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The modern railroad rail has a flat bottom, and its cross section is much like an inverted T. An English engineer, Charles Vignoles, is credited with the invention of this design in the 1830s. A similar design also was developed by Robert L. Stevens, president of the Camden and Amboy Railroad in the United States.
Present-day rail is, in appearance, very similar to the early designs of Vignoles and Stevens. Actually, however, it is a highly refined product in terms of both engineering and metallurgy. Much study and research have produced designs that minimize internal stresses under the weight of traffic and thus prolong rail life. Sometimes the rail surface is hardened to reduce the wear of the rail under extremely heavy cars or on sharp curves. After they have been rolled at the steel mills, rails are allowed to cool slowly in special boxes. This controlled cooling minimizes internal shatter cracks, which at one time were a major cause of broken rails in track.
In Europe a standard rail length of 30 metres (98 feet 5 inches) is common. The weight of rail, for principal main-line use, is from about 55 kg per metre (about 110 pounds per yard) to 65 kg per metre (130 pounds per yard).
Railroads in the United States and Canada have used T-rails of hundreds of different cross sections. Many of these different sections are still in use, but there is a strong trend to standardizing on a few sections. Most new rail in North America weighs 57.5 or 66 kg per metre (115 or 132 pounds per yard). The standard American rail section has a length of 12 metres (39 feet). Some ore mining railroads in Western Australia employ rail weighing about 68 kg per metre (about 136 pounds per yard).
One of the most important developments is the welding of standard rails into long lengths. This continuous welded rail results in a smoother track that requires less maintenance. The rail is usually welded into lengths of between 290 and 400 metres (320 yards and one-quarter mile). Once laid in track, these quarter-mile lengths are often welded together in turn to form rails several miles long without a break.
Welded rail was tried for the first time in 1933 in the United States. It was not until the 1950s, however, that railroads turned to welded rail in earnest. Welded rail is now standard practice, or extensively used, on railroads throughout the industrialized world and is being adopted elsewhere to the extent that railroads’ finances allowed.
Controlling the temperature expansion of long welded rails proved not so difficult as first thought. It was found that the problem could be minimized by extensive anchorage of the rails to the sleepers or ties to prevent them from moving when the temperature changes, by the use of a heavy ballast section, and by heating the rails before laying to a temperature close to the mean temperature prevailing in the particular locality.
Rail fittings
Whether in standard or long welded lengths, rails are joined to each other and kept in alignment by fishplates or joint bars. The offset-head spike is the least expensive way of fastening the rails to wooden crossties, but several different types of screw spikes and clips are used. The rails may be attached directly to wooden crossties, but except on minor lines it is standard practice to seat the rail in a tie plate that distributes the load over a wider area of the tie. A screw or clip fitting must be used to attach rails to concrete ties. A pad of rubber or other resilient material is always used between the rail and a concrete tie.
Sleepers (crossties)
Timber has been used for railroad sleepers or ties almost from the beginning, and it is still the most common material for this purpose. The modern wood sleeper is treated with preservative chemical to improve its life. The cost of wood ties has risen steadily, creating interest in ties of other materials.
Steel ties have been used in certain European, African, and Asian countries. Concrete ties, usually reinforced with steel rods or wires, or ties consisting of concrete blocks joined by steel spacing bars are the popular alternative to wooden ties. A combination of concrete ties and long welded rails produces an exceptionally solid and smooth-riding form of track. Concrete ties have been standardized for the main lines of most European railroads and in Japan. Use of concrete elsewhere is increasing—although in North America, which has no European- or Asian-style high-speed rail and where hardwood for traditional crossties is cheap, there is no widespread use.