I understand that unit trains are coupled all the time. Also I have read that they go through a rotary unloader to unload.Do they stop and start for each car or is it a continuos slow roll through. which ever method is used it must be time consuming to place each car just so.
Before I answer your question, I must clarify something. When you mention the term unit trains it is kind of an umbrella term that refers to a single train that can carry any commodity besides coal. There are unit trains of grain, ethanol, of course coal, and others.
Now, to answer your question when a coal unit train is dumped, the process is somewhat automated. The cars are parked along a positioner that moves the cars to be dumped.
http://www.youtube.com/watch?v=jd_StoBp6Sw
In regards to whether an entire train is broken up, as far as I know they are broken up, but someone may know of another instance where they unloaded without being uncoupled.
If you look at a typical unit coal train, note that one end of each wheeled bathtub is painted a contrasting color. The coupler on that end is a rotary coupler, and the cars can be rotated without being uncoupled as long as there is a rotary coupler at the end of the rotary dumper barrel. The coupler can be on the car in the barrel or the car standing on fixed ground - but one or the other has to have a rotary coupler.
If you use your favorite satellite viewing system to look at the loadouts at modern mines you will notice that they are usually located on reverse loops. Likewise, the destination facility will have its receiving track in the form of a loop. The entire train turns 180 degrees in the process of being converted from a loaded unit to an empty unit.
Chuck (Modeling Central Japan in September, 1964)
I have seen unit trains cut into blocks at older loadouts and during the unloading process where a loop wasn’t feasible or cost prohibitive.
A unit train is different from a train that happens to carry all the same commodity. As much as possible, unit train means the train is kept together as a unit - coal is picked up by the train at point A and taken to point B to be unloaded, then returned to point A for more coal. A 1950’s iron ore train going from the Mesabi Range to Duluth, Two Harbors, or Superior isn’t really a unit train, because it’s made up of cars from several different mines, and the cars will be broken down into different cuts to be unloaded - and some may even be interchanged with another railroad. It might look like a unit train, since it’s 100+ cars of the same railroad carrying the same thing, but it’s technically not a unit train.
Not true in every case – Tucson Electric’s tracks are dead-ended sidings. They have their own switcher to maneuver loaded cars from an inbound loaded track, through the rotary dumper, and then shove the empties onto the outbound track for later pickup. They break the inbound train into sections because their dumper’s track isn’t long enough for the entire train.
In Jeff Wilson’s book ‘Industries Along The Tracks’ che has a section on coal customers, which includes coal-fired power plants. In the article is a series of photos of the Tecumseh Energy Center (Topeka, Kan.), two photo’s of particular interest are of a covered hopper unloading spot, the second photo being the plants siding off the main with coal hoppers on and the caption mentioning unit trains of coal are left on the siding and brought to the unloading area in the plant 5 at a time by a 44-tonner industrial switcher.
Trains Magazine a while back had a special on the coal industry. It was a good issue and talked about how unit coal trains were unloaded. I can’t comment more than that because it’s been a while since I’ve read the article and can’t remember where I put it.
Not contradicting Stix on his description, a unit train technically is a train which is billed on a single waybill. So multiple cars are billed from the same origin to the same destination on the same single waybill. Since it is one shipment of one commodity from one origin to one destination on one waybill it tends to move together.
“units” can be as few as 10 cars, but mostly they have been in increments of 25 cars, up to 110, 115, 125, 150 cars.
A 1950’s coal train will individual cars billed on individual waybills. So even if they had 100 cars of coal from the same origin to the same destination it wouldn’t be a unit train because it wasn’t on the same waybill it would be on 100 different waybills.
Also remember unit trains gets a special shipping rate…
…and that’s why they didn’t show up until they did, there was no reason for them until the ICC allowed a discount rate for the unit.
There are 5 common methods for unloading unit coal trains:
- Rotary dump – either single car or tandem (two car). Both use an indexer to advance the train 1 or 2 cars at a time into position. The train is stopped while the car dumps. While many receivers equipped with rotary dumpers can accept an entire train without breaking the train apart for dumping, a substantial number must break the train into pieces for dumping. If you see a switch engine at the receiver, it’s a pretty good indication it’s breaking the train apart and needs the switch engine to move cuts of cars through the dumper. Rotary couplers enable one car to turn over while coupled to stationary cars to either side. Typically a single-car rotary dump has a maximum throughput of 4,000 tons per hour, and a tandem dump 6,000 tph. Rack-and-pinion indexers are very accurate regardless of temperature and there’s usually not much messing around with stopping the train with the car to be dumped in the right position. Cable indexers are not as accurate and there might be some back-and-forth to get the car into the correct location especially at the beginning or end of the train, or if there’s any gradient in the dumper track that the train wants to roll down, or be pulled up.
- Rapid-discharge. These are bottom-dump cars that are pulled through the dumper typically by the train’s road power. The hopper doors are electric-over-air controlled. A shoe on the side of the car contacts a rail to the side of the track (and about 5’ above ground level) that is electrified. Current flows from the rail through th