US3736124A - Method for electroslag remelting of metals with slag introduction - Google Patents

Abstract

MOLTEN SLAG IS INTRODUCED THROUGH THE LOWER PORTION OF A CRUCIBLE DEVICE INTO THE BOTTOM OF THE REMELTING ZONE IN AN ELECTROSLAG REMELTING PROCESS USING SINGLE OR PLURAL CONSUMABLE ELECTRODES IN AN AMOUNT SUFFICIENT TO ACHIEVE A PREDETERMINED DEPTH IN THE REMELTING ZONE. THE ACHIEVEMENT OF THE PREDETERMINED DEPTH IS SIGNALLED WHEN CURRENT FLOWS AS A RESULT OF THE SLAG LEVAL CONTACTING AND CLOSING A CIRCUIT THROUGH AN ENERGIZED ELECTRODE DISPOSED IN THE REMELTING ZONE.

Description

May 29, 1973 B PATQN ET AL 3,736,124

METHOD FOR EL ECTROSLAG REMELIING OF METALS WITH SLAG TNTRODUCTTON Filed Sept. 1, 1970 4 Sheets-Sheet 1 IO l2 1: is (5 o) vm'rons BORIS EVGENIEVICH PAFON,

JURY VADIMOVICH LATASH,

BORIS IZRAILEVICH MEDOVAR, JULY GEORGIEVICH EMELIANENKOB: MlKHAIL MARKOVICH KLJUEV ATTORNEYS May 29, 1973 B. E. PATON ET AL 3,736,124

METHOD FOR EuECTROSLAG REMEL'IING OF METALS WITH SLAG INTRODUCTION Filed Sept. 1, 1970 4 Sheets-$heet 2 I8 I F/G 4.

mvsmons BORIS EVGENIEVICH PATON,

JURY VADIMOVICH LATASH, BORIS IZRAILEVICH MEDOVAR, JULY GEORGIEVICH EMELIANENKO 8| MIKHAIL MARKOVICH KLJUEV May 29, 1973 Filed Sept.

8. E. PATON E A 3,736,124

METHOD FOR FILEC'FEOSLAG REMELTINC' OF METALS WITH SLAG INTRODUC'ITON L, 1970 4 Sheets-Shet raw?! .IIIIIIIIIIIJ INVENTORS BGRIS EVGENIEVICH PATON, JURY VADIMOVICH LATASH, BORIS lZRAILEVICH MEDOVAR JULY GEORGIEVICH EMELIANENkO a MIKHAIL MARKOVICH KLJUEV BW,M,M,MM

ATTORNEYS May 29, 1973 PATQN ET AL 3,736,124

METHOD FOR ELECTROSLAG REMELTING OF METALS WITH SLAG INTRODUCTION Filed Sept. 1, 1970 4 Sheets-Sheet 1 F/ata HNVENTORS BORIS EVGENIEVICH PATON,

/ JURY VADIMOVICH LATASH BORIS IZRAILEVICH MEDOVAR,

JULY GEORGIEVICH EMELIANENKO 8| MIKHAIL MARKOVICH KLJUEV WAM M7 ATTORNEY United States Patent 3,736,124 METHOD FOR ELECTRUSLAG REMELTING OF METALS WITH SLAG INTRODUCTION Boris Evgenievich Paton, Jury Vadimovich Latash, Boris Izrailevich Medovar, and July Georgievich Emelianenko, Kiev, and Mikhail Markovich Kljuev, Elektrosal, U.S.S.R., assignors to Institut Elektrosvarki Im. E. 0. Patona, Kiev, U.S..R.

Continuation-impart of applications Ser. No. 592,054, Nov. 4, 1966, Ser. No. 10,419, and Ser. No. 10,485, both Feb. 11, 1970, all now abandoned. Said Ser. Nos. 10,419 and 10,485 being a continuation-in-part of said application Ser. No. 592,054. This application Sept. 1, 1970, Ser. No. 68,661

Int. Cl. C22d 7/00; H05!) 7/18; CZlc 5/52 US. Cl. 75-10 C 38 Claims ABSTRAQT OF THE DISCLUSURE Molten slag is introduced through the lower portion of a crucible device into the bottom of the remelting zone in an electroslag remelting process using single or plural consumable electrodes in an amount sufficient to achieve a predetermined depth in the remelting zone. The achievement of the predetermined depth is signalled when current flows as a result of the slag level contacting and closing a circuit through an energized electrode disposed in the remelting zone.

This application is a continuation-in-part of abandoned application Ser. No. 592,054, entitled A Method of Electroslag Remelting of Metal and Plant Effecting Same filed Nov. 4, 1966. Also, this application is a continuation-in-part of Ser. No. 10,419 entitled Method and Ap paratus for Electroslag Remelting of Metals filed Feb. 11, 1970, now abandoned; and Ser. No. 10,485 entitled Slag Introduction Method For Electroslag Remelting Process filed Feb. 11, 1970, also abandoned. These two abandoned applications in turn being continuations-inpart of Ser. No. 592,054.

BACKGROUND OF THE INVENTION The present invention relates to a method of electroslag remelting of metal from consumable electrode means, and particularly to electroslag remelting utilizing introduction of molten slag at the bottom of a crucible device.

In the electroslag remelting of metals, a bath of molten slag is obtained in a remelting zone, for example, a crucible or a mold (often referred to as a crystallizer). At least one consumable electrode is disposed to extend into that zone with its lowermost end immersed in said molten slag bath. Electric current is caused to flow from the electrode to and through the slag bath. The passage of the current through the slag bath produces heat which causes the electrode to melt. As the electrode melts, the remainder of the electrode is lowered into the slag bath so that all of the electrode is progressively melted. Because the metal in the electrode has a density greater than that of the slag bath, a molten pool of metal is formed below the slag bath. This molten pool of metal progressively solidifies into an ingot of refined metal.

Known in the prior art are methods of electroslag remelting of metal, obtained from consumable electrodes in a cooled crucible, disposed on a bottom plate; for carrying out the remelting process, a pool of molten slag is formed in said crucible.

The molten slag pool is obtained in the crucible in one case due to the melting of a solid flux or a mixture of its charge constituents during the remelting of a consumable electrode directly in the crucible. In another case, nonconsumable electrodes, carbon or graphite, are employed 3,736,124 Patented May 29, 1973 for these purposes. This method is known as the dry start method.

There is also employed a flux premelted in a separate unit or a mixture of its charge constituents, followed by top pouring the molten slag thus obtained into the crucible. This method is referred to herein as top pouring.

In the first two cases of preparing the molten slag pool, the time as required for obtaining an ingot is increased by as much as 10 to 20 percent, since the melting of slag is carried out directly in the crucible, which is likely to decrease the production rate of the plant by as much as 10 to 20 percent.

Besides, when preparing the molten slag pool with the use of consumable electrodes, there occurs an incomplete melting of the flux in the peripheral zone of the crucible which is likely to drastically impair the surface of the ingot being melted and to increase the bottom discard to be cropped during the subsequent processing of the ingot up to 10 percent.

Though the preparation of the molten slag pool in the crucible by top pouring therein the molten slag is a progressive method, which allows increasing the production rate of the plant and ensuring a high quality of the bottom part of the ingot, this method possesses its disadvantages, too.

When placing the consumable electrode in the crucible, the gap therebetween is small, and the pouring of the molten slag therein presents difficulties. The molten slag gets on the crucible walls and consumable electrode, and is likely to produce slag sows or lumps thereon. The falling off of the slag sows into the slag pool during the melting process may result in market variations of electrical conditions of the melting process.

To eliminate said disadvantages requires that during the pouring of the molten slag the consumable electrode should be outside the crucible, for which reason the design of the plant must provide for lifting the electrode clamped in the electrode holder over the crucible so that the latter could be displaced from under the electrode for pouring the slag therein.

The short electric circuit is elongated thereby, and consequently, the losses of active energy increase therein, too, which results in a reduction of the power factor of the plant (cos a). After top pouring the molten slag into the crucible, a voltage is applied to the installation, and the consumable electrode is lowered at a maximum speed into the crucible until it is brought into contact with the slag. During this time, a crust or lining of the solid slag may form on the crucible walls and on the cooled bottom plate or a dummy bar, if it is to be placed on the bottom plate, which crust is likely to insulate the molten slag pool from the bottom plate and crucible, which results in a breaking occurring in the current circuit, and the melting process may not start.

Disadvantages of the existing plants employed for effecting the electroslag remelting of metal according to said method, consist in their excessive height, which is connected with a necessity of pouring the molten slag with the consumable electrode being raised, and with considerable losses of time as required for effecting auxiliary operations. Besides, there are required dummy bars or sacrificial plates for protecting the bottom plate against the burning through.

SUMMARY OF THE INVENTION In conformity with the present invention, the molten slag pool is produced in the crucible by pouring the molten slag into its bottom part, in other words, its lower portion. The consumable electrode (or electrodes) is inserted into the crucible until its lower end is at a predetermined distance from the bottom plate, and a voltage is applied to the plant simultaneously with the pouring of slag into the bottom portion of the crucible. When the level of slag in the crucible reaches the electrode, there occurs the completion (closing) of the electric circuit of the plant, and the process of remelting the consumable electrode begins.

Because of a rapid rising of the slag level in the crucible, there is insufficient time for a crust or lining of solidified slag to form on the bottom plate (or dummy bar) and on the crucible walls, and current begins to flow in the electric circuit of the plant, while the pouring of the molten slag continues to be carried out while current flows, the pouring of slag being discontinued only after the formation of the molten slag pool of a specifified depth.

According to the present invention, in the plant for carrying out the method, said plant being provided with an electrode holder complete with consumable electrodes that are disposed in a crucible placed on a bottom plate, in the lower part or portion of said plant there is disposed a pouring device for supplying the molten slag into the crucible through a channel (access port). The access port or channel for introduction of the slag can be constructed in many ways such as a bore or aperture adjacent the lower portion of the crucible through the crucible wall or through the crucible bottom plate. For convenience in cleaning out solidified slag in the channel such channel can be made separable, e.g., it can be formed by the linking of the bottom plate with the crucible.

In one embodiment of the realization of the present invention, the channel, through which the pouring device communicates with the crucible, is formed by an external boring (elongated recess) in the bottom plate, covered from above by the end surfaces of the crucible wall and syphon pouring device.

In another embodiment of the invention, the channel or passage for supplying the molten slag is formed in the lower end portion of the crucible wall by a radial boring or groove, covered from below by the bottom plate of the crucible.

The channel or passage for supplying the molten slag may be also formed by two borings or grooves facing each other, said borings or grooves being located in the lower end portion of the crucible wall and in and to the outside of the bottom plate of the crucible, respectively.

It is expedient to design tohe pouring device detachable along the longitudinal plane of its channel.

The engineering solutions set forth herein allow manufacturing a plant for electroslag remelting of metal, said plant being simple in operation and design.

In conjunction with the foregoing discussion, an object of the present invention is to provide unique methods of electroslag remelting which eliminate disadvantages of previously known methods and plants for carrying into effect same. This object is achieved by providing a novel method of supplying molten slag to a remelting zone whereby the above described disadvantages are overcome or minimized.

It is a further object of the present invention to provide a novel method of slag pouring which gives significantly improved results.

These objects are realized by the application of a methd of electroslag remelting of metal as discussed in the foregoing Summary, where pouring of molten slag into the crucible is effected in such a manner as to eliminate the possibility of the breaking of the current circuit of an electroslag remelting plant or apparatus, which would be adapted for carrying into effect the pouring of the molten slag in such a manner.

DESCRIPTION OF THE DRAWINGS The nature of the present invention will further become more fully apparent from a consideration of the following 4 description of an exemplary embodiment thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a general side elevation view of a plant for electroslag remelting of metal according to the present invention;

FIG. 2 is a front view of the plant shown in FIG. 1;

FIG. 3 is a vertical section detail view of the plant taken along line AA of FlG. 2 showing structural details of one embodiment of the bottom pouring device;

FIG. 4 is a cross-section view, taken along line BB of FIG. 1;

FIG. 5 is a vertical section view of a second embodiment of a bottom pouring device according to the present invention;

FIG. 6 is a cross-section view showing the bottom of a furnace similar to that illustrated in FIG. 4 and shows the use of a weld lug;

FIG. 7 is a vertical section taken along line CC of FIG. 6 showing details of the device for clamping the welding lug;

FIG. 8 is an elevation view partially in section schematically illustrating the system of the present invention as applied to a bifilar furnace; and

FIG. 9 is a sectional view taken horizontally through the mold shown in FIG. 8, illustrating the spaced apart arrangement of the electrodes in the mold.

The proposed plant for electroslag remelting of metal has a supporting column 1 (FIGS. 1 and 2) complete with carriages 2 and 3 disposed thereon, said carriages being displaced progressively relative to columns 1 along guides 4 by the aid of drives 5 and 6.

Attached to the carriage 2 is an electrode holder 7 of the clamp type complete with a drive 8, designed to secure a consumable electrode 9 moving relative to a crucible 10 during the progressive motion of the carriage 2.

The crucible part 10, to be placed on its bottom plate 11, is connected by a bracket 12 to the carriage 3 and during the displacement thereof it can rise relative to the bottom plate 11, placed, in its turn, on a carriage 13.

In the lower part of the plant, there is provided a pouring device 14, communicating with the crucible 10 and intended for supplying therein the molten slag which is premelted in a separate unit, for example, in an arc furnace.

The pouring device. 14 communicates with the crucible 10 through a channel or passage 15 (FIGS. 3 and 4) which terminates in an access port, as formed by the linking of the bottom plate 11 with the crucible 10. Thus, in the FIG. 3 embodiment the channel 15 has boundaries determined by the top surface of bottom plate 11 and the end surface of the sidewalls of crucible 10.

In the exemplary, preferred embodiment of the present invention, represented in FIGS. 3 and 4, the access port in channel 15 is formed by an external boring or aperture provided in the bottom plate 11, and is covered from above by the lower end surfaces of the crucible 10 and pouring device 14. This channel 15 has its upper surface determined by the lower end surfaces of crucible 10 and pouring device 14 and its lower surface determined by an extension of bottom plate 11.

To facilitate the removal of slag after the completion of melting, it is desirable that the boring provided in the bottom plate 11 should have in its cross section a trapezoidal or segment-shaped form. That is, for ease of removal of the slag from channel 15 after completion of remelting, it is desirable that the longitudinal and transverse cross section of the channel should be trapezoidal or segment-shaped, as is apparent in FIGS. 3 and 4.

The channel or passages 15 into the lower portion of the crucible may be formed by a radial boring or aperture (which is not shown in the drawing) provided on the lower end of the crucible 10 and covered from below by the bottom plate 11 or by borings or grooves (not shown in the drawing) provided on the lower end of the crucible and the bottom plate 11 facing each other. The access into the crucible can also be formed by spaced apart apertures (not shown in the drawing), in one or the other or both of the bottom plate 11 and the sidewall of crucible 10. All these embodiments of the channel provide for a rapid access thereto for cleaning it from the slag after the completion of the melting process.

The pouring device 14 is provided in its upper part with a receiving funnel 16, which may be made as a single piece integral with it or detachable therefrom. It is expedient to make the pouring device 14 detachable along the plane of its channel 17, if the cleaning operation is to be effected immediately after the pouring of the molten slag into the crucible 10. The pouring device 14 may be made non-detachable, if the cleaning of the channel 17 from the slag is effected after the completion of the melting process; in this case, however, the channel 17 should have a slight taper, as seen in FIG. 5, for instance, from 1 to 3 percent, with the big end down.

The top end of receiving funnel 16 ordinarily is at a distance above bottom plate 11 sufficient to insure an adequate head of slag in funnel 16 so that the slag reaches its predetermined depth inside crucible 10 and contacts the lowermost end of electrode 9. It is desirable that the lateral end of the pouring device 14 should repeat the shape of the lateral surface of the lower flange 18 of the crucible 10. The pouring device 14 may be fastened to the lower part of the crucible 10 or to the bottom plate 11, and may be made of metal or with a lining of the internal channel 17 and receiving funnel 16. Thus, when pouring device 14 has the same shape as flange 18 of the crucible 10, the pouring device 14 can be fastened to the flange 18 of crucible 10 or to bottom plate 11 or to both flange 18 and plate 11.

Since the pouring device 14 can be made of metal, part or all of the inside of channel 17, receiving funnel 16 and channel 15 can be lined as at in FIG. 5, to resist heat.

If desired, heating elements (not shown) can be placed on the receiving funnel 16 and/or channel 17 in order to maintain or to increase the temperature of the molten slag as it flows therethrough.

Apart from the described component members, the plant or apparatus is also provided with a system for supplying a cooling liquid to the crucible 10 and bottom plate 11; a system for electric supply (a transformer, bus bars, and flexible cables); a system for exhausting gases evolving from the crucible during the melting process; apparatus for controlling and adjusting the melting operation, that are not described herein detail as being not relevant to the essence of the present invention.

The proposed installation operates as follows.

The consumable electrode 9 (or electrodes) is introduced into the electrode holder 7 and is clamped there by the aid of drive 8. Then, due to a displacement of the carriage 2, the electrode 7 is adjusted down into the crucible so that its lower end is disposed at a distance from the bottom plate 11 somewhat smaller than the thickness of layer of the molten slag to be poured into' the crucible 10. Hence, when the layer of slag in the crucible is equal to, for example, 200 mm., the lower end of the electrode 9 should be spaced from the bottom plate 11 at a distance of 190 mm.

The voltage is applied to the crucible by switching in the transformer.

The molten slag is poured from a ladle into the receiving funnel 16 of the pouring device 14, and is supplied into the crucible 10 through channels 17 and 15. The pOuring of the slag is discontinued at the moment the level of the molten slag in the crucible reaches the lower end of the electrode 9, which is evidenced by the current flowing through the plant circuit.

Thereupon, desirable electrical conditions of the melting process are preset by the aid of an appropriate apparatus, said electrical conditions being maintained constant throughout the melting process involving the building up of the ingot, or may vary according to the present program, which is effected due to a variation in the speed of feeding the electrode 9 by adjusting the rotational speed of the drive 5, and to a variation of the voltage of the secondary winding of the transformer intended to supply the plant. Thus, as pointed out above, the electrode is lowered to a depth of immersion to obtain the desired current flow to maintain the desired slag temperature. As the electrode melts, it is fed into the mold to maintain the end of the electrode immersed in the molten slag.

The ingot of a required height having been built up in the crucible 10, the melting process is discontinued, for which purpose feeding of the electrode is stopped, the transformer switched off, and the carriage 2 then raised into its upper position. The remaining stub of the electrode 9 is thereafter removed from the electrode holder 7. Thereupon, the crucible part 10 is raised by the aid of the carriage 3 until the built-up ingot is made to leave it completely, whereupon the carriage 13 complete with the bottom plate 11 and ingot are rolled out aside from the crucible part 10. The ingot is then removed and the channels 15 and 17 are cleaned from the solidified slag. Sometimes, with a view of saving time, the pouring device -14 is to be cleaned from the slag in the course of the melting process.

Subsequently, carriage 13 together with the bottom plate 11 is again placed under the crucible part 10, which is lowered onto the bottom plate. The pouring device 14 is connected thereto, and the working procedure as described above is repeated.

The proposed plant may be made use of to manufacture ingots of a round, oval, square, rectangular or any other cross section depending upon the crucible shape.

The method and plant, realized according to the present invention, provide for a maximum possible coeflicient of utilization of the working time; allow obtaining ingots with the bottom portion thereof of a high quality, which permits practically to avoid cropping the bottom discard; facilitate the rapid performance of the operation of pouring the molten slag into the crucible and the preparation of the plant before starting the subsequent melting process. The greater the weight of the ingot being formed, the greater is the efficiency of the instant apparatus.

The proposed plant is of a comparatively small height.

Aside from the above-mentioned advantages, the proposed plant provides for carrying out the process of electroslag remelting without the use of metallic dummy bars that are to be placed in the existing units on the bottom plate with a view of preventing its damage during the beginning of the melting process.

The utilization of the proposed plant proves to be more efficient the greater the weight of ingots that are to be made therein. "t is also possibel to employ one or a plurality of the consumable electrodes for obtaining an ingot. Thus, one or a plurality of the consumable electrodes clamped together without insulation between and with power applied between electrodes and the bottom plate can be employed to obtain an ingot. Other electrical arrangements can be used when a plurality of electrodes are employed such as designing the circuitry so that the applied electric current flows between the ends of the electrodes when they are in contact with the molten slag rather than from the electrodes to the bottom plate. In such an arrangement the current can be caused to flow between two or four electrodes as shown in FIGS. 5 and 6 of Belgian Pat. No. 670,299 or between three electrodes as shown in FIG. 4 of British Pat. No. 979,583 wherein a three phase transformer is used for the elctrical supply.

Referring to the access port of channel 15 as above described, this access port and the radial cross section of channel 15 ordinarily have the same area. These areas ordinarily range from 6 to 120 sq. cm. for circular ingots of 651500 mm. diameter (or equivalent non-round cross sections). The use of these cross sections assures that the back pressure in channel will not be excessive and that slag will solidify in channel 15 blocking backflow through the access port from the crucible and the remelting proceeds.

The above-described lining of the internal channel 17 and receiving funnel 16, if desired, can be extended into channel 15, using shields of refractory material such as graphite as shown in FIG. 5, to prevent the molten flux from burning through the funnel wall. The graphite shields may be 8-10 mm. in thickness in a typical installation.

When electrode 9 (see FIG. 1), is clamped in electrode holder 7, it is adjustably lowered by means of carriage 2 so that its lower portion moves into the crucible 10 until its lowermost end is spaced above the bottom plate 11 a distance from 4% to 20% less than the thickness (that is, the depth) of the layer of the molten slag to be poured into crucible 10.

Illustrated in FIGS. 6 and 7, there is an exemplary use of a weld lug. To provide a perfect electrical connection between the ingot being formed in the mold and the bottom plate 21, a circular recess 22 is provided extending down into the bottom plate 21 from its top surface which forms the bottom of the mold. A circular piece of metal 23 of the same composition as the ingot which is to be formed in the mold by the electroslag remelting process is fitted in recess 22. FIG. 6 shows a pouring device 14 with a receiving funnel 16 and a connecting channel 17 attached to the mold 10 in a manner similar to that hereinbefore described for FIG. 4.

A cylindrical passage or bore '24 is defined in the bottom plate 21 extending horizontally from recess 22 to the outer side of the wall of bottom plate 21. Cylindrical passage 24 slidably mounts a spring biased clamp pin 25, the inner end of which engages the weld lug 23. The outer end of pin 25 is slidably guided through a U-shaped bracket 26 mounted on the sidewall of bottom plate 21. Pin 25 is provided with an abutment collar 27 on the portion disposed between bracket 26 and the bottom plate sidewall. A coil compression spring 28 surrounds the pin 25 between the collar 27 and the U-shaped bracket 26 and applies a force against the collar 27 which urges the pin 25 against the weld lug 23 which presses the weld lug 23 against the side of the recess 22. In this manner an excellent electrical contact is obtained between the weld lug 23 and the bottom plate 21. When the molten slag bath is first introduced into the mold, the heat of the molten slag will cause the top of the weld lug 23 extending up into the mold to melt and the mOlten pool. which is initially formed in the bottom of the mold, will come in contact with the melted upper portion of the weld lug. As a result, when the ingot starts to solidify, weld lug '23 will be welded to the bottom solidified portion of the ingot being formed and an excellent electrical contact will be obtained between the weld lug and the ingot and thus between the ingot and the bottom plate 21.

In an embodiment illustrated in FIGS. 8 and 9, a system in accord with the present invention may comprise a mold 30 including a bottom plate 32 and sidewalls 34. Although not shown in FIGS. 8 and 9, mold 30' is water cooled by conventional techniques, such as has been hereinbefore described. A pair of electrodes 36 are positioned over the mold 30 extending down into the open top of the mold. The electrodes are supported by an electrode holder 38 mounted on a carriage 40. Carriage 40 can be moved up and down a supporting tower 42 to feed the electrodes 36 together as a unit into the mold 30' as the electrodes melt. The sidewalls 34 of the mold are mounted on a second carriage 44 which also is movable up and down the tower 42. Drive motors, similar to drives 5 and 6 in FIG. 1 can provide the motive force for the carriages 40 and 44.

As can be seen in FIG. 9, a channel 46 is defined by a groove in the top surface of the bottom plate 32 extending from inside of the mold sidewalls to outside thereof and extending into a tongue 48 formed on the bottom plate. The channel 46 is preferably positioned as shown in FIG. 9 at a point half way between the two electrodes. A funnel 50 provided with a base plate 52 rests on the tongue 48 of the bottom plate and closes the top of the portion of the channel 46 which extends out into the tongue 48. The sidewalls are formed with a flange 54 which abuts against the plate 52 so that the portion of the channel 46 extending outside of the sidewalls 34 is completely covered. The passage of funnel 50 connects with the channel 46. As a result, a closed channel is provided between the bottom of the interior of the mold and the mouth of the funnel 50.

Each of the two electrodes 36 is connected to an opposite side of the secondary winding 56 of a transformer 58. The second winding has a center tap to which the mold bottom plate 32 is connected, preferably by means of a weld lug as hereinbefore described, but not shown in this embodiment. In operation, the assembly of electrodes 36 is first lowered into the mold 30 to a position determined by the desired depth of the bath of molten slag to be formed in the mold. AC power is applied between the electrodes from the transformer 58. Then superheated molten slag is poured into the bottom of the mold 30 through the funnel 50 and the channel 46. When the molten slag in the mold 30 reaches a depth sufi'lcient to contact the two electrodes 36, current will begin to flow between the electrodes through the molten slag thus heating the molten slag and beginning to melt the electrodes 36. This flow of current will be indicated by an indicator 60, which for example may be an ammeter connected in the conductor between one of the electrodes and the transformer 58. When the technician who is controlling the pouring of the molten slag into the mold observes that current begins to flow through the electrodes 36 as indicated by the indicator 60, he immediately stops pouring the molten slag. In this manner, by initially positioning the electrode at the proper depth in the mold, the desired amount of molten slag in the mold is readily obtained with precision. Because there will be some reaction time between the indication provided by indicator 60 and the time that pouring of slag actually stops, the slag will be poured to a depth a little above the ends of the electrodes in the mold. The desired amount of slag is nevertheless precisely obtained by initially positioning the bottom ends of the electrodes just below the desired level of slag in the mold.

As the electrodes 36 are melted, they are fed into the molten slag by the carriage 40 moving on the tower 42 to maintain the electrodes immersed at the desired depth in the molten slag. As the electrodes melt, they will form a molten pool beneath the bath of molten slag which will solidify into an ingot starting from the bottom of the mold with a pool of molten metal being maintained between the bath of molten slag and the solidified ingot. In FIG. 8, the solidified ingot in the mold is designated by the reference number 62, the bath of molten slag is designated by the reference number 64, and the pool of molten metal is designated by the reference number 66. The connection between the bottom plate 32 and the center tap of the secondary winding 56 serves to maintain the melting rates of the two electrodes equal. Should one of the electrodes melt slower than the other it will become more deeply immersed in the molten slag. The resistance between this electrode and the bottom plate 32 will be reduced relative to that between the other electrode and the bottom plate. As a result, some current will flow between the center tap and the more deeply immersed electrode, thus increasing the current flow through the more deeply immersed electrode relative to the other electrode. This action results in the more deeply immersed electrode melting at a greater rate until its immersion becomes less, the

current decreases and melting rate decreases. In this manner, the melting rates of the electrodes tend to equalize. As the ingot is formed, the bath of molten slag will rise in the mold 30. When the bath nears the top of the mold, the melting of the electrodes is ended and the molten pool of metal at the top of the ingot and the bath of molten slag is allowed to solidify. After the solidification has taken place, the sidewalls 34 are stripped from the ingot by moving the carriage 44 up on the tower 42. The sidewalls 34 are conical shaped with the large end down as shown in FIG. 8 to facilitate stripping.

In this manner, a high quality ingot is produced by an electroslag remelting system with a relatively high power factor. The ingot can be produced by remelting of ferrous or nonferrous metals from the consumable electrodes.

The dry start method of obtaining a molten slag bath, mentioned above as prior art, is time consuming and increases the time for producing finished product ingots by as much as compared to the time required when the slag is melted outside of the remelting zone. In addition, the dry start method has the disadvantage that the afore-mentioned arcing leads to oxygen release from the slag whereby the first portion of the metal melted from an electrode is out of specification. Furthermore, such arcing ordinarily does not melt the slag at the periphery of the remelting zone and as a result the heat produced by the current passing through the slag at the beginning of the remelting process is not sufiicient to adequately refine the metal being produced. As a result of the oxygen contamination and as a result of the initial incomplete slag melting, the bottom portion of the formed ingot is of inferior quality and is ordinarily trimmed or cropped from the rest of the ingot and reprocessed or discarded. This bottom portion can amount to up to 10% of the entire ingot.

The prior art top pouring method overcomes the aforementioned disadvantages of the dry start method but has disadvantages of its own as follows.

If top pouring is carried out with the electrode removed from the remelting zone, a crust of molten slag is often formed at the bottom of the remelting zone during the time the electrode is being lowered into the zone after pouring has been completed. This crust insulates the bottom of the remelting zone so as to block current flow whereby the electroslag remelting process is prevented from starting. When this occurs, the crust-containing slag must be removed from the remelting zone and a new batch of slag poured. This phenomenon is referred to as a false start.

Moreover, if the apparatus is designed so that the electrode can be positioned above the remelting zone, the apparatus is required to be of greater height than otherwise, requiring more factory space, and the lead attached to the electrode is required to be longer whereby inductance is increased so that the power factor is lowered requiring more power per pound of metal produced.

If top pouring is carried out with the electrode in place in the remelting zone, then a long eiectrode of small cross-section must be used in order to provide a sufficient gap between the electrode and the sidewalls of the remelting zone so that the slag stream does not contact and coat either the electrode or the walls with a scale of solid slag. Moreover, such scale falls in solid form into the molten slag during the remelting process and either can cause marked variation in the current applied during remelting thereby causing non-uniform results or else can be trapped within the metal melted from the electrode so as to form undesirable inclusions in the formed ingot.

The length of the electrode utilized in this method results in high inductance and a lower power factor thereby raising production costs. In addition, a tall tower must be provided for supporting and feeding the electrode. Such a tower adds significantly to the cost of the installation.

In order to ensure that the slag being top poured does not contact either the electrode or the remelting zone walls, the pouring stream must be of relatively small cross-section. As a result, pouring of the slag to a required depth in the remelting zone takes a significant amount of time so that often a crust of solidified slag forms at the bottom of the remelting zone whereby a false start occurs.

Both of the aforementioned techniques of top pouring have the disadvantage that the slag during pouring reacts with nitrogen in the air to form nitrides which dissolve in the metal being produced lowering the quality of the finished product ingot. In addition, moisture in the air dissolves in the slag during pouring and disassociates into hydrogen and oxygen which dissolve in the metal being produced; the hydrogen causes cracking to occur in the finished product ingot. These chemical reactions are encouraged due to the long period of time during which top pouring is carried out and by the large surface area of slag presented during pouring.

Both of the aforementioned techniques of top pouring are dangerous. The fact that the ladle from which the molten slag is poured during top pouring is in an elevated position presents considerable danger to personnel in case of accidental spilling. Moreover, energizing of the electrode can result in a small explosion due to short circuiting causing excess heating of the slag which explosion can upset the ladle if it is still in position over the remelting zone.

Furthermore, top pouring techniques have the very important disadvantage that the electrode cannot be energized previous to the completion of pouring. In top pouring with the electrode outside the remelting zone, the electrode cannot be energized previous to its insertion into the remelting zone for reasons of safety. In top pouring with the electrode in place, depending into the mold, the electrode or electrodes cannot be energized because slag splashing against them during pouring causes short circuiting resulting in explosion. Energizing of the electrode current circuit previous to the completion of pouring would result in a significant time savings so that the apparatus can be used more efficiently.

In addition to the foregoing, top pouring techniques have the disadvantage of requiring special measuring equipment to determine the slag level in the remelting zone at any particular time during top pouring.

As stated hereinbefore under the Summary of the Invention, the slag pool is produced by pouring the molten slag into the bottom part of the crucible 10. This bottom part of the crucible, as defined by the crucible sidewalls and its separate bottom plate 11, forms a remelting zone in which the electrode or electrodes, such as shown in the embodiment of FIG. 8, are melted by the electrical current as soon as the slag reaches its predetermined depth by rising to contact the electrode 2. The pouring is sufficiently fast and current flow begins sufficiently quickly after the pouring is started that the formation of a slag crust on the bottom of the remelting zone is prevented and thus false starts are eliminated. In fact, the time required for obtaining molten slag in the remelting zone with an energized electrode in place is minimized to a matter of a few minutes or less.

Because the electrode is already in place and because bottom pouring avoids pouring slag past the electrode, the gap between the electrode and the remelting zone walls, i.e., the sidewalls of the crucible, can be made very small thus permitting a larger diameter electrode to be used. As a result, a significantly shorter electrode can be used and the height of the tower required is accordingly reduced. With shorter electrodes, the inductance of the circuit is reduced and the power factor of the system is accordingly increased. Since the slag is poured into the bottom of the remelting zone, the possibility of formation of slag scale on the remelting zone walls is entirely eliminated.

With this technique of pouring the molten slag into the bottom of the remelting zone, the operator controlling the pouring can determine very precisely when to stop pouring the molten slag. When the molten slag reaches the electrode, current begins to flow in the electrode and that current flow provides a condition indicating to the operator that the slag bath has reached the predetermined depth. Accordingly, pouring of the slag is discontinued when current starts to flow through the electrode. Because the slag can be poured quickly through a closed channel into the bottom of the remelting zone, there is little opportunity for the slag to react with nitrogen in the air or to dissolve moisture from the air. Furthermore, because slag is poured into the bottom of the remelting zone, the ladleis positioned near the base of the furnace thus greatly reducing the danger to personnel.

The invention may be embodied in other specific forms without departing from the scope, spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope and spirit of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. In a method of electroslag remelting of metal from consumable electrodes in which at least one consumable metal electrode with upper and lower ends is disposed with its lowermost end arranged to be immersed in molten slag in crucible means having fluid cooled wall means and progressively melted in said slag through the application of electric current, said crucible means having a fluid cooled bottom portion at the lower end thereof, the improvement comprising, in the beginning of the remelting process, introducing slag in a molten state into the fluid cooled crucible means through at least one port formed through the crucible means adjacent the lower portion thereof, causing the molten slag to contact the lower end of the consumable electrode, and with the electrode in contact with the molten slag, passing electric current through a circuit including the electrode and the molten slag.

2. In a method of electroslag remelting of metal from a consumable electrode in which a consumable electrode with upper and lower ends is disposed in a fluid cooled crucible with its lowermost end immersed in molten slag and progressively melted in said slag through the application of electric current, the improvement comprising: in the initiation of the remelting process, introducing said slag in molten state through an access port in the lower portion of said fluid cooled crucible, a sufficient amount of slag being introduced to contact the lower end of said consumable electrode, and with the electrode in contact with the molten slag, passing electric current through a circuit including the electrode and the molten slag.

3. A method as defined in claim 2, in which said molten slag is introduced into said crucible at a point below the lowermost end of said consumable electrode.

4. A method as defined in claim 3, wherein the introduction of said molten slag into said crucible is discontinued when the molten slag in the crucible contacts said lower end of said consumable electrode.

5. A method as defined in claim 2, wherein the introduction of said molten slag into said crucible is discontinued when the molten slag in the crucible contacts said lower end of said consumable electrode.

6. A method as defined in claim 2 wherein all of the slag introduced into said crucible is introduced into said lower portion of said crucible.

7. A method as defined in claim 2 wherein the introduction of said molten slag into said crucible is discontinued when current commences to flow through the molten slag.

8. A method as defined in claim 2, in which said molten 12 slag is introduced through a passage in the bottom plate of the crucible.

9. In a method of electroslag remelting of metal in a fluid cooled crucible from a consumable electrode in which a consumable electrode with upper and lower ends is disposed with its lowermost end arranged to be immersed in molten slag within the crucible and progressively melted in said slag through the application of electric current passing through the electrode and the slag, the fluid cooled crucible having a bottom plate at the lower end thereof, the improvement comprising: in the initiation of the remelting process, introducing slag in molten state into the fluid cooled crucible through a passage formed through the crucible adjacent the lower portion thereof, a suflicient amount of slag being introduced to contact the lower end of the consumable electrode, and with the electrode in contact with the molten slag, passing electric current through a circuit including the electrode and the molten slag.

10. A method as defined in claim 9, wherein an ingot is formed in the crucible from metal melted from the consumable electrode and passed through the molten slag.

11. A method as defined in claim 9, wherein the crucible is free of slag prior to introduction of the slag through the passage adjacent the lower portion of the crucible.

12. A method as defined in claim 9, wherein said molten slag is introduced into the crucible at a point below the lowermost end of the consumable electrode.

13. A method as defined in claim 9, wherein said molten slag is introduced through an aperture located in the lowermost end of the crucible.

14. A method as defined in claim 9 wherein said molten slag completes the electrical circuit and permits electric current to flow when it contacts the lower end of said consumable electrode.

15. In a method of electroslag remelting of metal from consumable electrodes in which at least one consumable metal electrode with upper and lower ends is disposed with its lowermost end arranged to be immersed in molten slag in a fluid cooled crucible and progressively melted in said slag through the application of electric current, said crucible having a fluid cooled bottom plate at the lower end thereof, the improvement comprising, in the beginning of the remelting process, introducing slag in a molten state into the fluid cooled crucible through at least one passage formed through the crucible adjacent the lower portion thereof, causing the molten slag to contact the lower end of the consumable electrode, and with the electrode in contact with the molten slag, passing elecric current through a circuit including the electrode and the molten slag.

16. A method as defined in claim 15, wherein the passage through said crucible is located at a point above the bottom plate of the crucible wherein the slag is introduced through the side of the crucible.

17. A method as defined in claim 15, wherein the passage is located below the lowermost end of the consumable electrode, whereby the slag is introduced into the crucible at a location lower than the lowermost end of the consumable electrode.

18. A method as defined in claim 15, wherein the passage is located in the bottom plate of the crucible so that the slag is introduced through the bottom plates.

19. A method as defined in claim 15, wherein the voltage for driving said electric current is applied during the introducing of the slag and the slag rises in the crucible to contact the consumable electrode and to close the electrical circuit enabling current flow.

20. A method as defined in claim 15, wherein a plurality of consumable electrodes are disposed in the cru cible.

21. A method as defined in claim 15, wherein the crucible is initially free of slag and the slag introduced through the passage adjacent the lower Portion f the C cible is in an amount sufficient to immerse the lower end of the consumable electrode.

22. A method of electroslag remelting at least one consumable metal electrode having upper and lower ends in a receptacle which includes a crucible and a bottom plate at the lower end of said crucible with a channel extending from the outside to the inside of said receptacle located at the lower portion thereof, each of said crucible and bottom plate having means for cooling same, whereby an ingot is formed by applying electric power and progressively melting an electrode immersed in molten slag contained in the crucible, said method comprising: in initiating of the melting process, disposing an electrode within said crucible with the lower electrode end spaced apart from said bottom plate; supplying cooling liquid to the crucible and the bottom plate; melting slag outside said receptacle; introducing the slag in molten state into said receptacle through said channel at the lower portion of said receptacle and in an amount sufiicient for the molten slag to achieve a predetermined depth within the crucible, causing the molten slag and the lower electrode end to come into contact with one another, and with the electrode in contact with the molten slag, passing electric current through a circuit including the electrode and the molten slag. v

23. A method as defined in claim 22, wherein the molten slag is introduced into the crucible at the lowermost end thereof.

24. A method as defined in claim 22, wherein the slag is introduced into the crucible at a point below the electrodes lowermost end.

25. A method as defined in claim 22, wherein voltage is applied to the electrode while the molten slag is being introduced into the receptacle.

26. A method of electroslag remelting a plurality of consumable electrodes to form an ingot as defined in claim 22, wherein a plurality of electrodes are disposed within said crucible.

27. A method as defined in claim 22, wherein the crucible is free of slag prior to introduction of the slag through the channel located at the lower portion of the crucible.

28. A method of electroslag remelting at least one consumable metal electrode having upper and lower ends in a receptacle which includes a crucible and a bottom plate at the lower end of said crucible with a channel extending from the outside to the inside of said receptacle located at the lower portion thereof, each of said crucible and bottom plate having means for cooling same, whereby an ingot is formed by applying electric power and progressively melting an electrode immersed in molten slag contained in the crucible, said method comprising: disposing an electrode within said crucible with the lower electrode end spaced apart from said bottom plate; supplying cooling liquid to the crucible and the bottom plate; melting slag outside said receptacle; applying voltage to the electrode; introducing the slag in molten state into said receptable through said channel at the lower portion of said receptacle and in an amount sufficient for the molten slag to contact the consumable electrodes lower end and thus complete an electrical circuit including the consumable electrode and molten slag to initiate the electroslag remelting process; melting said consumable electrode by continued application of power and feeding of said electrode into the molten slag thus building up an ingot by solidification of melted electrode metal due to cooling liquid supplied to the crucible and base plate; and terminating the feeding of the electrode and the applying of power when the ingot reaches desired height.

29. A method as defined in claim 2, wherein the lower electrode end is spaced apart from the bottom plate less than the height of molten slag in the crucible established by the amount of molten slag introduced into the receptacle.

30. A method as defined in claim 28, wherein the voltage is applied between the electrode and the receptacle.

31. A method as defined in claim 28 wherein the molten slag is introducd into the receptacle via a channel at least a portion of which is formed in part of the bottom plate.

32. A method as defined in claim 28 wherein the molten slag is introduced into the receptacle via a channel which is formed by the linking of the bottom plate with the crucible.

33. A method of electroslag remelting a plurality of consumable electrodes to form an ingot as defined in claim 28 wherein a plurality of electrodes are disposed within said crucible with the voltage applied when the molten slag is introduced into the receptacle in sufiicient amount so that the slag will contact the lower ends of said electrodes.

34. A method as defined in claim 28 wherein the ingot is built up to desired height within the crucible and after the power is discontinued the crucible is raised away from the ingot.

35. A method as defined in claim 28, wherein the crucible is free of slag prior to introduction of the slag through the channel located at the lower portion of the crucible.

36. In a method of electroslag remelting of metal from consumable electrodes in which at least one consumable electrode with upper and lower ends is disposed with its lowermost end arranged to be immersed in molten slag in a fluid cooled crucible and progressively melted in the slag through the application of electric current, the crucible having a fluid cooled bottom plate at the lower end thereof, the improvement comprising: in the initiation of the electroslag remelting process, introducing slag in a molten state into the fluid cooled crucible through at least one passage formed through the crucible and located below the lowermost end of the electrode, said introducing of the slag occurring while the voltage for driving electric current is applied so that the slag rises in the crucible to contact the consumable electrode and to immerse the lowermost end thereof causing the electrical circuit for current fiow to be completed.

37. A method as defined in claim 36, wherein the crucible is free of slag prior to the introduction of slag through the passage located below the lowermost end of the electrode.

38. A method as defined in claim 36, wherein a plurality of consumable electrodes are disposed in the crucible.

References Cited UNITED STATES PATENTS 2,248,628 7/ 1941 Hopkins -10 3,342,250 9/1967 Treppschuh 75-10 1,814,584 7/1931' Bost 249-109 FOREIGN PATENTS 885,096 8,1953 Germany 75--10 910,418 5/1954 Germany 75--10 168,743 2/1965 U.S.S.R. 75----10 979,583 1/1965 United Kingdom 75-10 L. DEWAYNE RUTLEDGE, Primary Examiner P. D. ROSENBERG, Assistant Examiner US. Cl. X.R. 13-9; 75-11 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 736, 124 Dated May 29, 1973 inventofls) I Boris E. Paton et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below In column 1, at the proper line in the Heading, please ins ert --Foreign Application Priority Data I October 25, 1966 7 Austria A 9973/66 I U.S.S .R. Author's Certificate Applications March 5, 1966 [1.8 .S .R. 1060334 April 2, 1966 U.S .S .R. 1067222 Column 2, line 32, change "market" to ---marked Column 3, line 15, change "specifified" to --specified-. Column 3, line 47, change t'ohe" to -the. Column 5, line 51, change "herein" to --here in--. Column 6, line 57, change "t to --It-. f. Column 6 line 57, change "possibel" to --possible--. 1 Column 12, line 63, change plates" to ---plate-. Column 14, line 1, change "2" to --28- 1 Signed and sealed this 29th day of January 1974 i (SEAL) Attestz a 1 p g EDWARD M.PLETCHE R,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner -of Patents PC4050 (110459) I I v uscoMM-oc GOING-P69 v I (LS. GOVERNMFN'I FRINYING OIUCE 1 IQ'B 3-334 UNITED STATES PATENT OFFICE (IETEFICATE OF CURRECTIGN Patent No. 3, 736, 124 Datecl Nlay 29, 1973 Invenmfls) Boris E. Paton et a1 It is certified that error appears in the-above-identified patent and that said Letters Patent are hereby corrected as shown below In column l, at the proper line in the Heading, please its ert --Foreign Application Priority Data I October 25, 1966 Austria A 9973/66 US.S .R, Author 's Certificate Applications M r 1 U05 .5 .R. 1060334 Column 2, line 32, change "market" to ---marked-- Column 3, line 15, change "specifified" to --specified-. Column 3, line 47, change tnhe" to --the.

Column 5, line '51, change "herein" to --here in-*-.

Column 6, line 57, change "t to --It--.

Column 6, line 57, change "possibel" to --possible-. Column 12, line 63, change "plates" to -plate-.

Column 14, line 1, change "2" to -28-- Signed and sealed this 29th day of January 1974.

(SEAL) Attestz EDWARD M.FLETCHE R,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents ORM PO- 10 0( 1 I USC OMM' DC wave-poo I U.$. GOVERNMENT PRINT NG OFFICE I I969 0-366-334' 0;

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