Named after its Inventor Dr. James Bibby in 1917, this coupling is still one of the most sought after flexible
couplings for heavy shock applications. Let us now look at the constructional
features of the coupling.
○ The Coupling consists of two flanges or hubs
specifically mounted on the drive and the driven shafts respectively. These
hubs contain axial grooves cut on their circumference.
○ The two couplings are
joined or held together by means of a specially designed grid spring.
○ The total assembly is enclosed in a casing or
shell filled with grease for low speed applications or, in high speed application with high viscosity oil.
Now let’s look
at the working aspect of the coupling and how it tends to reduce vibration and
prevents the build up of resonance in the
system.
a.) The specially designed spring is
wound up through the grooves forming a series of resilient bridges throughout
the periphery of the coupling.
b.) The grooves are tapered up at the
edges (see photo) in order to provide extra flexible spans to the spring at
normal loads and tends to support the spring at the sides whenever overloading
occurs.
c.) The stiffness of the spring
depends on its unsupported length of each of its flexible span. The unsupported
length tends to vary with the loads producing a varying stiffness for the
coupling based on the loading.
d.) This action tends to produce a
detuning action altering the torsional vibration frequency of the system that
prevents the build-up of resonance.
Some applications of Bibby
Couplings are
○ Cement Mills – in grinding and crushing
machinery.
○ Cranes
○ Conveyors
○ Turbines
○ Marine Auxiliaries
○ Paper Mills
Bibby couplings can be used for
applications with powers varying from as low as 1 h.p to about 100,000 h.p.
per 100 rpm of the coupling. Correspondingly the
couplings are available in varying sizes ranging from 100mm diameter to 4000 mm
diameter.
Bibby couplings are capable of taking
axial and radial misalignments to a very small extent only. It is necessary for
the user to ensure that both axial and radial misalignments are kept to the minimum possible.
Selection procedure for Bibby
Couplings:
The selection of the Bibby
coupling is mainly based on the torque being
transmitted by the coupling. Each coupling has a characteristic value for the
torque transmitted by it to the revolutions per minute of the coupling.
The rating of the coupling is given by
Rating = Maximum power to be
transmitted in h.p/ r.p.m of
coupling
In order to account for contingencies
like shocks, sudden stops, stalling, etc. a factor of safety is to be considered during selection of the coupling.
Rating of coupling to be Selected =
Max. power of coupling* Factor/ r.p.m. of coupling
The chart containing the factors
to be considered is given below based on the
application and driving machinery.
See the selection chart below for the
selection of corresponding coupling based on the power. Note: This chart is an
indicative for the selection of the Bibby coupling. Kindly refer to an actual
manufacturer's catalog for selection as
ratings may vary from manufacturer to manufacturer.