Quantcast Ratchet and Pawl Mechanisms

Custom Search
 
  
 


MIL-HDBK-1038
It is customary to have the hooks equipped with a securing feature, such
as a clamped spring loaded latch across the throat opening or a D-ring installed
through a hole in the hook tip.  Welding, including that to repair forging flaws,
is prohibited.
5.3.17
Bumpers.  Bridge crane bumpers are selected according to the applicable
criteria of CMAA #70 and CMAA #74.  The bumpers may be either one of the two
standard commercial elastomeric or hydraulic types, or a custom designed spring
type.
Portal cranes are not normally equipped with bumpers on the travel
trucks.  Container cranes are equipped with spring or hydraulic bumpers on both
the travel trucks and trolley.  These bumpers should be designed for a
deceleration rate of 16 feet/second/second when contacted at 50 percent of the
corresponding rated speed.  (The stroke should be calculated using an efficiency
of 0.5 for spring bumpers and 0.8 for hydraulic bumpers.)  Additionally, the
bumpers must be designed to absorb/dissipate the total energy of the gantry or
trolley traveling at 100 percent of rated speed without sustaining any damage.
The boom bumpers (buffers) of floating and container cranes (mounted on the A-
frame or gantry structure) are selected to absorb and dissipate the kinetic energy
of the boom at its rated hoisting speed without any damage to the structural or
mechanical components of the crane.  (Portal cranes are not normally equipped with
boom bumpers.)
In determining the kinetic energy that a bumper must absorb and
dissipate, the hook block and load are not included if they are free to swing.
The elastomeric and hydraulic bumpers should be selected in accordance with the
manufacturer's published recommendations.
5.3.18
Spud Locks.  Spud lock pins must be designed for the torque/load due to
the maximum design wind velocity with the boom at maximum radius.  The shear
stress design factors must be 4.00 and 5.00 based on the material yield and
ultimate shear strengths, respectively.  The bearing stress on the pin and its
pocket bore must have a design factor of 4.00 based on the material tensile yield
strength.
On floating cranes, the loads due to list and trim must be added to the
wind load.
5.3.19
Rotate Holding Brakes.  The combined capacity of these brakes, multiplied
by the mechanical advantage of the back-driven speed reducer, must be adequate for
the imposed rotational loads that govern the design of spud locks.  The efficiency
and operational characteristics of the back-driven speed reducer must be confirmed
with the manufacturer.
5.3.20
Ratchet and Pawl Mechanisms.  The ratchet, its fasteners, the pawl, and
the pivot joint are designed for a hypothetical 150 percent rated hook load to
account for possible impact in engaging the ratchet.  This design approach has
been used on the older portal and floating cranes.  On newer cranes, in order to
avoid recalculation of the wire rope pull for this hook load, crane designers use
150 percent of the rated hook load drum line pull for the design of the ratchet
and pawl mechanism.  This conservative approach can be readily accommodated with a
practical design.  All pivoting joints are required to have grease lubricated
bushings.
157





 


Privacy Statement - Copyright Information. - Contact Us

Integrated Publishing, Inc.