Casting blank liquid core length detection method

Abstract

The invention discloses a casting blank liquid core length detection method, and belongs to the technical field of ferrous metallurgy continuous casting. According to the method, a high-density and high-melting-point metal tungsten ball is put into molten steel of a crystallizer to serve as a marker, the putting time point is recorded, and continuous length marking and sampling cutting are carried out on an output casting blank so as to locate the position of the tungsten ball. The sinking speed of the tungsten ball in molten steel is measured in advance, a synchronous relation model of the sinking time of the tungsten ball and the movement time of the casting blank is established, the identification length is corrected, and finally the actual liquid core length of the casting blank is accurately calculated. The method is safe, reliable, simple and convenient to operate, low in cost and high in detection precision, can provide an accurate basis for optimization of continuous casting process parameters, and is suitable for liquid core length detection of square billets and rectangular billets.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting technology in iron and steel metallurgy, and specifically relates to a method for detecting the length of the liquid core of a cast billet. Background Technology

[0002] The core length of a continuously cast billet refers to the distance from the surface of the molten steel in the crystallizer to the point where the billet has completely solidified. It is one of the most crucial parameters in the continuous casting process. Accurately determining the core length is of great significance for rationally setting the casting speed, optimizing the secondary cooling water distribution, adjusting electromagnetic stirring parameters, and implementing the light reduction process. It directly affects the internal quality of the billet and production efficiency.

[0003] Currently, methods for determining the length of the liquid core in continuously cast billets mainly include the nail-shot method, isotope tracing method, radioactive indicator method, puncture method, pressure feedback detection method, ultrasonic detection method, and numerical simulation calculation method. The nail-shot method involves injecting a sulfur-containing nail into the billet, sampling for corrosion, and inferring the solidification front position based on the sulfur distribution. This method is relatively simple to operate but is a destructive test, and its measurement accuracy is greatly affected by the sampling location and corrosion effect. The isotope tracing method and the radioactive indicator method use the distribution of radioactive substances in molten steel to determine the solidification end. Although they have high sensitivity, they pose radioactive safety risks, require strict supervision, and are limited in on-site implementation. The puncture method measures the internal temperature through mechanical drilling or directly probes the solid-liquid interface, providing intuitive results but is complex to operate and significantly interferes with production. The pressure feedback detection method and the ultrasonic detection method can achieve a certain degree of online detection, but the equipment investment is high, maintenance is complex, and the detection stability needs improvement due to the influence of the billet surface condition and internal structure. Numerical simulation calculations are based on heat transfer models to estimate the liquid core length. This method is low-cost and interference-free. However, the model parameters need to be calibrated in conjunction with actual operating conditions, and the accuracy depends on the setting of boundary conditions. It is difficult to use this method alone as a reliable basis for process adjustment.

[0004] In summary, existing methods for detecting the length of liquid cores suffer from various problems, including high safety risks, high costs, complex operation, large detection deviations, and poor operability, making it difficult to meet the requirements for refined control in continuous casting production processes. Therefore, developing a safe, simple, cost-effective, and highly accurate method for detecting the length of liquid cores has significant engineering application value. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide a method for detecting the length of the liquid core of a cast billet, so as to solve the technical problems of high safety risks, high cost, complex operation, low detection accuracy and poor operability of existing detection methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for detecting the length of the liquid core in a cast billet, comprising the following steps: (1) The continuous casting machine uses a stopper rod tundish to maintain a constant casting speed. V c Pour the solution to maintain a stable molten steel level in the crystallizer; (2) Select a tungsten ball as a marker and drop it into the molten steel from the center of the inner arc side of the crystallizer. Record the time of the drop. T 0 The output billet is continuously marked with its length starting from the outlet of the straightening machine. Based on the marking results, the distance from the molten steel surface in the crystallizer to the location of the tungsten ball on the billet is determined and recorded as the marking length. L 0 ; (3) Based on the sinking speed of the tungsten ball in molten steel V w ,by T = L 0 / V w The sinking time of the tungsten ball was calculated. T Based on the synchronization relationship between the sinking time of the tungsten ball and the movement time of the billet, the formula is used to... L y = L 0 + ( V c × T ) / 60 Calculate the actual length of the liquid core in the cast billet; in, L y This is the actual length of the liquid core in the cast billet, in meters. L 0 The unit for indicating length is meters (m). V c This refers to the casting speed of the continuous casting machine, expressed in m / min. T The sinking time of the tungsten ball is in seconds; 60 is the conversion factor between minutes and seconds.

[0007] The detection method provided in this invention corrects a neglected source of error in traditional tracer methods (such as the nail-shooting method)—the movement time of the marker itself. Traditional methods, whether using nails or isotopes, implicitly assume that "the marker reaches the solidification front instantaneously." However, in reality, it takes time for the marker to sink from the surface of the crystallizer to the end of the liquid core. During this time, the cast billet continues to move downwards. Therefore, the directly located marker point actually corresponds to an earlier point at the end of the liquid core, leading to an inaccurate measurement value. This invention introduces the sinking time of the tungsten ball. T and pulling speed V c For the length of the identifier L 0Make corrections using formulas L y = L 0 + ( V c × T The method calculates the actual liquid core length of the cast billet, thus eliminating systematic bias in principle. Therefore, this method is closer to the true value in terms of theoretical model than the uncorrected method.

[0008] Preferably, the tungsten ball is a high-temperature resistant pure tungsten ball with a purity ≥99.9%, a sphericity ≥0.95, and no cracks or pore defects on the surface.

[0009] The diameter of the tungsten ball is determined according to the cross-sectional dimensions of the cast billet using the following formula: d = k × D in, d The diameter of the tungsten sphere is in mm. D For characteristic dimensions of the billet, the cross-sectional side length is taken for square billets and the cross-sectional thickness is taken for rectangular billets, in mm. k This is a proportionality coefficient, with a value ranging from 0.05 to 0.07.

[0010] Preferably, the proportionality coefficient k The value is 0.0625; after calculation according to the above formula, the result is rounded to an integer millimeter and used as the final selected tungsten ball diameter.

[0011] Preferably, in step (1), the constant pulling speed V c The settings are based on the billet cross-section specifications and steel type of the continuous casting machine, and the stable working conditions for constant casting speed are: casting time ≥ 30 min, molten steel level fluctuation in the crystallizer ≤ ± 5 mm, and casting speed deviation ≤ ± 0.05 m / min.

[0012] Before adding the tungsten ball in step (2), preheat the tungsten ball to 100~150℃ and then vertically add it into the molten steel in the crystallizer.

[0013] Preferably, after marking the length of the billet in step (2), the billet in the marked section is continuously sampled, with a sampling length of 300~1000mm. The sampled billet is longitudinally cut along the center line of the billet to find the metal tungsten ball.

[0014] The sinking speed of the tungsten ball V w By conducting multiple pre-drop tests on the same continuous casting machine, the sinking speed of tungsten balls of different diameters was obtained based on measured data. Vw .

[0015] Preferably, the method is applicable to the detection of the liquid core length of square or rectangular billets.

[0016] The beneficial effects of this invention are: 1. This invention utilizes the high density and high melting point of tungsten spheres, allowing them to remain solid in molten steel and rapidly sink to the end of the liquid core, serving as a clear physical marker. By establishing a synchronous relationship model between the sinking time of the tungsten sphere and the movement time of the cast billet, the marking length is corrected and calculated, eliminating the influence of the tungsten sphere sinking process on the detection results and effectively improving the detection accuracy.

[0017] 2. The method of this invention has clear steps and a simple process, which can be mastered by on-site operators after simple training. Operations such as placing tungsten balls, recording time, marking length, and sampling and cutting can all be completed during normal production without interrupting production or interfering with the stable operation of the continuous casting process. It is highly operable and easy to promote and apply in various continuous casting production sites. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the solidification of a billet cast in a continuous casting machine.

[0019] In the diagram: 1-Crystallizer; 2-Molten steel level in the crystallizer; 3-End of the molten core in the billet; 4-Length of the molten core in the billet. L y . Detailed Implementation

[0020] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] As mentioned above, to solve the technical problem of difficulty in measuring the length of the liquid core of a billet in a continuous casting machine and the inability to meet the accuracy requirements for process optimization, this invention provides a method for detecting the length of the liquid core of a billet: The melting point of tungsten is 3410℃, and its density is 19.35 g / cm³. 3 Steel typically has a melting point of 1470-1530℃ and a density of 7.8 g / cm³. 3 Taking advantage of the high melting point and high density of tungsten, high-temperature resistant tungsten balls are added to the molten steel in the crystallizer. Under the influence of gravity, the tungsten balls sink rapidly to the end of the molten core of the billet. The length of the billet from the liquid surface of the crystallizer at the time of adding the tungsten balls is recorded. The billet is continuously sampled and longitudinally cut to find the tungsten balls. The length of the molten core of the billet is determined based on the recorded length of the billet from the liquid surface of the crystallizer at the time of adding the tungsten balls. Figure 1 This invention demonstrates the measurement of the liquid core length of the cast billet.L y The physical definition of is the arc-shaped distance along the centerline of the cast billet from the molten steel surface 2 in the crystallizer to the completely solidified end 3 of the billet. This invention determines this distance by inserting a tungsten ball and tracking its position. L y The value.

[0022] This invention uses a tungsten ball to detect the length of the liquid core in a cast billet. The method is simple, safe, low-cost, easy to operate, and highly accurate. It provides a reliable basis for controlling and optimizing parameters such as continuous casting speed, temperature, secondary cooling water distribution, electromagnetic stirring, and light and heavy pressure reduction, which can greatly promote the improvement of product quality.

[0023] The specific embodiments of the present invention will be described in further detail below with reference to examples. The following detailed descriptions are illustrative and intended to provide further explanation of this application, rather than limiting the scope of the invention.

[0024] Example 1: Measurement of the length of the liquid core of a rectangular billet in a continuous casting machine (1) Measurement of liquid core length The continuous casting machine produces billet with a cross-section of 320 mm × 420 mm (thickness × width). The machine uses a stopper-type tundish, and the steel grade is 40Cr. The molten steel temperature in the tundish is controlled between 1505 and 1515℃. A constant casting speed is set. V c = 0.58 m / min, secondary cooling adopts intermediate cooling mode to maintain the stability of the molten steel level in the crystallizer.

[0025] according to d = k × D Tungsten balls with a diameter of 20 mm (320 × 0.0625 = 20) were selected as markers. The tungsten balls had a purity ≥ 99.9%, a sphericity ≥ 0.95, and no surface cracks or porosity defects. Before being placed into the casting, the tungsten balls were preheated to 120℃ to avoid thermal stress on the surface due to excessive temperature difference. Furthermore, before the billet liquid core length measurement experiment, multiple preheated 120℃ tungsten balls with a diameter of 20 mm were pre-placed on the same continuous casting machine. Based on the measured data (average value), the sinking speed of the tungsten balls was obtained. V w = 0.3 m / s.

[0026] After the continuous casting production stabilizes, a special long-handled pliers is used to vertically drop the preheated tungsten ball into the molten steel from the center of the inner arc side of the crystallizer, while a high-precision timer is started to record the drop time. T 0 (Accurate to the second). When adding the tungsten ball, avoid it adhering to the crystallizer wall and ensure it sinks freely.

[0027] Based on the timing of tungsten ball placement T 0 The length of the cast billet was marked starting from the exit of the straightener. A length encoder was used to continuously record the length of the cast billet from the exit of the straightener. After the marked section of the cast billet had completely left the straightener and cooled to a cuttable temperature, samples were continuously taken from the marked section in the flame cutting zone. The sampling length was set at 500 mm, and a total of 6 cast billet samples were obtained, including possible liquid core ends, numbered S1 to S6, corresponding to the marked length. L 0 The measurements are 13.0 m, 13.5 m, 14.0 m, 14.5 m, 15.0 m, and 15.5 m, respectively.

[0028] Each specimen is longitudinally cut along the centerline of the cast billet (i.e., the center in the thickness direction). A large band saw is used, and precise markings are made before cutting to ensure that the cut surface passes through the geometric center of the cast billet. After cutting, two symmetrical halves of the specimen are obtained, exposing the internal longitudinal section.

[0029] Carefully inspect the longitudinal section after cutting. Because the density of tungsten spheres is much higher than that of the steel matrix, and their surface is smooth, they exhibit a bright white metallic luster on the freshly cut surface, making them easily identifiable. (The section numbered S5 corresponds to the marked length.) L 0 A tungsten ball was found on the longitudinal section of the sample (15.0 m). The tungsten ball was located on the center line of the cast billet, with no obvious melting marks around it, indicating that it was intact until the end of solidification.

[0030] According to the formula T = L 0 / V w Calculate the time it takes for the tungsten ball to sink from the surface of the molten steel in the crystallizer to the end of the liquid core. T : T =15.0 / 0.3 = 50 s.

[0031] Based on the synchronization relationship between the sinking time of the tungsten ball and the movement time of the billet, the actual length of the liquid core of the billet is calculated using a formula. L y : L y = L 0 + ( V c × T ) / 60 = 15.0 + (0.58 × 50) / 60 = 15.48 m.

[0032] (2) Repeatability test To evaluate the repeatability of the method of the present invention, the casting speed was maintained within the same stable casting cycle. V c = 0.58 m / min constant, using the same diameter (20 mm) and pre-calibrated sinking speed V w A tungsten ball with a velocity of 0.3 m / s was dropped and measured three times consecutively.

[0033] Because the continuous casting process itself involves permissible process fluctuations (such as fluctuations in molten steel temperature and slight fluctuations in casting speed), the position of the liquid core end will dynamically change within a certain range. Therefore, the marked length found through sampling and cutting in three measurements... L 0 There are slight differences; the specific measurement data and calculation results are as follows: Table 1: Measurement Data The range of the three measurement results was 0.07 m, and the standard deviation was 0.035 m. This indicates that even with normal process fluctuations and measurement errors, the method of this invention can still control the fluctuation of the detection results within a very small range, exhibiting excellent repeatability and stability. Furthermore, the measurement results are... L 0 The minute changes have reasonable sensitivity and can accurately reflect the dynamic changes in the liquid core length, providing a reliable basis for the fine adjustment of the continuous casting process.

[0034] (3) Measurement accuracy assessment To verify the measurement accuracy of this invention, the method of this invention (tungsten ball diameter 20mm, pre-calibrated) was simultaneously applied on the same rectangular billet continuous casting machine (section 320mm×420mm, casting speed 0.58m / min). V w = 0.3m / s) and the traditional nail shooting method were compared to detect the liquid core length, and numerical simulation was used for verification.

[0035] Testing revealed that, under the same operating conditions, the liquid core length measured by the nail-shooting method was 14.9 m. Simultaneously, the theoretical liquid core length calculated using a solidification heat transfer mathematical model corrected for on-site thermocouple data was 15.4 m. Comparison shows that the measurement result of the method of this invention (15.48 m) is closer to the theoretical calculation value than that of the nail-shooting method (14.9 m), with a deviation of only 0.08 m. This indicates that the present invention effectively eliminates systematic errors by correcting for the sinking time of the marker, resulting in a measurement result closer to the true liquid core length. Therefore, the method of this invention demonstrates higher measurement accuracy.

[0036] Example 2: Measurement of the length of the liquid core of a billet in a small billet continuous casting machine The billet cross-section of the small billet continuous casting machine is 160 mm × 160 mm. The continuous casting machine uses a stopper rod tundish, and the steel grade is No. 25 steel. The tundish temperature is controlled between 1515 and 1530℃. A constant casting speed is set. V c = 2.5 m / min, secondary cooling adopts intermediate cooling mode to maintain the stability of the molten steel level in the crystallizer.

[0037] according to d = k × D Tungsten balls with a diameter of 10 mm (160 × 0.0625 = 10) were selected as markers. The tungsten balls had a purity ≥ 99.9%, a sphericity ≥ 0.95, and no surface defects. The tungsten balls were preheated to 100℃ before being added to the casting. Before the slab core length measurement experiment, multiple preheated 100℃ tungsten balls with a diameter of 10 mm were pre-added to the same continuous casting machine for testing. Based on the measured data (average value), the sinking speed of the tungsten balls was obtained. V w = 0.2m / s.

[0038] After stable pouring, a tungsten ball is vertically inserted into the center of the inner arc side of the crystallizer, and the insertion time is recorded simultaneously. T 0 (Accurate to the second).

[0039] Based on the timing of tungsten ball placement T 0 The length of the cast billet is marked starting from the exit of the straightener. A length encoder is used to continuously record the length of the billet from the exit of the straightener. After the marked section of the billet has completely left the straightener and cooled to a cutable temperature, samples are continuously taken from the marked section in the flame cutting zone. The sampling length is 500 mm, and a total of 8 samples are obtained, corresponding to the marked length. L 0 The dimensions are 9.0 m, 9.5 m, 10.0 m, 10.5 m, 11.0 m, 11.5 m, 12.0 m, and 12.5 m, respectively.

[0040] Each sample was longitudinally cut along the centerline of the cast billet to expose its internal longitudinal section. At the corresponding marked length... L 0 On the longitudinal section of the sample with a diameter of 11.0 m, a tungsten ball was found to be placed in the center of the cast billet. The ball was intact and there were no traces of melting around it.

[0041] According to the formula T = L 0 / V w Calculate the time it takes for the tungsten ball to sink from the surface of the molten steel in the crystallizer to the end of the liquid core. T :T =11.0 / 0.2 = 55s.

[0042] Based on the synchronization relationship between the sinking time of the tungsten ball and the movement time of the billet, the actual length of the liquid core of the billet is calculated using a formula. L y : L y = L 0 + ( V c × T ) / 60 = 11.0 + (2.5 × 55) / 60 = 13.29m.

[0043] The above description is merely a preferred embodiment of this application and is not intended to limit the application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications made within the spirit and principles of this application are not permitted. Equivalent substitutions and improvements should all be included within the scope of protection of this application.

Claims

1. A method for detecting the length of the liquid core in a cast billet, characterized in that, Includes the following steps: (1) The continuous casting machine uses a stopper rod tundish to maintain a constant casting speed. V c Pour the solution to maintain a stable molten steel level in the crystallizer; (2) Select a tungsten ball as a marker and drop it into the molten steel from the center of the inner arc side of the crystallizer. Record the time of the drop. T 0 The output billet is continuously marked with its length starting from the outlet of the straightening machine. Based on the marking results, the distance from the molten steel surface in the crystallizer to the location of the tungsten ball on the billet is determined and recorded as the marking length. L 0 ; (3) Based on the sinking speed of the tungsten ball in molten steel V w ,by T = L 0 / V w The sinking time of the tungsten ball was calculated. T ; Based on the synchronization relationship between the sinking time of the tungsten ball and the movement time of the billet, the formula is used to... L y = L 0 + ( V c × T ) / 60 Calculate the actual length of the liquid core in the cast billet; in, L y This is the actual length of the liquid core in the cast billet, in meters. L 0 The unit for indicating length is meters (m). V c This refers to the casting speed of the continuous casting machine, expressed in m / min. T The sinking time of the tungsten ball is in seconds; 60 is the conversion factor between minutes and seconds.

2. The method for detecting the length of the liquid core of a cast billet according to claim 1, characterized in that, The tungsten spheres are high-temperature resistant pure tungsten spheres with a purity ≥99.9%, sphericity ≥0.95, and no cracks or pore defects on the surface.

3. The method for detecting the length of the liquid core in a cast billet according to claim 2, characterized in that, The diameter of the tungsten ball is determined according to the cross-sectional dimensions of the cast billet using the following formula: d = k × D in, d The diameter of the tungsten sphere is in mm. D For characteristic dimensions of the billet, the cross-sectional side length is taken for square billets and the cross-sectional thickness is taken for rectangular billets, in mm. k This is a proportionality coefficient, with a value ranging from 0.05 to 0.

07.

4. The method for detecting the length of the liquid core of a cast billet according to claim 1, characterized in that, In step (1), the constant pulling speed V c The settings are based on the billet cross-section specifications and steel type of the continuous casting machine, and the stable working conditions for constant casting speed are: casting time ≥ 30 min, molten steel level fluctuation in the crystallizer ≤ ± 5 mm, and casting speed deviation ≤ ± 0.05 m / min.

5. The method for detecting the length of the liquid core in a cast billet according to claim 1, characterized in that, Before adding the tungsten ball in step (2), preheat the tungsten ball to 100~150℃ and then vertically add it into the molten steel in the crystallizer.

6. The method for detecting the length of the liquid core of a cast billet according to claim 1, characterized in that, After marking the length of the billet in step (2), the billet in the marked section is continuously sampled. The sampling length is 300~1000mm. The sampled billet is longitudinally cut along the center line of the billet to find the metal tungsten ball.

7. The method for detecting the length of the liquid core of a cast billet according to claim 1, characterized in that, The sinking speed of the tungsten ball V w By conducting multiple pre-drop tests on the same continuous casting machine, the sinking speed of tungsten balls of different diameters was obtained based on measured data. V w .

8. The method for detecting the length of the liquid core of a cast billet according to any one of claims 1-7, characterized in that, The method is applicable to the detection of the liquid core length of square or rectangular billets.

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