Steel cable

Braided steel cable coil.

A steel cable is a type of mechanical cable made up of a set of steel wires that form a single body as a work element. These wires may be helically wound in one or more layers, generally around a central wire, forming spiral cables.

These cables, in turn, can be wound helically around a core or core, forming multiple strand cables. These cables can be considered as elements and can also be wound helically on a core, forming guard cables, or coupled one next to the other, to form flat cables. Originally, the steel cable was the invention of the German engineer, Wilhelm Albert.

Fundamental features

Diameter

The diameter of a cable is considered to be the circumcircle circumscribed to its section, expressed in millimeters (mm).

When a new cable enters service, the stresses it supports produce a decrease in diameter, accompanied by an increase in its length, due to the settling of the different elements that make up the cable. This decrease in diameter is greater the greater the proportion of textile fiber that forms it.

Composition

By combining the arrangement of the wires and the cords, cables of very different compositions are obtained. Those made with thick wires resist wear due to friction well, but they are highly rigid and have little resistance to bending. Cables made up of a large number of fine wires are not very flexible, and little resistant to friction and corrosion.

Souls or Cores

The core of the cable is the support of size and consistency suitable to offer a firm support to the strands, so that, even at maximum load, the wires of the strands do not become entangled with each other.

Generally, the core of the cables is made of textile fiber, as long as they are not worked in environments with a high percentage of humidity and high temperatures, since these factors differ with the resistance of the core, making it weak to such an extent that can be cut For this, metallic souls are used, which are not affected by these last factors.

Notation

The composition of a cable is expressed by a notation composed of three figures, for example 6x19+1 Seale. The first indicates the number of cords in the cable, the second the number of wires in each cord, and the third the number of textile cores. The word Seale indicates a special arrangement of the cords, which we will see in the winding classes.

If the core of the cable is metallic, made up of wires, the last figure is replaced by a notation between parentheses that indicates the composition of said core. For example, 6x19+(7x7+0). When the cords or branches of the cable are other cables, the second figure will be replaced by the notation that indicates its composition, also in parentheses. For example, 6x(6x7+1)+1.

Wrap

The wires of the cords are arranged in the form of a helix around a central wire, forming one or more layers.

The pitch of the cord is the length covered by a complete turn of the wire around its central core. This distance is measured parallel to the axis of the bead. In ordinary cables, the different layers of wires that make up the cords have different pitches.

The cords, in turn, are placed on the cable in the form of a helix around the soul. The pitch of the helix described by a bead is the pitch of the wire.

Coiling classes

Cross-left roll.

Right cross-rolling.

Rolling left lang.

Right lang roll.

Alternate left roll.

Right alternating roll.

Considering the winding directions of the wires in the cord, and of the cords in the cable, it is possible to distinguish:

• Cross or current development is the one in which the cords are rolled in the opposite direction of the wires that form them.
• Lang roll, wires on the cord and cords on the cable are rolled in the same sense.
• Alternate rolling, with cords that are alternatively rolled in the same sense as the cable and in the opposite sense.

In addition, these three groups can be rolled to the right or to the left.

Preformed

In the manufacturing process of ordinary cables, the wires adopt the shape of a helix and occupy their respective positions thanks to an elastic deformation, which causes internal stresses in said wires. Because of these internal stresses, when the ties are removed, or when a wire breaks, the ends tend to recover their original straight shape.

In preformed cables, both the wires and the cords undergo a permanent deformation during the manufacturing process, adopting the shape of a helix in accordance with the position they will occupy in the cable.

By suppressing the elastic deformation, the internal stresses existing in the wires of the non-preformed cables are eliminated and that contribute to the breakage of said wires due to fatigue.

The main advantages of preformed cables are:

• Increased flexibility, since the bending will not add internal manufacturing tensions to the bending effort due to the rolling of pulleys and drums. This therefore amounts to a reduction in bending efforts.
• It avoids cut-off effects, because the wire tips that are broken by fatigue are not entangled, these are not stuck between the cable and the pulley throats, thus avoiding cutting other wires.
• Increased duration, resulting from the two previous advantages.
• Easy handling. By cutting a preformed cable the cords and wires remain in place because they have no tendency to disable and unroll by forming cokes.
• It facilitates the use of the Lang roll-out, by reducing the inconveniences that are more likely to be developed, makes it possible to adapt it to more applications.

Materials

The drawn wire used to manufacture cables is obtained from Martin Siemens steel fermachine or electric furnace steel. its carbon content generally varies from 0.3% to 0.8%, obtaining mild, semi-hard and hard steels within this range.

The purity index can vary according to the characteristics required; however, these types of steel cannot contain more than 0.04% phosphorus and 0.04% sulfur.

Wire Types

Cables can also be classified according to their structure and most prominent characteristics in the following groups

• Spiral cables or cords
• Normal cables
• Equal-step cables
• Triangular cord cables
• Anti-routing cables
• Guard cables
• Flat cables
• Semi-closed and closed cables

Spiral cables or cords

They are also known as single-wound cables, in which the wires are placed in one or more layers wound in the form of a helix around a core. The core is usually made up of a single wire.

If this construction is already a finished cable, the wires of the different layers are wound in an alternating left and right direction and then it is called a spiral cable. When it is an element of another larger cable, the different layers of wires are wound in the same direction and then it is called a cord.

In general, spiral cables resist wear due to friction as they have a roughly cylindrical and very smooth surface. In them the section is used well since in a relatively small diameter a considerable load capacity is obtained. Being alternately wound, it resists torsion well.

They also have a high modulus of elasticity.

Because they are not very flexible, they are used mainly as static cables, in thin cables they are used for brakes and vehicle controls. They are also used as rail cables for cable cars, carrying cables for suspension bridges, guide cables in mining extraction, counterweight in very old elevators and freight elevators, more flexible cables with 6 and 8 cords are used in current elevators and elevators.

• • • Normal cables ***

They are formed with cylindrical cords wound helically around a core or core that can be made of fiber or metal.

The strands of these cables are made of wires of the same diameter and the number of wires in each layer increases by 6 by 6, in arithmetic progression. As all the wires have the same diameter, they are very homogeneous cables

The twists of the different layers all have the same direction and are wound with the same cabling angle, in this way the pitches of the different layers are different and proportional to the average diameters of each layer.

Since the layers of wires have different pitches, when they support pressure the wires cross and notch each other, producing bending stresses when bending the cable.

In these cables, the tensile stress is distributed evenly among all the wires as they are wound with the same cabling angle.

Its field of application is very extensive, its limitation in use is given by its little flexibility

Equal pitch cables

The different layers of wires that make up its strands are wired under the same pitch, therefore the wires of the strands of the different layers do not cross each other and rest along their entire length in the grooves that are They form between every two contiguous wires of the lower layer. Their external appearance is the same as that of normal cables and it is necessary to observe their section to be able to differentiate them.

The most frequent compositions are:

• Seale
• Warrington
• Warrington-Seale
• Filling (Filler Wire)

In general, cables with the same pitch have greater flexibility, great resistance to lateral compression and a high breaking load.

Triangular cord cables

These cables are made up of six strands roughly shaped like an equilateral triangle.

Anti-rotation cables

The conventional steel cable under the action of a load rotates on its own axis. This phenomenon is due to the spiral winding of the wires and cords, and to the direction of rotation, which is opposite to the direction of winding of the cable, so that the conventional cable always tends to unwind by turning.

When the lift height is considerable (depending on the cable diameter and other factors), this problem begins to become important and in systems of two or more lines, it is very likely that the cables will wrap around each other.

This generates a highly damaging condition for the cable and dangerous for the safety of people. There are installations that solve this problem by using left and right twist cables, working in pairs, with the caveat that left twist cables are generally only made to order.

In most cases, however, the solution is to use anti-rotation steel cables. In short, these cables are used to lift unguided loads (which can rotate freely), with considerable lifting heights. The design and constructive type of these cables is based on composing elements whose torsion moments balance each other, producing a practically zero resultant.

The most used designs are the so-called multi-strands, among which the most popular is 18x7+ 1x7, usually called “19x7”. In this design, two layers of 6 and 12 strands are made up respectively, on a core of one strand, all of these strands being practically the same, with 7 wires each. The result is a rope with highly anti-rotation properties, with excellent tensile strength, medium flexibility and crush resistance. There are other possible constructions, all based on the same principle. The 34x7 construction is more flexible and more efficient as an anti-twist, although it is also somewhat less stable.

Selection of anti-rotation cables

There are no precise rules for determining when to use an anti-twist cable. In the first instance, it is convenient to consider the experience obtained with cables previously used in the same installation or equipment. When there is no such experience, or in case of doubt, there are some applicable diagrams and formulas, although their results are for guidance only. The variables that affect the determination are:

• aging height.
• cable diameter.
• diameter of the pulleys.
• Number of lines.
• arrangement of the pulleys.
• specific cable torque.

It is recommended not to use anti-rotation cables when the load is guided (prevented from rotating) and it is also advisable to take some additional specific precautions. For example, due to their particular design, anti-twist cables present marked differences compared to 6-strand cables. The way they behave, wear and break, differs from conventional constructions. This brings with it the need to use specific handling, use and inspection criteria.

Handling of non-rotating cables

All the recommendations mentioned for the handling of any cable must be considered, with special attention to the fact that the anti-rotation cable must always be kept conditioned in reels and not in coils.

When it is unavoidable to make a coil, it must be properly strapped or tied, and when unrolling it, the coil must be rolled vertically until the cable is completely in a straight line on the ground. Special care must be taken not to introduce twist into the cable during handling or installation. All ends should have one, two, or three strong wire ties, depending on the diameter, unless they are welded.

Installation of anti-rotation cable

Anti-twist wire ropes are prone to knotting, crushing and becoming unbalanced, in characteristic “soul collapse” and “bird cage” shapes. Emphasis should be placed on avoiding operating practices that make it possible to reach such situations. A fundamental aspect is the method of installation, since many of the problems appear when the cable is newly installed. In general, the same recommendations that are given for the installation of any other cable apply, with the addition of the following:

• at all times keep the cable under tension, gently frying the coil that delivers the cable to the system.
• If the past through the system is done by pulling the new cable with the old one, the connection between both must have the possibility of turning.

Installation and operation environment conditions:

For 19x7 construction, the minimum winding diameter should be 30 to 40 times the cable diameter, although it is a fact that many kits are built with smaller ratios.

In installations with smaller diameters it is preferable to adopt a 34x7 construction cable or thoroughly check if a conventional construction cable can be used. Anti-rotation cables must always remain under tension.

Shocks, especially sudden ones, are harmful to the cable. If a sufficiently heavy block is not available, it is recommended to use additional counterweights or counterweight balls, in single line cases.

No rotation should be induced on the load. Said rotation could produce an unbalance of the torsion moments of the opposing helix strands, causing deformations in the cable.

An unwise practice is to attach swivels or swivels to the dead end anchorage. Free rotation of the cable will cause a reduction in resistance, load imbalance, and possible unbalance of the cable pair.

The angle of deviation between the pulleys and the drum must not exceed 1.5º. It is highly preferable to use grooved drums with the least amount of cable layers.

The ends of the cable must be firmly anchored with the full cross section and solidly retained.

The ideal method is with padding terminals. If wedge terminals are used, it is advisable to solder the ends of the cable or purchase the same with tapered ends. Cable clamps, although widely used, are not the best fixing method.

Inspection of anti-rotation cable

Inspection criteria for anti-rotation wire rope also differ from conventional ones. Any small reduction in diameter must be attended to with great care.

The criteria for counting broken wires also differs and once the decommissioning point is reached, non-twist ropes leave less time until breakage than conventional ropes.

Guardian wires

They could be called cables of cables, since they are made up of several cables, called branches, wound helically around a central fiber or metal core.

Flat cables

Flat cables are also called braided cables or ribbon cables, they are made up of several cables or branches of 4 strands each, arranged in parallel one next to the other and sewn together with sewing wires. The branches are normally arranged in an even number and are chosen so that their windings alternately twist to the right and to the left. Flat cables can be sewn with single seams or double seams.

Semi-enclosed and closed cables

They are cables with a single strand, generally formed by several layers of round wires covered by one or more layers of shaped wire. When the profile of the wires of the last layer is X-shaped, they are placed alternating with round wires and the cable is called semi-closed. When the profile of the wires is Z-shaped, they are all the same and fit together, thus being called a closed cable. As in the spiral cables, the wire layers of the closed ropes are laid alternately to the right and to the left in order to reduce their reaction to torsion.

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