KR100899689B1 - Discharge amount control method of upper flow nozzle - Google Patents

Abstract

According to the present invention, the amount of discharge of a rotary flow upper nozzle for controlling the opening degree of a slide gate is detected by measuring the surface level of the playing mold, measuring the argon back end pressure of the tundish upper nozzle, calculating the required opening amount of the slide gate to meet the target level. A control method, comprising the steps of: detecting a level of water level of a playing mold (3) by a level of water level detector (ECLM) provided at an upper end of the playing mold (3); When the detected water level is low or high with respect to the target level, the degree of opening of the slide gate 5 for the last few seconds from the movement information of the slide gate 5 for the last few seconds does not cause an amount of change in the water level. Determining whether the increase or decrease is repeated; If it is determined that the opening degree of the slide gate 5 is repeatedly increased or decreased within the range which does not cause the amount of change in the water level, the opening degree of the slide gate 5 is not changed, and the slide is made for the last few seconds. If the opening degree of the gate 5 is not judged to have been repeatedly increased or decreased within a range that does not cause the amount of change in the surface level, the required opening amount of the slide gate 5 for adjusting the target level is calculated and the slide gate 5 It provides a method for controlling the discharge amount of the upper flow nozzle of the rotary flow, characterized in that it comprises a step of opening.

Tundish, playing mold, level of water, eccentric slot nozzle, slide gate, upper nozzle

Description

TECHNICAL FOR CONTROLLING THE QUANTITY OF MOLTEN STEEL DISCHARGED THROUGH SWIRL TYPE UPPER NOZZLE}

1 is a schematic diagram of a typical continuous casting process;

2 is a schematic view of the nozzle clogging in the tundish upper nozzle area;

3 is a flow chart illustrating a flow control method of a conventional tundish upper nozzle;

Figure 4 is a cross-sectional view of the rotary flow upper nozzle to which the present invention is applied;

5 is a schematic diagram illustrating the presence and absence of rotational flow of the upper flow nozzle of the rotary flow to which the present invention is applied;

Figure 6 is a graph showing the fluctuations of the surface of the water flow when the rotary flow upper nozzle to which the present invention is applied induces and does not rotate.

FIG. 7 is a graph showing the surface fluctuation amplification and attenuation by interlocking the surface level of the tundish with the slide gate; FIG.

8 is a flowchart illustrating a method of controlling the discharge amount of the upper rotary nozzle according to the present invention.

♣ Explanation of symbols for main part of drawing ♣

1: Radar 2: Tundish 3: Performance Mold 4: Submerged Nozzle 5: Slide Gate

6: Upper nozzle 20: Eccentric slot nozzle 25: Elevation level detector (ECLM)                 

26: Argon post pressure

The present invention relates to a method for controlling the discharge amount of the upper flow nozzle of the rotary flow, and more particularly, the amount of the required opening amount of the slide gate for detecting the water level of the playing mold, and measuring the argon rear end pressure of the tundish upper nozzle to meet the target level. It relates to a discharge amount control method of the upper flow nozzle of the rotary flow to control the opening degree of the slide gate by calculating the.

In general, as shown in FIG. 1, in the continuous casting process, the molten steel 7 is injected from the ladle 1 through the tundish 2 into the playing mold 3 and is primarily formed in the playing mold 3. The molten steel 7 is solidified by cooling and continued cooling in the secondary cooling zone to produce the cast steel 7a.

FIG. 2 is an enlarged view of the upper nozzle of the tundish 2 shown in FIG. 1, and interpolates between upper and lower wall blocks (Well Blocks 8a and 8b) between the immersion nozzles 4 at the bottom of the tundish 2. Type or extrapolated upper nozzle 6 is installed, and the lower portion of the lower nozzle is composed of an upper plate 12, an intermediate plate 14, and a lower plate 15. (16) and immersion nozzle (4).

When the molten steel 7 moves from the tundish 2 to the playing mold 3, nonmetallic inclusions in the molten steel 7 adhere to the refractory inner wall, causing the nozzle clogging phenomenon 13 as shown in FIG.                         

The nozzle clogging phenomenon 13 mainly occurs in the upper nozzle 6 region, the slide gate 5 region, and the immersion nozzle 4 of the upper and lower wall blocks 8a and 8b. When the nozzle clogging occurs, the nozzle 4, 5) It is difficult to secure the amount of molten steel to reach the target casting speed because the internal molten steel flow path is blocked.

When nozzle clogging occurs in the immersion nozzle 4, casting operation can be continued using a new nozzle by a method of quickly replacing the immersion nozzle 4 (GTC; Gate Tube Change). 6) When the nozzle clogging phenomenon 13 occurs in the area, it is necessary to drill the blocking layer 13 temporarily or stop casting by using a punching rod.

However, in the case where the blockage layer 13 is forcibly drilled by using the above-described perforated rod, a large amount of non-metallic inclusions are temporarily incorporated into the playing mold 3 as well as causing sudden fluctuation of the surface.

This phenomenon is the cause of linear defects occurring in the cast steel 7a to be cast. Therefore, it is important to suppress the nozzle clogging in the upper and lower wall blocks 8a and 8b and the upper nozzle 6 in order to secure productivity and suppress quality deterioration due to repeated clogging of nozzles / drills.

As described above, the conventional method used to suppress the nozzle clogging in the upper and lower wall blocks 8a and 8b and the upper nozzle 6 region is made of nitrogen or after forming the gas channel. 4 to 15 L / min of argon gas is blown.

In this way, the nozzle clogging can be considerably suppressed in the method of blowing nitrogen or argon gas into the upper nozzle 6 (as disclosed in Korean Patent Application Nos. 1999-10971, JP-A 2-307654, and EP0982088). have.

Another method is to generate a swirl flow during molten steel movement between the tundish 2 and the mold 3 (Korean Patent Application No. 195-26284) to suppress nozzle clogging.

In addition, in the case of adjusting the amount of molten steel using a stopper, a method of using a vortex rotational flow by a PCV (Precision Control Valve) method was proposed by Arba, Wolftechnology, Switzerland, and an RTV (Revolving Tube Value) method by Interstop Didier, Switzerland. .

As described in Korean Patent 2000-81899, 2000-67323, 2000-81899, 1999-28920, 2000-38702 and the like, the method of adjusting the water level is performed by reading the water level, casting speed, mold size, tundish weight and contents. The feedback rate of the slide gate for adjusting the target level is fed back and adjusted using the tundish level.

By introducing each of the above nozzle clogging suppression methods, conventionally, the flow rate of the tundish upper nozzle is controlled by the following method.

3 is a flowchart illustrating a flow control method of a conventional tundish upper nozzle.

FIG. 3 is a logic for detecting the surface level of the mold 3 and inducing driving of the slide gate 5 in a conventional manner, and the surface level of the mold 3 by the surface level detector ECLM 25. If the flow rate control is necessary because the water level is lower than or higher than the target level, the opening amount of the slide gate 5 for determining the target level is determined and the slide gate 5 is determined. Move it.

When adopting the conventional flow control method that proceeds in one direction as described above, a change in the level of the water level of the mold 3 immediately changes the opening degree of the slide gate 5, and when the level of the water surface exhibits a periodic amplitude, The slide gate 5 is operated to adjust the level, and the surface level fluctuation is increased by repetitive amplification such that the surface level is changed again by amplitude and the slide gate 5 is operated again.

In order to solve the above problems, the present invention is to install an eccentric slot nozzle on the upper nozzle to the top of the upper nozzle to cause the flow of molten steel in the tundish immersion nozzle, and at the same time detect the molten steel discharged from the playing mold from the upper nozzle SUMMARY OF THE INVENTION An object of the present invention is to provide a method for controlling the discharge amount of a rotary flow upper nozzle for controlling the amount of molten steel discharged from the upper nozzle by measuring the rear end pressure of the argon gas blown into and the opening degree of the sliding gate.

In order to achieve the above object, the present invention provides a method for controlling the molten steel discharge amount of the upper nozzle by detecting the level of the molten steel discharged to the playing mold through the eccentric slot nozzle installed in the upper nozzle of the tundish, Detecting a floor level of the playing mold by means of the installed floor level detector; When the detected hot water level is low or high with respect to the target level, the increase and decrease of the sliding gate 5 for the last few seconds from the movement information of the slide gate for the last few seconds does not cause a change in the water level. Judging whether or not; If it is determined that the opening degree of the slide gate is repeatedly increased or decreased within a range that does not cause the amount of change in the level of the water level, the opening degree of the slide gate is not changed, and the opening degree of the slide gate is measured for the last few seconds. If it is not determined that the increase and decrease is repeated within a range that does not cause a change in the level, calculating the necessary opening amount of the slide gate to meet the target level and opening the slide gate, characterized in that A method of controlling the discharge amount of a nozzle is provided.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Figure 4 is a cross-sectional view of the rotary flow upper nozzle to which the present invention is applied.

As illustrated in FIG. 2 described above, in order to suppress clogging of the upper nozzle 6 of the tundish 2, as illustrated in FIG. 4, a refractory material is formed at the bottom of the tundish 2. When the eccentric slot nozzle 20 is installed to induce the swirl flow 22 when the molten steel 7 moves between the tundish 2 and the mold 3, the molten steel 7 injected into the mold 3 is swirled. It has more momentum than if 22 did not occur.

That is, when the molten steel moves while the vortex rotational flow 22 is generated, more momentum energy must be given at the inlet side to secure the same flow rate through the passage having the same length and the inner diameter.

This surplus momentum energy is used as energy for maintaining the rotary flow 22 while moving through the passage, and loss due to friction with the wall. However, at the point just exiting the passage, the surplus momentum energy moves together with the momentum energy of the moving fluid, so that the kinetic energy of the fluid is very large, unlike when the vortex rotational flow 22 does not occur, and is tundish in the continuous casting process. If the molten steel moves while the molten steel moves between the (2) -molds (3), the molten steel exits the immersion nozzle (4) and is injected into the mold (3). In case it is not, the momentum is so large that it causes fluctuation of the surface.

Theoretically considering the above facts is as follows.

5 is a schematic diagram illustrating the relationship between the flow of the upper flow nozzle and the flow of the present invention to which the present invention is applied.

FIG. 5 shows the positions of the top 23 and the bottom 24 of the tundish 2 of the molten metal in order to analyze the relationship between the presence and the flow of the vortex rotational flow. Assuming the incompressible steady flow and using Bernoulli's theorem, the energy at the surface of the melt and the energy at the bottom of the melt are expressed by Equations (1) and (2).

-Total energy per unit volume on the melt surface (23)

= Potential energy + kinetic energy + work by pressure

---------------------------------------(1)

---------------------------------------(One)

-Total energy per unit volume at the outlet (24)

= Potential energy + kinetic energy + work by pressure + loss energy

---------------------------(2)

---------------------------(2)

Here, the loss energy Eloss at the outlet 24 represents energy dissipation of viscous resistance due to turbulence. Since the total energy is conserved, the energy of the fluid at the molten metal surface 23 and the energy of the fluid at the outlet 24 are the same, and can be written as in Equation (3).

------------(3)

------------ (3)

There is almost no velocity at the surface of the molten metal, and there is almost no difference between the pressure at the molten surface 23 and the pressure at the outlet port 24, so that it can be summarized as in Equation (4).

------------------------------(4)

------------------------------(4)

Equation (4) shows that the potential energy for the difference between the height of the upper part and the lower part is converted into the kinetic energy and the loss energy of the outlet port 24.

In the absence of rotational flow, the kinetic energy at the outlet 24 will be equal to the kinetic energy of the axial velocity, and thus can be written as follows.

-------(5)

------- (5)

In the case of the rotational flow 22, the kinetic energy at the outlet 24 is the sum of the kinetic energy of the axial velocity and the kinetic energy of the tangential velocity.

-------------------------------------------------- ------------------ (6)

The potential energy is the same both in the case of the rotational flow 22 and in the absence of the rotational flow 22.                     

-------------------------------------------------- ------------------ (7)

If the kinetic energy of the axial speed when there is the rotational flow 22 on the left side and the kinetic energy of the axial speed when there is no gathering are summarized, the following equations can be obtained.

-------------------------------------------------- ------------------(8)

-----------------------(9)

----------------------- (9)

----------------------(10)

---------------------- (10)

------------------------------(11)

------------------------------ (11)

When comparing the flow rates with and without the rotating flow 22

-------------------------------------------------- ----------------- (12)

---------------------------------------(13)

--------------------------------------- (13)

Therefore, when the molten steel height of the same tundish 2 is the same, it turns out that the flow volume in the case of the rotational flow 22 is never greater than the flow rate in the case of the absence of the rotational flow 22.                     

Therefore, in order to secure a flow rate suitable for the target casting speed using the same equipment, the opening ratio of the slide gate 5, which is a flow control device, must be increased.

This means that the potential energy due to the molten steel height of the tundish 2 is more effectively transmitted to the molten steel moving through the immersion nozzle 4. That is, when the opening ratio is increased, the molten steel exiting the immersion nozzle 4 and injected into the mold 3 retains the energy used to generate the vortex rotational flow 22 and the energy lost by the friction of the nozzle wall. It is moved into the mold 3.

This means that the hot water surface in the mold 3 is more oscillated in applying the technique of inducing the vortex rotational flow 22 to suppress the nozzle clogging phenomenon, such as the eccentric slot nozzle 20.

FIG. 6 is a graph showing the fluctuations of the surface of the water when the rotary flow upper nozzle to which the present invention is applied is induced or not.

In FIG. 6, when the eccentric slot nozzle 20 is applied to guide the vortex rotation flow 22 in the nozzle and otherwise, the fluctuation of the surface of the mold 3 is shown. The induced surface is larger in amplitude than the induced case. In addition, not only the amplitude is large, but also as shown in (B) of FIG. 6, the surface forms a wave having a constant period.

This periodic amplitude reinforces fluctuations in the water level. That is, when the hot water level is measured by the ECLM which detects the water level level at the highest point of the amplitude, the opening level of the slide gate 5 is closed, and when the lowest point of the amplitude, the ECLM is measured as the water level is lowered and the slide gate 5 is measured. Opening is more open.

While the average level of the water level remains the same, the increase and decrease is gradually increased by allowing the ECLM to sense the change in the water level and adjust the slide gate 5 by the periodic increase and decrease.

This phenomenon may be formed by a cycle induced by bulging or vortex rotational flow of the slab in the secondary cooling zone. The periodic vibration of the hot water surface induced by the bulging of the cast steel can be easily detected because it depends on the roll pitch of the secondary cooling zone, and this frequency is automatically filtered in the ECLM to allow the slide gate Adjustment is possible by disabling (5).

However, the period of the water surface fluctuation induced by the vortex rotational flow 22 may include the length of the immersion nozzle 4, the strength of the vortex rotational flow 22, the amount of argon, the discharge angle of the immersion nozzle 4, and the immersion nozzle 4. Because it depends on the operating conditions such as the depth of immersion and tungsten molten steel level, it does not always have the characteristics induced by constant equipment conditions such as bulging of cast steel. Therefore, in this case, the water level should be controlled using other information.

FIG. 7 is a graph illustrating the surface fluctuation amplification and attenuation due to the interlocking of the tumble level and the slide gate.

As shown in FIG. 7, it can be seen that as the casting proceeds, the fluctuation amount of the hot water surface is gradually amplified, and the opening degree of the slide gate 5 is also fluctuating together.

Section 'A' of FIG. 7 is a section in which the operator manually operates the slide gate 5 to maintain the level of water level. When switching to the automatic operation of adjusting the slide gate 5 by detecting the surface level by the ECLM (depth level detector) again, it can be seen that the surface level fluctuation disappears rapidly and the opening of the slide gate is also stabilized.

At this time, since all other conditions such as casting speed and immersion nozzle application conditions were constant, the suggestion in FIG. It can be confirmed that it is a phenomenon.

As a countermeasure, if the sensitivity of the slide gate system for adjusting the flow rate is driven by an average of several seconds or the like, the sensitivity is lowered, but side effects such as the inability to prepare a quick response during abnormal operation are caused.

Therefore, the operation logic of the slide gate 5 should be constructed in such a manner that the operation sensitivity of the slide gate 5 is maintained as it is and does not respond to periodic fluctuations in the water level.

8 is a flowchart illustrating a method of controlling the discharge amount of the upper rotary nozzle according to the present invention.

FIG. 8 is a logic for controlling the fluctuation of the surface of the water provided by the present invention. In the present invention, the level of the surface of the playing mold 3 is detected by the surface level detector (ECLM) 25, and then the surface of the surface of the target mold is measured. If the level is low or high, information about the argon back pressure 26 and the opening of the slide gate 5 of the upper nozzle 6 for a few seconds immediately before is judged, so that even if the water level is required to be changed, Do not change the opening degree of the slide gate 5 if the argon back pressure 26 has not changed for the last few seconds or if the opening and closing of the slide gate 5 is repeated in a range that does not cause the amount of change in the water level in the previous few seconds. Do not.

However, if the argon back end pressure 26 of the upper nozzle 6 has changed for a few seconds immediately before and the opening and closing of the slide gate 5 for the last few seconds does not increase or decrease within the range that does not cause a change in the water level, the target level is changed. The necessary opening amount of the slide gate 5 for fitting is calculated, and the slide gate 5 is opened.

In the case of moving with the vortex rotational flow 22, since the periodic amplitude is displayed on the surface of the mold 3, the rear stage pressure 26 of the argon blown into the upper nozzle 6 and the slide gate 5 as well as the surface of the mold 3 By using the movement information it is possible to detect a change in the level of the water.

That is, even if the level of the water level of the playing mold 3 rises, if the argon back pressure 26 is constant or if the variation of the slide gate 5 within the previous few seconds is not large enough to cause the amount of change in the level of detected water level, the slide gate 5 ) Is not working.

When the opening degree of the slide gate 5 is adjusted by the logic controlling the flow rate using the rear end pressure 26 of the blown argon and the movement information of the slide gate 5 within a few seconds immediately before, Even if an amplitude is generated, the slide gate can be prevented from interchanging due to its height.

As described above, the present invention measures the rear end pressure of the argon of the tundish upper nozzle and the movement information of the slide gate within a few seconds immediately before controlling the amount of molten steel discharged from the upper nozzle, so that the amplitude is maintained even if a periodic amplitude occurs on the hot water surface. Since the slide gate can be prevented from interchanging by the height, the stable molten steel can be supplied from the tundish into the playing mold, thereby improving the quality of the final cast.

Claims (1)

In the method for controlling the molten steel discharge amount of the upper nozzle 6 by detecting the level of the molten steel discharged to the playing mold (3) through the eccentric slot nozzle 20 installed in the upper nozzle (6) of the tundish (2), Detecting a floor level of the playing mold (3) by a surface level detector (ECLM) 25 provided at an upper end of the playing mold (3); When the detected water level is low or high with respect to the target level, the degree of opening of the slide gate 5 for the last few seconds from the movement information of the slide gate 5 for the last few seconds does not cause an amount of change in the water level. Determining whether the increase or decrease is repeated; If it is determined that the opening degree of the slide gate 5 is repeatedly increased or decreased within the range which does not cause the amount of change in the water level, for the last few seconds, the opening degree of the slide gate 5 is not changed. If the opening degree of the slide gate 5 is not judged to have been repeatedly increased or decreased within the range which does not cause the amount of change in the water level, the required opening amount of the slide gate 5 for adjusting the target level is calculated. And a step of opening the slide gate (5).

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