Figure 6-36.Lays of wire rope.
Characteristics of Wire Rope
The main types of wire rope used consist of 6, 7,
12, 19, 24, or 37 wires per strand. Usually, the wire
rope has six strands laid around the core.
The two most common types of wire rope, 6 x 19
and 6 x 37, are shown in figure 6-37. The 6 x 19 type
(having six strands with 19 wires in each strand) are
the stiffest and strongest construction of the types of
wire rope suitable for general hoisting operations.
The 6 x 37 wire rope (six strands with 37 wires in each
strand) are very flexible, making it suitable for cranes
and similar equipment.
Several factors must be considered whenever a
wire rope is selected for use in a particular kind of
operation. The manufacture of wire rope which can
withstand equally well all kinds of wear and stress, it
Figure 6-37.A. 6 x 19 wire rope; B. 6 x 37 wire rope.
may be subjected to, is not possible. Because of this,
selecting a rope is often a matter of compromise
sacrificing one quality to have some other more
urgently needed characteristic.
TENSILE STRENGTH.Tensile strength is the
strength necessary to withstand a certain maximum
load applied to the rope. It includes a reserve of
strength measured in a so-called factor of safety.
CRUSHING STRENGTH.Crushing strength
is the strength necessary to resist the compressive and
squeezing forces that distort the cross section of a wire
rope, as it runs over sheaves, rollers, and hoist drums
when under a heavy load. Regular lay rope distorts less
in these situations than lang lay.
FATIGUE RESISTANCE.Fatigue resistance
is the ability to withstand the constant bending and
flexing of wire rope that runs continuously on sheaves
and hoist drums. Fatigue resistance is important when
wire rope must run at high speeds. Such constant and
rapid bending of the rope can break individual wires in
the strands. Lang lay ropes are best for service
requiring high fatigue resistance. Ropes with similar
wires around the outside of their strands also have a
greater resistance, since these strands are more
A B R A S I O N R E S I S T A N C E .Abrasion
resistance is the ability to withstand the gradual
wearing away of the outer metal, as the rope runs
across sheaves and hoist drums. The rate of abrasion
depends mainly on the load carried by the rope and its
running speed. Generally, abrasion resistance in a rope
depends on the type of metal of which the rope is made
and the size of the individual outer wires. Wire rope
made of harder steels, such as improved plow steel, has
a considerable resistance to abrasion. Ropes that have
larger wires forming the outside of their strands are
more resistant to wear than rope having smaller wires
which wear away more quickly.
resistance is the ability to withstand the dissolution of
the wire metal that results from chemical attack by
moisture in the atmosphere or elsewhere in the
working environment. Ropes that are put to static
work, such as guy wires, may be protected from
corrosive elements by paints or other special dressings.
Wire rope may be galvanized for corrosion protection.
Most wire rope used in crane operations must rely on
their lubricating dressing to double as a corrosion