diameters must be at least 40 times the wire rope diameter. Equalizer sheave
pitch diameters for all classes of wire ropes must be at least 18 times the wire
rope diameter. The groove depth must be at least 1.15 times the wire rope
diameter, the groove included (throat) angle 30 to 40 degrees, and the groove
radius 0.060 to 0.120 inch larger than the wire rope diameter. Rims of running
sheaves must be heat treated to a minimum hardness of 320 BHN in the groove.
Sheaves with higher hardness carburized groove surfaces are also available.
Travel Wheels. Travel wheels of portal and container cranes are sized
for the maximum imposed load. For portal cranes, the governing design load may be
due to the hook load/boom radius combination for the maximum moment, or it may be
due to the moment caused by the counterweight with no load on the hook and the
boom at minimum radius. In both cases, the upperworks is rotated approximately
over a corner of the portal base. (See paragraph 188.8.131.52 for the "beaming method"
of calculating the upperworks position and the maximum corner load.) For
container cranes, the trolley is positioned at the end of its boom travel limit
with the rated load, and with no load at the end of its travel position on the
main beam and the boom raised to its stored position.
With the maximum imposed corner loads calculated and the rail size
specified, the minimum wheel diameter is determined using the following equation:
MWL = K*W*D
MWL = maximum wheel load that is imposed on the wheel (in pounds).
= sizing factor, usually 1500 (dimensionless).
= effective width of rail head, which is the width of the rail
top minus the corner radii (in inches).
= wheel tread diameter (in inches).
Travel wheels are required to be steel forgings, heat treated to at least
320 BHN. Carburizing is the preferred hardening process, but flame hardening may
also be used, subject to NCC approval. The hardened case must extend to the inner
faces and outer diameters of the flanges. Industry standards for wheel sizes and
manufacturing requirements are prescribed by ASTM A504.
The standard rails are available in rail head hardness in the range of
200 BHN to 615 BHN. The common rails installed for portal and container cranes
have rail head hardness of 320 BHN, for which the K factor of 1500 is applicable.
For other rail head hardnesses, the maximum value of the K factor should be
determined as follows:
K = 2.5 (BHN of wheel tread + BHN of rail head)
There is no detriment to large differences between the wheel and rail
head hardnesses. Experience suggests that wear of both can only be improved by
increasing the hardness of either the wheel, rail head, or both.
The wheel profile is determined by the rail system; however, the wheel
treads (distances between interior faces of flanges) must be at least 1.0 inch
wider than the rail head. Flange thickness and flange height must be matched to
the rail system frogs and switches. The included angle between the flanges must