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7

01 - WIRE ROPE & STRAND

Wire Rope & Strand Characteristics

Size

Ropes are referred to by a diameter. The correct way to

measure wire rope is shown below.

Construction

The main components of wire rope are shown below.

In the example above, each individual wire is arranged around

a central wire to form a 7-wire strand. Six of these strands are

formed around a central core to make a wire rope. The rope is

specified at 6 x 7 (6/1) i.e., six strands of seven wires.

The actual range of wire rope Constructions is wide and varied

but the number could be limited to approximately twenty-five.

The size and number of wires in each strand, as well

as the size and number of strands in the rope greatly affect

the characteristics of the rope. In general, a large number of

small-size wires and strands produce a flexible rope with good

resistance to bending fatigue. The rope Construction is also

important for tensile load (static, live or shock) abrasive

wear, crushing, corrosion and rotation.

Cores

A number of core types is available and each gives

specified properties to the rope:

1.

Wire Strand Core (WSC) - Strand usually of the

same Construction as the outer strands.

2.

Fibre Core (FC) - Sisal or polypropylene.

3.

Wire Rope Core (WRC) - a wire rope usually of

6 x 7 (6/1)/1 x 7 (6/a) Construction.

Wire Strand Core (WSC)

These cores are chiefly for standing ropes (guys or rigging),

and offer high tensile strength and, owing to the larger wires in

the core, greater resistance to corrosion.

Fibre Core (FC)

A fibre core, generally sisal, provides a resilient foundation

for the strands in the rope structure. Fibre cores are used for

ropes that are not subjected to heavy loads and where flexibility

in handling is required. Fibre Cores are inadequate where wire

rope is subjected to heavy loading, prolonged outdoor exposure

and crushing on small drums and sheaves.

Wire Rope Core (WRC)

Wire rope core is preferred for operating ropes in applications

of high tensile stress, high compression loads on small drums

and sheaves (such as on earthmoving equipment) and high

operating temperatures (such as cranes handling large

quantities of molten metal). A rope with WRC is approximately

11% heavier and 7.5% stronger than fibre cored rope of the

same size.

Lay

This refers to the way the wires in the strands, and the

strands in the rope are formed into the completed rope.

The wire strands are essentially laid up in a planetary

motion with controlled twist being imparted to produce

a tightly formed rope.

The term Lay is used in three ways:

1.

To describe the direction in which the strands are laid in

the rope right or left.

In a Right Hand Lay strands are laid around the rope core

in a clockwise direction - see illustration. In a Left Hand Lay,

the strands are laid anti-clockwise - see illustrations. Steel

Wire Ropes are conventionally produced Right Hand Lay

unless special circumstances require Left Hand Lay.

2.

To describe the direction in which the wires are stranded in

relation to the direction of the strands in the completed rope,

e.g. Ordinary Lay or Lang’s Lay.

Ordinary Lay means the wires in a strand are laid in a

direction opposite to the direction in which the strands are

laid in the final rope.

Lang’s Lay means the wires in a strand are laid in the same

direction in which the strands are laid in the final rope.

Lang’s Lay ropes have superior properties in resistance to

wear, abrasion, fatigue and scuffing. This is illustrated below,

where it can be seen that wear on an outer wire is distributed

over a far greater area than in Ordinary Lay.

3.

‘Lay’ is also a measure of the ‘pitch’ of a strand in a rope.