JPS613645A - Method for controlling flow rate of cooling water for continuous casting mold - Google Patents

Abstract

PURPOSE:To economize cooling water and to decrease the generation of breakout by controlling the flow rate of the cooling water for cooling a casting mold so that the wall surface temp. of the mold is approximated to the target value of the wall surface temp. of the mold determined from the component values of the molten steel. CONSTITUTION:The wall surface temp. of the casting mold 4 is detected by a thermometer 5. The target value of the wall surface temp. of the mold 4 is determined in accordance with the solidifying point temp. estimated from the component values of the molten steel 2. The flow rate of the cooling water is so controlled that the detected value of the above-described wall surface temp. attains the above-described target value. The cooling water is economized and the generation of the breakout is decreased by the above-mentioned control method.

Description

[Detailed Description of the Invention] <Object of the Invention> Industrial Application Field The present invention relates to a cooling water control method for a continuous casting mold (hereinafter simply referred to as a mold). The present invention relates to a method of controlling the flow rate of cooling water so that this value matches a target value.

Conventional technology In general, continuous casting of molten steel involves sequentially transferring the molten steel to a ladle, a tundish, and a continuous casting mold. Thereafter, the solidified shell is used as an outer shell and is sequentially pulled downward in an unsolidified state, and is completely solidified by water spray cooling in a so-called secondary cooling zone below the mold. Therefore, cooling of molten steel in the initial stage, that is, cooling inside the mold, is considered to be an important issue from the viewpoint of speeding up casting and quality, and in the past, various methods of controlling cooling water for continuous casting molds have been proposed. However, there are the following problems.

In other words, the conventional continuous casting mold cooling water control methods can be roughly divided into (1) constant flow rate control method, and (2)
) A method of controlling the slab surface temperature to a constant level, and (3) a method of cascading the casting speed.

This constant flow rate control method is a method of controlling the flow rate of cooling water supplied to the continuous casting mold so as to always maintain a constant flow rate. However, even if the flow rate of cooling water is kept constant using the constant flow rate control method, the amount of heat passing through the continuous casting mold wall varies depending on many casting conditions such as the mold wall taper, powder distribution, slab size, steel type, etc. Therefore, the set flow rate is controlled as an excessive flow rate with a large safety factor.
There is a problem that cracks occur on the surface of the slab due to proper cooling.

Next, the method of controlling the surface temperature of the slab to be constant is to measure the surface temperature of the slab and control the flow rate of cooling water to keep it constant.

However, in this case, since the slab surface temperature is most influenced by the spray cooling water in the secondary cooling zone, the mold cooling water control has little to do with it, and the slab surface temperature measurement itself is the most basic. There are problems and very few places are implementing it.

Finally, the method of cascading the casting speed was developed in Japanese Patent Publication No. 4
9-107928 or JP-A No. 52-46331, the amount of heat removed is determined using the amount of cooling water passing through the mold and the temperature difference between the temperature of the cooling water on the mold supply side and the temperature on the mold discharge side. This method controls the casting speed according to the However, since this method uses a constant flow of cooling water m regardless of the temperature of the molten steel in the tundish, fluctuations in the pouring temperature cause the slab to absorb more heat than necessary, which is undesirable for casting high-temperature slabs. There is a problem of whether this can lead to a breakout.

Problems to be Solved by the Invention The present invention aims to solve the above-mentioned problems. Specifically, the mold wall temperature is detected and the flow rate of mold cooling water is adjusted so that this temperature becomes a target value. We propose a method for controlling the flow rate of cooling water to remove the minimum necessary heat from the mold and form a skin during solidification.

<Structure of the Invention> Means for solving the problem and its operation, that is, the method of the present invention detects the mold wall temperature when controlling the cooling water for cooling the continuous casting mold, and this detected value is determined by the temperature of the molten steel. It is characterized by controlling the flow rate of cooling water so that it reaches a target value determined based on the components, etc.

Therefore, according to the method of the present invention, the temperature of the mold copper plate is detected together with the flow rate of the mold cooling water, and these detection signals are used to
One of the features is that the flow rate of mold cooling water is controlled, and this feature makes it possible to achieve effects such as reducing the amount of cooling water used, reducing the occurrence of breakouts, and making it possible to produce high-temperature slabs.

Therefore, the above configuration will be explained in detail as follows.

As mentioned above, in a continuous casting mold, the cooling function is important, and if overcooling or insufficient cooling occurs, problems such as slab surface cracking and breakout will occur, as described above.

Therefore, it is important to cool the mold so as to adjust the necessary minimum appropriate amount of heat removal. However, in the conventional technology, the amount of cooling water is controlled based on the temperature of the slab drawn below the mold, or the amount of heat removed is maintained at a constant value by controlling the amount of cooling water, but as mentioned above, there are many problems. remains. In continuous casting, the amount of heat removal required in the mold is closely related to the molten steel composition as well as the temperature at which the molten steel is poured into the tandyssico. That is,
If the casting temperature is high, strong cooling is required in the mold, and if it is low, it is necessary to achieve slow cooling. This is nothing but the difference between the solidifying temperature and the freezing point temperature, which comes from the molten steel composition.

In short, the cooling necessary to prevent surface cracking and breakout problems in the mold during continuous casting is achieved by matching the freezing point temperature of the molten steel components and using the minimum amount of heat necessary to form a solidifying skin. This is the point.

From this point of view, one feature of the present invention is that, as described above, the temperature of the mold wall surface is measured and the flow rate of cooling water is controlled so that the wall surface temperature reaches a predetermined target value. By controlling the flow rate of cooling water in this way, no matter what the pouring temperature is, the molten steel will be cooled and solidified in the mold in just the right amount, and the cooling status in the mold can also be observed.

To explain in more detail, if the casting temperature is high, the mold wall temperature increases, and if it is low, the mold wall temperature decreases. Therefore, if the cooling water is controlled by the method of the present invention so that the mold wall surface temperature matches a predetermined target value, the mold heat extraction amount can be adjusted to an appropriate value since the casting temperature and the V-shaped wall surface temperature are correlated with each other. Can be controlled. Note that the amount of heat removed at this time can be determined based on the flow rate of cooling water and the temperature difference between cooling water supply and drainage.

Further, the present invention will be specifically explained using FIG. 1 and FIG. 2 as follows.

Note that FIG. 1 is a layout diagram of an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a sectional view of an example of a mold copper plate temperature measuring apparatus.

First, in Fig. 1, numeral 1 indicates tundish 2, molten steel, 4 indicates a mold, and molten steel 2 indicates tundish 1.
It is then cast into mold 4. The wall temperature of the mold 4 is measured by a temperature measuring device 5 embedded in the mold wall, and the level of molten steel 2 in the mold 4 is measured by a level meter 3, and the mold 4 is cooled via a cooling water supply pipe 24. Water is supplied, and this supply pipe 24 is provided with a flow meter 7 and a flow control valve 8, and the cooling water after cooling is discharged from a cooling water discharge pipe 25. The molten steel 2 injected into the mold 4 forms a solidified shell 9 by removing heat from the mold 4, and is continuously drawn out from below.

Next, when performing continuous casting as described above, the temperature of the mold wall surface is measured by the temperature measuring device 5, and the flow rate of cooling water is controlled so that this temperature coincides with a predetermined target value. By controlling in this manner, the amount of heat removed from the molten steel can be kept at an appropriate and minimum level, and continuous casting can be performed smoothly.

That is, the amount of heat removed from the molten steel 2 in the mold 4, 0, is given by equation (1).

In equation (1), h is a dimension correction coefficient, the flow rate of mold cooling water can be measured by flow meter 7, the mold size is determined from the beginning, and the depth of molten steel in the mold is determined from the value measured by level meter 3. can be easily determined.

Therefore, in order to appropriately maintain the amount of heat removed from the mold Q to a minimum value, the amount of heat removed from the mold 0 can be maintained constant by setting Δ■ in equation (1) to its target value. Setting the target value of Δ1 can be achieved by adjusting the mold wall temperature to a predetermined target value.

In other words, △■ indicates the temperature difference at which molten steel is washed away by mold cooling water, and Δ■ - pouring temperature - slab temperature in the mold (Ts
). In this case, the temperature of the slab in the mold (hereinafter referred to as Ts) can be easily determined by correcting the temperature of the mold copper plate measured by the temperature measuring device 5 using the heat transfer coefficient of the mold.

In addition, in order to keep this temperature difference △■ constant, since the molten steel is poured under normal conditions, the flow rate of cooling water must be controlled to keep the mold copper plate temperature constant so that it matches the target value. When the temperature is maintained, △■ becomes constant, and according to equation (1), the amount of heat removed 0 is appropriate, minimum, and kept constant.

In short, if the cooling water flow rate is controlled by the method of the present invention so that the temperature measurement value of the mold copper plate matches the preset target value, the heat removal period Q in the slab can be kept constant according to equation (1). This will allow the molten steel to cool properly. Note that when the amount of heat removed changes due to fluctuations in the casting speed, if △■ is set in consideration of the fluctuation, the influence of the casting speed fluctuation factor is included in this.

In addition, when controlling the flow rate of cooling water in this way, the mold wall temperature,
That is, the target value of the copper plate temperature is determined as follows in relation to the molten steel composition.

The composition of molten steel is known in advance during continuous casting,
From this molten steel composition, the freezing point temperature (hereinafter referred to as ■ ratio) is calculated as follows: When C<0.5%, TL=1538-(55x(%C)+80X(%H2)
+13×(%Sil+4,8X(%Mn)+1.5×(
%Cr) + 4.3×(%Ni) )・・・・・・(
2) When C>0.5%, TLL=1538- (44-24(%C1+52X(
%G)2+13×(%5i)−1−4,8X(%Mn>
+1.5X (%cr) 14.3X (%N1))...
...(3) Furthermore, in equations (2) and (3), (%C), (
%Si), (%Mn) (%Cr), and (%Ni) indicate the respective contents of C, St, Mn, Cr, and Ni in the molten steel. It can be calculated as follows. Therefore, based on this TLL, the target value can be set by taking the safe temperature into consideration and setting it to a low value.

Although the mold wall temperature measuring device can be constructed in any way as long as it can measure the temperature of the copper plate, it is usually constructed as shown in FIG.

That is, in FIG. 2, reference numeral 10 indicates a copper plate constituting the inner wall of the mold 4. A blind hole 11 is provided on the back side of the copper plate 10, and a thermal lightning pair 12 is disposed as a thermometer 58, which is pressed into the blind hole 11 and is in close contact with the copper plate 10. Reference numeral 13 indicates a protective tube for the thermocouple, 14 indicates a compensating conductor, and 15 indicates a spring.The spring mechanism presses the thermocouple 12 in the direction of the blind hole 11, allowing accurate temperature measurement.

Reference numeral 18 is a stopper, 17 is a fixed cap, and 18 is a warmer.
Installation of the meter 5 [Pucamp is shown, 19 is the guide vibe. A ring 20 is provided on the copper plate 10 to prevent the cooling water flowing inside the mold 4 from entering. In addition, code 2
1 is the mold assembly bolt, 21a is the back play 1/22
a and 22b, and 23 indicates a spacing piece fixing bolt. In addition, when controlling the flow rate of cooling water as described above, a control device 6 is provided as shown in FIG. It is also possible to have the calculation function and flow rate adjustment function performed automatically.

That is, the molten steel level signal in the mold, the mold copper plate temperature signal, and the mold cooling water flow rate signal are automatically measured, and the amount of heat removed is calculated using equation (1) from the target mold copper plate temperature and mold size set in advance by the control device 6. , the cooling water flow rate is controlled so as to keep this constant, that is, so that the mold copper plate temperature matches its target value.

<Effects of the Invention> As explained in detail above, when the amount of cooling water is controlled by the method of the present invention, heat removal ω is kept constant at an appropriate value, and the flow rate of cooling water is controlled based on the temperature of the mold copper plate. . For this reason, the actual cooling capacity is shown after integrating and controlling factors such as the distribution of Paragoo, the inner wall of the mold such as the steel type, and the contact situation of the molten steel slab with the inner wall of the mold such as the solidified skin. This eliminates the need for proper cooling or insufficient cooling as in the conventional case, prevents large thermal stress from occurring in the solidified layer that occurs in the mold, improves the surface properties of the solidified layer, and allows for proper cooling. Break Ala]・
It can also be prevented from occurring.

[Brief explanation of drawings]

FIG. 1 is a layout diagram of an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a sectional view of an example of a mold wall temperature measuring apparatus. Code 1・・・Tandish 2・Old・Molten steel 3・
... Molten steel level meter in mold 4 ... Mold 5 ... Mold copper plate thermometer 6 ... Mold cooling water control device 7 ... Mold cooling Water flow meter 8...Flow rate control valve

Claims (1)

[Claims] When controlling the cooling water that cools the continuous casting mold, the mold wall temperature is detected and the flow rate of the cooling water is controlled so that this detected value becomes a target value determined based on the molten steel composition, etc. A method for controlling the amount of cooling water in a continuous casting mold, characterized by: