbine, prior art sealing 
techniques require disassembly of the turbine. These prior art sealing 
procedures result in significant downtime of the turbine at a significant 
cost to the operator or customer. It is thus desirable to provide a 
sealing technique for retrofit application, allowing for sealing the gaps 
between turbine blade roots and corresponding grooves of a rotor disc 
while not requiring disassembly of any components of the gas turbine. 
SUMMARY OF THE INVENTION 
A sealing apparatus and method for delivering a sealing material to gaps 
between gas turbine blade roots and the corresponding grooves of a rotor 
disc are disclosed. The sealing apparatus comprises a tank for housing a 
pressurized sealing material, a delivery tube for delivering the sealing 
material from the tank to the rotor disc, a control valve for controlling 
the flow of the sealing material, a sealing fixture for distributing the 
sealing material to the gaps between the blade roots and the corresponding 
grooves, an O-ring seal for effecting a tight seal between the sealing 
fixture and the rotor disc, and jack screws for maintaining the sealing 
fixture securely in place. 
The method for delivering a sealing material to gaps between turbine blade 
roots and the corresponding grooves of a rotor disc comprises the steps of 
positioning the sealing fixture on the side face of a rotor disc, 
actuating the jack screws until their free ends abut the side face of an 
adjacent rotor disc, mixing a sealing material, which is preferably a 
resilient, high temperature resin, with a hardener or catalyst sealing and 
pressurizing the resin with an inert gas such as nitrogen, and actuating 
the control valve to control the flow of the sealing material. 
The resin is conducted through the sealing fixture until it reaches the 
side face of the rotor disc so as to deliver the resin to the gaps and 
resiliently seal the same. The sealing fixture is moved to enclose or 
cover the next series of rotor blade root/groove gaps to seal those gaps. 
The sealing fixture may be sized to seal any number of gaps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, wherein like numerals indicate like elements, 
there is shown in FIG. 1 a partial, side elevation view of a conventional, 
prior art rotor disc 20. The rotor disc 20, located on the periphery of a 
rotor body 22 in either a compressor section or turbine section of a gas 
turbine, has a plurality of grooves 18 situated around the circumference 
of the rotor disc 20. 
The rotor blades 10, each comprising an airfoil 12 and a blade root 14, fit 
into the grooves 18 of the rotor disc 20. The grooves 18 are designed to 
secure the rotor blades 10 in place on the rotor disc 20. Gaps 16 between 
the blade roots 14 and the corresponding grooves 18, however, result when 
the rotor blades 10 are mounted on the rotor disc 20 due to manufacturing 
tolerances and the need to provide space for expansion. 
FIG. 2 shows a preferred embodiment of a sealing apparatus 28 according to 
the present invention, and is illustrated in cooperation with a rotor disc 
20. The function of the sealing apparatus 28 is to deliver a sealing 
material 32 to the gaps 16. The sealing apparatus 28 comprises a tank 30 
for housing a pressurized sealing material 32, a delivery tube 40 for 
delivering the sealing material from the tank 30 to the rotor disc 20, a 
control valve 44 for controlling the flow of the sealing material 32, a 
sealing fixture 50 for distributing the sealing material 32 to the gaps 16 
between the blade roots 14 and the corresponding grooves 18, an O-ring 
seal 80 for effecting a tight seal between the sealing fixture 50 and the 
rotor disc 20, and jack screws 70 for maintaining the sealing fixture 50 
securely in place. 
The tank 30 houses the sealing material 32 and comprises an outlet port 38. 
The delivery tube 40 comprises an inlet end 42 and an outlet end 48. The 
sealing fixture 50 comprises an upper face 58, an open face 54, a closed 
face 56, an inlet port 52, and a mounting lip 82. Each jack screw 70 
comprises a fixed end 68 and a free end 72. 
The tank 30 is mechanically coupled in fluid communication with the 
delivery tube 40 at the junction of the tank's 30 outlet port 38 and the 
delivery tubels 40 inlet end 42. The control valve 44 is located on and 
mechanically coupled with the delivery tube 40, preferably in close 
proximity to its inlet end 42. The delivery tube is mechanically coupled 
in fluid communication with the sealing fixture 50 at the junction of the 
delivery tube's 40 outlet end 48 and sealing fixture's inlet port 52, 
preferably on the upper face 58 of the sealing fixture 50. 
The sealing fixture 50 is coupled with the side face 24 of the rotor disc 
20 by means of the O-ring seal 80. The mounting lip 78 which spans the 
border of the open face 54 of the sealing fixture 50 is coupled to the 
rotor disc 20 at 82. The jack screws 70 are imbedded in mounting holes 66 
in the sealing fixture 50 at the fixed ends 68 of the jack screws 70. The 
free ends 72 of the jack screws 70 abut the side face 26A of the rotor 
disc 20A adjacent (or facing) the closed face 56 of the sealing fixture 
50, as rotor discs 20 and 20A are spaced at intervals, e.g., six inches 
apart, along the length of a compressor section or turbine section of a 
gas turbine. 
FIG. 3 shows a front elevation view of the sealing fixture 50 according to 
the invention. In addition to the components mentioned above, the sealing 
fixture 50 further comprises a central channel 60 for conducting the 
sealing material 32 through the sealing fixture 50 and an outlet port 62. 
The central channel 60 extends from the inlet port 52 to the outlet port 
62 of the sealing fixture 50. As shown in FIG. 3, the O-ring seal 80 
extends all around the mounting lip 78 of the sealing fixture 80. 
FIG. 3A shows a more detailed cross-sectional view of the preferred 
embodiment of the sealing fixture 50 (jack screws 70 not shown). FIG. 3A 
depicts the approximate dimensions (in inches) of all of the components of 
a preferred embodiment of the sealing fixture 50. 
The operation of the present invention in cooperation with two rotor discs 
20 and 20A as shown in FIG. 2 will now be provided. The sealing fixture 50 
is positioned on the side face 24 of a rotor disc 20 as shown in FIG. 2 to 
seal a plurality of gaps 16 between blade roots 14 and corresponding rotor 
disc grooves 16. The O-ring seal 80 serves to effect a tight seal between 
the sealing fixture 50 and the rotor disc 20 as the jack screws 70 are 
actuated until their free ends 72 abut the side face 26A of the adjacent 
rotor disc 20A. 
Sealing material 32 is preferably resilient, is preferably a high 
temperature resin thoroughly mixed with a hardener or catalyst in the tank 
30, and is preferably capable of withstanding high pressure. More 
preferably, the sealing material 32 is a room temperature vulcanizing 
(RTV) silicone rubber having suitable operating temperatures. Even more 
preferably, the sealing material 32 is Dow Corning brand 3120 RTV 
silicone. The tank 30 is sealed and pressurized with an inert gas such as 
nitrogen, entering at the inlet port 34, to approximately 125 to 150 psi 
(lb/in.sup.2) that is displayed on the pressure gauge 36. 
The control valve 44, provided to control the flow of the sealing material 
32, is actuated to allow flow of the sealing material or resin 32 out of 
the tank 30 at its outlet port 38, through the inlet end 42 of the 
delivery tube 40 and through the delivery tube 40 toward the sealing 
fixture 50. The resin 32 exits the delivery tube 40 at its outlet end 48 
and enters the sealing fixture 50 at its inlet port 52. 
The resin 32 is then conducted through the central channel 60 of the 
sealing fixture 50 until it reaches the outlet port 62. At the outlet port 
62, the resin 32 fills in the space between the open face 54 of the 
sealing fixture 50 and the side face 24 of the rotor disc 20. The resin 32 
is then forced into the gaps 16, as shown in FIG. 1, between the blade 
roots 14 and corresponding grooves 18 on the rotor disc 20. When resin 32 
is visible on the other side face 26 of the rotor disc 20, the sealing of 
the gap 16 is complete. 
The jack screws 70 are then actuated to release the sealing fixture 50 from 
its tight seal. The rotor disc 20, especially the side face 24 of the 
rotor disc 20 where gaps 16 were just sealed is cleaned, i.e., any excess 
resin 32 is wiped away. The sealing fixture 50 is moved to enclose or 
cover the next series of rotor blade root 14/groove 18 gaps 16 to seal 
those gaps 16. The sealing fixture 50 may be sized to seal any number of 
gaps 16. 
The foregoing procedure is repeated for any gaps 16 that need sealing. 
Approximately 12 to 24 hours after application of the resin 32, the 
turbine can return to service. Thus, a sealing apparatus 28 and sealing 
technique for retrofit application, allowing for sealing the gaps 16 
between gas turbine blade roots 14 and corresponding grooves 18 of a rotor 
disc 20, is achieved. 
The foregoing detailed description provides a sealing apparatus 28 and 
procedure for sealing blade roots 14 of a compressor section or turbine 
section of a gas turbine. With a suitable sealing material 32 that can 
withstand the high temperatures of the turbine section of a steam turbine, 
however, the invention can also be used to seal the gaps 16 between blade 
roots 14 and the corresponding grooves 18 of a rotor disc 20 in the 
turbine section of a steam turbine. 
It is to be understood that even though numerous characteristics and 
advantages of the present invention have been set forth in the foregoing 
description, together with details of the structure and function of the 
invention, the disclosure is illustrative only, and changes may be made in 
detail, especially in matters of shape, size and arrangement of parts 
within the principles of the invention to the full extent indicated by the 
broad general meaning of the terms in which the appended claims are 
expressed.