NCC policy is to require both ends of pins to be locked this may be in
the form of a keeper bar on each end or a head on one end and a keeper bar on the
other end. The only exception to this practice is to permit only one end to be
secured with a keeper bar if the other end protrudes by at least
half the pin diameter, not including the chamfer. Keeper bars should never be
welded to the pins.
Wire rope drums of built-up hoists typically have welded stub shafts on
their end plates. These stub shafts are integral parts of the drum weldment.
Alternatively, a rotating through-shaft may be pressed and keyed into hubs of drum
end plates and supported by pillow blocks. Some cranes have end plates with hubs
and bronze bushings or bearings in place of stub shafts. With this arrangement,
the drum rotates on a stationary shaft passing through the length of the drum.
Couplings. Couplings are standard commercial assemblies of established
manufacturers. All torque carrying components of couplings, with a few exceptions
discussed below, must be steel. Couplings are designed to be full-flexible, semi-
flexible, or rigid. The first two types have provisions for grease lubrication.
The hubs have concentrically machined bore and outside diameters which permit the
installation of specialized equipment for precise shaft alignment. Coupling hubs
may be bored and slotted for the keys to the exact requirements of the customer or
may be purchased unfinished.
Full-flexible couplings have two hubs, which are pressed and keyed on the
shaft or axle ends, and a two piece flange connected sleeve fitted over the hubs.
The hubs have external gear teeth cut on their circumference and the sleeve has
internal gear teeth which mate with those on the hubs. Each sleeve flange has a
lubrication plug in its periphery and an O-ring seal on the hub seat. The torque
is transmitted through the two sets of gear teeth. This coupling design can
accommodate angular misalignment and parallel offset between the two ends. A
variation of the above design has the sleeve replaced with a steel spring grid
grid. A non-load bearing cover is installed over the hubs and the grid to keep
them engaged and contain the lubrication grease. Full-flexible couplings should
be limited to these two designs. (For lubrication, a plug in one sleeve flange is
temporarily replaced with a standard lubrication fitting, the plug in the other
flange is removed, fresh grease is injected and old grease is purged through the
open plug hole, and the plugs reinstalled.) Full-flexible couplings are mandatory
for connecting shafts and axles with adjacent bearing supports. When installed on
vertical shafts, the couplings must include a disc clamped between the sleeve
flanges to keep the sleeve from sagging out of its intended position on the hubs.
In gear type semi-flexible couplings, one of the hubs and its half-piece
of the sleeve are made into a single component. The deletion of one of the gear
tooth meshes limits the coupling to compensating only for angular misalignment.
Alternatively, a coupling with a steel grid installed over external teeth of two
coupling hubs, also functions as a semi-flexible coupling. Semi-flexible couplings
are mandatory for floating shafts and shaft arrangements where the bearing support
of one shaft is adjacent, and the other is distant, from the coupling.