JPH0663849B2 - Measuring method of material temperature in continuous heating furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring a material temperature in a continuous heating furnace, and particularly to a material to be heated which is moved and heated in a continuous heating furnace having a heating zone and a soaking zone. The present invention relates to a method for measuring a material temperature and a heating pattern for controlling the material temperature history of the above to a target value.

<Prior Art> Usually, a material to be heated such as a steel sheet that is reheated in a continuous heating furnace such as an annealing furnace is held in a predetermined temperature range for a predetermined time within the soaking zone. The material temperature at that time is mainly measured by a radiation thermometer installed at the heating zone outlet and the soaking zone outlet. In this case, it is essential to accurately obtain and correct the emissivity ε of the heated material. . Further, in order to confirm the soaking time, the temperature rise pattern is predicted by calculation. In this case, it is indispensable to determine the overall heat absorption rate φ _CG .
Further, it is difficult to maintain high detection accuracy unless the emissivity ε and the overall heat absorption coefficient φ _CG are identified in real time.

The reason will be described in detail below.

In normal measurement of material temperature, the necessary factors are surface temperature and average temperature. The surface temperature is necessary for evaluating the surface quality of the material, and the average temperature is necessary for evaluating the internal quality of the material. By the way, when a radiation thermometer is used for temperature measurement, the measured value of the surface temperature depends on the emissivity, and the measured value of the average temperature depends on the surface temperature and the heat transfer coefficient of the atmosphere.

On the other hand, there is a method to obtain the heat transfer coefficient as a function form of only the average temperature from the actual heating data, but since the average temperature itself depends on the heat transfer coefficient as described above, another method such as the radiation equation is used. , The surface temperature and the total heat absorption coefficient φ _CG have to be obtained as a functional form. Here, in the case of cooling in the atmosphere, the emissivity ε is equivalent to the overall heat absorption coefficient φ _CG , and also in the case of atmospheric heating, ε and φ _CG are the furnace dimensions, material dimensions and furnace wall. In any case, φ _CG can be represented by ε because they are combined as a function of emissivity.

Therefore, if there is a guarantee that the emissivity ε given to the radiation thermometer is a true value, the heat transfer coefficient is determined from the measured surface temperature and the average temperature is sequentially determined using this heat transfer coefficient. It is possible, but the reality is that there is currently no absolute means to test the emissivity ε itself. Therefore, emissivity and heat transfer coefficient, surface temperature, average temperature of 4
It can be said that, in principle, there is no way for any of them to be given as a truly correct thing by themselves, and these four are of the nature that they should be determined simultaneously by only one set of combinations.

Furthermore, it has been clarified that the overall heat absorption coefficient φ _CG changes depending on the furnace operating condition, and in-situ identification of φ _CG, that is, ε, is the first method for highly accurate material temperature measurement and control. Although there was only one condition, there was actually no method for that. Note that, as disclosed in Japanese Patent Publication No. 61-43649, there is disclosed a method of calculating and calculating the material temperature while calculating φ _CG .

<Problems to be Solved by the Invention> However, in Japanese Patent Publication No. 61-43649, when the material temperature at time t is calculated, the φ _CG value before Δt time is used, but the details of the invention are described. As described in the section of the explanation, "φ _CG
Is not necessarily constant even if the material or shape of the steel slab is the same, and is considered to be an uncertain factor that differs depending on the operating condition of the furnace (Publication 2, page 3, column 3, lines 21-24). " However, since it is unavoidable to handle such a situation, "Averaging by using statistical methods,
) ”, Φ _CG is applied, and there is a problem in accuracy, and in principle, fuel combustion heat, scale formation heat, heat input from upstream zone, heat loss from furnace wall, heat loss from exhaust gas, etc. Calculating φ _CG on the basis of the heat balance equation consisting of many uncertain parameters has limited accuracy.

Further, in the heat transfer equation for calculating the material temperature at the time t (equation (3) in the same column 3), there is no description of how to give the atmospheric heat transfer coefficient α. Therefore, considering that both φ _CG and α are parameters that largely depend on the furnace operating state, it cannot be said that the present invention has obtained a proper idea. In this respect, it is extremely rational if the operations for determining φ _CG , ε, α and the material temperature are performed at the same time. The present invention has been made in view of the above circumstances, and an object thereof is to provide a highly accurate method of measuring a material temperature in a continuous heating furnace.

<Means for Solving the Problems> The configuration of the present invention is based on the following procedure,
As a result, highly accurate heat treatment is achieved.

(1) The material temperature (T ₀ ) on the entrance side of the heating zone and the temperature (T _f ′, T _f ) inside the heating zone and the soaking zone are measured by any ordinary means.

(2) The brightness temperature ([T ₁ ], [T ₂ ]) of the material to be heated is detected by the radiation thermometer at two points, the heating zone exit side and the soaking zone exit side.

(3) the overall heat absorption rate phi _CG in the heating zone and _H at a constant value, regarded as a linear function type phi _s the overall heat absorption rate phi _CG increases in proportion to the standing furnace time in the soaking zone.

(4) Give the emissivity ε of the material to be heated as a function form of φ _CG .

(5) Convergence calculation and identification of _H from T ₀ , T _f ′, [T ₁ ] is performed to determine the heating zone outlet side material temperature T ₁ and heating pattern.

(6) Convergence calculation and identification of φ _s is performed from _H , T ₁ , T _f , and [T ₂ ] to determine the material temperature T ₂ of the soaking zone and the soaking pattern.

<Operation> The inventors of the present invention continuously run a thin steel plate equipped with a thermocouple in a continuous heating furnace having a heating zone and a soaking zone, and continuously measure the material temperature from the heating zone entrance side to the soaking zone exit side. I conducted an experiment. Based on the temperature measurement data obtained at that time, the radiant heat transfer coefficient was calculated back from the temperature rise calculation formula, and the total active heat absorption coefficient was calculated back from the radiant heat transfer coefficient formula. Then, as a result of analyzing enormous temperature measurement data obtained by variously changing the steel type, plate thickness, plate radiation, traveling speed, heating zone and soaking temperature of thin steel plates, the following important findings were obtained. Got

(1) Within the heating zone, the overall heat absorption coefficient φ _CG should be maintained at a substantially constant value, although its level varies depending on the steel type, heating conditions, etc.

(2) In the soaking zone, φ _CG should increase almost in proportion to the reactor time.

These phenomena can be uniformly interpreted by the difference ΔT between the temperature inside the furnace and the surface temperature of the material. That is, within the heating zone
T is usually large at a level of over 200 ° C, and φ _CG can be regarded as a value almost equal to the emissivity of the material at room temperature, while ΔT sharply decreases to 100 ° C or less in the soaking zone, and ΔT Asymptotically approaches 0 with the time spent in the furnace. In principle, since φ _CG = 1.0 when ΔT = 0, it is considered that when the ΔT approaches 0 in the near-heat reactor zone, φ _CG continuously increases. An example of the correlation between these ΔT and φ _CG is shown in FIG. From this figure, φ _CG is ΔT> 200 ℃
Becomes almost constant value and φ _CG = 1.
It is clear that it approaches a zero.

On the other hand, when we have made various investigations about the relationship between the emissivity ε and overall heat absorption rate phi _CG, we found generally to be combined in a particular relation to the overall heat absorption rate phi _CG emissivity ε . Therefore, since the unknown can be limited to either φ _CG or ε, if ε is given, the surface temperature (Ta) of the material can be determined by detecting the brightness temperature of the heated material with a radiation thermometer. If φ _CG is given, on the one hand, the radiant heat transfer coefficient is estimated from Ta and the average temperature a is converted from Ta. On the other hand, the average material temperature b at the radiation temperature measurement position is calculated by the temperature rise calculation. It can be calculated. Therefore, φ _CG or ε is determined by deriving an equation that makes the material average temperatures a and b, which are converted or calculated by different means equivalent, and that only φ _CG or ε is an unknown, and solves it. Is automatically ε or φ _CG
It is possible to construct a logic that simultaneously determines the temperature measured by the radiation thermometer and the temperature rise pattern.

The basic procedure of the present invention will be described below.

Radiation thermometers are installed on the heating zone exit side (that is, the soaking zone entrance side) and the soaking zone exit side respectively, and the material surface temperature of the material to be heated is continuously measured, and the temperature measurement values are calculated by the following procedure. To do.

First, although the set emissivity [ε] of the radiation thermometer may be arbitrary, it is set to 1.0, which is the most convenient for handling, and the detection values of the heating zone exit side radiation thermometer and the soaking zone exit side radiation thermometer ( That is, the brightness temperature) [T ₁ ] and [T ₂ ] are data-logged in real time.

On the other hand, the absorption wavelength λ ₀ of the detection element of the radiation thermometer, the material thickness d, the plate width W, the heating zone in-reactor time t _H , the soaking zone in-reactor time t _s ,
Thermal properties of the material (thermal conductivity λ, thermal conductivity a, etc.),
The heating zone entrance side material average temperature ₀ , the heating zone furnace temperature T _f ′, the soaking zone furnace temperature T _f, etc. are input.

Then _'Select, while the emissivity epsilon _1' temporary uniform overall heat absorption rate _H in the heating zone is converted with a function of, for example, the following (2) ₁ epsilon represented by formula _'(H', W) .

First, the emissivity ε ₁ ′ of the material temperature is generally expressed by the following equation (1).

ε ₁ ′ = { _H ′ ⁻¹ + 1− _CF ⁻¹ − (ε _f ⁻¹ −
1) · F _m / F _f } ^-1 (1) where C _F is a parameter for evaluating the state of heat exchange between the material to be heated and the furnace wall, which is generally called the view factor. When a furnace having a rectangular cross section completely encloses a material having no macroscopic concave surface such as a steel plate, it can be regarded as C _f ≈1.0. [epsilon] _f is the emissivity of the furnace wall made of brick, and is usually specified in the range of 0.8 to 0.9, so it can be given as a constant value. F _m / F _f is the ratio of the material surface area to the furnace wall surface area and can be treated as known in advance.

After all, ε ₁ ′ can be given as a function of _H ′ and the material size. For example, in the case of a thin plate, the plate thickness (d) << the plate width (W), so ε ₁ ′ is given by the following (2 ) Like the formula
_It can be calculated by the function of H'and W.

ε ₁ ′ = ( _H ′ ⁻¹ −b _H · W) ⁻¹ (2) where bH is a positive constant, and the heating zone outlet side material surface temperature T _1,1 is, for example, the following formula (3). The conversion is performed using the function of T ₁₁ ([T ₁ ], ε ₁ ′, λ ₀ ) shown by.

T ₁₁ = {([T ₁ ] +273) ⁻¹ + λ ₀ / C ₂ · l _n ε
₁ ′} ⁻¹ −273 (℃) ……… (3) where λ ₀ : absorption wavelength of the detection element of the radiation thermometer (μm) C ₂ : 1.43 × 10 ⁴ (μm · deg) The radiant heat transfer coefficient α ₁₁ at the hot point is
For example, α ₁₁ (T ₁₁ , T _f ′, _H ′) expressed by the following equation (4)
Boltzmann's heat radiation equation and Newton's heat transfer equation are combined to calculate the radiation heat transfer equation.

α ₁₁ = _H ′ ・ σ {(T ₁₁ +273) ² + (T _f ′ +273) ² } · (T ₁₁ + T _f ′ +546) (kcal / m ² h ° C) ……… (4) where σ : Stephan-Boltzmann constant (= 4.88 × 10 ⁻⁸ kcal / m ² hK ⁴ ) T _f ′: Temperature in the heating zone furnace (° C.) Further, the average temperature ₁₁ in the material at the temperature measuring point is expressed by the following formula (5), for example. It is converted by a function of ₁₁ (T ₁₁ , α ₁₁ , d, T _f ′) shown by. _{11 = T 11 · {1 +} N 11/2 · (1-T f '/ T 11) ·} (℃) _{where, N 11 = (α 11 ·} d / λ) × 10 -3 d: material OD lambda :Thermal conductivity : Average temperature position coefficient ₁₂ (T ₀ , T ₁₁ , t _H , d,
T _f ′, _H ′) heat conduction analysis solution Prediction calculation is performed by the temperature rise calculation formula. ₁₂ = (− T _f ′) · exp (−k · t _H ) + T _f ′ ... (6) where μ ₀ : 8.889 × 10 ³ a: Temperature propagation rate (m ² / h) t _H : Heating furnace residence time (s) m: Material shape factor Of course, the heating zone may be appropriately divided and the temperature increase calculation may be performed for each divided section.

By comparing the average temperature ₁₁ measured in terms of where the heating home use side average temperature ₁₂ obtained in the step, to determine whether the difference therebetween falls within the allowable error [delta], fit to overall heat absorption rate _H Repeat the selection of ′.

The ₁₁ When the difference of ₁₂ match within the required accuracy, _H to be identified that _H for time _', epsilon _{1', respectively,} epsilon ₁
As a result, the heating furnace outlet material surface temperature T ₁ (= T ₁₁ ) and the material average temperature ₁ (= ₁₁ ) are determined and simultaneously output.

Then, _H is given as the total heat absorption rate φ _{si on the} entrance side of the soaking zone, and the temporary average heat absorption rate _s ′ in the _soaking zone is selected. Here, on the premise that the total heat absorption rate in the _{soaking zone} increases in proportion to the in-reactor time, the total heat absorption rate φ _sθ at the temperature measuring point on the _{soaking zone} is _expressed by, for example, φ _sθ shown in the following equation (7). Calculation is performed using the function of ( _H , _s ').

φ _sθ = 2 _s −φ _si (7) Here, φ _si = _H , and from φ _sθ , the emissivity ε ₁ ′ at the temperature measuring point on the _{soaking zone} is _{given by the} above equation (2). Similarly, for example, it is converted using the function of ε ₂ ′ (φ _sθ , W) shown in the following formula (8), and the material surface temperature T ₂₁ is expressed as T in the following formula (9).
₂₁ ([T ₂ ], ε ₂ ′, λ ₀ ) function is used for conversion.

ε ₂ ′ = (φ _sθ −b _s · W) ⁻¹ (8) where b _s : positive constant T ₂₁ = {([T ₂ ] +273) ⁻¹ + λ ₀ / C ₂ · l _n ε ₂ ′} ⁻¹ −273 (° C.) ……… (9) Subsequently, the radiant heat transfer coefficient α at the radiation temperature measuring point
₂₁ is expressed by, for example, the following equation (10), α ₂₁ (T ₂₁ , T _f , φ
_sθ ) radiant heat transfer coefficient equation.

α ₂₁ = φ _sθ · σ {(T ₂₁ +273) ² + (T _f +273) ² } ・ (T ₂₁ + T _f +546) ……… (10) Where, T _f : temperature inside the soaking furnace (° C) Further, the average temperature ₂₁ in the material at the temperature measurement point is converted by, for example, a function of ₂₁ (T ₂₁ , α ₂₁ , d, T _f ) shown by the following equation (11). ₂₁ = T ₂₁ · {1 + N _21/2 · (1- _Tr / T ₂₁ ) ·
} ……… (10) Where, N ₂₁ = (α ₂₁ · d / λ) × 10 ⁻³ The average temperature in the material at the temperature measuring point at the soaking furnace outlet
₂₂ is represented by the following formula (12), for example, ₂₂ ( ₁ , ₂₁ , t
_s , d, T _f , _s ') are calculated by the heat conduction analysis solution temperature rise calculation formula. _{22 = (1 -T f) ·} eXp (-k · t s) + T f ......... (12) here, As in the case of the heating zone, the soaking zone may be appropriately divided and the temperature rise calculation may be sequentially performed for each of the dividing furnaces.

The soaking temperature average material ₂₂ obtained here is compared with the material average temperature ₂₁ measured and converted in the step, and it is determined whether or not the difference between the two falls within the allowable error δ, and the average is obtained until it falls. The selection of the overall heat absorption rate _s'is repeated.

The ₂₁ When the difference of ₂₂ match within the required accuracy, _s to be identified that _s when _', epsilon _{2', respectively,} epsilon ₂
As the mean temperature, the material surface temperature T ₂ (= T ₂₁ ) and the material average temperature ₂ (= ₂₁ ) are determined and simultaneously output.

These basic procedures are summarized in the flow chart and shown in FIG.

By using such a procedure, it is possible to detect the material surface temperature and the average temperature in the heating / soaking furnace with high accuracy.
Also, since all the arithmetic expressions used here are analytical solutions,
The calculation time is extremely short as compared with the case of solving a partial differential equation as described in JP-B-61-43649,
Since the feed back control can be performed in small increments, it is very advantageous for rapid and highly accurate material temperature control, and of course, it has higher precision than the simple model.

As is clear from the above description, the features of the present invention are that it is possible to simultaneously determine the overall heat absorption coefficient, emissivity, heat transfer coefficient of heat medium, surface temperature and average temperature of materials, which are mutually related. Is the most preferable method that does not exist in the idea of the prior art at all.

<Examples> Examples of the method of the present invention will be described below.

FIG. 3 is a side view showing an outline when the method of the present invention is applied to a heating / soaking annealing line for thin steel sheets. In this figure, the surface temperature of the material to be heated 1 is, for example, a Si element type radiation thermometer 5a having an absorption wavelength of 0.9 μm installed on the heating zone 2 exit side (ie, the soaking zone 3 entrance side) and the soaking zone 3 exit side, respectively. ,
5b, the temperature measurement signal is input to the data collection device 10 together with the heating and soaking chamber temperature signal measured by the thermoelectric body 9a ~ 9f, is processed by the arithmetic processing unit 11 . The control signal from the arithmetic processing unit 11 is fed back to the gas flow rate control valves 7a and 7b of the heating zone 2 and the soaking zone 3 via the control unit 12 to control combustion. The material to be heated 1 sent out from the payoff reel 21 is sequentially passed through the heating zone 2 and the soaking zone 3 to be heated and soaked, and finally wound up by the take-up reel 22.

In the figure, 4a to 4c are guide rolls installed in the furnace,
6a and 6b are cooling shield tubes for shielding the ambient light from the furnace, and 8a and 8b
Is a jet of fuel and air.

Further, the radiation thermometers 5a and 5b installed at the heating zone 2 outlet and the soaking zone 3 outlet are related to the present invention, and are provided with heat insulating measures,
The set emissivity [ε] is set to 1.0, for example. The data collection by these radiation thermometers 5a and 5b is performed continuously, but the following points should be considered. That is, (1) both are arranged to collect radiation from the central position in the plate width direction of the material to be heated 1 so that two radiation thermometers can measure the same portion of the material.

(2) As the measured values on the downstream side of the soaking zone 3,
Data is collected and arithmetically processed with a delay of the required travel time of the material from the heating zone 2 exit side. Further, the average temperature of the material 1 to be heated on the inlet side of the heating zone 2 is usually as small as less than 50 ° C and has a relatively large tolerance of 10 to 20 ° C. It is assumed that a so-called conventional average temperature estimated from the surface temperature measured by a radiation thermometer given a rate is given as a known value.

Applying the material temperature measuring device configured in this way to a continuous annealing furnace of the type that directly burns gas in the furnace with a heating zone, soaking zone length of 12 m, furnace height of 2.5 m, furnace width of 2.2 m ,
The surface temperature of a ferritic stainless steel sheet that was continuously heated while running at a line speed of 24 m / min with a sheet thickness of 1.0 mm and a sheet width of 1000 mm was measured.

A thermocouple was previously attached to this steel plate, and the measured value was used as the true temperature as a reference.

For comparison, a radiation thermometer with the emissivity of the conventional method fixed at 0.35 was attached in parallel and measured.

Table 1 shows the measurement results.

As is apparent from this table, in contrast to the method of the present invention in which the emissivity is identified online, the conventional method of the fixed emissivity setting method has a large measurement error as compared with the measurement value (true temperature) by the thermocouple. You can see that This is because the emissivity preset by the conventional method is larger than the emissivity identified in the present invention in the heating zone, and is conversely smaller in the soaking zone, and as a result, the material temperature has such a magnitude relationship. Is.
Therefore, the use of the method of the present invention improves the measurement accuracy of the material temperature, which is remarkable especially in a heating furnace having a small emissivity.

As described above, according to the present invention, the overall heat absorption coefficient of each of the heating zone and the soaking zone can be identified online, and at the same time, the emissivity at the radiation measuring point of the heating zone and the soaking zone can be identified. Can be measured. By performing the temperature control in the furnace by a normal feedback on the deviation from the target material temperature based on the measured value, the deviation can be surely reduced and a highly accurate annealing process can be realized.

In addition, in the present embodiment, the case of heating the steel sheet directly in the combustion atmosphere furnace was described, but the present invention is not limited to this.
It goes without saying that the present invention can be applied to shapes other than steel plates, such as round bars and metals, non-metals other than steel, and different atmosphere heating methods such as the radiant tube method.

If the heating furnace has a pre-tropical zone, the radiation zone thermometer may be used in addition to the connection between the pre-tropical zone and the heating zone, or the pre-tropical zone and the heating zone may be integrated into one heating zone. The method of the present invention can be applied without any problem.

<Effects of the Invention> As described above, according to the present invention, the emissivity essential for temperature measurement using a radiation thermometer is identified online,
In addition, since the overall heat absorption rate, which is indispensable for predicting the temperature rise in atmospheric heating, is identified online, the material temperature at the furnace outlet and the temperature rise pattern in the furnace can be detected with high accuracy, and the accurate temperature inside the furnace can be detected. As a result, it is possible to perform the heat treatment as targeted based on the correction of the above, and as a result, it is possible to obtain a high level and product quality with little fluctuation. Also, there is no waste of heat energy, and it is higher due to passing at maximum speed. It has many effects such as being able to maintain productivity.

[Brief description of drawings]

FIG. 1 is a flow chart showing the basic procedure according to the method of the present invention, FIG. 2 is a characteristic diagram showing the correlation between the difference between the furnace temperature and the material surface temperature, and the overall heat absorption rate, and FIG. 3 is the present invention. It is a side view which shows the outline of the application example of a method. 1 ...... Heated material, 2 ...... Heating zone, 3 ...... Soaking zone, 4 ...... Guide roll, 5 ...... Radiation thermometer, 6 ...... Ambient light shielding tube, 7 ...... Gas flow control valve, 8 ... … Gas / air ejection holes, 9 …… Thermocouple, 10 …… Data sampling device, 11 …… Computer processing device, 12 …… Control device, 21 …… Pay-off reel, 22 …… Take-up reel.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Sato 2-88 Wakihama Kaigan-dori, Chuo-ku, Kobe-shi, Hyogo Kawasaki Steel Co., Ltd. Hanshin Works

Claims (1)

[Claims] 1. A method for measuring a material temperature when a material to be heated is continuously heated while running in a continuous heating furnace composed of a heating zone and a soaking zone, which comprises: The ambient temperature in the soaking zone is measured, and the brightness temperature of the material to be heated is detected by the radiation thermometers installed at the two outlets of the heating zone and the outlet side of the soaking zone. The overall heat absorption rate in the heating zone is set to a constant value, and the total heat absorption rate in the soaking zone is defined as a linear function of the heating time of the heated zone. The emissivity of the material to be heated between the outlet of the heating zone and the outlet of the soaking zone was identified online from the temperature and the overall heat absorption rate of the heating zone. And rising of heated material in those furnaces Method of measuring the material temperature in a continuous furnace, characterized in that to determine the pattern, respectively.