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Installation
33
Misalignment & Couplers
Align the motor shaft and load as accurately as possible. In most applications,
some misalignment is unavoidable, due to tolerance variations in components.
However, excessive misalignment may degrade your system’s performance. The
three misalignment conditions, which can exist in any combination, are illustrated
and described in the next drawing.
Aligned
Parallel Misalignment
Combined Parallel & Angular Misalignment
End Float
Angular Misalignment
Misalignment Conditions
•
Angular Misalignment: The center lines of two shafts intersect at an angle other than
zero degrees.
•
Parallel Misalignment: The offset of two mating shaft center lines, although the
center lines remain parallel to each other.
•
End Float: A change in the relative distance between the ends of two shafts.
The type of misalignment in your system will affect your choice of coupler.
Single-Flex Coupling
Use a single-flex coupling when you have angular misalignment only. Because a
single-flex coupling is like a hinge, one and only one of the shafts must be free to
move in the radial direction without constraint. Do not use a double-flex coupling
in this situation: it will allow too much freedom and the shaft will rotate eccentri-
cally, which will cause large vibrations and catastrophic failure. Do not use a
single-flex coupling with a parallel misalignment: this will bend the shafts,
causing excessive bearing loads and premature failure.
Double-Flex Coupling
Use a double-flex coupling whenever two shafts are joined with parallel misalign-
ment, or a combination of angular and parallel misalignment (the most common
situation).
Single-flex and double-flex couplings may or may not accept end play, depending
on their design.
Rigid Coupling
Rigid couplings are generally not recommended, because they cannot compensate
for any misalignment. They should be used only if the motor or load is on some
form of floating mounts that allow for alignment compensation. Rigid couplings
can also be used when the load is supported entirely by the motor’s bearings. A
small mirror connected to a motor shaft is an example of such an application.
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