Wires are the basic building blocks of wire rope.
They lay around a "center" in a specified
pattern in one or more layers to form a strand.
The strands lay around a core to form a wire rope.
The strands provide all the tensile strength of a
fiber core rope and over 90% of the strength of a
wire rope with an independent wire rope core.
Characteristics like fatigue resistance and resistance
to abrasion are directly affected by the design of
strands. In most strands with two or more layers
of wires, inner layers support outer layers in such
a manner that all wires may slide and adjust freely
when the rope bends. As a general rule, a rope
that has strands made up of a few large wires will
be more abrasion resistant and less fatigue resistant
than a rope of the same size made up of strands with
many smaller wires.
Some basic strand constructions:
The most common example of the single layer
construction is a 7-wire strand. It has
a single-wire center with six wires of the same
diameter around it.
This construction has two layers of wires around
a center wire with the same number of wires
in each layer. All wires in each layer
are the same diameter. The strand is designed so
that the large outer wires rest in the valleys
between the small inner wires.
This construction has two layers of uniform-size
wire around a center wire with the inner layer
having half the number of wires as the outer
layer. Small filler wires, equal in number
to the inner layer, are laid in the valleys
of the inner layer.
This construction has two layers with one diameter
of wire in the inner layer, and two diameters
of wire alternating large and small in the outer
layer. The larger outer-layer wires rest
in the valleys, and the smaller ones on the
crowns, of the inner layer.
When a strand is formed in a single operation
using two or more of the above constructions,
it is referred to as a "combined pattern."