How Ropes are made
Background
A rope is a bundle of flexible fibers twisted or braided together to
increase its overall length and tensile strength. The use of ropes for
hunting, carrying, lifting, and climbing dates back to prehistoric
times. Ropes were originally made by hand using natural fibers. Modern
ropes are made by machines and utilize many newer synthetic materials to
give them improved strength, lighter weight, and better resistance to
rotting. More than half of the rope manufactured today is used in the
fishing and maritime industries.
Although the origin of rope is unknown, the Egyptians were the first
people to develop special tools to make rope. Egyptian rope dates back
to 4000 to 3500 B.C. and was generally made of water reed
fibers. Other Egyptian rope was made from the fibers of date palms,
flax, grass, papyrus, leather, or camel hair. The use of such ropes
pulled by thousands of slaves allowed the Egyptians to move the heavy
stones required to build the pyramids. By about 2800 B.C.,
rope made of hemp fibers was in use in China. Rope and the craft of rope
making spread throughout Asia, India, and Europe over the next several
thousand years. By the fourth century, rope making in India had become
so specialized that some makers produced rope intended only for use with
elephants. Leonardo da Vinci (1452-1519) drew sketches of a concept for
a rope making machine, and by the late 1700s several working machines
had been built and patented. Rope continued to be made from natural
fibers until the 1950s when synthetic materials such as nylon became
popular. Despite the changes in materials and technology, rope making
today remains little changed since the time of the ancient Egyptians.
Rope is sometimes generally referred to as cordage and can be divided
into four categories based on its diameter. Cordage under 0.1875 inches
(0.5 cm) in diameter includes twine, clothesline, sash cord, and a
tar-covered hemp line called marline. These are not considered to be
true rope. Cordage with a diameter of 0.1875 to 0.5 inches (0.5-1.3 cm)
is a light-duty rope and is some-times referred to as "small
stuff." Cordage with a diameter of 0.5 to about 1.5 inches (1.3-3.8
cm) is considered to be true rope. Cordage over about 1.5 inches (3.8
cm) in diameter is generally called a hawser and is used for mooring
large ships.
Rope construction involves twisting fibers together to form yarn. For
twisted rope, the yarn is then twisted into strands, and the strands
twisted into rope. Three-strand twisted rope is the most common
construction. For braided rope, the yarn is braided rather than being
twisted into strands. Double-braided rope has a braided core with a
braided cover. Plaited rope is made by braiding twisted strands. Other
rope construction includes combinations of these three techniques such
as a three-strand twisted core with a braided cover. The concept of
forming fibers or filaments into yarn and yarn into strands or braids is
fundamental to the rope-making process.
Raw Materials
Rope may be made either from natural fibers, which have been processed
to allow them to be easily formed into yarn, or from synthetic
materials, which have been spun into fibers or extruded into long
filaments.
Natural fibers include hemp, sisal, cotton, flax, and jute.
Another natural material is called manila hemp, but it is
actually the fibers from a banana plant. Sisal was used extensively to
make twine, but synthetic materials are replacing it. Manila rope is
still used by traditionalists, but it can rot from the inside, thus
losing its strength without giving any outward indication.
Synthetic fibers include nylon, polyester, polypropylene and aramid.
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Polypropylene costs the least, floats on water, and does not stretch
appreciably. For these reasons it makes a good water ski tow rope.
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Nylon is moderately expensive, fairly strong, and has quite a bit of
stretch. It makes a good mooring and docking line for boats because of
its ability to give slightly, yet hold.
- Polyester is more and more used in
ropes - good price/performance ratio.
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Aramid is the strongest, but is also very expensive.
Nylon and polyester may be spun into fibers about 4-10 inches (10-25 cm)
long. Ropes made from spun synthetic fibers feel fuzzy and are not as
strong as ropes made from long, continuous filaments. Some ropes use two
different synthetic materials to achieve a combination of high strength
and low cost or high strength and smooth surface finish.
Wire rope may be made from iron or steel wires. This is commonly
referred to as cable and is used in bridges, elevators, and
cranes. It is made by a different process than fiber or filament ropes.
The Manufacturing Process
Fibers and filaments are first formed into yarn. The yarn is then
twisted, braided, or plaited according to the type of rope being made.
The diameter of the rope is determined by the diameter of the yarn, the
number of yarns per strand, and the number of
strands or braids in the finished rope.
Processing the fibers and filaments
Forming twisted rope
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The bobbins of yarn are set on a frame known as a creel. For
three-strand, right-hand twist rope, Z-twist yarns would be used to make
each strand. The ends of the yarns are fed through a hole in a register
plate which keeps the yarns in the proper relation to each other. The
ends of the yarns are then fed into a compression tube. As the yarn is
pulled through the compression tube, the tube twists it in the S-twist
direction, opposite of the yarn twist, to produce a tight strand.
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The strands are either transferred to strand bobbins or fed directly
into the closing machine. For common three-strand rope, three S-twist
strands would be used. The closing machine holds the strands firmly with
a tube-like clamp called a laying top. The end of each strand is then
passed through a rotating die which twists the strands in the Z-twist
direction, locking them together. This process is called closing the
rope.
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The finished rope is wound onto a reel. When the end of the strands has
been reached, the finished coil of rope is removed from the reel and
tied together with bands of smaller rope. The ends are either taped or,
if the rope is a synthetic material, melted with heat to prevent them
from unraveling.
Forming braided rope
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Braided ropes are commonly made from synthetic materials. The bobbins of
yarn are set up on several moving pendants on a braiding machine. Each
pendant travels in an oscillating pattern, weaving the yarn into a tight
braid. A set of rollers pulls the braid through a guide to lock, or set,
the braid and keep tension on the rope. In some machines the braiding
process is accomplished by feeding the yarns through separate
counter-rotating register plates. One yarn is woven in one direction
followed by another in the opposite direction, and so on, to form an
interlocked braid.
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If a double-braided rope is being formed, the first braid becomes the
core, and the second braid is immediately woven on top of it to form the
outer covering, called the coat.
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As the rope emerges from the rollers, it is taken up on a reel. The
finished coil is then removed and banded, and the ends are taped or
melted.
Forming plated rope
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Eight-plaited rope consists of four S-twist strands and four Z-twist
strands. The strands are paired together with one S-twist and one
Z-twist in each pair. These pairs are then held together and braided
with the other pairs. The manufacturing process first follows the
twisted rope process to make the strands, then the braided rope process
to form the final rope.
Quality Control
The level of quality control depends on the intended use of the rope.
Ropes intended for general purpose use are sold by diameter and tensile
strength. Tensile strength is determined by breaking a sample piece
under load. Basic raw material specification and a visual inspection are
the only quality control measures used for these ropes. Ropes intended
for high-risk applications—such as rappelling, rescue work, and
lifting objects over people—are more closely inspected and tested.
These ropes have a finite service life and may also have a color code or
other coding to indicate the date of manufacture. Some ropes incorporate
some type of wear tracer formed into the rope. These tracers are usually
a single yarn of contrasting color placed just under the outer wrap of
yarn. Should any abrasion or overextension of the rope occur, this
filament would be exposed, indicating an unsafe condition and requiring
that the rope be replaced.
The Future
The future of rope making is directly linked to improvements in
materials. Over the years, almost every conceivable type of rope
configuration has been attempted. In the past, new materials have
allowed rope makers to reduce the diameter of the rope while maintaining
the tensile strength and improving the resistance to weathering and
abrasion. It is expected that a new generation of very strong, very
light fibers and forming techniques will produce even further
improvements in ropes.
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