T-155
17.1.8 Overload Factor, KO
Overload factor, KO, is the quotient of actual tangential force divided by nominal
tangential force, Ft . If tangential force is unknown, Table 17-4 provides guiding values.
Actual tangential force
KO = ––––––––––––––––––––––––––––
(17-11)
Nominal tangential force, Ft
Table 17-4 Overload Factor, KO
17.1.9 Safety Factor for Bending Failure, SF
Safety factor, SF, is too complicated to be decided precisely. Usually, it is set to at least 1.2.
17.1.10 Allowable Bending Stress at Root, sF lim
For the unidirectionally loaded gear, the allowable bending stresses at the root are
shown in Tables 17-5 to 17-8. In these tables, the value of sF lim is the quotient of the
tensile fatigue limit divided by the stress concentration factor 1.4. If the load is bidirectional,
and both sides of the tooth are equally loaded, the value of allowable bending stress
should be taken as 2/3 of the given value in the table. The core hardness means hardness
at the center region of the root.
See Table 17-5 for sF lim of gears without case hardening. Table 17-6 gives sF lim of
gears that are induction hardened; and Tables 17-7 and 17-8 give the values for carburized
and nitrided gears, respectively. In Tables 17-8A and 17-8B, examples of calculations are
given.
Uniform Load
(Motor, Turbine,
Hydraulic Motor)
Light Impact Load
(Multicylinder Engine)
Medium Impact Load
(Single Cylinder Engine)
1.0
1.25
1.5
1.25
1.5
1.75
1.75
2.0
2.25
Uniform Load
Medium Impact
Load
Heavy Impact
Load
Impact from Load Side of Machine
Impact from Prime Mover
