More manual

Added sections on the technic-specific kinds of item processing, and on
generic metal mechanics, and the specific trickery around iron (merging
in notes_on_iron).

1 files changed, 0 insertions, 68 deletions

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-Notes on iron and steel
-=======================
-
-Alloying iron with carbon is of huge importance, but in some processes
-the alloying is an implicit side effect rather than the product of
-explicit mixing, so it is a complex area.  In the real world, there is
-a huge variety of kinds of iron and steel, differing in the proportion
-of carbon included and in other elements added to the mix.
-
-The Minetest default mod doesn't distinguish between types of iron and
-steel at all.  This mod introduces multiple types in order to get a bit
-of complexity and flavour.
-
-Leaving aside explicit addition of other elements, the iron/carbon
-spectrum is here represented by three substances: wrought iron,
-carbon steel, and cast iron.  Wrought iron has low carbon content
-(less than 0.25%), resists shattering, and is easily welded, but is
-relatively soft and susceptible to rusting.  It was used for rails,
-gates, chains, wire, pipes, fasteners, and other purposes.  Cast iron
-has high carbon content (2.1% to 4%), is especially hard, and resists
-corrosion, but is relatively brittle, and difficult to work.  It was used
-to build large structures such as bridges, and for cannons, cookware,
-and engine cylinders.  Carbon steel has medium carbon content (0.25%
-to 2.1%), and intermediate properties: moderately hard and also tough,
-somewhat resistant to corrosion.  It is now used for most of the purposes
-previously satisfied by wrought iron and many of those of cast iron,
-but has historically been especially important for its use in swords,
-armour, skyscrapers, large bridges, and machines.
-
-Historically, the first form of iron to be refined was wrought iron,
-produced from ore by a low-temperature furnace process in which the
-ore/iron remains solid and impurities (slag) are progressively removed.
-Cast iron, by contrast, was produced somewhat later by a high-temperature
-process in a blast furnace, in which the metal is melted, and carbon is
-unavoidably incorporated from the furnace's fuel.  (In fact, it's done
-in two stages, first producing pig iron from ore, and then remelting the
-pig iron to cast as cast iron.)  Carbon steel requires a more advanced
-process, in which molten pig iron is processed to remove the carbon,
-and then a controlled amount of carbon is explicitly mixed back in.
-Other processes are possible to refine iron ore and to adjust its
-carbon content.
-
-Unfortunately, Minetest doesn't let us readily distinguish between
-low-temperature and high-temperature processes: in the default game, the
-same furnace is used both to cook food (low temperature) and to cast metal
-ingots (varying high temperatures).  So we can't sensibly have wrought
-iron and cast iron produced by different types of furnace.  Nor can
-furnace recipes discriminate by which kind of fuel is used (and thus
-by the availability of carbon).  The alloy furnace allows for explicit
-alloying, which appropriately represents how carbon steel is made, but
-is not sensible for the other two, and is a relatively advanced process.
-About the only option to make a second iron-processing furnace process
-readily available is to cook multiple times; happily, this bears a slight
-resemblance to the real process with pig iron as an intermediate product.
-
-The default mod's refined iron, which it calls "steel", is identified
-with this mod's wrought iron.  Cooking an iron lump (representing ore)
-initially produces wrought iron; the cooking process here represents a
-low-temperature bloomery process.  Cooking wrought iron then produces
-cast iron; this time the cooking process represents a blast furnace.
-Alloy cooking wrought iron with coal dust (carbon) produces carbon steel;
-this represents the explicit mixing stage of carbon steel production.
-Additionally, alloy cooking carbon steel with coal dust produces cast
-iron, which is logical but not very useful.  Furthermore, to make it
-possible to turn any of the forms of iron into any other, cooking carbon
-steel or cast iron produces wrought iron, in an abbreviated form of the
-bloomery process.  As usual for metals, the same cooking and alloying
-processes can be performed in parallel forms on ingots or dust.