(a)
Breaking Strength. All hoisting wire rope shall be of such breaking strength as
to provide a minimum factor of safety of seven. The factor of safety (F) shall
be calculated by the following formula:
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where
S = Manufacturer's rated breaking strength of one
rope.
N = Number of parts of ropes under load.
W = Maximum static load imposed on all ropes with the
platform, cage, or bucket, and its rated load at any position in the
hoistway.
(b) Wire Rope
Inspection.
(1) Inspector.
A representative of the user of the material hoist shall
be appointed and this representative shall keep written reports of the rope
condition on file at the work site. The representative shall have the authority
to order wire rope replacements and keep unsafe wire rope from being
used.
(2) Periods of
Inspection.
Inspection periods shall be set-up for each
material-hoist wire rope. The frequency of inspection shall be determined by
consideration of environment, degree of hazard to materials, frequency of
operation, and the frequency with which the rope is subjected to its capacity
limits. Inspections shall be made not less often than once each 30
days.
(3) Method of
Inspection.
The working length of the wire rope shall be unwound from
the hoist drum. Thorough inspection shall be made of the rope sections that
pass over sheaves, drums, or contact saddles, or which make opposing turns. The
rope close to end attachments shall be carefully inspected.
(4) Inspection of Used Wire Rope.
A used wire rope shall be thoroughly inspected prior to
installation.
(5) Inspection
of Wire Rope on Idle Equipment.
The wire rope on equipment that has been idle or shutdown
for a period of one month or more shall be completely inspected prior to
operation.
(6) Surfaces
Contacted by Wire Rope.
Sheaves, guards, guides, drums, flanges, and other
surfaces contacted by wire rope during operation should be examined at the time
of inspection. Any condition harmful to the rope in use at the time should be
corrected.
(c)
Wire Rope Removal and Replacement.
Wire rope with one or more of the following defects shall
be removed or replaced immediately:
(1) Corrosion. Severe corrosion shall be
cause for replacement. Any development of slight corrosion should be noted and
watched closely.
(2) Broken Wires.
One or more valley breaks shall be cause for replacement. (A valley break is a
wire break occurring in the valley between two adjacent strands.)
Six randomly distributed broken wires in one rope lay, or
three broken wires in one strand in one rope lay, shall be cause for
replacement. (A rope lay is the length along the rope in which one strand makes
a complete revolution around the rope.)
(3) End Attachments. Development of broken
wires in the vicinity of attachments shall be cause for replacement. If this
condition is localized in an operating rope and the section in question can be
eliminated by making a new attachment, this can be done rather than replacing
the entire rope.
(4) Abrasion.
Abrasion, scrubbing, flattening, or peening causing loss of more than one-third
of the original diameter of the outside wires shall be cause for
replacement.
(5) Kinking. Severe
kinking, crushing, birdcaging, or other damage resulting in distortion of the
rope structure shall be cause for replacement.
(6) Heat. Evidence of any heat damage
resulting from a torch, or any caused by contact with electrical wires shall be
cause for replacement.
(7)
Reduction of Rope Diameter. Reduction from nominal diameter of more than
3/64 -inch
for diameters up to and including ¾ -inch;
1/16 -inch
for diameters 7/8 to 1 1/8 inches; and
3/22 -inch
for diameter 1 ¼ to 1 ½ inches shall be causes for replacement.
Marked reduction in diameter indicates deterioration of the
core.
(d) Wire Rope
Installation. Hoisting ropes shall be installed in accordance with the wire
rope manufacturer's recommendations. The hoisting ropes shall be secured to the
drum by clamps or by an approved equivalent means.
(e) Drums and Sheaves.
(1) Pitch diameters of drums shall be a
minimum of 24 times the nominal rope diameter. The drum flange shall extend at
least 2 inches radially beyond the last layer of rope when all rope is coiled
on the drum.
(2) The winding drum
shall have not less than three turns of rope when the platform, cage, or bucket
is at the lowest point of travel.
(3) All hoisting wire rope shall be improved
plow steel grade or stronger, and equal in flexibility to 6 x 19 classification
wire rope. The joining of hoisting ropes by splicing is prohibited.
(4) There shall be at least 4 feet of
clearance between the cathead sheave and the hoisting-rope fastening on the
platform, cage, or bucket when either is at the uppermost terminal or
landing.
(5) The arc of the bottom
of the sheave groove shall be smooth and concentric with the bore or shaft of
the sheave. The center line of the groove shall be in a plane perpendicular to
the axis of the bore or shaft of the above sheave.
(6) Sheave grooves shall be machined or cast,
providing the bottom of the groove has a radius subtending an arc of 150
degrees and conforms to Table 1.
Table 1
Groove Radii for New and
Reconditioned Sheave Grooves
|
|
Wire Rope, Nominal
Diameter
|
Groove
Minimum
|
Root Radius
Maximum
|
--
|
|
¼
|
.140
|
.150
|
|
|
5/16
|
.170
|
.180
|
|
|
3/8
|
.205
|
.215
|
|
|
½
|
.265
|
.275
|
|
|
5/8
|
.330
|
.340
|
|
|
¾
|
.390
|
.400
|
|
|
7/8
|
.460
|
.475
|
|
|
1
|
.525
|
.540
|
|
|
1 1/8
|
.585
|
.600
|
|
|
1 ¼
|
.655
|
.670
|
|
(7) Load-bearing sheaves for wire rope shall
be grooved to accommodate the rope and shall have a diameter at least 20 times
that of the wire rope. For minimum tread diameter of sheaves see Table 2. (The
diameter of a sheave is measured at the bottom of the grooves.)
(8) Sheaves intended for use with fiber rope
shall not be used with wire rope.
(9) Defective and worn sheaves that may cause
equipment failure or damage to the wire rope shall be replaced. If pillow
blocks are used, they shall be mounted on top of beams and securely bolted.
Open bearings shall not be used.
(10) No snatch blocks or hood-type sheaves
shall be used on any hoist tower.
Table 2
Minimum Ratio of Rope Diameter to
Sheave Tread Diameter
|
|
Diameter of Hoisting Rope
(Inches)
|
|
Minimum Tread Diameter of
Sheaves* (Inches)
|
|
¼
|
|
|
5
|
|
5/16
|
|
|
6 ½
|
|
3/8
|
|
|
7 ½
|
|
½
|
|
|
10
|
|
5/8
|
|
|
12 ½
|
|
¾
|
|
|
15
|
|
7/8
|
|
|
17 ½
|
|
1
|
|
|
20
|
|
1 1/8
|
|
|
22 ½
|
|
1 ¼
|
|
|
25
|
* Based on 20 times rope diameter.
(11) All sheaves shall be of iron or
steel.
(12) All sheave bearings
shall be lined with babbit, or other equivalent bearing metal, or have ball or
roller bearings.
(13) Sheave
bearings shall be provided with adequate means for
lubrication.