SK283103B6 - Method and furnace for making a molten product - Google Patents

Abstract

A method and a furnace for melting a solid material to form an electrocast product, including at least two electrodes (4, 5). According to the method, the melting process is started by contacting the tops (13) of the electrodes (4, 5) with said solid material (23) to be melted while holding the electrodes close enough together to enable an electric current to flow therebetween, an electric arc is then generated between said electrodes to melt the solid material adjacent the tops (13) of the electrodes (4, 5), and said tops are subsequently gradually moved apart without breaking the contact with the material or cutting off the current flow between the electrodes.

Description

Technical field

The invention relates to a method for producing an electro-melted product by melting solid materials, in particular metals or ceramics, in an electric furnace equipped with at least two electrodes, between the free ends in which an electric current passes, e.g. in the form of an electric arc.

The invention relates to a simple and economical process for producing an electro-melted product by melting solid, electrically conductive and non-conductive materials, which is carried out at relatively high temperatures.

BACKGROUND OF THE INVENTION

Prior art methods favor melting of electrically conductive solids. If the charge is electrically non-conductive, a special measure, e.g. add carbon or graphite to the charge to allow the electric current to pass through the charge.

The prior art methods can only be applied at relatively low temperatures, e.g. from 1500 to 1600 ° C and thus do not suit the processing of refractory materials.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention is based on a process which largely eliminates the disadvantages of the established methods and can be used in the case of melting of both electrically conductive and non-conductive material, and it is not necessary to take additional measures with respect to non-conductive materials.

To start the melting process according to the invention, the free ends of the electrodes are placed on the solid material to be melted and at the same time are pushed together at a distance such that an electric current can pass therebetween. Once an arc is formed between the electrodes, the solid material melts first in the immediate vicinity of the free ends of the electrodes. Thereafter, the free ends of the electrodes are separated from each other following a gradually expanding hot melt focus, while still maintaining contact with the fused solid material and the passage of the electrodes through the electrodes is ensured between the free ends of the electrodes.

The present invention also provides an electric furnace for the production of an electro-melted product, which is arranged to meet the conditions for carrying out the method of the invention.

The furnace is characterized in that the electrodes converge with their free ends and are movable independently of one another between the proximity position when their free ends eventually touch, and the spacing position when there is a certain distance between the free ends. The furnace is provided with means for continuously moving the electrodes between these surfaces.

Each electrode is mounted in an electrically insulated support arm.

According to the invention, the electrodes are introduced laterally into the melting pot so that they can be moved between the zoom and zoom positions.

Overview of the figures in the drawing

The invention will be explained in more detail in the drawing, in which:

Fig. 1 shows a diagram of an electric furnace according to the invention (partly in cross-section), FIG. 2 is a cross-section along line II-II of FIG. 1, FIG. 3 is a schematic diagram of the connection of electrodes to an electrical circuit.

DETAILED DESCRIPTION OF THE INVENTION

In particular, the invention relates to a process for producing an electro-melted refractory product by melting solid materials of different kinds, in particular refractory materials.

The melting takes place in an electric furnace which is equipped with at least two electrodes, between the free ends of which, when connected, an electric current provides the necessary energy for melting.

If the charge is electrically non-conductive or less conductive, it is e.g. solid ceramic materials, in which case the free ends of the electrodes touch on starting the melting process, also touching the solid material to be melted. When connected to the circuit, an electric arc is formed between the electrodes, which heats and melts the solid material in the immediate vicinity of the free ends of the electrodes.

The free ends of the electrodes are gradually separated from each other as the melt focus expands while maintaining contact with the fused solid material. Care must also be taken to maintain the passage of electrical current between the electrodes and through the melt formed between their free ends. The heating in this melting step is due to Joule heat, due to the resistance of the molten material between the electrodes partially immersed in the melt to pass the electric current. As a result, the initially non-conductive solid fused material becomes conductive because it has been brought into a liquid state.

If the molten material is sufficiently electrically conductive and goes e.g. o metals, it is not necessary for the free ends of the electrodes to touch each other when melting is started. In this case, it is sufficient that the distance between the electrodes corresponds to the possibility of forming an electric arc. The heating produced in this melting step is partly due to the heat emitted by the electric arc and the penetrating solid material, partly by Joule heat, due to the resistance of the molten material to the passing electrical current in the portion of the melt into which the electrodes are partially immersed.

It will be appreciated that the distance between the electrodes may vary according to the type of molten material. In the case of an electrically non-conductive material, the electrodes touch or nearly touch each other so as to form an electric arc between their free ends, while in the case of the electrically conductive material the free ends of the electrodes may be spaced apart.

Thus, the distance between the electrodes depends on the conductivity of the molten material, but also on the strength of the electrical installation, and the distance between the free ends of the electrodes should ensure optimal melting performance.

The melt is homogenized by convection mixing before discharge from the ladle. According to the invention, this step takes place shortly after the melting is complete by re-approaching the free ends of the electrodes.

The attached figures illustrate an electric furnace for producing an electro-melted product by the method of the invention.

An electric furnace is the type used by the immersion electrode system.

The furnace is equipped with a ladle 1, which is closed at the top by a vault 2 with a chute 3, through which a charge is inserted into the ladle.

On both sides of the side of the ladle 1, two electrodes 4 and 5 are attached in the support arms 6 so that their free ends 13 point obliquely to each other. The support arms 6 are electrically insulated. The electrodes are retained in the support arms so as to be movable between the approach position when both free ends eventually touch each other and the offset position when there is a certain distance between the free ends. For this reason, the electrodes freely pass through the openings in the side walls 1 'of the ladle 1, their cross-section being designed to form a circular passage 19 around the electrodes through which air enters the furnace, and is large enough to deflect the electrodes. The electrode axes can be at an angle of 15 ° to 165 ° there.

The electrodes are deflected around the outer deflection point 28, which is sufficiently distant from the furnace wall, so as to deflect the free ends of the electrodes 4 and 5 in the furnace as much as possible, thereby achieving precise control of the melting independently of the quantity of molten material. The outer deflection point 28 is practically situated on the support arm 6.

Each support arm 6 is disposed from a base 7 in which the column 8 is recessed, and at its upper end, which is identical to said external deflection point 28, a hinge pin 9 is mounted in the hinge pin. The holder 9 is provided with a control wheel 11 by which it is possible (manually or by motor) to move the electrodes in the direction of the arrows 12, thereby varying the distance between their free ends 13 inside the ladle 1. This distance can also be varied by deflecting the electrodes around .

The outer cylindrical wall 15 of the bottom of the ladle 1 rests by means of rollers 16 on the base 14. The rollers are inserted into the rails 17 in the cylindrical wall 15 of the bottom of the ladle.

At about half the height of the side wall of the ladle 1 there is a discharge opening 18.

To discharge the electrothermal mass, the ladle is deflected on the pedestal 14 in the direction of the arrow 26 (FIG. 2).

The fact that the electrodes 4 and 5 pass quite freely through the walls 1 'of the furnace and do not touch them in any way significantly differentiates the furnace arrangement according to the invention from the electric melting furnaces used hitherto.

In the current technique, the electrodes are attached to the walls of the furnaces and are hinged on relatively complex devices that are exposed to elevated temperatures against which the electrodes need to be protected. However, these means are the reason why current furnaces can only operate at temperatures of the order of 1600 ° C.

Since the furnace according to the invention is equipped with circular passages 19 which are large enough to allow the flow of cool air along the electrodes in comparison with the present technique, and since each electrode passing through this opening is retained in a lateral support arm 6 which is sufficiently spaced from the side wall 1, it is not necessary to take sufficient measures against the high temperatures inside the ladle to protect the electrodes and their support arms.

This allows the refractory products to be processed at temperatures above 2500 ° C.

In FIG. 3 schematically illustrates the connection of electrodes 4 and 5 to an electrical circuit. The circuit is connected to the electrical network at terminals 29 in a conventional manner via a circuit breaker (not shown). A self-inducting coil 20 is inserted into the circuit and is connected in series with the electrodes 4 and 5 when the electrodes are in the proximity position.

By the switch 21 it is possible to briefly connect this coil when the electrodes 4 and 5 are in the offset position.

In addition, a transformer 27 is applied to the circuit, which applies voltage to the electrode terminals and provides the necessary current density to effect melting. It can be a classical transformer with permanent voltage transfer 220/11 000 V.

The main switch 22 can close the electrical circuit and connect the electrodes to the mains.

When the melting is started, the power circuit 22 closes the power circuit, the switch 21 remains open, the electrodes 4 and 5 are in the proximity position, with their free ends immersed in or at least in contact with the charge.

As soon as a certain amount of solid material 23 melts to form a melt 24, the electrodes 4 and 5 are gradually separated from each other and the switch 21 is closed to short-circuit the self-induction coil 20.

Following the expansion of the melt focus, an increase in the distance between the electrodes is made, making sure that the current density passing between the electrodes through the melt 24 is sufficiently large that the melting temperature is transferred to the surrounding solid material 23.

After all solid material has melted, it is preferable that the electrodes 4 and 5 approach each other again while immersed below the level of the melt, while disconnecting the switch 21 as needed to reduce the amount of current in the electrical circuit. As a result, a relatively large amount of energy is concentrated in a small volume of molten material which causes a local temperature increase. This results in a convective flow, resulting in perfect mixing of the molten material and the formation of a relatively homogeneous mass of high quality.

The following are some specific examples to illustrate the application of the method of the invention in a furnace previously described.

Examples: A furnace with a total weight of 1500 kg is charged in the composition: 33% zirconia, 50% alumina, 14% silica and 3% alkali salt in the form of sodium carbonate. The average grain size ranges from 0.5 mm to 15 cm (diameter size).

Before starting the melting, the two free electrode ends 13, 5, which in this example are made of graphite, approach each other and to the level of solid material previously embedded in the ladle 1. The two free electrode ends 13 are partially covered by the solid material so that submerged.

The electrical circuit is then closed by the main switch 22, the switch 21 being open. An electric arc is formed between the electrodes 4 and 5.

The energy on the electrodes is of the order of 300 kW. After about 5 minutes, a sufficient amount of melt 24 is generated in the vicinity of the free ends 13 of the electrodes 4 and 5, and the self-induction coil 20 can be short-circuited by switch 21. At the same time, the electrodes gradually move apart.

Because the melt 24 is of a liquid state, an electrical current passes between the electrodes through the melt. The total melting time is about 45 minutes and the melting temperature is about 2250 ° C.

The resulting melting temperature is large enough to allow the entire batch to gradually melt while continuously increasing the electrode gap until the batch melts completely.

Other types of materials were treated in a similar way in the furnace:

It was mainly a charge which contained 50% iron and 50% cobalt, charge containing 95% alumina and% alkali salt, 50% cobalt and 50% nickel, bronze, brass, etc.

Another example relates to melting glass shards. In this example, molybdenum or graphite electrodes were used.

SK 283103 Β6

The glass shards were melted in the previously described furnace together with the burnt waste containing e.g. heavy metals. It was mainly a waste extract from firing furnaces in a solid state.

Melting gave a glassy product containing said heavy metals, which could be used as a basic raw material for the production of beads by known technology to remove heavy metals.

The melting was carried out continuously in the inclined ladle 1 so that the glass product with the melting process flows out through the discharge opening 18, while the ladle is supplemented by the discharge opening 3 in the furnace crown.

The same continuous melting method was also used for incho material batches.

The method according to the invention and the arrangement of the electric furnace in which the method is carried out do not require additional specific steps to start and stop melting.

It is possible e.g. allow a portion of the non-conductive charge to solidify in the furnace. However, it should be ensured that the electrodes 4 and 5 are brought to a position above the level of the solidified charge prior to starting the melting, which will be carried out as described above. If the charge is electrically conductive, this measure does not need to be implemented.

The operating conditions of the furnace can be changed. A certain layer of electro-melted product 25 may be left on the ladle walls as a permanent protection of the ladle walls 1.

The furnace can be connected to direct current, single phase or three phase current.

The advantageous arrangement and positioning of the electrodes 4 and 5 with respect to the ladle 1 makes it possible to control the size of the angle and taking into account the level of the charge. To this end, it must be ensured that the electrodes can be deflected on the column 8 of the support arm 6 in an arc of a relatively large span. For this reason, the external deflection point must be sufficiently distant from the furnace wall.

The invention is not limited to these examples. Without departing from its scope, it is possible to use different types of electrodes that are suitable for electric furnaces operating in an immersion electrode system, and the structure of the electrode support arm 6 may also be arranged in another manner.

Also, the charge, its composition and grain size can be varied. It may be a powdered material or blocks with a diameter of several tens of centimeters.

Claims (2)

not to the proximity of the electrodes (4, 5), in particular to the space therebetween, while at the same time continuously discharging the melt (24). Method according to claim 1 or 2, characterized in that the melting is carried out in an oxidizing medium. Method according to any one of claims 1 to 3, characterized in that it is mixed with a conventional stream before the melt is discharged. An electric furnace for carrying out the method of claim 1, which is provided with a ladle, at least two electrodes passing through the furnace wall and means for forming an electric arc between the free ends of the electrodes that converge together and are movable between their proximity positions when the free ends optionally also touching, and a position of separation when there is a certain distance between their free ends but are still in contact with the fused material, wherein the displacement of the free ends between these positions is substantially continuous and is performed by means of the furnace characterized in that in the support arm (6) the electrodes (4) and (5) are mounted sliding and pivotable in their axis about an external deflection point (28) remote from the wall (1 ') and passing through the wall opening (1'), around the electrodes ( 4) and (5) is a circular passage (19) for deflecting the electrodes (4) and (5), the axes of which are at an angle α of 15 ° to 165 °, wherein the ladle (1) is closed at the top by a vault (2), which is provided with a chute (3) for filling the ladle (1) with solid melting material. An electric furnace according to claim 5, characterized in that each support arm (6) is electrically insulated and arranged from a base (7) in which a pillar (8) is arranged, the upper end of which is the outer deflection point (28) and is connected to the holder (9) by a hinge, the electrode (4, 5) being fixed to the holder (9) for moving and deflecting and for changing the distance between the free ends (13) of the electrodes (4, 5). An electric furnace according to claim 5 or 6, characterized in that a self-inducting coil (20) is inserted in series with the electrodes (4, 5) in their electrode supply circuit (4) and (5). the zoom position and briefly in their zoom position. 3 drawings 1. A process for melting solid materials, in particular metals or ceramics, in which an electrically melted product is produced in an electric furnace equipped with at least two electrodes, between the free ends of which an electric current can pass mainly in the form of an electric arc. and the distance between them allows the passage of an electric current or the formation of an electric arc in which solid material melts near the free ends of the electrodes and the electrical current also passes through the melt formed between the two free ends, characterized in that the free ends of the electrodes (13) are progressively separated from each other in the context of the expanding focus of the molten solid material (23), while still maintaining contact with the molten solid material (23) to maintain the flow of current between the electrodes. Method according to claim 1, characterized in that during melting the material is fed to the melt.