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A
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Casting, sintering and extruding metal
Metal can be formed into shapes using heat and
pressure. Casting involves heating metal until it becomes molten (liquid)
and pouring it, or forcing it under pressure, into a mould called a die. Instead
of being cast, metal components can be formed by sintering. This is done by
using metal powder instead of molten metal. The powder is placed in a die
and compressed into a solid mass. It is then heated (though not melted)
until it becomes sintered – that is, the powder particles join together
structurally, due to the heat.
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B
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Working metal
Traditionally,
many metal tools were made by heating iron bars in a fire, called a forge,
until they were red hot or (hotter still) white hot. The metal was then
worked – in other words, shaped by hammering it. Working metal using
compression (for example, hammering) is also called forging.
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C
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Heat treating metal
The properties of a metal can
be changed by heat treating it – that is, heating and cooling the metal. The
table below, from the technical information section of a steel supplier’s
website, summarize the main types of heat treatment.
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EXERCISES
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20.1
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Tick what is usually required in the metal forming processes (1-3). Look
at A opposite to help you.
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20.2
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Decide
whether the sentences below are true or false, and correct the false
sentences. Look at B opposite to help you.
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1. Metal must always be
heated before it can be forged.
2. When referring to metals,
the terms working and forging mean the same.
3. A common reason for
forging metal is to increase its hardness.
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20.3
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Make correct sentences using
one part from each column. Look at C opposite to help you. The first one
has been done for you.
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20.4
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Replaced the
highlighted expressions in the report extract with alternative words and
expressions from A, B and C opposite. Sometimes there is more than one
possible answer.
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The first stage in
manufacturing the blades for the cutting tools is to form them into an
approximate shape by (1) a process of squeezing molten metal through a die. Before
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