Open hearth process?

Open- hearth process:

Open-hearth was invented in 1860. It is a large firebrick bowl around 15 x 46 ft across and 40 ft high. The pigs from the blast furnace process are mixed with scrap steel and melted.

In this process, the steel is directed over the metal instead of through it. The hearth can hold 50-175 tons of metal and could take 11 hours to refine. At the end of this time, the alloying elements and exact carbon content are added and the steel is drawn of into large firebricks lined crucibles and cast into ingots.

In operation, a charge of limestone and scrap is placed in the furnace. Fuel usually hot gas and air under pressure, enters at one end near the top of furnace, ignites and is directed downward and over the metal. After the scrap metal is melted down- this usually takes upto 2 hours - hot metal from the blast furnace is added and the refinement of the metal continues. The flames touch the metal from above. Thus a very high temperature keeps the iron in a liquid form. Samples of the white-hot metals are taken, cooled and tested to find out if they contain the wanted amount of carbon. The carbon is gradually removed in the form of gas, which combines with the air of the furnace. If too much carbon has been burned out, more can be added. When the melted metal contains the right amount of carbon, it is poured into ingots.

Most of the silicon and manganese are oxidized and combine with limestone and other non-metallic elements to form a slag which floats on the top. This slag protects the metal from the direct action of the flame.

Steel made in open-hearth is called open-hearth steel and is used for bridges, rails, bolts, screws, shafts etc. It is also used for making high grade tool steel. Although slower and expensive to make, it is a better grade of steel and stronger than Bessemer steel.