NATIONAL CRANE
Published 03-23-2018 Control # 243-14
6-5
NBT50 OPERATOR MANUAL
MAINTENANCE CHECKLIST
6
the cable on the drum so that the wear is equalized along the
total length of the cable.
Wire Rope Replacement
No precise rules can be given for determination of the exact
time for replacement of wire rope since many variable factors
are involved. Determination regarding continued use or
replacement of wire rope depends largely upon the good
judgement of an appointed and qualified person who
evaluates the remaining strength in a used rope after
allowance for any deterioration disclosed by inspection.
•
Wire rope replacement should be determined by the
following information excerpted from a National
Consensus Standard as referenced by Federal
Government Agencies and as recommended by
Manitowoc. All wire rope will eventually deteriorate to a
point where it is no longer usable. Wire rope shall be
taken out of service when any of the following conditions
exist:
•
Six randomly distributed broken wires in one rope lay or
three broken wires in one strand in one lay. The rope is
unsafe for further use if there are either three broken
wires in one strand (Breaks 2, 3, 4) or a total of six
broken wires in all strands in any one lay.
•
In rotation resistant ropes: two randomly distributed
broken wires in six rope diameters or four randomly
distributed broken wires in 30 rope diameters
•
Wear of one-third the original diameter of outside
individual wires. Worn rope, usually indicated by flat
spots on the outer wires is unsafe for further use when
less than two-thirds the thickness of the outer wire
remains.
•
Necking down of the rope indicates core failure.
•
Kinking, crushing, bird caging, or any other damage
resulting in distortion of the rope structure.
•
Evidence of heat damage.
•
Reductions from nominal diameter of more than 5%:
-
.4 mm (0.0156 in) for rope diameters to 8 mm (0.313
in)
-
.8 mm (0.031) for rope diameters 9.5 mm (0.375 in)
to 0.50 in (12.7 mm)
-
1.2 mm (0.047 in) for rope diameters 14.3 mm
(0.561 in) to 19.1 mm (0.75 in)
-
1.6 mm (0.063) for rope diameters 22.2 mm (0.875
in) to 28.6 mm (1.125 in).
•
One outer wire broken at its point of contact with the core
of the rope which has worked its way out of, and
protrudes or loops out from the rope structure.
•
Manitowoc recommends that for cable extended booms,
a single damaged wire rope assembly shall require
replacement of the complete set of extension cables.
•
Manitowoc recommends that boom extension cables be
replaced every seven (7) years.
Care of Wire Rope
Handle wire rope with care to prevent damage to the
individual wires which affect the overall strength and
performance of the rope. Do not allow the formation of kinks,
because this displaces the strands of wire from their original
position and relation to each other causing severe bending
and unequal tensions in the strands. This distortion and wire
displacement cannot be corrected even under high tension
and a permanent weak point remains in the rope. Displaced
or raised wires indicate a previous kink, but does not show
the damaged condition of the inner rope wires.
Never pull wire rope over a non-rotating support such as a
spindle bar, a pin, or an inoperative sheave. This practice
causes severe abrasion to the outer strand wires. A properly
operating sheave or snatch block is essential to safety and
long service life of the rope.
Do not use worn sheaves or sheaves with flat grooves
because they do not provide sufficient support to prevent the
distortion and flattening of the rope. Sheaves with nicked or
broken flanges can cut or otherwise damage the rope.
An even distribution of rope coils over the hoist drum is
essential to smooth operation. This prevents the rope from
cutting down through or crushing other coils on the drum
resulting in damage to and difficulty in unwinding the rope.
REPLACEMENT CABLE
If the hoist cable needs to be replaced, care should be taken
in selecting a suitable replacement cable. The cable strength
requirements are shown on the crane load chart. The types
of cable are optional with 6 x 25 and Dyform being the most
common. A high strength, rotation resistant cable is
preferred and is furnished as standard by National Cranes.
This cable eliminates single part line load spin and prolongs
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Summary of Contents for National Crane NBT50 Series
Page 1: ...Operator Manual National Crane NBT50 Series ...
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Page 10: ...TOC 6 TABLE OF CONTENTS OPERATOR MANUAL NBT50 THIS PAGE BLANK ...
Page 12: ...INTRODUCTION OPERATOR MANUAL NBT50 1 2 Published 03 23 2018 Control 243 14 FIGURE 1 1 7650 66 ...
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