are a specialized type of rolling stock
Rolling stock comprises all the vehicles that move on a railway. It usually includes both powered and unpowered vehicles, for example locomotives, railroad cars, coaches and wagons...
designed for the transport of coils (i.e., rolls) of sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...
, particularly steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
. They are considered a subtype of the gondola
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...
car, though they bear little resemblance to a typical gondola.
Prior to the invention of this type, coils of sheet steel were carried on end or in cradles in open or covered gondolas. Load shifting, damage, and awkward loading and unloading were all problems with this type of loading, and since so much sheet steel is transported, a specialized car was designed for this use.
These cars started to appear in the 1960s. Early examples include the Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
G40 and G41 class cars, built in 1964-65.
The body of a coil car consists of a trough or series of troughs. Most commonly these run lengthwise, but there are transverse variants as well; in either case they may be lined with wood or other material to cushion the load. The coils are set on their sides in the trough, and stops may be applied across the trough to keep the coils from shifting.
The cars are equipped with hoods to cover the load. Some cars use a single hood, but more commonly a pair of hoods is provided. Each hood has a lifting point at its center, and often has brackets on the top at the corners in order to allow the hoods to be stacked when not in use. The hoods are largely interchangeable and it is common to see a car with mismatched hoods.