The saddle types of gudgeon assemblies are preferred because they preserve the
structural integrity of the equalizer and shield the joint against the weather.
The lateral movement between the gudgeon assembly and the equalizer is controlled
by the insertion of thrust washers between these components. Gudgeon pins do not
require bushings but they must be grease lubricated at the contact surfaces where
the rocker motion takes place.
The gudgeons seat in pockets at the ends of the mating equalizers. The
vertical loads are supported by thrust bearings or thrust washers; the bending
moments are distributed into bronze bushings installed inside the top and bottom
flanges of the equalizers. Portal base construction of the older cranes has
inherent flexibility that allows them to deform sufficiently to maintain wheel
contact on rails with some unevenness. The all-welded portal base construction of
the newer cranes, however, is too rigid to compensate for rail irregularities.
Consequently, their gudgeons in the upper level of equalizers must be free to
slide (drop down) in their bushings to allow the wheels of an unloaded corner to
maintain contact with the rails. When thrust bearings are used, the bearing
installation must include provisions to maintain the races and the rolling
elements in contact during lift-off conditions.
Float Pins. The gudgeon pins of the travel trucks that operate on curved
tracks, in addition to accommodating rocker motion, must also provide for the
lateral sliding (float) of the travel truck. The required amount of float is a
function of the rail gauge, rail radius of curvature, and the portal base
proportions; it must be calculated for each specific installation. Transition
between travel on curves and straight track changes the effective rail gauge and
causes the travel trucks to float and impose lateral squeezing or spreading forces
on the portal base and torsion on the equalizers. The magnitude of these forces
is the product of the wheel loads and the friction between the float pins and
their bushings. Figure 19 shows a typical design used on older cranes, and
Figures 20 and 21 show those preferred on newer cranes.
The sizing, material properties, and lubrication provisions for these
components are prescribed in detail in Section 5.2. Use these design requirements
to avoid binding at the float pin and the resulting heavy rail head/wheel flange
wear and cracked welds in the portal base.
Other float pin and gudgeon assembly configurations and materials may be
considered only in consultation with, and approval of, NCC.
Cranes that travel on straight tracks do not require
gudgeons. The rocker motion is provided in the form of rocker pins and reinforced
extensions of the webs or saddles, either upward or downward, at the pivot points.
Travel Trucks. Travel trucks are short box beam weldments that provide
mounting for the travel wheels, travel drive, and a rocker or float pin. The four
outermost travel trucks also have rail sweeps or bumpers on their outer faces.
Wheel axle bearing seats are designed so that wheel/axle bearing assembly can be
removed with no more that 3 inches of jacking.
The older cranes have a combination of powered and unpowered travel
in each corner complement. The powered trucks have both travel wheels
through an idler gear that mates with the wheel gears. These powered
normally include other open gears mounted between the webs. The unpowered
have only two free-wheeling travel wheels.