A continuous casting method of isothermal quenching nodular cast iron ADI

Abstract

The application relates to the technical field of metal casting, in particular to a continuous casting method of isothermal quenching nodular cast iron ADI, which comprises the following steps: collecting the temperature of a crystallizer used in the ADI continuous casting process in real time; calculating the heat exchange coefficient inside the crystallizer in real time; collecting the friction force generated when a casting blank is pulled out from the crystallizer in real time; presetting each period, obtaining the period steady-state index of the heat exchange coefficient, the temperature and the friction force in each period; obtaining each mutation point of the friction force and the temperature in time sequence in each period respectively, and screening each friction force change point and each temperature change point therefrom; obtaining the lag time length of each friction force change point; obtaining the continuous casting stability index and the stop confidence degree of each period; and evaluating the abnormal situation of the continuous casting process in each period through the stop confidence degree of each period. The application aims to discover abnormal phenomena in the continuous casting process in time, reduce non-scheduled shutdown caused by misjudgment and improve the continuous casting production efficiency of ADI.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of metal casting, in particular to a continuous casting method of isothermal quenching nodular cast iron ADI. BACKGROUND

[0002] The heat treatment of continuous nodular cast iron is usually carried out by isothermal quenching, and the nodular cast iron after isothermal quenching is referred to as ADI, also known as austempered nodular iron. Compared with steel, ADI has more excellent wear resistance, and is therefore widely used in many fields. Continuous casting is a process of converting metal liquid into a casting blank through forced cooling. The nodular cast iron profile produced by the horizontal continuous casting method has no shrinkage, shrinkage cavity, slag inclusion and other defects, and has the characteristics of dense structure, fine grain and high nodularity, and excellent comprehensive mechanical properties.

[0003] In order to improve the quality and production efficiency of the ADI continuous casting process, the prior art has obtained the optimal process parameters of different castings in the continuous casting process, such as the pulling speed, the cooling rate, the water spraying distance, etc., through finite element analysis combined with simulation, and carries out continuous casting production based on the optimal process parameters. In order to ensure the safety of production in the continuous casting process, the prior art usually relies on the threshold comparison method 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 by only using the threshold comparison method, which may cause errors in the state evaluation of the continuous casting process, and thus may cause the phenomenon of frequent start and stop of the continuous casting process, thereby affecting the production efficiency of the ADI continuous casting process. SUMMARY

[0004] In view of the above, it is necessary to provide a continuous casting method of isothermal quenching nodular cast iron ADI. Compared with the traditional continuous casting method of isothermal quenching nodular cast iron ADI, the method can timely find abnormal phenomena in the continuous casting process, reduce unplanned downtime caused by misjudgment, and improve the continuous casting production efficiency of ADI.

[0005] The continuous casting method of isothermal quenching nodular cast iron ADI provided by the application adopts the following technical scheme:

[0006] One embodiment of the application provides a continuous casting method of isothermal quenching nodular cast iron ADI, which comprises the following steps:

[0007] The temperature of the crystallizer used in the ADI continuous casting process is collected in real time; the heat exchange coefficient inside the crystallizer is calculated in real time by using the water channel axis curvature radius and the water channel equivalent diameter data of the crystallizer, and 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 casting blank is pulled out of the crystallizer is collected in real time;

[0008] 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;

[0009] 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;

[0010] 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.

[0011] The abnormal conditions of the continuous casting process in each cycle are evaluated by using the suspension confidence level.

[0012] In one embodiment, the process of obtaining the periodic steady-state index is:

[0013] 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;

[0014] 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;

[0015] 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;

[0016] 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.

[0017] In one embodiment, the cycle steady-state index is calculated as follows:

[0018] 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;

[0019] According to the calculation method of the periodic steady state index of the heat exchange coefficient in each period, the periodic steady state index of the temperature and the friction force in each period is calculated.

[0020] In one embodiment, the process of screening the friction force change point and the temperature change point from the mutation points of the friction force and the temperature in each period is as follows:

[0021] For the mutation point of the friction force in each period, the difference between the average value of the friction force before the mutation point and the average value of the friction force after the mutation point is calculated, and the mutation point with a negative difference value is taken as the friction force change point.

[0022] According to the screening process of the friction force change point, the temperature change point is screened from the mutation points of the temperature in each period.

[0023] In one embodiment, the process of obtaining the lag time is as follows:

[0024] The temperature change point with the smallest time interval between the friction force mutation point and the collection time is recorded as the temperature corresponding point of the friction force mutation point, and the time interval between the friction force mutation point and the temperature corresponding point is taken as the lag time of the friction force change point.

[0025] In one embodiment, the process of obtaining the continuous casting stability index is as follows:

[0026] The absolute value of the correlation coefficient between the heat exchange coefficient and the temperature in time sequence in each period is calculated.

[0027] The average value of the periodic steady state index of the heat exchange coefficient, the temperature and the friction force in each period is calculated.

[0028] The continuous casting stability index is directly proportional to the absolute value and the average value, and inversely proportional to the dispersion.

[0029] In one embodiment, the calculation method of the continuous casting stability index is as follows:

[0030] The product of the absolute value and the average value is calculated, and the dispersion is mapped to a first positive number.

[0031] The continuous casting stability index is the ratio of the product to the first positive number.

[0032] In one embodiment, the process of obtaining the termination confidence is as follows:

[0033] The slope of the fitting straight line of the continuous casting stability index in time sequence of each period and a preset number of periods before the period is calculated.

[0034] an arithmetic mean of the hysteresis time lengths of all the friction force change points in each cycle is recorded as a first arithmetic mean; an arithmetic mean of the hysteresis time lengths of all the friction force change points in a preset number of cycles before each cycle is recorded as a second arithmetic mean; a difference between the first arithmetic mean and the second arithmetic mean is calculated;

[0035] The suspension confidence degree is inversely proportional to the continuous casting stability index and the slope, and is proportional to the difference.

[0036] In one embodiment, the calculation process of the suspension confidence degree is as follows:

[0037] The slope is mapped to a second positive number, and a product value of the continuous casting stability index and the second positive number is calculated;

[0038] A sum value of the product value and a preset positive number is calculated, and the suspension confidence degree is a ratio of the difference and the sum value.

[0039] In one embodiment, the process of evaluating the abnormal situation of the continuous casting process in each cycle is as follows:

[0040] If the normalized value of the suspension confidence degree of the current cycle is greater than or equal to a preset threshold, it is determined that an abnormal phenomenon occurs in the current continuous casting process, otherwise, it is determined that no abnormal phenomenon occurs in the current continuous casting process.

[0041] The present application has at least the following beneficial effects:

[0042] The present application aims at the problem that the prior art only compares and analyzes by threshold, thereby resulting in poor detection effect of the continuous casting process state, frequent start and stop of the continuous casting process, and affecting the casting efficiency. By constructing a cycle stability index, the periodic stability of the crystallizer heat exchange and the distinctness of the main cycle characteristics in the continuous casting process can be reflected, which is beneficial to timely discovery of periodic abnormalities. By screening the friction force change points and the temperature change points, the time reflecting the sudden increase of the friction force and the temperature can be obtained, and then the hysteresis time length is calculated to reflect how long the temperature needs to respond after the friction force changes. Then, the continuous casting stability index is calculated to reflect the correlation stability of the heat exchange coefficient, the temperature and the friction force, and the stability of the hysteresis time length, which comprehensively considers the heat exchange coefficient, the temperature and the friction force, and can more comprehensively reflect the stability of the continuous casting process. By calculating the suspension confidence degree, the deviation degree of the current continuous casting process data compared with the historical continuous casting process can be reflected, the abnormal risk is dynamically evaluated, the misjudgment caused by the data fluctuation in a single cycle can be reduced by combining the historical data and the current data, and the reliability of the evaluation of the abnormal situation of the continuous casting process is improved. By the suspension confidence degree, the abnormal phenomenon in the continuous casting process can be timely discovered, the quality and safety problems caused by the abnormality are avoided, the non-scheduled downtime caused by the misjudgment is reduced, and the continuous casting production efficiency of the ADI is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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.

[0044] Figure 1 A flowchart of the steps of a continuous casting method for austempered ductile iron (ADI) provided in this application;

[0045] Figure 2 Schematic diagram of the process of obtaining termination confidence. DETAILED DESCRIPTION

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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:

[0051] Step 1, real-time acquisition of the temperature of the crystallizer used in the ADI continuous casting process; real-time calculation of the heat exchange coefficient inside the crystallizer through the curvature radius of the water channel axis of the crystallizer, the equivalent diameter data of the water channel, and the real-time flow rate, density, specific heat capacity, thermal diffusivity and dynamic viscosity of the cooling water in the crystallizer; real-time acquisition of the friction force generated when the cast blank is pulled out of the crystallizer.

[0052] The crystallizer is one of the most critical devices in the ADI continuous casting process. If the crystallizer has a problem, it will directly affect the cast iron quality, production efficiency and production safety. Therefore, the crystallizer is taken as the detection object to monitor and evaluate the state of the ADI continuous casting process in real time.

[0053] 18 columns of thermocouples are arranged equidistantly on the two wide copper plates of the crystallizer, and 2 columns of thermocouples are arranged on the two narrow copper plates respectively. Three rows of thermocouples are arranged equidistantly along the pouring direction, and a total of 120 thermocouples are arranged. The average temperature of all thermocouples collected at the same time is recorded as the temperature of the crystallizer.

[0054] The density of the cooling water in the crystallizer is obtained in real time by a densimeter, the thermal diffusivity and specific heat capacity of the cooling water in the crystallizer are measured in real time by a laser heat conduction instrument, and the thermal conductivity of the cooling water is obtained in real time through 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 by a flowmeter and a viscometer, the water channel axis curvature radius and water channel equivalent diameter data of the crystallizer are obtained according to the instruction manual of the crystallizer, and the Reynolds number of the cooling water is obtained in real time through the density, flow rate, dynamic viscosity and water channel equivalent diameter data. The Prandtl number is obtained in real time through the dynamic viscosity, specific heat capacity and thermal conductivity. The Nusselt number is obtained in real time through the Reynolds number, Prandtl number, water channel axis curvature radius and water channel equivalent diameter data. The heat exchange coefficient inside the crystallizer is obtained in real time through the thermal conductivity, water channel equivalent diameter data and Nusselt number. The specific calculation methods of the thermal conductivity, Reynolds number, Prandtl number, Nusselt number and heat exchange coefficient are known technologies, and will not be described herein.

[0055] The traction force of the cast blank when pulled out of the crystallizer is obtained by a traction machine, and is recorded as the friction force between the crystallizer and the cast blank.

[0056] The temperature data, heat exchange coefficient and friction force are collected in real time and synchronously. In this embodiment, the collection time interval of the temperature data, heat exchange coefficient and friction force is 1s. The value of the collection time interval is preset by human, and the implementer can set it according to the actual situation. The application does not have special limitations.

[0057] In order to eliminate the dimensional influence between data, the temperature, the heat exchange coefficient and the friction are normalized respectively. In this embodiment, the Min-Max normalization method is used to normalize the temperature, the heat exchange coefficient and the friction respectively, and the Min-Max normalization method is a known technology, which will not be described herein.

[0058] In step 2, the periodic steady-state index of the heat exchange coefficient, the temperature and the friction in each period is obtained by the autocorrelation in time sequence and the energy distribution in frequency domain of the heat exchange coefficient, the temperature and the friction in each period.

[0059] The movement mode of ADI in horizontal continuous casting production is a periodic movement of one pull and one stop. When the casting blank is pulled out from the crystallizer, the contact area between the inner wall of the crystallizer and the casting blank decreases, resulting in a decrease in local cooling intensity, and the heat transfer between the crystallizer and the casting blank is enhanced due to the increase of friction, and the temperature of the crystallizer is temporarily increased. Then the molten iron in the holding furnace flows into the crystallizer for cooling to form the casting blank, at this time the cooling water continuously flushes the inner wall of the crystallizer, and the heat is quickly taken away, and the temperature of the crystallizer gradually decreases. Therefore, if the continuous casting production process of ADI is stable, the heat exchange coefficient inside the crystallizer will also change periodically with the change of temperature. Therefore, whether the continuous casting production process of ADI has abnormal phenomenon can be analyzed by analyzing whether the heat exchange coefficient inside the crystallizer still has periodicity.

[0060] Based on the above analysis, the autocorrelation coefficients of the heat exchange sequence in each period at a plurality of preset lag periods are obtained by taking the heat exchange sequence in each period as the input of the autocorrelation function, and the maximum value of the autocorrelation coefficients of the heat exchange sequence in each period at all preset lag periods is counted. The maximum value can reflect whether the heat exchange sequence has periodicity, and the larger the maximum value is, the more significant the periodicity of the heat exchange sequence is. The autocorrelation coefficient is a known technology, which will not be described herein.

[0061] In this embodiment, the length of the period is 30 min, and the length of the period is artificially preset, and the implementer can set it according to the actual situation, and the present application does not make special limitation.

[0062] In this embodiment, the preset lag period is an integer in the range of wherein N represents the length of the heat exchange sequence, and the value range of the preset lag period is artificially preset, and the implementer can set it according to the actual situation, and the present application does not make special limitation.

[0063] Further, since the stop-start rhythm of the ADI level continuous casting process has strong periodicity, the heat exchange response of the crystallizer should also stably reflect this periodicity under normal circumstances. However, due to factors such as equipment aging phenomenon in the actual production process, weak changes in the temperature of the molten iron, etc., the heat exchange sequence may introduce complex disturbances, it is difficult to accurately identify the main period and distinguish complex disturbances through the autocorrelation coefficient, which will affect the judgment of the true periodicity, so further analysis is needed.

[0064] For each period, the heat exchange sequence is subjected to Fourier transform, and the period corresponding to the frequency component with the maximum energy is taken as the main period. The proportion of the energy of the frequency component corresponding to the main period in the total energy of all frequency components is calculated. The proportion can reflect the significance and stability of the main periodic component in the heat exchange sequence. The larger the proportion is, the more significant the main periodicity in the heat exchange process is, the more stable the heat exchange operation of the crystallizer is, and the more in line with the expected stop-start rhythm.

[0065] Further, the maximum value of the autocorrelation coefficient of the heat exchange sequence in each period at all preset lag periods and the proportion of the energy of the frequency component corresponding to the main period in the total energy of all frequency components are used to obtain the periodic steady-state index of the heat exchange coefficient in each period, and the expression is:

[0066] In the formula, represents the periodic steady-state index of the heat exchange coefficient in the i th period. represents the maximum value of the autocorrelation coefficient of the heat exchange sequence in the i th period at all preset lag periods. represents the proportion of the energy of the frequency component corresponding to the main period in the total energy of all frequency components in the i th period.

[0067] It should be noted that the periodic steady-state index can reflect whether the periodicity of the heat exchange coefficient of the crystallizer itself in the continuous casting process is stable. The larger the periodic steady-state index is, the better the stability of the crystallizer in the ADI continuous casting process is, the more stable the heat exchange process is, the temperature change is controllable, and thus the higher the stability of the continuous casting process is.

[0068] Since the rhythm of the casting blank pulled out from the crystallizer in the ADI continuous casting process is a stop-start cycle rhythm, the friction between the casting blank and the crystallizer also has strong periodicity. Therefore, the periodic steady-state index of the temperature and the friction in each period is obtained according to the method of obtaining the periodic steady-state index of the heat exchange coefficient in each period.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] When the casting blank is pulled, the friction force between the casting blank and the crystallizer begins to increase, which can cause local heat accumulation, so that the temperature of the crystallizer wall surface begins to rise rapidly. Therefore, the friction forces at all collection time points in each cycle are arranged in time sequence to form a friction force sequence in each cycle, and each mutation point in the friction force sequence and the temperature sequence in each cycle is obtained. For the mutation point of the friction force in each cycle, the difference between the mean value of the preset number of friction forces before each mutation point and the mean value of the preset number of friction forces after each mutation point is calculated, and the mutation point with the negative difference value is taken as the friction force change point. According to the screening process of the friction force change point, each temperature change point is screened from the mutation points of the temperature in each cycle. The collection time points of the friction force change point and the temperature change point can reflect the time points of sudden increase of the friction force and the temperature.

[0076] In this embodiment, the PELT (Pruned Exact Linear Time) algorithm is used to obtain each mutation point in the friction force sequence and the temperature sequence in each cycle. The PELT algorithm is a known technology, and will not be described herein. As other embodiments, on the basis of being able to obtain each mutation point in the friction force sequence and the temperature sequence in each cycle, the implementer can use other existing technologies, such as the Pettitt algorithm, the Mann-Kendall algorithm, etc. The present application does not make special limitations.

[0077] In this embodiment, the value of the preset number is 4, and the value of the preset number is preset by a person. On the basis of meeting the condition that the value of the preset number is in the range of [2, 5], the implementer can set it according to the actual situation.

[0078] Further, the lag length of each friction force change point is obtained through the occurrence time of the friction force change point and the temperature change point in each cycle. Specifically, the temperature change point with the smallest time interval between each friction force mutation point and the collection time point of the friction force mutation point in each cycle is recorded as the temperature corresponding point of the friction force mutation point, and the time interval between the friction force mutation point and the temperature corresponding point is taken as the lag length of the friction force change point. The lag length can reflect how long the temperature needs to respond after the friction force changes.

[0079] The dispersion degree of the lag length of all friction force change points in each cycle is calculated. The dispersion degree can reflect whether the lag degree of the temperature compared with the friction force in each cycle is stable. The larger the dispersion degree is, the more unstable the lag degree of the temperature compared with the friction force in each cycle is.

[0080] Further, the continuous casting stability index of each cycle is obtained by the absolute value of the correlation coefficient between the heat exchange sequence and the temperature sequence in each cycle, the average value of the periodic stability index of the heat exchange coefficient, the temperature and the friction in each cycle, and the dispersion of the lag length of all friction change points in each cycle, and the expression is:

[0081] In the formula, 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 stability index of the heat exchange coefficient, the temperature and the friction in the i th cycle; represents the first positive number mapped by the dispersion of the lag length of all friction change points in the i th cycle.

[0082] In this embodiment, the dispersion is mapped to the first positive number by calculating the sum of the dispersion and the preset positive number, wherein the value of the preset positive number is 0.006, and the value of the preset positive number is artificially preset. To avoid affecting the calculation result of the continuous casting stability index, the preset positive number should be a very small positive number. On the basis of meeting the value of the preset positive number in the range of (0.005, 0.01), the implementer can set the specific value of the preset positive number.

[0083] 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 is stable; the larger the continuous casting stability index, the more stable the change relationship between the friction and the temperature, the temperature and the heat exchange coefficient, and the more stable the operation of the continuous casting process.

[0084] Step 4, the stop confidence of each cycle is obtained by the change trend of the continuous casting stability index of each cycle and the previous preset number of cycles, the average level of the lag length of all friction change points in each cycle, and the difference compared with the average level of the lag length of all friction change points in the previous preset number of cycles, combined with the continuous casting stability index.

[0085] Further, considering that the working environment of the crystallizer is harsh and the maintenance period of the equipment is too long, the crystallizer and the internal sensor are prone to aging phenomenon, which may cause the continuous casting data to slowly drift. However, since a single cycle cannot reflect the slow change of the data, the cycles can be analyzed more deeply by combining historical data.

[0086] Arranging the continuous casting stability indexes of each period and the preceding preset number of periods in time sequence to form a continuous casting stability index sequence of each period, performing linear fitting on the continuous casting stability index sequence of each period, and calculating the slope of the fitted straight line; the slope can reflect the time sequence trend of the stability of the continuous casting process, the greater the slope, the more the stability of the ADI continuous casting process is gradually enhanced, the smaller the slope, the more the continuous casting stability is gradually reduced, and the greater the possibility of unstable factors such as equipment aging, and the greater the possibility of abnormal phenomena in the continuous casting process.

[0087] In the embodiment, the value of the preset number is 50, and the value of the preset number is preset by a person, and the implementer can set it according to the actual situation, and the application does not make special limitations.

[0088] In the embodiment, the least square method is used to perform linear fitting on the continuous casting stability index sequence of each period, and as other implementation manners, on the basis of realizing linear fitting on the continuous casting stability index sequence of each period, the implementer can use other existing technologies such as linear regression analysis and weighted least square method, and the application does not make special limitations.

[0089] Further, the arithmetic mean of the lag time of all friction change points in each period is recorded as a first arithmetic mean, the arithmetic mean of the lag time of all friction change points in the preceding preset number of periods is recorded as a second arithmetic mean, and the difference between the first arithmetic mean and the second arithmetic mean is taken as a lag difference value of each period; the lag difference value can reflect whether the lag relationship between the temperature and the friction in each period deviates from the historical data; since various abnormal factors such as bonding between the casting blank and the crystallizer, crack leakage and the like can cause the lag degree to change, the greater the lag difference value, the greater the possibility of abnormality in the continuous casting process in each period.

[0090] In the embodiment, the difference between the first arithmetic mean and the second arithmetic mean is the absolute value of the difference.

[0091] Further, through the change trend of the continuous casting stability index of each period and the preceding preset number of periods, and the average level of the lag time of all friction change points in each period, compared with the difference between the average level of the lag time of all friction change points in the preceding preset number of periods, the continuous casting stability index is combined to obtain the termination confidence of each period, and the expression is:

[0092] In the formula, C i represents the termination confidence of the i th period; D i represents the lag difference value of the i th period; and S i represents the continuous casting stability index of the i th period. C i represents the termination confidence of the i th period; D i represents the lag difference value of the i th period; S i represents the continuous casting stability index of the i th period. represents the slope of the fitting straight line of the continuous casting stability index sequence of the i-th period; τ represents a preset positive number for avoiding the denominator being 0, and the value of τ in the embodiment is 0.006; the value of τ is preset by human, and τ should be a very small positive number for avoiding the influence on the calculation result of the stop confidence; on the basis of meeting the value of τ being in the range of (0.005, 0.01), the implementer can set the specific value of τ by himself; exp( ) represents the exponential function with the natural constant as the base number. The exponential function with the natural constant as the base number is only one embodiment of the application, and on the basis of meeting the base number of the exponential function being greater than 1, the implementer can set the base number of the exponential function by himself.

[0093] It should be noted that the stop confidence can reflect the deviation degree between the continuous casting process data in each period and the historical continuous casting process; the greater the stop confidence is, the greater the possibility of the abnormal phenomenon of the continuous casting process in each period is, and the continuous casting process needs to be stopped in time to ensure the production safety. The acquisition process of the stop confidence is shown in the schematic diagram of Figure 2

[0094] Step 5: The abnormal situation of the continuous casting process in each period is evaluated through the stop confidence.

[0095] If the normalized value of the stop confidence of the current period is greater than or equal to the preset threshold value, it is determined that the abnormal phenomenon of the continuous casting process occurs in the current continuous casting process, and the continuous casting process needs to be stopped in time and the maintenance treatment needs to be performed in time to ensure the casting safety; otherwise, it is determined that the continuous casting process runs stably and no abnormal phenomenon occurs, and the continuous casting can be continued, thereby avoiding the problem of affecting the continuous casting efficiency due to the frequent start and stop of the continuous casting process.

[0096] In the embodiment, the sigmoid function is used to obtain the normalized value of the stop confidence, and the sigmoid function is a known technology, and the application will not be described here.

[0097] ​In summary, the present application is directed to the prior art only through threshold comparison analysis, and then leads to the detection effect of continuous casting process state is poor, makes the continuous casting process frequent start and stop, affects the casting efficiency problem, by constructing the periodic steady state index, so as to reflect the periodic stability and the significance of the main periodic characteristics of the crystallizer heat exchange in the continuous casting process, which is beneficial to timely discovery of periodic abnormalities; by screening the friction force change point and the temperature change point, the time reflecting the sudden rise of friction and temperature can be obtained, and then the lag time is calculated, reflecting how long the temperature needs to respond after the friction changes; then the continuous casting stability index is calculated, reflecting the correlation stability of heat transfer coefficient, temperature and friction and the stability of lag time, considering the heat transfer coefficient, temperature and friction multiple factors, which can more comprehensively reflect the stability of continuous casting process; by calculating the stop confidence, the deviation degree of the current continuous casting process data compared with the historical continuous casting process can be reflected, the abnormal risk is dynamically evaluated, by combining the historical data and the current data, the misjudgment caused by the data fluctuation in a single period can be reduced, and the reliability of the evaluation of the abnormal situation of the continuous casting process is improved; through the stop confidence, the abnormal phenomenon in the continuous casting process can be found in time, the quality and safety problems caused by the abnormality are avoided, the non-scheduled downtime caused by misjudgment is reduced, and the continuous casting production efficiency of ADI is improved.

[0098] The flow diagrams and the block diagrams in the drawings show the possible implementation architectures, functional and operational of the system, method, and computer program product according to embodiments of the present disclosure. In this regard, each block in the flow diagrams and the block diagrams can represent a module, a segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the blocks can occur out of the order noted in the drawings. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may, in fact, be executed in the reverse order, depending upon the functionality involved. These descriptions and representations are used by those skilled in the art of special computer languages to describe computations performed by the computer workstations, workstations, and computer programs. In the context of this document, the operations and steps can be re-ordered because effective and / or desirable results can be achieved even when operations are out of the order described. For example, two sequentially depicted operations or steps may, in fact, be executed substantially concurrently, or the blocks may, in fact, be executed in the reverse order, depending upon the functionality involved. Each block in the block diagrams and / or flow diagrams, and combinations of blocks in the block diagrams and / or flow diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or can be implemented by special purpose hardware and computer instructions, such as program code, computer programs, or portions of it.

[0099] It is apparent to a person skilled in the art that the present application is not limited to the details of the above-described exemplary embodiments, but can be implemented in other concrete forms without departing from the nature of the present application. Consequently, the above-described embodiments of the present application should be considered in all respects as illustrative and not 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 billet 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; calculate the absolute value of the correlation between the heat transfer coefficient and the temperature in each cycle in a time series, calculate the average value of the periodic steady-state index of the heat transfer coefficient, temperature and friction force in each cycle, and obtain the continuous casting stability index of each cycle in combination with the dispersion of the lag time of all friction force change points in each cycle; the continuous casting stability index is proportional to the absolute value and the average value, and inversely proportional to the dispersion; 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. By using the suspension confidence level, evaluating abnormal conditions of the continuous casting process in each cycle; 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 cycle, the periodic steady-state index of the temperature and friction force in each cycle is obtained; 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.

2. The continuous casting method of austempered ductile iron (ADI) according to claim 1, 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.

3. 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.

4. 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.

5. The continuous casting method of austempered ductile iron (ADI) according to claim 1, 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.

6. The continuous casting method of austempered ductile iron (ADI) according to claim 1, 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.

7. 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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