JPH0569454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for continuous temperature measurement 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, or other steps are taken, 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 temperature of molten steel 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, alumina 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 ensured, 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 desired method is an 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,
In this method, the molten steel surface is exposed and the radiant energy obtained from the surface is sampled using a radiation thermometer to detect the temperature. With this method, the protection tube has a simple shape and suffers only minimal wear and tear damage. Furthermore, since the running cost of the sensor itself is the most advantageous among temperature measurement 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.

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=
The temperature was 30-40°C, but recently, operational improvements and plant improvements have been carried out with the goal of achieving ΔT = 10-20°C. Therefore, it is possible to achieve the above-mentioned ΔT target, has low running costs, and is comparable to the current reproducibility of consumable immersion thermocouples (σ = 2°C), and is a continuous optical system with a reproducibility of σ = 5°C or less. There is a need to develop a method for temperature measurement.

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a temperature measurement method and apparatus that have low running costs and are capable of continuous temperature measurement with high accuracy.

[Means to solve the problem]

The method of the present invention for solving the above problems is to provide an optical thermometer on the base side of a submerged hollow tube with an open tip and measure the temperature based on the radiant energy of the tip. While the hollow tube is immersed in the molten metal, an inert gas is blown into the hollow tube at a predetermined flow rate and discharged from the open tip to bubble into the molten metal, while measuring the radiant energy from the molten metal using an optical thermometer. The method is characterized in that the average value of the maximum value of the radiant energy within the wave period of the interface with the molten metal is taken as the measured temperature value of the molten metal.

[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.

Further, in the present invention, an inert gas is blown into a hollow tube with an open tip at a predetermined flow rate, and is discharged from the tip to bubble into the molten metal. This bubbling is performed because if the molten metal is not stirred by bubbling, the static pressure balancing surface of the molten metal will be constantly exposed to inert gas, which will lower the surface temperature and make it impossible to detect the true molten steel temperature. This is because it disappears.

In this sense, bubbling is effective, but on the other hand, as a result of bubbling, the molten metal surface periodically exhibits uneven waves due to static pressure balance, and the radiant energy from the molten metal surface during concavity and convexity increases. The vector is no longer incident parallel to the radiation thermometer, resulting in temperature measurement errors because the apparent emissivity varies over time.

Therefore, according to the present invention, the temperature is detected with a sampling period equal to or less than the wave period of the molten metal surface, the maximum value of the radiant energy is averaged, and the temperature value is determined based on this. Highly accurate temperature measurement that is always consistent with temperature.

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

[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 the temperature measurement method described below is installed on the manhole cover 1. The device is fixed.

That is, a flanged cylindrical support metal fitting 2 is bolted to the manhole cover 1, and a gas blowing unit 3, an air cooling jacket 4 using air Ai, and a protective cap 5 are fixed in this order to the flange. A radiation thermometer 6 is provided in the air-cooled jacket 4, and its signal is taken into the arithmetic unit 10 via a conduit 7 and an AD converter 8, where the temperature result according to the arithmetic processing described later is displayed on a temperature display 11. It is becoming more and more common. Further, a ceiling window 16 is arranged in front of the radiation thermometer 6.

On the other hand, an immersion hollow tube 9 is disposed on the support hardware 2, and this hollow tube 9 has a double layered structure, with a slag-resistant protection tube 9A ₁ , a heat-resistant protection tube 9A ₂ , and It has a heat-resistant tip protection tube 9B,
It has a molten steel protection tube 9D with a protection tube aggregate 9C made of stainless steel or the like inside, and these tubes 9A to 9D are made of, for example, Al ₂ O ₃ -C, and have a metal socket 1.
1 to the supporting hardware 2 with ceramic bolts 12 made of Al ₂ O ₃ or the like.

Further, the gas blowing unit 3 is provided with a conduit 13 through which an inert gas such as Ar is blown, and a constant pressure valve 14 and a flow rate regulating valve 15 are disposed in the middle of the conduit 13. The tip of the conduit 13 communicates with the inside of the hollow tube 9.

In such a device, after the tip of the hollow tube 9 is partially immersed in the molten steel M, argon gas (Ar gas) is fed into the hollow tube 9 at a constant pressure and a constant flow rate, and bubbling occurs from the tip. let Bubbles are designated by the symbol B. In this state, the radiation thermometer 6 looks at the molten steel M, samples the radiant energy therefrom, and takes it out as a temperature signal.

In this case, as a result of bubbling, the static pressure balancing surface of the molten steel repeats uneven waves as shown in FIG. In the present invention, changes in radiant energy are grasped using a short sampling period equal to or less than this wave period, only the maximum value thereof is extracted, and this is averaged to be used as a temperature measurement value of the molten metal.

By the way, as the material for the hollow tube 9, in addition to the above-mentioned examples, Mo-ZrO ₂ based materials can also be used, but in terms of erosion resistance and heat shock resistance, Al ₂ O ₃ -C based materials are preferred. is the best. 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 13, which has the effect of eliminating the influence of the CO gas.

By the way, as the optical thermometer, a monochromatic thermometer, a multi-wavelength thermometer, etc. can be used. Additionally, fiber optics can also be used to sample the radiant energy.

The immersion depth L of the hollow tube into the molten steel M is preferably L≧2D, where D is the outer diameter of the hollow tube. More preferably, 2D≦L≦3D.

On the other hand, the hollow tubes described above wear out and are replaced after a certain period of use. The hollow tube is Al ₂ O ₃
-C type ceramics are well worth the replacement cost, but Mo--ZrO ₂ type ceramics result in higher costs. However, if this cost is ignored, a Mo-ZrO ₂ based material can be used.

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.

The temperature of the molten steel in the tundish was measured over a period of one month using the temperature measuring device shown in FIG. hollow tube is
It was made of Al ₂ O ₃ -C ceramic.

The measurement conditions are as follows.

The immersion length L of the outer tube 9 is 500 mm. The outer diameter is 60 mm. The inner diameter is 20 mm. Argon gas pressure: 3 Kg/cm ² Flow rate: 3 Kg/Hr. Molten steel temperature: 1510 to 1570°C. In this case, the molten steel wave period is 0.3 to 0.5. It was hot in sec. The relationship with the argon gas blowing flow rate is shown in Figure 4. Therefore, the sampling period was set to 10ms or less. According to this, the data after A/D conversion was at a level that could sufficiently reproduce the raw data. The relationship at this time is shown in FIG. As shown in Figure 5,
It can be seen that the temperature fluctuations caused by the molten steel waves caused by bubbling are perfectly reproduced.

As a result, the measurement accuracy of the temperature measuring device was found to be Δ=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 2.

In addition, the material of the hollow tube was changed to Mo-ZrO ₂ system,
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 3. Moreover, it was found that the lifespan was long, about 30 hours.

〔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 longitudinal cross-sectional view of an example of a temperature measuring device, Fig. 2 is a graph showing a comparison between the temperature measurement value of the present invention and the temperature measured by an immersion thermocouple, and Fig. 3 is a continuous temperature measurement at the beginning and end of casting. Graphs showing the results, FIG. 4 is a relationship diagram between Ar flow rate and molten steel wave period, and FIG. 5 is a relationship diagram between molten steel wave period and molten steel true temperature. 6... Radiation thermometer, 9... Hollow tube, 10... Arithmetic unit, 13... Inert blowing conduit.

Claims (1)

[Claims] 1. An optical temperature meter is provided on the base side of the immersed hollow tube with the tip open, and the temperature is measured based on the radiant energy of the tip, and the hollow tube is immersed in the molten metal. , detecting the radiant energy from the molten metal with an optical thermometer while blowing an inert gas into the hollow tube at a predetermined flow rate and discharging it from the open tip to bubble into the molten metal;
1. A method for continuous temperature measurement of molten metal, characterized in that the average value of the maximum values of the radiant energy within the wave period of the interface with the molten metal is taken as the temperature measurement value of the molten metal.