Claims:We claim:
1) A means provided inside a casing (C) of a turbine for reduction of hoop stresses on external bolts of the casing (C) comprising a top half labyrinth holder (202) and a bottom half labyrinth holder (204) having a semi curvilinear divergent cone shaped outer surface circumscribed by a rim (R1 and R2) and provided with flanges (F1 and F2) on their either extreme ends, said top half labyrinth holder (202) and said bottom half labyrinth holder (204) adapted to pass through a groove of the casing (C) and assembled over the horizontal plane with the help of said flanges (F1 and F2) encompassing a rotor of the turbine in such a way that said semi curvilinear divergent cone shaped outer surface of said top half labyrinth holder (202) mates with an opening (O) of an exhaust hood (EH) of said casing (C), said top half labyrinth holder (202) and said bottom half labyrinth holder (204) arrests the exposure of the working fluid to a portion (B3) of said casing (C).

2) A means provided inside a casing (C) of a turbine for reduction of hoop stresses on external bolts of the casing (C) as claimed in claim 1, wherein said top half labyrinth holder (202) and said bottom half labyrinth holder (204) takes the impact of pressure of working fluid without transferring it to external bolts of the casing (C) and prevents the leakage of working fluid.

3) A means provided inside a casing (C) of a turbine for reduction of hoop stresses on external bolts of the casing (C) as claimed in claim 1, wherein said top half labyrinth holder (202) and said bottom half labyrinth holder (204) finds their application in casings with extraction vents, bleed vents and exhaust hoods.
, Description:FIELD OF THE INVENTION:
The present invention relates to the field of reduction of hoop stresses on external bolts of a turbine casing. Particularly, the present invention relates to a provision of a means inside a turbine casing for reducing hoop stresses on external bolts of the turbine casing.

BACKGROUND OF THE INVENTION:
Turbine casings are generally subjected to high hoop stresses due to internal pressure of working fluid which results in loosening of bolts that are locking both halves of the turbine casings and ultimately resulting in leakage of working fluid. So, it is a general practice in turbine industry to use bolts of greater thickness for locking both halves of the turbine casing to withstand hoop stresses and thereby prevent leakage of working fluid.

Figure 1 illustrates an isometric view of a casing of a turbine.

It is evident from outer appearance of the casing of the turbine that addition of ribs on its outer surface to withstand hoop stresses is not possible.

Figure 2 illustrates a cross-sectional view of a turbine with a casing of figure 1.

Figure 3 illustrates an isometric view of a labyrinth holder of figure 2.

Figure 4 illustrates an isometric view of a labyrinth seal of figure 2.

According to the figure 2, there is provided a turbine comprising a casing 10, a rotor 12, a plurality of blades 14, a nozzle chest 16, a plurality of labyrinth holders 18 and a plurality of labyrinth seals 20. The plurality of blades 14 are mounted on a plurality of rotor discs of the rotor 12. The plurality of labyrinth holders 18 inserted in to grooves of the casing 10 includes the plurality of labyrinth seals 20 inserted in to the plurality of labyrinth holders 18 and encompasses the rotor 12. The working fluid enters the turbine through the nozzle chest 16, expands over the plurality of blades 14 resulting in drop of pressure and temperature of working fluid thereby converting the thermal energy in to mechanical energy. So, the impact of pressure of working fluid on the casing 10 at portion of the plurality of blades 14 generally indicated by a reference letter A is less when compared to the impact of pressure of working fluid on the casing 10 at portion indicated by a reference letter B. At portion B, the impact of pressure of working fluid on the casing 10 at portion indicated by a reference letter B1 is less due to provision of exhaust hood EH when compared to the impact of pressure of working fluid on the casing 10 at portion indicated by a reference letter B2.

Typically, the labyrinth holders 18 available in the market are of semi cylindrical shape assembled at horizontal plane and serve the purpose of prevention of leakage of working fluid and thereby improving the performance of the turbine.

Several techniques have been disclosed in the prior art to reduce hoop stresses in turbo machines.

US Patent no. 5605438 filed on December 29, 1995 titled “Casing distortion control for rotating machinery” discloses a turbine casing provided with structural members like circumferential ribs and axially extending ribs on its outer surface to withstand hoop stresses. In this granted patent, a method is taught to withstand hoop stresses by the turbine casing but there is no preliminary mechanism to stop the transfer of impact of pressure of working fluid to external bolts of the turbine casing. The provision of this type of ribs is not possible on all types of casings especially casings with extraction vents, bleed vents and exhaust hoods. Further, casting of this type of casings with circumferential ribs and axially extending ribs is complicated and takes a lot of time.

US Patent no. 7097422 filed on February 3, 2004 titled “Hoop Stress Relief Mechanism for Gas Turbine Engines” discloses a plurality of J-shaped slots provided radially around the circumference of a rotor disc to withstand hoop stresses caused by both thermal and centrifugal forces. The granted patent teaches about mechanism to withstand hoop stresses on a rotor of a turbine but the patent is silent on mechanism to withstand hoop stresses on a casing of a turbine.

Therefore, there is felt a need for provision of a means inside a casing of a turbine to overcome the drawbacks of the prior art and thereby reducing hoop stresses on external bolts of the casing of the turbine.

OBJECTS OF THE INVENTION:
An object of the present invention is to provide a simple means inside a casing of a turbine for reducing hoop stresses on external bolts of the casing.

Another object of the present invention is to provide a means inside a casing of a turbine to avoid contact of working fluid with inner surface of the casing.

One more object of the present invention is to reduce impact of pressure of working fluid on inner surface of a casing of a turbine towards working fluid exit end.

Still another object of the present invention is to provide a fool proof mechanism to prevent leakage of working fluid by reducing hoop stresses on external bolts of a casing of a turbine.

Further another object of the present invention is to reduce stress concentration on external bolts of a casing towards working fluid exit end.

Still one more object of the present invention is to provide an alternative means for reducing hoop stresses on external bolts of casings with extraction vents, bleed vents and exhaust hoods.

SUMMARY OF THE INVENTION:
In accordance with the present invention a means inside a casing (C) for reduction of hoop stresses on external bolts of the casing (C) is provided, the means comprising a top half labyrinth holder (202) and a bottom half labyrinth holder (204) having a semi curvilinear divergent cone shaped outer surface circumscribed by a rim (R1 and R2) and provided with flanges (F1 and F2) on their either extreme ends, the top half labyrinth holder (202) and the bottom half labyrinth holder (204) adapted to pass through a groove of the casing (C) and assembled over the horizontal plane with the help of the flanges (F1 and F2) encompassing a rotor of the turbine in such a way that the semi curvilinear divergent cone shaped outer surface of the top half labyrinth holder (202) mates with an opening (O) of an exhaust hood (EH) of the casing (C), the top half labyrinth holder (202) and the bottom half labyrinth holder (204) arrests the exposure of the working fluid to a portion (B3) of the casing (C).

Typically, the top half labyrinth holder (202) and the bottom half labyrinth holder (204) takes the impact of pressure of working fluid without transferring it to external bolts of the casing (C) and prevents the leakage of working fluid.

Typically, the top half labyrinth holder (202) and the bottom half labyrinth holder (204) finds their application especially in casings with extraction vents, bleed vents and exhaust hoods.

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 a casing of a turbine according to the prior art;

Figure 2 illustrates a cross-sectional view of a turbine with a casing of figure 1 according to the prior art;

Figure 3 illustrates an isometric view of a labyrinth holder of figure 2;

Figure 4 illustrates an isometric view of a labyrinth seal of figure 2;

Figure 5 illustrates a cross-sectional view of a turbine in accordance with the present invention; and

Figure 6 illustrates an isometric view of a top half labyrinth holder and a bottom half labyrinth holder of figure 5 assembled over the horizontal plane in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A preferred embodiment will now be described in detail with reference to accompanying drawings. The preferred embodiment does not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.

Figure 5 illustrates a cross-sectional view of a turbine.

Figure 6 illustrates an isometric view of a top half labyrinth holder and a bottom half labyrinth of figure 5 assembled over the horizontal plane.

In accordance with the present invention, there is provided a means inside a casing C of a turbine for reduction of hoop stresses on external bolts of the casing C comprising a top half labyrinth holder 202 and a bottom half labyrinth holder 204. The top half labyrinth holder 202 resembles a semi curvilinear divergent cone on its outer surface circumscribed by a rim R1 and provided with flanges F1 on its either extreme ends. The bottom half labyrinth holder 204 resembles a semi curvilinear divergent cone on its outer surface circumscribed by a rim R2, supported by a rib RB at its bottom end and provided with flanges F2 on its either extreme ends. The top half labyrinth holder 202 and the bottom half labyrinth holder 204 are adapted to pass through a groove of the casing C and assembled over the horizontal plane with the help of flanges (F1 and F2). The semi curvilinear divergent cone shaped outer surface of the top half labyrinth holder 202 facilitates in mating with an opening O of an exhaust hood EH of the casing C. The top half labyrinth holder 202 and the bottom half labyrinth holder 204 prevents the exposure of the working fluid to a portion B3 of the casing C.

The top half labyrinth holder 202 and the bottom half labyrinth holder 204 takes the impact of pressure of working fluid without transferring it to external bolts of the casing C and prevents the leakage of working fluid.

TECHNICAL ADVANCEMENTS:
A means provided inside a casing of a turbine for reduction of hoop stresses on external bolts of the casing has several technical advantages including but not limited to the realization of :
• a simple means inside a casing of a turbine for reducing hoop stresses on external bolts of the casing ;
• a means inside a casing of a turbine to avoid contact of working fluid with inner surface of the casing ;
• a means inside a casing of a turbine to reduce impact of pressure of working fluid on inner surface of the casing towards working fluid exit end ;
• a fool proof mechanism to prevent leakage of working fluid by reducing hoop stresses on external bolts of a casing of a turbine ;
• a means inside a casing of a turbine to reduce stress concentration on external bolts of a casing towards working fluid exit end ; and
• an alternative means for reducing hoop stresses on external bolts of the casings with extraction vents, bleed vents and exhaust hoods.

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.