Locomotive Frame
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A locomotive frame is the structure that forms the backbone of the
railway Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...
locomotive A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...
, giving it strength and supporting the superstructure elements such as a cab,
boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, centra ...
or bodywork. The vast majority of locomotives have had a frame structure of some kind. The frame may in turn be supported by axles directly attached to it, or it may be mounted on bogies (known as trucks in
American English American English, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lang ...
), or a combination of the two. The bogies in turn will have frames of their own.


Types of frame

Preserved GWR 9017 showing outside frames Three main types of frame on steam locomotives may be distinguished:, p 255.


Plate frames

These used steel plates about thick. They were mainly used in Britain and continental Europe. On most locomotives, the frames would be situated within the driving wheels ("inside frames"), but some classes of an early steam locomotive and diesel shunters were constructed with "outside frames". Some early designs were double framed where the frame consisted of plates both inside and outside the driving wheels. Others were ''sandwich frames'' where the frame was constructed of wood sandwiched between two metal plates.


Bar frames

Bar frames of a WAGR U class locomotive These are openwork girder structures built up from steel or iron bars which are usually thick, welded into a single load-bearing assembly. They were first used on the
Bury Bar Frame locomotive The Bury Bar Frame locomotive was an early type of steam locomotive, developed at the Liverpool works of Edward Bury and Company, later named Bury, Curtis, and Kennedy in 1842. By the 1830s, the railway locomotive had evolved into three basic ...
during the 1830s, and were widely used in nineteenth century American locomotives (including those exported to Australia and New Zealand; see Vogel railways).


Cast steel beds

Cast steel Steel casting is a specialized form of casting involving various types of steel cast to either final/net or near-net shape. Steel castings are used when iron castings cannot deliver enough strength or shock resistance.Oberg, p. 1332 Examples ...
locomotive beds were developed in the latter years of steam locomotive design in the United States, from where they were also exported to Britain and Australia.


Articulated locomotives

An articulated locomotive with no fixed wheels (i.e. excluding the
Mallet locomotive A Mallet locomotive is a type of compound locomotive, compound articulated locomotive, articulated steam locomotive, invented by the Swiss engineer Anatole Mallet (1837–1919). The front of the locomotive is articulated on a bogie. The Compou ...
but including other articulated
steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...
s, as well as most diesel and
electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a Battery (electricity), battery or a supercapacitor. Locomotives with on-board fuelled prime mover (locomotive), ...
s) may have a separate frame beneath the superstructure, or the bodywork's internal structure may be load-bearing. Rarely is a true
monocoque Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French term for "single shell". First used for boats, ...
structure used. Diesel and electric locomotives with a traditional, full-width body, known as
cab unit In North American railroad terminology, a cab unit is a railroad locomotive with its own cab and controls. "Carbody unit" is a related term, which may be either a cabless booster unit controlled from a linked cab unit, or a cab unit that con ...
s in
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
, tend to have their strength in an internal structure. This style of construction is still popular elsewhere, but North American locomotives nowadays are overwhelmingly
hood unit A hood unit, in North American railroad terminology, is a body style for diesel and electric locomotives where the body is less than full-width for most of its length and walkways are on the outside. In contrast, a cab unit has a full-width ca ...
s—with a strong frame beneath the superstructure that carries all the load, and bodywork made of removable panels for easy maintenance. Fully enclosed locomotives are used in some limited applications, mostly for
passenger train A passenger train is a train used to transport people along a railroad line, as opposed to a freight train that carries goods. These trains may consist of unpowered passenger railroad cars (also known as coaches or carriages) push-pull train, ...
s. These tend to be
cowl unit A cowl is an item of clothing consisting of a long, hooded garment with wide sleeves, often worn by monks. It was developed during the Early Middle Ages. The term may have originally referred to the hooded portion of a cloak, though contemporar ...
s, in which the body is not load-bearing.


See also

*
Chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of a manufactured object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...
*
Steam locomotive components __NOTOC__ Main components found on a typical steam locomotive include: File:Diagram_of_steam_locomotive_components_(March_2021_version).tif, center, 800px, The main components of a typical steam locomotive. Click or hover over numbers to see nam ...
* Underframe * Rigid-framed electric locomotive


References

Frame, Locomotive {{Loco-stub