Chapter 5 – Overview of Iron and Steel Production:

1. Main Steps in Iron and Steel Production (Overview)
The production process of iron and steel involves a sequence of steps:

Mining
Ore Concentration / Ore Dressing
Making Iron
Making Steel
Casting and Forming
Heat Treatment
Machining and Joining
Finished Products

2. Mining
Definition: Mining extracts ore from the ground. Ore is rock or minerals with sufficient metal deposits.

Types of Mining:

Open-Cast Mining: This method is used when ore is located in relatively horizontal strips of topsoil close to the earth's surface. The topsoil is removed using excavating machinery or jets of water to access and extract the ore. This technique is generally cheap, allows for significant mechanization, but can be environmentally unfriendly.
Open-Pit Mining: Similar to open-cast mining, but the ore is contained within rock formations rather than topsoil, and the ore-bearing rock is deep and wide. As the depth of the pit increases, so do the costs and safety risks. Like open-cast mining, it is cheap and highly mechanized, but also environmentally unfriendly.
Underground Mining: This method is used for ore located deep beneath the surface. It involves digging vertical shafts and tunnels to bring the ore to the surface. The ore-bearing rock is typically blasted with explosives, making it both expensive and dangerous. The soil or rock above the ore is called the overburden. While more expensive and dangerous, it has less environmental impact compared to surface mining methods.
Dredging: This technique is utilized when ore is found in shallow water. A specialized ship called a dredger is used, which employs a chain-and-bucket elevator system to bring ore material from the sea or river bed onto the ship. The ore is separated on the ship, and waste material is then dumped back into previously mined areas of the water. This method is less expensive than underground mining but is limited to shallow water environments.

Details: Mining is described in Chapter 6.

3. Ore Concentration / Ore Dressing
Definition: Separates valuable metal ore from waste ore material (called gangue).

Process: Iron ore is first crushed into fine pieces. Machines are used to separate the valuable metal deposits from the waste.

Main Ore Separation Techniques:

Gravity Separation
Magnetic Separation
Flotation (or Froth) Separation

Details: Ore concentration is described in Chapter 7.

4. Making Iron

Blast Furnace:

Makes molten pig iron from concentrated iron ore.
Pig iron is an iron-carbon alloy with a high percentage of carbon, making it brittle.
Pig iron is usually sent on to the next step to make cast iron or steel.

Cupola Furnace:

Used to make cast iron from pig iron and/or scrap metal.

Details: Making iron is described in Chapter 8 (for Blast Furnaces) and Chapter 9 (for Cupola Furnaces).

5. Making Steel

Basic Oxygen Furnace (BOF):
Makes steel from molten pig iron by injecting high-speed oxygen into it, which burns off carbon and impurities.

Electric Arc Furnace (EAF):
Makes steel by using high-voltage electric arcs to melt scrap metal or pig iron, and burn off carbon and impurities.

Details: Making steel is described in Chapter 8.

6. Casting and Forming
Processes: Iron and steel can be made into different shapes by:

Casting
Forging
Extrusion
Drawing
Rolling
Stamping (also called Pressing)

Details: Casting and forming are described in Chapter 10.

7. Heat Treatment, Machining, and Joining

Heat Treatment:
After forming, steel can be given heat treatment to change its properties (e.g., to make it harder, softer, tougher, or more ductile).

Details: Heat treatment is described in Chapter 12.

Machining:
Metal products can be further shaped by machining using tools like drills, saws, lathes, milling machines, and grinders.

Details: Machining is described in Chapter 13.

Joining:
Metal products can be joined via:

Welding
Adhesives
Mechanical fasteners (e.g., nuts and bolts, rivets)

Details: Joining is described in Chapter 14.

Chapter 6: Mining and Ore Concentration

Ore Terminology

Ore: Rock containing enough metal for economical extraction.
Ore Extraction (Mining): The process of extracting ore from rock and surrounding earth.
Ore Concentration (Ore Dressing): Separating metal-rich particles from waste particles in the ore (discussed in Chapter 7).
Metal Extraction: Using heat, chemical, or electrical methods to extract metal from concentrated ore (discussed in Chapter 8).

Common Metals and their Ores Metals typically exist in nature as chemical compounds, not in pure form. The type of compound determines the extraction method.

Iron: Found in Hematite, Magnetite, Limonite, and Iron Pyrite (Iron oxide). Extracted by smelting.
Aluminium: Found in Bauxite (Aluminium oxide). Extracted by electrolysis.
Copper: Found in Chalcopyrite, Chalcosite, and Bornite (Copper oxides and sulphides). Extracted by chemical methods.
Lead: Found in Galena (Lead sulfide). Extracted by smelting.
Tin: Found in Tin Pyrite (Tin oxide). Extracted by smelting.
Chromium: Found in Chromite (Iron chromium oxide). Extracted by chemical methods.
Zinc: Found in Zincite (Zinc oxide). Extracted by smelting.
Gold: Found as pure gold (Native Gold). Only cleaning is needed for extraction.

Types of Mining

Open-Cast Mining: This method is used when ore is in topsoil near the surface in horizontal strips. The topsoil is removed using excavating machinery or water jets.
- Advantages: Cheap, allows for much mechanization.
- Disadvantages: Environmentally unfriendly.
Open-Pit Mining: Similar to open-cast mining, but the ore is in deep, wide rock rather than topsoil.
- Advantages: Cheap, allows for much mechanization.
- Disadvantages: Environmentally unfriendly; cost and safety risks increase with pit depth.
Underground Mining: Used when ore is deep beneath the surface. Vertical shafts are dug, and tunnels bring the ore to the surface. Ore-bearing rock is often blasted with explosives, making it expensive and dangerous. The amount of soil or rock above the ore is called the overburden.
- Advantages: Less environmental impact.
- Disadvantages: Expensive, dangerous.
Dredging: Employed when ore is in shallow water. A dredger ship uses a chain-and-bucket elevator to bring material from the sea or river bed. The ore is separated on the ship, and waste is dumped back into a previously mined area.
- Advantages: Less expensive than underground mining.
- Disadvantages: Only works in shallow water.

Mining in Ireland Zinc and lead are mined in Tara, Co. Meath, Lisheen, Co. Tipperary, and Galmore, Co. Kilkenny. Imported bauxite is processed into alumina for export at Aughinish, Co. Limerick.

Chapter 7 – Ore Crushing and Grinding:

The initial step in concentrating ore is to create small particles. Raw ore is crushed and ground into a desired size using large machines like jaw-crushers, or cone or cylinder crushers. These crushed particles are then sorted by size.

Ore Separation Techniques:

Three common methods are used to separate ore particles: Gravity Separation, Magnetic Separation, and Flotation Separation.

Gravity Separation: This technique leverages the fact that metal-rich ore particles are heavier than waste particles. Crushed ore particles are introduced into running water that flows over a constantly shaken, grooved platform. The heavier metal particles sink into the grooves, while the lighter waste particles are washed away. Gravity separation is specifically used for tin and tungsten ores.
Magnetic Separation: This process is employed for ores containing magnetic metals such as iron, nickel, and cobalt. Crushed ore particles are passed by a strong magnet or a magnetic roller. Ore particles with little to no metal fall directly into one collector, while metal-rich particles are attracted by the magnet and fall into a separate collector.
Flotation Separation: This method is suitable for metals that exhibit a surface reaction against water, including silver, copper, lead, and zinc. Fine ore particles are mixed with water and oil, or other helpful chemicals, and then pumped into the bottom of a tank. Air is blown into the tank from the bottom, creating numerous small, constantly rising bubbles. The metal-rich ore particles adhere to these air bubbles because they are repelled by the water, forming a froth on the surface. This froth, containing the metal-rich particles, is then skimmed off. Ore particles with little or no metal exit through a waste outlet at the bottom of the tank.

Final Stage: Drying and Pelleting
After being separated by a wet process like gravity or flotation separation, the concentrated ore undergoes drying and clumping into larger sizes. This prepares the ore for transport to the subsequent stage, which is typically smelting in a furnace to extract the metal, as detailed in Chapter 8, "Furnaces and Metal Extraction".

Chapter 8 – Metal Extraction Methods:

There are three primary methods for extracting metals from their concentrated ores:

Pyrometallurgy: This method uses heat to extract metals. The most common form is smelting, which produces molten metal. Smelting often involves a chemical reaction called reduction, which means removing oxygen. For iron ore, carbon is used to reduce iron oxide, yielding iron and carbon dioxide. Metals commonly extracted via pyrometallurgy include zinc, tin, and lead.
Hydrometallurgy: This method uses liquids and chemical reactions. Concentrated ore is mixed with chemicals in a liquid solution, and chemical reactions separate the metal. Copper, silver, gold, and platinum are examples of metals extracted this way.
Electrometallurgy: This method employs electricity, specifically electrolysis. Electrodes are placed in a liquid solution containing the concentrated ore and other chemicals. The metal is then attracted out of the solution and deposits onto one of the electrodes. Aluminium and iron can be extracted using this method.

Furnaces for Iron and Steel Production:

Smelting and reduction processes are carried out in furnaces, which have refractory linings on their walls to prevent melting when holding molten metal. The material placed into a furnace is known as the charge.

The Blast Furnace: Making Pig Iron

A Blast Furnace produces pig iron from concentrated iron ore, coke, limestone, and hot air. Pig iron is an iron-carbon alloy containing about 4% carbon. The charge for a blast furnace includes iron ore, coke (a clean carbon fuel from coal), and limestone (a flux that collects impurities to form slag).

The operation of a Blast Furnace involves several steps:

The charge is loaded via charging bells, a double-door system preventing heat or gas escape by opening only one door at a time.
Hot air is blasted through tuyeres (air nozzles).
Chemical reactions occur: coke burns, producing heat and carbon monoxide; carbon monoxide reduces iron oxide to iron and carbon dioxide; and limestone collects impurities to form slag.
Gases escape through gas outlets and are collected. Molten iron falls to the bottom and is tapped off.
Molten slag floats on top of the iron and is also tapped off.

The Blast Furnace runs continuously, with molten iron and slag being tapped off regularly, and new charge loaded at the top. The hot rising gases are collected, cleaned, and used to pre-heat the incoming air blasts.

The Blast Furnace produces molten pig iron, which can be cast into shapes and cooled. Due to its high carbon percentage, pig iron is typically too brittle for most applications and is further smelted to make cast iron or steel.

Advantages of a Blast Furnace include:

Low cost
High volume production
Continuous operation
The ability to create its own heat

Disadvantages include:

The production of large amounts of polluting carbon dioxide
The requirement for a significant amount of space

The Cupola Furnace: Making Cast Iron

A Cupola Furnace produces cast iron from pig iron, scrap metal, coke, and limestone. It is a smaller, simpler version of a blast furnace, named after its cupola dome which acts as a spark guard.

The operation involves:

Starting a fire with a layer of coke at the furnace bottom
Adding layers of metal (pig iron, scrap iron/steel), coke, and limestone through a charging door
Pumping in air at regular intervals to aid burning
Tapping off molten metal regularly via a tap hole
Limestone collects impurities, forming slag that floats on top of the metal and is also tapped off regularly

Cast iron typically contains 2% to 3% carbon. The specific type of cast iron produced depends on the scrap metal used, carbon and silicon levels, and cooling rate.

Grey Cast Iron: The most common type, where added silicon causes excess carbon to form graphite, making the iron softer, more impact-resistant, and easier to cast and machine.
White Cast Iron: Produced by faster cooling and less silicon, leading excess carbon to form cementite, which makes the iron harder and more brittle than grey cast iron.

Cupola furnaces offer advantages such as:

Low cost
High volume production
Self-generated heat

Disadvantage: Inability to reduce carbon to the low percentages required for steel production.

The Basic Oxygen Furnace: Making Steel

The Basic Oxygen Furnace produces steel, an iron-carbon alloy with less than 2.1% carbon, from molten pig iron, scrap metal, flux, and oxygen. This furnace operates by blowing pure oxygen at high speeds into molten pig iron using a water-cooled lance, which burns off carbon and other impurities. The removed carbon combines with oxygen to form carbon dioxide gas. By varying the amount of oxygen, low-carbon or high-carbon steels can be produced.

The process involves:

Charging: Scrap metal, molten pig iron (often directly from a blast furnace), and flux (lime) are added.
The 'Blow': A fume hood is replaced, an oxygen lance is lowered, and oxygen is pumped in at supersonic speed.
Tapping Off: The oxygen lance is raised, the fume hood removed, and the furnace tilted to drain off molten steel, followed by molten slag.

Advantages:

Creates large quantities of steel cost-efficiently
Does not require an external heat source

Disadvantage:

Must be located near a blast furnace to receive molten pig iron

The Electric Arc Furnace: Making Steel

An Electric Arc Furnace is another method for making steel, primarily by melting scrap metal (and optionally pig iron) using electric arcs.

The process of the Electric Arc Furnace involves:

Lifting the roof and electrodes
Dropping scrap metal and flux (lime) into the furnace; molten pig iron may also be added
Closing the roof and lowering the electrodes into the charge
Creating high-voltage electric arcs by the electrodes, which melt the charge and burn off excess carbon and impurities
Oxygen can also be injected to assist burning and adjust carbon content
Lifting the roof and electrodes again
Tilting the furnace to pour out molten slag through an inspection door, then tilting it the other way to pour molten steel out through a tapping spout

Advantages:

Produces steel from cold scrap metal alone
Doesn't need to be near a blast furnace
Can produce very high-quality steel

Disadvantages:

Enormous electricity consumption
Generates polluting gases like carbon dioxide

Other Furnaces Mentioned Include:

Ladle or refining furnaces: For further metal improvement (e.g., gas/impurity removal, alloying)
Re-heat furnaces: For re-heating cold metal for rolling, casting, or heat treatment
Reverberatory furnaces: Used for extracting copper from its ore

Measuring Furnace Temperature: Pyrometers

Measuring and controlling furnace temperature is crucial for producing desired metal structures and ensuring correct furnace operation. A pyrometer is a device used to measure temperature at a distance. The two main types, thermoelectric and optical pyrometers, are inserted through furnace walls.

Thermoelectric / Thermocouple Pyrometer: This device uses a thermocouple, which is a junction between two different metals. When heated, the thermocouple generates an electric current. The flow of this current is detected and used to indicate the temperature, which is calculated relative to a cold thermocouple junction located outside the furnace.
Optical Pyrometer: This device measures heat by visually matching the color of an electrically-heated filament to the color of the furnace. A variable resistor is adjusted to change the current through the filament, making it glow brighter. When the filament's color matches the furnace's color, the reading on a meter indicates the furnace's temperature.

Chapter 9 – Types of Metal Manufacturing Processes:

Casting: This process creates different shapes by pouring or injecting molten metal into a mould and allowing it to cool.
Forming: Involves deforming an existing piece of hot or cold metal into a new shape by compressing or pulling it. Forging, rolling, extrusion, drawing, and pressing/stamping are all types of forming.
Shaping: Refers to cutting away excess material to create different shapes, often using tools like lathes, milling machines, grinders, and drills (further detailed in Section 4 – Workshop Processes).
Joining: Creates products by connecting existing metal pieces, for example, through welding, mechanical fasteners, or adhesives (also covered in Section 4 – Workshop Processes).

Casting

Casting is the process of creating shapes by pouring or injecting hot metal into a mould. It is well-suited for complex shapes and finds applications in producing engine parts such as cylinder heads, casings, pistons, and valves, as well as plumbing parts and cookware. However, cast parts are generally not as strong as forged parts.

Sand Casting: Used with ferrous metals like cast iron and steels because these metals have very high melting temperatures that would melt metal moulds. In this method, sand is bonded together using clay or chemicals. After the metal cools, the sand mould is broken and must be re-made for each new part.
Die Casting: Employs steel dies to form a mould and is used with non-ferrous metals such as aluminium, zinc, copper, and tin, as steel dies do not melt at their casting temperatures. Molten metal is injected into the closed dies, which are then separated to eject the item. Die casting is expensive to set up but is faster than sand casting because the moulds are reusable and the dies are water-cooled.

Forming Processes

Forming processes involve deforming metal into desired shapes.

Forging: This technique uses large compressive force to deform a piece of metal into the desired shape, often likened to a hammer-and-anvil process. Steel dies can be used as the workpiece is not melted. Forging is used for parts requiring high strength and toughness, such as car transmission components (axles, gears, crankshafts) and tools (hammers, wrenches).
- Open Die Forging: The metal piece is constrained only on the bottom side, with a hammer striking from the top.
- Closed Die Forging: Both the top (hammer) and bottom (anvil) parts, which are moulded dies, force the metal piece to take the shape of the cavity between them.
- Drop Forging: Uses a heavy weight as the 'hammer'.
- Press Forging: Uses a hydraulic ram to squeeze the dies together more slowly.
- Hot Forging: Involves heated metal, requiring less force for deformation. It allows the metal to re-crystallize, resulting in a less hard and stress-relieved part.
- Cold Forging: Requires more force and leads to a harder part due to work hardening effects.
Rolling: Involves rollers compressing metal to create sheet or bar shapes with required thicknesses. Applications include flat sheet metal, corrugated sheets, construction beams, and railway tracks. However, rolling cannot create complex shapes.
Extrusion: This process pushes metal through a die opening to create shapes with a uniform cross-section. Common applications include tubes, pipes, rods, railings, and window frames. Similar to rolling, extrusion cannot make complex shapes.
Drawing: Similar to extrusion, but the metal is pulled through the die opening. It is most commonly used to manufacture wire. Drawing also has a limitation in making complex shapes.
Thread Rolling: Utilizes two rollers to force a thread pattern into a part instead of cutting the thread. It is used for bolts, nuts, and other threaded parts. A significant advantage is that thread rolling produces harder and stronger threads than machined (cut) threads due to the cold working effect, and it results in no wasted metal.
Stamping / Pressing: This method forces a cold, thin metal sheet over a metal die to create various shapes. Applications include car body parts, corrugated roof panels, radiator panels, and coins. Stamping machines can also cut out required shapes, similar to a 'cookie cutter', and the process is very fast. However, it is limited to thin parts, requires expensive tooling, a lot of energy, and parts may need subsequent heat treatment.

Powder Metallurgy

Powder metallurgy manufactures metal and alloy parts by compacting metallic powders and other ingredients into a desired shape, which is then heated (sintered) in a furnace.

Manufacture of Tungsten Carbide Cutting Tools: Tungsten carbide, one of the hardest man-made alloys, is produced using powder metallurgy. The process involves:

Tungsten powder is mixed with carbon powder and heated to form tungsten carbide powder.
This tungsten carbide powder is then mixed with cobalt powder and other binders in a ball mill.
The mixture is compacted in a mechanical press to form the desired shape.
Finally, the shaped part is sintered (heated below its melting point) in an oven to fuse the particles together.

Choosing a Metal Manufacturing Process

The choice of manufacturing process depends on the desired part characteristics:

For a complex part, casting is a suitable choice.
For flat sheets, rolling or extrusion are appropriate.
Corrugated or bent sheets are best made by stamping/pressing.
Bars or tubes are typically produced via extrusion.
If a strong, impact-resistant part is needed, forging is recommended.
For wire, drawing is the primary method.

Chapter 10 – Introduction to Plastics Manufacturing:

Manufacturing processes for plastics can be broadly categorized based on the type of plastic used: thermoplastics or thermosets.

Manufacturing with Thermoplastics:
These are recyclable plastics. Thermoplastic pellets are easily heated to become molten, allowing them to take the shape of a mould. They are used for complex and high-volume products such as toys, CDs, packaging, toothbrushes, chairs, tubes, pipes, window frames, bottles, and various containers.

Manufacturing with Thermosets:
These are strong, heat-resistant, and non-recyclable plastics. With thermosets, the polymer is created for the first and only time within the mould or machine itself. They are typically used for products requiring high strength and heat resistance, like plugs, sockets, heat-resistant electrical parts, sports and aircraft parts, and boat parts.

Manufacturing with Thermoplastics

Several processes are used for manufacturing products from thermoplastics:

Injection Moulding: In this process, thermoplastic pellets are melted and then injected into a mould under high pressure. Once cooled, the product is ejected. This method is highly suited for high-volume and complex shapes, offering advantages like fast cycle times, the ability to create complex parts with a good finish, and suitability for high-volume production. Its disadvantages include expensive tooling and difficulty in changing moulds. Applications include DVDs, toys, chairs, packaging, cutlery, CDs, and toothbrushes.
Extrusion: Thermoplastic pellets are melted and forced through a die opening, after which the material is cooled to form a continuous shape. This process is ideal for long products with a uniform cross-section, such as tubes, pipes, window frames, long bars, gutters, cans, rods, and railings.
Blow Moulding: A plastic tube (parison) is extruded, then a mould closes around it, and air is blown into the parison to expand it against the mould walls. After cooling, the product is ejected. This method is perfect for hollow products with thin walls like bottles and containers.
Rotational Moulding: A mould is filled with thermoplastic powder, then heated while rotating on two axes. The plastic melts and coats the inside of the mould. After cooling, the hollow product is ejected. This is suitable for hollow products with thicker walls, such as footballs and large tanks.
Thermoforming / Vacuum Forming: A sheet of thermoplastic is heated until pliable, then a vacuum or pressure is used to pull or push the sheet over a mould. This method is suitable for simple parts with thin walls. Applications include simple packaging, casings, luggage, bathtubs, and helmets.
Calendaring: Plastic is melted and then passed between a series of rollers to form a continuous sheet. This process is used to make thin sheets or films, such as cling film.

Manufacturing with Thermosets

Processes for manufacturing with thermosets include:

Compression Moulding: A thermoset resin or powder is placed into a heated mould, then compressed, and allowed to cure (harden) before being ejected. This method is suitable for strong, heat-resistant products. Applications include plugs, sockets, and heat-resistant electrical parts.
Transfer Moulding: Similar to compression moulding, but the thermoset resin is first heated in a transfer pot and then injected into a closed mould under pressure, where it cures. This method is also used for mouldings for electronic components.
Lamination: Layers of thermoset resin and reinforcing fibers (like glass or carbon) are pressed and often heated to create strong, lightweight, and rigid panels. This process is used for sports, aircraft, and boat parts, as well as for electrical applications.
Pultrusion: This continuous process involves pulling fibers (such as glass or carbon) through a tank of thermoset resin. The resin-impregnated fibers then pass through a heated former, where the resin cures. The resulting strong, lightweight, and rigid rods are then cooled and cut to length.

Chapter 10 – Introduction to Plastics Manufacturing: