Page 28 - Curriculum Visions Dynamic Book

Cast and wrought iron
The molten iron that comes from a furnace is known as pig iron. This can be run off
into moulds to produce a variety of intricate shapes, collectively known as wrought iron. If pig iron is remelted and cooled it forms cast iron. The works in which castings are made is called a foundry.
Iron refined in a furnace is not entirely pure, as it contains carbon. The amount of carbon affects the properties of the iron to a large extent. Wrought iron is nearly pure iron, with a carbon content of less
than 0.035%. This makes it a relatively soft material that is easily worked with hammers (it is said to be easily forged).
Cast iron has a carbon content above 3%, which makes it harder than wrought iron but much more brittle. If cast iron is cooled quickly, hard but brittle white cast iron is formed; if it is cooled slowly, soft but tough grey cast iron is formed.
Wrought iron
Wrought iron is nearly pure iron, with a soft, fibrous structure. This allows it to be formed into intricate shapes, whether hot
or cold. It was used to make everything from ploughshares to rifles, from railway track to decorative grilles.
Wrought iron replaced bronze in ancient civilisations, and led to the Iron Age. It was originally formed simply by hammering the nearly molten ore to remove the impurities.
All the ironwork in old buildings is wrought iron. Cast iron was
only made after the mid-18th century when it replaced wrought iron because it is stronger and can be used more easily. In particular, less material is needed for structural purposes, such as bridges and buildings. Wrought iron continued to be used for railway tracks until it was replaced by steel.
 The world’s first iron bridge, built across the River Severn in England in 1778, ushered in the new Iron Age. It was made of wrought
iron metal. The fastenings are iron wedges rather than rivets because, at this stage, designers were still making bridges of wood and they had not yet learned the technique of riveting.
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