Pig iron re-melted to produce cast iron which is poured into moulds usually formed in sand. There are three main types:
i) Grey Iron. Although this is relatively easy and cheap to cast it is extremely brittle, in thin sections especially, and cannot be riveted, hammered or assembled with any ease.
ii) SG Iron. Although more durable than grey iron, it is difficult to cast into thin sections. It also does not inherit the toughness of malleable iron that is vital in everyday use of our door and window furniture.
iii) Malleable Iron. This is an iron that after casting is subjected to a heat treatment process known as annealing. In this process castings are heated to around 1000ºC for up to 100 hours whilst in contact with haematite ore. The ore acts as an oxidising agent, which removes carbon from the casting. It is the presence of carbon in cast iron that causes its brittleness and removing some makes the casting much stronger (malleable). This iron differs as it is stronger and more durable and can be cast and assembled into a wider range of products than the other two irons mentioned above.