A method for reducing the quantity of mixed pouring of different steel grades in a continuous casting tundish

Abstract

This invention relates to a method for reducing the amount of dissimilar steel grades mixed in the tundish during continuous casting. The method includes the following steps: Step 1: A ladle filled with dissimilar molten steel is transported by a crane to the ladle turret of the continuous casting machine, placing it in a waiting-for-casting position; Step 2: The slag discharge alarm value of the ladle is tightened; Step 3: The amount of remaining molten steel in the tundish is controlled; Step 4: While implementing Step 3, the opening of the tundish stopper is controlled to further reduce the amount of remaining molten steel in the tundish; Step 5: When the tundish tonnage (i.e., the amount of mixed steel grades) is controlled to the required amount of mixed dissimilar steel grades according to the above steps, the ladle of the previous furnace is moved to a non-working position, while the ladle of the waiting dissimilar molten steel grades is rotated to the casting position, and the ladle slide is opened for mixed casting. This completes the operation of reducing the amount of mixed steel grades.

Description

Technical Field

[0001] This invention relates to a method, specifically a method for reducing the amount of mixed steel grades poured into the tundish during continuous casting, belonging to the field of continuous casting control technology. Background Technology

[0002] In continuous casting production, mixing different steel grades is unavoidable to improve the continuous casting machine's operating rate. However, in actual production, two steel grades with significantly different compositions are often cast together, leading to cross-contamination and an increase in mixed-grade billets (if mixing is not carried out, it would affect the continuity of production and capacity utilization). Since mixed-grade billets cannot be used as the original steel grade, they must be downgraded or directly reduced to contracted products, causing significant losses to the enterprise. Furthermore, the uneven composition and varying strength of the mixed-grade billets at both ends cause inconvenience for hot rolling mills.

[0003] Currently, our competitors control the mixed casting volume at 60 tons / tundish, while our plant's mixed casting volume is 70 tons / tundish (the mixed casting volume consists of the remaining molten steel in the original tundish and the molten steel of the different steel grades to be cast). The mixed casting volume is relatively large, so it is necessary to reduce the mixed casting volume.

[0004] In order to both organize continuous production and reduce the amount of mixed castings of different steel grades, similar steel mills at home and abroad have made the following improvements:

[0005] Reference 1: Lu Yunwei et al. Transition time and influencing factors of continuous casting and pouring of mixed billets. Ansteel Technology. 1995, (3): 12-16;

[0006] Reference 2: Lu Yunwei et al. Transition time and influencing factors of continuous casting mixed billets. Steelmaking. 1995, (4): 30-33, 12;

[0007] Reference 3: Hou Jilin. Research on the determination of mixed steel zone in multi-furnace continuous casting of billets. Baogang Technology. 2000, 26(1):43-46. This paper introduces Baogang's research on the problem of mixed steel billets in continuous casting through mathematical calculations, water model experiments, and on-site sampling. Finally, the determination of the mixed steel zone was completed, a reasonable range for determining the mixed steel zone of the billet was proposed, and a length cutting table for mixed steel billets was formulated.

[0008] Reference 4: Liang Lei et al. Shanghai Meishan Iron & Steel Co., Ltd. Automatic insertion device for continuous casting of different steel grades in the same package. Chinese Patent. Application No.: 200720041903, 2008-10-08.

[0009] Reference 5: Chen Jikang et al. Baoshan Iron & Steel Co., Ltd. Automatic insertion device for iron plate for continuous casting of different steel grades. Chinese Patent. Application No.: 99205873, 2000-03-01.

[0010] References 1-3 respectively introduce the rapid initial changes in the chemical composition of molten steel and billets in the tundish during continuous casting of different steel grades, the slow transition to the chemical composition of the continuous casting furnace (ladle) in the later stage, the lag of the side flow over the middle flow, and the formation and influencing factors of mixed billets during continuous casting, such as the transition time and the amount of mixed billets, which are affected by the shape and structure of the tundish, the amount of residual molten steel, the composition difference and the mass flow rate.

[0011] Reference 4 provides an automatic insertion device for continuous casting of different steel grades in the same tundish, which is equipped with a quick-change mechanism at the bottom of the tundish and can solve the problem of continuous casting of different steel grades in the same tundish of a slab continuous casting machine.

[0012] Reference 5 provides an automatic plate insertion device for isolating continuously cast steel plates of different grades, which can ensure the quality of the junction of dissimilar steel grades.

[0013] This invention utilizes control measures to prevent slag from flowing from the tundish into the crystallizer during continuous casting (i.e., measures to control slag flow during continuous casting) to reduce the amount of mixed castings, which is not the same approach as the invention methods in the related patents retrieved above.

[0014] The amount of molten steel to be mixed is determined by the amount of molten steel remaining in the tundish before mixing; the smaller this amount, the less steel to be mixed. Therefore, a new solution is urgently needed to address the aforementioned technical problems. Summary of the Invention

[0015] This invention addresses the problems existing in the prior art by providing a method for reducing the amount of mixed steel grades poured into the tundish during continuous casting. This technical solution utilizes control measures to prevent slag from flowing from the tundish into the crystallizer during the continuous casting process (i.e., measures to control slag flow during continuous casting) to achieve the purpose of reducing the amount of mixed steel grades poured.

[0016] To achieve the above objectives, the technical solution of the present invention is as follows: a method for reducing the amount of mixed steel grades poured into the tundish of continuous casting, the method comprising the following steps:

[0017] Step 1: The ladle filled with molten steel of a different grade is transported by a crane to the ladle turret of the continuous casting machine, so that it is in the waiting position for casting. At this time, the molten steel in the ladle that was originally being cast (which is of a different grade than the molten steel in the ladle in the waiting position) is being cast into the tundish through the long nozzle at the bottom of the ladle.

[0018] Step 2: Tighten the slag discharge alarm value in the ladle. The purpose is to prevent slag mixed with the molten steel from flowing into the crystallizer, thereby improving the cleanliness of the molten steel in the tundish and reducing the amount of slag mixed in (because a higher cleanliness of the molten steel in the tundish allows more molten steel to flow into the crystallizer to produce slabs). When the molten steel in the ladle is almost finished casting, as mentioned above, the slag discharge detection and prediction device at the bottom of the ladle will sound. Once it sounds, it means that slag has flowed into the tundish with the steel flow. At this time, the sliding plate above the long nozzle of the ladle should be closed immediately. This means that the casting of this ladle of molten steel is complete, and preparations are made for the next ladle of molten steel to be cast into the tundish.

[0019] Step 2 Explanation: The alarm setting of the slag detection and prediction device is related to the slag area of ​​the steel flow cross-section at the long nozzle of the ladle. Specifically, when the slag area reaches a certain percentage of the long nozzle's cross-sectional area (the preset value is the percentage of the slag area to the nozzle's inner diameter cross-section, called the slag alarm value in production), the slag detection and prediction alarm will sound. Obviously, the larger the slag alarm value, the greater the amount of slag flowing. However, in normal production, the slag detection alarm value is always a fixed constant (M).

[0020] Step 3: Control the remaining molten steel in the tundish (i.e., reduce the amount of mixed casting). The method is as follows: before casting the next ladle of dissimilar steel, when the slag detection device alarms at the end of the casting process, adjust the alarm value M of the molten steel in the previously being cast ladle to a new, required alarm value (Y), and link it to the amount of molten steel (T) in the ladle.

[0021] T=(MY) / 5

[0022] In the formula: T - the amount of molten steel with less slag, in tons;

[0023] M - The daily fixed slag discharge alarm value (do not add the percentage sign %).

[0024] Y - Adjusted slag discharge alarm value (do not add the percentage sign %)

[0025] Step 3 Explanation: Regarding reducing the amount of molten steel mixed in the tundish, if the alarm value decreases by 5 (do not add the percentage sign here), then 1 ton of molten steel can be reduced from being poured into the tundish. That is, before mixing molten steel of different grades in the lower ladle, the remaining molten steel in the tundish can be reduced by 1 ton.

[0026] Step 3 differs from the previous method. When the molten steel in the tundish is reduced to the normal tonnage (around 30 tons), it can continue to be reduced. Previously, however, once reduced to the normal tonnage, it would stop (otherwise slag would be added), and instead, the next batch of dissimilar molten steel would be poured into the tundish, resulting in a larger mixing volume. Now, the above formula is used to control the mixing volume. This invention represents a method developed in production to approximately reduce the mixing volume of molten steel in the tundish.

[0027] Step 4: While implementing Step 3, control the opening of the tundish stopper rod to further reduce the amount of molten steel remaining in the tundish (i.e., further reduce the amount of mixed casting). The method is to establish the relationship between the opening of the tundish stopper rod and the reduction of the amount of mixed casting based on the different mixed casting steel grades with different quality requirements.

[0028] Step 4 Explanation: After the ladle slide is closed, the amount of molten steel in the tundish is controlled by the opening of the stopper rod. The larger the opening of the tundish stopper rod, the greater the amount of molten steel flowing into the crystallizer, and the faster the amount of molten steel in the tundish decreases, but the greater the slag entrapment. Conversely, the smaller the opening, the less molten steel flows into the crystallizer, the slower the amount of molten steel in the tundish decreases, and the less slag entrapment, or even no slag entrapment (the slag is blocked by the stopper rod). Based on this characteristic, in practice, the following relationship has been established between the stopper rod opening and the reduction in the amount of molten steel in the tundish (i.e., the molten steel waiting to be mixed and poured):

[0029] N=(100-K) / 25,

[0030] In the formula:

[0031] N - The amount of steel to be poured into the molten steel, in tons;

[0032] K - stopper opening value, substituted with a number without a percentage sign;

[0033] In the formula, "100" refers to the full opening value of the stopper rod.

[0034] Step 5: Once the tundish tonnage (i.e., the amount of mixed steel) has been controlled to the required level according to the above steps, the ladle from the previous heat is moved to the non-working position, while the ladle awaiting the mixed steel is rotated to the casting position, and the ladle slide is opened for mixing. This completes the operation of reducing the amount of mixed steel.

[0035] Compared with the prior art, the present invention has the following advantages: (1) The ladle slag detection technology is used to control slag at the end of ladle casting. It is a control technology for slag in molten steel in ladle during normal casting. The present invention uses this technology to control the amount of molten steel mixed in the tundish. It is an innovative technology that has not been reported before. Its core technical means is to improve the cleanliness of molten steel in the tundish by strictly controlling the amount of slag, so as to reduce the amount of molten steel mixed in the tundish (because if the cleanliness of molten steel in the tundish is high, too much molten steel in the tundish can flow into the crystallizer to produce slabs). When applying slag detection, the parameters were modified and not used directly, which reflects creativity. (2) The stopper rod to control the steel flow rate is a technical means that must be used in almost every heat of molten steel in the tundish during continuous casting to control the stability of the amount of molten steel in the tundish during the casting process. However, in the mixed casting process, the peers have never used the method of controlling the opening of the stopper rod to reduce the amount of mixed casting. The common situation is to use baffles and other technologies to reduce the amount of mixed casting. This invention uses stopper opening control to reduce the amount of mixed casting, which has not been reported before. Moreover, when using it, it does not directly control the stopper opening using conventional methods, but establishes a stopper opening control mode to reduce the amount of mixed casting, which reflects creativity. (3) The technology used in this invention to reduce the amount of mixed casting is simple, easy to implement, highly practical, requires no investment, is highly feasible, and has no pollution, reflecting the concept of green steelmaking production. Detailed Implementation

[0036] To enhance understanding of the present invention, detailed descriptions are provided below in conjunction with embodiments.

[0037] Example 1: A method for reducing the amount of dissimilar steel grades mixed in the tundish of continuous casting, the method comprising the following steps:

[0038] Step 1: The ladle filled with molten steel of a different grade is transported by a crane to the ladle turret of the continuous casting machine, so that it is in the waiting position for casting. At this time, the molten steel in the ladle that was originally being cast (which is of a different grade than the molten steel in the ladle in the waiting position) is being cast into the tundish through the long nozzle at the bottom of the ladle.

[0039] Step 2: Tighten the slag discharge alarm value in the ladle. The purpose is to prevent slag mixed with the molten steel from flowing into the crystallizer, thereby improving the cleanliness of the molten steel in the tundish and reducing the amount of slag mixed in (because a higher cleanliness of the molten steel in the tundish allows more molten steel to flow into the crystallizer to produce slabs). When the molten steel in the ladle is almost finished casting, as mentioned above, the slag discharge detection and prediction device at the bottom of the ladle will sound. Once it sounds, it means that slag has flowed into the tundish with the steel flow. At this time, the sliding plate above the long nozzle of the ladle should be closed immediately. This means that the casting of this ladle of molten steel is complete, and preparations are made for the next ladle of molten steel to be cast into the tundish.

[0040] Step 2 Explanation: The alarm setting of the slag detection and prediction device is related to the slag area of ​​the steel flow cross-section at the long nozzle of the ladle. Specifically, when the slag area reaches a certain percentage of the long nozzle's cross-sectional area (the preset value is the percentage of the slag area to the nozzle's inner diameter cross-section, called the slag alarm value in production), the slag detection and prediction alarm will sound. Obviously, the larger the slag alarm value, the greater the amount of slag flowing. However, in normal production, the slag detection alarm value is always a fixed constant (M).

[0041] Step 3: Control the remaining molten steel in the tundish (i.e., reduce the amount of mixed casting). The method is as follows: before casting the next ladle of dissimilar steel, when the slag detection device alarms at the end of the casting process, adjust the alarm value M of the molten steel in the previously being cast ladle to a new, required alarm value (Y), and link it to the amount of molten steel (T) in the ladle.

[0042] T=(MY) / 5

[0043] In the formula: T - the amount of molten steel with less slag, in tons;

[0044] M - The daily fixed slag discharge alarm value (do not add the percentage sign %).

[0045] Y - Adjusted slag discharge alarm value (do not add the percentage sign %)

[0046] Step 3 Explanation: Regarding reducing the amount of molten steel mixed in the tundish, if the alarm value decreases by 5 (do not add the percentage sign here), then 1 ton of molten steel can be reduced from being poured into the tundish. That is, before mixing molten steel of different grades in the lower ladle, the remaining molten steel in the tundish can be reduced by 1 ton.

[0047] Step 3 differs from the previous method. When the molten steel in the tundish is reduced to the normal tonnage (around 30 tons), it can continue to be reduced. Previously, however, once reduced to the normal tonnage, it would stop (otherwise slag would be added), and instead, the next batch of dissimilar molten steel would be poured into the tundish, resulting in a larger mixing volume. Now, the above formula is used to control the mixing volume. This invention represents a method developed in production to approximately reduce the mixing volume of molten steel in the tundish.

[0048] Step 4: While implementing Step 3, control the opening of the tundish stopper rod to further reduce the amount of molten steel remaining in the tundish (i.e., further reduce the amount of mixed casting). The method is to establish the relationship between the opening of the tundish stopper rod and the reduction of the amount of mixed casting based on the different mixed casting steel grades with different quality requirements.

[0049] Step 4 Explanation: After the ladle slide is closed, the amount of molten steel in the tundish is controlled by the opening of the stopper rod. The larger the opening of the tundish stopper rod, the greater the amount of molten steel flowing into the crystallizer, and the faster the amount of molten steel in the tundish decreases, but the greater the slag entrapment. Conversely, the smaller the opening, the less molten steel flows into the crystallizer, the slower the amount of molten steel in the tundish decreases, and the less slag entrapment, or even no slag entrapment (the slag is blocked by the stopper rod). Based on this characteristic, in practice, the following relationship has been established between the stopper rod opening and the reduction in the amount of molten steel in the tundish (i.e., the molten steel waiting to be mixed and poured):

[0050] N=(100-K) / 25,

[0051] In the formula:

[0052] N - The amount of steel to be poured into the molten steel, in tons;

[0053] K - stopper opening value, substituted with a number without a percentage sign;

[0054] In the formula, "100" refers to the full opening value of the stopper rod.

[0055] Step 5: Once the tundish tonnage (i.e., the amount of mixed steel) has been controlled to the required level according to the above steps, the ladle from the previous heat is moved to the non-working position, while the ladle awaiting the mixed steel is rotated to the casting position, and the ladle slide is opened for mixing. This completes the operation of reducing the amount of mixed steel.

[0056] Example 2:

[0057] The highlight of this invention is the establishment of a formula for reducing the amount of residual molten steel in the tundish by controlling slag discharge during the continuous casting process. This allows for the reduction of molten steel in the tundish (i.e., the amount of molten steel awaiting mixing), ensuring that even when the molten steel level falls below the critical vortex height (i.e., the critical slag entrainment height, which normally leads to slag entrainment into the crystallizer), slag entrainment into the crystallizer will not occur, thus minimizing the amount of molten steel to be mixed. In short, by reducing the amount of molten steel in the tundish (i.e., the amount awaiting mixing) to below the critical slag entrainment height, this invention prevents slag entrainment into the crystallizer. Normal methods for reducing the amount of molten steel to mix cannot reduce it below the critical slag entrainment height in the tundish.

[0058] The specific implementation method of this invention patent is as follows:

[0059] Step 1: Molten steel of different grades to be mixed enters the ladle turret of the continuous casting platform and is in the waiting position. At this time, the molten steel pouring in the ladle is almost finished. The predicted value of the slag discharge detection in the ladle is adjusted by 25% according to the formula: T=(MY) / 5, so as to close the bottom slide plate of the ladle in advance. The purpose is to reduce the amount of slag discharge (i.e., to prevent or reduce the slag in the ladle from flowing into the molten steel in the tundish below the ladle). This way, due to the high cleanliness of the molten steel in the tundish, more will flow into the crystallizer to produce slabs, thus reducing the amount of mixed molten steel poured into the tundish. The following are some scenarios for reducing the amount of mixed molten steel poured into the tundish by controlling the slag discharge detection, as shown in Table 1.

[0060] Table 1. Implementation methods for reducing the amount of molten steel mixed in the tundish by setting slag detection and prediction values.

[0061]

[0062] Step 2: When the slag detection alarm is heard during Step 1, immediately close the sliding plate at the bottom of the ladle to stop the molten steel from flowing down. At this time, the molten steel in the tundish below the ladle continues to flow into the crystallizer. To reduce the amount of molten steel mixed in the tundish and allow too much molten steel to flow into the crystallizer for slab production, the stopper opening is adjusted. This allows the molten steel in the tundish to continue flowing into the crystallizer while preventing slag from flowing into the crystallizer. The method is to reduce the stopper opening by adjusting the amount according to the formula: T=(100-K) / 25, as shown in Table 2.

[0063] Table 2. Implementation methods for reducing the amount of concrete poured using stopper rod opening adjustment

[0064]

[0065] Step 3: After step 2 is completed, return the molten steel from the ladle of different steel grades that was in the waiting position to the working position (or return it in advance during step 2), open the bottom slide plate of the ladle, and the molten steel of different steel grades will flow into the tundish, completing the mixing and casting task.

[0066] Through the implementation of the above measures, the average number of times per year that the tundish tonnage needs to be controlled for mixed casting is 1500. Generally, mixed casting of steel grades accounts for 15% of the total number of times, reducing the mixed casting volume by 2 tons / tundish. Specifically, step 1 (reducing the mixed casting volume by setting slag detection prediction values) reduces the mixed casting volume by 1 ton / tundish, and step 2 (reducing the mixed casting volume by adjusting the stopper rod opening) also reduces the mixed casting volume by 1 ton / tundish. Mixed casting of steel grades with higher downgrade requirements accounts for 85% of the total number of times, reducing the mixed casting volume by 4 tons / tundish. Specifically, step 1 (reducing the mixed casting volume by setting slag detection prediction values) reduces the mixed casting volume by 2 tons / tundish, and step 2 (reducing the mixed casting volume by adjusting the stopper rod opening) also reduces the mixed casting volume by 2 tons / tundish. Therefore, the annual reduction in mixed casting volume is calculated as follows:

[0067] 1500 * 15% * (1 + 1) + 1500 * 85% * (2 + 2) = 450 + 5100 = 5550 tons. Calculated annually, this reduces the amount of mixed-cast steel by 5550 tons / year. Based on actual production, 1 ton of remaining molten steel in the tundish can produce 2 tons of mixed-cast steel slabs, resulting in a total annual reduction of 5550 * 2 = 11,100 tons of mixed-cast steel. The actual annual economic benefit = downgrade loss per ton of steel (200 yuan / ton) * downgraded mixed-cast steel slab conversion amount = 200 yuan / ton * 11,100 tons = 2.22 million yuan.

[0068] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for reducing the amount of dissimilar steel grades mixed in the tundish of continuous casting, characterized in that, The method includes the following steps: Step 1: The ladle filled with molten steel of a different grade is transported by overhead crane to the ladle turret of the continuous casting machine, placing it in the waiting position for casting. Step 2: Tighten the slag discharge alarm value in the ladle. Step 3: Control the amount of molten steel remaining in the tundish. Step 4: While implementing Step 3, control the opening of the tundish stopper rod in order to continue to reduce the amount of molten steel remaining in the tundish; Step 5: When the tonnage of the tundish, i.e. the amount of mixed casting, is controlled to the required amount of mixed casting of different steel grades according to the above steps, the ladle of the previous furnace is moved to the non-working position, while the ladle of the waiting molten steel of different grades is rotated to the casting position, and the ladle slide is opened for mixed casting. At this point, the operation of reducing the amount of mixed casting is completed. Step 2: Adjust the slag discharge alarm value of the ladle. Specifically, the alarm setting of the slag discharge detection and prediction device is related to the slag area of ​​the cross-section of the steel flow at the long nozzle of the ladle. That is, when the slag area reaches a certain percentage of the cross-sectional area of ​​the long nozzle, the alarm setting value is the percentage of the slag area to the inner diameter of the nozzle cross-section. In production, this is called the slag discharge alarm value. The slag discharge detection and prediction device will then sound an alarm. Obviously, the larger the slag discharge alarm value, the greater the amount of slag discharged. However, in normal production, the daily fixed slag discharge alarm value M is a fixed constant. Step 3: Controlling the remaining molten steel in the tundish reduces the amount of mixed casting. Before casting the next ladle of dissimilar steel, when the slag detection device alarms at the end of the casting process, the normally fixed slag alarm value M is adjusted to a new, adjusted slag alarm value Y, and this is linked to the amount of molten steel T with less slag. T=(MY) / 5 In the formula: T - the amount of molten steel with less slag, in tons; M - The daily fixed alarm value for slag discharge; Y - Adjusted slag discharge alarm value; Regarding reducing the amount of molten steel mixed in the tundish, if the alarm value decreases by 5, then 1 ton of molten steel will be reduced from the tundish. That is, before mixing molten steel of different grades in the lower ladle, the remaining molten steel in the tundish will be reduced by 1 ton.

2. The method for reducing the amount of dissimilar steel grades mixed in the continuous casting tundish according to claim 1, characterized in that, Step 4: While implementing Step 3, control the opening of the tundish stopper rod to further reduce the amount of molten steel remaining in the tundish, i.e., to further reduce the amount of mixed casting. After the ladle slide is closed, the amount of molten steel in the tundish is controlled by the opening of the stopper rod. The larger the opening of the tundish stopper rod, the greater the amount of molten steel flowing into the crystallizer, and the faster the amount of molten steel in the tundish decreases, but the greater the degree of slag entrapment. Conversely, the smaller the opening, the less molten steel flows into the crystallizer, the slower the amount of molten steel in the tundish decreases, and the degree of slag entrapment is less, or even non-entrapment, i.e., the slag is blocked by the stopper rod. Based on this characteristic, in practice, the following relationship has been established between the stopper rod opening and the reduction of the amount of molten steel in the tundish, i.e., the amount of molten steel waiting to be mixed casting: N=(100-K) / 25, In the formula: N - The amount of steel to be poured into the molten steel, in tons; K - stopper opening value, substituted with a number without a percentage sign; In the formula, "100" refers to the full opening value of the stopper rod.

Images