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Rigid couplings are comprised of two flanged hubs bolted together.  Less
common but found most frequently on older bridge crane travel drives are the clam
shell types of rigid couplings.  There are single piece or matched pairs of steel
or ductile castings in the form of heavy-walled tubes.  The single piece design is
cut lengthwise on one side and slotted on the opposite side so that it can be
clamped with a row of bolts along the cut side.  The two piece coupling has a row
of clamping bolts on both sides of the coupling.  Machined key slots are usually
provided on both ends of these coupling shells.  Rigid couplings are permitted
only on long shafts (with distant bearing supports) where shaft deflection easily
compensates for any misalignment.
Special Couplings.  Couplings between the diesel engine and the electric
generator include elastomeric elements between the flange and hub.  The flange
that mates with the diesel engine flywheel is face mounted with a ring of bolts;
the hub is pressed onto the shaft of the electric generator and secured with a key
on the shaft.
Rotate drives on older cranes have unique "built-up" couplings, generally
known as "Olham" or jaw type.  They rotate slowly but carry the maximum torque of
the drive.  The most common designs feature two slots at right angles to each
other and a sliding key in each slot.  This arrangement compensates for
substantial parallel offset and limited angular misalignment.
Limit switches are connected to the shafts by small, light duty couplings
designed especially for that purpose.  One end of the coupling is face mounted on
the end of the wire rope drum shaft.  Functionally they are
Bearings.  Antifriction bearings are precision assemblies of hardened and
polished rolling elements and concentric races (rings).  There is a large variety
of bearing designs to fit every crane application.  Some bearings are available as
sealed, permanently lubricated assemblies; other types are open, requiring
installation of separate seals and provisions for lubrication.  Bearings which
require periodic grease lubrication have their races grooved and drilled for the
distribution of injected grease.  Installations of grease lubricated bearings must
include provisions for the purging of old grease either past the seal lips or
through relief fittings.  The press fits of inner races on the shafts and axles,
the fits of the outer races in the housings, and clamping of the races must follow
the bearing manufacturer's installation criteria to obtain satisfactory bearing
performance.  Ball bearings, having much lesser load carrying capacity than the
roller types, are used primarily within standard commercial assemblies such as
electric motors and disc brakes.
Double-row spherical roller bearings have two barrel-shaped
side-by-side rings of rollers which roll on the internal spherical surface of the
outer race.  This arrangement makes them inherently self-compensating for any
angular misalignment between the shaft and housing.  They are recommended for
support of shafts and axles without heavy axial loads.  Travel wheel axles, open
gearing shafts, and hoist drums are most often mounted on these bearings.


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