Steel wire rope (right hand lang lay)
Wire rope is several strands of metal
wire
Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm
A wire is a flexible strand of metal.
Wire is c ...
twisted into a
helix
A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helic ...
forming a composite
''
rope
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similar ...
'', in a pattern known as ''laid rope''. Larger diameter wire rope consists of multiple strands of such laid rope in a pattern known as ''cable laid''.
In stricter senses, the term ''wire rope'' refers to a diameter larger than , with smaller gauges designated cable or cords. Initially
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
wires were used, but today
steel is the main material used for wire ropes.
Historically, wire rope evolved from wrought iron 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. While friction between the individual wires and strands causes wear over the life of the rope, it also helps to compensate for minor failures in the short run.
Wire ropes were developed starting with mining hoist applications in the 1830s. Wire ropes are used dynamically for lifting and hoisting in
cranes and
elevator
An elevator or lift is a cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or decks of a building, vessel, or other structure. They a ...
s, and for
transmission of mechanical power. Wire rope is also used to transmit
force in mechanisms, such as a
Bowden cable
A Bowden cable ( )
is a type of flexible cable used to transmit mechanical force or energy by the movement of an inner cable relative to a hollow outer cable housing. The housing is generally of composite construction, consisting of an inne ...
or the
control surfaces of an airplane connected to levers and pedals in the cockpit. Only aircraft cables have WSC (wire strand core). Also, aircraft cables are available in smaller diameters than wire rope. For example, aircraft cables are available in diameter while most wire ropes begin at a diameter.
Static wire ropes are used to support structures such as
suspension bridges or as
guy wire
A guy-wire, guy-line, guy-rope, or stay, also called simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly for ship masts, radio masts, wind turbines, utility poles, and tents. A thi ...
s to support towers. An
aerial tramway
An aerial tramway, sky tram, cable car, ropeway, aerial tram, telepherique, or seilbahn is a type of aerial lift which uses one or two stationary ropes for support while a third moving rope provides propulsion. With this form of lift, the grip ...
relies on wire rope to support and move cargo overhead.
History
Modern wire rope was invented by the German
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...
engineer
Wilhelm Albert in the years between 1831 and 1834 for use in mining in the
Harz
The Harz () is a highland area in northern Germany. It has the highest elevations for that region, and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt, and Thuringia. The name ''Harz'' derives from the Middle High German ...
Mountains in
Clausthal
Clausthal-Zellerfeld is a town in Lower Saxony, Germany. It is located in the southwestern part of the Harz mountains. Its population is approximately 15,000. The City is the location of the Clausthal University of Technology. The health resort ...
,
Lower Saxony
Lower Saxony (german: Niedersachsen ; nds, Neddersassen; stq, Läichsaksen) is a German state (') in northwestern Germany. It is the second-largest state by land area, with , and fourth-largest in population (8 million in 2021) among the 16 ...
,
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. It was quickly accepted because it proved superior strength from ropes made of hemp or of metal
chains
A chain is a serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression but linear, rigid, and load-bearing in tension. A c ...
, such as had been used before.
Wilhelm Albert's first ropes consisted of three strands consisting of four wires each. In 1840, Scotsman
Robert Stirling Newall
Robert Stirling Newall FRS FRAS (27 May 1812 – 21 April 1889) was a Scottish engineer and astronomer.
Life and work
Born at Dundee on 27 May 1812, Newall began work in a local mercantile office before leaving for London, where, in the emplo ...
improved the process further. In America wire rope was manufactured by
John A. Roebling
John Augustus Roebling (born Johann August Röbling; June 12, 1806 – July 22, 1869) was a German-born American civil engineer. He designed and built wire rope suspension bridges, in particular the Brooklyn Bridge, which has been designated as ...
, starting in 1841
and forming the basis for his success in
suspension bridge building. Roebling introduced a number of innovations in the design, materials and manufacture of wire rope. Ever with an ear to technology developments in mining and railroading,
Josiah White
Josiah White (1781–1850) was a Pennsylvania industrialist and key figure in the American Industrial Revolution.
Career
White began early factory-centered mill production in 1808 in water powered ironworks near Philadelphia, along with his par ...
and
Erskine Hazard
Erskine Hazard (1790-1865), a younger son of the first U.S. Postmaster Ebenezer Hazard, became the partner of Josiah White about 1810 when around 19 years old. White and Hazard together established spearheaded efforts that enabled the Industrial R ...
, principal owners
of the
Lehigh Coal & Navigation Company (LC&N Co.) — as they had with the first blast furnaces in the Lehigh Valley — built a Wire Rope factory in
Mauch Chunk
Jim Thorpe is a borough and the county seat of Carbon County in the U.S. state of Pennsylvania. It is part of Northeastern Pennsylvania. It is historically known as the burial site of Native American sports legend Jim Thorpe.
Jim Thorpe is ...
,
[Modern History of Wire Rope - Donald Sayenga](_blank)
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
in 1848, which provided lift cables for the
Ashley Planes
Ashley Planes was a historic freight cable railroad situated along three separately powered inclined plane sections located between Ashley, Pennsylvania at the foot, and via the Solomon cutting the yard in Mountain Top over above and initially bu ...
project, then the back track planes of the
Summit Hill & Mauch Chunk Railroad, improving its attractiveness as a premier tourism destination, and vastly improving the throughput of the coal capacity since return of cars dropped from nearly four hours to less than 20 minutes. The decades were witness to a burgeoning increase in deep shaft mining in both Europe and North America as surface mineral deposits were exhausted and miners had to chase layers along inclined layers. The era was early in railroad development and steam engines lacked sufficient tractive effort to climb steep slopes, so incline plane railways were common. This pushed development of cable hoists rapidly in the United States as surface deposits in the Anthracite
Coal Region
The Coal Region is a region of Northeastern Pennsylvania. It is known for being home to the largest known deposits of anthracite coal in the world with an estimated reserve of seven billion short tons.
The region is typically defined as compri ...
north and south dove deeper every year, and even the rich deposits in the
Panther Creek Valley
In Eastern Pennsylvania, the valley of the Panther Creek tributary of the Little Schuylkill River, a very small and relatively short mountain creek, was historically important due to its stranglehold on energy production, a key region central to ...
required LC&N Co. to drive their first shafts into lower slopes beginning
Lansford and its
Schuylkill County twin-town
Coaldale.
The German engineering firm of
Adolf Bleichert & Co. was founded in 1874 and began to build bicable aerial tramways for mining in the
Ruhr Valley
The Ruhr ( ; german: Ruhrgebiet , also ''Ruhrpott'' ), also referred to as the Ruhr area, sometimes Ruhr district, Ruhr region, or Ruhr valley, is a polycentric urban area in North Rhine-Westphalia, Germany. With a population density of 2,800/km ...
. With important patents, and dozens of working systems in Europe, Bleichert dominated the global industry, later licensing its designs and manufacturing techniques to Trenton Iron Works, New Jersey, USA which built systems across America. Adolf Bleichert & Co. went on to build hundreds of aerial tramways around the world: from Alaska to Argentina, Australia and Spitsbergen. The Bleichert company also built hundreds of aerial tramways for both the Imperial German Army and the Wehrmacht.
In the last half of the 19th century, wire rope systems were used as a means of transmitting mechanical power including for the new
cable cars. Wire rope systems cost one-tenth as much and had lower friction losses than
line shaft
A line shaft is a power-driven rotating shaft for power transmission that was used extensively from the Industrial Revolution until the early 20th century. Prior to the widespread use of electric motors small enough to be connected directly to e ...
s. Because of these advantages, wire rope systems were used to transmit power for a distance of a few miles or kilometers.
Construction
Wires
Steel wires for wire ropes are normally made of non-alloy carbon steel with a carbon content of 0.4 to 0.95%. The very high strength of the rope wires enables wire ropes to support large tensile forces and to run over sheaves with relatively small diameters.
Strands
In the so-called cross lay strands, the wires of the different layers cross each other.
In the mostly used parallel lay strands, the lay length of all the wire layers is equal and the wires of any two superimposed layers are parallel, resulting in linear contact. The wire of the outer layer is supported by two wires of the inner layer. These wires are neighbors along the whole length of the strand. Parallel lay strands are made in one operation. The endurance of wire ropes with this kind of strand is always much greater than of those (seldom used) with cross lay strands. Parallel lay strands with two wire layers have the construction Filler, Seale or Warrington.
Spiral ropes
In principle, spiral ropes are round strands as they have an assembly of layers of wires laid helically over a centre with at least one layer of wires being laid in the opposite direction to that of the outer layer. Spiral ropes can be dimensioned in such a way that they are non-rotating which means that under tension the rope torque is nearly zero. The open spiral rope consists only of round wires. The half-locked coil rope and the full-locked coil rope always have a centre made of round wires. The locked coil ropes have one or more outer layers of profile wires. They have the advantage that their construction prevents the penetration of dirt and water to a greater extent and it also protects them from loss of lubricant. In addition, they have one further very important advantage as the ends of a broken outer wire cannot leave the rope if it has the proper dimensions.
Stranded ropes
Stranded ropes are an assembly of several strands laid helically in one or more layers around a core. This core can be one of three types. The first is a fiber core, made up of synthetic material or natural fibers like sisal. Synthetic fibers are stronger and more uniform but cannot absorb much lubricant. Natural fibers can absorb up to 15% of their weight in lubricant and so protect the inner wires much better from corrosion than synthetic fibers do. Fiber cores are the most flexible and elastic, but have the downside of getting crushed easily. The second type, wire strand core, is made up of one additional strand of wire, and is typically used for suspension. The third type is independent wire rope core (IWRC), which is the most durable in all types of environments. Most types of stranded ropes only have one strand layer over the core (fibre core or steel core). The lay direction of the strands in the rope can be right (symbol Z) or left (symbol S) and the lay direction of the wires can be right (symbol z) or left (symbol s). This kind of rope is called ordinary lay rope if the lay direction of the wires in the outer strands is in the opposite direction to the lay of the outer strands themselves. If both the wires in the outer strands and the outer strands themselves have the same lay direction, the rope is called a lang lay rope (from Dutch contrary to , formerly Albert's lay or langs lay). Regular lay means the individual wires were wrapped around the centers in one direction and the strands were wrapped around the core in the opposite direction.
Multi-strand ropes are all more or less resistant to rotation and have at least two layers of strands laid helically around a centre. The direction of the outer strands is opposite to that of the underlying strand layers. Ropes with three strand layers can be nearly non-rotating. Ropes with two strand layers are mostly only low-rotating.
Classification according to usage
Depending on where they are used, wire ropes have to fulfill different requirements. The main uses are:
* Running ropes (stranded ropes) are bent over sheaves and drums. They are therefore stressed mainly by bending and secondly by tension.
* Stationary ropes, stay ropes (spiral ropes, mostly full-locked) have to carry tensile forces and are therefore mainly loaded by static and fluctuating tensile stresses. Ropes used for suspension are often called ''cables.''
* Track ropes (full locked ropes) have to act as rails for the rollers of cabins or other loads in aerial ropeways and cable cranes. In contrast to running ropes, track ropes do not take on the curvature of the rollers. Under the roller force, a so-called free bending radius of the rope occurs. This radius increases (and the bending stresses decrease) with the tensile force and decreases with the roller force.
* Wire rope slings (stranded ropes) are used to harness various kinds of goods. These slings are stressed by the tensile forces but first of all by bending stresses when bent over the more or less sharp edges of the goods.
Rope drive
Technical regulations apply to the design of rope drives for cranes, elevators, rope ways and mining installations. Factors that are considered in design include:
* Number of working cycles allowed before replacement or breakage of the rope
*
Donandt force (yielding tensile force for a given bending diameter ratio /) - strict limit. The nominal rope tensile force must be smaller than the Donandt force .
* Rope safety factor, ratio between the rope's breaking strength and the maximum load to be expected
* Allowable number of broken strands before replacement
* Optimal rope diameter for a given sheave diameter, so as to obtain best working life
The calculation of the rope drive limits depends on:
* Data of the used wire rope
* Rope tensile force
* Diameter of sheave or drum
* Simple bendings per working cycle
* Reverse bendings per working cycle
* Combined fluctuating tension and bending per working cycle
* Relative fluctuating tensile force
* Rope bending length
Safety
The wire ropes are stressed by fluctuating forces, by wear, by corrosion and in seldom cases by extreme forces. The rope life is finite and the safety is only ensured by inspection for the detection of wire breaks on a reference rope length, of cross-section loss, as well as other failures so that the wire rope can be replaced before a dangerous situation occurs. Installations should be designed to facilitate the inspection of the wire ropes.
Lifting installations for passenger transportation require that a combination of several methods should be used to prevent a car from plunging downwards. Elevators must have redundant bearing ropes and a safety gear. Ropeways and mine hoistings must be permanently supervised by a responsible manager and the rope must be inspected by a magnetic method capable of detecting inner wire breaks.
Terminations
The end of a wire rope tends to fray readily, and cannot be easily connected to plant and equipment. There are different ways of securing the ends of wire ropes to prevent fraying. The common and useful type of end fitting for a wire rope is to turn the end back to form a loop. The loose end is then fixed back on the wire rope. Termination efficiencies vary from about 70% for a Flemish eye alone; to nearly 90% for a Flemish eye and splice; to 100% for potted ends and swagings.
Thimbles
When the wire rope is terminated with a loop, there is a risk that it will bend too tightly, especially when the loop is connected to a device that concentrates the load on a relatively small area. A thimble can be installed inside the loop to preserve the natural shape of the loop, and protect the cable from pinching and abrading on the inside of the loop. The use of thimbles in loops is industry
best practice
A best practice is a method or technique that has been generally accepted as superior to other known alternatives because it often produces results that are superior to those achieved by other means or because it has become a standard way of doing ...
. The thimble prevents the load from coming into direct contact with the wires.
Wire rope clips
![Wire rope clamps](https://upload.wikimedia.org/wikipedia/commons/b/ba/Wire_rope_clamps.jpg)
A wire rope clip, sometimes called a clamp, is used to fix the loose end of the loop back to the wire rope. It usually consists of a
U-bolt
A U-bolt is a bolt in the shape of the letter U with screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a ...
, a
forged
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...
saddle, and two nuts. The two layers of wire rope are placed in the U-bolt. The saddle is then fitted to the bolt over the ropes (the saddle includes two holes to fit to the U-bolt). The nuts secure the arrangement in place. Two or more clips are usually used to terminate a wire rope depending on the diameter. As many as eight may be needed for a diameter rope.
The
mnemonic
A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding.
Mnemonics make use of elaborative encoding, retrieval cues, and imag ...
"never saddle a dead horse" means that when installing clips, the saddle portion of the assembly is placed on the load-bearing or "live" side, not on the non-load-bearing or "dead" side of the cable. This is to protect the live or stress-bearing end of the rope against crushing and abuse. The flat bearing seat and extended prongs of the body are designed to protect the rope and are always placed against the live end.
The US Navy and most regulatory bodies do not recommend the use of such clips as permanent terminations unless periodically checked and re-tightened.
Eye splice or Flemish eye
An
eye splice
The eye splice is a method of creating a permanent loop (an " eye") in the end of a rope by means of rope splicing.
The Flemish eye is a type of circular loop at the end of a thread. There are several techniques of creating the eye with its k ...
may be used to terminate the loose end of a wire rope when forming a loop. The strands of the end of a wire rope are unwound a certain distance, then bent around so that the end of the unwrapped length forms an eye. The unwrapped strands are then
plaited back into the wire rope, forming the loop, or an eye, called an eye splice.
A Flemish eye, or Dutch Splice, involves unwrapping three strands (the strands need to be next to each other, not alternates) of the wire and keeping them off to one side. The remaining strands are bent around, until the end of the wire meets the "V" where the unwrapping finished, to form the eye. The strands kept to one side are now re-wrapped by wrapping from the end of the wire back to the "V" of the eye. These strands are effectively rewrapped along the wire in the opposite direction to their original lay. When this type of rope splice is used specifically on wire rope, it is called a "Molly Hogan", and, by some, a "Dutch" eye instead of a "Flemish" eye.
Swaged terminations
Swaging
Swaging () is a forging process in which the dimensions of an item are altered using dies into which the item is forced. Swaging is usually a cold working process, but also may be hot worked.
The term swage may apply to the process (verb) or ...
is a method of wire rope termination that refers to the installation technique. The purpose of swaging wire rope fittings is to connect two wire rope ends together, or to otherwise terminate one end of wire rope to something else. A mechanical or hydraulic swager is used to compress and deform the fitting, creating a permanent connection. Threaded studs, ferrules, sockets, and
sleeves
A sleeve ( ang, slīef, a word allied to '' slip'', cf. Dutch ) is the part of a garment that covers the arm, or through which the arm passes or slips.
The sleeve is a characteristic of fashion seen in almost every country and time period, ac ...
are examples of different swaged terminations. Swaging ropes with fibre cores is not recommended.
Wedge sockets
A wedge socket termination is useful when the fitting needs to be replaced frequently. For example, if the end of a wire rope is in a high-wear region, the rope may be periodically trimmed, requiring the termination hardware to be removed and reapplied. An example of this is on the ends of the drag ropes on a
dragline
A dragline excavator is a piece of heavy equipment used in civil engineering and surface mining.
Draglines fall into two broad categories: those that are based on standard, lifting cranes, and the heavy units which have to be built on-site. ...
. The end loop of the wire rope enters a tapered opening in the socket, wrapped around a separate component called the wedge. The arrangement is knocked in place, and load gradually eased onto the rope. As the load increases on the wire rope, the wedge become more secure, gripping the rope tighter.
Potted ends or poured sockets
Poured sockets are used to make a high strength, permanent termination; they are created by inserting the wire rope into the narrow end of a conical cavity which is oriented in-line with the intended direction of strain. The individual wires are splayed out inside the cone or 'capel', and the cone is then filled with molten lead-antimony-tin (Pb
80Sb
15Sn
5) solder or 'white metal capping',
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, or now more commonly, an unsaturated
polyester resin Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins. Unsaturated polyester res ...
compound.
See also
*
Fiber rope
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similarly ...
*
Tensile structure
A tensile structure is a construction of elements carrying only tension and no compression or bending. The term ''tensile'' should not be confused with tensegrity, which is a structural form with both tension and compression elements. Tensile ...
*
Wire rope spooling technology
Wire rope spooling technology is the technology to prevent wire rope getting snagged when spooled, especially in multiple layers on a drum.
History
Ever since the development of wire rope, comprising multiple wire strands, spooling the wire has ...
References
External links
Types and construction of wire rope strand and cableU.S. Navy Technical Manual for Wire and Fiber RopeModern history of wire ropeHandbook of Oceanographic Winch, Wire and Cable Technology US Federal Specification RR-W-410 for Wire Rope and Strand
{{Authority control
Cables
Mechanical power transmission
Ropes
Wire
German inventions