The rail profile is the cross-sectional shape of a rail as installed on a railway or railroad, perpendicular to its length.
Early rails were made of wood, cast iron or wrought iron. All modern rails are hot rolled steel with a cross section (profile) approximate to an I-beam, but asymmetric about a horizontal axis (however see grooved rail below). The head is profiled to resist wear and to give a good ride, and the foot profiled to suit the fixing system.
Unlike some other uses of iron and steel, railway rails are subject to very high stresses and are made of very high quality steel. It took many decades to improve the quality of the materials, including the change from iron to steel. Minor flaws in the steel that may pose no problems in other applications can lead to broken rails and dangerous derailments when used on railway tracks.
Generally, the heavier the railway tracks, the heavier and faster the trains which run through these tracks.
Rails represent a substantial fraction of the cost of a railway line. Only a small number of rail sizes are made by steelworks at one time, so a railway must choose the nearest suitable size. Worn, heavy rail from a mainline is often reclaimed and downgraded for re-use on a branch line, siding or yard.
History
The earliest rails used on horse-drawn wagonways were wooden. In the 1760s strap-iron rails were introduced with thin strips of cast iron fixed on to the top of the wooden rails, increased their durability. Both wooden and strap-iron rails were relatively inexpensive, but could only carry a limited weight. The metal strips of strap-iron rails sometimes separated from the wooden base and speared into the floor of the carriages above, creating what was referred to as a "snake head". The long-term maintenance expense involved outweighed the initial savings in construction costs.
Cast-iron rails with vertical flanges were introduced by Benjamin Outram of B. Outram & Co. which later became the Butterley Company in Ripley. The wagons that ran on these plateway rails had a flat profile. Outram's partner William Jessop preferred the use of "edge rails" where the wheels were flanged and the rail heads were flat - this configuration proved superior to plateways. Jessop's (fishbellied) first edge rails were cast by the Butterley Company.
The earliest of these in general use were short, cast-iron fishbelly rails, named for their shape. Rails made from cast iron were brittle and broke easily. They could only be made in short lengths, which soon led to unevenness of the track. As rolling techniques improved, John Birkinshaw's 1820 patent introduced wrought iron in longer lengths, replaced cast iron, and contributed significantly to the explosive growth of railroads in the period 1825–40. The cross-section varied widely from one line to another, but were of three basic types, as shown in the diagram. The parallel cross-section which developed in later years was referred to as bullhead.
Meanwhile, in May 1831, the first flanged T rail (also called T-section) arrived in America from Britain and was laid into the Pennsylvania Railroad by Camden and Amboy Railroad. They were also used by Charles Vignoles in Britain.
The first steel rails were made in 1857 by Robert Forester Mushet, who laid them at Derby station in England. Steel is a much stronger material, which steadily replaced iron for use on railway rail and allowed much longer lengths of rails to be rolled.
The American Railway Engineering Association (AREA) and the American Society for Testing Materials (ASTM) specified carbon, manganese, silicon and phosphorus content for steel rails. Tensile strength increases with carbon content, while ductility decreases. AREA and ASTM specified 0.55 to 0.77 percent carbon in rail, 0.67 to 0.80 percent in rail weights from , and 0.69 to 0.82 percent for heavier rails. Manganese increases strength and resistance to abrasion. AREA and ASTM specified 0.6 to 0.9 percent manganese in 70 to 90 pound rail and 0.7 to 1 percent in heavier rails. Silicon is preferentially oxidised by oxygen and is added to reduce the formation of weakening metal oxides in the rail rolling and casting procedures. AREA and ASTM specified 0.1 to 0.23 percent silicon. Phosphorus and sulfur are impurities causing brittle rail with reduced impact-resistance. AREA and ASTM specified maximum phosphorus concentration of 0.04 percent.
The use of welded rather than jointed track began in around the 1940s and had become widespread by the 1960s.
Types
Strap rail
The earliest rails were simply lengths of timber. To resist wear, a thin iron strap was laid on top of the timber rail. This saved money as wood was cheaper than metal. The system had the flaw that every so often the passage of the wheels on the train would cause the strap to break away from the timber. The problem was first reported by Richard Trevithick in 1802. The use of strap rails in the United States (for instance on the Albany and Schenectady Railroad 1837) led to passengers being threatened by "snake-heads" when the straps curled up and penetrated the carriages.
T-rail T-rail was a development of strap rail which had a 'T' cross-section formed by widening the top of the strap into a head. This form of rail was generally short-lived, being phased out in America by 1855.
Plate rail
Plate rail was an early type of rail and had an 'L' cross-section in which the flange kept an unflanged wheel on the track. The flanged rail has seen a minor revival in the 1950s, as guide bars, with the Paris Métro (Rubber-tyred metro or French Métro sur pneus) and more recently as the Guided bus. In the Cambridgeshire Guided Busway the rail is a thick concrete beam with a lip to form the flange. The buses run on normal road wheels with side-mounted guidewheels to run against the flanges. Buses are steered normally when off the busway, analogous to the 18th-century wagons which could be manoeuvered around pitheads before joining the track for the longer haul.
Bridge rail
Bridge rail or box rail is a rail with an inverted-U profile. Its simple shape is easy to manufacture, and it was widely used before more sophisticated profiles became cheap enough to make in bulk. It was notably used on the Great Western Railway's gauge baulk road, designed by Isambard Kingdom Brunel.
Barlow rail
Barlow rail was invented by William Henry Barlow in 1849. It was designed to be laid straight onto the ballast, but the lack of sleepers (ties) meant that it was difficult to keep it in gauge.
Flanged T-rail Flanged T-rail or T-section rail is the name used in North America for flat-bottom rail. Colonel Robert L. Stevens, the president of the Camden and Amboy Railroad, considered that wrought-iron rail would be better than the iron-strapped wooden rails used on all United States railroads. No steel mills in North America were capable of rolling long lengths, so he sailed to the United Kingdom, which at the time was the only place where flanged T-rail could be rolled. In May 1831, the first 500 rails, each long and weighing , reached Philadelphia and were spiked on to crossties, marking the first use of the flanged T-rail in the United States. Flanged T-rail quickly became the standard pattern adopted by all US railroads.
Colonel Stevens also invented the hooked spike for attaching the rail to the crosstie. In 1860, the screw spike was introduced in France where it was widely used. Screw spikes are the most common form of spike in use worldwide in the 21st century.
Flat-bottom rail
Flat-bottom rail is the dominant rail profile in worldwide use.
Vignoles rail is a commonly used name for flat-bottom rail, after engineer Charles Vignoles who introduced it to Britain. Charles Vignoles observed that wear was occurring with wrought iron rails and cast iron chairs on stone blocks – the most common system at that time. In 1836 he recommended flat-bottom rail to the London and Croydon Railway, to which he was the consulting engineer. His original rail had a smaller cross-section than the Stevens rail, with a wider base than modern rail, fastened with screws through the base. Other lines that adopted it were the Hull and Selby, the Newcastle and North Shields, and the Manchester, Bolton and Bury Canal Navigation and Railway Company.
In the UK, when it became possible to preserve wooden sleepers with mercuric chloride (a process called Kyanising) and creosote, a much steadier, quieter ride resulted than with stone blocks. Rails were fastened directly to the sleepers using rail spikes. Their use, and Vignoles's name, spread worldwide. However, UK railway companies strongly preferred bullhead rail, fixed by wooden keys in cast-iron chairs, until the 1970s.
The joint where the ends of two rails are connected to each other is the weakest part of a rail line. The earliest iron rails were joined by a simple fishplate or bar of metal bolted through the web of the rail. Stronger methods of joining two rails together have been developed. When sufficient metal is put into the rail joint, the joint is almost as strong as the rest of the rail length. The noise generated by trains passing over the rail joints, described as "the clickity clack of the railroad track", can be eliminated by welding the rail sections together. Continuously welded rail has a uniform top profile even at the joints.
Double-headed rail
In late 1830s, Britain's railways used a range of different rail patterns. The London and Birmingham Railway, which had offered a prize for the best design, and was one of the earliest lines to use double-headed rail, where the head and foot of the rail had the same profile. These rails were supported by chairs fastened to the sleepers.
The advantage of double-headed rails was that, when the rail head became worn, they could be turned over and re-used. In 1835 Peter Barlow of the London and Birmingham Railway expressed concern that this would not be successful because the supporting chair would cause indentations in the lower surface of the rail, making it unsuitable as the running surface. Although the Great Northern Railway did experience this problem, double-headed rails were successfully used and turned by the London and South Western Railway, the North Eastern Railway, the London, Brighton and South Coast Railway and the South Eastern Railway. Double-headed rails continued in widespread use in Britain until the First World War.
Bullhead rail
Bullhead rail was developed from double-headed rail. The profile of the head of the rail is not the same as the foot. Because it does not have a symmetrical profile, it was not possible to reverse bullhead rail over and use the foot as the head. It was an expensive method of laying track as heavy cast iron chairs were needed to support the rail, which was secured in the chairs by wooden (later steel) wedges or "keys", which required regular attention.
Bullhead rail was the standard for the British railway system from the mid-19th until the mid-20th century. In 1954, bullhead rail was used on of new track and flat-bottom rail on . One of the first British Standards, BS 9, was for bullhead rail, which was originally published in 1905, and revised in 1924. Rails manufactured to the 1905 standard were referred to as "O.B.S." (Original), and those manufactured to the 1924 standard as "R.B.S." (Revised).