Jul. 22, 2024
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Good quality track ballast is made of crushed stone. The sharp edges help the particles interlock with each other. Track ballast supports railway sleepers, which carry railway track.
Track ballast is the material which forms the trackbed upon which railroad ties (UK: sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the compression load of the railroad ties, rails, and rolling stock; to facilitate drainage; and keep down vegetation that can compromise the integrity of the combined track structure. Ballast also physically holds the track in place as the trains roll over it. Not all types of railway tracks use ballast.[2]
A variety of materials have been used as track ballast, including crushed stone, washed gravel, bank run (unwashed) gravel, torpedo gravel (a mixture of coarse sand and small gravel), slag, chats, coal cinders, sand,[3] and burnt clay.[4] The term "ballast" comes from a nautical term for the stones used to stabilize a ship.
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The appropriate thickness of a layer of track ballast depends on the size and spacing of the ties, the amount of traffic on the line, and various other factors. Track ballast should never be laid down less than 150 mm (6 inches) thick, and high-speed railway lines may require ballast up to 0.5 metres (20 inches) thick.[6] An insufficient depth of ballast causes overloading of the underlying soil, and in unfavourable conditions, overloading the soil causes the track to sink, usually unevenly. Ballast less than 300 mm (12 inches) thick can lead to vibrations that damage nearby structures. However, increasing the depth beyond 300 mm (12 inches) confers no extra benefit in reducing vibration.[8]
In turn, track ballast typically rests on a layer of sub-ballast, small crushed stones which provide a solid support for the top ballast and reduces ingress of water from the underlying ground. Sometimes an elastic mat is placed between the sub-ballast and ballast, significantly reducing vibration.[8]
It is essential for ballast to both cover the ties and form a substantial "shoulder" to restrain lateral movement of the track. This shoulder should be at least 150 mm (6 inches) wide, and may be as wide as 450 mm (18 inches).[10] Most railways use between 300 and 400 mm (12 and 16 inches).
Ballast must be irregularly shaped to work properly.Stones must be irregular, with sharp edges to ensure they properly interlock with each other and the ties to fully secure them against movement. Speed limits are often reduced for a period of time on sections of track where fresh ballast has been laid in order to allow it to properly settle.[11]
Ballast can only be cleaned so often before it is damaged beyond re-use. Ballast that is completely fouled can not be corrected by shoulder cleaning.[12] One method of "replacing" ballast is to simply dump fresh ballast on the track, jack the whole track on top of it, and then tamp it down. Alternatively, the ballast underneath the track can be removed with an undercutter, which does not require removing or lifting the track.[12]
The dump and jack method cannot be used through tunnels, under bridges, or where there are platforms. Where the track is laid over a swamp the ballast is likely to sink continuously, and needs to be "topped up" to maintain its line and level. After 150 years of topping up at Hexham, Australia, there appears to be 10 m (33 ft) of sunken ballast under the tracks.[14] Chat Moss in the United Kingdom is similar.[citation needed]
Regular inspection of the ballast shoulder is important. The shoulder acquires some amount of stability over time, being compacted by traffic, but maintenance tasks such as replacing ties, tamping, and ballast cleaning can upset that stability. After performing those tasks, it is necessary either for trains to run at reduced speed on the repaired sections, or to employ machinery to compact the shoulder again.[15]
If the trackbed becomes uneven, it is necessary to pack ballast underneath sunken ties to level the track again, which is usually done by a ballast tamping machine. A more recent, and probably better,[6] technique is to lift the rails and ties, and to force stones, smaller than the track ballast particles and all of the same size, into the gap. That has the advantage of not disturbing the well-compacted ballast on the trackbed, which tamping is likely to do. The technique is called pneumatic ballast injection (PBI), or, less formally, "stoneblowing". However, it is not as effective as fresh ballast, because the smaller stones tend to move down between the larger pieces of ballast and degrade its bonds.[19]
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The quantity of ballast used tends to vary with gauge, with the wider gauges tending to have wider formations, although one report states that for a given load and speed, narrowing the gauge only slightly reduces the quantity of earthwork and ballast needed. The depth of ballast also tends to vary with the density of rail traffic, as faster and heavier traffic requires greater stability. The quantity of ballast also tends to increase over the years as more and more ballast is piled onto an existing roadbed. Some figures from an report listing requirements for light railways (usually narrower than standard gauge) are:
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For more information, please visit Rail Shoulder.
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Feb 22,
This is an informational post, please check the rail components page if you are searching for the product.
Railway track components means the components for the railway track. As the necessary parts of rail track, railway components also called rail track parts. All railway track components play different roles in the railway track. Railway track components give the foundation of whole railway track system like steel rail and railway sleeper. Besides, rail components also ensure the railway safety by fixing rails and railway sleepers, such as railway fastening system, railway fish plate and fish bolt. As a manufacturer that is specialized in making rail products over 20 years, AGICO Rail sum a list of common railway track components, including steel rail, railway sleeper, turnout, rail fastening system and railway fish plate.
As the main part of railway track, steel rail always act as two parallel lines. In general, steel rail is used to provide a surface for train and guide the train forward. Steel rail also transmit the pressure from locomotive to railway sleepers. According to the kilos per meter, steel rail normally include light rail, heavy rail and crane rail. For different markets, steel rail can be classified into many standards, such as GB, UIC, DIN, ASTM, AREMA, As , BS11-, JIS E-93/JIS E-93, ISCR, ISCOR standard, etc.
Railway sleeper, also known as railroad tie, cross tie, is laid perpendicular to steel rail. Railway sleeper can be properly deformed to trimmer pressure when the train passes through, after that, cover as much as possible. By the raw materials, railway sleeper generally can be divided into three types: wooden sleeper, steel sleeper and concrete sleeper. The main function of railway sleeper as follow:
Railway fish plate, also called rail joint, splice bar or joint bar, is a metal bar that is used to the connect end of two rails by fish bolts. As the connection part between two rails, railway fish plate is used in combination with the steel rail. According to the steel rail standard, railway fish plate has three types:
According to the national standards, there are some typical rail joints that are applied to different markets, including American Australian, Canadian, DIN, BS, UIC, African standard, and so on.
Rail fastening system refers to a group of railway fasteners that are used to fasten steel rail to railway sleeper. Common components of rail fastening system include rail clip, railroad spike, rail bolt, rail tie plate, rail pad, washer, plastic dowel, rail insulator and rail shoulder, etc.
The main function of rail fastening system is preventing steel rail from lateral and horizontal movement. Besides that, rail fastening system also can absorb and transfer the pressure from locomotive to railway sleeper. In a word, rail fastening system ensures the rail in gauge and protects rail safety. Rail fastening system has a lot of types that is composed of different fasteners. Typical rail fastening system includes SKL, KPO, E-type, NABLA, and etc.
Railway switch is a special component of railway track, which is applied in the railway crossing. Railway switch has another name-turnout. Railway switch is simply a rail component for converting track. Railway switch increase the trafficability of railroad track, and it is important to transport safety and efficiency.
All these railway track components work together, which keep the railway safety and reliability. Besides, there are many other railway track parts do the same thing like them, such as rail anchor, rail clamp, etc. As a professional rail components manufacturer, AGICO Rail can custom any component parts of railway track with national standards. Free sample and fast shipping are available.
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