Welcome to Bharat Wire

We discuss the structure of wire rope as follows.

1)	Diameter
2)	Core
3)	Wire rope Lay
4)	Strand construction
5)	Wire Rope Construction
6)	Wire rope properties
7)	Care & Maintenance
8)	Engineering Details

DIAMETER :

DIAMETER of a wire rope is the diameter of the circle which would completely enclose it. Care should be taken to see that the correct method of measurement is used.

Nominal Diameter inches	Undersize inches	Oversizr inches
0 to 3/4	0	1/32
13/6 to 1 1/8	0	3/64
1-3/16 to 1 1/2	0	1/16
1-9/16 to 2 1/4	0	3/32

TOLERANCE – Wire Ropes are usually made slightly larger than nominal diameter to allow for reduction in size which takes place due to the compacting of the structure under load.

Core :

There are two general types of wire rope, one is made of fibre and the another of wire. Cores made from wire are usually a small wire rope of sutable size to serve as a core, this is called an independent wire rope core, usually referred to as IWRC. The other type of wire core is a wire strand structure, it is called a strand core and usually abbreviated to S.S.

Fibre cores are mainly manufactured from a natural fibre, either manila or sisal. Present day condition of operation subject a wire rope to severe pressures, and as fibre core ropes will not withstand these condition their use is restricted to conditions where the loading is light, e.g. chair lifts. Some fibre cores are manufactured from polypropolene or Nylon but the use of synthetic fibre cores until recently has been confined to a few types of service where they are able to stand up to chemical agents which would attack a natural fibre.

FUNCTION OF THE CORE:

The core is the foundation of wore rope and its primary function is to support the wire strands of which the rope is composed, keeping them in their correct relative position during the operating the life of rope. As the wire is loaded – the strand imbed themselves more firmly into the core, the resulting axial movement increases the interstrand pressure existing at the place where the strand contact each other. It is necessary that the core be hard enough to restrict the magnitude of the interstrand pressure. In most wire rope applications the rope is in motion over sheaves and winding drums. These contacts apply lateral pressure to the rope causing flattening and increase of interstrand pressure. This calls for additional support from the core above that needed o restrict the interstrand pressure due to rope tension only. Heavily loaded ropes operating over small drums are subjected to extremely heavy interstrand pressure. The severity of the operating conditions are increasing because of the need for handling heavier loads with smaller, more compact equipment, therefore, there is an increasing need for cores which can supply a more substantial support.

INDEPENDENT WIRE ROPE CENTRE:

In most instances an independent wire rope center is the answer to the problem of interstrand pressure. This core is a small wire rope itself and acts as a support for the strands of the wire rope. This combination of a wire rope within a wire rope has greatly improved the ability of wire rope to operate with success under conditions where a fibre rope would fail. An other advantage of independent wire rope centers is that of reduced stretch. There are two types of stretch affecting wire rope, elastic and constructional. Constructional stretch usually occurs during the early part of the ropes life and results in permanent elongation. Elastic stretch is proportionate to the load imposed. When an IWRC rope is used elastic stretch is about 30% less and constructional stretch is about 50% less than when a fibre core rope is used.

Other advantages are:

1. Reduced tendency for the rope to rotate.

2. Longer rope life when operating at high temperatures.

3. 7 1/2 % strength increases over that of high temperatures.

The ability of an independent wire rope center to support the strands of a rope often makes the difference between satisfactory and unsatisfactory rope service.

FIRE CORE:

There are two main types of fibre core, one being synthetic the other natural. Sisal is the most commonly used natural fibre but polypropylene and other synthetic are becoming more widely used each year.

Wrights Canadian Ropes sisal core is treated with a copper napthanate solution which has a rot proofing affects on the fibre and thus extends its life. This is found to be beneficial where ropes are used under corrosive conditions such as in sea water and damp mine shafts. The synthetic cores, polypropylene and Nylon have proven satisfactory in many applications, especially where ropes are subjected to extremely corrosive atmospheres, such as is found in oil wells where hydrogen sulphide is present.

Both synthetic and natural fibres contribute approximately the same strength to a wire rope.

WIRE ROPE LAY NOMENCLATURE:

ORDINARY LAY OR REGULAR LAY:

A standard wire rope is a right hand regular lay rope composed of six strand laid around a core. This is the rope that is usually furnished unless otherwise specified or indicated by the intended service. In this rope the indiviaual wires of the strand have been laid in a left hand direction and the strand themselves have been laid in a right hand direction around the core of the rope. This rope is easily identified because the indiviaual wires as they appear on the surface of the rope are parallel with the axis of the rope and the strands appear as a right hand thread.

If the individual wires of the component strands have been laid in a right hand direction and the strands have been laid in a left hand direction around the core of the rope it would be called a left hand regular lay wire rope. Here again the individual wires appearing on the surface of the rope are parallel with the axis of the rope but the strands appear as a left hand thread.

Left lay ropes are used where drum and anchorages are such that right lay ropes wound under load would tend to roll away from adjacent laps, resulting in uneven winding. They are also used to counter the rotation of a right hand lay rope when two ropes are used as a pair.

LANG LAY:

Right hand lang lay wire rope is one in which the individual wires of the strand have been laid in a right hand direction and the strands themselves have been laid in a right hand direction around the core of the rope. The individual wires as they appear on the surface of the rope make an angle with the axis in the same general direction as the strands themselves appearing as a right hand thread. Lang lay rope composed of six strands around a core has many uses, particularly in construction and mining applications, it is more flexible and has greater abrasion resistance due to greater length of wire exposed to wear than ordinary lay rope of the same strength, grade and construction.

Left lay lang lay rope can be manufactured but has very limited application and is rarely used.

ALTERNATE LAY:

A six strand wire rope in which three strands are ordinary lay and three strands are lang lay is known as alternate lay wire rope and combines some the desirable properties of both the regular lay and the lang lay type of rope.

LENGTH OF LAY:

Each strands in a wire rope is helical in shape. The distance measured parallel to the axis or the centre line of a rope in which the strand makes one complete spiral around the rope is the length of rope lay.

The length of the helix of the individual wires in the strands may also vary. This length is measured in the same manner as rope lay and is referred to as strand lay.

PERFORMING :

Performing is the process in which each individual strand and each individual wire is permanently formed in the helical shape it will assume in the finished wire rope. This process causes the strands to lay in place and removes the tendency of wires and strands to fly apart when cut. There are many advantages of performed wire rope, some of which are as follows.

1)	Performed wire rope will not unravel when seizing are removed therefore there is no great loss of lay
	or wasted rope.
2)	Performed wire rope is better able to resist severe bending conditions.
3)	Performed wire rope tends to hold on small drums better than non-performed ropes and will wind
	more uniformly.
4)	Performed rope is more inert than non-performed rope that makes it easier to handle during
	installation and less susceptible to the formation of kinks.

THE Structure of wire rope may be analysed as follows :

1) SIZE :

Generally denoted by its diameter, it is equal to the diameter of the circle which will completely enclose the rope. Denoted by inch(‘) or millimeter (mm).


2) STRAND FORMATION:

It is the number of strands in a rope, as well as numbers and arrangement of wires in a strand. Example – 6 (=No. of strands) X 19 (12/6 + 6f/1) (=No. and arrangement of wires in the strand) A majority of wire ropes are composed of strands having symmetrical cross sections that fit smoothly into a circumscribed circle, and which are made of round wires. The following basic designs are used.


3) CENTRELESS Formation:

This is the simplest from, in which all the wires are of equal size, and are twisted to assume a helical shape in the strand, with no centre.


4) SINGLE LAYER Formation:

In this design, the outer wires are wound around a centre wire.


5) MULTIPLE LAYER Formation:

In this design, there is more than one operation. The layers are formed one over the other in succession. It is a straight formation and equal sizes of wires are used.


6) SEALE Formation:

In this design, the outer layer has a predetermined number of large wires. They are laid around an equal number of small inner wires in such a manner that the outer wires lie in the valley of the under-lying wires. The advantage of this is in its more abrasive surface.


7) FILLER Formation:

In this design, even number of wires are laid around an inner layer of half that number. In each valley between two layers a small wire is filled. The advantage of this construction is in its greater strength and shock absorption capacity because of compact design.


8) WARRINGTON Formation:

In this design, a layer of pairs of wires (one large and one small) is laid over an inner layer of wires. The number of wires in the inner layer is half of thosein the outer layer. By its formation the strand is more roundish. It has more wearing surface without losing its flexibility.


9) COMBINATION Formation:

In many compound constructions, when there are more than two layers of wire over the centre wire, a combination of any two from among Filler, Seale and Warrington is designed. Example : In the Warrington Seale construction, the intermediate layer has a Warrington relationship with the inner layer and a Seal relationship with the outer.


10) TRIANGULAR Formation (Flattened Strand):

The strands are triangular in shape instead of round, thus offering a greater surface area of steel. The Flattened Strand rope has a 15% greater cross-sectional metallic area, hence they are stronger and have longer life. They are made in Lang Lay. This formation prevents overwinding and heavy loading and is mainly used in the mining industry as haulage rope.