Civil Engineering Reference
In-Depth Information
FIGURE 3.2
Steel rebars used to reinforce portland cement concrete wall.
oxides in the ore. Limestone is used to help remove impurities. Prior to re-
duction, the concentration of iron in the ore is increased by crushing and
soaking the ore. The iron is magnetically extracted from the waste, and the
extracted material is formed into pellets and fired. The processed ore con-
tains about 65% iron.
Reduction of the ore to pig iron is accomplished in a blast furnace. The
ore is heated in the presence of carbon. Oxygen in the ore reacts with carbon
to form gases. A flux is used to help remove impurities. The molten iron,
with an excess of carbon in solution, collects at the bottom of the furnace.
The impurities, slag, float on top of the molten pig iron.
The excess carbon, along with other impurities, must be removed to pro-
duce high-quality steel. Using the same refining process, scrap steel can be
recycled. Three types of furnaces are used for refining pig iron to steel:
1. open hearth
2. basic oxygen
3. electric arc
The open hearth and basic oxygen furnaces remove excess carbon by re-
acting the carbon with oxygen to form gases. Lances circulate oxygen through
the molten material. The process is continued until all impurities are removed
and the desired carbon content is achieved. Open hearth furnaces have been
used since the early 1900s. Now, due to greater efficiency and productivity,
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