Iron Production - Techniques and History

Iron Production - Techniques and History , Bo Justusson

Basic Steps Iron is produced from ore in two steps. First ore is mixed with charcoal (or coke) in a blastfurnace and heated to high temperature to get iron. Then this iron is further processed to reduce carbon and slag, and to add alloys. There are many alternate methods that has been used throughout history for those two steps. When charcoal was used, countries with both iron ore and large forests (like Sweden) had an advantage.

Blast-furnace Iron ore and charcoal (or coke) are charged from the top. Air is blown in at the bottom. The coal burns to CO which reacts with the ore and reduces it.
In principle:
Fe3O4 + CO --> Fe + CO2
The waste rock in the ore is lighter than iron and floats as slag. The melted iron and slag are tapped at the bottom.
(GIF-image 3k)
Blast-furnaces have been used since the 12th century. Their size has increased. Charcoal was first used, but from around 1800 coke could be used.

Iron and Steel To obtain high quality iron and steel from the the blast-furnace iron (pig iron), it is heated and treated with air or pure oxygen. Left a Bessemer converter where air is blown in at bottom and passes through melted iron.
Below a Siemens-Martin furnace where air goes into a pre-heater (regenerator) and passes above the melted iron and then onto another regenerator which gets heated. The direction of the air flow is changed after a time to make use of the heat! Both methods were invented around 1860.
(GIF-images 4k+4k)

Older Methods Older methods were based on heating and hammering. One used water-wheels to drive the hammers. The pig iron blocks were heated in a hearth and hammered to long thin pieces (rod iron). See images on following page.

Number of Plants To-day. Now there are only two iron mines: in Sweden Kiruna and Malmberget, both in the northmost part of Sweden. The last two mines in southern Sweden were Grängesberg closed 1989 and Dannemora closed 1992 (D. had been in production since the 13th century!).
There are also only two ironworks with blast-furnaces, one in Luleå and one in Oxelösund.
Old times. There have been hundreds of iron mines and blast-furnaces, and around thousand iron mills. Most of them in Bergslagen (far north-west of Stockholm, see map on Early Railways-page). This reduction has of course meant enormous changes for the people working in the Bergslag region. However, manufacturing of products based on iron is still very important in the region.

Basic Steps	Iron is produced from ore in two steps. First ore is mixed with charcoal (or coke) in a blastfurnace and heated to high temperature to get iron. Then this iron is further processed to reduce carbon and slag, and to add alloys.	There are many alternate methods that has been used throughout history for those two steps. When charcoal was used, countries with both iron ore and large forests (like Sweden) had an advantage.

Blast-furnace		Iron ore and charcoal (or coke) are charged from the top. Air is blown in at the bottom. The coal burns to CO which reacts with the ore and reduces it. In principle: Fe3O4 + CO --> Fe + CO2 The waste rock in the ore is lighter than iron and floats as slag. The melted iron and slag are tapped at the bottom. (GIF-image 3k) Blast-furnaces have been used since the 12th century. Their size has increased. Charcoal was first used, but from around 1800 coke could be used.

Iron and Steel		To obtain high quality iron and steel from the the blast-furnace iron (pig iron), it is heated and treated with air or pure oxygen. Left a Bessemer converter where air is blown in at bottom and passes through melted iron. Below a Siemens-Martin furnace where air goes into a pre-heater (regenerator) and passes above the melted iron and then onto another regenerator which gets heated. The direction of the air flow is changed after a time to make use of the heat! Both methods were invented around 1860. (GIF-images 4k+4k)

Older Methods	Older methods were based on heating and hammering. One used water-wheels to drive the hammers. The pig iron blocks were heated in a hearth and hammered to long thin pieces (rod iron). See images on following page.

Number of Plants	To-day. Now there are only two iron mines: in Sweden Kiruna and Malmberget, both in the northmost part of Sweden. The last two mines in southern Sweden were Grängesberg closed 1989 and Dannemora closed 1992 (D. had been in production since the 13th century!). There are also only two ironworks with blast-furnaces, one in Luleå and one in Oxelösund.	Old times. There have been hundreds of iron mines and blast-furnaces, and around thousand iron mills. Most of them in Bergslagen (far north-west of Stockholm, see map on Early Railways-page). This reduction has of course meant enormous changes for the people working in the Bergslag region. However, manufacturing of products based on iron is still very important in the region.

For more information use links at: Railways - Start Page