Title of Invention

A METHOD OF MANUFACTURE OF A STEEL WORM AND WORM WHEEL PAIR FOR A WORM DRIVE

Abstract A method of manufacture of a steel worm and worm wheel pair comprising the steps of cleanning the worm; rotating the said worm and coating the same with TIN in a vacuum chamber by physical vapour deposition (cathodic evaporation); cleaning the worm wheel; preheating the worm wheel to 400 deg.C; and immersing the same in a molten bath containing alkaline cyanates and carbonates of potassium, sodium, and lithium with sulphur activated catalyst, maintained at a temperature of 500 deg.C; slow cooling the worm wheel; and clearing the same.
Full Text

This invention relates to method of manufacture of a worm and worm wheel pair for a worm driva.
Our other invention relates to a method of manufacture of a steel worm and worm wheel for a worm drive under co-pending Application
N0.1737/MAS/96.
Worm drives transmit power and motion between crossed axes by a combination of sliding and rolling motion. Due to the contact being predominantly sliding, at higher reduction ratio, the mode of failure is scuffing and scoring rather than pitting and tooth fracture as in the case of other gear drives,
Thus for compatibility reasons and to obtain a low coefficient of friction in sliding, dissimilar materials are favoured for their use. Existing commercial units for most industrial applications invariably use a hardened steel worm mating with a bronze (phosphor, tin or tinless) wheel; other material combinations like steel and cast iron are also in use, however, not so widely, as that of ferrous non-ferrous pairs.
This invention proposes worm and worm wheel pairs of steel mating with steel which can replace the existing steel non ferrous combination economically without sacrificing performance.
The worm and worm wheel proposed herein have better strength compared to the existmg non-ferrous combination; better compatibility, and are economical.

The method of manufacture of a steel worm and worm wheel pair according to this invention, comprises the steps of cleaning the worm; rotating the said worm and coating the same with TiN (TITANIUM NITRIDE) in a vacuum chamber by physical vapour deposition (cathodic evaporation); cleaning the worm wheel; preheating the worm wheel to 400 deg.C; and immersing the same in a molten bath containing alkaline cyanates and carbonates of potassium, sodium and lithium with sulphur activated catalyst, the bath being maintained at a temperature of 500 deg.C; slow cooling the worm wheel; and cleaning the same.
EXAMPLE
The worm is cleaned by degreasing with kerosene, in trichloroethylene (TCE), again in TCE at 80 deg.C by wet blasting or liquid honing under high pressure water rinse, by ultrasonic cleaning in liquid detergent solution, in de-ionised water sprayed under pressure, by dry air and UV dying.
The worm is then coated with TiN (Titanium Nitride) in a vacuum chamber by physical vapour deposition (also called cathodic evaporation). The chamber pressure is maintamed at 18.3X10-5 Torr during coating, the medium being highly pure nitrogen gas and the temperature being maintained at 358 deg.C to 362 deg.C, with current rating at 46 aanps/hr and emissivity at 0.2. During the operation, the worm is given a negative bias of minus 1000 volts and rotated at 1.2rpm.

The worm wheel is cleaned by TCE vapour degreasing, by hot water and by dry air.
The worm wheel is then preheated to 400 deg.C
The worm wheel is then immersed in a molten bath containing alkaline cyanates and carbonates of potasium, sodium and lithium with sulphur activated catalyst. The bath is maintained at a temperature of 500 deg.C and the immersion is carried out for 150 minutes.
The worm wheel is then taken out of the bath and slow cooled in air.
Thereafter it is cleaned in detergent solution, by hot water and by dry air.
No post finishing operation is necessary.
The terms and expressions in this specification are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described, having regard to the scope and ambit of this invention.


We Claim:
1. A method of manufacture of a steel worm and worm wheel pair comprising the steps of cleaning the worm; rotating the said worm and coating the same with TiN (TITANIUM NITRIDE) in a vacuum chamber by physical vapour deposition (cathodic evaporation); cleaning the worm wheel; preheating the worm wheel to 400 deg.C; and immersing the same in a molten bath containing alkaline cyanates and carbonates of potassium, sodium and lithium with sulphur activated catalyst, maintained at a temperature of 500 deg.C; slow cooling the worm wheel; and cleaning the same.
2. A method as claimed in Claim 1 wherein the worm is cleaned by degreasing with kerosene, in TCE by wet blasting or liquid honing, under high pressure water rinse, by ultrasonic cleaning in liquid detergent solution, in de-ionised water sprayed under pressure, by dry air and UV drying.
3. A method as claimed in Claim 2 wherein the chamber pressure
is maintained at 18.3 x 10 Torr during coating, the medium
being highly pure nitrogen gas and the temperature being
maintained at 358 deg.C to 362 deg.C. with current rating at 46
amps/hr and emissivity at 0.2-
4. A method as claimed in any one of the preceding Claims
wherein the worm is biased at minus 1000 Volts and rotated at
1.2 rpm.

5. A method as claimed in any one of the preceding Claims wherein the worm wheel is cleaned by TCE (TRICHLOROETHYLENE) vapour degreasing, hot water and dry air.
6. A method as claimed in any one of the preceding Claims wherein the worm wheel is immersed in the bath for 150 minutes.
7. A method as claimed in any one of the preceding Claims
wherein after cooling in air, the worm wheel is cleaned in
detergent solution, by hot water and by dry air.
8. A method of manufacture of a steel worm and worm wheel pair
for a worm drive substantially as herein described and as
illustrated by the Example.
9. A worm and worm wheel pair for a worm drive whenever
manufactured by a method as claimed in any one of the preceding
Claims.


Documents:

1738-mas-1996 abstract granted.pdf

1738-mas-1996 abstract.pdf

1738-mas-1996 claims granted.pdf

1738-mas-1996 claims.pdf

1738-mas-1996 correspondence others.pdf

1738-mas-1996 correspondence po.pdf

1738-mas-1996 description (complete) granted.pdf

1738-mas-1996 description (complete).pdf

1738-mas-1996 form-1.pdf

1738-mas-1996 form-26.pdf


Patent Number 228524
Indian Patent Application Number 1738/MAS/1996
PG Journal Number 10/2009
Publication Date 06-Mar-2009
Grant Date 05-Feb-2009
Date of Filing 03-Oct-1996
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address I.I.T. P.O., CHENNAI 600 036,
Inventors:
# Inventor's Name Inventor's Address
1 DR. MINNAL MUTHUVEL MAYURAM INDIAN INSTITUTE OF TECHNOLOGY, I.I.T. P.O., CHENNAI 600 036,
2 MOKKAPATI SURYANARAYANA INDIAN INSTITUTE OF TECHNOLOGY, I.I.T. P.O., CHENNAI 600 036,
PCT International Classification Number B23F11/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA