Vacuum Melting Furnace And Method

Abstract

Vacuum metallurgical refining plant having adjoining vacuum chambers with intermediate valve for selectively interconnecting or isolating the chambers with respect to each other to permit simultaneous interdependent or independent operations within each. Furnace in first chamber receives cold or molten charge during initial refining treatment. Refining effected during pouring and stirring of metal in furnace chamber and during tapping into mobile ladle. During final refining, ladle traverses throughout second chamber and successively advances over rows of mobile molds statically arranged in files within second chamber for vacuum teeming into abreast mold assemblies without using an intermediate refractory conduit, such as a tundish.

Description

BACKGROUND OF INVENTION

This invention relates to an apparatus and method for vacuum refining of molten metals. More particularly, this invention is concerned with the means by which the molten metal is handled from the time of charging of the furnace to the casting of ingots, and especially while being subject to an evacuated environment.

In the past, molten metals, such as alloy steel, were poured from a refining furnace through an intermediate refractory conduit, such as a tundish or launder which directed the flow of the molten metal sequentially into a series of advancing molds. The molds themselves were supported on carriages or cars which were moved and indexed into position below the fixed tundish nozzle. To pour a second row of molds, the pivotally actuated tundish or launder with their refractory pouring basins and spouts had to be shifted or swung into a second position under which the second row of mold cars were being sequentially indexed for receiving the metal being poured. Since cooling of the metal within the mold produces progressive solidification from the exterior to the interior, movement of the mold cars changed the solidification pattern and rate and hence a variation in the structure of the ingots or castings. Where each car was moved a different number of times or through a different distance, an attendant lack of uniformity in the ingots was effected even within the same batch of molten metal.

Other problems resulting from the use of intermediate conduit devices were refractory inclusions, drain drippings, difficulty in accurately indexing the molds sequentially below the nozzle, clogging of the nozzles and pouring basins, the need for a large independent mold area or chamber under vacuum, and need for additional chamber height occasioned by the space occupied by the tundish or launder, and the necessity to juxtapose complex and extremely vulnerable mechanical devices to the splashings of metal being poured.

The advantages in using a pouring or teeming ladle have become quite evident in the steel refining art, but only recently with the adoption of vacuum refining techniques for producing ultra clean steels and alloys. For example, where molten metal was poured into molds by tipping a coreless tiltable furnace, a portion of the slag and other impurities which had collected on the top of the melt in the furnace would very likely be first poured into the initial molds with some into each subsequent mold. As a result, all castings or ingots would have a percentage of impurities, the earliest poured having a somewhat greater degree of contamination. Thus, the batch would be nonuniform, and would be subject to rejection because of slag and refractory inclusions, dirt and other porosities, producing flaws repugnant to the precision and integrity of top grade aircraft engine alloys. By the use of a ladle, one can obtain gravimetric flotation of the slag and other impurities, while tapping the ladle from the bottom permits teeming of a slag-free and contamination-free uniform metal.

Where a single high vacuum chamber was used to contain the furnace for refining the molten metal and to hold the molds into which metal from the furnace was tapped or poured, the furnace could not be recharged while the molds were cooling nor could the molten metal in the furnace be subject to a refining action while the molds were being moved into or out of the chamber. Thus, full productivity during melting or casting under vacuum refining conditions was unattainable. While mold tunnel vacuum locks have been in use in the past, the prior constructions necessitated movement of the molds to the detriment of uniform solidification patterns.

It is, therefore, an object of this invention to provide an apparatus and method for the vacuum refining of molten metal during charging into and refining within a furnace and then casting the molten metal into ingots.

Another object of this invention is to provide a molten degassing plant in which perfectly uniform and ultraclean metals may be produced in a smaller installation at a faster rate with minimum labor forces.

Still another object of this invention is to provide a metal vacuum refining plant in which the use of intermediate refractory conduits, such as tundishes and/or launder are completely eliminated.

Yet another object of this invention is to provide a metal refining and casting plant in which the furnace may be charged and the metal refined therein while being subject to high vacuum treatment without interfering with loading, casting, or unloading operations of a previous batch of molds.

A still further object of this invention is to provide a metal refining and casting plant in which metal being cast into ingots under higher vacuum degassing treatment does not interfere with charging operations of the refining furnace.

Yet a further object of this invention is to provide a degassing plant for refining and casting molten metal which will occupy a much smaller space than those heretofore erected for producing a similar annual capacity.

Yet still another object of this invention is to provide a steel degassing plant which will eliminate the need for overhead cranes.

Another object of this invention is to provide a steel casting plant in which higher cycle pouring efficiency can be obtained either under atmospheric or vacuum conditions.

Still another object of this invention is to provide a steel refining, casting and degassing plant in which a single operator can control all operations under full field of vision from a remote and safe distance with comfort.

Yet another object of this invention is to provide a steel refining, casting and degassing plant in which the operators can control all systems without being subject to exposure to great heat or splashing molten metal.

Yet another object of this invention is to provide a new and improved method for handling molten metal being cast into ingots while subject to high vacuum degassing.

Still another object of this invention is to provide a vacuum metallurgical refining plant in which conventional and less expensive accessory equipment can be employed, for example, mold cars and locomotion devices.

Other objects of this invention are to provide an improved device and method of the character described which is easily and economically produced, which is sturdy in construction, and both highly effective and efficient in operation.

The foregoing objects are achieved through the use of a multiple chambered vacuum refining plant in which charging of the furnace together with heating, melting, stirring, refining, and pouring of the metal are effected in a first chamber having a high vacuum applied thereto. The second chamber which is for casting is adjoined the first chamber and also has means for applying a high vacuum thereto. The two chambers are adapted to be isolated from each other by means of a valve in the form of a sliding door which can be sealed against either chamber. The molten metal from the furnace is tilted to discharge its molten contents into a mobile ladle which is now in the first chamber. The ladle is optionally rotatable and is mounted upon wheels for conveyance on tracks through the door valve into the second chamber, the latter having been already evacuated and in communication with the first chamber. Mold cars have been previously moved into the second chamber prior to its evacuation and are now arranged therein two abreast. The mobile ladle is then caused to advance through the second chamber which is under vacuum and in its advancement is swung from side to side about the rotatable axis for tapping the molten metal contained therein into the molds without using a tundish or other secondary refractory device. While the casting is occurring under vacuum conditions in the second chamber, the sliding door valve can be closed, and the furnace may be recharged or even repaired under atmospheric conditions without affecting operations in the second or casting chamber. Similarly, the mold cars can be rolled out of the second chamber through another tunnel door after first isolating via the valve door the first chamber which may be under vacuum during refining operations. Hence, operations can be conducted in either chamber without interfering with the simultaneous operation of the other chamber.

With the above and related objects in view, this invention consists of the details of construction and combination of parts as will be more fully understood from the following detailed description when read in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view and partly broken away of a molten metal degassing plant embodying this invention.

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1.

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2.

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 2.

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 3.

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 3.

FIG. 7 is a sectional view taken along lines 7-7 of FIG. 1.

FIG. 8 is a sectional view taken along lines 8-8 of FIG. 7.

DETAILED DESCRIPTION

Referring now in greater detail to the drawings in which similar reference characters refer to similar parts, there is shown a molten metal degassing plant comprising a first chamber, generally designated as A, a furnace B for melting and refining molten metal in the first chamber under high vacuum conditions, a second chamber C for pouring molten metal into molds D under high vacuum conditions and a rotatable ladle and wagon, generally designated as E, receiving the molten metal from the furnace for transportation and delivery to the molds.

Referring now to FIG. 2, the vacuum chamber A comprises a reinforced steel housing 12 of such a configuration and cubic dimensions as will freely contain the furnace B, the mobile ladle E, and permit free access to and operation of both the ladle and the furnace, the latter being tiltable for pouring. The housing 12 may have a metal shell surrounding an interior refractory surface in order to provide insulation and prevent heat loss to the exterior. Both the housing 12 and the furnace B are supported on a steel deck 14 which is mounted on a pad 16 of I-beams in turn supported upon suitable reinforced concrete construction. A hopper 18 is coupled to the upper portion of the housing 12 and over an opening 19 therein directly above the furnace B. The hopper 18 is adapted to be loaded with a hot or cold charge of metal, alloying materials, slag forming materials, and other oxidizers or deoxidizing ingredients. Control of the feeding of the material within the hopper 18 is effected through an interlock valve 20 interposed above flange 22. When bulk charging, the valve 20 is opened and a predetermined amount of material is fed through the interlock and the charge lowered into the furnace B. As the material is loaded into the furnace B, it is exposed to the evacuated environment within the chamber A whereupon it is preliminarily degassed. Where a hot charge of molten metal is teemed through the opening 19 via a ladle 24 mounted on flange 22, the action is similar to the stream degassing technique. A sight port 26 permits observation of the interior operations.

Transversely extending across the top of the chamber A are a pair of rails 28 on which charging cars 30 are carried. Bulk charging containers 32 are carried to the site by rail trucks 34 and are elevated to the charging cars 30 by means of a crane (not shown). In a similar manner, the preliminary teeming ladle 24 may be mounted upon the top of the chamber A and the crane may load the hot charge of metal into the teeming ladle for stream degassing into the furnace B.

The chamber A is coupled to a multistage steam jet high vacuum system 36 through a conduit 38 so that the pressure within the chamber can be evacuated down to a few microns. A separate conduit 40 couples the evacuation system 36 to the chamber C.

The furnace B may be any suitable high temperature device for heating, melting, stirring, and refining metal, such as steel, under high vacuum conditions. The preferable refining apparatus is a coreless induction furnace because of its compatibility with an evacuated environment and because of its ability to produce stirring as well as heat by the eddy currents produced thereby. The furnace B includes a generally cylindrical container portion 42, of 15 ton capacity for example, and which has a lip 44 for pouring molten metal therefrom into the ladle E. The container portion 42 includes interior refractories which are resistant to high temperature and chemical attack of molten metal therein, and the induction coils (not shown) are mounted in a conventional manner, not forming an integral part of this invention. Trunnions 46 extending outwardly from the container portion are carried in pillow blocks 48 on either side. The pillow blocks 48 are themselves mounted upon stationary stanchions 50 through piston drive cylinders 52 and 54. All controls for the furnace B are located exterior to the chamber A so that its charging, heating, and pouring can all be accommodated at a safe, remote position. To discharge the contents of the furnace, the drive cylinders 52 and 54 are actuated to raise and then tilt the furnace and its contents will be poured from its lip 44 into the ladle E.

The chamber C includes a portion below the level of the chamber A, which is known as the mold tunnel for containing the mold cars, and an upper portion in which is suspended tracks 60 at the same level as track section 56 supporting the ladle E in chamber A. The chamber C is also of reinforced steel beam construction and includes an I-beam bed 64 for supporting tracks 66 on which the mold cars E roll. A blind wall 68 of the chamber C defines the end of the mold tunnel immediately adjacent chamber A. The ceiling 70 is suspended from overhanging girders 72. Valve member F, which constitutes a sliding door panel, is suspended from the girders 72 to isolate when sealably closed by pressure in either direction or to permit communication between the two chambers A and C when open. A sliding closure G is supported from the opposite entrance to the chamber C to permit ingress and egress of the mold cars D and to seal off the end of the chamber C as desired.

The mold cars D are of generally conventional construction and each includes a compartmentalized cart 80 in which is carried a plurality of molds 82. The molds 82 are of a convenient configuration and cubic dimensions for forming ingots of the desired size. One or more generally cylindrical molds 82 may be supported within each compartment in the cart 80. At the outside of the chamber C, the mold cars D are delivered by a transfer carriage 84 which is wheeled over tracks 86. Two sets of tracks 88 and 90 are carried upon the transfer carriages 82 in perpendicular relationship to the tracks 86. An electric motor 92 is employed on each of the mold cars D to drive them two abreast through bridge 94 carrying intermediate transfer tracks 96. Thereafter, the mold cars are driven through the entranceway G to the mold tunnel C two abreast onto the tracks 66 therein. The mold transfer carriage 84 is operable by a piston-cylinder drive assembly 98 to permit moving of the mold cars D to a storage station for the ingots.

Referring now to FIGS. 2, 3 and 4, the mobile ladle assembly E comprises an electrically or hydraulically driven wagon 100 which is mounted on flanged wheels 102 for rolling engagement with tracks 56 in the furnace chamber A, with tracks 60 in the casting chamber C over the mold tunnel, and on tracks 104 at a ladle heating station on top of bridge 94. Pivotal track sections 106 and 107 permit continuity of the rail guide line through the chamber passageway and entranceway and can be operated to be swung out of the way to allow sealing engagement of door valve F and entrance gate G as required. The ladle wagon 100 includes a turntable cradle 106 rotatably supported thereon for detachably carrying ladle 108. The cradle 106 has a plurality of casters 110 which are guided in a circular raceway 112 on the platform of the wagon 100. A heavy chain 114 is welded to the periphery of the cradle 106 and is engaged by sprockets 116 driven by remote controlled electric or hydraulic motors 118. While the cradle 106 can rotate through a 360.degree. arc, in the application of teeming the molten metal in the ladle 108 into the molds, only approximately 135.degree. to 160.degree. arc (shown in broken lines in FIG. 3) is required to pour into the molds 82 on adjacent abreast mold cars. The ladle wagon 100 can be caused to traverse the tracks 56, 106, 60, 107, and 104 by means of sprocket gears 120 carried on jack shaft 122 driven by a remote controlled drive motor (not shown) the sprocket gears 120 engage chain links 124 supported intermediate the tracks 60. It is also possible to use a winch for causing longitudinal motion in the chain 124 which could be transferred into a direct drive for the ladle wagon 100.

The ladle 108 is a conventional teeming ladle which includes a refractory lining. Referring to FIGS. 3, 4, and 5, a stopper rod 128 suspended from cross arm 130 is used to plug the nozzle opening 132 at the bottom of the ladle. Crossarm 130 is coupled to the upper end of piston actuator 134 which is reciprocably operated in drive cylinder 136. Drive cylinder 136 is suitably mounted upon the exterior of the ladle 108, as shown in FIG. 5, or it may be carried by the ladle car 100. Raising the stopper rod 128 from its plugged engagement with outlet nozzle 132 by a remote control will permit the molten contents in the ladle 108 to teem into the molds 82 carried in the now stationary mold cars D therebelow. A suitable cover 138 may be lowered upon the top of the ladle 108 to act as a radiation shield, as an insulation lid, and to prevent splashing.

Referring to FIGS. 1, 7, and 8, the door valve F which is located between the furnace chamber A and mold chamber C in this case may suitably be a sliding steel panel 140 which is suspended from a trolley 142. The trolley 142 includes a bracket 144 bolted to the top of the panel 140 adjacent each end thereof and sheave wheels 146 on which the brackets depend. The sheave wheels 146 are guided along rails 148 carried by a superstructure 150. A tie rod 152 connects the trolleys 142 and is reciprocably operative by a suitable drive piston 154. A rectangular frame 156 which is channel or U-shaped in cross section at its bottom and one side peripherally encloses the passageway between the two chambers A and C. The inverted U-shaped superstructure 150 encloses the spaced apart upper portion of the frame 156 and the other side of the passageway. The frame 156 thus defines a vacuum tight box. The panel 140 is slidable between the channel sections of the frame 156 upon being carried therein by the suspending trolleys 142. Annular elastomeric seals or gaskets 158 and 160 are carried upon each of the opposing surfaces of the panel 140 in annular grooves formed therein and define complete margins thereabout. See U.S. Pat. No. 3,248,119. When the panel 140 is moved into the frame 156 piston actuating members 162 and 164 urge the panel against the opposite inside wall of the frame. As best seen in FIG. 1, the piston actuators 162 are perimetrically spaced about the exterior wall of frame 156 adjacent chamber C. These actuators 162 would be operative to urge the panel 140 toward the opposite wall of the frame 156 when the furnace chamber A was evacuated. The seals 168 would thus form a positive closure thereagainst as a result of atmospheric pressure in the chamber C forcing the panel toward the furnace chamber A now operating under vacuum. Similarly, the actuators 164 would urge the panel 140 and its seal 160 against the chamber C wall of the frame 156 when the mold tunnel was under vacuum to effect a closure thereabout and isolate furnace chamber A from mold chamber C. When the panel 140 is retracted from within the frame 156, the two chambers A and C are in full communication with each other and the superstructure 150 and the opposing side and bottom of the frame 156 would maintain a vacuum tight enclosure about the mouth of the passageway.

As is best shown in FIGS. 1 and 2, the entranceway G to the mold tunnel is closed by another sliding panel or door 170 which carries an annular surface seal 172 on only one side. That is, the entranceway G need only be sealed in one direction, and that would occur whenever vacuum would be applied to the chamber C. The door 170 is also suspended by a trolley 174 carried on overhanging rails 176 adjacent the upper portion of the mold tunnel entrance. When the door 170 is reciprocated to close over the entranceway G, the seal 172 is urged against a flanged buck 178 peripherally extending thereabout.

The mode of operation of the present invention can either be under full vacuum conditions in order to effect maximum refining of hydrogen, nitrogen, and oxygen entrainment as well as carbon deoxidation and reduction of oxides and silicates. Where desirable the plant may be operated under full atmospheric conditions or also in an environment of inert gas, such as nitrogen, argon or helium. It is to be particularly noted that the ladle 108 is carried on wheels from its loading position adjacent the furnace B over to and above the molds 82. At no time is an intermediate conduit or tundish required since the ladle is teemed directly into the molds one at a time. At no time are the molds moved until after solidification of the metal into ingots occurs. No mold car indexing is required since the ladle 108 is rotated or pivoted from side to side by its cradle 106 in its advancement over the molds.

For full vacuum treatment, valve door F is closed and the chamber A isolated from chamber C. The furnace chamber A is evacuated and charging, melting and alloying begun. At the convenience of the operator, the mold cars D are then moved through the entranceway G into the tunnel C. With entranceway G closed, the mold chamber C is separately pumped down. Valve door F may now be opened so that the two chambers A and C are in full communication with each other. When the furnace B is not charged with molten metal, the charge is stream degassed in its fall into the furnace. Melting, stirring, and refining within the furnace are all effected under vacuum conditions, and the same is true in pouring the molten metal from the furnace into the ladle 108. The mobile ladle wagon E is wheeled through the open passageway and is advanced over the mold cars D. While the ladle 108 is pivoted by its cradle 106 and the metal tapped into the molds 82 therebelow on each side, the valve door F may be closed. Actuators 164 move the valve door 140 against the mold chambers side of the frame 156. The furnace chamber A may be brought up to atmospheric conditions since the mold chamber C is fully isolated. A new charge can be effected in the furnace B without interfering with the pouring operation in the adjacent mold tunnel C. Similarly, when the mold cars D are removed through the entranceway G, with the valve door F interposed between the two chambers, there is no reason why the furnace cannot be charged under vacuum. It is to be observed that the pouring from the furnace 42 into the ladle 108 can be observed through sight port 26.

As is apparent from the foregoing description, the use of the rotatable mobile ladle completely avoids the necessity of using a tundish or launder together with their attendant problems of clogging. The elimination of the intermediate refractory conduit removes the refractory contamination caused by such vessels. Furthermore, the instant invention fully eliminates the need for accurate indexing the molds under the tundish pour point. Since the molds do not have to be removed during indexing, a shorter mold chamber or area is required. In addition, because the molds need not be moved at all during metal solidification, greater uniformity in ingots and castings is obtained. The use of a ladle stopper rod to stop the flow of steel provides a more precise cutoff then tipping the ladle and also eliminates tundish drain dripping. By utilizing a bottom-tapped ladle during teeming, we avoid the problems of uncontrolled lateral motion occuring from the momentum of the stream of molten metal being tilted. Furthermore, gravimetric flotation is afforded to allow slag-free and contamination-free pourings. Faster pouring from the furnace (or from another ladle, not shown) into the preheated mobile ladle results in a smaller heat loss between the furnace and mold pouring. The use of the ladle on wheels frees the overhead crane which is customarily required during the conventional teeming operation. The operator can control the entire operation at a safe distance, since the entire system is automated. By closing the sliding door to seal off the second chamber during vacuum pouring, the furnace can be charged at atmospheric pressure or in an atmosphere which will not contaminate casting. Similarly, by sealing off the furnace chamber, the charging, melting, heating, stirring, refining, and pouring into the ladle can be conducted under high vacuum conditions while the mold cars are unloaded and/or loaded into the casting chamber. The apparatus of the instant invention therefore provides greater efficiency with less peak loads and cleaner mold pouring with smaller installation sites and fewer personnel. The rotatable ladle arrangement permits servicing of any pattern or configuration of molds within the range of the stopper rod area coverage without altering or adjusting the equipment.

Although this invention has been described in considerable detail, such description is intended as being illustrative rather than limiting, since the invention may be variously embodied, and the scope of the invention is to be determined as claimed.

Claims

We claim:

1. Metal degassing apparatus comprising a first chamber, means for melting metal in said first chamber, a second chamber communicating with said first chamber, statically arranged mold means for casting metal in said second chamber, means for evacuating said first and second chambers, ladle means for receiving molten metal from said means for melting, means for conveying said ladle means for receiving from said first chamber into said second chamber to permit tapping the molten metal from said ladle means for receiving into said statically arranged mold means for casting metal.

2. The apparatus of claim 1 including means constituting a valve intermediate said first and second chambers, said valve when open permitting passage therethrough of said means for conveying to allow interdependent operations in the two chambers and when closed acting as a seal therebetween to permit isolation of said first and second chambers whereby independent operations in either chamber will not interfere with those in the other.

3. The apparatus of claim 2 wherein said means for conveying comprises a wheeled vehicle transportable on guides between said first and second chambers.

4. The apparatus of claim 3 including means in said vehicle for pivoting said means for receiving about a vertical axis.

5. The apparatus of claim 2 wherein said means constituting a valve comprises a panel interposable between adjacently spaced apart walls framing the passageway between said first and second chambers, an annular seal supported upon the surface of each side of said panel substantially complementary with the spaced apart walls, means to urge said panel and one of said seals against one of said spaced walls, means to urge said panel and the other of said seals against the other of said walls whereby a higher pressure in one of said chambers with respect to the other will reinforce sealing action of said panel against the said other chamber.

6. The apparatus of claim 2 including means for detachably closing an entranceway between said second chamber and atmosphere to permit ingress and egress of said means for casting.

7. The apparatus of claim 1 including means for charging said means for melting by stream degassing.

8. The apparatus of claim 6 wherein each of said means is operatively controlled from a remote station external to said first and second chamber.

9. A method for refining molten metal comprising the steps of melting metal in a furnace contained within a first chamber operating under vacuum conditions, pouring the molten metal from the furnace into a ladle in the first chamber to permit gravimetric flotation of slag and other impurities, transporting the ladle to a second chamber in communication with the first chamber and also operating under vacuum conditions, advancing the ladle over molds statically arranged in at least one file within the second evacuated chamber, and teeming the molten metal from the ladle into successive molds all without using an intermediate refractory conduit.

10. The method of claim 9 including the additional step of charging the furnace under vacuum conditions.

11. The method of claim 10 wherein the step of charging is performed in a molten state.

12. The method of claim 9 including the additional step of stirring the molten metal being heated in the furnace.

13. The method of claim 9 including the additional step of isolating the two chambers from each other and performing operations in one chamber under vacuum conditions while the other chamber is under atmospheric conditions.