JPH0238932A - Continuous temperature measuring method for molten metal - Google Patents

Abstract

PURPOSE:To measure temperature continuously with high accuracy by detecting radiant energy from the molten metal by an optical temperature measuring meter while bubbling inert gas in the molten metal. CONSTITUTION:The tip of a hollow pipe 9 is dipped partially in the molten steel M and then the argon gas is supplied into the hollow pipe 9 under constant pressure at a constant flow rate and bubbled from the tip. In this state, the radiant energy from the molten steel M is sampled by the radiation thermometer 6 and led out as a temperature signal. In this case, variation of the radiant energy is grasped at a sampling period shorter than the waving period of the bubbling to extract only maximum values, which are averaged to obtain a temperature value.

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 tie dish.

[Prior Art and Problems to be Solved by the Invention] The /$w4 temperature in the tundish of continuous casting equipment fluctuates due to various disturbances during casting.

Generally, a certain amount of molten steel is poured from a ladle into a tundish,
It is distributed and injected into several molds from the tundish,
In the continuous casting process, where rapid solidification is completed, the tandai is located at an intermediate plant. In the first place, the main roles of the tundish are: ■ temporarily holding molten steel, ■ floating and separating inclusions, and ■ distributing 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 tundish is determined 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 because it is located in the middle of the 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. In addition, if no heating, cooling, etc. are added to the final stage of casting,
Although the temperature gradually decreases, the rate of temperature decrease varies depending on the number of castings of the tundish used and variations in preheating before casting. If the molten steel temperature in the tundish is lowered, the effect of floating inclusions is reduced and the casting nozzle is clogged, so it is extremely important to accurately grasp the molten steel temperature in the tundish.

In order to solve the above problems, recently, Japanese Patent Application Publication No. 6
Attempts have been made to employ a molten steel heating device in a tundish shell disclosed in Japanese Patent No. 1-249655.

This is to feed 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 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 becomes impossible to measure at intervals of about 3 minutes or less, and as a result, it cannot be used to control the temperature of molten steel, which fluctuates by about ±10°C every few tens of seconds, which occurs in the early stages of casting. In view of running costs, it is simply not possible to measure temperature each time. Therefore, as a method to reduce running costs, a commercially available probe with a platinum-platinum rhodium thermocouple inserted inside a protective tube (made of zirconia ceramics, alumina carbon, etc.) that is highly heat resistant to molten metal is available. be. However, this is because the cost of the thermocouple is a little high, and although the lifespan of about 10 hours is ensured, the thermocouple is affected by carburization etc. due to the CO gas generated from the protective tube itself, and the thermocouple ages over time. Problems remain, such as poor reproducibility and, in the worst case, a disconnection situation.

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 JP-A-56-60323 and JP-A-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 surface of the molten steel is exposed, and the temperature is detected by sampling the radiant energy obtained from the surface using a radiation thermometer. With this method, the protection tube has a simple shape and suffers only minimal wear and tear damage. Furthermore, the running cost of the sensor itself is the most advantageous among temperature sensors, so in the future,
Optical temperature measurement methods are expected to become mainstream in the steel industry.

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 about 7°C to 10°C. In this case, it is assumed that it is difficult to correct the base down with the true value by adjusting the flow rate of the inert gas.

Optimum control of the molten steel temperature in the tundish requires that the difference from the molten steel solidification temperature be extremely small, and this is due to the energy-saving effect of 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°C, but recently, operational improvements and plant improvements have been carried out with the goal of reducing ΔT to -10 to 20°C. Therefore, the target of ΔT can be achieved, the running cost is low, and the current reproducibility of consumable immersion thermocouples (σ=2℃) is achieved.
There is a need for the development of a continuous optical temperature measurement method with a reproducibility of σ = 5°C or less, which is comparable to that of the conventional method.

SUMMARY OF THE INVENTION Therefore, 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 continuously measuring temperatures with high accuracy.

[Means to solve the problem]

In order to solve the above problems, the method of the present invention is to provide an optical thermometer on the base side of a submerged hollow tube with an open tip, which measures the temperature based on the emissivity 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 temperature value is determined based on the average value of the maximum value of the radiant energy within the wave period of the interface with the molten metal.

[For production]

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.
It is possible to measure the temperature with high accuracy, which is always different from the temperature of a pseudo-smooth surface of molten metal.

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 a 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 protection camp 5 are fixed in this order to the flange. A radiation thermometer 6 is provided inside the air cooling jacket 4, and its signal is transmitted through the guide path 7 and the A radiation thermometer 6.
The temperature results are taken into the arithmetic unit 10 via the D converter 8 and subjected to arithmetic processing, which will be described later, and are displayed on the temperature display 1). Further, a ceiling window 1) is arranged in front of the radiation thermometer 6.

On the other hand, an immersion hollow tube 9 is arranged on the support hardware 2, and this hollow tube 9 has a double layered structure, and has slag protection tubes 9A, 9A and a tip protection tube 9B on the outside thereof, 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, AI! 203
-C material, and is attached to the supporting hardware 2 via a metal socket 1) with a ceramic bolt 12 made of Aj'zOz or the like.

Further, the gas blowing unit 3 is provided with a conduit 13 for blowing inert gas such as a meter, and a constant pressure valve 14 is provided in the middle of the conduit 13.
and a flow rate adjustment valve 15 are arranged. 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 shown in Figure 3, along with bubbling,
The static pressure balancing surface of molten steel repeats uneven waves. In the present invention, changes in radiant energy are grasped using a short sampling period less than this wave period, only the maximum value is extracted, and this is averaged to determine the temperature value. shall be.

By the way, as for the material of the hollow tube 9, in addition to the above examples,
Mo-Zr0t type materials can also be used, but in terms of erosion resistance and heat shock resistance, Aj! zO*-
C type ones are optimal. However, in this system, CO gas is mainly generated due to the heat of the molten steel. This CO gas has a wavelength band (500 nm to 1
500nm) has the effect of absorbing that wavelength6
Therefore, in order to prevent the accuracy from decreasing due to this, the C
Purging O gas by blowing out Ar gas through the conduit 13 also has the effect of eliminating the influence of CO gas.

By the way, as the optical thermometer, a monochromatic temperature needle, a multi-wavelength thermometer, etc. can be used. Furthermore, sampling of radiant energy can also be performed using optical fibers.

The immersion depth L of the hollow tube into the melt@M is preferably L≧2D, more preferably 2D≦, where D is the outer diameter of the hollow tube.
L≦3D.

On the other hand, the hollow tubes described above wear out and are replaced after a certain period of use. Hollow tube is Aj! ! O.

-C type ceramics are well worth the replacement cost, but Mo-Zr0t type ceramics lead to higher costs. However, if we ignore this cost point, Mo.
Zr0z-based materials can be used.

In addition, the present invention can be applied not only inside the 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 A1.02-C
It is made of ceramic.

The measurement conditions are as follows.

The immersion length of the outer tube 9 is 500fi. The outer diameter is 60mφ and the inner diameter is 20mφ. Argon gas pressure: 3kg/aJ. Flow rate: 3kg/Hr. Molten steel temperature: 71510~1570℃. In this case, the molten steel wave period is 0.3~0. It was .5 seconds. Figure 2 shows the relationship with the argon gas blowing flow rate. Therefore, the sampling period was set to 10 m5 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. 3. As shown in FIG. 3, it can be seen that the temperature fluctuations caused by the molten steel waves caused by bubbling are completely 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 4.

In addition, when we tried continuous temperature measurement during connected casting by changing the material of the hollow tube to a Mo-Zr0z system, we found that the temperature suddenly increased at the beginning and end of casting, which had been difficult to ascertain until now. I was also able to understand the fluctuations. Furthermore, it was found that the lifespan was as long as 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]

Figure 1 is a longitudinal cross-sectional view of an example of a temperature measuring device, Figure 2 is a diagram showing the relationship between the molten steel wave period and Ar flow rate, Figure 3 is a relationship diagram between the molten steel wave period and true temperature of molten steel, and Figure 4 shows the measurement accuracy. The graph shown in FIG. 5 is a graph of the results of continuous temperature measurement. 6... Radiation thermometer, 9... Hollow tube, 10... Arithmetic unit, 13... Inert blowing conduit. 50 Memory Peng Shame-Sho-Kusu-I Bo 7 Edition - Meiichi

Claims (1)

[Claims] (1) An optical temperature meter is provided on the base side of the immersion hollow tube whose tip is open, and measures the temperature based on the emissivity of the tip by looking at the tip, and the hollow tube is immersed in the molten metal. At the same time, while 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, the radiant energy from the molten metal is detected with an optical thermometer,
1. A method for continuous temperature measurement of molten metal, characterized in that the temperature value is determined based on the average value of the maximum value of the radiant energy within the wave period of the interface with the molten metal.