KR20170074355A - A method and an arrangement for improving heat transfer for tundish plasma heating - Google Patents

Abstract

The invention relates to an apparatus for heat transfer to a melt (60) in a tundish (1) of a continuous casting process, said tundish comprising at least one outlet (12, 12 ') and an inlet (42) The apparatus comprises a heating chamber (20); A plasma heating apparatus (30) comprising a plasma torch (32) positioned in the heating chamber, wherein the plasma heating apparatus (30) is mounted on an arm and spaced a distance relative to the melt (60) Said plasma heating device being arranged to operate through a hole in said plasma heating device; And an electromagnetic stirrer (50) located outside the heating chamber (20) and arranged to electromagnetically stir the melt (60). The heating chamber 20 further comprises a pair of weirs 22 and 22 'installed in the upper part of the heating chamber and a pair of dams 24 and 24' installed in the lower part of the heating chamber, The stirrer 50 is arranged to electromagnetically stir the melt in the region of the heating chamber 20 and the region is surrounded by the weirs 22 and 22 'and the dams 24 and 24' .

Description

[0001] METHOD AND APPARATUS FOR IMPROVING HEAT TRANSFER FOR TUNDLESS PLASMA HEATING [0002]

The present invention relates to a method and apparatus for improving turn-dissipative plasma heat transfer wherein the turn-off includes lasers having an outlet and an inlet, the apparatus comprising a pair of weirs disposed in the upper portion of the heating chamber, And a plasma heater mounted in the heating chamber at a distance relative to the melt.

Tundish plasma heating is used in continuous casting of metals to precisely control the casting temperature change of the molten metal in the tundish. Tundish plasma heating applies a plasma torch to deliver heat directly to the melt surface of the tundish, which is then transported into the melt by the designed fluid flow. The plasma torch is housed in a tundish to generate a plasma arc, operates with a controlled current having a maximum current of about 5000 Amp during casting, and also requires a certain argon flow rate to form a plasma arc. The tundish is covered with a high-grade refractory lid and thus forms a heating chamber, which establishes an inert atmosphere on the molten metal to protect the molten metal from re-oxidation and nitrogen pick-up. The surface area of the heating chamber must be slug free to ensure the current circuit of the plasma.

The normal temperature of the plasma arc is about 10000 ° C. This heat is transferred from the plasma arc and radiated in the heating chamber to increase the temperature of the melt surface to a higher level. The high temperature of the melt surface leads to a high temperature gradient in the upper part of the heating chamber, which in turn leads to a large buoyancy. The buoyancy reacts to the convection flow from the inlet stream, thus forming a stagnation zone in the upper portion of the heating chamber. The stagnation zone thus results in a low heat transfer rate from the top to the bottom of the heating chamber. This means that the main disadvantage of plasma heating is low heating efficiency, and typically only about 60% of the heating can be utilized.

JP04089160 discloses a system for injecting molten steel from a ladle through a nozzle in a tundish and additionally from a tundish nozzle into a mold. The system further includes a plasma heating device positioned between the ladle nozzle and the tundish nozzle for heating the molten steel, and a molten steel stirring device located near the plasma heating device for stirring the molten steel by an electromagnetic force. An AC linear motor electromagnetic coil or an electric magnet is used for the molten steel stirring device.

It is an object of the present invention to provide a method for improving the heat transfer efficiency of a melt at the time of turning of a continuous casting process.

In a first aspect of the present invention, a method is provided for improving the heat transfer of a melt in a tundish of a continuous casting process. The method includes the steps of mounting a plasma heating device with a plasma torch positioned in a heating chamber, the heating chamber being positioned above the tundish with a distance to the melt, Providing a pair of weirs in an upper portion of the chamber, installing a pair of dams in a lower portion of the heating chamber, removing the outer surface of the tundish to electromagnetically stir the melt, Applying an electromagnetic stirrer through the heating chamber, applying plasma heating to the melt inside the turn-dish through the heating chamber, and electromagnetically stirring the melt in the region of the heating chamber, And electromagnetically stirring the melt, surrounded by weirs and the dams.

Electromagnetic agitation establishes agitation forces along the wall of the tundish, and agitating forces induce rotational flow in the heating chamber, which in turn homogenizes the temperature and improves the heat transfer from the plasma torch to the melt. The melt may be electromagnetically agitated in an upward or downward direction with respect to the axis.

Only the area enclosed by the dams and weirs is electromagnetically agitated, thus preventing a short-cut flow from the heating chamber to the outlets of the tundish.

It is advantageous to apply electromagnetic stirring because the stirrer can be operated independently without contact with the tundish melt and therefore better reliability is achieved.

Also, since the melt flow in the tundish can be controlled with a constant flow pattern, excellent reproducibility is achieved, regardless of melt temperature or refractory conditions.

Additional advantages include:

- maintains the stable free surface of the melt, and therefore the stability of the plasma arc is not affected.

- Possible slag on the melt surface moves away from the plasma heating zone.

The melt flow is controlled by the desired properties; The dead zone is minimized; A stronger and larger mixed volume is achieved.

According to one embodiment of the present invention, the method further comprises the step of controlling the stirring speed of the electromagnetic stirring in the range of 0.2-0.5 m / sec to establish a similar rotational flow rate of the melt.

In a second aspect, there is provided an apparatus for heat transfer of melt in a turn-on of a continuous casting process, wherein the turn-off includes an outlet and an inlet. The apparatus includes a heating chamber; A plasma heating apparatus (30) comprising a plasma torch (32) positioned in the heating chamber, wherein the plasma heating apparatus (30) is mounted on an arm and spaced a distance relative to the melt (60) The plasma heating device 30 arranged to operate through the holes in the heating chamber 20 and an electromagnetic stirrer located outside the heating chamber 20. [ Wherein the heating chamber further comprises a pair of weirs disposed in an upper portion of the heating chamber and a pair of dams disposed in a lower portion of the heating chamber, wherein the electromagnetic stirrer electromagnetically agitates the melt in the region of the heating chamber, And the region is surrounded by the weirs and the dams.

In a first embodiment of the invention, the dams and weirs are located between the exit and entrance of the turn-dish.

In a third aspect, a tundish for continuous casting of the melt is provided, including the apparatus of the present invention. The turn-off may be a multi-strand turn-off including the second exit.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail by way of illustration of different embodiments of the invention and with reference to the accompanying drawings, in which: FIG.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A shows a flow chart for improving the heat transfer of a melt of a tundish in a continuous casting process according to an embodiment of the present invention. Fig.
1B shows a flowchart for improving the heat transfer of the melt of the tundish in a continuous casting process according to another embodiment of the present invention.
Figs. 2A to 2C show schematic top, side and front views of an apparatus for heat transfer of melt of a tundish in a continuous casting process according to a third embodiment of the present invention. Fig.
Figure 3 shows the speed fields of the different configurations, in particular the device without electromagnetic stirring, and the device of the embodiment of Figures 2a to 2c, of turn-off.

The concept of the present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the concept of the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Referring to Figures 2a-2c and 1a-1b, an apparatus 1 of the present invention for heat transfer of melt 60 in a tundish includes a mold 10 in a continuous casting process. The turn-dish 10 further includes an outlet marked as a turn-around nozzle 12. In this example, two outlets 12, 12 ', indicated by turn-off nozzles, are arranged on each side of the turn-off. To feed the melt to the tundish, a ladle (40) comprising an inlet (42) is disposed. The tundish 10 is disposed to connect the ladle 40 and the continuous casting machine, and as a reservoir, distributes and feeds the melts continuously to the casting machine. In order to provide a high quality metal, the tundish 10 provides the melt 60 to the continuous casting machine at the desired temperature and at a uniform flow rate. Melt 60, or molten metal, may be any of iron, steel, aluminum, copper, and alloys or mixtures thereof.

In this exemplary embodiment, the turn-dish 10 is a T-shaped tundish divided into two parts, an inlet chamber 12 and an outlet chamber 14, and has a weight of 30 tons. The exit chamber is essentially a T-shaped arm portion and has a rectangular shape. The inlet chamber 12 is essentially a T-shaped central leg portion and is located directly on one side of the longer sides of the outlet chamber 14 while the ladle 40 is positioned directly above the inlet 42, Is located above the inlet chamber (12) which receives the melt conveyed from the nozzles (40).

The apparatus 1 comprises a heating chamber 20 partially made of a high-grade refractory lid, a plasma heater 30 mounted in the heating chamber at a distance from the melt, and an electromagnetic stirrer 50. The heating chamber 20 establishes an inert atmosphere on the molten metal to protect the molten metal against reoxidation and nitrogen pick-up. In this exemplary embodiment, the heating chamber is located above the outlet chamber 14.

The plasma heater 30 is mounted in the heating chamber 20 at a distance from the melt surface and between the ladle inlet 42 and the outlets 12, 12 'of the turn-dish (step S10). A plasma heating apparatus 30 including a plasma burner for generating a plasma torch 32 is arranged to heat the melt 60.

The heating chamber 20 further includes a pair of weirs 22 and 22 'installed in the upper part of the heating chamber and a pair of dams 24 and 24' installed in the lower part of the heating chamber (steps S20 and S30) . The arrangement of the weirs 22, 22 'also prevents slag from the heating chamber and seals the heating chamber with argon gas to avoid re-reoxidation of the melt and to provide sufficient plasma heating to sustain the plasma arc Lt; RTI ID = 0.0 > a < / RTI > The dams 24, 24 'increase the mixing of the melt and enable one rotational flow in the heating chamber. In addition, the arrangement of the dams 24, 24 'prevents short-path flow from the heating chamber to the outlets 12, 12'. In this exemplary embodiment, a further third weir 23 is disposed between the inlet chamber 12 and the outlet chamber 14.

The electromagnetic stirrer 50 is located on the outside of the turn-off, on the other side of the longer side of the outlet chamber 14 in this example (step 40). This is because when plasma heat is applied to the inner melt of the tundish (step 40), the electromagnetic force is used to move the melt in the area surrounded by the weirs 22, 22 ', 23 and the dams 24, 24' (Step S50). This is because the heat transfer between the plasma torch and the melt occurs mainly in the heating chamber. Stirring outside the heating chamber is not efficient in promoting heat transfer. Preferably, in order to equalize the temperature of the heating chamber and to avoid strong turbulence in the heating chamber, the stirring speed of the electromagnetic stirring is controlled in the range of 0.2-0.5 m / sec (step S70). The agitation speed is based on a numerical simulation and is fine-tuned based on the quality feedback of the continuous casting process. The minimum stirring speed limit ensures the mixing effect in the heating chamber while the maximum stirring speed limit prevents strong turbulence in the heating chamber and slag capture into the melt. For top slagless turn-off, a stirring speed higher than 0.5 m / sec is possible.

Also, the electromagnetic stirrer 50 is arranged to electromagnetically agitate the melt in an upward or downward direction (step S80 or S80 ') so that an upward or downward agitating force is generated along the inner wall of the turn-dish, 2c, which causes upflowing melt at the turn-off, so that the plasma torch rotates up to the surface of the melt positioned above so that the low temperature melt is uniformly heated. This eventually equalizes the temperature of the melt and improves the heat transfer from the plasma arc to the melt.

Although the exemplary embodiment of Figs. 2A-C illustrates a T-type multi-strand turn-off, the present invention is not limited to a single strand turn-on and other shapes of single or multi- It should be understood that the present invention can also be applied to C type or H type.

The combination of plasma heating and electromagnetic agitation greatly improves rotational flow, i.e., heat transfer efficiency, which is evident by simulation as shown in Fig. 3 in which different configurations are compared.

Figure 3 shows a simulated velocity field of a different configuration, particularly a device without electromagnetic stirring and a turn-dish in the device of the embodiment of Figures 2a-c.

Table 1 below shows the different simulated configurations of plasma heating and electromagnetic stirring.

Plasma heating Electromagnetic stirring Case 1 no no Case 2 Yes no Case 3 Yes Yes

In the first case, a configuration without plasma heating and electromagnetic agitation is simulated and a weak rotational flow appears in the heating chamber. In the second case, a configuration with plasma heating but no electromagnetic stirring is simulated and a suitable rotational flow appears in the heating chamber. In the third case, a configuration having both plasma heating and electromagnetic stirring is simulated, and a strong rotational flow appears in the heating chamber.

Claims (11)

CLAIMS 1. A method for improving heat transfer of a melt in a tundish of a continuous casting process,
- mounting a plasma heating device with the plasma torch positioned in a heating chamber, said heating chamber being located above the tundish with a distance to the melt (S10)
- installing (S20) a pair of weirs in the upper part of the heating chamber,
- installing (S30) a pair of dams in the lower part of the heating chamber,
- mounting an electromagnetic stirrer (S40) on the outer surface of the tundish to electromagnetically stir the melt,
Applying (S50) plasma heating to said melt inside said turn-dish through a heating chamber, and
- electromagnetically stirring the melt in the region of the heating chamber, the region being surrounded by the weirs and the dams, - electromagnetically stirring the melt (S60)
≪ / RTI > A method for improving heat transfer of a melt in a tundish of a continuous casting process. The method according to claim 1,
Further comprising the step (S70) of controlling the stirring speed of the electromagnetic stirring in the range of 0.2 - 0.5 m / sec. The method according to claim 1,
Controlling the stirring speed of the electromagnetic stirring to be higher than 0.5 m / sec. ≪ RTI ID = 0.0 > 11. < / RTI > The method according to claim 1,
Further comprising: electromagnetically stirring the melt in an upward or downward direction (S80, S80 '). ≪ Desc / Clms Page number 20 > As an apparatus for heat transfer to the melt (60) in the tundish (1) of a continuous casting process,
The turn-off includes at least one outlet (12, 12 ') and an inlet (42)
The device
- heating chamber (20),
- a plasma heating device (30) comprising a plasma torch (32) located in said heating chamber, said plasma heating device (30) being mounted on an arm and being spaced a distance relative to said melt (60) , Said plasma heating device (30) being arranged to operate through a hole
An electromagnetic stirrer (50) located outside the heating chamber (20) and arranged to electromagnetically stir the melt (60)
Lt; / RTI >
The heating chamber 20 further comprises a pair of weirs 22 and 22 'installed in the upper part of the heating chamber and a pair of dams 24 and 24' installed in the lower part of the heating chamber, The stirrer 50 is arranged to electromagnetically agitate the melt in the region of the heating chamber 20 and the region is surrounded by the weirs 22 and 22 'and the dams 24 and 24' , A device for heat transfer to the melt (60) in the turn-around (1) of a continuous casting process. 6. The method of claim 5,
Wherein the electromagnetic stirrer is arranged to agitate the melt at a stirring rate in the range of 0.2 - 0.5 m / sec. 6. The method of claim 5,
Wherein the electromagnetic stirrer is arranged to agitate the melt at a stirring speed greater than 0.5 m / sec. The apparatus for heat transfer to the melt (60) in the tundish (1) of a continuous casting process. 6. The method of claim 5,
Wherein the dams and the weirs are located between the inlet of the ladle and the outlet of the turn-dish. ≪ RTI ID = 0.0 > 8. < / RTI > 6. The method of claim 5,
Characterized in that the electromagnetic stirrer is arranged to agitate the melt in an upward or downward direction. ≪ RTI ID = 0.0 > 1 < / RTI > A tundish for continuous casting of a melt, comprising the apparatus of any one of claims 5 to 9. 11. The method of claim 10,
Wherein the tundish is a multi-stranded tundish having two or more outlets.

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