Field of Invention:
This invention relates to a fixture and the process for drilling locking holes
with the same on the rotor for fixing the Fans in a TARI type Turbo Generator by
Horizontal Boring machine .
Background of the invention:
TARI is the nomenclature given to an air cooled Turbo Generator in which
the cooling gas in the casing is air. The Rotor winding cooling is done by radial
air, while stator winding cooling is done through indirect air.
In turbo generator, heat is produced while running due to eddy current,
hysteresis, copper and other losses in Stator and rotor winding and stator core.
This heat increases the temperature inside the Turbo Generator winding.
If this heat is not quenched or cooled off, temperatures will keep on rising
due to cumulative effect and the temperature may go detrimentally high. This
high temperature causes deterioration of the insulation properties and may
ultimately cause breakdown of the Turbo Generator.
For the above said requirement of cooling in TG, on Rotor both the sides Fans
are assembled for cooling the Rotor Coil (as heat is generated in coil due to
copper losses). Circular air flow happens due to natural phenomenon of "Thermo
siphon" in which hot air being lighter tends to go up and cold air being heavier
tends to go down but to accelerate this flow axially, fans are provided on both
side of rotor shaft (refer fig. 4), by mounting fan blades on the hub of the rotor.
One group of 27 blades is mounted on each side of the Rotor. Each blade is
mounted on blower half in M60X2 hole(10) and each blade is locked by 2 no.

pins mounted on M10 holes (11). These M60 holes (10) are used to assemble
and clamp the fixture (F) on the rotor to drill the required M10 holes (11) which
are subsequently to be used for locking the Fans to be fixed in the M60 holes
(10) subsequently.
Since the rotor is rotated at a very high speed of 3000 rpm therefore fans
mounted on its periphery are exposed to high centrifugal force. Any loosening of
the fan blade from shaft shall cause extensive damage in the winding and may
lead to total failure. For avoiding this, fan blades are required to be properly
locked.
This being a new rating projects, it was necessary to perform this
important operation carefully and without any hazards. Without a jig, it was not
possible to make these holes. The holes were tired with the old jig of hydrogen
cooled design rotors but the jig could not be fitted in the shaft and could not give
desired result. The operation was tried directly with a drill but substantial amount
of rework had to be done as the drill was not going straight and there was a risk
of total rejection. The time taken without jig was very high and job quality very
poor. Also drilling the locking holes directly without a fixture using a hand drill,
resulted frequent breakage of drill bit. Above process was time consuming as
time taken to drill holes by hand drill is phenomenal and time is also consumed
to takeout the broken drill if the broken drill bit is left inside the hole.
Brief description of the accompanying drawings:
Fig.l : Shows a guiding fixture according to the invention.
Fig.2 : Shows the threaded nut to be assembled with the fixture according
to the invention.
Fig.3 : Shows the fixture according to the invention along with the nut.
Fig.4 : Shows the position of locking holes and Fan holes on a rotor
according to the invention.

Objects of the Invention:
Therefore, the object of the invention is to propose a fixture and a
process for drilling locking holes with the same on a rotor for fixing the Fans in
TARI type Turbo Generator by Horizontal Boring Machine, which is capable of
eliminating the disadvantages of prior art.
Another object of the invention is to propose a fixture and a process for
drilling locking holes with the same on a rotor for fixing the Fans in TARI type
Turbo Generator by Horizontal Boring Machine, which is able to reduce the
operational time by 50% compared to direct drilling.
Further object of the invention is to propose a fixture and a process for
drilling locking holes with the same on a rotor for fixing the Fans in TARI type
Turbo Generator by Horizontal Boring Machine, which can avoid the breakage of
drill bit in the holes and produce quality holes without rework thus saves
substantial time and money.
A still another object Fixture and a process for drilling locking holes with
the same on a rotor for fixing the Fans in TARI type turbo generator by
Horizontal Boring machine, which is capable of maintaining the dimensional
accuracy of the size of the holes as well as distance between the pair of locking
holes.
Detailed description of a preferred embodiment of the invention:
As shown in Fig. 3, the fixture (F) is made of the three components. One
is a plate (1) called a metallic fork with its contour in one side of the thickness
machined to a first bracket or arc shape matching to the outside circumference
of a metal bush (12). The plate (1) and the bush (12) is welded (7) together. A
plate (2) is fixed to the plate (1) and having guided holes (13) with bushes drive
fit to the holes for guiding the drill bit. The plate (2) is fixed to the plate (1) at
right angle and vertically down. The guiding holes (13) on plate (2) guides the

drill bit in such a way that holes are accurately done at the place of requirement
as per drawing. The holes have to be done in such a way that the holes are at
desired margin from the outer edge of the rotor while the distance between the
holes are maintained within tolerance. In case, the guiding is not proper, there
would be a noise at the very beginning of the process as because of the fouling
between the holes and the drill bit, thus, the process can be stopped before any
damage to the rotor. The bush (12) the fixture is strategically designed in such a
way that inner diameter of item (12) is just greater than the threaded diameter
(5) of threaded nut (4) and outer diameter is bigger than the same such that it
acts as a collar (6) to support tightening force from item (4). The threaded nut
(4) has a diameter (6) for holding and gripping the nut (4). This diameter (6) is
knurled so that the grip is firm. As shown in Fig.2, the knurled portion is shown
by hatch marks on diameter 6.
As shown in Fig.3, the fixture (F) has the threaded nut in the fabricated
part (1,2). The threads (5) of the nut (4) is made same as that of Fan holes
thread M60X2 on the rotor.
As shown in Fig.3, the threaded nut (4) is pushed inside the holes of
fabricated part (1,12). Now the fixture (F) is fixed to the rotor (9) by tightening
the nut (4) with the help of grip (6) when the thread of item 4 gets tightened
with the thread of Fan blade holes(lO) as shown in Fig.4. The fixture (F) is
clamped to the Fan holes' in such a manner that the plate(2) with guiding holes
(13) is in perfect position forth drilling the required holes on the rotor as per
drawing. There are two guiding holes (13) on the plate for making two holes as
per the requirement of the drawing. After clamping the fixture (F), the machine
spindle is brought near the plate (2) and then passes through the guiding bush
and drills the hole (11). The process is repeated with other guiding bush for the
other hole (11). The rotor is then rotated a bit to create next two hole (11)
maintaining the distance between the holes.

Benefits incurred:
Productivity: Since the hole can be made in a self guided manner, the
time to make locking holes is less thus leading to higher productivity;
Quality : By carrying out the operation in a fool-proof manner, the
quality of the job has increased and problems rework is no more.
Monetary benefits:
1. One time saving in cost of importer jig: Rs. 15,00,000
2. Regular saving
A. On account of reduction in time to produce locking ring holes : per rotor
saving = 48 hour * 2 person * 186 Rs/hour = Rs 17856 * 10 rotors per year =
Rs 1.78,560/-
B. Saving on account of reduction in horizontal machining time = 44 hours
per set., m/c per hr cost= Rs 2000; Total savings= 44X2000X10=Rs 8,80,000
C. Saving on account of rework involving repeat drilling: 28 hours per set X
m/c per hr cost= Rs2000: 28X2000X10= Rs 5,60,000
D. Less cost of developing tooling:
Manpower cost = 24 hours * 2 persons * 186= Rs 8928/-
Machining cost = 4 Hrs * 1250 per hour = Rs 5,000/-
ANNUAL SAVING (A+B+C-D)= 16,04,632 Rs.

We Claim
1. A Fixture and a process for drilling locking holes with the same on a rotor for
fixing the Fans in TARI type Turbo Generator by Horizontal Boring Machine, the said
fixture (F) comprising;
a plate (1) or a metallic fork having one side arc shape for welding with a metal bush
(12);
a metal bush (12) with hole for accommodating a threaded nut (4); a threaded nut (4)
with knurled grip (6) and having a threaded part (3) at the bottom
characterized in that;
a plate (2) fixed at right angle and vertically down to the plate (1) is disposed with
guiding holes (13) filled with guiding bush for guiding the drill bit for producing the
required locking holes (11) on the rotor wherein, the threaded part (5) of the said nut
(4) of the fixture (F) is disposed in the fan holes (10) having the same thread when the
said nut (4) is tightened to clamp the fixture on the rotor (9) by the knurled dia (6) of
the said nut (4) acting as a collar.
2. The fixture (F) as claimed in claim 1 is made of alloy steel.
3. A process for drilling locking holes on a rotor for fixing the Fans comprising;
assembling the fixture (F) by disposing the threaded nut (4) in the hole of metal
bush (12);
putting the threaded part (5) of threaded nut (4) of the fixture (F) on the Fan
holes (10);
clamping the fixture (F) on the rotor by tightening the thread of the said nut (4)
with the matching thread of the Fan holes;
bringing the machine spindle in front of the plate (2); drilling the locking holes
wherein , the rotor is rotated to align the next locking holes of the rotor when all the
locking holes of the rotor are drilled accurately.

ABSTRACT

The fixture (F) for making locking holes is made of a metallic fork (1)
having one side arc shaped for welding with a metal bush (12) which has a hole
at the middle to a accommodate a threaded nut (4) which has a knuhe diameter
(6) in one end and a threaded part (5) at the other. A plate (2) is fixed to the
metallic fork (1). The plate (2) has the guiding holes to guide the drill bit. The
nut (4) is disposed in the Fan holes of the rotor. The thread of the nut matches
with that of the Fan holes. The fixture is clamped on the rotor by tightening the
thread of the part (5) with the help of knurled dia .(6) which acts as a collar
while sitting on the face of the metal bush (12). The guiding holes of the plate
(2) guides the drill bit for producing the required locking holes (11) of the rotor.