JPS6195766A - Method and device for holding or elevating temperature of liquid metal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method according to the preamble of claim 1 and to a device for carrying out this method.

Temperature losses occur during tapping from the melting furnace, during metallurgical work-up, during ladle transfer and ladle holding, and in particular during pouring of the molten steel into the tundish of continuous casting installations. Metallurgical post-treatments include, during copper melting, e.g. alloying, washing with inert gas, blowing with desulfurization agents and vacuum degassing of the molten steel for the purpose of adjusting the desired composition, deoxidation and separation of products by deoxidation, Homogenization, desulfurization and reduction of the hydrogen and nitrogen content of the metal as well as controlled adjustment of the casting temperature may be mentioned. Such post-treatments are carried out, for example, in a casting ladle, in a vacuum processing vessel or in a tundish.
A container through which the melt flows while forming a dam is also included in the intake container referred to in the present invention.

The above-mentioned temperature losses can be compensated by corresponding heating of the melt in the melting furnace. In this case, however, it must be accepted that the furnace lining is heavily loaded by the high temperatures and that the production rate of the melting furnace is reduced by the time required for overheating.

It is known to re-supply the thermal energy lost from the liquid metal in the manner described above by means of a heating device located outside the melting furnace. Such heating devices, which are generally installed in the casting ladle, are multiphase AC-arc heaters each working with three graphite electrodes; The device is equipped with an expensive lifting structure and electrode control for rapid up-and-down movement. Subject to the diameter of the electrodes, the dimensions of the current supply and the electrode holder, the spacing between the electrodes is relatively large and the spacing to the ladle wall is correspondingly small.

Furthermore, the polyphase alternating current arc of the graphite electrode, which is inherently unstable, burns toward the ladle wall due to the force of the electromagnet, and due to cracking, the ladle wall is subjected to an extremely strong load due to heat, causing wear and tear on the ladle lining. increase accordingly. To avoid these disadvantages, graphite electrodes are operated with the shortest possible arc, but this increases the risk of recarburization of the melt by the electrode graphite. Furthermore, the known heating equipment requires that the protection of the heated graphite electrode in the ladle jacket be made gas-tight only by means of constructionally expensive measures, which is therefore detrimental to the metallurgical process, and which cannot be used under high pressure. Ingress of air by costly blowing with inert gases shall be prevented.

To avoid periodic wall wear, an electrode assembly consisting of two graphite electrodes is immersed in liquid metal, with the inner rod-shaped electrode set back and offset relative to the outer tubular electrode. It is known. However, with this known heating device there is a risk that the liquid metal will be carburized. Furthermore, the external tubular electrodes are subject to significant wear.

Furthermore, it is known to heat liquid metals by induction. However, this requires that all of the uptake vessels used be equipped with an induction coil. Moreover, even with this heating mode, significant wear of the ladle lining occurs.

The underlying problem of the invention is that the liquid metal is chemically unaffected and that the walls of the uptake vessel are protected. The object of the present invention is to create a method for maintaining or increasing the temperature of liquid metal present in the intake vessel after tapping from the melting furnace by supplying energy.

The device equipped with the electrodes for carrying out this method is constructed in such a way that a good sealing of the covering of the uptake vessel to the atmosphere is achieved.

Moreover, it must be easily and compactly constructed to enable subsequent integration of the device into existing installations.

This subject is limited to a method in the patent claims ts1.
The problem is solved by the features described in section.

Due to the water cooling, the plasma burner has a temperature at its rear end such that it is possible to implement a gas-tight seal for the plasma burner in the cladding of the intake vessel. Although the plasma burner has the same heating efficiency, the graphite electrode also has a significantly smaller diameter, so the method according to the invention moves the focus further away from the wall and towards the center of the container. The inner wall of the container can be provided with a thermal load, thereby unloading the inner wall of the container.

By limiting the central distance of the focal point from the solid axis of the intake vessel with the arrangement according to claim 2, the desired protection of the casting ladle wall is particularly facilitated. If the plasma burner is arranged symmetrically as usual, a subterm is formed resulting from the focus, the diameter of which corresponds to twice the central distance of the focus from the central axis of the intake vessel. If the arrangement of the containers is not rotationally symmetrical, the proportions according to claim 2 apply correspondingly to the dimensioning of the plane of symmetry of the containers.

Further advantageous developments according to the invention are specified in the patent claims 3 to 27.

According to claim 6, enrichment due to carbonization nitrogen is also effectively avoided when argon is used. The ranges stated in claims 4 and 5 of the arc length ensure a reliable energy supply, and the maintenance of the working elements according to claim 6 characterizes the unobjectionable progression of this method. The arrangements according to claims 7 and 8 represent advantageous measures for reaching a limit on the central distance of the focal point from the central axis of the intake vessel.

When working with the method according to claims 10 and 11, a current circuit is formed through the plasma burner, the arc column generated by the plasma burner and the liquid metal.

In this mode of operation, therefore, there is no need to provide the uptake vessel with an expensive counter electrode.

By injecting an inert gas into the liquid metal from below, the liquid metal is set in motion, thereby achieving a good distribution of the thermal energy generated by the plasma burner.

By laterally injecting an inert gas into the liquid metal at a uniform height, the thermal energy provided by the plasma burner is distributed advantageously within the entire layer of liquid metal present at this height. . This achieves a temperature gradient that allows stepwise pouring of the melt.

The arrangement set forth in claim 15 enables reliable ignition of the plasma burner in a simple manner.

In order to make it possible to carry out the method without harmful air influences, the space existing above the liquid metal in the intake vessel is as defined in claim 15 before igniting the plasma burner. Due to the configuration, the ignition between the plasma burners, which are filled with inert gas, and the lowering of the plasma burners and their proximity to the liquid metal, dissolves any sludge layer present, and with this, the sludge layer in the liquid metal and this Allows current to flow through.

The device for implementing the method described above has a gas-tight sheathing, which can be carried out in a simple manner by means of a circular cord ring due to the low temperatures of the plasma burner.

Since plasma burners allow a significantly greater scattering of the arc length than graphite electrodes, the device according to claim 18 is advantageously constructed with a holding and lifting mechanism common to all plasma burners. Is possible. In this case, the plasma burner is fixed in a simple manner in the bottom insert of the tube, so that only one cut-out opening in the jacket of the intake container has to be hermetically sealed. In order to keep the structural height as low as possible, the tube is constructed in a telescopic manner.

In accordance with claim 24, υ the sheathing is constructed with a separate central region. If the plasma burner is equipped with a separate lifting device - this is the case when the plasma burner is installed at an angle. It is advantageous to fasten the lifting device to the cover of the intake container when the device is in use.

If the covering here has a separate central area, as proposed in claim 24, the lifting device can be used for uptake containers of different sizes, in which case the uptake The cover of the container need only have openings of the same size to accommodate the separate central area.

When the covering part is formed not only as a cover existing on the intake container, but also as a boiler capable of accommodating the intake container or accommodating itself, as described in claim 25, In a similarly advantageous manner, it is possible to operate intake vessels of different sizes using the same heating device.

The invention will now be described in detail with reference to the embodiments illustrated in the accompanying drawings.

tJ! In the embodiment according to FIG. 11, a casting ladle 2 filled with liquid molten metal 1 rests on a transport vehicle 3. In the embodiment according to FIG.

The casting ladle 2 carries on its seven flange 4 a cover 5 which is provided on its underside with a heat shield 6 made of a refractory material. This cover is furthermore connected to a metering device 7 for the alloy material and to a waste gas conduit 10, which is schematically shown in FIG.
It is equipped with This waste gas conduit 10 is connected to the switching mechanism 1
1 is alternatively connected to the atmosphere via a pressure limiting valve 12 or a vacuum pump 13.

The heating device comprises three water-cooled plasma burners 4 operated by multiphase alternating current, these plasma burners being concentric - as described for example in U.S. Pat. No. 5,147,529. The burner nozzle surrounds the electrodes and the burner nozzle surrounding the electrodes. The parallel oriented burners are held by a common carrier arm 15 which can be moved up and down by means of a lifting device 16. Supply conduits 17 for supplying electric current, water and gas leading to the individual plasma burners 14 are laid out on the carrier arm 15 .

For guiding the plasma burner 14 through the cover 5, this cover is provided with a water-cooled gas-tight cut-out opening 18. In this case, the sealing takes place, for example, by means of a circular cord ring.

The cover 5 is furthermore equipped with a laser transmitter 19, which works on the echosounder principle, in order to determine the height of the liquid metal filling level or bath level and to cause the plasma burner 14 to follow these accordingly.

The casting ladle 2 is equipped in its bottom with a scavenging block 20 and in its side walls with gas inlet channels 21 uniformly distributed over the circumference. Both the scavenging block 20 and the conduit 21 are provided with a connection port 22f for supplying inert gas, especially argon.

To start the process, the waste gas line 10 is switched to the switching mechanism 1
1 to a pressure limiting valve 12. The space between the liquid metal 1 and the cover 5 is filled with argon under slight overpressure by means of a plasma burner 14. Therefore, the free air initially present is discharged out of the container by the pressure limiting valve. At the same time, argon is introduced into the liquid metal via the scavenging block 20 and the line 21, through which it reaches the space above the bath level. The slag crust present on the liquid metal 1 (not shown in detail) is destroyed by the rising gas and the accompanying bath movement and is silted to the side.

The contactless ignition of the plasma burner 14 is heated in the plasma gas (argon) flowing past by an internal ignition arc, and the 1! An insulated gas conduit is formed between the pole and the liquid metal 1. In this electrically conductive gas line a main arc 23 is ignited, which leads to each plasma burner 14 uniformly distributed around the central axis 2' of the casting ladle 2. forms a focal point 24 above the bath level of the liquid metal 1. Focal points 24 spaced apart
At its center, it has a spacing r't- with respect to the central axis 2'. This distance r corresponds to half the diameter dK of the partial ring 25 virtually formed by the center of the focal point 24. Casting ladle 2
In order to protect the inner wall of the wall, the diameter d is the respective inner diameter of the casting ladle 2, preferably the customer. is limited to the value of

In order to evenly distribute the heat generated within the liquid metal 1 by the plasma burner, argon is injected into the liquid metal 1 from below through the scavenging block 2° so that the liquid metal is heated in the bath. This creates a movement and creates a uniform temperature within the L1 liquid metal 1.

If the ladle contents are cast in two ways, it is advantageous to heat the upper layer to be cast later to a higher temperature. This is achieved by injecting argon into the liquid metal via lateral conduit 21. Therefore, the upwardly rising argon causes only the upper layer to undergo bath movement, whereby the thermal energy supplied by the plasma burner 14 advantageously remains in the upper layer), so that the temperature gradient It is formed over the whole area.

The waste gas conduit 10 which carries out the vacuum treatment of the liquid metal 1 is connected via a switching mechanism 11 to a vacuum pump 13 .

During the vacuum treatment of the plasma burner 14, the flow opening 18 of the cover 50 is closed so that a sealing gap between the cover 5 and the plasma burner 14 is ensured. The large spacing to the liquid metal 1 created by this K protects the plasma burner against splashes above the liquid metal 1. For heating purposes, the plasma burner 14 is lowered into its working position after vacuum treatment.

In the embodiment according to FIG. 3, the casting ladle 2a has a covering part 27
a), the sheathing b includes a concentric cut-out 30 formed by the annular collar 28 and the flange 29. This cutout 50 is closed by a cover insert 32 which rests airtight on the flange 29. The cover insert 32 is provided with three burner operating devices 34 arranged uniformly distributed over the center axis 2').
, these burner operating devices are arranged at an angle α relative to the central axis 2'. The plasma burner 14', which is held at its tip in the burner operating device 54, is guided through a gas-tight cut-out opening 18' through the cover insert 32.

The cover insert 32 can also be placed in the cutout 50 of the covering portion 27b of the casting ladle 2b, which is shown by the dashed line in FIG. 3 and is larger than the tiger. It is therefore possible to use the heating device fixed on this cover insert 32 and consisting of a plasma burner 14' also for casting ladles of different sizes.

In order to be able to adapt to casting ladles of different sizes, it is advantageous to design the tilting position of the burner actuator to be adjustable.

In the embodiment according to FIG. 4, the casting ladle 2 is housed in a steel container 36 surrounding it. This container 3
6 carries a cover 57t which is provided with burner actuating devices 34 which are uniformly distributed around the central axis 2' and whose inclination position is adjustable. Furthermore, this cover is equipped with a heat protection shield 6, a metering device 7 and a waste gas connection 8t, as already mentioned in connection with the other embodiments. The ninth covering of the liquid metal 1 is formed in this embodiment by a combination of a cover 37 and a container 36. Inside the container 36 are casting ladles 21, - of different sizes.
This container can therefore be used universally with a heating device equipped with a plasma burner 14'.

Prior to adding and @, an inert gas atmosphere has already been added to the container
6, the container wall is fully equipped with nozzles 39. The inert gas is also supplied by burner 14' and also by nozzle 3.
9 is also introduced into the container.

The ninth plasma burner 14' for ignition is installed at an angle so that its axes intersect at a point located above the bath level. The raw flow first flows directly through the electrodes of the plasma burner 14 without taking a route through the liquid metal. Due to the arc radiation) the slag layer present on the liquid metal 1 is dissolved and becomes electrically conductive. The plasma burner 14' is now brought into working condition by means of a steep angle adjustment, in which case it is integrated together with the liquid metal 1 (into the current circuit).

In the embodiment according to FIG. 5, the plasma burner 14' is arranged in an insert 41, which is present at the lower end of the guide or carrier tube 42. The tube 42 is guided through a concentric flow opening 43 in the cover 42.

The insert 41, the tube body 42, and the water flow opening 43Fi formed airtightly with respect to the tube body are cooled.

Furthermore, the insert 41 and the tube 42 are laminated with a refractory material. The tube 42 is held by a carrier arm 45 by which it can be moved up and down through the cover 44t. In the embodiment shown in FIG. 5, liquid metal is introduced into a continuous casting facility (not shown), in which a tundish 46 is provided below the bottom of the casting ladle at the ninth point of introduction. is charged with liquid metal via an outlet opening 47 which is present in the bottom of the casting ladle 2 and is provided with a sliding closure. The arrangement shown in FIG. 5 allows, on the one hand, a common movement of the plasma burners 14' with only one lifting device and, on the other hand, the use of very short plasma burners; this is due to constructional reasons. It is advantageous when heating large quantities of liquid metal for long periods of time during casting. The supply conduit 17 of the plasma burner 14' is guided through the tube 42 and the carrier arm 45.

In the embodiment according to FIG. 6, the central tube 49 is of telescopic construction) and has three tube sections 50, 51.5.
2), in this case the inner tube section 52Fi is off with an insert 53 at its front end, into which two plasma burners 54 oriented parallel are provided. Both plasma burners 54 are operated with single-phase alternating current, with the current circuit running alternately from one plasma burner through the liquid metal to the other plasma burner. Due to the telescopic design of the central tube 49, it is possible to increase the lifting height if the original construction height is low.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a casting ladle with all plasma burners installed parallel to each other and the associated heating device; Figure 2 is a cross-sectional view of the casting ladle along line l-11 in Figure 1; 3 is a plan view of a heating device consisting of three plasma burners, FIG. 4 is a view of a heating device installed on the container, and FIG. 5 is a plan view of a heating device consisting of three plasma burners, and FIG. FIG. 6 is a schematic longitudinal sectional view of a telescope-shaped support tube with two plasma burners; FIG. Reference numerals in the figure are 5... Covering section 14... Plasma burner 18... Cutting opening

Claims (1)

[Claims] 1. A method for maintaining or increasing the temperature of a liquid metal existing in an intake container after being tapped from a melting furnace by supplying energy, the method comprising: A method as described above, characterized in that it is supplied by an arc conducted through at least two plasma burners cooled with water and operated with a gas inert to the liquid metal. 2. The focal point of the arc generated by the individual plasma burner does not exceed 3/■ of the radius of the inner wall of the intake vessel at the height of the respective bath level from the central axis of the intake vessel above the liquid metal bath level. The method according to claim 1, wherein the center distance is adjusted to have a center distance. 3. Operate the plasma burner using argon.
A method according to claim 1. 4. Plasma burner not smaller than 100mm, 50mm
2. A method according to claim 1, wherein the distance from the liquid metal is maintained at a distance of no greater than 0 mm. 5. The plasma burner should be no smaller than 200mm and 40mm.
holding at a distance from the liquid metal not greater than 0 mm;
A method according to claim 4. 6, - the distance of the focal point from the central axis of the uptake vessel (r/
mm) - - Distance of the burner jet from the bath level (1/mm) - and - Arc current radiated via the burner electrode (1/KA)
- by the following relational expression: r=(0.375...0.625)1×(0.755+O
Adjust within the framework of P315KA^-^1^/^3√1),
A method according to claim 4 or claim 5 for carrying out the operation. 7. Apparatus according to claim 1, in which the plasma burner is operated in a position not parallel to the central axis of the intake vessel and at a small distance from said central axis of the burner jet. 8. The method of claim 7, wherein the plasma burner is operated at an acute angle to the central axis of the intake vessel. 9, - Center distance from the central axis of the focal point uptake vessel (
r/mm) - - Distance between burner radiation port and bath level (1/mm) -
The arc radiation flow (1/KA) flowing through the electrodes of the burner and the acute angle (α) at which the plasma burner is inclined with respect to the central axis of the uptake vessel are expressed by the following relation: r=(0.375...0 .625)1×(0.755+O
Z315KA^-^1^/^■√1-0.75tanα
9. The method according to claim 8, wherein the method is regulated within the framework of . 10. The method according to claim 1, wherein two or one plasma burner is operated with two-phase alternating current. 11. Three or one 3 plasma burners are operated with multiphase alternating current in a center-tap connection, with the liquid metal being the central point on the consumer side, according to claim 1. Method described. 12. The method according to claim 1, wherein during at least part of the energy supply by the plasma burner a gas inert to the liquid metal is fed into the liquid metal from below. 13. A method as claimed in claim 1 in which a gas inert to the liquid metal is laterally applied from a height into the liquid metal during at least a certain time interval of the energy supply by the plasma burner. 14. The slag crust that has solidified to some extent on the melt is destroyed by gas introduced into the liquid metal from below before igniting the plasma burner, and is washed away to the side. Method described. 15. A method as claimed in claim 1, characterized in that the space in the intake vessel above the liquid metal is filled with inert gas at overpressure before igniting the plasma burner. 16. First ignite the plasma burner above the liquid metal,
16. The method of claim 15, wherein the method is then brought into close proximity to liquid metal. 17. Intake after tapping from the melting furnace, comprising an uptake vessel with a sheath for the liquid metal and an electrode guided through a flow opening present in this sheath. A device for carrying out a method for maintaining or increasing the temperature of a liquid metal present in a container by supplying energy, comprising a concentric arrangement of a plasma burner (14) whose electrodes are cooled by water. device, characterized in that the sheathing (5) is provided with a flow opening (18) which is formed in a gas-tight manner with respect to the plasma burner (14). . 18. Plasma burner (14) lifts device (16)
18. Device according to claim 17, comprising a common holding mechanism (15) operated by. 19. Plasma burner (14″) is in the center tube (42)
is fixed in the bottom insert (41) of the tube, which can be moved up and down in the sheathing (44) through the air-tight flow opening (43), in which case the bottom insert (41) also 19. The device according to claim 18, wherein the jacket wall of the central tube (42) is also water cooled. 20. The device according to claim 19, wherein the bottom insert (41) and the jacket wall of the central tube (42) are laminated with a fire-resistant material. 21. The central tube carrying the parasma burner (54) (
21. The device according to claim 20, wherein 49) is of telescoping design. 22, the plasma burner (14') takes in the intake vessel (2,
2a, 2b) in a position not parallel to the central axis (2') of the burner, in which case the burner nozzle has a very short distance from the central axis (2'). Apparatus according to any one of clauses 17 to 21. 23, the plasma burner (14') takes in the intake vessel (2,
23. Device according to claim 22, located at an acute angle (α) with respect to the solid axis (2') of 2a, 2b). 24, a separate central region (3) in which the covering (27a, 27b) is provided with one or multiple flow openings (18');
18. The device according to claim 17, comprising: 2). 25, a container (3) in which the covering part accommodates the uptake container (2);
Claim No. 6, 37)
The device according to item 7. 26, the cladding (5) is provided with a waste gas connection pipe (8), which waste gas connection pipe can alternatively be connected to the pressure limiting valve (12);
18. Device according to claim 17, which can alternatively communicate with the atmosphere via a vacuum pump (13). 27. The covering part (5) is provided with a distance measuring device (19) oriented in the direction of the internal space of the intake container,
Apparatus according to claim 17.