The term “high” of course is relative
but with pitch line velocities of several thousand feet per minute the
lubrication of gears is not simple. Naturally, a low viscosity oil is required and the problems are : to have assurance that a film of oil
is present when the gear teeth
mesh; to have an abundance of oil to remove heat; and to be sure that the leaving oil
will get out of the way of fast moving gear teeth. If a problem is
encountered as to delivery of oil to the
mating surfaces of high speed gears, the experience of Dern^20 may help. This
investigator found that when
gears run at 16,000 to 18,000
feet per minute, “more satisfactory results may
be obtained by spraying oil radically into the
teeth of both gears at a point as close as
possible to the mash”. For the purpose, one or two jets of 0.040 to
0.060 inch in diameter, delivering a solid stream of oil, were used. Where the
pitch line velocity was 20,000 to 25,000 feet per minute, jets on the leaving
side of the gears removed most heat.
Trouble may be encountered with
high speed gears churning the gear oil which in turn causes heating. This is one
reason directional baffles
or even
a shroud around the gears may be necessary in order to keep leaving oil
away from the gears and directed toward
a gear case outlet.
