Preamble
This is a bit of a long one. I've come up with hopefully a convincing framework for adding a Blast Furnace to the game as well as Cast Iron as a new metal with many potential uses. This is a very comprehensive post which goes into detail on how the in game mechanics could work.
I will update this post as needed to tweak things based on feedback, if you have any ideas or suggestions let me know.
Blast Furnace
Rationale
The Blast Furnace serves as a late game upgrade to the crucible, allowing the player to make large batches of metal items, ingots, etc fairly quickly. The blast furnace also allows for the creation of Cast Iron and its associated items, which would be used for upgrading automation drive trains among other things. (more on this below).
It does not outright replace bloomeries however. You must still use bloomeries to create glass, as well as to make iron tools/plates/rods/armor etc as Cast Iron is not suitable for forging. Cast Iron plates, rods, etc can only be used for recipes that call for Cast Iron. Cast Iron and regular Iron are not interchangeable with one exception, Cast Iron Ingots can be used in place of regular iron ingots in a cementation furnace for steel, so it can help speed up steel production once you've reached the steel age.
Importantly, Steel is not required for Cast Iron production. Any level of Refractory bricks can be used to make the furnace, but Tier 3 is recommended. The very high heat of the furnace will damage the bricks of the furnace at a much higher rate than the cementation furnace. Tier 2 bricks will break more often, but will work well enough. Tier 1 bricks are not recommended.
In game concept:
New blocks & Items
Some new blocks and items would need to be added in order for the blast furnace to work as a concept.
They are as follows:
Refractory brick opening
A refractory block with an opening.
Used to allow air from bellows into the furnace as well as molten metal and slag to flow out of the furnace.
One for each Refractory block type.
Spill Chute
Used with Refractory brick openings to direct molten metal and slag out of the furnace.
The molten metal Spill chutes will pour only when there is a crucible directly underneath them. No threat of waste.
Using multiple crucibles for large smelts is recommended.
I've used fireclay here only for visibility. They would be made from Refractory bricks.
Crankshaft
Made from cast iron.
When attached to a bellows it allows mechanical power to automate pumping of the bellows.
Hopper w/ Flap
Serves as the interface for filling the furnace.
Referred to as Flap hopper and flapped hopper. can't think of a better name
Ore Charge block
A technical block used by the game to populate the furnace.
There should be one for each metal in the game.
When fully melted the molten slag and metal will automagic out the spill chutes.
Solidified metal
If you wait too long to pour the metal in the furnace it will solidify into blocks.
You will have to use a hammer and chisel to bust them up into bits and try again.
Molten slag
New kind of liquid that pours out of the blast furnace after each smelt.
If you do not have a spillway to catch the slag it will flow everywhere.
Can set fire to flammable objects and players.
Solidifies over time into slag blocks.
The amount of slag produced depends on how many charges are smelted. At the full 36 charges 18 slag blocks will be created (1 slag for every 2 charges).
Slag blocks
The solidified molten slag from the furnace
Mine with a pickaxe to get slag rocks.
Building the blast furnace
Layer 1-4
Layer 1
5x5 Refractory brick with 3x3 of any Raw Igneous Stone. (Hearthstone)
Layer 2
Increase wall height by 1 block.
Up to 3 Refractory openings in the front, with spill chutes attached. The finished melt will flow from here into placed crucibles.
Up to 3 Refractory openings on one side. These are the openings for the bellows to stoke the flames. More Bellows equals faster smelt times!
Layer 3
Increase wall height by 1 block
One Refractory opening in the back with spill chute attached.
This is for the slag to spill out from.
Layer 4
Increase wall height by 1 block.
Layer 5-8
Layer 5
Increase wall height by 1 block, ignore corners.
Layer 6
Increase wall height by 1 block. Fill in center leaving a one block opening.
Layer 7
Diagonal square shape with a one block opening in the center.
Put the Flap Hopper in the center.
Layer 8
3x3 Horseshoe shape with opening facing the back of the furnace.
Layer 9-12
Layer 9
Repeat layer 8.
Layer 10
One block on the front, 2x3 horseshoe shape with the opening facing the front.
Layer 11
Diagonal square shape with a one block opening in the center.
Layer 12
Repeat layer 11.
Filling the blast furnace
In order to smelt ore in the furnace you must fill it with “Charges”. This is done by interacting with the Flap Hopper in the charging arch. A "Charge" consists of Ore nuggets, Fuel, and, if smelting Iron ore, flux. The player can smelt ANY metal in the game except for steel in the blast furnace including alloys, so long as the alloy rations are correct. Flux (Lime or Powdered Borax) and Coke are specifically required for Cast Iron smelts. Any other ore or alloy can use Black Coal, Anthracite or Charcoal and doesn't require flux.
Each charge = 2 ingots of metal, or 40 ore nuggets.
Each Charge requires 4 fuel
Each charge when placed by the hopper is a full block.
A full blast furnace can smelt 2 x 9 x 4 or 72 ingots at a time.
Hopper w/ Flap
This is placed in the charging arch and is what the player uses to fill the furnace. The hopper has an inventory and a flap that remains shut until the charge recipe is entered correctly by the player. The player will have to place the charge materials into the inventory in a specific ratio. Once the ratio of fuel/flux/and ore are correct, the player can press a “Release!” button in the gui.
The hopper flap will open and populate the blast furnace with the appropriate amount of charge blocks automagically.
The minimum number of charges that can be smelted is 4.
Smaller smelts are better done on the firepit!
You can put more than one charge into the furnace at a time, as long as the ratios are correct!
Doesn't let the player overfill the furnace and will warn the player if they attempt to do so. Will also prevent the player from mixing multiple different kinds of charges in the furnace (ex. Tin Bronze and Iron charges)
When the player is done populating the furnace with charges they can light the furnace
Lighting the furnace
To light the furnace, use a torch through one of the bellows openings, targeting an ore charge block. The ore charge will light and then slowly light any nearby charges. Once lit, the furnace will begin to smelt the ore. The bellows will need to be pumped during the smelt either manually, or automatically using a crankshaft and mechanical power. If done manually, the player will have to pump the bellows for at least ¼ the total smelt time. This is cumulative and doesn't need to be continuous. The bellows GUI should let the player know when they have pumped enough. Making a crankshaft or two for your first smelt is recommended!
The speed of the smelt is determined by how many bellows are used to provide air to the furnace, as well as how many charges are in the furnace.
More bellows will decrease the smelt time.
More Charges will increase the smelt time.
These numbers can be tweaked for balance!
1 bellows w/ 12 charges (⅓ full): ~8 in-game hours.
2 bellows w/ 12 charges: ~4 in-game hours.
3 bellows w/ 12 charges: ~2 in-game hours.
A fully automated blast furnace will smelt rather quickly!
Once the furnace is finished smelting, molten slag will spill out of the rear chute and into your spillway and molten metal will spill out of the spill chutes into your placed crucibles. Fireclay Crucibles are recommended as molten iron is too hot for regular crucibles and will break them! You can then grab your crucibles with tongs as normal and begin pouring them into molds.
Cast Iron
Cast Iron is used for a variety of different applications in real life, from furniture to cookware to machine parts. For Vintage Story I feel the same breadth should be represented! You would be able to upgrade that old ceramic cooking pot with something a bit larger, as well and create mechanical components for use in mechanical power trains, and hopefully much more!
As previously mentioned Cast Iron requires Coke as the smelting fuel as well as a form of flux (lime or powdered borax) for each Charge.
For One Iron Charge:
This ratio can be tweaked for balance!
2x lime or 2x P. Borax
40 iron ore (2 ingots worth)
4 Coke
When smelting cast iron, the crucible you use to catch the molten iron must be a fireclay crucible. Regular crucibles won't cut it! They will break and you will lose your metal. Also keep in mind, If the molten iron solidifies in the crucible there is no way to melt it again! You will have to bust out the hammer and chisel and break your crucible to get the iron out.
Sand Casting
Unlike other metals Cast iron cannot use standard ceramic molds. Instead the player will need to create sand casting molds.
These molds have an associated durability. With the sandstone and olivine sand having around 15 durability, or 15 casts before the mold breaks, whereas the fireclay derived Chamotte molds have double that at 30 casts. These numbers may seem fairly low, but most molds will get used only a few times and the player will likely make many molds for bulk items anyway, so this seems about right.
In order to imprint the mold with the desired shape, the player must use a “Pattern Item”. These are items that will form the sand casting mold. Some Pattern items are made by the player by smithing specifically for use as mold patterns, but most are regular items you can make, find, or purchase.
Don't leave your sand molds out in the rain or they will break, even without any molten metal in them!
Minimum number of units that can be smelted by the furnace is 800, prepare your molds accordingly.
Mold making process
Cast Iron molds require sand casting and only certain "base sands" will work.
Sandstone sand (high in silica content)
Peridotite sand (in place of “olivine sand”)
“Chamotte sand” - Calcine fireclay in a firepit
Once you have your base sand you must mix it with a binder, water and clay, in a barrel. This will create casting sand (or chamotte casting sand)
To make a mold you need
A mold form. (crafted from boards and nails and strips.)
Casting Sand
A mold “Pattern Item”
Now you can make your mold.
Place the mold form on a solid surface.
Right click and add casting sand into the mold. 4 casting sand is required for one mold
Place in the appropriate “pattern item” to create the mold you want.
Wait a short while for the mold to set
Once the mold sets you can extract the pattern item with right click.
Your sand casting mold is now ready for use!
In real life it takes 2 halves to make a mold, but for simplicity and player convenience only one will be necessary.
Pattern Items:
These are Items used to form sand casting molds. There is no associated durability loss; you can use pattern items as many times as you want to make as many molds as you want. Smithed patterns can be placed on the ground for convenience.
[Pattern] -> [Mold the pattern makes]
Smithed on an anvil using any suitable metal
Cast Iron Pot Base Pattern -> Cast Iron Cooking Pot Base mold
Cast Iron Pot Lid Pattern -> Cast Iron Cooking Pot Lid mold
Cast Iron Pan Pattern -> Cast Iron Pan mold
Cast Iron Stove Door Pattern -> Cast Iron Stove Door mold
Cast Iron Stove Legs Pattern -> Cast Iron Stove Legs mold
Cast Iron Stove Body Pattern -> Cast Iron Stove Body mold
Crankshaft Pattern -> Crankshaft mold
Uses items as a pattern
Chandelier -> Cast Iron chandelier mold
Any Planter -> Cast Iron Planter mold
Any Pot -> Cast Iron Pot mold
Cast Iron Chair -> Cast Iron Chair mold
Cast Iron Table -> Cast Iron Table mold
Brazier -> Cast Iron Brazier mold
Rusty gear -> Small Cast Iron Gear mold
Large Rusty Gear -> Large Cast Iron Gear mold
Any Metal Plate -> Cast Iron Plate mold
Any Metal Rod x2 -> Cast Iron Rod mold
Wooden axle x2 -> Cast Iron axle mold
Flywheel -> Cast Iron Flywheel mold
Aged or Brass Torch Holder -> Cast Iron Torch Holder mold
Cauldron -> Cast Iron Cauldron
Iron Fence/Ornate Iron Fence -> Iron Fence/Ornate Iron Fence mold
Iron Fence Top/Ornate Iron Fence Top -> Iron Fence Top/Ornate Iron Fence Top mold
Candle Holder -> Candle Holder mold
Candelabra -> Candelabra mold
Cast Iron Post x2 -> Cast Iron Post mold
Any Metal Ingot x2 -> Cast Iron Ingot mold
Cast Iron Items
These are various ideas I've come up with for items that could be made using Cast Iron as a material.
If you have any other suggestions feel free to let me know!
Cookware
Cast Iron Cooking Pot
Made from multiple casted parts which are crafted together
Can cook 24 meal portions at once
Cannot cook non meal recipes
Cast Iron pot base (300 units)
Cast Iron Pot lid (100 units)
Too large for an Elk to carry!
Cast Iron Pan (200 units)
Can cook meat more quickly than just on a firepit, requiring less fuel and extracting more satiety (320 sat from “well cooked redmeat” instead of 280 for example)
Can be placed over a firepit or on a Cast Iron stove
Can be placed on your elk in the cooking pot slot
Could also be used to fry foods
Cast Iron Stove
Made from multiple casted parts which are crafted together
Cast Iron Stove Door (100 units)
Cast Iron Stove Body (500 units)
Cast Iron Stove Legs (200 units)
More efficient than the clay oven for baking. keeps heat longer and can hold more firewood.
Can also be used to cook with pots or pans on top!
Cast Iron furniture
Iron fence (and iron fence top) (200 units for 8 )
The vanilla iron fence
Iron fence gate
Crafted with iron fence sections and iron nails and strips
Ornate Iron fence (and top) (200 units for 8 )
An iron fence with a more ornate design
Purchased from trader or found in ruins
Cast Iron Chair (200 units)
Purchased from trader or found in ruins
Cast Iron Table (200 units)
Purchased from trader or found in ruins
Cast Iron Lantern
An ornate lantern crafted with Cast Iron plate and glass
Cast Iron Post (200 units for 2)
Purchased from trader or found in ruins
Great for placing your lanterns onto!
Cast Iron Planter (200 units)
Cast Iron Pot (100 units)
Candle Holder (100 units)
Purchased from trader or found in ruins
Holds one candle
Can be placed on floor or walls
Light level 11
Candelabra (300 units)
Purchased from trader or found in ruins
Holds 3 candles.
Can be placed on floor or walls
Light level 16
Cast Iron chandelier (800 units)
Holds 8 candles
Light level 24
Cast Iron Brazier (400 units)
Light level 16
Permanent light source
Must be filled with 4 firewood and lit manually
Cast Iron Torch Holder (200 units)
holds torches
Cast Iron Cauldron (400 units)
Good for making large batches of non meal recipes.
24 portions of non meal recipes
Can’t cook meal recipes.
Cast Iron Mechanical components
Given the recent rumors about a limit on torque or speed for wooden drive trains, the need for an upgrade that can handle high speed high stress mechanical power sources seems like a no brainer!
Small Cast Iron Gear (100 units)
Large Cast Iron Gear (600 units)
Cast Iron Axle (200 units for 2)
Cast Iron Flywheel (800 units)
Could be retrieved from story location 1 or found in ruins
Cast Iron Crankshaft. (200 units)
Used for crafting mechanisms and automating bellows and maybe other mechanical stuff!
Gearbox which can shift rotation speed up or down via lever
Requires Cast Iron components to craft
4 way gear junctions both vertical and horizontal
Requires Cast Iron components to craft
Metal Clutch, Brake, and Transmission
Requires Cast Iron components to craft
MISC Cast Iron Stuff
Cast Iron Ingot (200 units for 2)
Can’t be made into tools, etc, but can be used in a cementation furnace for steelmaking.
Cast Iron Plate (200 units)
used for crafting lanterns and mechanical components
Cast Iron Rod (200 units for 2)
used for crafting mechanical components