Technology



Rolling stock
Railway rolling stock comes in a variety of forms. The most common types of passenger services railway rolling stock are described below.

Locomotives:
Examples of LocomotivesThe sole purpose of locomotives is to pull or push trains; they carry no passengers or freight. Locomotives are distinguished by the prime mover or energy source used to propel them. Modern locomotives are either electric or diesel-electric. Electric locomotives draw power from an overhead wire or third rail, and use electric motors to turn the wheels. The prime-mover is a transformer on the locomotive that converts the overhead electricity to the type of electricity needed in electric traction motors that turn the wheels. Instead of a transformer, diesel-electric locomotives use a diesel engine to drive an alternator and generate electricity that powers traction motors that turn the wheels.

Some diesel locomotives use a hydraulic torque converter rather than electric motors—these are referred to as diesel-hydraulic locomotives. Older generation steam locomotives, powered by coal, oil, or wood, are now used only in tourist operations or for occasional work on smaller railways or in museums.




Passenger rolling stock:
Examples of Passenger Rolling StockDescriptions of passenger rolling stock types can be found in . “Multiple-unit” passenger rolling stock is an important category, with two basic types—electric multiple-units, called EMUs and diesel multiple-units, called DMUs. The MU equipment has no locomotive; multiple cars can be connected and operated from a single location. Some multiple-unit cars have powered axles; the cars that do not are called ‘trailer’ cars. Typically, the first car has a driver’s station and accommodates passengers. Multiple unit (MU) equipment is popular for many reasons.

•   MU trains can respond to changes in demand levels because cars can be added to or dropped from a train.
•   MU trains can be driven from either end so two person crews can quickly prepare for return trip, making MUs popular for commuter services.
•   MU trains offer more passenger space per track length, since they operate without a locomotive.
•   MUs distributes traction power throughout the train, thus achieving higher power-to-weight ratios and greater acceleration rates.

The MUs’ flexibility and design characteristics are also ideal for high-speed train services because higher power levels are needed to overcome aerodynamic drag.

Some TGV and ICE trains are considered push-pull trains with power cars at each end, some with as much as 16,300 horsepower (12,200 kW). For example, the EuroStar train service has a configuration (1 power set, 18 trailer cars, 1 power set) with a total of 24,400 kW (32,600 hp) that can carry 794 passengers in bi-level coach configurations.

Freight wagons:
Examples of Freight Wagons Railway freight wagons come in a variety of designs aimed at accomplishing specific freight tasks most efficiently.

Box Wagons are commonly used for many commodities such as auto-parts, canned goods, bags of cement, and even loose grains. Some box wagons offer interior loading restraints (equipped boxes), a range of door types and sizes, insulation, refrigeration, and temperature control so goods will not overheat or freeze, and a range of grades-high-grade wagons are used to ship food or other products that must avoid contamination by other commodities.

‘Open-top’ Hopper Wagons can be loaded in many different ways and carry commodities that will not be damaged by exposure to weather such as aggregates, coal, and mineral ores. The name derives from the ‘hoppers’ at the bottom of the wagons that are opened to discharge contents easily and quickly.

Covered Hopper Wagons haul commodities such as grains, cement, sand, fertilizers, flour and sugar, or chemical or powdery materials that may be damaged by exposure to the elements. Some covered hopper wagons are ‘unload-assist’ and have vibrating sides or air injection systems to aid unloading. Covered hopper wagons are often categorized by size (cubic meters/feet) and larger wagons are used for lighter density commodities such as flour or grains; smaller wagons are used for high-density products such as cement and sand.

Gondola wagons have open tops but no bottom hoppers for unloading. Most gondolas are unloaded by a crane or bucket but some have drop floors; often they are unloaded using a rotary dumping device (see photo at left). High-sided gondolas are used for aggregates, coal, and other relatively low-density materials, including cement in 10-ton bags. Low-sided gondola wagons are used for heavier materials such as steel slabs, steel structural members, machinery, and other materials that can tolerate exposure to the weather.

Flat Wagons carry machinery, logs, plywood, containers, and road transport trailers. Many flat wagons include special features to extend their utility—for example, an automobile rack converts it to an automobile carrier; stakes added to the sides can contain pipes and lengths of raw timber; bulkheads can be added to transport logs, or lumber. Trucks, tanks, turbines, and other commodities are carried on flat wagons or modified flat wagons.

Tank Wagons carry liquids such as oil or oil products, chemicals, or consumables such as seed oils, milk, beer, or water. Some tank wagons carry gases in their liquid forms, such as liquefied petroleum gas or LPG, or pressurized fluids in a liquid/gaseous state, such as liquefied natural gas (LNG). Tank wagons are often specialized for the type of commodity they carry, for example, chemicals, oils, and oil products use a special tank lining, and milk or beer may be carried in a stainless steel tank. In many countries, tank wagons transporting hazardous materials are required to have safety features, such as shelf couplers that prevent wagons from detaching during a train derailment, or reinforced end shields that prevent couplers from puncturing the tank during derailment. In addition, pressurized tank wagons have pressure relief valves and special venting systems.

These basic freight wagons types have many variations; many railways collaborate with shippers and tailor freight wagons to specific needs.


Rolling stock components:
Examples of Rolling Stock Components Railway rolling stock includes some major common components. Most railway freight and passenger wagons sit on top of bogies (or ‘trucks’ in North America; see photo at left). Most bogies have two wheel sets so rollingstock can manouver around curves while supporting heavy loads. The two side frames contain two wheel sets (each wheel set is two wheels and a solid axle mounted together as one piece). Roller bearings are used between the axles and the side frames to permit the wheel sets to turn freely. Usually, wagons bodies are not fastened to the bogies but rest on and pivot around a center support. Generally, bogies on passenger rolling stock support a suspension system that isolates them from the wheels and infrastructure. Bogies also support the braking systems. Most passenger and freight rail cars use brakes operated by air pressure. Freight braking systems use air pressure to press brake pads to each wheel tread. Some passenger systems use the same type of braking system, but most high speed trains are equipped with disk brakes attached directly to wheelset axles in addition to tread brake systems.

Couplers are designed to allow railway cars to be joined together quickly and easily while draft gears provide the mechanism to transmit the longitudional forces that propel the train through the car body to the next car, without interfering with the workings of the bogies. Some couplers, like those shown at left, have top and bottom extensions (shelf couplers) to ensure that cars stay coupled even if one car leaves the tracks. Draft gear and coupler system strength determine the safe weight at which a train can operate on a railway. Many rail systems use buffer pads alongside coupler mechanisms to reduce ‘slack action’, the tendency of a group of wagons to elongate or contract when in motion.

    








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