1.1 Applicability. This Standard provides a
method to determine the power rating of gear sets
for cylindrical grinding mills, kilns, coolers, and
dryers. The formulas are applicable to steel gears
with machined spur, single helical, double helical,
or herringbone gear teeth commonly used for this
purpose. Calculations determine the allowable rating
for pitting resistance and bending strength of
external spur and helical involute gear teeth.
1.2 Limitations.
(1) Rating procedures are limited to open or
semi-enclosed gearing where the gear reaction
forces are transmitted through a structure which
provides independent bearing support for the gear
and pinion. Open gears operate without any enclosure.
Semi-enclosed gears operate with a guard
that provides some degree of protection against
contamination from dust or dirt and retains lubricant.
(2) Enclosed gear drives or speed reducers
are expressly excluded from this Standard.
(3) This gear rating practice is limited to
maximum operating speeds of 2000 feet per minute
(10.2 m/s) gear pitch line velocity or 450
revolutions per minute of the pinion.
(4) When dual motors and pinions are used,
each pinion will be designed for 60 percent of the
total input power of both motors unless otherwise
specified by contractual agreement.
(5) This Standard does not include gearing
which has been surface hardened by nitriding or
flame hardening. This gear rating practice is limited
to through hardened gears operating with
through hardened, carburized, or induction hardened
pinions.
(6) Face contact ratio of helical gear sets must
be greater than 1. O.
1.3 Metallurgy. The allowable stress numbers,
sac and %t , included herein are based on commercial
steel making and heat treating practice.
Hardness and tensile strength are the criteria for
allowable stress numbers. Variation in microstructure
will result in variation in gear capacity.