No abstract

No abstract

In tests made on spur gears with mineral oils of various viscosities, it was observed that a relationship exists between the maximum horsepower which the gears can transmit without scoring, and the product of gear speed and lubricant viscosity. An analysis of the factors entering into this relation indicates that these are the same that occur in Lewis’ equation used in gear design, except that the latter does not contain the lubricant viscosity. If this viscosity is introduced into the Lewis equation, the latter represents the experimental points for horsepower transmitted at the onset of scoring very well over a wide range of speeds and lubricant viscosity. This modified Lewis equation appears to apply to spur gears, in general, and indicates that the influence of lubricant viscosity on the power-transmitting capacity of gears is much too great to be neglected in the design of gears.

Accinelli, et al. [5], showed that high-speed bearings, when operated with varieties of lubricants, showed this same sharp increase in friction with temperature. In fact, the silicone oil which had the most favorable viscosity characteristics for maintaining a hydrodynamic film in the face of rising temperature was the first to show the sharp friction increase resulting from desorption. Inasmuch as many ball bearings are forced by geometrical considerations to have a considerable amount of spinning, designers would be well advised to remember this when specifying lubricants. In particular for high-temperature operation, the use of liquid lubricants does not seem feasible because of the desorption problem. The use of solid-film lubricants either applied mechanically to the surface or chemically formed in situ would seem more practical.