FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A method of manufacturing a wound stator pack with dimensional accuracy
APPLICANTS
Name : Crompton Greaves Limited
Address : CG House, Dr Annie Besant Road, Worli, Mumbai
400 030, Maharashtra, India Nationality : an Indian Company
INVENTOR
Name : Dabeer Vivek Divakar
Address : Crompton Greaves Ltd, LT Motors Division (M3), A-6/2
MIDC, Ahmednagar 414001, Maharashtra, India Nationality : Indian national
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 a method of manufacturing a wound stator pack with
dimensional accuracy.
This invention also relates to a wound stator pack with dimensional accuracy manufactured by the above method.
PRIOR ART DESCRIPTION
A stator body is generally aluminium casted and machined and is provided with a spigot at its one end at which the drive end endshield of an electric motor is fitted. Usually the stator body and spigot are cylindrical. A wound stator pack is manufactured by heating a casted and machined aluminium stator body with a spigot at its one end to 300°C and shrink fitting a wound pack in the stator body through the spigot followed by cooling the stator body with the wound pack to room or ambient temperature. During heating of the stator body and shrink fitting of the wound pack in the stator body, the stator body and spigot undergo dimensional changes and get deformed. On cooling the stator body with wound pack, the deformed spigot usually becomes oblong. Due to the oblongness of the spigot, fitment of the drive end endshield on the spigot during assembly of the electric motor becomes difficult in that the endshield will have to be hammered onto the spigot with great force. Too much hammering of the endshield may result in breakage of the endshield and wastage of material. The manufacturing cost of the electrical motor also increases correspondingly. Due to the oblongness of the spigot there can be misfit and misalignment between the endshield and the spigot. This will reduce the concentricity of the stator and rotor and cause the motor to malfunction thereby
2

reducing its efficiency. The rotor and the stator may also touch each other and get damaged.
OBJECTS OF THE INVENTION
An object of the invention is to provide a method of manufacturing a wound stator
pack with dimensional accuracy.
Another object of the invention is to provide a wound stator pack with dimensional accuracy manufactured by the above method.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a method of manufacturing a wound
stator pack with dimensional accuracy, the method comprising :
i) locating a retainer ring over the cylindrical spigot of a casted and machined aluminium stator body, the retainer ring having a step at the lower end inner circumference thereof matching with a corresponding step at the upper end outer circumference of the spigot to allow the retainer ring to sit in position in the step at the upper end outer circumference of the spigot, the retainer ring being made of a material having a thermal coefficient of expansion lower than that of aluminium, a uniform clearance of 0.3 to 0.5 mm being provided between the abutting radial faces of the steps of spigot and retainer ring;
ii) heating the stator body and the retainer ring to 300 °C and shrink fitting a wound pack in the stator body through the retainer ring and spigot; and iii) cooling the stator body with wound pack to room temperature.
3

According to the invention there is also provided a wound stator pack with dimensional accuracy manufactured by the above method.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a schematic partially sectional view of a casted and machined aluminium stator body fitted with a retainer ring; and
Fig 2 is an enlarged view at X in Fig 1.
As illustrated in Figs 1 and 2 of the accompanying drawings, a casted and machined aluminium stator body 1 is fitted with a retainer ring 2 over the spigot 3 of the stator body. Both the stator body and spigot are cylindrical. The retainer ring has a step 4 at the lower end inner circumference thereof matching with a corresponding step 5 at the upper end outer circumference of the spigot. The retainer ring sits in position in the step at the upper end outer circumference of the spigot. A clearance of 0.3 to 0.5 mm is provided between the abutting radial faces 4a and 5a of the steps of the spigot and retainer ring, respectively. 6 and 7 are the bearing bore and terminal box of the stator body. The stator body and the retainer ring are heated to 300 °C preferably in a electric oven (not shown) and a wound pack (not shown) is shrink fitted in the stator body through the retainer ring and spigot. The stator body with the wound pack and the retainer ring are allowed to cooled down to room temperature. The retainer ring is removed from the spigot and the stator body with the wound pack
4

is then taken for further processing to make a stator assembly. The retainer ring is made of a material having a thermal coefficient of expansion lower than that of aluminium. Preferably, the retainer cap is made of mild steel or alloy steel which has a thermal coefficient of expansion of 11.1 (j. - meter / m - °C which is lower than that of aluminium namely 23.8 u - meter / m - °C. During heating of the stator body, the stator body and the spigot expand. The clearance of the order of 0.3 to 0.5 mm between the abutting radial faces of the steps of the spigot and retainer ring provides space for uniform expansion of the spigot. Due to the retainer ring being made of a material of lower thermal coefficient of expansion, the retainer ring does not practically undergo any expansion. On cooling the stator body with the wound pack shrink fitted therein and the retainer ring, the spigot also cools down to the room temperature to its original size and the circularity and uniformity of the spigot is maintained. As the circularity and dimensional accuracy of the spigot is maintained, fitment of the drive end endshield on the spigot during assembly of the motor becomes easy. Possibility of too much hammering of the endshield onto the spigot is avoided. Breakage and damage to the endshield and wastage of material are avoided and manufacturing cost of the motor is correspondingly reduced. Misfit and misalignment between the spigot and the endshield are avoided; concentricity of the stator and the rotor is maintained; malfunctioning of the motor is avoided, and efficiency of the motor is improved. Possibility of the stator and rotor touching each other and getting damaged is also avoided.
Wound packs were shrink fitted in stator bodies with and without the retainer ring. The stator bodies with and without the retainer ring were heated to 300 °C in an
5

electric oven. The results of the comparative studies were as shown in the following Table 1 :
Table 1

Experiment No Wound stator packs made without retainer ring Oblongness ofspigotmm
Diameters of spigots at every 90° mm
1 485.92 486.2 486.56 485.5 1.06
2 485.76 486.3 486.3 485.84 0.54
3 486.04 485.66 486.58 485.68 0.92
4 485.84 485.9 486.7 485.4 1.3
5 486.06 486.2 486.34 485.84 0.5
Average oblongness of spigot 0.864
Experiment No Wound stator packs made with retainer ring Oblongness ofspigotmm
Diameters of spigots at every 90° mm
1 485.84 485.7 485.7 485.9 0.2
2 486 486 486 486.1 0.1
3 486 486 486 486.2 0.2
4 486.1 485.9 485.9 486 0.2
5 486.12 486.9 485.9 486 0.22
Average oblongness of spigot 0.184
It is clearly seen in Table 1 that the average of deformation of the spigots in the case of stator bodies fitted with the retainer ring as against stator bodies without the retainer ring was reduced from 0.864 mm to 0.184 mm indicating an improvement in the circularity and dimensional accuracy of the spigots by 369.5 %. This clearly shows that the circularity and dimensional accuracy of the spigots of the stator bodies shrink fittd with wound packs ie the wound stator packs as obtained by the method of the invention were greately improved and were excellent.
6

We claim :
1. A method of manufacturing a wound stator pack with dimensional accuracy,
the method comprising:
i) locating a retainer ring over the cylindrical spigot of a casted and machined
aluminium stator body, the retainer ring having a step at the lower end inner circumference thereof matching with a corresponding step at the upper end outer circumference of the spigot to allow the retainer ring to sit in position in the step at the upper end outer circumference of the spigot, the retainer ring being made of a material having a thermal coefficient of expansion lower than that of aluminium, a uniform clearance of 0.3 to 0.5 mm being provided between the abutting radial faces of the steps of spigot and retainer ring;
ii) heating the stator body and the retainer ring to 300 °C and shrink fitting a wound pack in the stator body through the retainer ring and spigot; and iii) cooling the stator body with wound pack to room temperature.
2) The method as claimed in claim 1, wherein the retainer ring is made of mild steel or alloy steel.
3) A wound stator pack with dimensional accuracy manufactured by the method as claimed in claim 1 or 2.

7

ABSTRACT
A method of manufacturing a wound stator pack with dimensional accuracy. A retainer ring (2) is located over the cylindrical spigot (3) of a casted and machined aluminium stator body (1). The retainer ring has a step (4) at the lower end inner circumference thereof matching with a corresponding step (5) at the upper end outer circumference of the spigot to allow the retainer ring to sit in position in the step at the upper end outer circumference of the spigot. The retainer ring is made of a material having a thermal coefficient of expansion lower than that of aluminium. A uniform clearance of 0.3 to 0.5 mm is provided between the abutting radial faces (4a, 5a) of the steps of spigot and retainer ring, respectively. The stator body and the retainer ring are heated to 300 °C and a wound pack is shrink fitted in the stator body through the retainer ring and spigot. The stator body with wound pack is then cooled to room temperature (Fig 1).