GB1583514A

GB1583514A - Electroslag refining process

Info

Publication number: GB1583514A
Application number: GB1780377A
Authority: GB
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1978-04-27
Filing date: 1978-04-27
Publication date: 1981-01-28

Description

(54) ELECTROSLAG REFINING PROCESS (71) We, BRITISH STEEL CORPORATION, a Corporation incorporated and existing under the Iron and Steel Act 1967 whose principal office is at 33 Grosvenor Place, London, S.W.1, do hereby declare the in-vention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly des cribed in and by the following statement: This invention relates to the electroslag refining process and more especially to elec trodes for use in this process.

.Tn-the electroslag refining process a slag within an open ended mould is maintained in a molten state and at a temperature above the melting point of the metal to be refined.

Unrefined metal is introduced into the mould and is refined as it passes in droplet form through a bath of molten slag, refined droplets collecting to.form a pool beneath the slag bath. The mould walls- are-cooled by the circulation of a coolant, normally water, and a solidified ingot is built up be neath the molten metal pool. The metal to be refined may be introduced to the mould in the form of a consumable elec trode and the slag maintained molten by passage of an electric current from the elec- - trode to the base plate on which the mould stands.

Alternatively, unrefined material in liquid, particulate or similar form may be fed into the mould; in this case the electric current may be conveyed to the slag through a solid non-consumable electrode produced from, for example, carbon, tungsten or molybdenum or an internally water-cooled electrode manufactured from copper.

Such non-consumable electrodes suffer from a number of disadvantages. Firstlyj their use can result in contaminants being introduced into the ingot to be produced Secondly, operation with water-cooled elec trodes can be dangerous and can lead to erratic performances caused by slag freez- ing - on to .that surface of the electrode which is immersed in the molten slag. The frozen slag barrier so formed is less conductive electrically than is required for satisfactory operation of the process and is produced because copper and other suitable materials have temperatures lower than the majority of slags employed in the process.

According to - the present invention in one aspect, an electroslag refining furnace includes an electrode, means for supporting the electrode so that its lower end protrudes into the upper open end of a mould mounted on a base plate, and means for cooling the interior of that portion only of the electrode which -in use of the apparatus is positioned above the level of molten slag contained in the mould, the lower end of the electrode being so constructed that when immersed in molten slag its surface will melt through contact with the slag until the heat imput to the electrode is balanced. by the heat extracted from -the electrode through the aforementioned internal cooling.

The internally cooled portion of the elec-- trode may be manufactured from copper; preferably, the lower end portion of the electrode which is- in the slag is of the same composition or of a composition compatible with the metal to be refined in theprocess. The lower - end of the electrode may be brazed -or welded to the internally cooled portion of the electrode.

In an alternative embodiment, the internally cooled portion of the electrode is made of steel and the tip portion of the electrode consists.of a solid extension to the internally-cooled portion of the electrode.

The metal to be refined may be- introduced into the mould as a powder or in: particulate or pelletized form; the metal may be introduced into mould from above at a rate controlled in- dependence- upon the rate at which an ingot is built up within the mould. If the metal is introducedas a powder, it may be preheated- by meansof, for example, a radio frequency heating device.

Alternatively, -the metal to be refined may be introduced in the form of a consumable electrode which extends with the non-consumable electrode into the slag located in the mould. In this arrangement current may pass between the two electrodes in a bifilar circuit or both electrodes may be connected to separate phases of a threephase alternating current supply or the current source and the current conveyed to the other may be from a source of direct current.

According to the present invention in another aspect, there is provided an electroslag refining process which comprises the steps of supporting an electrode with its lower end immersed in a quantity of molten slag contained in a mould mounted on a base plate and applying coolant to the interior of that part only of the electrode which is positioned above the surface of said molten slag, the lower immersed end of the electrode being so constructed that its stirface melts through contact with the slag until the heat input to the electrode is balanced by the heat extracted from the electrode through the afore-mentioned internal cooling.

The invention will now be described by way of example with reference to the accompanying drawing in which the sole figure is a side elevation in section of an electrode in accordance with the invention supported with its lower end protruding into the upper open end of the mould.

The electrode 1 illustrated in the drawing has an upper internally cooled portion 2 and a lower uncooled tip portion 3. The upper portion 2 of the electrode is provided with internal passageways connected to lead a coolant, for example water, to and from a coolant source (not shown). A plug 5 is located towards the lower end of the electrode portion 2 to close off the lower run of the passageway. The electrode portion 2 may be manufactured from a number of materials, these including, copper and steel. The lower tip portion 3 of the electrode consists of a steel block which is brazed or welded to the lower end of the upper electrode portion 2.

The electrode is supported so that in use it protrudes into an open ended mould 8 mounted on a base plate 9. The electrode and the base plate are connected in circuit to a transformer 10. The level of molten slag which in use of the apparatus is present in the mould is indicated by broken line 12.

In operation, a quantity of molten slag is introduced into the mould 8 to the level indicated by the line 12. Electric current is passed between the electrode tip and the base plate to heat, by joule effect, the slag to the required temperature. Initially, the surface of the electrode tip portion 3 will melt back due to its contact with the slag until equilibrium is reached between the heat input to the electrode tip and the heat cess will proceed with what is, in effect, a extracted from the tip by the water cooling of the upper electrode portion 2. Once this equilibrium has been reached, the process will proceed with what is, in effect, a non-consumable electrode. Unrefined material in liquid, powder, particulate, pelletized or like form is introduced into the mould through its open upper end.This unrefined material passes through the slag and collects to form a pool of molten refined metal below the slag. In time the metal pool solidifies to form a refined ingot. The ingot may be withdrawn from the. mould by lowering the base plate 9 to maintain the molten slag at the level indicated by line 12. Alternatively; the ingot may grow progressively within the mould. In this event, the electrode 1 is progressively raised to maintain the level of the molten slag at the electrode length indicated by line 12.

In an alternative arrangement, the electrode 1 comprises a single casing of steel, the lower tip portion 3 forming what is, in effect, a solid uncooled extension to the upper internally cooled portion 2.

WHAT WE CLAIM IS:- 1. An electroslag refi.ning furnace ineluding an electrode, means for supporting the electrode so that its lower end protrudes into the upper open end of a mould mounted on a base plate and means for cooling the interior of that portion only of the electrode which in use of the apparatus is positioned above the level of molten slag contained in the mould, the lower end of the electrode being so constructed that when immersed in molten slag its surface will melt through contact with the slag until the heat input to the electrode is balanced by the heat extracted from the electrode through the aforementioned internal cooling.

2. A furnace as claimed in claim 1 wherein the internally cooled portion of the electrode is manufactured from copper.

3. A furnace as claimed in claim 1 or claim 2 wherein the tip portion of the electrode which is immersed in molten slag is of the same composition or of a composition compatible to the metal to be refined in the process.

4. A furnace as claimed in any one of claims 1 to 3 wherein the electrode tip is brazed or welded to the internally cooled portion of the electrode.

5. A furnace as claimed in any one of claims 1 to 3 wherein the internally cooled portion of the electrode is made of steel and the tip portion of the electrode consists of a solid extension to the internally cooled portion of the electrode

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. may be introduced in the form of a consumable electrode which extends with the non-consumable electrode into the slag located in the mould. In this arrangement current may pass between the two electrodes in a bifilar circuit or both electrodes may be connected to separate phases of a threephase alternating current supply or the current source and the current conveyed to the other may be from a source of direct current. According to the present invention in another aspect, there is provided an electroslag refining process which comprises the steps of supporting an electrode with its lower end immersed in a quantity of molten slag contained in a mould mounted on a base plate and applying coolant to the interior of that part only of the electrode which is positioned above the surface of said molten slag, the lower immersed end of the electrode being so constructed that its stirface melts through contact with the slag until the heat input to the electrode is balanced by the heat extracted from the electrode through the afore-mentioned internal cooling. The invention will now be described by way of example with reference to the accompanying drawing in which the sole figure is a side elevation in section of an electrode in accordance with the invention supported with its lower end protruding into the upper open end of the mould. The electrode 1 illustrated in the drawing has an upper internally cooled portion 2 and a lower uncooled tip portion 3. The upper portion 2 of the electrode is provided with internal passageways connected to lead a coolant, for example water, to and from a coolant source (not shown). A plug 5 is located towards the lower end of the electrode portion 2 to close off the lower run of the passageway. The electrode portion 2 may be manufactured from a number of materials, these including, copper and steel. The lower tip portion 3 of the electrode consists of a steel block which is brazed or welded to the lower end of the upper electrode portion 2. The electrode is supported so that in use it protrudes into an open ended mould 8 mounted on a base plate 9. The electrode and the base plate are connected in circuit to a transformer 10. The level of molten slag which in use of the apparatus is present in the mould is indicated by broken line 12. In operation, a quantity of molten slag is introduced into the mould 8 to the level indicated by the line 12. Electric current is passed between the electrode tip and the base plate to heat, by joule effect, the slag to the required temperature. Initially, the surface of the electrode tip portion 3 will melt back due to its contact with the slag until equilibrium is reached between the heat input to the electrode tip and the heat cess will proceed with what is, in effect, a extracted from the tip by the water cooling of the upper electrode portion 2. Once this equilibrium has been reached, the process will proceed with what is, in effect, a non-consumable electrode. Unrefined material in liquid, powder, particulate, pelletized or like form is introduced into the mould through its open upper end.This unrefined material passes through the slag and collects to form a pool of molten refined metal below the slag. In time the metal pool solidifies to form a refined ingot. The ingot may be withdrawn from the. mould by lowering the base plate 9 to maintain the molten slag at the level indicated by line 12. Alternatively; the ingot may grow progressively within the mould. In this event, the electrode 1 is progressively raised to maintain the level of the molten slag at the electrode length indicated by line 12. In an alternative arrangement, the electrode 1 comprises a single casing of steel, the lower tip portion 3 forming what is, in effect, a solid uncooled extension to the upper internally cooled portion 2. WHAT WE CLAIM IS:-

1. An electroslag refi.ning furnace ineluding an electrode, means for supporting the electrode so that its lower end protrudes into the upper open end of a mould mounted on a base plate and means for cooling the interior of that portion only of the electrode which in use of the apparatus is positioned above the level of molten slag contained in the mould, the lower end of the electrode being so constructed that when immersed in molten slag its surface will melt through contact with the slag until the heat input to the electrode is balanced by the heat extracted from the electrode through the aforementioned internal cooling.

6. Apparatus for producing the metal ingot substantially as herein described with reference to the accompanying drawing.

7. An electroslag refining process which comprises the steps of supporting an electrode with its lower end immersed in a quantity of molten slag contained in a mould mounted on a base plate and applying coolant to the interior of that part only of the electrode which is positioned above the surface of said molten slag, the lower, immersed end of the electrode being so constructed that its surface melts through contact with the slag until the heat input to the electrode is balanced by the heat extracted from the electrode through the aforementioned - internal cooling.