What BlueScope did with some of its old blast furnaces is perhaps the ultimate in recycling.
They pulled down furnaces 1-3, took out some of the metals and melted it down to make new steel.
That was the fate of the earlier blast furnaces, while Numbers 5 and 6 are still standing.
Only No5 is working, No6 having been shut down in 2011 when BlueScope exited the loss-making steel market.
Those obsessed with numerical order may wonder why it wasn’t No5 that was switched off – No5 had recently been relined, which gave it a longer life than No6.
The No5 furnace runs 24 hours a day, seven days a week because it’s too expensive to regularly turn off and on again.
The blast furnace structure is more than eight storeys high and includes three four storey-high silo-like stoves full of bricks.
One of these is heated up and then cold air is shot into it, which comes out hot and is used to get things happening in the blast furnace itself.
You don’t see much of what is happening in the furnace, which is fully enclosed.
Which is a smart thing to do, when you think about, because it’s making molten iron, which could eat through metal in seconds were it to escape.
That’s why the furnace’s insides are insulated, as is anything the iron touches on its way to the next stage in the steelmaking process.
You can think of the blast furnace as a giant bottle, where ingredients are constantly added to the top, and the finished product removed from the bottom by drilling and resealing a hole.
At the top of the furnace coke, iron ore and blended material called flux sits in two feeder bins.
These are poured into the furnace in alternating layers of ore and coke.
Twenty-eight jets called tuyeres shoot the heated air from the stoves into the furnace, which ignites the coke and starts the chemical process that makes molten iron.
The iron flows down to the bottom of the furnace. While the molten iron is running to the bottom, more raw materials are going in at the top in a never-ending loop
To get the iron out a hole is drilled in the side of the furnace, known as a taphole. There are three locations around the furnace where this happens, each of which also includes a trough, into which the molten iron flows.
After the iron has poured out, a “gun” shoots clay into the hole, which sets because of the heat of the furnace and seals things up.
The iron - which is around 1500 degrees, flows down the trough and into odd-looking insulated railway cars known as torpedo ladles.
The torpedo ladles then trundle along an internal rail line to the next stage, which some think is the most spectacular part of steelmaking.