For the first hundred years of so of railroad history, dry bulk items such as sand and cement were put into bags or boxes and loaded into boxcars for shipment. This required considerable labor to load and unload. In the 20th Century, a new type of car, the covered hopper, was developed. As the name impliles, these cars were essentially an open-top hopper with a roof and hatches for loading. At first, they were just used for special commodities such as carbon black, while more common items like cement were still hauled in boxcars. This began to change dramatically in the late 1940s and 1950s as the railroads and sh ippers ordered more and more covered hoppers. By the 1970s, almost all dry bulk items from sand to grain to plastic pellets were shipped in covered hoppers.
One of the important builders of covered hoppers was American Car and Foundry (ACF). The first ACF covered hopers were rib-side like almost all others. Then in the early 1960s, ACF began building cylindrical cars. These were in production for only a few years, when ACF changed the design to a rounded-side design without ribs, that they called the Center Flow?. The Center Flow? cars ranged from 2-bay 2970 cubic feet cars, through 3-bay 4600 cubic feet cars, to 4-bay 4700 cubic feet cars. The cars were built at several ACF plants, but the Huntington, West Virginia plant built only Center Flow? cars since their inception and was the primary builder.
The first 2-bay 100 ton 2970 Center Flow? cars built at Huntington were the 150 cars for Chicago & North Western, under building lot 11-02475, with an "on track" date of August 19, 1966. The largest batch was building lot 11-02493, 500 cars for Rock Island, on track May 8, 1967.

Era: 1960s to Present
? New tooling
? Razor-sharp printing and painting
? Weighted for optimal performance
? Fully assemble
? Etched metal roof walks
? Machined metal wheels
? Installed wire grab irons