Rail profile

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A Rail profile is a hot rolled steel profile of a specific shape or cross section (an asymmetrical I-beam).

Unlike some other uses of iron and steel, railway rails are subject to very high stresses and have to be 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 pose no problems in reinforcing rods for buildings, can, however, lead to broken rails and dangerous derailments when used on railway tracks.

By and large, the heavier the rails and the rest of the trackwork, the heavier and faster the trains these tracks can carry.

The rails represent a substantial fraction of the cost of a railway line. Only a small number of rail sizes are made by the steelworks at the one time, so a railway must choose the nearest suitable size. Worn, heavy rail from a mainline is often cascaded down to branchline, siding or yard use.

Rail sizes

Rails in Canada, the United Kingdom, and United States are still described using imperial units. However, in Australia they are now described in metric units and always have been on mainland Europe.

Depending on the use of imperial or metric units, rail sizes are usually expressed in terms of pounds per yard or kilograms per metre. Coincidentally, the pounds-per-yard figure is almost exactly double the kilograms-per-metre figure, making rough conversions easy.

Europe

Rails are made in a large number of different sizes. Some common European rail sizes include:

40 kg/m (81 lb/yd)
50 kg/m (101 lb/yd)

54 kg/m (109 lb/yd)
60 kg/m (121 lb/yd)

In the countries of former USSR 65 kg/m rails are common. Thermally hardened 75 kg/m rails also have been used on heavy-duty railroads like Baikal-Amur Mainline, but have proven themselves deficient in operation and were mainly rejected in favor of 65 kg/m rails.

North America

The American Society of Civil Engineers (or ASCE) specified rail profiles in 1893 for 5 pound increments from 40 to 100 pounds per yard. ASCE tee-rail profiles specified fixed proportions -- height of rail equaled width of foot and proportion of weight in head, web and foot were 42%, 21% and 37%, respectively. ASCE 90 pound profile was adequate; but heavier weights were less satisfactory. In 1909 the American Railway Association (or ARA) specified standard profiles for 10 pound increments from 60 to 100 pounds per yard. The American Railway Engineering Association (or AREA) specified standard profiles for 100, 110 and 120 pound rails in 1919, for 130 and 140 pound rails in 1920, and for 150 pound rails in 1924. The trend was to increase rail height/foot-width ratio and strengthen the web. Disadvantages of the narrower foot were overcome through use of tie-plates. AREA recommendations reduced the relative weight of rail head down to 36%, while alternative profiles reduced head weight to 33% in heavier weight rails. Attention was also focused on improved fillet radii to reduce stress concentration at the web junction with the head. AREA recommended the ARA 90 pound profile. Old ASCE rails of lighter weight remained in use, and satisfied the limited demand for light rail for a few decades. AREA merged into the American Railway Engineering and Maintenance-of-Way Association in 1997. By the mid-20th century, most rail production was medium heavy (112 to 119 pound) and heavy (127 to 140 pound.) Some common North American rail sizes include:

75 lb/yd (38 kg/m) (ASCE)
85 lb/yd (43 kg/m) (ASCE)
90 lb/yd (45 kg/m) (ARA)
100 lb/yd (50 kg/m) (AREA)
105 lb/yd (52 kg/m) New York Central Railroad
115 lb/yd (57 kg/m) (AREA)
119 lb/yd (59 kg/m) Colorado Fuel and Iron

127 lb/yd (63 kg/m) New York Central Railroad
132 lb/yd (65 kg/m) (AREA)
133 lb/yd (66 kg/m) (AREA)
136 lb/yd (67 kg/m) Colorado Fuel and Iron
140 lb/yd (69 kg/m) (AREA)
141 lb/yd (70 kg/m)
155 lb/yd (77 kg/m) Pennsylvania Railroad

Some common North American crane rail sizes include:

12 lb/yd (6 kg/m)
20 lb/yd (10 kg/m)
25 lb/yd (12 kg/m)
30 lb/yd (15 kg/m)
40 lb/yd (20 kg/m)

60 lb/yd (30 kg/m)
80 lb/yd (40 kg/m)
85 lb/yd (42 kg/m)
104 lb/yd (52 kg/m)

105 lb/yd (52 kg/m)
135 lb/yd (67 kg/m)
171 lb/yd (85 kg/m)
175 lb/yd (87 kg/m)

Australia

Some common Australian rail sizes include:

30 kg/m (60 lb/yd)
36 kg/m (73 lb/yd)
40 kg/m (81 lb/yd)
47 kg/m (95 lb/yd)

50 kg/m (101 lb/yd)
53 kg/m (107 lb/yd)
60 kg/m (121 lb/yd)
68 kg/m (137 lb/yd)

50 kg and 60 kg are the current standard, although some other sizes are still manufactured.
Some American sizes are used on northwest Western Australian iron ore railways.

History

Early rails were used on horse drawn wagonways. In the early days the rails were flanged (i.e 'L' shaped) with the wagon wheels being flat. Over time it was realised that flanged wheels with flat rails worked better.

Early rails were sometimes strap-iron rails, which consisted of thin strips of iron strapped onto wooden rails. These rails were too fragile to carry heavy loads, but because the initial construction cost was less, this method was sometimes used to quickly build an inexpensive rail line. Strap 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." However, the long-term expense involved in frequent maintenance outweighed any savings.

The earliest in general use were the so-called cast iron fishbelly rails from their shape. In time it became possible to roll longer lengths in wrought iron. 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.

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.

Early fishbelly metal rails made from cast iron were brittle and broke easily. They could only be made in short lengths which would soon become uneven. By 1840, wrought iron in longer lengths replaced cast iron as rolling techniques improved. The first steel rails were made in 1857 by Robert Forester Mushet, who laid them at Derby station in England. Steel was 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 rail, 0.67 to 0.80 percent in rail weights from 90 to 120 pounds, 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 improves steel by increasing density. 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.

References

External links

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Last updated on Saturday March 08, 2008 at 06:26:59 PST (GMT -0800)
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