The Bessemer process

The Bessemer converter turns molten pig iron into steel by blowing air through it. Nothing is burned: the carbon and silicon already in the pig are the fuel, and oxidising them is what keeps the bath hot. Carbon falls steadily while the blast is on, so the product depends entirely on when the blow is stopped. Stop at the target and the charge is Bessemer steel; blow past it and the same metal turns into soft iron.

The machine

Four blocks work together. The Bessemer Control is the anchor and the lever; the Bessemer Transmission sits directly under it and takes the axle; the Bessemer Converter vessel stands two blocks in front of the control; the Bessemer Gas Intake sits two blocks beyond the vessel and takes the blast. A molten canal tap feeds the vessel from the side, and a molten canal start takes the pour away below it.

The intake and the transmission must face the same way as the control. The multiblock accepts any orientation, so a misaligned one completes the structure and then refuses to run, with the reason on the readout.

The full operational readout is on the vessel, not on the control. Looking at the control shows only whether the axle is turning.

How it works

What it needs to run

Requirement	Value
Blast	8 L/s of air at 2.5 atm or more, drawn through the gas intake
Mechanical power, to tilt	any geared speed above 0.1 on the transmission
Vessel capacity	4800 units of metal, scrap included

Air below 2.5 atm is not blast, and the blow pauses without it. The gas intake is a machine port, not a length of pipe: the network has to be in the cell against its face, so a pipe segment goes between the blower and the intake. Blast pressure out of an Air Blower is the engine's inlet steam pressure times 0.75, so keep the engine's steam above 3.4 atm or the blast falls under the gate partway through a blow. A twin-tub blower cannot reach it at all.

The blow

Carbon starts at 4.0 % in fresh pig, and every litre of blast that reaches the bath burns 0.000016 of it away. At the full 8 L/s that is 0.0128 percentage points a second.

Carbon	What the bath is	Time at full blast
4.0 %	molten pig iron	the start
0.2 %	Bessemer steel	about 5 minutes in
0.05 %	soft iron (the vanilla iron ingot)	about 12 seconds later

That last row is the whole skill of the process. The blow does not stop itself at the target. At 0.20 % the status flips from Blowing... carbon X to Over-blowing past steel... carbon X and the bath keeps decarburising, so that flip is the signal to move: about twelve seconds separate it from soft iron. The Bessemer steel ready line is printed only on a tick where no blast arrives, so a running blow never shows it.

Heat

The bath holds whatever the heat balance says, recomputed every second:

T_process = T_in - T_loss
T_in      = 1250 C + 600 C x the fraction of the demanded blast that arrived
T_loss    = 50 C + 0.35 C per unit of cold scrap in the vessel

At full blast with no scrap that is 1800 C. Refining needs 1500 C, the steel liquidus. Below it the blow stalls and the bath cools toward freezing. Nothing else heats the converter; there is no fuel and no burner.

Cold scrap

Steel bits, or anything else carrying the scrap role, can be charged by right-clicking the control while holding them. Each bit is 5 units of mass and 97 % of it becomes steel when the heat reaches the carbon target. Scrap is pure cold mass: it is not refined, it only loads T_loss.

There is no scrap cap. The limit is arithmetic: at 0.35 C per unit, about 860 units of scrap, some 170 bits, drags a full-blast bath under the 1500 C floor and stalls the blow. More freezes it. Scrap goes into an empty vessel or into raw pig, never into a finished heat.

What comes out

Per 100 units of pig charged: 90 units of steel, 6 units of molten slag, 4 units gone as gas. Slag accumulates in its own pool during the blow and floats on the steel, which is why it is poured first.

The vessel pours at 44 units a second, so a full 4800-unit heat takes about 110 seconds to drain. The bath cools at half the usual molten-metal rate, which is what leaves time to skim, pour and work the canal valves.

Slag from the converter is the same slag the furnaces make. Ground to powder, 8 of it with 1 litre of slaked lime in a barrel makes 4 mortar.

Running a heat

1. Build the structure, spawn the vessel by right-clicking the control with one large gear and eight iron or steel rods in the hotbar, then raise the vessel through its seven build stages. The Bessemer converter page carries the figure, the materials and the stage list.
2. Connect the axle to the transmission and start it turning.
3. Connect the blast main to the gas intake through a pipe, and get it above 2.5 atm before starting.
4. Charge cold scrap now if any is wanted, by right-clicking the control holding steel bits.
5. Sneak and right-click the control to tilt the vessel to filling, and open the molten canal tap. The vessel takes pig from the tap cell until it is full or the tap runs dry.
6. Right-click the control with no modifier to bring the vessel upright. The blow starts by itself and the readout counts the carbon down.
7. Watch the carbon count. At 0.20 % the line flips from Blowing... to Over-blowing past steel..., and that flip is the signal; the Bessemer steel ready line appears only once the blast has stopped. Sprint and right-click at once: the first tilt skims the slag off the top.
8. When the slag pool reads empty, sprint and right-click again and hold for a second. The vessel tilts further and pours the steel into the output canal.

What goes wrong

The pressure drops the moment the blow starts. The converter draws 8 L/s of air. If the blast main sits just over 2.5 atm the draw pulls it under and the blow pauses. Raise the engine's steam pressure rather than the blower count: the blower's ceiling is the steam pressure times 0.75.

No blast at all. The gas intake is not a network block. There must be a pipe segment between the blower and the intake, presenting a connector back at the intake's face.

"No mechanical power." The transmission under the control is not turning, or is not aligned with the control. Both the intake and the transmission have to carry the same facing as the control.

The status says misaligned. Same cause; break the offending block and place it facing the same way as the control.

The axle stopped mid-blow. Power is the lever, not the blast: the blow carries on, over-blows to soft iron and then freezes, while the vessel cannot be tilted or poured. Get the axle turning again before anything else.

Over-blown to soft iron. The blow ran twelve seconds too long. The heat is not wasted, it is just plain iron now; pour it and start again sooner.

"Foreign metal! Pour it out." Something other than pig, Bessemer steel or iron is in the vessel. Only pig blows. Pour it out and refill from a pig tap.

The bath will not refine. Too much cold scrap. The readout names the heat loss and the 1500 C floor. A stall from cold scrap does not clear itself: below 1500 C the bath stops refining, so the carbon never reaches the target that would melt the scrap in, and the heat only cools further. Pour it out and charge less next time. A stall from weak blast is the other message, Blow paused! Needs air, and that one clears when the pressure comes back.

The pour does nothing. There is no molten canal at the output cell, or the canal is full or already carrying the other medium. Slag and steel go through the same cell, so the slag has to be drained clear before the steel follows.

Solidified residue. A charge left to freeze latches. Under a fifth of capacity, about 960 units, and once it has hardened, it chisels out of the upper hatch and the metal comes back whole. At or above that, only breaking the vessel clears it, and breaking loses up to 10 units.