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, 2005
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A method for obtaining induction heat treated cold rolled motor laminations for use in motors, and motors thereof.
APPLICANTS :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Mudragada Sathyanarayana, Hiwarkar Vijay and Ingle Asha; all of Crompton Greaves Limited, CG Global R&D Centre, Kanjurmarg (E), Mumbai, Maharashtra, India; all 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:
This invention relates to the field of metal treatment.
Particularly, this invention relates to cold rolled motor laminations for use in motors.
Specifically, this invention relates to a method for obtaining induction heat treated cold rolled motor laminations for use in motors, and motors thereof
BACKGROUND OF THE INVENTION:
Motors are machines that convert electrical energy to mechanical energy. The main components of a motor are stator and rotor. The Rotor is a rotating part of the motor while the stator is the stationary part of the motor. Stampings are used in the manufacture of stators as well as rotors for motors and /or other electrical or rotary machine equipment. Stampings are typically made of electrical steel sheets in the thicknesses of 0.35mm to 1.0mm.
Electrical steel which is also known as lamination steel, silicon steel or transformer steel is a sub-group of magnetic material family which is being used in the electric products like transformers, motors, generators, pumps etc. as a core material.
The magnetic properties like lower core loss, higher saturation flux density, lower coercivity and high permeability of electrical steel grade makes it a suitable candidate for the use as core material in transformers or motors. The core loss of the electrical steel being the most important parameter for its suitability as a core material needs to be controlled precisely.
The core loss is of three basic types: i. Hysteresis loss; ii. Eddy current loss and iii. Anomalous losses.

CRNO electrical steel has two basic types depending on their supply condition of heat treatment: (1) fully processed; and (2) semi processed electrical steels. Fully processed steels are those for which decarburizing annealing is done at supplier's end. Fully processed steels are further coated with organic or inorganic coating and hence, there is no need of any further heat treatment at stamping manufacturers' end. Semi-processed steels are those for which the last operation carried out is normally a skin pass rolling and further heat treatment is carried out at stamping manufacturer's end. The semi-processed steels are also known as cold rolled motor lamination (CRML) steel.
Semi-processed electrical grades are vastly being used for motor applications. Various annealing treatments are being performed on the semi-processed electrical grades in order to reduce the core loss of the laminations. In order to maintain the lower core loss, the lamination thickness needs to be as low as possible without hampering the punchability of the sheets. However, lower sheet thickness always comes with higher raw material cost due to extra rolling operations of the sheets which are critical to perform.
Non-oriented electrical steel laminations are being used in motors, generators, fans and pumps applications. The stator pack manufacturing process using fully processed non-oriented electrical steel grade consists of:
1. Slitting of coil
2. Punching to the required lamination dimensions
3. Stacking of laminations to the required core length
4. Pack building by riveting/clittingAvelding the laminations
In last two decades, semi-processed electrical steel technology has emerged as one of the cheapest technologies in the electrical steel laminations industry. The cost of

semi-processed steel is much lower than that of fully processed steel. In case of semi-processed electrical steel grade, a material supplier gives a skin pass rolling as a final operation to the steel coil and a heat treatment operation needs to be performed at stamping manufacturer's end. The heat treatment operation was successfully developed at stamping manufacturers' end by using conventional heat treatment process for loose laminations and final pack building operation was done by riveting, clitting or welding process.
According to the prior art, electrical /gas heat treatment process (es) are used in order to treat the laminations conventionally. These result in disadvantages such as high cycle time, low energy efficiency of the heat treatment process, high cost and the like.
PRIOR ART:
Patent document GB58097 discloses heat treatment of armour metal plates of moderate thickness. The purpose of induction heating is case hardening followed by quenching of armour plates. However, it does not specifically disclose heat treatment processes of stator pack laminations with 0.5mm thickness. And it does not disclose annealing treatment benefits.
Patent document US2010295412 discloses a process wherein high efficiency induction head is positioned in the central opening of the circular core and relates to applications in electrical generators. The purpose for induction heating is harden-drying varnish impregnation the stator coil. However, it does not disclose steps of method in order to reduce the stresses that are generated in the punching operation and to increase the grain size in the stator coil.
Patent document JP2006088581 discloses the purpose induction heating of resin film laminations is to producing enough adhesive strength. It also discloses a

manufacturing method of the layered product of a resin film and at least one layer of resin film consist of an exothermic layer (photo thermal transducing material and holding water) of metal which generates heat by electromagnetic induction. However, it does not disclose steps or method in relation to exposing cold rolled laminations without any resin film to induction heating in order to obtain improved magnetic properties of coils.
The book, 'Heat treating' relates to heat treatment of laminations wherein the stacking factor is 0.75 to 0.80 and further relates to CRGO laminations 'with insulation coating'. This refers to the curing of the applied coating. However, it does not disclose induction heating or changing magnetic properties for laminations without insulation coating with a stacking factor of 0.90 to 0.95 for a sheet of 0.5mm thickness.
The paper, 'Layered alloys for effective magnetic flux concentration in induction heating; V. LESCHYNSKY et al; Materials Science-Poland, Vol. 25, No. 2, 2007' relates to heat treatment of CRGO laminations with coating wherein the stacking factor is 0.75 to 0.80 and wherein induction heating of 0.05 mm to 0.2 mm with frequency about 10 kHz is used. However, it does not disclose induction heating or changing magnetic properties for laminations with a stacking factor of 0.90 to 0.95 for a sheet of 0.5mm thickness.
The 'Fluxtrol LRM product' relates to sheets with coating and relates to localized heating. However, it does not disclose steps or processes or products with laminations having sharp edges or having no coating. Also, it does not disclose the scope of localized heating and also does not disclose steps of obtaining desired magnetic properties.

OBJECTS OF THE INVENTION:
An object of the invention is to provide a heat treatment method and process for cold rolled motor laminations, subjected to induction heating, for use in motors.
Another object of the invention is to provide an induction heating method for loose laminations which will reduce the cycle time reduction.
Yet another object of the invention is to maintain performance of induction heating of loose laminations with respect to conventional heating of loose laminations.
Still another object of the invention is to provide a low cost stator/rotor manufacturing process.
An additional object of the invention is to provide cold rolled motor laminations, subjected to induction heating for achieving desired magnetic properties.
Yet an additional object of the invention is to provide an induction heating method and technique for cold rolled motor laminations of 0.5mm thickness.
Still an additional object of the invention is to provide an induction heating method and technique for cold rolled motor laminations having no coating.
Another additional object of the invention is to provide an induction heating method and technique for cold rolled motor laminations having sharp edges.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a method for heat treating metal loose laminations, said method comprises:

a. first step of induction heating said metal loose laminations up to temperatures in
the range of about 600°C to 800°C;
b. second step of maintaining said metal loose laminations in heated temperature
in the range of about 600°C to 800°C for a pre-determined period of time in
relation to the total amount of mass to be heated; and
c. third step of cooling said metal loose laminations to room temperature.
According to this invention, there is provided a motor made by loose stack of heat treated metal laminations to obtain a stator pack, said treated metal laminations obtained using a method, said method comprises:
A. first step of induction heating said metal loose laminations up to temperatures in
the range of about 600°C to 800°C;
B. second step of maintaining said metal loose laminations in heated temperature
in the range of about 600°C to 800°C for a pre-determined period of time in
relation to the total amount of mass to be heated; and
C. third step of cooling said metal loose laminations to room temperature.
Typically, said metal loose laminations are cold rolled laminations.
Typically, said metal loose laminations are of 0.5mm in thickness.
Preferably, said metal loose laminations are in the range of 0.35mm to 1.0mm in thickness.

Typically, said metal loose laminations are Cold Rolled Closed Annealing (CRCA) laminations.
Typically, said metal loose laminations are semi-processed steel laminations. Typically, said metal loose laminations are sharp cornered laminations.
Typically, said stator packs are heat treated using an induction coil for heat treatment method.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a flowchart of the method for treating metal laminations.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a method for treating metal loose laminations.
Figure 1 illustrates a flowchart of the method for treating metal laminations.
In accordance with an embodiment of this invention, there is provided a first step (10) of induction heating the metal loose laminations up to temperatures in the range of about 600°C to 800°C. The metal loose laminations are cold rolled laminations. The metal loose laminations are preferably of 0.5mm but may be in the range of 0.35mm to 1 mm in thickness.
In accordance with another embodiment of this invention, there is provided a second step (20) of maintaining the metal loose laminations in heated temperature in the range of about 600°C to 800°C for a pre-determined period of time in relation to the total amount of mass to be heated.

In accordance with yet another embodiment of this invention, there is provided a third step (30) of cooling the loose laminations to room temperature.
The laminations are Cold Rolled Closed Annealing (CRCA) laminations, i.e. semi-processed steel laminations.
This method of induction heating is developed for stator pack loose laminations for heat treatment. This method and process is relatively rapid and is also a cost saving process. In induction heating method, heat is generated in the material itself as per the Eddy current principle. The heating speeds are extremely high because of the high power density. The principle of induction heating is mainly based on the two physical phenomena:
I. Electromagnetic induction
II. Joule effect
According to this invention, there is provided a motor made by a stack of said treated metal loose laminations. The stator packs are heat treated using an induction coil for heat treatment process; the process, described above, is specifically selected for the lamination material.
The induction heat treatment has many benefits which are listed below:
1. Low cost
2. Cycle time reduction
3. Better magnetic properties due fast heating and cooling
4. Accurate temperature control
5. High energy efficiency
All these benefits resulted in to a direct use of induction heating system for heat treatment of laminations for various applications like stator packs of motor

applications. A large number of trials have been taken to do the heat treatment operation by induction heating system for better magnetic properties and motor performance. All stamping manufacturers use only the heat treatment process of the prior art for heat treating the laminations of semi processed grades of electrical steels. Also, with the use of the method of this invention, laminations with sharp corners can be induction heated for better properties and better motor characteristics without burning corners of the laminations.
Magnetic properties of induction heating of loose laminations semi-processed cold rolled non-oriented electrical steel can be seen in Table 1 below.
Table 1 illustrates magnetic properties of induction heating system of loose
laminations.

Sr.
No Process Plate
thickness
(mm) At 1.5T, 50Hz

AT/m W/Kg
1 600° C @ 30min. 0.5 857.58 7.87
2 650° C @ 20min. 0.5 791.59 7.50
3 650° C @ 30min. 0.5 657.85 7.11
4 700° C @ 5min. 0.5 816.92 7.64
5 700° C @ 20min. 0.5 690.43 6.96
6 750° C @ 5 min. 0.5 780.59 7.25
7 750° C @ 10 min 0.5 750.76 7.21
8 750° C @ 15 min. 0.5 668.76 6.96

From Table 1, it was seen that the magnetic properties of the packs treated by induction system matches with the heating system of the prior art (normally 7-8 W/kg). This indicates that the use of cold rolled semi-processed electrical steel for induction heating method does not compromise on the magnetic properties of the stator packs, but reduces costs and time. The motor performance results of induction heated packs and conventional heated packs are listed in Table 2. The use of this method results in low cost and cycle time reduction. Also, accurate temperature control can be achieved with high energy efficiency.

Table 2 illustrates motor testing results comparison of induction heated packs and conventional pack.

Rating 1HP, 4P Induction heating packs Conventional heated pack Market-declared Performance Min. Values Subtracting Tolerance Max. Values including
750° C @ 5min 600° C @ 30 min 750° C @ 10 min 650° C @ 20 min

upper Tolerance

KIAM1282
4 KIAM1282 6 KIAM1282 9 KIAM13
314 JKAM14219


Parameter
Type Test FL efficiency 76.2 76.87 76.73 76.36 76.16 77 - -

FLPF 0.74 0.75 0.74 0.75 0.75 0.75 0.71 -

Slip at FL 6.53 6.71 6.64 6.76 7.01 6 4.8 7.2

Temp, rise 43 56.2 47.1 47.6 50.2 70 - -

Starting torque 212 174 212 222 203 200 170 250

% sec 317 324 317 319 317 500 - 600

F& W 16.92 9.11 10.74 13.24 16.35 - - -

Core loss 31.7 33.33 33.07 35.91 38.04 - - -

Stator Copper loss 125 123.96 123.98 121 116.12

Rotor Copper loss 53.35 55.13 54.4 55.22 57.73

Tested output kW 0.74 0.75 0.75 0.74 0.74

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. A method for heat treating metal loose laminations, said method
comprising:
a. first step of induction heating said metal loose laminations up to
temperatures in the range of about 600°C to 800°C;
b. second step of maintaining said metal loose laminations in heated
temperature in the range of about 600°C to 800°C for a pre
determined period of time in relation to the total amount of mass to be
heated; and
c. third step of cooling said metal loose laminations to room temperature.
2. A method as claimed in claim 1 wherein, said metal loose laminations are cold rolled laminations.
3. A method as claimed in claim 1 wherein, said metal loose laminations are of 0.5mm in thickness.
4. A method as claimed in claim 1 wherein, said metal loose laminations are in the range of 0.35mm to 1mm in thickness.
5. A method as claimed in claim 1 wherein, said metal loose laminations are Cold Rolled Closed Annealing (CRCA) laminations.
6. A method as claimed in claim 1 wherein, said metal loose laminations are semi-processed steel laminations.
7. A method as claimed in claim 1 wherein, said metal loose laminations are sharp cornered laminations.
8. A motor made by loose stack of heat treated metal laminations to obtain a stator pack, said treated metal laminations obtained using a method, said method comprising:

A. first step of induction heating said metal loose laminations up to
temperatures in the range of about 600°C to 800°C;
B. second step of maintaining said metal loose laminations in heated
temperature in the range of about 600°C to 800°C for a pre
determined period of time in relation to the total amount of mass to be
heated; and
C. third step of cooling said meta.1 loose laminations to room temperature.
9. A motor as claimed in claim 8 wherein, said metal loose laminations are cold rolled laminations.
10. A motor as claimed in claim 8 wherein, said metal loose laminations are of 0.5mm in thickness.
11. A motor as claimed in claim 8 wherein, said metal loose laminations are in the range of 0.35mm to 1mm in thickness.
12. A motor as claimed in claim 8 wherein, said metal loose laminations are Cold Rolled Closed Annealing (CRCA) laminations.
13. A motor as claimed in claim 8 wherein, said metal loose laminations are semi-processed steel laminations.
14. A motor as claimed in claim 8 wherein, said metal loose laminations are sharp cornered laminations.
15. A motor as claimed in claim 8 wherein, said stator packs are heat treated using an induction coil for heat treatment method.