JPH10319030A - Method of measuring molten steel flow velocity in casting mold and detection rod for measuring molten steel flow velocity used in this method - Google Patents

Abstract

(57) [Summary] [Object] In a molten metal flow velocity measuring apparatus and method for estimating a flow velocity from vibration detection of a detection rod caused by Karman vortex discharge, a further improvement in measurement accuracy is achieved by enhancing erosion resistance of the detection rod. It is intended to improve. [Constitution] The dimensions of the detection rod are 5 to 30 mm in diameter and 10 in length.
The material is set to 0 to 400 mm, and the material is 60 to 80% by weight of a high melting point metal represented by molybdenum, 10 to 30% by weight of ceramics represented by zirconia, and 10 to 20% by weight of antioxidant represented by graphite. It is characterized by being made into a sintered body having as a main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the flow rate of molten steel capable of continuously and directly measuring the flow rate of molten steel injected from a tundish into a casting mold through an immersion nozzle, for example, in continuous casting. More specifically, the present invention relates to a technique for improving measurement accuracy by improving erosion resistance to molten steel and molten steel powder.

[0002]

2. Description of the Related Art In a continuous casting process of molten steel, there is a process of distributing and injecting molten steel from a tundish into a casting mold through an immersion nozzle. In this step, it is important to control the flow rate of molten steel in the casting mold. This is for the following reason. FIG. 2 shows a conceptual diagram of a cross-sectional structure around the immersion nozzle in this step. In the figure, reference numeral 1 denotes a water-cooled casting mold, and its planar shape is a square shape having short side walls 1a and 1b and long side walls 1c and 1d as shown in FIG.
In the figure, reference numeral 2 denotes an immersion nozzle, and reference numeral 3 denotes a molten powder. The molten powder has a function of preventing oxidation of the surface of the molten metal, lubricating between the casting mold and the slab, catching floating inclusions, and keeping the molten metal warm.

The immersion nozzle 2 is generally provided with a plurality of discharge ports in the vicinity of the lower portion. For example, as shown in the drawing, the lower side wall has two discharge ports 2a and 2b.
The same amount of molten metal is discharged from a and 2b, and the discharge direction coincides with the longitudinal direction of the space 4 in the casting mold. The molten metal discharged from the immersion nozzle 2 is supplied while being controlled so that the interface height in the casting mold is maintained at substantially the same level, and the molten metal filled in the casting mold is discharged by the casting mold. In addition, it is possible to continuously obtain cast slabs by continuously drawing out from the cooled and solidified lower side.

[0004] When molten steel is injected from the immersion nozzle 2 into the casting mold 1 of such continuous casting, the molten steel flow colliding with the short side wall 1a of the casting mold 1, as shown in FIG. The rising flow d is divided into a rising flow d toward the casting mold and a descending flow e toward the lower part of the casting mold. The rising flow d raises the level of the molten metal near the short side wall 1a as shown in FIG. This fluctuation of the molten metal level affects the thickness of the molten powder. That is, the thickness of the molten powder layer 3 becomes smaller at the position where the molten steel surface rises and becomes larger at the position where the molten steel surface descends. As the casting speed increases, the discharge flow rate from the immersion nozzle also increases, and the speed of the ascending flow of the molten steel increases. If the speed of the ascending flow of the molten steel increases, the amount of swelling of the molten steel surface increases, and accordingly, the wavy frequency and the amount of vertical fluctuation of the molten steel surface also increase. As a result, the thickness of the solidified shell fluctuates and becomes non-uniform, which causes problems in the quality of the slab, such as fouling flaws and vertical cracks. Therefore, in a continuous casting facility, it is important to control the flow rate of molten steel in a casting mold so as not to cause variation and unevenness in the thickness of a solidified shell.

In order to improve the surface quality of the slab, it is important to suppress the occurrence of entrainment of the molten powder into the molten steel, and the flow rate of the molten steel is also closely related to this. The molten powder 3 is used as a lubricant between the casting mold and the slab, but when the molten steel flows excessively, a phenomenon occurs in which the powder is caught in the molten steel. Then, as a result, slime bites and the like are generated, and the quality of the cast slab is deteriorated. On the other hand, when stagnation occurs in the flow of molten steel in the casting mold, the temperature of the molten steel in the stagnation portion is lower than in other portions, and the growth of the solidified shell is locally slowed. As a result, the thickness of the initially solidified shell becomes non-uniform, and the stress acting on the slab differs in the width direction of the casting mold, causing vertical cracks and the like. If the flow of molten steel is irregular, the powder layer itself may be lost. That is, a refractory nozzle immersed in the molten steel is used to inject the molten steel into the casting mold, but due to the effect of the discharge flow from the immersion nozzle, the flow of the molten steel in the casting mold becomes irregular, and the flow rate is constant. Disappears.
As a result, the surface of the molten steel (hereinafter referred to as the molten metal surface) is wavy and fluctuates up and down, the temperature of the molten metal surface in the casting mold is not uniform, and the thickness of a part of the molten powder layer existing on the molten metal surface is reduced. The thinned powder layer or a portion where the molten powder layer itself disappears may occur. As a result, the unmelted powder present on the molten powder layer comes into contact with the molten steel, and the frequency of being caught and trapped in the molten steel increases, so that slime bites occur. In addition, when the molten metal surface fluctuates, the amount of molten powder entering between the molten steel and the casting mold locally changes, and the amount of heat transfer from the molten steel to the casting mold is not uniform in the width direction of the casting mold, so that the thickness of the solidified shell is not uniform. It becomes uniform and vertical cracks occur.

[0006] In order to improve the quality of the slab, the thickness of the solidified shell should not be varied or non-uniform.
It is important to suppress the entrainment of the molten powder into the molten steel and to make the growth of the initial solidified shell uniform in the width direction of the casting mold, and so on. It is necessary to control the flow, and for that purpose, it is indispensable to grasp the molten steel flow velocity accurately. As an apparatus for measuring the flow rate of molten steel, one of the applicants has already filed Japanese Patent Application Laid-Open No. 7-20139 (Japanese Patent Application No. 5-165817). According to this method, the detection rod 5 is inserted and immersed in the molten metal so as to cross the flow as shown in FIG. 4, and the discharge cycle of the Karman vortex discharged to the downstream side of the detection rod 5 as shown in FIG. Is detected by the cycle of the impact applied to the detection rod 5. Specifically, this shock cycle is measured by a vibration detecting means such as a strain gauge attached to the detecting rod 5 as shown in FIG. 6, and the measurement result is obtained in advance and the frequency of the detecting rod and the molten metal are measured. The flow velocity of the molten metal is calculated by applying the relational expression to the flow velocity, and the flow velocity of the molten steel that changes every moment is continuously measured by such a method.

According to this method, it is possible to directly measure the flow velocity of the discharge flow from the immersion nozzle or the flow velocity of the surface flow, and it is possible to control the peripheral devices by feeding back the obtained measurement data to the control system. In addition to this, it has become possible to carry out flow velocity analysis in a casting mold to find out the optimal conditions for high-speed casting.

[0008]

However, this measuring method still has problems to be solved. This is a problem that when long-term continuous measurement is performed, the measurement accuracy decreases with time. The decrease in measurement accuracy is due to the following reasons. In this measurement method, the frequency of occurrence of Karman vortices generated behind the detection rod is obtained from the frequency of the detection rod, and is calculated by a dimensionless relational expression consisting of the molten steel speed, the frequency of the detection rod, and the diameter of the detection rod. However, in order to guarantee the reliability of the calculation result, the diameter of the detection rod must not change. However, in practice, when the sensing rod is immersed in molten steel in a casting mold for a long time and the flow rate of the molten steel is continuously measured, the sensing rod is exposed to the flow of hot molten steel and molten powder, so that the sensing rod is eroded by these. As a result, the diameter of the detection rod becomes unknown, and the molten steel flow velocity obtained from the dimensionless relational expression becomes inaccurate.

Further, when this phenomenon that the sensing rod becomes thinner and thinner particularly occurs at a contact point with the molten powder existing on the molten steel, the sensing rod is broken by a force received from the molten steel flow, and the broken part is cast. It is expected to be trapped in the solidified shell growing in the mold and cause defects in the slab. In addition, cooling is delayed at locations where broken parts are mixed, causing breakage.
Out (a phenomenon that the measurement is not completed within the specified time) is also expected to occur. As described above, thinning of the sensing rod must be avoided because it causes a decrease in the measurement accuracy of the molten steel flow rate, defects in the slab, and further breakout. An important issue is to improve the erosion resistance of the rod.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and provides a method for measuring the flow rate of molten steel from a frequency of the detection rod caused by Karman vortices generated downstream of the detection rod immersed in the molten steel. In addition, by increasing the erosion resistance of the detection rod, it is possible to prevent a decrease in measurement accuracy with the passage of time, and specifically, a material for a detection rod having excellent erosion resistance is proposed. In addition, it is not proposed to propose a range of an optimum dimension of the detection rod using this material.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors examined the erosion resistance of the detection rod. When considering the erosion resistance, the erosion resistance to molten steel and the melting powder It was necessary to consider both the erosion resistance, and concluded that the durability as a sensing rod was meaningless unless it was effective for both. Then, the present invention was completed as a result of exploring a material satisfying the above conditions and examining a range of an optimum dimension of the detection rod using the material. Claim 1 of the present invention
Is immersed in molten steel so that one end is fixed and the other end is a free end on the free end side of the sensing rod so as to cross the molten steel flow, and is caused by Karman vortex generated downstream of the sensing rod. In the method of measuring the vibration of the detection rod and estimating the molten steel flow velocity in the casting mold by applying the relational expression between the detection rod frequency and the molten steel flow velocity determined in advance, the dimensions of the detection rod are 5 to 30 mm in diameter. 100-400 mm in length, and the material of the detection rod is: a) One or more refractory metals selected from molybdenum, vanadium, niobium, tantalum, chromium, tungsten, manganese, technetium, and rhenium 6
0 to 80 wt% b) 10 to 30 wt% of one or more kinds of ceramics selected from zirconia, alumina, yttrium oxide, silica, silicon carbide and silicon nitride c) A mixture of one or both of graphite and boron nitride 10 This is a method for measuring the flow velocity of molten steel in a casting mold, characterized in that a sintered body having a main component of a, b and c of up to 20 wt% is formed.

If the diameter of the detection rod is smaller than 5 mm, the pressure received from the molten steel flow is too small, so that when the molten steel flow is slow, it becomes difficult to detect vibration. On the other hand, the diameter is 30m
If it exceeds m, the pressure received from the molten steel flow becomes extremely large and the weight of the detection rod also increases, so that it becomes difficult to suspend and support the detection rod. The length of the sensing rod is usually 7
Set to more than double. The range of the length that the detection rod can take is 100 to 400 mm in length. It has a length of 100
If it is less than mm, the detection rod weight is too light and a vibration of a detectable swing width cannot be obtained.On the other hand, if it exceeds 400 mm, the pressure applied to the detection rod from the molten steel flow becomes excessive and its weight also increases, It becomes difficult to suspend and support. Appropriate range of detection rod size is 5-30mm in diameter, length 1
It is 00 to 400 mm.

The conditions for determining the material of the detection rod are as follows:
High melting point, excellent erosion resistance to molten steel and molten powder, does not degrade product quality even if it melts into product slab, does not bend or break even if exposed to molten steel flow for a long time It has sufficient mechanical strength, easy molding, and the like. That is, since the detection rod is immersed in molten steel for a long time, its heat resistance must be higher than the temperature of molten steel, that is, 1550 ° C., which is the melting temperature of iron. In the present invention, approximately 2
The standard is around 000 ° C. Further, it is required to have a workability capable of being processed into a rod shape and a mechanical strength typified by stickiness to withstand pressure and vibration received from a molten steel flow.

Both the component a and the component b have excellent heat resistance, the high melting point metal as the component a has excellent erosion resistance to molten steel, and the ceramic as the component b has excellent erosion resistance to molten powder. That is, although the high melting point metal as the component a has a high melting point, it has excellent erosion resistance to molten steel, but slightly inferior erosion resistance to molten powder, which is an oxide. Molten powder has a stronger oxidation reaction than molten steel, and easily oxidizes and corrodes a component such as metal. In addition, since the component a is a metal, it has excellent workability and is sticky, and facilitates molding of the detection rod and contributes to imparting mechanical strength necessary for the detection rod. The compounding amount of the component a for this purpose is 60 to 80 wt%. 60w
If the content is less than t%, the erosion resistance to molten steel is insufficient, forming is also difficult, and the adhesiveness is insufficient, resulting in brittleness. Also 8
If the content exceeds 0 wt%, the amount of the component b is relatively reduced, so that the erosion resistance to molten powder is reduced. Ceramics that are component b have excellent erosion resistance to both molten steel and molten powder, but are hard and brittle,
There is a disadvantage of poor processability. Therefore, if the compounding amount is too large, it is difficult to form the detection rod, and the stickiness is reduced, which may cause breakage when exposed to the molten steel flow for a long time. From these facts, the blending range of the ceramic as the component b is set to 10 to 30 wt%.

[0015] Graphite or boron nitride as a component c is an antioxidant, and protects a high melting point metal such as molybdenum from an oxidizing atmosphere. If the amount is too small compared to the amount of the high melting point metal, the antioxidant effect is inferior,
If the amount is too large, a phenomenon occurs in which the detection rod becomes thinner and thinner due to oxidation of the antioxidant itself. From these facts, the compounding range of the component c is set to 10 to 20 wt%.

[0016]

When a detection rod is immersed in molten steel of a casting mold, Karman vortices are regularly generated behind the detection rod, and an impact having a frequency corresponding to the frequency of occurrence acts on the detection rod to vibrate the detection rod. I do. This vibration is measured by the vibration detecting means.
Between the frequency of the sensing rod and the diameter of the sensing rod and the flow rate of molten steel,
Since the dimensionless relational expression (Strohhal number) = (vibration frequency of the detection rod) x (diameter of the detection rod) / (flow rate of molten steel) exists, it was obtained by measurement with the known diameter of the detection rod. The molten steel flow velocity can be calculated from the frequency of the detection rod. By making the material of the detection rod a sintered body containing the above-mentioned a, b and c as main components, the erosion resistance to molten steel and molten powder is improved, and the life of the detection rod is extended. Even if these components a, b, and c are mixed in a slab as a product, they do not cause a problem in the quality of the slab. The detection rod has a diameter of 5 to 30 mm,
By setting the length to 100 to 400 mm, a sufficient vibration output can be obtained even for a slow molten steel flow.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will now be described with reference to the illustrated embodiments. FIG. 1 is an explanatory view of a main part of a flow velocity measuring device according to the present invention. This flow velocity measuring device is composed of a measuring rod 30, a strain gauge 25 as a vibration detecting means, and a calculator (not shown). The measuring rod 30 is further composed of a detecting rod 11 and a supporting rod 20 supporting the same. .

As the detection rod 11, a cylindrical hollow rod with a bottom is mainly used. The detection rod 11 may be solid, but is preferably hollow from the viewpoint of mechanical strength when the material is the same amount. If it is hollow, the detection rod 11
In addition, it is possible to provide a thermocouple internally, and to perform temperature control of the molten metal to be discharged while simultaneously detecting an abnormal situation such as melting and breakage of the detection rod 11 at an early stage. In addition, the tip of the detection rod 11 does not need to be particularly hemispherical, and generally, planar processing is sufficient.

The dimensions of the detection rod 11 are 5 to 30 mm in diameter,
Select a length in the range of 100 to 400 mm. Detection rod 11
Has an influence on the detection sensitivity of the molten steel flow. The larger the diameter r, the greater the pressure received from the molten steel flow, so that a sufficiently large vibration output can be obtained even with a slow molten steel flow. The length also affects the detection sensitivity. The detection rod 11 has a tip
A range of 180 mm is immersed in molten steel for use.

As a material of the detecting rod 11, a refractory having sufficient heat resistance and corrosion resistance (melting resistance) at the operating temperature is selected. For example, molybdenum 60-80 wt%, zirconia 10-30 wt%, graphite 10-20 wt%
Can be used. Molybdenum is used because it has a high melting point (2630 ° C.), is excellent in erosion resistance to molten steel, is sticky, and is excellent in workability. Other refractory metals can be used instead of molybdenum. Other high melting point metals include, for example, vanadium (melting point: 1835 ° C), niobium (2520 ° C),
Examples include tantalum (2990 ° C.), chromium (1890 ° C.), tungsten (3380 ° C.), manganese (1244 ° C.), technetium (2170 ° C.), and rhenium (3180 ° C.). These may be used alone or in the form of an alloy. Considering costs and the like, molybdenum is realistic. If the amount exceeds 80% by weight, the rate of erosion to molten powder increases, and
If the content is less than wt%, the rate of erosion to molten steel increases, so the proper compounding range is in the range of 60 to 80 wt%.

Zirconia is used for the purpose of improving the erosion resistance to molten powder as a metal oxide. Other ceramics can be used instead of zirconia, and examples thereof include alumina, yttrium oxide, silica, silicon carbide, and silicon nitride. These can be used alone or in combination. If the amount is too large, molding of the detection rod becomes difficult, and if the amount is too small, the erosion resistance to molten powder becomes insufficient. The proper mixing range is in the range of 10 to 30 wt%.

Graphite is an antioxidant and prevents oxidation of high melting point metals such as molybdenum. The proper range of the amount is 10 to 20 wt%.

Next, a test performed for evaluating the erosion resistance of the detection rod of the present invention will be described. (Test 1) A erosion test was performed on molten steel and molten powder by changing the refractory used as the material of the detection rod, and these were compared. The refractories to be tested include those made of only high-melting-point metals, molybdenum and tungsten, those made of ceramics, only of zirconia and alumina, and those made of a mixed sintered body of high-melting-point metal and ceramic. Alumina graphite, zirconia graphite which is a mixed sintered body of nitride, ceramics and graphite as an antioxidant,
Furthermore, molybdenum-zirconia-graphite, which is a mixed sintered body of a refractory metal, ceramics and an antioxidant, was taken up. The erosion rate is expressed as a erosion index with respect to the erosion rate of molybdenum-10wt% zirconia-10wt% graphite, which exhibited the best erosion resistance for both molten steel and molten powder, as 1.0. did. Table 1 shows the results of the melting test of these refractories. still,
The erosion conditions were as follows. Detecting rod diameter: 10mm Detecting rod length: 300mm Immersion depth: 60mm Molten steel: Medium carbon steel Molten powder: Melting point: 1100 ° C, basicity: 1.2 Test temperature: 1550 ° C Test time: 5 hours Looking at the test results, molybdenum- 10wt% zirconia
As described above, 10 wt% graphite has the best erosion resistance to molten steel and molten powder, and is most suitable as a detection rod for a molten steel flow meter. Alumina and zirconia also have excellent erosion resistance to molten steel and molten powder, but these ceramics are inferior in workability, are brittle, and need to be preheated due to the occurrence of cracks against rapid temperature rise. For reasons such as
These cannot be used alone. Further, high melting point metals such as molybdenum and tungsten have excellent workability and have excellent erosion resistance to molten steel, but are slightly inferior to erosion resistance to molten powder as compared with the ceramics. Alumina graphite and zirconia graphite are extremely excellent in erosion resistance to molten steel and molten powder, but cannot be used as a material for forming a detection rod due to poor workability.

[0024]

[Table 1]

(Test 2) Molybdenum-10 wt.
% Zirconia-10 wt% graphite was confirmed to have the best erosion resistance to molten steel and molten powder. Next, the erosion test was performed while changing the mixing ratio of molybdenum, zirconia, and graphite. Table 2 shows test results
Shown in In order to compare the erosion resistance, the erosion index of molybdenum-10 wt% zirconia-10 wt% graphite was set to 1.0 as in the case of Example 1. The test conditions are the same as in Test 1. Since molybdenum is a high melting point metal and has good erosion resistance to molten steel, the higher the molybdenum content, the better the detection rod of the molten steel flow meter. However, it is difficult to measure the flow velocity for a long time by itself because it is eroded by the molten powder which is an oxide. From these, various contents of molybdenum, zirconia, and graphite were changed to produce various refractories, and erosion tests were performed on molten steel and molten powder.
The applicability of the molten steel current meter as a refractory was examined.

[0026]

[Table 2]

According to the test results, the composition of the refractory is such that the molybdenum content is 60 to 80 wt% and the zirconia content is 1%.
0-30wt%, graphite content 10-20wt
%, The erosion resistance was good, and it was confirmed that it was suitable as a refractory for a molten steel flow meter.

(Test 3) Molybdenum-10 wt.
A plurality of types of refractory detection rods of 10% zirconia-10% by weight graphite were manufactured by changing the diameter and length, and each of these detection rods was tested for accuracy of flow rate measurement. In the test, an experiment was conducted in which the flowmeter was rotated after immersing the molten steel flowmeter in the static molten steel in the melting furnace, and the flow rate calculated from the rotation speed was compared with the flow rate obtained from the measured value of the flowmeter. The conditions of the flow velocity measurement experiment are as follows. Table 3
Shows the measurement results. Molten steel: medium carbon steel Melting temperature: 1550 ° C Melting furnace diameter: 500 mm Depth of immersion of detection rod in molten steel: 20 to 200 mm As a result of the test, detection rod has a diameter of 5 to 30 mm and a length of 100 to 100
The flow rate measurement accuracy at 400 mm was as small as ± 5% or less, which proved to be a dimension suitable as a detection rod of a molten steel flow meter.

[0029]

[Table 3]

(Test 4) The durability of the detection rod of the present invention was tested using an actual casting mold. When the molten steel flow meter was set on the actual casting mold and the molten steel flow rate was continuously measured, ±
It was possible to measure continuously for 5 hours while maintaining the accuracy in the range of 5%. The flow rate of the molten steel measured at this time was 15 to 2
It was 0 cm / s. The continuous casting conditions of medium carbon steel slab applied in the actual machine test are shown below. Detector rod composition: molybdenum-10 wt%, zirconia-10 wt%, graphite Detector rod diameter: φ10 mm Detector rod length: 300 mm Detector rod immersion depth: 60 mm Casting speed: 1.8 m / min Casting mold width ( Length of inner side of long side): 1250mm Thickness of casting mold (length of middle side of short side)): 250mm Length of casting mold: 900mm Heating temperature of molten steel in tundish: 5 to 40 ° C Immersion nozzle shape: Downward 30 degrees, 2 Hole type Immersion nozzle immersion depth: 300mm From the test results above, the detection rod for molten steel flow velocity measurement of the present invention is excellent in erosion resistance to both molten steel and molten powder, and this detection rod is continuously used for a long time. It was confirmed that the material could withstand the measurement.

As shown in FIG. 1, such a detection rod 11 is used by being mounted on a support rod 20. The support rod 20 is composed of a mounting part 21, a thin part 22, and a fixing part 23. The detection rod 11 is mounted on the mounting part 21, and is detachably attached to the support rod 20 by externally fitting the tubular member 15. It has a configuration.

The fixing portion 23 is a portion to be gripped by a lifting mechanism (not shown), and is firmly fixed to the lifting mechanism so as not to be affected by peripheral vibrations.

The vibration of the detection rod 11 is detected by strain gauges 25, 25 attached to the side surfaces of the thin portion 22, which is the fulcrum of the vibration. The strain gauges 25, 25 are configured to detect the bending of the thin portion 22 and detect the frequency of the thin portion 22, that is, the frequency of the detection rod due to Karman vortex, from the repetition period of the bending. As the vibration detecting means, an optical displacement meter using an LED, an infrared ray, a laser, or the like can be used instead of the strain gauges 25, 25. However, when light in the infrared wavelength range is emitted from molten steel, use of infrared light is not preferable. When a light-shielding substance such as smoke is present, it is preferable to use the strain gauges 25.

In such a molten metal flow rate measuring device, the detection rod 11 is attached to the support rod, and the support rod fixing portion 2
3 is lifted and lowered by a lifting device (not shown).
Is positioned so as to cross this flow in the flow of the molten metal, and the shock repeatedly received due to the release of the Karman vortex is measured and recorded in the form of a vibration frequency, and after the measurement or in real time, the discharge flow from the vibration frequency is measured. The flow velocity V is calculated. Derivation of the flow velocity of the molten metal from the vibration frequency is performed by previously obtaining a relational expression between the vibration frequency f and the flow velocity V using the same measurement rod, and applying the measured vibrational frequency f to this relational expression. The flow velocity V is calculated as follows: V = a · f · D + b (where D: diameter of detection rod, a, b: constants)
The flow velocity V and the frequency f should be in a linear relationship, but actually deviate from the linear relationship because the stiffness of the portion where the strain gauge is attached is also involved. For this reason, when more accuracy is required, a calibration curve indicating the relationship between the flow velocity V and the vibration frequency f × the diameter D of the detection rod is obtained for each type of the measurement rod 30, and this calibration curve is used for subsequent actual measurement. It is used to calculate the flow velocity from the vibration frequency in.

[0035]

According to the present invention, the erosion resistance of the detection rod for measuring the flow velocity of molten steel is increased for both molten steel and molten powder, and the life thereof can be greatly extended. Therefore, it becomes possible to continuously measure the molten steel flow velocity in the casting mold for a long time, and it is possible to obtain an evaluation standard of the molten steel flow in the casting mold for producing a high-quality cast slab. The measurement result is fed back to a variable device of the molten steel supply amount to control the flow of the molten steel in the casting mold, thereby making it possible to produce a high quality cast slab.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a detection rod for measuring molten steel flow velocity of the present invention and its peripheral structure.

FIG. 2 is a schematic view showing various flows of molten steel in a casting mold.

FIG. 3 is an illustration showing an immersion nozzle positioned in a casting mold.

FIG. 4 is an explanatory diagram of a basic principle of measuring a flow velocity from vibration detection caused by a Karman vortex.

FIG. 5 is a schematic view showing a state in which Karman vortices are emitted downstream of the detection rod.

FIG. 6 is a graph showing a relationship between a frequency detected by a vibration detection unit and an output.

[Explanation of symbols]

c Karman vortex d Upflow in casting mold e Downflow in casting mold 1 Casting mold 1a, 1b Short side wall 1c, 1d Long side wall 2 Immersion nozzle 2a, 2b Discharge port 3 Melting powder 4 Space in casting mold 5 Detecting rod 5a Long side surface 11 Detection rod 15 Cylindrical member 20 Support rod 21 Mounting part 22 Thin part 23 Fixed part 25 Strain gauge 30 Measurement rod

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Mizukami 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Masafumi Hanao 4-chome, Kitahama, Chuo-ku, Osaka-shi, Osaka No. 5-33 Sumitomo Metal Industries, Ltd. (72) Inventor Masayuki Kawamoto 4-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Inventor Atsushi Hayashi Minami-Beppu-cho, Settsu-shi, Osaka 16-16 Inside Heraeus Electronight Co., Ltd. (72) Inventor Yukio Terauchi Inside 16-16 Heraeus Electronight Co., Ltd.

Claims (3)

[Claims] 1. A method for immersing a predetermined range on a free end side of a detection rod having one end fixed and the other end as a free end into molten steel so as to cross a molten steel flow, and to generate Kalman generated downstream of the detection rod. In a method of measuring the vibration of a detection rod caused by a vortex and estimating the flow rate of molten steel in a casting mold by applying the relational expression between the detection rod frequency and the flow rate of molten steel determined in advance, the dimensions of the detection rod are set to a diameter 5-30mm, length 100-400m
m) and the material of the sensing rod is: a) One or more refractory metals selected from molybdenum, vanadium, niobium, tantalum, chromium, tungsten, manganese, technetium and rhenium
0~80wt% b) zirconia, alumina, yttrium oxide (Y ₂ O
₃ ), silica, silicon carbide (SiC), silicon nitride (Si ₃
Sintering by no N ₄ mixture 10-20 wt% of a one or both of one or more kinds of ceramics 10 to 30 wt% c) graphite or boron nitride is selected from among the), b, a main component c A method for measuring the flow velocity of molten steel in a casting mold, comprising: 2. The material of the detecting rod is molybdenum 60-80.
wt%, zirconia 10-30 wt%, graphite 1
A method for measuring a flow rate of molten steel in a casting mold, comprising a sintered body containing 0 to 20 wt% as a main component. 3. A detection rod for immersing in molten steel in a casting mold and measuring the flow velocity of the molten steel based on vibration generated by the flow of the molten steel, the size of which is 5 to 30 m in diameter.
m, the length is 100 to 400 mm, and the material is
Molybdenum 60-80wt%, zirconia 10-30w
A sensing rod for measuring a flow rate of molten steel used in a method for measuring a flow rate of molten steel in a casting mold, wherein the detection body is made of a sintered body mainly containing t% and 10 to 20% by weight of graphite.