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Back Chapter 1 Construction Support | Up Construction Electrician Basic - Electricity handbook for electricians | Next Synthetic-Fiber Lines |
the loop at the end of the line, as shown in the figure.
Wind the standing part around the line covering the loop
of the whipping. Leave a small loop uncovered, as
shown. Pass the remainder of the standing end up
through the small loop and pull the dead end of the
twine, thus pulling the small loop and the standing end
back towards the end of the line underneath the
whipping. Pull the dead end of the twine until the loop
with the standing end reaches a point midway
underneath the whipping. Trim both ends of the twine
close up against the loops of the whipping. Before
cutting a line, place two whippings on the line 1 or 2
inches apart and make the cut between the whippings.
This will prevent the ends from unraveling after they are
cut.
Stowing Line
Before stowing a fiber line, you must take certain
precautions to safeguard the line against deterioration.
You should never stow a wet line. Always dry the line
well before placing it in stowage.
After a line has been used, you should coil it down
in a clockwise direction (assuming it is a right-hand
lay). Should the line be kinked from excessive turns,
remove the kinks by the procedure known as "thorough
footing."
You do this by coiling the line down
counterclockwise and then pulling the bottom end of the
coil up and out the middle of the coil. If the line is free of
kinks as it leaves the coil, make it up in the correct
manner. If it is still kinked, repeat the process before
making up the line for stowage.
Choose your stowage space for line carefully. Line
deteriorates rapidly if exposed to prolonged dampness.
Furthermore, it is important for the stowage area to be
dry, unheated, and well ventilated. To permit proper air
circulation, you should either place the line in loose
coils on a wood grating platform about 6 inches (15 cm)
above the floor or hang the line in loose coils on a
wooden peg.
You should NEVER expose a line to lime, acids, or
other chemicals, or even stow it in a room containing
chemicals. Even the vapors may severely damage line.
As a final precaution, avoid continually exposing line to
sunlight. Excessive sunlight will also damage the line.
Strength of Fiber Line
Overloading a line poses a serious threat to the
safety of personnel, not to mention the heavy losses
likely to result through damage to material. To avoid
overloading, you must know the strength of the line you
are working with. This involves three factors: breaking
strength, safe working load, and safety factor.
BREAKING STRENGTH.Refers to the
tension at which the line will part when a load is applied.
Line manufacturers have determined breaking strength
through tests and have set up tables to provide this
information
SAFE WORKING LOADBriefly defined, the
"safe working load" (SWL) of a line is the load that can
be applied without causing any kind of damage to the
line. Note that the safe working load is considerably
less than the breaking strength. A wide margin of
difference between breaking strength and safe working
load is necessary to allow for such factors as additional
strain imposed on the line by jerky movements in
hoisting or bending over sheaves in a pulley block.
SAFETY FACTOR. safety factor of a line is
the ratio between the breaking strength and the safe
working load. Usually, a safety factor of 4 is acceptable,
but this is not always the case. In other words, the safety
factor will vary, depending on such things as the
condition of the line and circumstances under which it is
to be used. While the safety factor should NEVER be
less than 3, it often should be well above 4 (possibly as
high as 8 or 10). For best, average, or unfavorable
conditions, the safety factor indicated below may often
be suitable.
BEST conditions (new line): 4
AVERAGE conditions (line used but in good
condition): 6
UNFAVORABLE conditions (frequently used line,
such as running rigging): 8
Table 1-1 lists some of the properties of manila and
sisal line, including strength. The table shows that the
minimum breaking strength is considerably greater than
the safe working capacity. The difference is caused by
the application of a safety factor. The safe working load
(SWL) of line is obtained by dividing the breaking
strength (BS) by a factor of safety (FS). A new 1-inch-
diameter No. 1 manila line has a breaking strength of
9,000 pounds, as indicated in table l-l. To determine
the safe working load of the line, you would divide its
breaking strength by a minimum standard safety factor
1-2
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