JPH0567893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for measuring the temperature of molten metal, such as molten steel in a tundish.

[Problems to be solved by conventional technology and invention]

The temperature of molten steel in the tundish of continuous casting equipment fluctuates due to various disturbances during casting. Generally, in a continuous casting process, a certain amount of molten steel is injected from a ladle into a tundish, and distributed from the tundish into several molds to complete rapid solidification, and the tundish is located in an intermediate plant. In the first place, the main role of tandaitsuyu is to
It plays the role of temporarily holding molten steel, floating and separating inclusions, and distributing it to multiple molds. In either case, temperature conditions are the dominant process, and in order to ensure efficient operation, it is important to understand the molten steel temperature in the tundish. The temperature of the molten steel in the tandate is affected by the large amount of heat removed from the furnace wall bricks or the surface of the molten steel in the early stages of casting, and since it is located in the middle of a continuous process, there is an imbalance between the amount of molten steel injected from the ladle and the amount of molten steel discharged into the mold. , the molten steel capacity fluctuates sharply, and the temperature fluctuates widely. Also,
Towards the end of casting, if no heating, cooling, etc. are applied, the temperature will gradually drop, but the rate of temperature drop will vary depending on the number of castings of the tundish used and variations in preheating before casting. When the molten steel temperature in the tundish decreases, the effect of floating inclusions decreases and clogging of the casting nozzle occurs, so it is extremely important to accurately grasp the molten steel temperature in the tundish.

In order to solve the above problems, recently,
Attempts have been made to employ a device for heating molten steel in a tundish, which is disclosed in Japanese Unexamined Patent Publication No. 61-249655. This system feeds back the results of measuring the molten steel temperature to the power control section of the induction heating device to compensate for the temperature drop from the initial stage to the final stage of casting.

By the way, the currently most widely used method for measuring the temperature of molten steel of this type uses a consumable immersion thermocouple. However, since this is a discontinuous temperature measurement, it is impossible to measure the temperature at intervals of about 3 minutes or less, and as a result, it is difficult to control the temperature of molten steel, which fluctuates by about ±10 degrees Celsius every few tens of seconds, as seen in the early stages of casting. It cannot be used at all. Furthermore, in view of the running costs of consumable immersion thermocouples, it is completely impossible to measure temperature each time. Therefore, as a method to reduce running costs, as a commercially available product,
There is a probe in which a platinum-platinum-rhodium thermocouple is inserted inside a protective tube (made of zirconia ceramics, aluminum carbon, etc.) that is highly heat resistant to molten metal. However, this is due to the slightly higher cost of the thermocouple, and although the lifespan of about 10 hours is guaranteed, the thermocouple generates heat from the protective tube itself.
Problems remain, including carburization and other effects caused by CO gas, which deteriorates reproducibility over time and, in the worst case, can lead to wire breakage.

Under the current state of temperature measurement, the most promising method is the optical temperature measurement method. Examples of this include the techniques described in Japanese Patent Application Laid-open Nos. 56-60323 and 60-105929, in which a heat-resistant conduction pipe is inserted into molten steel and an inert gas is supplied. Since the tip of the conduit is perforated, the molten steel surface is exposed, and the radiant energy obtained from that surface is sampled with a radiation thermometer.
This is a method of detecting temperature. With this method, the protective tube has a simple shape and suffers only the necessary minimum wear and tear damage. Furthermore, since the running cost of the sensor itself is the most advantageous among temperature sensors, it is thought that optical temperature measurement methods will become mainstream in the steel industry in the future.

However, as is well known, when an inert gas is blown into the molten steel, the surface of the molten steel facing the opening of the conduction pipe is rapidly cooled.
In fact, it has been reported that when Ar gas is sprayed onto the surface of molten steel, the temperature decreases by approximately 7°C to 10°C. In this case, it is assumed that it is difficult to correct the base down from the true value depending on how the flow rate of the inert gas is adjusted. Furthermore, since variations in the surface shape of the molten steel also occur, there is naturally a variation in the apparent emissivity, which is expected to reduce measurement reproducibility.

For optimal control of molten steel temperature in tandem production,
It is required that the difference from the solidification temperature of molten steel be extremely small, and this is to save energy by lowering the temperature base of the previous process. In the past, the temperature difference (referred to as ΔT) was ΔT=30
The temperature was ~40℃, but recently, operational improvements and plant improvements have been implemented with the goal of achieving ΔT=10~20℃. Therefore, the target of ΔT can be achieved, the running cost is low, and the reproducibility is continuously σ = 5℃ or less without color loss compared to the current reproducibility of consumable immersion thermocouples (σ = 2℃). There is a need to develop an optical temperature measurement method.

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a temperature measuring device that has low running costs, has high responsiveness and reproducibility in temperature measurement, and is capable of continuous temperature measurement.

[Means to solve the problem]

The present invention for solving the above problems includes an outer tube whose distal end is closed and an inner tube inserted into the outer tube with a gap and whose distal end is spaced apart from the inner surface of the distal end of the outer tube. an immersion tube in which the tip of the tube is immersed in molten metal; an optical type that is disposed on the base side of the inner tube and measures the temperature of the radiant energy inside the tip by looking at the tip of the outer tube through the inner tube; and a thermometer; blowing a purge gas from a position above the surface of the molten metal into the atmosphere from an opening formed at a position above the surface of the molten metal in a space communicating with the gap, and purging the gas in the gap. It is characterized by comprising: a gas purge means that induces gas and forcibly discharges it into the atmosphere; and;

[Effect]

Unlike a consumable immersion thermocouple, the present invention measures temperature continuously, so it is possible to grasp the temperature change of the molten metal over time, and based on this, when controlling the temperature of the molten metal. It is an effective method.

In addition, in the present invention, unlike the conventional method in which the emissivity of molten metal is measured while injecting inert gas into a hollow tube with an open tip, the tip of the immersion tube with a closed tip measures the heat of the molten metal. Since the optical thermometer detects the optical radiation emitted by Temperature measurement can be performed with no fluctuation and high measurement reproducibility accuracy.

Furthermore, unlike the one-time use of consumable immersion thermocouples, it can be used continuously and repeatedly, significantly reducing running costs.

On the other hand, JP-A No. 62-217129 and Utility Model Application No. 50-
Publication No. 87979 describes that the temperature is measured by gazing at the tip of a tube immersed into molten metal using a radiation pyrometer. does not have.

However, according to the present invention, an inner tube is provided that is inserted into the outer tube with a gap and whose tip is spaced from the inner surface of the tip of the outer tube, and further, the gas in the gap is forcibly discharged to the outside of the outer tube. Gas purge means were provided. As described later, for example, A
When _{a 2} O ₃ -C type material is used, it mainly generates CO gas, which absorbs the wavelength in the wavelength band used in the radiation thermometer, resulting in a decrease in measurement accuracy.

In contrast, according to the present invention, by providing a gas purge means and forcibly expelling, for example, CO gas in the inner tube and the gap between the inner tube and the outer tube to the outside, the above-mentioned decrease in measurement accuracy can be prevented. It is possible to perform highly accurate temperature measurement.

[Specific structure of the invention]

The present invention will be explained in more detail below.

FIG. 1 shows a first embodiment. For example, in order to measure the temperature of molten steel M in a tundish, a manhole cover 1 is provided in the temperature measurement hole of the lid, and a temperature measurement device described below is attached to the manhole cover 1. is fixed.

That is, a flanged cylindrical support metal fitting 2 is bolted to the manhole cover 1, and a purge unit 3, an air cooling jacket 4, and a protective cap 5 are sequentially fixed to the flange. A radiation thermometer 6 is provided inside the air-cooled jacket 4, and its signal is transmitted via a guide path 7 to an external signal processing device (not shown).
It is beginning to be given to A ceiling window 8 is arranged in front of the radiation thermometer 6.

On the other hand, on the support hardware 2, the immersion tubes, that is, the outer tube 9 and the inner tube 10 are arranged concentrically with a gap S.
It is installed with The outer tube 9 has a double layer structure, and has a slag-resistant protection tube 9A ₁ , a heat-resistant protection tube 9A ₂ , and a heat-resistant tip protection tube 9B on the outside, and a protection tube made of stainless steel or the like on the inside. It has a molten steel protection tube 9D with an aggregate 9C, and these tubes 9A to 9D are made of a material of, for example, A ₂ O ₃ -C, and are supplied with A ₂ O ₃ or the like to the supporting hardware 2 via a metal socket 11. It is attached by ceramic bolts 12.

The tip of the outer tube 9 is sealed with a closure 13 made of A ₂ O ₃ -C or the like, and a target 14 made of high alumina or the like is provided thereon.

On the other hand, the inner tube 10 is made of, for example, alumina or stainless steel, and is fixed to the inner surface of the support metal fitting 2, for example, by welding.

Further, the purge unit 3 is provided with a conduit 15 for blowing an inert gas such as Ar, the tip of which passes through the inner tube 10 and extends through the opening 2 of the support metal fitting 2.
They are arranged with a gap in a. As a result, when Ar gas is blown from the conduit 15 and discharged from its tip, gas, which will be described later, in the gap S between the outer tube 9 and the inner tube 10 is attracted, and the ejector effect causes the opening 2a and the conduit 15 to flow. It is discharged through between the tip and the tip. Reference numeral 16 denotes a gas blowing pipe for cooling the radiation thermometer 6, such as Ar gas, since the ambient temperature is about 200°C.

When the tip of such a device is immersed in molten steel M, the temperature of the target 14 eventually reaches a state of thermal equilibrium with the temperature of molten steel M due to the heat of the molten steel M. In this state, the radiation thermometer detects target 1.
4, grasp the heat from there, and extract it as a temperature signal. Thereby, the molten steel temperature at that point in time is detected. Then, the temperature is continuously measured while the tip is immersed in the molten steel M for a certain period of time.

By the way, as the material for the outer tube 9, in addition to the above-mentioned examples, Mo- _ZrO2- based materials can also be used, but in terms of erosion resistance and heat shock resistance,
A ₂ O ₃ -C type is most suitable. However,
In this system, CO gas is mainly generated by the heat of molten steel. This CO gas has the effect of absorbing wavelengths in the wavelength band (500 nm to 1500 nm) used in radiation thermometers. Therefore, in order to prevent the accuracy from decreasing due to this, the CO gas is purged by blowing out Ar gas through the conduit 15.

In the above example, as the material of the inner tube, other materials with a dense structure such as SiO ₂ or ZrO ₂ can be used. This inner tube prevents the aforementioned CO gas from entering the radiation temperature measurement zone.

The emissivity of the target can be easily measured in advance using a blackbody furnace or the like, but it is desirable to have good reproducibility and a value close to 1.0. The shape of the target need not be flat, but may be convex or concave at the center, as shown in FIGS. 3a and 3b. Furthermore, it is possible to use the plug 13 itself as a target, but if the plug 13 generates CO gas or the emissivity of its material is not clear in advance, it is possible to use a target as shown in the example in Figure 1. , it is preferable to provide a separate target 14.

In FIG. 1, the small hole 10a is formed at the tip of the inner tube 10 so that gas (Ar gas, etc.) blown from the blowing tube 16 passes directly into the gap S through the small hole 10a, and the target 14 is cooled. This is to prevent it from happening.

Furthermore, as an optical thermometer, a monochromatic thermometer, a multi-wavelength thermometer, etc. can be used, and an optical fiber is inserted into the inner tube to optically connect the target and the thermometer. Good too.

In the example in Figure 1, the inner tube has an open tip, but as in the example in Figure 2, the inner tube 10' made of, for example, Mo-ZrO ₂ is closed, and its tip is connected to the outer tube. The target 13 may be provided in close contact with the inner tube 9 and inside the inner tube 10'. In this case, it is desirable to provide a heat transfer material 17 made of graphite or the like between the tubes 9 and 10' to improve thermal conductivity. In this case as well, purge the CO gas.

The immersion depth L of the immersion tube into the molten steel M is preferably L≧2D, where D is the outer diameter of the immersion tube. More preferably, 2D≦L≦3D. This is to ensure desired measurement accuracy as shown in FIG.
Furthermore, this condition is true regardless of the wall thickness or material of the inner and outer tubes.

On the other hand, only the outer tube described above is subject to wear and tear and is replaced after a certain period of use. The outer tube is A
When using ₂ O ₃ --C ceramics, the replacement cost is sufficient, but when using Mo--ZrO ₂ ceramics, the cost increases. However, if you ignore this cost point, you can also use Mo-ZrO ₂ type materials, and in that case, no CO gas will be generated, so you will need to use double pipes to purge the CO gas. It can be used as a single tube.

The present invention can be applied not only inside a tundish but also inside a blast furnace gutter, torpedo, ladle, converter, iron pouring ladle, mold, etc.

〔Example〕

Next, examples will be shown.

(Example 1) Using the temperature measuring device shown in FIG. 1, the temperature of molten steel in a tundish was measured over a period of one month. The outer tube was made of A ₂ O ₃ -C ceramic, and the inner tube was made of Mo-ZrO ₂ ceramic.

As a result, the measurement accuracy of the temperature measuring device was found to be σ=4°C. When we attempted to compare the results with a consumable immersion thermocouple, which has a high measurement accuracy of σ = 2°C, we found a high correlation as shown in Figure 5.

In addition, the material of the outer tube was changed to Mo-ZrO ₂ type,
When we attempted continuous temperature measurement during continuous casting, we were able to detect rapid temperature fluctuations at the beginning and end of casting, which had been difficult to detect until now, as shown in Figure 6. Moreover, it was found that the lifespan was long, approximately 30 hours.

(Example 2) The temperature of molten steel in a mold was measured using the immersion tube shown in the example shown in FIG. In this case, both the inner and outer tubes are Mo−ZrO ₂
The device was made of ceramic, and an optical fiber was installed inside to optically connect it to a narrow-field multi-wavelength thermometer. As a result, continuous temperature measurement for about 10 hours was possible.

〔Effect of the invention〕

As described above, according to the present invention, the measurement accuracy is sufficiently high for practical use, and continuous temperature measurement is possible while reducing running costs.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the first temperature measuring device example, Fig. 2 is a longitudinal cross-sectional view of another example, Fig. 3 is an illustration of targets a and b, and Fig. 4 is L/D ratio and measurement. A correlation diagram with accuracy, FIG. 5 is a graph showing measurement accuracy, and FIG. 6 is a graph of continuous temperature measurement results. 1... Manhole cover, 6... Radiation thermometer, 9...
...outer tube, 10,10'...inner tube, 13...obstruction, 14...target, 15...conduit, S...
gap.

Claims (1)

[Scope of Claims] 1. An outer tube with a closed tip, and an inner tube inserted into the outer tube with a gap and whose tip is spaced apart from the inner surface of the tip of the outer tube, the tip of the outer tube being separated from the inner surface of the tip of the outer tube. an immersion tube which is immersed in molten metal; an optical thermometer that is disposed on the base side of the inner tube and measures the temperature of the radiant energy inside the tip of the outer tube by looking through the inner tube; ; Purge gas is blown into the atmosphere from a position above the surface of the molten metal through an opening formed at a position above the surface of the molten metal in a space communicating with the gap, thereby attracting the gas in the gap and releasing it into the atmosphere. A temperature measuring device for molten metal, comprising: gas purge means for forcibly discharging the metal into the molten metal.