CA1090587A - Apparatus and method for in-line degassing and filtration of molten metal - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure teaches an improvement in the degassing and filtration of molten metal, especially aluminum, using an apparatus which employs a pair of sequentially placed, removable filter-type plates and at least one fluxing gas inlet positioned therebetween. Fluxing gas is provided to the melt trough the inlet and flows upward through the first of said plates into counter-current contact with the melt.
Said plate serves to break up said fluxing gas into a fine dispersion to assure its intimate and extensive contact with the molt. Dissolved gases and non-metallic inclusions are thereby abstracted and removed from the melt.

Description

V~ t7 The present invention relates to the degassing and iltration of molten metal, and particularly to the treatment of said metal with a fluxing gas.
Molten metal, particularly molten aluminum, in practice generally contains entrained and dissolved impurities, both gaseous and solid, which are deleterious to the final cast product. These impurities may affect the final cast product after the molten metal is solidified, whereby processing may be hampered or the final product may be less ductile, or have poor finiqhing and anodizing characteristics. The impurities may originate from several sources. For example, the impuri-ties may include metallic impurities such as alkaline and al-kaline earth metals, and occluded hydrogen gas and dissolved surface oxide filmq which have become broken up and are en-trained in the molten metal. In addition, the inclusions may originate as insoluble impurities, such as carbides, borides and others or eroded furnace and trough refra~tories.
It is naturally highly desirable to improve the de-gassing and filtration of molten metals in order to remove or minimize quch impurities in the final cast product, particu-larly with respect to molten aluminum and especially, for ex-ample, when the resultant metal is to be used in a decorative product, such as decorative trim or sheet, or products bearing critical specifications, such as aircraft forgings and extru-~ions, and light gauge foil stock. Impurities as aforesaid cause loss of properties such as tensile strength and corro-sion resistance in the final solidified alloy and lead to de-gradation of processing efficiency and loss of properties in the final product. For example, one type of finishing flaw which is particularly significant in decorative trim or sheet is a stringer defect known as a linear defect.

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~V~ 7 Conventionally conducted gas fluxing processes, such as general hearth fluxing, have involved the introduction of the fluxing gas to a melting or holding furnace containing a quan-tity of molten metal. This procedure required that the furna-ce be shut down while the fluxing gas is circulated, so that the metal being treated would remain constant and treatment could take place. This procedure had many drawbacks, among them, the reduced efficiency resulting from the prolonged idleness of the furnace during fluxing, as well as the lack of efficiency due to the low surface area to volume ratio between the gas flux and the molten metal. Further factors comprised the reqtriction of location to the furnace which permitted the re-entry of impurities to the melt before casting, and the high emissions resulting from both the sheer quantity of flux required and the location of its circulation.
A~ an alternative to the batch-type fluxing operations employed as set out above, certain fluxing operations were employed in an in-line manner, that is, the operation and as-sociated apparatus were located outside the melting or holding furnace and often between the melting furnace and either the holding furnace or the holding furnace and the casting station.
m is helped to alleviate the inefficiency cauRed by furnace shut-down, but was not a~ ~uccessful in improving the effi-ciency of the operation itself, in that undesirably large quan-tities of fluxing gas were often required per unit of molten metal, which was both costly and detrimental to air purity.
Some of these processes utilized in conjunction therewith con-ventional filter media such as open-weave glass cloth screens, and bed filters made up, for example, of tabular alumina, which both exhibit as a primary disadvantage the inability to main-tain a uniform pore size.

10~0~ 7 Porous ceramic foam materials are known in the art, for example, having been described in U.S. Patents 3,090,094 and 3,097,930. mese porous ceramic foam materials are known to be particularly useful in filtering molten metal as des-cribed in U.S. Patent 3,893,917 for "Molten Metal Filter" by Michael J. Pryor and momas J. Gray, patented July 8, 1975, and also as described in our copending Canadian Patent Appli-cation No. 249,110 filed March 26, 1976. Said Canadian Patent Application also describes an apparatus and method for the fil-tration of molten metals which employs filter plates preparedfrom said porous ceramic materials.
Porous ceramic foam materials are particularly useful for filterin~ molten metal for a variety of reasons included among which are their excellent filtration efficiency resulting in part from their uniform, controllable pore size, and low cost, as well as ease of use and replaceability. me fact that these ceramic foam filters are convenient and inexpen-sive to prepare and use has prompted the development of means for easily and conveniently employing these porous, molten metal filters in an in-line degassing and filtration unit which provides a highly efficient assembly.
Accordingly, it is a principal object of the present invention to provide an improved method and apparatus for the degassing and filtration of molten metal which employs filter-type plates of uniform porosity.
It is a particular object of the present invention to provide an apparatus and method as aforesaid which achieves improved degasæing by counter-current contact between molten metal and fluxing ga~ taking place within and above one of the filter-type plates.
It i~ a still further object of the present invention 10~VS~7 to provide improvements as aforesaid which are convenient and inexpensive to utilize and which result in highly efficient metal degas3ing and filtration.
Further objects and advantages of the present inven-tion will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages are readily attained.
The pre~ent invention comprises a highly efficient de-gassing and filtration apparatus comprising a chamber having respective metal inlet~ and outlets, and wall ~urfaces for the support of at least a first and a second removable filter-type medium in sequential spaced-apart relationship, and at least one conduit providing at least one fluxing gas inlet port positioned between said first and said second medium, wherein said port is so positioned that fluxing gas issuing therefrom is capable of disper~ion and percolation through said first medium. The filter-type media differ in pore size and permea-bility whereby said first medium possesses a relatively coarser pore structure, higher permeability and larger available flow area than said second medium. In a preferred embodiment, filter-type media are provided which posses~ an open cell structure characterized by a plurality of interconnected voids, and are preferably prepared from a ceramic foam wherein said voids are surrounded by ceramic material. Ihe filter media may comprise plates having bevelled peripheral surfaces adapt-ed to mate with bevelled wall surfaces on said chamber. A
resilient sealing means is provided on each of said bevelled filter plate surfaces which is resistant to said molten metal to sealably engage the bevelled wall surface~ of said chamber upon installation of the filter plates.
In accordance with the method of the present invention, lt)~t~ff7 degassing and filtration of molten metal is conducted by the passage of a melt through a chamber wherein said melt travels through at least two sequentially placed, spaced-apart filter-type media, whereby said melt is brought into counter-current contact with a fluxing gas while within and above the first of said media, said fluxing gas, having issued from at least one inlet port provided within said chamber between the first and second of said media, dispersing and percolating up into con-tact with said melt within said first medium.
During the operation of the present method, the surfa-ce of said first filter-type medium is maintained below the le-vel of the melt. The method may employ a fluxing gas such as an inert gas, preferably carrying a small quantity of an active gaseous ingredient such as chlorine or a fully halogenated car-bon compound. Optionally, a supernatant salt cover comprised of alkali and alkaline earth chlorides and a fluoride may be located on the surface of said melt residing above the first of said filter-type media.
The present apparatus and method provide a considerable increase in productivity in the degassing of molten metal as degassing is conducted without interruptions of the melting furnace. Further, the design of the apparatus enables its placement near to the casting station, whereby the possibility of further impurities entering the melt is substantially eli-minated.
me employment of the filter-type medium of the present invention in the above apparatus enables the gaseous flux to achieve a greater dispersion throughout the melt whereby greater surface areas of flux contact with a unit of melt volu-me is achieved. me improved kinetics attributable to the pre-sent invention contribute to its greater efficiency.

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In addition, the efficiency of the present invention permits degassing to be conducted with a sufficiently lowered amount of flux material whereby the level of effluents result-ing from the fluxing operation is greatly reduced.
The present apparatus and method provide considerable increase in productivity in the degassing of molten metal as degassing is conducted without interruption of the melting furnace. Further, the design of the apparatus permits its placement near to the casting. me present invention enables the operation of a fluxing and filtering process which achieves significant reduction in the level of effluents normally result-ing from processing of this kind.
By virtue of the employment of conveniently removable filter-type media possessing a carefully controlled gradation of filter properties, the apparatus and method of the present invention are capable of achieving levels of melt purity here-tofore attainable only with the most rigorous of processing.
Also, the employment of a relatively coarse first filter-type medium to abstract larger entrained non-metallic particulate before the melt reaches the second fine filter greatly extends the useful life of the latter. In addition, these high levels of purity are attained utilizing inexpensively manufactured filter-type media.
The invention will now be described with reference to the accompanying drawings which show a preferred form thereof and wherein:
Pigure 1 is a side sectional view of the apparatus of the present invention depicting the filter-type plates in pla-ce therein substantially horizontally disposed.
Figure 2 is a perspective view, partly broken away, of a filter-type medium illustrative of the present invention.

1050S~7 Figure 3 is a side sectional view of an alternate em-bodiment of an apparatus in accordance with the present inven-tion wherein the second filter-type medium is disposed in substantially side-by-side relationship to the first medium.
Referring to Figure 1, an apparatus is illustrated in location within a molten metal transfer system which may inclu-de pouring pans, pouring troughs, transfer troughs, metal treatment bays or the li~e. As will be discussed later on, the apparatus and method of the present invention may be em-ployed in a wide variety of locations occurring intermediatethe melting and casting stations in the metal processing sys-tem. m us, Figure 1 depictq apparatus 10 in location adjacent the exit port 11 of holding furnace 12. The rate of flow of me-tal from holding furnace 12 is controlled by a valve means com-prising a check rod 13. Metal flows into apparatus 10 via a short transfer pasqageway 14 leading to chamber 15 wherein the de~assing and filtration operations of the present inven-tion take place. By the control of metal flow into transfer passageway 14 by the positioning of check rod 13, melt level 16 is maintained at a point above the first of said filter-type media, at a level depicted in Figure 1 selected for pur-poses of illustration only.
Chamber 15 is illustrated as roughly bowl-shaped and is disposed with its bottom recessed below the level of trans-fer passageway 14 so that molten metal travelling thereto will flow downwardly through the filter-type media. Chamber 15 is characterized by the provision of at least two peripheral rims 17 and 1~, comprising, respectively, a first and a second peripheral rim. First peripheral rim 17 is located at the upper portion of chamber 15 and, in Figure 1 is positioned at a level continuous with the bottom of transfer passageway 14.

109~S~ ~' Second peripheral rim 18, as depicted in Figure 1, is disposed within chamber 15 so as to effectively divide it into sub-cham-bers 19 and 20. As with the first peripheral rim 17, second downwardly converging bevelled surface which enables the ex-peditious installation and replacement of appropriately con-figured filter-type media. Though rims 17 and 18 are illus-trated as having bevelled surfaces, the invention is not li-mited thereto, as rims possessing other means for retaining in place the filter-type media of the present invention may be employed as will be noted later on. Rim 18 is shown to be reduced in size from first rim 17 to enable the unobstructed manipulation of the filter medium located therein.
First sub-chamber 19 comprises the area residing ~et-ween the first and second filter-type media labeled 21 and 22, respectively. As illustrated herein, filter-type media 21 and 22 may likewise possess bevelled peripheral surfaces 23 adapted to mate with correspondingly configured peripheral rims 17 and 18. me bevelled peripheral surfaces 23 when em-ployed are provided with resilient sealing means 24 thereonwhich are resistant to molten metal, and the respective fil-ter media 21 and 22 including sealing means 24 are sequential-ly inserted into chamber 15 so that sealing means 24 in each instance engages the respective bevelled surfaces of rims 17 and 18.
As noted earlier, the provision of peripheral rims 17 and 18 supporting respective filter media 21 and 22 effective-ly divides chamber 15 into sub-chambers 19 and 20. Referring again to Figure 1, in accordance with the present invention sub-chamber 19 is provided with at least one inlet port 25 comprising the opening or openings of a conduit 26 or mani-5~3~

fold through which a fluxing gas may be introduced to the meltfrom an outside source, not shown. The flux material which may be employed in the present apparatus and method comprises a wi-de variety of well-known components including chlorine gas and other halogenated gaseous materials, carbon monoxide as well as as certain inert gas mixtures derived from and includ-ing nitrogen, argon, helium and the like. A preferred gas mix-ture for use in the present invention comprises a mixture of nitrogen with from about .1 to about 5% by volume dichlorodi-fluoromethane, wherein the inert gaq component may further in-clude an inert carrier such as helium, argon and mixtures thereof, and dichlorodifluoromethane may be replaced in whole or in part by chlorine or fully chlorinated or chlorofluorina-ted lower hydrocarbon components containing one to six carbon atoms and free of hydrogen. In conjunction with this gas mix-ture, a liquid salt mixture may be employed on the surface of the melt residing within transfer passageway 14 which would compri~e mixtures of alkali and alkaline earth chlorides and a fluoride. A specific such formulation may, for example, inclu-

2~ de 40-50% NaCl, 45-55% KCl and 5% Na3AlF6. me foregoing flux materials are fully disclosed in U.S. Patent No. 3,854,934, by James E. Dore et al,, commonly assigned, the disclosure of which is incorporated herein by reference. As indicated above, the foregoing compositions are presented for purposes of illus-tration only and do not form a material limitation on the pre-sent invention.
Referring further to Figure 1, one of the primary fea-tures of the present invention comprises the location of the flux inlet comprising port 25 as illustrated herein in rela-tion to the first filter-type medium comprising filter plate 21. Specifically, the placement of port 25 is such that flux-ing gas issuing therefrom is capable of percolating up through _g_ ~0~0 ~'7 the melt residing within sub-chamber 19 to pass through first filter-type medium 21 where it is broken up and dispersed, and makes counter-current contact with molten metal flowing in the opposite direction through said filter-type medium. It is at this point in filter 21 that the unexpectedly efficient impu-rity removal takes place whereby relatively coarse undesirable particulate inclusions,undesirable gases and certain dissolved metallic elements are separated from the melt and then percola-te up to the melt surface by the counter-current action of the fluxing gas, where the particulate material may be subsequent-ly removed if so desired by conventional surface treatment techniques, such as skimming and the like. The action of the fluxing gas is schematically illustrated in Figure 1 wherein the gas is depicted as a plurality of bubbles 27 issuing from inlet port 25 and passing through and above filter medium 21 to the melt surface or level 16. Further, though not illus-trated herein, melt surface 16 may optionally possess thereon the liquid salt cover noted earlier in conjunction with a pre-ferred fluxing material useful with the present invention.
After contacting the fluxing gas upon passage through filter medium 21, the molten metal flows through sub-chamber 19 and continues through filter medium 22 comprising in the illustration a filter plate possessing a relatively fine pore size. Whereas the primary purpose of first filter-type medium 21 is to break up the fluxing gas into a fine dispersion to assure intimate and extensive contact with the melt, the pur-pose of second filter-type medium 22 is to remove any remaining non-metallic particulate material from the melt as it passes therethrough. mus, the molten metal issuing from filter me-dium 22 into second sub-chamber 20 is purified and is ready for transfer to either a casting station or, if desired, fur-ther processing, through exit trough 28.

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A further primary feature of the present invention re-sides in the provision of filter-type media of uniform, close tolerance at a significant reduction in cost. Accordingly, the filter-type medium of the present invention comprises a filter plate such as that illustrated in E~igure 2. Filter plate 29 possesses an open cell structure, characterized by a plurality of interconnected voids, such that the molten metal may pass therethrough to remove or minimize entrained solids from the final cast product, or to facilitate the exchange of impurities between the melt and a fluxing gas. Such a filter may comprise, for example, a solid filter plate made from sintered ceramic aggregate, or a porous carbon plate. In the preferred embodi-ment, a ceramic foam filter is utilized as described in the aforesaid copending application. In accordance with the teach-ing of said copending application, ceramic foam filters may be prepared which have an open cell structure characterized by a plurality of interconnected voids surrounded by a web of said ceramic material. The ceramic filters have an air permea-bility in the range of from 400 to 8000 x 10 7 cm2, preferably from 400 to 2500 x 10 7 cm2, a porosity or void fraction of 0.80 to 0.95 and from 5 to 45 pores per linear inch, preferably from 20 to 45 pores per linear inch. ~he molten metal flow rate through the filter may range from 5 to 50 cubic inches per square inch of filter area per minute. The ceramic foam filter described in said copending application is particularly suitable in the present invention since it is of low cost and may be readily employed on a throwaway basis. Furthermore, this filter is surprising effective in the filtration of mol-ten metal, especially aluminum, at a low cost achieving sur-prising filtration efficiency with considerable flexibility.
In accordance with the present invention, first filter-type ~v~s~l~

medium 21 may be prepared of a relatively coarse pore size ranging from 5 to 20 ppi, which possesses an air permeability ranging from 2500 to 8000 x 10 7 cm2, while second filter me-dium 22 would comprise a relatively fine filter possessing a pore count of from 20 to 45 ppi and an air permeability from 400 to 2500 x 10 7 cm2. Naturally, as noted earlier, both permeability and pore size of the respective filter-type media may be varied to suit the particular material being filtered, and the present invention should not be limited to the afore-noted exemplary ranges.
The ceramic foam filter preferably utilized in thepresent invention is prepared from an open cell, flexible foam material having a plurality of interconnected voids surrounded by a web of said flexible foam material, such as polyurethane foamq or cellulosic foams. m e ceramic foam filter may be pre-pared in accordance with the general procedure outlined in U.S.
Patent 3,893,917 wherein an aqueous ceramic slurry is prepared and the foam material impregnated therewith qo that the web thereof is coated therewith and the voids substantially filled therewith. me impregnated material is compressed so that a portion of the slurry is expelled therefrom and the balance uniformly distributed throughout the foam material. The coat-ed foam material is then dried and heated to first burn out the flexible organic foam and then sinter the ceramic coating, thereby providing a fused ceramic foam having a plurality of interconnected voids surrounded by a web of bonded or fused ceramic in the configuration of the flexible foam. Naturally, a wide variety of ceramic materials may be chosen depending upon the particular metal to be filtered. Preferably, a mixture of alumina and chromia is employed, however, these materials may naturally be utilised separately or in combination with other ceramic materials. Other typical ceramic materials 109~ '7 which may be employed include zirconia, magnesia, titanium dioxide, silica and mixtures thereof. Normally, the slurry contains from about 10 to 40% of water and one or more rheolo-gical agents, binders or air setting agents.
As shown in Figure 2, the filter plate of the present invention 29 may have a bevelled peripheral surface 30 adapted to mate with the similarly bevelled rims of the filter chamber illustrated in Figures 1 and 3. Naturally, variations in design are contemplated within the scope of the present invention and thus a wide variety of geometric configurations may be contemplated within the scope of the apparatus disclosed herein, and the illustration of Figure 2 is not meant to be li-miting thereto.
In the instance where the filter plate of the present invention is designed to be a throwaway item, it is essential to provide an effective means of sealing the filter plate in place in its holder which is easy to assemble, disassemble and clean up. The holder or filter chamber itself is normally an integral part of a trough, pouring pan or tundish, etc. and should be constructed of refractory materials resistant to the molten metal similar to those used in standard trough construc-tion. It iQ greatly preferred to seal the filter plate in pla-ce using a resilient sealing means or gasket type seal as il-lustrated and discussed earlier, which peripherally circum-scribes the filter plate at the bevelled portion thereof. The gasket type sealq ensure a leak free installation and also pro-vide an effective parting medium which is essential for ease of disassembly. In addition, since the gaskets or sealing means prevent ingress of metal to the sealing faces of the holder unit, their use considerably eases clean up and effectively prolongs the life of the unit by eliminating problems of metal 0~

attack. Furthermore, because of its resiliency, the gasket may provide sufficient frictional force to hold the filter body in place in the holder or filter chamber without resort to other types of hold down devices. The resilient sealing means should be non-wetting to the particular molten metal, resist chemical attack therefrom and be refractory enough to withstand the high operating temperatures.
Plate type filter units of the present invention may be sealed by gaskets around their edges and/or at the periphe-ry of their large faces. The plate type filter units of thepresent invention are preferably sealed by an edge type seal along the peripheral surface of the filter plate thus provid-ing a positive seal and, in conjunction with the gasket, a mechanical advantage to hold the filter in place. In the event that a simple press fit is insufficient to hold the filter in place, naturally a variety of mechanical devices such as wed-geq and hold down weights may be employed. Alternatively, apparatus 10 in Figure 1 can be made to be split at rims 17 and 1~, in a manner not shown, ~o that pressure can be applied to the sealq by the vise-like action of closing the split unit.
The bevelled angle of the filter chamber and corresponding be-velled angle of the filter plate tends to form a positive seal and hold the filter in place against buoyancy forces acting thereupon. Naturally, as indicated above, the gasket or seal should be resistant to the molten metal utilized. Typical ~eal materials utilized in aluminum processing include fi-brous refractory type seals of a variety of compositions, as the following illustrative seals: (1) a seal containing about 45% alumina, 52% silica, 1.3% ferric oxide and 1.7% titania, (2) a seal containing about 55% silica, 40.5% alumina, 4%
chromia and 0.5% ferric oxide, and ~3) a seal containing about 53% silica, 46% alumina and 1% ferric oxide.

)$~7 In accordance with a further embodiment of the present invention, an apparatus 31 is depicted in Figure 3 which com-prises a transfer passageway 32 leading to a continuous filter chamber _ . Chamber 33 differs from chamber 15 of Figure 1 in_ that it is continuous rather than partitioned into sub-chambers.
In this embodiment, coarse filter-type medium 21' is located in essentially side-by-side relationship with fine filter-type me-dium 22'. The respective filter-type media are separated by partition wall 34 which is integral with and of identical height to transfer passageway 32 and exit trough 35. As in the apparatus of Figure 1, a flux inlet port 25' is located in chamber 33 adjacent and below filter medium 21' and is fed in a similar manner by conduit 26'. Thus, flux material comprising a gaseous fluxing agent may issue from port 25' and will perco-late through filter medium 21' to achieve the desired counter-current contact and exchange with the downwardly moving melt.
me difference in the configuration of chamber 33 dictates that the melt will flow downward around partition wall 34 and will receive its final filtration aq it passes upward through filter medium 22' on its way to exit trough 35. As in the illustra-tion of Figure 1, apparatus 31 is provided with bevelled peri-pheral rims to accomodate the placement and support of the res-pective filter media. Likewise, the filter media are provided with resilient sealing means to effect the desired securement of the filters within the rims.
A wide variety of instances exist where the apparatus and method of the present invention in all of the above dis-closed variations may be employed. Specifically, in the ins-tance of a continuous casting operation, a pair of flux fil-tration chambers may be employed in parallel arrangement. Insuch an operation, the great length and associated total flow of metal involved may require the frequent changing of filter lO~VS~

media in mid-run. Such changes may be facilitated by the em-ployment of parallel flow channels each containing a filtration chamber, together with a mean~ for diverting flow from one channel to the other, by valves, dams or the like. Flow would thus be restricted to one filtration chamber at a time and would be diverted to an alternate channel once the head drop across the first filtration chamber became excessive. It can be seen that such a switching procedure could supply an end-less stream of filtered metal to a continuous casting station.
In addition to the above, the present apparatus and method are capable of several modifications within the scope of the invention to accomodate variations in operating proce-dure. For example, in the instance where small, individual lots of molten metal are prepared and cast, it is desirable that the filter-type media remain operable for s~veral such lots. To this end, the filter media may be recessed somewhat from the levels of the transfer passageway and exit trough whereby, after melt flow has ceased, residual melt remains which fill~ the chamber and covers both filters. In conjunc-tion with this modification, at least one cover unit may be employed which would reside above the remaining melt, and would be provided with heating means such as a plurality of radiant heaters to keep the melt in the liquid state. In the event that such modifications are employed with the apparatus of Figure 1, peripheral rim 17 would be recessed and the cover member, not illu~trated herein, would be placed thereover.
Likewise, the bottom of exit trough 28 would be brought into alignment with the bottom of passageway 14 and a similar cover member would be employed at the location where the exit area of sub-chamber 20 abuts with trough 28. In the illustration of Figure 3, filter-type media 21' and 22' could simply be re-05~3~7 cessed to permit the residence of melt thereover, and appro-priately configured cover members could be located thereat.
Other modifications contemplated within the scope of the invention include the provision of a plurality of inlet ports surrounding the respective chambers immediately below the respective first filter-type media. In addition, and likewise not illustrated herein, the inlet ports could be extended to the center of said chambers by the extension of the respective conduits thereinto, whereby fluxing gas may enter the melt from a point centrally located within the chamber. Both the provision of a manifold of fluxing gas inlet ports, and an in-let port or ports centrally located within the chamber, neither of which illustrated herein, comprise modifications which are, themselves, subject to alterations of design, etc., and accord-ingly, the invention should not be strictly interpreted thereby.
It is to be understood that the invention is not limi-ted to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are suitable of modification of form, size, arrangement of parts and details of operation.
m e invention rather is intended to encompass all such modi-fications which are within its spirit and scope as defined by the claims.

Claims (28)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for the degassing and filtration of molten metal which comprises a chamber having respective metal inlets and outlets, wall surfaces adapted for the support of at least a first and a second removable filter-type medium in sequential, spaced-apart relationship, and a conduit providing a fluxing gas inlet port positioned between said first and said second filter-type medium in such relation to said first filter-type medium that fluxing gas issuing from said port is capable of percolation therethrough.

2. The apparatus of Claim 1 wherein said filter-type media comprise filter plates having peripheral surfaces adapted for mating relationship with said wall surfaces.

3. The apparatus of Claim 2 further including resilient sealing means in engagement between said mating surfaces, said sealing means resistant to said molten metal.

4. The apparatus of Claim 2 wherein said plates com-prise ceramic foam filter plates having an open cell struc-ture characterized by a plurality of interconnected voids surrounded by a web of said ceramic.

5. The apparatus of Claim 4 wherein said filter plates have air permeabilities ranging from 400 to 8000 x 10-7 cm2, porosities of 0.80 to 0.95, pore sizes of 5 to 45 ppi and thicknesses of from 1/2 to 4 inches.

6. The apparatus of Claim 5 wherein said first filter-type medium comprises a relatively coarse filter plate, and said second filter-type medium comprises a relatively fine filter plate.

7. The apparatus of Claim 6 wherein said coarse filter plate possesses an air permeability ranging from 2500 to 8000 x 10-7 cm2 and a pore size of from 5 to 20 ppi, and said fine filter plate possesses an air permeability ranging from 400 to 2500 x 10-7 cm2 and a pore size of from 20 to 45 ppi.

8. The apparatus of Claim 1 wherein said chamber is partitioned into at least two sub-chambers by the disposi-tion of said filter-type media in parallel, stacked relationship therein.

9. The apparatus of Claim 6 wherein said chamber is partitioned into at least two sub-chambers by the disposition of said filter plates in parallel, stacked relationship therein, and said coarse filter plate is located above said fine filter plate.

10. The apparatus of Claim 1 wherein said chamber is partially divided by a vertical partition wall and said filter-type media are disposed in side-by-side relation-ship against opposite surfaces of said wall.

11. The apparatus of Claim 6 wherein said chamber is partially divided by a vertical partition wall, said filter plates are disposed in side-by-side relationship against opposite surfaces of said wall, and said coarse filter plate and said fine filter plate are disposed in the same plane.

12. The apparatus of Claim 2 wherein said meting surfaces are provided with a downwardly converging bevel.

13. The apparatus of Claim 12 wherein said meting surfaces are bevelled at substantially the same angle.

14. The apparatus of Claim 3 wherein said sealing means is a ceramic gasket.

15. The apparatus of Claim 1 wherein said fluxing gas is selected from the group consisting of halogenated gaseous materials, inert gases and mixtures thereof.

16. The apparatus of Claim 15 wherein there is employed in addition to said fluxing gas, a liquid salt mixture applied directly to the surface of said molten metal.

17. A method for the degassing and filtration of molten metal which comprises passing said molten metal through a chamber wherein said metal travels through at least two sequentially placed, spaced-apart filter-type media and is brought into counter-current contact with a fluxing gas while traveling through the first of said filter-type media, and wherein said fluxing gas issues from an inlet provided within said chamber between the first and second of said filter-type media and percolates through the first of said media to contact said molten metal.

18. The method of Claim 17 wherein said filter-type media comprise removable filter plates having per-ipheral surfaces adapted for mating relationship with corresponding wall surfaces located in said chamber.

19. The method of Claim 18 wherein said chamber further includes a resilient sealing means in engagement between said mating surfaces, said sealing means resistant to said molten metal.

20. The method of Claim 18 wherein said plates comprise ceramic foam filter plates having an open cell structure characterized by a plurality of interconnected voids surrounded by a web of said ceramic.

21. The method of Claim 20 wherein the first of said filter-type media comprises a relatively coarse filter plate, the second of said filter media comprises a relatively fine filter plate, and said flux material percolates through said coarse filter plate.

22. The method of Claim 21 wherein said coarse filter plate possesses an air permeability ranging from 2500 to 8000 x 10-7 cm2 and a pore size of from 5 to 20 ppi, and said fine filter plate possesses an air permeability ranging from 400 to 2500 x 10-7 cm2 and a pore size of from 20 to 45 ppi.

23. The method of Claim 19 wherein said sealing means is a ceramic gasket.

24. The method of Claim 17 wherein said fluxing gas 19 selected from the group consisting of halogenated gaseous materials, inert gases, and mixtures thereof.

25. The method of Claim 24 wherein there is employed in addition to said fluxing gas, a liquid salt mixture applied directly to the surface of said molten metal, said salt mixture comprising salts prepared from halogen-containing compounds.

26. The method of Claim 17 which further comprises the steps of providing a chamber having a metal inlet and a metal outlet, and wall surfaces adapted for the support of said filter-type media, providing fiter-type media comprising filter plates having open cell structure characterized by a plurality of interconnected voids, said plates having peripheral surfaces adapted to mate with the wall surfaces of said chamber and including a resilient sealing means on said peripheral surfaces resistant to said molten metal, and sequentially inserting said respective filter plates and sealing means in said chamber to engage the wall surfaces of said chamber, wherein the foregoing steps are conducted prior to the passage of molten metal therethrough.

27. The method of Claim 26 wherein said wall surfaces and said peripheral surfaces all define a down-wardly converging bevel.

28. The method of Claim 27 wherein said wall surfaces and said peripheral surfaces of said filter plates are bevelled at substantially the same angle.