Misalignment and parallel offset:
Flexible couplings are not designed to operate in
excessive misalignment and parallel offset situations
deliberate or otherwise. Generally the couplings flexibility
allows for operating conditions where angular, parallel
and end float situations occur as machinery wears or
bed-in. There are other situations to consider such as
shaft deflection, thermal expansion and other conditions
that may cause misaligning situations. When selecting
a coupling it is important to take note of the couplings
misalignment and offset values as previously explained,
operating conditions do vary. Some couplings require
less force to misalign or work better than others in overcoming
acceptable degrees of misalignment and offset.
Excessive misalignment and offset does put extra load
and causes increased vibration on the coupled machines
bearings, gears, and other parts which in turn could
cause premature failure.
Types of shaft misalignments
Torsional flexibility:
This is a term used to describe a coupling design feature
which allows the flexible medium between two coupling
halves to absorb and dampen any shock, vibration or
pulsating loads the coupling maybe subjected too. It
can be thought of as a twisting force (torsional-torque
refers to twisting). If the coupling selection process has
been correctly calculated and also the coupling correctly
aligned torsional flexibility will be accounted for. This will
cause the flexible medium to function correctly within its
designed limits and give a rated life.
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