阅读说明：本技术 结晶器表面附近钢液流速的测量方法 (Method for measuring flow velocity of molten steel near surface of crystallizer ) 是由 杨健 蒋鹏 张涛 于 2020-06-28 设计创作，主要内容包括：本发明公开了一种结晶器表面附近钢液流速的测量方法,进行测量时,将测速棒插入到结晶器液面以下,测速棒在钢液冲击作用下发生偏转,在重力、钢液对测速棒的冲击力和浸入到钢液中的测速棒所受的浮力的作用下达到力矩平衡,通过测量偏转角度和测速棒插入钢液深度,从而计算得到钢液流速。对于一根测速棒,通过多次测量读取该偏转角度和测速棒的插入钢液深度值,可以计算得出钢液流速的测量值。通过多根测速棒的流速测量值求平均,可以获得该连铸工艺条件下的结晶器表面附近钢液流速。该速度平均值结果具有良好的稳定性,随着连铸工艺条件的变化,呈现规律性的变化趋势,能够很好地反映了结晶器表面附近钢液流速随连铸工艺条件的变化规律。(The invention discloses a method for measuring the flow velocity of molten steel near the surface of a crystallizer, wherein a speed measuring rod is inserted below the liquid level of the crystallizer during measurement, the speed measuring rod deflects under the impact action of the molten steel, the moment balance is achieved under the action of gravity, the impact force of the molten steel on the speed measuring rod and the buoyancy force borne by the speed measuring rod immersed in the molten steel, and the flow velocity of the molten steel is calculated by measuring the deflection angle and the depth of the speed measuring rod inserted into the molten steel. For one speed measuring rod, the deflection angle and the depth value of the inserted molten steel of the speed measuring rod are read through multiple measurements, and the measured value of the flow velocity of the molten steel can be calculated. The flow velocity of the molten steel near the surface of the crystallizer under the continuous casting process condition can be obtained by averaging the flow velocity measurement values of the plurality of speed measuring rods. The speed average value result has good stability, presents a regular change trend along with the change of the continuous casting process condition, and can well reflect the change rule of the molten steel flow speed near the surface of the crystallizer along with the continuous casting process condition.)

1. The utility model provides a measuring method of near crystallizer surface molten steel velocity of flow, adopts mainly to constitute measuring device by balancing piece, angle indicator board, pointer, deflection bearing, the stick that tests the speed, the outer lane of deflection bearing is connected with the stick fixed mounting that tests the speed, the balancing piece is as testing the weight center adjustment preparation part that the stick deflected, angle indicator board and pointer are as the device of the stick deflection angle that indicates testing the speed, its characterized in that: when measurement is carried out, the speed measuring rod is inserted below the liquid level of the crystallizer, the speed measuring rod deflects under the action of flow impact of molten steel, and a certain deflection angle is formed under the balance of the gravity of the speed measuring rod, the impact force of the molten steel and the moment of buoyancy borne by the speed measuring rod immersed in the molten steel; for one speed measuring rod, reading the deflection angle of the speed measuring rod and the depth value of the inserted molten steel of the speed measuring rod through multiple measurements, and calculating to obtain the measured value of the flow speed of the molten steel; and averaging the flow velocity measurement values of the plurality of speed measuring rods to obtain the flow velocity of the molten steel near the surface of the crystallizer under the continuous casting process condition.

2. The method for measuring the flow rate of molten steel in the vicinity of the surface of a mold according to claim 1, wherein: under the condition that the gravity of the speed measuring rod, the impact force of the molten steel and the moment of buoyancy borne by the speed measuring rod immersed in the molten steel are balanced, the deflection angle of the speed measuring rod and the depth value of the speed measuring rod inserted into the molten steel are measured and read, and therefore the measured value of the flow speed of the molten steel is calculated.

3. The method for measuring the flow rate of molten steel in the vicinity of the surface of a mold according to claim 1, wherein: the speed measuring rod is made of stainless steel or refractory materials; the diameter of the speed measuring rod is 5-30mm, so that the speed measuring rod starts to be fused when the staying time of the speed measuring rod in the molten steel is not less than 15s, a plurality of deflection angle values are read within the staying time of the speed measuring rod in the molten steel, and the measured value of the flow speed is obtained through calculation.

4. The method for measuring the flow rate of molten steel in the vicinity of the surface of a mold according to claim 1, wherein: the depth of the speed measuring rod inserted into the molten steel is controlled to be 10-100 mm.

5. The method for measuring the flow rate of molten steel in the vicinity of the surface of a mold according to claim 1, wherein: and for a certain continuous casting process condition, measuring the speed by using a plurality of speed measuring rods, and averaging the flow speed measurement values of the plurality of speed measuring rods to obtain the average value of the flow speed of the molten steel under the continuous casting process condition.

6. The method for measuring the flow rate of molten steel in the vicinity of the surface of a mold according to claim 1, wherein: under different continuous casting process conditions, the flow velocity of the molten steel near the surface of the crystallizer is measured, the result of the average value of the velocity has stability, and the change rule of the flow velocity of the molten steel near the surface of the crystallizer along with the continuous casting process conditions is reflected.

Technical Field

The invention relates to the technical field of continuous casting processes, in particular to a method for measuring the flow velocity of molten steel near the surface of a crystallizer. The method can realize high-temperature online measurement of the flow velocity of the molten steel near the surface of the slab continuous casting crystallizer, the measurement result of the flow velocity of the molten steel has good stability, and the influence of the change of continuous casting process parameters on the flow velocity of the molten steel near the surface of the crystallizer can be regularly reflected. The accurate and stable measurement of the flow velocity of the molten steel near the surface of the crystallizer can help to optimize the flow field of the molten steel in the slab crystallizer, and plays an important role in improving the surface defects of ultra-low carbon steel caused by steel making, particularly automobile outer plates.

Background

The production technology of the automobile outer plate comprises molten iron pretreatment, converter, refining, continuous casting and machine cleaning in a steelmaking process, hot rolling, cold rolling, hot galvanizing and other process technologies in a subsequent process and a surface quality control technology. The surface defects of the automobile outer plate caused by the steel-making process can be detected only in the quality inspection process of the final hot-galvanized plate after hot rolling, cold rolling and hot galvanizing processes, the history of defect formation is long, the processes are multiple, and the steel-making defects are interwoven with the defects generated by the hot rolling, cold rolling and hot galvanizing processes and are difficult to identify and judge. The whole process is long in period and poor in correspondence from surface defect analysis and judgment, process improvement and effect verification feedback, and particularly steel-making defects on the surface of a thin plate are sporadic and random, so that the difficulty in defect identification, source tracing and targeted process optimization is extremely high. Therefore, the research on the control technology of the surface defects of the automobile outer panel caused by steel making is a representative research and development subject with great difficulty and strong comprehensiveness.

The crystallizer is the last link before the molten steel is solidified, is also the core part in the continuous casting process, and is called as the heart of a continuous casting machine. The metallurgy of the crystallizer is the final opportunity for removing inclusions in molten steel, so the continuous casting crystallizer is also a key link for controlling surface defects of an automobile outer plate caused by steel making. After molten steel enters the crystallizer from the tundish through the submerged nozzle, an initial solidification process is completed in the crystallizer, and an initial solidified shell with a certain thickness is formed. Because the initial solidified shell is positioned at the outermost layer of the continuous casting billet, the surface defects of the cold-rolled sheet product are closely related to the defects of whether covering slag, large-scale inclusions, bubbles and the like are captured in the initial solidified shell.

The molten steel has larger kinetic energy after entering the crystallizer through the submerged nozzle, and due to the impact action, the stream generally impacts the narrow surface of the crystallizer along the inclination angle direction of the nozzle and is divided into an upper stream and a lower stream to respectively form an upper reflux area and a lower reflux area in the crystallizer, and the flowing form is a typical double-circulating stream. However, when the impact force of the stream is weak or the flow of argon gas blown into the submerged nozzle is too large, the stream may not impact the narrow face of the crystallizer and may move upward in advance, and thus the flow pattern formed is a single circulation flow. The two flow forms have important influences on the formation of defects on the surface of the outer plate of the automobile, such as floating of inclusions in molten steel, fluctuation of the liquid level of the surface of the crystallizer, slag entrapment of casting slag, and capture of argon bubbles formed in the crystallizer by blowing argon into the crystallizer by the submerged nozzle.

At present, the method for researching the flow field of the molten steel in the crystallizer mainly comprises physical simulation and numerical simulation. Physical simulation generally uses water to simulate molten steel and oil to simulate mold powder. However, the density of water and molten steel is greatly different, so that the floating behavior of bubbles in the molten steel is greatly different from that of bubbles in water; in addition, the mold flux has a three-layer structure of a liquid slag layer, a sintering layer and a powder layer, and the behavior of the mold flux is difficult to simulate by adopting oil; the bias flow phenomenon in the crystallizer is difficult to simulate due to the irregular blockage of the submerged nozzle; in addition, the influence of mold vibration is difficult to physically simulate. Therefore, it is difficult to accurately simulate the actual crystallizer flow field by using a physical simulation method.

On the other hand, the mathematical simulation has the following limitations. The unsteady flow field is difficult to accurately simulate by mathematical simulation; because bubbles in the molten steel are not of a single size, the behavior of the bubbles is difficult to simulate; the interaction between the protective slag with the three-layer structure and the molten steel is very complex, and a mathematical model is difficult to accurately simulate; mathematical models of anomalies occurring in the crystallizer cannot usually be simulated; the influence of the crystallizer vibration is difficult to accurately simulate by a mathematical model. Therefore, only phenomena can be explained by adopting mathematical simulation, and new laws are difficult to find.

Therefore, metallurgists at home and abroad are always developing a method for directly measuring the flow velocity near the surface of the crystallizer. Chinese patent No. ZL201210485150.7 discloses a device and method for measuring flow velocity near the surface of molten steel, the device includes a speed measuring rod and a speed measuring rod deflection device, the method calculates the distance between the rotation fulcrum and the center of gravity and the distance between the rotation fulcrum and the impact force point according to the center of gravity, the rotation fulcrum and the impact force point of the speed measuring rod, measures the gravity value of the speed measuring rod, inserts the speed measuring rod into the molten steel to obtain the rotation angle and the insertion depth, thereby calculating the flow velocity of the molten steel. Chinese patent number ZL201210487402.X discloses a continuous measuring device and method for flow velocity near the surface of molten steel.

Although the flow field of molten steel in the crystallizer has very important significance for controlling the inclusions and the surface quality in the continuous casting billet, the common liquid flow velocity measuring device cannot play a role because the temperature of the molten steel is as high as more than 1600 ℃, and the measurement of the actual flow velocity of the molten steel becomes a technical problem in the field of steel making. Although the prior art provides a device and a method for measuring the flow velocity near the surface of molten steel and a device and a method for continuously measuring the flow velocity near the surface of molten steel, in the actual measurement process, it is found that the measured flow velocity near the surface of the crystallizer greatly fluctuates due to the three-dimensional turbulent motion of the molten steel flowing in the crystallizer, the flow velocity near the surface of the crystallizer is difficult to obtain a reasonably stable result, and the change of the flow velocity is not regular when the continuous casting process parameters are changed. Therefore, the method for measuring the flow velocity near the surface of the crystallizer needs to be innovated and improved, and becomes a technical problem to be solved urgently.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects of the prior art and provide a method for measuring the flow velocity of the molten steel near the surface of the crystallizer, which can obtain a stable and reliable result when the flow velocity of the molten steel near the surface of the crystallizer is measured, so that the flow velocity of the molten steel near the surface of the crystallizer can be regularly changed along with the change of continuous casting process parameters. The invention relates to a method for measuring the flow velocity near the surface of molten steel, which is particularly suitable for measuring the flow velocity of the molten steel near the surface of a crystallizer. The flow field of the molten steel in the crystallizer can be controlled and the flow field of the molten steel in the crystallizer can be optimized by directly measuring the flow velocity of the molten steel near the surface of the crystallizer, so that the surface defects of the continuous casting billet caused by slag entrapment, inclusion, bubbles and the like are effectively reduced, and the surface defect incidence rate of an automobile outer plate caused by steel making is further reduced.

In order to achieve the purpose of the invention, the invention adopts the following inventive concept:

the measuring device mainly comprises a balance block, an angle indicating plate, a pointer, a deflection bearing and a speed measuring rod, wherein the outer ring of the deflection bearing is fixedly installed and connected with the speed measuring rod, the balance block is used as a gravity center adjusting and preparing part for deflection of the speed measuring rod, and the angle indicating plate and the pointer are used as devices for indicating the deflection angle of the speed measuring rod. During the measurement, will test the speed the stick and insert below the crystallizer liquid level, test the speed the stick and take place to deflect under the molten steel impact force effect, reach moment balance under the buoyancy effect that the stick receives of the impact force of gravity, molten steel to testing the speed the stick and the stick that tests the speed of soaking in the molten steel, consequently can obtain following moment balance formula:

GL₁sinθ-F_fL₂sinθ＝F_DL₂cosθ (1)

wherein G is gravity (N), L₁Arm of force (m) of gravity, theta is the deflection angle of the speed measuring bar, F_fIs buoyancy (N), F_DFor the speed-measuring rod to be subjected to the impact force of the molten steel, L₂The moment arm (m) is the moment arm of impact force and buoyancy, and is obtained by conversion of the immersion depth of the measurement speed measuring rod.

Wherein the buoyancy that the speed measuring stick receives is:

F_f＝ρgV (2)

in the formula: rho is the density (kg/m) of the molten steel³) And V is the volume (m) of the part of the speed measuring rod immersed into the molten steel³) G is the acceleration of gravity (m/s)²)。

The impact force of the molten steel on the speed measuring rod is equal to the streaming resistance of the molten steel, and the calculation formula is as follows:

wherein: rho is the density (kg/m) of the molten steel³)，U₀Is the flow velocity (m/s) of the molten steel, A is the projection area (m) of the streaming object in the direction vertical to the flow velocity of the molten steel²)，C_DIs the coefficient of resistance to streaming.

The streaming resistance coefficient of the velocity measuring rod has a certain relation with the Reynolds number. The streaming resistance coefficient of the speed measuring rod can be obtained by calculating the Reynolds number, and is substituted into the formula (3) to calculate the streaming resistance of the molten steel impact speed measuring rod.

Substituting the calculation formula of the streaming resistance into the torque balance formula (1) of the speed measuring rod to calculate the flow velocity U of the molten steel₀The method comprises the following steps:

the method for measuring the flow velocity of the molten steel near the surface of the crystallizer is carefully analyzed, and the influence of the buoyancy on the speed measuring rod, except the gravity of the speed measuring rod and the impact force of the molten steel on the speed measuring rod, is considered in the moment balance analysis of the speed measuring rod deflecting a certain angle. The influence of buoyancy on the speed measuring rod inserted into the molten steel is considered, so that the measurement accuracy of the flow velocity near the surface of the crystallizer can be greatly improved.

According to the invention, research and analysis are carried out on the method for measuring the flow velocity of the molten steel near the surface of the crystallizer, and the actual flow of the molten steel in the crystallizer is three-dimensional turbulent motion, so that the measured flow velocity near the surface of the crystallizer is greatly fluctuated, and the result that the reasonable and stable measurement of the flow velocity of the molten steel near the surface of the crystallizer is difficult to obtain is found.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

a method for measuring the flow velocity of molten steel near the surface of a crystallizer mainly comprises a balance block, an angle indicator plate, a pointer, a deflection bearing and a speed measuring rod, wherein the outer ring of the deflection bearing is fixedly installed and connected with the speed measuring rod, the balance block is used as a gravity center adjusting and preparing part for deflection of the speed measuring rod, the angle indicator plate and the pointer are used as devices for indicating the deflection angle of the speed measuring rod, when measurement is carried out, the speed measuring rod is inserted below the liquid level of the crystallizer, the speed measuring rod deflects under the action of flowing impact of the molten steel, and a certain deflection angle is formed under the balance of the gravity of the speed measuring rod, the impact force of the molten steel and the moment of buoyancy borne by the speed measuring; for one speed measuring rod, reading the deflection angle of the speed measuring rod and the depth value of the inserted molten steel of the speed measuring rod through multiple measurements, and calculating to obtain the measured value of the flow speed of the molten steel; and averaging the flow velocity measurement values of the plurality of speed measuring rods to obtain the flow velocity of the molten steel near the surface of the crystallizer under the continuous casting process condition.

As the preferable technical scheme of the invention, under the condition that the gravity of the speed measuring rod, the impact force of the molten steel and the moment of buoyancy borne by the speed measuring rod immersed in the molten steel are balanced, the deflection angle of the speed measuring rod and the depth value of the speed measuring rod inserted into the molten steel are measured and read, so that the measured value of the flow velocity of the molten steel is calculated.

As the preferred technical scheme of the invention, the speed measuring rod is made of stainless steel or refractory material; the diameter of the speed measuring rod is 5-30mm, so that the speed measuring rod starts to be fused when the staying time of the speed measuring rod in the molten steel is not less than 15s, a plurality of deflection angle values are read within the staying time of the speed measuring rod in the molten steel, and the measured value of the flow speed is obtained through calculation. The material that tests the speed the stick adopts stainless steel, or materials such as refractory material because adopt stainless steel and refractory material, can avoid testing the speed the stick and receive crystallizer electromagnetic force's interference, the improvement that not only does benefit to the accuracy of testing the speed, also is favorable to the security that tests the speed. The diameter of the speed measuring rod is 5-30mm, because the speed measuring rod is too thin, the speed measuring rod is fused too fast and is fused within 15s, and the angle deflection value of the speed measuring rod read is too small, or the angle deflection is difficult to reach a stable state, so that the numerical value of the angle deflection value lacks representativeness. If the diameter of the speed measuring rod is larger than 30mm, the speed measuring rod is too heavy and inconvenient to operate; meanwhile, the diameter is too large, so that the flow field of molten steel in the crystallizer is easily interfered, and the measurement error is increased.

As the preferred technical scheme of the invention, the depth of the speed measuring rod inserted into the molten steel is controlled to be 10-100 mm. The depth of the speed measuring rod inserted into the molten steel is 10-100mm, because the insertion depth of the speed measuring rod is too shallow, when the speed measuring rod deflects, the end part of the speed measuring rod leaves the molten steel and enters the protective slag layer, and the accuracy of a measuring result is influenced; if the insertion depth is too deep, the flow velocity of the molten steel measured by the speed measuring rod deviates from the vicinity of the surface, and the accuracy of the measurement result is also influenced.

As a preferable technical scheme of the invention, for a certain continuous casting process condition, a plurality of speed measuring rods are used for measuring the speed, and the flow speed measurement values of the plurality of speed measuring rods are averaged to obtain the average value of the flow speed of the molten steel under the continuous casting process condition. The measuring method comprises the steps of reading a plurality of deflection angle values for one speed measuring rod and converting the deflection angle values to obtain a measured value of the flow speed, measuring the speed by using a plurality of speed measuring rods for one continuous casting process condition, and averaging the measured values of the flow speed of the plurality of speed measuring rods to obtain a speed average value under the continuous casting process condition. The purpose is to reduce measurement errors through multiple measurements, so that the measurement result can better reflect the characteristic value of the flow velocity of the molten steel near the crystallizer under the continuous casting process condition.

As the preferred technical scheme of the invention, the flow velocity of the molten steel near the surface of the crystallizer is measured under different continuous casting process conditions, and the change rule of the flow velocity of the molten steel near the surface of the crystallizer along with the continuous casting process conditions is reflected. The speed average result of the invention has good stability, presents a regular change trend along with the change of the continuous casting process condition, and can well reflect the change rule of the molten steel flow speed near the surface of the crystallizer along with the continuous casting process condition and the actual fluid condition of the molten steel flow speed.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. the gravity of the speed measuring rod, the impact force of the molten steel and the moment balance of the buoyancy force borne by the speed measuring rod immersed in the molten steel are comprehensively considered, various main acting forces borne by the speed measuring rod can be comprehensively considered, and the precision of the molten steel flow velocity obtained through the conversion of the deflection angle of the speed measuring rod is improved;

2. the average value result of the molten steel flow velocity measured by the method has good stability, presents a regular change trend along with the change of the continuous casting process condition, and can well reflect the change rule of the molten steel flow velocity near the surface of the crystallizer along with the continuous casting process condition;

3. the method is simple and easy to implement, low in cost and suitable for popularization and application.

Drawings

FIG. 1 is a schematic diagram of the structure of the measuring device and a force analysis diagram of the speed measuring rod adopted by the method of the present invention.

FIG. 2 is a graph of the resistance coefficient of cylindrical streaming versus Reynolds number for the process of the present invention.

FIG. 3 is a graph showing the measurement results of the flow velocity of molten steel in the vicinity of the surface of the mold under different casting speeds in accordance with one embodiment of the present invention.

FIG. 4 is a graph showing the results of measuring the flow rates of molten steel in the vicinity of the surface of the mold under different argon gas flow conditions in the second embodiment of the present invention.

Detailed Description

The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below: