US3712365A

US3712365A - Electroslag process for the production of metal castings

Info

Publication number: US3712365A
Application number: US00093887A
Authority: US
Inventors: V Baglai; B Medovar; J Latash; B Paton
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-11-30
Filing date: 1970-11-30
Publication date: 1973-01-23
Anticipated expiration: 1990-01-23

Abstract

A process of operating an electric furnace as set out wherein the electrode is melted within the furnace mold by application of electric current while the electrode is held in a fixed axial position. The molten slag bath is maintained in contact with the electrode during melting thereof.

Description

United States Patent [191 Paton et al.

ELECTROSLAG PROCESS FOR THE PRODUCTION OF METAL CASTINGS Inventors: Boris Evgenievich Paton, ulitsa Kolsjubinskogo 9, kv. 2i; Boris Izrailevich Medovar, Bulvar Lesi Ukrainki 2, kv. 8', Jury Vadimovich Latash, Vazdukhoflotsky prospekt, 87, kv. l4; Vitaly Mikhailovich Baglai, ulitsa Semashko l0, kv. 54/3, all of Kiev, U.S.S.R.

Filed: Nov. 30, 1970 Appl. No.: 93,887

Related U.S. Application Data Continuation of Ser. No. 707,088, Feb. 21, 1968, abandoned.

U.S. Cl. ..l64/52, 13/18, 13/15 Int. Cl. ..B22d 27/02 Field of Search...l64/52, 50, 252, 250; 75/10 C,

Primary Examiner-J. Spencer Overholser Assistant Examiner-V. K. Rising Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT A processof operating an electric furnace as set out wherein the electrode is melted within the furnace mold by application of electric current while the electrode is held in a fixed axial position. The molten slag bath is maintained in contact with the electrode during melting thereof.

45 Claims, 5 Drawing Figures PATENTEDJM 23 I975 SHEET 1 OF 2 BACKGROUND OF THE INVENTION The present invention relates to processes for the production of metal castings.

More particularly, the invention relates to a process for the electroslag remelting of consumable electrodes and can be used, in particular, to produce ingots from ball-bearing, heat-resistant and high-strength construction steels and alloys.

Known in the prior art is a process of electroslag remelting, consisting in that a pool of liquid slag is created in a cooled ingot mold, into which the lower ends of one or several metal blanks are immersed serving as a consumable electrode, an electric current being passed through the electrode and the slag pool. The electric current causes the heat necessary for melting of the metal blank to be liberated in the slag pool; the metal melted off the blank is given the required shape in the ingot mold, forming a casting.

As a rule, the cross section of the consumable electrode is much less than that of the mold space, for this reason the height of the ingot obtained is much less than the length of the electrode being remelted. To maintain the electrode melting process, the mold or the electrode must be moved so to preclude breaking of the electric circuit which would take place if the electrode leaves the slag pool.

The known plants, in particular, those described in Soviet lnventors Certificate No. 195,482, have mechanisms for moving the electrode or mold, which comprise carriages with an electrode holder or a platform with the mold, travelling along guide columns. The guide columns are usually cumbersome and have a considerable height, especially in plants for casting ingots weighing over tons, and the mechanisms for moving the electrode or mold must have a large lifting capacity. It can therefore be stated that such plants are of a complicated design, require considerable working area and high shop structures.

An object of the present invention is to eliminate the above disadvantages and difficulties.

The specific object of the invention is to provide an improved process for the production of metal castings by electroslag remelting of a consumable electrode, in which, according to the invention, no mutual movement of the mold and the electrode is required to maintain the process of melting of the consumable electrode.

Disclosed in the present invention is an improved process for producing metal castings by electroslag remelting of a consumable electrode in a cooled ingot mold. According to the invention, remelting is run with the electrode in a fixed position relative to the mold, and with slag being added to the slag pool to maintain the process of melting of the'consumable electrode as it is used up.

It is good practice to use solid pulverized slag and fill the space between the electrode and the mold with it, so as to provide a layer of solid slag above the slag bath in the process of melting which would gradually enter the slag pool as the electrode is consumed.

This ensures uniforms feeding of the slag pool in the mold and protection of the pool from the surrounding atmosphere; at the same time the layer of solid slag above the bath serves as an adsorbent for the gases liberated in the process of melting the metal.

In addition, in the proposed process the slag pool is constantly refreshed as new portions of the solid slag are melted, whereby refining of the metal is improved.

It is also possible to pre-fill the space between the electrode and the mold with liquid slag beforehand and let it solidify; the solid slag will replenish the slag pool as the electrode melts under its own weight.

It is also possible to run the process by periodically adding liquid slag to the slag pool as the electrode melts, the slag being poured in from above through the gap between the electrode and the mold.

It will sometimes be expedient to use a tapered consumable electrode and place it into a conical mold with its greater base upward. With the taper of the electrode and the mold being the same, notwithstanding the addition of slag, the depth of the slag pool can be insured to remain constant, while its volume will increase as the mold widens upward.

It will be preferable to have the taper of the electrode somewhat greater than that of the mold space to ensure that the height of the built-up ingot will be less than the length of the remelted portion of the electrode, and that with the slag pool moving in accordance with the ingot growth along the height of the mold, the depth of said pool should increase and insure the optimal ratio between the depth of the slag pool and the diameter of the mold space at the place of the slag pool location at the given moment. 1 The advantage of using tapered electrodes consists in that such electrodes can be produced by casting the metal in cast iron molds, whereas they were previously manufactured by forging, rolling or in continuous metal-casting plants.

Practice has also proved that the tapered shape of the mold, widening upward, results in a more favorable crystallization of the ingot, the crystallization proceeding upward.

To produce untapered ingots it is desirable to use prismatic or cylindrical electrodes and remelt them in untapered molds or in molds slightly widening downward. In this case the cross-sectional dimensions of the electrode should be at least nine-tenths of the respective dimensions of the internal cross section of the mold. This is done to ensure that the depth of the slag pool at the end of melting should not exceed technologically tolerable limits.

When using tapered, prismatic and cylindrical electrodes it is desirable to make them with a shoulder in the upper portion, so as to make it possible to do without an electrode holder and place the electrode in the mold by arranging its shoulder directly on the current-feeding contact device. In the plant for effecting the process, according to the invention, this contact device is installed in the upper portion of the mold and is electrically insulated from it.

In a plant for the production of tapered castings the mold is made of at least two parts split along a vertical plane, which can be connected to a mechanism for moving them apart when the ingot is being extracted.

An advantage of the invention as a whole resides, first of all, in the simplification and lower cost of the plants for electroslag remelting, and also in the simplification of their operation.

Another advantage stems from the high electrotechnical characteristics of the plants owing to the current conductors from the source of power to the plants having a comparatively short length and being arranged parallel to each other at a close distance (-bifilarly). This, in turn, made it possible to reduce the resistance and inductive reactance of the electric circuit of the plant.

The invention made it possible to appreciably reduce the height of theplants and, accordingly, the height of the shop structures accommodating them, and also to reduce the floor space used.

The nature of the present invention will become more fully apparent from a consideration of the following description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 represents a schematic view of a plant according to the invention, with a tapered mold, used for effecting the process of producing metal castings;

FIG. 2 is a top view of the same plant, without the consumable electrode;

FIG. 3 shows schematically the mutual arrangement of the consumable electrode and the mold, when the electrode and the mold have the same taper;

FIG. 4 shows schematically the mutual arrangement of the consumable electrode and the mold, when the taper of the electrode is greater than that of the mold;

FIG. 5 is a schematic view of a plant according to the invention, with a cylindrical mold, used for effecting the process of producing metal castings.

In one of the possible embodiments, shown in FIGS. 1 and 2, the plant comprises a cooled taperedmold l widening upward and installed on a base 2 with a siphon device 3, which communicates by means of a duct 4 in the base 2 with a space 5 of the mold and serves for pouring liquid slag into the mold. The top edge of the mold 1 carries current-feeding contact devices 7, insulated from the mold edge bymeans of a dielectric gasket 6, said contact devices 7 being made as two halfsrings, connected via feeders 8 to a busbar 9, the latter being connected to a source of alternating or direct current (not shown). 7

. A consumable tapered electrode 10 (an ingot cast in a cast iron mold being usable for the purpose), with a cross-section close to the internal cross section of the mold 1 is so placed in the latter that its lower end is immersed in the slag pool (not shown), said electrode bearing with its shoulder 11 that is in the upper portion thereof, against the contact devices 7.

In the upper part of the mold 1 two current-feeding contact devices 12 are also secured connected via feeders. 13 to a busbar 14, connected to the same source of current. The electrode 10 can have the same taper as the mold, or a greater one. I

Solid pulverized slag, which is fed into the slag pool as the electrode 10 melts for stabilizing the process, is charged into the space between the electrode 10 and the mold 1 from a bin 15 along a chute 16 via a hole (not shown) in the-shoulder 11 of the electrode 10.

For extracting the finished ingot (not shown) from the mold I the latter is made of two parts 1a and 1b, split along a vertical plane, each said part carrying said contact device 7 made as a half-ring. The parts In and 1b of the mold 1 are moved apart for extracting the ingot by means of a mechanism 17, provided with turning levers 18 in a plane perpendicular to the axis of the mold 1. The levers 18 are connected to the parts la and lb of the mold. An open mold is shown in FIG. 2.

Thus a novel feature of the plant described hereinabove is the design of the electrode 10 and the mold l which are made tapered, widening upward, with identical or close tapers, and also the fixed position of the electrode 10 relative to the mold l.

The principle of operation of the plant and the process for producing ingots in this plant are described herein below for embodiments when the tapers of the electrode 10 and the mold l are equal, and when the taper of the electrode 10 is greater than that of the mold 1.

By switching on the source of current, voltage is applied to the electrode 10 and mold 1. Preliminarily melted slag is poured into the mold 1 through the device 3 in such an amount, as indicated above, that the lower end of the electrode 10 should be immersed in the slag. When this takes place the process of melting the electrode 10 commences. The space between the electrode 10 and the mold l is filled with solid slag. It is desirable that in the process of melting the slag pool be covered by a layer of solid slag, which would gradually drop into it as the electrode 10 melts; this also contributes to better refining of the metal.

The volume of the slag pool can: be maintained by periodically feeding liquid slag into the gap between the electrode 10 and the mold 1. It is also possible to prefill this space with liquid slag and let it solidify owing to the intensive removal of heat through the walls of the mold l and the electrode 10. As the electrode 10 melts, the solidified slag will also drop into the slag pool under its own weight. i

The diagrams presented in FIGS. 3 and 4 show the relation between the length of the melted portion of the electrode, the height of the built-up ingot and the depth of the slag pool in the process of remelting, depending on the taper of the electrode 10 and the mold l.

In case the angles a and B of taper of the mold 1 (FIG. 3) and those of the electrode 10 are equal'and the depth h of the slag pool is specified, it is possible to insure, in the process of melting, the equality of the cross-sectional areas of the electrode 10 at the place where its melting begins (levels AA or A'A along the surface of the slag pool at the beginning and the end of the melting process, respectively) and of the surface of a metal bath 19 (levels BB or B'B') of an ingot 20 being built up. v

Under these conditions in the process of melting with theaddition of solid slag in the space between the electrode 10 and the mold 1 the depths h and h of the slag pool are constant, but the ratio-between the depth of the slag pool and the diameter of the mold (at the place where the slag pool is located) decreases, whereby the discharge gap 8' between the electrode 10 and the surface of the metal bath 19 at the end of the process becomes less than the discharge gap 8 at the beginning of the process, and an arc may strike between the electrode 10 and the metal bath l9.

When the taper of the electrode exceeds that of mold 1 (FIG. 4) so that during the entire process of melting the ratio between the depth of the slag pool and the diameter of the mold remains constant, with B a we have h' h and '6 6.

Since in these instances the volume of the slag pool continuously grows, it is good practice to increase the power supplied by raising the voltage.

Upon completion of the melting process the stub of the electrode is removed and the ingot is extracted from the mold.

It is most expedient to use conical ingots thus produced for forging on hammers and presses.

In another embodiment of the invention (FIG. 5), in contrast to the first one, the plant comprises a prismatic or cylindrical mold 21, in which a prismatic or tapered electrode 22 is similarly installed, said electrode 22 bearing with its shoulder 23 against an annular currentfeeding contact device 24 installed on the upper edge of a mold 21 and electrically insulated from it by means ofa gasket 25.

The plant is supplied from a source of alternating or direct current (not shown) by means of feeders 26.

The internal cross-section of the mold 21 may somewhat increase toward the bottom for the extraction of the ingot to be facilitated.

A base 27 and a siphon device 28 are similar to those described above. For the extraction of the ingot from the mold the base 27 is made vertically movable on a bed-plate 29 connected to a lowering mechanism (not shown).

, A condition prereguisite for the operation of this plant is that the cross-sectional dimensions of the electrode 22 must be at least nine-tenths of the corresponding dimensions of the internal cross-section of the mold 21.

This is done to insure that the difference between the linear rates of electrode melting and ingot building up should be minimum, and that the depth of the slag pool at the end of melting should not exceed the appropriate tolerances.

In the process of melting the volume of the slag pool also increases with melting of the electrode 22, and the power supplied to the plant must be increased. The ingots produced in this plant are designed mainly for processing in rolling mills.

Described herein are the most easily realizable exemplary embodiments of the invention with one consumable electrode. It is also possible, however, to remelt two or three electrodes, connected correspondingly in se ries (a bifilar circuit), or with a star or delta connection. Here the total cross section of the electrodes should then approach the internal section of the ingot mold.

The invention is not limited to the exemplary embodiments described herein and may have modifications within the scope of the following claims.

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

1. A process for the production of metal castings by the remelting of at least one consumable electrode immersed in a slag pool which is created in a cooled mold; said process consisting in that remelting is carried on with the portion of said electrode, at which said electrode is mounted, maintained in a fixed position relative to the mold, and slag is added to the slag pool as the electrode melts.

2. A process as in claim 1, wherein the space between the electrode and the mold is filled with solid, preferably pulverized, slag, which enters the slag bath from this space as the electrode melts.

3. A process as in claim 1, wherein liquid slag is poured into the space between the electrode and the mold and is kept there until it solidifies, so that it should be supplied into the slag pool during the remelting process as the electrode is consumed.

4. A process as in claim 1, wherein in the process of melting of the electrode, liquid slag is periodically added to the slag pool through the gap between the electrode and the mold.

5. A process as in claim I, wherein the consumable electrode is made tapered and is placed into a tapered mold with its greater base upward.

6. A process as in claim 5, wherein the electrode is made with a taper equal to that of the mold.

7. A process as in claim 5, wherein the electrode is made with a taper greater than that of the mold.

8. A process as in claim 1, wherein prismatic electrodes are used with cross-sectional dimensions at least nine-tenths of the corresponding dimensions of the internal cross-section of the mold.

9. A process as in claim 1, wherein cylindrical electrodes are used with cross-sectional dimensions at least nine-tenths of the corresponding dimensions of the internal cross-section of the mold.

10. A process as in claim 1, wherein use is made of electrodes with a shoulder in their upper portion, by means of which the electrodes when installed in place bear against the current-feeding contact devices of the mold.

11. A process for the melting of at least one consumable electrode in a cooled mold of an electric furnace comprising the steps of: retaining the mounted portion of the electrode in fixed position with respect to themold during melting and maintaining a molten slag bath in contact with the electrode during melting.

12. A process as defined by claim 11, wherein at least two consumable electrodes are melted simultaneously in the mold.

13. A process as defined by claim 12, wherein said at least two consumable electrodes are melted in an electrical circuit in which the electrodes are connected in series.

14. A process as defined by claim 11, wherein said molten slag bath is maintained by addition of slag components to the molten slag bath during melting.

15. A process as defined by claim 14, wherein at least a portion of the slag components which are added include, slag in molten state.

16. A process as defined by claim 14, wherein at least a portion of the slag components which are added include slag in solid state.

17. A process as defined by claim 16, wherein the added solid slag is introduced in pulverized form.

18. A process as defined by claim I], wherein said maintaining step is performed by filling the space between the electrode and the mold with solid slag, which during melting enters the molten slag bath as the electrode melts.

19. A process as defined in claim 18, wherein the solid slag used in filling the space is pulverized.

20. A process as defined by claim 11, wherein said maintaining step is performed by pouring molten slag into the space between the electrode and the mold, the molten slag is cooled until solidification occurs and is thereafter supplied into the slag pool during melting as the electrode is melted.

21. A process as defined by claim 11, wherein said maintaining step is performed by periodically adding molten slag to the molten slag bath.

22. A process as defined by claim 21, wherein the mounted position of said electrode provides a gap between electrode and mold, and molten slag is added through the gap between the electrode and the mold.

23. A process as defined by claim 11, wherein said process is initiated by the steps of placing a tapered electrode into a mold having a tapered internal wall, the tapers of both the electrode and the mold converging from top to bottom.

24. A process as defined in claim 23, wherein the axes of the electrode and the mold are disposed on a common vertical axis.

25. A process as defined by claim 24, wherein the taper of the electrode is substantially equal to the taper of themold.

26. A process as defined by claim 24, wherein the taper of the electrode is greater than the taper of the mold.

27. A process as defined by claim 24, including the preliminary steps of producing the tapered electrode for use in said process by casting metal in a cast iron mold.

28. A process as defined by claim 25, wherein said step of maintaining the molten slag bath is carried out so that thedepth of the molten slag bath increases during the melting.

29. A process as defined by claim 11, wherein the cross-sectional area of the electrode is nine-tenths of the cross-sectional area defined by the internal wall of said mold.

30. A process as defined by claim 29, wherein the cross-sectional area of the electrode is nine-tenths of the cross-sectional area of the mold at all axial locations. I

31. A-process as defined by claim 29, wherein the electrode is made with wall surfaces parallelto its axis.

32. A process as defined by'claim 29, wherein the mold is madewith internal wall surfaces parallel to its axis.

33. A process as defined by claim 11, wherein the electrode is made with wall surfaces parallel to its axis.

34. A process as defined by claim 11, wherein the mold is made with internal wall surfaces parallel to its axis.

35. A process as defined by claim 11, wherein said process is initiated by placing the electrode into the mold and adding molten slag to the bottom portion of the mold under the electrode.

36. A process as defined by claim 1], wherein said process is initiated by placing the electrode into the mold, energizing a source of electric current which is serially connected to the electrode and the mold, adding molten slag to the bottom portion of the mold through a siphon device connected to the base portion of the mold, and continuing the molten slag addition until the slag contacts the electrode'and the electric circuit.i s completed.

37..A process as defined by claim 11, wherein a source of electric current is serially connected to the mold and to the electrode.

38. A process as defined by claim 37, wherein the connection of the electric current to the mold is closely spaced to the connection of the electric current to the electrode in order to reduce inductive power losses.

39. A process as defined by claim 38, wherein the electrode is connected to a contact device which rests upon electrical insulation which is in turn supported by the mold, and the contact device is connected to one side of the source of electric current in the serial connection.

40. A process as defined by claim 39, wherein the weight of the electrode presses it into electrical contact with the contact device.

41. A process as defined by claim 11, wherein at least one of the mold walls is moved away from the formed ingot to facilitate removal of the ingot from the mold.

42. A process as defined by claim 41, wherein said mold is formed in two parts which are relatively moved apart to facilitate removal of the ingot from the mold.

43. A process as defined by claim 42, wherein the mold parts join one another along lines parallel to the axis of the closedmold.

44. A process .as defined by claim 41, wherein the base of the mold is moved relative to the mold to facilitate removal of the formedingot.

45. A process as defined by claim 44, wherein the movement of the base is in an axial direction away from the mold.

Claims

5. A process as in claim 1, wherein the consumable electrode is made tapered and is placed into a tapered mold with its greater base upward.

11. A process for the melting of at least one consumable electrode in a cooled mold of an electric furnace comprising the steps of: retaining the mounted portion of the electrode in fixed position with respect to the mold during melting and maintaining a molten slag bath in contact with the electrode during melting.

18. A process as defined by claim 11, wherein said maintaining step is performed by filling the space between the electrode and the mold with solid slag, which during melting enters the molten slag bath as the electrode melts.

25. A process as defined by claim 24, wherein the taper of the electrode is substantially equal to the taper of the mold.

28. A process as defined by claim 25, wherein said step of maintaining the molten slag bath is carried out so that the depth of the molten slag bath increases during the melting.

30. A process as defined by claim 29, wherein the cross-sectional area of the electrode is nine-tenths of the cross-sectional area of the mold at all axial locations.

31. A process as defined by claim 29, wherein the electrode is made with wall surfaces parallel to its axis.

32. A process as defined by claim 29, wherein the mold is made with internal wall surfaces parallel to its axis.

36. A process as defined by claim 11, wherein said process is initiated by placing the electrode into the mold, energizing a source of electric current which is serially connected to the electrode and the mold, adding molten slag to the bottom portion of the mold through a siphon device connected to the base portion of the mold, and continuing the molten slag addition until the slag contacts the electrode and the electric circuit is completed.

37. A process as defined by claim 11, wherein a source of electric current is serially connected to the mold and to the electrode.

43. A process as defined by claim 42, wherein the mold parts join one another along lines parallel to the axis of the closed mold.

44. A process as defined by claim 41, wherein the base of the mold is moved relative to the mold to facilitate removal of the formed ingot.