JPH0775766B2 - Method for detecting vertical crack in slab in continuous casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to detection of vertical cracks among scratches that may occur on the surface of a slab in continuous casting.

[Prior Art] In the process of continuous casting, elongated scratches, that is, vertical cracks, may occur on the surface of the slab in the direction of its progress, that is, in the longitudinal direction. Conventionally, this type of defect has been detected by cooling a cast piece after casting, and then performing visual inspection by an inspector, inspection by a detection device, or a flaw inspection after completion of rolling. However, with such a detection method, a decrease in yield due to the occurrence of vertical cracks cannot be avoided, and it is also difficult to detect a perfect flaw.

Therefore, a method for detecting flaws in a slab during casting is proposed in Japanese Patent Publication No. 63-53904. In this method, detection is performed by focusing on the distribution of the amount of heat removed, and it is possible to detect defects even during casting. If a flaw can be found during casting, it can be fed back to the operating conditions to prevent the flaw or minimize its size to prevent the yield from decreasing.

[Problems to be Solved by the Invention] However, the conventional vertical crack detection method has not been able to obtain very high detection accuracy. In the technique of Japanese Patent Publication No. 63-53904, when the predetermined condition indicating the possibility of vertical cracking is detected, the casting speed is controlled so as to be reduced.
If vertical cracks are erroneously detected frequently, the predetermined casting time becomes longer than necessary.

Then, this invention makes it a subject to raise the detection precision of the slab vertical crack detection method in continuous casting.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, an output from a temperature detecting means for detecting respective temperatures at different positions in the longitudinal direction and the lateral direction of a mold wall of a continuous casting facility is provided. The temperature information at each position is monitored, and the first condition indicating whether a predetermined descending pattern appears in the time-series change for the detected temperature at each position, and the detected temperature at a plurality of horizontal positions Regarding the position distribution pattern, a second condition indicating whether or not a predetermined abnormal temperature drop has appeared in the temperature of the detection target position with respect to the temperature of the peripheral position, and further, the first condition and the second condition are identified. The presence or absence of vertical crack detection is recognized by discriminating whether or not the detection positions satisfying both of the above are present at a plurality of positions having substantially the same horizontal position and different from each other in the vertical direction.

[Operation] In the present invention, vertical cracks are detected by paying attention to the time-series change in temperature and the position distribution pattern detected at each position on the mold surface during casting.

That is, according to the experiments by the present inventors, when vertical cracking occurs, an abnormal temperature drop is observed in the time-series change of the detected temperature during casting in that portion, and further, in the lateral direction of the detected temperature. It was found that the position distribution pattern had an abnormal pattern in which the temperature was abnormally lowered at the position where vertical cracking occurred, compared with the surrounding area. Further, since the vertical cracks are elongated in the vertical direction, that is, in the traveling direction of the slab, these abnormal temperature changes are detected at a plurality of positions having the same horizontal position but different vertical positions at substantially the same time. I knew it would be done.

Therefore, by identifying each of the above conditions, it is possible to detect or predict the presence or absence of vertical cracks during casting.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Example] Fig. 5a shows the appearance of a mold used in continuous casting. A passage of cooling water is formed inside the wall of the mold, and the molten steel in the mold is cooled by the cooling water. The molten steel injected into the mold is gradually solidified in the mold as the cooling progresses, and is slowly drawn out from below the mold at a constant speed. The casting width varies depending on the specifications of the product, but in this example, the maximum casting width is 222 cm.

In this embodiment, the casting system is constructed as shown in FIG. The process controller 100 controls the speed of the drive roll that pulls out the slab.
In addition, normally, the drawing speed of the slab, that is, the casting speed is maintained constant. The diagnostic device 200 is a process controller 100.
The temperature information on the mold is obtained via the, the vertical crack is diagnosed based on the temperature information, and the result is output to the process controller.

Next, a process of causing vertical cracks in the slab will be briefly described.

When the inflow of powder and the non-uniform lubrication occur, the solidification rate of the molten steel in the mold is partially reduced, and the development of the solidified shell becomes non-uniform. As a result, stress concentrates on the portion where the solidification delay has occurred, and longitudinal elongated cracks occur at that portion.
It should be noted that when the scale of the vertical cracks is small, only a defect is generated on the surface of the slab, but when the scale is large, it may lead to a breakout.

According to the experiments conducted by the present inventors, when vertical cracking occurs,
The symptom appears as a temperature change on the mold wall. In other words, looking at the change over time in the temperature at the point where vertical cracks occur,
As shown in the figure, there is a phenomenon in which the temperature temporarily drops compared to the steady temperature. In addition, as seen from the lateral position distribution of the mold temperature, for example, as shown in FIG. 3, there is locally recognized an abnormally low temperature portion as compared with the normal portion. Also, the low temperature part is located at the same position in the horizontal direction and different positions in the vertical direction at almost the same time (T3i and T4i in Fig. 2).
The phenomenon is observed.

Therefore, in the present invention, the temperature is measured at each position of the mold and whether an abnormal temperature drop occurs over time, whether an abnormal temperature pattern occurs in the lateral position distribution of temperature,
And vertical cracks are detected or predicted by identifying whether or not those phenomena are detected at a plurality of positions substantially at the same time.

In this embodiment, as shown in FIGS. 5b and 5c, a large number of thermocouples TC are embedded in each of the four faces of the mold. Specifically, a rod made of constantan is covered with an insulating material except for the tip, and the rod is inserted and fixed in holes formed at respective positions on a copper plate constituting the mold. By processing the electrical signal obtained from each thermocouple,
The temperature of each part can be measured.

In this embodiment, of the many thermocouples shown in FIGS. 5b and 5c, all the thermocouples in the third and fourth stages were used for vertical crack detection, and the other thermocouples were not used. .

The details of the processing of the diagnostic device 200 that detects vertical cracks are
Shown in Figures a, 4b, 4c and 4d. First, the contents of the process shown in FIG. 4a will be described.

In step 2, temperature data is input. That is, the temperature data obtained from each thermocouple is input via the process controller 100. The temperature data of each thermocouple is repeatedly sampled at a constant cycle (two seconds in this example). Of these data, the latest data and the data sampled immediately before are simultaneously held in the memory. It R2 (i, j) is the register that holds the latest data, and R1 (i, j) is the register that holds the latest data. Note that i and j
Are identification symbols corresponding to the horizontal position and the vertical position of the thermocouple, respectively.

When the data input for all the third and fourth thermocouples is completed, the process proceeds to step 4 and subsequent steps through step 3.

In step 4, various calculation processes are performed. In the calculation of the width-direction average temperature TM (j), for each thermocouple in each stage, the value obtained by dividing the sum of the detected temperatures in the horizontal direction by the number of thermocouples in each stage, that is, the average detected temperature (j = 3, Four). Standard deviation σ
(J) is calculated by the following equation.

Square root of σ (j) = ((Σ (T (i, j) -TM (j)) ² ) / n) T (i, j): Detection temperature of each thermocouple n: Number of thermocouples Time series temperature The gradient δT (i, j) corresponds to the changing speed (° C / sec) of the detected temperature at each position, and is calculated by the following equation.

δT (i, j) = (T (i, j) −T ′ (i, j)) / ts ts: Sampling period (2 seconds) T (i, j): R1 (i, j) content T ′ (I, j): Content of R2 (i, j) Width direction temperature deviation or Th (i, j) is the width direction average temperature TM
It is the difference between (j) and the thermocouple detection temperature T (i, j) at each position.

The process after step 5 is for detecting whether or not there is an abnormality in the detected temperature of the thermocouple at each position, and is sequentially executed for the data of all thermocouples, and the process of all data is performed. When is completed, the process returns to step 2 and the process is repeated. Note that this entire process is performed once every 2 seconds, which is the same as the temperature data sampling period.

When no abnormality is detected, the procedure goes to step 5, and steps 6, 7, and 8 are checked. In step 6, δ
The value of T (i, j) is compared with the threshold value C ₁ to identify whether or not the temperature has abnormally decreased with time (in this example, C ₁ =
-1).

When an abnormal fall is detected, the process proceeds to step 12, and since the content (fall detection time) of the register t ₁ (i, j) is 0 at _first , step 13 is executed, and t ₁ (i, j) and t ₂ (i, j) Store the initial value C ₃ in j). C ₃ is the calculation cycle (2 seconds).

If the detected temperature continues to drop abnormally, step 5,
Continue through 6, 12 to 14. In step 14, register t
₂ (i, j) contents (falling duration) are updated, and in the next step 15, contents of register t ₁ (i, j) are updated.

When the condition of step 6 is no longer satisfied after detecting the abnormal decrease in the detected temperature, step 7 is executed.
When the temperature gradient δT (i, j) cannot be seen as either falling or rising (between gradients C ₁ and C ₂ : C ₂ =
For 0.5), go through steps 7 through 10 to 15. That is, in this case, the fall detection time (t ₁ (i, j)) is updated (counted), but the fall continuation time (t ₂ (i, j)) holds the value up to that point.

Fall detection time t ₁ (i, j) during counting and fall duration t ₂ (i, j
When the values of j) are both relatively small, steps 15 to 16,
After passing through 11, the process proceeds to step 9, and the same process is executed for the detected temperatures at other positions.

When the actual temperature decrease amount is small, the decrease detection time t
₁ (i, j) falling duration as compared to t ₂ (i, j) since the change of the slow, t ₁ (i, j) even reaches a predetermined value _{C 4 t 2 (i, j} ) is given The value C ₅ is not reached. In this case, the process proceeds to 22 through steps 15, 16 and 17, and registers t ₁ (i, i, which holds the value of each time).
Clear the contents of j), t ₂ (i, j), and t ₃ (i, j).

In addition, after detecting an abnormal decrease in the detected temperature, the temperature gradient δT
Even when (i, j) changes to ascending, the process proceeds from step 8 to 22, and the contents of t ₁ (i, j), t ₂ (i, j) and t ₃ (i, j) are cleared.

When the actual temperature drop amount is large, the drop detection time t
_{Since 1} (i, j) and the fall duration time t ₂ (i, j) have the same value, 18 from step 15 to 16 and 11 or step 1
Continue from 5 through 16, 17 to 18.

In step 18, the value of the temperature deviation Th (i, j) in the width direction is compared with the threshold value C ₆ . For example, in the abnormal pattern as shown in FIG. 3, the temperature deviation Th (i, j) with respect to the position average temperature (TM (j)) becomes extremely large at the position of the vertical crack. In that case, proceed to steps 18 to 19. Step
At 19, the content (abnormal establishment time) of the register t ₃ (i, j) is updated.

Temperature deviation with respect to the position average temperature (TM (j)), even though the fall duration time t ₂ (i, j) has exceeded the predetermined value (C ₅ ).
If Th (i, j) is small, proceed from step 18 to 20. When the temperature deviation Th (i, j) temporarily increases due to a cause other than vertical cracking, step 19 is executed and then step 20 is executed, so that t ₃ (i, j) is larger than 0. In that case, with respect to the time data at another position having the same horizontal direction (i) and different vertical direction (j) with the thermocouple position of the data being processed, each time t ₁ (i), t ₂ (i), t ₃ Clear all (i) (step 21). In the next step 22,
Time data t ₁ (i, j), t ₂ (i, j), t at the processing position
₃ Clear (i, j).

Even if t ₃ (i, j) is 0, if t ₁ (i, j) is equal to or larger than the predetermined value (C ₄ ), the process proceeds to 22 through steps 20 and 23, and Clear the time.

The processing shown in FIG. 4c is periodically interrupted with respect to the processing of the main routine shown in FIGS. 4a and 4b, and vertical cracking is determined based on the processing result of the main routine.

This will be described with reference to FIG. 4c. At step 30, the initial value (1) is set to the counter i indicating the position in the horizontal direction (same as the width direction).
To store. The subsequent processing is repeatedly executed for each horizontal position until i reaches the maximum value (i max).

In step 32, it is discriminated whether or not a predetermined abnormality detection condition is satisfied for the third stage thermocouple, and the next step 33
Then, it is determined whether or not the abnormality detection condition is satisfied for the fourth thermocouple. If both conditions are met, proceed through step 32, 33, 34 to 35. In step 34, 4
The difference Δt ₃ between the time when the abnormality is detected in the thermocouple in the third stage and the time when the abnormality is detected in the thermocouple in the third stage is calculated. In step 35, it is checked whether the calculation result of step 34 is within a predetermined range. That is, when vertical cracks occur, the detected temperatures T3i and T4i at the third and fourth thermocouple positions at the same horizontal position and adjacent vertical positions are the second
Although there is some deviation as shown in the figure, an abnormal temperature drop appears at about the same time, so if these time differences are within a predetermined range (± 40 seconds in the example), all vertical cracking conditions are met. It is considered that the condition is satisfied, and the process proceeds to step 44.

In step 44, the status StA is checked. Since StA is not set at first, the process proceeds to step 45 and the status StB is checked. At first, StB is not set either, so go to Step 50 and check the status StB.
Is set, and the initial value f ₃ (corresponding to one cycle of processing) is set to the vertical crack B occurrence time tB.

When executing this processing after the status StB has been set, the routine proceeds from step 45 to step 46. In step 46, the value of the vertical crack B occurrence time tB is updated. In the next step 47,
The value of the vertical crack B occurrence time tB is set to a threshold value f ₄ (60 in this example).
Seconds). When the time tB becomes f ₄ or more, the process further proceeds to step 48.

In step 48, the temperature deviation Th in the width direction of the position of the third thermocouple
(I, 3) is compared with the threshold value f ₅ (40 ° C.), and in step 49, the widthwise temperature deviation Th (i, 4) at the position of the fourth thermocouple is compared with the threshold value f ₅ .

When all the conditions of steps 47, 48 and 49 are satisfied, the routine proceeds to step 36, and the rank of the detected vertical crack is switched from rank B to rank A. The A rank of the vertical cracks is a serious vertical crack that leads to a breakout if left as it is, and the B rank means a vertical crack that does not reach the breakout. The statuses StA and StB show the occurrence of vertical cracks of A rank and B rank, respectively.

When the status StB is set in step 36, the next step 37 clears StB and time tB. In Step 38, the status StA is checked, and if it is not set, the status StA is checked in the next Step 39.
Set. In step 40, the value of the vertical crack A occurrence time tA is updated.

The process shown in FIG. 4d is periodically interrupted with respect to the process of the main routine shown in FIGS. 4a and 4b, and the casting speed is obtained by using the result obtained in the process of FIG. 4c. Control.

This will be described with reference to FIG. 4d.

In step 61, check the status StA, and in step 6
In 2 check status StB. If StA is 1, that is, if vertical crack A is occurring, the routine proceeds to step 68, the display of abnormality A is turned on, and the display of abnormality B is cleared. If StB is 1, that is, if vertical crack B is occurring, the routine proceeds to step 63, where the display of abnormality B is turned on and the display of abnormality A is cleared.

Proceed to step 64 from step 63 or 68. If the abnormality has just occurred, the process proceeds from step 64 to 65. In step 65, the steady-state casting speed V _ZO is compared with a predetermined threshold value V1 (1 m / min in this example), and depending on the result, step 66 or 6
Run 9

When the casting speed is low, it is often possible to suppress the generation of further vertical cracks by further reducing the speed, but during restraint, damage will increase unless the withdrawal of the slab is stopped. Therefore, in this embodiment, in step 65, the magnitude of the casting speed (value in steady state) V _ZO at that time is identified, when the speed is slow, the deceleration mode is turned on in step 66, and when the speed is fast, the slab of Stop pulling out. That is, the process controller 100 is instructed to control the driving of the roll so as to decelerate or stop it. In the next step 67, the deceleration flag is set.

When both the status of StA and StB are cleared, that is, when the condition of vertical crack is not satisfied, step
Proceed to 70 to clear the deceleration flag and cancel deceleration. That is, the process controller 100 is instructed to control the roll driving speed to return to the steady speed.

In the above embodiment, the ranks A and B of the vertical cracks are determined by the vertical crack B occurrence time tB and the magnitude of the temperature deviation in the width direction of each stage, but they may be identified by other conditions.
For example, as the constants C ₄ , C ₅ , and C ₆ of the above-described embodiment, two sets different from each other corresponding to A rank and B rank are prepared, and the A rank is processed in the processing of FIGS. 4a and 4b. When the condition of is satisfied, the status StA may be set immediately after step 44 of FIG. 4c.

[Effect] As described above, according to the present invention, vertical cracks in continuous casting can be detected with high accuracy while casting.

In actual operation, a vertical crack detection rate of about 60% was obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a casting system for carrying out the present invention. FIG. 2 and FIG. 3 are graphs showing changes in the detected temperature with time and the lateral position distribution of the detected temperature, respectively. FIG. 4a, FIG. 4b, FIG. 4c and FIG. 4d are flowcharts showing the contents of the processing of the diagnostic device of FIG. 5a, 5b, and 5c are a perspective view, a front view, and a side view, respectively, showing the appearance of the mold and the arrangement of thermocouples of the embodiment. 100: Process controller 200: Diagnostic device 300: Drive controller TC: Thermocouple

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Kusumoto 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Stock Co., Ltd. Inside the Kimitsu Works, Kaisha (56) Reference JP-A 1-210160 (JP, A)

Claims (1)

[Claims] 1. The temperature information at each position output from temperature detecting means for detecting the temperature at different positions in the longitudinal direction and the lateral direction of the mold wall of the continuous casting equipment is monitored, and the detected temperature at each position is monitored. Regarding the first condition indicating whether or not a predetermined descending pattern appears in the time series change, and the position distribution pattern of the detected temperature at a plurality of positions in the horizontal direction, regarding the temperature of the detection target position and the temperature of the peripheral position On the other hand, the second condition indicating whether or not a predetermined abnormal temperature drop has appeared is identified, and further, the detection position where both the first condition and the second condition are satisfied substantially at the same time is the lateral position. A method for detecting vertical cracks in a continuous casting, which recognizes the presence or absence of vertical cracks by identifying whether or not they are present at a plurality of positions that are substantially the same and different from each other in the vertical direction.