FIELD OF INVENTION
The present invention relates to a grinding attachment and a method for preparation of reference diameter for machining large capacity turbo generator Rotor. More particularly, the invention relates to a grinding attachment and a method for grinding the journal diameter as well as other diameters of a rotor based on the reference diameter which is also known as belt diameter.
BACKGROUND OF INVENTION
A turbo generator is the combination of a turbine directly connected to an electrical generator for the generation of electrical power.
Rotor is a vital component of Generator. Rotor rotates 3000 RPM during operation and journal is most important part of rotor because journal rest on bearing.
A large steam turbine rotor must run with low vibration levels during operation and when going through critical speeds. Rotors must be straight and true within a tight tolerance. Mechanical Runout is a measure of the shaft's deviation from a perfectly uniform radius as its circumference is traversed. This type of runout can

be measured by a dial indicator. For most TG rotors, runout at journal area should not exceed 20 microns as any excessive runout at journal during operation life may result in:
1) Local rubbing resulting in permanent metallurgical changes
2) Local expansion and yielding that results in permanent bowing and cracking
3) Residual stresses and material hardness
4) Bowing that cannot be balanced out
Due to high speed of rotor, micron level gap (200 micron) is being maintained between journal and bearing. To maintain micron level gap between journal and bearing, tolerance in journal diameter is 40 micron, journal run out should be less than 20 micron and cylindricity less than 10 micron. For a rotating shaft, physical out-of-roundness results in a reduction in gap between journal and bearing.
It is a very difficult task to obtain these design parameter. To maintain these micron gaps, grinding is done on the rotor diameter.
Some of the technical terms are described hereunder for better understanding of the prior art:

1) Tolerance: In a manufacture of a machine, quality is a primary consideration. Precision manufacturing of a product determines its quality, its cost and selling price. Parts of a machine are designed in order to make a function. The working parts have a definite relationship with each other: free rotation, free longitudinal movement, clamping action, and permanent fixed position. Precision is the degree of accuracy necessary to ensure the functioning of a part as intended. Tolerance is the allowable variation for any given size in order to achieve a precision job to function properly.
2) Runout: Mechanical Runout is a measure of the shaft's deviation from a perfectly uniform radius as its circumference is traversed
3) Cylindricity: Cylindricity is a condition of a manufacturing part surface of revolution in where all points of the circular surface are equi-distant from
actual axis
4) Belt preparation: preparing the belt diameters tolerances, runouts and
cylindricity as per design requirements
5) Steady: Long workpieces often need to be supported in the middle, as cutting
tools can push (bend) the work piece away from where the centers can
support them, because cutting metal produces tremendous forces that tend
to vibrate or even bend the workpiece. This extra support can be provided by
a steady.
6) Exciter End of rotor: The end of the rotor which is towards the exciter.

7) Turbine End of rotor: The end of the rotor which is towards the turbine
8) Journal: The part of a rotor that rests on bearings.
9) Bearings: A bearing is a machine element that constrains relative motion and reduces friction between moving parts to only the desired motion.
10)Sagging: to sink or bend downward by weight or pressure, especially in the middle
Earlier method: - Rotor is placed on lathe with the help of its
• journals resting on steady,
• exciter end clamp in chuck jaw, and
• turbine end it tail stock centre.
The prime target is to maintain a micron level gap (200 micron) between journal and bearing. For that belt is used as base/reference for machining journal as well as all other diameter of rotor.
As per technology, belt preparation is required before machining journal which means belt diameter should be within 5 micron. Before belt preparation setting of rotor is required. For belt preparation turning, grinding as well as rolling of belt diameter is done. After all these machining operation, we shift steady to belt

diameter with the help of EOT crane. After setting the rotor, we measure run out of belt over the belt diameter.
As per technological requirement, the run out of belt should be within 5 micron but generally it is on the higher side of the required 5 microns. Again we shift the steady to journal with the help of crane and set the rotor. Repeat the machining operation to get belt run out less than 5 micron but we cannot get it even after 3-4 attempts. To perform this repeatedly is not easy as the rotor size is around 12-14 meter in length and 75 tonnes in weight. In every attempt shifting of steady as well as all machining operation were repeated. It was very hectic because sometimes even after 3-4 attempts, achievement of required run out of belt is not possible.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a grinding attachment and a method for preparation of reference diameter for machining large capacity turbo generator Rotor which is capable of grinding the reference or belt diameter without shifting the steady resting below the said diameter.

Another object of the invention is to propose a grinding attachment and a method for preparation of reference diameter for machining large capacity turbo generator Rotor which is capable of achieving a reference diameter of rotor having a runout on diameter less than 5 microns.
A still another objection of the invention is to propose a grinding attachment and a method for preparation of reference diameter for machining large capacity turbo generator Rotor which is capable of eliminating the hazards of shifting the steady for a number of times.
A further objection of the invention is to propose a grinding attachment and a method for preparation of reference diameter for machining large capacity turbo generator Rotor which is able to eliminate the problem of sagging on belt diameter.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.l - "Apparent" probe gap for a) an out-of-round shaft with uniform
electrical properties and b) a perfectly round shaft with non-uniform electrical properties.

Fig.2 - Shows how cylindricity due to sagging was delivering to wrong
runout measurement at the dial.
Fig.3 - Shows Rotor and related components
Fig.4 - Shows belt (point A shown in figure above) is rested on steady to
eliminate sagging effect at belt (B)
Fig.5 - Shows developed Grinder
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Since sagging of rotor was the main problem due to which it was unable to make journal with the help of this technology. We did not get this problem in case of small rotor, but we face this problem in case of higher rating rotor.
Weight of higher rating rotor is more than 60 ton hence, sagging effect cannot be neglected. Sagging problem was eliminated by placing steady on belt diameter as deflections at the supports is zero for simply support cylindrical objects.

Earlier, the machining of belt was done through turning but now since placing steady on belt diameter eliminates the sagging issue, it interrupts in turning operation on the belt for limiting runout.
After setting the rotor all machining operation (grinding & rolling) is done in situ to get belt run out within 10 micron. Hence, there need a change in technology for preparing the belt.
Once belt of the rotor is prepared than, we start the final machining of rotor journal. After machining of journal, steady is shifted to the journal with the help of crane. Hence repeated use of crane and handling staff is eliminated through this process. Also we defer the earlier technology to make belt (i.e. basic reference of the rotor). Due to this all problems regarding machining parameters are achieved in first step correctly.
Thus sagging effect of rotor on belt diameter has been completely nullified because Belt diameter of rotor resting on steady (earlier journal diameter resting on steady) during Belt preparation of rotor.
Item wise description of the developed grinding machine is as below:
Item 1. otor

Item 2. Pulley
Item 3. Belt
Item 4. Grinding wheel
Item 5. Motor base
Item 6. Vertical support
Item 7. Horizontal support
Item 8. Housing clamping bolt
Item 9. Shaft
Item 10. Housing
Item 11. Housing clamping unit
Item 12. Belt adjustment bolt
The motor (1) which drive the whole system rests on the motor base (5). Plurality of pulleys (2) are present to transfer the power from motor (1) to the grinding wheel (4) through a belt (3).
The arrangement of pulleys (2) is vertical i.e., one pulley is vertically above the second.
The height to the whole system is provided through the vertical support (6) which is supporting the motor (1) through its base (5).

The stability to the vertical structure is provided through horizontal support (7) which through its threaded joints attaches to housing clamping unit (11) through Housing clamping bolt (8) which contains the housing (10) of the shaft (9) that drives the grinding wheel (4).
There is provided a bolted arrangement (12) that is used to tighten the belt that transfers the power from motor to the pulley shaft (9).
When the motor (1) is turned on, it will rotate the grinding wheel (4) and the grinding operation can be done on the belt while the steady is also supporting the same so as to eliminate any possible sagging of the rotor.
The grinding attachment (G) is fixed to a boring bar (not shown) unit which is attached to the carriage of the machine. By moving the carriage manually, the boring bar along with the grinding wheel moves towards the job and feed is given as per requirement to achieve a reference or belt diameter to a predetermined size allowing a runout of less than 5 microns. The grinding attachment is made and implemented in such a way that it does not foul with the steady while grinding operation is done.

WE CLAIM
1. A grinding attachment for preparation of reference diameter for machining large capacity turbo generator Rotor comprising:
a motor (1) resting on a base (5) of a grinding attachment (G) for driving the whole system;
a plurality of pulleys (2) placed vertically one above the other for transferring the motion of the motor to a pulley shaft (9) through a belt (3) attached to said pulleys;
vertical support (6) supporting the motor (1) through the base (5) for providing height to the whole system;
horizontal support (7) providing stability to the vertical structure;
a housing (10) of a pulley shaft (9);
a bolted arrangement (12) for tightening the belt that transfers power from motor (1) to pulley shaft (9);
Characterized in that,
the pulley shaft (9) attached to the pulley (2) at one end and to a grinding wheel (4) at the other end receives motion from the motor through belt and pulley and transfers the motion to the grinding wheel (4) wherein the whole attachment is fixed on carriage of the machine when the feed of the grinding wheel for grinding the belt diameter is obtained by moving the carriage

manually so that reference diameter is achieved with the steady holding the reference diameter, within a run out of the said diameter less than 5 microns.
2. A grinding attachment as claimed in claim 1, wherein the horizontal support (7) through its threaded joints, is fixed to the housing clamping unit (11) by housing clamping bolt (8).
3. Method for preparation of reference diameter for machining large capacity turbo generator Rotor with a grinding attachment as claimed in claim 1, the
said method comprising;
transferring the motion of the motor to pulley (2) placed vertically one
above the other through belt (3);
transferring the motion of the bottom pulley (2) to a pulley shaft (9) attached to the pulley (2) in one end and transferring the motion of the pulley shaft (9) to a grinding wheel (4) attached to the shaft;
wherein the whole grinding attachment is fixed to a carriage of the machine which imparts feed manually to the grinding wheel (4) for grinding the reference diameter keeping the steady holding the belt diameter throughout the grinding operation.