Title of Invention

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

Abstract

ABSTRACT A method of manufacture of a steel worm and worm wheel comprising the steps of cleaning the worm; rotating the said worm and plasma spraying molybdenum thereon, finishing the same; cleaning the worm wheel; preheating the worm wheel to 400 deg. C; and immersing the same in a molten bath containing alkaline cyan ates and carbonates of potassium, sodium and lithium with sulphur activated catalyst, the bath being maintained at a temperature of 570 deg. C; quenching in water and cooling the worm wheel, and cleaning the same.

Full Text

This invention relates to a method of manufacture of a steel worm and worm wheel for a worm drive. Worm drives tranmit 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 unless) 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 existing steel non-ferrous combination; better compatibly, and are economical. The method of manufacture of a steel worm and worm wheel, according to this invention, .comprises the steps of cleaning the worm; rotating the said worm and plasma spraying molybdenum thereon J'fihislurig the same; cleaning the worm wrteell preheating the worm wheel to 400 deg.C; and immersing the same hi 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 570 deg.C; quenching in water and cooling the worm wheel; and cleaning the same. EXAMPLE The worm is cleaned by decreasing in trichloroethylene (TCE), by dry air, by abrasive grit blasting and then again by dry air. The blast media is AL2O3 of mesh size 40 and air pressure 0.3MPa. The worm is then held in a rotating chuck and molybdenum (used in powder form) is plasma sprayed on the rotating worm. The plasma spraying is carried out at 36 V 800 A. The plasma gas and the carrier gas are argon at flow rates 112 SCFH and 12.8 SCFH respectively. The spray rate is 2kg/hr with the gun distance 120 mm. The handling is manual. After plasma spraying, the worm is finished by profile grinding. The worm wheel is cleaned by CTC (carbon tetrachloride) 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 570 deg.C and the immersion is carried out for 150 minutes. The worm wheel is then taken out of the bath, quenched in water and 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 inetention 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: LA method of manufacture of a steel worm and worm wheel comprising the steps of cleaning the worm; rotating the said worm and plasma spraying molybdenum thereon J finishing the same; cleaning the worm wheel; C^c\racf-£y(se^ by" ^preheating the worm wheel to 400 deg.C; and immersing the same in a molten bath containing alkaline eyanates and carbonates of potassium, sodium and lithium with sulphur activated catalyst, the bath being maintained at a temperature of 570 deg.C; quenching in water and cooling the worm wheel; and cleaning (he same. 2.A method as claimed in Claim I wherein the worm is cleaned by degreasing in TCE, by dry air, abrasive grit blasting and again by dry air. 3.Amethod as claimed in Claim 2 wherein the blast media is Al2O3 of mesh size 40 and air pressure 0.3 MPa. 4.A method as claimed in any one of the preceding Claims wherein the plasma spraying is carried out using a plasma dyne SG 100 gun, 36 Volts and 800 amperes, the plasma gas and the carrier gases being argon at flow rates of 112 SCFHand 12.8 SCFH respectively. 5.A method as claimed in Claim 4 wherein the molybdenum is used in 6. A method as claimed in any one of the preceding Claims wherein the worm is finished by profile grinding. 7.A method as claimed in any one of the preceding Claims wherein the worm wheel is cleaned by CTC and dry air. 8 A method as claimed in any one of the preceding Claims wherein the worm wheel is immersed in the bath for 150 minutes. 9. 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 dry air. 10 A method of manufacture of a steel worm and worm wheel for a worm drive substantially as herein described and as illustrated by the Example. 11. A steel worm and worm wheel for a worm drive whenever manufactured by a method as claimed in any one of the preceding Claims.

Documents:

1737-mas-1996 abstract.pdf

1737-mas-1996 claims.pdf

1737-mas-1996 correspondence others.pdf

1737-mas-1996 correspondence po.pdf

1737-mas-1996 description (complete).pdf

1737-mas-1996 form-1.pdf

1737-mas-1996 form-26.pdf