Rotate bearing bolts, studs, and nuts must be left unpainted.
(These items require periodic inspections and checks of their tension.)
Non-structural fasteners, such as those retaining keeper bars, etc.,
should be painted without blast cleaning.
Mechanical. The vast majority of mechanical components are standard
commercial items, usually designed and built to existing industry standards. They
range from the complete hoist assemblies to load hooks. The standard commercial
items are described in catalogs and advertising literature; however, such
descriptions must be reviewed and understood to ensure that the desired ratings
and design factors are being provided.
Hoists. The hoists are the most critical assemblies of any
crane - they raise, lower, hold, and stop moving loads and warrant the most
attention to their design and quality of workmanship. Depending on the
application, the hoists may be built-up to the precise specification requirements
or they may be standard commercial units designed to a particular service or duty
class. The built-up hoists are always electric motor driven and with wire rope
reeving. The standard commercial hoists may be electrically, hydraulically, or
manually driven and may use either wire rope or chain reeving.
Built-Up Hoists. In the typical arrangement, the electric motor is
connected to the gear reducer input (high speed) shaft by a full-flexible coupling
with one shoe brake installed on the opposite end of the input shaft and another
brake installed either on the outboard (tail) end of the motor or on the coupling
hub on the gear reducer input shaft. There are several options for connecting the
gear reducer output shaft to the wire rope drum:
The output shaft may be connected directly to one stub shaft of the
wire rope drum by a full-flexible coupling, in which case the drum must be
supported independently on two stub shafts, each mounted in a bearing.
The output shaft may be pressed directly into the drum hub, in which
case the inboard drum stub shaft and support bearing may be omitted if the
adjacent gear reducer bearing has adequate capacity. Alternatively, a bearing of
adequate capacity may be installed to support the inboard drum stub shaft and the
adjacent gear reducer bearing removed. In both of these arrangements, the three
bearings must be mounted on solid foundations, aligned/shimmed very accurately to
preclude built-in stresses. It should be noted that although self-aligning
bearings are commonly used in these applications, they take up the angular, but
not the parallel, misalignments.
To avoid the stringent alignment requirements of (b) above, the
inboard stub shaft may be replaced by a barrel type coupling to provide the radial
support and to transmit the drive torque. Barrel couplings are designed for
angular misalignments of up to 2.0 degrees (similar to semi-flexible couplings)
and have much greater radial load capacity than the shaft-to-shaft couplings. The
barrel couplings are flange mounted by a ring of bolts to the drum end plate. The
adjacent gear reducer bearing must have adequate capacity for the imposed radial
The output shaft may terminate with a gear pinion, which engages a
ring gear on the drum. In this arrangement the drum is supported independently by