Bloomery

A smelting furnace was a device for the extraction of iron from iron ore.

In this case, it was built of clay or stone shaft furnaces of about 50 to 220 cm in height. In addition to the shaft was in some cases a hearth pit for the slag discharge, the so-called race pit. The Rennöfen were hot heated with charcoal, wood or peat and then for the smelting of wechselschichtig up with fuel, usually softwood charcoal, and filled comminuted ore of the highest possible iron content. The Erzausbeute was a maximum of 50%. At a temperature of 1100 to 1350 ° C - depending on the design of the oven - a part of the iron ore is reduced to iron in the solid state; same time, there was a slagging. The melting temperature of iron ( 1539 ° C) should preferably not be achieved, so that no iron was produced, which is brittle and not forgeable. The slag ran ( ran, hence the name) from openings from the oven and stove in the pit.

Another theory that better explains the rather large crystals in the billet is that the top of the furnace reduces the ore and as strong as cast iron is carburized, so that it is located in the further decrease in the liquid state. It connects to a structure that grows on the outside. This is done in an area with an excess of oxygen in the vicinity of / air inlets ( s ) which thus leads to the increase of the melting point and decarburization.

The ventilation was usually carried out by a bellows. There were also high, chimney-like pie dishes, where sufficient natural draft, or which were operated by tunnel with wind; such Rennöfen were happy to create ridges. The product of the smelting process was interspersed with slag Eisenluppe (no cast iron), remained in the smelting furnace. The resulting material is also referred to as a racing iron. These billet or " salamander " now had to be forged for their further processing. Here, charcoal and slag residues were expelled. As a final product directly malleable iron, but depending on furnace operation also steel with a non-uniform carbon content, which is called after tanning to compensate for the properties and uniform distribution of the ingredients as refined steel was born.

Since the smelting furnace technology in Central Europe was use for more than 3,000 years until the early modern period, no general description of the furnace operation is possible with the numerous procedures and designs. Experiments showed, however, that to obtain one kilogram of iron about 30 kilograms of charcoal were needed in total ( with the reforge ). In European ovens ore is mostly used for coal in the ratio of 1:2.5 to 1:3. In Japanese Tatara, a rectangular baking dish, mixtures of 1:2 and even 1:1 are possible then why not coal quantities of Ausschmiedens and welding ( tanning ) / ( Gerbstahl ) need to be added are expected to arrive to the suitable steel.

Per smelting several pounds could be won to a hundredweight of steel, depending on the ore, furnace size, process time and other factors. In particular, from the rust-brown limonite encountered in wet heathlands or waters iron was recovered. The ore also ortstein, is formed in the boundary of the reduction to the oxidation zone in the ground.

This process took place in prehistoric times since the Iron Age with the Celts, Romans, Germans and other peoples application and was only replaced in modern times by blast furnaces, the generated liquid pig iron. An intermediate stage were the low shaft, which were in use until the end of the 19th century in some places. The technology of iron making is an art in itself; This fact also explains why iron was first discovered and used so late ( in Europe from about 700 BC).

• Experimental reconstruction of a Celtic race furnace

Bloomery with groove and pit stove for slag

Meilerbau

Furnace campaign