Continuous caster breakout

Catastrophic failure mode: skin breaks, fifty tons of molten steel dump out, machine down for weeks, millions in losses.

Yes, I'm going to show you that in a second. They didn't originally — they would just do rectangular bars or round bars, mostly rectangular bars because it's easier to bend them, or slabs, which would be up to a ten-inch-thick slab by eight feet wide. But they now roll I-beams. These are some of the details that go along inside this bath. They show the steel kind of wavy here, and it has a skin. If you have a breakout — breakouts are really exciting in a continuous caster, that means the skin broke and you dump about fifty tons of steel on the ground. So you don't want to be walking under one of these things, just in case. It will kill you. And it typically shuts the caster down for several weeks. You're talking a four- or five-hundred-million-dollar machine here, down for weeks. Millions of dollars of loss.

Running too fast breaks the solid skin and dumps 20-30 tons of steel on the floor; ~2 weeks shutdown plus $1-2M/day losses.

You have a ladle that brings the steel from the BOF, about 200 to 300 tons at a time. You drop it into a tundish, which is a holding tank. You have a stopper rod, you bottom-pour, and it comes in here. You have water-cooled copper molds — the blue stuff or purple, whatever the color, I'm colorblind. It forms the solidified skin against the copper, and it's still pliable enough that you can actually bend it, rather than cooling it straight down. Bring it down — you can see the red — it solidifies in the yellow, and you have a torch that comes along. You can cut through 10 inches of steel with that oxygen torch like butter, and you have a slab, and it goes off to storage. Liquid metal, solid metal, and slag. Continuous casters will run for two and a half years before needing to shut down, continuously, 24/7, 365 days a year. The only problem is if you have a breakout, where you try to run too fast and you break through the solid skin, and all of a sudden you dump 20 or 30 tons of steel on the floor — not a good day. About two weeks shut down to clean it up and get started again, and a million or two million dollars a day, you run into real losses. So lots of things people do to try to improve things. Any questions on basic steelmaking?

Breakouts happened once or twice a year in the '70s, take a week to clean up — 300–400 tons of molten steel hitting the shop floor, 25,000 tons of lost production, hundreds of millions to rebuild. Today rare due to process controls and IR sensors.

But then some people — again I think it was Austria — decided they could try continuous casting. Continuous casting had been done on lower temperature metals like brasses, copper alloys, and I told you they were doing it on gold alloys, which is not all that different than brass. In continuous casting, you have a ladle with molten metal that you melt somewhere else, and you pour it into something called the tundish, which is just a bathtub holding things, and it drops the metal into a mold. The mold is water-cooled copper, and you solidify a little skin on this. In this yellow band, you actually have molten metal, and the whole thing is pliable, and so you have these rolls. This whole thing stands about seven stories tall, with liquid metal in the center. If you get a breakout, it takes about a week to clean it up, because you've got three or four hundred tons of molten steel hitting the floor of this shop. They do have a stopper in the tundish, but even there you've still got this thing that can be ten feet wide and ten inches thick, and it's 50% liquid on average. If that skin breaks — and they did break, we'd have breakouts once or twice a year in the '70s when I worked at the steel company. They almost never have it today because they've got all kinds of process controls and infrared temperature sensors, and it's too expensive to have a breakout.