Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the art of iron and
steel-making, and the refining of other metals, and partic-
ularly relates to a process of recovering, from a blast
furnace operation, high-grade metal having a substantial
amount of impurity, and then removing the impurity to allow
the metal commercially to be used.
In the normal operation of iron blast furnaces,
liquid iron is continuously collected in the hearth, and
liquid slag is simultaneously forming and collecting as a
separate, completely immiscible layer on top of the iron.
As used herein, the term "slag" means any material having
a high degree of impurities. "Iron slag", the precise
composition of which can vary substantially, is produced
in the production of blast furnace iron and typically will
` have an approximate composition of 38 percent by weight of
calcium oxide, 13 percent of magnesium oxide, 36 percent
of silicon dioxide, 10 percent of aluminum oxide, 1.5
percent of sulfur, and minor amounts of other metallic
oxides.
In all iron blast furnaces, the liquid iron slag
must be flushed out every few hours. This iron slag is -
usually removed by allowing it to flow through a tap hole,
known as a "slag notch" or "cinder notch", which is located
high in the blast furnace at approximately the normal level
of the slag. The molten iron slag is thus allowed to run
out of the blast furnace every few hours, in order to
prevent accumulation of undue amounts of the slag. However,
because iron is constantly migrating through the slag layer
during the operation of the furnace, the pouring of the
iron slag will result in a concomitant loss of approximately
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one percent by weight of the total amount of iron produced
by the blast furnace.
A typical blast furnace will produce approximately
3,000 tons of iron per day, and large blast furnaces may
produce as much as 10,000 tons of iron per day or more. It
is therefore quite common to experience a loss of from about
30 to 100 tons per day of iron with the removal of the iron
slag from the blast furnace. Iron, with an acceptable low
level of impurities contained therein, as is found in normal
blast furnaces, has a very substantial value. Thus, such
losses of up to 100 tons of iron per day are obviously sub-
stantial and are desired to be minimized or eliminated
completely.
In the common prior art process, the molten blast
furnace iron slag is conveyed into one of two large, walled-
in slag pits located right next to the furnace, where it is
allowed to solidify and cool. The slag pit contains primarily
slag, having, however, substantial irregular-shaped masses
of iron of widely-varying size scattered throughout the slag,
like raisins in a cake. Depending primarily on the quality
of the raw materials entering the blast furnace, i.e., iron
ore, coke and limestone, the amount of iron slag produced per
ton of iron will vary substantially, and the amount of iron
distributed throughout the slag pit is usually in the range
from about two to five percent by weight of the total slag
pit contents. The iron distributed through the iron slag in
the slag pit is the same as the regular blast furnace iron
product, having a relatively low level of impurities and high
economic value, if it can be separated adequately from the
surrounding iron slag.
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When the slag pit being worked is full, the slag
from the blast furnace is then channelled to the other slag
pit, which is then empty, having earlier been emptied by
power shovels and trucks while the other slag pit was being
filled. These power shovels and trucks are moved over to
the full pit, after a period of time has elapsed to allow
solidification of the iron slag, and the trucks are filled
by the power shovels with large chunks of slag from the
slag pit, which are transported to a slag processing facility,
generally located nearby.
In the slag processing facility, the large chunks
- of slag, having dimensions of up to several feet, are impacted
by heavy wrecking balls, to crush the slag into pieces
generally of up to two feet in maximum dimension. In the
past, when the slag processor had broken the iron pieces
contained in the slag down to a size which could be accommo-
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` dated by an open hearth furnace-charging pan, this iron-
containing material, called blast furnace slag iron herein,
was separated from the pieces of iron slag by use of an
electromagnet, to be recycled to an open hearth furnace.
These blast furnace slag iron pieces are highly variable in
their iron and iron slag content, but will frequently
comprise about sixty to eighty percent of blast furnace
iron, having a low sulfur content of typically about .03
percent by weight, and twenty to forty percent of iron
slag, having a sulfur content of about one to two percent
by weight. ;
~- Because of the substantial time involved in
producing steel using an open hearth furnace, due to the
inherently long melting, refining and superheating cycle,
the blast furnace slag iron pieces, which have a high sulfur -
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content -- since there is one to two percent of sulfur in
- the slag -- were still reusable, and could be used in open
hearth steel production. The c~nsiderable melting and
refining time inherent in the operation of open hearth
furnaces allowed ample opportunity for all of the sulfur to
be removed in the open hearth furnaces. Therefore, so long
as open hearth furnaces were popular, no major problem was
encountered in recycling blast furnace slag iron.
However, basic oxygen furnace steelmaking is
steadily replacing basic open hearth steelmaking as the
process of choice for converting blast furnace iron to steel.
It is expected that, in a relatively short period of time,
substantially all blast furnace iron in the United States
will be refined to steel by the basic oxygen furnace method.
Although the basic oxygen furnace process is vastly superior
- to the open hearth process in most ways, the basic oxygen
furnace is inferior with respect to its flexibility in hand-
ling scrap metals, such as the blast furnace slag iron pieces
described above. In particular, most basic oxygen furnace
operators prefer to exclude these blast furnace slag iron
pieces from their charges, because these pieces are usually
- considered to be too high in sulfur content for optimum
efficiency steelmaking, due to their excess iron slag content.
Unimproved blast furnace slag iron is not suitable for basic
oxygen furnace processing, because of the relatively short
residence time of the iron in the basic oxygen furnace. This
residence time is usually not adequate to achieve sufficient
desulfurization of the relatively high sulfur content blast
furnace slag iron pieces. Therefore, in any integrated steel
mill having only basic oxygen furnace steelmaking production,
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the blast furnace slag iron pieces produced from the mill's
blast furnace slag are commonly accumulated in large stock-
piles as a low grade form of scrap, too good to haul to the
dump, but not good enough to charge, as is, into the steel-
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..~king basic oxygen furnace. This scrap has had a very low
economic value in the past because, in addition to its
unsuitability for basic oxygen steelmaking, it could not be
utilized in any other sector of the ferrous industries, such ~.
as in iron foundaries.
In accordance with one aspect of the present invention,
there is provided a product of manufacture comprising: a multi-
plicity of irregularly shaped masses of blast-furnace slag-iron
having a random size distribution throughout the range of up to
a thickness of about 6 inches and a lateral dimension of about
three feed and each article having a relatively low amount of
slag substantially uniformly dis~ributed therethrough and having
at or in contact with its surface a large number of irregularities,
crevices and fissures, a quantity of a contaminating slag rigidly
- adhered to the iron, at least part of said slag being located
within said crevices and fissures, said slag comprising less than
about ten percent by weight of the total weight of the product,
said product having been produced by breaking blast-furnace iron-
. slag into pieces having a substantial amount of such slag exposed
at or to the surface of each piece; continuously tumbling a mass
of such pieces against each other in order to achieve a relatively
uniform redistribution of such pieces within such mass; and
while effecting such redistribution substantially continuously
imparting such pieces with a shower of a substantial quantity
of small particles having a hardness greater than the hardness -
of the slag impurities and at a high velocity and for a period
of time sufficient to abrade such impurities from the iron.
The invention also provides a process for recovering ~ .
a relatively pure metal having a slag content not exceeding 10 --
percent by weight from a piece of such metal containing a softer
slag impurity rigidly adhered thereto and located at least in
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bstantial part within crevices and fissures accessible to
the surface of said metal, comprising: a. breaking said metal
containing impurities into pieces having a substantial amount
of such slag impurities exposed at or to the surface of each
piece; b. continuously tumbling a mass of such pieces against
each other in order to achieve a relatively uniform redistribution
of such pieces within such mass; and c. while effecting such
redistribution, substantially continuously impacting such pieces
with a shower of a substantial quantity of small particles
having a hardness greater than the hardness of the slag impurities
and at a high velocity of at least about 10,000 feet per minute,
and for a period of time sufficient to abrade such impurities
from the metal to produce a product containing not more than
10 percent by weight of said slag impurities.
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The process of this invention involves the use of
a shot blasting and tumbling machine, of a type well known
in the art and more fully described below. This machine is
frequently used to clean loosely adherent sand from foundry
castings. However, this use does not entail the removal
of a hard material, firmly attached to the iron, from minute
fissures and crevices such as is involved in the process of
this invention to remove almost all of the slag from blast
furnace slag iron pieces.
The instant invention overcomes the shortcomings
of prior art processes and products by providing a process
for recovering relatively low sulfur content, low slag
content blast furnace iron from a crude material, called
blast furnace slag iron pieces, having a large amount of
iron slag contained on the surface thereof and extending
from the surface thereof into the body thereof through
cavities, fissures and the like. This process, although
disclosed to be utilized to remove blast furnace slag
from blast furnace slag iron pieces, may also be utilized
20 to remove slag impurities from other refined metals such ~ -
as aluminum, zinc, copper and the like.
In the practice of the process of this invention,
the slag and metal chunks are broken up into pieces, having
sizes of up to a maximum dimension of about two or three
feet, in order to make it possible to charge them into
conventional shot blasting machines and, when most of the
slag has been removed, to charge them into basic oxygen
furnaces, electric furnaces, iron foundry cupolas and the ~
like, for further use of the iron. A typical piece will ~ -
have a non-geometric shape and dimensions up to about two
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feet by two feet by six inches. However, because of the
random way in which the slag is broken into pieces, any
given slag pit will produce blast furnace slag iron pieces
having a wide variety of shapes and sizes, down to as little
as about one-quarter inch.
In the practice of this process, the blast furnace
slag iron pieces, or pieces of other metal and slag, are
; first prepared into suitable sizes, by the use of wrecking
balls or similar well-known techniques. The pieces containing
significant quantities o~ blast furnace iron or other metal
to be recovered are then separated from the other, principally
slag~containing, pieces. In the case of iron, this separation
may easily be effected by the use of an electromagnet. The
suitably sized pieces are then transported, as by trucks,
conveyor belts, railroad cars, or the like to the slag
processing unit.
The slag processing unit is a tumbling and shot
blasting machine, of a general type which is known in the
art and commercially available. In this machine, the
charge of slag-metal pieces, such as blast furnace slag
iron, are placed in a suitable location, such as in a
container, wherein they are operated on by a conveyor,
rotating and tumbling the mass of individual pieces about,
in order to achieve a continuing redistribution of the
pieces. As this continuing redistribution is taking place,
the pieces on at least one face of the tumbling mass are
subjected to the impact of a continuous flow of relatively
high velocity, hard pellets or similarly shaped particles,
commonly called shot or grit. Shot is relatively uniformly
shaped, usually spherical, particles of metal, typically a
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relatively hard high carbon steel alloy. Grit is similar to
shot, but instead of being spherical, it has facets and
sharp corners. The hardness of the shot or grit must be
substantially greater than the hardness of the slag, so
that the shot or grit will erode the slag when the slag metal
pieces are impacted with the high velocity shot or grit. -
This shot or grit is impacted against the slag-
metal pieces, using a relatively high velocity impeller, for
taking large quantities of the shot or grit and impelling
them against the slag-metal pieces at relatively high velocity.
This impact, occurring relatively continuously, while contin-
uously redistributing the slag-metal pieces, such as blast
furnace slag iron pieces, throughout the mass of such pieces, ~
allows the achievement of relatively uniform exposure of all ;
surfaces of all of the slag-metal pieces to the impact of the
shot or grit. As a result of this process, in a relatively
short period of time, on the order of about ten minutes to
about one or two hours, a surprisingly good removal of the
slag from the pieces is achieved, not only at the surface
of each piece, but also extending substantially downwardly
into most, if not all, of the crevices and fissures in the
piece. If the process begins with blast furnace slag iron
pieces which have a slag content of about twenty to forty
percent by weight and a corresponding blast furnace iron
content of about sixty to eighty percent by weight, enough
slag may be removed by this process that the final pieces
will have a slag content as low as about two percent by -~
weight. `~
The precise slag content of the final product
3a can be regulated by varying the conditions of the process,
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and particularly the size of the shot or grit, the amount
of shot or grit used, the velocity imparted to the shot or
grit, the duration of the shot blasting process, and the
extent to which the shot blasting enclosure is filled with
slag-metal pieces. To a lesser extent, some of the superficial
removal of slag is dependent upon the amount of tumbling of
the individual pieces which is achieved by the conveyor for
these pieces. However, this tumbling only removes surface
slag, and is definitely not capable of removing, by itself,
the slag located in fissures and crevices, which must be
removed as well in order to be able to achieve a commercially
valuable product having relatively low slag content, on the
order of ten percent by weight or preferably even less.
The product of the invention is a body of metal,
blast furnace iron when the process is applied to blast
furnace slag iron pieces, comprising an irregularly shaped
body, the dimensions of which may vary within wide limits
from a fraction of an inch to approximately two or three
feet, and which has a multiplicity of surface-exposed fissures
and crevices throughout the body, these fissures and crevices
being relatively free of slag, the individual pieces having
- a total slag content of up to about ten percent by weight
and preferably no more than about two or three percent by
weight.
It is important to note that, because of the
nature of the process, the slag which is located in deep
crevices or fissures which extend to the surface of the
individual pieces is accessible to the shot or grit and can
be removed substantially completely by the impacting of shot
or grit on those pieces.
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In the process of the invention, the shot or grit
` impacting the slag produces a large quantity of relatively
fine slag particles, as a residue of the process. These
particles may be utilized as a component of Portland cement
or the like in order to realize some economic value from this `
otherwise useless slag.
In the accompanying drawings:
Figure 1 is a schematic representation, in perspec-
tive, of a tumbling and blasting machine which may be utilized
in the practice of the process of this invention;
Figure 2 is a top plan view of a representative
piece of blast furnace slag iron prior to treatment by the
process of the invention;
Figure 3 is a cross-sectional view taken along 3-3
of Figure 2;
Figure 4 is a top plan view of the product of this
invention, corresponding essentially to the raw material of
Figure 2 with a majority of the slag removed, so that the
final slag content of the product is no more than about two
percent by weight; and
Figure 5 is a cross-sectional view, taken along
line 5-5 of Figure 4.
Viewing Figure 2, the numeral 10 generally designates
a representative blast furnace slag iron piece. The piece
illustrated, which will have a maximum dimension of approx-
imately two or three feet and a maximum thickness of
approximately six inches, comprises a principal continuous
phase of blast furnace iron, generally designated by the
numeral 12, and an outer covering of slag, generally designated
by the numeral 14.
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Viewing Figure 3, it will be seen that the body of
iron contains a large number of crevices and fissures, of
varying depths, sizes and shapes. Many of these fissures,
which are generally designated by numeral 16, are substantially
filled with varying amounts of hard, tough, tightly adhering
slag.
Viewing Figure 3, it will be seen that such
portions of iron as are generally designated by numeral 12
are seen in Figure 2 as being quite small and superficially
exposed iron segments on the surface of piece 10. In Figures
4 and 5, the final blast furnace iron product of this
invention is generally designated by numeral 18.
It should be understood that Figures 2 to 5 inclusive
are intended merely to be general schematic representations
of what a piece of blast furnace slag iron may look like
before and after the process of this invention and do not
correspond precisely to any given piece of material.
Pieces 10 are formed from a blast furnace when
the molten slag, containing about two to about five percent
of molten iron, is "tapped off" through the slag notch or
cinder notch of a conventional blast furnace. That iron
and slag mixture is flowed, in the molten state, into
suitable slag pits, where it is allowed to harden. This
pit material is broken up and removed to a slag processing
facility, where relatively large chunks of iron and slag
are broken down into substantially smaller blast furnace
slag iron pieces, such as by the use of a wrecking ball.
In a typical example, a wrecking ball weighing
at least 15 tons would be dropped onto the pieces of iron
and slag from a height of at least 60 feet. This process
shatters the slag into a large number of small pieces, from
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which the iron~containing blast furnace slag iron piecesmay be separated by the use of a suitable electromagnet
which can be ad]usted to separate out only pieces having a
predetermined amount of iron. Therefore, although the slag
pit contains a predominant amount of slag and a relatively
minor amount of iron (two to five percent), the blast
furnace slag iron pieces which are removed at the slag
processing facility will comprise only those pieces having
some significant amount of iron. The pieces which are
utilized in the process of this invention will desirably have
sizes of up to approximately two or three feet in maximum
dimension, any larger pieces being impacted again with the
wrecking ball, to reduce their size to a suitable handleable
size. The maximum size of these pieces is determined by
the size of piece that can be charged into and efficiently
processed in, a shot blasting machine and subsequently
accommodated in a melting furnace.
These blast furnace slag iron pieces, having
maximum dimensions of up to two or three feet, are then
transported, as by conveyor, truck, or railroad car to
the final processing facility.
Figure 1 illustrates schematically one form of
tumbling and shot blasting machine usable in the process `-
of this invention, which is commercially available. One
suitable such tumbling and shot blasting machine is sold
by Wheelabrator-Frye Inc. under the "Super-Tumblast"
trademark. These machines, which come in different sizes
and capacities, essentially comprise an enclosed chamber -
in which a given quantity of material is charged, and in
which the mass of pieces is tumbled while it is impacted
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by a recirculating, high velocity continuous stream of
pellets of shot or grit, which are discharged downwardly
onto the mass of rotating pieces.
Viewing Figure 1, the tumbling and shot blasting
machine, which is generally designated by numeral 20, is
seen to comprise a housing 22 in which is formed an enclosure
24 into which the pieces to be worked on are charged.
Enclosure 24 has a door 29 which can be opened for inserting
and removing the pieces 10, and which is closed during the
actual tumbling and shot blasting operation. Located within
enclosure~24 is conveyor 26, which is an L-shaped conveyor,
comprising individual metal slats 28, each of which has
a plurality of circular apertures 30. Each of the apertures
- 30 has a diameter of approximately 5/8 inch. The conveyor
26 is mounted for counterclockwise movement, during the shot
blasting step, on a plurality of drive wheels 36 which are
driven by a suitable drive motor (not shown). The conveyor
direction is reversed to discharge finished product from
the shot blasting machine.
The conveyor 26 has a vertical section and a
horizontal section, forming an L-shape. When the pieces
10 to be treated are loaded into enclosure 24, they are
placed on top of the horizontal surface of the conveyor 26.
The drive motor for conveyor 26 may be reversible, so that
it may be reversed to facilitate discharge of the finished
pieces when door 29 is opened. A typical drive speed for
conveyor 26 is fifteen feet per minute.
Located in the upper portion of the housing 20
are one or two rotatably mounted thrust members 32 called
throwing wheels or impellers, the purpose of which is
continuously to deliver large quantities of shot or grit,
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at high velocity, against the upper face of the mass of
pieces 10 located in enclosure 24. For simplicity, only
one throwing wheel is illustrated, but, if two wheels are
utilized, as is preferred, both wheels are of the same size
and the two wheels are parallel. The two throwing wheels
~2 are, in a preferred embodiment of the invention, rotated
at approximately 3,600 rpm, and are each 15 inches in diameter.
The two wheels 32 may each be driven by a motor (not shown)
of about 60 to about 75 horsepower, and each imparts to the
shot a tangential velocity of approximately 19,000 feet per
minute. The throwing wheels will preferably deliver in the
range from about two thousand to about four thousand pounds
of shot per minute, if an enclosure 24 having a capacity to
handle about fifty cubic feet of slag iron pieces 10 is
used. The design of the throwing wheels and their details
are well known.
As illustrated in Figure 1, the shot is generally
designated by numeral 34 and preferably comprises small,
hard spherical balls, more fully described below.
It is important to note that, for optimum operating
efficiency, the enclosure 24 is filled with pieces 10 only
to a level of about four-tenths of the total height of the
enclosure, thus occupying about forty percent of the
enclosure volume. It is this optimum volume which is
occupied which is used to designate the machine capacity.
Thus a fifty cubic foot machine contains material occupying
fifty cubic feet, when it is forty percent filled. This
design capacity is selected to give the optimum efficiency
of the shot blasting operation, and other volumes may be
used, but with less efficiency.
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- The shot 34 impacts the upper surfaces of the mass
of blast furnace slag iron pieces 10 and, because of the
substantial hardness and kinetic energy of the shot, abrades
away the slag 14 in small pieces, generally on the order of
less than several hundredths of an inch in size. Also, some
larger pieces of slag are broken away from the pieces 10 by
' virtue of the impact of the various pieces 10 against each
other as they are tumbled about enclosure 24 because of
the movement of conveyer 26.
10The movem~nt of conveyor 26 effects a continuous
tumbling movement and redistribution of the pieces 10 within
enclosure 24, so that different pieces and different surfaces
of each piece are continuously exposed to the direct impact
of the high velocity shot 34, thereby to effect a uniform
abrasion of the slag from the iron or other metal to be
recovered. After each piece of shot impacts one or more
pieces 10, it passes downwardly through the mass of those
pieces to the conveyor 26, where the movement of the pieces
10 on the conveyor 26 causes a flow of the individual shot
members. The pieces of shot exit the enclosure 24 by passing
downwardly through apertures 30 in the slats 28 of conveyor
26. The apertures 30 are appro~imately 5/8 of an inch in
diameter, and will also, therefore, pass appropriately small
pieces of slag, and occasional small pieces of iron which may
also be abraded in the enclosure 24. These small pieces of
shot, slag and iron, all of which are necessarily less than
5/8 inch in maximum dimension, pass through the apertures
30 in the slats 28 and fall into enclosure 40 in the bottom
of the unit 20, where they are transported by conveyor
screw 38.
The conveyor 38 may be a screw conveyor or a
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shaking conveyor, which transports the combination of shot,
slag and iron across a screen of 1/4 inch mesh (not shown).
- The particles which are greater than 1/4 inch in size remain
on the screen, and constitute mostly slag particles and some
iron. These particles are then passed, by a suitable
conveyor (not shown), past a magnetic separator, which
recovers the highly magnetic materials, comprising both
iron and slag, but having enough iron to merit recovery for
subsequent recovery and reuse. The particles which are less
than 1/4 inch in diameter, comprising all of the shot, most
of the slag particles generated by the shot blasting operation
and some iron particles, drop freely vertically through the
screen and are conveyed by bucket elevator 42 and screw
conveyor 46 to an air separator (not shown) where the
cascading stream of particles is contacted by a high velocity
air stream. This air separator is located in the upper
chamber 48. secause the slag is of substantially lower
density than the shot (or grit), it is blown further away
by the air stream and is blown into a ducting system (not
shown) which transports the slag to a bag house. The
heavier shot and smaller slag iron pieces are not blown as
far as the larger slag pieces, and they fall into shot
hoppers (not shown) in chamber 48. These shot hoppers
have adjustable discharge openings, and they function to
keep the throwing wheels loaded with shot.
It is notable that the slag particles which pass
through the screen, having a 1/4 inch or less size, as
well as the very fine slag collected in the bag house,
could be used as a component of certain types of cement
3Q which normally incorporate blast furnace slag therein.
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It is to be noted that the structural details of
the tumbling and shot blasting mechanism 20 are well known
in the art and form no part of this invention. In the
most preferable embodiment of the invention, the tumbling
and shot blasting unit is of at least fifty cubic foot size,
that is to say, the optimum working capacity of enclosure 24
is fifty cubic feet.
In the operation of the process of this invention,
it is first necessary to reduce the slag iron pieces to usable
sizes of up to approximately two or three feet in maximum
dimensions. A substantial number of these pieces, typically
comprising a charge weighing about 5,500 to 6,000 pounds, when
- a fifty cubic foot enclosure 24 is used, are then placed in
a suitable tumbling and shot blasting mechanism 20 for the
purpose of providing a relatively continuous tumbling and
agitation of the individual pieces.
The individual pieces are then subjected to the
impact of a high velocity stream of small spherical steel
shot or hard grit 34, having a flow rate in the range from
about 2,000 to about 4,000 pounds per minute and a hardness
which is substantially gréater than the hardness of the slag
and having a size which is in the range of up to about 1/10
of an inch, and is preferably in the range from approximately
.025 inches to approximately .060 inches for a period in
the range from about ten to about sixty minutes. It has
been found that the smaller particles, preferably about
.039 inches nominal size, provide a more effective cleaning, -i
in that they are better able to penetrate deeply into any
crevices and fissures in the blast furnace slag iron pieces.
It is to be noted that when shot is sold the individual
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particles usually cover a range of sizes around thespecification size. Therefore, if .039 inch shot is
specified, some of the pieces supplied will be somewhat
less than .039 inches in diameter and some slightly greater
than that size.
It is also notable that there are approximately
400,000 shot pellets per pound, if a .039 inch diameter
steel shot is used, and that this would desirably produce
a flow rate of approximately 3,000 pounds per minute using
two fifteen inch diameter throwing wheels 32, each driven
by a 75 horsepower motor. The shot consists of a high
carbon steel alloyed with chromium, having about 1 percent
carbon, and having a hardness of approximately 48 on the
Rockwell C scale. A desirable shot having these character-
istics is sold by Wheelabrator-Frye Inc. under the
designation S-390.
The velocity imparted to the shot or grit and its
flow rate may be varied within wide ranges, and the precise
velocity and flow rate utilized will depend upon the size of
the available drive motor for the throwing wheel and the
time period within which it is desired to clean the slag
from the iron. Desirably, the velocity imparted to the
shot or grit, for a fifty cubic foot volume of charge, will
be in the range from approximately 10,000 to approximately
35,000 feet per minute, leaving the throwing wheel. It is
most preferred to impart a velocity of approximately 19,000
feet per minute at the throwing wheel, when utilizing a 50
cubic foot machine. The optimum flow rate for a fifty cubic
foot charge would be about 3,000 pounds per minute.
3Q
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Example 1
Approximately 20,000 pounds of blast furnace slag
iron having sizes of up to two or three feet in maximum
dimensions and thicknesses of up to about six inches, were
processed using the method of this invention. The machine
utilized for the processing was a 50 cubic foot wheelbrator
Super-Tumblast, having two 60 horsepower throwing wheels and
utilizing steel shot having a .055 inch nominal diameter,
and designated as S-550 shot. This machine imparts approx-
imately 19,000 feet per minute of linear velocity to thesteel shot at the point of departure from the throwing wheel
at a flow rate of about 2,400 pounds per minute. The conveyor
26 was set at an operating speed of approximately 15 linear
feet per minute.
In one instance, the enclosure was loaded with
approximately 4,200 pounds of the slag iron pieces, and in
each of two other instances it was loaded with approximately
7,500 pounds of the slag iron pieces. The 4,200 pound batch
was processed for fifteen minutes, one of the 7,500 pound
batches was processed for twenty-five minutes~, and the other
was processed for forty minutes.
The 4,200 pound batch was inspected at various
stages during the fifteen minute blast period. After five
minutes of processing, cleaning was well under way, but the
product was not yet satisfactory. After ten minutes, the
product was judged to be at least ninety percent metallic,
and after fifteen minutes the material was at least 96 to
97 percent metallic.
The two 7,500 pound batches constituted grossly
overloaded conditions for the 50 cubic foot Super-Tumblast,
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... .
~037~0
which really should not be charged with more than 5,500 to
6,000 pounds of slag iron for efficient processing. It was
a matter of practical interest, however, to observe just how
well the machine would do under these conditions.
With the first 7,500 pound test, fifteen minutes
of processing gave good results, but the percentage of
metallics was not as high as it was in the case of the 4,200
pound batch after the same blasting time. This was to be
expected, because in the case of the 7,500 pound load, the
pieces did not receive the degree of exposure to the shot
that they received in the 4,200 pound load. After a total
of twenty-five minutes of processing, this load had been
cleaned of slag up to the same percentage of metallics as
was observed after fifteen minutes of processing with the
4,200 pound batch.
In the second 7,500 pound test, the material was
inspected after thirty minutes of processing, and it was
found to be at least 96 percent metallic. After forty
minutes of processing, the product was at least 98 percent
metallic
Example II
A different 50 cubic foot Super-Tumblast unit was
employed for a second series of tests. It was decided that,
although the equipment performs rather well when overloaded,
it is better to charge the machine with no more than the
recommended fifty cubic feet of slag iron, which weighed
about 5,700 to 6,000 pounds.
The only other significant difference in the test
conditions between Example I and II was that in Example II,
the shot diameter was 0.039 inches, compared to 0.055 inches
in Example I.
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~(137~20
- Four tests were conducted for this Example, in
order to prepare material of varying cleanliness (freedom
from slag) by varying the length of the processing time.
One load was processed for twenty minutes, one for thirty
minutes, and two for forty minutes.
The results of the thirty and forty minute
processing cycles were excellent; at least 98 percent metallics
had been achieved in all three tests. Essentially 95 percent
metallics was reached in the twenty minute processing.
Generally speaking, the results of the second
series of tests were superior to those of the first. This
conclusion is attributed mainly to the smaller shot diameter,
which apparently penetrated the crevices of the pieces more
thoroughly than did the coarser shot of the first series.
It is notable that the process of this invention
is equally applicable to the steel metallics magnetically
extracted from the slag produced by basic oxygen furnaces,
open hearth furnaces, and electric arc furnaces, and to iron
metallics recovered from various foundry melting slags.
The product of this invention is a body of a
relatively high purity metal, which may be blast furnace
iron, steel, aluminum, zinc, copper or the like. The product
has an irregular surface having a substantial number of
crevices and fissures, which are free of slag, the total
slag content of each piece being no more than about ten
percent by weight and preferably being no more than about -~
two percent by weight.
The iron product of this invention can be used
in all forms of steel making. That is to say, the cleaned
3Q blast furnace iron can be used in making steel by any
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,: ' . .' ' ~. ' . ~ .'
.. ... ~, , .
~\ ~
1~377~0 :
process, as well as in making iron castings, as a substitutefor the cast iron scrap and pig iron normally used in making
iron castings, The ultimate composition of the product of
this invention would most desirably be no less than about 98
percent iron and no more than 2 percent slag, and have a
total of no more than up to approximately 0.05 percent by
weight of sulfur. It is to be noted that this is to be
compared with conventional blast furnace iron which has up
to about approximately .05 percent sulfur maximum, and the
slag from the blast furnace which has up to approximately
two percent by weight of sulfur. The reason why the sulfur
content of the cleaned blast furnace iron produced by this
process is about 0.05 percent or less, notwithstanding the
relatively high sulfur content of the slag, is because the
; amount of slag is so low as to be virtually insignificant
as a sulfur contributor.
It is notable that the process of this invention
can be varied within reasonable limits without departing
from the spirit and scope of the invention. For example,
the particular hardness, size or shape of the shot or grit
used, the velocity imparted thereto and the flow rate thereof,
the linear speed of the conveyor, and the precise size and
quantity of the metal-slag pieces, as well as the time during
which the process is applied, can be varied without departing
from the spirit and scope of the invention.
It is also notable that the process of this
invention may be used to treat aluminum, brass, copper or
other metals to remove slag from the crevices and fissures
thereof.
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