Fluid lubricants can be applied to gear sets by sprays, which are air borne, or by jets of the liquid alone. Such methods of application are employed when the peripheral speed exceeds the limits for splash lubrication or when the gears are not adapted to the dip method. The size and shape of spray patterns can be controlled by the use of different type of nozzles, the distance from the nozzle to the target, or the pressure and temperature of the lubricant. If the gearing has a wide face, two or more jets can be used on one gear set.
Since one function of the gear oil is to cool as well as lubricate, a fan shaped spray or jet should spread the oil across the entire gear face. Adjustments of such sprays are a matter of experience, and firms supplying such equipment can give the best advice. For any cases, except exceedingly high speed, most authorities prefer to apply the oil spray on the incoming side of the gears so that the oil will be spread across the entire gear face. For moderate speeds the application should not be directly at the point of mesh, due to air turbulence. However, Dern^15 suggests that, for pitch line velocities above 16,000 to 18,000 feet per minute, the most satisfactory results are obtained by spraying a solid stream of oil radially into the teeth of both gears at a points as close as possible to the mesh. Further, in speaking of gears operating at pitch line velocities of 20,000 to 25,000 feet per minute, Dern^15 agrees that such gears should be lubricated on the leaving side of the mesh where the oil will do the most good as a coolant and not contribute to high dynamic loads.
In high speed operation of gears, lubricated by jets of oil, scavenging of the lubricant is sometimes a problem. Special baffles or even a change in gear case design may be necessary in order to remove considerable volumes of oil rapidly enough so that interference with gear operation does not result.
Automatic spray application is used on open gears where a controlled amount of lubricant is sprayed over the gears at desired intervals. By heating the oil, high viscosity lubricants can be used or better still, cut back oils are applied. Gesdorf^21 offers details of such applications and the problems involved in the development and use of the same.
For high speed worm gears, which tend to throw oil rather than carry it to the mesh, a high velocity jet stream of gear oil is more satisfactory than a spray. In fact two jets can be used, one striking the worm wheel teeth in a direction parallel to the axis and the other in a direction perpendicular to the axis.
