Continuous casting method for isothermal quenching nodular cast iron ADI

Abstract

The invention relates to the technical field of metal casting, in particular to an isothermal quenching nodular cast iron ADI continuous casting method which comprises the steps that the temperature of a crystallizer used in the ADI continuous casting process is collected in real time; calculating a heat exchange coefficient in the crystallizer in real time; friction force generated when the casting blank is pulled out of the crystallizer is collected in real time; presetting each period, and obtaining period steady-state indexes of the heat exchange coefficient, the temperature and the friction force in each period; respectively acquiring abrupt change points of friction force and temperature in each period on a time sequence, and screening friction force change points and temperature change points from the abrupt change points; the lag time length of each friction force change point is obtained; the continuous casting stability index and the suspension confidence coefficient of each period are obtained; and evaluating the abnormal condition of the continuous casting process in each period through the stopping confidence coefficient of each period. According to the method and the device, the unplanned shutdown caused by misjudgment is reduced by timely finding the abnormal phenomenon in the continuous casting process, and the continuous casting production efficiency of ADI is improved.

Description

Technical Field

[0001] The present application relates to the field of metal casting technology, and in particular to a continuous casting method of austempered ductile iron (ADI). Background Art

[0002] Continuous ductile iron (ductile iron) is typically heat-treated through austempering. Ductile iron after austempering is referred to as ADI, also known as austempered ductile iron (ADI). Compared to steel, ADI offers superior wear resistance, leading to its widespread application in various fields. Continuous casting is a process in which liquid metal is converted into ingots through forced cooling. Ductile iron profiles produced by horizontal continuous casting are free of defects such as shrinkage, shrinkage cavities, and slag inclusions. They exhibit dense microstructure, fine grains, a high degree of spheroidization, and excellent overall mechanical properties.

[0003] In order to improve the quality and production efficiency of the ADI continuous casting process, the existing technology has obtained the optimal process parameters of different casting materials in the continuous casting process, such as casting speed, cooling rate, water spray distance, etc., through finite element analysis combined with simulation, and carried out continuous casting production based on the optimal process parameters. In order to ensure production safety during the continuous casting process, the existing technology usually relies on threshold comparison to monitor various parameter data in the ADI continuous casting process. However, it is difficult to fully reflect the complex process of the continuous casting process through the threshold comparison method alone, which can easily lead to errors in the state assessment of the continuous casting process, which may cause the continuous casting process to frequently start and stop, thereby affecting the production efficiency of the ADI continuous casting process. Summary of the Invention

[0004] In view of the above, it is necessary to provide a continuous casting method for austempered ductile iron ADI. Compared with the traditional continuous casting method for austempered ductile iron ADI, the continuous casting production efficiency of ADI can be improved by timely detecting abnormal phenomena in the continuous casting process, reducing unplanned shutdowns caused by misjudgment.

[0005] The continuous casting method of austempered ductile iron ADI of the present application adopts the following technical solution: One embodiment of the present application provides a continuous casting method for austempered ductile iron (ADI), the method comprising the following steps: The temperature of the crystallizer used in the ADI continuous casting process is collected in real time. The heat transfer coefficient inside the crystallizer is calculated in real time using the crystallizer's water channel axis curvature radius, water channel equivalent diameter data, as well as the real-time flow rate, density, specific heat capacity, thermal diffusivity, and dynamic viscosity of the cooling water in the crystallizer. The friction force generated when the cast embryo is pulled out of the crystallizer is collected in real time. Each cycle is preset, and the periodic steady-state index of the heat transfer coefficient, temperature, and friction force in each cycle is obtained through the autocorrelation of the heat transfer coefficient, temperature, and friction force in the time series and the energy distribution in the frequency domain; Obtain each mutation point of the friction force and temperature in each cycle in a time series, and select each friction force change point and each temperature change point from the mutation points of the friction force and temperature in each cycle by comparing the friction force and temperature at the nearest moments before and after each mutation point; obtain the lag time of each friction force change point by the appearance time of the friction force change point and the temperature change point in each cycle; obtain the continuous casting stability index of each cycle by the correlation between the heat transfer coefficient and the temperature in the time series in each cycle and the cycle steady-state index, combined with the dispersion of the lag time of all friction force change points in each cycle; The confidence level of termination of each cycle is obtained by combining the continuous casting stability index with the change trend of the continuous casting stability index of each cycle and the preset number of cycles before it, and the average level of the hysteresis time of all friction force change points in each cycle, compared with the average level of the hysteresis time of all friction force change points in the preset number of cycles before it. The abnormal conditions of the continuous casting process in each cycle are evaluated by using the suspension confidence level.

[0006] In one embodiment, the process of obtaining the periodic steady-state index is: Arrange the heat transfer coefficients at all acquisition moments in each cycle in time sequence to form a heat transfer sequence in each cycle, obtain the autocorrelation coefficients of each heat transfer sequence at each preset lag period, and calculate the maximum value of the autocorrelation coefficients of each heat transfer sequence at all preset lag periods; Calculate the proportion of the energy of the frequency component with the largest energy in the frequency domain in each heat exchange sequence to the total energy of all frequency components; Combining the maximum value and the proportion in each cycle, a periodic steady-state index of the heat transfer coefficient in each cycle is obtained; According to the method for obtaining the periodic steady-state index of the heat transfer coefficient in each period, the periodic steady-state index of the temperature and the friction force in each period is obtained.

[0007] In one embodiment, the cycle steady-state index is calculated as follows: The product of the maximum value and the proportion in each cycle is used as the periodic steady-state index of the heat transfer coefficient in each cycle; The temperature and friction force cycle steady-state indices in each cycle are calculated according to the calculation method of the cycle steady-state index of the heat transfer coefficient in each cycle.

[0008] In one embodiment, the process of selecting each friction force change point and each temperature change point from the friction force and temperature mutation points in each cycle is as follows: For each mutation point of the friction force in each cycle, the difference between the average of a preset number of friction forces before each mutation point and the average of a preset number of friction forces after each mutation point is calculated, and the mutation point where the difference is negative is taken as the friction force change point; According to the screening process of friction force change points, each temperature change point is screened from the temperature mutation points in each cycle.

[0009] In one embodiment, the process of obtaining the lag time is as follows: The temperature change point in each cycle that is after each friction mutation point and has the shortest time interval with the acquisition moment is recorded as the temperature corresponding point of each friction mutation point, and the time interval between each friction mutation point and its temperature corresponding point is recorded as the lag time of each friction change point.

[0010] In one embodiment, the process of obtaining the continuous casting stability index is: Calculate the absolute value of the correlation coefficient between the heat transfer coefficient and the temperature in each cycle; Calculate the average values ​​of the heat transfer coefficient, temperature and friction period steady-state index in each cycle; The continuous casting stability index is respectively proportional to the absolute value and the average value, and inversely proportional to the dispersion.

[0011] In one embodiment, the continuous casting stability index is calculated as follows: Calculating the product of the absolute value and the average value, and mapping the dispersion into a first positive number; The continuous casting stability index is the ratio of the product to the first positive number.

[0012] In one embodiment, the process of obtaining the suspension confidence is as follows: Calculate the slope of the fitting line of the continuous casting stability index of each cycle and a preset number of cycles before it in the time series; Recording the arithmetic mean of the hysteresis time of all friction force change points in each cycle as a first arithmetic mean; recording the arithmetic mean of the hysteresis time of all friction force change points in a preset number of cycles before each cycle as a second arithmetic mean; calculating the difference between the first arithmetic mean and the second arithmetic mean; The termination confidence is inversely proportional to the continuous casting stability index and the slope, and is directly proportional to the difference.

[0013] In one embodiment, the calculation process of the suspension confidence is: Mapping the slope to a second positive number, and calculating a product value of the continuous casting stability index and the second positive number; The sum of the product value and a preset positive number is calculated; and the termination confidence is the ratio of the difference to the sum.

[0014] In one embodiment, the process of evaluating abnormal conditions of the continuous casting process in each cycle is as follows: If the normalized value of the termination confidence of the current cycle is greater than or equal to the preset threshold, it is determined that a casting abnormality has occurred in the current continuous casting process; otherwise, it is determined that no abnormality has occurred in the current continuous casting process.

[0015] This application has at least the following beneficial effects: This application addresses the problem that the existing technology only uses threshold comparison analysis, which leads to poor detection of the continuous casting process status, frequent start and stop of the continuous casting process, and affects the casting efficiency. By constructing a periodic steady-state index, it is possible to reflect the periodic stability of the crystallizer heat exchange and the significance of the main period characteristics during the continuous casting process, which is conducive to timely detection of periodic anomalies; by screening the friction force change points and the temperature change points, it is possible to obtain the moment reflecting the sudden increase in friction force and temperature, and then calculate the lag time to reflect how long it takes for the temperature to respond after the friction force changes; and then calculate the continuous casting stability index to reflect the correlation stability of the heat transfer coefficient, temperature and friction force. As well as the stability of the lag time, it comprehensively considers multiple factors such as heat transfer coefficient, temperature and friction, and can more comprehensively reflect the stability of the continuous casting process; by calculating the termination confidence, it can reflect the degree of deviation of the current continuous casting process data compared with the historical continuous casting process, and dynamically evaluate the abnormal risk. By combining historical data with current data, it can reduce the misjudgment caused by data fluctuations in a single cycle and improve the reliability of the assessment of abnormal conditions in the continuous casting process; through the termination confidence, abnormal phenomena in the continuous casting process can be discovered in time, and quality and safety problems caused by abnormalities can be avoided. At the same time, unplanned shutdowns caused by misjudgment can be reduced, thereby improving ADI's continuous casting production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 A flowchart of the steps of a continuous casting method for austempered ductile iron (ADI) provided in this application; Figure 2 Schematic diagram of the process of obtaining termination confidence. DETAILED DESCRIPTION

[0018] In the description of the embodiments of this application, words such as "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "or," and "for example" is intended to present the relevant concepts in a concrete manner.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application relates. The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be understood that, unless otherwise indicated, " / " represents or.

[0020] It should also be noted that the terms "first" and "second" in this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0021] The specific scheme of the continuous casting method of austempered ductile iron ADI provided by the present application is described in detail below with reference to the accompanying drawings.

[0022] An embodiment of the present application provides a continuous casting method for austempered ductile iron ADI. Specifically, the following continuous casting method for austempered ductile iron ADI is provided. Figure 1 , the method comprises the following steps: Step 1: Real-time acquisition of the temperature of the crystallizer used in the ADI continuous casting process; real-time calculation of the heat transfer coefficient inside the crystallizer using the crystallizer's water channel axis curvature radius, water channel equivalent diameter data, as well as the real-time flow rate, density, specific heat capacity, thermal diffusion coefficient, and dynamic viscosity of the cooling water in the crystallizer; and real-time acquisition of the friction force generated when the cast embryo is pulled out of the crystallizer.

[0023] The crystallizer is one of the most critical equipment in the ADI continuous casting process. If there is a problem with the crystallizer, it will directly affect the quality of cast iron, production efficiency and production safety. Therefore, this application uses the crystallizer as the detection object to monitor and evaluate the status of the ADI continuous casting process in real time.

[0024] 18 rows of thermocouples were arranged at equal distances on the two wide copper plates of the crystallizer, and 2 rows of thermocouples were arranged on each of the two narrow copper plates. Three rows of thermocouples were arranged at equal distances along the pouring direction, for a total of 120 thermocouples. The average temperature collected by all thermocouples at the same time was recorded as the temperature of the crystallizer.

[0025] The density of the cooling water in the crystallizer is obtained in real time using a densitometer, and the thermal diffusivity and specific heat capacity of the cooling water in the crystallizer are measured in real time using a laser thermal conductivity meter. The thermal conductivity of the cooling water is obtained in real time using the density, thermal diffusivity, and specific heat capacity. The flow rate and dynamic viscosity of the cooling water in the crystallizer are collected in real time using a flow meter and a viscometer. The curvature radius of the water channel axis and the equivalent diameter of the water channel are obtained according to the crystallizer manual. The Reynolds number of the cooling water is obtained in real time using the density, flow rate, dynamic viscosity, and equivalent diameter of the water channel. The Prandtl number is obtained in real time using the dynamic viscosity, specific heat capacity, and thermal conductivity. The Nusselt number is obtained in real time using the Reynolds number, Prandtl number, curvature radius of the water channel axis, and equivalent diameter of the water channel. The heat transfer coefficient inside the crystallizer is obtained in real time using the thermal conductivity, equivalent diameter of the water channel, and Nusselt number. The specific calculation methods of the thermal conductivity, Reynolds number, Prandtl number, Nusselt number, and heat transfer coefficient are well known in the art and will not be described in detail in this application.

[0026] The pulling force when the billet is pulled out of the crystallizer is obtained by the pulling machine and recorded as the friction force between the crystallizer and the billet.

[0027] Temperature data, heat transfer coefficient, and friction are collected in real time and synchronously. In this embodiment, the collection time interval for temperature data, heat transfer coefficient, and friction is 1 second. The value of the collection time interval is preset by the implementer and can be set according to actual conditions. This application does not impose any special restrictions.

[0028] In order to eliminate the dimensional influence between the data, the temperature, heat transfer coefficient and friction force are normalized separately. In this embodiment, the Min-Max normalization method is used to normalize the temperature, heat transfer coefficient and friction force separately. The Min-Max normalization method is a well-known technology and will not be described in detail in this application.

[0029] Step 2: Preset each cycle and obtain the periodic steady-state index of the heat transfer coefficient, temperature, and friction force in each cycle through the autocorrelation of the heat transfer coefficient, temperature, and friction force in the time series and the energy distribution in the frequency domain.

[0030] During ADI's horizontal continuous casting production, the movement of the cast material is a cyclical movement of pulling and stopping. When the billet is pulled out of the crystallizer, the contact area between the inner wall of the crystallizer and the billet decreases, resulting in a decrease in the local cooling intensity. The increase in friction also enhances the heat transfer between the crystallizer and the billet, causing the temperature of the crystallizer to rise briefly. The molten iron in the holding furnace then flows into the crystallizer for cooling to form the billet. At this time, the cooling water continuously flushes the inner wall of the crystallizer, quickly carrying away the heat, and the temperature of the crystallizer gradually decreases. Therefore, if the continuous casting production process of ADI is stable, the heat transfer coefficient inside the crystallizer will also show periodic changes with changes in temperature. Therefore, by analyzing whether the heat transfer coefficient inside the crystallizer is still periodic, it is possible to preliminarily analyze whether there are any abnormalities in the continuous casting production process of ADI.

[0031] Based on the above analysis, each data collection cycle is preset, and the heat transfer coefficients at all collection moments within each cycle are arranged in time series to form a heat transfer sequence within each cycle. The heat transfer sequence within each cycle is used as the input of the autocorrelation function, and the autocorrelation coefficient of the heat transfer sequence within each cycle at each preset lag period is output. The maximum value among the autocorrelation coefficients of the heat transfer sequence within each cycle at all preset lag periods is calculated. This maximum value can reflect whether the heat transfer sequence is periodic; the larger the maximum value, the more significant the periodicity of the heat transfer sequence. The autocorrelation coefficient is well known in the art and will not be further described in this application.

[0032] In this embodiment, the duration of the cycle is 30 minutes. The duration of the cycle is preset manually and can be set by the implementer according to actual conditions. This application does not impose any special restrictions.

[0033] In this embodiment, the range of the preset lag period is Integer in, where N represents the length of the heat exchange sequence, the value range of the preset lag period is preset manually, and the implementer can set it according to the actual situation. This application does not impose any special restrictions.

[0034] Furthermore, because the pull-and-stop rhythm of the ADI horizontal continuous casting process exhibits a strong periodicity, the mold's heat exchange response should normally also stably reflect this periodicity. However, due to factors such as equipment aging and subtle variations in molten iron temperature during actual production, complex perturbations can be introduced into the heat exchange sequence. Using the autocorrelation coefficient alone makes it difficult to accurately identify the primary cycle and distinguish complex perturbations, which can affect the determination of true periodicity. Therefore, further analysis is necessary.

[0035] For each cycle, the heat exchange sequence is Fourier transformed, and the cycle corresponding to the frequency component with the largest energy is taken as the main cycle. The proportion of the energy of the frequency component corresponding to the main cycle in the total energy of all frequency components is calculated; the proportion can reflect the significance and stability of the main periodic components in the heat exchange sequence; the larger the proportion, the more significant the main periodicity in the heat exchange process, the more stable the heat exchange operation of the crystallizer, and the more consistent with the expected pull-stop rhythm.

[0036] Furthermore, the periodic steady-state index of the heat transfer coefficient in each cycle is obtained by taking the maximum value of the autocorrelation coefficient of the heat transfer sequence in each cycle under all preset lag periods and the proportion of the energy of the frequency component corresponding to the main cycle in the total energy of all frequency components. The expression is: Where, Represents the periodic steady-state index of the heat transfer coefficient in the i-th cycle; It represents the maximum value of the autocorrelation coefficient of the heat exchange sequence in the i-th cycle under all preset lag periods; It represents the proportion of the energy of the frequency component corresponding to the main period in the i-th period to the total energy of all frequency components.

[0037] It should be noted that the periodic steady-state index can reflect whether the periodicity of the heat transfer coefficient of the crystallizer itself is stable during the continuous casting process; the larger the periodic steady-state index, the better the stability of the crystallizer during the ADI continuous casting process, the more stable the heat transfer process, and the more controllable the temperature change, which further indicates that the stability of the continuous casting process is higher.

[0038] Because the billet is pulled from the mold in an alternating rhythm of pull-and-stop during the ADI continuous casting process, the friction between the billet and the mold also exhibits a strong periodicity. Therefore, the cyclical steady-state indices of temperature and friction within each cycle are obtained using the same method for obtaining the cyclical steady-state indices of the heat transfer coefficient within each cycle.

[0039] Calculate the average of the cycle steady-state indices for the heat transfer coefficient, temperature, and friction within each cycle. This average value reflects whether the ADI continuous casting process is operating within the expected steady-state continuous casting rhythm within each cycle. A larger average value indicates more stable changes in the heat transfer coefficient, temperature, and friction during the continuous casting process, which in turn indicates a more stable continuous casting rhythm and a lower likelihood of anomalies.

[0040] Step 3: Obtain each mutation point of the friction force and temperature in each cycle in the time series, and screen each friction force change point and each temperature change point from the mutation points of the friction force and temperature in each cycle by comparing the friction force and temperature at the adjacent moments before and after each mutation point; obtain the lag time of each friction force change point through the appearance time of the friction force change point and the temperature change point in each cycle; obtain the continuous casting stability index of each cycle through the correlation between the heat transfer coefficient and the temperature in each cycle in the time series and the cycle steady-state index, combined with the discreteness of the lag time of all friction force change points in each cycle.

[0041] Furthermore, considering that the heat transfer coefficient changes with the temperature during the continuous casting process of ADI, and the temperature is also periodic, the correlation between temperature and heat transfer coefficient can be further combined to deeply analyze the stability of the ADI continuous casting process.

[0042] The temperature data at all collected moments in each cycle are arranged in time series to form a temperature sequence within each cycle. The absolute value of the correlation coefficient between the heat exchange sequence and the temperature sequence within each cycle is calculated. The absolute value of the correlation coefficient can reflect whether the correlation between the heat exchange coefficient and temperature of the crystallizer during the ADI continuous casting process is stable.

[0043] In this embodiment, the correlation coefficient between the heat exchange sequence and the temperature sequence is the Pearson correlation coefficient. The calculation method of the Pearson correlation coefficient is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to measure the correlation between the heat exchange sequence and the temperature sequence, the implementer may adopt other existing technologies, such as the Spearman correlation coefficient, the Kendall rank correlation coefficient, etc., and this application does not impose any special restrictions.

[0044] Furthermore, temperature changes exhibit a hysteresis. When the billet is subjected to tension, friction is first generated between the billet and the mold, while temperature changes only gradually become apparent some time after the billet is pulled from the mold. If the continuous casting process is stable, the lag between temperature changes and friction changes will also be stable. However, if an abnormality occurs during the continuous casting process, such as a sudden increase in friction due to adhesion between the billet and the mold, or a sudden decrease in friction due to breakout, the heat transfer path in the mold will fluctuate, leading to an abnormal change in the lag between temperature and friction.

[0045] As the billet is pulled, the friction between it and the mold begins to increase, leading to localized heat accumulation and a rapid rise in the mold wall temperature. Therefore, the friction forces collected at all sampling moments within each cycle are arranged in chronological order to form a friction sequence within each cycle. Each mutation point in the friction and temperature sequences within each cycle is then determined. For each friction mutation point within each cycle, the difference between the average of a preset number of friction forces before and after each mutation point is calculated. Mutation points where this difference is negative are considered friction change points. Following the friction change point screening process, temperature change points are selected from the temperature mutation points within each cycle. The sampling moments at which friction and temperature change points occur can reflect the moments when friction and temperature suddenly increase.

[0046] In this embodiment, the PELT (Pruned Exact Linear Time) algorithm is used to obtain the friction force sequence and each mutation point in the temperature sequence within each cycle respectively. The PELT algorithm is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to obtain the friction force sequence and each mutation point in the temperature sequence within each cycle respectively, the implementer may adopt other existing technologies, such as the Pettitt algorithm, the Mann-Kendall algorithm, etc., and this application does not impose any special restrictions.

[0047] In this embodiment, the value of the preset number is 4. The value of the preset number is preset manually. On the basis of ensuring that the value of the preset number is within the range of [2, 5], the implementer can set it according to actual conditions.

[0048] Furthermore, the hysteresis duration of each friction change point is determined by the occurrence times of the friction change points and temperature change points within each cycle. Specifically, the temperature change point within each cycle that follows each friction mutation point and has the shortest time interval with the acquisition time is recorded as the temperature corresponding point of each friction mutation point. The time interval between each friction mutation point and its temperature corresponding point is used as the hysteresis duration of each friction change point. The hysteresis duration reflects how long it takes for the temperature to respond to a change in friction.

[0049] The dispersion of the hysteresis time of all friction force change points in each cycle is calculated. The dispersion can reflect whether the hysteresis degree of temperature compared to friction force in each cycle is stable. The larger the dispersion, the more unstable the hysteresis degree of temperature compared to friction force in each cycle.

[0050] Furthermore, the continuous casting stability index of each cycle is obtained by the absolute value of the correlation coefficient between the heat transfer sequence and the temperature sequence in each cycle, the average value of the periodic steady-state index of the heat transfer coefficient, temperature and friction force in each cycle, and the discreteness of the hysteresis time of all friction force change points in each cycle. The expression is: Where, represents the continuous casting stability index of the i-th cycle; represents the absolute value of the correlation coefficient between the heat exchange sequence and the temperature sequence in the i-th cycle; represents the average value of the periodic steady-state index of heat transfer coefficient, temperature and friction force in the i-th cycle; Represents the first positive number obtained by discrete mapping of the hysteresis duration of all friction force change points in the i-th cycle.

[0051] In this embodiment, the discreteness is mapped to a first positive number by calculating the sum of the discreteness and a preset positive number, wherein the value of the preset positive number is 0.006. The value of the preset positive number is preset manually. In order to avoid affecting the calculation result of the continuous casting stability index, the preset positive number should be an extremely small positive number. On the basis of satisfying that the value of the preset positive number is within the range of (0.005, 0.01), the implementer can set the specific value of the preset positive number by himself.

[0052] It should be noted that the continuous casting stability index can reflect whether the heat transfer effect of various factors in the continuous casting process within each cycle is stable; the larger the continuous casting stability index, the more stable the relationship between friction and temperature, and temperature and heat transfer coefficient, and thus the more stable the operation of the continuous casting process.

[0053] Step 4: Obtain the termination confidence of each cycle by combining the continuous casting stability index with the changing trend of the continuous casting stability index of each cycle and the preset number of cycles before it, and the average level of the lag time of all friction change points in each cycle compared with the average level of the lag time of all friction change points in the preset number of cycles before it, and the continuous casting stability index.

[0054] Furthermore, considering the harsh working environment of the crystallizer and the long maintenance cycle of the equipment, it is easy for the crystallizer and internal sensors to age, which may cause the continuous casting data to drift slowly. However, since a single cycle is difficult to reflect the slow changes in data, a more in-depth analysis of each cycle can be carried out by combining historical data.

[0055] The continuous casting stability indexes of each cycle and a preset number of cycles before it are arranged in time series to form a continuous casting stability index sequence of each cycle. A straight line fitting is performed on the continuous casting stability index sequence of each cycle, and the slope of the fitted straight line is calculated. The slope can reflect the time series trend of the stability of the continuous casting process. The larger the slope, the more stable the ADI continuous casting process is. The smaller the slope, the more stable the continuous casting stability is. The greater the possibility of unstable factors such as equipment aging, and the more likely abnormal phenomena are to occur in the continuous casting process.

[0056] In this embodiment, the value of the preset number is 50. The value of the preset number is preset manually and the implementer can set it according to actual conditions. This application does not impose any special restrictions.

[0057] In this embodiment, the least squares method is used to perform linear fitting on the continuous casting stability index sequence of each period. As other implementation methods, on the basis of being able to perform linear fitting on the continuous casting stability index sequence of each period, the implementer may adopt other existing technologies, such as linear regression analysis, weighted least squares method, etc., and this application does not impose any special restrictions.

[0058] Furthermore, the arithmetic mean of the lag time of all friction force change points in each cycle is recorded as the first arithmetic mean; the arithmetic mean of the lag time of all friction force change points in a preset number of cycles before each cycle is recorded as the second arithmetic mean; the difference between the first arithmetic mean and the second arithmetic mean is used as the lag difference of each cycle; the lag difference can reflect whether the lag relationship between temperature and friction force in each cycle deviates from historical data; since various abnormal factors such as adhesion between the ingot and the crystallizer, cracks and steel leakage can cause the lag degree to change, the larger the lag difference, the greater the possibility of abnormality in the continuous casting process in each cycle.

[0059] In this embodiment, the difference between the first arithmetic mean and the second arithmetic mean is an absolute value of the difference.

[0060] Furthermore, the confidence level of termination of each cycle is obtained by combining the continuous casting stability index with the change trend of the continuous casting stability index of each cycle and the preset number of cycles before it, and the average level of the hysteresis time of all friction force change points in each cycle with the average level of the hysteresis time of all friction force change points in the preset number of cycles before it. The expression is: Where, represents the termination confidence of the i-th cycle; represents the lag difference of the i-th period; represents the continuous casting stability index of the i-th cycle; Represents the slope of the fitted straight line of the continuous casting stability index sequence of the i-th cycle; τ represents a preset positive number used to avoid the denominator being 0. In this embodiment, the value of τ is 0.006. The value of τ is preset manually. To avoid affecting the calculation result of the termination confidence, τ should be an extremely small positive number. On the basis of satisfying that the value of τ is within the range of (0.005, 0.01), the implementer can set the specific value of τ at will; exp() represents an exponential function with a natural constant as the base. Among them, the exponential function with a natural constant as the base is only one embodiment of the present application. When the base of the exponential function is greater than 1, the implementer can set the base of the exponential function at will.

[0061] It should be noted that the termination confidence can reflect the degree of deviation between the continuous casting process data in each cycle and the historical continuous casting process; the greater the termination confidence, the greater the possibility of abnormal phenomena in the continuous casting process in each cycle, and the more necessary it is to stop the continuous casting process in time to ensure production safety. The diagram of the process flow for obtaining the termination confidence is as follows: Figure 2 shown.

[0062] Step 5: Evaluate abnormal conditions of the continuous casting process in each cycle using the termination confidence level.

[0063] If the normalized value of the termination confidence of the current cycle is greater than or equal to the preset threshold, it is determined that an abnormal continuous casting phenomenon has occurred in the current continuous casting process, and the continuous casting process needs to be stopped and repaired in time to ensure casting safety. Otherwise, it is determined that the current continuous casting process is running stably and no abnormal phenomenon has occurred, and continuous casting can continue, thereby avoiding the problem of affecting continuous casting efficiency due to frequent starts and stops of the continuous casting process.

[0064] In this embodiment, a sigmoid function is used to obtain a normalized value of the termination confidence. The sigmoid function is a well-known technology and will not be described in detail in this application.

[0065] In summary, the present application addresses the problem that the prior art only uses threshold comparison analysis, which leads to poor detection of the continuous casting process status, frequent start and stop of the continuous casting process, and affects the casting efficiency. By constructing a periodic steady-state index, it is possible to reflect the periodic stability of the crystallizer heat exchange and the significance of the main period characteristics during the continuous casting process, which is conducive to timely detection of periodic anomalies; by screening the friction force change points and the temperature change points, it is possible to obtain the moment reflecting the sudden increase in friction and temperature, and then calculate the lag time to reflect how long it takes for the temperature to respond after the friction force changes; and then calculate the continuous casting stability index to reflect the relationship between the heat transfer coefficient, temperature and friction. The stability and hysteresis time stability take into account multiple factors such as heat transfer coefficient, temperature and friction, and can more comprehensively reflect the stability of the continuous casting process. By calculating the termination confidence, it can reflect the degree of deviation of the current continuous casting process data compared with the historical continuous casting process, and dynamically evaluate the abnormal risk. By combining historical data with current data, it can reduce misjudgment caused by data fluctuations within a single cycle and improve the reliability of the assessment of abnormal conditions in the continuous casting process. Through the termination confidence, abnormal phenomena in the continuous casting process can be discovered in time to avoid quality and safety problems caused by abnormalities, while reducing unplanned shutdowns caused by misjudgment and improving ADI's continuous casting production efficiency.

[0066] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architectures, functions and operations of the systems, methods and computer program products according to the embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for implementing the specified logical functions. In some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different boxes can also occur in an order different from that disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified function or action, or may be implemented by a combination of dedicated hardware and computer instructions.

[0067] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the basic characteristics of the present application. Therefore, from all perspectives, the above embodiments of the present application should be regarded as exemplary and non-restrictive.

Claims

1. A continuous casting method for austempered ductile iron (ADI), characterized in that: The method comprises the following steps: The temperature of the crystallizer used in the ADI continuous casting process is collected in real time. The heat transfer coefficient inside the crystallizer is calculated in real time using the crystallizer's water channel axis curvature radius, water channel equivalent diameter data, as well as the real-time flow rate, density, specific heat capacity, thermal diffusivity, and dynamic viscosity of the cooling water in the crystallizer. The friction force generated when the cast embryo is pulled out of the crystallizer is collected in real time. Each cycle is preset, and the periodic steady-state index of the heat transfer coefficient, temperature, and friction force in each cycle is obtained through the autocorrelation of the heat transfer coefficient, temperature, and friction force in the time series and the energy distribution in the frequency domain; Obtain each mutation point of the friction force and temperature in each cycle in a time series, and select each friction force change point and each temperature change point from the mutation points of the friction force and temperature in each cycle by comparing the friction force and temperature at the nearest moments before and after each mutation point; obtain the lag time of each friction force change point by the appearance time of the friction force change point and the temperature change point in each cycle; obtain the continuous casting stability index of each cycle by the correlation between the heat transfer coefficient and the temperature in the time series in each cycle and the cycle steady-state index, combined with the dispersion of the lag time of all friction force change points in each cycle; The confidence level of termination of each cycle is obtained by combining the continuous casting stability index with the change trend of the continuous casting stability index of each cycle and the preset number of cycles before it, and the average level of the hysteresis time of all friction force change points in each cycle, compared with the average level of the hysteresis time of all friction force change points in the preset number of cycles before it. The abnormal conditions of the continuous casting process in each cycle are evaluated by using the suspension confidence level.

2. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of obtaining the periodic steady-state index is as follows: Arrange the heat transfer coefficients at all acquisition moments in each cycle in time sequence to form a heat transfer sequence in each cycle, obtain the autocorrelation coefficients of each heat transfer sequence at each preset lag period, and calculate the maximum value of the autocorrelation coefficients of each heat transfer sequence at all preset lag periods; Calculate the proportion of the energy of the frequency component with the largest energy in the frequency domain in each heat exchange sequence to the total energy of all frequency components; Combining the maximum value and the proportion in each cycle, a periodic steady-state index of the heat transfer coefficient in each cycle is obtained; According to the method for obtaining the periodic steady-state index of the heat transfer coefficient in each period, the periodic steady-state index of the temperature and the friction force in each period is obtained.

3. The continuous casting method of austempered ductile iron (ADI) according to claim 2, characterized in that: The calculation method of the cycle steady-state index is: The product of the maximum value and the proportion in each cycle is used as the periodic steady-state index of the heat transfer coefficient in each cycle; The temperature and friction force cycle steady-state indices in each cycle are calculated according to the calculation method of the cycle steady-state index of the heat transfer coefficient in each cycle.

4. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of selecting each friction force change point and each temperature change point from the friction force and temperature mutation points in each cycle is as follows: For each mutation point of the friction force in each cycle, the difference between the average of a preset number of friction forces before each mutation point and the average of a preset number of friction forces after each mutation point is calculated, and the mutation point where the difference is negative is taken as the friction force change point; According to the screening process of friction force change points, each temperature change point is screened from the temperature mutation points in each cycle.

5. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of obtaining the lag time is as follows: The temperature change point in each cycle that is after each friction mutation point and has the shortest time interval with the acquisition moment is recorded as the temperature corresponding point of each friction mutation point, and the time interval between each friction mutation point and its temperature corresponding point is recorded as the lag time of each friction change point.

6. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of obtaining the continuous casting stability index is as follows: Calculate the absolute value of the correlation coefficient between the heat transfer coefficient and the temperature in each cycle; Calculate the average values ​​of the heat transfer coefficient, temperature and friction period steady-state index in each cycle; The continuous casting stability index is respectively proportional to the absolute value and the average value, and inversely proportional to the dispersion.

7. The continuous casting method of austempered ductile iron (ADI) according to claim 6, characterized in that: The calculation method of the continuous casting stability index is: Calculating the product of the absolute value and the average value, and mapping the dispersion into a first positive number; The continuous casting stability index is the ratio of the product to the first positive number.

8. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of obtaining the suspension confidence is as follows: Calculate the slope of the fitting line of the continuous casting stability index of each cycle and a preset number of cycles before it in the time series; Recording the arithmetic mean of the hysteresis time of all friction force change points in each cycle as a first arithmetic mean; recording the arithmetic mean of the hysteresis time of all friction force change points in a preset number of cycles before each cycle as a second arithmetic mean; calculating the difference between the first arithmetic mean and the second arithmetic mean; The termination confidence is inversely proportional to the continuous casting stability index and the slope, and is directly proportional to the difference.

9. The continuous casting method of austempered ductile iron (ADI) according to claim 8, characterized in that: The calculation process of the suspension confidence is: Mapping the slope to a second positive number, and calculating a product value of the continuous casting stability index and the second positive number; The sum of the product value and a preset positive number is calculated; and the termination confidence is the ratio of the difference to the sum.

10. The continuous casting method of austempered ductile iron (ADI) according to claim 1, characterized in that: The process of evaluating abnormal conditions of the continuous casting process in each cycle is as follows: If the normalized value of the termination confidence of the current cycle is greater than or equal to the preset threshold, it is determined that a casting abnormality has occurred in the current continuous casting process; otherwise, it is determined that no abnormality has occurred in the current continuous casting process.

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