FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
An improved shaft and an improved process for shaft mounting of rotor.
APPLICANTS (S)
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S)
Dhokane Prakash and Bhagawa Popat; both of Crompton Greaves Limited, LT Motors Division, A/6-2, MIDC Industrial Area, Ahmednagar - 414111, Maharashtra, India; both Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of the Invention:
The invention relates to the field of motors.
Particularly, this invention relates to an improved shaft and an improved process for shaft mounting of rotor.
Background of the Invention:
An 'electrical rotating machine' or a 'rotating electrical machine' is any form of apparatus, equipment, or system which has a rotating member and generates, converts, transforms, or modifies electric power. These include apparatus such as a motor, generator, or synchronous converter.
Essentially all of the world's electric power is produced by rotating electrical generators, and about 70% of this energy is consumed in driving electric motors. Electric machines are electromechanical energy converters; generators convert mechanical energy into electrical energy and motors convert electrical energy into mechanical energy.
An electric machine can be constructed on the principle that a magnet will attract a piece of permeable magnetic material such as iron or magnetic steel. For example, a pole structure along with a magnetic block is allowed to rotate. The magnetic block will experience a torque tending to rotate it counterclockwise to the vertical direction.

One type of an 'electrical rotating machine' or a 'rotating electrical machine' is a motor. A motor for electrical purposes, i.e. an electric motor, is a device which converts electrical energy to mechanical energy. For industrial use, the ratings of motor may typically be very high. They may be placed in housings or frames. It contains two main components; stator, rotor. The rotor is the non-stationary part of a rotary motor, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor's axis. The stator is the stationary part of a rotor system. The rotor has a fanning action.
An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than a commutator or slip rings as in other types of motor. These motors are widely used in industrial drives.
A rotor includes two types of stampings; 1) core or central stampings which essentially form the central body of a rotor and 2) bunch of stacked end stampings which form the end portions of a rotor. A rotor essentially consists of a core assembly with rotor bars and resistance rings. The stampings of the rotor are stack mounted. The rotor is, typically, a shaft mounted rotor.
There are problems relating to the prior art systems, assemblies, and methods of rotor shaft mounting.
There is a need for a system and method which obviates the problems of the prior art.

Objects of the Invention:
An object of the invention is to provide a relatively accurate geometry of rotor and shaft.
Another object of the invention is to prevent incorrect dimensions of rotor after its mounting on a shaft.
Yet another object of the invention is to provide a structurally stable rotor.
Still another object of the invention is to provide a low residual unbalance in relation to shaft mounted rotor.
An additional object of the invention is to provide a shaft mounted rotor with reduced vibration level.
Summary of the Invention:
According to this invention, there is provided an improved shaft and an improved process for shaft mounting of rotor, said process comprises the steps of:
a. refraining from machining bearing seats on a shaft, located on either side of
the area about which rotor is to be mounted, up to a pre-determined
thickness;
b. inserting a rotor on to said shaft with relatively un-machined bearing seats;
c. heating in order to achieve shrink fitting of rotor on said shaft;

d. turning said rotor and said bearing seat in order to achieve finished diameter
according to designed air gap; and
e. machining said relatively un-machined bearing seats along with said rotor in
order to achieve improved concentricity between outer diameter of said rotor
and said bearing seat.
Preferably, said step of refraining from machining bearing seats on a shaft comprises the step of leaving about 20 microns of extra material on said bearing seat.
Typically, said process comprises the step of removing extra material from outer diameter of said rotor, after pressing of said motor, by holding rotor between centres of shaft.
Brief Description of the Accompanying Drawings:
Figure 1 illustrates a finished / machined shaft used in a motor for rotor mounting;
Figure 2 illustrates a die cast rotor; and
Figure 3 illustrates a shaft mounted rotor.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 4 illustrates a shaft, in accordance with this invention;

Figure 5 illustrates a die cast rotor; and
Figure 6 illustrates a shaft mounted rotor, in accordance with this invention.
Detailed Description of the Accompanying Drawings:
Figure 1 illustrates a finished / machined shaft (10) used in a motor for rotor
mounting.
The shaft is a machined shaft.
Figure 2 illustrates a die cast rotor (20).
The rotor is made by stacking various laminations and then die-casting this stack in
a furnace. The laminations, may be of 0.5mm thickness. The concentricity of the
outer surface of the rotor with respect to rotor inner diameter (ID) is not
maintained, in this process.
Reference numeral B refers to extra material provided on the outer diameter of
rotor. Typically, the extra material is of 1mm thickness.
Figure 3 illustrates a shaft (10) mounted rotor (20).
The rotor and shaft is shrink fitted.
Die Cast rotor is inserted by heating (Shrink fitting) on the machined shaft.
Die Cast Rotor is turned in order to achieve finished diameter according to the
designed air gap.

When rotor (20) is inserted onto the shaft (10) and turned, it becomes concentric with shaft center.
As the bearing seat (12) is machined before rotor (20) insertion, perfect concentricity between bearing seat (12) and outer diameter of rotor is not maintained which causes residual unbalance in the rotor assembly.
After the rotor (20) is pressed, the extra material B on the rotor outer diameter is removed and finished diameter is maintained by holding rotor (20) between centres of shaft referenced by numeral D.
According to this invention, there is provided an improved shaft and an improved process for shaft mounting of rotor.
Figure 4 illustrates a shaft, in accordance with this invention.
Figure 5 illustrates a die cast rotor.
Figure 6 illustrates a shaft mounted rotor, in accordance with this invention.
In accordance with an embodiment of this invention, there is provided a shaft comprising bearing seats (112), located on either side of the area about which rotor is to be mounted. The bearing seats are improved bearing seats, in that, the bearing seats are not completely machined.

According to one exemplary embodiment, about 20 microns of extra material is left on the bearing seat (112).
Further, the die cast rotor (20) is inserted on to the improved shaft (110) by heating in order to achieve shrink fitting of rotor on shaft.
Still further, the die cast rotor (20) and bearing seat (112) are turned in order to achieve finished diameter according to the designed air gap.
Since, the bearing seat (112) is machined again along with the outer diameter of the rotor (20), better concentricity between outer diameter of rotor (20) and bearing seat (122) is achieved, which reduces residual unbalance which causes the vibration of the motor using this rotor and rotor shaft.
After the rotor (20) is pressed, the extra material B on the rotor outer diameter is removed and finished diameter is maintained by holding rotor (20) between centres of shaft referenced by numeral D.
According to one non-limiting exemplary embodiment, motor vibration was reduced from 2.3 mm/sec to 1.6 mm/sec due to the use of the rotor -shaft and process of this invention.
The technical advancement of this invention lies in provisioning a shaft mounted rotor in such a process that better concentricity of rotor a bearing seat of shaft is achieved. This results in a low residual unbalance and vibration level of motor using the shaft mounted rotor according to this invention.

While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. An improved shaft and an improved process for shaft mounting of rotor, said
process comprising the steps of:
a. refraining from machining bearing seats on a shaft, located on either side of
the area about which rotor is to be mounted, up to a pre-determined
thickness;
b. inserting a rotor on to said shaft with relatively un-machined bearing seats;
c. heating in order to achieve shrink fitting of rotor on said shaft;
d. turning said rotor and said bearing seat in order to achieve finished diameter
according to designed air gap; and
e. machining said relatively un-machined bearing seats along with said rotor in
order to achieve improved concentricity between outer diameter of said rotor
and said bearing seat.
2. The process as claimed in claim 1, wherein said step of refraining from machining bearing seats on a shaft comprising the step of leaving about 20 microns of extra material on said bearing seat.
3. The process as claimed in claim 1, wherein said process comprising the step of removing extra material from outer diameter of said rotor, after pressing of said motor, by holding rotor between centres of shaft.