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Basic Oxygen Furnace (BOF)
WHAT A pear-shaped furnace, lined with refractory bricks, that
refines molten iron from the blast furnace and scrap into steel. Up to
30% of the charge into the BOF can be scrap, with hot metal accounting
for the rest.
WHY
BOFs, which can refine a heat (batch) of steel in less than 45
minutes, replaced open-hearth furnaces in the 1950s; the latter
required five to six hours to process the metal. The BOF's rapid
operation, lower cost and ease of control give it a distinct advantage
over previous methods.
HOW
Scrap is dumped into the furnace vessel, followed by the hot metal
from the blast furnace. A lance is lowered from above, through which
blows a high-pressure stream of oxygen to cause chemical reactions
that separate impurities as fumes or slag. Once refined, the liquid
steel and slag are poured into separate containers.
Bars
Long steel products that are rolled from billets. Merchant bar and
reinforcing bar (rebar) are two common categories of bars, where
merchants include rounds, flats, angles, squares, and channels that
are used by fabricators to manufacture a wide variety of products such
as furniture, stair railings, and farm equipment. Rebar is used to
strengthen concrete in highways, bridges and buildings (see Sheet
Steel).
Billet
A semi-finished steel form that is used for "long" products: bars,
channels or other structural shapes. A billet is different from a slab
because of its outer dimensions; billets are normally two to seven
inches square, while slabs are 30-80 inches wide and 2-10 inches
thick. Both shapes are generally continually cast, but they may differ
greatly in their chemistry.
Black Plate
Cold-reduced sheet steel, 12-32 inches wide, that serves as the
substrate (raw material) to be coated in the tin mill. |
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Blast Furnace
A towering cylinder lined with heat-resistant (refractory) bricks,
used by integrated steel mills to smelt iron from its ore. Its name
comes from the "blast" of hot air and gases forced up through the iron
ore, coke and limestone that load the furnace.
Blanking
An early step in preparing flat-rolled steel for use by an end user. A
blank is a section of sheet that has the same outer dimensions as a
specified part (such as a car door or hood) but that has not yet been
stamped. Steel processors may offer blanking for their customers to
reduce their labor and transportation costs; excess steel can be
trimmed prior to shipment.
Bloom
A semi-finished steel form whose rectangular cross-section is more
than eight inches. This large cast steel shape is broken down in the
mill to produce the familiar I-beams, H-beams and sheet piling. Blooms
are also part of the high-quality bar manufacturing process: Reduction
of a bloom to a much smaller cross-section can improve the quality of
the metal.
Breakout
An accident caused by the failure of the walls of the hearth of the
blast furnace, resulting in liquid iron or slag (or both) flowing
uncontrolled out of the blast furnace.
Burr
The very subtle ridge on the edge of strip steel left by cutting
operations such as slitting, trimming, shearing, or blanking. For
example, as a steel processor trims the sides of the sheet steel
parallel or cuts a sheet of steel into strips, its edges will bend
with the direction of the cut (see Edge Rolling).
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