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Rail profile

Cross sectional shape of a railway rail

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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 70-to-90-pound-per-yard (34.7 to 44.6 kg/m) rail, 0.67 to 0.80 percent in rail weights from 90 to 120 lb/yd (44.6 to 59.5 kg/m), 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.

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