JP3369926B2 - Auto start method for continuous casting - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting of molten steel using a mold, by accurately grasping the level position of the molten metal in the mold or the rising speed thereof, and thereby causing an accident due to molten steel overflow or a breakout at the time of start casting. The present invention relates to an automatic start method for continuous casting that prevents such problems.

[0002]

2. Description of the Related Art Continuous casting of molten steel using a mold is started by first pouring the molten steel into the mold from above with a dipping nozzle to a steady level of the molten metal level with a dummy bar inserted at the lower end of the mold. Casting and steady casting in which the molten metal surface level becomes a steady level and drawing of the slab is started. In the start casting in which the molten steel is first poured into the mold, it is important to accurately grasp the level of the molten metal after the start of pouring and the rising speed thereof. However, since the molten metal level in the mold and the rising speed of the molten metal level constantly fluctuate due to clogging occurring in the sliding nozzle or nozzle and the difference in molten steel head, the molten steel overflows from the mold and casting is interrupted. In some cases, a shortage of molten steel holding time in the mold (solidification time of molten steel) at the start of drawing may lead to a situation such as breakout, which is a factor that makes automatic operation (automatic start) of casting particularly difficult. As a method for preventing casting accidents such as molten steel overflow and breakout, in Japanese Patent Application Laid-Open No. 9-1304, as shown in FIG. 4, a plurality of eddy current sensors 41 are provided above the mold 40 and vertically below the mold 40. The thermocouples 42, 43, and 44 are provided, and this value is input to the arithmetic unit 51 to obtain the deviation between the predetermined rising speed of the molten metal surface and the actual rising speed of the molten metal surface, and this deviation is small. The opening of the sliding nozzle is adjusted so that The start casting in this case is
The dummy bar 45 is inserted and fixed to the lower end of the mold 40, the sliding nozzle is opened, and molten steel is poured from the immersion nozzle 46. The level of the molten metal raised by this pouring gradually rises from (a) to the steady level of (c), and the rising speed is also detected based on the thermocouples 42, 43, 44. When the molten metal level reaches the steady level (C), the slab support device 47
At the same time, the drawing is started in the direction of the arrow in the figure, and at the same time, the level control of the molten metal surface is switched by the eddy current sensor 41 to shift to the steady casting. Further, in Japanese Unexamined Patent Publication No. 8-206805, a plurality of thermocouples are provided in the lower part of the mold in the vertical direction to detect the level of the molten metal below, and the value is used to correct the device for detecting the molten metal level provided in the upper part of the mold. Then, a method of automatically adjusting the opening of the sliding nozzle and starting the withdrawal of the slab has been proposed.

[0003]

However, by the thermocouples 42, 43, 44 provided in the vertical direction of the eddy current sensor 41 and the mold 40, the predetermined rising speed of the molten metal surface and the actual molten metal surface The method of obtaining the deviation from the rising speed and adjusting the opening of the sliding nozzle to reduce the deviation has the following problems. First, the rising level
For example, when the temperature is detected at the level of the metal surface (b) which is almost the same as that of the thermocouple 42, and when the level of the metal surface is detected at the point (b), the thermocouple 42 is detected.
May be located between and 43. In either case, as shown in FIG. 4, the thermocouples 42, 43, and 44 are shallow in the copper plate 49 on which the plating layer 48 is applied, and are embedded on the water cooling box 50 side (counter casting side). . Therefore,
Even at the level of the molten metal in (a), since the heat of the molten steel is transferred to the thermocouple 42 via the plating layer 48 and the thick copper plate 49, it takes time to transfer the heat, and There is a delay in response when rising to. Further, the temperature itself detected is low, and a large measurement error occurs because the judgment is made based on this low value. Further, in the case of being located between the thermocouples 42 and 43 like the level of the molten metal in (b), there is no change in the temperature measured by the thermocouple 43, and the position of the molten metal level is unknown. Become. As a result, the actual level of the molten metal in the start casting and its rate of rise become unclear, making it difficult to adjust the opening of the sliding nozzle, etc. according to the target rate of rise of the level of molten steel, and the molten steel overflows from the mold to cause casting. There is a high possibility of interruption or shortage of the solidification time of the molten steel in the mold at the start of drawing, resulting in thinning of the solidified shell and defects such as breakout and cracking of the slab. Furthermore, auto-starting (automatic casting) including the transition from start casting to steady-state casting becomes difficult, and automation of continuous casting itself becomes impossible. Further, also in the initial casting control method disclosed in Japanese Patent Laid-Open No. 8-206805, the response delay of the thermocouple provided below the mold or the measured temperature is the same as in the case of reducing the deviation between the molten metal level and the rising speed. There is a problem such as low. As a result, a large measurement error occurs, and even if the level meter above the mold is corrected based on this measured temperature and casting is performed, molten steel overflow, breakout, slab cracking, and other defects are introduced. There is.

The present invention has been made in view of the above circumstances. By accurately grasping the molten metal level and its rising speed and adjusting the molten metal level to a target value, molten steel overflows from the mold and molten steel An object of the present invention is to provide a continuous casting auto-starting method capable of preventing defects such as breakout and slab cracking due to insufficient solidification time.

[0005]

A method according to the above-mentioned object.
Auto-start method of continuous casting described, the level of molten metal in the mold is measured by a thermocouple, in the automatic casting method of continuous casting to adjust the nozzle opening from the molten metal level, in the vertical direction of the mold, Embedding a plurality of the thermocouple, exposing the tip of the thermocouple to the copper plate surface of the mold, from the temperature of the copper plate surface of the mold, to determine the molten metal level, the thermocouple response is high. , The rising speed of the surface level can be measured accurately.

[0006]

In this continuous casting auto-start method, the temperature of the thermocouple embedded in the mold is 135
The position at which the temperature rises to 0 to 1510 ° C. and shows the maximum temperature when the temperature continues for 1 to 5 seconds is the level of the molten metal.
If the temperature change of this thermocouple is lower than 1350 ° C, the actual level of the molten metal does not reach the thermocouple or the heat transfer to the thermocouple is bad due to the adhered substances such as powder and metal. There is an error in the value. Also, the temperature of the thermocouple is 1
If the temperature is higher than 510 ° C, the temperature of the molten steel itself becomes too high and solidification in the mold becomes insufficient, causing breakout due to insufficient solidification time. Further, if the temperature duration is shorter than 1 second, an increase in temperature due to splashing of molten steel or the like will be erroneously detected, resulting in an error from the actual molten metal level. On the other hand, if the duration of the temperature is longer than 5 seconds, erroneous detection that the actual molten metal level is stagnant occurs even though the actual molten metal level is rising.

[0008] Then, autostart method of continuous casting of claim 2, in the auto-starting method of a continuous casting according to claim 1, and the coating layer is applied to the copper plate surface of the mold, through the coating layer Since the temperature is measured by using the above method, it is possible to reliably prevent an abnormal temperature rise due to splash or flame in the initial stage of casting.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an auto-start method for continuous casting according to an embodiment of the present invention will be described with reference to the accompanying drawings for the understanding of the present invention. Figure 1
2 is a conceptual diagram of a continuous casting apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of one thermocouple in FIG. 1, and FIG. The figure which shows the temperature change of a thermocouple, (b) is a figure which shows the transition of the elapsed time (second) from casting start and the actual molten metal level (mm) in a mold. In FIG. 1, the continuous casting apparatus 10 includes a molten steel 11
Is once received by the tundish 12, and is poured into the mold 13 by the sliding nozzle 14 and the dipping nozzle 15 which are examples of nozzles. The mold 13 is composed of a copper plate 16 having a thickness of 30 to 60 mm, and the surface of the copper plate 16 on the casting side has
0.5 to 0.5 by plating or thermal spraying composed of a single element such as nickel, chromium, molybdenum, etc. or a composition of two or more
A coating layer 17 having a thickness of 5 mm is formed. A water cooling box 18 for cooling the copper plate 16 is provided on the non-casting side of the copper plate 16. The mold 13 includes thermocouples 19a, 19b, 19c, 19d, 19e, 19 having a diameter of 3 to 10 mm.
f and 19g are embedded in the up and down direction at intervals of 100 mm on the left and right sides of the mold 13, respectively, and the level 20 of the molten metal and the rising state are measured. Further, below the mold 13, there are provided a slab support segment 21 for cooling and supporting the slab having the solidified shell formed therein and a pinch roll 22 for pulling out the slab, and a dummy bar 23 is provided at the initial stage of start casting. Are set so as to close the lower end of the mold 13. Further, the electromotive force generated in the thermocouples 19a to 19g is converted into a temperature by the converter 24 and is input to the general arithmetic and control unit 25, where the temperature is recorded and the molten metal level 2
The calculation of the position 0 and the ascending speed and the recording for each elapsed time are performed. The total arithmetic and control unit 25 gives the nozzle opening and closing control unit 26 the opening of the sliding nozzle 14 as a target value, based on the obtained position of the molten metal level 20 and the rising speed. The opening of the sliding nozzle 14 is adjusted by a generally used advancing / retreating device such as a hydraulic cylinder (not shown). On the other hand, the dummy bar 23 set in the mold 13 is instructed to drive the pinch roll 22 at the same time when the total arithmetic and control unit 25 outputs that the molten metal level 20 reaches either of the thermocouples 19a and 19b. And the extraction is started.

The embedding of the above-mentioned thermocouples 19a to 19g in the mold 13 has the same structure, so the thermocouple 19a will be described as a representative. The thermocouple 19a, as shown in FIG.
And the copper wire 28 are made of alumina or zirconia or the like, which can be electrically insulated.
An insulating coating layer 30 having a thickness of m was provided, the entire diameter was formed to 6 mm, and the insulating coating layer 30 was inserted into a hole 31 having a diameter of 10 mm penetrating the copper plate 16 and the water cooling box 18. This thermocouple 1
The tip of 9a is the tip 27a of the constantan wire 27.
And the tip end portion 28a of the copper wire 28 is exposed, and each of the tip end portions 27a and 28a is made of copper or a copper alloy to form a short-circuit portion 32 capable of electrical conduction on the surface of the copper plate 16. is there. In this thermocouple 19a, a brazing layer 33 is provided in the gap between the hole 31 and the insulating coating layer 30, and the copper plate 16
It is fixed to the frame 34 of the water cooling box 18 on the non-casting side.
The O-ring 35 and the flange 36 are attached so as to prevent water leakage or falling accident. Further, 37 is a water channel for cooling water for cooling the copper plate 16,
It flows from below to above and is discharged out of the system. The molten metal level 20 for each thermocouple 19g to 19a output by the total arithmetic and control unit 25 is colored in a plurality of color tones in the height direction of the mold 13 and displayed on a monitor (not shown). The monitoring may be performed including the rising state.

Next, the operation when the continuous casting apparatus 10 is used in the continuous casting automatic start method according to the embodiment of the present invention will be described. As the molten steel 11, a low carbon steel containing 0.08% by weight of carbon and 0.50% by weight of Mn as main components was received in the tundish 12. In this state,
After closing the lower end of the mold 13 having a width of 1800 mm, a thickness of 250 mm and a length of 900 mm with a dummy bar 23, an opening command is given to the sliding nozzle 14 from the nozzle opening / closing control device 26, and molten steel 11 is poured from the dipping nozzle 15 to start automatically. Casting started. As for the opening command of the sliding nozzle 14, half-opening and closing operations were performed 2 to 4 times, and then half-opening (50%) was performed for pouring, and the molten metal level 20 was sequentially increased. The relationship between the elapsed time (seconds) from the start of casting of the thermocouples 19g to 19e and the measured temperature of the thermocouple is shown in FIG.
It was shown to. The thermocouple 19g is located at a position where the level 20 of the molten metal is first measured after starting the casting, and the temperature thereof gradually rises at the start of casting due to the influence of the ambient temperature due to the heat of the molten steel 11, When the position of the level 20 approaches, it rises sharply, and when the level 20 reaches the position of the thermocouple 19g (t ₁ second), the maximum is 1350 to 15
The temperature becomes 10 ° C., and after the temperature continues for 1 to 5 seconds, the temperature drops to about 610 to 1200 ° C. Further, similarly, the measured temperatures of the thermocouples 19f and 19e which respond next rise gradually in the range of 150 to 200 ° C. due to the influence of the ambient temperature caused by the rise of the molten metal level 20 and the molten metal level 20. When the positions approach each other, the temperature rises sharply and the level 20 reaches the positions of the thermocouples 19f and 19e (t
_It reaches a maximum temperature of 1350 to 1510 ° C. in ₂ seconds and t ₃ seconds), and after the temperature continues for 1 to 5 seconds, it is approximately 610 to 1
It tends to decrease to a temperature of 200 ° C. Therefore, at the position of the molten metal level 20, the temperature measured by the thermocouples 19a to 19g is in the range of 1350 to 1510 ° C, and the temperature is 1
Indicated by the time point lasting ~ 5 seconds. Here, if the display of the high temperature continues for less than 1 second, there is a high possibility that it is an erroneous detection due to fluctuations caused by the bumping of the molten metal.
If the time is longer than the second, since the actual molten metal level is rising but the solidification is not progressing, it may be an erroneous detection that the actual molten metal level is stagnant. For this reason, the duration of temperature is more preferably 1 to 3 seconds.

Further, in the case of the thermocouple 19g, the rate of rise of the molten metal level 20 is Lmm / from the elapsed time t ₁ seconds from the start of casting and the vertical spacing Lmm between the thermocouple 19g of the mold 13 in the vertical direction. Calculated in t ₁ seconds. For thermocouple 19f, the embedded interval Lmm thermocouples 19g and thermocouple 19f, can be determined by a Lmm / (t ₂ -t ₁₎ seconds, 19e also determined by the same procedure. In this way, the maximum temperature of the thermocouples 19g to 19e is 20
The reason for expressing the absolute position itself is that the temperature of the surface of the copper plate 16 immediately below the extremely thin coating layer 17 having a thickness of 0.5 to 5 mm can be directly measured. It is to transfer heat as it is. Further, even when the molten steel 11 is momentarily attached to the coating layer 17 covering the thermocouples 19g to 19e by splash (scattering of the molten steel 11), the temperature once rises, but the coating layer 17 of 0.5 to 5 mm. By cooling the mold 13, the temperature gradually decreases without exceeding 1350 ° C., and the abnormality is identified.

Next, the following control was performed according to the measurement of the molten metal level 20 of the thermocouples 19g to 19e.
FIG. 3B shows the elapsed time (seconds) from the automatic start of the thermocouples 19g to 19a and the actual molten metal surface level (m in the mold).
m) is the transition result, and the thick solid line shows the target molten metal level and its rising value when pouring into the mold 13 with the opening of the sliding nozzle 14 being half open (50%), and the thin line is the thermocouple. The measured value of the molten metal level 20 of 19 g to 19 a is shown. The dotted line is a conventional example described later. First, length 9
Between the lower end of the 00 mm mold 13 and the upper 800 mm, 2
The thermocouples 19g to 19a are arranged at 100 mm intervals with the position of 00 mm as the starting point at intervals of 100 mm, and pouring is performed in the mold 13 to convert the electromotive force of each thermocouple 19g to 19a. At the same time as the temperature was converted by the device 24, the start of the auto start was input to the general arithmetic and control unit 25. After ₁ second from the start of auto start, thermocouple 19g
The maximum temperature of 1450 ° C. was detected from the converter 24 and the total arithmetic control unit 25 output that the molten metal level 20 reached. As shown by the thin line, this result substantially coincides with the position of the target molten metal level indicated by the thick solid line, and the accurate molten metal level 20 is measured. Similarly, after t ₂ seconds, the maximum temperature 1455 ° C. of the thermocouple 19f was measured, and 300 m from the lower end of the mold 13 was measured by the general arithmetic and control unit 25.
It was output that the surface level 20 reached the position m. In this case as well, the position substantially matches the position of the target molten metal level, and the total arithmetic control unit 25 causes the molten metal level difference (that is, the distance between the thermocouple 19g and the thermocouple 19f) to be 100 mm (t ₂
The rising speed of the molten steel level 20 was calculated from −t ₁ ) seconds, but it was close to the target value, and the sliding nozzle 14
The opening degree and the discharge amount of the immersion nozzle 15 were normal, and casting was continued in this state. In addition, the opening / closing adjustment of the sliding nozzle 14 by the nozzle opening / closing control device 26 is automatically performed by the total calculation control device 25 so that the rising speed of the molten metal level 20 and the target rising speed of each thermocouple 19g to 19a match. I went there. As a result, thermocouple 19g ~ 19
The molten metal level 20 detected in a has substantially the same value as the target molten metal level in the actual molten metal level and its rising speed, and the controlled opening of the sliding nozzle 14 is half open (50%). Good follow-up control was achieved between ~ 40% opening. After that, at t ₇ seconds after the start of casting, it was detected that the molten metal surface level 20 reached the thermocouple 19a. Therefore, the total arithmetic and control unit 25 outputs a pullout start command to the pinch roll 22 and the pullout amount is commensurate. Set the sliding nozzle opening to level 2
0 was controlled within the range of 10 mm to shift to steady casting.

As described above, the thermocouples 19g to 19a are
Immediately below the very thin coating layer 17 of 0.5 to 5 mm (copper plate 1
The temperature of the surface of 6) can be measured, so that the reached molten steel 1
Since the temperature of No. 1 is transferred without any delay, the solidified state of the inner surface of the mold 13 can be grasped as it is, and the temperature to be measured can be measured in a high temperature range, so that the position of the molten metal level 20 can be accurately represented. it can. On the contrary, by covering the coating layer 17 having a thickness of 0.5 to 5 mm and the mold 13, the disturbance such as splash can be prevented and more accurate measurement can be performed. Further, regarding the rising speed of the molten metal level 20, each thermocouple 19
Since g to 19a quickly respond to the position of the molten metal level 20, the thermocouples 19g to 19a are determined by the arrival times t _{1 to} t ₇ of the molten metal level 20 or the thermocouples of FIG. 3B. 19g ~ 19a level rise line (thin line in the figure)
Therefore, it may be obtained by a general means such as a quadratic equation, and in any case, the deviation from the target value can be reduced. Also, the dotted lines in FIG. 3B are thermocouples 19e, 19c, 19
The copper plate 16 on the side of the water cooling box 18 at the same height of the mold 13 as a
The conventional thermocouple (marked with x) inserted in the
When viewed at the same position as the thermocouple 19e, there is a large response delay from the start of casting to t ₄ seconds (t ₃ seconds for the thermocouple 19e of this embodiment). Further, when viewed at the level height, the target molten metal level at the same height position of the mold 13 is 30 to 40 m due to the response delay.
It is out of the high position of m. In particular, at the level 20 of the steady molten metal surface after t ₇ seconds when the drawing is started, the target value is greatly exceeded, and it is understood that there is a high possibility of a molten steel overflow accident.

In the continuous casting auto-start method according to the embodiment of the present invention, the thermocouples 19a to 19g are used and the interval is set to 100 mm. However, in addition to this, many intervals may be set to less than 100 mm. This distance is preferably 6 mm to 70 mm so that the level 2
The measurement accuracy of 0 is significantly improved, and there is no heat removal or reduction in strength when attached to the copper plate 16. Also, thermocouple 19
It is also possible to form a thermocouple unit in which a to 19 g is embedded in a copper block in advance and to embed the thermocouple unit on the front surface side of the copper plate. Further, as the thermocouple wires constituting the thermocouples 19a to 19g, constantan and copper were used, but other commonly used ones such as chromel, alumel, platinum, platinum rhodium can be applied. It is also possible to combine the above-mentioned thermocouple and eddy current sensor to control the steady state by the eddy current sensor. In addition to the above, thermocouples may be provided in the molten metal level 20 in a high-density inclined manner to control the molten metal level 20 in the steady state, and this value may be used. Although the auto casting method for continuous casting according to the embodiment of the present invention has been described above, the scope of the present invention is not limited to this and includes a range that does not depart from the gist of the present invention.

[0016]

The automatic casting start method for continuous casting according to claims 1 and 2 is a continuous casting auto start method in which the nozzle opening is adjusted from the molten metal level measured by a thermocouple in the casting mold. Since the level of the molten metal is determined from the temperature measured by the thermocouple exposed on the surface of the copper plate, the heat transfer is quick and the position and the rising speed of the molten metal level can be accurately grasped. Further, since the molten metal surface level and the like are measured in a high temperature range where the temperature change is large, erroneous detection can be prevented and molten steel overflow accident, breakout, slab cracking defect, etc. can be prevented.

[0017]

[0018] Then, autostart method of continuous casting, the temperature of the thermocouple embedded in the mold 1350-15
Since the position showing the maximum temperature when the temperature rises to 10 ° C and continues for 1 to 5 seconds is taken as the molten metal level, it is possible to prevent erroneous detection due to the influence of splash of molten steel, ambient temperature, etc. And its rising speed can be measured accurately.

In the continuous casting auto-starting method according to the second aspect , a coating layer is provided on the surface of the copper plate of the mold, and the temperature is measured through the coating layer. Therefore, abnormalities due to splash, flame, etc. at the initial stage of casting are caused. The temperature rise can be prevented, the wear of the thermocouple due to molten steel can be prevented, and the measurement can be performed for a long time.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a continuous casting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of one thermocouple in FIG.

FIG. 3A is a diagram showing a temperature change of a thermocouple in a mold at an early stage of casting. (B) is a diagram showing the elapsed time (seconds) from the start of casting and the actual molten metal surface level (mm) in the mold.

FIG. 4 is a diagram showing a conventional molten metal level control method at the initial stage of casting using a thermocouple and an eddy current sensor.

[Explanation of symbols]

10: Continuous casting device, 11: Molten steel, 12: Tundish, 13: Mold, 14: Sliding nozzle, 15:
Immersion nozzle, 16: copper plate, 17: coating layer, 18: water-cooled box, 19a to 19g: thermocouple, 20: bath level, 2
1: slab support segment, 22: pinch roll, 23:
Dummy bar, 24: converter, 25: integrated arithmetic and control unit,
26: Nozzle opening / closing control device, 27: Constantan wire, 27a: Tip part, 28: Copper wire, 28a: Tip part,
29: Insulation filling layer, 30: Insulation coating layer, 31: Hole, 3
2: short circuit part, 33: brazing layer, 34: frame, 35:
O-ring, 36: flange, 37: waterway

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-8-117945 (JP, A) JP-A-58-159961 (JP, A) JP-A-8-206805 (JP, A) JP-A-6- 114520 (JP, A) JP-A-8-294754 (JP, A) JP-A-58-205821 (JP, A) JP-A-9-174214 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/08 B22D 11/16 104 B22D 11/18

Claims (2)

(57) [Claims] 1. An automatic start method for continuous casting, wherein a molten metal level in a mold is measured by a thermocouple, and a nozzle opening is adjusted from the molten metal level, in the vertical direction of the mold, a plurality of the thermocouples are provided. Embedded individually, exposing the tip of the thermocouple to the copper plate surface of the mold, from the temperature of the copper plate surface of the mold, to determine the level of the molten metal , moreover, the temperature of the thermocouple embedded in the mold Is 13
Raises to 50-1510 ° C, and the temperature continues for 1-5 seconds
An automatic start method for continuous casting, characterized in that the position showing the maximum temperature at the time is set to the molten metal level . 2. The auto-start method for continuous casting according to claim 1 , wherein a coating layer is provided on the surface of the copper plate of the mold, and the temperature is measured through the coating layer.