You may not realize it, but steel wire ropes are all around us. They are used in bridges, elevators and locks. In cranes and in various industrial applications. What are the origins of this versatile product? Let’s take a look at the rich history of the steel wire rope.
The history of the steel wire ropes goes way back, because rope is considered its predecessor. As early as prehistoric times, ropes were made from plant fibers, skin and hair. In 1250, the Incas used rope to build a bridge of suspension cables. And in ancient Egypt, rope acted as a lifting device in the construction of pyramids.
As of the nineteenth century, iron chains became a good alternative. The mining industry, among others, made eager use of them. Mining engineer Julius Albert foresaw a risk. Although chains had a high breaking load, they didn’t have parallel strans like wire ropes. With wire ropes, the break of one wire was absorbed by the other wires, but this was not the case with chains. As a result, fatigue fractures of chains were a real danger in the mining industry as the entire chain would fail with only one facture.
In 1824, Albert focused his efforts on this issue and seeks a way to combine the advantages of wire ropes and chains. He builds a tensile machine to test the fatigue of chains. After numerous tests, he concluded that chains were inadequate: they quickly showed signs of fatigue and are not safe enough.
In 1834, Albert manufactured the first successful steel wire rope. He used the weaving technique that was also used to make rope. He struck the rope with three strands, each consisting of four wires. The result was a steel wire rope with a diameter of 19 millimeters and a length of 600 meters. The great advantage of this steel wire rope: if one strand breaks, the other strands will absorb the blow.
On 23 July 1834, the first steel wire rope using this technique was used in the Caroline quarry in Clausthal, Germany. This quarry was some 464 meters deep.
The story of the steel wire rope doesn’t end here. In the following years, the steel wire rope is further developed. New techniques are invented for wire ropes with a higher breaking load. In England, Robert Stirling Newall designs a machine to mechanically strike steel wire ropes. Experiments are also carried out with multiple layers of wire.
Although experts are continually taking the steel wire rope to the next level, wire breaks remain a nasty issue. In 1884, Thomas Seale came up with a new construction, which consisted of sturdy outer wires and an equal number of inner wires with a smaller diameter. This made the wire rope more flexible. Seale also ensured that the wires are parallel to each other, preventing wire crossings.
Nevertheless, the Seale construction ultimately did not prove to be the dream solution for wire breakage. The large outer wires made the wire rope less flexible and the steel wire rope still became quickly fatigued. In response, James B. Stone reduced the diameter of the outer wires. He filled the space created between the outer wires with smaller wires. The filler wire rope construction was a reality. This technique is still widely used today.
During the nineteenth century, another construction was added: the Warrington construction. This consists of six strands from one core wire, with six wires in the first layer around it. In the grooves of the six thick wires in the second layer are another six wires. The second layer thus consists of 12 threads. The large number of threads in the outer layer increases the flexibility. A disadvantage is that the thin wires on the outside reduce the resistance to destruction and corrosion. Also, the construction is relatively unstable.
Of course, the search for higher-quality materials continued. In 1855, Henry Bessemer received a patent for the so-called “bessemer process”: a production method for steel from pig iron. From 1865 onwards, it was possible to mass produce steel. The steel wire ropes that were manufactured from this steel mass had much greater tensile strength than iron rope wires. In 1883, steel wire ropes were used for the first time in a suspension bridge, and not the least either: the Brooklyn Bridge in New York City.
The producers of steel wire ropes found out that “all beginnings are difficult”. Because iron is a lot more flexible than steel, it took some getting used to working with the “stiff” steel wire ropes. During the manufacturing of the steel wire ropes, steel wires and strands have a continuous tendency to get back into their original shape. In 1920, a solution to this problem was devised. The wires and strands were pre-shaped.
The result: a steel wire rope that is more resistant to fatigue, has a better recovery capacity (after bending) and is more flexible (in an unloaded state). A solution from which we continue to benefit today.
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Modern History of Wire Rope
by Donald Sayenga
It wasn't until recent history (the 1600-1700s) that most of the technical breakthroughs in the modern history of wire rope were achieved in Europe. This was followed by a remarkable 40-year period, between 1849-89, when a majority of the basic forms of wire rope still in use today all over the world were devised in the United States.
Early German
and English Ropes
The first operative
wire ropes of the modern era, employed in vertical shafts as hoisting
cables in the Harz Mountain silver mines of Germany from 1834 to 1854,
were not very complicated inventions. Three lengths of wrought-iron wire,
all the same size, were twisted around each other by hand to make a strand.
Next, three or four identical strands were twisted around each other in
a similar manner to make a rope. The process was similar to prehistoric
techniques for making ropes of hemp fibers.
These handmade ropes, known as Albert Ropes (after William Albert, the Harz mining official who pioneered the practice) were not very flexible because the wires were relatively large and stiff. But, they gave good service compared to chains or hemp ropes, where large hoists, drums, and sheaves were in use. Chains tended to part without warning, and hemp rope rotted in the damp mineshafts. Unfortunately, the tedious process of making Albert Ropes discouraged trials in other applications. Several versions were tested, but none contained an internal core for support of the outer strands. First attempted in 1834, they were abandoned after the 1850s.
Meanwhile, at the same time the Germans were achieving wire rope success in the Harz mines, a London inventor named Andrew Smith was experimenting with various ways to apply wire ropes to ship's rigging. He manufactured several kinds of wire rope for this purpose, using the ropewalk techniques of the hemp cordage industry. In 1840, a new rapid transit system known as the Blackwall Railroad opened for business in London. Smith substituted his wire ropes for the hemp haulage on the Blackwall Railroad.
In the meantime, another Englishman, Robert Newall, learned about the Albert ropes. He devised a way to make wire ropes in a factory using machinery rather than the hand-twisting method. His ropes were tested with success on the Blackwall Railroad, but Smith opposed Newall's efforts during a patent fight in the mid-1840s, in which Newall prevailed. The companies established by Smith and Newall later merged, remaining in business to the present.
Smith soon left England for California and the Gold Rush. Newall's style of wire rope--comprised of six strands, each containing its own fiber core, all twisted around a central fiber core--soon dominated the English market. Their major English contribution to the industry, however, was the idea of making strands on a machine known as a strander.
Wire Ropes
and American Railroads
Word about
the English and German experiments spread quickly to the United States.
Prior to the advent of the high-pressure steam locomotive, the early railroads
overcame higher elevations with a combination of hemp rope hoists and
gravity descent, operated much like a modern ski-lift system.
In Pennsylvania, a cross-country transportation system known as the Allegheny Portage RR agreed to test a handmade wire rope in 1842 as a substitute for hemp ropes, which tended to rot after little more than one year of service. The test was a success, so the Portage converted to wire ropes. The new wire ropes attracted attention at the Morris Transportation System in New Jersey, and at several anthracite coal transportation companies including the Delaware & Hudson Co. in New York and the Lehigh Co. in Pennsylvania. These wire ropes were made by a surveyor named John Roebling. Although he twisted the wires together by hand, like the Albert ropes, he adopted the six-strand-plus-core arrangement favored by Smith and Newall. Roebling's ropes, however, were made entirely of wire, utilizing a core that was identical to the six outer strands, each comprised of 19 wires.
Roebling soon learned that his process for twisting 19 wires together created a strand that tended to become hexagonal rather than round. He launched a series of experiments with machine-made ropes looking for a way to make strands that were rounder. Meanwhile, one of his customers, the Lehigh Co., moved forward rapidly, building its own wire-rope factory in 1848. This factory (now owned by Bridon International--the same company that absorbed the original Smith and Newall companies in the UK), is still in business near Wilkes-Barre, Pa. And Roebling gave up surveying to concentrate on ropemaking, building a large factory in Trenton, N.J., in 1849.
Roebling's
Three-Size Construction
At the time
that his factory began operations in Trenton, Roebling achieved the first
American advancement in wire-rope theory. Realizing that the defects of
six-strand ropes could be corrected by combining wires of different diameters
in the strands, he devised a three-size construction (now known as Warrington
construction). By starting with a seven-wire strand made of one wire size,
Roebling added an outer layer containing 12 wires of two different alternating
sizes.
After numerous tests, Roebling's three-size ropes provided slightly better service in some applications. Although the original aim of the invention was to create improved roundness, the new strands yielded a side-effect of even greater significance. Because there was less hollow space within the strand itself, the greater fill-factor permitted the strands to be made by what is known as the equal-lay principle, whereby each wire in an outer layer is cradled by two wires in an inner layer, creating greater support without the effect of internal crossovers. The importance of the equal-lay principle did not become obvious until the introduction of modern high-speed stranders in the 1850s.
Unfortunately, in an accident with his own machinery, Roebling's arm and shoulder were mangled in 1849. Several years passed before he regained full mobility. During this period, he diverted his attention to the construction of wire-cable suspension bridges, for which he is most famous today. This diversion prevented him from fully exploiting the merits of three-size construction. When it was introduced again later, under the name Warrington, many people thought three-size construction was an English invention. Roebling never patented his achievement, so the history of his invention remains obscure.
Meanwhile, during Roebling's recovery, English ropemaking techniques were introduced in California. The inventor, Andrew Smith, had returned to Great Britain in 1853 but his son, Andrew H. Smith, remained in California to seek his fortune in the gold fields. After starving for several years, he moved to San Francisco, changed his name to A.S. Hallidie and launched a wire-rope business in 1857. Hallidie devoted himself to the concept of improvements in wire rope tramways for the gold and silver mines of California and Nevada.
Hallidie's mining tramways were a success in the 1860s. He also built numerous wire-cable suspension bridges and he devised his own version of equal-lay stranding, known as California Cable, using triangular-shaped wires. In some ways, Hallidie's method was superior to Roebling's three-size method, except that triangular wire is costly and difficult to manufacture. All this aside, Hallidie is better known for adapting his mining tramway cables to the streets of San Francisco in 1872 and the birth of the city's famous cable-car system.
Thomas
Seale's Patent
The original
Hallidie cable car on Clay Street was an instant success as a transportation
system. Overnight, competitors went into business on other hilly streets
nearby. Cable cars differed from overhead tramways because the ropes were
subjected to more severe service conditions. Constant starting and stopping
of the cars with a sliding grip, combined with numerous deflection sheaves
required to allow the underground cable to conform to the surface profile
of the streets, destroyed wire ropes in short order. San Francisco quickly
became the world's largest wire rope market.
One of Hallidies major transportation competitors was wealthy Leland Stanford. He had been involved in numerous successful ventures including the transcontinental railroad. Stanford intended to make his new California Street cable car line the city's finest. To this end, he hired an earthmoving contractor named Thomas Seale to be his superintendent. Born in Ireland, Seale had come to California with his brother during the gold rush, where they attained considerable wealth by grading streets near the San Francisco waterfront. The Seale brothers owned a huge ranch adjacent to Stanford's ranch in Palo Alto.
Roebling's three-size construction ropes were not very suitable for cable-car service because the alternately small-sized outer wires invariably wore out first, breaking up and tangling machinery in the underground tubes. English inventors were experimenting with elliptical- and triangular-shaped strands to solve this problem. These so-called flattened strands did provide improvement when tested, but they were very expensive to produce. Ultimately, the enormous demand for wire rope in San Francisco stimulated intense competition between Roebling's company and Hallidie, driving prices downward.
The cable car demand next spread all over the United States as other cities installed cable cars in the 1870s and 1880s. The three existing American manufacturers could not cope with the demand, which brought many other companies into the ropemaking arena. In San Francisco, the dilemma of short-rope service was tackled by Thomas Seale, whose solution soon became the accepted answer to the problem of severe outer wear combined with multiple reverse bending over small-diameter sheaves.
Seale's patent (#315,077 April 7, 1885) is based upon rearranging the three wire sizes into an entirely different pattern so that all the largest wire sizes are side-by-side on the exterior of the strand. The aim was to achieve increased abrasion resistance without losing flexibility. More important, the patent also described, for the first time, the basic concept of equal-lay stranding, which is inherent in the Roebling three-size approach, but had not been previously explained as the solution to internal cross-wire nicking.
Unfortunately, Seale's notes are gone and details of how he devised his famous construction remain unknown.
James Stone's
Filler Wire Patent
Most of the
wire rope companies, including Roebling's, adopted Seale's principles,
even though it became apparent that Seale-type strands, although much
more abrasion-resistant, had a tendency to be slightly less flexible and
therefore less fatigue-resistant. Further analysis of the problem was
launched by James B. Stone, who was rope-mill superintendent for Washburn
& Moen in Worcester, Mass., in the 1880s. (Washburn & Moen later
became known as American Steel & Wire and, after 1900, became an important
part of the conglomerate known as United States Steel.)
Stone had already invented high-speed stranding equipment for the rope mill. He also had studied several cable-car systems in detail and concluded that four different sizes of wire, not three, would be needed to create the most perfect fill factor for strand concentricity. The smallest of the wires, known as filler wires, were to be inserted into the rope for cushioning purposes.
After toying with that concept, Stone realized that six fillers provided a key to making round, equal-laid strands at high speed from 19 wires of nearly the same size. James Stone's patent (#416,189 December 3, 1889) described what is now known as 6 by 25 filler wire construction.
The significance of the American developments in wire rope construction cannot be understated. Today, James Stone's 6 by 25 wire rope is the most widely-used wire rope construction in the world for general purpose applications. Thomas Seale's patented form of wire rope is also widely-used, particularly in any kind of application where severe abrasion is encountered, and John Roebling's three-size Warrington construction remains popular for small-diameter ropes where the filler wire principle cannot be applied.
A.S. Hallidie's municipal cable cars were supplanted by electromotive traction railways, which, in turn, were driven out of business by General Motors and Ford everywhere except in their original home in San Francisco. Motorists trapped in commuter traffic jams perhaps occasionally question the wisdom of driving the cable cars out of business, but the innovations in fundamental wire rope construction derived from American transportation experiments have benefited wire rope users everywhere.
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