mechanism. Acceleration and deceleration controls shall meet requirements
specified in this section.
2.3.1.3
Micro-Drives
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NOTE: Include those motions where a micro-drive is
required. If micro-drive is not specified, delete
these paragraphs. Micro-drives are generally
required when slow speeds are required for an
extended amount of time. If precision movement is
required for limited time for final positioning of
loads, use adjustable frequency or dc variable
voltage crane controls instead of micro-drives.
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The following crane motions shall be provided with a separate micro-drive:
[main hoist], [auxiliary hoist], [trolley drive] [and] [bridge drive]. The
micro-drives shall be used to precisely position loads. Each micro-drive
shall consist of an electric motor, gear reducer, magnetic coupling clutch
and necessary controls. The output shaft of the reducer shall be connected
to an extension of the primary drive high-speed shafting with a magnetic
coupling clutch. Coupling shall normally be disengaged and shall be
engaged only if the micro-drive is required. Electrical clutch components
required for proper operation shall conform to the requirements specified
in paragraph ELECTRICAL COMPONENTS. Clutches shall be the magnetic
coupling type, and shall engage and disengage the micro-drives from the
high speed shafts of the main drive arrangement. The clutch shall be
engaged by electromagnet and released by springs. Clutch ratings shall be
not less than 150 percent of the micro-motor rated torque as amplified by
the intervening gearing. Clutch enclosures shall facilitate easy access
for wear inspection of the friction elements and visual examination of the
clutch assemblies.
2.3.2
Load Blocks
2.3.2.1
Main and Auxiliary Hoist Load Blocks
Load blocks shall be of welded steel construction. Load blocks shall be
provided with hot-rolled or forged steel fixed crosshead separate from the
sheave pin with swivel mounting for forged steel hook. Each lubrication
fitting for sheave pins shall be an independent type recessed within the
sheave pin or adequately guarded to prevent damage. The pitch diameter of
the sheaves shall be not less than 16 times the rope diameter. Sheaves
shall be supported by roller type bearings on steel sheave pins.
Provisions for external lubrication shall be provided to allow pressure
relief and purging of old grease. Sheave blocks shall be constructed to
provide maximum personnel safety and to prevent the hoist rope from leaving
the sheaves under normal operating condition.
2.3.2.2
Hook Assembly
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NOTE: If specific hook dimensions are provided in
the drawings, include the appropriate sentence;
otherwise manufacturer's standard hook will be
provided. If hooks are required to be disassembled
and inspected, include appropriate sentence.
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SECTION 14630A
Page 21
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