Method for prolonging service life of slab continuous casting tundish

Abstract

The invention provides a method for prolonging the service life of a slab continuous casting tundish, which comprises the following steps: S1, before baking the tundish, wrapping a stopper head with asbestos cloth; s2, the tundish is subjected to staged baking; s3, in the last 1.5 hours before casting, when an upper nozzle needs to be preheated, the asbestos cloth is taken down; and S4, when the tundish is baked, compressed air is upwards blown to the stopper rod head from the interior of the upper nozzle of the tundish, and blowing of the compressed air is stopped when the upper nozzle is preheated. In the process of baking the tundish, the rod head of the stopper rod is wrapped with asbestos cloth, and compressed air is blown to the rod head of the stopper rod in a matched mode, so that corrosion to the rod head of the stopper rod in the baking process can be reduced, it is guaranteed that the stopper rod can still effectively control flow after 16 hours, and it is guaranteed that the phenomenon that steel is clamped on the plate face of a small strand of steel flow in the flow intercepting process is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of continuous casting devices, and in particular to a method for extending the service life of a tundish for slab continuous casting. Background Art

[0002] The basic process of continuous casting is ladle → long shroud → tundish → submerged shroud → crystallizer → fan-shaped segment → flame cutting → spraying machine. The tundish is an important transition container between the refining ladle and the crystallizer. The length of time for each batch of continuous casting is mainly restricted by the service life of the tundish, so extending the service life of the tundish can create higher economic benefits. The tundish uses a magnesium coating as a working layer, and the tundish mainly contains flow field control devices (turbulators, retaining walls, dams) and flow control devices (stopper rods). Among them, the stopper rod of the flow control device is mainly used to control the speed of the molten steel in the tundish flowing to the crystallizer, and to cut off the steel flow to facilitate the replacement of the submerged shroud or stop casting. The main measures to extend the service life of the tundish are mainly through the flow field design in the tundish, the construction process and the baking time of the tundish.

[0003] The stopper rod head contains a certain proportion of MgO and C, which are unstable in high temperature environment and are prone to decomposition reaction: MgO+C=Mg+CO. The stopper rod must be installed before the tundish is baked. Under normal circumstances, the tundish baking takes 5 hours (the baking time is even longer when the production rhythm changes). The rod head is affected by the above reaction in a high temperature environment for a long time. In addition, during the production process, the stopper rod will also be affected by the erosion of the molten steel, resulting in the production process. The submerged nozzle can only be replaced once through the stopper rod interception, and the service life of the submerged nozzle is 8 hours. Therefore, in the prior art, one tundish can only be used with two submerged nozzles, and the service life is only 16 hours. In addition, the stopper rod head is severely corroded and cannot meet the interception requirements. If the interception is unsuccessful, a small stream of steel will be sandwiched on the nozzle plate surface, causing batch inclusion defects and leading to the degradation or scrapping of the ingot. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for extending the service life of a slab continuous casting tundish, reduce the erosion of the stopper rod during the baking process, extend the service life of the tundish, and improve the quality of the product.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for extending the service life of a slab continuous casting tundish, comprising the following steps:

[0007] S1. Before baking the tundish, wrap the plugging rod head with asbestos cloth;

[0008] S2. Use staged baking for the tundish;

[0009] S3. Remove the asbestos cloth when the water inlet needs to be preheated in the last 1.5 hours before pouring;

[0010] S4. When baking the tundish, compressed air is blown upward from the water inlet of the tundish to the head of the plug rod, and the blowing of compressed air is stopped when the water inlet is preheated.

[0011] Furthermore, in the step S2, the tundish is baked in stages using blast furnace gas or lignite gas.

[0012] Further, in the step S2, the staged baking includes low-fire baking, medium-fire baking and high-fire baking;

[0013] The first stage: bake at low heat for 1 hour to make the temperature inside the tundish reach 300℃;

[0014] The second stage: baking at medium heat for at least 2 hours, so that the temperature inside the tundish reaches 500-800℃;

[0015] The third stage: Bake at high heat for at least 2 hours to make the temperature inside the middle bag reach 1000-1100℃.

[0016] Furthermore, the method further comprises step S5, when replacing the submerged nozzle, when the slag surface of the protective slag in the crystallizer drops to the lower edge of the side hole of the submerged nozzle, replacing the new submerged nozzle.

[0017] Furthermore, the replacement of the submerged water nozzle is performed by an oil cylinder, and the action time of the oil cylinder is 0.6-0.8 seconds.

[0018] The advantages of the present invention are that during the baking process of the tundish, by wrapping the asbestos cloth around the head of the stopper rod and blowing compressed air toward the head of the stopper rod, the erosion of the head of the stopper rod during the baking process can be reduced, thereby ensuring that the stopper rod can still effectively control the flow after 16 hours and ensuring that the small stream of steel in the interception process will not cause the phenomenon of steel clamping on the plate surface.

[0019] In addition, the present application prolongs the casting length of a pouring, improves the continuous casting operation rate and the yield rate, while reducing the weight of the fixed scrap removed during a pouring and the weight of the remaining steel in the tundish. The use time of the refractory in the tundish is extended. The cost of fixed grinding treatment during the pouring process is reduced, and by comparing the surface quality of the cast billet and the quality feedback from downstream customers, the service life of the tundish is extended and the casting first-class product rate is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0021] Figure 1 The present invention is a schematic flow chart of a method for extending the service life of a slab continuous casting tundish.

[0022] Figure 2 It is a schematic diagram of the structure of the continuous casting tundish of the present invention.

[0023] Figure 3 The present invention is a structural schematic diagram of the relative positions of the submerged nozzle and the slag surface of the protective slag in the crystallizer when the submerged nozzle is replaced.

[0024] Description of the numbers in the figure:

[0025] 1. Tundish body; 2. Tundish cover; 3. Turbulator; 4. Impact plate; 5. Retaining wall; 6. Dam; 7. Long water inlet; 8. Stopper rod; 9. Tundish upper water inlet; 10. Immersed water inlet. DETAILED DESCRIPTION

[0026] See also Figures 1 to 3 The present invention provides a method for extending the service life of a slab continuous casting tundish. The structure of the continuous casting tundish of the present application includes a tundish body 1 and a cover 2 arranged on the tundish body 1. When the tundish is baked, the flame sprays from the cover 2 into the tundish. A turbulator 3, an impact plate 4, a retaining wall 5 and a dam 6 are arranged in the tundish body 1. The impact plate 4 is arranged below the turbulator 3. The long water nozzle 7 and the stopper rod 8 extend through the cover 2 into the cavity of the tundish body 1, and the long water nozzle 7 is located above the turbulator 3. A tundish upper water nozzle 9 is arranged at the bottom of the tundish body 1. The tundish upper water nozzle 9 is opened at an end away from the turbulator 3. The stopper rod 8 is located above the tundish upper water nozzle 9. The bottom of the tundish upper water nozzle 9 is connected to an immersion water nozzle 10.

[0027] The long nozzle 7 is responsible for introducing molten steel from the ladle into the tundish. The turbulator 3, retaining wall 5 and retaining dam 6 are devices for adjusting the flow field of molten steel in the tundish. The stopper rod 8 is a flow control device in the tundish. The stopper rod 8 is controlled by a linear motor to reciprocate up and down to control the size of the steel flow and to replace the submerged nozzle 10 and cut off the flow when the pouring is stopped. The upper nozzle 9 of the tundish and the submerged nozzle 10 are responsible for introducing molten steel from the tundish into the crystallizer. The submerged nozzle 10 is in contact with the plate surface of the upper nozzle 9 of the tundish, and the submerged nozzle 10 is moved left and right by the track to achieve the purpose of replacing the submerged nozzle 10.

[0028] The method for extending the service life of a slab continuous casting tundish comprises the following steps:

[0029] S1. Before baking the tundish, wrap the plug rod head with asbestos cloth to prevent the high temperature flame from directly contacting the plug rod head during baking;

[0030] S2. Use staged baking for the tundish;

[0031] The staged baking includes low-fire baking, medium-fire baking and high-fire baking. The intermediate package is baked in stages using gas. When baking with low fire, the gas flow rate is 300Nm 3 / h; when baking on medium fire, the gas flow rate is 700Nm 3 / h; when baking with high fire, the gas flow rate is 1000Nm 3 / h;

[0032] The first stage: bake at low heat for 1 hour to make the temperature inside the tundish reach 300℃;

[0033] The second stage: baking at medium heat for at least 2 hours, so that the temperature inside the tundish reaches 500-800℃;

[0034] The third stage: Bake at high heat for at least 2 hours to make the temperature inside the middle bag reach 1000-1100℃.

[0035] Under normal circumstances, the baking time for medium heat is 2 hours, and the baking time for high heat is 2 hours. If there is an unplanned production delay, the baking time for medium heat and high heat will be extended according to the actual situation.

[0036] S3. Remove the asbestos cloth when the water inlet needs to be preheated in the last 1.5 hours before pouring;

[0037] S4. When baking the tundish, the compressed air is blown upward from the water inlet of the tundish to the plug rod head, and the compressed air is stopped when the water inlet is preheated. The compressed air is blown upward from the water inlet of the tundish to the plug rod head to cool the rod head.

[0038] During the baking process of the tundish, the erosion of the rod head of the stopper rod can be reduced by wrapping the rod head with asbestos cloth and blowing compressed air to the rod head of the stopper rod, so as to ensure that the stopper rod can still effectively control the flow after 16 hours, and ensure that the small stream of steel will not be clamped on the plate surface during the interception process, so that the service life of a tundish with three immersion nozzles can be extended to 24 hours. At the same time, it also avoids the problem of small molten steel dripping on the plate surface of the new immersion nozzle when replacing the immersion nozzle due to severe erosion of the rod head.

[0039] Specifically, in step S2, the tundish is baked in stages using blast furnace gas or lignite gas.

[0040] There is another reason for the problem of steel clamping on the surface of the submerged nozzle: after the stopper rod is closed, there is a distance of about 35 cm between the position of the stopper rod head and the nozzle surface. When the molten steel within this distance has not completely stopped dripping, the submerged nozzle is replaced, resulting in steel clamping on the surface of the new submerged nozzle. To address this problem, the method for extending the service life of the slab continuous casting tundish disclosed in the present invention also includes step S5, when replacing the submerged nozzle, when the slag surface of the protective slag 12 in the crystallizer 11 drops to the lower edge of the side hole of the submerged nozzle, replace the new submerged nozzle, such as Figure 3 As shown. By extending the timing of replacing the submerged nozzle, the molten steel between the plug rod head position and the nozzle plate surface can have sufficient time to drip. At the same time, the replacement of the submerged nozzle is performed by the oil cylinder, and the action time of the oil cylinder to replace the submerged nozzle is 0.6-0.8 seconds.

[0041] A specific application of the present application is that the tundish needs to be baked before use because it contains a certain amount of moisture.

[0042] When baking, use staged baking;

[0043] The first stage: bake at low heat for 1 hour to make the temperature inside the tundish reach 300℃;

[0044] The second stage: baking at medium heat for at least 2 hours, so that the temperature inside the tundish reaches 500-800℃;

[0045] The third stage: Bake at high heat for at least 2 hours to make the temperature inside the middle bag reach 1000-1100℃.

[0046] Before production, the rod head that plays a role in the stopper flow cut-off process is protectively baked. That is, before baking the tundish, the rod head of the stopper is pre-wrapped with asbestos cloth. The asbestos cloth is removed only when the upper nozzle is preheated in the last 1.5 hours before pouring. When baking the tundish, compressed air is blown upward from the upper nozzle of the tundish to the rod head of the stopper to cool the rod head. When preheating the upper nozzle, stop blowing compressed air. By wrapping the rod head of the stopper with asbestos cloth and blowing compressed air to the rod head of the stopper, the problem of the stopper rod head being prone to decomposition reaction due to being in the high temperature zone of medium fire and high fire for a long time, thereby reducing the performance of the stopper rod, can be avoided. Ensure that the stopper rod can still effectively control the flow and adjust the timing of replacing the immersed nozzle after 16 hours of production, and ensure that there will be no plate surface clamping due to the appearance of small steel flows during the cut-off process.

[0047] After the plug rod head is intercepted, when the slag surface of the protective slag in the crystallizer drops to the lower edge of the side hole of the submerged nozzle, a new submerged nozzle is replaced, so that the molten steel between the plug rod head position and the nozzle plate surface can have sufficient time to drip. The action time of the oil cylinder for replacing the submerged nozzle is 0.6-0.8 seconds. This avoids the replacement of the submerged nozzle when the molten steel between the plug rod head position and the nozzle plate surface position has not completely stopped dripping, resulting in the plate surface of the new submerged nozzle clamping the steel.

[0048] The method disclosed in the present application can extend the service life of the tundish, extend the casting length of the tundish casting, improve the continuous casting operation rate and yield rate, and reduce the weight of the fixed waste billets cut off during the casting (a fixed length of billets at the beginning and end of each casting in the tundish is waste). Under the same output, the weight of the remaining steel in the tundish is less by adopting this method (for production safety, a fixed amount of molten steel must be left in the tundish at the end of the casting). The service life of the refractory materials in the tundish is extended. The cost of fixed grinding treatment during the casting process is reduced (normal billets within a fixed length at the beginning and end of the casting need to be ground), and by comparing the surface quality of the casting billets and the quality feedback from downstream customers, the service life of the tundish is extended and the casting first-class product rate is increased. Comprehensive calculations show that the use of one casting can save $1,174.5 in costs. Based on a continuous casting machine producing 300 castings per year, the annual cost savings are approximately $352,000.

[0049] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for extending the service life of a slab continuous casting tundish, characterized in that: The steps include: S1. Before baking the tundish, wrap the plugging rod head with asbestos cloth; S2. Use staged baking for the tundish; S3. Remove the asbestos cloth when the water inlet needs to be preheated in the last 1.5 hours before pouring; S4. When baking the tundish, compressed air is blown upward from the water inlet of the tundish to the head of the plug rod, and the blowing of compressed air is stopped when the water inlet is preheated.

2. A method for extending the service life of a slab continuous casting tundish according to claim 1, characterized in that: In the step S2, the tundish is baked in stages using blast furnace gas or blue coal gas.

3. A method for extending the service life of a slab continuous casting tundish according to claim 1, characterized in that: In step S2, the staged baking includes low-heat baking, medium-heat baking and high-heat baking; The first stage: bake at low heat for 1 hour to make the temperature inside the tundish reach 300℃; The second stage: baking at medium heat for at least 2 hours, so that the temperature inside the tundish reaches 500-800℃; The third stage: Bake at high heat for at least 2 hours to make the temperature inside the middle bag reach 1000-1100℃.

4. A method for extending the service life of a slab continuous casting tundish according to claim 1, characterized in that: The method further includes step S5, when replacing the submerged nozzle, when the slag surface of the protective slag in the crystallizer drops to the lower edge of the side hole of the submerged nozzle, replacing the new submerged nozzle.

5. A method for extending the service life of a slab continuous casting tundish according to claim 4, characterized in that: The replacement of the submerged nozzle is performed by a cylinder, and the action time of the cylinder is 0.6-0.8 seconds.

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