Lewis Dartnell is an astrobiologist in England who wants to help you save the world after civilization collapses. To that end, he's written a book called The Knowledge: How to Rebuild Our World from Scratch. It's the one post-apocalyptic guide you'll ever need. We've got an excerpt.
In this chapter, Dartnell describes how we can regain our ability to work with metals — and why we'd want to. While writing this chapter, Dartnell learned to forge (that's him in the pictures above) just to be sure an ordinary person could actually do all this. Here's the excerpt.
Metals offer a suite of properties not provided by any other materials. Some are exceptionally hard and strong, making them ideal for tools, weapons, or structural components like nails or whole girders. But, unlike brittle ceramics, they also exhibit elasticity and plasticity—if stressed they flex rather than shatter and can be pulled into thin wire suitable for fastening, fencing or conducting electricity. Many metals can also resist very high temperatures, making them ideal for high-performance machinery.
What you ideally want to be able to re-attain as rapidly as possible after the Fall is not just the mastery of iron but its carbon alloy, steel. Steel contains a blend of iron and carbon atoms and is so much more than the sum of its parts. The inclusion of carbon changes the metal's properties substantially, and by varying the proportion of carbon soaked into the alloy recipe you can control the strength and hardness of the steel to suit different applications.
We'll see later how to create iron and steel from scratch, because in the immediate aftermath you'll be able to easily scavenge them. Salvaged items can be repurposed by relearning the traditional skills of the blacksmith: working by an open hearth, or forge, to keep the workpiece glowing hot as you reshape it between hammer and anvil. The reason that we've been able to exploit hard iron through the history of civilization is that it temporarily changes its physical properties when hot, softening to become malleable enough to be beaten into shape, rolled into sheets or drawn into pipes and wires. This is a fundamental point, because it means you can use iron tools to work on iron to produce more tools.
The crucial knowledge for fully exploiting iron for tools is the principle of hardening steel—quenching and tempering. Steel is hardened by heating it red-hot so that the internal structure of iron-carbon crystals converts to a particularly rigid conformation (which is non-magnetic, allowing a simple test during heating). If allowed to cool slowly afterwards, though, this crystal reverts back to its previous form and so you need to chill it rapidly to essentially freeze the desired structure: quenching the piece by dunking it sizzling into water or oil. However, a hard substance is also brittle—and a steel hammer, sword or spring that shatters is useless—so after quenching a piece needs to be tempered. You do this by reheating to a lower temperature for a period of time so that a proportion of the crystal structure relaxes—you are deliberately trading off some of the strength to return a little elasticity to the material. Tempering allows you to tune the combination of rigidity and elasticity of steel, a crucial ability for designing the appropriate metal for the intended task.
Another key technology, only more recently available, is welding: gluing metal together with molten metal. Acetylene yields the hottest flame of any fuel gas, reaching over 3,200°C when it is burned in a stream of oxygen. A welding torch can be created by separately controlling the pressurized flow of oxygen and acetylene gas through a lit nozzle. Pure oxygen can be produced by electrolysis of water or later in the reboot by distilling liquefied air. Acetylene is released by the reaction of water with lumps of calcium carbide, which is itself made by heating quicklime and charcoal (or coke) together in a furnace: substances that we have already covered. As well as being useful for metal joining, an oxyacetylene flame can also be wielded as a cutting torch for steel, a jet of oxygen combusting the hot metal out in a neat line.
An even higher temperature of around 6,000°C is generated by an electric arc welder: brandishing the power of lightning. Rigging up a row of batteries, or a generator, will produce enough of a voltage that a constant spark, or arc, will leap between the target metal and a carbon electrode to weld or cut as the electrode is drawn across the surface. Such jury-rigged oxyacetylene torches or arc cutters would be indispensable equipment for salvage crews sent into the dead cities to disassemble the ruins and scavenge the most valuable materials. One very effective way for melting down scrap steel for recycling is the electric arc furnace. It's essentially a giant arc welder: large carbon electrodes surge electricity through the metal to melt it, with limestone flux used to remove impurities as slag on top and the molten steel being poured as if from a kettle. Running an arc furnace from renewable electricity would be an important technology to try to leapfrog to in order to relieve demands on fuels for thermal energy in the post-apocalyptic world.
But retaining access to metals as a material is only half of the story: you'll also need to be able to adeptly work them into the forms you need. If you can't salvage any working versions of these essential machine tools how might you construct them from scratch?
An incredibly elegant example has been provided by a machinist in the 1980s who created a fully equipped metal-working shop—complete with lathe, metal shaper, drill press and milling machine—starting with little more than clay, sand, charcoal, and some lumps of scrap metal. Aluminum is a good choice as it has a low melting point for easy casting and is very corrosion-resistant so will be scavengeable even long after the apocalypse.
The heart of this phenomenal project is a small-scale foundry, consisting of a salvaged metal bucket fitted with a refractory inner lining of clay, and fired by charcoal intensified with a stream of air through the bucket side. This back-garden furnace is more than sufficient to melt the scavenged aluminum, and the molten metal can then be poured to cast a whole variety of machine components. Casting molds can be constructed from fine sand mixed with clay as a binder and a little water, packed around carved patterns in a two-part wooden frame.
The first machine to create is a lathe. A simple lathe is composed of a long, flat beam called the bed, with a headstock fixed at one end and a tailstock at the other that can be unlocked to slide left and right along the bed track. The workpiece is attached to the spindle on the headstock - perhaps by bolting to a faceplate, or gripped in a chuck with moveable jaws - and then the whole piece spun around this center, driven by a pulley or gear system from whatever motive force you've harnessed (waterwheel, steam engine or electric motor). The tailstock can be used to support the other end of the workpiece, sliding along the bed to accommodate different lengths, or else to bear a tool like a drill to bore through the center of the workpiece as it turns. A carriage also slides along the bed, mounted with a cutting tool on a cross slide so that it can be precisely positioned around the workpiece, shaving into it as it turns to create any desired profile. Astoundingly, not only is the lathe capable of duplicating all of its own components to create more lathes, but starting from absolute scratch you can even produce during the rudimentary stages of construction of your first lathe the remaining components needed to complete it.
In order to cut precisely spiraling threads on your workpiece you would want to fit a long lead screw alongside the bed to smoothly move the carriage, and ideally couple this with gears to the headstock spindle to perfectly co-ordinate their motion. In a post-apocalyptic world you would really hope to be able to scavenge a ready-made long threaded screw, as cutting a thread with a constant pitch is fiendishly difficult otherwise. In our history it took a long process of reiterative refinement to make the first precise metal screw thread, from which many others can then be constructed, and you would want to avoid having to repeat this.
Once you have a lathe you can use it to construct the parts of other, far more complex machine tools such as the milling machine. Whereas the lathe applies a tool to a rotating workpiece, the milling machine bears a rotating tool against the workpiece, and is exceedingly versatile –once you have a milling machine you can create pretty much anything else. So this demonstration is a microcosm of the history of technology itself: simple tools making more complex tools, including more precise versions of themselves, and repeating this cycle to ratchet upwards.
But what if you can't find any ready-purified metals for forging or casting, or you've already used all that was scavengeable. How do you get metal out of rocks in the first place? The general principle of smelting is to remove the oxygen, sulfur, or other elements the metal is compounded with in the ore. This requires a fuel to attain high temperatures, a reducing agent and a flux. Charcoal (or coke) performs admirably for the first two functions: it burns fiercely, and as it combusts in the smelter it releases carbon monoxide, a powerful reducing agent that strips the oxygen away to leave pure metal. The overall blueprint for a rudimentary iron-smelting furnace is similar to that of a kiln for burning lime. The furnace is charged with layers of charcoal fuel and the crumbled iron ore rock. Some limestone mixed in with the ore serves as a flux, lowering the melting point of the refractory gangue (the worthless rocky stuff) so that it turns fluid in the furnace, absorbing the impurities away from the metal. The flux forms a slag that is drained away, and your metallic prize can be extracted from the furnace.
Learn more on the official The Knowledge website.