Metals are chemical elements that are placed in the left hand side of the periodic table of the elements. Their main common characteristic is that they loose electrons easily to form ions. In a piece of metal, the ions are surrounded by an electronic cloud, the electrons that form the cloud are free to move through the metal. The cloud of electrons balances the electrostatic repulsion between adjacent ions and binds them together forming metallic bonds.
According to this description metals have the following general properties: malleability, ductility, thermal and electrical conductivity, opacity, and luster. Some have also good mechanical strength, hardness and toughness.
In addition many of them are also hard, tough and strong.
Examples of metals are Aluminium, Copper (and its alloys Brass and Bronze), Iron, Zinc, Lead, Mercury.
Metals can be There are categorized in many different ways, we're going to classify them into Ferrous and Non-Ferrous.
Ferrous Metals
Ferrous metals are those that contain iron as their main component, usually alloyed with carbon.
Iron based alloys include always carbon, depending on the concentration of carbon there are three main types ferrous materials.
Pure Iron (0% carbon)
Steel (alloy of iron + carbon between 0,03% and 1,76% of carbon): Strong, malleable, ductile, flexible, tough.
Cast iron (alloy of iron + carbon between 1,76% and 6,67% of carbon): Brittle and hard, used to cast complex shape pieces.
Animation that shows a blast furnace in action.
Here we have some videos that show the steel making process
Imagine a world without steel: Steel is a super-material that combines strength and flexibility, that can withstand very high forces, that's
the reason why it is widely used to build tools, cars, ships, and big structures such as skyscrapers and bridges. It is thought that 90%
of the metal used in the world is steel.
Steel brigdes: Steel is a flexible and elastic material that can also withstand very high forces, that's why is used to build big structures such
as long bridges.
Iron ore mining: The iron ore is a mineral from which iron can be extracted, they're rich in iron oxides mixed with other worthless minerals named
gangue.
Iron ore pellets: The iron ore that contains around 25% of iron is crashed up and enriched by removing as much gangue as possible using magnets to reach a concentration of iron of around 60%. To separate the iron oxides from the gangue we use magnets. The enriched powder obtained is compacted into pellets with the size of a marble.
Iron ore to steel: Este vídeo muestra como se convierte el mineral de hierro (normalmente un óxido de hierro) en
hierro fundido + 4% de carbono (arrabio o pig iron en inglés) en un alto horno.
En el horno se introduce por arriba el mineral y el carbón de coque, mientras por debajo se inyecta
un chorro de aire sobrecalentado a 1600ºC que quema el carbón de coque mientras se alcanzan
temperaturas de unos 4000ºC, a esta temperatura el oxígeno se separa del hierro
y se obtiene hierro fundido (arrabio) con impurezas como Silicio, Manganeso, Azufre, Fósforo etc. El problema
ahora es otro, el arrabio contiene demasiado carbono que lo hace frágil.
Creating steel: Vídeo sobre el convertidor LD, que transforma el arrabio en acero quemando
el exceso de carbono con oxígeno inyectado a través del fondo del convertidor. Literalmente el arrabio (pig iron)
arde. El porcentaje de carbono al final se queda en torno al 0,5%.
Recycling steel I, Recycling steel II: Vídeos que muestran como se obtiene el acero a partir de chatarra.
Non-Ferrous Metals
Aluminium
Aluminium is one of the most abundant metals on Earth, is three times lighter than steel, excellent thermal and electrical conductor and resists corrosion. It is easy to alloy with other materials such as Copper or Magnesium to make ultra-light alloys.
Australia is the world's largest producer of Aluminium, here we can see the Aluminium making process. In the Video we see how Bauxite, the Aluminium ore, is extracted by surface mining. Bauxite contains Aluminium-Oxide (Alumina) but also sand and Iron-Oxide which make up the gangue and have to be removed by crushing the bauxite in giant rolling drums filled with steel cannon balls. The crusher pulverizes bauxite to the consistency of sand. The Alumina (Aluminium Oxide) is separated from the gangue and transferred to another facility where pure Aluminium ingots are obtained by electrolysis.
A more detailed and advanced video on the Aluminium making process. The pure Aluminium-Oxide (Alumina) is dissolved in molten Cryolite and then electrolysis is used to separate (reduce) Aluminium from Oxygen and to obtain pure Aluminium. This process consumes a lot of energy.
This video explains how aluminium foil is made. An ingot of Aluminum with approximate dimensions of 4x2x0,7 meters is rolled out several times to transform it into 12Km of Aluminium foil.
A myriad of Aluminium cans are consumed every day, this video describes their making process.
Copper
Is one of the first metals discovered by Man, is abundant and easy to extract and refine. Is the basic metal used by the electric and electronic industry because is a good electrical and thermal conductor. Is also very malleable and ductile, easy to weld using tin as binding metal. Corrodes easily, but the initial layer of oxide created stops corrosion. (is self protected or passivated) that's why is used to make pipes tanks for liquids (such as beer).
Shaping techniques
In the web page How things are made we can find plenty of videos that show the different shaping techniques and processes.
Once extracted from the ore, the molten metal is purified and transformed into cylindrical bars, slabs, ingots, sheets, profiles, wires etc. These materials are then supplied to factories where they are shaped to create a great variety of objects. The most important shaping techniques are: Rolling, Extrusion, Traditional Forging, Press forging, Punching, Bending, Wire drawing, Casting, Powder Metallurgy and Machining (Turning and /or Milling).
Rolling: This technique is used to reduce the thickness of an slab or strip, to obtain flat planks, sheets, beams of any profile (H, U, T ...), tubes, rails etc. It can be applied to flat pre-shapes at low of high temperatures. Low temperature rolling achives high tolerances and accuracies in the thickness of the sheets and slabs up to 10 microns. Is suitable for steel, Copper, Brass, Bronze, Aluminium and Titanium.
Extrusion: This process can only be used with soft metals with low melting points such as Aluminium. The metal is heated until it becomes plastic enough to be shaped and then is introduced in a kind of huge syringe where a piston forces it to pass through a dye that has an opening with the desired profile. Is a method used to make Aluminium profiles and tubes. Very common also to shape plastics. Aluminium extrusion plant in action.
Forging: For two thousand years it's been, along with casting the main shaping technique, specially for steel. In traditional forging the blacksmith heats an steel bar until it glows red to make it plastic and then is hammered on an anvil to give it the desired thickness and shape. In factories three main types of industrial forging are used. These processes use presses and dye casts to speed up the process and to achieve high tolerances. It's the most commonly used method to manufacture solid objects (without internal cavities) with any shape out of a cylindrical steel preformS.
Punching: Is used to make holes with a given shape on a thin sheet of metal. The sheet is placed between a punch and a die, and then an hydraulic press squeezes the punch against the die. Both the die and punch have the cross section that corresponds with the hole shape we want to obtain. Is used to manufacture flat pieces with one or more holes out of any metallic sheet.
Stamping: Is similar to punching, but instead of making holes with a given shape on a sheet of metal we obtain flat solid pieces with a given exterior shape. The stamping machine sometimes bends also the sheets to obtain the desired piece. Suitable to manufacture any flat piece out of any metallic sheet.
Bending: Is used to bend a strip of metal at a given angle and tip shape (mainly sharpened or rounded). Used for any metallic sheet.
Casting: First of all a mold with the desired shape is created, then the mold is filled with molten metal, when it solidifies the piece is extracted from the mold and the imperfections are removed. Using this technique we can obtain hollow pieces with very complex shapes practically finished in one single operation and with quite accurate measurements (approximately 0,1mm maximum accuracy), such as, for example the cylinder block of a motor. This technique is used mainly with Aluminium, Bronze and Cast Iron, but rarely with steel.
Milling: Is similar to a 3D printer, using a rotating cutting tool (like a drill bit) controlled by a computer (CNC) the piece is machined by removing the metallic chips or swarf. This is very accurate technique that achieves maximum accuracies of around 0,005 mm adequate to make pieces of any shape such as gears, die-casting molds etc. Is used mainly with Steel, Aluminium, Brass, Bronze, Titanium, can't be used with Cast Iron.
Turning: Is used to machine pieces with cylindrical shape. The piece is fastened to a rotating plate (spindle) and the cutting tool moves along the rotation axis removing chips of extra material to obtain the desired shape. This is also a very accurate technique that achieves maximum accuracies of around 0,005 mm. It is used to machine threads, screws, nuts, pistons etc. Is used mainly with steel, Aluminium, Brass, Bronze, Titanium, can't be used with Cast Iron.