Train wheel

Source: Wikipedia, the free encyclopedia.
Not to be confused with Training wheels.
Railroad car wheels are fixed rigidly to their axle, ensuring both wheels of the wheelset rotate at the same rate

A train wheel or rail wheel is a type of

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] The International Union of Railways has defined a standard wheel diameter of 920 mm (36 in), although smaller sizes are used in some rapid transit railway systems and on ro-ro carriages.[3]

Wheel geometry and flange

See also: Derailment, Adhesion railway, and Hunting oscillation
A railway wheel's tread and flange and its relationship to the load-bearing rail

The running surface of most train wheels is conical, which serves as the primary means of keeping the train aligned with the

track while in motion. The wheels are fixed on an axle, and when rounding a curve the mass of the train pushes the wheelset towards the outside of the track. The outside wheel rides up to contact the rail at a larger diameter, while the inside wheel drops down to contact its rail at a smaller diameter. The difference between the distances travelled by each wheel for each rotation of the axle causes the wheelset to follow the curve of the track. [4]

Almost all train wheels have a projection, called a flange, on one side to keep the wheels, and hence the train, running on the rails when the limits or tests of alignment are reached: when a bend is taken at appropriate speed, when there are strong side-winds, and to withstand most common defects in trackbed, rail and mild debris. Some wheels do not have a conical profile and instead are cylindrical, such that the flanges are essential to keep the train on the track.

Wheel arrangement

Main article: Wheel arrangement

The number of wheels per locomotive or car varies 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.[4]

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
should comply with the requirements of AS7514.4, which is the Australian standard for infrastructure maintenance vehicle wheels.

Railway wheel and tire

Main article: Railway tire

Modern railway wheels are usually machined from a single casting, also known as monoblock wheels.

rubber, between the wheel and tire. Failure of such kind of wheel was one of the causes leading up to the Eschede high-speed train crash.[5]

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 normal operation, a wheel may obtain a tread temperature of 550 °C (1,022 °F).[6] 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.[7]

Guide wheel

Rubber-tyred metros with a central guide rail, such as the Busan Metro, Lille Metro and the Sapporo Municipal Subway as well as rubber-tyred trams have guide wheels.

Left: diagram of the Translohr guide rail (green) and the tram's guide wheels (red). Right: cross section of the guide rail and guide wheel of the Bombardier's GLT

See also

References

  1. ISBN 9781845694128
    . Retrieved 2020-10-29.
  2. OCLC 500906475
    .
  3. ISBN 978-0-203-84812-8
    .
  4. ^ a b "Book : The Contact Patch". the-contact-patch.com. Retrieved 2020-10-29.
  5. ^
    ISBN 978-0-08-049073-1
    .
  6. S2CID 135684020
    .
  7. ISBN 978-1-84569-412-8. Retrieved 2020-10-29. {{cite book}}: |work= ignored (help
    )

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

External links
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