INABILITY of the roller-bearing company with which the author of this paper is connected to obtain from oil manufacturers or others the information it desired regarding the properties of lubricants for transmissions and rear axles caused the company to undertake to secure the information at first hand itself. It began testing lubricants for their abrasive qualities and their load-carrying capacities.
The investigators soon realized that the usual physical tests do not prove the effects of lubricants on gears. Therefore two machines were built, one to give the scuffing properties and the other to give the abrasive properties, the latter being the more important as regards antifriction bearings. Lubricants of mineral origin that were free from fillers and metallic substances were satisfactory in this respect, but many gears require a lubricant that will withstand gear-tooth loads as high as 1800 lb. per in. of tooth length, which is higher than the straight mineral oils can carry without scuffing.
The test machines built and their operation are described. Results obtained with various oils and compounds are shown in photographs of test blocks and in autographic records made with apparatus designed at the University of Michigan for checking the roughness of plane or curved surfaces. Charts are also given of coefficients of friction, oil temperatures, maximum load carried at different rubbing speeds before scuffing begins, and abrasion of bearings during test runs that were continued for 200 hr.
The lubricants tested included straight mineral oils and the same oils with the addition of varying percentages of free sulphur, combined sulphur, lead and copper oleates, lead oxide, aluminum stearate, inorganic fillers, cutting-oils and castor-oil.
The facts as determined up to the present with reference to lead-soap-base oils and sulphurized oils are enumerated and the desirable properties of a lubricant for heavily-loaded gears and hypoid gears are set forth.
In conclusion, the author states that the carrying capacities indicated are only comparative and that the results given are merely observations made in checking oils on the machines described. Since this investigation was initiated, several other gear, automobile and oil companies have done considerable work along the same line that is already beginning to be reflected in better oil products.
Written discussion* on lead-soap-base lubricants and other types of lubricant for use in present-day transmissions and rear axles was contributed by five speakers, who present arguments for and against the use in them of lead soap, sulphur and other inorganic ingredients. A compromise between tooth scuffing and bearing wear seems to be necessary, according to one discusser, and the importance of designing gears with reference to the possible lubricating qualities of oils or greases is pointed out.