Pump Drives. As the name implies, these units were developed
specifically for driving multiple hydraulic pumps from a single power source.
However, they have been modified for other applications. Pump drives have the
gears arranged so that a single input shaft, usually from an electric motor or a
diesel engine, can drive several hydraulic pumps or electric generators. The
power source connection may be in the form of a spline, key, clutch, or a manually
engaged/disengaged cutout coupling. Unlike the speed reducers, pump drives are
intended to function primarily as power splitters; the speed reduction is a
secondary function and is limited to a single stage (gear mesh).
Open Gearing. Open gearing is often used as the last gear set to obtain
the desired output from a drive. The most common applications are the built-up
hoist drives, rotate drives, and travel drives of older portal cranes. It is the
slowest and the most heavily loaded set of gear train. Accordingly, spur
(straight) gearing, which does not produce any axial loads on the support
structure, is recommended. The pinion should have its teeth crowned to avoid
damaging edge loading of the teeth, which can be expected due to the high loads
and uncertain structural support. The design of open gearing of all types is
governed by AGMA standards. Open gear sets are normally grease lubricated.
Whenever feasible, they should be protected by a metal cover with spring loaded
lids for inspection of the gear teeth, tooth contact at the mesh, and lubrication.
Travel drives of the older portal cranes typically drive the two wheels
of the powered travel truck through an idler gear. The teeth of the idler gear
are subjected to constant load reversals due to their engagement with the drive
pinion and the wheel gears regardless of the direction of rotation. In order to
account for this severe operating conditioning, the bending strength rating of the
idler gear is reduced to 70 percent of its normal rating.
Shafts, Axles, and Pins. All gears and travel wheels, with the exception
of those in the rotate assembly and carrier yokes, should be pressed on and turn
with their shafts or axles. All gears and driven wheels should also be keyed to
their axles. Additionally, helical gears should be seated against a shoulder
machined on their shafts to absorb the axial force due to the helix angle.
Diameter differences at the shoulders should be minimized and the radius of the
fillet should be as large as the design permits so as to mitigate the stress
concentration factors. Squaring and floating shafts, which normally have coupling
hubs pressed on their ends, should not have their end diameters reduced below 90
percent of the shaft diameter. Mechanical pins are stationary members which
support pivoting components of operating mechanisms (such as ratchet pawls or spud
locks) or sheaves. It is common practice to drill numerous holes through these
pins to serve as lubrication passages to the bushings or sheave bearings mounted
on them. The loss of strength due to these holes must be considered in the design
of the pins. The location and geometry of the keyseat must be evaluated for its
effect on the fatigue strength of the shaft or axle.
Squaring shafts and floating shafts are usually obtained as standard
commercial turned-ground-polished steel shafting. Fleeting sheave pins, which are
exposed to the weather and carry bushings that turn and slide on them, must be
either corrosion resistant steel or plated with nickel and hard chrome to make
them corrosion resistant. These shafts are not drilled for lubrication. The
fleeting sheave bushings are lubricated through grease passages in the sheave hub
and the bushing.