A ballast cleaner (also known as an undercutter, a shoulder ballast cleaning machine) is a machine that specialises in cleaning the railway track

ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, ...

(gravel, blue stone or other

aggregate Aggregate or aggregates may refer to: Computing and mathematics * collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...

) of impurities.

Background and development

Over time, ballast becomes worn, and loses its angularity, becoming rounded. This hinders the

tessellation A tessellation or tiling is the covering of a surface, often a plane, using one or more geometric shapes, called ''tiles'', with no overlaps and no gaps. In mathematics, tessellation can be generalized to higher dimensions and a variety of ge ...

of pieces of ballast with one another, and thus reduces its effectiveness. Fine pieces of granite, like sand, are also created by attrition, known simply as "fines". Combined with water in the ballast, these fines stick together, making the ballast like a lump of concrete. This hinders both track drainage and the flexibility of the ballast to constrain the track as it moves under traffic. Ballast cleaning removes this worn ballast, screens it and replaces the "dirty" worn ballast with fresh ballast.
The advantage of ballast cleaning is that it can be done by an on-track machine without removing the rail and

sleepers ''Sleepers'' is a 1996 American legal crime drama film written, produced, and directed by Barry Levinson, and based on Lorenzo Carcaterra's 1995 book of the same name. The film stars Kevin Bacon, Jason Patric, Brad Pitt, Robert De Niro, Dustin Ho ...

, and it is therefore cheaper than a total excavation. In the 19th century and early 20th century, ballast was shoveled or forked, then screened by hand using portable devices. Early automated cleaners used vacuum pressure built by a

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, oil or, rarely, wood) to heat water in the loco ...

to suck ballast up from the track to feed it into the sifting grates. Link-Belt produced a small machine that would clean the ballast between tracks on a multiple track line; it used a small gasoline engine and was small enough to be operated by a small crew of men, and it was built such that it would not need to be moved as trains passed on adjacent tracks. More fully automated ballast cleaners were developed in the early- to mid-20th century by several companies including

Speno Speno International SA is a manufacturer of railway track maintenance machines. The Speno company was founded by Frank Speno in 1960 and is now headquartered in Switzerland. It operates maintenance trains in many countries. The ''Speno'' trains ar ...

and

Pullman-Standard The Pullman Company, founded by George Pullman, was a manufacturer of railroad cars in the mid-to-late 19th century through the first half of the 20th century, during the boom of railroads in the United States. Through rapid late-19th century ...

; a version of Pullman-Standard's machine was demonstrated in 1949 that was estimated to save railroad companies about $1,000 per mile of track on their maintenance . As the century progressed, other manufacturers entered the market with their own versions.

Modern ballast cleaner operations

A cutter bar runs beneath sleeper level excavating all of the ballast under the sleepers to a specified, variable depth. A conveyor then moves the ballast into the cleaner, where it gets forced through a mesh by a shaking chamber. Pieces of ballast which are smaller than the mesh size fall through and are rejected, those that are bigger than the mesh are returned to the track along with fresh ballast. Some ballast cleaners have both ballast and spoil wagons attached to it, to which the materials are fed by a series of conveyor belts. Others simply undercut the ballast, and allow for a work train to come through to dump fresh ballast. This process can be done in short sections, meaning that track life can be considerably extended with the minimum of disruption.

References

External links

Grandad's Railway Section: Ballast Cleaners
Maintenance of way equipment {{Rail-transport-stub