Deviation from these criteria is permitted only with the approval of NCC.
The following design standards apply to portal cranes, floating cranes,
container cranes, and unique portions of cantilever cranes. Design and selection
of mechanical drive components is governed by the rated torque of the drive motor;
and that of the wire rope drum and supporting components by the drum line pull.
(Drive motor selection method is described in paragraph 22.214.171.124 below.)
Mechanical design procedures are based on the assumption that the full rated
torque of the drive motor will be applied to the mechanical components. Many
mechanical components have unique, industry-wide design procedures and standards
which, to a large extent, are followed by the NCC. The general design criteria
for all other components are minimum design factors of 4.00 on the yield strength
and 5.00 on the ultimate strength of the material. Other unique design and
selection criteria follow.
Wire Rope Users Manual is the wire rope industry's comprehensive
reference for design issues relating to wire ropes and reeving system components.
It provides background material on wire rope construction and classification,
physical properties, behavior under load, handling and installation, all types of
end terminations, field lubrication, and inspection. Particularly useful are the
recommended reeving system features to lessen hook block spinning and reduce the
probability of wire rope cabling. The wire rope selections in the manual include
constructions and sizes which are not listed in Federal Specification RR-W-410
(the standard reference for wire ropes), and there are minor inconsistencies in
the breaking strengths of some wire ropes listed in the two documents. NCC policy
is to accept wire ropes and listed nominal breaking strengths of either document.
However, all other design criteria of reeving systems are governed by the
requirements of this handbook.
Gear Reducers. All standard commercial gear reducers have nameplates
ratings stamped on them. The ratings are based on a specific input speed
(normally 1170 or 1750 RPM) and 5000 hours of bearing life. If the actual
operating input speed is different from that on the nameplate, the ratings are
prorated accordingly, but the rated torque associated with the nameplate
horsepower may not be exceeded. Neither the bending strength rating nor the
pitting resistance rating may be less than the drive motor rating. The nameplate
ratings are established by the gear reducer manufacturer in accordance with the
standards and procedures of the American Gear Manufacturers Association (AGMA).
The inherent safety margins are adequate to account for the increased loads due to
drive motor starting torque and brake application. However, the limitations on
the magnitude of the "overhung" load, usually on the output shaft, must be
considered if a significant load is imposed on the shaft.
There are no industry rating standards for cycloidal speed reducers
(since they are proprietary designs of a limited number of manufacturers) and
their selection and applicability should be based on the manufacturer's published
data. These speed reducers possess unique performance and operating
characteristics, such as capacity for high shock loading and backdriving, which
make them desirable for some applications. Their selection should be made in
consultation with the manufacturer's engineering staff.