of larger wires is more resistant to external abrasion but
is less flexible.
The CORE, the element around which the strands
are laid to form the wire rope, may be of hard fiber, such
as manila, hemp, plastic, paper, or sisal. Also, a wire-
strand core may be used. Each type of core serves the
same basic purposeto support the strands laid around
A FIBER CORE offers the advantage of increased
flexibility. Also, it serves as a cushion to reduce the
effects of sudden strain and acts as a reservoir for the oil
to lubricate the wires and strands to reduce friction
between them. Wire rope with a fiber core is used in
places where flexibility of the wire rope is important.
A WIRE-STRAND CORE not only resists heat
better than a fiber core but it also adds about 15 percent
to the strength of the wire rope. On the other hand, the
wire strand makes the wire rope less flexible than a fiber
An INDEPENDENT WIRE-ROPE CORE is a
separate wire rope over which the main strands of the
wire rope are laid. It usually consists of six seven-wire
strands laid around either a fiber core or a wire-strand
core. This core strengthens the wire rope more,
provides support against crushing, and supplies
maximum resistance to heat.
Wire rope may be made by either of two methods.
If the strands or wires are shaped to conform to the
curvature of the finished wire rope before laying up, the
wire rope is termed preformed. If they are not shaped
before fabrication, the wire rope is termed
nonpreformed. When cut, preformed wire rope tends
not to unlay, and it is more flexible than nonpreformed
With nonpreformed wire rope, twisting
produces a stress in the wires; and, when it is cut or
broken, the stress causes the strands to unlay. In
nonpreformed wire rope, unlaying is rapid and almost
instantaneous, which could cause serious injury to
someone not familiar with it.
The main types of wire rope used by the Navy have
6, 7, 12, 19, 24, or 37 wires in each strand. Usually, the
wire rope has six strands laid around a fiber or steel
Two common types of wire rope, 6 by 19 and 6 by
37 wire rope, are shown in figure 1-4. The 6 by 19 type
of wire rope, having six strands with 19 wires in each
strand, is commonly used for rough hoisting and
skidding work where abrasion is likely to occur. The 6
by 37 wire rope, having six strands with 37 wires in each
strand, is the most flexible of the standard six-strand
wire ropes. For that reason, it is particularly suitable
when you are going to use small sheaves and drums,
such as are used on cranes and similar machinery.
Grades of Wire Rope
Wire rope is made in a number of different grades,
three of which are mild-plow steel, plow steel, and
MILD-PLOW STEEL wire rope is tough and
pliable. It can stand up under repeated strain and stress,
and it has a tensile strength of 200,000 to 220,000
pounds per square inch (psi).
PLOW STEEL wire rope is unusually tough and
strong. This steel has a tensile strength (resistance to
lengthwise stress) of 220,000 to 240,000 psi. This wire
rope is suitable for hauling, hoisting, and logging.
IMPROVED-PLOW STEEL wire rope is one of the
best grades of wire rope available, and most, if not all, of
the wire rope you will use in your work will probably be
made of this material. It is stronger, tougher, and more
resistant to wear than either plow steel or mild-plow
steel. Each square inch of improved-plow steel can
stand a strain of 240,000 to 260,000 psi.
Measuring Wire Rope
The size of wire rope is designated by its diameter.
The true diameter of a wire rope is considered as being
the diameter of the circle that will just enclose all of its
strands. Both the correct and incorrect methods of
measuring wire rope are shown in figure 1-5. Note, in
particular, that the CORRECT WAY is to measure from
the top of one strand to the top of the strand directly
opposite it. Use calipers to take the measurement; if
calipers are not available, an adjustable wrench will do.
To ensure an accurate measurement of the diameter
of a wire rope, always measure the wire rope at three
Figure 1-4.Two types of wire rope.