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Rail tracks are used on Railway s (or railroads), which, together with Railroad Switch es (or points), guide Trains without the need for steering. Tracks consist of two parallel Steel Rails , which are laid upon Sleepers (or cross ties) that are embedded in Ballast to form the Railroad track. The Rail is fastened to the ties with Rail Spike s, lag Screw s or clips such as Pandrol clips. The type of fastener depends partly on the type of sleeper, with spikes being used on wooden sleepers, and clips being used more on Concrete sleepers. Usually, a baseplate (or Fishplate , although a fishplate is also a bar used to join rails) is used between the rail and Wood en sleepers, to spread the load of the rail over a larger area of the sleeper. Sometimes spikes are driven through a hole in the baseplate to hold the rail, while at other times the baseplates are spiked or screwed to the sleeper and the rails clipped to the baseplate. Steel rails can carry heavier loads than any other material. Railroad ties spread the load from the rails over the ground and also serve to hold the rails a fixed distance apart (called the Gauge .) Rail tracks are normally laid on a bed of coarse stone chippings known as '' Ballast '', which combines resilience, some amount of flexibility, and good Drainage . Steel rails can also be laid onto a concrete slab (a slab track). Across bridges, track is often laid on ties across longitudinal Timber s or longitudinal Steel Girder s. Additional detail on tracks used for Tram and Light Rail operations, as opposed to Heavy Rail , is available at Tramway Track . RAILWAY RAIL See Also: Rail profile See also JOINTED TRACK There are different ways of joining rails together to form tracks. The traditional method was to bolt rails together in what is known as jointed track. In this form of track, lengths of rail, usually around 20 metres (60 feet) long, are laid and fixed to ''sleepers'' (UK) (''crossties'', or simply ''ties'' in North American parlance), and are joined to other lengths of rail with steel plates known as ''fishplates'' (UK) or ''joint bars'' (N.A.). Historically, North American railroads until the mid to late 20th Century used sections of rail that measured 39 feet (11.9 m) long so they could be carried to and from a worksite in conventional Gondola s, which often measured 40 feet (12.2 m) long; as car sizes increased, so did rail lengths. Fishplates or joint bars are usually 60 centimetres (2 feet) long, and are bolted through each side of the rail ends with bolts (usually four, but sometimes up to six.) Small gaps known as Expansion Joint s are deliberately left between the rails to allow for expansion of the rails in hot weather. The holes through which the fishplate bolts pass are oval to allow for expansion. British practice was always to have the rail joints on both rails adjacent to each other, while North American practice is to stagger them. Because of the small gaps left between the rails, when trains pass over jointed tracks, they make a "clickety clack" sound. Unless it is well maintained, jointed track doesn't have the ride quality of welded rail, and is unsuitable for High Speed Trains . A major problem is cracking around the bolt holes, which can lead to the rail head breaking. This was the cause of the Hither Green Rail Crash which caused British Railways to begin converting much of its track to Continuous Welded Rail. However, it is still used in many countries on lower speed lines and Siding s. Jointed track is still extensively used in poorer countries due to the lower construction cost and lack of modernisation of their railway systems. Insulated joints Where Track Circuit s exist for Signalling purposes, insulated block joints are required. These compound the weakness of ordinary block joints. Specially made glued joints, where all the gaps filled with Epoxy Resin increases the strength again. Audio Frequency track circuits such as those made by CSEE replace the conventional block joint with a tuned loop which uses say 20m of the rail as part of the blocking circuit. Axle Counter s can also reduce the number of track circuits and thus the number of insulated rail joints. CONTINUOUS WELDED RAIL Most modern railways use continuous welded rail (CWR); in this form of track, the rails are Welded together by utilising the Thermite reaction or flash butt welding to form one continuous rail that may be several kilometres long. Because there are few joints, this form of track is very strong, gives a smooth ride, and needs less maintenance. Welded track has become common on main lines since the 1950s. Because of the increased strength of welded track, trains can travel on it at higher speeds and with less friction. Welded rails are more expensive to lay than jointed tracks, but have much lower maintenance costs. Rails expand in hot weather and shrink in cold weather. Because welded track has very few expansion joints, if no special measures are taken it could become distorted in hot weather and cause a Derailment (a condition known in America as Sun Kink , referred in Britain as "buckling"). To avoid this, welded rails are very often laid on Concrete or steel Sleepers , which are so heavy they hold the rails firmly in place. After new segments of rail are laid, or defective rails replaced (welded in), the rails are artificially Stress ed. Great attention is paid to compacting the ballast effectively, particularly the shoulder over the ends of the sleepers, to prevent them from moving. Even so, in Extreme Weather , foot patrols monitor sections of track known to be problematic. The Stressing Process , involves either heating the rails causing them to expand,1 or stretching the rails with Hydraulic equipment. They are then fastened (clipped) to the sleepers in their expanded form. This process ensures that the rail will not expand much further in subsequent hot weather. In cold weather the rails try to contract, but because they are firmly fastened, cannot do so. In effect, stressed rails are a bit like a piece of stretched Elastic firmly fastened down. Engineers try to heat the rail to a temperature roughly midway between the average extremes of hot and cold (this is known as the 'rail neutral temperature'). If temperatures reach outside normal ranges however, welded rail can buckle in a hotter than usual summer or can actually break in a colder than anticipated winter. Joints are used in continuously welded rail when necessary; instead of a joint that passes straight across the rail, producing a loud noise and shock when the wheels pass over it, two sections of rail are sometimes cut at a steep angle and put together with a gap between them - a Breather Switch (referred to in Britain as an expansion joint). This gives a much smoother transition yet still provides some expansion room. METHODS OF FIXING RAIL TO SLEEPERS/TIES s which sit in chairs (not shown).]] There are several methods used to fasten rail to wooden sleepers / ties. The worldwide standard type of rail used today is ''flat-bottomed rail'' ( Vignoles Rail ), which has a flat base and can stand upright without support. A flat-bottomed rail has a cross-section like that of an upside-down 'T' and is usually held to the sleeper with a '' Baseplate '', a metal plate attached to the sleeper; although for lower cost construction FB rails can be laid directly onto the sleepers. Modern sleepers can be made of , a low voltage passed through the rails for signalling purposes. This is different from a "traction current," which powers electric trains. See also {Link without Title} A variety of different types of heavy-duty clips are used to fasten the rails to the underlying baseplate, one common one being the ''Pandrol'' fastener (Pandrol clip), named after its maker, which is shaped like a sturdy, stubby paperclip. [http://www.pandroluk.com/casestudies/prj31_bdy.htm and Another one is the Vossloh Tension Clamp.[http://www.vossloh-fastening-systems.de/fs_cms/en/index.html North American practice normally uses '' Rail Spike s'', which are very large nails with over hanging heads to clasp the flat-bottomed rail. These are cheaper and simpler to install but can loosen if the tie rots, much more easily than the British chair (a type of baseplate) does. This is mitigated by using very large and solid Creosoted ties or using another rot-proofing Preservative . See also Timber Treatment . ]] In traditional British practice, cast metal ''chairs'' were Screw ed to the sleepers, which took a style of rail known as ''bullhead'' that was somewhat figure-8 in cross-section — wider at top and bottom (known as the ''head'' and ''foot'' respectively) and smaller in the middle (the ''web''). ''Keys'' (wedges of wood or sprung steel) were then driven in between chair and rail to hold it in place. This was common practice on British railways until the 1950s, but is now largely obsolete. The idea behind ''bullhead'' rails was that because both the top and bottom of the rails were the same shape, when one side of the rail became worn, the rail could be turned over to the unused side, thus extending the rail's lifespan. However the bottom head turned out to get dented, rendering the original idea useless. Since the turnover requirement was no longer needed, ''bullhead'' rails came to have a flat base (narrower than flat-bottomed rail), and the top part has curved edges that fit the profile of the train wheels. In recent years, methods have been developed to put tracks on concrete without using conventional sleepers or track ballast. While this method's construction cost is high, this system is expected to have significantly lower maintenance cost than conventional tracks. It is mainly used on high-speed lines and in tunnels, where maintenance access is difficult. |
Image:Adelaide Darwin Railway Line Between
| "http://wwwinformationdelightinfo/information/entry/Adelaide_River" class="copylinks">Adelaide River and Pine Creek DSC03643jpgConcrete Sleepers |
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| "http://wwwinformationdelightinfo/information/entry/Roaring_Camp_and_Big_Trees_Narrow_Gauge_Railroad" class="copylinks">Roaring Camp And Big Trees Narrow Gauge Railroad trestle burned in 1976 showing damage to sleepers and rails |
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