Method for online control of continuous casting slab quality

Abstract

The application discloses a method for online controlling the quality of continuous casting billets, which comprises the following steps: setting a temperature measuring device in front of a straightening and correcting machine, measuring the surface temperature of the continuous casting billets in real time through the temperature measuring device, adjusting the amount of secondary cooling water according to the surface temperature of the continuous casting billets, setting a weight and size setting device, measuring the cutting length and weight of the continuous casting billets, monitoring the cross-sectional size of the continuous casting billets, calculating the cutting cross-sectional area, combining the length and weight of the continuous casting billets to calculate the average density value of the continuous casting billets, and adjusting the cooling water amount of each partition of the secondary cooling of the continuous casting machine according to the cross-sectional size of the continuous casting billets and the average density value of the continuous casting billets. The method for online controlling the quality of continuous casting billets can quickly judge the internal quality of the continuous casting billets, does not need to additionally increase equipment investment, and improves the quality judgment efficiency of the continuous casting billets.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of casting billet production process, and particularly relates to a method for online control of continuous casting billet quality. BACKGROUND

[0002] The existing casting billet quality control system mainly adopts mathematical calculation model, and in the actual production process, the parameters such as the temperature of molten steel, the temperature of crystallizer water and the temperature of secondary cooling water have an influence, there is a large deviation between the calculation model and the actual working condition, the quality control is poor, and the casting billet quality is often detected by the most commonly used method of internal quality of casting billet, the feedback of quality information is relatively slow, and the casting billet quality is difficult to monitor in real time.

[0003] Continuous casting is a cooling and solidification process of solidifying molten steel into a casting billet, and the parameters such as the temperature of molten steel, the cooling water flow and the temperature will affect the cooling strength, if the cooling is uneven or the cooling strength is too large, the casting billet has the following two quality risks: 1. Surface cracks are prone to occur when the straightening temperature before the straightening machine is lower than the third brittle temperature (about 700-900℃); 2. When the casting billet cooling process is uneven shrinkage or the billet shell strength is not enough, the casting billet has shape defects such as bulging and off-square, which is easy to cause porosity and intermediate crack defects, and further produce internal cracks, serious segregation, porosity, shrinkage and other defects, that is, there is a certain corresponding relationship between the shape and internal defects of the casting billet.

[0004] The patent document with the publication number CN202639268U discloses an online control system for the surface quality of continuous casting billet, which comprises a casting billet quality determination and product quality diagnosis system server, a high-temperature casting billet surface defect online detection system server and a casting billet surface quality control system process station server. The surface quality of the casting billet provided by the casting billet surface quality defect online detection system is fed back to the casting billet surface quality online control system process station server, the process station server combines the abnormal situation of the process parameters determined by the casting billet quality tracking and determination system, accurately judges the problems existing in the quality defects, timely adjusts the process and equipment parameters, avoids causing more waste products to the next rolling process, reduces the production cost and energy consumption, improves the production efficiency, improves the yield and product quality. The technical solution disclosed in the patent document cannot solve the above-mentioned technical problems. SUMMARY

[0005] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application provides a method for online control of continuous casting billet quality, which aims to quickly judge the internal quality of the continuous casting billet and improve the determination efficiency.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for online control of the quality of continuously cast billets, wherein a temperature measuring device is set in front of the straightening machine to measure the surface temperature of the billet in real time, and the secondary cooling water volume is adjusted according to the surface temperature of the billet; and a fixed weight and fixed length device is set to measure the cutting length and weight of the billet, monitor the cross-sectional dimensions of the billet and calculate the cutting cross-sectional area, calculate the average density value of the billet in combination with the length and weight of the billet, and adjust the cooling water volume of each zone of the secondary cooling of the continuous casting machine according to the cross-sectional dimensions and average density value of the billet.

[0007] The temperature measuring device is an infrared thermometer.

[0008] The fixed weight and fixed length device includes a first infrared camera for measuring the cutting length of the billet and a billet weight measuring device for measuring the weight of the billet. The first infrared camera is set at the cutting position of the continuous casting machine, and the billet weight measuring device is set on the post-cut roller conveyor.

[0009] The method for online control of continuous casting billet quality includes the following steps:

[0010] S1. Based on the mathematical calculation model, determine the standard water volume of the zero section, I section, II section, III section, and IV section of the secondary cooling zone of the continuous casting machine under different steel grades and corresponding casting speed conditions;

[0011] S2. After the casting process is normal and the casting speed is stable, the temperature measuring device is turned on to measure the surface temperature of the billet in real time.

[0012] S3. After the billet reaches the cutting position, the length of the billet is measured by the fixed weight and fixed length device.

[0013] S4. The weight of the cut billet is measured by the fixed weight and length device, and the cross-sectional dimensions of the billet are checked. Finally, based on the length, cross-sectional dimensions and weight of the billet, the average density value of the billet is calculated to confirm whether there are any defects in the billet.

[0014] In step S2, if the surface temperature of the billet is lower than the third brittle temperature range of the corresponding steel grade, the amount of secondary cooling water in sections III and IV is first reduced to increase the surface temperature of the billet before the straightening machine. The amount of secondary cooling water reduction is critically measured by the billet surface warming rate in sections III, IV, and the air cooling zone from section IV to the straightening machine being less than or equal to the first set value. If the amount of secondary cooling water reduction in sections III and IV still cannot meet the requirement that the surface temperature of the billet before the straightening machine is higher than the third brittle temperature range, then following the principle that the billet surface warming rate is less than or equal to the first set value, the amount of secondary cooling water in sections II, I, and zero is reduced sequentially.

[0015] The first setting value is 100℃ / m.

[0016] In the step S2, if the surface temperature of the casting blank before the straightening machine is higher than the second set value, firstly, the water quantity of the second cooling in the section III and the section IV is increased to reduce the surface temperature of the casting blank before the straightening machine, and the water quantity increasing of the second cooling in the section III and the section IV is taken as the critical value and the cooling intensity is not greater than that of the previous section; if the water quantity increasing of the second cooling in the section III and the section IV reaches the critical value and still cannot satisfy the surface temperature of the casting blank before the straightening machine being lower than the second set value, then the water quantity of the second cooling in the section II, the section I and the zero section is sequentially increased according to the principle that the surface temperature reducing speed of the casting blank is taken as the critical value and the cooling intensity is not greater than that of the previous section, so that the surface temperature of the casting blank in the straightening machine is within a reasonable range.

[0017] The second set value is 1050℃, and the third set value is 200℃ / m.

[0018] In the step S4, the weight of the casting blank is measured by the roller scale, and the cross section size of the casting blank is detected by the second infrared camera arranged on one side of the roller scale.

[0019] The method for controlling the quality of the continuous casting blank in line provided by the application can quickly judge the internal quality of the casting blank, does not need to additionally increase equipment investment, and improves the judgment efficiency of the quality of the casting blank. DETAILED DESCRIPTION

[0020] The specific embodiments of the application are further described below through the description of the embodiments, which aims to help the skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the application, and to help the implementation.

[0021] The application provides a method for controlling the quality of a continuous casting blank in line, which measures the surface temperature of the casting blank in real time by arranging a temperature measuring device before the straightening machine, adjusts the water quantity of the second cooling according to the surface temperature of the casting blank, arranges a weight and size determining device to measure the cutting length and weight of the casting blank, monitors the cross section size of the casting blank and calculates the cutting cross section area, calculates the average density value of the casting blank according to the length and weight of the casting blank, and adjusts the water quantity of the second cooling of each section of the continuous casting machine according to the cross section size and the average density value of the casting blank.

[0022] Preferably, the temperature measuring device is an infrared temperature measuring device. The infrared temperature measuring device is arranged before the straightening machine to measure the surface temperature of the casting blank in real time, the water quantity of the second cooling of the continuous casting machine is reduced to reduce the cooling intensity and then increase the surface temperature of the casting blank if the surface temperature of the casting blank is lower than the third brittle temperature, and the water quantity of the second cooling of the continuous casting machine is increased to increase the cooling intensity and then reduce the surface temperature of the casting blank if the surface temperature of the casting blank is greater than 1050-1150℃.

[0023] As preferred, the gauge length and weight setting device comprises a first infrared camera for measuring the cutting length of the cast slab and a cast slab weight measuring device for measuring the weight of the cast slab, the first infrared camera is arranged at the cutting position of the continuous casting machine, the cast slab weight measuring device is arranged on the post-cut roller table, the cutting position of the continuous casting machine is provided with a cutting machine, the post-cut roller table is located behind the cutting machine, and the cast slab weight measuring device is used for measuring the weight of the cut cast slab. By arranging the gauge length and weight setting device (i.e. arranging the first infrared camera at the cutting position to determine the cutting length of the cast slab, and arranging the cast slab weight measuring device on the post-cut roller table), the cutting length and weight of the cast slab are measured, a second infrared camera is arranged on one side of the roller table, the second infrared camera is used for monitoring the cross-sectional shape and size of the cast slab and calculating the cutting cross-sectional area, the average density value of the cast slab is calculated in combination with the length and weight of the cast slab, and the control system of the continuous casting machine adjusts the water quantity of each partition of the secondary cooling zone according to the shape of the cast slab and the average density value of the cast slab.

[0024] The method for controlling the quality of the continuously cast slab on line according to the present application comprises the following steps:

[0025] S1, determining the standard water quantity of the zero section, the I section, the II section, the III section and the IV section of the secondary cooling zone of the continuous casting machine under the corresponding casting speed of different steel grades according to a mathematical calculation model;

[0026] S2, after the casting is started normally and the casting speed is stable, turning on the temperature measuring device arranged in front of the withdrawal and straightening machine, and measuring the surface temperature of the cast slab in real time by the temperature measuring device;

[0027] S3, after the cast slab reaches the cutting position, measuring the length of the cast slab by the gauge length and weight setting device;

[0028] S4, measuring the weight of the cut cast slab by the gauge length and weight setting device, detecting the cross-sectional size of the cast slab, and finally calculating the average density value of the cast slab according to the length, cross-sectional size and weight of the cast slab, and confirming whether the cast slab has defects.

[0029] In the embodiment, the continuous casting machine is a 6-machine 6-flow square billet machine, the cross section is 220mm*220mm, and the arc radius of the continuous casting machine is 12m. The secondary cooling zone of the continuous casting machine is divided into five cooling sections from top to bottom, namely the zero section, the I section, the II section, the III section and the IV section, and the cooling intensity of the zero section, the I section, the II section, the III section and the IV section decreases in turn.

[0030] In step S2, if the surface temperature of the casting blank is lower than the third brittle temperature value range corresponding to the steel grade, the casting blank is prone to straightening cracks in the straightening process. The system first reduces the secondary cooling water quantity of the III section and the IV section to increase the surface temperature of the casting blank before the withdrawal straightening machine. The secondary cooling water reduction quantity is taken as a critical value when the surface temperature of the casting blank in the III section, the IV section and the air cooling zone before the IV section to the withdrawal straightening machine is greater than the first set value. The critical value is based on a mathematical calculation model. If the secondary cooling water reduction quantity of the III section and the IV section reaches the critical value and still cannot satisfy the surface temperature of the casting blank before the withdrawal straightening machine being higher than the third brittle temperature value range, the secondary cooling water quantity of the II section to the I section and the zero section is sequentially reduced in the principle that the surface temperature of the casting blank is greater than the first set value as a critical value. The distance between the III section and the IV section and the withdrawal straightening machine is short, and the adjustment of the water quantity of the III section and the IV section has a greater influence on the surface temperature of the casting blank before the withdrawal straightening machine. As an optimization, the secondary cooling water quantity of the III section and the IV section is preferentially adjusted.

[0031] In the embodiment, the first set value is 100℃ / m. The heat source of the surface temperature reheat of the casting blank is the core of the casting blank. The greater the surface temperature reheat of the casting blank is, the weaker the cooling at the position is, the worse the cooling uniformity in the whole cooling process is, the easy to cause solidification bridging, and the more the internal defects such as center porosity and intermediate crack are. In addition, the surface temperature reheat of the casting blank will make the surface temperature of the casting blank increase. The higher the temperature is, the faster the grain growth is, the faster the alloy element precipitates at the grain boundary is, the more the grain boundary and the grain boundary weakening are intensified, the mechanical properties of the surface of the casting blank are reduced, and the surface crack trend is increased. Therefore, the upper limit of the surface temperature rise of the casting blank should be strictly controlled. In combination with the related documents and the actual situation on site, the surface temperature reheat of the casting blank is less than 100100℃ / m, which has a smaller influence on the quality of the casting blank. Therefore, the first set temperature is set to 100℃ / m.

[0032] In step S2, if the surface temperature of the casting blank before the withdrawal straightening machine is higher than the second set value, the strength of the casting blank is low, and the casting blank is prone to defects such as bulging and intermediate crack. The system first increases the secondary cooling water quantity of the III section and the IV section to reduce the surface temperature of the casting blank before the withdrawal straightening machine. The secondary cooling water increase quantity is taken as a critical value when the surface temperature of the casting blank in the III section and the IV section is less than the third set value and the cooling intensity is not greater than that of the previous section. The critical value is based on a mathematical calculation model. If the secondary cooling water increase quantity of the III section and the IV section reaches the critical value and still cannot satisfy the surface temperature of the casting blank before the withdrawal straightening machine being lower than the second set value, the secondary cooling water quantity of the II section to the I section and the zero section is sequentially increased in the principle that the surface temperature of the casting blank is less than the third set value and the cooling intensity is not greater than that of the previous section, so that the surface temperature of the casting blank in the withdrawal straightening machine is in a reasonable range. The surface temperature of the casting blank before the withdrawal straightening machine is controlled in an optimal temperature range, and then the risk of the surface and internal quality defects of the casting blank is reduced to a minimum.

[0033] Due to the oxidation of the casting blank and the air, the surface of the casting blank produces iron oxide scale. The temperature of the iron oxide scale is far lower than the surface temperature of the casting blank. The casting blank temperature measuring device can automatically exclude the abnormally low temperature measurement value.

[0034] In the present embodiment, the second set value is 1050℃, and the third set value is 200℃ / m. The second set value is set too high, and the interval of the slab surface temperature adjustment is too large. The excessively high slab surface temperature can cause the slab to have low strength, and can easily cause defects such as bulging and center cracks, which is not conducive to the quality control of the slab. If the second set value is set too low, the interval of the slab surface temperature adjustment is too small, and the operability is too low. In consideration of the quality of the slab and the operability, the second set value is set to 1050℃. If the third set value is set too high, the range of the slight adjustment of the cooling intensity of the slab is large. When the cooling intensity is too large, the temperature difference between the inside and the outside of the slab is large, that is, the thermal stress is large, and cracks are easily generated. In addition, the columnar crystal is abnormally grown, and internal defects such as center porosity, segregation, and center cracks are difficult to control. If the third set value is set too low, the range of the adjustment of the cooling intensity is small, and the operability is low. In consideration of the quality of the slab and the operability, the third set value is set to 200℃.

[0035] In the above step S3, after the slab reaches the cutting machine, the length of the slab is detected by the first infrared camera, and the slab is measured according to the set cutting length value. The production process needs to cut the slab into single slabs with the required weight. However, the cutting process cannot be weighed. As a preferred embodiment, a slab length measuring device is provided. The distance from the end of the slab to the cutting torch is detected by the slab length detection device, and the cutting position of the slab is determined in combination with the single meter weight value of the slab (that is, the weight of the slab per 1 meter length), so as to accurately control the cutting of the slab.

[0036] In the above step S4, the cut slab is conveyed to the roller scale (roller with weighing function) position through the conveying roller, and is stopped at the roller scale position. The weight of the slab is measured. The second infrared camera provided on one side of the roller scale detects the cross-sectional size of the slab, and transmits the weight and cross-sectional size information of the slab to the system. The system determines whether the slab has defects such as off-square, bulging, and concave according to the length, cross-sectional size, and weight of the slab, and calculates the average density value of the slab. The setting of the roller scale can quickly measure the weight of the cut slab. If the cutting weight is not within the range, the single meter weight value of the slab (that is, the weight of the slab per 1 meter length) is adjusted. The cutting length is adjusted in real time according to the adjusted single meter weight value of the slab, which can reduce the long and short size defects of the slab, and thus improve the production efficiency. That is, the combination of the roller scale and the first infrared camera can realize the accurate cutting of the slab. The present system needs to determine the cross-sectional shape of the online slab. Therefore, as a priority, the second infrared camera is provided. The present system also needs to determine the average density value. Therefore, as a priority, the first infrared camera is provided to detect the length of the slab, the roller scale is provided to measure the weight of the slab, and the average density value of the slab is calculated. In addition, the infrared camera and the roller scale are widely used and have stable use stability.

[0037] In step S4, if the cast blank has bulging or off-side defects, the control system first increases the secondary cooling water quantity of the zero section and the first section to increase the cooling intensity, and then increases the shell strength to control the bulging value. The secondary cooling water increase quantity is less than the fourth set value, which is the critical value of the surface temperature of the cast blank before the puller, and the surface temperature of the cast blank is greater than the third brittle temperature. The critical value is based on the mathematical calculation model. If the secondary cooling water increase quantity of the zero section and the first section reaches the critical value, the cast blank still cannot meet the shape size of the cast blank, and the principle of the surface temperature of the cast blank before the puller being less than the fourth set value and the surface temperature of the cast blank being greater than the third brittle temperature is followed to sequentially increase the secondary cooling water quantity of the second section to the third section and the fourth section to control the bulging value or off-side quantity of the cast blank. If the secondary cooling water quantity of each section has reached the maximum critical value, and the bulging defect of the cast blank is still over the standard, the cast blank is poured according to the maximum critical value of the secondary cooling water quantity, and an alarm is given to indicate that the cast blank has bulging or off-side defects. The thinner the shell is, the lower the surface strength is, and the easier the shape defects are to occur. Therefore, as an optimization, the secondary cooling water quantity is preferentially increased in the zero section and the first section when the cast blank has shape defects. The shape defects such as bulging and off-side are also affected by the shape of the inner cavity of the crystallizer copper pipe (and the mold size), the cooling uniformity and other working conditions. Especially when the secondary cooling spray gun is seriously blocked or the spray pipe is cracked and leaks, increasing the cooling water quantity will aggravate the uneven cooling, and then aggravate the shape defects. The shape of the inner cavity of the crystallizer copper pipe, the cooling uniformity and other working conditions need to be checked and confirmed after shutdown. Therefore, as a priority, the shape defect alarm function is set to ensure that the maintenance personnel check the inner cavity size of the copper pipe and the spraying effect immediately after shutdown, and replace or process the problematic parts.

[0038] In the present embodiment, the fourth set value is 200℃ / m. The fourth set value and the third set value are actually the same value, which is a critical value of the cooling intensity to ensure that the cooling intensity is within a certain range.

[0039] In step S4, if the cast blank has a concave defect, the control system gives an alarm to indicate that the cast blank has a concave defect, and the operator checks whether there is equipment abnormality such as nozzle falling off or dead roll on site.

[0040] According to the daily production records, a standard average density table under different steel grades and different pulling speeds is drawn. When the real-time calculated density of the cast blank is lower than the average density by 5%, the cast blank is prone to have serious center porosity or intermediate crack defects. At this time, the system automatically pops up an alarm signal of the low cast blank density value, and each secondary cooling partition increases the secondary cooling water quantity by 3% of the actual water quantity. If the cast blank density value is still over the standard, each secondary cooling partition increases the secondary cooling water quantity by 3% of the actual water quantity. If the cast blank density value is still low after the water quantity is adjusted twice, the system produces according to the adjusted actual water quantity, and gives an alarm signal of the cast blank density being low and the pulling speed needing to be reduced.

[0041] In the prior art, if the surface temperature of the casting blank is too high, the total amount of the second cooling water is increased. In the present application, when the surface temperature of the casting blank is controlled, the amount of water is preferentially increased in the specified area. The water amount adjustment mode is controlled according to the casting blank shape and the surface temperature. The first section and the second section have a great influence on the blank shape. When there is a shape defect, the water amount of the first section and the second section is preferentially adjusted. The third section and the fourth section have a great influence on the surface temperature of the casting blank. When the surface temperature of the casting blank is too high or too low, the water amount of the third section and the fourth section is preferentially adjusted, instead of directly adjusting the water amount of each section in proportion. Therefore, the present method can more quickly adjust the shape size of the casting blank and the surface temperature of the casting blank, and further control the quality of the casting blank.

[0042] The above examples have exemplarily described the present application. It is obvious that the specific implementation of the present application is not limited by the above method. As long as various non-essential improvements are made by using the method concept and technical scheme of the present application, or the above concept and technical scheme of the present application is directly applied to other occasions without improvement, they are all within the protection scope of the present application.

Claims

1. A method for online control of the quality of continuously cast billets, characterized in that, By installing a temperature measuring device in front of the straightening machine, the surface temperature of the billet is measured in real time, and the amount of secondary cooling water is adjusted according to the surface temperature of the billet; by installing a fixed weight and fixed length device, the cutting length and weight of the billet are measured, the cross-sectional dimensions of the billet are monitored and the cutting cross-sectional area is calculated, and the average density value of the billet is calculated by combining the length and weight of the billet, and the cooling water volume of each zone of the secondary cooling of the continuous casting machine is adjusted according to the cross-sectional dimensions and average density value of the billet. The method for online control of continuous casting billet quality includes the following steps: S1. Based on the mathematical calculation model, determine the standard water volume of the zero section, I section, II section, III section, and IV section of the secondary cooling zone of the continuous casting machine under different steel grades and corresponding casting speed conditions; S2. After the casting process is normal and the casting speed is stable, the temperature measuring device is turned on to measure the surface temperature of the billet in real time. S3. After the billet reaches the cutting position, the length of the billet is measured by the fixed weight and fixed length device. S4. The weight of the cut billet is measured by the fixed weight and length device, and the cross-sectional dimensions of the billet are detected. Finally, based on the length, cross-sectional dimensions and weight of the billet, the average density value of the billet is calculated to confirm whether there are any defects in the billet. In step S2, if the surface temperature of the billet before the straightening machine is higher than the second set value, the amount of secondary cooling water in sections III and IV is increased first to reduce the surface temperature of the billet before the straightening machine. The increase in secondary cooling water is based on the principle that the cooling rate of the billet surface in sections III and IV is less than the third set value and the cooling intensity is not greater than that of the first section. If the increase in secondary cooling water in sections III and IV reaches the critical value but still cannot meet the requirement that the surface temperature of the billet before the straightening machine is lower than the second set value, then following the principle that the cooling rate of the billet surface is less than the third set value and the cooling intensity is not greater than that of the first section, the amount of secondary cooling water in sections II, I and zero is increased in sequence to keep the surface temperature of the billet inside the straightening machine within a reasonable range.

2. The method for online control of continuously cast billet quality according to claim 1, characterized in that, The temperature measuring device is an infrared thermometer.

3. The method for online control of continuously cast billet quality according to claim 1, characterized in that, The fixed weight and fixed length device includes a first infrared camera for measuring the cutting length of the billet and a billet weight measuring device for measuring the weight of the billet. The first infrared camera is set at the cutting position of the continuous casting machine, and the billet weight measuring device is set on the post-cut roller conveyor.

4. The method for online control of continuously cast billet quality according to any one of claims 1 to 3, characterized in that, In step S2, if the surface temperature of the billet is lower than the third brittle temperature range of the corresponding steel grade, the amount of secondary cooling water in sections III and IV is first reduced to increase the surface temperature of the billet before the straightening machine. The amount of secondary cooling water reduction is critically measured by the billet surface warming rate in sections III, IV, and the air cooling zone from section IV to the straightening machine being less than or equal to the first set value. If the amount of secondary cooling water reduction in sections III and IV still cannot meet the requirement that the surface temperature of the billet before the straightening machine is higher than the third brittle temperature range, then following the principle that the billet surface warming rate is less than or equal to the first set value, the amount of secondary cooling water in sections II, I, and zero is reduced sequentially.

5. The method for online control of continuously cast billet quality according to claim 4, characterized in that, The first setting value is 100℃ / m.

6. The method for online control of continuously cast billet quality according to any one of claims 1 to 3, characterized in that, The second setting is 1050℃, and the third setting is 200℃ / m.

7. The method for online control of continuously cast billet quality according to any one of claims 1 to 3, characterized in that, In step S4, the weight of the billet is measured by a roller scale, and the cross-sectional dimensions of the billet are detected by a second infrared camera located on one side of the roller scale.