A method for slag entrapment prevention and replacement for submerged entry nozzle

Abstract

The application provides a slag roll-up prevention replacement method suitable for submerged nozzles, and is applied to a continuous casting machine with a set structure fixed submerged nozzle, and comprises the following steps: stopping adding protective slag into a crystallizer before nozzle replacement, reducing the pulling speed in stages according to the thickness of the protective slag, and exhausting the protective slag in the crystallizer when the second pulling speed is reached; maintaining the stopper opening degree, keeping the casting flow continuity, keeping the steel liquid surface in the crystallizer at a first liquid level based on the influence of the old nozzle volume on the liquid level safety height, and dismounting the old nozzle by top flow; keeping the steel liquid surface in the crystallizer at a second liquid level based on the influence of the new nozzle volume on the liquid level safety height, and installing the new nozzle by top flow; and adding the protective slag in stages after the new nozzle is installed, improving the pulling speed according to the thickness of the protective slag, and completing the nozzle replacement. The application solves the nozzle replacement problem under the condition that the crystallizer cross-section space is limited, avoids the slag roll-up leakage and the formation of the casting billet scar waste product caused by the casting flow break in the tundish, and improves the casting billet yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steelmaking, and particularly relates to a slag-rolling prevention replacement method suitable for submerged nozzles. BACKGROUND

[0002] Only one submerged nozzle can be accommodated in the crystallizer of a small square billet continuous casting machine, so that the nozzle replacement cannot adopt the slab nozzle quick replacement mechanism, and can only adopt the method of stopping casting flow, stopping the casting machine, disassembling the old nozzle, installing the new nozzle, and then continuously casting to replace the nozzle, which causes the flow in the crystallizer to be interrupted and the casting blank to form a scab defect, and the scab blank is a waste product that can only be cut off; due to the existence of the protective slag in the crystallizer, the liquid level is greatly lifted and lowered during the nozzle replacement, slag is clamped, and the risk of leakage is increased; and the long time of stopping the casting flow of the tundish also causes the upper nozzle to freeze and stop casting.

[0003] Therefore, it is necessary to provide a nozzle replacement method which can keep the casting flow continuous, does not produce scab blank, and can prevent slag rolling. SUMMARY

[0004] According to the above technical problems, a slag-rolling prevention replacement method suitable for submerged nozzles is provided. The present application mainly solves the problem of nozzle replacement under the condition that the cross-sectional space of the crystallizer such as small square billet is limited, realizes high-quality nozzle replacement, avoids slag rolling and leakage, eliminates the scab waste product of the casting blank formed by the interruption of the casting flow of the tundish, and improves the yield of the casting blank.

[0005] The technical means adopted by the present application are as follows:

[0006] A slag-rolling prevention replacement method suitable for submerged nozzles is applied to a continuous casting machine with a set structure fixed submerged nozzle, and comprises the following steps:

[0007] Before the nozzle replacement, the protective slag is stopped from being added to the crystallizer, the casting speed is reduced in stages according to the thickness of the protective slag, and the protective slag in the crystallizer is exhausted when the lowest safe casting speed is reached;

[0008] The stopper opening degree is maintained to keep the casting flow continuous, the liquid level in the crystallizer is kept at a first liquid level based on the influence of the volume of the old nozzle on the safe height of the liquid level, and the old nozzle is disassembled in top flow;

[0009] The liquid level in the crystallizer is stabilized at a second liquid level based on the influence of the volume of the new nozzle on the safe height of the liquid level, and the new nozzle is installed in top flow;

[0010] After the installation of the new nozzle is completed, the protective slag is added in stages, the casting speed is increased according to the thickness of the protective slag, and the nozzle replacement is completed.

[0011] Further, the casting speed is reduced in stages according to the thickness of the protective slag, and specifically comprises the following steps:

[0012] At a standard working pulling speed, stop adding the protective slag into the crystallizer before the nozzle is replaced; when the thickness of the protective slag is consumed to a first slag thickness H1, start the first stage of reducing the pulling speed; when the pulling speed is reduced to a first pulling speed, stop the speed reduction, consume the slag, and when the thickness of the protective slag is consumed to a second slag thickness H2, start the second stage of reducing the pulling speed, and reduce the pulling speed to a second pulling speed;

[0013] The first stage of reducing the pulling speed adopts a first speed rate, and the second stage of reducing the pulling speed adopts a second speed rate.

[0014] The first stage of reducing the pulling speed adopts a first speed rate, and the second stage of reducing the pulling speed adopts a second speed rate; the first speed rate means that the pulling speed is reduced or increased at a frequency of 0.05 m / min per 10 s, and the second speed rate means that the pulling speed is reduced or increased at a frequency of 0.10 m / min per 5 s.

[0015] Further, the maintaining of the stopper opening degree and the continuity of the casting flow specifically comprises:

[0016] When the pulling speed is reduced to the second pulling speed, the control mode of the stopper is switched from the automatic mode to the manual mode, and the opening degree of the stopper is maintained unchanged before and after the switching of the control mode.

[0017] The stopper is always in an open state, the continuity of the casting flow is maintained, and the casting blank has no rejoining process.

[0018] Further, the top flow of removing the old nozzle specifically comprises:

[0019] The liquid level control of the crystallizer is switched from the automatic mode to the manual mode, the liquid level is manually controlled, the molten steel surface in the crystallizer is maintained at a first liquid level based on the influence of the volume of the old nozzle on the safe height of the liquid level, and the removal of the old nozzle is completed in a state of continuous casting flow and no protective slag.

[0020] Further, the top flow of installing the new nozzle specifically comprises:

[0021] After the removal of the old nozzle is completed, the molten steel surface in the crystallizer is stably maintained at a second liquid level based on the influence of the volume of the new nozzle on the safe height of the liquid level, and the installation of the new nozzle is completed in a state of continuous casting flow and no protective slag.

[0022] Further, the protective slag is added in stages according to the pulling speed increasing with the thickness of the protective slag, and specifically comprises:

[0023] After the installation of the new nozzle is completed, the molten steel surface is manually controlled to be stably maintained in a third liquid level range, the liquid level control mode is switched from the manual mode to the automatic mode, a small amount of protective slag is added into the crystallizer, the thickness of the protective slag only meets the requirement that the molten steel surface in the crystallizer is not exposed, the first stage of increasing the pulling speed is started, and the pulling speed is increased to a first pulling speed.

[0024] After the first stage of increasing the casting speed, the thickness of the protective slag is recovered to the safe range, and the second stage of increasing the casting speed is started until the casting speed is increased to the standard working casting speed, and the water gap replacement is completed.

[0025] The second stage of increasing the casting speed uses the first rate of increasing the casting speed.

[0026] Further, the first casting speed can meet the minimum casting speed for the stability of the automatic control of the stopper and the long-time safe casting.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] The anti-entrainment slag replacement method for the submerged water gap provided by the present application comprises the following steps: stopping adding the protective slag into the crystallizer before the water gap replacement, decreasing the casting speed in stages according to the thickness of the protective slag, and exhausting the protective slag in the crystallizer when the minimum safe casting speed is reached; maintaining the opening of the stopper to keep the continuity of the casting flow, keeping the liquid level of the steel liquid in the crystallizer at a first liquid level based on the influence of the volume of the old water gap on the safe height of the liquid level, and removing the old water gap in the top flow; keeping the liquid level of the steel liquid in the crystallizer stable at a second liquid level based on the influence of the volume of the new water gap on the safe height of the liquid level, and installing the new water gap in the top flow; and adding the protective slag in stages after the installation of the new water gap is completed, and increasing the casting speed according to the thickness of the protective slag to complete the water gap replacement. The present application mainly solves the problem of water gap replacement under the condition that the space of the crystallizer such as the billet crystallizer is limited, realizes high-quality water gap replacement, avoids the entrainment slag leakage and eliminates the waste products of the billet caused by the broken flow of the tundish, and improves the yield of the billet.

[0029] The anti-entrainment slag replacement method for the submerged water gap provided by the present application keeps the casting flow continuous and the casting speed constant during the replacement of the water gap, so that the billet has no marks and the surface quality meets the requirements of rolling, and the billet does not need to be cut, thereby improving the yield of the billet; at the same time, the technical problem of slag leakage during the replacement of the water gap of the billet is safely solved; the method has good operability, small safety hazard to production, and does not increase the risk of freezing of the upper water gap.

[0030] Based on the above reasons, the present application can be widely popularized in the field of steelmaking. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating labor intensity.

[0032] Figure 1 Flow chart for the slag entrapment prevention replacement method for submerged nozzle in the present application.

[0033] Figure 2 Schematic diagram of the casting state of the continuous caster in the present application.

[0034] Figure 3 Open stream casting state for replacing the nozzle in the present application.

[0035] In the figure: 1, tundish; 2, tundish upper nozzle; 3, submerged nozzle; 4, molten steel surface; 5, crystallizer; 6, stopper; 7, molten steel in the tundish; 8, hook; 9, counterweight weight; 10, nozzle tongs; 11, protective slag; 12, open stream steel flow; 13, new nozzle; 14, molten steel; 15, billet shell. DETAILED DESCRIPTION

[0036] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0038] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, operation, device, component and / or combination thereof.

[0039] The foregoing is considered as merely illustrative of the principles of the application, and not in limitation thereof since modifications of the teachings of the present application will occur to those skilled in the art upon reading and understanding the description of the exemplary embodiments. Therefore, the scope of the application should be determined by the following claims, along with their full scope of equivalents, rather than by the embodiments described above.

[0040] In addition, it should be noted that the use of "first", "second", and the like, terminology merely to distinguish one identifiable element from another, and unless otherwise stated, the terms are not intended to indicate a special ranking of importance or a special preference. Thus, the terms are used merely to distinguish one element from another.

[0041] As shown in Figure 1 The present application provides a slag entrapment prevention method for submerged nozzle, which is applied to a continuous casting machine with a set structure fixed submerged nozzle, and comprises the following steps:

[0042] Before the nozzle is replaced, the protective slag is stopped from being added into the crystallizer, the casting speed is reduced in stages according to the thickness of the protective slag, and the protective slag in the crystallizer is consumed when the lowest safe casting speed is reached;

[0043] In the implementation, as an embodiment of the present application, the step of reducing the casting speed in stages according to the thickness of the protective slag specifically comprises:

[0044] Before the nozzle is replaced, the protective slag is stopped from being added into the crystallizer under the standard working casting speed; when the thickness of the protective slag is consumed to a first slag thickness H1=30mm, the first-stage reduction of the casting speed is started; when the casting speed is reduced to a first casting speed, the reduction is stopped, the protective slag is consumed, when the thickness of the protective slag is consumed to a second slag thickness H2=5mm, the second-stage reduction of the casting speed is started, and the casting speed is reduced to a second casting speed;

[0045] In the implementation, the first casting speed represents a buffer working casting speed, and is taken as 1.0m / min in production, and the second casting speed represents a lowest safe casting speed, and is taken as 0.6m / min in production.

[0046] The first-stage reduction of the casting speed is performed at a first reduction rate, and the second-stage reduction of the casting speed is performed at a second reduction rate.

[0047] The first stage reduces the pulling speed by a first rate, and the second stage reduces the pulling speed by a second rate; the first rate means reducing or increasing the pulling speed by 0.05 m / min every 10 s, and the second rate means reducing or increasing the pulling speed by 0.10 m / min every 5 s.

[0048] When the pulling speed is reduced to the minimum safe pulling speed, the reduction is stopped, and the consumption of the slag and the depletion of the protective slag in the crystallizer are performed at the minimum safe pulling speed.

[0049] The stopper opening degree is maintained to keep the casting continuity, the liquid level is kept at a first liquid level in the crystallizer based on the influence of the old nozzle volume on the liquid level safety height, and the old nozzle is removed by top flow;

[0050] The first liquid level is a high liquid level in production, and the high liquid level ranges from 65 mm to 75 mm from the upper opening of the crystallizer.

[0051] In specific implementation, as an embodiment of the present application, the maintenance of the stopper opening degree and the keeping of the casting continuity specifically include:

[0052] When the pulling speed is reduced to the second pulling speed, the control mode of the stopper is switched from the automatic mode to the manual mode, and the stopper opening degree is maintained unchanged before and after the control mode switching;

[0053] The stopper is always in an open state to keep the casting continuity, and the casting blank has no rejoining process.

[0054] In specific implementation, as an embodiment of the present application, the removal of the old nozzle by top flow specifically includes:

[0055] The liquid level control of the crystallizer is switched from the automatic mode to the manual mode, the flow is manually controlled, the liquid level in the crystallizer is kept at the first liquid level based on the influence of the old nozzle volume on the liquid level safety height, and the removal of the old nozzle is completed in the state of continuous casting and without protective slag.

[0056] The liquid level in the crystallizer is stabilized at a second liquid level based on the influence of the new nozzle volume on the liquid level safety height, and the new nozzle is installed by top flow.

[0057] The second liquid level is a low liquid level in production, and the low liquid level ranges from 85 mm to 95 mm from the upper opening of the crystallizer.

[0058] In specific implementation, as an embodiment of the present application, the installation of the new nozzle by top flow specifically includes:

[0059] After the removal of the old nozzle is completed, the liquid level in the crystallizer is stabilized at the second liquid level based on the influence of the new nozzle volume on the liquid level safety height, and the installation of the new nozzle is completed in the state of continuous casting and without protective slag.

[0060] After the new water gap is installed, the protective slag is added in stages, the casting speed is increased according to the thickness of the protective slag, and the water gap replacement is completed.

[0061] In specific implementation, as an embodiment of the present application, the protective slag is added in stages, and the casting speed is increased according to the thickness of the protective slag, which specifically includes:

[0062] After the new water gap is installed, the steel liquid surface is manually controlled to be stable in the third liquid level range, the third liquid level represents that the steel liquid surface is 80mm±2mm from the upper opening of the crystallizer, the liquid level control mode is switched from manual mode to automatic mode, a small amount of protective slag (1mm-3mm) is added to the crystallizer, the thickness of the protective slag only meets the requirement that the steel liquid surface in the crystallizer is not exposed, the first stage of increasing the casting speed is started, and the casting speed is increased to the first casting speed.

[0063] The casting speed is maintained stable at the first casting speed, and it is confirmed that the crystallizer state is normal and the water gap is well positioned vertically with the crystallizer, then the protective slag is added again, the thickness of the protective slag is restored to the safe range (20mm-30mm), the second stage of increasing the casting speed is started, and the casting speed is increased to the standard working casting speed, and the water gap replacement is completed.

[0064] The standard working casting speed is the casting speed under the normal working state in production, which is 2.8m / min.

[0065] The first stage of increasing the casting speed uses a second speed rate, and the second stage of increasing the casting speed uses a first speed rate.

[0066] In specific implementation, as an embodiment of the present application, the first casting speed can meet the minimum casting speed for automatic control stability of the stopper and long-time safe casting at the same time, and provides a feasible time for full melting of the slag or protective slag. In implementation, the first casting speed is related to the cross section.

[0067] Example 1

[0068] In this embodiment, a small square billet continuous casting machine with a crystallizer size of 160mmx160mm is taken as an example, a general carbon steel is cast, the standard working casting speed is 2.8m / min, the thickness of the protective slag under the standard working casting speed is 60mm, the steel liquid surface height set value under the automatic mode is =80mm, the buffer working casting speed is 1.0m / min, the minimum safe casting speed is 0.6m / min, and the preheating temperature is >1100℃ before the new water gap is installed.

[0069] The replacement process of the submerged entry water gap of the small square billet continuous casting machine using the method of the present application is as follows:

[0070] 1, stop adding protective slag into the crystallizer before the water gap is replaced, at this time the casting machine pulling speed Vc = 2.8 m / min, the flow length observation crystallizer inside protective slag, with the crystallizer copper pipe upper mouth as the reference object, confirm the current thickness of the protective slag, the protective slag thickness H = 80 mm - the distance from the slag surface to the upper mouth of the crystallizer.

[0071] 2, according to the protective slag thickness, reduce the pulling speed in stages, when the thickness of the protective slag is consumed to the standard working pulling speed V = 2.8 m / min, the lowest safe slag thickness H1 = 30 mm, start the first stage of reducing the pulling speed, use the low speed rate to reduce the speed, every 10 s reduce the pulling speed by 0.05 m / min; when the pulling speed is reduced to the buffer working pulling speed V a = 1.0 m / min, stop reducing the speed, consume the slag, when the thickness of the protective slag reaches the buffer working pulling speed lowest safe slag thickness H2 = 5 mm, at this time the steel liquid surface in the crystallizer appears partial exposure, start the second stage of reducing the pulling speed, this stage uses the high speed rate to reduce the speed, every 5 s increase the pulling speed by 0.10 m / min.

[0072] 3, when the pulling speed is reduced to the lowest safe pulling speed V b = 0.6 m / min, stop reducing the speed, consume the protective slag in the crystallizer.

[0073] 4, switch the stopper control from the automatic mode to the manual control mode, before and after the switch, the stopper opening degree remains unchanged, that is, the stopper is always in the open state, keep the casting flow continuity, and the casting blank has no recombination process.

[0074] 5, based on the influence of the old water gap volume on the liquid level safety height, manually control the flow, increase the steel liquid surface to 65-75 mm away from the upper mouth of the crystallizer; complete the old water gap removal under the condition of continuous casting flow and no protective slag.

[0075] 6, under the open flow pouring state, clean the residual steel around the lower water gap of the tundish, and clean the foreign matters in the crystallizer.

[0076] 7, based on the influence of the new water gap volume on the liquid level safety height, stabilize the steel liquid surface in the crystallizer at 85-95 mm away from the upper mouth of the crystallizer, complete the new water gap installation under the condition of continuous casting flow and no protective slag.

[0077] 8, after the new water gap installation is completed, manually control the steel liquid surface to be stable in the liquid level height range set by the automatic control mode, stabilize the steel liquid surface at 80 mm away from the upper mouth of the crystallizer, switch the liquid level control mode from the manual mode to the automatic mode; at the same time, add a small amount of protective slag (5 mm) into the crystallizer, the protective slag thickness only meets the condition that the steel liquid surface in the crystallizer has no exposure, then start the first stage of increasing the pulling speed, use the high speed rate to increase the speed, every 5 s increase the pulling speed by 0.10 m / min, increase the pulling speed to the buffer working pulling speed V a=1.0m / min; Maintain a stable pulling speed under the buffer working pulling speed, and after confirming that there are no abnormalities in the crystallizer and that the nozzle and crystallizer are properly vertically positioned, the protective slag is fully melted. Add protective slag again to restore the thickness of the protective slag to the safe range, that is, when the slag thickness H1 = 30mm, and then start the second stage of increasing the pulling speed. Use a low speed to increase the speed, and increase the pulling speed once every 10s at a frequency of 0.05m / min until the pulling speed is increased to the target working pulling speed.

[0078] 9. Gradually restore the slag thickness inside the crystallizer to 60mm according to the pulling speed, and complete the sprue replacement.

[0079] Example 2

[0080] like Figure 1 As shown, the present invention provides a method for replacing slag-resistant nozzles suitable for immersion nozzles. When replacing nozzles using the method of the present invention, it is necessary to have two people working together. One person controls the pulling speed and stopper rod to maintain a stable liquid level, while the other person completes the disassembly, cleaning and installation of the nozzle. Figure 2 This is a schematic diagram of a continuous casting machine, showing the casting structure under normal conditions. Figure 3 This refers to the open-flow pouring process during mouthwash installation. Additionally, the new inlet needs to be preheated to >1100℃ before installation. Any debris on the old inlet should be removed promptly. Open-flow pouring time <5 seconds.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preventing slag entrapment during replacement of submerged entry nozzles, applicable to continuous casting machines where the submerged entry nozzle is fixed using a fitted structure, characterized in that... The method comprises the following steps: stopping adding protective slag into the crystallizer before replacing the water gap, reducing the pulling speed in stages according to the thickness of the protective slag, and depleting the protective slag in the crystallizer when the second pulling speed is reached; maintaining the opening degree of the stopper, keeping the continuity of the casting flow, keeping the liquid level in the crystallizer at a first liquid level based on the influence of the volume of the old water gap on the safe height of the liquid level, and removing the old water gap by top flow; stabilizing the liquid level in the crystallizer at a second liquid level based on the influence of the volume of the new water gap on the safe height of the liquid level, and installing the new water gap by top flow; after the installation of the new water gap is completed, adding the protective slag in stages and increasing the pulling speed according to the thickness of the protective slag, and completing the replacement of the water gap.

2. The anti-entrainment replacement method for a submerged entry nozzle according to claim 1, characterized by, The method of reducing the pulling speed in stages according to the thickness of the protective slag comprises the following steps: stopping adding the protective slag into the crystallizer before replacing the water gap at the standard working pulling speed; starting the first stage of reducing the pulling speed when the thickness of the protective slag is reduced to a first slag thickness H1; stopping the speed reduction when the pulling speed is reduced to a first pulling speed, depleting the protective slag, starting the second stage of reducing the pulling speed when the thickness of the protective slag is reduced to a second slag thickness H2, and reducing the pulling speed to a second pulling speed. The first stage of reducing the pulling speed adopts a first speed rate, the second stage of reducing the pulling speed adopts a second speed rate, the first speed rate means reducing or increasing the pulling speed at a frequency of 0.05 m / min per 10 s, and the second speed rate means reducing or increasing the pulling speed at a frequency of 0.10 m / min per 5 s.

3. The anti- skull replacement method for a submerged entry nozzle according to claim 1, wherein The method of maintaining the opening degree of the stopper and keeping the continuity of the casting flow comprises the following steps: when the pulling speed is reduced to the second pulling speed, the control mode of the stopper is switched from the automatic mode to the manual mode, and the opening degree of the stopper is maintained unchanged before and after the switching of the control mode. The stopper is always in the open state, the continuity of the casting flow is kept, and the casting blank has no re-solidification process.

4. The anti- skull replacement method for a submerged entry nozzle according to claim 1, wherein The method of removing the old water gap by top flow comprises the following steps: the liquid level control of the crystallizer is switched from the automatic mode to the manual mode, the liquid flow is manually controlled, the liquid level in the crystallizer is kept at a first liquid level based on the influence of the volume of the old water gap on the safe height of the liquid level, and the removal of the old water gap is completed in the state of continuous casting flow and no protective slag.

5. The anti- skull replacement method suitable for a submerged entry nozzle according to claim 1, wherein The method of installing the new water gap by top flow comprises the following steps: after the removal of the old water gap is completed, the liquid level in the crystallizer is stabilized at a second liquid level based on the influence of the volume of the new water gap on the safe height of the liquid level, and the installation of the new water gap is completed in the state of continuous casting flow and no protective slag.

6. The anti- skull replacement method suitable for a submerged entry nozzle according to claim 1, wherein The method of adding the protective slag in stages and increasing the pulling speed according to the thickness of the protective slag comprises the following steps: after the installation of the new water gap is completed, the liquid level is manually controlled to be stabilized in a third liquid level range, the liquid level control mode is switched from the manual mode to the automatic mode, a small amount of protective slag is added into the crystallizer, the thickness of the protective slag only meets the requirement that the liquid level in the crystallizer is not exposed, the first stage of increasing the pulling speed is started, and the pulling speed is increased to a first pulling speed; the pulling speed is kept stable at the first pulling speed, and it is confirmed that the state of the crystallizer is normal and the water gap is well positioned with the crystallizer, then the protective slag is added again to make the thickness of the protective slag return to the safe range, the second stage of increasing the pulling speed is started, and the pulling speed is increased to the standard working pulling speed, and the replacement of the water gap is completed; the first stage of increasing the pulling speed adopts the second speed rate, and the second stage of increasing the pulling speed adopts the first speed rate.

7. The anti- skull replacement method suitable for a submerged entry nozzle according to claim 2, wherein The first drawing speed is the lowest drawing speed that can meet the stability of automatic control of the stopper and long-time safe pouring at the same time.

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