Re: boxcar design evolution


soolinehistory <destorzek@...>
 

--- In STMFC@..., "Pieter_Roos" <pieter_roos@...> wrote:

OTOH, hoppers and gondolas, both composite and all steel, continued to use more specialized shapes in their framing. The early PRR single sheathed designs (R7 and X23) also used special pressed members, so USRA was clearly not the first.
But then again, the ARA reverted to standard mill shapes for the stakes in MOST of the ARA standard twin, triple, and quad hoppers.


The USRA single sheathed design would appear to have been a step forward in height, as the 1920's ARA standard called for scaling the IH back by 6 inches, with the original USRA size as an option.
There was a reasonable amount of resistance to the 9'-0" IH of the USRA cars as being "too big", wasteful since with most loads the cars would reach their load limit before they cubed out. Indeed, the ARA standard cars of 1923 reverted to the formerly common 8'-7" IH, although they retained the use of purpose designed pressings for posts and diagonals.

The same debate about mill shapes vs. pressings continued in the steel car era; cars built with structural shapes for posts tend to have a single line of rivets on the lap seam of the side sheets; those with double rows have pressed "hat" section posts. Meanwhile, coal hoppers swung back to using pressed posts in the exterior stake designs of the fifties. Ultimately, pressings won out... ALL the modern exterior post cars of recent years have pressed posts, although the fabricating techniques are vastly different from the cars of the teens. It did, however, take a good fifty years for the design features that make pressing superior to all come together. Contrast this with pressed steel ends, or roofs for that matter, which essentially replaced the earlier way of doing things in a brief five or ten years.

Dennis

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