JPS5937146B2 - How to detect the level of molten steel in the mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection method for reliably detecting the level of molten steel in a mold, for example in a continuous casting apparatus.

Conventionally, it has been difficult to continuously detect the level of molten steel in the mold in continuous casting equipment because the molten steel as the object is at a high temperature. In Japanese Patent No. 142848, an electrode is inserted into the slag in the lower layer of flux floating on the surface of molten steel in a mold, and changes in electrical resistance due to temperature changes at the electrode insertion part are detected, and the detected value is always constant. A method has been proposed in which the level of molten steel in the mold is detected by moving the electrode up and down and measuring the amount of movement.

The present invention relates to an improvement of the method for detecting the level of molten steel in a mold disclosed in Japanese Patent Publication No. 54-42848. In addition to using a heat insulating flux as the electrode, the electrode is always kept in the slag with the heat insulating flux being poured onto the molten steel so that the depth of the slag into which the electrode is inserted is always within the range of 3 to 15 mm. The electrode is moved up and down so that its resistance value remains constant, and the level of molten steel in the mold is detected based on the amount of movement.

In other words, by using an insulating flux that is difficult to form into slag, a sufficiently thick flux layer is formed on the molten steel, and the slag and the electrode inserted into the flux layer are sufficiently insulated. The slag layer is formed with a thickness of 3 mm or more to ensure that the tip of the electrode remains in the slag at all times, while preventing the electrode from being damaged or becoming abnormal due to so-called slag bears, which are likely to occur at the tip of the slag. The change in electrical resistance caused by the gradually changing temperature within the thick slag layer is accurately detected using an electrode, and the amount of movement is detected when the electrode protrudes outside the detection area and vibrates, a so-called hunting phenomenon of the electrode. This method is designed to improve detection accuracy and to easily put this detection method into practical use. Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

In FIG. 1, molten steel 2 is poured into a mold 1 of a continuous casting apparatus during casting, and a heat insulating flux is thrown on top of the molten steel. A layer of heat insulating flux 4 is present on the slag 3.

A rod-shaped electrode 5 made of a material with a high melting point such as carbon is inserted into the flux 4 from the upper part of the mold 1, and its lower end stays in the slag 3. It is suspended so that it can freely move up and down via a mechanical lifting device 6 made of a wire or the like that is wound up and pulled out on a drum.

The lifting device 6 is driven by a servo motor 7, and moves the electrodes up and down by rotating it forward or backward. Also,
A linear potentiometer 8 is mechanically interlocked with the lifting device 6 so that the displacement of the electrode 5 can be taken out as the output of the potentiometer 8. A constant current is passed through the electrode 5 from a constant current generator 9, and the resistance between the electrode 5 and the molten steel 2 is measured as a voltage, for example, using a resistance measuring device.
Take out at 0.

The output of this resistance measuring device 10 is compared with a constant resistance or voltage set in advance by a resistance setting device 11 using a differential amplifier 12, and the difference value between the two is used to control the servo motor using a power amplifier 13. The output is converted to an output, and the output controls the drive of the reservo motor 7 to move the lifting device 6 up and down. In other words, the level of molten steel 2 in the mold 1 fluctuates, and the resistance measuring device 1
When the output of 0 changes, the elevating device 6 is moved up and down by the drive of the servo motor 7 while the output of the differential amplifier 12 is output due to the difference between the output and the setting value of the resistance setting device 11.
The electrode 5 is always moved to a position where the resistance between the electrode 5 and the molten steel 2 is constant. Such vertical movement of the electrode 5 is measured by a potentiometer 8 to detect the level of the molten steel 2. The output of the resistance measuring device 10 and the output of the potentiometer 8 are recorded every moment by a recorder 14. For example, Figure 2 A, 2, and 3 respectively show the recording of the output of the resistance measuring device 10 in the recorder 14, and in Figure 2 A, the voltage output v of the resistance measuring device is approximately constant during the measurement time t. Show that. Further, FIG. 3 is a diagram showing the relationship between the distance S' between the top surface of molten steel and the electrode measured by the potentiometer 8 in the recorder 14 and the resistance value v between the molten steel and the electrode measured by the resistance measuring device 10, with curves Al, A2, A3 has a molten steel temperature of 150
At 0°C, the depth of the slag, that is, the thickness of the slag layer 3 is 311Lζ6m7! L. The case of lO relation is shown. Generally, the slag layer 3 in which the electrode is to stay has a certain resistance gradient corresponding to the temperature gradient that develops from the high temperature part facing the molten steel to the low temperature part contacting the flux layer, as shown in Fig. 3. Therefore, the distance between the electrode and the molten steel can be detected based on the resistance value between the electrode and the molten steel. When detecting such a level, the slag layer 3 is formed by melting the flux 4 thrown onto the top surface of the molten steel.
The slag layer needs to be thick enough so that its resistance gradient changes slowly so that the respective resistance value at each location can be reliably measured.

As a result of various experiments, the present inventors have found that by using an adiabatic flux as the flux 4, it is possible to easily form a flux layer with a sufficient thickness and a good heat retention effect for the electrodes, and the depth of the slag 3 can be easily formed. It has been found that the resistance value at each position can be reliably measured if the resistance is always within the range of 3 to 15 times. The adiabatic flux is, for example, SlO2: 36.6%, CaO: 34%, Al2
Consisting of O3: 5.5%, F: 4.6%, conventional Na2
Unlike molten fluxes whose main components are SiO3 and CaF2, it is difficult to turn into slag, and it is also difficult to form slag hair (clumps of slag) when cooled. A slag layer of sufficient thickness can be formed. In addition, when insulating flux is poured onto the molten steel, the flux close to the molten steel melts to form a slag layer, and an unmelted flux layer is formed on top of it, so the flux layer exerts a heat insulating effect on the slag layer. This stabilizes the thickness and properties of the slag layer, while the electrode that penetrates the flux layer and is inserted into the slag layer is also kept warm by the flux layer and does not cool down rapidly. This prevents adhesion and formation of so-called bumps that adversely affect the measurement accuracy and properties of the electrode. The depth of the slag layer formed in this way is too shallow;
In other words, the thickness of the slag layer is so thin that when it exceeds a certain limit, it becomes difficult to detect its resistance with electrodes. Figure 2A shows the normal state of →1 in which the voltage corresponding to the resistance can be detected by the electrodes as approximately constant, and the slag layer is 10m7L. The figure shows the case where the flux layer is about 10+α, and the opening in Figure 2 shows the case where the thickness of the slag layer and flux layer is around 51L1, and the output of the resistance measuring device at this time is about 20mm wide. In this state, the slag layer is less than 3 m1, and as soon as the electrode moves up and down to keep its resistance constant, it immediately plunges into the molten steel and is heated.
It is thought that it protrudes into the flux layer and is rapidly cooled, so that it is no longer in the detection area. In this case, if adiabatic flux is added and poured onto the molten steel as shown in Fig. 2C, and the thickness of the slag layer is increased as a result, the hunting phenomenon as described above disappears and the followability is improved as shown in Fig. 2. This can be seen from the fact that it returns to a state like this. Furthermore, as shown in the curve A3 in Figure 3, when the thickness of the slag layer becomes 3 nm or less, the resistance gradient initially becomes approximately horizontal, but suddenly becomes a curve that rises vertically near the flux layer. Therefore, it can be seen that the distance that the electrode can move within the slug is short, and that it becomes extremely difficult to detect the resistance value at each position as the electrode moves. In other words, as shown in Figure 3A and A2, when the thickness of the slag layer is large, the resistance gradient becomes a curve that changes smoothly, so the moving distance of the electrode can be increased, and the electrode It is possible to detect different resistance values corresponding to each position more reliably and with better responsiveness, and therefore the detection becomes easier and more accurate. Incidentally, if the thickness of the slag layer exceeds 1,511 mm, more flux than necessary is used, and the economical efficiency as a unit of flux becomes poor.

As shown in the above examples, the present invention inserts an electrode into the lower slag of flux floating on the surface of molten steel in a mold, detects changes in electrical resistance due to temperature changes at the electrode insertion part, and The detection power method for the level of molten steel in the mold is made by moving the electrode up and down and measuring the amount of movement so that the detected value is always constant, and using an adiabatic flux as the flux, The heat insulating flux is introduced onto the molten steel so that the depth of the slag into which the flux is inserted is always within the range of 3 to 15 m1, and a preferred embodiment of the present invention includes: At least when the electrode moving up and down in the slag generates vibration due to a hunting phenomenon, the hunting phenomenon is detected, and at this time, the depth of the slag is determined to be 3 mm or less and is determined to be outside the above range. This method has the outstanding advantage that the level of molten steel in the mold can be detected easily and reliably as expected through such a simple process.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a schematic configuration of the detection device used in the present invention, Fig. 2 A, C and C are time-electrode measurement voltage diagrams measured with the device of Fig. 1, and Fig. 3 is FIG. 2 is a diagram showing the relationship between electrode distance and resistance measured with the device shown in FIG. 1; 1...Mold, 3...Slag, 4...
...Flux, 5...Electrode, 6...
・Lifting device, 7... Servo motor, 8...
...Potentiometer, 10...Resistance measuring device.

Claims (1)

[Claims] 1. An electrode is inserted into the lower slag of flux floating on the surface of molten steel in a mold, and changes in electrical resistance due to temperature changes at the electrode insertion part are detected, and the detected value is always The method for detecting the level of molten steel in a mold comprises moving the electrode up and down so that the electrode remains constant and measuring the amount of movement, using an adiabatic flux as the flux, and a slag layer into which the electrode is inserted. A method for detecting the level of molten steel in a mold, characterized in that the heat insulating flux is poured onto the molten steel so that the thickness of the molten steel is always within the range of 3 to 15 mm. 2. In the method for detecting the level of molten steel in a mold as set forth in claim 1 above, at least when the electrode moving up and down in the slag generates vibrations due to the hunting phenomenon, the hunting phenomenon is detected. The thickness of the above slag layer is 3m
The heat insulating flux is poured onto the molten steel until the hunting phenomenon disappears, assuming that the flux is below m.