JPS59159255A - Controlling method of heating molten metal in tundish - Google Patents

Abstract

PURPOSE:To prevent the decrease in the temp. of a molten metal without pinching by charging and heating the molten metal in the large quantity in excess of heat absorption and radiation in the initial period of charging the molten metal into a tundish then charging and heating the molten metal so as to compensate the heat absorption and radiation. CONSTITUTION:The charging flow rate of a molten metal to be accepted in a tundish from a transporting ladle, etc. is regulated to >=3t/min in the initial period of charging and is increased according to the capacity of the tundish. The quantity of the electric power to be thrown to an electromagnetic induction heater for compensating the decrease in the temp. of the molten metal in the tundish is controlled. More specifically, the quantity of the electric power to be thrown when a reference level is attained is designated as 100% and the quantity of the electric power to be thrown is controlled to 20-30% until 35% of the reference level is attained and 50-65% until 70% is attained so that the continued flow of the molten metal in the bypassing route of the heater is assured. The electric power below the max. power is thrown after the reference level is attained so that the decrease in the temp. of the molten metal is prevented.

Description

[Detailed Description of the Invention] (Technical Analysis) Regarding the handling of molten metal, such as molten steel (hereinafter referred to as molten metal), for example, in a pouring operation, a typical example of which is pouring into a continuous casting mold, , an intermediate container called a tanditshu (hereinafter abbreviated as TD) is used to receive tapped steel that has undergone refining in a steelmaking furnace via a transport ladle, and is transported by a flow system of molten steel including this TD. It is extremely important when handling molten steel to maintain the properties of the molten steel as refined as possible during the transfer, otherwise most of the refining effort will be lost to Karasu. It is.

Conventionally, various considerations have been added to this, but among the properties of the molten steel mentioned above, it is necessary to appropriately reduce the influence of the humidity drop due to the severe heat removal G that inevitably occurs when molten steel is received for the first time in the TD. What is described below in connection with this is mainly positioned as a summary of technologies that include continuous casting.

(Problem) The above heat absorption occurs during the initial stage of injection of molten steel received into the TD from a transportation ladle, etc., due to heat absorption by the lining refractory of the TD and heat radiation from the poured molten steel to the environment at the bath surface G. Due to the heat loss caused by the above, the temperature of the molten steel suddenly decreases.

Of course, the heat removal rate decreases with the subsequent injection of high-temperature molten steel, so the TD content w4 temperature gradually increases as time passes from the start of injection and eventually settles to a constant value, but generally continuous casting mold In actual operation, the influence of the above-mentioned initial heat removal is not taken into account when determining the degree of superheating of the tapping temperature that is suitable for casting into steel.

Therefore, in the transient unsteady transfer period as mentioned above,
Due to the low casting temperature in continuous casting molds, solidified metal structure and other quality defects are forced to the drawing tip of the continuously cast slab, that is, the so-called bottommost slab. This also occurs particularly at joints between slabs during continuous casting operations.

In order to prevent such a drop in the temperature of the steel in the TD at the initial stage of injection, a channel-type electromagnetic induction heating device (hereinafter abbreviated as an inductor) should be attached to the TD, and this should be used to heat the molten steel as appropriate. is advantageous.

The inductor is connected to the T on the side of the path of the main flow of molten steel in the TD, that is, the flow toward the transfer/spool.
A molten steel channel is formed in a detour path that partially protrudes from the side wall of D, and resistance heat generation based on electromagnetic induction is generated in response to the molten steel channel.

However, it has often been experienced that, depending on the power supply schedule for this inductor, the desired heating of molten steel does not proceed smoothly and appropriately.

At the initial stage of injection, when molten steel heating is most needed, partial replacement of the gas phase that filled the detour path of the inductor until the start of molten steel injection is performed. Under the influence of the temperature of the molten metal that enters the path from G, various gases generated from the refractories that form the path are mixed in the detour path, and these also expand under the influence of the temperature of the molten steel that enters. This is because even if it is dissipated out of the path, it does not mean that it is removed from grace.

When the normal rated output of the inductor is applied to the molten steel channel that is forced to occupy a portion of the detour path in this way, resistance heats up based on the induced current in the molten steel channel, and at the same time, the induced current The pinch effect caused by this heat generation accelerates the expansion of the gas phase, causing a local reduction in the cross section of the molten steel channel, resulting in separation of the molten steel channel in the longitudinal direction, and electrical conduction interruption due to so-called binching. be done. If the induced current ceases to flow in this way, the power necessary to heat the molten steel channel can no longer be sustained effectively and stably, and once continuity is interrupted, it takes time to restore continuity to the molten steel channel. Second, similar binning occurs repeatedly.

Regarding this point, we first attempted to control the power input to the inductor according to changes in the level of molten steel in the TD based on the clarification of the interaction with the bath surface level (Japanese Patent Application No. 1983).
8-6091-1), obtained two improvements, but such limitations on input power do not have the disadvantage of reducing the effect of heating at the initial stage of injection of molten steel in the TD.

(Objective of the invention) A large amount of molten steel is injected for a short period of time to temporarily overwhelm the heat loss that should not cause a temperature drop in the molten steel received at TD, especially in the initial stage of injection, and then the heat loss is It is the aim of this proposal to achieve stable operation of compensable inductors without disturbances due to binching.

(Structure of the invention) The object of item 1 is advantageously achieved by the following configuration.

A channel-type channel that forms a detour on the side of the main flow of molten steel in the TD during operations in which molten steel received from a transport ladle etc. is transferred to a continuous mold or similar facility. When heating the molten steel with an inductor, the injection flow rate of the molten steel received from the above-mentioned transport ladle or the like must be injected for a short period of time, exceeding a minimum limit of 3 tons per minute, and increasing the amount as the TD capacity increases. , while the bath level of the molten steel in the TD increases due to this injection, the maximum power input of the inductor is determined according to the TD capacity and is necessary to compensate for the temperature drop of the molten steel in the TD after the start of the injection. Based on the bath surface level at the time of
17Jj until reaching the maximum power of 80 to 20% and 65 to 50% of the maximum power, respectively.
Applying a phased power input pattern to ensure continuous flow of molten steel in the detour route described above, ``After reaching the reference level in 1, reduce the temperature of the molten steel in the TD by applying less than the maximum power required. A method for controlling heating of molten steel in a TD, which combines prevention of rJ.

What is important here is that at the initial stage of pouring into the TD, the molten steel humidity as a whole should overwhelm the drop due to heat absorption by the TD lining refractory, heat radiation from the bath surface, etc., in as short a time as possible. The idea is to first perform a rapid injection like this, and then add power in stages in a timely and appropriate manner to achieve heating by the inductor to compensate for the heat absorption and heat dissipation described above without the occurrence of binching. This effectively prevents the temperature of the molten steel in the TD from decreasing throughout the entire casting period.

Now, in FIG. 1, an example of a TD equipped with an inductor is shown with a partial cutaway to illustrate the main part structure.

In the figure, 1 is the TD, 2 is its transfer nozzle, and 3 is the inductor. There are various capacities of TDI, but in the case of 7 tons, large cases such as 35 tons, and even 75 tons, as described below, the casting speed in normal continuous casting machine operation is not that much. Since there is no difference, the official rated power of the inductor required to secure the molten steel temperature during pouring is 11000k for the former and 1500kW for the latter, which suits the purpose.

In TDI, a refractory lining is applied to the steel shell in accordance with customary practice, and a stopper (not shown in the figure) that controls the blockage of the transfer nozzle 2 is installed, and a transport ladle is placed in the upper right part of the figure away from the transfer nozzle 2. (not shown) receives injected molten steel.

The inductor 3 has a refractory case 44 forming a detour path on the side of the main flow facing the injection nozzle 2G of injected molten steel.
and a core 6 having a primary coil 5.

For example, the detour route can be formed in a circular ring shape (doughnut shape).
Inside the case 4, hold the template made from the gun side (-m f T D ], +7. of this template).
While inserting and incorporating the primary coil 5 and core 6 into the central hole of the template through the water-cooling jacket while protruding from the inner surface of the side wall, preferably magnesia is inserted around the template and between it and the case 4. A dry ramming type refractory of yarn is used to compact the material by vibration compaction, and then the ramming material is sintered by the Joule heat of the induced current generated in the template by energizing the primary coil 5. However, it is possible to open the inner surface of the side wall of the TDl at two locations in the form of a C-shaped groove, for example, by increasing the current supply power during the initial injection into the TD to cause template dissolution. Of course, it doesn't matter if it's by law.

FIG. 2 illustrates the relationship between the magnetic flux φ generated in the core 6G by energizing the primary coil/115G and the induced current j-.

Next, FIGS. 3(a) and 3(b) compare the time course of the molten steel temperature in the TD, which is caused only by the magnitude of the injection flow rate into the TD.

As is clear from the figure, due to rapid injection with a large injection flow rate, the difference ΔT between the temperature (and the lowest temperature) when the steady casting region is reached, even if the time t until the humidity in the steady casting region is restored is prolonged. On the other hand, when the injection flow rate is small, the time t is short, but ΔT
Therefore, although short-time injection with a high injection flow rate is advantageous, due to various constraints in actual operation, the injection behavior shown in Figure 3 (a) (which cannot be achieved, At best, we have to aim to get closer to figure (a), which is between the intermediate level and figure (b).

Well, first of all, the capacity is 7 tons (bath depth 600 myn when full)
We conducted an operation experiment using a TDI with an injection flow rate of 7 tons/min, and when one minute elapsed after the start of injection, the normal rated output was 100.
When the maximum power was applied using the 0kW inductor 3, as shown in Fig. 4(a), the above-mentioned binning occurred, and the resistance heat generation due to the induced current IG was not achieved, and continued for 1.2 minutes. At this point, 1,000kw of power was applied again, but binching occurred. Then, when 2.5 minutes had passed after injection, I turned it on again and was able to perform stable current heating for the first time. Depending on the heating, it is of little use in preventing the temperature of the molten steel in the TD immediately after injection, and as shown in Figure 4), Δ
T is quite large 0 Therefore, in the middle of the injection at 7 tons/min, first 200 kw and then 300 kw as shown in the fifth ('A(a))
By energizing the inductor 3, which injects the suppressed πL force into the l1li D for 17 seconds each, an attempt is made to discharge residual gas bubbles by stirring the molten steel channel, and one minute after the start of injection, the 1000 kW I turned on the power, but binching still occurred. Then, after 5 minutes, the injection was restarted and we were finally able to perform stable current heating, but as shown in Fig. 5 (b), the humidity temperature change in the TD was still unsatisfactory, and ΔT was approximately -10°C. Reached. From this result, the output to generate the melt agitation necessary for gas discharge in the molten steel channel is 200~
It turns out that 300 kW is insufficient.

Therefore, in order to promote the evacuation of the gas bubbles shown in Section 61M(a), power of 800 kW and 650 kW was introduced in stages for 17 seconds each, and then 1 minute after the start of injection, power of 1000 kW was introduced. When the n°C force is applied, there is no interruption in the molten steel channel due to pinch wobbling, and stable current heating is possible, and as shown in Figure 6 (b), the temperature drop in the molten steel in the TD can be ignored for the first time. decreased to

In addition, this advance and staged power input will be 800 kw'9
When we tried it at 50 kW, we were unable to avoid pinching.

In each of the above cases, if the capacity of the TDI is 7 tons, the time to apply the maximum required power to the inductor is set at 1 minute after the start of injection, and the bath depth at that time of 600 m is considered to be the reference bath surface level, and this is reached. As the bath level rose, 38% (200w+s) and 67% (4
80% (300kw) of the regular rated power of 11000k for G iron and inductor 3 at each point in time when G iron and inductor 3 reached
, 65% (equivalent to 6501 (W)) The operation shown in Fig. 6 (a), which applies a stepwise power input pattern that is suppressed to correspond to 65% (6501 (W)), eliminates interference due to pinching until the maximum power is input after reaching the standard level. As a result, it was possible to perform casting without actually reducing the humidity of the IA melt in the TD, as shown in the same figure ('b).

Next (herein, the injection time to reach the above reference level is 1.
4 minutes (5 tons, 7 minutes), 2.8 minutes (8 tons, 7 minutes) Compared to the case of rapid RT, the effect of preventing the melt's temperature from decreasing was reduced, and ΔT was -3°C and -6°C, respectively.
In the case of an injection time of 8°5 minutes (2 tons/min), that is, at an injection flow rate lower than 3 tons/min, ΔT increases rapidly (-13°C), so that the initial It was found that it was not possible to secure the casting temperature.

Next, large TDs with capacities of 85 tons and 75 tons, respectively.
When the capacity of each inductor is increased to 1500 kW and the injection flow rate is 12 tons/min and 15 tons/min, respectively, the initial casting melt is effectively The relationship between the tundish capacity and the elapsed time after the start of injection until the maximum power is applied, which should be suitable for the initial heating of the injection to ensure the expected lA temperature, was obtained, and the results shown in Figure 7 were obtained. It was confirmed that the above conformity could be achieved in the shaded area.

From this figure, it is clear that increasing the TD capacity increases the injection flow rate, delays the time when the maximum power is applied by the inductor, and suppresses the blockage until the time when the maximum power is applied. Also, applying an appropriate stepwise power-on pattern is necessary for effective temperature compensation of the molten steel in the TD by the inductor without binching.

As mentioned above, when the injection flow rate of molten steel in the TD is less than the minimum 3 tons per minute, effective temperature compensation of the molten steel in the TD cannot be achieved, and as the TD capacity increases, the flow rate cannot be further increased. is necessary. The upper limit of the injection flow rate depends on the operating conditions and cannot be increased unnecessarily; in the case of 7 tons, it is 7 tons/min, in the case of 35 tons, it is 12) tons/min, and in the case of 75 tons, it is 15 tons/min. This is almost the limit.

Next, the standard level for the steel bath surface in the TD that can avoid the occurrence of binning when the maximum power is applied after the application of the stepwise power-on pattern during two consecutive rapid short-term injections is determined by the TD capacity. However, for a relatively small size of about 7 tons, the full level is 4, and for a large size of about 35 tons, it is about 1. It is necessary to set it to about /2.

For the phased power application pattern listed above, 80-20% of the maximum power and 65-50% of the maximum power are applied during the rise of the bath level which does not reach 85% and then 75% of the maximum reference level, respectively. It is necessary to apply each range sequentially, and neither is timely, and each range is 20%,
If the power input is too low (less than 50%), binching cannot be effectively avoided when the maximum power is applied once the reference level is reached, while excessive power input exceeding 30% and 50%, respectively, will result in binching at that point. Pinching occurs, and stable operation of the inductor cannot be obtained thereafter.

Below, each TD with a capacity of 7 tons, 35 tons, and 75 tons
Heating the molten steel in the TD using
Table 1 below shows the results of verifying the effects of this invention using an example, in comparison with a comparative example where the injection flow rate is too small, when the latter two are performed using an inductor of 1.500 kW. be.

Table 1 Concerning the phased power input pattern, experiments were carried out by changing the timing of application of conformance examples 1, 3, and 5 that had the best results on the upper side, and it was found that ΔT was virtually eliminated in the cases shown in the following table. Obtained.

Table 2 From this, the input of maximum power becomes slower as the capacity of the TD becomes larger, 1 minute for 7 tons, 2.2 minutes for 85 tons, and 2.5 minutes for 75 tons, but the important point is that these times In order to completely avoid a drop in the temperature of the inner mesh steel in the TD, it is possible to input power in a preliminary step-by-step manner that allows the maximum power to be input stably without occurrence of binning, in conjunction with the rapid injection into the TD. G is necessary.

Thus, according to the present invention, it is possible to effectively eliminate current flow interference due to pinching that has conventionally been associated with inputting the maximum power necessary for timely heating of the melter in the TD by the inductor, and to simplify During transfer to a mold or similar facility, the temperature drop that occurs, especially at the beginning, can be properly compensated for and virtually matched to that during steady-state pouring, so that the deterioration in product quality resulting from the temperature drop is avoided. , can be advantageously prevented.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the TD with the inductor attached to it broken to reveal the main structure. Figure 2 is an explanatory diagram of the behavior of induced current generated by the inductor. Figures 3 (a) and (b) are the TD. This is a comparative chart of the influence of the injection flow rate of internally received molten steel on the temperature of the molten steel, and it is the 41st
1A (a), (1:l), Fig. 5 (a), (b
), 6 m(a) and (b) are graphs of the inductor power input pattern and the corresponding molten copper temperature transition, respectively, and Figure 7 is a diagram showing the suitability of the logo TD capacity and the maximum power input timing. It is.

Claims (1)

[Claims] 1- Molten metal received from a transport ladle etc. into a tundish is cast into a continuous casting mold or similar IIJ.
When the molten metal is heated by a channel-type electromagnetic induction heating device that forms a detour on the side of the main flow of molten metal in the tundish during the operation of transferring the molten metal to the tundish, the above-mentioned transportation Regarding the injection flow rate of molten metal received into the tundish from a ladle etc., the minimum limit is 3 tons per minute, and the larger the tundish capacity, the higher the amount, and the injection is carried out for a short time, and the bath level of the molten metal in the tundish due to this injection. During the rising G, the tundish volume h (determined according to Based on the bath surface level, until it reaches 35% of the standard level, and for a further 70% of the standard level.
% of the maximum power above, respectively.
) to 20% and 65 to 50%, respectively, to ensure continuous flow of molten metal in the detour route; A method for controlling heating of molten metal in a tundish, comprising: preventing a drop in temperature of the molten metal in the tundish by inputting power below a maximum ηL force.