U.S. patent number 3,796,563 [Application Number 05/256,276] was granted by the patent office on 1974-03-12 for method of manufacturing metal sheet and foil.
This patent grant is currently assigned to Bethlehem Steel Corporation. Invention is credited to Eugene M. Rudzki, George E. Wieland, Jr..
United States Patent |
3,796,563 |
Wieland, Jr. , et
al. |
March 12, 1974 |
METHOD OF MANUFACTURING METAL SHEET AND FOIL
Abstract
An aqueous slurry of superconcentrated iron ore powder and a
binder is continuously deposited on a supporting carrier, dried,
and the resultant coating heated in a reducing atmosphere to about
1,500.degree. to 2,100.degree. F. for several minutes to partially
reduce the oxygen content of the ore. The coating is then stripped
from the carrier and rolled to provide a strip of increased
density. The strip is open coiled and heat treated to completely
reduce the oxygen content of the ore, as well as to sinter the
strip, and rolled to final gauge. The strip is then annealed, which
both softens and further sinters the strip, and finish rolled.
Inventors: |
Wieland, Jr.; George E.
(Bethlehem, PA), Rudzki; Eugene M. (Bethlehem, PA) |
Assignee: |
Bethlehem Steel Corporation
(Bethlehem, PA)
|
Family
ID: |
22971627 |
Appl.
No.: |
05/256,276 |
Filed: |
May 24, 1972 |
Current U.S.
Class: |
419/40; 419/26;
419/29; 419/53; 419/28; 419/43 |
Current CPC
Class: |
B22F
5/006 (20130101); B22F 3/18 (20130101); B22F
3/001 (20130101) |
Current International
Class: |
B22F
3/18 (20060101); B22F 5/00 (20060101); B22F
3/00 (20060101); B22f 001/00 (); B22f 003/18 ();
B22f 003/24 (); B22f 003/00 () |
Field of
Search: |
;148/126
;75/211,214,200,5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Quarforth; Carl D.
Assistant Examiner: Hunt; B.
Claims
1. A method of producing a strip of metal from a powder of at least
one member of the group consisting of metal oxides and oxide ores,
said oxides and ores being reducible by hydrogen, comprising:
a. preparing a slurry comprising said powder and a thickening and
binding means,
b. depositing said slurry on a supporting carrier to provide a
coating,
c. drying said coating on said carrier,
d. heating said coating, while still on said carrier, in a reducing
atmosphere at a temperature and for a time sufficient to partially
reduce the oxygen content of said powder whereby at least about 10
percent of the metal of the powder is in a metallic state, the
balance of said metal being combined as one or more oxides, as well
as to cause the particles of said coating to cohere,
e. removing the coating from the carrier to provide a formed
layer,
f. rolling said formed layer into a strip having a density of about
50 to 95 percent that of the theoretical density of the metal,
g. open coiling the strip and heating it in a reducing atmosphere
for a time sufficient to reduce the oxygen content of the strip to
about 2 wt. percent max., and
h. rolling the strip to increase its density to substantially
said
3. A method of producing a strip of ferrous metal from a powder of
iron ore, comprising:
a. preparing a slurry comprising said powder and a thickening and
binding means,
b. depositing said slurry on a supporting carrier to provide a
coating,
c. drying said coating on said carrier,
d. heating said coating, while still on said carrier, in a reducing
atmosphere to a temperature within the range of 1,500.degree. to
2,100.degree. F. for a period of time sufficient to partially
reduce the oxygen content of said ore whereby at least about 10
percent of the iron is in a metallic state, the balance of said
iron being combined as one or more oxides, as well as to cause the
particles of said coating to cohere,
e. removing the coating from the carrier to provide a formed
layer,
f. rolling said formed layer into a strip having a density of 3.8
to 7.3 gm./cc.,
g. open coiling the strip and heating it in a reducing atmosphere
for a time sufficient to reduce the oxygen content of the strip to
about 2 wt. percent max., and
4. A method as recited in claim 3, in which:
1. said slurry comprises 60 to 80 wt. percent of said powder,
balance water and a thickening and binding means,
2. in step (g), said strip is heated to 1,500.degree. to
2,100.degree. F. for 4 to 6 hours, and
5. A method as recited in claim 4, in which said iron ore is
superconcentrated.
Description
BACKGROUND OF THE INVENTION
This invention relates to powder metallurgy, and more particularly
to a method of producing metal strip and foil from an aqueous
slurry of a powder of metal oxides and/or oxide ores.
It is broadly old to produce strips or foils of metal from metallic
powders, e.g., iron powder. One well-known method for producing
such strips may comprise, for example, preparing slurry of iron
powder and a liquid binding and thickening agent and depositing the
slurry on a supporting member. The resultant coating is dried and
either sintered or removed from the supporting member and cold
rolled into strip. Subsequently, the strip may be subjected to
various combinations of heating and rolling operations.
While the above-described processing operations are satisfactory
for producing strip from metals, such a process has not been
successful for producing strip from metal oxides, oxide ores, and
combinations thereof. It has been found that a dried slurry of
metal oxides or oxide ores has insufficient strength to be removed
from a supporting member and cold rolled, and sintering of the
dried slurry prior to removal from the supporting member and
rolling is not effective, since the particles of which the dried
slurry is comprised will not satisfactorily cohere.
Thus, prior processes of producing sheet and foil from metal oxides
or oxide ores, e.g., magnetite or hematite, comprised, for example,
conventional processing comprising the production of pig iron in a
blast furnace, the conversion of the iron into steel in an open
hearth furnace and the mechanical reduction of ingots of said steel
into slabs and hot-rolled strip. The hot-rolled strip was
subsequently cold-rolled into sheet and foil. Alternatively, the
magnetite or hematite could be crushed, beneficiated, pelletized,
chemically reduced, and re-crushed to produce metal powder suitable
for the above-described powder-processing steps.
It is an object of this invention to provide a method of producing
sheet and foil from metal oxides and oxide ores, said method
bypassing the above-described pyrometallurgical steps, e.g., in the
case of magnetite or hematite, the steps of ironmaking and
steelmaking, as well as the roughing and hot-rolling operations; it
is also an object to bypass the pelletizing and re-crushing
operations of the prior art powder metallurgy practice.
SUMMARY OF THE INVENTION
We have discovered that, when a slurry of a powder of a metal oxide
or an oxide ore is prepared, and said slurry is deposited on a
supporting member and given a relatively short, high temperature
heat treatment in a reducing atmosphere until about 10 percent of
the metal of the powder is in a pure metallic state, the resultant
coating has sufficient strength so that it can be stripped from the
supporting member and rolled into strip. Sufficient additional
strength is developed during the rolling operation to permit the
strip to be open coiled and heat treated in a reducing atmosphere
wherein the oxygen content of the strip is substantially completely
reduced. The strip is then rolled to substantially final gauge. It
may then be annealed and finish rolled, e.g., skin passed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The first step of the process of the invention is the preparation
of a slurry of superconcentrated oxide ore and a thickening and
binding means. Preferably, the slurry is aqueous, although organic
liquid slurries, e.g., alcohols, could be used. While the invention
is applicable to oxide ores such as copper ore, nickel ore and iron
ore, as well as to metal oxides, e.g., iron oxide, provided that
such ores and oxides are reducible by hydrogen, the preferred
embodiment will be described in connection with a superconcentrated
oxide ore of iron. By "superconcentrated oxide ore" is meant an
oxide ore which is highly beneficiated whereby no more than about 2
percent of the ore, and preferably less than 1 percent thereof, is
foreign matter. Such foreign matter includes, for example,
silica.
The slurry is prepared by admixing a solution comprising about 70
percent by weight, of a powder of superconcentrated magnetite,
hematite, or mixtures of magnetite and hematite, and about 30
percent, by weight, of an aqueous solution of a thickening and
binding agent, e.g. a solution of ethyl or methyl cellulose. The
powder, preferably, has a particle size of -100 mesh. The slurry is
prepared so as to have an apparent viscosity of about 700 to 25,000
cps., and is deposited on a supporting carrier to provide a coating
about 0.005 to 0.250 inch thick. The carrier may be, for example,
an endless belt.
The endless belt, with the coating thereon, is transported into
heating means, e.g., a furnace, where the coating is first dried
and then heated in a reducing atmosphere to a temperature of about
1,500.degree. to 2,100.degree. F. for a period of time sufficient
to reduce the oxygen content of the ore to a point where at least
about 10 percent of the iron is in a metallic state. If the
temperature of the furnace is about 1,800.degree. F., this period
of time may be from about a few seconds up to about 2 minutes,
depending on the thickness of the coating. At lower temperatures
this period is somewhat longer, depending upon the thickness of the
coating, while at higher temperatures this period is
correspondingly shorter.
It is essential for the powder to be reduced to a point where at
least about 10 percent of the iron is in a metalllic state. At only
very slightly lower percentages of metallic iron, the particles of
the coating will not cohere satisfactorily and the coating will
crumble when removed from the belt. At his point in the process,
the iron ore cannot be substantially completely reduced, as unduly
long times would be required.
In order to reduce the oxygen content of the iron ore sufficiently
for 10 percent of the iron to be metallic, it is necessary to
reduce the total oxygen content of the ore by 33 percent, if the
ore is magnetite, and 40 percent if the ore is hematite. That is,
the oxygen content of magnetite must be reduced from about 27 wt.
percent to about 18.5 wt. percent, while the oxygen content of
hematite must be reduced from about 30 wt. percent to about 18 wt.
percent. For mixtures of magnetite and hematite, the required
oxygen reduction is somewhere between 33 and 40 percent, depending
upon the relative amounts of each ore.
It is important to note that these first four steps of the subject
process, viz., preparing an iron ore slurry, depositing the slurry
on a substrate, drying the slurry, and partially chemically
reducing the ore, can be done continuously. This greatly enhances
the commercial feasibility of the subject process.
The coating of partially reduced ore has sufficient strength so
that it can be removed from the carrier. The coating is then hot or
cold rolled to provide a strip of increased density. At this point
in the process, the density of the strip is equal to 50 to 95
percent of the theoretical density of iron, i.e., 3.9 to 7.5
gm./cc..sup.3.
The strip is next open coiled and heated in a reducing atmosphere
to reduce the oxygen content of the strip from about 18 wt. percent
to a maximun of 2 wt. percent, and preferably to less than 0.2 wt.
percent. A temperature within the range of
1,500.degree.-2,100.degree. F. for a time period of 4 to 6 hours is
suitable, although longer times are of course permissible.
The strip is then hot or cold rolled to increase its density to the
theoretical density of iron, viz. 7.9 gm./cc., and thus
substantially eliminate porosity. The strip may be used in this
condition. However, preferably its thickness is reduced to within
about 2 percent of final gauge, and it is then annealed and finish
rolled, e.g., skin passed.
As a specific example of our invention, a slurry of 70 wt. percent
superconcentrated magnetite (containing 0.7 wt. percent gangue), 30
wt. percent of a 1 percent solution of Methocel 4,000, manufactured
and sold by the Dow Chemical Company, which is a methyl cellulose
solution having a viscosity of 4,000 cps., was prepared. The slurry
was deposited on a stainless steel endless belt to provide a
coating 0.060 inch thick and 4 inches wide. The coating was then
transported through a heat treatment furnace containing a reducing
atmosphere, e.g., hydrogen, at 1,800.degree. F., where the coating
was in the heating zone for about 2 minutes. It was then cooled, in
a manner to prevent oxidation, to room temperature. It was 0.038
inches thick, and about 12 percent of the iron was in the metallic
state.
The coating of partially reduced ore was then cold rolled into
strip, thereby increasing its density to 6.0 gm./cc. and decreasing
its thickness to 0.013 inch. The strip was open coiled and heat
treated in a reducing atmosphere at 1,8000.degree. F. for 16 hours
to decrease the oxygen content of the strip to 0.1 wt. percent. The
strip was then hot rolled to substantially final gauge of 0.007
inch. The hot rolling was done at 1,800.degree. F. The density of
the strip was 7.74 gm./cc. The hot-rolled strip was then annealed
at 1300.degree.-1400.degree. F. and finish rolled. The strip was
tested, and it was found to have a tensile strength of 32,900 psi.
and a tensile elongation of 14.1 percent. Strip of similar
compositions, but produced by the aforementioned prior art iron
powder metallurgy techniques, had a tensile strength of 30,400 psi.
and a tensile elongation of 13.5 percent. The strip is suitable for
fabrication into metal containers or heat exchangers, for
example.
While the subject process has been described in connection with
unalloyed iron ore, it is permissible to add powders of alloying
elements, e.g., carbon, to the ore.
* * * * *