01.
General
Characteristics. Wire rope comes in many grades and dimensions, and
every rope has its own characteristics with regard to strength and resistance
to crushing and fatigue. A larger rope will outlast a smaller rope of the same
materials and construction, used in the same conditions, because wear occurs
over a larger surface. Similarly, a stronger rope will outlast a weaker rope,
because it performs at a lower percentage of its breaking strength, with
reduced stress. (3-31-22)
02.
Wire Rope Terms. Common grades of wire rope include extra improved
plow steel (EIPS) and swaged powerflex, among others. The following terms are
commonly used for wire rope: (3-31-22)
a.
Abrasion Resistance. Ability of outer wires to resist wear. Abrasion resistance
is greater with larger wires. (3-31-22)
b. Core. The foundation of a wire rope which
is made of materials that will provide support for the strands under normal
bending and loading conditions. A fiber core (FC) can be natural or synthetic.
If the core is steel, it can be a wire strand core (WSC) or an independent wire
rope core (IWRC). (3-31-22)
c.
Crushing Resistance. Ability of the rope to resist being deformed. A rope with
an independent wire core is more resistant to crushing than one with a fiber
core. (3-31-22)
d. Die-form Line.
Made from strands that are first compacted by drawing them through a drawing
die to reduce their diameter. The finished rope is then swaged or further
compressed. (3-31-22)
e. Fatigue
Resistance. Ability of the rope to withstand repeated bending without failure
(the ease of bending a rope in an arc is called its "bendability"). Fatigue
resistance is greater with more wires. (3-31-22)
f. Strength. Referred to as breaking
strength, usually measured as a force in pounds or tons. The breaking strength
is not the same as the load limit, which is calculated as a fraction of the
breaking strength to ensure safety. (3-31-22)
g. Swaged Line. Manufactured by running a
nominal-sized line through a drawing die to flatten the outer crown and thus
reduce the rope diameter. This compacted rope allows for increased drum
capacity and increased line strength. (3-31-22)
03.
Typical Wire Rope
Specifications. The table below lists a few examples of wire-rope
breaking strengths. (3-31-22)
TABLE 454.03 - Typical Wire
Rope Specifications
|
6x26 Improved Plow
Steel
|
6x26
Swaged
|
Swaged
Compact-Strand
|
Diameter
(inches)
|
Weight
(lbs/ft)
|
Breaking Strength
(tons)
|
Weight
(lbs/ft)
|
Breaking Strength
(tons)
|
Weight
(lbs/ft)
|
Breaking Strength
(tons)
|
1/2
|
0.46
|
11.5
|
0.6
|
15.2
|
0.63
|
18.6
|
9/16
|
0.59
|
14.5
|
0.75
|
19
|
0.78
|
23.7
|
5/8
|
0.72
|
17.9
|
0.93
|
23.6
|
1.01
|
28.5
|
11/16
|
1.10
|
28.8
|
1.18
|
35.3
|
3/4
|
1.04
|
25.6
|
1.37
|
34.6
|
1.41
|
42.2
|
13/16
|
1.56
|
39.6
|
1.63
|
49.3
|
7/8
|
1.42
|
34.6
|
1.83
|
46.5
|
1.91
|
56.0
|
15/16
|
1.95
|
53.3
|
2.20
|
66.1
|
1
|
1.85
|
44.9
|
2.42
|
60.6
|
2.53
|
73.7
|
1-1/8
|
2.34
|
56.5
|
2.93
|
75.1
|
2.97
|
92.9
|
1-1/4
|
2.89
|
69.3
|
3.52
|
92.8
|
3.83
|
112.1
|
1-3/8
|
3.5
|
83.5
|
4.28
|
108.2
|
4.62
|
128.6
|
Source: Cable Yarding Systems Handbook. 2006. Worksafe BC.
Table lists typical breaking strengths. See manufacturer's specifications for
specific lines. (3-31-22)
04.
Synthetic Rope. High-tensile
strength synthetic lines are considerably lighter than standard wire rope;
however, some lines are dimensionally as strong as standard wire rope.
Accordingly, high-tensile strength synthetic lines are permitted to be used in
appropriate logging applications, including as substitutes for brush straps,
tree straps, tail and intermediate support guylines, guyline extensions,
skyline extensions, and haywire. Manufacturers' standards and recommendations
for determining usable life or criteria for retirement of such lines shall be
followed. Personnel shall examine the lines for broken or abraded strands,
discoloration, inconsistent diameter, glossy or glazed areas caused by
compression and heat, and other inconsistencies. Rope life is affected by load
history, bending, abrasion, and chemical exposure. Most petroleum products do
not affect synthetic ropes. (3-31-22)
05.
Inspection and Care.
(3-31-22)
a. Wire rope shall be inspected
daily by a qualified individual and repaired or taken out of service when there
is evidence of any of the following conditions: (3-31-22)
i. Twelve and five tenths percent (12.5%) of
the wires are broken within a distance of one (1) lay. (3-31-22)
ii. Evidence of chafing, sawing, crushing,
kinking, crystallization, bird-caging, corrosion, heat damage, or other damage
that has weakened the rope structure. (3-31-22)
b. Qualified personnel shall closely inspect
those points subject to the most wear, including the knob ends of lines, eye
splices, and those sections of line that most often run through blocks or
carriages. If there is doubt about the integrity of the line, it is far safer
to replace a suspect line, or cut out and resplice a defective area, than risk
a failure during operation. Evaluation of the load-bearing yarder lines shall
be stringent. A qualified person shall also inspect all other lines used on
site and remove any that are unsafe. (3-31-22)
06.
Additional Precautions. The
following precautions shall also be observed: (3-31-22)
a. Ensure the working load limit for any line
is adequate for the intended use. (3-31-22)
b. The manufacturer's specifications with
regard to assigned breaking strength shall be followed. Such specifications as
determined by engineering test results should factor the grade of the wire,
number of strands, number of wires per strand, filler wire construction, lay
pattern of the wires, and the diameter of the line.
(3-31-22)
07.
Safety Factor. Operators shall follow the manufacturer's
specifications in determining load limits. The working load limit is a fraction
of a line's breaking strength - a factor of three (3), or one-third (1/3) the
breaking strength, is commonly used as a safety factor for running and standing
lines, when workers are not exposed to breaking lines or loads passing
overhead. A safety factor of three (3) is commonly used to determine the
working load limit for a standing or running line. A standard six (6) x
twenty-six (26) IWRC wire rope with a diameter of one (1) inch has a breaking
strength of approximately forty-five (45) tons - divide by three (3) - equals
fifteen (15) tons working load limit. (3-31-22)
08.
Wire Labeling. (3-31-22)
a. The elements of a typical wire rope are
labeled, for example, six (6) x twenty-five (25) FW PRF RL EIPS IWRC. The label
indicates a six (6)-strand rope with twenty-five (25) wires per strand (six (6)
x twenty-five (25)), filler-wire construction (FW), strands pre-formed in a
helical pattern (PRF), laid in a right-hand lay pattern (RL), using an
extra-improved plow steel (EIPS) grade of wire, and strands laid around an
independent wire rope core (IWRC). See figure 013.08-A for proper labeling of
wire rope. (3-31-22)
FIGURE 454.08.a.
Click
here to view image (3-31-22)
b. Out of Service Standard Example. A six (6)
x twenty-five (25) IWRC wire rope = six (6) strands in one (1) lay with
twenty-five (25) wires per strand = one hundred fifty (150) wires. The rope
must be taken out of service when twelve and five tenths percent (12.5%), or
one-eighth (1/8), of the wires are broken within the distance of one (1) lay =
one hundred fifty (150) divided by eight (8) = eighteen and seventy-five one
hundredths (18.75), or nineteen (19) broken wires.
(3-31-22)
09.
Wire
Line Life. Table 454.09 provides the allowable life of a line in million
board feet in accordance with line size and use. Figure 454.09.a. illustrates
both the correct and incorrect manner in which to measure line size (diameter).
(3-31-22)
TABLE 454.09
LINE LIFE BY WOOD
HAULED
|
System
|
Use
|
Line Size
(inches)
|
Line Life (million board
feet)
|
Standing Skyline
|
Skyline
|
1-3/4
|
20-25
|
1-1/2
|
15-25
|
1-3/8
|
8-15
|
Mainline
|
1 to 1-1/8
|
15-20
|
1
|
10-15
|
Haulback
|
3/4 to 7/8
|
8-12
|
Live Skyline
|
Skyline
|
1-1/2
|
10-20
|
1-3/8
|
8-15
|
1
|
6-10
|
Mainline
|
1
|
10-15
|
3/4
|
8-12
|
5/8
|
8
|
Haulback
|
3/4 to 7/8
|
8-12
|
1/2
|
6-10
|
Dropline
|
7/16
|
5-8
|
High Lead
|
Mainline
|
1-3/8
|
8-15
|
1-1/8
|
6-12
|
Source: Willamette Logging Specialist's Reference by Keith L
McGonagill. 1976. Portland, OR: Willamette National Forest. Calculations of
line life refer to EIPS 6x21 wire rope for the skyline, and EIPS 6x26 for other
lines. Figures will be different for other classes of wire rope.
(3-31-22)
FIGURE 454.09.a.
Click
here to view image
(3-31-22)
10.
Dynamic Loads. Operators
shall consider high dynamic loads when calculating safe working limits of wire
ropes. Wire ropes are often subjected to high dynamic loads, which greatly
multiply the force on a line and may exceed the safe working limit. Even a
split second of time over the limit can lead to premature failure of a line.
Typical dynamic loads occur when a turn hits a stump, a turn comes down off of
the back hillside to full suspension, or when excessive force is applied to
pulling a turnout of its bed. A high dynamic load or a sudden shock load that
exceeds the working limit may not result in immediate failure, but rope strands
may stretch and weaken, and may fail at a later time. (3-31-22)
11.
Other Common Wire Rope
Considerations. (3-31-22)
a. Wire Rope
Stretching and Line Diameter. A stretched wire rope has a reduced diameter.
Operators shall check for stretched lines by measuring the diameter,
particularly on older lines and any line used in stressful situations.
(3-31-22)
b. Older Wire Rope.
Standing lines and guylines are often kept in service for multiple years (four
(4) to five (5), and as long as ten (10) years in some instances) without
exhibiting any obvious signs of excessive wear other than rust. Operators shall
check date stamps of wire rope and evaluate line life. Operators shall also
inspect the core of older lines periodically for a fractured or dry core, which
could indicate other deficiencies such as broken wires, excessive wear, or line
deformation. (3-31-22)
c. Hard Use.
The life of a wire rope is also affected by hard use. Line life can be measured
by the volume of wood hauled (see Table 459.09). Line life is reduced when a
line exceeds its elastic limits, is heavily shocked, or rubbed against rocks or
other lines. As a line wears, the safe working load limit shall be lower and
the payload adjusted appropriately. (3-31-22)
d. Wire Rope endurance and elastic limits.
Working within the endurance and elastic limits of lines can help preserve line
life. The following principles shall be observed when evaluating the integrity
and safe use of wire rope: (3-31-22)
i. The
"endurance limit" for all lines is fifty percent (50%) of the breaking
strength. If wire rope tensioning regularly exceeds the endurance limit, the
life of the line is reduced through fatigue. (3-31-22)
ii. The "elastic limit" for all lines is
sixty to sixty-five percent (60-65%) of the breaking strength. When a wire rope
is loaded to its normal safe working limit, the line stretches, but then
returns to its original size when the load is released. If a load increases
past the elastic limit through prolonged exertion or repeated stress, the line
will stretch and stay stretched, resulting in a permanent reduction in the
breaking strength. (3-31-22)
e. Lubrication and Abrasion. Wire rope is
lubricated in the factory to reduce internal friction and corrosion, and
prolong the life of the rope. Heat from friction causes the internal lubricant
to deteriorate. Friction occurs when the rope stretches under load,
particularly in places where it bends around sheaves or other objects. An
improperly lubricated line can pick up particles of dirt and sand that will
increase abrasion. Accordingly, operators shall: (3-31-22)
i. Check for and ensure the proper
lubrication of all lines and wire rope, following the manufacturer's
instructions. Commercial wire rope lubricants are available.
(3-31-22)
ii. Carefully inspect
lines for faults in areas where dust and sand may collect. (3-31-22)
iii. Store all wire rope and lines off the
ground. (3-31-22)
12.
Line Connections. (3-31-22)
a. Inspection. Operators shall regularly
inspect shackles, hooks, splices, and other connecting equipment for damage and
wear, as well as ensure the connectors are the correct type and size for the
line and intended use. (3-31-22)
b.
Wire Splicing. Splices are used to form an eye at the end of a line, extend the
length of a line, or repair a broken or damaged line. The splicing of wire rope
requires special skill and shall only be performed under the supervision of a
competent person with using the proper tools. Reference materials are available
with detailed instructions for numerous types of splices. Individuals splicing
wire shall always wear appropriate eye protection while splicing or assisting
with a splicing procedure. (3-31-22)
c. The logger's eye splice and three
(3)-pressed eye are the most common methods to form an eye for use as a skyline
terminal. See Figure 454.12.c. The spliced eye is approximately eighty percent
(80%) efficient. A three (3)-pressed eye can reach ninety percent (90%) line
strength. The pressed eye is typically performed at the rigging shop. Spliced
eyes may be placed in the field, but may require additional time to install.
(3-31-22)
FIGURE 454.12.c.
Click
here to view image
(3-31-22)
d. When Flemish (Farmers, Rolled) eye splices are used
on load-bearing lines, the strand ends must be secured by: (3-31-22)
i. Hand tucking each strand three (3) times;
or (3-31-22)
ii. Applying a
compression (pressed-eye) fitting. (3-31-22)
e. Guyline Care. Guylines are a vital link in
holding up a tower. Guyline extensions shall not be excessively moved around by
dragging on the ground, or left on the ground for long periods of time as they
will deteriorate faster. (3-31-22)
f. Guyline extensions must be connected by:
(3-31-22)
i. A bell shackle using a safety pin
to connect spliced eyes or pressed eyes; or (3-31-22)
ii. Poured nubbins (buttons) and a
double-ended hook. (3-31-22)
g. Line Deformity. A line may deform where it
loops around a shackle or pin, producing weakness that may result in line
failure. A thimble in the loop protects the line. Thimbles may be used on
standing lines, but not on running lines. Examples of the appearance of
deformed lines and the use of thimbles in shackles are illustrated in Figure
454.12.g. (3-31-22)
FIGURE 454.12.g.
Click
here to view image
(3-31-22)
13.
Shackles and Hooks.
(3-31-22)
a. Hooks. Hooks shall be inspected
to ensure that they have not sprung open. Ensure that shackles are positioned
correctly to bear the load. Haywire swivels shall be inspected frequently, due
to their susceptibility to wear rapidly. (3-31-22)
b. Shackle Safety. Proper bells or shackles
shall be used to connect the guylines to the stumps, and the guyline lead
blocks to the ring at the top of the tower. Connections shall have at least one
and a half (1-1/2) times the strength of the guyline. The pins of the shackles
must be secured to protect against dislodgement, and a nut and cotter key, or a
nut and molly may be used for that purpose. The use of loops or mollies to
attach guylines is prohibited. Examples of the appearance of some shackle
equipment is illustrated in Figure 454.13.b.
FIGURE 454.13.b.
Click
here to view image
(3-31-22)
c. The following practices shall be observed
in order to ensure the safe use of shackles: (3-31-22)
i. A shackle must have a rated breaking
strength greater than the rated breaking strength of the lines attached to it,
and the manufacturer's rated strengths to determine oversized requirements
shall be used. Accepted industry standards shall be utilized and adhered to
when determining the correct shackle size based on the type and nature of the
logging operation being performed. Examples of the appearance of some shackle
equipment for the purposes of proper selection is illustrated in Figure
454.13.c.i (3-31-22)
ii. Shackles
with pins, and securing nuts with mollies or a cotter key shall be used on
standing or overhead rigging. (3-31-22)
iii. Screw shackle pins shall not be used in
any standing or overhead rigging. (3-31-22)
iv. Screw shackle pins, where allowed to be
used, shall be tightened securely. (3-31-22)
v. Shackle pin mollies shall be rolled
sufficiently and fit the pin hole fully. Mollies shall be tucked a minimum of
three (3) times. (3-31-22)
vi. The
shackle shall always be placed with the pin nearest to the yarder, so that in
the event the shackle fails the least amount of hardware may be thrown at the
yarder. (3-31-22)
vii. Replace
shackles that are bent, broken, or show excess wear on the inner surfaces.
Examples of the appearance of some damaged or non-conforming shackles are
illustrated in Figure 454.13.c.vii. (3-31-22)
FIGURE 454.13.c.vii.
Click
here to view image
viii. Sleeve shackles or choker bells must be
used when choked lines are permitted. (3-31-22)
FIGURE 454.13.c.i.
Click
here to view image
(3-31-22)
14.
Knobs, Ferrules, and Eyes.
(3-31-22)
a. Poured nubbins and a double-end
hook are acceptable connectors in place of shackles in some instances. The use
of quick nubbins (wedge buttons) as guylines and skyline end fittings is
prohibited unless attaching guy lines to guy line drums. Operators shall follow
the manufacturer's recommendations when attaching sockets and similar end
fastenings. (3-31-22)
b. Poured
nubbins achieve ninety-nine percent (99%) of line strength and may be used.
Quick nubbins only achieve a maximum of sixty-five percent (65%) under ideal
conditions, and accordingly operators shall consider whether they are
appropriate for safe use in any given application. Pressed ferrule are not
certifiable for strength, and shall not be used. Examples of the appearance of
some knob, ferrule, and nubbin equipment are illustrated in Figure 454.14.
(3-31-22)
c. Operators shall
inspect knobs, ferrules, and eyes at cable ends for loose or broken wires, and
corroded, damaged, or improperly applied end connections. Poured nubbins shall
be date stamped.
FIGURE 454.14
Click
here to view image
(3-31-22)
15.
Brush Blocks. Brush blocks
shall be thoroughly inspected for cracks, wear, or deterioration.
Operators shall closely examine the areas subject to the most
wear, including bearings, sheave, frame, yoke, and pins. Defective parts shall
be replaced immediately. Blocks shall be greased every time before each
use.
FIGURE 454.15
Click
here to view image
(3-31-22)
16.
Chains and Straps. Chains or
straps shall always be sized and used correctly for the intended purpose.
Determining which size to use may depend on various factors. Oversized trailer
lift straps, for example, shall have a breaking strength equal to five (5)
times the load to be lifted. Towing chains shall have a tensile strength
equivalent to the gross weight of the towed vehicle. The manufacturer's
specifications or other appropriate reference materials shall always be
consulted to ensure the right chain or strap is used for a task. (3-31-22)
a. Operators shall periodically inspect
chains for damaged, worn, or stretched links. Chains with more than ten percent
(10%) wear at the bearing surface shall be replaced. Operators shall
periodically inspect straps, and examine them for broken wires or wear.
Examples of the appearance of damaged and safe chains are illustrated in Figure
454.16.a.
FIGURE 454.16.a.
Click
here to view image
Click
here to view image
(3-31-22)