JP2023104890A - Liquid level measuring device - Google Patents

Abstract

To provide a liquid level measuring device capable of stably measuring a liquid level in a container for handling high-temperature molten metal.SOLUTION: A liquid level measuring device includes: liquid level measuring means which transmits electromagnetic waves for the liquid level detection such as light waves and microwaves toward the liquid surface of the molten metal M stored in a container V having an open upper part represented by the tundish and measures the liquid level of the molten metal M by receiving the reflected electromagnetic waves after the electromagnetic waves are reflected on the liquid surface of the molten metal M; and reflection means which includes the reflection surface with a surface roughness Ra of 0.2 or less for reflecting the electromagnetic waves to change the traveling direction of the electromagnetic waves before and after the reflection to a predetermined direction, respectively and is formed of, preferably, a plate-like body equipped with gas blowing means for blowing gas onto the reflecting surface.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a liquid level measuring device, and more particularly to a liquid level measuring device that measures the liquid level of molten metal stored in a container without contact by using electromagnetic waves.

In facilities that handle high-temperature molten metal (also called molten metal), as typified by metal smelting plants, a predetermined amount of molten metal is received and various processes are performed. Various containers are used for the purpose of temporarily storing metals. For example, in a facility for casting molten steel as molten metal, a generally rectangular container with an open top called a tundish is used for temporary storage of molten steel. This tundish has a discharge port at the bottom, and the molten steel produced in the previous smelting process is poured into the tundish via a ladle and temporarily stored, so that the downstream It becomes possible to stably supply molten steel from the bottom outlet toward the mold located on the side.

When molten steel is supplied to the mold, if the amount of molten steel supplied fluctuates, there is a risk that the quality of the castings cast in the mold will vary. Therefore, by providing a sliding plate at the lower discharge port of the ladle and adjusting the opening degree of the lower discharge port, the amount of molten steel poured from the ladle into the tundish according to the amount of molten steel stored in the tundish. is being controlled. As a result, the amount of molten steel stored in the tundish can be maintained at a constant amount, so that the amount of molten steel supplied to the mold can be stabilized.

In order to control the amount of molten steel poured into the tundish from the ladle as described above, it is necessary to grasp the amount of molten steel stored in the tundish. This can be determined indirectly by measuring the liquid level of molten steel stored in the tundish. Since the temperature of molten steel handled in a tundish reaches a high temperature exceeding about 1000° C., a thermocouple was conventionally used to measure the liquid level of molten steel in the tundish. For example, in Patent Document 1, a thermocouple is inserted into a protective tube that penetrates the side wall of the tundish and protrudes inward. A technique for determining that the installation position (height) of the thermocouple is passed is disclosed. In other words, if the molten steel level drops below the thermocouple installation position, the temperature detected by the thermocouple will drop rapidly, and the molten steel level will rise and the thermocouple installation position will drop. If it exceeds, the temperature detected by the thermocouple rises sharply, making it possible to grasp the liquid level of the molten steel in the dundish.

JP-A-5-31558

However, in the liquid level measurement method of Patent Document 1, it is necessary to bring the protective tube containing the thermocouple into contact with the high-temperature molten steel. Since the thermocouple is repeatedly exposed to a high temperature environment and a low temperature environment each time it moves up and down, it sometimes breaks. If the thermocouple is disconnected, it is of course impossible to ascertain the liquid level of the molten steel in the tundish. Otherwise, the molten steel may overflow from the upper end of the tundish and injure workers working near the casting equipment. Furthermore, in the liquid level measurement method of Patent Document 1, it is possible to grasp only whether the liquid level is above or below the mounting position of the thermocouple as a reference. If multiple liquid levels were to be sensed, for example low, medium and high, multiple thermocouples would have to be provided.

The present invention has been made in view of the problems of the liquid level measurement method using the thermocouple as described above. It aims at providing the liquid level measuring device which can measure.

In order to achieve the above object, a liquid level measuring device according to the present invention transmits an electromagnetic wave for detecting a liquid level toward the liquid surface of a molten metal stored in a container with an open top, and A liquid level measuring means for measuring the liquid level of the molten metal by receiving the reflected electromagnetic wave after being reflected by the liquid surface of the molten metal; and a reflecting means comprising a plate-like body having a reflecting surface with a surface roughness Ra of 0.2 or less for reflecting light.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to stably measure the liquid level of the molten metal in the container, so its industrial value is extremely high.

1 is a perspective view showing a state in which a liquid level of molten metal in a container is being measured using the liquid level measuring device of the first embodiment of the present invention; FIG. 2 is a schematic configuration diagram of an optical displacement gauge included in the liquid level measuring device of FIG. 1. FIG. 2 is a configuration diagram of control means, input means, and output means of the liquid level measuring device according to the first embodiment of the present invention; FIG. It is a graph which shows the relationship between the wavelength of the light which the liquid level measuring apparatus of the 1st Embodiment of this invention emits, and the spectral radiance which the molten steel which is a measuring object emits. FIG. 3 is a schematic front view of a PSD included in the optical displacement gauge of FIG. 2; FIG. 2 is a perspective view of reflecting means included in the liquid level measuring device of FIG. 1; It is a block flow diagram showing how to use the liquid level measuring device of the first embodiment of the present invention. FIG. 5 is a graph showing the relationship between the incident position and the liquid level, which is the basis of arithmetic processing performed in the liquid level measuring device according to the first embodiment of the present invention; FIG. FIG. 8 is a perspective view showing a state in which the liquid level of the molten metal in the container is being measured using the liquid level measuring device of the second embodiment of the present invention; FIG. 7A is a schematic front view of various types of microwave displacement gauges included in the liquid level measuring device according to the second embodiment of the present invention; FIG. 10 is a graph showing the principle of measuring the liquid level with the liquid level measuring device of FIG. 9; FIG. FIG. 7 is a configuration diagram of control means, input means, and output means of the liquid level measuring device according to the second embodiment of the present invention. FIG. 10 is a perspective view showing a tubular body preferably provided in a liquid level measuring device according to a second embodiment of the present invention, together with a microwave level meter and reflecting means; FIG. 10 is a cross-sectional view of a reflector preferably formed on the top surface of the container of FIG. 9; It is a block flow diagram showing how to use the liquid level measuring device of the second embodiment of the present invention.

An embodiment of the liquid level measuring device of the present invention for non-contact measurement of the liquid level of a liquid level measurement object in a container using electromagnetic waves will be described below. The liquid level measuring device of this embodiment of the present invention transmits an electromagnetic wave for detecting the liquid level toward the liquid level of the molten metal in a container with an open top, and the electromagnetic wave is transmitted at the liquid level of the molten metal. A liquid level measuring means for measuring the liquid level of the molten metal by receiving the reflected electromagnetic wave after reflection, and a reflecting surface for changing the advancing direction of the electromagnetic wave before and after reflection on the liquid surface to a predetermined direction, respectively. and a reflecting means comprising a plate-like body having a reflecting surface with a roughness Ra of 0.2 or less.

The above liquid level measurement using electromagnetic waves can be broadly classified into an optical type using visible light or infrared rays and a radio wave type (microwave type) using microwaves. Therefore, in the following description, first, a first embodiment in which an optical displacement meter (level meter) that employs a light wave (light) as the electromagnetic wave is used as a liquid level measuring means will be described. A second embodiment in which a microwave displacement meter (level meter) employing is used as a liquid level measuring means will be described.

1. First Embodiment As shown in FIG. 1, a liquid level measuring apparatus according to a first embodiment of the present invention is a liquid level measuring object stored in a container V with an open top represented by a tundish. A radiation part 11 that emits detection light D for detecting the liquid level toward the liquid surface of the molten metal M that becomes It has an optical displacement gauge (laser displacement gauge) 10 having a light receiving portion 12 for receiving light R. This liquid level measuring device further comprises a plate-like body provided with a reflecting surface 20a having a surface roughness Ra of 0.2 or less for reflecting the detection light D and the reflection detection light R in order to change the directions of travel of the detection light D and the reflected detection light R into predetermined directions. It has a reflecting means 20 of .

As shown in FIG. 1, the reflecting means 20 is supported by a support (not shown) above the container V, so that it is exposed to the heat of the high-temperature molten metal M in the container V. As shown in FIG. Therefore, it is preferable that the material of the plate-like body constituting the reflecting means 20 has such excellent heat resistance that it does not easily deform even when exposed to such a high-temperature atmosphere. Examples of materials having such excellent heat resistance include ceramic materials and SUS materials. Ceramic materials are more preferable because they are less likely to be deformed by heat.

The liquid level measuring device of the first embodiment of the present invention is different from the conventional liquid level measuring device using a thermocouple, and the liquid level measuring device is non-contact with the molten metal M stored in the container V and the liquid level is to be measured. In addition to being able to measure the liquid level, the optical displacement gauge 10 can be arranged at a position avoiding the top of the container V by providing the reflecting means 20 above the container V as described above. As a result, it is possible to prevent the radiation heat emitted from the high-temperature molten metal M and the convection heat rising upward from exposing the radiation part 11 and the light receiving part 12 of the optical displacement gauge 10 . Further, since the optical axis of the detection light D can be incident almost perpendicularly to the liquid level of the molten metal M to be measured, which is stored in the container V, a wide measurement range can be obtained. . That is, it is possible to stably measure the liquid level of the molten metal M in the container V within the range from the empty state to the full liquid state over a long period of time. Hereinafter, each element constituting the liquid level measuring device of the first embodiment of the present invention will be specifically described.

1-1 Optical Displacement Gauge As described above, the optical displacement gauge 10 of the liquid level measuring device of the first embodiment of the present invention is the molten metal M to be measured, which is stored in the container V. and a light receiving portion 12 for receiving reflected detection light R after the detection light D is reflected by the liquid surface of the molten metal M. As shown in FIG. 2, the radiation unit 11 is mainly composed of a light source 11a for generating detection light D and a projection lens 11b for condensing the detection light D emitted from the light source 11a and projecting the light onto the object to be measured. , the light receiving section 12 is mainly composed of a light receiving element 12a for receiving the reflected detection light R and a light receiving lens 12b for forming an image of the reflected detection light R on the light receiving element 12a. By arranging these as shown in FIG. 2, the liquid level of the molten metal M can be measured by a triangulation method.

That is, Q is the distance between the center of the light projecting lens 11b and the center of the light receiving lens 12b, which are separated from the liquid surface of the molten metal M to be measured by the same distance P, and the center of the light receiving lens 12b is the light receiving element. The distance from the light-receiving surface of the light-receiving element 12a is defined as F, and the distance from the point at which the perpendicular drawn from the center of the light-receiving lens 12b to the light-receiving surface of the light-receiving element 12a intersects the light-receiving surface to the position where the reflected detection light R is incident on the light-receiving surface. When the distance is X, the distance P can be obtained from the following formula 1.

[Formula 1]
P = (F/X) Q

Of the four variables in Equation 1, Q and F are values determined by the structure of the optical displacement gauge 10, so the distance P can be uniquely obtained from the distance X. As will be described later, a CPU (Central Processing Unit) or the like performs arithmetic processing for determining the liquid level of the molten metal M in the container V based on the output value corresponding to the incident position of the reflected detection light R output from the light receiving element 12a. can be performed by the control means of This CPU, for example, as shown in FIG. It is composed of a calculation unit 14 . The CPU may be incorporated in the optical displacement gauge 10, or the optical displacement gauge 10 and the CPU may be separate devices. In the storage unit 13, a reference liquid level of the molten metal M can be input as will be described later from a reference liquid level input means 15 such as a keyboard or a touch screen. The liquid level data is output to a liquid level display means 16 such as a display and displayed there.

(1) Radiation Unit The radiation unit 11 is composed of a light source 11a including a laser oscillator that oscillates, for example, a laser beam as the detection light D, and a projection lens 11b that collects the laser beam emitted from the light source 11a. The light source 11a is not particularly limited as long as it can oscillate a laser beam having a wavelength suitable for detecting the liquid level of the high-temperature molten metal M, and a general one can be adopted. Here, the wavelength suitable for liquid level detection is a wavelength at which the reflected detection light R after the detection light D is reflected by the liquid surface of the molten metal M can be accurately received by the light receiving unit 12. When the metal M is molten steel, a laser beam with a wavelength of 400 nm to 700 nm is preferable, and a green laser beam with a wavelength of 500 nm to 550 nm or a violet or blue laser beam with a wavelength of 400 nm to 500 nm is more preferable. The reason for this is the graph in FIG. 4, which shows the relationship between the wavelength of light emitted by molten steel and the spectral radiance, which is a physical quantity that indicates the intensity of light emitted from (or passes through) a certain area, using the melting temperature as a parameter. As can be seen from , the light emitted by molten steel contains a large amount of infrared light with a wavelength of 780 nm or more, so it is possible to measure the liquid level more accurately by using a laser beam with a different wavelength as the detection light. Because it becomes

Specifically, referring to FIG. 4, for green laser light with a wavelength of 500 nm to 550 nm, if the temperature of the molten steel is 2000 K, the dispersed radiance in the region of 500 nm to 550 nm (green light) emitted by the molten steel However, it is less than 1/10 of the dispersed radiance in the region of 780 nm to 820 nm (red light) emitted by molten steel. That is, since the light emitted by molten steel does not contain much light with a wavelength of 500 nm to 550 nm compared to infrared rays with a wavelength of 780 nm or more, green laser light having a wavelength region corresponding to this wavelength of 500 nm to 550 nm is oscillated. By using the oscillator, it becomes easier to distinguish between the light emitted by the molten steel and the reflected detection light R. Moreover, since the green laser light is visible light and is easy to see, the work of positioning the reflected detection light R to be incident on the light receiving section 12 is easier than in the case of using the red laser light.

On the other hand, regarding purple or blue laser light with a wavelength of 400 nm to 500 nm, when the temperature of molten steel is 2000 K, the dispersed radiance in the region of 400 nm to 500 nm (green light) emitted by molten steel is 780 nm to 820 nm emitted by molten steel. It is 1/100 or less of the diffused radiance in the (red light) region, and this ratio becomes 1/1000 or less when the molten steel temperature reaches 1500K. Therefore, when using an oscillator that oscillates violet or blue laser light having a wavelength range corresponding to this wavelength range of 400 nm to 500 nm, the light emitted by the molten steel and the reflection detection light R can be more easily distinguished.

(2) Light-receiving part The light-receiving part 12 includes a light-receiving element 12a composed of, for example, a PSD (Position Sensitive Detector), and a laser beam as the detection light D emitted from the light source 11a of the optical displacement meter 10 and stored in the container V. and a light-receiving lens 12b that collects the reflected detection light R, which is a laser light that has returned to the optical displacement meter 10 again after being reflected by the liquid surface of the molten metal M, onto the light-receiving element 12a as a spot light. there is An interference filter that allows only light of a specific wavelength to pass may be attached to the light receiving section 12 . For example, by attaching an interference filter that allows only the light of the wavelength used for the detection light D to pass through, it is possible to effectively suppress the incidence of light other than the spot light.

The above PSD has a structure in which a pair of electrodes for signal extraction are provided at both ends of a uniform resistance layer formed on one side or both sides of a high resistance semiconductor substrate. As a result, when the reflected detection light R is incident on the surface of the resistive layer as spot light, an electric charge proportional to the amount of light is generated at the incident position. The generated charge reaches the resistance layer as a photocurrent, is divided in inverse proportion to the respective distances to the pair of electrodes, and is extracted from the output electrode. For example, when the PSD has the structure shown in FIG. 5, the following equations 2 and 3 are provided between the incident position of the reflected detection light R and the output currents I _X1 and I _X2 of the output electrodes X ₁ and X ₂ , respectively. The relationship shown in is established. Therefore, the incident position _XA of the spot light can be obtained based on the formula 4 which can be derived from the formulas 2 and 3, regardless of the amount of light and its change. where I _X1 is the output current of electrode _X1 , I _X2 is the output current of electrode _X2 , _I0 is the total photocurrent (I _X1 + I _X2 ), L _X is the length of the light receiving surface, and X _A is the PSD Each represents the distance from the electrical center position to the incident position.

[Formula 2]
I _X1 =((L _X /2−X _A )/L _X )×I ₀
[Formula 3]
I _X2 =((L _X /2+X _A )/L _X )×I ₀
[Formula 4]
(I _X2 −I _X1 )/(I _X1 +I _X2 )=2×X _A /L _X

(3) Storage Unit The storage unit 13, which is a storage area allocated inside a CPU (Central Processing Unit) generally built in the optical displacement gauge 10, stores the values of the molten metal M in addition to Equation 4 above. In addition to storing the equations necessary for calculating the liquid level, it also plays the role of storing values output from the later-described calculation unit 14 and values input to the reference liquid level input means 15 .

(4) Calculation unit The calculation unit 14, which is a calculation area allocated inside the CPU generally built in the optical displacement meter 10, extracts the information stored in the storage unit 13 and performs a predetermined algorithm. , and outputs the calculation result to the storage unit 13 .

(5) Reference liquid level input means and liquid level display means The output value output from the light receiving element 12a is data relatively representing the distance from the optical displacement meter 10 to the liquid level of the molten metal M to be measured. Therefore, it is necessary to input the reference liquid level in order to carry out the arithmetic processing in the arithmetic unit 14 described above. Therefore, the reference liquid level can be input to the storage unit 13 via the reference liquid level input means 15 consisting of an input terminal.

For the reference liquid level input means 15, for example, a touch panel, which is an input device capable of performing an input operation by directly touching a menu screen displayed on the display with a finger, is preferably used. By adding a correction value that uniquely changes according to the displacement of the incident position on the light-receiving element 12a to the reference liquid level information input from the reference liquid level input means 15 in this manner, the liquid in the container V is The liquid level of the molten metal M to be measured can be calculated. The liquid level data obtained by the above arithmetic processing is output to a liquid level display means 16 such as a display provided in the instrument chamber, and displayed there.

1-2 Reflecting Means The reflecting means 20 provided in the liquid level measuring device of the first embodiment of the present invention is a reflecting means for changing the advancing directions of the detection light D and the reflected detection light R to predetermined directions, respectively, as described above. Preferably, the plate-like body is substantially rectangular in plan view and has a reflecting surface 20a that allows the light to pass through. The plate-like body is preferably made of a ceramic material having excellent heat resistance. The type of ceramic material is not particularly limited, but one having a lower coefficient of thermal expansion is preferred, and one having a higher Young's modulus is more preferred. As such a ceramic material, for example, a ceramic material containing 99.9% by mass or more of alumina can be mentioned. By using a ceramic material for the plate-like body as described above, it is possible to provide the reflecting means 20 almost right above the vessel V in which the molten metal M whose liquid level is to be measured is stored. As a result, the optical axis of the detection light (laser light) D emitted from the radiation part 11 of the optical displacement meter 10 provided avoiding the upper part of the container V is aligned with the liquid level of the molten metal M to be measured. can be incident almost perpendicularly to the

That is, if a glass mirror or a resin prism, which are generally used as laser light reflecting means, is used as the material of the plate-like body that constitutes the reflecting means 20, it is likely to be deformed under the influence of heat. There is a concern that the direction of travel of the detection light D and the reflected detection light R will shift during use, and the liquid level of the molten metal M may not be measured accurately. In addition, the mirror made of glass has a very low thermal conductivity, and a difference in thermal expansion tends to occur between the reflective surface side and the opposite side, so there is concern that the mirror may break. On the other hand, by making the plate-shaped body of the reflecting means 20 made of ceramic as described above, even if the reflecting means 20 is heated by radiant heat or convection heat from the molten steel in the container V, deformation due to the thermal influence will occur. can be prevented. As a result, the liquid level of the molten metal M to be measured can be stably measured over a long period of time.

In the plate-like body constituting the reflecting means 20, the surface roughness of the reflecting surface 20a for reflecting the detection light D and the reflected detection light R is Ra 0.2 or less. As a result, irregular reflection can be suppressed and the regular reflectance of the detection light D and the reflected detection light R can be increased on the reflection surface 20a of the reflection means 20, so that the liquid level can be measured more stably. The surface roughness of Ra 0.2 or less can be achieved by subjecting the plate-like body to a polishing process, for example. Further, it is preferable that the thickness of the plate-like body constituting the reflecting means 20 is 4 mm or more. By setting such a thickness, it is possible to suppress the transmission of the detection light D and the reflected detection light R in the thickness direction of the plate-shaped body, and reflect 85% or more of the laser light in the wavelength range of 300 nm to 1000 nm. Therefore, more stable liquid level measurement can be expected.

The reflecting means 20 may further include gas blowing means for blowing gas such as compressed air onto the reflecting surface 20a. As a result, the plate-like body constituting the reflecting means 20 can be appropriately cooled, so that deformation due to heat can be more reliably suppressed, and fine particles such as fumes generated from the molten metal M in the vessel V can be reflected. Adhesion to the surface 20a can be prevented. The above gas blowing means can be realized by the structure shown in FIG. 6, for example.

That is, the reflecting means 20 shown in FIG. 6, which is formed of a plate-like body which is substantially rectangular in plan view, has a substantially L-shaped shape when viewed from the side because one end of the plate-like body protrudes toward the reflecting surface 20a. A gas introduction passage 21 is provided in this projecting portion. A plurality of branched passages 22 extending obliquely downward communicate with the gas introduction passage 21, and the tip openings 23 of the respective branched passages 22 form a reflecting surface 20a on a stepped surface 20b of the projecting portion. It has an opening facing the With this structure, by supplying compressed air from a compressed air supply source (not shown) to the gas introduction path 21 through a heat-resistant flexible tube 24 such as Teflon (registered trademark), the reflecting surface 20a is effectively compressed. Air can be blown.

The number of reflecting means 20 is not limited to one as shown in FIG. may be reflected by the reflecting means. Moreover, each of the detection light D and the reflected detection light R may be reflected twice or more by using two or more reflecting means. By using a plurality of reflection means as described above, the degree of freedom in the installation position of the optical displacement gauge and the reflection means increases. It becomes possible to adopt the liquid level measuring device of the second embodiment of the present invention.

1-3 Method of using the liquid level measuring device An example in which molten steel is stored as the molten metal M will be described with reference to the block flow diagram of FIG. First, in step 1, the inside of the tundish before charging the molten steel is emptied so that the optical displacement gauge 10 is not adversely affected by the molten steel flowing down into the tundish or the molten steel stored in the tundish. An optical displacement gauge 10 constituting the liquid level measuring apparatus of the first embodiment of the present invention is installed at a position obliquely above the tundish in the state of (1) and horizontally spaced from the tundish.

Next, in step 2, the reflecting means 20 constituting the liquid level measuring device of the second embodiment of the present invention is arranged above the tundish. At that time, the optical displacement meter 10 is activated, and the detection light (laser light) D emitted from the light source can be reflected by the reflecting surface 20a of the reflecting means 20 and then reflected by the bottom surface of the tundish. The position and angle of the reflecting means 20 are adjusted so that the reflected detection light R can be received by the light receiving part 12 of the optical displacement meter 10 after being reflected again by the reflecting surface 20a of the reflecting means 20 . Also, the position and angle of the optical displacement meter 10 are adjusted as necessary.

Next, in step 3, a standard molten steel liquid level L ₀ (for example, zero) is input from the standard liquid level input means 15 to store the value in the storage unit 13 . Then, in order to obtain the incident position of the reflected detection light R in the PSD as the light receiving element 12a when the liquid level is _L0 , the optical displacement meter 10 is activated and the detection light D is emitted from the light source of the radiation part 11. are reflected by the bottom surface of the tundish, and the output currents I _x1 and I _x2 generated when the reflected detection light R is incident on the PSD of the light receiving section 12 of the optical displacement meter 10 are output to the storage section 13 . As a result, the calculation unit 14 calculates the incident position _X0 of the spot light (reflected detection light R) when the tundish is empty and the liquid level _{is L0} based on the equation 4 stored in advance in the storage unit 13. and store the value of the calculation result in the storage unit 13 .

Next, in step 4, a box-shaped body having a height of _LB is placed in the tundish as a molten steel dummy, and the liquid level _LB is input from the reference liquid level input means 15, and the value is stored in the storage unit 13. Memorize. Then, in the same manner as in step 3 above, in order to obtain the incident position in the PSD when the liquid level is _LB , the optical displacement meter 10 is activated to radiate the detection light D from the light source of the radiating section 11. Output currents I _X1 and I _X2 generated when reflected detection light R is incident on the PSD of the light receiving section 12 of the optical displacement meter 10 are output to the storage section 13 . As a result, the calculation unit 14 calculates the incident position _XB of the spot light (reflection detection light R) at the liquid level _LB based on Equation 4 stored in advance in the storage unit 13, and the value of the calculation result is calculated. Store in the storage unit 13 . After measuring the liquid level with the box-shaped body, the box-shaped body is taken out from the tundish.

Next, in step 5, the parameters of the arithmetic expression of the following formula 5 for uniquely obtaining the liquid level of the molten steel with respect to the incident position _XL of an arbitrary spot light (reflection detection light R) are set to the above steps 3 and 4, based on the set of the liquid level _L0 and the incident position _X0 and the set of the liquid level L _B and the incident position _XB stored in the storage unit 13, the calculation unit 14 calculates the value of the calculation result is stored in the storage unit 13. FIG. 8 shows a graph showing the relationship between the variables in Equation 5, with the horizontal axis representing the incident position [X] and the vertical axis representing the liquid level [mm].

[Formula 5]
L=L ₀ +((L _B −L ₀ )/(X _B −X ₀ ))×(X _L −X ₀ )

Preparations for measuring the liquid level are completed, and finally in step 6, compressed air is supplied to the gas introduction path 21 of the reflecting means 20 through the flexible tube 24, and molten steel is charged into the tundish. At the same time, the optical displacement meter 10 is activated to radiate the detection light D from the light source 11a of the radiation part 11, and after being reflected by the reflection means 20 and reflected by the liquid surface of the molten steel, the reflected detection light R is reflected by the reflecting means 20 and is incident on the PSD of the incident section 12 . As a result, the CPU calculates the incident position X _L of the spot light (reflection detection light) by substituting the current values I _x1 and I _x2 output from the PSD into Equation 4, and stores it in the storage unit 13 . , into Equation 5 to calculate the liquid level L of the molten steel in the tundish. The calculated liquid level is displayed on a liquid level display means 16, such as a display in an instrument room.

As described above, by using the liquid level measuring device of the first embodiment of the present invention, the liquid level can be measured without contact, unlike the liquid level measurement by the conventional thermocouple, and the molten metal can be stored. Since the optical displacement gauge can be arranged at a position spaced apart from the container, it is possible to prevent the optical displacement gauge from being adversely affected by radiant heat and convection heat emitted from the molten metal. In addition, any liquid level can be measured in a wide measurement range from an empty state in which no molten metal exists in the container to a full liquid state.

2. Second Embodiment As shown in FIG. 9, a liquid level measuring device according to a second embodiment of the present invention has a Both the role of transmitting the detection microwave W for liquid level detection and the role of receiving the reflection detection microwave U after this detection microwave W is reflected by the liquid surface of the molten metal M to be measured. It has a microwave type displacement meter 30 having a transmitting/receiving section 31 that is responsible for it. This liquid level measuring device is further provided with a plate-like reflecting surface 40a having a surface roughness Ra of 0.2 or less for reflecting the detection microwave W and the reflection detection microwave U in order to change the direction of travel of the detection microwave W and the reflection detection microwave U to predetermined directions. It has a reflecting means 40 consisting of a body.

As shown in FIG. 9, the reflecting means 40 is supported by a support (not shown) above the container V, so that the reflecting means 40 is exposed to the heat of the high-temperature molten metal M in the container V. As shown in FIG. Therefore, it is preferable that the material of the plate-shaped body constituting the reflecting means 40 has such excellent heat resistance that it does not easily deform even when exposed to a high-temperature atmosphere. and SUS materials. Among them, as will be described later, in the case of the liquid level measuring device of the second embodiment of the present invention that uses microwaves for liquid level measurement, It is preferable to use a SUS material from the viewpoint of suppressing absorption.

Also in the liquid level measuring device of the second embodiment of the present invention, similarly to the liquid level measuring device of the first embodiment, the liquid level of the molten metal M stored in the container V is measured. In addition to being able to measure the liquid level by contact, by providing the reflection means 40 above the container V as described above, the microwave displacement gauge 30 can be arranged at a position avoiding the upper part of the container V. FIG. This prevents the transmitting/receiving section 31 of the microwave displacement gauge 30 from being exposed to radiant heat emitted from the high-temperature molten metal M and convection heat rising upward. Further, since the microwave axis of the detection microwave W can be incident almost perpendicularly to the liquid level of the molten metal M to be measured, which is stored in the container V, the measurement range can be widened. can be done. That is, it is possible to stably measure the liquid level of the molten metal M in the container V within the range from the empty state to the full liquid state over a long period of time.

Further, the microwaves used for the detection microwave W and the reflected detection microwave U are electromagnetic waves having a wavelength of about 0.1 mm to 1000 mm and a speed of about 300,000 km/sec, which is about the same as light. It is almost unaffected by atmospheric conditions such as the temperature, pressure, flow velocity, etc. of the gas present in the path. Since the wavelength is sufficiently long, and the wavelength is sufficiently longer than the wavelength of the visible light shown in FIG. 4, it is easy to distinguish between the infrared light and the visible light. Therefore, it is possible to perform measurement with higher accuracy than when using visible light.

In the method of measuring the liquid level with the above-described microwave displacement meter 30, the detection microwave transmitted while changing the frequency with time is reflected by the liquid surface of the liquid level measurement target and returns. FMCW (Frequency Modulated Continuous Wave) method for obtaining the liquid level from the deviation, and the pulse-shaped detection microwave transmitted toward the liquid surface of the liquid level measurement target is reflected by the liquid surface and returned as a reflected detection microwave There is a pulse method that measures the time until the liquid level is reached to determine the liquid level, and any of the above-described microwave displacement meters can be employed. Hereinafter, each element of the liquid level measuring apparatus according to the second embodiment of the present invention will be specifically described by taking up a case where an FMCW type microwave displacement gauge is adopted.

2-1 Microwave Displacement Gauge As described above, the microwave displacement gauge 30 of the liquid level measuring device of the second embodiment of the present invention is a liquid level measurement object stored in the container V. A transmission/reception unit 31 is provided for transmitting the detection microwave W toward the liquid surface of the metal M and receiving the reflection detection microwave U after the detection microwave W is reflected by the liquid surface of the molten metal M. . As shown in FIG. 9, the transmitting/receiving unit 31 has an antenna extending in the transmitting direction, and transmits a detection microwave W having a frequency of about 5 GHz to 30 GHz, and also transmits the molten metal M whose liquid level is to be measured. can receive the reflected detection microwave U that has been reflected by the liquid surface of the

The type of the transmitting/receiving section 31 is not particularly limited as long as it can properly transmit and receive microwaves. As shown in FIG. A rod antenna type (a), a horn antenna type (b) with a megaphone-shaped horn attached to the tip of the antenna, and a wave with a pipe-shaped probe attached to propagate microwaves. A guide type (c) or the like can be preferably used.

In the above-described microwave displacement gauge 30, when measuring the liquid level of the molten metal M, the detection microwave W is transmitted from the antenna of the transmitting/receiving unit 31, and the detection microwave W reaches the liquid level of the molten metal to be measured. The transmitting/receiving unit 31 receives the reflection detection microwave U that has returned after being reflected by the liquid surface of M. At this time, the frequency of the detection microwave W to be transmitted is changed continuously and linearly within a predetermined range. Then, by measuring the difference between the frequency of the received reflection detection microwave U and the frequency of the detection microwave W transmitted at the time of reception, the transmitted microwave is reflected by the liquid surface of the molten metal M. Since the time until it returns is indirectly known, the liquid level of the molten metal M can be measured.

The principle of liquid level measurement by the FMWC method will be described in detail with reference to FIG. For example, as shown in FIG. 11, the frequency of the detection microwave W transmitted from the transmitter/receiver 31 is continuously and linearly modulated in a sawtooth pattern with a sweep time T between the maximum frequency _fmax and the minimum frequency _fmin . , the detection microwave W transmitted at time t(0) when the transmission frequency becomes f(0) is reflected by the liquid surface of the molten metal M to be measured, and then has the same frequency f(0) as the transmission frequency. ) is returned to the transmitting/receiving unit 31 and received by the transmitting/receiving unit 31 is t(1), the time required for the round trip of this microwave is Δt=t(1)−t( 0)” passes, the transmission frequency of the detection microwave W transmitted from the transmitter/receiver 31 changes from the transmission frequency f(0) at time t(0) to the transmission frequency f(1) at time t(1). Change.

As described above, the transmission frequency of the detection microwave W transmitted from the transmitting/receiving unit 31 is continuously and linearly modulated, and the rate of increase α, which is the change over time, is α=(f _max −f _min )/T, the transmitted frequency f(0) of the detection microwave W at time t(0) and the reception of the reflected detection microwave U having a frequency equal to this frequency f(0) By detecting the transmission frequency f(1) of the detected microwave W at the time of , when Δf, which is the difference between these frequencies, is “Δf=f(1)−f(0)”, it is derived from the proportional relationship Δt can be obtained from the following equation 6.

[Formula 6]
Δt=Δf·T/(f _max −f _min )

The time Δt obtained by Equation 6 above is the time required for the microwave to make a round trip between the antenna of the transmitting/receiving section 31 and the liquid surface of the molten metal M. Therefore, as shown in Equation 7 below, this By multiplying the time Δt by the speed V of the microwave and dividing by 2, the distance L traveled by the microwave from the liquid surface of the molten metal M to be measured to the antenna of the transmitter/receiver 31 can be obtained. When the liquid level of the molten metal M in the container V is the reference liquid level (for example, when the liquid level is zero and the container is empty), the distance L is obtained in advance using a liquid level measuring device. Any liquid level of the molten metal M in the vessel V can be measured by the liquid level measuring device.

[Formula 7]
L=Δt・V・(1/2)

As described above, after substituting the frequency values f(0) and f(1) output from the transmitting/receiving unit 31 into the equation 6, the molten metal M in the container V is calculated based on the equation 7. Arithmetic processing for obtaining the liquid level can be performed by control means such as a CPU (Central Processing Unit). This CPU, for example, as shown in FIG. and a calculation unit 33 for performing the calculation. The CPU may be incorporated in the microwave displacement gauge 30, or the microwave displacement gauge 30 and the CPU may be separate devices.

The storage unit 32 stores the liquid level of the molten metal M, which serves as a reference to be described later, which is input from a reference liquid level input means 34 such as a keyboard or a touch screen, as well as formulas necessary for calculating the liquid level of the molten metal M. It also plays a role of storing a value output from a calculation unit 33, which will be described later. Further, the calculation section 33 takes out the information stored in the storage section 32 , performs calculation according to a predetermined algorithm, and outputs the calculation result to the storage section 32 . Further, the liquid level data obtained by the above arithmetic processing is output to a liquid level display means 35 such as a display, and is displayed there. The value calculated based on the output value output from the transmitter/receiver 31 is the distance from the antenna of the transmitter/receiver 31 to the liquid level of the molten metal M to be measured. In order to calculate the liquid level of the molten metal M in the container V, it is necessary to input the liquid level in the container V as a reference. A reference liquid level input means 34 is provided as an input terminal for inputting the reference liquid level.

2-2 Reflecting Means The reflecting means 40 of the liquid level measuring apparatus of the second embodiment of the present invention changes the direction of travel of the detection microwave W and the reflection detection microwave U to predetermined directions as described above. Preferably, the reflecting means 40 is a substantially rectangular plate-like body provided with a reflecting surface 40a for reflecting the liquid level of the molten metal M to be measured. Therefore, it is preferable that the material of the plate-like body has excellent heat resistance. Ceramic materials, SUS materials, and the like can be mentioned as such materials having excellent heat resistance. By forming the plate-shaped body from a material with excellent heat resistance in this way, the detection microwave W transmitted from the transmitting/receiving section 31 of the microwave displacement gauge 30, which is provided avoiding the upper side of the container V, It can be made incident almost perpendicularly to the liquid surface of the molten metal M to be measured.

Among the above materials, the SUS material is more preferable because it can reflect microwaves with a higher reflectance. That is, since ceramic materials are generally formed by sintering inorganic powder, they have a myriad of fine voids microscopically. Therefore, when microwaves are reflected on the surface of the ceramic material, the microwaves are attenuated by transmission and absorption in this ceramic material. On the other hand, in the case of the SUS material, unlike the ceramic material described above, the surface (that is, the reflecting surface 40a) of the SUS material has almost no minute voids and is dense. By forming the body, it is possible to suppress the attenuation of the detection microwave W and the reflection detection microwave U when the detection microwave W and the reflection detection microwave U are reflected in order to change their traveling directions. As a result, the liquid level can be measured more satisfactorily than when a ceramic material is used as the material of the plate-like body. Although the thermal expansion coefficient of the SUS material is almost the same as that of the glass material, the thermal conductivity of the SUS material is sufficiently higher than that of the glass material. Therefore, it also has the advantage that bending due to heat is less likely to occur.

Although austenitic stainless steel such as SUS304 may be used as the SUS material used for the plate-like body, a ferritic stainless steel such as SUS430 or a martensitic stainless steel such as SUS410 may be used, which has a lower coefficient of thermal expansion. It is more preferable to use stainless steel with Carbon steel is a material that corrodes more easily than stainless steel, and an oxide film is easily formed on the surface, making it difficult to maintain a high reflectance on the reflecting surface. It is not preferable to use carbon steel for the material of

In the plate-shaped body constituting the reflecting means 40, the surface roughness of the reflecting surface 40a for reflecting the detection microwave W and the reflected detection microwave U is Ra 0.2 or less. As a result, irregular reflection can be suppressed on the reflecting surface 40a of the reflecting means 40, and the specular reflectance of the detection microwave W and the reflection detection microwave U can be increased, so that the liquid level can be measured more stably. Become. The surface roughness of Ra 0.2 or less can be achieved by subjecting the plate-like body to a polishing process, for example.

Similar to the reflecting means 20 of the first embodiment shown in FIG. 6, the reflecting means 40 may include gas blowing means for blowing gas such as compressed air onto the reflecting surface 40a. As a result, the plate-like body constituting the reflecting means 40 can be appropriately cooled, so that deformation due to heat can be more reliably suppressed, and fine particles such as fumes generated from the molten metal M adhere to the reflecting surface 40a. can prevent you from doing it.

In the liquid level measuring device of the second embodiment of the present invention, as shown in FIG. 13, the reflection means 40 is provided at one end of a tubular body 41 made of, for example, a metal pipe with both ends open. , the antenna of the transmitting/receiving section 31 of the microwave displacement meter 30 is preferably inserted into the other end of the tubular body 41 . As a result, the antenna of the transmitting/receiving section 31 can be more reliably protected from radiant heat, hot air, and the like generated from the molten metal M in the container V. As shown in FIG. Further, since the traveling direction of the microwave can be guided in the extending direction inside the tubular body 41, it becomes possible to measure the liquid level with higher accuracy.

The length of the tubular body 41 is not particularly limited, but the transmitting/receiving section 31 can be sufficiently separated from the vessel V in the horizontal direction so as not to be affected by the heat of the molten metal M in the vessel V. It preferably has sufficient length. Even when the transmitting/receiving unit 31 is separated from the container V in this way, the detection microwave W and the reflection detection microwave U can be guided inside the tubular body 41, so that the microscopic measurement can be performed without impairing the liquid level measurement accuracy. It becomes possible to more reliably protect the wave displacement meter 30 from thermal influences. In addition, since the tubular body 41 also plays the role of supporting the reflecting means 40, there is no need to separately provide a support for the reflecting means 40, so the installation cost can be reduced. Even if there is no space, the reflecting means 40 and the tubular body 41 can be easily arranged.

As shown in FIG. 14, which is a cross-sectional view of the container V of FIG. 9 taken along the line AA, the upper end surface of the side wall of the container V whose top is open is made of a castable refractory material over the entire circumference. It is preferable that a reflective portion _V1 having a substantially triangular cross section is formed. As a result, the detection microwaves _W2 and _W3 incident on the upper end surface of the side wall of the container V can be reflected in a direction different from the direction in which the reflecting means 40 is provided. The microwaves _W2 and _W3 reflected by the upper end face and the microwave _W1 reflected by the liquid surface of the molten metal M in the vessel V are both received by the transmitting/receiving unit 31, resulting in an inaccurate measurement of the liquid level. can be effectively avoided.

2-3 Method of Using the Liquid Level Measuring Device Next, regarding the method of using the liquid level measuring device of the second embodiment of the present invention, a container V having an open top is placed in a dundish to measure the liquid level. A case where molten steel is stored as the molten metal M will be described as an example with reference to the block flow diagram of FIG. First, in step 1, in order to prevent the microwave displacement gauge 30 from being adversely affected by the molten steel flowing down into the tundish or the molten steel stored in the tundish, the inside of the tundish before charging the molten steel is A microwave displacement gauge 30 constituting a liquid level measuring apparatus according to a second embodiment of the present invention is installed obliquely above the empty tundish and horizontally away from the tundish.

Next, in step 2, the reflecting means 40 constituting the liquid level measuring device of the second embodiment of the present invention is arranged above the tundish. At that time, the microwave displacement meter 30 is activated, and the detection microwave W transmitted from the transmitter/receiver 31 can be reflected by the reflecting surface 40a of the reflecting means 40 and then reflected by the bottom surface of the tundish. The position and angle of the reflecting means 40 are adjusted so that the detection microwave U can be received by the transmitting/receiving section 31 of the microwave displacement meter 30 after being reflected by the reflecting surface 40a of the reflecting means 40 again. Also, the position and angle of the microwave displacement meter 30 are adjusted as necessary.

Next, in step 3 , a reference liquid level L ₀ (for example, zero) of molten steel is input from the reference liquid level input means 34 to store the value in the storage unit 32 . For example, when the liquid level _L0 is the liquid level in an empty state where molten steel does not exist in the tundish, the detection microwave W is transmitted in this empty state, and the transmission frequency f(0) is stored. stored in the unit 32; Then, the reflected detection microwave U reflected by the bottom surface of the tundish is received, and the transmission frequency f(1) of the detection microwave W at the time of reception is stored in the storage unit 32 . f(0) and f(1) stored in the storage unit 32, the transmission frequency increase rate α with time stored in the storage unit 32 in advance, and the microwave velocity V, the transmission/reception unit 31 The path distance L ₀ ′ of the microwave from the antenna to the bottom surface of the tundish is calculated based on the following equation 8, and the value is stored in the storage unit 32 .

[Formula 8]
L ₀ ′=((f(1)−f(0))/α)×V×(1/2)

Preparations for liquid level measurement are now complete. Finally, in step 4, after supplying compressed air to the gas introduction path of the reflecting means 40 through the flexible tube, molten steel is charged into the tundish, The microwave displacement meter 30 is activated to start measuring the liquid level L of the molten steel. That is, the transmission/reception unit 31 transmits the detection microwave W, and the transmission frequency F(0) is stored in the storage unit 32 .

Then, the reflected detection microwave U reflected by the liquid surface (liquid level L) of the molten steel is received, and the transmission frequency F(1) of the detection microwave W at the time of reception is stored in the storage unit 32 . Then, from F(0) and F(1) stored in the storage unit 32, the transmission frequency increase rate α with time stored in the storage unit 32 in advance, and the microwave velocity V, the transmission/reception unit 31 to the liquid surface (liquid level L) of the molten steel is calculated based on the following formula 9, and the value is stored in the storage unit 32.

[Formula 9]
L'=((F(1)-F(0))/α)×V×(1/2)

Then, by substituting L ₀ stored in the storage unit 32 and the calculated microwave path distances L ₀ ' and L' into the following equation 10, the liquid level L of the molten steel in the tundish is calculated. . The calculated liquid level can be displayed on, for example, a display in the instrument room as the liquid level display means 35 .

[Formula 10]
L = L ₀ + (L ₀ '-L')

As described above, by using the liquid level measuring device of the second embodiment of the present invention, it is possible to perform non-contact measurement unlike the conventional liquid level measurement using a thermocouple. Since the microwave displacement gauges can be arranged at separated positions, it is possible to prevent the microwave displacement gauges from being adversely affected by radiant heat and convection heat emitted from the molten metal. In addition, any liquid level can be measured in a wide measurement range from an empty state in which no molten metal exists in the container to a full liquid state.

REFERENCE SIGNS LIST 10 optical displacement meter 11 radiation unit 11a light source 11b light projection lens 12 light receiving unit 12a light receiving element 12b light receiving lens 13 storage unit 14 calculation unit 15 reference liquid level input means 16 liquid level display means 20, 40 reflection means 20a, 40a reflection surface 20b Stepped surface 21 Gas outlet 22 Communication hole 23 Gas introduction hole 24 Flexible tube 30 Microwave displacement meter 31 Transmission/reception unit 32 Storage unit 33 Calculation unit 34 Reference liquid level input means 35 Liquid level display means D Detection light W Detection microwave M Molten metal R Reflection detection light U Reflection detection microwave V Vessel _V1 Reflector I _x1 , I _x2 Output current _X1 , _X2 Output electrode

Claims (6)

An electromagnetic wave for detecting the liquid level is transmitted toward the liquid surface of the molten metal stored in a container with an open top, and the reflected electromagnetic wave after the electromagnetic wave is reflected on the liquid surface of the molten metal is received. Liquid level measuring means for measuring the liquid level of the molten metal by
and reflecting means comprising a plate-like body having a reflecting surface with a surface roughness Ra of 0.2 or less for reflecting to change the traveling direction of the electromagnetic wave before and after the reflection to a predetermined direction. 2. The liquid level measuring device according to claim 1, wherein said reflecting means has gas blowing means for blowing gas onto said reflecting surface. The electromagnetic wave is a light wave, the liquid level measuring means is an optical displacement gauge including a radiation part that plays the role of transmission and a light receiving part that plays the role of reception, and the plate-like body is made of ceramic. , The liquid level measuring device according to claim 1. 4. The liquid level measuring device according to claim 3, wherein said plate-like body contains 99.9% by mass or more of alumina. The electromagnetic waves are microwaves, the liquid level measuring means is a microwave displacement gauge including a transmitting/receiving part that performs both the transmission role and the reception role, and the plate-like body is made of stainless steel. , The liquid level measuring device according to claim 1. A tubular body for guiding the traveling direction of the microwave is provided between the transmitting/receiving section and the reflecting means, and has a substantially triangular cross section made of castable refractory over the entire circumference of the upper end face of the side wall of the container. 6. The liquid level measuring device according to claim 5, wherein a reflecting portion is formed.

Images