Locomotive frame
Encyclopedia
A locomotive frame is the structure that forms the backbone of the railway locomotive
, giving it strength and supporting the superstructure elements such as a cab, boiler 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 (UK
) / trucks (US
), or a combination of the two. The bogies in turn will have frames of their own.
Three main types of frame on steam locomotives may be distinguished:
were constructed with outside frames.
Some early designs were Double framed where the frame conisted of both plates both inside and outside the driving wheels. Others were sandwich frames where the frame was constructed of wood sandwiched between two metal plates.
during the 1830s, and were widely used in the USA throughout the nineteenth century.
s were a development of the final years of steam locomotive design in the United States. They were also imported to Britain from the USA.
An articulated locomotive
with no fixed wheels (i.e. excluding the Mallet locomotive
but including other articulated steam locomotive
s, as well as most diesel
and electric 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
structure used.
Diesel and electric locomotives with a traditional, full-width body, known as cab unit
s in North America
, 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
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 trains. These tend to be cowl unit
s, in which the body is not load-bearing.
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
, giving it strength and supporting the superstructure elements such as a cab, boiler 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 (UK
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
) / trucks (US
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
), or a combination of the two. The bogies in turn will have frames of their own.
Types of frame
Plate frames
These used steel plates about 1-2" thick. They were mainly used in Britain and continental Europe. On most locomotives the frames would be situated within the driving wheels, but some classes of early steam locomotive and diesel shuntersSwitcher
A switcher or shunter is a small railroad locomotive intended not for moving trains over long distances but rather for assembling trains ready for a road locomotive to take over, disassembling a train that has been...
were constructed with outside frames.
Some early designs were Double framed where the frame conisted of both 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
These were made of two steel bars which are usually 4-7" thick. They were first used on the Bury Bar Frame locomotiveBury Bar Frame locomotive
The Bury Bar Frame locomotive was an early type of steam locomotive, developed at the works of Edward Bury and Company, later named Bury, Curtis, and Kennedy....
during the 1830s, and were widely used in the USA throughout the nineteenth century.
Cast steel beds
Cast steel bedLocomotive bed
A locomotive bed is a one-piece steel casting for a steam locomotive that consists of the locomotive frame, the cylinders and valve chests, steam pipes, and smokebox saddle, all as a single component. It was a development of the final years of steam locomotive design in the United States. Most...
s were a development of the final years of steam locomotive design in the United States. They were also imported to Britain from the USA.
Articulated locomotives
Main article Articulated locomotiveArticulated locomotive
Articulated locomotive usually means a steam locomotive with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves...
An articulated locomotive
Articulated locomotive
Articulated locomotive usually means a steam locomotive with one or more engine units which can move independent of the main frame. This is done to allow a longer locomotive to negotiate tighter curves...
with no fixed wheels (i.e. excluding the Mallet locomotive
Mallet locomotive
The Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet ....
but including other articulated steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
s, as well as most diesel
Diesel locomotive
A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...
and electric locomotive
Electric locomotive
An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage device...
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
Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...
structure used.
Diesel and electric locomotives with a traditional, full-width body, known as cab unit
Cab unit
A cab unit and a carbody unit are body styles of locomotives in railroad terminology. While closely related, they are not exactly the same....
s in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, 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
Hood unit
A hood unit, in railroad terminology, is a body style for diesel and electric locomotives. On a hood unit, the body of the locomotive is less than full-width for most of the locomotive's length, with walkways on the outside of the locomotive. In contrast, a cab unit has a full-width carbody for...
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 trains. These tend to be cowl unit
Cowl unit
A cowl unit is a body style of diesel locomotive. The terminology is a North American one, though similar locomotives exist elsewhere. A cowl unit is one with full-width enclosing bodywork, similar to the cab unit style of earlier locomotives, but unlike the cab unit style, the bodywork is merely...
s, in which the body is not load-bearing.