JP5906945B2 - How to prevent ladle leakage - Google Patents

Description

  The present invention receives molten steel melted in a primary refining furnace such as a converter or an electric furnace, and conveys the received molten steel to a continuous casting process via a vacuum degassing refining process, if necessary. Regarding the method of preventing leakage steel in the ladle to supply, in detail, due to the wear of the refractory lining installed in the ladle, the contained molten steel melts the ladle iron skin from the ladle. The present invention relates to a method for preventing leakage.

  The ladle for receiving molten steel melted in a converter or electric furnace and transporting and supplying the received molten steel to the continuous casting process has an outer surface of the ladle and a refractory inside the iron skin. It has a structure where objects are constructed. This refractory is usually composed of two layers, a permanent refractory (also called “permanent brick”) and a lining refractory (also called “work brick”). A lining refractory is applied at the site where it is constructed and in direct contact with the molten steel. The lining refractory is worn with the number of times of use due to mechanical wear due to contact with the molten steel, erosion due to slag mixed in the molten steel and spalling due to rapid temperature changes, etc. At that time, it was dismantled and the lining refractory was constructed again.

  However, it is rare that the lining refractory is evenly worn, and in many cases, a portion having a large amount of wear locally occurs. In recent years, a slag modifier has been added to the ladle for the purpose of improving the quality of the molten steel, and the slag that has reacted with the slag modifier adheres to the inner wall of the ladle. The remaining thickness cannot be accurately grasped.

  Under such circumstances, the ladle may be used without noticing local damage to the lining refractory. In such a case, the molten steel contained in the ladle melts the iron skin of the ladle. There may be a trouble (referred to as “leakage steel”) that flows out from the side wall or the bottom of the ladle (the bottom surface is referred to as the “laying portion”). The flow of hot molten steel will cause serious damage to nearby equipment.Therefore, it is not possible to detect leakage of the refractory lining the ladle in advance and prevent leakage steel by appropriate repair of the refractory. It is extremely important, and therefore a means for preventing steel leakage has been proposed.

  For example, in Patent Document 1, the temperature of the iron skin of a ladle containing molten steel is measured with an infrared radiation thermometer, and if the measured temperature or temperature rise rate is equal to or higher than a preset threshold value, an alarm is issued. There has been proposed a method for preventing leakage steel by adding a refractory elution inhibitor to the slag presenting on the molten steel in the ladle.

  Patent Document 2 proposes a method for determining the remaining thickness of the refractory lining the topped car based on the temperature of the outer wall of the topped car measured before and after the hot metal discharge timing inside the topped car.

JP 2009-19249 A JP 2009-35789 A

  However, the above prior art has the following problems.

  That is, even if the remaining thickness of the lining refractory is the same, the ladle iron skin temperature is affected by the residence time in the empty state before receiving the steel and the elapsed time after receiving the molten steel, In Patent Document 1, the temperature threshold is determined to be a certain constant temperature without taking these into consideration. If the staying time in the empty state before receiving steel is longer than usual and the elapsed time after receiving molten steel is shorter than usual, the iron skin temperature of the ladle becomes low, and in such a case In some cases, the iron skin temperature does not reach the threshold value. In other words, Patent Document 1 cannot accurately grasp the remaining thickness of the lining refractory, and there is a risk of steel leakage.

  Patent Document 2 is a technique for determining the remaining thickness of the lining refractory based on the characteristics of the outer wall temperature of the topped car, in which the outer wall temperature gradually rises even after the hot metal is discharged in the toped car. The topped car discharges the hot metal contained in a short time in a short time, but the ladle gradually discharges the molten steel over 30 minutes depending on the casting speed of the continuous casting machine. The temperature behavior is different from the behavior of the outer wall temperature of the topped car. That is, even if the technique of Patent Document 2 is applied to a ladle as it is, the remaining thickness of the refractory lining the ladle cannot be grasped.

  The present invention has been made in view of the above circumstances, and the purpose of the present invention is to use the ladle even if the stay time in the empty state before receiving steel and the elapsed time after receiving the molten steel change. By providing a ladle steel leakage prevention method that can reliably and inexpensively prevent molten steel contained in the ladle from melting and leaking during secondary refining or casting. is there.

The gist of the present invention for solving the above problems is as follows.
[1] Receives molten steel from the primary smelting furnace, supplies the received molten steel to the continuous casting machine, and repeats the process of receiving the molten steel from the primary smelting furnace again after the supply to the continuous casting machine is completed. This is a ladle leakage prevention method. The surface temperature of the ladle's skin is measured with an infrared radiation thermometer, and the highest temperature among the measured surface temperatures has been supplied to the continuous casting machine. The relationship between the time from receiving the molten steel to the time when the molten steel is received and the iron skin temperature, the relationship between the time after receiving the molten steel and the time at which the iron temperature is measured, and the iron temperature, and When the temperature threshold required from the relationship between the remaining thickness of the lining refractory of the pan and the iron skin temperature is exceeded, the refractory lining of the ladle is inspected and repaired. How to prevent ladle leakage.
[2] Leakage of ladle according to [1] above, wherein the surface temperature of the empty ladle iron shell immediately after the supply of the molten steel contained in the continuous casting machine is measured Steel prevention method.
[3] The temperature threshold is set to a different value depending on a portion of the ladle, and the maximum temperature is determined according to the portion of the ladle, [1] or [2] The method for preventing steel leakage in a ladle as described in 1.
[4] The measurement of the surface temperature of the iron ladle of the ladle is a position where the ladle stops in the vicinity of the continuous casting machine in order to carry the ladle into or out of the continuous casting machine. The method of preventing steel leakage from a ladle according to any one of [1] to [3] above, wherein the method is performed at a position where the side wall surface and the bottom surface can be observed.

  According to the present invention, the relationship between the time from the completion of the supply of the previous molten steel to the continuous casting machine to the time of receiving the current molten steel and the core temperature, and the temperature of the core after receiving the molten steel The temperature threshold is determined from the relationship between the time until the measurement time and the iron skin temperature, and the relationship between the remaining thickness of the refractory lining refractory and the iron skin temperature. When the iron skin temperature exceeds this temperature threshold, it is judged that the remaining thickness of the lining refractory cannot secure the target thickness, and the lining refractory of the ladle is inspected and repaired. It is possible to prevent steel leakage.

It is a figure which shows the relationship between the maximum temperature of the side wall part surface of the ladle of the state holding the molten steel, and the residual thickness of the lining refractory of a ladle. It is a figure which shows the relationship between the maximum temperature of the side wall part surface of a ladle and the remaining thickness of the lining refractory of a ladle immediately after supply of the accommodated molten steel to a tundish is completed. It is a figure which shows the relationship between the maximum temperature of the bottom face part surface of the ladle immediately after completion of supply of the accommodated molten steel to a tundish, and the residual thickness of the refractory lining the ladle. It is a figure which shows the relationship between the maximum temperature of a side wall surface iron skin temperature, and an empty pan time. It is a figure which shows the relationship between the maximum temperature of a side wall surface iron skin temperature, and a filling pot time.

  Hereinafter, the present invention will be specifically described.

  The present inventors measure the iron shell surface temperature of the ladle used in the steel making process with an infrared radiation thermometer, and compare the measured temperature with the temperature threshold value to reliably and inexpensively leak steel. We studied how to prevent it. Here, the ladle used in the steelmaking process is a process of receiving molten steel melted in a primary refining furnace such as a converter or electric furnace. After passing through the next refining, after the supplied molten steel is supplied to the tundish of the continuous casting machine and the supply of the molten steel to the tundish is completed, the inspection and replacement of the molten steel spill nozzle installed on the bottom surface of the tundish is carried out. It is a cup-shaped container that is used by repeating the process of receiving molten steel from the primary smelting furnace again. Hereinafter, the examination results will be described.

  As a result of examining the position where the ladle iron skin temperature is measured, the place where the infrared radiation thermometer is installed is in the vicinity of the continuous casting machine, and both the surface of the ladle and the bottom surface can be observed. Was found to be suitable. Specifically, for example, when placing a ladle that is lifted by a crane or the like in the vicinity of a facility for placing a ladle directly above the tundish of a continuous casting machine (referred to as a “swing tower”) Alternatively, when the ladle is lifted by a crane or the like and removed from the swing tower, it has been found that a place where the iron skin temperature can be measured from below the ladle is suitable.

  In this position, after receiving the molten steel from the primary smelting furnace, a long time of 30 minutes or more has elapsed, and the ladle iron skin temperature is close to the maximum temperature during the ladle use cycle. It is most suitable for judging leakage steel from the iron skin temperature of the ladle. Also, immediately after hanging the ladle on the swing tower or immediately after lifting it from the swing tower, the ladle is stopped at that position due to the characteristics of the crane, so measure the temperature while the ladle is stopped. This improves the accuracy of the temperature measurement position. Furthermore, since the ladle stops at the same lifting position near the swing tower both when the ladle is brought into and out of the swing tower, both measurements can be performed with the same radiation thermometer.

  Fig. 1 and Fig. 2 show the relationship between the maximum temperature of the ladle side wall surface measured with an infrared radiation thermometer and the remaining thickness of the refractory lining the ladle at the position near the swing tower where the ladle is lifted by a crane. Indicates. FIG. 1 is a measurement result of a ladle (hereinafter, also referred to as “at the time of filling pot”) in a state where the ladle is held immediately before the ladle is carried into the swing tower of the continuous casting machine, and FIG. 2 is accommodated. Immediately after supplying the molten steel to the tundish (within 10 minutes after completion of supply), the measurement result of the empty ladle (hereinafter also referred to as “when empty pan”) when removing the ladle from the swing tower is there.

  FIGS. 1 and 2 compare that the empty pot time and the full pot time are the same, but the iron pot temperature in the empty pot shown in FIG. 2 is higher than that in the gun pot shown in FIG. all right. Here, “empty pot time” means that the last molten steel that was contained (the molten steel that was contained one time before the temperature measurement) was supplied to the continuous casting machine after the completion of the supply of this molten steel (measured). It is the time from receiving the molten steel accommodated at the time of warming) from the primary smelting furnace. The empty ladle time includes the time for maintenance of the molten steel outflow nozzle etc. at the bottom of the ladle after completion of casting, and the time for moving to the converter for receiving steel. In the filling pot time, after receiving the steel in the converter, the refining time in the LF furnace (the ladle refining furnace) and the RH vacuum degassing device, moving to the continuous casting machine, continuous casting time, supplying molten steel to the continuous casting machine It includes the travel time to the temperature measurement position after completion. The reason why the temperature measurement result at the time of the empty pan shown in FIG. 2 is higher is that the iron skin surface temperature at the bottom of the ladle rises due to the heat from the molten steel during continuous casting.

  1 and 2, even if the remaining thickness is the same, there is a variation in the surface temperature of the iron skin, but in order to reliably prevent leakage steel, the relationship line where the remaining thickness is the lowest among the variations in the measured temperature. Therefore, for example, when the control value of the remaining thickness of the lining refractory is set to 20 mm, the relational line with the minimum remaining thickness among the measurement variations is used as a reference from FIGS. 1 and 2. It can be seen that the temperature threshold value of the side wall surface temperature at the time of the filling pot should be 400 ° C., and the temperature threshold value of the side wall surface temperature at the time of the empty pot should be 405 ° C. It is preferable to measure temperature at the time of the empty pan shown in FIG.

  Moreover, in FIG. 3, the relationship between the maximum temperature of the ladle bottom part surface at the time of an empty pan and the residual thickness of a lining refractory is shown. As shown in FIG. 3, even if the remaining thickness of the lining refractory is the same, the bottom surface temperature is lower than the side wall surface temperature of FIGS. 1 and 2, and the temperature control value depends on the ladle part. It can be seen that it is preferable to change. For example, in the example of FIG. 3, when the management value of the remaining thickness of the lining refractory is set to 20 mm, the temperature threshold value of the bottom surface temperature at the time of the empty pan may be set to 344 ° C.

  When changing the temperature control value according to the ladle part, of course, the maximum temperature to be compared with the temperature threshold is not the maximum temperature of the entire ladle, but the maximum temperature at that part. To do.

  FIGS. 1 to 3 show that the pan time is 60 to 75 minutes (referred to as “standard time” in the present invention) and the pot time is 60 to 90 minutes (referred to as “standard time” in the present invention). Since the surface temperature of the ladle iron skin changes as the empty pot time and the full pot time become longer or shorter outside the range of these standard times, It has been found that it is necessary to determine the temperature threshold according to the actual values of the pot time and the pot time.

  4 and 5 show the maximum temperature of the side wall surface iron skin temperature measured using a ladle in which the remaining thickness of the refractory lining is substantially the same, changing the empty pot time or the filling pot time. It is a figure which shows the result of having investigated the relationship between empty pot time, and the relationship between the maximum temperature of a side wall surface iron skin temperature, and a filling pot time. In addition, this temperature measurement result is a measurement result in the ladle at the time of an empty pan immediately after completion of supply of molten steel to a tundish.

  FIG. 4 is a diagram showing the relationship between the maximum temperature of the side wall surface iron skin temperature and the empty pan time. From FIG. 4, when the empty pan time becomes longer, the side surface iron on the side wall is affected by the effect of cooling before receiving steel. The skin temperature was found to be low. Moreover, FIG. 5 is a figure which shows the relationship between the maximum temperature of a side wall part surface skin temperature, and a filling pot time, and when a filling pot time becomes long, a side wall part surface iron temperature rises by the heat transfer from molten steel. I understood.

As a result of quantifying the data of FIGS. 4 and 5 by multiple regression analysis, the inventors determined that the surface iron surface temperature (T) of the ladle side wall shown in FIGS. 4 and 5 depends on the empty ladle time and the filling time. It confirmed that it changed with the following (1) Formula.
T (° C) = 0.30 x Pot time (min)-0.19 x Empty pot time (min) + 338.3 (1)
That is, by extending the filling time by 1 minute from the maximum value in the standard time range (90 minutes in FIGS. 1 to 3), the surface iron surface temperature (T) of the ladle side wall increases by 0.30 ° C. On the other hand, the ladle side surface iron skin temperature (T) decreases by 0.19 ° C by extending the empty pan time by 1 minute with respect to the maximum value in the standard time range (75 minutes in FIGS. 1 to 3). I found out that

  By using this relationship, it was found that the temperature threshold for ladle management can be accurately set according to the filling time and empty time in the ladle for measuring the surface temperature of the iron skin. For example, with respect to the temperature threshold value (405 ° C.) obtained when the empty pot time and the filling pot time are standard time in FIG. 2, the filling pot time is extended outside the range of the standard time (60 to 90 minutes). In this case, the temperature threshold value may be increased by 0.30 ° C. per minute, which is the difference from the maximum standard time (90 minutes) of the filling pot time, and the empty pot time is the standard time (60 to 75 hours). In the case where the temperature threshold is extended beyond the range of (min), it is understood that the temperature threshold may be reduced by 0.19 ° C. per minute, which is the difference from the highest standard time (75 minutes) of the empty pan time.

  On the other hand, when the filling pot time and the empty cooking pot time are shorter than the standard time range, calibration may be performed by reversing the sign ± based on the difference from the minimum value of the standard time. That is, when the filling pot time is shorter than the standard time (60 to 90 minutes), the temperature threshold is set to the difference between the standard value of the filling pot time and the minimum value (60 minutes) per minute. It is only necessary to lower the temperature by 0.30 ° C. Also, when the empty pan time is shorter than the range of the standard time (60 to 75 minutes), the temperature threshold is set to the minimum value of the standard time of the empty pan time ( What is necessary is just to raise 0.19 degreeC per minute of the difference with 60 minutes).

  The present invention is based on the above knowledge, and the ladle leakage prevention method of the present invention is a ladle leakage prevention method used in a steelmaking process, and the surface temperature of the ladle iron skin is infrared. Measured with a radiation thermometer, the maximum temperature of the measured surface temperature is the time (= empty pan time) and iron skin after the last molten steel is supplied to the continuous casting machine until this molten steel is received. The relationship between the temperature, the time from receiving the molten steel to the measurement time of the iron skin temperature (= pot time) and the iron skin temperature, and the remaining thickness of the refractory lining the ladle When the temperature threshold required from the three-part relationship with the iron skin temperature is exceeded, it is determined that the remaining thickness of the lining refractory cannot secure the target thickness, and inspection and repair of the refractory lining the ladle It is characterized by performing.

  As the infrared radiation thermometer used in the present invention, one that can measure the temperature distribution two-dimensionally, such as a thermoviewer, is particularly preferable. At this time, it is preferable to install two or more infrared radiation thermometers in order to observe a wide range of the surface of the side wall and the bottom of the ladle. In addition, if a relational expression such as the above expression (1) is obtained according to the processing process and equipment, the present invention can be applied to different processes.

  As described above, according to the present invention, the relationship between the empty pan time and the iron skin temperature, the relationship between the filling pan time and the iron skin temperature, the remaining thickness of the refractory lining the ladle and the iron skin The temperature threshold is determined based on the relationship between the temperature and the relationship between the temperature, and when the iron skin temperature of the ladle exceeds the temperature threshold, it is determined that the remaining thickness of the refractory lining cannot secure the target thickness, and the Since the inspection and repair of the lining refractories are performed, it is possible to prevent steel leakage accurately and reliably at low cost.

  The surface temperature of the side wall of the ladle in the empty state immediately after the supply of molten steel to the continuous casting machine is completed (after 5 minutes) using a thermoviewer installed in the ladle lifting part near the swing tower of the continuous casting machine. Was measured. The ladle time in this ladle was 75 minutes, the empty pan time was 180 minutes, and the maximum temperature of the ladle side wall surface was 395 ° C.

  From FIG. 2, the temperature threshold at the standard emptying pot time (60 to 75 minutes) and the standard filling pot time (60 to 90 minutes) is 405 ° C. In this measurement, the filling pot time is within the standard range. However, since the empty pan time is 105 minutes longer than the standard maximum value, the temperature threshold is controlled to be lower by 0.19 × 105 ° C. (= 180−75) = 19.95 ° C., and the temperature threshold is set to 385 C.

  That is, the measured surface temperature is lower than 405 ° C. shown in FIG. 2, but it is found that the measured surface temperature is equal to or higher than the temperature threshold (= 385 ° C.) in consideration of the empty pot time and the filling pot time. Stopped and inspected and repaired the refractory. Thereby, it was possible to prevent steel leakage.

Claims (4)

The ladle used to receive the molten steel from the primary smelting furnace, supply the received molten steel to the continuous casting machine, and repeat the process of receiving the molten steel from the primary smelting furnace again after the supply to the continuous casting machine is completed. This is a steel leakage prevention method, in which the surface temperature of the ladle iron skin is measured with an infrared radiation thermometer, and the maximum temperature among the measured surface temperatures is the remaining thickness of the ladle refractory and the iron skin temperature. The temperature threshold determined from the relationship between the time after the supply of the last molten steel to the continuous casting machine and the time of receiving the current molten steel (empty pan time) , and the skin temperature after receiving the molten steel of this time When the time until the measurement time of (the pot time) exceeds the temperature threshold corrected based on the difference from the standard time when it deviates from the preset standard time, the ladle refractory of the ladle A method for preventing steel leakage in a ladle, characterized by performing inspection and repair.   The ladle steel leakage prevention method according to claim 1, wherein the surface temperature of the empty ladle iron shell immediately after supplying the molten steel contained in the continuous casting machine is measured.   The ladle according to claim 1 or 2, wherein the temperature threshold value is set to a different value according to a portion of the ladle and the maximum temperature is determined according to the portion of the ladle. Steel leakage prevention method.   Measurement of the surface temperature of the ladle iron skin is a position where the ladle stops in the vicinity of the continuous casting machine in order to carry the ladle into or out of the continuous casting machine, and the surface of the side wall of the ladle The method for preventing steel leakage in a ladle according to any one of claims 1 to 3, wherein the method is performed at a position where the surface of the bottom portion can be observed.

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