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Train wheel

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Flanged railway wheel
Railway wheel flange (left)
Tram wheel flange (right)
Railroad car wheels are affixed to a straight axle, such that both wheels rotate in unison. This is called a wheelset.

A train wheel or rail wheel is a type of wheel specially designed for use on railway tracks. The wheel acts as a rolling component, typically pushed onto an axle and mounted directly on a railway carriage or locomotive, or indirectly on a bogie (in the UK), also called a truck (in North America). Wheels are initially cast or forged and then heat-treated to have a specific hardness.[1] New wheels are machined using a lathe to a standardized shape, called a profile, before being installed onto an axle. All wheel profiles are regularly checked to ensure proper interaction between the wheel and the rail. Incorrectly profiled wheels and worn wheels can increase rolling resistance, reduce energy efficiency and may even cause a derailment.[2]

Wheel geometry and flange

Train wheels have a flange on one side to keep the wheels, and hence the train, running on the rails when the limits of the geometry-based alignment are reached, e.g. due to some emergency or defect. See Hunting oscillation. Most train wheels have a conical geometry, serving as the primary means of keeping the train's motion aligned with the track while others have a cylindrical geometry such that the flanges are essential to keep the train on the rail track.[3]

Wheel arrangement

Main article: Wheel arrangement

The number of wheels per locomotive or car vary in both size and number to accommodate the needs of the railcar or locomotive. Regardless of these factors, pairs of identically sized wheels are always affixed to a straight axle as a singular unit, called a wheelset.[3]

Wheels for road-rail vehicles

The small rail wheels fitted to road-rail vehicles allow them to be stored away when the vehicle is in road-going mode.

Wheels used for road-rail vehicles are normally smaller than those found on other types of rolling stock (such as locomotives or carriages). This is because the wheel has to be stored clear of the ground when the vehicle is in road-going mode - Such wheels can be as small as 245 mm (9.65 in) in diameter. In Australia, wheels for road-rail vehicles should comply with the requirements of AS7514.4, which is the standard for infrastructure maintenance vehicle wheels.

Railway Wheel and Tire

Main article: Railway tire

Historically, a railroad wheel consisted of two main parts: the wheel itself, and the tire (or tyres in British English, Australian English and others) around the outside. The wheels of many rail vehicles, especially steam locomotives and older types of rolling stock, are fitted with these steel tires to provide a replaceable wearing element on a costly wheel. A rail tire was usually made from iron or steel, and is typically heated and pressed onto the wheel where it remains firmly as it shrinks and cools. Resilient rail wheels have a resilient material, such as rubber, between the wheel and tire.

Causes of damage

The most common cause of wheel damage is severe braking. This activity includes sudden braking, braking on steep gradients and braking with high weight loads. The brake shoes (or blocks) are applied directly to the wheel surface which generates immense amounts of thermal energy. Under severe braking conditions, the generated thermal energy can contribute to thermal shock or alteration of the wheel's mechanical properties. Ultimately, acute thermal loading leads to a phenomenon called spalling. Alternatively, severe braking or low adhesion may stop the rotation of the wheels while the vehicle is still moving, which may cause a flat spot on the wheel-rail interface and localized heat damage.

Modern railway wheels are manufactured reasonably thick to provide an allowance of wear material. Worn wheels or wheels with a flat spot are machined on a wheel lathe if there is sufficient thickness of material remaining.[4]

See also

References

  1. ^ "Wheel–Rail Interface Handbook | ScienceDirect". www.sciencedirect.com. Retrieved 2020-10-29.
  2. ^ Wheel-rail interface handbook. Lewis, R. (Roger), Olofsson, U. (Ulf). Boca Raton, FL: CRC Press. 2009. ISBN 978-1-61583-153-1. OCLC 500906475.{{cite book}}: CS1 maint: others (link)
  3. ^ a b "Book : The Contact Patch". the-contact-patch.com. Retrieved 2020-10-29.
  4. ^ Nielsen, J. (2009-01-01), Lewis, R.; Olofsson, U. (eds.), "8 - Out-of-round railway wheels", Wheel–Rail Interface Handbook, Woodhead Publishing, pp. 245–279, doi:10.1533/9781845696788.1.245, ISBN 978-1-84569-412-8, retrieved 2020-10-29

ISO 1005 Parts 1-9 BS 5892 Parts 1-6 AS7414.4

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