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
An improved method for the production of stator packs.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Dumbre Jayshri, Hiwarkar Vijay and Ingle Asha, all of Crompton Greaves Limited, Advanced Materials and Process Technology Center, CG Global R&D Centre, Kanjur Marg (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:

Technical field:
The present invention relates to an improved method for the production of stator pack.
Background of the invention:
Electrical steel is a special type of steel used in the construction the cores of the stator and rotor of motors and generators. The material is usually manufactured in the form of cold-rolled strips less than 2 mm in thickness. In electric machines such as transformers, motors, etc., the coated steel is punched in the form of thin laminations of required design. These punched laminations are stacked together in required height to form a core.
Generally, after punching electrical steel sheet coil, the punched laminations undergo stress relieving treatment to eliminate stresses generated during punching operation. The heat treatment to the semi processed electrical steel sheet to develop magnetite layer on the sheet surface is called 'bluing treatment'. The motor laminations are Subjected to 'grain growth annealing1 treatment which is normally carried out at higher temperature at around 800°C under reduced atmosphere. Both these heat treatments are essential to get desired magnetic properties.
The laminations are stamped by a manufacturer thereof from cold rolled steel strip which is usually subjected to a decarburizing anneal either before the stamping operation, by the steel maker, or after the stamping operation,

by the manufacturer of the laminations. The considerations involved in the composition and processing of the cold rolled steel strip before stamping, in the decarburization thereof and in the stamping, annealing and other operations performed by either the steel maker or the manufacturer of the laminations, are discussed in US 4,390,378 and US 4,601,766.
It is usually more desirable for the decarburizing anneal to be performed by the steel maker rather than by the lamination manufacturer. In those situations where the manufacturer of the lamination does not perform a decarburizing anneal after stamping the lamination, another type of anneal is usually performed to relieve the stresses resulting from the stamping operation and to enhance the magnetic properties of the lamination.
All anneals performed by the manufacturer of the laminations, whether a decarburizing anneal or a stress relieving anneal, are usually conducted at a location remote from the stamping press at which the laminations were made. Typically, the laminations are conducted away from annealing furnace as well as annealing is conducted away from the stamping press. Thus, laminations have to be transported or handled to submit the same for stamping press. Once laminations have been stamped on the press, then the punched laminations are submitted to annealing furnace.
US 4,602,969 discloses a method for subjecting core blanks (laminations) to a stress relieving anneal after the core blanks have undergone blanking, presumably at a stamping press. The core blanks are transported by a conveyor, presumably from the stamping press, to annealing equipment wherein the core blanks are initially elevated upwardly through a vertical

tube containing induction heating coils. The core blanks are subjected to loading and unloading operations at an annealing furnace, as well as other material handling operations, separate and discrete from those employed to conduct the core blanks away from the stamping press.
Typically, semi processed steel technology is vastly used by stamping manufacturer as it is less costly as compared to fully processed steel. Performance of such steel can be improved by means annealing treatment and achieve excellent permeability and lower core loss. Traditionally, the annealing treatment is carried out on stamped lamination or punched lamination in which laminations are loosely bounded together. After annealing treatment, loose laminations are finally riveted or cleated or welded to make a stator pack for motors. During the production of stator or rotor pack, laminations have been handled by loading or unloading at stamping, annealing, etc till pack formation and other handling of the stamped laminations during transportation if required. Heat treatment involves additional handling of motor laminations before and after annealing. However, wrong bending or rough handling can adversely affect the magnetic properties of the steel. The laminations are soft and are prone to mechanical damage while handling and results in wastage of end laminations. The magnetic properties are likely to get deteriorated due to mechanical stresses induced in the stator packs.
Thus, there is need to invent modified method for the production of stator which substantially eliminates loading, unloading and other handling of the stamped laminations.

Objects of the invention:
An object of the invention is to provide an improved method for the production of stator pack which eliminates loading, unloading and other handling of the stamped laminations.
Another object of the invention is to provide an improved method for the production of stator pack which eliminates loading, unloading and other handling of the stamped laminations thereby preventing deterioration of magnetic properties.
Another object of the invention is to provide an improved method for the production of stator pack which improves mechanical stability of motor laminations.
Another object of the invention is to provide an improved method for the production of stator pack which eliminates loading, unloading and other handling of the stamped laminations thereby reducing scrap generation and making the method cost-effective.
Another object of the invention is to provide an improved method for the production of stator pack which eliminates loading, unloading and other handling of the stamped laminations thereby reducing time and manpower and increasing the productivity.

Detailed Description:
According to the invention there is provided, an improved method for the
production of stator pack;
said method comprises
a preparing stator pack by cleating motor laminations; and
b. subjecting stator pack to heat treatment at temperature in the range of 400° C to 600° C in the furnace to form magnetite layer on the surface of the laminations followed by cooling the pack to 200° C.
The motor laminations are made of semi processed electrical steel having 0.03 weight % carbon, 0.40 to 0.75 weight % aluminum and silicon together and 0.007 weight % phosphorous.
The motor laminations are cleated to form stator pack. The cleating of the motor laminations is carried out by pressing the laminations in the required core length and holding them in place by passing a steel strips of specific width in the grooves provided on the outer diameter of the stator laminations.
The heat treatment in the present invention is carried out in ambient atmosphere to form magnetite layer on the surface of the laminations.
The present invention is directed to a method for subjecting stamped motor laminations to cleating to form pack and then subjecting the same to heat treatment which minimizes loading, unloading and other handling of the stamped laminations and shortens the production time. Since the method of

the invention eliminates loading, unloading and other handling of the stamped laminations thereby preventing deterioration of magnetic properties, improving mechanical stability of motor laminations, reducing scrap generation, reducing man power and making the method cost-effective. The present invention increases the productivity.
The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
Examples 1 to 4
The motor laminations were made from semi processed electrical steel which were equivalent to grade 50 M 800. The laminations were cleated to form stator packs for different frames like D80 4P, ND100 4P, ND112 4P and ND132 6P and for motor rating lH, 3H, 5H and 5H respectively. The stator packs obtained were subjected to heat treatment at temperature 550±10° C in the furnace to form magnetite layer on the surface of the laminations. The stator pack was allowed to cool down by cooling the furnace to 200° C. These stator packs were tested for core loss and the results have been incorporated in table 1.
Comparative Examples 5 to 8 :
The motor laminations made from 50 M 800 were punched and subjected to heat treatment at temperature 780±10'3 C in the furnace for 120 minutes in reducing atmosphere. The laminations obtained after treatment were cleated to form stator pack for different frames like D80 4P, ND100 4P, ND112 4P and ND132 6P and for motor rating 1H, 3H, 5H and 5H respectively. These

stator packs were tested for core loss and the results have been incorporated in table 1.
Table 1: Comparative core loss value of stator packs produced according to Examples and Comparative Examples.

Sr Frame Motor core loss of stator core loss of stator
No. rating Pack prepared according to comparative examples 5 to 8 (W/Kg at 1.5T,50Hz) Pack prepared according to examples 1 to 4 (W/Kg at 1.5T, 50Hz)
1 D80 4P 1HP 7.79 7.69
2 ND100 4P 3HP 7.93 8.43
3 ND112 4P 5HP 11.85 11.98
4 ND132 6P 5HP 9.08 9.76
*The core loss values given are the average of at least 5 packs.
It can be seen from comparison that the core loss values of the cleated stator packs prepared according to examples 1 to 4 are closer to the core loss values of the stator pack which were conventionally prepared according to examples 5 to 8 and are within acceptable limits. Retention of magnetic properties in heat treatment of cleated packs can be seen from Table 1 for various frames.

We claim,
1. An improved method for the production of stator or pack;
said method comprises
a. preparing stator pack by cleating punched laminations; and
b. subjecting stator pack to heat treatment at temperature in the
range of 400° C to 600° C in the furnace to form magnetite layer on
the surface of the laminations followed by cooling the pack to 200° C.
2. The method as claimed in claim 1, wherein the motor laminations used are made of semi processed electrical steel having 0.03 weight % carbon, 0.40 to 0.75 weight % aluminum and silicon together and 0.007 % phosphorous.
3. The method as claimed in claim 1, wherein the cleating of the motor lamination is carried out by pressing the laminations in the required core length and holding them in place by passing a steel strips of specific width in the grooves provided on the outer diameter of the stator laminations.
4. The method as claimed in claim 1, wherein the heat treatment is carried out in air to form magnetite layer on the surface of the laminations.