FIELD OF INVENTION
The present invention relates to a method of manufacturing gland steam holes opening in shaft seal area of steam turbine casing through machining. More particularly, the invention relates to a manufacturing process for the formation of intricate gland steam Holes by the means of machining in shaft seal area of steam turbine which could not be formed through casting.
BACKGROUND OF INVENTION
A steam turbine module consists of three main components viz. Outer casing, inner casing and bladed rotor. Bladed Rotor of the turbine is first kept in inner casing or cylinder and inner casing is then covered by the outer casing of the turbine. The outer casing is divided into two halves i.e., upper and lower half.
A steam turbine ordinarily has a shaft, or rotor, resting in bearings and enclosed in one or more casings, referred to as cylinders. At the point where the rotor penetrates the outer cylinders some means is required in order to prevent leakage of air into, or steam from, the cylinders. Members known as glands having labyrinth-type seal rings in conjunction with a gland sealing steam system are provided to perform this function.

During startup or at relatively low load conditions, sealing steam for the glands is provided by a steam supply such as an auxiliary boiler designed for this purpose. Once the turbine is running at higher load levels, the steam for sealing the gland is provided from within the turbine itself such as by exhaust steam, during which condition the system is self-sealing.
These glands sealing steam is passed through casting of the turbine.
Casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process.
One of metal casting’s strongest selling points is its ability to encompass several parts, often in the form of a welded assembly, into one component. This is possible because the nature of the metal casting process lends itself to complex geometries. At the heart of many of these complex geometries is a core or core assembly.
A core is a shaped body, usually made of sand, which forms the interior part of the casting, like the cavity the pit makes in the flesh of a peach. In metal casting, the mold provides a space for the molten metal to go, while the core keeps the metal from filling the entire space.

Cores allow you to incorporate holes in your design, but these holes don’t have
to be limited to the see-through kind you’d find in a length of pipe. Cores can
take on a variety of angles and shapes, and more than one can be used per
casting. Sometimes, an assembly of cores is constructed to create a web of
internal passageways and chambers.
Most cores are generally made of sand, although they also can be made of
ceramic or metal. The core acts as a negative, displacing molten metal as it is
poured into the casting mold. Following the solidification of the metal, the sand
core is shaken out, revealing the void.
In order for a core to successfully produce a quality casting, the core must have
several different types of strength. It must be strong enough to maintain its form
while it is prepared and handled, withstand the hot metal poured into a mold,
and exhibit minimal expansion or contraction in order to maintain good
dimensional accuracy. These necessary strengths should be considered during
casting design in order to ensure an accurate component can be cast in an
efficient and productive manner.
A typical job, its pattern and the mold cavity with core and core print is shown in
Figure 12.
Outer (Lower Half) consists of intricate curved paths for gland sealing steam in
shaft seal area. These paths for gland sealing steam should have been formed
during casting of Outer casing in casting facility. These steam paths have 3-

dimensional trajectory which is impossible to machine and must be casted, but due to technological problem in designing of cores operating at very high elevated temperatures, these paths could not be incorporated at foundry and forging facility. So, casting design was reviewed with a view to form these curved paths for in shaft seal area in such a way, so that the formation of such gland sealing steam passage holes can come under the ambit of conventional machining.
OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose a method of manufacturing gland steam holes in shaft seal area of steam turbine casing through a machine which is capable of drilling four compound holes and four corresponding holes on a cast surface of a steam turbine casing, both intersecting each other to obtain a path of gland sealing stem flow.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the

accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which
Figure 1A & 1B are perspective view of Outer Casing having intricate hollow curved path for movement of gland sealing steam as in the prior art.
Figure 2 is yet another perspective view of Outer Casing having intricate hollow curved path for movement of gland sealing steam as in the prior art.
Figure 3 is a perspective view of the new uniform trajectory substituting the previous curved path for the movement of gland sealing steam according to the invention.
Figure 4, 5, 6, 7 are perspective view of the new uniform trajectory substituting the previous curved path for the movement of gland sealing steam according to the invention.
Figure 8A & 8B are perspective view of the new uniform trajectory substituting the previous curved path for the movement of gland sealing steam in accordance with the invention.
Figure 9 is a perspective view of the drilling machine setup for new uniform trajectory substituting the previous curved path for the movement of gland sealing steam as per the invention.

Figure 10, 11 are perspective view of the new uniform trajectory substituting the previous curved path for the movement of gland sealing steam according to the invention
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Designing of gland sealing steam holes
Casting of Outer casing requires hollow curved paths (P) in shaft seal area as per figure 1A & 1B. This path has rectangular cross section at the beginning of shaft seal and gets constantly blended with circular cross section and this circular hole finally get blended with smaller circular opening as per section CC. This path with above cross section has 3 dimensional trajectory (refer section CC, View –X in Figure 1A) at the beginning then transcends in curved path and finally get ended as per Sec CC of figure -1A. This is further shown in simplified figure-2. The above path with variable cross section is changed to uniform circular cross section throughout the new trajectory substituting the previous path. The trajectory is shown in figure-3. It is clear from figure-3 that first straight hole (1) starts from shaft seal portion at compound angle (13.3 degree and 20 degree) and get merged with the second straight hole (2). Any kind of Geometrical error

in the calculation of angles and start points of both the holes could lead the mismatching of the two non-coplanar holes causing major deviation. Refer figure 4, figure 5, figure 6 & figure 7.
Manufacturing of gland sealing steam holes
For manufacturing of gland sealing steam holes in Outer casting, layout marking of pipe trajectory is done (Marking line M1 & M2 in Figure 8A) on the turbine end and generator end faces after machining of reference faces (R1) on both the ends (refer figure 8A and 8B) to ensure correct intersection during machining. The center of the hole (C1) refer figure 8B, is marked on the casting projection for pipe (P1) with reference to the already machined reference faces (R1) on the Turbine end and generator ends. Projection of the other hole (1 Refer Figure 3) at 13.3 degree angle is drawn on the above projected pipe end with taking center for the hole (C1) marked in figure 8B. The projection of the line (L1) figure 8B drawn at 13.3 degree is taken with the help of Plum and other marking devices on the outer skin surface of the casting and the point (C2) at which it meets the projection of 20 degree line (M2) figure 8A is marked as the starting point for the other skewed hole. This point location is verified again by comparing the dimensions calculated by CAD drawings. Location of both the hole should be so accurate such that it does not get punctured at any other undesired location.

This gland sealing steam holes are drilled in the following sequence:
- Job is placed with joint plane downwards height block to suit the height and orientation of machine. Job is leveled and the machine is set with respect to the job by properly touching the machine spindle to the pre machined surface (Refer figure 10). As two compound angles are needed for hole drilling, so two heads of machine are broken in degrees such a way that minimum load goes on machine. Angle 13.3 degree is taken on small head and angle 20 degree is taken on bigger head. Hole start point on the outer skin of casing is reached with the dead center on machine spindle. Seat is made for drilling the hole and then step by step drilling ranging dia 30, dia 50, dia 70, and dia 75 or 80 is to be made. Proper puncturing of hole is be ensured with pilot drill. Either long drill or drill with extension sleeves can be used. Care for chip removal and coolant supply is being taken to avoid any breakage of drill during deep drill operation.
- Similarly for each four holes, two on Turbine end and Two on Generator end Drill machine is set and drilling on hole diameter 80 mm is done as above.
- After drilling the four compound holes job is taken to Radial arm drilling machine for drilling of corresponding hole which intersects the already drilled holes to complete the path of gland sealing steam flow.
- Job is leveled on bed plate area of Radial drill machine with joint plane facing downward.

- Now four holes dia 80 mm are drilled one by one on the radial drill machine. After drilling of holes undesired opening are plugged by weld deposition and subsequent stress relieving is done in furnace as per metallurgical instructions. (Refer figure 10 & 11).
It is now apparent that the embodiment of the invention, as described hereinabove, will provide an extremely feasible method of formation of gland sealing steam holes opening in shaft seal area of steam turbine casing through machining.
The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact machining operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

WE CLAIM
1. A method of manufacturing gland steam holes opening in the shaft seal area of steam turbine casing through machining, the said method comprising;
machining reference faces (R1) on both turbine and generator ends of casing to ensure correct intersection of hole (1) and hole (2) during machining;
marking center (C1) of the hole (1) on the top face of projected casting of pipe (P1) by marking line M1 and M2 drawing projection of line of other hole (1) at 13.3 degree angle on said projected pipe with marking devices on outer skin surface of casting;
marking the point (C2) at which the 13.3 degree line intersects projection of 20 degree line to make the point as starting point for other skewed hole;
verifying and comparing dimensions of the said point location with dimensions calculated by CAD drawings;
placing the marked job (casing) with joint plane downwards on a height block suiting the height and orientation of machine;
leveling the job;
setting the machine (3) with respect to the job by making the machine spindle to touch the pre-machined surface;

distributing the machine load in two heads of the machine such that 13.3 degree angle implemented on small head and 20 degree angle implemented on bigger head;
making seat for drilling the hole;
drilling the hole step by step starting with diameter 30 mm followed by 50 mm dia, 70 mm dia and finally 80 mm dia; wherein,
each of the four holes, two being on turbine end and two on Generator end are then drilled to a diameter of 80 mm on the drill machine, when the job after being drilled for said compound holes (1) is placed on the Radial arm drilling machine to drill corresponding hole of 80 mm (2) one by one to intersect already drilled holes to complete the path of gland sealing steam flow when undesired opening is plugged (4) by weld deposition wherein subsequent stress relieving is done in furnace.