Method for prolonging service life of crystallizer nozzle

Abstract

The invention provides a method for prolonging the service life of a crystallizer nozzle, and relates to the technical field of metallurgical continuous casting, and the method comprises the following steps: starting casting and initializing a nozzle protection system, and determining nozzle protection related parameters according to on-site process data; the upward variation and the downward variation of the water gap protection system are calculated; asymmetric trapezoidal wave control is started, and upper limit adjustment of the liquid level is carried out; adjusting the lower limit of the liquid level; the liquid level is recovered and adjusted; and the third step, the fourth step and the fifth step are repeated till the crystallizer is not used. By adopting the asymmetric trapezoidal wave control model, accurate control and uniform erosion of the slag line position of the water gap are realized, the problem of ') '-shaped non-uniform erosion is effectively avoided, the service life of the water gap is effectively prolonged, the number of continuous casting furnaces is increased, and the consumption cost of refractory materials is reduced.

Description

Technical Field

[0001] This application relates to the technical field of metallurgical continuous casting, and particularly relates to a method for improving the service life of a mold nozzle. Background Art

[0002] During the continuous casting production process, changing the nozzle in the slab is the most important step in the continuous casting process. The existing submerged nozzle is located between the tundish and the mold. By controlling the molten steel flow state and injection speed, it can effectively prevent secondary oxidation and splashing of the molten steel in the air, and can protect the stable operation of the casting system. However, it is often eroded by the mold powder and molten steel during continuous casting, resulting in a shortened service life.

[0003] To extend the service life of the submerged nozzle, in the prior art, steel mills usually use a nozzle protection system to adjust the position of the slag line of the submerged nozzle in the mold. By changing the contact area between the submerged nozzle and the mold powder, the uniform distribution of erosion is achieved. However, the existing nozzle protection system has many technical defects: the sine wave control model of the existing nozzle protection system is difficult to avoid technical problems such as uneven nozzle erosion and short service life. These technical limitations not only fail to achieve the expected goal of extending the nozzle life, but may also cause quality problems such as slab cracks and sticking breakout, bringing process risks and economic losses to continuous casting production. Summary of the Invention

[0004] This application is made in view of the above problems, and its purpose is to provide a method for improving the service life of a mold nozzle, which adopts an asymmetric trapezoidal wave control model to achieve precise control and uniform erosion of the slag line position of the nozzle, so that the slag line position of the nozzle changes uniformly, effectively avoiding the ")"-type uneven erosion problem caused by the traditional sine wave. Compared with the sine wave control model, it can effectively extend the service life of the nozzle, increase the number of continuous casting furnaces, and reduce the refractory consumption cost.

[0005] Specifically, the first aspect of this application provides a method for improving the service life of a mold nozzle, including the following steps: Step 1: Initialization of starting casting and nozzle protection system, determining the nozzle protection offset value ±A, the overall downward offset value B of the asymmetric trapezoidal nozzle protection, and the nozzle protection period T according to process data; The protection period T of the nozzle needs to be approximately a straight line after the liquid level is amplified, generally taking more than 120 minutes. The value of T should make the calculated value of [the smelting period of one furnace of molten steel (generally 40 minutes) × the number of continuous casting furnaces in a casting heat / the nozzle protection period] as close to an integer as possible to ensure that the slag line position of the nozzle is evenly distributed under the total production cycle.

[0006] Starting casting refers to the process of smoothly introducing the molten steel after refining treatment from the tundish into the mold for casting during the iron and steel production process.

[0007] The mold is the core component of the continuous casting machine. Its main function is to control the flow state of the molten steel and ensure that a uniform shell is formed during the solidification of the molten steel. The flow state of the molten steel in the mold directly affects the quality of the cast slab, including liquid level fluctuations, flow velocity distribution, and the floating-up of inclusions. If the flow field in the mold is uneven or the liquid level fluctuates too much, it may lead to defects such as cracks and slag inclusions on the surface of the cast slab. The design and operating parameters of the mold (such as taper, cooling water distribution, etc.) need to be carefully adjusted to ensure that the molten steel can solidify smoothly into a shell.

[0008] The submerged entry nozzle is located between the tundish and the mold. By controlling the flow state and injection speed of the molten steel, it can effectively prevent secondary oxidation and splashing of the molten steel in the air and protect the stable operation of the pouring system.

[0009] Step 2: Calculate the upward change amount and downward change amount of the nozzle protection system, which are (A - B) and (-(A + B)) respectively; Step 3: Enable asymmetric trapezoidal wave control to perform the upper limit adjustment of the liquid level; Traditional sinusoidal wave vibration control is to make the mold vibrate up and down with a certain amplitude and frequency, so as to improve the flow state of the molten steel and reduce the defects of breakout and oscillation marks. However, sinusoidal wave vibration has certain limitations. For example, it has poor effect at low casting speeds and cannot completely avoid the problems of breakout and oscillation marks.

[0010] Step 4: Perform the lower limit adjustment of the liquid level; Step 5: Perform the recovery adjustment of the liquid level; Step 6: Repeat Step 3, Step 4, and Step 5 until the mold is no longer in use.

[0011] Furthermore, the process data specifically includes: the total range R of the liquid level detection system, the best linearity point S%, and the erosion-resistant area range of the nozzle.

[0012] The total range R of the liquid level detection system is related to the device of the detection system and is generally 150 mm - 200 mm.

[0013] Furthermore, the best linearity point S% is the point with the best measurement linearity of the liquid level detection system, generally 70% - 80% of the total range R of the liquid level detection system.

[0014] The point with the best measurement linearity of the liquid level detection system is generally 70% - 80% of the total range R of the detection system, and the height from the copper tube opening of the mold is generally 80 - 100 mm.

[0015] Furthermore, the nozzle protection offset value ±A is the offset amount of the actual molten steel moving up and down at the optimal linearity point S%, and it is required that the upper and lower limit thresholds of the molten steel still remain within the erosion-resistant area of the nozzle.

[0016] The upper limit threshold of the molten steel is S%×R + A, and the lower limit threshold is S%×R - A. It is required that the upper and lower limit thresholds of the molten steel still remain within the erosion-resistant area of the nozzle. Generally, the erosion-resistant area of the nozzle is 60 mm to 180 mm above the tapping hole of the nozzle. In order to make the quality of the steel billet more consistent, the steel mill generally controls the difference in the insertion depth of the nozzle under different conditions (different nozzles, different heats of molten steel), and the change range of the molten steel is within 30 mm. Therefore, the value of A is generally calculated as 2A + the thickness of the liquid slag layer + the amplitude of the liquid level fluctuation ≤ 30 mm.

[0017] Furthermore, the overall downward offset value B of the asymmetric trapezoidal nozzle protection is the overall downward offset amount of the upper and lower limit thresholds after the asymmetric nozzle protection of the molten steel is enabled. It is necessary to make the upper and lower limit thresholds of the molten steel after offset still remain within the erosion-resistant area of the nozzle and erode the optimal linearity point S% as little as possible. The value range is 3 mm to 5 mm.

[0018] The upper limit threshold of the molten steel after offset is S%×R + A - B, and the lower limit threshold of the molten steel after offset is S%×R - (A + B). It is necessary to make the upper and lower limit thresholds of the molten steel after offset still remain within the erosion-resistant area of the nozzle.

[0019] Furthermore, the regulation ramp-up time of the liquid level: upper limit hold time: lower limit hold time = 1: 0.9 to 1.1: 0.9 to 1.1.

[0020] Furthermore, the slope of the change in the molten steel liquid level during the regulation ramp-up time is (2A) / (T / 6).

[0021] Furthermore, the upper limit regulation is specifically to use the optimal linearity point S% of the liquid level detection system plus the upward change amount as the upper limit threshold A1 for controlling the liquid level with a trapezoidal wave, and regulate the liquid level to reach A1 within T / 18 time and hold for T / 3 time.

[0022] Furthermore, the lower limit regulation is specifically to use the optimal linearity point S% of the liquid level detection system plus the downward change amount as the lower limit threshold A2 for controlling the liquid level with a trapezoidal wave, and regulate the liquid level to reach A2 within T / 6 time and hold for T / 3 time.

[0023] Furthermore, the recovery regulation is specifically to regulate the liquid level to return to the optimal linearity point S% of the liquid level detection system within T / 9 time.

[0024] Furthermore, the upper limit of the liquid level cannot be higher than the upper limit alarm value of the system, and the lower limit of the liquid level cannot be lower than the lower limit alarm value of the system. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of this accompanying drawing or the prior art, the accompanying drawings required for use in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of this accompanying drawing. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on the structures shown in these accompanying drawings.

[0026] Figure 1 It is the flowchart of the steps of the present invention; Figure 2 It is the variation control diagram of the asymmetric trapezoidal wave control model in the embodiments of the present invention; Figure 3 It is the schematic diagram of the submerged nozzle erosion situation in the embodiments of the present invention.

[0027] The realization of the purpose of this accompanying drawing, functional features and advantages will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed implementation manners

[0028] In order to make the purpose, technical solutions and advantages of this application clearer, the following describes and explains this application in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of this application.

[0029] Obviously, the accompanying drawings in the following description are only some examples or embodiments of this application. For those of ordinary skill in the art, without creative efforts, this application can also be applied to other similar scenarios based on these accompanying drawings. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in this application, some designs, manufacturing or production changes based on the technical content disclosed in this application are only conventional technical means and should not be understood as the content disclosed in this application being insufficient.

[0030] If there is no special indication, all the implementation manners and optional implementation manners of this application can be combined with each other to form new technical solutions.

[0031] If there is no special indication, all the technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0032] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, when the method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0033] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed may also be included or comprised, or it may only include or comprise the listed components.

[0034] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0035] To better understand the solutions of the embodiments of this application, some related terms and concepts that may be involved in the embodiments of this application will be introduced below.

[0036] (1) The mold is a device in the continuous casting machine used to solidify molten steel. It is usually a cuboid or cylindrical container with a cooling system inside. By controlling the cooling intensity, it affects the solidification rate of molten steel and the shape of the billet. The design and operating parameters of the mold directly affect the surface quality and internal structure of the billet. Its main function is to control the flow state of molten steel and ensure that a uniform shell is formed during the solidification of molten steel. The flow state of the molten steel in the mold directly affects the quality of the billet, including liquid level fluctuations, flow velocity distribution, and the floating of inclusions. If the flow field in the mold is uneven or the liquid level fluctuates too much, it may cause defects such as cracks and slag inclusions on the surface of the billet.

[0037] (2) The submerged entry nozzle is an important passage connecting the tundish and the mold, usually installed at the bottom of the tundish and inserted below the molten steel surface in the mold. Its main functions are to prevent the secondary oxidation of molten steel, control the flow rate of molten steel when it enters the mold, and promote the floating of inclusions in the molten steel. The design of the submerged entry nozzle includes its shape, size, material, and insertion depth, etc. These factors will have a significant impact on the flow field and temperature field in the mold. For example, the shape of the nozzle (such as straight hole, concave, convex, etc.) will affect the stability of molten steel flow, while the insertion depth of the nozzle will affect the occurrence of liquid level fluctuations and slag entrainment phenomena.

[0038] (3) The sinusoidal wave control of the mold refers to, in the continuous casting process, optimizing the quality of the cast slab and improving the production efficiency by controlling the vibration waveform of the mold to be a sinusoidal wave. Sinusoidal vibration is a common vibration form, characterized by a constant vibration frequency and amplitude, and is usually used to reduce the depth and spacing of oscillation marks on the surface of the cast slab, thereby improving the surface quality of the cast slab.

[0039] In this embodiment, as Figure 1 shown, a method for improving the service life of the mold nozzle includes the following steps: Step 1: Initialization of the starting casting and nozzle protection system, determine the nozzle protection offset value ±A, the overall downward offset value B of the asymmetric trapezoidal nozzle protection, and the nozzle protection period T according to the on-site process data; The protection period T of the nozzle needs to be approximately a straight line after the liquid level is amplified, generally taking more than 120 minutes. The value of T needs to make the calculated value of [the smelting period of a ladle of molten steel (generally 40 minutes) × the number of consecutive casting furnaces per casting sequence / the nozzle protection period] as close as possible to an integer to ensure that the nozzle slag line position is evenly distributed under the total production cycle.

[0040] Starting casting refers to the process of smoothly introducing the molten steel after refining treatment from the tundish into the mold for casting during the iron and steel production process.

[0041] The mold is the core component of the continuous caster, and its main function is to control the flow state of molten steel to ensure that the molten steel forms a uniform shell during solidification. The flow state of the molten steel in the mold directly affects the quality of the cast slab, including liquid level fluctuations, flow rate distribution, and the floating of inclusions. If the flow field in the mold is uneven or the liquid level fluctuation is too large, it may lead to defects such as cracks and slag inclusions on the surface of the cast slab. The design and operating parameters of the mold (such as taper, cooling water distribution, etc.) need to be carefully adjusted to ensure that the molten steel can solidify into a shell smoothly.

[0042] The submerged entry nozzle is located between the tundish and the mold. By controlling the flow state and injection speed of molten steel, it can effectively prevent the secondary oxidation and splashing of molten steel in the air and protect the stable operation of the casting system.

[0043] Step 2: Calculate the upward change amount and downward change amount of the tundish protection system, which are (A - B) and (-(A + B)) respectively; Step 3: Enable the asymmetric trapezoidal wave control to adjust the upper limit of the liquid level; Traditional sine wave vibration control is to make the mold vibrate up and down with a certain amplitude and frequency, so as to improve the molten steel flow state and reduce breakout and oscillation mark defects. However, sine wave vibration has certain limitations. For example, it has poor effect at low casting speeds and cannot completely avoid breakout and oscillation mark problems.

[0044] Step 4: Adjust the lower limit of the liquid level; Step 5: Adjust the restoration of the liquid level; Step 6: Repeat Step 3, Step 4 and Step 5 until the mold is no longer in use.

[0045] Furthermore, the on-site process data specifically includes: the total range R of the liquid level detection system, the best linearity point S%, and the erosion-resistant area range of the tundish nozzle.

[0046] The total range R of the liquid level detection system is related to the device of the detection system, which is 180 mm in this embodiment.

[0047] Furthermore, the best linearity point S% is the point with the best measurement linearity of the liquid level detection system, generally 70% - 80% of the total range R of the liquid level detection system.

[0048] In this embodiment, the point with the best measurement linearity of the liquid level detection system is 75% of the total range R of the detection system, and the height from the mold copper tube opening is 100 mm.

[0049] Furthermore, the tundish protection offset value ±A is the offset amount of the actual molten steel moving up and down at the best linearity point S%, and it is required that the upper and lower limit thresholds of the molten steel are still within the erosion-resistant area of the tundish nozzle.

[0050] The upper limit threshold of the molten steel is S%×R + A, and the lower limit threshold is S%×R - A. It is required that the upper and lower limit thresholds of the molten steel are still within the erosion-resistant area of the tundish nozzle. The erosion-resistant area of the tundish nozzle is 60 mm - 180 mm above the tundish nozzle outlet. And in order to make the quality of the steel billet more consistent, the steel mill generally controls the difference in the tundish nozzle insertion depth under different conditions (different tundish nozzles, different heats of molten steel), and the change range of the molten steel is within 30 mm. Therefore, the value of A is generally calculated as 2A + slag layer thickness + liquid surface fluctuation amplitude ≤ 30 mm.

[0051] Further, the overall downward offset value B of the asymmetric trapezoidal nozzle protection is the overall downward offset of the upper and lower limit thresholds after the molten steel enables the asymmetric nozzle protection. It is necessary to ensure that the upper and lower limit thresholds of the molten steel after offset are still within the erosion-resistant area of the nozzle and as little as possible erode the best linearity point S%. In this embodiment, the value is 3 mm.

[0052] The upper limit threshold of the molten steel after offset is S%×R + A - B, and the lower limit threshold of the molten steel after offset is S%×R - (A + B). It is necessary to ensure that the upper and lower limit thresholds of the molten steel after offset are still within the erosion-resistant area of the nozzle.

[0053] Further, the adjustment ramp time of the liquid level: upper limit hold time: lower limit hold time = 1:1:1.

[0054] Further, the slope of the molten steel liquid level change during the adjustment ramp time is (2A) / (T / 6).

[0055] Further, the upper limit adjustment is specifically to use the best linearity point S% of the liquid level detection system plus the upward change amount as the upper limit threshold A1 for controlling the liquid level of the trapezoidal wave, adjust the liquid level to reach A1 within T / 18 time, and hold for T / 3 time.

[0056] Further, the lower limit adjustment is specifically to use the best linearity point S% of the liquid level detection system plus the downward change amount as the lower limit threshold A2 for controlling the liquid level of the trapezoidal wave, adjust the liquid level to reach A2 within T / 6 time, and hold for T / 3 time.

[0057] Further, the recovery adjustment is specifically to adjust the liquid level to return to the best linearity point S% of the liquid level detection system within T / 9 time.

[0058] Further, the upper limit of the liquid level cannot be higher than the upper limit alarm value of the system, and the lower limit of the liquid level cannot be lower than the lower limit alarm value of the system.

[0059] In this embodiment, the process conditions of the steel mill are that the thickness of the liquid slag layer is 6 mm, and the liquid level fluctuation range is ±3 mm (i.e., the liquid level fluctuation amplitude is 6 mm). Therefore, A ≤ (30 mm – 6 mm – 6 mm) / 2 = 9 mm. In this embodiment, A is taken as 9 mm, R = 180 mm; S% = 75%, T = 60 min, ±A = ±9 mm, B = 3 mm. The upward change amount of the liquid level height is A1 = A - B = 6 mm, and the downward change amount of the liquid level height A2 = -(A + B) = -12 mm. The best point position of the linearity of the molten steel is S%×R = 135 mm. The upper limit threshold of the molten steel is S%×R + A = 144 mm, and the lower limit threshold is S%×R - A = 126 mm. After enabling the asymmetric nozzle protection, the upper and lower limit thresholds are shifted downward as a whole. After the shift, the upper limit threshold of the molten steel is S%×R + A - B = 141 mm, and the lower limit threshold after the shift is S%×R - (A + B) = 123 mm. The change amount control chart of the asymmetric trapezoidal wave control model is as Figure 2 shown. The erosion curve after applying the nozzle protection with the asymmetric trapezoidal wave control of this embodiment is as Figure 3 shown. Figure 3 In it, the actual erosion situation is on the left, the ideal erosion situation is on the right, and the arrow indicates the best point position of the linearity. As can be seen from Figure 3 , the liquid level control is good, the slag line erosion is relatively uniform, and the erosion of the best point position of the linearity of the liquid level detection system is reduced, making the liquid level control more accurate, reducing the liquid level fluctuation and abnormal fluctuation, and achieving the effect of extending the service life of the nozzle.

[0060] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments with the same composition and the same function and effect as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various deformations that can be thought of by those skilled in the art are applied to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for improving the service life of the mold nozzle, characterized in that, It includes the following steps: Step 1: Initialize the casting start and nozzle protection system, and determine the nozzle protection offset value ±A, the overall downward offset value B of the asymmetric trapezoidal nozzle protection, and the nozzle protection period T according to the process data; Step 2: Calculate the upward change amount and downward change amount of the nozzle protection system; Step 3: Enable the asymmetric trapezoidal wave control to perform the upper limit adjustment of the liquid level; Step 4: Perform the lower limit adjustment of the liquid level; Step 5: Perform the restoration adjustment of the liquid level; Step 6: Repeat Step 3, Step 4 and Step 5 until the mold is no longer in use.

2. The method for improving the service life of the nozzle of the mold according to claim 1, characterized in that The process data specifically includes: the total range R of the liquid level detection system, the best linearity point S%, and the erosion-resistant area range of the nozzle.

3. A method for improving the service life of the nozzle of a mold, as claimed in claim 2, wherein The best linearity point S% is 70% - 80% of the total range R of the liquid level detection system.

4. A method for improving the service life of a mold nozzle according to claim 1, characterized in that, The nozzle protection offset value ±A is the offset amount of the actual molten steel moving up and down at the best linearity point S%, and it is required that the upper and lower limit thresholds of the molten steel are still within the erosion-resistant area of the nozzle.

5. A method for improving the service life of the nozzle of a mold, characterized in that, The overall downward offset value B of the asymmetric trapezoidal nozzle protection ranges from 3 mm to 5 mm.

6. The method for improving the service life of the mold nozzle according to claim 1, wherein, For the adjustment ramp time of the liquid level: upper limit holding time: lower limit holding time = 1: 0.9 - 1.1: 0.9 - 1.

1.

7. A method for improving the service life of the nozzle of the mold according to claim 6, characterized in that, The slope of the molten steel liquid level change during the adjustment ramp time is (2A) / (T / 6).

8. A method for improving the service life of the nozzle of a mold, characterized in that, The upper limit adjustment is specifically to use the best linearity point S% of the liquid level detection system plus the upward change amount as the upper limit threshold A1 for the trapezoidal wave control of the liquid level, adjust the liquid level to reach A1 within T / 18 time, and hold for T / 3 time.

9. A method for improving the service life of the nozzle of a mold, characterized in that The lower limit adjustment is specifically to use the best linearity point S% of the liquid level detection system plus the downward change amount as the lower limit threshold A2 for the trapezoidal wave control of the liquid level, adjust the liquid level to reach A2 within T / 6 time, and hold for T / 3 time.

10. A method for improving the service life of the nozzle of a mold, characterized in that, The restoration adjustment is specifically to adjust the liquid level to restore to the best linearity point S% of the liquid level detection system within T / 9 time.

Images