Rotary car dumper - AbsoluteAstronomy.com

A rotary car dumper or wagon tippler (UK) is a mechanism used for unloading certain railroad car

Railroad car

A railroad car or railway vehicle , also known as a bogie in Indian English, is a vehicle on a rail transport system that is used for the carrying of cargo or passengers. Cars can be coupled together into a train and hauled by one or more locomotives...

s such as hopper car

Hopper car

A hopper car is a type of railroad freight car used to transport loose bulk commodities such as coal, ore, grain, track ballast, and the like. The name originated from the coke manufacturing industry which is part of the steel industry ....

s, gondolas

Gondola (rail)

In railroad terminology, a gondola is an open-top type of rolling stock that is used for carrying loose bulk materials. Because of its low side walls, gondolas are used to carry either very dense material, such as steel plates or coils, or bulky items such as prefabricated pieces of rail...

or lorries (tipplers, UK). It holds the rail car to a section of track and rotates the track and car together to dump out the contents. Used with gondola cars, it is making open hopper cars obsolete. Because hopper cars require sloped chutes in order to direct the contents to the bottom dump doors (hatches) for unloading, gondola cars allow cars to be shorter, thus lowering their center of gravity

Center of gravity

In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...

, while carrying the same gross rail load.

Overview

Originally, individual cars would be decoupled and placed in the dumper, but now it is possible to dump an entire unit train

Unit train

A unit train, also called a block train, is a railway train in which all the cars making it up are shipped from the same origin to the same destination, without being split up or stored en route...

of coal without uncoupling any of the cars. The cars used for these trains are equipped with AAR

Association of American Railroads

The Association of American Railroads is an industry trade group representing primarily the major freight railroads of North America . Amtrak and some regional commuter railroads are also members...

Type F rotary couplers on one end, with this end generally indicated with contrasting paint color. The dumper rotates

Rotation

A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

the cars on the axis of the couplers.
The cars must all oriented the same way, failure to do will result in a broken coupler when the dumper rotates.

Rotary dumping of cars provides a number of advantages and disadvantages:

Rotary dumping eliminates the need for maintaining the additional components of a traditional hopper car
Hopper car
A hopper car is a type of railroad freight car used to transport loose bulk commodities such as coal, ore, grain, track ballast, and the like. The name originated from the coke manufacturing industry which is part of the steel industry ....

, such as hopper doors and door locks.
- While Hopper cars may be used in rotary service, they are occasionally first converted into Bathtub Gons
Rotary dump installations are generally associated with faster train unloading times, although this time varies widely depending primarily on the ability of the system to remove product once dumped.
- A unit train of coal (perhaps 100 cars) can be unloaded in approximately two and a half hours using a rotary dumper.
- Some older rotary dumpers require that cars be separated, significantly reducing efficiency.
- Some newer rotary dumpers may be capable of dumping two cars at a time.
- Hopper cars bottom-dumped individually may take 2-3 minutes per car for freely-flowing product, not including thaw time.
- Hopper cars bottom-dumped over a trestle
  Trestle
  A trestle is a rigid frame used as a support, especially referring to a bridge composed of a number of short spans supported by such frames. In the context of trestle bridges, each supporting frame is generally referred to as a bent...
  
  may see the entire train emptied as quickly as 4 minutes
Loads that have gotten wet and/or frozen can still be unloaded quickly.
- A frozen load of coal in a "bottom dump" car has to be thawed out to be emptied.
- Since railroads charge demurrage
  Demurrage
  The term demurrage originated in vessel chartering and refers to the period when the charterer remains in possession of the vessel after the period normally allowed to load and unload cargo . By extension demurrage refers to the charges that the charterer pays to the shipowner for its extra use of...
  
  for holding cars beyond an arranged time period, a frozen load represents an unwanted expense.
- Most methods to thaw the car quickly in freezing weather present safety hazards, including setting the coal on fire.
- Thaw sheds may cause significant damage to the cars themselves, such as melting rubber air brake components and burning paint.
Unfortunately, poorly designed or poorly maintained rotary dumpers can significantly reduce the serviceable life of a car.
- Most rotary dumpers do not provide a full bearing surface on the side of the car, resulting in bent side stakes.
- Rotary dumpers set too far from the side of the car results in a shock load when the car is rotated, particularly when the product is frozen together.

Alternatives

Alternatives to the rotary dump cars are bottom dump cars with bottom doors, and back end hoes which unload gondola cars. The former has the disadvantage that any imperfection in the seals of the doors allows material to spill onto the track.

Overview

Alternatives

See also