In todays Trains newswire one of the articles mentions the possible cause of a derailment as a broken sill. I am not familiar with that term. Is it part of the frog or what?
A sill is the main longitudinal structural member of the car, the underframe if you will.
Mac
Thank you PNWRMNM
Mac described the center sill, which is the main structural member. All of the energy used to move or stop a car is transmitted through this member. Attached to it are the bolsters that support the trucks and attached to its (the sill) ends are the coupler pockets and draft gear.
But there are more than one sill. With the possible exception of only tank cars, every car also has side sills which run down the sides of each car and support its walls (and doors if it is a box car). And there is the end sill which supports the end wall and may or may not also have an anti-climber to deflect any coupler bypass.
If the center sill had broken, probably (but not absolutely) that car would have been the one to derail because it probably (but not absolutely) would have come apart and collapsed onto the track where the break occurred.
So probably, since it was the car behind that went on the ground, it was either a side sill or an end sill that broke-- and I would think that the end sill would be the most likely culprit since, generally, part of its job is to hold up parts of the draft gear along with the center sill.