Use Wire Rope Safely

Wire rope is widely used instead of fiber rope because :

It has greater strength for the same diameter and weight.

Its strength is constant whether wet or dry.

its length remains the same under varying whether condition.

it has greater durability.

Compacted Wire Rope

Compacted strand wire rope is manufactured from strands which have been reduced in diameter by one of several swaging processes. The outer wires of the strand are flattened and the internal wires are no longer round. Compared to standard wire rope of the same diameter, a compacted rope has a greater cross-sectional metallic area resulting in higher strength and its smoother surface makes it more abrasion resistant.

Low-Rotation Wire Rope

A certain amount of rope spin is natural during the operation of most cranes.  This should be kept to a minimum as excessive rotation can cause serious fatigue.  On single-fall cranes, the damaging effect of spin can be reduced by installing a free-moving ball bearing swivel between the rope and the load.  In cases where spin is particularly troublesome it is often advisable to change to a low-rotating construction.

A low-rotation or an anti-twist wire rope consists of an inner layer of strand laid in one direction covered by a layer of strand laid in the opposite direction.  This has the effect of counteracting torque by reducing the tendency of the finished rope to rotate. 

Strand Construction of Wire Rope

The strand construction refers to the pattern in which the wires are placed within the strands.

Take for example this 6x19 FC wire.

The actual construction is 6x19 Filler (12/6+6F/1) fibre core. That is 6 strands each made up of 19 wires.  Each wire made up of 12 outer wires over 6 inner wires plus 6 filler wires over 1 centre wire.  The word filler relates to the strand pattern of which there are three.

Filler, Seale and Warrington.

Filler – characterised by the small spacer wires which lie in the interstices of the inner layer to help position and support the outer layer.

Seale – characterised by having equally sized wires in the outer layer with the same number of uniform but smaller sized wires in the inner layer.

Warrington – characterised by having one of its wire layers (usually the outer) made up of an arrangement of alternately large and small wires.

In 6x36 construction, because of the greater number of wires, combinations of the three strand patterns are used.  Wire sizes would become too large if only one of the three fundamental patterns were used.  For example, Warrington Seale is a blend of the Seale and Warrington patterns.  The outer layer has equally sized wires whilst the layer underneath has wires of alternately large and small diameter.

Wire And Strands

Wire ropes are made up by laying wire strands around a core.  The strands themselves are made up of between 3 - 91 wires.  The more wires per strand the more flexible the rope will be.

6x36 FC = 6 strands each made up of 36 wires. 

Strands laid around a Fibre Core.

  

6x19 IWRC = 6 strands each made up of 19 wires. 

Strands laid around a Steel Core. 

 

 

Rope Core

         The purpose of the core is to provide support and maintain the position of the outer strands during operation.  The core provides an elastic bed to enable movement or relative displacement and allow deformation of the wire strands when the rope is flexed round a sheave.  A core of incorrect size or inferior material will cause a rope not to function properly and will shorten its life.

There are two main types of rope core – Fibre (FC) and Steel (IWRC or WSC)

FC                   Fibre core around which wire strands are laid.

FC ropes provide excellent flexibility.  Additionally, the fibre core is impregnated with lubricant during manufacture thus providing internal lubrication to reduce internal corrosion and wear between wires.

IWRC             Independent wire rope core around which wire strands are laid.  IWRC ropes have increased strength and provide good resistance to crushing, distortion and heat. The steel core also provides better support for the outer strands thus ensuring even stress distribution and retention of the rope shape.

WSC               Wire strand core around which wire strands are laid. 

Used in ropes below 13mm dia. 

Has the same benefits as IWRC.

Definition of Wire rope

          Wire rope is a type of rope which consists of several strands of metal wire laid (or 'twisted') into a helix. Initially wrought iron were used, but today steel is the main material used for wire ropes. Historically wire rope evolved from steel chains which had a record of mechanical failure.  While flaws in chain links or solid steel bars can lead to catastrophic failure, flaws in the wires making up a steel cable are less critical as the other wires easily take up the load. 

        Friction between the individual wires and strands, as a consequence of their twist, further compensates for any flaws. This method of minimising the effect of flaws may also be seen in Damascus steel, employing multiple folding or laminations.