JP2001239353A - Detecting method of abnormal casting condition inside mold in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detecting method with high precision of abnormal casting conditions inside a mold such as a breakout, a defect on the casting surface or an abnormal flow of molten metals. SOLUTION: A mold temperature is measured with means for temperature measurement 16, 17 buried in a plurality of places inside the mold 11 leaving a space to the casting direction, and based on a temperature measuring value inside the mold, a thermal flux inside the mold 12 on each measuring point is estimated using a means for heat transfer inverse problems. A breakout is detected in a lapsed time when a random point on the mold piece 1 inside the mold passes the two measuring points or when the thermal flux estimated values around that time are lowered at more than the threshold values set up in advance on respective measuring points and concurrently in the order of measured points.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to casting abnormalities in continuous casting, in particular, breakouts occurring in slabs in molds,
The present invention relates to a method for online detection of surface defects, abnormalities in molten metal flow, and the like.

[0002]

2. Description of the Related Art Knowing the solidification state of molten metal in a mold of a continuous casting machine during casting requires online detection, breakout, scene vibration, etc. of slab surface defects caused by uneven formation of solidified shells. This is a necessary condition for predicting the abnormal operation of the steelmaking, and is important for the continuous casting operation and quality control. Therefore, conventionally, many methods for detecting an abnormality in casting in a mold have been proposed.

In order to know the solidified thickness of the molten metal and the temperature profile of the solidified shell, it is necessary to know the heat flux on the inner surface of the mold. Conventionally, the heat flux in the mold of the molten metal is determined by using two thermocouples in the direction of heat removal from the mold. From the thermal conductivity λ of the mold material, the distance d between the two thermocouples, and the temperature difference ΔT obtained from the temperature measured by the thermocouples, q = (λ / d) -Attempts have been made to obtain the equation ΔT. However, placing two thermocouples in a narrow space between the inner surface of the mold and the water cooling groove,
There was a problem that it was difficult to maintain and manage. Furthermore, the heat flux derived by this method is based on the assumption that the temperature distribution in the mold is in a steady state, and as the degree of the unsteady state increases, the estimation error with respect to the actual heat flux value increases. There is a problem.

[0004] In Japanese Patent Application No. 9-273745, "Method of judging abnormality in mold in continuous casting equipment", the tip of a thermocouple is exposed on the surface of a copper plate of a mold, and the temperature at the casting side of the copper plate surface of the mold is adjusted. The solidification state and the powder lubrication state of the molten metal in the mold are measured to determine abnormalities during casting. As a result, the occurrence of a casting interruption accident (breakout) due to the outflow of molten metal or the like and the occurrence of slab surface defects are minimized, and the yield is improved. In this method for determining an abnormality in a mold, since the heat flux in the slab is not determined, the solidification state in the mold and the thickness of the solidified shell cannot be known.
For this reason, surface defects, abnormalities in the flow of molten metal, and the like cannot be detected online. Also, it is necessary to attach a large number of thermocouples to the mold with their tips exposed on the mold surface.

[0005]

SUMMARY OF THE INVENTION The present invention estimates the heat flux not only in the steady state but also in the unsteady state of the molten metal mold from the measured temperature of the mold disposed between the inner surface of the mold and the water cooling groove. An object of the present invention is to provide a method for detecting a casting abnormality in a mold such as a breakout, a surface defect, or a molten metal flow abnormality with high accuracy.

[0006]

According to a first aspect of the present invention, there is provided a method for detecting abnormal casting in a mold in continuous casting, wherein the temperature of the mold is measured by temperature measuring means embedded in a plurality of locations of the mold at intervals in the casting direction. Based on the measured values, the heat flux at the inner surface of the mold at each measurement point is estimated by using the inverse heat transfer method. Then, at or near the elapsed time when an arbitrary point of the slab in the mold passes through the two measurement points, the heat flux estimation value drops below the preset limit value for each measurement point and in the order of the measurement points. Detect breakouts.

[0007] Breakout occurs when a portion where the thickness of the slab solidified layer is thinned is partially damaged due to a foreign substance caught between the mold and the slab or a crack of the slab and molten metal flows out. . When a solidified layer that leads to breakout passes through the mold, heat transfer from the solidified layer to the mold is hindered by the influence of foreign substances or cracks that cause the solidified layer to cause a decrease in heat flux. Therefore, the occurrence of breakout can be detected from the amount of decrease in heat flux at each measurement point obtained by the above method.

[0008] In the second invention, the method for detecting an abnormality in casting in a mold in continuous casting is to measure a mold temperature by temperature measuring means embedded in the mold and to determine a heat flux on the inner surface of the mold based on the measured value of the mold temperature. Estimate using a method. Then, the surface defect of the slab in the mold is detected based on the time series value of the fluctuation component and the average component for each fluctuation period obtained by performing the wavelet transform on the heat flux estimation value.

[0009] Cracks in the slab can be considered to have a small degree of the breakout. Therefore, a large crack can be detected by changing the level value of the heat flux reduction in the breakout determination described above, but as the size of the crack decreases, the determination becomes difficult due to the influence of disturbance or the like. The slab cracks are caused by uneven solidification in the mold, and the cause of uneven solidification is mainly governed by the state of the powder layer flowing between the mold and the slab. Is reflected in the heat flux on the inner surface of the mold. Therefore, in the time series change of the heat flux derived by the method of the first invention,
Information on the state of the powder layer that causes cracks is embedded, and the wavelet transformation detects the amount of heat flux turbulence at every fluctuation cycle, and the casting is performed through the evaluation of the soundness of the powder layer heat transfer resistance. One surface defect can be determined. Specifically, the size of the surface defect can be determined from the fluctuation period in which the heat flux disturbance occurs, and the frequency of the surface defect can be determined from the amplitude of the heat flux fluctuation amount in each fluctuation period band. The surface defects detected are vertical cracks, horizontal cracks having a smaller crack length than the vertical cracks, and fine barbs.

In a third aspect of the invention, there is provided a method for detecting an abnormality in a casting in a mold in continuous casting, wherein the temperature of the mold is measured by temperature measuring means embedded in a plurality of locations of the mold at intervals in the casting direction, and the mold temperature is measured based on the measured temperature of the mold. Estimate the heat flux on the inner surface using the heat transfer inverse problem method, estimate the convection heat transfer caused by molten metal outflow from the heat flux inside the slab based on the heat flux estimation value, and An abnormality in the flow of the molten metal in the mold is determined.

Since there is a causal relationship between the convective heat transfer amount calculated as described above and the molten metal flow rate, it is possible to determine the abnormality in the flow in the mold from the convective heat transfer amount on the molten metal side. . Abnormal flow in the mold causes internal defects such as powder entrainment in the scene and trapping of inclusions (alumina clusters, pot slag) in the slab.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described by taking continuous casting of a slab as an example. FIG. 1 schematically shows a mold and a slab (consisting of a molten metal and a solidified shell) in a mold in a longitudinal section along a slab width direction.

As shown in FIG. 1, a water cooling groove 1 is provided in a mold 11.
The cooling water temperature measuring means 15 for measuring the temperature of the cooling water is provided in the water cooling groove 13. The cooling water amount is measured by the flow meter 14. The mold 11 is cooled with cooling water passing through the water cooling groove 13, and heat is removed from the in-mold slab 1. The first mold temperature measuring means 16 and the second mold temperature measuring means 17 are embedded between the inner surface 12 of the mold and the water cooling groove 13 with an interval d in the vertical (casting) direction. In order to obtain heat flux, mold temperature distribution, etc. with high accuracy,
The mold temperature measuring means 16 is preferably arranged at or near the molten slag liquid phase portion 7 or the solidification start point, and the second mold temperature measuring means 17 is arranged at the solidified shell 5. The interval d between the two temperature measuring units 16 and 17 is set to an interval suitable for detecting a casting abnormality based on operation results in accordance with casting conditions, slab dimensions, and the like. In FIG. 1, two mold temperature measuring means are arranged in the vertical direction. However, for example, three to five mold temperature measuring means may be arranged in the vertical direction as needed. The distribution of the heat flux and the mold surface temperature in the casting direction can be obtained with higher accuracy as the number of mold temperature measuring means (temperature measuring points) is increased. Also, a pair of upper and lower mold temperature measuring means 1
6, 17 are, for example, 2 to 2 in the slab width direction according to the width of the slab 1.
Six sets may be arranged. In the direction perpendicular to the casting direction, only one temperature measuring means may be used. The cooling water temperature measuring means 15 and the mold temperature measuring means 1
For example, a thermocouple, a thermistor, or the like is used as 6 and 17. The temperature measurement value and the flow measurement value are stored in the computer 1
9 The computer 19 is preliminarily input with necessary data and a calculation program for calculating the casting conditions, the thermal conductivity of the material of the mold, the distance of the temperature measurement point from the inner surface of the mold, the heat flux, the temperature distribution, and the amount of convection heat transfer. .

According to a first aspect of the present invention, the temperature of the mold is measured by temperature measuring means 16 and 17 embedded in a plurality of places of the mold 11 at intervals d in the casting direction, and the mold inner surface at each measurement point is measured based on the measured mold temperature. The heat flux at 12 is estimated using the inverse heat transfer method. The method of estimating the heat flux will be described later together with the estimation of the temperature distribution and the like.

At or near the elapsed time when an arbitrary point on the in-mold slab 1 passes through the two measurement points, the heat flux estimation value drops below a preset limit value for each measurement point and in the order of the measurement points. By doing so, a breakout is detected. The elapsed time or a time τ near it is expressed by the following equation. _{d / v c ≦ τ ≦ (} 1 + α) d / v c where, d is the distance between the upper and lower temperature measuring point, v _c is the casting speed. α is a margin coefficient, which is about 0.01 to 0.1. The margin coefficient α is, when the movement of the foreign matter biting portion of the slab in the mold is delayed from the first measurement point to the second measurement point,
This is a coefficient considering the delay time. Limit values are casting conditions,
Set based on operation results according to slab dimensions and the like.

FIG. 2A shows the relationship between the elapsed casting time and the mold temperature measured by the thermocouple, and FIG. 2B shows the relationship between the elapsed casting time and the heat flux estimated from the measured mold temperature. I have. The first temperature measurement point is 180m from the top of the mold
m, the second temperature measurement point is 340 mm. From these figures, it can be seen that the change in heat flux is finer, sharper, and clearer than the change in mold temperature. Therefore, the detection of a breakout due to a change in the heat flux can detect a smaller breakout with higher reliability than a change in the mold temperature.

In FIG. 2B, the heat flux estimation value at the first measurement point drops below the limit value a, and the heat flux estimation value at the first measurement point falls below the limit value b within the elapsed time. If it falls, it is determined that a breakout has occurred. Note that FIG.
As shown by the circled portion in FIG. 7B, foreign matter can be detected.

The second invention detects a surface defect such as a vertical crack based on the heat flux. The slab cracks can be considered to have a small degree of the breakout. Therefore, a large crack can be detected by changing the limit values a and b in the above-described breakout determination. However, as the size of the crack becomes smaller, the determination becomes difficult due to disturbance or the like.

FIG. 3A shows the relationship between the elapsed casting time and the mold temperature measured by a thermocouple when a vertical crack occurs. FIG. 3B shows the relationship between the elapsed casting time and the heat flux estimated from the mold measurement temperature in the same case as described above. Due to the heat transfer delay due to the heat transfer resistance from the temperature measuring means to the inner surface of the mold, it can be detected only in a state where the change in the heat transfer on the inner surface of the mold is slow as shown in FIG. FIG.
3B, the change in the heat flux is finer, sharper, and clearer than the change in the mold temperature, as described in FIG. However, when the cracks are small as described above, it is difficult to detect the small cracks as shown in FIG.

In the second invention, a small crack is detected by performing a wavelet analysis on a change with time of the estimated heat flux shown in FIG. 3B. 4 (a) to 4 (d) and FIG.
(A)-(d) have shown the fluctuation | variation result of the period of the heat flux of 8 seconds, 16 seconds, 32 seconds, and 64 seconds by a wavelet analysis, respectively. FIG. 4 shows the case where the slab has vertical cracks.
Is the case of sound slabs. The lower part of FIG. 4D shows the care rate of vertical cracks, that is, the rate of occurrence of vertical cracks. From these wavelet analysis results, it can be understood that the slab having the vertical cracks has a larger disturbance of the heat flux fluctuation in the period band of 8 seconds to 32 seconds than the sound slab. The magnitude (amplitude) and frequency of these fluctuations correspond well to the degree of the vertical crack care rate, and vertical cracks can be detected by managing the heat flux fluctuations in these periodic bands. The size of the vertical crack can be determined by the amplitude, and the position in the slab length direction can be determined by the elapsed casting time. The vertical crack generation slab has the same upper and lower heat flux behavior in the 64 second period band, which is considered to represent the lifting behavior of the slab from the mold, indicating the possibility of detecting the vertical crack cause system. I have.

In FIG. 4, there are two measurement points, an upper thermocouple position and a lower thermocouple position. Although surface defects such as vertical cracks can be detected based on the heat flux variation measured at one location, the defect detection accuracy is higher when measured at two locations. In the case of measurement at two locations, the presence / absence, size, and position of the slab in the length direction of the slab are determined by the larger amplitude of the heat flux variation.

In the third invention, the heat transfer inverse problem method is applied to a slab solidified layer in a mold. Heat flux value on the inner surface of the mold calculated from the thermocouple measurement value to the known boundary conditions of the outer surface of the slab solidified layer, the heat transfer to the slab solidified layer surface temperature determined by the heat history calculation of the molten metal in the mold as the observation point The inverse problem is solved, the thickness of the solidified layer and the heat flux on the inner surface of the solidified layer are calculated, and the convective heat transfer amount on the molten metal side is calculated from the heat flux on the inner surface of the solidified layer. Since there is a causal relationship between the amount of convective heat transfer and the molten metal flow rate, it is possible to determine the flow in the mold based on the amount of convective heat transfer on the molten metal side. The convective heat transfer amount at the time of occurrence of the abnormal flow in the mold is accumulated as operation result data, and is compared with the estimated convective heat transfer amount to determine the abnormal flow in the mold.

As described above, in the first invention and the second invention, the heat flux on the inner surface of the mold is estimated from the mold temperature measured by the temperature measuring means embedded between the inner surface of the mold and the water cooling groove, and the breakout or Detect surface defects. In the third invention, an abnormality in the flow in the mold is detected based on the convective heat transfer amount on the molten metal side obtained based on the heat flux. Less than,
A method for obtaining the heat flux and the convective heat transfer amount based on the mold temperature measurement value will be described.

The heat flux on the inner surface of the mold is determined by James V. BECK's method of non-linear heat transfer problem [Int. J. Masss Transfer, vol.
pp703-716 (1970)], and based on the numerical solution of the unsteady heat transfer equation, the heat flux that can best explain the measured value of the temperature of one mold buried between the mold surface and the water cooling groove is time-series. Sequentially. In addition, the heat flux and the mold inner surface temperature obtained as a solution of the unsteady heat transfer difference equation are simultaneously determined.

FIG. 6 is a conceptual diagram showing heat transfer between the mold inner surface 12 and the mold water cooling groove 13. Mold 11 from molten metal 2
The heat flux flowing into the mold 11 passes through the mold 11 and the mold water cooling groove 1
Heat is removed by the cooling water w flowing through the cooling water 3. In order to detect a heat flux, a thermocouple 16 is provided at a position at a vertical distance E from the mold inner surface 12 to the mold water cooling groove.

In FIG. 6, considering only the one-dimensional heat transfer in the thickness direction of the mold, the equation governing the heat transfer from the inner surface of the mold to the mold water cooling groove is expressed by the following equation. _{ρc p ∂T / ∂t = -∂ (} λ∂T / ∂x) / ∂x (1) T (E, t) = Y (t) (2) λ∂T (F, t) / ∂x = hw (T (F, t) -Tw) (3) T (x, 0) = T0 (x) (4) where ρ is the density of the mold material, c _p is the specific heat of the mold material,
x is the vertical distance at an arbitrary position from the inner surface of the mold to the water cooling groove, E is the vertical distance from the inner surface of the mold to the mold thermocouple installation point, and Y is the measured value. F represents the vertical distance from the mold inner surface 12 to the mold water cooling groove 13, and hw and Tw respectively represent the overall heat transfer coefficient of water-side cooling and the water temperature. T0
(X) shows the initial temperature distribution in the vertical direction between the mold inner surface 12 and the mold water cooling groove 13, and all are set to room temperature immediately before the start of casting.

The mold temperature T (E, t) and the measured temperature Y at the thermocouple measurement point calculated from the equations (1), (3) and (4)
The square error of (t) is defined by the following equation (5), and the heat flux q (t, 0) ≡λ∂T / ∂x _{= 0} such that the square error is minimized.
Is determined from equation (6). F (q) = (T (E, t) −Y (t)) ² (5) ∂F (q) / ∂q = 0 (6)

In the above description, the heat flux was obtained for the upper temperature measurement point (the position of the temperature measurement means 16) in FIG. 6, but the lower temperature measurement point (the position of the temperature 17 in FIG. 1) or the measurement point was 3 points. The heat flux at the measurement point can be obtained in the same manner even when there are more than two places. The heat flux distribution in the casting direction is obtained by extrapolation using the obtained heat flux. The heat flux is a function of the direction of casting position and time, the following briefly q _m
Expressed by

Next, the thickness of the solidified shell, the temperature distribution in the solidified shell, and the surface temperature of the solidified shell are determined based on the heat flux.

FIG. 7 is a conceptual diagram showing heat transfer in the molten metal. When the molten metal 2 in the molten metal pool is drawn downward from the meniscus 3 at a speed corresponding to the casting speed, it is cooled by the heat flux by the mold 11 to form the solidified shell 5. Using the temperature of the molten metal in the meniscus 3 as an initial condition and the heat flux of the mold surface obtained above as a boundary condition, a one-dimensional unsteady heat transfer calculation in the x direction of the molten metal 2 is performed. For convenience of calculation, the x direction is set in a direction opposite to that in FIG.
Here, since the thermal inertia of the powder layer is small, it is assumed that the heat transfer in the powder layer between the solidified shell and the mold surface is in a pseudo-steady state, and the heat flux on the mold surface is equal to the heat flux on the solidified shell surface. C _s ρ _s ∂T / ∂t _meni = ∂ (−λ _s ∂T / ∂x) / ∂x (7) T = T0 where t _meni = 0 (8) -λ _s ∂T / ∂x = q _m where x = 0 (9) T = TL where x = δ (10) −λ _s ∂T / ∂x = ρ _s L (dδ / dt) where x = 0 (11) where t _meni is Elapsed time from the meniscus, x is the distance from the mold surface at any position in the solidified shell, δ is the solidified shell thickness, L is the solidification latent heat, λ _s is the thermal conductivity of the solidified shell, C _s is the specific heat of the solidified shell, TL indicates the solidification temperature.

By solving the equations (7) to (11), the temperature distribution in the solidified shell is determined simultaneously with the thickness of the solidified shell.
The solidified shell surface temperature at an arbitrary position in the casting direction from the meniscus can be determined.

Next, the heat flux of the solidified shell surface is estimated,
A method for obtaining a heat flux caused by thermal convection (molten metal flow) will be described. As before, the method of JVBECK's nonlinear inverse heat transfer problem is used.

Considering only one-dimensional heat transfer in the thickness direction of the solidified shell as shown in FIG. 7, the governing equation can be expressed by the following equation. ρ _s C _s ∂T / ∂t = −∂ (λ _s ∂T / ∂x) / ∂x (12) T (0, t) = Y (t) (13) λ _s ∂T (0, t) / ∂t = q _m (14) T (x, 0) = Ti (x) (15) Here, t represents an arbitrary time and is different from t _meni which indicates an elapsed time from the meniscus.

Assuming a certain solidified shell thickness, the above (1)
By solving equations 2) to (15), the assumed heat flux and temperature on the inner surface of the solidified shell are obtained. By setting this solidified shell thickness to an appropriate value, it is possible to match the solidified shell inner surface temperature and the molten metal solidification temperature obtained by calculation,
Heat flux in this case is the heat flux q _m on solidified shell surface. The heat flux q _m is composed of the heat flux caused by the heat convection of the molten metal, the heat flux moving to the solidification shell by heat conduction, and the amount of heat used as the latent heat of solidification of the molten metal. These relations are expressed by the following equation (16). expressed. _{q m -ρL (dδ / dt)} = [1 / {(1 / α) Ten Δx / λ _s}] (Tb-Tx) (16) where, alpha is the heat transfer coefficient due to the molten metal convection, Tx coagulation The solidified shell temperature at a distance of Δx from the inner surface of the shell, Tb indicates the bulk temperature of the molten metal. (16) from equation _{q conv = α (Tb-Tx} ) = (Tb-Tx) / [(Tb-Tx) / {q m -ρL (dδ / dt)} -Δx / λ s ] (17) heat This is the heat flux caused by convection.

The calculation for obtaining the heat flux and the like is executed by the computer 19 shown in FIG. 1 in accordance with the instructions in the flowchart shown in FIG.

In step 1, zero is set for the time t, and in step 2, the minute time interval Δt is added to the time t to update the time. In step 3, the measured value of the thermocouple installed in the casting direction in the casting direction is read into the computer 19, and in step 4, the heat flux of the mold surface and the temperature of the inner surface of the mold are determined based on the measured value of the thermocouple read in step 3. Calculate T _ms .

Specifically, the above equation (4) is used as an initial condition,
Equation (1) is discretized and solved using equations (2) and (3) as boundary conditions. The mold temperature T (E, t) and the measured temperature Y (t) at the thermocouple measurement point calculated from the equations (1) to (4)
Is calculated by the following equation (5).

As shown in the above equation (6), the square error F
Partial differential coefficient for heat flux q of (q) is closer to zero, modifying the heat flow flux value q ₀ on the assumption according to the following procedure.

The calculated mold temperature at the mold temperature measurement point calculated using the assumed heat flux q ₀ as a boundary condition is represented by T (E,
t) 0, the mold temperature calc'd mold temperature measurement point the heat flux q ₁ was modified was calculated boundary conditions T (E, t)
When T is 1, T (E, t) 1 is Taylor-expanded with respect to Δq≡q ₁ −q _{0 as} follows. T (E, t) 1 = T (E, t) 0+ (∂T (E, t) 0 / ∂q 0) · (q 1 -q 0) (18) Here, following equation sensitivity coefficient beta ₀ Is defined as β ₀ ≡∂T (E, t) 0 / ∂q ₀ = (T (E, t) 1 -T (E, t) 0) / εq ₀ (19) Here, ε is a minute value set for searching for an optimum value of q, for example, 0.001 And (18) and (19) substituted formula (6) below, is rearranged with respect to _{q 1, q 1 = q 0} + (T (E, t) 0-Y (t)) / β 0 (20) q ₁ and q ₂ are compared, and if the following convergence judgment formula is satisfied, q ₁
Is the desired heat flux. _{(Q 1 -q 0) / q} 0 <0.001 (21)

If equation (21) is not satisfied, q _i is calculated according to the following equation (22) based on q ₁ in the same procedure as above, and the calculation is repeated until equation (23) is satisfied. , Heat flux q, and at the same time, the mold inner surface temperature T (0, 0,
t) is calculated. q _i = q _i−1 + (T (E, t) _i−1 −Y (t)) / β _i−1 i = 2, 3,... (22) (q _i −q _i−1 ) / q _i-1 <0.001 i = 2,3, ... (23)

In step 5, the solidified shell thickness δ and the solidified shell surface temperature TL are determined using the equations (7) to (11). At this time, the heat flux value q _m used in the equation (9) is
The extrapolation value in the casting direction of the heat flux value obtained by the inverse problem from the thermocouple measurement value is used.

In step 6, the heat flux inside the solidified shell surface is determined by the equations (12) to (15). At that time, (1
Y (t) in equation 3) is the value of step S5 at each thermocouple position.
In using the billet surface temperature obtained, (14) is the q _m using a mold inner surface heat flux values obtained by solving the inverse problem in step S4.

In step 7, the convection heat transfer caused by the flow of the molten metal is determined by the heat flux inside the solidified shell (17).
Obtain from the formula.

Although the slab is a slab in the embodiment of the present invention described above, the present invention is not limited to this. For example, the slab may be a billet, a thick plate, a round bar, or the like, and can be applied to horizontal continuous casting.

[0045]

According to the method of the present invention, the heat flux of the molten metal mold surface or the solidified shell surface in the unsteady state as well as the steady state is obtained from the measured temperature of the mold disposed between the inner surface of the mold and the water cooling groove. Since the temperature and the like are estimated, the solidification state in the molten metal mold can be clearly detected.
As a result, it is possible to detect a casting abnormality in a mold online and with high accuracy, and to manage a casting operation method that can obtain a sound solidification state. Further, in order to obtain the mold surface temperature, it is not necessary to expose the tip of a temperature measuring means such as a thermocouple to the mold surface.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of an apparatus for implementing a method of the present invention.

FIG. 2 (a) is a diagram showing a change over time of a thermocouple temperature change of a slab having a breakout, and FIG. 2 (b) is a diagram showing a change over time of a heat flux of the slab.

FIG. 3 (a) is a diagram showing a change over time of a thermocouple temperature change of a slab having a vertical crack, and FIG. 3 (b) is a diagram showing a change over time of a heat flux of the slab.

FIG. 4 is a diagram showing a wavelet analysis result of a heat flux of a slab in which a vertical crack has occurred.

FIG. 5 is a diagram showing a wavelet analysis result of a heat flux with respect to a sound slab.

FIG. 6 is a conceptual diagram showing heat transfer between an inner surface of a mold and a mold water cooling groove.

FIG. 7 is a conceptual diagram illustrating heat transfer in a molten metal.

FIG. 8 is a calculation flowchart according to the present invention.

[Description of Signs] 1: Cast slab 2: Molten metal 3: Meniscus 5: Solidified shell 7: Molten slag 11: Mold 12: Mold inner surface 13: Water cooling groove 14: Flow meter 15: Cooling water temperature measuring means 16: No. 1 mold temperature measuring means 17: second mold temperature measuring means 19: computer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Koichi Hirai 1 Nishinosu, Oji, Oita City, Oita Prefecture Inside Nippon Steel Corporation Oita Works (72) Inventor Hiroaki Iiboshi 1 Nishinosu, Oita City, Oita City, Oita Prefecture New Japan F-term (reference) in Oita Works of Steel Corporation 4E004 MA05 MC12

Claims (3)

[Claims] 1. A method for measuring a mold temperature by a plurality of temperature measuring means embedded in a mold and detecting an abnormality in the casting in the mold based on the measured value of the mold temperature. The mold temperature is measured by the temperature measuring means, and the heat flux on the inner surface of the mold at each measurement point is estimated using the heat transfer inverse problem method based on the measured mold temperature value. A continuation characterized in that a breakout is detected when the heat flux estimation value falls below a preset limit value for each measurement point and in the order of the measurement points at or near the elapsed time passing through two measurement points. A method for detecting abnormal casting in a mold in casting. 2. A method for measuring a mold temperature with temperature measuring means embedded in a mold and detecting an abnormality in casting in the mold based on the measured temperature of the mold, wherein the temperature of the mold is measured by temperature measuring means embedded in the mold. Estimate the heat flux on the inner surface of the mold using the heat transfer inverse problem method based on the temperature measurement value, and time-series values of the fluctuation component and average component for each fluctuation cycle obtained by wavelet transform of the heat flux estimation value A method for detecting an abnormality in a casting in a mold in continuous casting, wherein the method detects a surface defect of a slab in the mold based on the method. 3. A method for measuring a mold temperature with temperature measuring means embedded in a mold and detecting an abnormality in casting in the mold based on a measured value of the mold temperature, wherein the temperature embedded in a plurality of locations of the mold at intervals in the casting direction. The mold temperature is measured by the measuring means, the heat flux on the inner surface of the mold is estimated using the inverse heat transfer method based on the measured mold temperature, and the molten metal flows from the heat flux inside the slab based on the estimated heat flux. A method for detecting abnormality in casting in continuous casting, comprising estimating the amount of convective heat transfer caused by the heat and detecting an abnormality in molten metal flow in the mold based on the estimated value of convective heat transfer.