Bibby Transmissions Torque Limiting
Modules have been specifically designed to
provide overload protection for applications
where very high torque’s are transmitted,
and to extend the range covered by
Bibbigard Type A units.
The modular system provides facilities for
virtually unlimited torque capacity and
lends itself to many transmission
applications – chain, belt and gear drives,
or shaft-to-shaft gear or flexible coupling
drives.
The maximum release torque depends on
the number and size of Torque Limiting
Modules that can be incorporated, and the
size of the unit that can be accommodated
within the confines of the installation.
Internally & Externally adjusted modules
provide repeatability better than 5%,
however Externally adjusted modules are
preferred when the application is required
to operate within minimal variations
between static & dynamic disengagement.
The Bibbigard Torque Limiting Module is
constructed from the finest quality
materials. Many of the vital components
are made from high quality tool steels,
through hardened to Rockwell C62, and
precision ground to close tolerances.
Normal Operation
The flanges X and Y are driven by a large
steel ball (2), located in the detent
pocket (1), which is retained by a plunger
(3). This in turn is retained axially by
means of a system of angled races (6,8)
biased by pressure from the Belleville
springs (5), acting on a circle of balls (7).
Disengagement
On overload, relative angular movement
between flanges X and Y imparts a
tangential force (Fu) on the large steel
ball, forcing it clear of the detent pocket
back against the plunger. This in turn
causes the plunger to be forced through
the circle of balls overcoming the spring
loading on the angle races. In this
position, the balls are resting on the
large diameter of the plunger, and once
this condition is reached the flanges are
completely free to rotate independently.
A suitable switch can be incorporated in
the assembly to switch off the drive
motor or operate a warning device when
the Torque Limiting assembly disengages.
Resetting is a simple matter of first realigning
the flanges X and Y and then
tapping each module plunger back with
a soft mallet to allow the circle of balls
to return to their original position and
the large steel ball to return to its
location in the detent pocket.
Internally & externally adjusted modules
can be through hole or blind hole detent
fixing (see diagrams left and on page 59).
The type of detent fixing is dependant
upon the design constraints.
All modules require to be preloaded, this
is done by, in the case of the through
hole fixing by tightening the grubscrew
at the base of the detent pocket. In the
case of the blind hole fixing this is done
by the means of shims under the module.
Selection
To apply the modules in the form of a
torque limiter it is necessary to
determine the quantity of modules
needed for the required torque capacity
at a specific radius from the axis of
rotation.
