JPH0318462A - Method and instrument for measuring molten layer thickness of mold powder on molten steel surface in mold for continuous casting - Google Patents

Abstract

PURPOSE:To stably measure thickness of molten mold powder layer with good accuracy even at high temp. by injecting gas from upper part of molten steel surface to blow off unmelting mold powder layer and the molten mold powder layer and measuring. CONSTITUTION:At the time of injecting the supplied gas on molten steel surface through a gas injection hole 5b, the unmelting mold powder layer 4 and a part of the molten mold powder layer 3 are blown off to expose the meniscus 2a surface of the molten steel 2. At the time of stopping the gas injection, the molten steel 2, molten mold powder layer 3 and unmelting mold powder layer 4 are accumulated toward the blowing-off center successively and returned back to the condition before gas-injecting, but the accumulating velocity is different corresponding to each layer. At the time of continuously measuring height at blowing-off center part after stopping the gas injection with a range finder 6, the level to the meniscus 2a surface of the molten steel 2, the level to the upper face 3a of the molten mold powder layer 3 and the level to the upper face 4a of the unmelting mold powder layer 4 can be detected. By inputting the detected level signals into an arithmetic unit 7, the layer thickness of the molten mold powder layer 3 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method and apparatus for measuring the thickness of a molten layer of mold powder on the surface of a molten steel bath in a continuous casting mold. <Conventional technology> In continuous steel forming, a powdered or granular additive called mold powder is added to the surface of the molten steel in a mold to form a layer of molten mold powder that coats the surface of the molten steel. ．． This molten layer of molten steel is: ■ Prevents oxidation of the molten steel that occurs when the molten steel surface comes into contact with air; ■ Prevents heat loss from the molten steel surface and keeps the molten steel surface warm; ■ Non-metals floating from the molten steel. Absorbs inclusions and cleans molten steel, ■
By flowing between the mold and the slab while covering the surface of the molten steel and acting as a lubricant, it plays a role such as improving the surface properties of the slab and ensuring stable drawing of the slab.
It is one of the very important control targets from the standpoint of quality assurance of slabs and prevention of breakouts. Therefore, it is necessary to control the mold powder molten layer thickness to an optimal value by adjusting the amount of mold powder input and casting speed, but to do this, it is necessary to measure the mold powder molten layer thickness to a positive value. ．． By the way, conventionally used methods for measuring the thickness of the molten layer of mold powder can be roughly divided into two types: the contact method, in which a detection part is inserted into the molten steel, and the non-contact method, in which it is measured away from the molten steel bath surface. Can be done. One of the representative contact methods is the wire method. In this method, the thickness of the molten mold powder layer is determined from the length of the molten mold powder that adheres to the surface of the iron wire rod when the iron wire rod is immersed in the meniscus surface of the mold for a predetermined period of time and then pulled up. .

Furthermore, Japanese Patent Application Laid-Open No. 14451/1983 discloses a method of measuring the thickness of the molten layer of mold powder based on the buoyancy force exerted on the float when the float is immersed. Furthermore, JP-A No. 57-1 09555 and JP-A No. 62-248547
There is a method of dipping an electrode and detecting its resistance change, which is disclosed in Japanese Patent Publication No. 63-242451, and a method of dipping an aluminum coated steel wire and then pulling it up to measure the length of melted aluminum. There are methods such as measuring with a television camera. On the other hand, as a non-contact measurement method, for example,
- Publication No. 46361 discloses that the transmittance of γ rays is different from that of an unmelted mold powder layer and a molten mold powder layer. A method has been proposed for measuring mold powder melt N1 using a gamma ray source and its detector, taking advantage of the fact that it differs depending on the molten steel.

Also, the literature "Powder film thickness gauge. Development of molten powder pool thickness gauge" [Steel Research No. 324 (1987)]
) reported a method of measuring the thickness of the molten layer of mold powder using the eddy current method. The method using this eddy current involves passing alternating currents of two frequencies through a coil, and melting NY! due to the difference in impedance change. The purpose is to measure L.

Furthermore, in Japanese Patent Application Laid-Open No. 60-123714, ? 8 A device has been proposed that measures the slag thickness by blowing gas from above the slag on the steel bath surface using a nozzle and detecting the back pressure of the nozzle and the brightness of the molten steel bath surface. A new invention tries to solve the problem! ! ! ! Subject: However,
In the case of the contact type described above, steel wires and electrodes are immersed in the molten steel bath surface. There is a problem that detection parts such as floats are melted and the measurement accuracy is reduced, and in the worst case, it becomes impossible to measure. In addition, when these detection parts are immersed in the molten steel bath surface, unmelted mold powder adhering to the detection part settles as foreign matter in the molten steel in a solidified state, causing a deterioration in the quality of the slab. It also causes problems.

On the other hand, in the case of a non-contact type, Japanese Patent Application Laid-Open No. 61-463 (i
Regarding the γ-ray detection method of No. 1, there is a problem that the equipment is large and it is difficult to actually install the γ-ray source on the side of the mold, and it is difficult to measure the molten layer thickness in a sensitive manner. Furthermore, when using the eddy current method, it is easily affected by the ambient temperature, so it not only requires a temperature compensation mechanism and cooling device, but also has a low S/N ratio, making it difficult to guarantee measurement accuracy. Have difficulty.

Furthermore, with regard to the slag thickness measuring device disclosed in JP-A-60-123714, sufficient measurement accuracy is required due to the large fluctuation range of back pressure measurement values, temperature changes in molten steel, and brightness detection errors due to differences in grade. difficult to obtain.

The present invention was made to solve the above problems, and is a non-contact method that does not affect the quality of slabs, is not affected by ambient temperature, and is highly accurate and stable. An object of the present invention is to provide a method and apparatus for measuring the thickness of a molten layer of mold powder on the surface of a molten metal bath in a continuous casting mold.

<Means for Solving the Problems> The first aspect of the present invention is to measure the thickness of the mold powder molten layer on the molten steel bath surface in the mold of continuous casting.
A part of the unmelted mold powder layer and a part of the molten mold powder layer floating on the molten steel bath surface are removed by blowing gas from above the molten steel bath surface, and the level of the exposed molten steel bath surface and the molten mold powder layer are removed. A method for measuring the thickness of a molten M layer of mold powder on a molten steel bath surface in a continuous casting mold, characterized by detecting the level and the level of an unmolten mold powder layer and measuring the thickness of each layer individually. A second aspect of the present invention is a device for measuring the thickness of a mold powder molten layer on a molten steel bath surface in a continuous casting mold, the device being mounted above the molten steel bath surface. 8. A gas injection port that sprays gas vertically toward the steel bath surface, a gas injection port that removes a part of the unmelted mold powder layer and a part of the molten mold powder layer floating on the molten steel bath surface, and A level measuring means attached to the upper part of the gas transmission port to detect the level of the molten steel bath surface, the level of the molten mold powder layer, and the level of the unmelted mold powder layer, and the level of each layer detected by the level measuring means. a calculation device that individually calculates the level of the molten mold powder layer and the layer thickness of the unmolten mold powder layer; This is a measuring device. <Specific structure and operation> Below, the specific structure of the present invention will be explained in detail with reference to the drawings. FIG. 1 is a block diagram schematically showing a mold powder melt layer thickness measuring device according to the present invention. As shown in the figure, inside a mold 1 for continuous casting, a meniscus 2a of molten steel 2 is poured from a tundish (not shown). The mold powder layer 3 is covered with a molten mold powder layer 3, and the upper surface 3a of the molten mold powder layer 3 is further covered with an unmelted mold powder layer 4.

? A gas injection chamber 5 is provided on the 8w4 bath surface, that is, on the unmelted mold powder layer 4, and gas having a predetermined pressure supplied from the gas supply port 5a is supplied to the gas injection port 5b.
It is then sprayed onto the surface of the molten steel bath. In the upper part of the gas injection chamber 5, for example, a laser type or a microwave type. Millimeter wave type. A distance meter 6 such as an ultrasonic type is installed so as to soften the molten steel bath surface through the gas injection port 5b, and measures the distance to the molten steel bath surface. Note that when an ultrasonic type distance meter 6 is used, as described above, it is strongly affected by the ambient temperature, so it is necessary to perform temperature correction or maintain the ambient temperature constant. The signal measured by the distance meter 6 is input to an arithmetic device 7 and subjected to arithmetic processing, and the result of the arithmetic operation is displayed on a display device 8 such as a CRT. Next, the operation of this mold powder melt layer thickness measuring device will be explained. from the gas supply port 5a (the supplied gas is
When injected onto the molten steel bath surface through step b, as shown in Figure 2,
Unmelted mold powder layer 4 and molten mold powder N
By blowing away a part of molten steel 2, the surface of meniscus 2a of molten steel 2 is exposed. Therefore, when the gas injection is suddenly stopped, the molten wJ2, molten mold powder layer 3. The unmelted mold powder M4 gradually accumulates toward the center of the blowout and returns to the state before gas injection 1.1, but the accumulation speed differs depending on each layer. That is, as illustrated in FIG. 3, after the gas injection stops, the molten steel 2 first accumulates, and then the molten mold powder layer 3
, and the unmelted mold powder layer 4 accumulates, creating a step between these layers. Therefore, if the height of the center of the blowout after the gas injection is stopped is continuously measured using the distance jill'+6, the level h1 to the surface of the meniscus 2a of the molten steel 2, and the upper surface 3a of the molten mold powder N3. The level ha up to the upper surface 4a of the unmelted mold powder layer 4 can be detected, and the level h up to the upper surface 4a of the unmelted mold powder layer 4 can be detected. And these detected level signals h+? t. hs
By inputting and calculating into the calculation device 7, the layer thickness h+x of the molten mold powder [3] and the layer thickness hts of the unmelted mold powder 7114 can be determined by the following equations (1) and (2), respectively.

h1■”” h + h!・・・−・１・−・・−−−−１−１−・−・−・− {I）hts
-hz hx −・・・−・１・・・・−・・−
・−・・・・・・・・−−−−−・− (2) By outputting and displaying these results on the display device 8, the operator can reflect them in the operation. Next, we will explain the precautions when using the optical cutting method instead of the distance meter 6. By utilizing the phenomenon that the molten mold powder 1113 and the unmelted mold powder layer 4 do not completely return to the state before the gas injection within a certain period of time after the gas injection is stopped, it is possible to observe a state in which each layer appears to be separated. can do. Therefore, by three-dimensionally measuring this state, the level of each layer can be detected. In the conventional technology, optical cutting methods and moiré methods can be considered as methods for instantaneously performing three-dimensional measurements of objects, but considering the limitations of the installation space of the equipment, the ease of implementation, and the measurement environment conditions, etc.
Optical sectioning is preferred. Figure 4 schematically shows the configuration of a mold powder molten layer thickness measuring device using the optical cutting method. That is,
In the figure, a laser 9 is used because a strong light source is required, and a laser beam 10 is guided into the mold 1 using an optical fiber 1l. Laser beam 1 emitted from optical fiber l1
0 is made into a slit light by a cylindrical drill lens 12 and melted into rfA2. tlj is projected onto the molten mold powder III 3 and the unmelted mold powder layer 4, and the slit image l
Take care of 3. When this slit image l3 is photographed by the photographing device 1G via the reflecting mirror 14 and filter 15, measurement results as shown in FIG. 5 are obtained. That is, now the level ht+7 of the molten steel bath surface up to the meniscus 2a {}the level h up to the upper surface 3a of the molten mold powder layer 3! The portions corresponding to the slit images 13 at the level h3 up to the upper surface 4a of the unmelted mold powder layer 4 are h+', h,'
, hs', these parts are imaged as flat images. Therefore, the difference between each level, that is, the displacement corresponding to the slint image l3 of the rfJ thickness h+z of the molten mold powder layer 3 and the layer thickness h of the unmelted mold powder N4, is expressed as h
+z' l L,', the following (3) is performed in the arithmetic unit l7. (By formula 41, hat' = tl+
'hz'---------------・----(31h
zs' = h t ' h x ' ---1 ---
−−・１−−−−−− (/l)h+z' + L
2' is determined, and the installation angle of the imaging device 16 and the projection angle of the slit light are determined. By multiplying by a coefficient determined by the magnification of the photographed image, the actual difference between each level, that is, the layer thickness h I! of the molten mold powder layer 3 is calculated. and the layer thickness h0 of the unmelted mold powder layer 4 can be determined. Note that the light source for the slit light is not limited to a laser, and may be any source that clearly projects a slit image. Further, for example, a fiber scope or the like may be used to photograph the slit image l3. Furthermore, the gas injection port 5b shown in FIG. 1 above is replaced with an inner gas injection port l8 and an outer gas injection port 19 as shown in FIG.
As a dual structure, if the molten mold powder layer 3 is separately blown at the inner gas injection port 1/L port 18, and the unmelted mold powder N4 is separately blown from the outer gas injection port 19, during gas injection. Level h1, ht of each layer,
hx can be detected respectively. The injection gas used here is preferably one that does not react with the molten steel or mold powder; for example, it is preferable to use an inert gas such as gas. Also,
In order to prevent cooling of the molten steel by the injection gas, it is desirable to use preheated gas.

In this way, by using the mold powder molten layer r\ measurement device of the present invention, by blowing gas from above the molten steel bath surface, a part of the unmolten mold powder layer floating on the molten steel bath surface and a melted mold powder layer are removed. After removing a part of the mold powder layer, the layer thickness of the molten mold powder layer and the unmelted mold powder layer can be determined by detecting the level of the exposed molten steel bath surface immediately after stopping the gas injection. They can be measured simultaneously. <Example> First, in order to evaluate the measurement characteristics of the present invention, mold powder was melted 1.5 kg in a 50 kg melting furnace that simulated the inside of a continuous mold. ! Experiments were conducted using various methods of Ir¥ measurement equipment.
In addition, in order to determine the reference values necessary to confirm the validity of the measured values in each experiment, we used the wire method to measure the thickness of each layer intermittently while the gas injection was stopped during each experiment. It was measured. [Experimental Example I] An experiment was conducted using the distance meter method shown in Figure 1 as a mold powder melt Nw measuring device. At this time, a gas laser type distance meter was used. This is because A
This is because the r-gas laser type can provide high output with a relatively short wavelength. In addition, the distance distance and the installation position of the gas injection port are 7011111 from the top surface of the unmelted mold powder layer, respectively.
, set the height to 3011111. [Experimental Example ■] A similar experiment was also conducted using the optical cutting method shown in Figure 4. A slit beam of a bamboo gas laser beam with a width of approximately 0.5 m was used as the optical cutting slint beam at this time, and the state of the molten steel bath was measured three-dimensionally approximately 0.7 seconds after the gas injection stopped. [Experiment example ■] Furthermore, an experiment using the light cutting method using the double injection method shown in Fig. 6 was also conducted in the same manner. The injection gas used at this time was Ar gas preheated to about 200'C, with 70 1/win from the inner gas injection port and 6/win from the outer gas injection port.
Each was injected at 0 N/min. Note that the light-cutting light has a width of approximately 0.0 mm, as in the above experiment.
A 5M 8R gas laser slit light was used. [Comparative Example] Measurement was carried out under the same conditions using the conventional float immersion method.

Table 1 summarizes the results of comparing 20 measurements each of Experimental Examples 1, It, III, and Comparative Example with the standard values obtained by the wire method as their maximum errors and standard deviations. It was shown. Table 1 As is clear from this table, both the rangefinder method in Experimental Example [2] and the light sectioning method in Experimental Example (■) can be used to measure with a very high degree of coverage, and the double injection method in Experimental Example (■) It can be seen that it is possible to measure with almost the same degree of topography as the float immersion method used in the comparative example. From these results, it is clear that even when applied to measuring the melt N thickness of mold powder in the mold of actual continuous casting, it is possible to measure with higher accuracy than the conventional method. <Effects of the Invention> As explained above, according to the method and apparatus for measuring the thickness of the molten layer of mold powder on the surface of the molten steel bath in a continuous casting mold according to the present invention, the following effects can be obtained. ■ Measurement is performed by injecting gas from above the surface of the molten steel bath to separate the unmelted mold powder layer and the molten mold powder layer, so the degree of particle diameter is stable even at high temperatures without being affected by the unmelted mold powder layer. The thickness of the molten mold powder layer can be measured with good accuracy. ■ Since it is a non-contact measurement method, there is no risk of foreign objects being inserted into the molten steel, so measurements can be performed without deteriorating the quality of the slab. ■ By using the measurement results according to the present invention, it is possible to control the thickness of molten mold powder N to an optimum value, which contributes to improving the quality of slabs.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram schematically showing the mold powder melt layer thickness measuring device according to the present invention, Fig. 2 is an explanatory diagram showing the state of gas injection onto the molten metal bath surface, and Fig. 3 is a diagram showing the gas injection state. Temporal variation of the molten steel bath surface when stopped! 1! FIG. 4 is an explanatory diagram showing the state of the transfer, and FIG.
The figure is a characteristic diagram showing an example of measurement results by the optical cutting method, and FIG. 6 is a side sectional view showing another example of the gas injection port. l
... Mold, 2... Molten steel, 2a... Meniscus 3... Molten mold powder layer. 4...Unmelted mold powder layer. 5... Gas injection chamber.
5a...Gas supply port, 5b...Gas injection port. 6... Distance meter (level measuring means). 7...
・Arithmetic device. 8...Display device, 9...Laser. 10... Laser beam. 11...Fiber, 1
2...Cylindrical lens l3...Slit image,
14...Reflector. 15...filter, 16...
- Photographing device, 17... Arithmetic device, 1B... Internal injection port, 19... External injection port.

Claims (1)

[Claims] 1. When measuring the thickness of the molten mold powder layer on the molten steel bath surface in a continuous casting mold, gas is blown from above the molten steel bath surface to form an unmolten mold powder layer floating on the molten steel bath surface. and a part of the molten mold powder layer, and detect the level of the exposed molten steel bath surface, the level of the molten mold powder layer, and the level of the unmolten mold powder layer,
A method for measuring the thickness of a molten layer of mold powder on a molten steel bath surface in a continuous casting mold, the method comprising measuring the thickness of each layer individually. 2. When detecting the level of the exposed molten steel bath surface, the level of the molten mold powder layer, and the level of the unmelted mold powder layer, the unmolten mold powder after blocking the gas blown from above the molten steel bath surface. 2. The method for measuring the thickness of a molten mold powder layer on a molten steel bath surface in a continuous casting mold according to claim 1, wherein the accumulation state of the molten mold powder layer and the molten mold powder layer is measured using a level measuring means. 3. A device for measuring the thickness of the mold powder molten layer on the molten steel bath surface in a continuous casting mold, comprising a gas injection port that is attached to the upper part of the molten steel bath surface and blows gas vertically toward the molten steel bath surface; A gas injection port for removing a part of the unmolten mold powder layer and a part of the molten mold powder layer floating on the surface of the molten steel bath, and a gas injection port that is attached to the upper part of the gas injection port to remove a part of the unmolten mold powder layer and a part of the molten mold powder layer floating on the surface of the molten steel bath. Level measurement means for detecting the level of the powder layer and the level of the unmelted mold powder layer, and the level of the molten mold powder layer and the respective layer thicknesses of the unmelted mold powder layer from the level of each layer detected by the level measuring means. an arithmetic device that individually calculates the
A device for measuring the thickness of a molten layer of mold powder on a molten steel bath surface in a continuous casting mold, characterized by comprising: 4. The device for measuring the thickness of a molten layer of mold powder on a surface of a molten steel bath in a continuous casting mold according to claim 3, wherein the level measuring means is a distance meter. 5. An apparatus for measuring the thickness of a molten layer of mold powder on a bath surface of molten steel in a continuous casting mold according to claim 3, wherein the level measuring means is a measuring apparatus using an optical cutting method.