FIELD OF INVENTION
The invention generally relates to drilling of helium leak test holes in the rotor
shaft of high capacity turbo generator. More particularly, the invention relates to
a device for drilling holes for helium leak test on a rotor shaft of high capacity
turbo generators.
BACKGROUND OF INVENTION
A turbo generator is a major constituent of Thermal Power Stations. The Turbo
Generator consists of two main parts, a Stator and a Rotor. The Rotor is a
rotating part and the stator is a static part of the Turbo Generator.
As the rotor rotates at a speed around 3000 RPM, it generates a change in the
magnetic flux inside the stator. Due to change in the flux inside the stator, the
induced EMF gets generated in the conductor of the stator which provides the
current through the conductors of the stator.
During manufacturing of a turbo generator, a plurality of operations are to be
configured on the generator shaft. Initially, a forged shaft is placed on a Lathe
machine for turning operation. After completion of the turning operation, the
shaft undergoes marking operation. During the marking operation, a plurality of
operations for example, Winding slots, coupling holes, balancing holes and
Helium Leak Test holes are marked on the shaft. At least two helium leak test
holes are first marked at a position of 3 & 9 O'clock on the outer diameter of the
Exciter End coupling. After marking the shaft as described hereinabove, a slotting
operation is done, then the shaft is shifted to a Horizontal Boring machine for
configurating said helium leak test holes.
Accordingly, the Shaft is placed on two rollers (supported on the Journal, the
diameter being parallel to the machine column traverse (X-axis). The shaft is so
set that the coupling face becomes parallel to the machine spindle. The rollers
are then rotated to bring the marking of the helium-leak test holes (two
numbers) parallel to the machine spindle. After setting the spindle parallel to the
marking of the hole, firstly a hole of M18 x 1.5 mm up to a
depth of 18 mm is drilled with a counter shank of 024 x 5. Then, a second hole
of 08 is drilled upto a depth of 45 mm, then a hole of 07 is drilled upto a depth
45 mm, and finally the hole is punctuated in side of the field third lead bore by
05 m. After completion of this operation, the shaft is rotated for the next hole,
and same steps of operation is carried out.
During the drilling operation with the existing devices, the following problems
arise:
1. Breaking of Drills: As the depth of the hole 05 to be drilled is very
large (175 mm from outer diameter), a long drill of length around 250
mm is normally required. During the drilling operation; the drill often
breaks and gets stuck inside the hole. It becomes very difficult to
remove the broken drill from the hole because of the smaller diameter
and high depth of the drill-hole.
2. High setting time: According to the existing process/firstly the two
roller are disposed corresponding to the distance between two journals
of the shaft, and a gap between the shaft and the machine spindle is
maintained. Then, the job is being placed on the rollers. After loading,
the setting of the job is done to make the hole parallel to the face of
the Exciter End coupling. As the weight of the job is normally above
40 tons, a 50 tons crane is used to load the job. Setting of the job has
to be very accurate for which hydraulic jacks to shift/align the job is
adapted, which is quite cumbersome and costly.
3. High cycle time : As the depth of the hole is very high, the drilling
process cannot be operated at high feed and speed. Thus, a feed of
0.5 mm/min and 250 rpm while drilling is normally used. After drilling
each 2mm of depth, the chips from the hole is to be removed.
Accordingly, the cycle time for the process is substantially high.
Objects of the Invention :
It is therefore an object of the invention to propose a device for drilling holes
for helium leak test on a rotor shaft of high-capacity turbo generators, which
eliminates the disadvantages of the prior art.
Another object of the invention is to propose a device for drilling holes for
helium leak test on a rotor shaft of high-capacity turbo generators, which
eliminates the use of a costly Horizontal Boring Machine for carrying out the
drilling operation.
A still another object of the invention is to propose a device for drilling holes
for helium leak test on a rotor shaft of high-capacity turbo generators, which
reduces the frequency of breakage of the drills.
A further object of the invention is to propose a device for drilling holes for
helium leak test on a rotor shaft of high-capacity turbo generators, which
reduces the cycle time and increases productivity.
Brief Description of the accompanying drawings:
Figure 1: Shows a Prior Art Process Mapping chart for a drilling operation
Figure 2 : Shows an isometric view of a device for drilling helium-leak test
holes according to the invention.
Figure 3 : Shows a schematic view of the device of Fig.l without hearing the
clamping means mounted.
Figure 4 : Shows a detailed schematic view of the body of a drilling head of
the device of Figure -1.
Figure 5 : Shows a detailed schematic view of a bearing housing of the device
of Figure -1.
Figure 6 : Shows in detail the tool adaptor of the device of figure 1
Figure 7 : Shows the details of a sliding means of the device of Figure 1.
Figure 8 : Shows an examplary strip of the sliding means of Figure 7.
Figure 9 : Shows a guiding plate of the device of Figure 1.
Figure 10:Shows an angle for coupling a guide plate of the device of Figure 1.
Figure 11 : Show three different bushes used between the angle and the
guide plate of the device of Figure - 1.

Figure 12 : Shows a feeding Lever of the device of Figure 1.
Figure 13 : Shows the end covers of the device of figure - 1.
Figure 14:Shows the clamping means for mounting on the device of Figure 1.
Figure 15 : Shows a photographical view of the inventive device mounted on
a rotor shaft.
Summary of the invention
Accordingly, there is provided A device for drilling holes for helium-leak test
on a rotor shaft of high capacity turbogenerators, the devices being
mountable on the rotor shaft, the device comprising; a rotatable drilling head
disposed inside a housing ; at least two bearings (2b, 2b) accommodated in a
bearing housing detachably attached to the drill-head housing ; a guide plate
supporting a slide, the slide being attached to the drill head housing , the
guide plate releasably fixed on the coupling face of the rotor shaft via a bush
including an angle, the angle providing a clearance between the guide plate
and the slide enabling the slide to move to the extreme end of the guide
plate ; a tool adopter allowing a direct coupling of a taper shank drill, and
having at least one each of a bevel gear and a bearing (2a); a feeding lever
having a hole at a first end for attaching the slide, and a pin at a second end
which engages one of the plurality holes provided to the guide plate
depending on the location of the slide and a depth including speed of the
feed to be provided to the taper shank drill; and a clamping means on which

the drill-head housing being mountable, the drill-head can be rotated 360°
inside the housing by loosening or tightening the clamping means, the driven
end of the clamping means is attached to the side, and the driving end being
provided with a driving motor.
Detail description of the invention
Figure - 2 Shows an isometric view of a device for drilling helium-leak test
holes mounted on a rotor shaft.
Figure - 3 Shows a schematic view of the device mountable on the rotor
shaft for implementing the hole drilling operation on the rotor shaft.
As shown in figure 3, the inventive Drill Device comprises :
- a body of drilling head (1);
- a bearing housing (2);
- a tool adopter (3);
- a slide (4);
- at least one strips for the slide (19);
- a guide plate (6);
- an angle (7);
- a bush (8);
- a feeding lever (9);
- at least two end covers (10); and
- a Clamping means (11) for the drilling head (1)

Figure - 4 Shows the body of drilling head : (1) which is the main part of the
drilling device. With this part (1) all the other major components of the device
are assembled. The body (1) can rotate 360° along with the components
assembled in it. With the help of the rotatable body (1), one is enabled to drill
both from outer and inner diameter of the job.
Figure - 5 Shows the Bearing housing (2) which is push fitted into the Body of
the drilling head (1). At least two bearings (2b,2b) which support a driving shaft
(17) is fitted in it.
Figure - 6 Shows the Tool adopter (3) which constitutes a modified adaptor (3)
for a standard MT-5 sleeve, according to the Device. In this adopter (3) one can
directly fit a taper shank drill (18). One bevel gear (15) and one bearing (2a) is
fitted in the tool adopter (3).
Figure - 7 Shows the Slide (4) on which the Drill body (1) is fitted on the slide
(4) rests on a guide plate (6). A feed is given to this slide (4) with a feed lever
(9).
Figure - 8 Shows the Strips (19) for the slide (4). At least two numbers of strips
(19) are used to provide a grip to the slide (4) onto the guide plate (6) from the
bottom sides. Three Holes of M6 are used to clamp the strips (19) with the slide
(4) from the bottom side.

Figure - 9 Shows the Guide plate (6) on which the Slide rests. The Guide plate
(6) is fitted to the plurality of holes provided on the coupling face of the rotor via
a Bush (8) and an angle (7). At least two Pin (20) of 010 provided to the
feeding lever (9) is engaged into a plurality of 010 holes, for example,
seventeen holes to provide a feed to the slide (4) during drilling.
Figure - 10 Shows an angle (7) which is used to fit the guide plate (6) on the
coupling face of the rotor shaft.
As shown in figure 11, the Bush (7) is placed between the guide plate (6) and
the angle (7) for clamping of the guide plate (6). This angle (7) provides a
clearance between the guide plate (6) and the slide (4) for clamping the guide
plate (6). Due to this clearance, the slide (4) can move to the extreme ends of
the guide plate (6).
As shown in figure 12, the feeding lever (9) is used to provide a feed to the drill
(18). One end of the lever (9) having a hole 0 6 is fitted to the Slide (4) and the
other end having a pin 0 10 rests in the plurality of holes of 0 10 configured on
the guide plate (6).The pin is engaged to the holes of the guide plate (6)
according to the feed and the location of the slide (4). The lever (9) is used on
both side of the Slide (4).
As shown in figure 13, the End covers (10) are used to seal the ends of the
drilling head (1). Oil is filled inside the drilling head (1). One end cover (10) acts
as the housing (2) for the bearings (2b, 2b).

Figure -14 Shows the Clamping means (11) for the drilling head (1). The Drilling
head (1) is clamped inside a clamping means (11). The Drilling head (1) can
rotate 360° inside the clamping means (11). To rotate the drilling head (1), the
clamping means is first loosened, and the head is rotated, and thereafter the
clamp is tightened. One end of the clamping means (11) is fixed with the slide
(4) and on the other end, a driving motor (12) is fitted.
The present invention eliminates the requirement for presetting of the rollers
everytime and setting the job with respect to X-axis and Y-axis of the machine.
The drilling device is now directly mountable on the Exciter end coupling face.
The coupling holes which are very accurately machined are adapted to fix the
device on the coupling face. According to the invention, one each hole of 08 and
07 mm is first drilled from outer diameter then the drilling head of the device is
rotated by 180° and a second hole of 0 5 mm is drilled from the inner diameter
of the job. For the second hole, the drilling head (1) is moved on the slide and
rotated by 180° to drill on the outer diameter the hole of 08 and 07 mm. The
head(l) is further rotated to drill the hole 05 mm from the inner diameter. As a
hole of 05 from inside of the job is drilled, a short drill is used to puncture inside
the hole of 07. Thus, the chance of breaking the drill is substantially reduced.
Advantages of the invention.
1. As the steps of repeated presetting and setting of the job has been
eliminated, the cycle time has been reduced.
2. Chance of breaking of drills has been reduced.

WE CLAIM :
1. A device for drilling holes for helium-leak test on a rotor shaft of high
capacity turbogenerators, the devices being mountable on the rotor
shaft, the device comprising :
- a rotatable drilling head disposed inside a housing (1);
- at least two bearings (2b, 2b) accommodated in a bearing housing (2)
detachably attached to the drill-head housing (1);
- a guide plate (6) supporting a slide (4), the slide (4) being attached to the
drill head housing (1), the guide plate (6) releasably fixed on the coupling
face of the rotor shaft via a bush (8) including an angle (7), the angle (7)
providing a clearance between the guide plate (6) and the slide (4)
enabling the slide (4) to move to the extreme end of the guide plate (6);
- a tool adopter (3) allowing a direct coupling of a taper shank drill (18),
and having at least one each of a level gear (15) and a bearing (2a);
- a feeding lever (9) having a hole at a first end for attaching the slide (4),
and a pin at a second end which engages one of the plurality holes
provided to the guide plate (6) depending on the location of the slide (4)
and a depth including speed of the feed to be provided to the taper shank
drill (18); and
- a clamping means (11) on which the drill-head housing (1) being
mountable, the drill-head (1) can be rotated 360° inside the housing by
loosening or tightening the clamping means (11), the driven end of the
clamping means (11) is attached to the side (4), and the driving end
being provided with a driving motor (12).
2. The device as claimed in claim 1, wherein the drill-head housing (1)
supports via the bearings (2b, 2b) a driving shaft (17).
3. The device as claimed in claim 1, wherein the slide (4) is provided with
at least two strips (19) having at least one hole to clamp the slide (4)
with the clamping means (11).
4. The device as claimed in claim 1, comprising at least two end covers
(10) to seal the two ends of the drill head housing (1).
5. A device for drilling holes for helium-leak test on a rotor shaft of high
capacity turbogenerators, the devices being mountable on the rotor
shaft as substantially described and illustrated herein with reference to
the accompanying drawings.

The invention relates to a device for drilling holes for helium-leak test on a
rotor shaft of high capacity turbogenerators, the devices being mountable on
the rotor shaft, the device comprising a rotatable drilling head disposed inside
a housing (1); at least two bearings (2b, 2b) accommodated in a bearing
housing (2) detachably attached to the drill-head housing (1); a guide plate
(6) supporting a slide (4), the slide (4) being attached to the drill head
housing (1), the guide plate (6) releasably fixed on the coupling face of the
rotor shaft via a bush (8) including an angle (7), the angle (7) providing a
clearance between the guide plate (6) and the slide (4) enabling the slide (4)
to move to the extreme end of the guide plate (6); a tool adopter (3)
allowing a direct coupling of a taper shank drill (18), and having at least one
each of a level gear (15) and a bearing (2a); a feeding lever (9) having a hole
at a first end for attaching the slide (4), and a pin at a second end which
engages one of the plurality holes provided to the guide plate (6) depending
on the location of the slide (4) and a depth including speed of the feed to be
provided to the taper shank drill (18); and a clamping means (11) on which
the drill-head housing (1) being mountable, the drill-head (1) can be rotated
360° inside the housing by loosening or tightening the clamping means (11),
the driven end of the clamping means (11) is attached to the side (4), and
the driving end being provided with a driving motor (12).