A logical judgment method for longitudinal surface cracks of continuous casting billets based on temperature characteristics

Abstract

The present invention discloses a logical judgment method for longitudinal surface cracks of continuous casting billets based on temperature characteristics, belonging to the field of iron and steel metallurgy. The method is characterized by including: establishing a sample database for longitudinal surface cracks of continuous casting billets; calculating the temperature characteristic values of thermocouples in the continuous casting mold; obtaining the temperature characteristic value range of longitudinal surface cracks of continuous casting billets; and judging the longitudinal surface cracks of continuous casting billets. It can accurately and quickly identify the longitudinal surface cracks of continuous casting billets, providing an effective method for on-line detection of longitudinal surface cracks of continuous casting billets. It is scientific, reasonable, highly applicable and has good effects.

Description

Technical Field

[0001] The present invention belongs to the technical field of continuous casting in iron and steel metallurgy, and is a logical judgment method for longitudinal surface cracks of continuous casting billets based on temperature characteristics. Background Art

[0002] The longitudinal surface crack of a continuous casting billet refers to a crack generated along the drawing direction on the surface of the billet. The longitudinal surface crack originates near the meniscus inside the mold and is affected by many factors such as molten steel composition, mold powder performance, and liquid level fluctuation. Under the coupling action of multiple factors, the cooling of the billet shell is uneven, resulting in excessive local stress. When the local stress at the thinner part of the billet shell exceeds its tensile strength, the initial crack form is generated. When longitudinal cracks appear on the surface of the continuous casting billet, in the lightest case, finishing is required. In severe cases, the continuous casting billet will be scrapped or even cause a longitudinal crack breakout accident, seriously interfering with the normal production order and becoming a key factor restricting the efficient production of continuous casting billets.

[0003] Patent Publication No.: CN1428216A discloses a method for predicting longitudinal surface cracks of continuous casting slabs named: A method for predicting longitudinal surface cracks of continuous casting slabs based on the change characteristics of thermocouple temperature data. In this method, a transverse array and at least three longitudinal rows of thermocouples are buried below the molten steel liquid level position in the mold, and these temperatures are read through a data acquisition system and data analysis is carried out. Under the condition of stable drawing speed, when the temperature of a certain row of thermocouples suddenly shows a downward trend, and the temperature drop rate exceeds the set threshold, and at the same time, the temperatures of the two rows of thermocouples below show the same change trend, by checking whether the product of the initial temperature drop time difference between two adjacent thermocouples and the drawing speed is equal to the distance between the two thermocouples, and whether the temperature change trends of the three thermocouples in the same column where the crack occurs are synchronous, the identification of longitudinal surface cracks is realized. This method is a logical judgment method for longitudinal surface cracks. Its advantage is to judge by the movement of longitudinal surface cracks between the upper and lower rows of thermocouples, which has certain theoretical significance and helps to improve the accuracy of identifying longitudinal surface cracks. However, in the actual production process, due to the diversity of temperature drops caused by longitudinal surface cracks of continuous casting billets, sometimes there will be a large difference in the temperature drops of the three rows of thermocouples, and the movement of longitudinal surface cracks is closely related to the temperature drop characteristics. Therefore, the situation where the movement distance of longitudinal surface cracks is not equal to the distance between two thermocouples often occurs, and it is easy to produce the situation where longitudinal surface cracks cannot be identified.

[0004] Patent Publication Number: CN111618265A discloses a method for on-line detection of longitudinal cracks in continuous casting billets named "An On-line Detection Method for Longitudinal Cracks in Continuous Casting Billets Based on K-Nearest Neighbor Classification". This method splices the temperature change rates of longitudinal cracks and the thermocouple temperatures in the same column under normal conditions to obtain temperature samples and a sample library, and uses the KNN classification algorithm to identify and predict the longitudinal cracks in continuous casting billets. It is characterized in that, with the temperature change rate as the input and combined with the fast classification method KNN that does not require training of the sample library, it can directly detect the longitudinal cracks in the casting billet, which helps to improve the accuracy of longitudinal crack identification. However, this method only relies on the temperature change rate as the model input and does not comprehensively consider features such as temperature amplitude and standard deviation, and false alarms are likely to occur during the judgment of surface longitudinal cracks. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and propose a scientific, reasonable, highly applicable and effective logical judgment method for surface longitudinal cracks in continuous casting billets based on temperature characteristics, so as to solve the problem of low accuracy in the judgment of surface longitudinal cracks in existing continuous casting billets and provide necessary conditions for on-line detection of surface longitudinal cracks in continuous casting billets.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a logical judgment method for surface longitudinal cracks in continuous casting billets based on temperature characteristics, characterized in that the method includes the following steps:

[0007] 1) Establish a sample database for surface longitudinal cracks in continuous casting billets

[0008] ① At least two rows of thermocouples are arranged on the copper plate of the mold, and based on the on-line monitoring system of the continuous casting mold, the temperature data of the thermocouples in the continuous casting mold are obtained in real time;

[0009] ② According to the temperature data of the thermocouples in the continuous casting mold and combined with the manual detection results of the surface longitudinal cracks of the continuous casting billet on site, a sample database for surface longitudinal cracks in continuous casting billets is established;

[0010] 2) Calculate the temperature characteristic values of the thermocouples in the continuous casting mold

[0011] ① Calculate the temperature drop amplitude T of the thermocouple in the mold according to formula (1) f ,

[0012] T f =T min -T max1 (1) [[ID=3`6]]

[0013] In the formula, T max1 is the maximum temperature before the occurrence of longitudinal cracks, °C; T min is the minimum temperature during the occurrence of longitudinal cracks, °C;

[0014] ② Calculate the temperature rise amplitude T of the thermocouple in the mold according to formula (2) r ,

[0015] T r = T max2 -T min (2)

[0016] In the formula, T max2 is the maximum temperature after the occurrence of longitudinal cracks, in °C;

[0017] ③ Calculate the temperature drop amplitude R of the mold thermocouple according to formula (3) f ,

[0018]

[0019] In the formula, T av is the average temperature within 300 seconds before the occurrence of longitudinal cracks, in °C;

[0020] ④ Calculate the temperature rise amplitude R of the mold thermocouple according to formula (4) r ,

[0021]

[0022] ⑤ Calculate the thermocouple temperature rate. When the thermocouple temperature rate is greater than 0, it is recorded as the heating rate V r ;

[0023] ⑥ Calculate the thermocouple temperature rate. When the thermocouple temperature rate is less than 0, it is recorded as the cooling rate V f ;

[0024] ⑦ Calculate the temperature standard deviation within n seconds according to formula (5);

[0025]

[0026] In the formula, σ i is the temperature standard deviation at the i-th second; T i is the temperature at the i-th second; T av is the average temperature within n seconds;

[0027] 3) Obtain the temperature characteristic value range of the longitudinal cracks on the surface of the continuous casting slab

[0028] ① Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude of the first row is T fmax1 and the minimum temperature drop amplitude is T fmin1 . Similarly, extract the maximum temperature drop amplitude T fmax2 and the minimum temperature drop amplitude T fmin2 of the second row of thermocouples;

[0029] ②Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude of the first row is T rmax1 and the minimum temperature rise amplitude is T rmin1 , similarly, extract the maximum temperature rise amplitude T rmax2 and the minimum temperature rise amplitude T rmin2 ;

[0030] ③Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude of the first row is R fmax1 and the minimum temperature drop amplitude is R fmin1 , similarly, extract the maximum temperature drop amplitude R fmax2 and the minimum temperature drop amplitude R fmin2 ;

[0031] ④Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude of the first row is R rmax1 and the minimum temperature rise amplitude is R rmin1 , similarly, extract the maximum temperature rise amplitude R rmax2 and the minimum temperature rise amplitude R rmin2 ;

[0032] ⑤Extract the maximum value of the temperature rise rate of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise rate range. The maximum temperature rise rate of the first row is V rmax1 and the minimum temperature rise rate is V rmin1 ; similarly, extract the maximum temperature rise rate V rmax2 and the minimum temperature rise rate is V rmin2 ;

[0033] ⑥Extract the maximum value of the temperature drop rate of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature drop rate range. The maximum temperature drop rate of the first row is V fmax1 and the minimum temperature drop rate is V fmin1 ; similarly, extract the maximum temperature drop rate V fmax2 and the minimum temperature drop rate V fmin2 ;

[0034] ⑦Extract the maximum value of the temperature standard deviation of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature standard deviation range. The maximum temperature standard deviation of the first row is σ max1 and the minimum temperature standard is σ min1 , similarly, extract the maximum temperature standard deviation σ max2 and the minimum temperature standard deviation σmin2 ;

[0035] 4) Judgment of longitudinal surface cracks in continuous casting billets

[0036] ① Obtain the first and second row cooling amplitude values T f1 and T f2 . If T fmin1 ≥ T f1 ≥ T fmax1 and T fmin2 ≥ T f2 ≥ T fmax2 , then proceed to the next judgment. Otherwise, determine the sample to be measured as non-longitudinal crack;

[0037] ② Obtain the first and second row heating amplitude values T r1 and T r2 . If T rmax1 ≥ T r1 ≥ T rmin1 and T rmax2 ≥ T r2 ≥ T rmin2 , then proceed to the next judgment. Otherwise, determine the sample to be measured as non-longitudinal crack;

[0038] ③ Obtain the first and second row cooling rate values R f1 and R f2 . If R fmin1 ≥ R f1 ≥ R fmax1 and R fmin2 ≥ R f2 ≥ R fmax2 , then proceed to the next judgment. Otherwise, determine the sample to be measured as non-longitudinal crack;

[0039] ④ Obtain the first and second row heating rate values R r1 and R r2 . If R rmax1 ≥ R r1 ≥ R rmin1 and R rmax2 ≥ R r2 ≥ R rmin2 , then proceed to the next judgment. Otherwise, determine the sample to be measured as non-longitudinal crack;

[0040] ⑤ Obtain the first and second row maximum heating rate values V r1 and V r2 . If V rmax1 ≥ V r1 ≥ V rmin1 and V rmax2 ≥ V r2 ≥ V rmin2 , then proceed to the next judgment. Otherwise, determine the sample to be measured as non-longitudinal crack;

[0041] ⑥ Obtain the maximum cooling rates V f1 and V f2 of the first and second rows of the sample to be tested. If V fmin1 ≥V f1 ≥V fmax1 and V fmin2 ≥V f2 ≥V fmax2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack;

[0042] ⑦ Obtain the maximum standard deviations σ1, σ2, and σ of the first and second rows of the sample to be tested. If σ max1 ≥σ1≥σ min1 and σ max2 ≥σ2≥σ min2 , then determine the sample as a longitudinal crack sample; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0043] Furthermore, n in step 2)-⑦ is set to 10 s.

[0044] Furthermore, N in step 3) is set to 140 s; the first row of thermocouples T fmax1 is set to -22.5 °C, T fmin1 is set to -4 °C; the second row of thermocouples T fmax2 is set to -22.6 °C, T fmin2 is set to -4.8 °C; the first row of thermocouples T rmax1 is set to 21.2 °C, T rmin1 is set to 6.8 °C; the second row of thermocouples T rmax2 is set to 28.2 °C, T rmin1 is set to 3.4 °C; the first row of thermocouples R fmax1 is set to -19.1%, R fmin1 is set to -3.6%; the second row of thermocouples R fmax2 is set to -23.5%, R fmin2 is set to -5.8%; the first row of thermocouples R rmax1 is set to 19.3%, R rmin1 is set to 5.5%; the second row of thermocouples R rmax2 is set to 37.6%, R rmin2 is set to 3.4%; the first row of thermocouples V rmax1 is set to 1.51 °C / s, V rmin1 is set to 0.32 °C / s; the second row of thermocouples V rmax2 is set to 1.64 °C / s, V rmin2 is set to 0.32 °C / s; the first row of thermocouples V fmax1 is set to -1.46 °C / s, V fmin1Set to -0.42 °C / s; the second row of thermocouples V fmax2 Set to -1.52 °C / s, V fmin1 Set to -0.38 °C / s; the first row of thermocouples σ max1 Set to 3.96 °C, σ min1 Set to 1.34 °C; the second row of thermocouples σ max2 Set to 4.47 °C, σ min2 Set to 1.71 °C.

[0045] Furthermore, the method is applied to the judgment of longitudinal surface cracks in continuous casting billets of slab and round billet.

[0046] The beneficial effect of a method for logical judgment of longitudinal surface cracks in continuous casting billets based on temperature characteristics of the present invention is: extracting the temperature characteristic value range of longitudinal surface cracks on the billet surface in the mold, and using the method of logical judgment to judge the longitudinal surface cracks in continuous casting billets, which can accurately and quickly identify the longitudinal surface cracks in continuous casting billets, and provide an effective method for on-line detection of longitudinal surface cracks in continuous casting billets. It is scientific, reasonable, highly applicable and has good effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is the flow chart of logical judgment of longitudinal surface cracks in continuous casting billets;

[0048] Figure 2 is the schematic diagram of the thermocouple arrangement in the mold;

[0049] Figure 3 is the temperature curve diagram of the first and second rows of thermocouples when longitudinal cracks occur;

[0050] Figure 4 is the schematic diagram of the relationship between the cooling and heating amplitudes when longitudinal cracks occur;

[0051] Figure 5 is the schematic diagram of the relationship between the cooling and heating ranges when longitudinal cracks occur;

[0052] Figure 6 is the schematic diagram of the relationship between the cooling and heating rates when longitudinal cracks occur;

[0053] Figure 7 is the schematic diagram of the temperature standard deviation when longitudinal cracks occur. DETAILED DESCRIPTION OF THE INVENTION

[0054] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited thereto.

[0055] As Figure 1 shown, a method for logical judgment of longitudinal surface cracks in continuous casting billets based on temperature characteristics includes the following steps:

[0056] 1) Establish a sample database for longitudinal surface cracks in continuous casting billets

[0057] ① At least two rows of thermocouples are arranged on the copper plate of the mold. As Figure 2 shown, temperature-measuring thermocouples are installed inside the copper plate of the mold. There are 19 columns arranged on the wide-face copper plate and 1 column arranged on the narrow-face copper plate. A total of 3 rows of thermocouples are arranged along the pouring direction. The transverse spacing of the thermocouples on the wide-face copper plate is 0.15 m. The distances of the 3 rows of thermocouples from the top of the mold along the pouring direction are 0.21, 0.325, and 0.445 m respectively. Based on the on-line monitoring system of the continuous casting mold, the temperature data of the thermocouples of the continuous casting mold are obtained in real time;

[0058] ② According to the temperature data of the thermocouples of the continuous casting mold and combined with the manual inspection results of the longitudinal surface cracks of the continuous casting billet on site, a sample database of the longitudinal surface cracks of the continuous casting billet is established.

[0059] 2) Calculate the temperature characteristic values of the thermocouples of the continuous casting mold

[0060] Figure 3 are the temperature curves of the first and second rows of thermocouples when the longitudinal crack occurs. When the longitudinal crack appears between the first and second rows of thermocouples, the temperature curve of the thermocouple will show the phenomenon of "decrease - stability - increase". Therefore, extract the temperature characteristic values of the thermocouple that can capture this phenomenon.

[0061] ① Calculate the temperature drop amplitude T of the thermocouples of the mold within 30 seconds according to formula (1) f , as Figure 3 shown,

[0062] T f = T min - T max1 (1)

[0063] In the formula, T max1 is the maximum temperature before the longitudinal crack occurs, °C; T min is the minimum temperature during the occurrence of the longitudinal crack, °C;

[0064] ② Calculate the temperature rise amplitude T of the thermocouples of the mold within 30 seconds according to formula (2) r , as Figure 3 shown,

[0065] T r = T max2 - T min (2)

[0066] In the formula, T max2 is the maximum temperature after the longitudinal crack occurs, °C;

[0067] ③ Calculate the temperature drop rate R of the thermocouples of the mold according to formula (3) f ,

[0068]

[0069] In the formula, T av is the average temperature within 300 seconds before the occurrence of longitudinal cracks, in °C;

[0070] ④ Calculate the temperature rise amplitude R of the mold thermocouple according to formula (4) r ,

[0071]

[0072] ⑤ Calculate the thermocouple temperature rate. When the thermocouple temperature rate is greater than 0, it is recorded as the heating rate V r ;

[0073] ⑥ Calculate the thermocouple temperature rate. When the thermocouple temperature rate is less than 0, it is recorded as the cooling rate V f ;

[0074] ⑦ Calculate the temperature standard deviation within n = 10 seconds according to formula (5);

[0075]

[0076] In the formula, σ i is the temperature standard deviation at the i-th second; T i is the temperature at the i-th second; T av is the average temperature within n = 10 seconds.

[0077] 3) Obtain the temperature characteristic value range of the longitudinal cracks on the surface of the continuous casting slab

[0078] ① Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude in the first row is T fmax1 and the minimum temperature drop amplitude is T fmin1 . Similarly, extract the maximum temperature drop amplitude T fmax2 and the minimum temperature drop amplitude T fmin2 of the second row of thermocouples;

[0079] ② Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude in the first row is T rmax1 and the minimum temperature rise amplitude is T rmin1 . Similarly, extract the maximum temperature rise amplitude T rmax2 and the minimum temperature rise amplitude T rmin2 of the second row of thermocouples;

[0080] ③ Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude in the first row is R fmax1and the minimum temperature drop is R fmin1 , similarly, extract the maximum temperature drop R fmax2 and the minimum temperature drop R fmin2 ;

[0081] ④ Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude of the first row is R rmax1 and the minimum temperature rise amplitude is R rmin1 , similarly, extract the maximum temperature rise amplitude R rmax2 and the minimum temperature rise amplitude R rmin2 ;

[0082] ⑤ Extract the maximum value of the temperature rise rate of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature rise rate range. The maximum temperature rise rate of the first row is V rmax1 and the minimum temperature rise rate is V rmin1 ; similarly, extract the maximum temperature rise rate V rmax2 and the minimum temperature rise rate is V rmin2 ;

[0083] ⑥ Extract the maximum value of the temperature drop rate of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature drop rate range. The maximum temperature drop rate of the first row is V fmax1 and the minimum temperature drop rate is V fmin1 ; similarly, extract the maximum temperature drop rate V fmax2 and the minimum temperature drop rate V fmin2 ;

[0084] ⑦ Extract the maximum value of the temperature standard deviation of all longitudinal crack samples passing through the first row of thermocouples within 140 seconds to obtain the maximum temperature standard deviation range. The maximum temperature standard deviation of the first row is σ max1 and the minimum temperature standard is σ min1 , similarly, extract the maximum temperature standard deviation σ max2 and the minimum temperature standard deviation σ min2 .

[0085] Figure 4 are the temperature drop and rise amplitudes when the longitudinal crack occurs. As can be seen from the figure, the first row of thermocouple T fmax1 is set to -22.5°C, T fmin1 is set to -4°C; the second row of thermocouple T fmax2 is set to -22.6°C, T fmin2 is set to -4.8°C; the first row of thermocouple T rmax1 is set to 21.2°C, T rmin1 is set to 6.8°C; the second row of thermocouple Trmax2 Set to 28.2 °C, T rmin1 Set to 3.4 °C.

[0086] Figure 5 is the temperature drop and rise amplitude when longitudinal cracks occur. As can be seen from the figure, the first row of thermocouples R fmax1 Set to -19.1%, R fmin1 Set to -3.6%; the second row of thermocouples R fmax2 Set to -23.5%, R fmin2 Set to -5.8%; the first row of thermocouples R rmax1 Set to 19.3%, R rmin1 Set to 5.5%; the second row of thermocouples R rmax2 Set to 37.6%, R rmin2 Set to 3.4 °C.

[0087] Figure 6 is the temperature drop and rise rate when longitudinal cracks occur. As can be seen from the figure, the first row of thermocouples V rmax1 Set to 1.51 °C / s, V rmin1 Set to 0.32 °C / s; the second row of thermocouples V rmax2 Set to 1.64 °C / s, V rmin2 Set to 0.32 °C / s; the first row of thermocouples V fmax1 Set to -1.46 °C / s, V fmin1 Set to -0.42 °C / s; the second row of thermocouples V fmax2 Set to -1.52 °C / s, V fmin1 Set to -­0.38 °C / s.

[0088] Figure 7 is the temperature standard deviation when longitudinal cracks occur. As can be seen from the figure, the first row of thermocouples σ max1 Set to 3.96 °C, σ min1 Set to 1.34 °C; the second row of thermocouples σ max2 Set to 4.47 °C, σ min2 Set to 1.71 °C.

[0089] 4) Judgment of longitudinal cracks on the surface of continuous casting billets

[0090] ① Obtain the temperature drop amplitudes T f1 、T f2 of the first and second rows of the sample to be measured. If T fmin1 ≥T f1 ≥T fmax1 and T fmin2 ≥T f2 ≥T fmax2 , then proceed to the next judgment; otherwise, judge the sample to be measured as non-longitudinal crack;

[0091] ② Obtain the first and second row temperature rise amplitudes \(T\) r1 and \(T\) r2 of the sample to be tested. If \(T\) rmax1 ≥ \(T\) r1 ≥ \(T\) rmin1 and \(T\) rmax2 ≥ \(T\) r2 ≥ \(T\) rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0092] ③ Obtain the first and second row temperature drop amplitudes \(R\) f1 and \(R\) f2 of the sample to be tested. If \(R\) fmin1 ≥ \(R\) f1 ≥ \(R\) fmax1 and \(R\) fmin2 ≥ \(R\) f2 ≥ \(R\) fmax2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0093] ④ Obtain the first and second row temperature rise amplitudes \(R\) r1 and \(R\) r2 of the sample to be tested. If \(R\) rmax1 ≥ \(R\) r1 ≥ \(R\) rmin1 and \(R\) rmax2 ≥ \(R\) r2 ≥ \(R\) rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0094] ⑤ Obtain the first and second row maximum temperature rise rates \(V\) r1 and \(V\) r2 of the sample to be tested. If \(V\) rmax1 ≥ \(V\) r1 ≥ \(V\) rmin1 and \(V\) rmax2 ≥ \(V\) r2 ≥ \(V\) rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0095] ⑥ Obtain the first and second row maximum temperature drop rates \(V\) f1 and \(V\) f2 of the sample to be tested. If \(V\) fmin1 ≥ \(V\) f1 ≥ \(V\) fmax1 and \(V\) fmin2 ≥ \(V\) f2 ≥ \(V\) fmax2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.

[0096] ⑦ Obtain the first and second row maximum standard deviations \(\sigma_1\), \(\sigma_2\), \(\sigma\) max1≥σ1≥σ min1 and σ max2 ≥σ2≥σ min2 , then the sample is determined as a longitudinal crack sample; otherwise, the sample to be measured is determined as a non-longitudinal crack.

[0097] Finally, based on the casting data of a domestic steel plant, the temperature characteristics of 28 non-surface longitudinal crack samples and 28 surface longitudinal crack samples were statistically analyzed. According to the method for logically judging surface longitudinal cracks in continuous casting billets proposed by the present invention, the temperature characteristics were compared. P1 to P7 of the first row and the second row of thermocouples represent the temperature drop amplitude, temperature rise amplitude, temperature drop rate, temperature rise rate, maximum heating rate, maximum cooling rate, and maximum standard deviation of the sample in sequence. The results are shown in Table 1. Among the 28 non-surface longitudinal crack samples from No. 1 to No. 28, only 1 sample was determined as a longitudinal crack, and the remaining 27 samples were determined as non-surface longitudinal cracks. All 29 to 56 surface longitudinal crack samples were correctly judged, and the accuracy rate of the selected 56 samples reached 98.21%.

[0098] Table 1 Longitudinal crack identification results

[0099]

[0100]

[0101] The above-described embodiments only represent the implementation manners of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A logical judgment method for longitudinal surface cracks of continuous casting billets based on temperature characteristics, characterized in that The method includes the following steps: 1) Establish a sample database of longitudinal surface cracks on the continuous casting billet ①Arrange at least two rows of thermocouples on the copper plate of the mold. Based on the on-line monitoring system of the continuous casting mold, obtain the thermocouple temperature data of the continuous casting mold in real time; ②According to the thermocouple temperature data of the continuous casting mold and combined with the manual inspection results of the longitudinal surface cracks on the continuous casting billet at the site, establish a sample database of longitudinal surface cracks on the continuous casting billet; 2) Calculate the temperature characteristic values of the thermocouples in the continuous casting mold ① Calculate the amplitude of the temperature drop of the mold thermocouple T according to formula (1) f , T f = T min -T max1 (1) where, T max1 is the maximum temperature before the occurrence of longitudinal cracks, in °C; T min is the minimum temperature during the occurrence of longitudinal cracks, in °C. ② Calculate the amplitude of the temperature rise of the mold thermocouple T according to formula (2) r , T r = T max2 - T min (2) Where, T max2 is the maximum temperature after the occurrence of longitudinal cracks, °C; ③ Calculate the temperature drop amplitude R of the mold thermocouple according to formula (3). f , where T av is the average temperature within 300 seconds before the occurrence of longitudinal cracks, in °C; ④ Calculate the temperature rise amplitude R of the mold thermocouple according to formula (4) r , ⑤ Calculate the temperature rate of the thermocouple. When the temperature rate of the thermocouple is greater than 0, record it as the heating rate V r ; ⑥ Calculate the temperature rate of the thermocouple. When the temperature rate of the thermocouple is less than 0, it is recorded as the cooling rate V f ; ⑦Calculate the temperature standard deviation within n seconds according to formula (5); Where, σ i is the temperature standard deviation at the i-th second; T i is the temperature at the i-th second; T av is the average temperature within n seconds; 3) Obtain the range of temperature characteristic values of the longitudinal surface cracks on the continuous casting billet ①Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples within N seconds passing through the first row of thermocouples to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude of the first row is T fmax1 and the minimum temperature drop amplitude is T fmin1 . Similarly, extract the maximum temperature drop amplitude T fmax2 and the minimum temperature drop amplitude T fmin2 ; ②Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude of the first row is T rmax1 and the minimum temperature rise amplitude is T rmin1 . Similarly, extract the maximum temperature rise amplitude T rmax2 and the minimum temperature rise amplitude T rmin2 ; ③Extract the maximum value of the temperature drop amplitude of all longitudinal crack samples within N seconds passing through the first row of thermocouples to obtain the maximum temperature drop amplitude range. The maximum temperature drop amplitude of the first row is R fmax1 and the minimum temperature drop amplitude is R fmin1 . Similarly, extract the maximum temperature drop amplitude R fmax2 and the minimum temperature drop amplitude R fmin2 ; ④Extract the maximum value of the temperature rise amplitude of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise amplitude range. The maximum temperature rise amplitude of the first row is R rmax1 and the minimum temperature rise amplitude is R rmin1 . Similarly, extract the maximum temperature rise amplitude R rmax2 and the minimum temperature rise amplitude R rmin2 ; ⑤Extract the maximum value of the temperature rise rate of all longitudinal crack samples passing through the first row of thermocouples within N seconds to obtain the maximum temperature rise rate range. The maximum temperature rise rate of the first row is V rmax1 and the minimum temperature rise rate is V rmin1 ; Similarly, extract the maximum temperature rise rate V rmax2 and the minimum temperature rise rate is V rmin2 ; ⑥Extract the maximum value of the temperature drop rate of all longitudinal crack samples within N seconds passing through the first row of thermocouples to obtain the maximum temperature drop rate range. The maximum temperature drop rate in the first row is V fmax1 and the minimum temperature drop rate is V fmin1 ; Similarly, extract the maximum temperature drop rate V fmax2 and the minimum temperature drop rate V fmin2 ; ⑦Extract the maximum value of the temperature standard deviation of all longitudinal crack samples within N seconds passing through the first row of thermocouples to obtain the maximum temperature standard deviation range. The maximum temperature standard deviation of the first row is σ max1 and the minimum temperature standard is σ min1 . Similarly, extract the maximum temperature standard deviation σ max2 and the minimum temperature standard deviation σ min2 ; 4) Judgment of longitudinal surface cracks on the continuous casting billet ①Obtain the first and second row temperature drop amplitudes T f1 and T f2 . If T fmin1 ≥T f1 ≥T fmax1 and T fmin2 ≥T f2 ≥T fmax2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack. ②Obtain the first and second row temperature rise amplitudes T r1 and T r2 . If T rmax1 ≥T r1 ≥T rmin1 and T rmax2 ≥T r2 ≥T rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack. ③Obtain the first and second row temperature drop amplitudes R of the sample to be measured f1 and R f2 If R fmin1 ≥R f1 ≥R fmax1 and R fmin2 ≥R f2 ≥R fmax2 , then proceed to the next judgment; otherwise, determine the sample to be measured as a non-longitudinal crack ④Obtain the first and second row temperature rise amplitudes R r1 and R r2 of the sample to be tested. If R rmax1 ≥R r1 ≥R rmin1 and R rmax2 ≥R r2 ≥R rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack. ⑤Obtain the maximum heating rates V r1 and V r2 of the sample to be tested. If V rmax1 ≥ V r1 ≥ V rmin1 and V rmax2 ≥ V r2 ≥ V rmin2 , then proceed to the next judgment; otherwise, determine the sample to be tested as a non-longitudinal crack.​​​​​​​​​​​​​​​​ ⑥Obtain the maximum cooling rates V f1 and V f2 of the first and second rows of the sample to be tested. If V fmin1 ≥ V f1 ≥ V fmax1 and V fmin2 ≥ V f2 ≥ V fmax2 , then proceed to the next judgment; otherwise, determine the sample to be tested as non-longitudinal crack.​​​​​​​​​​​​​​​​ ⑦ Obtain the maximum standard deviations σ1 and σ2 of the first and second rows of the sample to be measured, σ max1 ≥σ1≥σ min1 and σ max2 ≥σ2≥σ min2 , then determine the sample as a longitudinally cracked sample; otherwise, determine the sample to be measured as a non-longitudinal crack.

2. The logical judgment method for longitudinal surface cracks of continuous casting billets based on temperature characteristics according to claim 1, wherein In step 2)-⑦, n is set to 10 s.

3. A method for logically judging longitudinal surface cracks of continuous casting billets based on temperature characteristics according to claim 1, characterized in that, Step 3) Set N to 140 s; the first row of thermocouples T fmax1 is set to -22.5 °C, T fmin1 is set to -4 °C; the second row of thermocouples T fmax2 is set to -22.6 °C, T fmin2 is set to -4.8 °C; the first row of thermocouples T rmax1 is set to 21.2 °C, T rmin1 is set to 6.8 °C; the second row of thermocouples T rmax2 is set to 28.2 °C, T rmin1 is set to 3.4 °C; the first row of thermocouples R fmax1 is set to -19.1%, R fmin1 is set to -3.6%; the second row of thermocouples R fmax2 is set to -23.5%, R fmin2 is set to -5.8%; the first row of thermocouples R rmax1 is set to 19.3%, R rmin1 is set to 5.5%; the second row of thermocouples R rmax2 is set to 37.6%, R rmin2 is set to 3.4%; the first row of thermocouples V rmax1 is set to 1.51 °C / s, V rmin1 is set to 0.32 °C / s; the second row of thermocouples V rmax2 is set to 1.64 °C / s, V rmin2 is set to 0.32 °C / s; the first row of thermocouples V fmax1 is set to -1.46 °C / s, V fmin1 is set to -0.42 °C / s; the second row of thermocouples V fmax2 is set to -1.52 °C / s, V fmin1 is set to -0.38 °C / s; the first row of thermocouples σ max1 is set to 3.96 °C, σ min1 is set to 1.34 °C; the second row of thermocouples σ max2 is set to 4.47 °C, σ min2 is set to 1.71 °C.

4. A method for logically judging longitudinal surface cracks of a continuous casting billet based on temperature characteristics according to claim 1, characterized in that, The logical judgment method is applied to the judgment of longitudinal surface cracks on the continuous casting billets of slab and round billet.

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