JPS62197257A - Pouring method for molten steel in continuous casting - Google Patents

Abstract

PURPOSE:To control a gas blowing rate with respect to the fluctuation of an operation and to improve an ingot quality by controlling the ratio of the actual volume of the blowing gas to the amt. of the molten steel to be passed through an immersion nozzle within a set range. CONSTITUTION:The total pressure of the molten steel in the gas blowing part is first determined from the depth of the molten the flow rate of the molten steel, etc., and the flow rate of the gas necessary for generating foam in the molten steel 3 acted with said total pressure is determined. The actual volume Vg(m<3>/sec) of the gas is then calculated from the flow rate of the gas and the then calculated from the flow rate of the gas and the diameter and number of gas blowing holes. The amt. Vl(m<3>/sec) of the molten steel to be passed through the nozzle is calculated from the inside diameter of the nozzle and the flow rate of the molten steel or width, thickness and drawing speed of the molten steel. The gas blowing rate is so controlled that the ratio Vg/Vl=R of the actual volume Vg of the blowing gas to the amt. Vl of the molten steel to be passed in the nozzle attains the predetermined set range. The ratio R is obtd. by the empirical equation.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for pouring molten steel in continuous casting, and more specifically, a method for removing impurities in the molten steel by blowing an inert gas into the molten steel flow during the process of pouring it into a mold. The present invention relates to a continuous casting method that produces high-quality slabs by pouring while preventing nozzle clogging and the like.

[Conventional technology]

As is well known, in continuous steel casting, molten steel transported in a ladle is usually stored in a tundish and then injected into the mold from the tundish through an immersion nozzle (hereinafter simply referred to as the nozzle). It is.

At this time, the molten steel contains deoxidation products such as A (1203), or impurities such as powder, slag, and sulfide (hereinafter collectively referred to as inclusions), and these inclusions are When the inclusions are captured and remain as inclusions, various problems occur such as surface scratches and internal defects called slag slag.Also, among the inclusions, A7!203 etc. are trapped when passing through the nozzle. It often adheres and accumulates on the inner surface of the nozzle, clogging the nozzle and interfering with stable operation.

For this reason, methods have been proposed to efficiently separate the inclusions from molten steel and float them, and methods to capture the floated inclusions with powder supplied into the mold, and some of them have not been put into practical use. It has become so. For example, Japanese Patent Publication No. 49-28569 discloses a technique in which the inclusions are effectively floated by blowing an inert gas such as Ar gas or N2 gas into the molten steel flow in the process of being poured into the mold. It has been widely adopted in recent years.

Further, Japanese Utility Model Publication No. 56-48440 proposes a nozzle for further enhancing the effect of blowing the inert gas.

However, in order to enhance the floating effect of inclusions and prevent nozzle clogging by blowing the inert gas,
Often accompanied by operational difficulties.

In other words, if the amount of inert gas blown exceeds a certain amount, the flow rate of the inert gas becomes unstable, the molten metal level in the mold is greatly disturbed, and a phenomenon called boiling occurs, in which the molten steel no longer flows into the nozzle. It starts to occur. In extreme cases, such a boil phenomenon may lead to a breakout. For this reason, conventionally, based on past experience, it has been common for operators to operate while constantly monitoring the state of the mold surface in order to inject gas in an area where the boiling phenomenon does not occur. However, especially when there are variations in the depth of molten steel in the tundish, casting speed, etc., or when changing the casting width, it is difficult for the operator to make appropriate adjustments and control based on his/her judgment, and the boiling phenomenon described above frequently occurs. .

On the other hand, for the purpose of reducing manufacturing costs, attempts have been made to reduce the amount of inert gas blown into the steel, depending on the type of steel, to reduce its consumption. However, with conventional methods, there was no way to quantitatively understand this, so workers could visually check the
It is common practice to judge the blowing status, and as a result, the amount of blown gas becomes too small, causing nozzle clogging, making stable operation difficult.

[Problem that the invention seeks to solve]

As mentioned above, the setting and control of the inert gas injection amount in conventional methods relies on the operator's experience and intuition. There was no attempt to quantitatively understand blowing and apply it to actual operations. For this reason, it is difficult to control the amount of inert gas blown to accurately follow changes in operating conditions such as steel type, size, casting speed, and depth of molten steel in the tundish. The amount of inert gas blown tends to be too small due to concerns about major problems such as breakouts. As a result, inclusions are not removed sufficiently and the number of inclusions remaining in the slab increases, leading to unstable slab quality and, as mentioned above, operational troubles due to nozzle clogging. was occurring.

Particularly for steel types such as tinplate materials and thin plate materials for which severe requirements are placed on quality, the residual inclusions have been a major problem even if the boiling phenomenon does not occur.

Therefore, in order to avoid boiling and nozzle clogging, and to stabilize quality, operators must constantly monitor the situation under high temperatures, which places an extremely heavy mental and physical burden on them.

The present invention aims to solve the above-mentioned conventional problems in the inert gas blowing method when pouring molten steel, and it is possible to accurately follow the fluctuations in the operating conditions without causing boiling phenomenon, and to achieve an economical method. The purpose of the present invention is to provide a method for ensuring the optimum amount of blowing to obtain the quality required for casting, thereby improving the quality of slabs and preventing nozzle clogging.

[Means for solving problems]

FIG. 1 is a structural diagram showing a casting part in a general continuous casting equipment, and in the figure, 1 is a ladle and 2 is a tundish. Molten w43 once stored in Tanditshu 2
is injected into the mold 5 through a submerged nozzle 4. The nozzle 4 of this embodiment includes an upper nozzle 41 attached to the bottom wall of the tundish 2, a sliding nozzle 42 attached to the bottom of the tundish 2 in contact with the upper nozzle 41, and a movable plate of the sliding nozzle 42 integrally formed. It consists of an attached injection nozzle 43. Reference numeral 6 denotes a gas supply system, the tip of which is connected to the upper nozzle 41, through which gas is blown into the molten steel flow.

In the present invention, the molten m3 stored in the tundish 2 is injected into the mold 5 through the nozzle 4 while blowing an inert gas into the molten steel flowing down the nozzle 4 (hereinafter referred to as molten tA flow). In the injection of molten steel 3 in continuous casting, the actual volume V of the blown gas with respect to the amount of molten steel passing through the nozzle 4 Vβ (m3/sec) during the molten steel injection
g (m3/5ee) ratio V g / V j!
The present invention relates to a molten steel injection method in which the amount of gas blown is controlled so that R is within a predetermined setting range.

The present invention also relates to the above molten steel injection method in which the ratio R is set and controlled at the minimum total pressure portion of the nozzle 4.

In order to evaluate the quality of slabs, the number of platters per unit area obtained by observing the sulfur prints on slabs can be used as a guideline, as described below.
Further, in the present invention, the correlation between the actual volume of the blown gas and the number of blank spots per unit cross-sectional area of the slab is determined in advance, the allowable range of the number of black spots is determined for each steel type, and then the operating conditions are The present invention relates to a molten steel injection method in which an amount of blown gas at which the number of black spots falls within the allowable range is determined, and the ratio R is set and controlled from the amount of gas.

[For production]

As is well known, the inert gas (hereinafter referred to as gas) blown from the upper nozzle 41 forms fine bubbles and mixes into the molten steel, traps inclusions in the molten steel, and floats to the surface. As a result, inclusions are removed from the molten steel, improving the quality of the manufactured slab. Therefore, in order to promote the effect of removing inclusions by the gas, it is necessary for the blown gas to form fine bubbles of a spherical shape or a shape similar to it, and to mix evenly into the molten steel (hereinafter referred to as healthy bubbles). ). For this purpose, the gas pressure injected into the molten steel is calculated by the total pressure of the molten steel at the injection section (total pressure is the sum of the dynamic pressure due to the molten steel flow, the static pressure due to the molten steel bed, and the atmospheric pressure).
It is extremely important to increase the pressure by a predetermined pressure.

The inventors of the present invention repeatedly conducted various experiments and research in actual operation in order to obtain the above-mentioned healthy bubbles. As a result, when the amount of blown gas is expressed as the actual volume (hereinafter referred to as the actual volume) Vg under the pressure and temperature at the time of injection, the amount of molten steel passing through, that is, the amount of molten steel passing through, as shown in equation (1) below. We have found that this problem can be effectively solved by appropriately controlling the gas amount.

Vg/vβ=R...(1) However, Vg: Actual volume of blown gas (m3/sec)■
7! : Amount of molten steel passing through (volume of molten steel passing through m37sec) In other words, the actual volume of the gas is determined by calculating the total pressure of molten steel at the gas injection part from the depth of molten steel in the tundish, the inner diameter of the nozzle, the flow rate of molten steel, etc. Find the gas flow rate necessary to generate bubbles in the molten steel, and then calculate the following (2) from this gas flow rate, the gas blowing hole diameter (hereinafter referred to as the porous diameter), and the number of gas blowing holes.
It can be obtained as shown in the formula.

V g = tJA, x (π/4)d2 ×n ・
...(2) However, UAriAr law speed (m/sec) d;
Inner diameter of the nozzle (m) n: The number of gas injection holes and the amount of molten steel passing through are determined by the following formula (3) from the inner diameter of the nozzle, the flow rate of molten steel, or the width, thickness, and drawing speed of the slab to be produced. You can ask for it.

V 1 = U, Lx S = WX D X V c
−=(3) However, Usti nozzle flow rate of molten steel (m
/ 5ec) S: Nozzle opening (cross-sectional area) (d) W: Width of slab (m) D: Thickness of slab (m) c: Slab drawing speed (m/sec) Figure 2 shows the above It is a diagram showing the correlation between the actual gas volume Vg for obtaining healthy bubbles and the amount of passed molten steel v1, in which the vertical axis shows the actual gas volume Vg and the horizontal axis shows the amount of passed molten steel VX. The solid line is the lower limit necessary for the gas pressure to overcome the total pressure of molten steel and obtain healthy bubbles, and if the actual gas volume Vg is equal to or higher than the solid line 4, healthy bubbles can be stably obtained. The solid line m indicates the amount of gas required to prevent nozzle clogging, and the solid line l indicates the elapsed time from the start of nozzle use (cumulative casting time) and the amount of precipitation of inclusions such as A n 203. It is an amount that takes into account a correction coefficient that is empirically set from the relationship, and for example, if the slab drawing speed VC is 1.6 on average.
m/min, slab width W of 580 to 1350 fins, slab thickness D of 250 fins, tundish capacity of 60 ton, and curved slab continuous casting equipment equipped with a sliding nozzle, the equation (4) below is obtained.

Vm=Vn (1+t/4xl O')...(
4) ■n; Gas amount required for healthy bubble generation (m3/sec
)t: Cumulative casting time (sec) As can be seen from FIG. 2, there is a close relationship between the actual gas volume VgO ratio R and the amount of molten steel passing through vp.

On the other hand, when gas is blown into the molten steel flow in the nozzle, as the amount of gas blown increases, the buoyancy increases, making it difficult for the molten steel to flow smoothly, and when this exceeds a certain limit, it stops the molten steel from flowing down. Molten steel stops flowing downward,
Alternatively, the flow will be intermittent, and once this phenomenon occurs, the pressure in the molten steel flow will drop rapidly, and the gas in the gas supply system will flow into the molten steel flow all at once, and the above phenomenon will become more intense, resulting in the boiling phenomenon. .

The present inventors focused on the relationship between the actual volume of gas at the time of boiling generation and the amount of passed molten steel in the injection of molten steel in the continuous casting equipment, and as a result of a follow-up investigation, it was found that 11 VIl of passed molten steel It has been found that there is a close relationship between the ratio Vg/Vp=R of the actual gas volume Vg.

The solid line X in FIG. 2 shows the ratio R determined from the boiling limit, and if it is below the solid line X, no boiling phenomenon will occur, so the solid line X is almost the limit at which the maximum gas injection amount can be ensured. be. In this case the ratio R
A specific formula can be expressed by the following formula (5), for example, based on the experimental results of the curved slab continuous casting equipment.

Vg=0.0267xVA+5.3xlO-5R=Vg
/VA −(5,3×IO−′/ (II−D −Vc)) +
0.0267...(5) Therefore, by controlling the gas amount with respect to the amount of molten steel passing through at the time so that R is in the range between the nozzle clogging limit indicated by the solid line m and the boiling limit indicated by X, the operating conditions can be adjusted. It is possible to accurately follow fluctuations in gas flow, prevent boiling, and effectively obtain the required quality with an economical amount of gas. In addition, as the casting time becomes longer, (boiling limit
Although it is conceivable that an operating range may occur where the nozzle clogging limit (m) is reached, in such a case, it is desirable to control the temperature below the boiling limit (X) where operational troubles are greater. In other words, it is preferable to control using the smaller ratio R of the boil limit X and the nozzle clogging limit m.

By the way, as will be described later, the ratio R is the part where the total pressure in the nozzle is the lowest when the molten steel is injected, where the gas volume is maximum and the volume relationship with the molten steel is greatly influenced, that is, the minimum total pressure part referred to in the present invention. Therefore, it is effective to control the air flow with particularly high accuracy (it can be set and based on it).

Note that the Vg, VA, and R at the minimum total pressure portion are hereinafter expressed as Vog, VoIl, and Ro.

Figure 3 shows the boil generation situation in actual operation, the amount of molten steel passing through the minimum total pressure area ■0! 2 is a chart showing an example of the results of an investigation based on the relationship between Vog and actual gas volume Vog. In the figure, the vertical axis represents the actual gas volume Vog, and the horizontal axis represents the amount of passed molten steel vOl, the ○ mark indicates a normal case without boiling, and the X mark indicates boiling. In this example, the straight line a
shows the relationship: Vog=0.029 ・Voi247)
m ”?: ;jo This is almost the limit at which the maximum gas injection amount can be secured without causing reboiling.

Therefore, the ratio PO, ie, V o g /V o 14, was 29/1000. Therefore, the said RO is 29/10
It has been found that if the gas amount is controlled according to the operating conditions so that it falls within the range of 0.00 or less, the maximum flow rate can be ensured without causing boiling.

Next, a specific method of controlling the gas flow rate to the predetermined ratio R will be described.

In actual operation, the flow rate adjustment device system (for example, the flow rate adjustment valve 60 shown in FIG. 1) of the gas supply system 6 has a volume under standard temperature and standard pressure (0° C., latm) (with respect to the actual volume as follows: Since it is necessary to control the actual volume using the standard volume, the pressure and temperature are corrected using the following equation (6).

Vng-(P/Po)X(273/T)XVg...
・(6) However, Vng; standard volume of gas (Nm'/5
6c) PO: Atmospheric pressure (10336 kg/m) P: Gas pressure (kg/I) T: Gas temperature (K) Vg: Actual volume of gas (m'/sec) Note that changes in molten steel temperature are usually small, and The effect of change is extremely small compared to the effect of pressure change. Therefore, in actual operation, it is sufficient to ignore changes in molten steel temperature and correct only pressure changes. In this case, the actual volume does not take into account expansion due to molten steel temperature,
It is treated as the volume at standard temperature.

The total pressure of the molten steel flow varies greatly from the upper nozzle 41 of the nozzle 4 to the lower end of the injection nozzle 43 located in the mold 5, but the location that has a large effect on the occurrence of the boiling phenomenon is the location where the pressure is lowest. Become. One possible method for determining the pressure at the minimum total pressure area is to install a pressure detection device at the minimum total pressure area and directly detect it, but it is difficult to detect it at a location where extremely high temperature molten steel flows down while pulsating. There are many limitations, and it is difficult to expect highly accurate measurements. For example, it may be calculated using the well-known Bernoulli equation as shown in equation (7) below.

P = (Po + p・H-(%)-(ρ/g
)・(Ust/ に)”−Δp) N
...(7) However, FI: Distance from the gas injection part to the molten metal surface in the tundish (molten steel head m) g: Acceleration of gravity (m/sec"); Flow velocity resistance ρ: Specific gravity of molten steel (kg/m1) Δp; Pressure loss in the nozzle (kg/n ()N; Index (The index N in Equation 71 is 1 under ideal conditions, but in actual operation, it depends on the distance from the gas injection position to the meniscus, the actual inner diameter of the nozzle, An error often occurs between the calculated total pressure and the actually measured total pressure due to the flow rate of molten steel, etc. In such cases, the error can be eliminated by adjusting the index N. For example: The distance from the gas injection position to the meniscus is 500m.
m, and when the nozzle inner diameter is 110 fins, by setting the index N to 2, the actual gas volume calculated by the above equation (7) and the above equation (6) based on this equation (7) can be calculated from the calculation. The value obtained is very close to the value experimentally measured off-line, etc., and it was confirmed that there is no problem in practical use of equation (7).

As a result of the above, the optimal gas amount during operation can be determined if the flow velocity of the molten steel flow at the smallest cross-sectional area in the molten steel head H and nozzle during continuous casting, that is, the most constricted part, can be determined. The molten steel head H is determined by, for example, detecting the weight of molten steel in the tundish 2 and calculating from a correlation between the molten steel weight in the tundish and the depth of molten steel in the tundish, which has been determined in advance, or by optical or electrical level detection. It can be determined by adding the molten steel depth inside the tundish, which was found by calculating the deviation from the reference level using a device, and the distance from the bottom surface of the tundish to the gas injection part. on the other hand,
It is not easy to detect the flow velocity at the most constricted portion, and current measurement techniques have extremely low accuracy. Therefore, the amount of molten steel flowing down the nozzle can be detected directly using, for example, a non-contact flowmeter, or indirectly from the width, thickness, and drawing speed of the slab, and at the same time, the amount of molten steel flowing down the nozzle can be detected directly using a non-contact flow meter, or indirectly from the width, thickness, and drawing speed of the slab. It is effective to calculate the flow velocity from the actual cross-sectional area (the actual cross-sectional area is the nozzle opening multiplied by the contraction coefficient, etc.).

In FIG. 1, 7 is a speed detection device for the slab 8;
The drawing speed can be detected from the slab movement speed. 9 is a weight detection device for detecting the weight of the tanditsh 2 mentioned above;
61 is a gas flow rate system.

Further, 10 is an arithmetic and control device, and the speed detection device 7,
The above-mentioned R, Ro and the gas amount based thereon are calculated based on the detection signal of the weight detection device 9 and other data input in advance, and a flow rate control signal is issued to the gas supply system.

As a result of the above, it is possible to quantitatively understand the limit of gas injection amount at which the boiling phenomenon occurs as a function of factors such as casting speed, molten steel depth, and slab size. It became possible to control gas blowing. In actual operation, it is also possible to control the gas amount without boiling by using the approximate equation shown in the following equation (8), which was obtained through experiments by combining the above equations (5) to (7).

Vng=H”'・(0,0267・WD−Vc+5
．． 3X10-')...(8) On the other hand, as mentioned above, for steel types with strict quality where internal defects such as slag bite are a problem, the ratio R is calculated from the boil limit and nozzle clogging limit. There is a problem with setting only.

Figure 4 shows the number of black spots detected by the sulfur printing method and the number of inclusions, A j22
It is a chart showing an example of the results of investigating the relationship between the residual amount of the 03 cluster and the amount of slag chewing. Black spots are gas bubbles blown into molten steel that are taken into the slab, and these appear as black spots due to the sulfur print.As the amount of gas increases, the number of black spots increases, and vice versa. As the amount of gas decreases, the number of black spots also decreases. The example shown in FIG. 4 is the amount per 1250 csM (50 cm x 25 cm) of the slab cross section. As can be seen from Figure 4, there is a close relationship between the number of black spots per unit cross-sectional area, the type of inclusions, and the amount of inclusions remaining in the slab. As the number decreases, the score of the A6203 cluster increases.

In addition, in the above-mentioned steel types with strict quality, the allowable amount of inclusions is determined based on past experience so that, depending on the steel type, for example, the he β203 cluster score is below the value and the slag bite score is also below the value. Therefore, the allowable range of the number of black spots for keeping the inclusions below a predetermined allowable amount can also be determined for each steel type. Based on this knowledge, the present inventors conducted research on the relationship between the number of black spots and the amount of gas. As a result, both have the following (
It was found that the relational expression shown in equation 9) holds true.

BSM=β(α・Dg3・Vg−Vc)...(
9) However, BSM, number of black spots (pcs/1250
cJ) Dg: Gas bubble diameter (m) at the injection site ■g
Actual volume of gas (m″/sec) VC: Slab drawing speed (m/5ec) β; Proportionality constant α: Constant determined from porous pore diameter, molten steel viscosity, etc. 1.6m/
The actual number of blank spots on the slab when manufactured under various operating conditions with 1Ilin and molten steel head H of 1.2m and varying the amount of gas (in this example, argon gas is used),
It expresses the correlation with the number obtained by calculation based on the above formula (9), where α is the porous pore diameter, molten steel viscosity, and 3
×1O10, and β was 3.0.

As is clear from Fig. 5, by determining β and α for each steel type, the number of black spots that occur in actual operation can be accurately estimated from the gas amount and slab drawing speed based on equation (9) above. It is possible to do so.

Therefore, the slab withdrawal speed Vc during the relevant operation,
When the gas bubble diameter Dg is determined from the blown gas pressure, etc., the actual gas volume Vg for obtaining a predetermined number of blank spots is determined, and the ratio R to the amount of passed molten steel can be accurately set and controlled.

As described above, the optimum ratio rs is set according to the operating conditions, the slab size, casting speed, molten copper head, etc. are detected during actual operation, and the gas is adjusted so that the ratio R is achieved according to the detected values. By controlling the amount, slabs of desired quality can be efficiently produced without causing the boiling phenomenon. If the arithmetic and control device 10 shown in FIG. 1 is configured to have the functions as shown in the block diagram of FIG. 6, for example, it will be possible to automatically control the gas amount from the setting of the ratio R described above. is also possible.

That is, in FIG. 6, 101 is an input section for inputting predetermined operating conditions, a molten steel head in operation, a slab drawing speed, etc. as necessary. 102 is an R setting section;
The ratio R is calculated according to a predetermined method according to the operating conditions, boil limit, nozzle clogging limit, quality optimum value, etc. manually entered from the input section 101, and its range is set. 103 is R
A setting pattern selection section selects the optimum R under the operating conditions from the setting range of the ratio R described above according to the operating conditions from the input section 101, the setting location of the ratio R, the steel type, etc.
Select a setting pattern. Reference numeral 104 denotes a gas amount calculation section, which is detected from time to time during operation and is calculated by the R setting pattern selection section 103 based on information such as the slab speed, the molten steel head, the slab size, and the nozzle diameter that are manually input. Calculate the standard gas amount to achieve the selected ratio R. The results of the calculation unit 104 are input to the control unit 105, and the control unit 105 issues control commands to the flow rate regulating valve 60 and the like, thereby automatically controlling the gas amount.

In this way, the ratio R of gas amount and molten steel flow rate is determined by the boiling limit, nozzle clogging limit, and blank bot number (slab quality).
The actual gas amount control is determined by
Relationships with fewer quality problems can be selected and controlled.

〔Example〕

Example 1 In the curved slab continuous casting equipment of 5,000 tons/day,
The present invention was carried out when producing aluminum semi-killed steel for a section steel with a thickness of 250 fl and a width of 1200 fl.

The operating conditions in this example are as shown in Table 1,
Since nozzle clogging tends to occur frequently with this steel type, the boiling limit was used as an indicator for operation.

Therefore, the ratio R is set in advance from the boiling limit (25/10
00).

Table 1 Figure 7 shows a control chart under the above operating conditions, where the solid line indicates the depth of molten steel in the tundish, the solid line C indicates the gas pressure, and the solid line f indicates the amount of molten steel passing through. The fI is changing.

f2. f3 represents width change. the molten steel depth;
In response to changes in the gas pressure and the amount of molten steel passing through, the gas amount was controlled as indicated by the solid line e in order to bring the ratio R closer to (25/1000). As a result, there were no breakouts, and nozzle clogging and quality deterioration were significantly reduced. In contrast, with the conventional method of controlling the gas amount based on the operator's judgment, the gas amount fluctuated significantly not only due to changes in the molten steel depth but also during regular operation, resulting in variations in quality and frequent breakouts. .

A and B in FIG. 8 are based on the above-mentioned present invention. 20: An example of the results of a survey on the number of l clusters is shown in comparison.

As is clear from FIG. 8, it has been confirmed that the implementation of the present invention can significantly reduce nozzle clogging and improve quality.

Example 2゜Example 1. 250mmJ in the same continuous casting equipment!
JX ] The present invention was carried out when manufacturing tinplate material with a width of 20 Ovsm. In this tinplate material, the number of black spots is 2/Cl11, which is an acceptable range in terms of quality.

Therefore, from equation (9) above, the gas amount is 9ρ/min/l-s
is required, and the ratio R in this operation is 19/1000
was set. Next, as a result of operating while controlling the gas amount so that the ratio was 19/1000, the variation in the number of black spots in the manufactured slabs was extremely small.
As shown in FIG. 9, the quality was within the acceptable range. On the other hand, in the conventional method, there was a large variation as shown by the dotted line in FIG. 9, and many slabs were produced that were outside the above-mentioned tolerance range, resulting in a large number of inferior quality materials.

〔Effect of the invention〕

As described in detail above, by carrying out the present invention, it has become possible to accurately control the amount of inert gas blown during injection of molten steel in response to momentary changes in operation.

As a result, we were able to improve the quality of slabs and significantly reduce nozzle clogging.

[Brief explanation of drawings]

Fig. 1 is a structural diagram showing an example of implementing the present invention in general continuous casting equipment, Fig. 2 shows boiling limit, sound bubble generation limit,
Figure 3 shows an example of the correlation between the amount of molten steel passing through and the actual volume of gas when determining the generation limit of slag formation. A chart showing an example of the results of investigation based on the relationship, Figure 4 shows the number of black spots in manufactured slabs and AI! A chart showing the correlation between the 203 class and the amount of slag bite. Fig. 5 is a chart showing the correlation between the number of blank slats actually generated in the slab and the number calculated by calculation. Fig. 6 shows the function of the arithmetic and control unit. The block diagram, FIG. 7 is a chart 1 diagram showing an embodiment of the control chart based on the present invention, and FIG. 8 is the block diagram based on the present invention shown in FIG.
Nozzle clogging occurrence situation in the example and conventional control method (
Figure 8A is a chart comparing the number of inclusions remaining in the product (Figure 8B), and Figure 9 is based on the present invention. This is a diagram showing the following. 1; Ladle, 2; Tundish, 3; Container steel, 4; Immersion nozzle, 41; Upper nozzle, 42; Sliding nozzle, 43: Injection nozzle, 5; Mold, 6; Gas supply system, 60
Flow rate control valve, 7; Speed detection device, 8; Slab, 9; Weight detection device, 10; Arithmetic control device, 101; Input section,
102; R setting pattern selection section, 103; R setting section, 104; gas amount calculation section, 105; control section.

Claims (1)

[Claims] (1) A molten steel injection method in continuous casting in which molten steel stored in a tundish is injected into a mold through a submerged nozzle while blowing inert gas into the molten steel flow, wherein: The amount of gas blown is adjusted so that the ratio Vg/Vl=R of the actual volume of blown gas Vg (m^3/sec) to the amount of molten steel passing through the nozzle Vl (m^3/sec) falls within a predetermined setting range. (2) A method for injecting molten steel in continuous casting, characterized in that the ratio R is set and controlled at a minimum total pressure portion of the nozzle. Method for injecting molten steel in casting (3) In advance, determine the correlation between the actual volume of the blown gas and the number of black spots per unit cross-sectional area of the slab, determine the allowable range of the number of black spots for each steel type, and then molten steel in continuous casting according to claim 1, wherein the amount of blown gas at which the number of black spots falls within the allowable range is determined according to the operating conditions, and the ratio R is set and controlled from the amount of gas. Injection method