JPS6222089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an in-furnace device that can be suitably used for measuring the temperature of objects to be heated in a relatively high-temperature furnace, such as measuring the surface temperature of a slab in a heating furnace prior to the manufacturing process of hot-rolled steel sheets. This invention relates to a method for measuring the surface temperature of a heated object.

There is a strong demand for measuring the surface temperature of a slab, which is an object to be heated, continuously and as accurately as possible in the above-mentioned heating furnace.

In other words, if the surface temperature of the slab can be measured accurately, it will be possible to extract the slab from the furnace and proceed to the rolling process immediately after it reaches the predetermined extraction temperature, resulting in efficient and accurate heat management. This is because it is extremely effective from the viewpoint of energy saving.

However, the conventional method of measuring the temperature of a slab inside a heating furnace is to house a thermocouple in a protective tube.
The thermocouple is protruded into the heating furnace, and the temperature of the atmosphere inside the furnace is measured by the thermocouple, thereby controlling the operation of the heating furnace. Therefore, since the temperature of the slab is not directly measured, it cannot be said that the temperature is accurately measured. Therefore, in actual operation, the extraction temperature of the slab is set slightly higher than the predetermined temperature so as not to interfere with the subsequent rolling process, and the furnace time is set to be sufficiently longer than the baking time. As a result, more energy was wasted than necessary.

Note that the temperature of the slab can be accurately measured by bringing a contact thermometer into direct contact with the slab. However, if the thermometer is brought into contact with the slab while it is moving through the heating furnace, the thermometer will be worn out, making it unsuitable for continuous temperature measurement. Therefore, at present, there is no choice but to rely on a method of estimating the slab temperature by measuring the furnace atmosphere temperature as described above.

Therefore, attention has been paid to the radiation thermometry method, which is suitable for continuous temperature measurement, and various proposals have been made. However, various problems remain to be solved regarding the measurement of the surface temperature of objects moving within a heating furnace. These problems will be explained with reference to FIG. FIG. 1 is a schematic diagram showing the positional relationship between a furnace, a slab, and a radiation thermometer. The slab 1 in the heating furnace 3 is heated by radiant heat from the direction of the inner wall of the furnace 3. It is assumed that the slabs 1 in the heating furnace 3 are sequentially transported in a direction perpendicular to the plane of the paper. The radiation thermometer 4 brings radiation from the slab surface onto a conversion element 4b using an optical system 4a to obtain an output corresponding to the radiation energy.
4c is a cylinder surrounding the optical axis.

Since the slab 1 is heated from the surroundings, the ambient temperature T ₃ is much higher than the slab temperature T ₁ . Therefore, if radiant energy from the surroundings reaches the conversion element 4b for some reason, its influence will be significant. This interference from the surroundings is called the stray light noise component.

Furthermore, since the slab surface is rough with oxidation, stray light from the surroundings easily enters the radiation thermometer due to diffuse reflection. Due to the diffuse reflection of the slab surface, it is difficult to identify and quantify the source of stray light.

Various proposals have been made to reduce this stray light noise as much as possible or to quantify the influence of stray light noise. For example, this application or Japanese Patent Publication No. 53-
No. 47713, title of the invention, proposes providing a shielding mechanism for shielding stray light in the furnace in a method and apparatus for measuring the temperature of objects inside the furnace. This shielding mechanism has a shape in which a disk facing the slab 1 is added to the lower end of the cylinder 4c shown in FIG. This shielding mechanism is water-cooled and does not itself emit a large amount of radiant energy, so there is no problem of radiation from the shielding mechanism being reflected on the surface of the slab 1 and affecting the readings of the thermometer.

However, in the case of a heating furnace, the temperature inside the furnace is usually over 1000℃, and the temperature of the slab is also high, so when the moving speed of the slab inside the furnace is low,
The slab surface faces a relatively cold shield for a considerable period of time and is cooled, creating disturbance problems. Furthermore, malfunctions such as water leaks may lead to major accidents.

An object of the present invention is to provide a method for measuring the surface temperature of an object in a furnace, which solves the above-mentioned problems in radiation temperature measurement and enables continuous temperature measurement with high accuracy.

In order to achieve the above object, the inventors of the present invention masked the uncertain stray light noise with a known reference noise source, since it is difficult to completely remove the noise component, and at the same time, they masked the influence of the quantifiable reference noise. We focused on the fact that the temperature of the object to be heated can be obtained by removing it. That is, in the method for measuring the temperature of an object in a furnace according to the present invention, radiant energy from the direction of the object obtained from the central opening of a shielding plate placed opposite to the surface of the object to be measured in the furnace is used as a radiation thermometer. In a method for measuring the surface temperature of an object in a furnace, the shielding plate is used as a reference noise source at a known high temperature, and the shielding plate, which is the reference noise source, is used to measure radiation noise from the direction of the furnace inner wall to the radiation thermometer. The present invention is characterized in that the surface temperature of the object to be measured is obtained by blocking the interference and subtracting the contribution of the reference noise source from the indication obtained by the radiation thermometer.

The method of the present invention will be explained in more detail below with reference to the drawings and the like.

FIG. 2 shows an apparatus for carrying out the method of the invention. FIG. 2A is a schematic plan view. Parts common to those previously described in connection with FIG. 1 are given the same reference numerals. The temperature measurement error in radiation thermometry is a function of the detection wavelength, temperature, etc. of the radiation thermometer, and is proportional to the wavelength. Therefore, in this embodiment, the detection wavelength λ of the radiation thermometer 4 is made as short as possible, for example, λ=0.65λm.
It is as follows. Since the temperature measurement range is high, sufficient sensitivity can be obtained even at the above wavelengths. The emissivity ε ₁ of the slab 1 in the wavelength range is about 0.8, and fluctuations are small. As mentioned above, the ambient temperature T ₃ is high and fluctuates greatly depending on the combustion state, but the shielding plate 2 prevents the interference to a negligible extent. The surface of this shielding plate 2 facing the slab 1 forms a reference noise source. Since the shielding plate 5 is naturally heated in the furnace, a material with excellent heat resistance that can withstand temperatures higher than the temperature of the slab 1 is used. For example, silicon carbide (SiC) has a heat resistance of 1400℃ or more, has a thermal conductivity similar to that of carbon, has a small coefficient of thermal expansion, and can be machined, so this shielding plate 2
It can be used as a material. As is known, this emissivity is 0.8, but by roughening the surface,
It can be set to about 0.85.

The temperature of this shielding plate 2 is constantly measured by a thermocouple 5 embedded close to the bottom surface. The output of radiation thermometer 4 and the output of thermocouple 5 are respectively
The signal is applied to the arithmetic processing circuit 8 via the AD conversion circuits 6 and 7.

The arithmetic processing circuit 8 performs the arithmetic processing of equation (12), which will be described later, and outputs the blackbody temperature Eb (T ₁ ) of the surface of the slab 1.

Next, the temperature measurement principle underlying the method of the present invention will be explained using equations.

The temperature and emissivity of slab 1 are T ₁ and ε _1, respectively.
shall be. The temperature and emissivity of the shielding plate 2, which is the reference noise source, are assumed to be T ₂ and ε ₂ , respectively. The surrounding space wall is considered as a black body cavity with temperature T ₃ .

The reference noise source is a disk, its radius is R, and the distance between it and the slab is H. The surfaces of the slab and the reference noise source can both be regarded as diffuse reflection surfaces, so if the effective radiation energy per unit area from each surface is G _i (i = 1, 2, 3,), the following formula generally holds: G _i =εi・Eb(Ti)+(1−εi)〓〓GK・Fik
(1) Here, Eb(Ti): Blackbody radiation energy at temperature Ti FiK: View factor representing the proportion of radiation reaching surface from surface i to surface k (however, Fjj=0,
j=1, 2) By applying equation (1) to Figure 2, the following equations are obtained.

G ₁ = ε ₁・Eb(T ₁ )+ (1−ε ₁ )(G ₂ F ₁₂ +G ₃ F ₁₃ ) (2) G ₂ =ε ₂・Eb(T ₂ )+(1−ε ₂ )( G ₁ F ₂₁ +G ₃ F ₂₃ ) (3) G ₃ =Eb(T ₃ ) (4) When formulas (2) to (4) are rearranged and summarized for G ₁ , the following formula is obtained.

G ₁ = ε ₁ /1−(1−ε ₁ )(1−ε ₂ )F ₁₂ F ₂₁ ·Eb(T ₁ )+(1−ε ₁ )ε ₂ F ₁₂ /1−(1−ε ₁ ) (
1- _ε2 ) _F12F21・Eb( _T2 )+(1- _ε1 ){ _F13 +(1- _ε2 ) _F23F12 }/1- ₍ 1- _{ε1 )} (1-ε ₂ ) F ₁₂ F ₂₁・Eb(T ₃
)(5) G ₁ in equation (5) represents the value detected by the radiation thermometer, the first term on the right side is the apparent radiation from the slab, the second term is the contribution from the reference noise source, and the third term is the contribution from the surroundings. Indicates stray light noise. Rewrite equation (5) as the following equation.

G ₁ = εa・Eb (T ₁ ) + γa・Eb (T ₂ ) + η・Eb
(T ₃ ) (6) where ε _a =ε ₁ /1−(1−ε ₁ )(1−ε ₂ )F ₁₂ F _2
1 (7) γa=(1-ε ₁ )ε ₂ F ₁₂ /1-(1-ε ₁ )(1
−ε ₂ )F ₁₂ F ₂₁ (8) η=(1−ε ₁ ) {F ₁₃ +(1−ε ₂ )F ₂₃ F ₁₂
}/1-(1-ε ₁ )(1-ε ₂ )F ₁₂ F ₂₁ (9) F ₁₃ =F ₂₃ =1−F ₁₂ (11) In equation (6), if η can be made very small compared to ε _a and γ _a , the third term on the right side can be ignored. Therefore, the temperature of the slab can be determined from the following equation.

Eb(T ₁ )=1/ε _a {G ₁ −γ _a・Eb(T ₂ ) (12) The establishment of equation (11) can be easily understood as follows. In the model shown in Figure 2, F ₁₁ +F ₁₂ +F ₁₃ = 1, F ₁₁
= 0, so F ₁₃ =1−F ₁₂ . In addition, the diameter of the opening in the center of the shielding plate 5 is approximately 10 mm, and the diameter of the shielding plate is
If it is about 400 mm, the area of the central opening can be ignored and mutual reflection can be considered to occur between disks of radius R and distance H, so F ₁₂ = F ₂₁ (10)
The establishment of the equation is similarly easy to understand.

Next, we introduce specific numerical values and examine equation (12).
When H/R=0.05, each form series is as follows.

By setting F ₁₂ =F ₂₁ =0.951 F ₁₃ =F ₂₃ =0.049 ε ₁ =ε ₂ =0.85 and calculating equations (7), (8), and (9) from these, the following (13) is obtained.

That is, it can be seen that η≪γa, εa hold, and the blackbody temperature Eb (T ₁ ) of the slab can be obtained using equation (12).

In addition, in the method of the present invention, the following two measures can be considered in order to further reduce the influence of stray light noise from the direction of the inner wall of the furnace, which is a noise source.

(1) Reduce H/R as much as possible. That is, the radius of the shielding plate 5, which is the reference noise source, is increased to be as close to the slab 1 as possible. This is to block stray light by increasing the area of the shielding plate and reducing the height of the stray light entrance. In Equation (10), F ₁₂ is brought closer to 1. Using Equation (11), all view factors in Equation (9) are replaced with F ₁₂ , and it can be seen that as F ₁₂ approaches 1, η decreases. . Note that making H extremely small poses a problem in terms of operation, but even if they are placed close together, the reference noise source has a high temperature comparable to the temperature of the slab 1, so no disturbance will occur due to cooling.

(2) Bring the emissivity _ε2 of the reference noise source close to 1.0.
Qualitatively, this is to reduce the influence of stray light by increasing the absorption of the stray light by the shielding plate 5. In equation (9), ε ₁ is 1
It can be seen that as it approaches , the numerator decreases, the denominator increases, and η decreases.

The method of the present invention will now be further explained with reference to Examples. FIG. 3 shows the arrangement of the slab 1 in the slab heating furnace 3 during actual operation and the arrangement of the temperature measuring system for carrying out the method of the present invention.

The thickness (t) of slab 1, which is the object of temperature measurement, is 200
mm, width (W) is approximately 200 mm, and length is approximately 9000 mm. The radius (R) of the shielding plate 2, which is the reference noise source, is
200 mm, the opening radius (d) was 10 mm, and the distance (H) between the shielding plate 2 and the slab 1 was 10 mm. This heating furnace is of a type in which heavy oil is blown into the furnace through a large number of heavy oil injection ports 10 arranged on the furnace wall and heated with a gas burner. In this type of heating, the temperature of the furnace wall T ₃
The temperature distribution is considered to be quite large. The slab 1 and the shielding plate 2 are heated by the radiant heat from the direction of the wall surface. A PR thermocouple 9 was welded to the surface of the slab 1 to actually measure the temperature, and the measured value was compared with the slab temperature indication obtained by the method of the present invention. In this example, a silicon photoelectric conversion element with a detection wavelength of λ = 0.65 μm is used as the conversion element of the radiation thermometer 4, the temperature of the shielding plate 2 is constantly monitored with the above-mentioned configuration, and the emissivity of the slab 1 is ε ₁ is effectively
0.86, and the slab temperature indication was obtained based on the above equation (12).

In FIG. 4, the indication of the PR thermocouple 9 is plotted on the horizontal axis, and the corresponding temperature indication obtained by the method of the present invention is plotted on the vertical axis with white circles.

This was obtained by changing the furnace wall temperature T ₃ and the slab temperature T ₁ over a wide range by significantly changing the combustion state by the gas burner.

From Figure 4, the slab temperature measured by the PR thermocouple is 900℃.
It can be seen that even when the temperature changes from 1250°C to 1250°C, the temperature obtained by the method of the present invention is within an error of ±10°C at each measurement point. Note that the points indicated by black circles in FIG. 4 indicate the measured temperature of the reference noise source. Even if the temperature of the reference noise source changes in this way,
As long as it is known, there is no problem at all.

Next, another experimental example will be shown for comparison. In this experiment, the shielding plate 2 was removed and the magnetic tube 1 was measured using a radiation thermometer 4.
The experiment was carried out under exactly the same conditions as in the previous example, except that the slab 1 was looked through the lens 1. In FIG. 6, the indications of the radiation thermometer 4 relative to the indications of the PR thermocouple 9 are shown by white circles. As is clear from FIG. 6, the indications are much higher than the true temperature of the slab and have extremely large variations. This is due to the influence of stray light noise. By the method of the present invention, the influence of stray light noise is nearly completely blocked, so excellent results as shown in FIG. 4 can be obtained.

Since the method of the present invention is carried out as described above, it not only enables highly accurate non-contact continuous temperature measurement, but also provides the following numerous advantages.

First, the principle is extremely simple and clear, making it easy to understand and implement in the field.

Next, the output G ₁ of the radiation thermometer can be subjected to simple arithmetic processing as shown in equation (12), so real-time processing can be performed with a simple system.

Next, since the detection wavelength can be shortened, an inexpensive silicon photoelectric conversion element can be used as the sensor of the thermometer.

Various modifications can be made to the embodiments described in detail above within the scope of the present invention. Although an example has been shown in which a buried thermocouple is used to measure the temperature of the reference noise source, it is also possible to measure the temperature with a surface thermometer by providing a small hole 2a to eliminate surface reflection, as shown in FIG. It is also possible to configure the shielding plate 2 to have a cylindrical cavity shape as shown in FIG. 8 so as to increase _ε2 .

Furthermore, although we have described an example in which the temperature T ₂ of the reference noise source is obtained by natural heating in the furnace, it is also possible to actively heat the reference noise source from within, or to perform temperature control to maintain it at a constant known temperature.

Although silicon carbide is shown as the material for the shielding plate 2, which is the reference noise source, for example, alumina, heat-resistant steel, etc. can also be used.

Further, although the method of the present invention has been described in detail with respect to a slab heating furnace, it can be similarly applied to high-temperature furnaces other than slab heating furnaces.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining problems in measuring the surface temperature of objects in a furnace, Fig. 2 is a principle diagram showing an apparatus for carrying out the method of the present invention, and Fig. 3 is an implementation of temperature measurement according to the present invention. A layout diagram showing an example; Figure 4 is a graph showing the measurement results; Figure 5 is a layout diagram showing an experimental example of temperature measurement without using a reference noise source;
The figure is a graph showing the measurement results, FIG. 7 is a perspective view showing a modification of the temperature measurement of the reference noise source, and FIG. 8 is a perspective view showing a modification of the shielding plate. 1: Slab, 2: Shielding plate (reference noise source), 3:
Furnace, 4: Radiation thermometer, 4a: Optical system, 4b: Conversion element, 4c: Shade tube, 5: Thermocouple, 6, 7: AD
Conversion circuit, 8: Arithmetic processing circuit, 9: PR thermocouple,
10: Heavy oil inlet.

Claims (1)

[Claims] 1. In a method for measuring the surface temperature of an object in a furnace, the temperature of the object is measured using a radiation thermometer. , the shielding plate is used as a reference noise source of known high temperature, and
The shielding plate, which is the reference noise source, blocks radiation noise from entering the radiation thermometer from the direction of the inner wall of the furnace, and the contribution of the reference noise source is subtracted from the indication obtained by the radiation thermometer. A method for measuring the surface temperature of an object in a furnace, characterized by obtaining the surface temperature of a hot object.