Airborne oil mist or fog is being used to advantage in the lubrication of gear sets. The fog, consisting of oil atomized by compressed air into particles in the order of 2 microns in size, can be carried in pipes for long distances. At the point of application these will have to be reclassified to larger particles so that they will wet a metal surface. The air carrier must be vented from the lubricated part and is said to carry away heat. However, perhaps the heat dissipated will not be as great as in cases where gear oils splash or flow over gear sets.
The oil is used on a once through basis; consequently, clean, unoxidized oil is applied continuously. The amount of lubricant used is quite low, and the gears expend no energy in overcoming fluid friction of gear oils. With such a system, gear boxes are under some pressure; hence, no contaminants, such as dust, will enter.
Fog lubrication is only practical where sufficient points for lubrication justify a centralized system or where compressed air is available for use with a few points. The latter reason, therefore, probably rules out such systems in the case of aircraft and vehicles. If properly adjusted, definite amounts of oil can be applied by fog, and the system requires little attention, provided there are no air failures.
