Metal Classification

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By the end of this unit (L5-L6), you should have developed a knowledge and understanding of:

The specific names and classifications of metals and alloys
The processing from source into a usable material
The performance characteristics of different types of metal
Why different types of metal or alloy are suitable for different applications
Stock forms of metals

Ferrous and Non-ferrous metals

Ferrous metals

A metal containing iron and carbon. This classification of metal are magnetic and will rust.

e.g. Pig Iron, Cast Iron, medium carbon steel, high carbon steel, mild steel

Non-ferrous metals

A metal that does not contain iron

e.g. Aluminium, copper, zinc, titanium, silver and gold

Alloys

A combination of metals (two or more or two or more elements including one metal) to enhance their properties (similar to composites)

Ferrous; Stainless Steel

Non-ferrous: bronze, brass, duralumin, pewter

Metals are made up of crystals that contain atoms and molecules.

Metals have good strength in both compression and tension, due to the very strong metallic bonds holding the atoms together.

These metallic bonds also allow free electrons to be shared amongst molecules making metals good conductors of heat and electricity.

All metals are extracted from Ores which are found in the earth.
As a result, they are considered a finite material (one day they will run out).
Ores need to be processed in order to extract the metal from the other minerals, rocks and soil.

25% of the Earth’s crust is made up of metal ores with Aluminium (Bauxite) being the most common followed by Iron.

Gold is the only metal that can be found in a usable form while the rest have to be processed.

The metals produced do not always reflect the name of the ore:

Metals have been used for thousands of years in the form of Copper, Bronze and Iron

Metal materials such as Aluminum and Steel are considered more modern developments.

Steel is derived from Iron Ore which is one of the easiest to separate from its ore using a blast furnace to melt the ore leaving the waste (slag) to float to the top.

Metals fall into two main categories:

those containing Iron (Fe) known as Ferrous metals
those that do not contain Iron known as Non-ferrous metals.

Essentially Iron is the only ferrous metal but, with the addition of other elements, it can be made into other metals.

When Iron is separated from its ore it is known as Pig Iron. This is a very high carbon Iron (3.5-4.5%) and is therefore very brittle and not useful as a building material.

It is often transferred within a foundry while still molten to be made into steel otherwise it is cast into ingots for transportation to be processed elsewhere.

Wrought Iron (0.04-0.08% Carbon) was traditionally used before the introduction of Steel as a building material for bridges, fencing, gates and structures as a large as the Eiffel Tower - It is no longer in commercial production and any reference to it likely means it is simply steel worked (wrought) by hand.

Ingot

Ferrous metals

Cast Iron

Cast Iron is simply Pig Iron that has been liquefied and poured into a mould (cast) and as such is has up to 3.5% carbon as well as Silica. It is brittle unless it is heat treated to make it malleable. Cast iron is used to make anvils and cast engine casings.

With the addition of small amounts of carbon, iron is made stronger and is classed as Steel. As the carbon amount is increased so too are the hardness properties of the Steel. However, larger amounts of carbon (over 2%) render the iron brittle as in Pig and Cast Iron.

Mild Steel

Mild Steel, sometime known as Bright Drawn Mild Steel (BDMS), is used for the

majority of metal construction work from girders in building to the casing on your

fridge, from the body of a car to the legs on a table. It is Iron plus 0.15 to 0.3%

carbon.

Medium Carbon Steel

The addition of 0.3-0.7% Carbon produces Medium Carbon Steel which is used for springs and general gardening tools. It is also referred to as Tool Steel.

High carbon steel

High Carbon Steel (0.7-1.7% Carbon) is also referred to as High Speed Steel (HSS) and is used for tools, cutting and drilling bits, blades etc.

These can also be considered Alloys.

One major disadvantage of using Iron is the fact that it oxidises. While all metals are prone to oxidization, in Iron it can be very destructive to the metal. Iron Oxide is better known as rust.

Unless treated, Iron and Steel will oxidise quickly forming a layer of Iron Oxide which can easily be brushed away and prevented by coating in a layer of oil.

If left untreated the oxide will begin to erode the surface of the metal and, although it can still be removed, it will leave noticeable marks in the metal. Eventually the oxide, or rust, will erode the metal away completely to an orange/brown powder.

rust

Mr Kennedy Oils the tools and machines in Dt regularly to avoid oxidisation (rust)

Non-ferrous metals

As its name implies, these metals contain no Iron therefore they cannot rust but they have other properties which make them more suitable for other applications.

Non-ferrous metals also encompass precious metals such as Gold, Silver and Platinum.

Despite being the most abundant ore on earth, the processing of Bauxite into Aluminium is difficult and requires a great deal of energy. This explains why it is often 3-4 times more expensive than steel. However, Aluminium has a good strength to weight ratio. This means that given its relatively light weight it is also quite strong.

Aluminium

Aluminium is a third of the weight of steel yet it is roughly half as strong. This is a good example of ‘strength to weight ratio’; you may lose half the strength, but you lose two thirds of the weight of a similar size piece of material. As it does not corrode, Aluminium is often used to replace steel in outdoor applications and, due to being lightweight, is also used for portability in sports and camping applications. It is also an excellent conductor of heat so it is used in cooking and for heat sinks and electrical casings (iPod, iPad, Macbook etc.) to help dissipate the heat. It melts at 660 degrees C

Copper

Copper is equally difficult and expensive to produce and is becoming very expensive to buy. Like Aluminium, it requires an electrolytic process and a similar process is used for Tin and Zinc. Copper is an excellent conductor of both heat and electricity which is why it is still used for electrical circuits, plumbing and for electric and data cables.

For those that don’t have fiberoptic broadband, you still rely on Copper for bringing the internet into your home and copper piping to keep you warm.

It melts at 1083 degrees C.

Tin

Tin is rarely used in its pure state, but applications include food wrapping/foil (now replaced with aluminium) and coating for steel plate in the production of food cans. It is also mixed with Lead to make Solder.

It melts at 232 degrees C.

Lead

Lead is a very soft but heavy material which has excellent resistance to chemicals and can block a variety of wavelengths from passing through such as X rays. It is used to line the containers for radioactive material as well as flashing in buildings where the roof meets the wall.

It melts at 330 degrees C.

Zinc

Zinc is used primarily for coating steels which is known as galvanizing. This is done for steel support beams, buckets, wheelbarrows and bins for use outdoors. It can also be die cast to produce high detail products such as lock mechanisms and small gears.

It melts at 419 degrees C.

titanium

Titanium is also classed as a modern material. It has the highest strength to weight ratio of metals and is a very clean material making it suitable for medical and surgical applications. It is also used in high performance sports equipment and in spectacle frames.

It melts at 1675 degrees C.

You should also be familiar with a range of precious metals used primarily in jewelry due to their high cost.

Silver melts at 960 degrees C.

Gold melts at 1063 degrees C.

Platinum melts at 1755 degrees C.

Prep 5

2.23 Alloys / Stock forms >

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