Wire rope

A cable (also wire) is a rope which is made of wire and not from natural or synthetic fibers. The wires are of metal, usually steel.

The term wire refers almost always a so-called Twisted rope in which the wires into strands or Kardeelen and these twisted rope to be so struck. For special applications, it is also braided ropes. In contrast, the ropes of large suspension bridges consist of many parallel lying, compressed wires.

History

While ropes lying parallel wires are older and have been used by Marc Seguin for his from 1823 built suspension bridges, cable Slapped 1834 by Oberbergrat Julius Albert was invented in Clausthal. The chains used until then in the Upper Harz mining were damaged by the stress of setting up and rolling, breaking again and again, sometimes with devastating consequences. To prevent total failure of the entire chain in the breaking of only a single element, Albert started to test a wire rope. It consisted of three strands of four wires made of wrought iron diameter of 3.5 mm. The rope was manufactured in the same stroke (also called Albert impact ). Initial field trials were successfully conducted in February 1834 in the pit Carolina Clausthal.

Production

The beating of the wires is at the stranding. It carries a rotatable stranding a certain number of reels of wire, the wires of which run through the twisting head ( a disk with the appropriate number of holes ) to the stock and it wrapped helically around a core wire. The outgoing from the camp finished strand is again wound up on a reel. The stranding comes about through the interaction of the train on the strand and simultaneous rotation of the stranding. The product thus produced is referred to as a spiral cable, provided that it is used in this form, for example as a stay cable. Strands, however, are intended for further stranding.

In the next operation more strands are beaten by another stranding a deposit around the finished rope. The insert can be made of natural or synthetic fibers, steel wire, with or without plastic wrap or a plastic profile. The stranded cables usually used are stranded twice, but there are also ropes with several layers.

Manufacturer

The cable industry in the German-speaking area is characterized by medium. It co-ordinates in the wire rope Association.

Construction

The wires from which ropes are composed generally consist of mild steel with a high carbon content of 0.4 to 0.9%. The very high strength of the wires is produced by cold drawing.

Because of the higher life of the rope usually Langs lay ropes are used, in which the wires of the wire layers do not intersect. The ropes are called Langs lay ropes if the wire strands have the same lay direction as the strands themselves, and they are called lay ropes when the shock direction is opposite.

A stranded cable or round strand, the simple shape of the rope is referred to, in which the outer strands are visible. You can bright, galvanized or coated with various plastics in different colors. Ropes with the additional designation Seale have strands of a steel core, a thinner layer and a layer of thicker wires. Warrington - Seale called ropes with a wire insert, two layers of thinner wires and a layer of thicker wires. Commercial ropes have diameters of 1.5 to 60 mm.

In a compacted or densified cable the outer strands are passed through a drawing die and thereby flattened. Characterized the rope diameter is reduced, and the cable passes readily smoothed over rollers and pulleys, or the sheath of a Bowden cable. Other stranded cables, the wires are pressed on an insert made ​​of a plastic rod, the plastic of the interior space between the strands completely fills that the strands and prevent their stabilized contact.

Locked coil ropes have an outer layer of profiled wires, the mesh so that the rope has a smooth surface and is largely protected against the ingress of moisture and dirt. Your outer wires can not escape from the rope bundle at break. Fully Locked coil ropes have to better protect two such layers of shaped wires. They are mostly used as supporting ropes for cableway installations. There are full locked supporting cables with a diameter of 90 mm, a minimum tensile strength of 918 t and a weight of 48 kg per meter. Fully Locked coil carrying ropes can also be equipped with integrated power and optical waveguides.

Designations such as 6 × 7 mean that the rope strands consists of 6 each with 7 wires. A 6 × 19 standard cable therefore has 6 strands, each consisting of 19 wires; a 8x36 WS has 8 strands with 36 wires in the type Warrington - Seale. Letters such as FC ( fiber core) denote a fiber core, NFC a liner made ​​of natural fibers, synthetic fibers and SFC a toilet a steel insert.

After its construction ( building ) the cables according to DIN EN 12385 are divided into classes. It also sets the cable sizes are defined.

Limiting factors for the tensile strength or the length of the rope are not only the size of the stranding, but often also the total weight of the cable reel with the finished rope and the transportation to the site.

Use

Wire ropes are used in different sizes and styles for various purposes, ranging from thin and flexible traction cable for the shifter on the bike, the less ductile and stronger Bowden cable for the brakes and the more rigid holders for halogen lamps, via cables to service medical examination devices control cables for the control of aircraft, particularly black ropes for the rigging loft of theaters, on different ropes for lifts and lifting floodgates for winches, excavators, cranes and cable cars up to the ropes for cable-stayed bridges.

Easy Braided ropes are indeed elastic, but stretch under load, are thereby thinner and turn in freely suspended loads. Ropes but have to fulfill different requirements. By special design and manufacturing methods certain ropes are therefore particularly elastic and flexible to run on small rolls, and have beneficial bending fatigue properties. For other low wear is emphasized. Still others are resistant to high temperatures or non-magnetic or particularly corrosion resistant. Elevator ropes will have a constant diameter as possible, so as not to slip in the drive wheels. Ropes for the rigging of masts and similar lashings shall be less extensible, they are therefore sometimes pre-stretched at the factory. Supporting cables of cable cars to bend under the rollers slightly and be a smooth run externally smooth and vibration. Slings to carry large loads, but will not break at the edges of the load and also twisting.

The four main cable types are:

• Running cables ( stranded ropes ) are claimed due to tensile and bending by swelling when running over sheaves.
• Static ropes (usually spiral ropes ) are caused by traction forces - usually little swelling - claimed.
• Suspension ropes ( locked coil ropes ) are loaded by tensile forces and supporting roles by transverse forces. The carrier ropes do not take it because the cable bending stiffness to the curvature of the supporting roles.
• Slings ( stranded ropes ) are stressed by tensile forces, but mainly by bending at the usually quite sharp deflection at the load.

Accessories

There is a wide range of accessories, the ropes often only ever be used, such as ferrules to prevent unraveling of the cable end, thimbles for amplifying a rope eye, various rope end, turnbuckles, turnbuckles and so on. Applicable only by experienced specialists are ultimately the specific tendon anchorages in prestressed concrete and the rear anchorages of the cables from the cable cars.

Rope breaking force

The rope breaking strength of the cables is determined by the diameter ( d ) in mm, the filling factor ( f), the Verseilfaktor ( k) and the resistance ( Rm) of the steel. A diameter (d) is the maximum outer diameter of the cable (edge ​​measurement). The fill factor determines the proportion of the steel section to the total cross section. The Verseilfaktor due to its design; Cables always have a lower by about 5 to 15% strength than the strength of the sum of the individual wires.

The minimum tensile strength ( MBK ), that is, the force that must reach the rope in a tensile test at least, is then calculated using the following formula:

For the much- used parallel laid ropes with steel core and strength Ro = 1770 N / mm ² for example, the minimum tensile strength in accordance with DIN EN 12385 -:

Rated

Considered running ropes, which are used in many ways. For applications in which could come to harm at break of the ropes persons or property, there are standards for the design of rope drives. With these standards, especially the ratio of minimum rope breaking strength of cable force and the ratio of pulleys and rope diameter is indicated. A commonly accepted design method for rope drives, which is also often used in addition to the standards, calculates the five income thresholds:

• Work cycles ( life of the rope ) to the rope discard criteria or until the rope breaking. The work cycles must meet the requirements of the user.
• Donandt ( yield strength of the rope wires, depending on the bending diameter ratio D / d). Strict limit. The cable force S in the nominal stress must be less than the Donandt SD1 (1 % level ).
• Violence fraction (ratio of minimum rope breaking force of impact force). The ratio of the minimum breaking strength rope / cable force Fmin / S = 2,5 ..... 12, depending on the nature of the particular rope drive, partly determined in standards.
• Depositing number of wire breaks ( recognizability of the rope discard criteria ). For hoists in which a load crash should be prevented by inspection, the deposition number of wire breaks should be based on a reference length of rope diameter is at least 30X BA30 = 8 be.
• Optimum rope diameter ( economy ). For a given line pull and a given pulley diameter, the maximum rope life is achieved with the optimum rope diameter. The rope diameter should be as large as or slightly smaller than the optimum rope diameter, since above the optimum rope diameter rope service life decreases again.

This limits the calculation is relatively complicated. A computer program Seilleb1.xls, which can be found below and can be used free of charge, calculated these limits.

Before using this method, the effective tractive force, the type and number of bends, which undergoes the most stressed piece of rope per cycle, and the approximate length of this wire piece must be determined.

Security

The wire ropes are stressed by pulsating voltages, due to wear, corrosion and, in rare cases, by acts of violence. Your life is therefore - apart from a few exceptions - at last. The safe use of wire ropes is conditional on their replacement state is discovered in time, before a dangerous situation occurs. The main departure criterion is the number of broken wires on reference lengths. The reference length, for example 30 times the rope diameter is used, because the wires fully endorse again because of twisting by few turns off from its breakage. It is an essential advantage of the cables to other traction means, a portion of the wires may be broken before the safety is impaired. The security is growing because of better visibility with the size of the depositing number of wire breaks.

The use of the ropes for the support persons, the usual visual and tactile inspection of rope is not sufficient. In elevators therefore supporting parallel ropes and safety gear are used to prevent a crash. Ropeways and in mine hoists the ropes are tested by magnetic methods in the run, with those internal wire breaks can also be discovered.

Parallel cables

Parallel cables are mainly used as supporting cables of suspension bridges. They are so large that they could previously only produced directly on the bridge itself in the so-called air -spinning process. Here, an auxiliary rope was pulled over the pylons that it describes the same curve as the planned suspension rope. At the auxiliary rope a very large number of individual wires was successively drawn from a reciprocating bike across the bridge. The supporting cables of the Golden Gate Bridge were prepared in this manner. Each cable consists of 27 572 individual wires. Parallel adjacent and non-twisted or twisted filaments were each fixed so that all wires have the same load. Finally, the wires were encased and compressed by cable clamps.

Since the 60s, prefabricated parallel wire cables are used which are abbreviated as PPWS for Prefabricated Parallel Wire beach. This was only possible after it was investigated how these ropes can be wound onto reels without obtaining permanent deformations. Typically, 37, 61, 91 or 127, the wires together to form a hexagonal cross-sections. A cable drum with a parallel cable can weigh up to 85 tons today. The technology was first introduced on a large scale in Japan. Examples of bridges with suspension cables of prefabricated parallel cables are the Jiangyin bridge in China or the Kammon Bridge and the Akashi - Kaikyo Bridge in Japan.

Phrase

As a high-wire act is referred to except the original demonstration of acrobatic acrobats on a tightrope figuratively a dangerous or difficult undertaking, in which the practitioner must keep the balance.

People with " nerves of steel wire ropes " are extremely strong mentally.