Worm gears are unique in their ability to achieve large speed reductions in a compact space with gear ratios of 20:1, 60:1 and 200:1 or even higher in some cases and have transmission efficiency between 50% and 70%. One of the major drawback in worm drive design is the relative motion between the two mating elements is entirely sliding. This sliding motion continuously expels the lubricant aside leading to higher wear and increase in temperature. This phenomenon leads to high wear and higher temperatures, which are the limiting factors in the worm drives. Nano particles have gained a greater attention in the recent years because of their highly enhanced thermal and tribological properties when blended with conventional lubricants. In the present investigations the addition of Al2O3 nano particles with average particle size of 30 nm in SAE 140 gear oil resulted in reducing the coefficient of friction, wear and enhanced the heat transfer coefficient. It is observed that coefficient of friction is decreased by 8.98%, 10.11% and 16.85% at nano particle volume concentration of 0.1%, 0.2% and 0.5% respectively at room temperature. Frictional force was found reduced by 26.02% at room temperature for 0.5% volume concentration. Further it was also noted 32.25% and 18.55% reduction in frictional force at the temperatures 60°C and 90°C respectively for 0.2% volume concentration. Convective heat transfer coefficient is increased with increasing particle volume concentration and maximum enhancement of 46.35% in heat transfer coefficient observed at 0.5% volume fraction. The results depict that lubricants blended with nano particles exhibit enhanced tribological and heat transfer properties.

The sliding motion between worm and worm wheel is the inherent factor that makes the worm and worm wheel drives less efficient among all the gear drives. Efficiency of these gears varies between 40 to 90%. They need good lubricants, which has high heat dissipation capacity and low coefficient of friction for improving the efficiency. The lubricants considered in the current investigation play a significant role in decreasing the power losses in gearbox besides the geometry of the gears. Nano blended lubricants are found to have efficient tribological and thermal physical properties such as, less frictional coefficient and high heat transfer coefficient. Al2O3 Nano particles of 30 nm size dispersed in SAE 140 mineral oil at different volume fractions resulted decrease in frictional coefficient and found varying from 0.1 to 0.5% nano particle volume fractions. Further, heat transfer coefficient is enhanced by 46.35% for volume fraction of 0.5% and also temperature rise of nano blended lubricant was found to be less than that of base lubricant. The overall efficiency of the selected gearbox with which the experimentation has been done was found to be increased with usage of nano blended lubricant. The performance of the gearbox using nano lubricant at 0.5 volume percent is found improved by 4.85 and 7.86% at operating temperatures 35 and 60oC, respectively compared to the performance of the gearbox using base lubricant.