In the framework of IS0 Technical committee TC60,
a new work item concerning the calculation of load
capacity of worm gear is in Focess since 4 years.
The future reference of the standard IS0 14521:
load capacity calculation of worm gear. This
standard is based on DIN 3996 which has been
adopted in Germany in September 1998.
The following conditions that can limit the rated
load capacity :
o wear: such damage usually appears on the
tooth flanks of bronze wormwheels
pitting : this form of damage may appear on the
flanks of wormwheel teeth. Its development is
strongly influenced by the load transmitted and
the loadsharing conditions.
tooth breakage : shear failure of wormwheel
teeth or worm threads can occur when teeth
become thin due to wear or overload. Worm
thread and worm shaft breakage: shaft breakage
can occur as a result of bending fatigue or
overload.
worm shaft deflection : excessive deformation
under load modifying contact pattern between
worm and worm wheel.
o scuffing : this form of damage often appears
suddenly. It is strongly influenced by
transmitted load, sliding velocities and the
conditions of lubrication.
working temperature : when excessively high
working temperature leads to accelerated
degradation of the worm gear lubricant.
Among this, IS0 14521 defines criteria for: wear,
pitting, tooth breakage of worm wheel, worm shaf?
deflection.
Table 1 indicates the rdationship between different
forms of capacity limits in combination with speed
and torque.
In order to illustrate the behaviour of IS0 14521,
this paper :
presents result calculations based on 3 worm
gears sets which are those used in our
laboratory for testing,
o presents synthesis of influencing parameters for
each criteria calculation, with comments, and
an identification of the best choice for some
parameters.