FIELD OF THE INVENTION
The present invention relates to a device required to perform caulking near
balancing masses used for balancing the turbine rotors. More particularly, the
invention relates to a device which is capable of performing caulking process
near the edges of balancing masses as well as on the head of the grub screw
used for fixing the balancing masses, where the space is too less to perform
manual or automated hammering.
The present invention also relates to a process to perform the caulking
operation at the edge of the balancing weight groove on the turbine rotors so
as to fix the balancing weights at their defined position.
BACKGROUND OF THE INVENTION
Unbalance exists in a rotor when the mass centre axis is different to its
running centre axis. Practically all newly machined parts have asymmetrical
mass distribution due to its design and manufacturing, uneven number and
position of bolt holes, parts fitted off-center, machined diameters eccentric to
the bearing locations etc.
An unbalanced rotor, when rotating, wants to revolve around its mass centre
axis. Because the bearings restrict this movement, the centrifugal force, due
to the unbalance, causes the rotor to vibrate. These vibrations cause wear to
the bearings and, in extreme cases it may damage the whole turbine set up
during its operation. It is therefore necessary to reduce the unbalance to an
acceptable limit as per product design standards.
Removal of material by drilling, milling etc. from the heavy position on the
component is used to correct the unbalance. Alternatively it can be corrected
by adding material or mass called balancing weights to the “lighter” side of
the component to reduce the unbalance.
Since, a turbine runs at a very high RPM for a prolonged period of time, these
balancing weights try to move from their position leading to unbalance of the
turbine from its centre line again. To restrict the balancing weight’s
movement, caulking (act of punching or striking a material’s face or head so
hard, they are knocked out) is done near the edges of the weights as the
knocked out material blocks the movement of balancing weight (Refer figure
2).
To utilize the fossil fuel more efficiently in power plants and to achieve the
goal of reduction in global warming, higher rating power plant with advance
technology, such as supercritical parameter technology, are coming up that
require increasingly higher input steam temperature and pressure as to
increase the efficiency of steam power plants. But higher the temperature of
operation, lesser is the resistance of material to creep (a time-dependent
failure of materials at elevated temperature under applied stresses). The
utility of materials, exposed to elevated temperature and pressure, is limited
by their capacity to sustain elevated temperatures without undergoing loss of
strength over prolonged exposure. Therefore materials with higher
mechanical strength at lower as well as elevated temperatures are put into
use.
Though, caulking is done manually through hammering but advance and high
strength materials limit the use of conventional method of caulking i.e.,
hammering. Also in rotors pertaining to supercritical parameters, the center
distance is very less and hammering cannot be done in such a small space at
it will restrict the motion required for hammering (Refer figure 1). Also,
hammering is a repeated process that generates fatigue related issues to
the worker performing the caulking process. There are several ergonomics
related issues in situations where operator has to perform repeated manual
hammering. If hammering is not proper, it can also trigger crack initiation
which in the long run can damage the turbine and thereby affects electricity
generation. This causes serious losses to the power plant economics.
This situation is overcome by the invention of the device to perform caulking
process where the hammering cannot be done due to high material strength
and insufficient centre space.
OBJECTS OF THE INVENTION
In accordance with the structure mentioned above, it is an object of the
invention to propose a device (D) for performing caulking (punching)
adjacent to balancing masses required for balancing turbine rotors.
Another object of the invention is to propose a device (D) for performing
caulking (punching) adjacent balancing masses applicable for balancing
turbines, which allows punching /caulking of materials adjacent the edges of
balancing weights as well as on the head of the grub screw used for fixing
the balancing masses in such a way that the free movement of the weights is
restricted.
A further object of the invention is to propose a process to perform the
caulking operation in a device at the edge of the balancing weight groove on
rotors so as to fix the balancing weights at their defined position.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device (D) for performing caulking (punching)
adjacent balancing masses applicable for balancing turbines. The device is
enabled to perform caulking near balancing weight in order to restrict the
displacement of balancing weights when the turbine rotates at high RPM
during the operation. The caulking device comprises a caulking tool (1) shrink
fitted through a hole (13) constructed in front of a supporting stand (2) to
support and hold the caulking tool (1) in desired positions of
punching/caulking at the Edge of a groove (6) that holds balancing masses
(5). The front supporting stand (2) is joined to the base (9) through a welded
rigid joint. A Hydraulic jack (8) having a ram (4) is supported on rear
hydraulic stand (10) through welded joint the ram (4) opening through a
electric motor (3) connected to an Electric Power Source (EPS) (12). An
operating switch (11) controls the operation of start and end of the device
operation.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 Bladed Rotor
Figure 2 Balancing weight and punching process
Figure 3 Photographic view of the bladed rotor taken into Over Speed
Balancing Tunnel (OSBT) for balancing purpose
Figure 4 Developed device (D)
REFERENCE NUMERALS FOR IMPORTANT FETURES
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:
ITEM 1 represents the developed caulking tool with a pointed nose that is
able to do the shear deformation at the edge of the balancing weight groove
as well as on the head of the grub screw used for fixing the balancing masses
to successfully perform caulking operation.
ITEM 2 represents a front supporting stand to support and hold Item 1 as
desired
ITEM 3 represents a an electric motor connected to hydraulic Jack (8)
ITEM 4 represents a supporting platform for holding hydraulic jack’s ram
which can exert pressure against to provide the required shearing force for
caulking operation
ITEM 5 represents balancing masses placed in the turbine’s groove for
balancing purpose (refer figure 3)
ITEM 6 represents balancing weight groove (refer figure 3) in which
balancing masses (5) shall be rigidly held
ITEM 7 represents Steam Turbine rotor (refer figure 3) that has to be
balanced at its axis through placing the balancing masses (5) in groove (6)
ITEM 8 represents hydraulic jack having in it an electric motor (3)
ITEM 9 represents base of the front supporting stand (2)
ITEM 10 represents base of the rear supporting stand for hydraulic jack (8)
ITEM 11 represents electric switch to operate hydraulic jack
ITEM 12 represents electric power source required to drive hydraulic jack (8)
ITEM 13 represents circular hole through which caulking tool (1) shall have a shrink
fitted connection with front supporting stand (2)
DETAILED DESCRIPTION OF THE INVENTION
Description of the present invention, i.e., a device for performing caulking near
balancing masses is as per below :
The pointed tool (1) of the invented device (D) is designed in such a way that it
can exert the required caulking forces near the balancing masses (5) without
initiating a crack. Rounded portion at the back of the pointed tool (1) forms a
shrink fit kinetic pair with front supporting stand (2).
The caulking process using the invented process can be performed on turbine rotor
(7) having very less center area (which does not allow manual or automated
hammering process) and for those having material with high mechanical strength.
The hydraulic jacks (8) rating can be determined in a way that it can generate
enough force required to shear the material at the edge of the groove, as the
stress required to shear the material at the edge of the groove shall be less due to
stress concentration. A stress concentration (often called stress raisers or stress
risers) is a location in an object where stress is concentrated and therefore requires
less force to deform that area. An object is strongest when force is evenly
distributed over its area, so a reduction in area e.g., caused by a crack, notch, and
sharp edge results in a localized increase in stress.
The caulking tool (1) is shrink fitted in front supporting stand (2) to support and
hold caulking tool (1) in desired positions of punching/caulking at the edge of the
groove (6) that holds balancing masses (5).
Front supporting stand (2) is joined to the base (9) through a welded rigid
joint.
Hydraulic jack (8) is supported on rear hydraulic stand (10) through welded
joint.
The ram (4) of the hydraulic jack (8) operates through a hydraulic electric
motor (3) connected to an Electric Power Source (EPS) (12).
In order to provide flexibility of operation/working of the hydraulic jack, an
operating switch (11) is provided foreseeing the precision required for the
working of the ram (4) and shearing the edge of the groove (6) in and
around balancing masses (5).
The device (D) as described hereinabove shall be used for performing
caulking operation as per following steps :
Step 1 : Caulking tool (1) shrink fitted in front supported stand (2) for
performing caulking on the edge of balancing weight groove (6) and adjacent
to balancing masses (5) is to be placed and adjusted precisely at the tip of
the groove (6) where caulking is to be performed. Accurate positioning of tool
(1) is a must in order to ensure proper fastening of balancing weights in their
desired position. Inaccurately placed tool with respect to the desired position
shall lead to improper caulking which may cause vibration of balancing
masses during the operation of the steam turbine (rotating at 3000 rpm).
These vibrations will unbalance the rotor during its operating period that
leads to breakdown, outage and even failure of steam turbine resulting in
commercial losses.
Step 2 : Hydraulic jack (8) equipped with electric motor (3) and supported on
rear supporting stand (10) is placed in such a way that the hydraulic jack
supports itself from the reaction forces coming from caulking through aligning
itself with the turbine in a direction opposite to the ram movement.
Step 3 : Operating switch (11) is switched on so that the electric motor starts
operating and the ram (4) of the hydraulic jack (8) is made to move forward
in the direction of the edge of the groove (6).
Step 4 : Forward axial movement of Ram (4) gradually pushes the caulking
tool (1) in such a way that pointed nose of tool (1) shear the edge of groove
(6) in which balancing weights (5) are to be held through caulking operation.
Step 5 : Precise attention is required during this stage as large shearing force
is involved, which can permanently deform the material of rotor and damage
it, if the movement of ram is not stopped at right time. It is important to note
here that since the line of action of the reaction forces will always opposes
ram motion, the jack (8) will tend to move backwards, turbine would restrict
that motion.
It is further important to note that in addition to providing a device that
performs precise and controlled caulking operation, it is apparent that the
embodiment of the invention, as described hereinabove, shall provide an
extremely critical device to perform caulking for almost every rating and
material of the turbine, providing an even further versatile scope of use.
Since, the foregoing is considered as illustrative only of the principles of the
invention. Further, since numerous modifications and changes will readily
occur by those skilled in the art, it is not desired to limit the invention to the
exact construction and 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 device (D) for performing caulking (punching) adjacent balancing
masses applicable for balancing turbines, comprising :-
- a caulking tool (1) shrink fitted through a hole (13) configured on the
front face of a supporting stand (2) to support and hold the caulking
tool (1) in desired positions at the edge of a groove (6) that holds
balancing masses (5);
- the front supporting stand (2) rigidly joined to a base (9);
- a hydraulic jack (8) having a ram (4) and supported on a rear
hydraulic stand (10) through welded joint;
- the ram (4) of the hydraulic jack (8) operable through a hydraulic
electric motor (3) connected to an Electric Power Source (EPS) (12);
and
- an operating switch (11) to control the start and end operation of the
device;
2. A process of performing caulking operation in a device (D) as claimed
in claim 1, comprising the steps of :-
- fastening of a plurality of balancing weights (5) in their desired
position and precisely placing the caulking tool (1) at the tip of the
groove (6) where the caulking is to be performed;
- placing the hydraulic jack (8) equipped with electric motor (3) and
supported on rear supporting stand (10) in such a way that the
hydraulic jack supports itself from the reaction forces coming from
caulking through aligning itself with the turbine in a direction opposite
to the ram movement;
- switching on the operating switch (11) so that the electric motor
connected to an Electric Power Source (EPS) (12) starts operating
and the ram (4) of the hydraulic jack (8) is caused to move forward in
the direction of the edge of the groove (6); and
- gradually pushing the caulking tool (1) based on the forward axial
movement of Ram (4) in such a way that the pointed nose of the tool
(1) shear the edge of the groove (6) in which the balancing weights
(5) are held through the caulking operation.
3. The device as claimed in claim 1 wherein the tool (1) is having a
pointed nose such that by applying forces, the nose is able to deform
the edge of balancing weight groove plastically in order to perform
successful caulking.
4. The device as claimed in claim 1 or claim 3, wherein the material of
the pointed tool (1) is selected in such a way that it can sustain and
transfer the forces from the ram (4).
5. The device as claimed in claim 3, wherein the pointed tool (1) has a
rounded portion which forms a shrink fit kinematic pair with the front
supporting stand (2).
6. The device (D) as claimed in claim 1 wherein the hydraulic jack (8)
rating is determined in a way that it can generate enough force
required to shear the material at the edge of the groove.
7. The process as claimed in claim 2, wherein the caulking process can be
performed on a turbine rotor (7) having very less center area (which
does not allow manual or automated hammering process) and for
these having material with high mechanical strengths.