For over a hundred years, heavy-duty flat cars have ridden on
more than four axles; but these cars have typically been built in very small numbers and have
not been very common. The most widespread use of 6-wheel trucks under freight cars took
place between 1912 and 1922 when the three major Pocahontas Region coal roads – Norfolk & Western, Virginian and Chesapeake & Ohio – purchased
over 5,000 of their so-called Battleship Gons with a nominal capacity of 100 tons, although the actual capacity varied from 90 to 115 tons. While a few of these cars survived into the 1960's, the construction of 6-axle freight cars has never been repeated on such a large scale.
At about the same time as the N&W was building its first production (i.e. not a prototype) 6-axle gondolas, the U.S. steel industry began buying 6-axle hot metal cars. This design, sometimes referred to as a bottle or torpedo car, was patented by John D. Pugh in 1915 and the first examples were built by the M.H Treadwell Co. of Easton, PA the next year. The first cars had a capacity of 80 tons, but the typical capacity of a 6-axle car is 125-150 tons. Standard hot metal cars have also built with four 4-axle trucks (200-250 tons) and four 6-axle trucks (300 tons). A few 150-ton cars were built with 10 axles instead of eight, having two 4-wheel and two 6-wheel trucks, to provide a lower axle load. About 500 cars have been built, most notably by Treadwell and by the William B. Pollock Co. of Youngstown, OH. They are still available from Reichard Industries of Columbus, OH; although 12-axle cars now use six 4-axle trucks instead of four 6-wheel trucks, just like some modern heavy-duty flat cars.
After the Battleship Gon Era, the next large purchase of 6-axle freight cars occured in 1952 and 1953 when the U.S. Army
bought 755 flat cars with a nominal capacity of 100 tons, and most of these remained in service
into the early 1990's. Between 1981
and 1992, the Department of Defense supplemented its heavy-duty flat car fleet with almost
600 new 6-axle 150-ton cars. DOD also has a small fleet of special-duty flat cars with six, eight,
or twelve axles.
What followed Big John was a significant increase in the size of many freight cars. Some cars didn't look much different, although they had a higher load limit; but many car types got bigger, and in some cases, a LOT bigger! Box cars which had been 40 or 50 feet long became 60, 70 and even 86 feet long. Other cars got bigger too, but in most cases their nominal capacity seldom exceeded 100 tons. During this time, the 125-ton 4-axle truck (7x12-inch journal
bearings) was introduced; but relatively few 125-ton cars were built.
Almost all of these big cars rode on 4-wheel trucks. The 819 RailWhales were the most notable exception; but after the first 8-axle tank car was completed in 1963, a few other 6- and 8-axle cars were built, mostly gondolas and open hoppers; but all of these were developmental dead-ends.
In September 1963, six months after the first RailWhale, a 146-ton, 6-axle hopper rolled out of the Norfolk & Western's Roanoke Shops. N&W 76950 rode on a pair of 6-wheel Buckeye trucks and was almost 70 feet long. It had a light weight of 101,300 pounds, a load limit of 293,200 pounds, and a volume of 5460 cubic feet. Unfortunately, the car had two drawbacks: its size was incompatible with
the railroad's rotary car dumpers at Norfolk; and its size only enabled it to haul 133 tons
of coal, 13 tons less than its capacity. It was retired and scrapped after five years.
In June 1964 Pullman-Standard constructed a 135-ton, 6-axle covered hopper for the
Atlantic Coast Line.
ACL 500000 made extensive use of stainless steel and rode on a pair of
6-wheel American Steel Foundries trucks. The car had a light weight of 93,500 pounds and a volume of 5,006 cubic feet. While its trucks gave it a theoretical load limit of 301,000 pounds, its official capacity was 271,500 pounds. Like N&W 76950, ACL 500000 was also a one-of-a-kind car; but it has fared much better than the N&W hopper and remained in service through the end of the 20th century. After being sold for scrap, the car was purchased by the North Carolina Department of Transportation and is on display at Rocky Mount.
In August 1965, aircraft builder Aeronca Manufacturing Co. of Middletown, Ohio built a 260-ton, 8-axle aluminum hopper car for the Southern Railway. Unlike typical 8-axle cars, this 103-foot car consisted of four permanently-connected 25-foot units, each riding on two axles. Southern 100 was loaded with inovations, including disk brakes, 7x12 bearings, and 38-inch wheels. The latter features gave the car a gross rail load of 630,000 pounds. It had a light weight of 96,000 pounds and load limit of 534,000 pounds, giving it a very impressive net-to-tare ratio with a volume of 9,000 cubic feet.
The Chesapeake & Ohio and Bethlehem Steel jointly developed a 120-ton, 6-axle hopper car. C&O 300011 consisted of two articulated parts and rode on three conventional 4-wheel trucks. Built in November 1968, the 56-foot car had a light weight of 65,200 pounds, a load limit of 243,300 pounds, and a volume of 4186 cubic feet.
The cars already mentioned in this section were one-off prototypes, but in 1970 Thrall built seventy-five 150-ton bathtub gondolas
for the Kansas City Southern. These 404000-series cars were built to form a unit train for service between a coal mine near Howe, Oklahoma and an export terminal at Port Arthur, Texas; but they spent most of their
lives hauling wood chips in Louisiana. The 70 remaining cars were sold to General American in 2005, right around their 35th birthday, and were renumbered GACX 914-983. All of the GACX cars had 4-wheel trucks and were retired by 2011.
BACK TO FOUR WHEELS
Four-wheel freight cars have been common in much of the world, and a couple of prototypes were built in the U.S. in the 1950's. Southern hopper 100 consisted of four 4-wheel sections; and after 1970, car designers briefly moved back in this direction.
Greenville developed its fully-enclosed 129-foot Auto Guard, a
tri-level automobile carrier which could hold 18 full-size autos.
Each Auto Guard consisted of three permanently-connected 40-foot units, each riding
on two axles; but only two were built – Southern Railway 599000 and 599001 – in September 1973.
The cars had a light weight of 84,600 pounds and an indicated load limit of 100,000 pounds.
They utilized truck components from hopper car 100, although these were refitted with 6½x12
bearings and 33-inch wheels. The 599001 was retired after an accident when it was only a
couple of years old, but the other remained in service for 20 years. Norfolk Southern retired
the 599000 in October 1993 and donated it to the Virginia Transportation Museum in Roanoke.
A decade after the Auto Guard was introduced, Trailer Train had a brief fling
with 2-axle cars for intermodal service. First came 101 TTFX 4-Runners in 1981, which consisted of four permanently-coupled 4-wheel platforms. These were followed two years later by the first TTOX (later TTUX) Front Runner stand-alone cars, and about 3,240 were built before production ended in 1989. By that time TTX, the carbuilders and the railroads had decided that articulated cars using conventional 4-wheel trucks could achieve almost the same weght savings as the 4-wheel cars, while offering better tracking and simpler maintenence.
AXLE and JOURNAL BEARING APPENDIX
How much weight a freight car can carry is detemined by several factors, such as the structural design of
the car and the design of the trucks, including wheel and bearing size, springs and the number of axles. Of course, the quality and
condition of the track can affect how much a car can carry too. Factors such as rail
size, cross tie spacing, and bridge design
strength figure into this; but even heavy rail can't
support much weight if it hasn't been properly maintained.
Most track can accomodate almost any load, if the weight is spread out over enough axles;
but this principle doesn't apply to bridges. A bridge is designed to accomodate a specific
maximun weight, referred to as its Cooper's Rating. The number of axles required
to support a specific load on a rail line are determined by the track's maximum axle loading.
The maximum axle loading permitted for unrestricted interchange in the United States is
currently 65,750 pounds, although there is a move on to raise this to 71,000 pounds, and
some cars are built for a maximum axle loading of 78,750 pounds. The heaviest 6-axle locomotives
have an axle loading of around 72,000 pounds, but some 4-axle units have a higher loading.
In 1920 the railroad industry adopted a standard system for identifying standard journal bearing sizes, and it is still used today. The nominal capacity is the gross weight for a 4-axle car minus the weight of a typical car, typically 50,000-65,000 pounds. Below is a list of standard bearing sizes up through 1970.
|MAXIMUM GROSS WEIGHT
||7 x 12
Most 4-axle cars built on or after 1 January 1995 with Type F bearings have a maximum gross weight
of 286,000 pounds, and some older cars have had their maximum gross weight increased from 263,000 to 286,000 pounds through the installation of new truck springs. The owners of these
older cars also had to submit engineering documentation to the Association of American Railroads which showed that these cars are structurally capable of handling the extra load. In 2002 the AAR adopted the Type K 6½x9 bearing for 286,000 pound cars.
|© 2003-2013 Michael M. Palmieri