A method for on-line detection and automatic control of residual steel height in continuous casting tundish

Abstract

The application discloses a kind of continuous casting tundish residual steel height on-line detection and automatic control method, comprising the following steps: setting liquidus temperature measuring point in tundish;Casting operation starts, liquid steel enters tundish;Temperature measured by temperature measuring instrument continues to rise and is higher than 1450 DEG C, start into continuous casting state;Temperature measured by temperature measuring instrument is maintained at 1500-1550 DEG C, continuous casting state continues to carry out;Temperature measured by temperature measuring instrument drops and is lower than 1500 DEG C, start to detect temperature drop rate;Temperature drop rate measured by temperature measuring instrument reaches per minute cooling more than 12.5 DEG C, judge tundish residual steel as low liquid level state;Record current tundish tonnage data;Close tundish outlet, end casting operation.The application solves the security risk when manual operation, prevents abnormal accident from happening due to manual judgment, effectively controls production logistics stability and safety, solves production safety and the effect of controlling continuous casting production quality problem.

Description

Technical Field

[0001] This invention relates to online detection technology in the steel industry, and more specifically, to a method for online detection and automatic control of residual steel height in continuous casting tundish. Background Technology

[0002] Continuous casting is an important process in steel production. Figure 1 The process of continuous casting was revealed. For example... Figure 1 As shown, the continuous casting process includes: molten steel from ladle 11 mounted on rotary tower 10 is first poured into tundish 12, and then the molten steel from tundish 12 is poured into crystallizer 13. The molten steel cools in crystallizer 13 to form a billet, which is then pulled out of crystallizer 13 by dredger 14. Support rollers 15, agitator 16, and cooling nozzles 17 are installed along the billet's pull-out path to ensure continuous cooling and gradual solidification of the billet during the pull-out process, ultimately resulting in cutting by flame cutter 18.

[0003] In continuous casting, the tundish is one of the key pieces of equipment in the production process. The tundish plays a crucial role in stabilizing, distributing, and storing molten steel, flotating inclusions, and homogenizing the temperature and composition of the molten steel. It is vital for smooth continuous casting operations and ensuring steel quality. Among the various production parameters related to the tundish, the weight control of the molten steel in the tundish is a key indicator for continuous casting production and quality control. The weight of the molten steel involves the following four aspects:

[0004] Tundish flow field stability: When the tundish tonnage is too low and the tonnage changes too rapidly, the internal flow is disordered, and a large number of inclusions will not have time to float to the surface and will be drawn into the crystallizer, causing defects in the quality of the billet or even steel leakage accidents.

[0005] The impact of changes in molten steel static pressure on the stability of the casting surface in the mold. Typically, during rapid changes in the weight of the tundish, the static pressure in the casting channel from the tundish to the mold changes significantly. Insufficient response speed of the flow control system leads to large fluctuations in the casting surface, which is a significant factor contributing to slag inclusions and impurities in the billet.

[0006] Excessive molten steel content in the tundish can easily cause molten steel to overflow from the tundish overflow port or even the top edge of the tundish, leading to on-site safety accidents.

[0007] The residual steel height in the tundish near the low critical height has multiple impacts on casting safety, quality control, and continuous casting yield. Specifically, during abnormal continuous casting operations (disruption of subsequent ladle connections), continuous casting of different steel grades using iron plates (physically isolating molten steel from successive heats using iron plates inside the crystallizer), tundish replacement for continuous casting, and before the final casting of continuous casting CAST, if the residual steel height in the tundish falls below the critical height and the stopper (or flow control device such as a slide plate) is not closed in time, a vortex will form above the injection port of the crystallizer's casting channel, drawing in the acidic slag, covering agent, and a large amount of inclusions accumulated in the tundish into the crystallizer. This can easily lead to steel leakage, bulging, and severe slag and inclusion defects in the billet. Conversely, if the stopper (or slide plate) is closed too early, there will be too much residual molten steel in the tundish, resulting in steel loss and increasing the difficulty of the tundish removal process.

[0008] Currently, all tundishes used in continuous casting processes have weighing devices. These devices typically consist of several weighing pressure sensors mounted on the tundish car's lifting platform. The weighing composition includes the weight of the tundish itself and the weight of the molten steel inside. Before casting begins, a tare elimination function removes the weight of the tundish itself to obtain the weight of the molten steel inside. However, because this weighing device has a large weighing range—for example, the maximum capacity of molten steel in a slab continuous casting tundish at a steel plant is 70 tons, and the weight of the tundish itself is 60 tons—the weighing range of this casting machine is between 0 and 130 tons. Its weighing linearity cannot meet the weighing accuracy requirements of such a wide range. Furthermore, because the weighing device is mounted on a movable lifting platform, the flatness of this platform and the dust and debris around each weighing head significantly affect the weighing accuracy. In addition, due to the temperature control issues during continuous casting, the varying degrees of solidification of molten steel inside the tundish at low tonnage levels can interfere with the on-site judgment of the actual height of the molten steel inside the tundish.

[0009] Therefore, the weighing device in the tundish can only serve as a trend indicator of the molten steel weight. In actual production, after casting begins, operators need to visually inspect or use specialized tools to correct the actual weight of the molten steel in the tundish. In cases of continuous casting with different steel grades using tundish plates, tundish replacement for continuous casting, abnormal operations leading to extremely low tundish tonnage, and before the final casting of continuous casting, the molten steel in the tundish must be repeatedly corrected through manual measurement. This involves the operator standing on the tundish lid or rim, inserting an oxygen rod into a specific position within the molten steel, removing the oxygen rod, measuring the height of the molten steel on the rod, and then roughly calculating the actual weight based on the shape of the tundish. However, this operation is highly dangerous, and variations in individual operating techniques can lead to significant errors, hindering the automation and de-manning of continuous casting. Due to the high risk of direct manual measurement, robotic arms have been used to perform high-risk sampling, and cameras have replaced visual observation of the molten steel surface on the tundish rods. However, this method still requires manual judgment and estimation. Manual judgment and estimation cannot effectively and accurately determine the amount of residual molten steel in the tundish, and misjudgments are frequent. In the event of human error or oversight, slag may easily be introduced into the tundish, resulting in slag inclusions in the slab, or even blockage of the drain outlet, causing quality and safety accidents. Summary of the Invention

[0010] This invention discloses a method for online detection and automatic control of residual steel height in a continuous casting tundish, comprising the following steps:

[0011] Set up liquid phase temperature measurement points inside the intermediate batch;

[0012] The casting operation begins, and molten steel enters the tundish;

[0013] The temperature measured by the thermometer continued to rise and exceeded 1450 degrees Celsius, indicating that the continuous casting process had begun.

[0014] The temperature measured by the thermometer was maintained at 1500-1550 degrees Celsius, and the continuous casting process continued.

[0015] When the temperature measured by the thermometer drops below 1500 degrees Celsius, the rate of temperature drop is monitored.

[0016] The temperature drop rate measured by the thermometer reached more than 12.5 degrees Celsius per minute, indicating that the residual steel in the tundish was in a low liquid level state.

[0017] Record the current tonnage data of the intermediate package;

[0018] Close the tundish outlet and end the casting operation.

[0019] According to one embodiment of the present invention, the liquid phase temperature measuring point is a temperature measuring instrument set inside the tundish. The temperature measuring instrument is placed in the lower middle part of the tundish and is wrapped with refractory material to isolate the temperature measuring instrument from the liquid steel.

[0020] According to one embodiment of the present invention, a preheating step is further included before the casting operation begins, in which the intermediate ladle is preheated and baked. During the preheating step, the temperature measured by the thermometer gradually rises from room temperature to 1150 degrees Celsius.

[0021] According to one embodiment of the present invention, after the preheating step is completed, the baking of the intermediate bread is stopped, and the temperature measured by the thermometer decreases due to natural heat dissipation.

[0022] According to one embodiment of the present invention, the temperature measured by the thermometer continues to rise and exceeds 1450 degrees Celsius, indicating that the molten steel has submerged the temperature measuring point.

[0023] According to one embodiment of the present invention, the temperature measured by the thermometer drops and falls below 1500 degrees Celsius, indicating that the liquid steel level has fallen below the measuring point, but the measuring point is still surrounded by steel slag.

[0024] According to one embodiment of the present invention, when the temperature drop rate measured by the thermometer reaches more than 12.5 degrees Celsius per minute, it indicates that the temperature measuring point has been separated from the liquid steel and slag and is exposed to the air.

[0025] According to one embodiment of the present invention, the placement of the temperature measuring instrument in the tundish satisfies the following condition: when the temperature measuring instrument is exposed to air, the liquid steel level is at the tundish outlet, while the slag and inclusions in the tundish have not yet reached the tundish outlet.

[0026] According to one embodiment of the present invention, after closing the tundish outlet and ending the casting operation, the actual weight W2′ of the molten steel is obtained according to the compensation algorithm of the host computer, as follows:

[0027] After the pouring is completed, the casting speed is reduced to a safe casting speed V2 based on the casting cross-section and the current speed V1.

[0028] The host computer simultaneously calculates the required molten steel volume W4 for decelerating from V2 to maintaining the casting speed V3 before final pouring under different cross sections and deceleration rates, as well as the required molten steel volume W5 for the holding time required to obtain the shrinkage cavity in the billet.

[0029] Then, based on the theoretical weight W6 of the intermediate ladle calculated from the critical height H3 for preventing slag entrapment, the weight W3 of the intermediate ladle at the starting point of the second deceleration is calculated.

[0030] When the tonnage of the tundish drops to H1′, the tonnage of the tundish is automatically corrected to W2′.

[0031] When the tonnage of the intermediate tundish reaches W3, the second deceleration begins, and the pulling speed drops from V2 to V3;

[0032] When the tonnage of the tundish is equal to W6, close the outlet of the tundish and end the casting operation of the tundish.

[0033] The online detection and automatic control method for residual steel height in the continuous casting tundish of this invention can solve the safety hazards of manual operation and prevent abnormal accidents caused by human judgment, effectively controlling the stability and safety of production logistics, and achieving the effect of solving production safety and controlling continuous casting production quality problems. This invention uses the temperature measured by a thermometer in the tundish to intuitively determine the liquid steel level height in the tundish, and based on this, a model mechanism for predictive lead time can be used to perform online measurement and judgment during continuous casting. This method is simple and convenient, with mature technical principles, and is also convenient and practical in practice. Attached Figure Description

[0034] Figure 1 The process of continuous casting was revealed.

[0035] Figure 2 The flowchart of the method for online detection and automatic control of residual steel height in continuous casting tundish of the present invention is disclosed.

[0036] Figure 3 The temperature change trend of the tundish during the preheating stage is revealed by the graph.

[0037] Figure 4 The temperature variation trend of the tundish during the continuous casting stage is revealed.

[0038] Figure 5 The graph reveals the temperature change trend of the tundish when it enters a low liquid level state.

[0039] Figure 6 The diagram reveals the rate of temperature decrease in the tundish when it enters a low liquid level state.

[0040] Figure 7 The schematic diagram of the online detection and automatic control method for residual steel height in continuous casting tundish of the present invention is disclosed. Detailed Implementation

[0041] As an important aspect of automated continuous casting production, continuous temperature measurement in the tundish has been widely adopted in casting machines. This invention utilizes the continuous temperature measurement function of the temperature measuring instrument equipped in the tundish. Based on the inflection point of the continuous temperature measurement value, combined with the change in the tundish weighing value, and the characteristics of the cast steel grade and the trend model of superheat change, it comprehensively calculates the residual steel height and steel production in the tundish at low tonnage.

[0042] Figure 2A flowchart of the online detection and automatic control method for residual steel height in continuous casting tundish of the present invention is disclosed. (Reference) Figure 2 As shown, the online detection and automatic control method for residual steel height in the continuous casting tundish includes the following processes:

[0043] A liquid phase temperature measuring point is installed inside the tundish. In one embodiment, the liquid phase temperature measuring point is a temperature measuring instrument installed inside the tundish. The temperature measuring instrument is placed in the lower middle part of the tundish and is wrapped with refractory material to isolate the temperature measuring instrument from the molten steel. As mentioned earlier, with the advancement of automation in continuous casting processes, more and more tundishes are being equipped with temperature measuring instruments. The temperature measuring instruments are usually installed in the lower middle position of the tundish and wrapped with refractory material to prevent the temperature measuring instrument from being damaged by direct contact with the high-temperature molten steel.

[0044] The preheating step involves preheating the intermediate bread, during which the temperature measured by the thermometer gradually rises from room temperature to 1150 degrees Celsius. After the preheating step is completed, baking of the intermediate bread is stopped, and the temperature measured by the thermometer drops due to natural heat dissipation. Figure 3 The temperature change trend of the tundish during the preheating stage is revealed by the graph. Figure 3 The horizontal axis represents time, and the vertical axis represents temperature. For example... Figure 3 As shown, the tundish needs to be preheated before casting, and the preheating temperature can reach up to about 1150 degrees Celsius. After preheating, the molten steel is poured, and the temperature reading on the thermometer shows an upward trend. Figure 3 The leftmost box represents the temperature during the tundish preheating process. Once preheating begins, the tundish is gradually heated from room temperature to approximately 1150 degrees Celsius. The middle box represents the preparation stage after the tundish leaves the preheating stage. During this stage, due to the lack of a heat source, the tundish undergoes heat dissipation, resulting in a temperature rise (cooling down). The rightmost box represents the stage where molten steel is added to the tundish for casting, causing a rapid temperature increase.

[0045] The casting process begins, and molten steel enters the tundish. The ladle's outlet is opened, and molten steel flows from the ladle into the tundish.

[0046] When the temperature measured by the thermometer continues to rise and exceeds 1450 degrees Celsius, the continuous casting process begins. When the temperature measured by the thermometer continues to rise and exceeds 1450 degrees Celsius, it indicates that the molten steel has submerged the measuring point, meaning that the molten steel level in the tundish is higher than the position of the thermometer.

[0047] The temperature measured by the thermometer was maintained at 1500-1550 degrees Celsius, and the continuous casting process continued.

[0048] From the start of the casting operation to the ongoing process of casting, the temperature changes as follows: Figure 4 As shown, Figure 4The temperature variation trend of the tundish during the continuous casting stage is revealed. Figure 4 The horizontal axis represents time, and the vertical axis represents temperature. During this stage, molten steel flows from the ladle into the tundish, gradually submerging the temperature measuring point of the thermometer. At this point, the temperature measured by the thermometer will accelerate from the moment the molten steel enters the tundish (representing the entry of molten steel into the tundish) until the molten steel submerges the thermometer. The temperature will reach the molten steel temperature (around 1550 degrees Celsius) in a stepped manner, and then enter a stable temperature state.

[0049] When the temperature measured by the thermometer drops below 1500 degrees Celsius, the rate of temperature drop is monitored. After one CAST (casting sequence) in continuous casting, the tundish needs to be replaced. At this time, it is desirable to drain as much molten steel as possible from the tundish to maximize resource utilization, while also preventing solid inclusions such as slag and covering agent from falling into the crystallizer to avoid accidents. When the temperature measured by the thermometer drops below 1500 degrees Celsius, it indicates that the molten steel level is below the measuring point. This places the measuring point at the critical surface between molten steel and slag, surrounded by slag. Figure 5 The graph reveals the temperature change trend of the tundish when it enters a low liquid level state. Figure 5 The horizontal axis represents time, and the vertical axis represents temperature. Figure 5 This is the temperature curve captured by the thermometer during the final stage of CAST. The inflection point circled in the image indicates the point where the temperature drops, highlighting the boundary between the thermometer and the molten steel / slag. From this, it can be determined that the relative liquid level of the molten steel is lower than the temperature measurement point, meaning that the temperature measured at this point is actually the temperature of the slag.

[0050] After the temperature drops below 1500 degrees Celsius, the rate of temperature decrease is monitored. A temperature decrease rate exceeding 12.5 degrees Celsius per minute, as measured by the thermometer, indicates a low liquid level in the tundish. As mentioned earlier, below 1500 degrees Celsius, the measuring point is at the critical point between molten steel and slag. Subsequently, as the liquid level in the tundish continues to decrease, the measuring point gradually separates from the slag and is exposed to the air, causing the temperature to decrease at an even faster rate. However, due to the insulation effect within the tundish and the thermal radiation from the molten steel, the measured temperature will still remain within the range of 1400 to 1450 degrees Celsius. Therefore, at this point, the rate of temperature decrease, rather than the endpoint of the temperature drop, should be used as the basis for judgment. Figure 6 The diagram reveals the rate of temperature decrease in the tundish when it enters a low liquid level state. Figure 6 The horizontal axis represents time, and the vertical axis represents temperature. When the temperature drop rate measured by the thermometer reaches more than 12.5 degrees Celsius per minute, it indicates that the measuring point has separated from the molten steel and slag and is exposed to the air.

[0051] Record the current tonnage data of the tundish. Record the tonnage data of the tundish at this time and enter it into the database to provide a data foundation for building a mathematical model to more accurately calculate and correct the molten steel level.

[0052] Close the tundish outlet and end the casting operation. When it is determined that the tundish has entered a low molten steel level state, close the stopper rod to prevent solid inclusions such as slag and covering agent from falling into the crystallizer. Based on the above design requirements, after calculations using a mathematical model and multiple tests, the placement of the temperature measuring instrument inside the tundish meets the following conditions: when the temperature measuring instrument is exposed to air, the molten steel level is at the tundish outlet, while the slag and inclusions inside the tundish have not yet reached the tundish outlet.

[0053] Figure 7 The schematic diagram of the online detection and automatic control method for residual steel height in continuous casting tundish of the present invention is disclosed.

[0054] refer to Figure 7 Online detection of residual steel height in continuous casting tundish: Utilizing the widely adopted continuous temperature measurement method in the tundish, a continuous temperature measuring coupler is installed in the lower part of the tundish wall of the tundish 20. The signal transmitted by the continuous temperature measuring coupler is acquired at a high frequency of less than 1 second. The continuous temperature signal exceeding and falling below the liquidus temperature of the steel grade being cast are taken as two points for measuring the height H1 of the molten steel 21 in the tundish at the start of casting and the height H1′ of the molten steel 21 at the end of casting. The weight W1 of the tundish 20 when the molten steel 21 reaches height H1 at the start of casting and the weight W2 of the tundish when the molten steel 21 reaches height H1′ at the end of casting are recorded. The actual weight W2′ of the molten steel 21 is obtained according to the compensation algorithm of the host computer.

[0055] Control method: After the large ladle is poured, the casting speed is reduced to a safe casting speed V2 based on the casting cross-section and the current speed V1.

[0056] The host computer simultaneously calculates the required steel water volume W4 for decelerating from V2 to maintaining the casting speed V3 before final pouring under different cross sections and deceleration rates, as well as the required steel water volume W5 for holding time to obtain the shrinkage cavity of the composite billet (no holding time is required for tundish replacement and the insertion of iron plates of different steel types).

[0057] Then, based on the theoretical weight W6 of the tundish calculated from the critical height H3 for preventing slag entrapment, the weight W3 of the tundish at the starting point of the second deceleration is calculated (i.e., W3 = W4 + W5 * α + W6). Note that α is the retention coefficient (different steel grades have different retention coefficients; α = 0 when inserting iron plates or replacing the tundish).

[0058] When the tonnage of tundish 20 drops to H1′, the tonnage of tundish 20 is automatically corrected to W2′.

[0059] When the tonnage of the intermediate tundish 20 reaches W3, the second deceleration begins, and the pulling speed is reduced from V2 to V3;

[0060] When the tonnage of tundish 20 is equal to W6, close the outlet of tundish 20 and end the casting operation of tundish 20.

[0061] The online detection and automatic control method for residual steel height in the continuous casting tundish of this invention can solve the safety hazards of manual operation and prevent abnormal accidents caused by human judgment, effectively controlling the stability and safety of production logistics, and achieving the effect of solving production safety and controlling continuous casting production quality problems. This invention uses the temperature measured by a thermometer in the tundish to intuitively determine the liquid steel level height in the tundish, and based on this, a model mechanism for predictive lead time can be used to perform online measurement and judgment during continuous casting. This method is simple and convenient, with mature technical principles, and is also convenient and practical in practice.

Claims

1. A method for on-line detection and automatic control of residual steel height in a continuous casting tundish, characterized in that, include: A liquid phase temperature measuring point is set in the tundish. The liquid phase temperature measuring point is a temperature measuring instrument set in the tundish. The temperature measuring instrument is placed in the lower middle part of the tundish and is wrapped with refractory material to isolate the temperature measuring instrument from the liquid steel. The casting operation begins, and molten steel enters the tundish. Before the casting operation begins, there is also a preheating step to preheat and bake the tundish. During the preheating step, the temperature measured by the thermometer gradually rises from room temperature to 1150 degrees Celsius. The temperature measured by the thermometer continued to rise and exceeded 1450 degrees Celsius, indicating that the continuous casting process had begun. The temperature measured by the thermometer was maintained at 1500-1550 degrees Celsius, and the continuous casting process continued. When the temperature measured by the thermometer drops below 1500 degrees Celsius, the rate of temperature drop is monitored. The temperature drop rate measured by the thermometer reached more than 12.5 degrees Celsius per minute, indicating that the residual steel in the tundish was in a low liquid level state. Record the current tonnage data of the intermediate package; Close the tundish outlet and end the casting operation. After closing the tundish outlet and ending the casting operation, the actual weight W2′ of the molten steel is obtained according to the compensation algorithm of the host computer, as follows: After the pouring is completed, the casting speed is reduced to a safe casting speed V2 based on the casting cross-section and the current speed V1. The host computer simultaneously calculates the required molten steel volume W4 for decelerating from V2 to maintaining the casting speed V3 before final pouring under different cross sections and deceleration rates, as well as the required molten steel volume W5 for the holding time required to obtain the shrinkage cavity in the billet. Then, based on the theoretical weight W6 of the intermediate ladle calculated from the critical height H3 for preventing slag entrapment, the weight W3 of the intermediate ladle at the starting point of the second deceleration is calculated. When the tonnage of the tundish drops to H1′, the tonnage of the tundish is automatically corrected to W2′. When the tonnage of the intermediate tundish reaches W3, the second deceleration begins, and the pulling speed drops from V2 to V3; When the tonnage of the tundish is equal to W6, close the outlet of the tundish and end the casting operation of the tundish.

2. The method for on-line detection and automatic control of residual steel level in a continuous casting tundish according to claim 1, characterized in that: After the preheating step is completed, the baking of the intermediate bread is stopped, and the temperature measured by the thermometer drops due to natural heat dissipation.

3. The method for on-line detection and automatic control of residual steel level in a continuous casting tundish according to claim 1, characterized in that: The temperature measured by the thermometer continued to rise and exceeded 1450 degrees Celsius, indicating that the molten steel had submerged the measuring point.

4. The method for on-line detection and automatic control of residual steel level in a continuous casting tundish according to claim 1, characterized in that: The temperature measured by the thermometer dropped and fell below 1500 degrees Celsius, indicating that the liquid steel level was below the measuring point, but the measuring point was still surrounded by steel slag.

5. The method for on-line detection and automatic control of residual steel level in a continuous casting tundish according to claim 1, characterized in that: The temperature drop rate measured by the thermometer reached more than 12.5 degrees Celsius per minute, indicating that the measuring point had separated from the molten steel and slag and was exposed to the air.

6. The method according to claim 5, characterized in that: The placement of the temperature measuring instrument inside the tundish satisfies the condition that when the temperature measuring instrument is exposed to air, the liquid steel level is at the tundish outlet, while the slag and inclusions inside the tundish have not yet reached the tundish outlet.

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