Editing Hopper car (section)

== History ==
[[File:6619.JPG|left|thumb|This covered hopper car originally was built in the 1950s for the [[Atlantic Coast Line Railroad]]. After the 1967 SCL merger, these cars were fitted with [[Rotary car dumper|rotary couplers]] and used in [[Bone Valley]] phosphate service.]]
The word "hopper", meaning a "container with a narrow opening at bottom", goes back to the thirteenth century,<ref>{{cite web |title=Hopper |url=http://www.etymonline.com/index.php?search=hopper |website=Online Etymology dictionary}}</ref> and is found in [[Chaucer]]'s story "[[The Reeve's Tale]]" (written late fourteenth century) in reference to a machine for grinding grain into [[flour]].

Historically, open hopper cars were used to carry coarse mined products like [[coal]], [[ore]], and [[gravel]], while [[Boxcar|boxcars]] were used for granular materials requiring protection from the elements.

Weatherproof covers were added to hopper cars, creating the covered hopper.  Early production emphasized two-bay cars very similar to open coal hoppers and suitable for materials of similar density, like [[Portland cement]] or [[rock-salt]]. Some cars were available in the 1910s, and became more common by the 1940s. These early cars were volume-limited for less dense commodities like grain or [[sugar]], so later designs include longer covered hopper cars with higher sides and three or more bottom bays.<ref name="abc">{{cite book |last1=Sweetland |first1=David R. |title=Northern New England Color Guide to Freight and Passenger Equipment |last2=Horsley |first2=Stephen |date=1994 |publisher=Morning Sun Books |location=Edison, New Jersey |pages=35, 36 & 51 |lccn=94075695 |oclc=32243319}}</ref> Increasing [[axle load]] limits have allowed some of the heavier loads formerly assigned to two-bay hoppers to be assigned to larger, more efficient three-bay hoppers.

Some covered hopper cars retain the conventional centersill as a strength member transmitting [[Compression (physics)|compression]] and [[Tension (physics)|tension]] [[Force|forces]] from one car to the next. Beginning in the 1960s, designs distributing these forces along the sides of the car eliminated the centersill beam to simplify [[bulk material handling]] with wider hopper openings reducing the tendency for bridging to restrict gravity flow when unloading the car.<ref>{{cite web |title=Centerflow Cars |url=http://www.americanrailcar.com/Manufacturing/CenterflowCars |access-date=24 June 2020 |publisher=American Railcar Industries, Inc.}}</ref>