U.S. patent number 3,904,180 [Application Number 05/361,589] was granted by the patent office on 1975-09-09 for apparatus for fluxing and filtering of molten metal.
This patent grant is currently assigned to Southwire Company. Invention is credited to Joseph A. Bass, Lewis A. McKenzie, Frank M. Powers.
United States Patent |
3,904,180 |
Bass , et al. |
September 9, 1975 |
Apparatus for fluxing and filtering of molten metal
Abstract
This disclosure relates to a system for continuously treating
molten metal for substantially removing gas and finely-divided
solids therefrom. A two-stage tandem system is provided wherein
hydrogen gas is fluxed from the molten metal in the first stage,
and finely-divided solids are filtered from the molten metal in the
second stage by passing the molten metal through a refractory
granular filtering medium. The hydrogen is fluxed in the first
stage by passing a fluxing gas upwardly therethrough consisting of
approximately 15% chlorine gas and approximately 85% nitrogen gas.
The granular filtering material in the second stage is adapted to
assume a buoyant condition as molten metal is passed upwardly
therethrough thereby prohibiting the quick clogging of the
material.
Inventors: |
Bass; Joseph A. (Bremen,
GA), McKenzie; Lewis A. (Carrollton, GA), Powers; Frank
M. (Carrollton, GA) |
Assignee: |
Southwire Company (Carrollton,
GA)
|
Family
ID: |
23422631 |
Appl.
No.: |
05/361,589 |
Filed: |
May 18, 1973 |
Current U.S.
Class: |
266/215; 75/412;
266/220; 266/230; 75/681; 266/225 |
Current CPC
Class: |
C22B
9/055 (20130101); C22B 21/066 (20130101); C22B
9/05 (20130101) |
Current International
Class: |
C22B
21/06 (20060101); C22B 21/00 (20060101); C22B
9/00 (20060101); C22B 9/05 (20060101); C22B
021/06 () |
Field of
Search: |
;75/68R,46,93A
;266/34R,34PP,34T,35 ;210/20,434 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rutledge; L. Dewayne
Assistant Examiner: Andrews; M. J.
Attorney, Agent or Firm: Wilks; Van C. Hanegan; Herbert M.
Tate; Stanley L.
Claims
We claim:
1. A two-stage tandem apparatus for continuously treating molten
metal to substantially remove gas and finely-divided solids
therefrom, comprising a treating chamber including an inlet and an
outlet for the molten metal and having side walls and a floor, a
refractory weir dividing said chamber into first and second
sections, said weir extending vertically and being spaced from said
floor for providing communication between said first and second
sections, a removable lid completely covering said first and second
sections, means for introducing a fluxing gas into said first
section for fluxing hydrogen gas from molten metal contained
therein, a filtering medium disposed only in said second section
for filtering finely-divided solids from molten metal passed
upwardly therethrough, and means for providing a protective
atmosphere above the surface of the molten metal in said first and
second sections to prevent the reabsorption of hydrogen gas into
the metal after it has been fluxed therefrom, said means for
providing including sealing means associated with said removable
lid.
2. Apparatus as defined in claim 1 wherein said filtering medium is
adapted to assume a buoyant condition as molten metal is passed
upwardly therethrough, and including means disposed over said
filtering means for preventing floatation thereof.
3. Apparatus as defined in claim 2 wherein said floatation
preventing means is a perforated screen.
4. Apparatus as defined in claim 1 wherein said filtering medium
includes alumina balls.
5. Apparatus as defined in claim 1 wherein said filtering medium
includes crushed alumina.
6. Apparatus as defined in claim 1 including means for by-passing
molten metal past said filtering medium in the event of clogging
thereof.
7. Apparatus as defined in claim 6 wherein said by-passing means
includes spacing said weir from said removable lid to define a
by-pass flow path for the molten metal from said first section to
said outlet over the top of said weir.
8. Apparatus as defined in claim 7 wherein said weir is adjustably
mounted in oppositely facing grooves formed in opposite ones of
said side walls whereby the spacing of said weir from said
removable lid may be varied.
9. Apparatus as defined in claim 1 wherein said means for
introducing a fluxing gas includes at least one tube extending
downwardly through said first section and having a porous carbon
head disposed at the lower end thereof for dispersing fluxing gas
bubbles into the molten metal adjacent the bottom of said
chamber.
10. Apparatus as defined in claim 1 wherein said means for
introducing a fluxing gas includes at least one porous carbon block
mounted in the bottom of said first section for dispersing fluxing
gas bubbles upwardly through the molten metal.
11. A two-stage tandem apparatus for continuously treating molten
metal to substantially remove gas and finely-divided solids
therefrom, comprising a treating chamber having side walls, a floor
and a removable lid, a refractory weir dividing said chamber into
first and second sections, said weir extending vertically and being
spaced from said floor for providing communication between said
first and second sections, means for introducing a fluxing gas into
said first section for fluxing hydrogen gas from molten metal
contained therein, a filtering medium disposed only in said second
section for filtering finely-divided solids from molten metal
passed upwardly therethrough, and means for providing a protective
atmosphere above the surface of the molten metal to prevent the
reabsorption of hydrogen gas into the metal after it has been
fluxed therefrom, said means for providing including sealing means
associated with said removable lid.
12. Apparatus as defined in claim 11 wherein said means for
introducing a fluxing gas includes at least one porous carbon block
mounted in the bottom of said first section for dispersing fluxing
gas bubbles upwardly through the molten metal.
13. Apparatus as defined in claim 11 wherein said filtering medium
is adapted to assume a buoyant condition as molten metal is passed
upwardly therethrough, and including means disposed over said
filtering means for preventing floatation thereof.
14. Apparatus as defined in claim 13 wherein said floatation
preventing means is a perforated screen.
15. Apparatus as defined in claim 11 wherein said filtering medium
includes alumina balls.
16. Apparatus as defined in claim 11 wherein said filtering medium
includes crushed alumina.
17. Apparatus as defined in claim 11 including means for by-passing
molten metal past said filtering medium in the event of clogging
thereof.
18. Apparatus as defined in claim 17 wherein said by-passing means
includes spacing said weir from said removable lid to permit the
flow of molten metal over said weir from said first section into
said second section on the downstream side of said filtering
medium.
19. Apparatus as defined in claim 11 wherein said means for
introducing a fluxing gas includes at least one tube extending
downwardly through said first section and having a porous carbon
head disposed at the lower end thereof for dispersing fluxing gas
bubbles into the molten metal adjacent the bottom of said chamber.
Description
This invention relates generally to the treatment of metals and
metal alloys. More particularly, this invention relates to a method
of and apparatus for the treatment of metals and metal alloys in
the molten state prior to the casting thereof to provide molten
metal substantially free of gas and finely-divided solid
particles.
In the casting of light metals, e.g. aluminum and aluminum alloys,
it has been a common practice to melt the metal in open hearth or
other type melting furnaces which are heated by the burning of
conventional fuels. In preparing the metal for casting, the charges
of metal and desired alloying constituents are generally added to
the melting furnace to be melted, and thereafter the molten metal
is transferred to a holding furnace where close control of both the
composition and the temperature of the molten metal may be
maintained. Thereafter, the molten metal may be transferred by
suitable means from the holding furnace to either a transfer
crucible or directly to the pouring tundish of a casting
machine.
In the melting of the metal and its transfer from receptacle to
receptacle and finally to the casting machine, hydrogen gas may be
entrapped or dissolved within the molten metal. The hydrogen gas is
generated by the reaction of the metal with any moisture existing
throughout the system. Moreover, oxides of the metal and its
alloying constituents may be formed and dispersed throughout the
molten metal. Consequently, in the casting of the metal, e.g. in a
continuous process, the cast product may contain a large proportion
of the hydrogen gas in solution in the solid metal, as well as
small occluded oxide particles which tend to nucleate about
hydrogen-filled voids within the solidified metal.
The presence of hydrogen gas and finely-divided particles within
the cast product is, of course, a serious problem inasmuch as the
final product worked from the cast bar, such as continuously-formed
rod and wire, will have poor grain structure and, consequently,
reduced mechanical properties. Moreover, when the product is used
as an electrical conductor, the existence of undesirable
constituents may seriously reduce the electrical conductivity of
the product. The prior art has, therefore, proposed several methods
for fluxing molten metals with inert gases to reduce the hydrogen
content thereof, as well as for filtering the molten metal through
refractory filter media to remove finely-divided solid particles
therefrom.
Conventionally, molten metals have been batch fluxed by treating
the entire body of the melt in the holding furnace or in an
intermediate receptacle, such as a ladle. However, this method has
not been totally satisfactory because it is time-consuming and
requires large quantities of fluxing gas. Moreover, large
quantities of the hydrogen gas generally remain in the cast article
even after the batch fluxing due, primarily, to reabsorption of the
hydrogen gas and further generation thereof by reaction of the
metal with moisture that may be present throughout the system.
Moreover, while prior art methods of filtering molten metals
through refractory filter media to remove finely-divided solid
particles have been generally satisfactory in this respect, they
have not been beneficial in appreciably reducing the gas content of
a molten metal.
U.S. Pat. Nos. 3,039,864 and 3,172,757 granted, respectively, June
19, 1962 and Mar. 9, 1965 to P. D. Hess et al, disclose methods of
treating molten metals to both flux hydrogen gas therefrom as well
as to filter out finely-divided non-metallic solids. The method
according to each of these patents involves passing the molten
metal downwardly through a bed of refractory filter medium while,
at the same time, passing an inert gas therethrough. In U.S. Pat.
No. 3,039,864 the fluxing gas is disclosed as being passed in
counter-current flow relation to the flow of molten metal, while in
U.S. Pat. No. 3,172,757 the fluxing gas is disclosed as being
passed in co-current flow relation to the flow of molten metal.
While chlorine gas is generally recognized by the prior art as the
superior and desirable gas for use in fluxing hydrogen from molten
aluminum, each of the two above-noted prior art patents teaches
that chlorine gas is unsuitable for use in the methods disclosed
therein because of its tendency to form chlorides as well as to
result in clogging of the filter medium after only short periods of
operation. Consequently, the Hess et al patents disclose the use of
inert fluxing gases for use in fluxing hydrogen from aluminum, as
well as the use of nitrogen gas where the problem of
nitride-formation is not of significance.
It has been suggested that the reason that chlorine gas is superior
for fluxing hydrogen gas from molten aluminum is that the chlorine
will break down or otherwise overcome some film or surface
phenomenom that exists about the hydrogen gas bubbles, thereby
facilitating diffusion of the hydrogen gas into the fluxing
chlorine gas. Apparently, this surface phenomenon or film is not
broken down as completely with other inert fluxing gases.
It should be apparent, therefore, that even though the methods
disclosed in the Hess et al patents recognize the superiority of
chlorine gas for fluxing molten aluminum, the fact that the Hess et
al methods involve passing the fluxing gas directly through the
filter medium prohibits the use of chlorine gas because the
formation of chlorides will tend to clog the filter medium.
It is, therefore, a primary object of this invention to provide an
improved system for fluxing and filtering of molten metal.
More particularly, it is an object of this invention to provide a
system for both fluxing and filtering of molten metals,
particularly aluminum and aluminum alloys, that permits the fluxing
gas to at least partially include chlorine gas.
Still more particularly, it is an object of this invention to
provide a two-stage tandem treating system for fluxing and
filtering molten metals wherein the molten metal is fluxed in the
first stage of the system to remove hydrogen gas therefrom, and
then filtered through a granular filtering medium contained in the
second stage to remove finely-divided solids therefrom.
Another object of this invention is to provide a method for
continuously fluxing and filtering molten aluminum by passing a
fluxing gas at least partially comprised of chlorine gas through
the molten aluminum to flux hydrogen gas therefrom and to form
chlorides and other reacted solid products therewith, and then
separating the fluxed hydrogen gas, chlorides and other reacted
solid products from the fluxed molten aluminum before passing the
fluxed molten aluminum through a filtering medium to remove
finely-divided solids therefrom.
Still another object of this invention is to provide a method as
above described wherein a buoyant condition is effected on the
filtering medium as the molten metal is passed upwardly
therethrough which tends to prohibit the quick clogging of the
filtering medium thus extending the operating time thereof.
Yet another object of this invention is to provide a two-stage
tandem apparatus for continuously treating molten metal to
substantially remove hydrogen gas and finely-divided solids
therefrom, comprising a treating chamber having a refractory weir
which divides the chamber into first and second sections, the
fluxing gas being admitted near the bottom of the first section and
permitted to sweep the hydrogen gas and any solid particles that
may be formed by reaction of the fluxing gas with the molten metal
upward unobstructedly to the surface of the molten metal in the
first section, and a filtering medium disposed in the second
section for filtering finely-divided solids from molten metal
passed upwardly therethrough.
Briefly, these and other objects that may become hereinafter
apparent are accomplished in accordance with this invention by
providing a two-stage or double-compartment receptacle into which
the molten metal to be treated is introduced. A fluxing gas
consisting preferably of approximately 15% chlorine gas and 85%
nitrogen gas is introduced into the receptacle at or near the
bottom of the first compartment or section and passed upwardly
through the molten metal contained therein. Approximately 50 cubic
feet per hour of this gas mixture is required for completely
removing hydrogen gas from an aluminum alloy such as No. 5005 when
the metal flow rate is 8000 pounds per hour. This is approximately
5% of the chlorine gas normally used to batch flux a holding
furnace of molten aluminum. In one embodiment of the invention, the
gas is introduced through a suitable number of carbon or metallic
tubes and dispersed in small bubbles through porous carbon heads,
thereby furnishing a multitude of bubbles which facilitates contact
with a maximum amount of molten metal. In another embodiment of the
invention, the fluxing gas is introduced into the receptacle
through porous carbon blocks located in the bottom of the fluxing
compartment. The chloride and nitrogen gas is metered through
valves, regulators and flow meters in such a way as to provide the
melt with the proper amount of gas mixture. The top of the
receptacle may be sealed with a removable lid and suitable gaskets
thereby facilitating the creation of a positive pressure, such as
of aluminum chloride, inside the compartment which prohibits the
entrance of oxygen and hydrogen-bearing air from the outside, and
provides an atmosphere control over the top of the surface of the
metal inside the container thereby preventing the molten metal from
reabsorbing hydrogen gas fluxed therefrom.
After the molten metal has been fluxed in the first stage of the
receptacle, it is then admitted into the second stage and passed
upwardly through a granular filtering medium consisting preferably
of alumina in the form of balls, crushed alumina, crushed anode
butts, or other suitable inert filtering material. By passing the
molten metal upwardly through the filter medium, the medium is
caused to be buoyant which prohibits the quick clogging of the
filter material. Inasmuch as the material has a tendency to float,
a perforated screen of stainless steel, cast iron, carbon or other
suitable material is placed over the filter material to prohibit
the floatation of the filter material downstream into the casting
system.
The fluxed and filtered metal is then passed out of the double
compartment receptacle through a suitable launder, down spout and
float assembly. This structure prevents any turbulence in the
pouring tundish and provides gas-free clean metal at the pour
point.
With the above and other objects in view that may become
hereinafter apparent, the nature of the invention may be more
clearly understood by reference to the several views illustrated in
the attached drawings, the following detailed description thereof,
and the appended claimed subject matter.
IN THE DRAWINGS
FIG. 1 is a perspective view of a two-stage tandem system according
to this invention, and illustrates the removable lid disposed above
the two-compartment receptacle, and having two gas inlet tubes
extending downwardly therefrom for admitting mixtures of fluxing
gas into the interior of the receptacle;
FIG. 2 is a vertical sectional view taken along line 2--2 of FIG.
1, and illustrates details of the system including the refractory
weir spaced from both the lid and floor of the receptacle which
divides the compartment into first and second sections, as well as
alternate valve and metering lines for controlling the mixture of
fluxing gas.
Referring now to the drawings in detail, there is illustrated a
two-stage tandem treating system in accordance with this invention
and designated generally by the numeral 10. The system 10 includes
a double compartment receptacle 12 having side walls 14, 16, 17 and
19, a floor 18, and a removable lid 20, all of which are formed of
suitable refractory material. An inlet launder 22 and an outlet
launder 24 extend from the side walls 14, 16, respectively.
Molten metal M is introduced into the system from the melting or
holding furnace (not shown) through an intermediate launder 26
which communicates with the inlet launder 22 through a suitable
trough 28. Skimmer blocks 30, 32 seal off the interior of the
receptacle 12, while permitting molten metal M to flow thereunder.
The skimmer blocks 30, 32, in cooperation with the removable lid 20
and suitable gaskets 33, provide a sealed protective atmosphere
within the interior of the receptacle 12 above the surface of the
molten metal M for a purpose to be described in more detail
hereinafter.
As seen most clearly in FIG. 2, the receptacle 12 is divided into
first and second sections 34, 36, respectively, by means of a
refractory weir 38 adjustably mounted in oppositely facing grooves
39 formed in the side walls 17 and 19. The weir 38 is spaced from
the floor 18 so as to provide for communication between the
sections 34 and 36. Moreover, the weir 38 is also spaced downwardly
from the lid 20 in the fashion of a dam so as to permit overflow of
the molten metal M from section 34 to section 36 under certain
conditions as will be described hereinafter.
After the metal has been treated in the receptacle 12, it may be
conveyed from the outlet launder 24 into a pour pot or tundish 40
through a down spout 42 in the bottom of the outlet launder 24. A
float valve 44 may be provided in the tundish 40 for automatically
controlling the admission of molten metal M thereto.
In accordance with this invention, fluxing gas may be introduced
into the first section 34 of the receptacle 12 through tubes 50, 52
which extend downwardly therein through the lid 20. The tubes 50,
52 may be formed of carbon or suitable refractory metal and include
porous carbon heads 54, 56 through which the fluxing gas may be
dispersed in small bubbles. In the preferred embodiment of this
invention, chlorine and nitrogen gas from suitable sources (not
shown) may be supplied and proportioned through meters 58, 60 and
conducted through a line 62 to metered valves 64, 66 which admit
the suitably proportioned gas to the tubes 50, 52 for admission
into the first section 34 of the receptacle 12.
Alternatively, the chlorine and nitrogen gases may be proportioned
through meters 68, 70 and conducted through line 72 to metered
valves 74, 76 which admit the gas mixture through porous carbon
blocks 78, 80 located in the floor 18 of the receptacle 12.
The second section 36 is filled to a predetermined level with a
filtering medium 82 consisting of a granular refractory material of
suitable mesh size, preferably 3-14 mesh. The filter medium 82 may
be any suitable material that is inert with respect to the molten
metal which, in the case of aluminum, may be alumina in the form of
balls, crushed alumina, crushed carbon anode butts, or other
suitable material. The particles comprising the filter material 82
are so chosen and arranged such that they become buoyant upon the
occurrence of molten metal being passed upwardly therethrough. This
tendency of the part of the filter material 82 to float prohibits
the quick clogging of the filter material 82 with small solid
particles and thus facilitates longer operating times. Because of
the tendency of the filter material 82 to float, however, a
perforated screen 84 is disposed over the filter material 82 so as
to retain the material 82 in the lower portion of the second
section 36. The screen 84 may be formed of stainless steel, cast
iron, carbon or other suitable material.
In operation of the system 10, molten metal is introduced into the
interior of the receptacle 12 through the inlet launder 22 and is
flowed through the first section 34, the second section 36, and out
through the outlet launder 24. While the molten metal M is in the
first section 34, a suitable proportion of chlorine and nitrogen
fluxing gases is introduced either through the tubes 50, 52 or the
carbon blocks 78, 80. The fluxing gas will bubble upwardly through
the molten metal M thereby diffusing hydrogen gas therefrom and
sweeping the hydrogen gas upwardly to the top of the receptacle 12
along with any chlorides, nitrides, and other solid oxide particles
that are either in the molten aluminum or that have been formed by
reaction with the fluxing gases. Thus, a positive pressure of
aluminum chloride is maintained inside the sealed receptacle 12
above the surface of the molten metal M which prohibits the
entrance of oxygen and hydrogen-bearing air from the outside, and
provides an atmosphere control over the top of the surface of the
metal M inside the sealed receptacle 12 thereby preventing the
molten metal M from reabsorbing the fluxed hydrogen gas. Moreover,
the reacted solid particles can be simply skimmed from the surface
of the molten metal M periodically or when the buildup so
dictates.
The molten metal M then flows under the weir 38, which is
preferably spaced approximately one-half inch from the floor 18,
and into the second section 36 where it flows upwardly through the
filter medium 82, which thus assumes a buoyant condition as above
described, thereby having finely-divided solid particles filtered
therefrom.
In the event that the filter medium 82 does in fact become clogged
with solid particles, the molten metal M in the first section 34
will simply overflow the top of the weir 38 into the second section
36, thus by-passing the filter medium 82 and thereby preventing an
overflow of molten metal M from the receptacle 12.
It should be apparent that providing the filtering medium 82 only
in the second section 36 of the receptacle 12 leaves the first
section 34 free for the fluxing treatment. Thus, the fluxing gas
may bubble unobstructedly upward through the molten metal M to the
top of the first section 34, thereby sweeping the hydrogen gas and
reacted solid particles to the surface of the molten metal M.
Inasmuch as the fluxing gas does not have to travel through the
filtering medium 82, it does not matter that chlorides or other
solid particles may be formed by reaction of the fluxing gas with
the molten metal M. Consequently, the fluxing gas may contain a
suitable percentage of the superior chlorine fluxing gas, and any
chlorides that are formed will be merely swept to the top of the
first section 34 and in no way be caused to clog the filtering
medium 82.
In view of the foregoing, it should be apparent that there is
provided in accordance with this invention a novel method of and
apparatus for degassing and filtering molten metals, particularly
molten aluminum and aluminum alloys, consisting of a two-stage
tandem system for fluxing hydrogen gas and filtering finely-divided
solids therefrom which both permits the use of chlorine in the
fluxing gas and facilitates long-period operation of the filter
section.
Although the invention has been specifically illustrated and
described herein with reference to specific embodiments thereof, it
is to be understood that further minor modifications could be made
therein without departing from the spirit of the invention.
* * * * *