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 INVENTION
Plastic cooling fan for a totally enclosed fan cooled AC induction motor
INVENTOR
Desale Rajgopal, Technology Department, LT Motors (M3), Crompton Greaves Ltd, A6/2 MIDC Area, Ahmednagar, India, Indian national
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality: Indian Company
Address : CG House, Dr Annie Besant Road, Worli, Mumbai 400025, Maharashtra, India
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 INVENTION
This invention relates to a plastic cooling fan for a totally enclosed fan cooled AC induction motor.
BACKGROUND OF INVENTION
Cooling fans for totally enclosed fan cooled (TEFC) AC induction motors are made of plastics or aluminium. Aluminium fans are generally made by sand casting, whereas plastic fans are generally made by injection moulding. Plastic fans are advantageous over aluminium fans in several respects. Plastic fans can be mass produced in large numbers with high degree of dimensional accuracy and close tolerances and smooth surfaces. They do not require machining for achieving dimensional accuracy as in the case of aluminium fans. They can be easily fitted on the motor shaft and do not require heating to expand or hammering to be fitted on the motor shaft as in the case of aluminium fans. They ensure smooth air flow and have increased fan efficiency and reduced power consumption as compared to aluminium fans. Noise level of the plastic fan is also reduced as compared to aluminium fan.
A plastic fan comprises a conical shaped body having a tubular hub and a plurality of blades radially spacedly provided on the conical shaped body along the length thereof. The conical shaped body is reinforced by reinforcing radial ribs between the hub and the body. A key is provided in the tubular hub and a pair of oppositely placed openings are provided in the conical shaped body to provide a grip for the fan. During operation of the motor at high speeds the blades of the fan become dynamically imbalanced due to their distal ends (outer ends) being free thereby increasing vibration and noise level of the
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motor. The blades may also break offthereby reducing the life of the fan. Leakage of air takes place through the openings in the fan body thereby reducing the volume of air being delivered or blown by the fan.
OBJECTS OF INVENTION
An object of the invention is to provide a plastic cooling fan for a totally enclosed fan cooled ac induction motor which fan reduces vibrations and noise level of the motor.
Another object of the invention is to provide a plastic cooling fan for a totally enclosed fan cooled AC induction motor which fan has increased life.
Another object of the invention is to provide an improved totally enclosed fan cooled AC induction motor which fan increases the volume of air delivered or blown by the fan.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a plastic cooling fan for a totally enclosed fan cooled AC induction motor, the fan comprising a reinforcing ring formed around the distal ends of the blades provided along the conical shaped fan body radially spaced, the reinforcing ring being provided with a plurality of balancing weights spacedly.
The following is a detailed description of the invention with reference to the accompanying drawings, in which Figs 1 to 5 are front view, front perspective view,
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back view, back perspective view and crosssectional view of a plastic cooling fan for totally enclosed fan cooled AC induction motor according to an embodiment of the invention. The fan 1 as illustrated in Figs 1 to 5 of the accompanying drawings comprises a conical shaped body 2 having a tubular hub 3. 4 is a key provided in the tubular hub so as to mount the fan on the motor shaft (not shown) provided with a
corresponding key way (not shown). 5 is a slit provided in the key so as to render certain flexibility to the key. The fan body is reinforced by reinforcing ribs 6 provided between the hub and the fan body. A plurality of blades 7 are radially spacedly provided on the fan body along the length thereof. The blades are located on the fan body radially equidistantly spaced or radially displaced with respect to one another upto 10°. 8 is a reinforcing ring provided around the distal ends of the blades. The ring is provided with a plurality of holes 9 around it spacedly. Balancing weights comprising metallic rollers 10 are tightly held against the ring by bolts 11 passing through the rollers and the holes in the ring from one side of the ring and by nuts 12 engaged over the bolts and tightened against the ring from the opposite side of the ring. 13 are a pair of oppositely placed thinned or weakened portions. The fan is injection moulded with plastic materials preferably with mineral filled nylon such as nylon 6 or nylon 66. During operation of the motor even at higher speeds, vibration and noise level of the motor are considerably reduced as the distal ends of the blades are held by the reinforcing ring and the fan is dynamically balanced by the balancing weights. Besides the reduction in the noise level and vibration, chances of the distal ends of the blades getting damaged during high speed operation of the motor are also prevented by the reinforcing ring. Therefore, the life of the fan is increased. The thinned or weakened portions 13 can be easily knocked off so as to provide a grip for the fan and facilitate easy removal or handling of the fan. Until
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such time, the thinned or weakened portions prevent leakage of air through the openings formed at the thinned or weakened portions during operation of the fan which would have occurred in the case of the conventional plastic fan thereby improving air delivery or sweep by the fan. The thinned or weakened portions are, however, optional. The number of fan blades can vary. The construction of the balancing weights and the manner of mounting thereof on the reinforcing ring can vary. The rollers can be made of metals such as steel. The rollers can be non-metallic also. The profile of the thickened or weakened portions can vary. Such variations of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.
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We Claim
1. A plastic cooling fan for a totally enclosed fan cooled AC induction motor, the fan comprising a reinforcing ring formed aroimd the distal ends of the blades provided along the conical shaped fan body radially spaced, the reinforcing ring being provided with a plurality of balancing weights spacedly.
2. A plastic cooling fan as claimed in claim 1, wherein each of the balancing weights comprises a metallic roller tightly held against the ring by bolt and nut.
3. A plastic cooling fan as claimed in claim 1 or 2, wherein the fan body is provided with a pair of oppositely placed thinned or weakened portions.
4. A plastic cooling fan as claimed in anyone of claims 1 to 3, wherein the fan is injection moulded with mineral filled nylon such as nylon 6 or nylon 66.
5. A plastic cooling fan as claimed in any one of claims 1 to 4, wherein the blades are located on the fan body radially equidistantly spaced or radially displaced with respect to one another upto 10°.
Dated this 19th day of February 2007.
(Jose M A)
ofKhaitan&Co
Agent for the Applicants
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