Pig iron and Blast Furnace

Pig iron 

crude form of the iron and is used as raw material for the formulation of different ferrous metals, such as cast iron, wrought iron and steel. The pig iron is produced by smelting iron ores in a blast furnace. So we can call that the product of blast furnace is pig iron.

The blast furnace is a chimney like structure made form heavy steel plates lined with fire bricks to the thickness up to 1.5 meters. Its approximately height is up to 30 meters and 9 meters round in the diameter. The portion of the furnace above its wide cross-sectional area is called stack.

The top side of the stack is called throat, From throat the raw material is fed into the furnace. Below portion of the cross-section is known as bosh or burning zone. The bosh is provided with holes for a number of water jacketed iron blowing pipes known as tuyers. The tuyers are 12-15 in quantity and are connected to bustle pipe surrounding the furnace.

In the lower part of the furnace (Zone of fusion) the temperature is 1200 to 1300⁰. In the center of the furnace (Zone of absorption) the temperature is 800 to 1000⁰. The top portion of the furnace (Zone of reduction) the temperature is 400 to 700⁰. At the bottom of the furnace the molten iron sinks down while 

Above this floats the fusible slag which protects the molten iron from dioxdation. This molten iron produced is called pig iron. The slag from the blast furnace contains aluminum, calcium and ferrous silicates. It is used as ballast for rail road’s, mixed with tar for road making and in cement industry.

The Pig iron produced from the blast furnace contains 90 to 92% of iron. Other composition of the pig is carbon (1-5%), manganese (1-2%), sulphar and phosphorus (1-2%). 

The carbon is very important element in the iron which exists in iron in two forms, either in a free form as graphite or in a combined form as cementite and pearlite. The presence of free carbon in iron imparts softness and crystalline structure to the metal, while combined carbon makes the metal hard and gives a fine grained crystalline structure.