US 2821472 A
Description (OCR text may contain errors)
1958 w. s. PETERSQN ETAL 2,821,472 7 METHOD FOR FLUXING MOLTEN LIGHT METALS PRIDR' TO THE CONTINUOUS CASTING THEREOF Filed April 18, 1955 3 Sheets-Sheet 1 FIGl.
JN WT R WARREN PETERSON ILLIAM H-KLEMM ,QTTORNEY 7 2,821,472 METHOD FOR FLUXING MOLTEN LIGHT METALS PRIOR 28, 1953 w. s. PETERSON T TO THE CONTINUOUS CASTING THEREOF 3 Shefas-Sheet 2 Filed. April 18, 1955 T b b r z I l 1 I m m n WA 5. PETER5 N WTLLIBM g. ,KJJ'ZMM Ai'rbRNEY 0 05 o o o ll 1958 w. s. PETERSON ETAL 2,821,472
METHOD FOR FLUXING MOLTEN LIGHT METALS PRIOR TO THE commuous CASTING THEREOF WARREN PETERs ON ILLIAM A. KLRM M :JQTTORNEY nited States METHOD FOR FLUXWG MOLTEN LIGHT METALS gIFQ IOR TO THE CONTINUOUS CASTING THERE- Application April 18, 1955, Serial No. 501,916
17 Claims. (CI. 75-93) This invention relates to the treatment of metals and alloys. More particularly, this invention relates to the treatment of light metal and alloys in molten state prior to the casting thereof to provide molten metal free or substantially free of gas and other non-metallic impurities.
This application is a continuation-impart of application Serial Number 326,036, filed December 15, 1952, now abandoned.
In the casting of light metals, e. g. aluminum and alumihum alloys, one common practice is to melt the metal in open hearth or reverberatory furnaces which may be heated by means of oil, gas, coal, or coke. The open hearth furnace usually comprises a melting hearth and a holding hearth. In preparing the metal for casting the charges of metal and any desired alloying constituents are generally added to the melting hearth to be melted and thereafter the molten metal is transferred to the holding hearth where it is subjected to cleaning treatments and where control may be had of the composition and temperature of the molten bath. The treated molten metal may then be transferred from the holding hearth to the casting station. While in some instances the relative positions of the casting station and furnace maybe such as to permit the molten metal to flow directly from the furnace into the casting station, it is common to find the furnace spaced a given distance away from the casting station and use made of transfer troughs for conveying the molten metal to the casting station. Also, in certain instances the molten metal may be tapped from the holding hearth into a heated holding ladle and the ladle moved to the casting station where the molten metal is poured into a suitable transfer trough.
The cleaning treatment utilized in these conventional processes for preparing the molten metal for casting, as for example, continuous casting, comprises fluxing the metal by treating the entire body of the melt in the holding hearth or in an intermediate receptacle, such as a ladle, as a batch operation. Suitable materials for fluxing include gases such as chlorine or nitrogen and volatile substances such as aluminum and other chlorides, salt fluxes, etc. The purpose of this treatment is to remove dissolved gas and non-metallic impurities such as the oxides and nitrides of aluminum and magnesium, refractory material, etc., from the melt. The molten metal, after completion of the fluxing operation, is usually skimmed and thereafter the furnace is tapped and the casting operation commenced. In the case of the ladle, the molten metal is poured into the transfer trough by tipping the ladle. It is common practice to pour the metal from the furnace or ladle in astream from a spout or lip to an open transfer trough from where it flows to the mold in the casting station. The term continuous casting referred to hereinabove is intended to include casting procedures which may be of a strictly continuous nature .(in which the casting is cut to length without interruption of the casting procedure or Wh 'B the casting is of a semi-continuous nature, i. e., a casting of desired length may be cast, the flow of metal stopped, the
' atent casting removed and the procedure commenced anew. tn the casting of aluminum and aluminum alloys, one method commonly used is that disclosed in the Ennor Patent No. 2,301,027.
These prior known practices for treatment of the molten metal preparatory to the casting thereof have not proven completely satisfactory for production of sound castings. Moreover, it has been found extremely difficult to successfully continuously cast sound high strength aluminum alloys, such as 248 (3.8-4.9% copper, 0.50% silicon max, 0.50% iron max, 03-09% manganese, 1.2-l.8% magnesium, 0.25% zinc max., 0.10% chromium max., balance aluminum) and S (ll-2.0% copper, 0.50% silicon II1&X., 0.70% iron max., 0.30% manganese max, 2.l-2.9% magnesium, 5.66.l% zinc, 0.180.40% chromium, 0.20% titanium max., balance aluminum) of large cross-sectional area, as for example, 18 by 18 inches square or 32 inches in diameter, using metal subjected to these prior known metal treating processes. One disadvantage of prior art processes is brought about by the fact that aluminum and aluminum alloys melted in the presence of combustion products containing moisture, as in the case of oil, gas, coal, or coke-fired furnaces, invariably contain considerable amounts of dissolved hydrogen. Moreover, it has been found that even during the period of tie-gassing by various fluxing means, the molten metal in contact with the moisture bearing atmosphere tends to reabsorb hydrogen. Consequently, even though the gas has been removed from the molten metal melt by the during treatment, reabsorption of gas occurs. It has been found .by use of this manner of fluxing of the melt that although the first portion of the melt cast produces a casting section of relatively low porosity, the balance and major portion of the melt produces a casting containing progressively greater porosity due to the reabsorption of gas. This porosity is oftentimes the cause of high scrap loss in the casting or, if fabricated, results in poor metal quality.
Another disadvantage to be found in prior art methods of metal treatment arises from the fact that absorption of gas into the molten metal takes place during transfer of the metal from the furnace or ladle to the mold because of the fall of the metal into the transfer trough and also because of exposure of the metal to moisture containing air While in the open trough. The fall of the metal from the furnace or ladle to the trough results in a splashing of the metal which causes a breaking of the protective oxide film on the metal and absorption of hydrogen into the melt from moisture in the air. This fall of the metal, splashing, and passage through the open transfer trough also tends to increase the amount of dross and non-metallic films which may find their way into the ultimate casting.
Prior known methods of metal treatment further have the disadvantage that the heat loss from the metal transfer operation in the open transfer trough necessitates the melt in the furnace or ladle being maintained at a temperature higher than the desired pouring temperature. Molten aluminum and its alloys dissolve more gas as the temperature increases and therefore it is highly desirable and oftentimes necessary to keep as low a metal temperature as possible in the furnace or ladle to minimize gas absorption.
Various modifications of the hereinbefore discussed methods of metal treatment have been proposed in an attempt to overcome the various disadvantages attendant therein. Complicated furnaces employing vacuum chambers and inactive insoluble gas to agitate the melt to facilitate removal of dissolved gases by vacuum treatment have been proposed. Additionally, other complicated furnaces which are gas-tight or use fuels other than gas, oil, coke, or coal have been proposed. All of these pro posed structures have been found impracticable and unsatisfactory, particularly for large scale operations, for one or more reasons such as the complexity, cost, and operational difliculties encountered.
This invention embraces the discovery that satisfactory metal may be produced for subsequent casting by fiuxing, during the casting operation, substantially only that portion of the molten metal to be cast. This fiuxing treatment takes place in a restricted zone closely adjacent the point of exit of the metal from the furnace or other metal holding receptacle from which the molten metal is continuously flowing. By satisfactory metal is meant metal which is metallurgically correct in respect to composition, homogeneity, temperature, and freedom or substantial freedom from dissolved gas and other nonmetallic impurities. By fiuxing only that portion of the metal passing from the holding receptacle the effectiveness of the gas removal and cleaning operation is greatly increased. In other words, reabsorption of gas into the fluxed molten metal through the action between the receptacle atmosphere containing moisture and the molten metal is eliminated. Moreover, by such fiuxing operation the tendency of inclusion of dross and other nonmeta'llic impurities in the molten metal melt within the receptacle caused by prior known manual procedures for stirring the melt with a suitable tool in order that the bulk of the metal will be exposed to the action of the fiuxing agent is substantially eliminated.
This invention further embraces the concepts of underpouring and level-pouring the molten metal from the holding receptacle to the transfer trough, where such trough is used, which prevents the free fall and splashing of metal entering the transfer trough with the result that the reabsorption of gas and inclusion of other non-metallic impurities is prevented. The invention also includes the discovery that it is highly desirable and often necessary in the casting of light metals to protect the molten metal flowing through a transfer trough by means of maintaining a protective atmosphere cover in contact with the flowing metal to thereby insure against any reabsorption of gas into the molten metal just prior to passage into the casting mold. As an additional feature, this invention embraces the provision of a zone of relatively quiet metal flow subsequent to the zone of fiuxing treatment and prior to passage of the metal into the casting station or entry of the metal into a transfer means for movement to the casting station. Such feature has particularly significant application in those instances where large metal flow rates are desired, e, g., where metal bodies of large cross-section are being cast or where a single molten metal holding receptacle is to be used for simultaneously feeding several casting molds.
It is therefore the primary purpose and object of this invention to provide a novel method of treating molten metals and their alloys prior to the casting thereof which overcomes or substantially reduces the disadvantages present in prior known methods.
Another object of the invention is to provide a'novel method for fiuxing and degassing molten light metals and their alloys just prior to the casting thereof, such that sound castings having a cross-sectional area greater than those heretofore cast can be satisfactorily produced.
Another object of the invention is to provide a novel method for the fiuxing and degassing of molten light metals within a furnace or other receptacle which eliminates or substantially eliminates reabsorption of gas or inclusion of other non-metallic impurities in the treated metal.
Another object of the invention is to provide a novel method for treating molten metal prior to the' casting thereof wherein molten metal free or. substantially free of gas and other non-metallic impurity inclusion is passed from the holding receptacle or furnace to a transfer trough without exposing the metal to the atmosphere.
Another object of the invention is to provide a novel method for protecting molten metal flowing to a casting station to insure that the gas and non-metallic impurity content of the metal is maintained at a minimum.
Another object of the invention is to provide a novel method for fiuxing and degassing molten aluminum alloys of the high strength type wherein the gas and nonmetallic impurity content of the metal entering the casting mold can be readily controlled to provide metal suitable for casting sound metal bodies having a massive cross-sectional area.
Another object of the invention is to provide a novel method for treating molten light metals and their alloys to remove all or substantially all of the gas andother non-metallic impurities therefrom and wherein the molten metal being treated is flowing at a relatively high rate.
Further objects and advantages of the invention will be apparent from the following detailed description taken in conjunction with the drawings which illustrate various forms of apparatus for performing the method of'the invention and wherein:
Figure 1 is a fragmentary diagrammatic illustration of one form of apparatus embodying the principle of the invention;
Figure 2 is a front elevation sectional view taken along the line 2--2 of Figure 1 with parts removed for purpose of clarity and showing the position of the means for providing the fiuxing material relative to the exit opening from the furnace;
Figure 3 is a fragmentary diagrammatic illustration of a modification of the apparatus of Figures 1 and 2 where in fiuxing means pass out through the roof of the furnace;
Figure 4 is a fragmentary diagrammatic illustration of a modified form of apparatus wherein fiuxing material is introduced through the furnace bottom into the molten metal passing from the furnace;
Figures 5 and 6 are fragmentary diagrammatic illustrations of'modified forms of apparatus for introducing fiuxing material adjacent the exit opening of the furnace wherein the fiuxing zone is outside the furnace proper;
Figure 7 is a fragmentary diagrammatic illustration of a modified structure for transferring the molten metal from the furnace into the transfer trough without subjecting the metal to free fall in the atmosphere;
Figure 8 is a fragmentary diagrammatic top plan view of a further modified form of apparatus wherein provision is made for a zone of relatively quiet molten metal flow subsequent to the zone of fiuxing;
Figure 9 is an elevation sectional view taken along the line 9-9 of Figure 8; and
Figure 10 is an elevation sectional view taken along the line 1010 of Figure 8.
In accordance with the present invention and with reference to the drawings, the melting of metals, e. g., aluminum and aluminum alloys, may be carried out in a gas, coal, coke or oil-fired reverberatory melting furnace 1 which also performs the function of a holding hearth. It is to be understood, however, that furnace 1 may be used only as a holding hearth which can be put in molten metal flow relationship with a separate melting hearth, when desired. The details of the furnace structure per se form no part of the present invention and since such furnaces are in common use, further description is deemed unnecessary. Aluminum pig and/or scrap aluminum of the desired composition can be charged into the furnace to provide the molten bath 2. During this period of melting, the exit opening 3 of the furnace, hereinafter referred to as the furnace tap hole, is closed by suitable means such as a plug (not shown) commonly termed a doughball comprising a mixture of flour, water and asbestos. As a general rule, the composition of the melt is thereafter determined and corrected, if necessary by suitable metal additions.
After the melt has been brought to suitable composition, it may be stirred or agitated with a suitable furnace tool for a period sufiicient to provide a homogeneous melt. This tool, as well as the furnace refractories, are made of materials which prevent or minimize the introduction of impurities into the molten metal. It has been found that after adjusting the composition of the melt and stirring or agitating to provide homogeneity that it is undesirable to further disturb the protective skin layer on top of the melt. Such disturbances as result from additions or" metal, stirring, and skin layer removal increase the tendency for gas absorption and entrapment of non-metallic impurities in the melt to occur. The skin layer is allowed to remain on the molten metal to aid in protection from the furnace atmosphere. It is to be noted that a suitable molten salt flux could also be used as a protective medium.
Just prior to the start of the casting operation a suitable fiuxing apparatus 4 is turned on to pass a suitable fiuxing material such as chlorine or nitrogen gas into the melt. Fluxiug apparatus 4 may comprise a liquid cooled tube 5 which may be formed from steel pipe. Aflixed to the forward end of tube 5 is an interiorly threaded coupling member 6. to which is threadedly connected a tubular extension 7 of which the major portion of the length thereof is adapted to be submerged in the molten metal 2'. This tubular extension is made from a material inert or substantially inert to the purging gas as well as to the molten metal. Materials such as graphite, silicon carbide and other refractories, as well as enameled pipe, are suitable for this purpose. Passing through the length of tube 5 is an inner conduit 8 of relatively small size for carrying the fiuxing material to tubular extension 7 when in use. The outer end of conduit 8 is attached to a suitable source of fiuxing material (not shown) such as a cylinder of chlorine gas. There may also be an additional conduit 9 provided Within tube 5 for purposes of introducing a cooling liquid (water, oil, etc.) to the forward end of tube 5. A suitable outlet for the coolant may be provided at 10 in tube 5. It has been found desirable in the use of such fiuxing apparatus to provide suitable rotating means (not shown) whereby tube 5 may be rotated approximately 90 when not in actual use in the melt to move the normally submerged extension 7 out of contact with the bath. When the casting operation is not in progress tubular extension 7 is out of contact with the melt. At such time as the melt is of the proper composition and homogeneity the fiuxing gas is turned on and apparatus 4 is rotated to submerge tubular extension 7 in the melt at the desired position relative to the tap hole. When the casting operation is halted for any reason, extension 7 can be moved out of the melt and the fiuxing gas turned ofi.
When fiuxing apparatus of the type shown in Figure 1 is used, it has been found preferable to use a graphite or silicon carbide tube as the tubular extension 7. A relatively thick wall should be provided to give adequate mechanical strength. For example, a graphite tube having an outside diameter of about 2 inches and an inside diameter of about /2 inch has proven very satisfactory. It has also been found preferable to make the length of extension 7 approximately 4-5 inches longer than the maximum liquid metal depth in the furnace to avoid any tendency of over-heating outer tubular member 5. Where gas is used as the fiuxing medium, it is desirable to provide a suitable needle valve at the gas supply to enable accurate control of the gas flow. A short tube containing a T member with a pressure gauge mounted thereon can be provided in the gas line between the gas supply and the furnace.
It is important to the successful practice of the invention, using apparatus as shown in Figure 1, that the forward end of fiuxing apparatus 4, that is, the forward end of tubular extension 7, be positioned closely adjacent the tap hole 3 such that the molten metal passing out of the furnace through the tap holeis intimately mixed with the fiuxing material. It has been found highly advantageous to cause the flux material to pass upwardly through the molten metal stream. By performing the fiuxing operation in this manner, the conventional practice of batch fiuxing with its attendant disadvantages of gas reabsorption and non-metallic impurity entrapment is entirely or substantially eliminated. Where desired, the melt may be also treated in this old manner but no particular advantage has been shown to flow from this additional operation. Such a pretreatment would partially degas the melt and tend to remove non-metallic inclusions therefrom, but this procedure is not necessary by practice of the instant invention. Not only are the hereinbefcre mentioned disadvantages of prior known processes for furnace fiuxing completely or substantially overcome, but by practicing the instant invention wherein substantially only that portion of the metal being poured is being treated, the effectiveness of the fiuxing medium is greatly increased thereby reducing the total quantity of flux necessary for treatment of a given quantity of metal. This is highly desirable in large plant installations existing in this country today for obvious economic reasons. During the fiuxing operation the surface of the molten metal in the area above the tap hole is caused to bubble but this bubbling metal will be protected from contamination by moisture or products of combustion by a cover of gas emitted from the fiuxing operation. It is to be noted with reference to Figure 1 that although only one fiuxing tube is shown, more than one such tube could be provided within the fiuxing zone.
To insure proper fiuxing it has been found preferable to provide a restricted chamber in the form of walls 11, 11 (Figures 1 and 2) of suitable refractory material on each side of tap hole 3. These walls join the furnace wall in which the tap hole is located and extend outwardly into the furnace proper. The upper extremity of these walls preferably extends above the molten metal level in the furnace. The molten metal flowing out of the tap hole therefore must flow between walls 11, ll insuring the intimate mixture of the fiuxing material with the metal. Any excess or unreacted fiuxing material will rise through the melt and cover the top surface thereby excluding the bubbling metal at the surface from contact with the atmosphere. Further protection of the metal in the fluxing zone from the products of combustion of the oil, coal, coke, or gas fuel can be afforded by the use of an additional wall 12 connecting the outer ends of walls 11, 11 and wherein wall 12 does not extend downwardly to the furnace fioor as in the case of walls 11, 11, thereby permitting a passageway through which the molten metal may pass to the fiuxing zone. Where desired, the walls 11, 11 and 12 can extend upwardly to the roof of furnace 1 to exclude any possibility of contact of metal in the fiuxing Zone with the products of combustion or the atmosphere. In such case, however, it is necessary to pro vide a suitable flue in the furnace roof for escape of the excess or unreacted fiuxing material as well as the volatile products of reaction.
Another advantageous feature of the present invention involves the transfer of the suitably degassed and fluxed metal from the furnace or other holding receptacle to the casting station. Although by practice of the invention the molten metal will be significantly cleaner and be productive of sounder castings than by methods previously used, it has been found desirable and in certain instances to be necessary, as in the casting of high strength aluminum alloys (e. g., 245 and S alloy) of massive cross-section, that the transfer operation be closely controlled such that the cleanliness of the molten metal passing from the furnace be maintained. In general, casting operations of the type dealt with in this invention necessitate the transfer of molten metal from the furnace to the casting station by means of a transfer trough not only be cause of the obvious space difficulties encountered in attempting to place the casting, station closely adjacent the furnace tap hole, but also because of the desirability of placing the casting stations such that they can be supplied with molten metal from a plurality of furnaces. It has been discovered that a large part of the reabsorption of gas and inclusion of non-metallic impurities during transfer of the molten metal from the furnace to the casting station can be eliminated by preventing the metal from freely falling through the air into the transfer trough.
In order to accomplish this method of metal transfer the molten metal from the furnace is underpoured into the transfer trough. As can be seen from Figure l, there is provided an underpouring mechanism 13 which operates in metal flow fashion with furnace tap hole 3 and the transfer trough 21. Underpour mechanism 13 generally comprises a relatively short trough or receptacle 14 suitably attached in a sealed fashion to furnace 1 in communication with tap hole 3. As in the case of furnace 1, receptacle 14 should be provided with suitable refractory lining material to withstand the washing action of the molten metal. Additionally, cast iron or other suitable metal could be used for the receptacle. Receptacle 14 is provided with a suitable cover member 15 to prevent free access of atmosphere to the molten metal. Cover member 15 is preferably removable and suitable lifting means (not shown) are provided such as an overhead crane.
Resting on cover member 15 is a flow regulator 16 which generally comprises an externally threaded elongated member 17 mounted in threaded relationship within a nut member 18 which is located on cover member 15. On
the top of member 17 is a suitable turning handle 19 5 ward or downward with respect to the lower end portion of member 20 the rate of flow of metal can be increased or decreased, respectively.
It will be seen that the lower end of member 20 is submerged in the molten metal 22 contained in transfer trough 21. It is preferable that the exit or lower end of member 20 be relatively close to the bottom of trough 21 such that the metal passing from the furnace 1 into transfer trough 21 will always enter the trough well below the molten metal level existing in the trough. Accordingly, it is thus seen that by under-pouring is meant that the molten metal entering the transfer trough from the furnace flows into the trough under the molten metal level therein thereby preventing the free fall and splashing of metal into the trough with its attendant difficulties of gas reabsorption and entrapment of non-metallic impurities.
To insure that the molten metal flowing along the transfer trough to the casting station is maintained in a state of high cleanliness it has been found desirable to provide a dry gas cover in contact with the metal. This is accomplished by using a suitable removable cover member 23 provided with one or more gas inlets 24. Since the cover member 23 generally rests on trough 21 and is not rigidly attached thereto in sealing engagement there may be no necessity of providing gas outlet means. However, should this be necessary, suitable gas outlets can be provided. preferably at the far end of the transfer trough away from furnace 1. By dry gas is meant any gas which is free of hydrogen and hydrogen containing materials to avoid reabsorption of hydrogen by the flowing metal. Suitable gases for this use may be dry air, carbon dioxide, nitrogen, argon and helium or other essentially non-reactive gases.
When the flow of molten metal nears the far end of trough 21 it passes downwardly into a suitable casting station through a second flow control regulator 16 the same as that hereinbefore described in connection with underpouring the metal into trough 21 from furnace 1. The metal is under-poured into a suitable baffle or distributing cup 25 located in a relatively short open-ended mold 26 to continuously produce casting 27. It is desirable to provide a screen member (not shwon) through which the molten metal must pass prior to entrance into the mold 26 in order to prevent any impurities in particulate form which might be present from entering the mold. It is to be noted that it is contemplated, within the scope of the invention, to provide a suitable mold cover (not shown) over mold 26 and maintain a suitable dry gas atmosphere therein to prevent contact of the surface of the molten metal head in the mold with the atmosphere. The baflle 25 is preferably of the type which is subject of invention in the co-pending application of Stanley A. Kilpatrick, Serial Number 307,579, now U. S. Patent No. 2,754,556, issued July 17, 1956, wherein the baflle comprises a cup-shaped member provided with directional feed apertures 28 near the bottom thereof for controlling the direction and velocity of flow of metal within the molten metal head to attain the desired distribution of the metal within the mold. Since the casting station structure forms no part of the present invention, further description of same is deemed unnecessary.
It has also been found desirable in the casting of light metal bodies, particularly high strength aluminum alloy castings of massive cross-section, to provide for accurate control of the temperature of the metal flowing in transfer trough 21. These troughs generally are constructed of insulating refractory materials which allow a minimum of heat loss from the metal flowing therein. Alternatively, troughs may be made of metal not attacked by the corrosive and erosive effect of the molten metal, but such troughs should be properly insulated. Where the transfer trough is of relatively great length it may also be desirable to provide suitable heating elements in the troughs and/or in the cover member.
Figure 3 illustrates a modification of the apparatus shown in Figures 1 and 2, wherein rather than using liquid cooled fluxing apparatus 4, a plurality of refractory tubes 29 may be passed through suitable openings 30 in the furnace roof with the lower ends of these tubes being positioned close to the furnace floor adjacent the tap hole 3. Tubes 29 may be made of graphite, silicon carbide or other suitable material. The upper end of each of the tubes is connected to a fluxing gas supply manifold (not shown) and the gas flow in any given tube may be separately controlled by suitable valve means. The fluxing chamber of Figures 1 and 2, comprising side walls 11 and front walls 12 may be used in this modification and in addition a suitable refractory removable cover 31 may be provided to further protect the surface of the melt within the fluxing chamber from the furnace atmosphere. Where such a cover is used, however, suitable openings 32 are provided to facilitate entrance and removal of the flux tubes. Additionally, a suitable exhaust port 33 should be added to permit the escape of fluxing fumes and the gaseous products of reaction between the flux and the molten metal. The fluxing tubes may be staggered in their positions relative to each other in order to provide the most complete metal treatment with a minimum number of tubes.
Figure 4 illustrates another means for treating the molten metal in accordance with the invention. In this embodiment the furnace bottom in the area or zone of the tap hole may be modified to provide a chamber 35 covered by a member 36 made of refractory or other suitable material. This member preferably is provided with a plurality of relatively small openings 37 which lead into larger openings 38. Within openings 38 are placed suitable porous refractory plugs 39. Chamber 35 is connected to conduit member leading to a suitable source of fiuxing gas. In operation, the fluxing gas is introduced into chamber 35 through conduit 40. The gas then passes upwardly through openings 37 and porous plugs 39 and thence into the melt just below the tap hole 3. Although the structure set forth with regard to member 36 is preferred when using this type of fluxing 9 means, other structure can be used as, for example, where the-member is composed solely of a porous refractory material or where it merely has a plurality of perforations therein. Although the furnace bottom in the area of fiuxing, as illustrated, is on the same level with the remainder of the furnace bottom, this portion of the bottom can be recessed to provide increased depth of metal in the fluxing zone and thereby facilitate increased contact between the fluxing material and the metal. As in Figures 1' and 2, a suitable fluxing chamber, comprisingj side walls 11 and front wall 12 may be used. Additionally, a suitable cover member 41 may be provided to further protect the metal within the fluxing chamber from the furnace atmosphere. When a cover. is used, one or more exhaust ports' 42 should be provided for reasons iven for exhaust port 33in Figure 3.
Figures and 6 illustrate modifications of the metal treatment of the invention wherein the fluxing chamber isin effect an extension or projection of the furnace as shown. in Figures 1-4 and wherein the chamber extends in depth below the furnace bottom to facilitate increased contact between the fluxing materials and the molten metal. In these. embodiments of the invention, reabsorption of gas from products.- of. combustion in the furnace atmosphere is completely eliminated since the fluxing chamber is outside of the furnace or hearth proper. As shown in Figure 5, the bottom of the furnace is provided with an extension 45 together with an additional wall 46 to define a chamber 47. Covering the chamber 47 is a suitable covermember 48 in which is positioned a suitable fluxingtube 49 which may be similar to fluxing tubes 29 in Figure 3. The fluxing tube, as in Figure 3, is movable vertically with respect to the cover 48 to facilitate entrance and removal of the tube. Cover member 48 is preferably made removable for purposes of cleaning chamber 47, when necessary, and is. provided with a suit able exhaustport 50 to enable removal of fluxing fumes. and the gaseous products of reaction between the fluxand, the molten metal. Alternatively, these fumes and reaction products may be vented back to the furnace itself. Cover member 48 may also be provided with suitable heating elements to maintain close control of the molten metal temperature. In the lower portion of wall- 46 isprovided a tap hole 51 for passage of metal into the: transfer trough. Additionally, an emergency or cleanout taphole 52 may be provided at the bottom of the fluxing. chamber.
Figure 6 illustrates a fluxing chamber wherein it is a unit in itself which is suitably secured to furnace 1. This unit comprises bottom 55, sides 56, 57 and cover 58. The. cover may be removable and heated as in the. case of cover member 48 in Figure 5 and additionally contains a suitable exhaust port 59. Side wall 56 is. provided with a tap hole 60 and can also be provided with an emergency or cleanout tap hole 61. In. this particular embodiment of the invention cover 58 is provided with two or more fluxing tubes 62 similar to tube 29 shown in Figure 3. A baffie 63, which may or may not be removable, is provided between tubes 62 in order to deflect the flow of molten metal to the bottom of the chamher and thereby aid in obtaining maximum contact be tween the fluxing material and the metal.
It is to be noted that in the case of fluxing chambers such as those shown in Figures 5 and 6, the fluxing tubes may be replaced by porous or perforated areas located in the chamber bottom. Additionally, it is desirable to locate the metal exit from the chamber, i. e. the tap hole, below the molten metal level in order that any liquid or solid products of reaction between gaseous or other flux and the molten metal which rises to the surface of the melt will not be carried out with the molten metal flowing from the tap hole. An example of this is the formation of magnesium chloride during the fluxing of alloys containing magnesium. Since magnesium chloride possesses near #72 a lower density than does the molten aluminum alloy, it rises to the surface. By locating the tap hole below the molten metal level, the magnesium chloride remains onthe surface and will not be drawn off with the molten stream into the transfer trough and thence into the casting mold. When utilizing fluxing chambers which are extensions or projections of the furnace hearth proper as shown in Figures 5 and 6, it may be desirable to provide the chambers with a trapezoidal cross-section on the horizontal plane with the tap hole being located in the short parallel front side. Such a configuration has the advantage of minimizing heat loss from the molten metal contained therein.
Figure 7 illustrates a modification in the manner of metal transfer from the furnace to the transfer trough shown in Figure l, and wherein the elimination of free fall and splashing of the metal is accomplished by means of level pouring of the metal from the furnace into the transfer trough. The fluxing chamber, in this embodiment, comprises an extension of furnace 1 along the lines of that shown in Figure 5. This chamber is preferably trapezoidal in cross-section as referred to above in discussing Figures 5 and 6. A plurality of suitable flux tubes 65-, a cover member 66 and suitable exhaust means 67 similar to members 49, 48, and 54) of Figure 5 are provid'ed. The number of flux tubes 65 utilized may vary in number and may be staggered with respect to each other relative to their position within the fluxing chamber, the primary objective being that a sufficient number of such tubes be used to give the desired fluxing and degassing of the metal passing through the fiuxing chamber. it has also been found desirable in this type of chamber to replace a portion of the end wall of the furnace proper in the area of the fiuxing chamber with a refractory wall or plate 68. The material of this plate should be one possessing good thermal conductivity such as silicon carbide or other suitable material in order to provide heat for the metal in' the fluxing chamber by conduction from the melt proper and thereby avoid temperature differences in the molten metal. This feature can also be used to advantage in the embodiments shown in Figures 5 and 6. The tap hole is of tapered configuration and is provided in a separate annular member 69 which is securely cemented within the chamber wall. Member 69 may be made of cast iron or a suitable refractory such as zircon. A cooperating tapered plug member 70, which may be made of zircon or other suitable material, is provided for coaction with the tap hole to control the rate of flow of metal. Member 70 is actuated by means of an L-shaped arm 71, one end of which is attached to plug member 70, while the other end passes upwardly through a small slot 72 in the transfer trough cover, the slot 72 allowing lateral movement of arm 71 to adjust the rate of metal flow.
While the apparatus for practice of the instant invention illustrated in Figures 1 to 7 has been found particularly applicable for treating molten metal flow rates up to pounds of molten metal per minute, it has been found that where greatly increased molten metal flow rates are desired, e. g., 200 to 300 pounds of molten metal per minute, or over, that the modification of the invention discussed with reference to Figures 8 to 10 is preferable.
As shown in Figures 8 to 10 of the drawings, the fluxing chamber comprises an extension of furnace 1 along the lines of that shown in Figure 7. In this case the chamber is rectangular in cross-section and the wall 75' separating the hearth from the chamber is provided with a suitable opening 76 to permit molten metal to flow from the hearth into the fluxing chamber. As in the case of the apparatus of Figure 7 (wall or plate 68) the wall 75 is preferably made of a material possessing good thermal conductivity, e. g., silicon carbide, in order to provide heat for the metal in the chamber by conduction from the melt proper and thereby avoid temperature differences in the molten metal.
The chamber in efiect is composed of two zones, zone 77 which pertains to that portion of the chamber provided with flux tubes 78 and zone 79 which does not contain any flux tubes but permits establishment of a zone of quiet flow, i. e. substantially non-turbulent, for the molten metal passing through the chamber subsequent to passage through the zone containing the flux tubes and just prior to exit from the chamber through tap hole 80. While four flux tubes have been shown, it will be understood that the size and number of tubes used can be varied as conditions require.
Covering the chamber is a suitable cover 81, preferably removable and in contact with the top of the walls of the chamber through the medium of a conventional sand or alumina seal. The cover 81 is provided with an elongated opening 82 over zone 77 through which flux tubes 78 are received. The width of opening 82 is preferably made greater than the diameter of the flux tubes 78. Such opening allows the flux tubes to be disposed at various angles to the bottom of the chamber, lengthwise and/or crosswise of the chamber. On top of cover 81, and surrounding the flux tubes, may be provided a hood-like member 83, including a suitable stack 84, for the purpose of removing fluxing fumes and gaseous products of reaction between the flux and the molten metal. It will be obvious that other suitable hooding arrangements could be provided.
The fiuxing chamber may be provided with various doors 85, 86, and 87 for aiding in cleaning the chamber. As in Figure 7, the tap hole 80 may be of tapered configuration and is provided in a separate member which is securely cemented within the chamber wall. Likewise, as has been mentioned hereinbefore with reference to Figures -7, cover member 81 may be provided with suitable heating elements to maintain close control of the molten metal temperature. Although not shown, use can also be made of one or more suitable burners in the fiuxing chamber of Figures 8 to 10, as well as those in Figures 5 to 7, for the purpose of reducing the original heat-up time of the hearth and fiuxing chamber prior to passage of molten metal into the hearth and chamber and to be available for adding heat to molten metal in the chamber prior to or subsequent to fiuxing operations when necessary.
As mentioned hereinabove, Where the molten metal flow rates are-large, as where one holding receptacle is feeding metal for simultaneous multiple casting of bodies having a relatively large cross-section, it is preferable to use the treatment modification as described with refis reached where the turbulence created by the increased flux material is sufficiently great to tend to entrap nonmetallic impurities which would normally have sunk to the bottom of the chamber and/ or impurities which normally would float on the surface of the molten metal in the chamber with the resultant disadvantage of such impurities getting into the ultimate casting. By extending the length of the fiuxing chamber and providing increased contact between fiuxing medium and molten metal, and providing a zone of quiet metal flow subsequent to passage of the metal past the flux tubes, as shown in Figures 8 to 10, it has been found that the treatment of metal flowing at very high rates can be very satisfactorily accomplished. it will be understood, however, that the treatment discussed with reference to Figures 1 to 7 can be desirably applied to very high flow rates to produce molten metal significantly cleaner than that treated by conventional practices as heretofore known. Also, the treatment modification illustrated by Figures 8 to 10 can be applied in the casting of metal wherein conventional molten metal flow rates are used.
the efficiency of cleaning per unit time for a given quantity of gaseous or other types of flux has been greatly increased, particularly where the flux material is added from a position below the level of the place of exit such that it is caused to pass upwardly through the molten metal. As an example of the effectiveness of the invention, reference is made to the table below which sets forth the relative gas contents of 75S aluminum alloy (1) when no fiuxing treatment is performed, (2) when fiuxed in the furnace with solid aluminum trichloride (AlCl under the conventional batch process, wherein the flux is encased in aluminum foil and submerged in' the melt by means of an elongated tool, and (3) when continuously fiuxed adjacent the tap hole by means of chlorine gas (C1 according to the invention.
TABLE Fluxing Procedure Casts Ob- Relative Gas Content served of Molten Metal 1 None 5 Very High. A101; before casting on1y 5 High to Moderate." Cl; at tap hole during casting 13 "Low to None.
1 The relative gas content designated was made in terms of the number of gas bubbles evolved during freezing under vacuum according to the following: uH g n :Moderate" over 12 bubbles.
6-12 bubbles. 1-5 bubbles. 0 bubbles.
In the casts referred to in the above table, the relative amount of gas was determined in the molten metal from the transfer trough outside the furnace by means of the Vacuum Freeze Test. In this test molten metal samples, weighing about one pound, were taken with a hot'ladle and poured into a hot steel crucible (3 diameter x 3" high). The crucible was quickly placed in a vacuum desiccator with a glass lid and the desiccator evacuated to less than one millimeter pressure within two minutes time before the molten metal sample started to solidify. The number of gas bubbles evolved during freezing of the sample was observed until complete solidification of the sample was reached. Samples containing large amounts of gas evolved many bubbles and the metal sample became frothy and solidified with a very irregular top surface. Those samples which contain low to no gas evolved five or less small bubbles and solidified with a smooth top surface.
As will be seen from the table above, there is a marked difference in gas removal between the use of conventional practices and that of the instant invention. The attainment of this low gas content is highly desirable in the casting of metals and is necessary in the production of sound high strength aluminum alloy ingots, such as 248, 75S, etc., of relatively massive cross-section. By sound is meant that the structure of the ingots renders them usable as forging, extrusion, or rolling stock.
Moreover, by means of the present invention, the molten metal can be transferred from the furnace to the transfer trough without free fall or splashing of the metal as in prior practices wherein the metal is subject to reabsorption of gas and entrapment of non-metallic impurities. Additionally, by means of the invention the molten metal can be transferred to the casting station and still remain in the same condition of high cleanliness as when it was treated in the furnace. It has been found 13 that even where the metal withinthe furnace or other holding receptacle was rendered relatively clean by prior known practices that this result was partially nullified by open pouring of the metal into an open transfer trough due to reab's'orption of gas and inclusion of nonmeta'llic impurities.
The following are examples of the practice of the invention:
Examplel This example pertains to the casting of an 18 by 18 inch square 75S aluminum alloy ingot having. a length on the order of 90 inches. Approximately 11,000 pounds of 75S aluminum alloy were charged and melted in an oil-fired open hearth furnace. The molten metal was stirred for about minutes and sampled for spectrometric analysis. Upon receipt of the analysis, the alloy composition was corrected to the 75S alloy composition desired by adding the necessary alloying constituents. The composition of the melt was approximately 0.16% silicon, 2.48% magnesium, 1.68% copper, 5.92% zinc, 0.22% chromium, 0.20% iron, 0.03% titanium, balance aluminum. The skim was left on the molten metal surface for protection of the metal from the water vapor contained in the furnace atmosphere. The tap hole area of the furnace contained a fluxing chamber similar to that shown in Figures 1 and 2. Four fluxing tubes similar to apparatus 4 in Figure 1' were used. Chlorine gas was the flux material used and at a rate of flow ofabout pounds per hour per tube. These tubes were introduced from several furnace openings. A short period before casting, the chlorine was turned on, and the exit end of the flux tubes were positioned such that they were very close to the furnace bottom in front of the tap hole. This was done to assure proper operationof the fiuxing tubes and adjustment of chlorine flow. The temperature of the metal was on the order of 1350 F. The metal flowed through the tap hole of the furnace and was underpoured into a covered transfer trough maintained at a temperature of 1400 F. by means of resistance heaters in the cover. An argon atmosphere was maintained over the molten metal in the transfer trough. From the transfer trough, the metal was poured into a continuous casting mold and an ingot made therefrom. Samples of metal were taken from the transfer trough by suitable means and the samples showed a low gas content.
The 755 aluminum alloy ingot produced above had excellent metallurgical properties, and was satisfactory for the production of high quality products by rolling, forging or extrusion operations. The ingot had very fine grain size 0.03-0.04 inch mean diameter) and had extremely low porosity.
Example II This example pertains to the casting of a 32 inch diameter 75S aluminum alloy having a length of about 95 inches. The approximate composition of the alloy was 0.12% silicon, 2.56% magnesium, 1.56% copper, 5.90% zinc, 0.19% chromium, 0.18% iron, 0.05% titanium, balance aluminum. The method of preparing the melt and the fiuxing and metal transfer methods were the same as in Example I above, with the exception that a dry air atmosphere was maintained over the metal in the transfer system. The gas sampling tests showed the metal to have a low gas content.
The ingot produced was of excellent quality. Micro and macro examining techniques applied to various crosssections 'of the ingot failed to indicate any porosity, segregation or shrinkage cracks. The grain size was very fine, being approximately 0.02 inch mean diameter.
Example III The example pertains to the'casting of a 32 inch diameter 75S aluminum alloy ingot having a length of about 90 inches. The approximate composition of the alloy was 0.13% silicon, 2.70% magnesium, 1.62% copsampling tests showed the metal to have a low-to-no gas content. The ingot produced was of excellent quality as was determined in Example 11.
Example IV This example pertains to the casting of an 11" x 44" 753 alloy ingot having a length of 101 inches. Approximately 11,000 pounds of 75S aluminum alloy were charged and melted in an oil-fired open hearth furnace. The molten metal was stirred for about 5 minutes and sampled for spectrographic analysis. Upon receipt of the analysis the composition was corrected to the 75S alloy composition desired by adding the necessary constituents. The composition of the meltwas approximately 0.11% silicon, 2.57% magnesium, 1.80% copper, 5.42% zinc, 0.21% chromium, 0.21% iron, 0.05% titanium, .13% manganese, balance aluminum. A fluxing chamber similar to that shown in Figures 8 to 10 of the drawings was employed. Chlorine gas was the flux material used. Two fluxing tubes similar to tubes 78 in Figure 10 were employed with a chlorine flow of about 15 pounds of chlorine per hour total for both tubes. Approximately /2 hour before casting, the chlorine was turned on and the exit end of the flux tubes were positioned such that they were very close to the chamber bottom. This was done to ensure proper operation of the fiuxing tubes and adjustment of the chlorine now. The temperature of the metal was on the order of 1350 F. The metal flowed through the exit passage from the furnace at a rate of to 200 pounds of aluminum per minute. The metal was trailsferred through a covered transfer trough maintained at a temperature of 1400 F. by means of resistance heaters in the cover. From the transfer trough the metal was poured into a continuous casting mold and an ingot made therefrom. Samples were taken from the transfer trough by suitable means and subjected to a vacuum freeze test. None of the samples indicated any gas in the metal in the transfer trough. The ingots produced were subjected to reflectosc ope' tests and aside from usual head and butt defects no evidence of porosity was found. The ingot was sectioned and the ingot sections showed no cracks, porosity or other defects.
Example V This example pertains to the casting of an 11" by 44 35 aluminum alloy ingot having a length of about 84 inches. The approximate composition of the alloy was 0.19% silicon, 0.04% magnesium, 0.18% copper, 0.55% iron, 0.03% titanium, 1.10% manganese, balance aluminum. The method of preparing the melt and the fluxing and metal transfer methods were similar to that given in Example IV, above. Four chlorine fiuxing tubes. were used with a chlorine flow of about 20 pounds of chlorine per hour total through the 4 tubes. The metal flowed through the exit passage from the furnace at a rate of approximately 150 pounds per minute. Samples of metal were taken from the transfer trough by suitable means and subjected to a vacuum freeze test. All samples showed no gas. The ingot cast was given a reflectoscope test and aside from usual head and butt defects no evidence of porosity was found. The ingot was sectioned and the ingot sections showed no cracks, porosity or other defects.
Example VI This example pertains to the casting of a 14 inch dimeter 7 55 aluminum alloy ingot having a length of'about 97 inches. The approximate composition of the alloy was 0.16% silicon, 2.63% magnesium, 1.62% copper, 6.09% zinc, 0.23% chromium, 0.35% iron, 0.03% titanium, balance aluminum. The method of preparing the melt was the same as in Example IV, above. Use was made of a fluxing chamber similar to that used in Examples IV and V. Four chlorine fluxing tubes were used with a total chlorine flow of 25 pounds of chlorine per hour. The metal flowed through the exit passage from the furnace at a rate of approximately 50 pounds per minute. Samples of metal were taken from the transfer trough by suitable means and subjected to a vacuum freeze test, the results of which showed no gas at all times. The ingot cast was subjected to reflectoscope tests which showed no unsoundness.
Accordingly, by practice of the invention the gas and non-metallic impurity content of light metals, such as aluminum alloys, can be eliminated or substantially eliminated thereby aiding greatly in the production of sound ingots and in certain cases facilitating the casting of sound metal bodies heretofore not possible. This invention is particularly suited for the continuous casting of high strength aluminum alloy ingots (e. g., 248 and 75S alloy) where extremely close control of gas and impurity contents is necessary. Moreover, it has been found that the practice of the invention can be advantageously applied to the continuous casting of any aluminum alloy or other metals such as magnesium and its alloys where the problems of gas absorption and non-metallic impurity entrapment exist.
Although the instant invention is particularly suited for the treatment of metals in open hearth or reverberatory furnaces which are normally oil, coal, coke or gas-fired, it can be advantageously employed in the treatment of metals melted in other types of furnaces such as electric resistance heated or induction heated furnaces inasmuch as the surface of the melts will be subject to the atmosphere which contains hydrogen although to a lesser extent than in the case of combustion-type heating. Additionally, the present invention is eminently suited in foundry casting as a replacement for the conventional pot furnaces. Heretofore, open hearth or reverberatory furnaces were not suitable for foundry purposes due to excessive gas porosity. However, by practice of the present invention, open hearth or reverberatory furnaces can now be used for producing more satisfactory metal in large quantities and generally at a lower cost for heating than in the case of pot furnaces.
Several forms of specific apparatus have been described for carrying out the invention, but it will be apparent that various additional modifications may be employed in performing the method. It will also be understood that various changes, omissions and additions may be made to the method without departing from the spirit and scope of the invention as set forth in the appended claims.
What is claimed is:
1. A method for treating light metals in a receptacle having a moisture-containing atmosphere prior to the casting thereof to provide metal free or substantially free of gas and other non-metallic impurities, comprising the steps of providing a molten metal body in the receptacle, withdrawing said metal from the receptacle in a continuous stream at a point below the surface of said molten metal body, flowing said met-a1 past a source of fluxing material, passing the fluxing material through the metal whereby substantially only that portion of the molten metal being withdrawn from the receptacle is in intimate mixture with the fluxing material, and immediately thereafter pouring said treated metal into a conveying trough for transfer to the casting station.
2. A method for treating light metals prior to the continuous casting thereof to provide molten metal free or substantially free from gas and non-metallic impurities, comprising the steps of providing a body of molten v metal in a reverberatory furnace, withdrawing molten metal from the furnace in a continuous stream, continuously passing fluxing material upwardly through the metal forming said streams such that substantially only that metal is in intimate mixture with said fluxing material, and immediately thereafter transferring said treated metal to a conveying surface by level-pouring said metal from said furnace to said surface, and moving the metal along said surface to a casting station under a protective cover.
3. A method according to claim 2 wherein prior to transferring said metal to the conveying surface, there is established a zone of relatively quiet flow for said metal under a protective atmosphere.
4. A method for treating light metals in a receptacle having a moisture-containing atmosphere prior to the continuous casting thereof to provide metal free or substantially free of gas and other non-metallic impurities, comprising the steps of providing a body of molten metal in a receptacle, withdrawing the metal from said recept-acle below the liquid level thereof in a continuous stream, passing the flowing metal into an adjoining restricted receptacle under the surface of the molten metal contained therein, passing fluxing material upward through said metal entering said restricted receptacle to intimately mix therewith, and thereafter withdrawing the treated metal from the restricted receptacle under the liquid level therein and conveying said metal to a casting station.
5. A method according to claim 4 wherein said treated metal leaving the restricted receptacle is level-poured into a transfer trough for passage to the casting station.
6. A method according to claim 5 wherein prior to Withdrawal of said metal from said restricted receptacle, the metal is caused to pass through a zone of relatively quiet metal flow under a protective atmosphere.
7. A method according to claim 6 wherein said treated metal is conveyed to the casting station under a protective atmosphere cover thereby preventing reabsorption of gas in the metal.
8. A method according to claim 4 wherein said treated metal leaving the restricted receptacle is under-poured into a transfer trough.
9. A method according to claim 8 wherein said treated metal is conveyed to the casting station under a protective atmosphere cover thereby preventing reabsorption of gas in the metal.
10. A method for treating light metals to remove gas and other non-metallic impurities therefrom prior to the casting thereof, comprising the steps of providing a body of molten metal in the chamber of a reverberatory furnace, withdrawing the metal from said chamber below the liquid level thereof in a continuous stream, passing the flowing metal into an adjoining and restricted second chamber containing a protective atmosphere, passing fluxing material upward through said metal entering said second chamber to intimately mix therewith, and thereafter withdrawing the treated metal from the second chamber under the liquid level therein and conveying said metal under a protective atmosphere to a casting station.
11. A method for treating light metals prior to the continuous casting thereof to provide metal free or substantially free of gas and other non-metallic impurities,
comprising the steps of providing a body of molten metal in the chamber of a reverberatory furnace, withdrawing the metal from said chamber below the liquid level thereof in a continuous stream, passing the flowing metal into an adjoining restricted chamber comprising a fluxing zone and a quiet metal flow zone, said fluxing zone being closest to the point of withdrawal of said metal from the first mentioned chamber, passing fluxing material upward through said metal entering the restricted chamber to intimately mix therewith in said fluxing zone, passing said metal through said quiet zone un- 17 der a protective atmosphere, and thereafter withdrawing said treated metal from said restricted chamber.
12. A method according to claim 11 wherein the fluxing material is a gas selected from the group consisting of chlorine, nitrogen and mixtures thereof.
13. A method according to claim 12 wherein the treated metal withdrawn from the restricted chamber is poured into a transfer trough at a level substantially the same as that of the place of emergence of the metal from said restricted chamber.
14. A method according to claim 13 wherein said metal is conveyed in the transfer trough under a protective atmosphere.
15. A method for treating light metals in a furnace having a moisture-containing atmosphere to remove gas and other non-metallic impurities therefrom prior to the casting thereof, comprising the steps of providing a molten metal body in the furnace, withdrawing said metal from the furnace in a continuous stream at a point below the surface of said molten metal body, flowing said metal past the source of a gaseous flnxing material selected from the group consisting of chlorine and nitrogen and mixtures thereof, introducing the fluxing material into the metal whereby substantially only that portion of the molten metal being withdrawn from the furnace is in intimate mixture with the fluxing material, and immediately thereafter pouring said treated metal into a conveying trough for transfer to the casting station.
16. A method for treating light metals in a furnace having a moisture-containing atmosphere to remove gas and other non-metallic impurities therefrom prior to the casting thereof, comprising the steps of providing a molten metal body in the furnace, withdrawing said metal from the furnace in a continuous stream at a point below the surface of said molten metal body, flowing said metal past a source of chlorine fluxing material, passing said 18 fluxing material upwardly through said metal whereby substantially only that portion of the molten metal being withdrawn from the furnace is in intimate mixture with said fluxing material, and immediately thereafter pouring said treated metal into a conveying trough for transfer to the casting station.
17. A method for treating molten aluminum and aluminum alloys in a furnace having a moisture-containing at mosphere prior to the casting thereof to provide metal free or substantially free of gas and other non-metallic impurities, comprising the steps of providing a molten metal body in the furnace chamber, continuously withdrawing molten metal from said chamber below the liquid level of said body of molten metal, passing said metal into an adjoining restricted area comprising a fiuxing zone and a quiet metal flow zone, said fiuxing zone being closest to the point of withdrawal of said metal from said chamber, passing chlorine gas upward through said metal as it enters the fluxing zone of said restricted area in intimate mixture therewith, passing said metal through said quiet metal flow zone under a protective atmosphere, withdraw ing the treated metal from said restricted area below the liquid level therein, level-pouring said metal into a transfer trough for passage to the casting station, and providing a protective atmosphere cover within said transfer trough during passage of said metal therein to prevent reabsorption of gas in the treated metal.
References Cited in the file of this patent UNITED STATES PATENTS 2,472,465 Cornell June 7, 1949 2,528,209 Bonsack et a1 Oct. 31, 1950 2,618,477 Short Nov. 18, 1952 2,648,715 Lillienberg Aug. 11, 1953