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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.
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).
Busheling
Steel scrap consisting of sheet clips and stampings from metal
production. This term arose from the practice of collecting
the material in bushel baskets through World War II.
Butt-Weld Pipe
The standard pipe used in plumbing. Heated skelp is passed
continuously through welding rolls, which form the tube and
squeeze the hot edges together to make a solid weld. |
