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Blasting Away- Steel Building

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					?There are three general uses of the term "Blast" in the making of steel.

It's hard to overstate the importance of the steel industry in the United States,
especially in the late 1800's and early 1900's. This article gives a glimpse of insight
into one critical area of steel making: Blasting.

First, it is the name given to air under pressure used for purposes of combustion, etc.,
as in the blast furnace or the Bessemer converter; in some cases for cooling purposes,
as in the case of tools. If preheated, it is termed hot blast or warm blast; if not
preheated, cold blast. A blast under considerable pres- sure is sometimes referred to as
a cutting blast; if weak, a soft blast.

Blast Box. - Of a Bessemer converter: A shaft furnace supplied with blast for
producing pig iron by smelting iron ores. It is continuous in operation, the solid raw
materials being charged at the top, and the molten pig iron and slag tapped out at the
bottom at intervals. Large furnaces are about 80 to 200 feet high, have an output up to
600 or 700 (commonly 300 to 600) tons per day, and employ blast at a pressure of 5 to
25 (usually 1 to 15) pounds per square inch, and at a temperature of about 900° to
1400° F. (485° to 7600 C.) The modern equipment consists essentially of the furnace
proper or stack; blowing engines for compressing the air for the blast; stoves for
preheating the blast; appliances for charging the raw materials; and a cast house for
disposing of the molten iron.

Stack. - There are three well defined divisions, usually circular - practically never oval
or square - in section. At the bottom is the hearth (well, laboratory, or crucible) of
cylindrical shape; above this the walls diverge, forming an inverted truncated cone,
called the bosh (also the name for the greatest diameter of the furnace), above which
the walls converge to the top (throat or mouth), forming another truncated cone set
upright. In a furnace with saucer bosh or belly walls, the walls above the bosh, instead
of being straight, are slightly convex. The furnace is built of fire-brick (cold blast
furnaces are built of stone), usually but not always encased in a general steel jacket
extending part or all the way up. The section above the bosh is supported on a mantle
(mantel) ring (lintel plate) and columns. Up to a certain distance from the bottom of
the furnace the walls are protected from corrosion by cooling plates of bronze or other
metal through which water circulates. Sometimes water is caused to flow down the
outside.

Blast. - Formerly the blast was always used cold (hence the term cold blast) but this
practice is now restricted to a few small furnaces, as a rule employing charcoal for
fuel. Hot blast was introduced by Neilson about 1828, and affected a great economy
in fuel. The blast is introduced near the bottom of the bosh through a number of pipes
or tuyeres (twyers, tweers) which are protected from burning by being encased in
water-cooled metal castings (tuyere blocks). The overhang of a tuyere is the amount it
projects into the furnace beyond the inner wall.
Of course, modern steel making uses much more sophisticated, computer-aided
technologies, but the basics, as described above, remain.

				
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posted:4/11/2011
language:English
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