Apparatus for fluxing and filtering of molten metal

Abstract

This disclosure relates to a method of and apparatus for treating molten metal for substantially removing gas and finely-divided solids therefrom. A two-stage tandem apparatus is provided comprising a treating chamber divided into first and second sections by a vertically extending weir which is spaced from the floor of the chamber. Hydrogen gas is fluxed from the metal in the first section by means of a chlorine-nitrogen fluxing gas which is bubbled upwardly therethrough. After fluxing, the molten metal is passed upwardly through a refractory filtering medium disposed in the second section for filtering finely-divided solids therefrom. The filter media is supported in the chamber on a perforated filter media table which permits even flow of the metal upwardly therethrough. The chamber includes a removable lid by means of which a protective atmosphere is maintained within the chamber. Burner block assemblies having damper controls are mounted in the lid.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending application Ser. No. 361,589, filed May 18, 1973.

Description

BACKGROUND OF THE INVENTION

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 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 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, therfore, 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-comsuming 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 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.

SUMMARY OF THE INVENTION

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.

A further object of this invention is to provide apparatus as above-described wherein the treating chamber includes a removable lid having suitable sealing means for providing a sealed protective atmosphere within the interior of the chamber, and wherein burner block means are mounted in the lid for mounting gas burners whereby heat may be supplied to the metal in the chamber, and damper means for closing the passage through the burner block assemblies when the burners are turned off so as to maintain the protective atmosphere within the chamber.

Still another object of this invention is to provide apparatus as above-described wherein the filtering medium is supported in the second section of the chamber on a perforated filter media table which acts as a distributor plate to assume an even flow of the molten metal upwardly therethrough.

Yet another object of this invention is to provide apparatus as above-described which facilitates cleaning and replacement of the filter media, in particular a clean-out door provided in the side of the chamber adjacent the lower portion of the second section thereof, the door adapted to be swung open thereby permitting raking out of the filter media. 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 receptable 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 8,000 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 receptable through porous carbon blocks located in the bottom of the fluxing compartment. The chlorine 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 meterial 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 an exploded perspective view of a two-stage tandem system according to this invention, and illustrates the removable lid disposed above the two-compartment receptacle, the lid having two gas inlet tubes extending downwardly therefrom for admitting mixtures of fluxing gas into the interior of the receptacle, and further including two burner block assemblies having gas burners mounted thereon for admitting heat into the interior of the receptacle;

FIG. 2 is a vertical sectional view taken through the treating chamber or receptacle of this invention, 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, alternate valve and meter lines for controlling the mixture of fluxing gas, as well as two refractory burner blocks extending into the interior of the compartment for providing heat to the molten metal;

FIG. 3 is an exploded perspective view of the burner block assembly of this invention, and illustrates the damper plate which is adapted to close the passage through the assembly thereby closing the interior of the compartment and providing a sealed protective atmosphere therein; and

FIG. 4 is a perspective view of the filter media table which supports the filter media in the second section of the compartment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings in detail, there is illustrated a two-stage tandem treating system constructed 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, 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. 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. The float valve 44 includes a conical plug portion 45 which is adapted to controllably close the outlet of the down spout 42. Inasmuch as the plug 45 is constructed preferably from cast iron or other heavy material, it does not float sufficiently on the molten metal M to regulate the flow of metal through the down spout 42. Consequently, the float valve 44 is provided with an arm 46 pivotably mounted on an edge of the tundish 40 and having a slidable weight 48 mounted at the end thereof whereby the effective weight of the float valve 44 can be adjusted, allowing it to more precisely regulate the flow of metal M from the launder 24 to the tundish 40.

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 on the part of the filter material 82 to float during metal flow 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 during metal flow, 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.

The filter medium 82 is supported on a filter media table 86, most clearly illustrated in FIG. 4. The filter media table 86 is constructed from refractory material approximately one-half inch in thickness and generally about the same surface area as the cross-sectional area of the second section 36. Ih a preferred embodiment, the filter media table 86 is perforated with approximately 200 holes of five-eighths inch diameter which are somewhat smaller than the diameter of the aluminum balls, from which the filter material 82 is preferably constructed, in order that the balls may be supported while the molten metal M is flowing upwardly therethrough without permitting the balls to fall through the holes in the table 86.

The filter media table 86 includes legs 88 whereby the table 86 is positioned a predetermined distance above the floor 18, preferably at a distance corresponding to the distance at which the weir 38 is spaced from the floor 18. This arrangement prevents the filter medium 82 from clogging the entrance to the section 36 beneath the weir 38, and assures an even flow of the molten metal M upwardly through the medium 82 which accomplishes a more complete and satisfactory filtering of finely-divided particles out of the molten metal M than was accomplished in prior art construction. Moreover, provision of the filter media table 86 prevents channeling of the molten metal M upwardly along the inside edge of the weir 38 which tendency has been found to prevail when the filter medium 82 extends completely to the bottom of the second section 36.

Furthermore, provision of the table 86 prevents the filter medium 82 from sliding back down under the weir 38 into the first section 34 of the receptacle 12. Consequently, the first section 34 is always maintained free of the filter medium 82 and the fluxing gas is thus permitted to bubble unobstructedly upward through the molten metal M in the first section 34 without ever coming in contact with the filter medium 82. Accordingly, the efficiency of the system is maximized due to the fact that the fluxing gas does not react with the filter medium 82 to form oxide particles which would normally tend to clog the filter medium 82 and thus necessitate more frequent cleaning thereof.

It should be further understood that even though the filter medium 82 is disclosed herein as preferably being buoyant when the molten metal M is passed upwardly therethrough, this condition does not negate the necessity for providing the filter media table 86. Consequently, it should be apparent that in the absence of the table 86 the portion of the filter medium 82 nearest the weir 38 will tend to be forced upwardly by the flowing metal while the remainder thereof will tend to shift somewhat to the right and downward as viewed in FIG. 2. This will, of course, result in channeling the molten metal M upwardly along the edge of the weir 38.

During periods when the casting operation is stopped, heat must be applied to the interior of the receptacle 12 so that the temperature of the molten metal M does not drop to the point where it begins to solidify or freeze-up. To this end, as seen in FIGS. 1 and 2, gas burners 90 are provided for providing heat to the interior of the receptacle 12. These burners 90 are mounted in burnerblock assemblies 91 situated in suitable openings 92 in the lid 20.

As seen most clearly in FIG. 3, the burnerblock assemblies 91 include a refractory burner block 93 having an axial bore 94 extending therethrough whereby the heat from the burners 90 is adapted to communicate with the interior of the receptacle 12. Suitable mounting plates 95, 96, having circular openings 97, 98, concentric with the bore 94, are adapted to be disposed on the upper portion of the block 93. A U-shaped plate 99 having leg portions 100 which define a rectangular opening 101, is adapted to be disposed over the plate 96. The leg portions 100 include suitable tracks 102 for slidably receiving a damper plate 103 which is adapted to selectively open and close the opening 101.

A burner holder 104, having a mounting plate 105, is adapted to be secured to the U-shaped plate 99. The burner holder 104 includes a burner bracket 106 having circular ring portions 107, 108, in which the burner 90 is adapted to be suitably retained.

When the burnerblock assembly 91 is in assembled condition by securing the plates 95, 96, 99 and 105 by means of suitable bolts 109, an axial opening will extend through the burnerblock assembly 91 from the tips of the burners 90 to the interior of the receptacle 12. During operation of the burners 90, the damper plate 103 is maintained in its outermost position on the tracks 102. However, when the burners 90 are not being used, the damper plate 103 is simply slid inwardly so as to close the opening 101, thereby closing the axial opening through the burnerblock assembly 91. This will effectively seal the interior of the receptacle 12, thereby maintaining a positive pressure within the receptacle 12 and preventing the entrance of so-called tramp air and moisture to come into communication with the molten metal M.

Another feature of this invention includes the provision of a clean-out door 110 provided in a side of the receptacle 12 which communicates with the interior of the second section 36. The clean-out door 110 is suitably hinged at 111, 112 so as to be readily swung open whereby the filter media 82 can be readily cleaned or replaced. Additionally, a drain port 115 is provided in a side of the receptacle 12 communicating with the interior of the first section 34.

In prior art filters, when it was time to change the filter medium and put in a newly reconditioned medium, the molten metal had to be drained and the receptacle removed from the operating area whereupon it was turned on its side and the filter medium raked out. However, this lapse of time between the draining of the metal and the raking out of the filter medium was often sufficient to permit the molten metal adhering to the filter medium to freeze and cause the medium to stick, making it impossible to remove it from the receptacle except by reheating or breaking it out with a jackhammer. On the other hand, with the construction according to the instant invention, the molten metal can be drained through the port 115 and the clean-out door 110 immediately opened whereupon the filter medium 82 can be raked out and cleaned while the temperature is still high enough for the adhering metal to be in the molten condition, thereby saving considerable amount of time and effort.

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 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 permits both 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.

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 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, means for introducing a fluxing gas into said first section for fluxing gas from molten metal contained therein, a filtering medium disposed in said second section for filtering finely-divided solids from molten metal passed upwardly therethrough, a removable lid having sealing means associated therewith disposed over said chamber for preventing the infusion of air and moisture from the surrounding atmosphere and for providing a protective atmosphere over molten metal contained therein, burner means mounted on said lid and communicating with the interior of said chamber through at least one opening extending therethrough for providing heat to the molten metal, means for closing said at least one opening when said burner means are not in use whereby said protective atmosphere may be maintained, said burner means being mounted in at least one burnerblock assembly mounted in said at least one opening, said at least one burnerblock assembly including a refractory burner block extending into said chamber and having an axial bore extending therethrough and communicating with the atmosphere during operation to provide secondary air for supporting combustion, and wherein said means for closing said at least one opening includes damper means for closing said axial bore thereby preventing said communication.

2. Apparatus as defined in claim 1, wherein said damper means is a damper plate slidably mounted in a U-shaped plate carried by said at least one burnerblock assembly and disposed between said burner means and said burner block.

3. Apparatus as defined in claim 2, wherein a said burner-block assembly is provided in said lid for each of said first and second sections of said chamber.

4. Apparatus as defined in claim 1, further including a filter media table disposed in said second section for supporting said filter medium a predetermined distance above said floor, said table including a plurality of perforations whereby molten metal may flow evenly upwardly therethrough.

5. Apparatus as defined in claim 4, wherein said table is spaced from said floor a distance corresponding to the spacing of said weir therefrom.

6. Apparatus as defined in claim 1, wherein said lid is removable from said chamber.

7. Apparatus as defined in claim 1, further including a clean-out door disposed in one of said side walls of said chamber adjacent said second section whereby said filter medium can be readily raked out.

8. 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 medium for preventing floatation thereof.

9. Apparatus as defined in claim 8, wherein said floatation preventing means is a perforated screen.

10. Apparatus as defined in claim 1, wherein said filtering medium includes alumina balls.

11. Apparatus as defined in claim 1, wherein said filtering medium includes crushed alumina.

12. Apparatus as defined in claim 1, including means for by-passing molten metal past said filtering medium in the event of clogging thereof.

13. Apparatus as defined in claim 12, 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.

14. 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.

15. 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.

16. A two-stage tandem apparatus for continously treating molten aluminum to remove hydrogen 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 thereunder between said first and second sections, an inlet for admitting molten aluminum into said first section and an outlet for discharging molten aluminum from said second section, said inlet and outlet, together with said weir, defining a flow path for molten aluminum through said first section, under said weir and upwardly through said second section, means for introducing a chlorine-containing fluxing gas into said first section for fluxing hydrogen gas from molten aluminum contained therein, and a filtering medium disposed in said second section and supported on a perforated filter media table for filtering finely-divided solids from molten aluminum passed upwardly therethrough, said table being spaced from said floor at least a distance corresponding to the spacing of said weir therefrom thereby acting as a distributor plate to assure an even flow of molten aluminum upwardly through said filter medium and prevent molten aluminum by-passing said table and channeling upwardly through said filtering medium along the surface of said weir.

17. Apparatus as defined in claim 16, wherein said filtering medium is adapted to assume a buoyant condition as molten aluminum is flowed upwardly therethrough, and including means disposed over said filtering medium for preventing flotation thereof.

18. Apparatus as defined in claim 17, wherein said floatation preventing means is a perforated screen.

19. Apparatus as defined in claim 16, wherein said filter media table is constructed from refractory material and has a surface area substantially equivalent to the cross-sectional area of said second section.

20. Apparatus as defined in claim 16, wherein said table is spaced from said floor by means of a plurality of legs extending from the underside of said table.

21. Apparatus as defined in claim 16, wherein said filtering medium includes crushed alumina.

22. Apparatus as defined in claim 16, wherein said filtering medium includes alumina balls.

23. Apparatus as defined in claim 22, wherein said filter media table is perforated with a plurality of holes of a diameter less than the diameter of said alumina balls.