Rugby School Thailand Design & Technology Senior School

8.4 Metals

In this section of Unit 8, we’ll explore the interesting world of metals, focusing on three main categories: ferrous metals, non-ferrous metals, and alloys. Understanding these materials is crucial because they play a vital role in everything around us, from buildings and vehicles to everyday tools and gadgets.

Ferrous metals are those that contain iron, which gives them strength and durability. We’ll look at common examples like steel and cast iron, discussing their properties and uses.

Non-ferrous metals, on the other hand, do not contain iron. These metals, such as aluminum, copper, and zinc, have unique characteristics that make them suitable for different applications. We will discover why non-ferrous metals are important in industries like electronics and transportation.

Finally, we’ll dive into alloys, which are mixtures of two or more metals. Alloys often have improved properties compared to their individual components. For instance, stainless steel is an alloy that resists rust and corrosion.

As we explore metal materials, it’s also important to consider their environmental impact. The extraction and processing of metals can lead to significant pollution and habitat destruction. Mining operations can disrupt ecosystems, and the energy required for metal production contributes to greenhouse gas emissions. This is why recycling metals is so crucial! Recycling helps reduce the demand for new metal extraction, conserves natural resources, and minimizes waste. When we recycle metals like aluminum and steel, we not only save energy but also reduce the harmful effects on our planet. Throughout this unit, we’ll discuss the importance of recycling and how it can help us create a more sustainable future while still enjoying the benefits of metal materials.

As a part of your D&T Course, you need to know about the working properties, stock forms, sizes and extrusions, common uses and environmental impact of the metals listed below. The image to the right is for illustrative purposes only and does show some metals that will not appear in your exam.

– ferrous metals

○ cast iron

○ mild steel

○ stainless steel

○ high speed steel

○ carbon steels

– non-ferrous metals and their alloys

○ aluminium

○ copper

○ lead

○ tin

○ zinc

○ titanium

○ tungsten

○ duralumin.

ferrous metals

○ cast iron

○ mild steel

○ stainless steel

○ high speed steel

○ carbon steels

non-ferrous metals

○ aluminium

○ copper

○ lead

○ tin

○ zinc

○ titanium

○ tungsten

Alloys

Ferrous; Stainless Steel

Non-ferrous:

bronze, brass, duralumin, pewter

Metals and the environment

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.

Open cast mining

Mining for metals can have a devastating impact on the environment.

Metal ores

METAL ORES PROCESSED INTO STOCK FORMS

Look at the image below. Not only does it take a lot of energy to extract the metal ores out of the ground, the processing of metal ores into useable stock forms also uses a large amount of energy.

METALS IN MORE DEPTH

Ferrous metals

Cast Iron

Cast Iron is 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.

Larger amounts of carbon (over 2%) render the iron brittle like Pig and Cast Iron.

Mild Steel

Mild Steel, sometimes known as Bright Drawn Mild Steel (BDMS), is used for the majority of metal construction work from girders in buildings 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

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 include 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. 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 fiber optic broadband, you still rely on Copper for bringing the internet into your home

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 for electrical circuits.

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.