JPH1072616A - Method for refining molten metal in ladle and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method of molten metal refined with a melting furnace or an arc electric furnace, etc., by arc-heating the molten metal in a ladle with a graphite electrode line constituted by connect the graphite electrodes in order, during shifting to an ingot-making equipment, etc., through the ladle, and a refining apparatus therefor. SOLUTION: When heat-refining the molten metal 1 by utilizing the arc- heating with the graphite electrode line 40 constituted by connecting the graphite electrodes 41 in order each through a nipple in the ladle, at the upper part of a furnace cover 31 for closing the top opening part of the ladle, cooling liquid is sprayed incliningly upward to cool the outer periphery of the graphite electrodes 41 in the graphite electrode line 40. On the other hand, the top parts of the graphite electrode line 40 are dipped into slag 2 on the molten metal 1 to execute the arc-heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining a ladle for molten metal and a refining apparatus therefor.
While the molten metal refined in the electric furnace is transferred to the ingot making equipment via the ladle, the molten metal arc in the ladle is heated by the graphite electrode group to which the graphite electrodes are sequentially connected. The present invention relates to a refining method and a refining device.

[0002]

2. Description of the Related Art Recently, among molten steels refined by a converter, an electric arc furnace and other melting furnaces, steel grades such as so-called high-grade steels, low-alloy steels and special steels are processed in some form of vacuum refining process. Have been. At present, it is being processed in an out-of-pile smelting process instead.

[0003] The reasons for this are (1) that the quality requirements on the user side have become stricter with the progress of technology, and (2) that restrictions on tapping temperature and the like have been eased by the pure oxygen converter ( 3) Peripheral technologies such as high-efficiency steam ejectors have made great progress.

The out-of-pile smelting process itself was originally developed with a primary focus on preventing hydrogen-induced defects in large cast and forged steel products by vacuum casting, tapping and degassing. The development and commercialization of DH and RH suitable for mass production of rolled products has been accelerated, and their use has been accelerated. At times, they have been widely adopted in line with the rise of pure oxygen converters.

[0005] Then, for the purpose of higher-grade processing, V
A so-called ladle refining method typified by the AD method, the LF method, and the like has been developed. The ladle refining method is used as a simple out-of-pile refining method because it is a simpler and lower-cost process.

In this ladle refining method, heating and refining of molten metal such as molten steel is performed in a ladle. Usually, arc heating is performed by a graphite electrode by a three-phase arc power source, and flux is introduced into the ladle. When added, dissolve this flux,
At the same time, the temperature of the molten metal such as molten steel in the ladle is heated and raised.

[0007] A method has also been proposed that takes into account the stirring of molten metal such as molten steel in a ladle along with the progress of such a refining reaction. A porous plug of a porous refractory is installed at the bottom of the pot, and the molten metal is stirred by bubbling argon gas blown through the porous plug.

As described above, in the refining in the ladle, the use of arc heating by the graphite electrode has a great advantage as compared with other heat sources.

That is, in the arc heating, the gas particles are heated by a high-temperature arc generated by heating, dissociation, excitation and the like, and a high temperature of 1650 to 3000 ° C. can be easily obtained. Heating and refining of the molten metal can be effectively achieved in the ladle via the surface slag or the like.

However, if it is used to take advantage of the fact that an extremely high temperature can be obtained by arc heating, the graphite electrode is exposed to an extremely high temperature, and the oxidative consumption of the outer periphery is greatly reduced. The basic unit of electrode is greatly increased due to the progress of the process, and the improvement is a major point from this aspect.

Therefore, as in the refining by the electric arc furnace, it is considered that the cooling rate is reduced by spraying a cooling liquid onto the graphite electrode used for the arc heating in the ladle refining to reduce the basic unit. Can be

[0012] However, as for the spraying of the cooling liquid, the refining reaction in the arc electric furnace can be tolerated to some extent,
It is said that it is not suitable for refining in the ladle to meet the strict quality requirements from the side. Furthermore, compared to the operation of an arc electric furnace, the diameter of the graphite electrode used is relatively small, and it is desired to spray cooling liquid corresponding to such a small diameter electrode to cool it. .

From this point up to now,
Cooling is performed by spraying a cooling liquid onto a graphite electrode in refining in a ladle, and there is no proposal or found any equipment or apparatus used for cooling.

That is, when the coolant is sprayed on the outer peripheral surface of the graphite electrode used for refining in the ladle, when the spray amount of the coolant is excessive, a part of the coolant enters the ladle as it is, It flows down along the outer peripheral surface of the graphite electrode and enters the ladle. The coolant that has entered inside reacts on the surface of the slag layer on the molten metal such as molten steel, and part of the coolant that flows along the surface of the graphite electrode enters the slag, causing a hydrogen explosion and causing the ladle to fire. The lining will be damaged, and the refractory basic unit will be greatly increased. Further, hydrogen generated by the water gas reaction enters a molten metal bath such as molten steel, and the resulting steel type tends to cause hydrogen embrittlement. For this reason, in high-grade steels that strongly require toughness and the like, spraying a coolant on the graphite electrode for refining in a ladle has been regarded as dangerous.

If the degree of cooling by spraying the cooling liquid becomes excessive, the heat loss increases, and the power loss increases and the operating time increases with the extension of the heating time.

[0016]

The object of the present invention is to solve the above-mentioned drawbacks. Specifically, in refining a molten metal in a ladle, the basic unit of a graphite electrode used for arc heating is large. We propose a refining method and a device that can be reduced to a minimum.

[0017]

That is, the method of the present invention comprises immersing the tip of a graphite electrode array in which graphite electrodes are sequentially connected via nipples into a slag existing on a molten metal bath in a ladle. A ladle refining method for heating and refining a molten metal bath by generating a high-temperature arc in the slag, wherein an upper open part of the ladle is closed by a furnace lid, and graphite is placed on the upper part of the furnace lid. The graphite electrode is cooled by spraying a cooling liquid on the outer periphery of the electrode in an inclined upward direction.

The upward spray angle of the cooling liquid is set to be not more than 0 ° and not more than 60 ° with respect to the horizontal level.

The spraying rate of the cooling liquid is set to 2 to 10 liter / minute.

Further, water is injected as a cooling liquid.

The cooling liquid contains an antioxidant and the balance substantially consists of water.

A ladle for receiving the molten metal from the refining furnace is configured to be able to run on a traveling carriage, and a furnace lid for closing an open portion at an upper portion of the ladle is fixed to a predetermined place. An annular conduit disposed around the graphite electrode, the tip being immersed in a slag on a molten metal bath in a ladle on the furnace lid to generate an arc, and at least an inner portion of the annular conduit inside the annular conduit. In some parts, an injection nozzle for jetting the coolant upward is provided.

The spray hole of the injection nozzle is inclined upward with an inclination angle of more than 0 ° and 60 ° or less.

The configuration of these means and the operation thereof will be specifically described below with reference to the drawings.

FIG. 1 shows an example of an apparatus used for refining a molten metal while spraying and cooling a cooling liquid onto a graphite electrode to be subjected to refining in a ladle according to the method of the present invention. FIG.

FIGS. 2 (a), 2 (b), 2 (c) and 2 (d) are explanatory views showing respective steps of one example of refining in a ladle by the method of the present invention.

FIG. 3 is an explanatory diagram showing an enlarged example of the annular cooling pipe in the refining apparatus shown in FIG.

First, referring to FIG.
The molten steel melted and refined by a refining furnace (not shown) such as an electric furnace, that is, the molten metal 1 is received by the ladle 10. In the ladle 10, slag 2 mixed on the molten metal 1
Emerges.

The ladle 10 runs on a traveling carriage 20 as described later (see FIG. 2 (b)) and reaches a ladle refining device 30 in which a furnace lid and a graphite electrode array 40 are arranged. Then, the graphite electrode array 40 is inserted into the ladle (FIG. 2).
(C)).

FIG. 2 (c) shows a ladle refining apparatus 30 in which a furnace lid and a graphite electrode array 40 are arranged as shown in FIG. With this refining device 30, the molten metal 10 in the ladle is arc-heated by the graphite electrode. That is, in FIG. 1, reference numeral 41 denotes a graphite electrode, and the graphite electrodes 41 are sequentially connected via nipples to form a graphite electrode array 40. The graphite electrode array 40 penetrates through the inside of the furnace lid 31 of the ladle refining apparatus 30, and the upper graphite electrode 41 above the furnace lid 31 is heated by an electrode holder 42 (a part of which is shown in FIG. 1). It is held up and down independently of the lid.

The furnace lid 31 is supported by a pair of suspension beams 32 so as to be able to move up and down. When the ladle 10 is placed on the traveling carriage 11 and reaches below the furnace lid 31, the suspension beam 32 operates to lower the furnace lid 31, and the upper opening of the ladle 10 is closed. The traveling trolley 11 is driven by wheels 12, and the ladle 10 is received by a receiver 13. Receiver 13 is configured to be rotatable about the central axis of ladle 10 by ball 14. A graphite electrode array 40 penetrates substantially at the center of the furnace cover 31, and a dust collecting hood 33 is provided around the furnace electrode if necessary, so that dust such as dust generated during refining is removed by suction.

Further, a supply shot 34 is provided on the furnace cover 31, and a metal, an alloy, a slag-making agent, etc. necessary for refining are added as required.

The graphite electrode array 40 penetrates the furnace lid 31, and its tip is buried in the slag 2 on the molten metal 1, and the slag 2 is augmented by graphite electrodes 41 involved in refining in the slag 2. The molten metal 1 is heated by the arc heating in the slag 2 to perform refining.

When degassing is performed by refining in the ladle, a porous plug 15 is provided at the bottom of the ladle 10, and argon gas or the like is blown from the plug 15 to give a predetermined agitation to the molten metal 1. You can also.

When a three-phase AC voltage is applied to the graphite electrode array 40 to heat it, the graphite electrode array 40 is placed on a circular circuit having a predetermined radius centered on the center of the furnace lid 31 via a nipple at intervals. Three graphite electrode rows 40 that are sequentially connected to each other through the furnace lid 31.

In the case of performing DC heating instead of AC heating, one graphite electrode array 40 is disposed substantially through the center of the furnace cover 31, and a DC voltage is applied to the graphite electrode array 40. DC heating.

In the ladle refining apparatus constructed as described above, an annular conduit 50 is provided on the furnace lid 31 so as to surround the periphery of the graphite electrode array 40 (see FIGS. 1 and 3). That is, as shown in FIG. 1, when a three-phase AC voltage is applied using three graphite electrode arrays 40, the annular conduits 50 are provided for each graphite electrode array 40.

Injecting nozzles 51 are provided at intervals inside each of the annular conduits 50, and the cooling liquid 53 is sprayed from each of the injecting nozzles 51 while being inclined upward. The annular conduit 50 may be formed in a circular shape, but may be partially cut to form a cutout in order to eliminate the magnetic effect of the current flowing through the graphite electrode array 40. .

That is, as shown in FIGS. 1 and 3, an annular conduit 50 is arranged around the graphite electrode 41 in order to spray the cooling liquid 53, and the cooling liquid is sent to the annular conduit 50. An injection nozzle 51 is attached to the inner surface of the annular conduit 50 so as to be inclined upward, and the cooling liquid 53 is injected upward from the injection nozzle 51 and is sprayed onto the outer peripheral surface of the graphite electrode 41.

Each of the injection nozzles 51 on the inner surface of the annular conduit 50 is directed toward the center of the graphite electrode 41,
As shown in FIG. 3, the tip is inclined obliquely upward at an angle exceeding 0 ° and an upward inclination angle θ of 60 ° or less.

When the injection nozzle 51 is attached as described above,
The continuously supplied cooling liquid 53 is injected obliquely upward from each injection nozzle 51 through the annular conduit 50, and the cooling liquid 53 forms a loop indicated by reference numeral 531 in FIG.
It turns downward, flows along the outer peripheral surface of the graphite electrode 41, and cools the graphite electrode 41 while the coolant 53 descends downward.

The coolant 53 ejected upward forms a loop 531 once, in which the energy at the time of ejection is considerably lost, and then flows in a layered manner along the outer peripheral surface of the graphite electrode 41. Therefore, the cooling liquid 53 flowing on the outer peripheral surface of the graphite electrode 41 hardly scatters and covers the outer peripheral surface of the graphite electrode 41 uniformly. Further, even if the coolant enters the ladle 10 through the furnace lid 31, the coolant is vaporized by the internal heat and disappears, leaving no room for an aqueous reaction or the like, and hydrogen generated by the reaction may enter the molten steel. Absent.

More specifically, in the ladle 10, the surface of the molten metal 1 is covered with the slag 2, and the tip of the graphite electrode array 40 is immersed in the slag 2 to be heated by the arc. By this arc heating, the slag 2 and the furnace lid 31 are heated.
Are heated to a considerably high temperature by radiant heat transfer by arc heating.

For this reason, even if a part of the cooling liquid 53 enters the ladle 10, if the amount is within an allowable range to some extent, the cooling liquid 53 is immediately vaporized and disappears. Furthermore,
Even if hydrogen is generated at this time, there is almost no room to enter the molten metal 1 because it is covered by the slag 2.

However, if the intrusion of the coolant 53 exceeds the allowable limit, a hydrogen explosion or intrusion of hydrogen into the molten metal occurs.

On the other hand, the fuel is injected upward, and
When the coolant 531 is formed, most of the cooling liquid 53 comes into contact with the outer periphery of the graphite electrode 41, and the uniform and smooth contact of the cooling liquid 53 can form a uniform film layer 532 on the outer periphery of the graphite electrode 41. The formation of such a film layer 532 can also be understood from the fact that the outer periphery of the graphite electrode 41 is uniformly blackened. With such cooling, cooling with a cooling liquid simply reduces the amount of spray to each graphite electrode 41. Effective cooling can be achieved simply by adjusting.

When strict quality is required,
After that, as shown in FIG. 2D, a process such as degassing may be performed with the molten metal 1 kept in the ladle 10.

In the case of spraying in such a manner as to be inclined upward, the spray rate is 2 to 10 liters / minute, preferably 3 to 10 liters / minute.
It is preferable to keep it within an appropriate range of up to 9 liters / minute.
Further, an optimum value is determined within a proper range corresponding to the diameter of the graphite electrode, and cooling is performed by spraying a cooling liquid having the optimum value.

When the cooling liquid 53 is cooled in this way, the cooling liquid 53 hardly scatters, and almost all of the cooling liquid 53 flows on the outer peripheral surface of each graphite electrode 41 of the graphite electrode array 40. The cooling is properly performed without overcooling to the tip of the graphite electrode 41, and the basic unit of the electrode is greatly reduced.

In this case, the upward inclination angle θ is 0 ° (0 °
), The range of adjustment of the spraying or injection pressure is expanded to some extent. Even if the injection pressure is not so adjusted, if the loop is formed properly, it is reflected by the graphite electrode. The amount to be cooled is small, the cooling effect to the tip is sufficient, and the electrode unit consumption is reduced.

The lower limit of the appropriate range of the flow rate of the coolant is 2
The reason why the rate is 3 liters / minute, especially 3 liters / minute, is because, below that, even if the upward inclination angle θ is within the above range, the flow rate of the cooling liquid is insufficient and the predetermined cooling effect cannot be achieved. is there.

Further, the flow rate of the cooling liquid is set to 1 which is the upper limit of the appropriate range.
If it exceeds 0 liters / minute, the graphite electrode having a diameter sufficient to be used for refining in the ladle will overcool the entire graphite electrode array, and will require extra power to heat the supercooled part,
This is because the power consumption increases, which is not preferable.

In the above description, an example in which the cooling liquid is blown out from a plurality of nozzles has been described. However, under the above conditions, the cooling liquid can be blown out from one nozzle.
Further, the nozzle may be omitted only by a plurality of spray holes. In this case, the structure of the cooling device itself can be made compact.

[0054]

【Example】

Embodiment 1 FIG. First, as shown in Table 1, using a graphite electrode row in which graphite electrodes of various diameters were connected via a nipple, a cooling liquid mainly composed of tap water was inclined upward θ (= 20 °) above the furnace lid. ), The molten steel melted in the arc electric furnace was placed on a ladle while being sprayed and cooled while inclined, and the ladle was refined by the apparatus shown in FIG.

At this time, the flow rate of the tap water as the cooling liquid was changed for the graphite electrode of each diameter, and the basic unit of the electrode and the basic unit of the power with respect to the diameter and the flow rate of the graphite electrode were obtained. In the conventional example, unlike the present invention, the cooling liquid is not sprayed.

The results are as shown in Table 1.

[0057]

[Table 1]

As shown in Table 1, the size of the graphite electrode was 12
In the range of ~ 18 inches, the cooling water amount for each electrode was 4
The range is preferably 9 to 9 liters / minute, and especially
In the case of a 4-inch electrode, when the amount of cooling water is set to 5 to 6 liters / minute, the basic unit of the electrode is improved by nearly 20%.

When the contents of [H] and [O] in the molten steel after the ladle refining were determined, [H] was determined.
Was 3 ppm and [O] was 20 ppm, and these values were almost equal to those of the conventional example.

[0060]

As described above in detail, the present invention heats and refines a molten metal bath using arc heating by a graphite electrode array in which graphite electrodes are sequentially connected via nipples in a ladle. At this time, the upper open part of the ladle is closed with a furnace lid, and the coolant is sprayed on the furnace lid in an inclined manner to the outer periphery of the graphite electrode row while the tip of the graphite electrode row is molten metal. Ladle refining method and apparatus for molten metal to be heated and refined by immersing a slag layer on a bath.

Therefore, the entire periphery of the graphite electrode to be subjected to arc heating is covered with a cooling liquid which is looped downward and can be cooled effectively, oxidation consumption can be minimized, and a large width can be obtained. A reduction in the basic unit of electrode can be achieved.

Furthermore, since the surface of the molten metal in the ladle is covered with slag, and the slag is used effectively, the quality is not impaired even if coolant enters.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus used for refining molten metal while spraying a cooling liquid onto a graphite electrode to be subjected to ladle refining and cooling the molten metal according to the method of the present invention.

FIGS. 2 (a), (b), (c) and (d) are explanatory views showing respective steps of one example of ladle refining by the method of the present invention.

FIG. 3 is an explanatory diagram showing an enlarged example of an annular cooling pipe in the refining device shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Molten metal 2 Slag 10 Ladle 20 Ladle 20 Ladle refining apparatus 31 Furnace lid 40 Graphite electrode row 41 Graphite electrode 50 Annular conduit 51 Injection nozzle

Claims (6)

[Claims] When a molten metal is heated and refined using arc heating by a graphite electrode array in which graphite electrodes are sequentially connected via nipples in a ladle, an upper open portion of the ladle is removed. At the top of the furnace lid to be closed, cooling is performed by spraying a cooling liquid by inclining upward with respect to the outer periphery of the graphite electrode of the graphite electrode row, while immersing the tip of the graphite electrode row in slag on the molten metal. A ladle refining method for molten metal, which comprises arc heating. 2. The ladle refining method for molten metal according to claim 1, wherein an inclination angle at the time of spraying the cooling liquid upward is set to not more than 0 ° and not more than 60 ° with respect to a horizontal level. 3. The ladle refining method for molten metal according to claim 1, wherein the spray amount of the cooling liquid is set to 2 to 10 liters / minute. 4. The ladle refining method for a molten metal according to claim 1, wherein water is injected as the cooling liquid. 5. The cooling liquid according to claim 1, wherein the cooling liquid contains an antioxidant and the balance substantially consists of water.
A ladle refining method for the molten metal according to the above. 6. A furnace lid for closing an opening at an upper portion of the ladle is provided on a traveling route on which a ladle traveling on a traveling carriage travels. An array of graphite electrodes for arc heating the molten metal in the ladle is provided, and an annular conduit surrounding the array of graphite electrodes and on which a cooling liquid is introduced is provided on the furnace lid. At least a part of the inside of the conduit is provided with a spray hole or a spray nozzle for spraying the coolant upward and looping and spraying the coolant on the outer periphery of the graphite electrode row. Ladle refining equipment for molten metal.