Yes, I dutifully searched prior to posting - couldn’t find this.
While stopped at a railroad crossing today I saw a number of cars go by with HOT and ASPHALT stenciled on the side (I’ve also seen MOLTEN SULFUR - gosh, I feel so comfortable with that rolling through my town… anyhoo…) Presumably, the tanks are filled with hot asphalt. Which got me to thinking…
How do they keep it hot?
Also presumably, there’s some sort of insulation involved here. But how effective? Are they only for short hauls or is it effective on cross-continental journies? Or do these tank cars have electric heaters of some sort to keep the cargo nice and toasty?
What happens if the stuff inside cools down and solidifies? Gosh, would hate to have to explain that to the boss… what do they do? Use pickaxes to dig it out?
How about they pour the stuff in hot and molten, then it cools and solidifies for the trip, then is heated by internal coils to remelt the solid for removal?
And the ones carrying tar for roofs too… My first summer job, I worked for the gas company, and I got to see several tar trucks up close. I call them hellburners.
When I was in high school, we toured the steel mills in Hamilton. There I saw rail tanker cars carrying molten steel (or possibly slag, I donèt remember). They looked normal in the bright sunlight, but as we passed their shaded side, we could see that they were glowing red-hot. The bus was at a distance but we could all feel the heat.
Assuming it stays hot/liquid the whole time (instead of hardening and being re-melted like Sigene suggests), it has to be a combination of insulation/heating element.
On the reverse side of the scale, I once took a tour of the Coors brewery in Colorado. One of the things that was pointed out to us was railroad cars used to haul freshly brewed beer from the brewery to their bottling plant in N. Carolina (?), about 1600 miles away. The two things I remember about those cars: 1) If you were to drink 6 12-oz beers a day, it would take you 40 years to empty a car; and 2) The beer only warms up 2 degrees F over the course of the 1600 mile journey, and there is no active cooling in any of the cars.
I’ve never seen self-heating railroad cars, but I have seen jacketed ones. There is essentially a second tank around the first with a small space inbetween. If the stuff inside has solidified, steam could be piped into the jacket.
I can’t remember if the jacket was pressure rated. If so, you could heat to 360 deg F (or whatever the jacket and steam system pressure would allow), and if not only to 212 F, which could take a long time to thaw something that melts at, say, 210.
This jacket, with its air surround, also acts as an insulator during the trip, so you might end up with a temp not much lower than when you started.