JPH07208965A - Measuring method for plate thickness of steel plate by radiation - Google Patents

Abstract

PURPOSE:To provide a measuring method in which the measuring error of a plate thickness is reduced in the measurement of the plate thickness by a radiation. CONSTITUTION:A radiation source 3 which detects the plate thickness of a steel plate 1 and a dose detector 4 are installed in a finishing rolling mill 2. By the operation of a control panel 5, a radiation is radiated to the steel plate by the dose detector 4, a value which has been measured actually by a thermometer 6 detecting a radiation detection amount is sent to a temperature converter 7, and the value is sent to a thickness-measurement control device 8 together with the radiation detection amount. In addition, the thickness-measurement control device 8 is coupled to a display device 9, a recorder 10 and a control panel 11. Before an operation by a radiation thickness gage, the component composition of the steel plate is stored in a computer 14 in advance. Then, the decision means of a crystal structure which is changed so as to be dependent on a temperature, on the component composition and on a working state, of a volume change due to heat, of a volume change due to a solid solution and of a mass change is set in a correction and operation part 13 in the previous stage of a plate-thickness operation part 12. Then, the plate thickness of the steel plate which takes a metallurgical factor into consideration is computed in the plate-thickness operation part 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the thickness of a plate by counting the amount of radiation passing through the plate.

[0002]

2. Description of the Related Art In general, a radiation thickness meter projects a fixed amount of radiation from one side of the thickness of the object to be measured, measures the amount of radiation that has penetrated into the other side of the object to be measured, and measures this measured value. , The thickness of the object to be measured is obtained by comparison with a calibration curve (hyperbolic function indicating the relationship between the amount of transmitted radiation and the thickness) set in advance on this thickness gauge, and displayed by an appropriate method. Since it is a non-contact type, it is used as an online thickness gauge in a hot rolling line for steel sheets.

In such a radiation thickness gauge, since the method of measuring the thickness of a steel sheet changes depending on the components of the steel sheet, appropriate density and mass absorption coefficient are required to realize the highly accurate thickness measurement. It is essential to make a decision. Therefore,
For example, as in Japanese Examined Patent Publication No. 5-15206, when calculating the plate thickness of the steel plate by calculation, the steel composition is analyzed for each steel plate to be measured, and the calculation of the steel plate is performed by a preset calculation formula based on this analysis result. A plate thickness measuring method for a steel plate is disclosed in which the density and the mass absorption coefficient are calculated, and the plate thickness of the steel plate is measured using the calculation result.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The steel composition is analyzed for each steel plate to be measured, which is disclosed in Japanese Patent Publication No. 5206/1993, which is the above-mentioned prior art, and the steel plate is calculated by a calculation formula preset based on the analysis result. In the method of calculating the density and mass absorption coefficient of, and measuring the plate thickness of the steel sheet using this calculation result, temperature, component composition, change of phase (crystal structure) determined by processing state, volume change due to heat, There is a problem that it is not possible to measure the plate thickness with high accuracy because it cannot cope with volume change and mass change due to solid solution. That is, the temperature, component composition, and processing state of the steel sheet to be measured have a great influence on the metallurgical factors such as phase (crystal structure), volume change due to heat, volume change due to solid solution, and mass change. Since it affects the number of atoms in the unit cell and the volume and atomic number of the unit cell, which are the determinants of the absorption coefficient, there is a problem that a complete correction cannot be made unless correction is performed in consideration of these factors.

Therefore, as a result of intensive studies by the present inventors, the crystal structure which is a metallurgical factor and the volume change due to heat,
It is intended to provide a highly accurate plate thickness measuring method by performing correction corresponding to a change in volume and a change in mass due to solid solution.

[0006]

The present invention has been made in order to solve the above-mentioned problems, and the gist of the invention is to count the amount of radiation passing through a steel plate and measure the plate thickness. At the time of calculating the plate thickness of the steel plate by calculation, the temperature of the steel plate to be measured, the phase (crystal structure) determined by the composition and working state, the volume change due to heat, etc. are estimated, and based on this estimation result A method of measuring the thickness of a steel sheet by radiation is characterized in that the linear absorption coefficient of radiation is calculated according to a preset arithmetic expression, and the thickness of the steel sheet is measured using the result of this arithmetic operation.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram for implementing the present invention. As shown in FIG. 1, a steel plate 1 to be measured is a radiation source 3 serving as a hot γ-ray source for detecting the plate thickness of the steel plate 1 at an appropriate position during a finish rolling process by a finish rolling mill 2.
And a radiation dose detector 4 for receiving the radiation emitted from the radiation source 3. Then, by operating the machine side operation panel 5, the radiation detector 4 emits radiation to the steel plate,
It is configured to detect a radiation detection amount. on the other hand,
The value measured by the thermometer 6 of the steel plate is sent to the thermometer converter 7, and is sent to the thickness measurement controller 8 together with the radiation detection amount. Further, the thickness measurement control device 8 includes a display device 9 and a recorder 1.
0 and operation panel 11.

Prior to the calculation by the radiation thickness meter,
The composition of the steel sheet is stored in the calculator 14 in advance. A plate (specifically based on the formula described later) for determining a phase (crystal structure) that changes depending on temperature, component composition, and processing state, volume change due to heat, volume change due to solid solution, and mass change It is set in the correction calculation unit 13 in the preceding stage of the thickness calculation unit 12. Here, the plate thickness calculation unit 12 calculates the plate thickness of the steel plate considering the metallurgical factors.

[0009]

[Operation] γ as the measurement principle of the γ-ray thickness gauge according to the present invention
The attenuation of the amount of linear transmission follows the following formula. I / I ₀
= Exp (−μ · T) (1) where T: plate thickness I ₀ : strength before transmission I: strength after transmission μ: linear absorption coefficient Therefore, in the γ-ray thickness gauge, the plate thickness T of the steel plate is It is calculated by the formula. T = 1 / μ · ln (V ₀ / V) (2) However, V ₀ : Count number without plate V: Count number with plate The temperature and material (component composition) of the steel plate to be measured are different from this. In this case, since the linear absorption coefficient in equation (2) is different,
It is necessary to make a correction according to the component composition and the processing state.

Elastic absorption (Tho
There are three types: mson scattering), inelastic scattering (Compton scattering), and photoelectric effect (incident light completely disappears). Depending on the wavelength (energy) of radiation, which of the three types of absorption dominates is determined. For γ rays, Compton scattering and photoelectric effect may be taken into consideration. Therefore, the absorption cross section by Compton scattering is α _S = α _T 3/4 × [(1 + α) / α {(2 + 2α) / (1 + 2α) -ln (1 + 2α) / α} + ln (1 + 2α) / Zα- ( 1 + 3α) / (1 + 2α) ² (3) where α _T and α are α _T = 6.7 × 10 ⁻²⁵ (cm ² ) α = hν / (mc ² ) = (γ-ray energy) / (Mass energy of electron) α _S = 2.5785 × 10 ^-25 (cm ² ) (γ-ray energy = 662 kev) (4)

Also, regarding the absorption cross section due to the photoelectric effect, if only the effect of K-shell electrons is considered, since the incident energy of γ-rays is sufficiently larger than the binding energy of K-shell electrons, α _P = α _T 4√2 · α ⁴ · Z ⁵ · (mc ² / hν) ^7/2 (5) where α _T = 6.7 × 10 ⁻²⁵ (cm ² ) Z = atomic number α = 1/137 ( Fine structure constant) mc ² / hν = (electron mass energy) / (γ-ray energy). α _P = Z ⁵ × 4.3475 × 10 ⁻³³ (cm ² ) ... (6)

From the above, the linear absorption coefficient μ of γ rays can be obtained by the following equation. μ = ΣZ μ _a / V = ΣZ (α _P + Zα _S ) / V (7) where μ _a = α _P + Zα _S where z: number of atoms in unit lattice V: volume of unit lattice μ _a : Atomic absorption coefficient Z: Atomic number α _S : Scattering cross section (= 2.5785 × 10 ^-25 (c
m ² )) α _P : photoelectric absorption cross section (= Z ⁵ × 4.3475 × 10
^-33 (cm ² )) Therefore, it can be seen that the linear absorption coefficient of γ rays is determined by z (the number of atoms in the unit lattice), V (volume of the unit lattice) and Z (atomic number). In particular, when the photoelectric effect can be ignored (the atomic number is small), considering that ρ≈2ΣzZ / V, μ = α _S · ΣzZ / V≈α _S × ρ / 2 (8) However, , Ρ: density.

Next, as the correction factors depending on the material, the plate thickness of the steel plate to be measured, the linear absorption coefficient, and the count number are T ₁ and T, respectively.
₂ , μ ₁ , μ ₂ , V ₁ , V ₂ , μ ₁ T ₁ = ln (V ₀ / V ₁ ) μ ₂ T ₂ = ln (V ₀ / V ₂ ) ... (9) When they are equal (V ₁ = V ₂ ) μ ₁ T ₁ = μ ₂ T ₂ (10), the correction factor α depending on the material is α = T ₂ / T ₁ −1 = μ ₁ / μ ₂ − 1 (11)

Further, the linear absorption coefficient is influenced by metallurgical factors. As described above, the linear absorption coefficient of γ rays is determined by z (the number of atoms in the unit cell), V (the volume of the unit cell) and Z (the atomic number) (equation 7).
Therefore, as for the metallurgical factors affecting the linear absorption coefficient, the factors affecting z, V and Z may be targeted. Therefore, first, the external factors that affect the structure of steel include temperature, component composition, and processing. As the constituent factors of the microstructure determined by these external factors, phase (crystal structure) as a factor affecting z, V, and Z, volume change due to heat (temperature), and solid solution (penetration, substitution) Volume change, mass change, etc.

First, Table 1 shows the difference in z / V depending on the phase (crystal structure). Table 2 shows the coefficient of thermal expansion (coefficient of linear expansion) of αFe with respect to volume change due to heat (temperature). Table 3 shows the calculated z / V according to Table 2. Further, regarding the volume change and the mass change due to solid solution, for example, as elements that perform substitutional solid solution, Be, Al, Si, P, T
i, V, Cr, Mn, Ni, Cu, Zn, Nb, Mo,
Sn and W can be mentioned. The change in the lattice constant associated with the substitutional solid solution into αFe has a certain degree of correlation with the atomic radius difference between Fe and the solute. The lattice expansion is 0.361 at the maximum.
Since it is × 10 ^-12 m / wt% (Ti), the amount of change in the lattice constant when an arbitrary element is dissolved in 0.1 wt% is ±
It is about 0.04 × 10 ^-12 m.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

Therefore, in general, an element having a large atomic weight has a large atomic radius, so that upon solid solution (substitution), the lattice expands and z / Z decreases or the atomic mass Z increases.
The difference caused by the effect of lattice expansion and mass increase is that the change of zZ / V is ± 5.0 × 1 at most due to substitutional solid solution in αFe.
It is about 0 ^-2 %, and the substitutional solid solution with γFe is about the same as the substitutional solid solution with αFe. Further, H, B, C, and N are listed as the elements that form an interstitial solid solution, and it is sufficient to consider only C for the interstitial solid solution in Fe. The change of zZ / V by that is αFe, γF
e At most 5.0 x 10 ^-2 % to 10.0 x 10 ^-2 %
Is. The effects of these metallurgical factors on Z and z / V are summarized in Table 4. From this, it is understood that when the phase is completely transformed or when the temperature changes over the entire area, the influence of the volume change due to the phase and thermal expansion is large.

[0020]

[Table 4]

[0021]

Embodiment An embodiment according to the present invention will be described below with reference to FIG. FIG. 2 is a diagram showing a flowchart for implementation according to the present invention. As shown in FIG. 2, first, at the start, the reading of the component composition values of the steel plate to be measured is started, and subsequently, the temperature and the plate thickness of the steel plate are calculated by the estimation calculation in each rolling pass. The temperature distribution inside the steel sheet, the transformation rate (crystal structure), the volume change due to heat, etc. are estimated from the working state, and the number of atoms in the unit cell, the atomic number, and the volume of the unit cell are determined. As a result, the linear absorption coefficient is calculated by the equation (7), and the plate thickness is completely corrected by the equation (11) based on the measured radiation transmission amount by the γ-ray and the linear absorption coefficient. Is calculated.

FIG. 3 is a diagram showing the relationship between the plate thickness measurement error and the slab number ratio between the method of the present invention and the conventional method. As shown in FIG. 3, as the thickness measurement error, (radiation thickness meter measurement value-offline thickness measurement value) / (offline thickness measurement value) x 1
The value of 00 indicates that the method of the present invention has an extremely small plate thickness measurement error as compared with the conventional method.

[0023]

As described above, the present invention is a method for counting the amount of radiation that has passed through a steel plate and measuring the plate thickness. In calculating the plate thickness of the steel plate by calculation, the temperature component composition and Estimate the phase (crystal structure) determined by the processing state, volume change due to heat, etc., and based on this estimation result, calculate the linear absorption coefficient of radiation according to the preset calculation formula, and use this calculation result. Since the thickness of the steel sheet is measured, it has an extremely excellent effect that can contribute to the improvement of the quality of the steel sheet.

[Brief description of drawings]

FIG. 1 is a block diagram for implementing the present invention,

FIG. 2 shows a flow chart for implementation according to the invention,

FIG. 3 is a diagram showing a relationship between a plate thickness measurement error and a slab number ratio between the method of the present invention and the conventional method.

[Explanation of symbols]

 1 Steel Plate 2 Finishing Rolling Machine 3 Radiation Source 4 Radiation Dose Detector 5 Machine Side Operation Panel 6 Thermometer 7 Thermometer Converter 8 Thickness Measurement Control Device 9 Display 10 Recorder 11 Operation Panel 12 Plate Thickness Calculation Unit 13 Correction Calculation Unit 14 calculator

Claims (1)

[Claims] 1. A method for measuring the plate thickness by counting the amount of radiation that has passed through the steel plate, the phase being determined by the temperature, composition and working state of the steel plate to be measured when calculating the plate thickness of the steel plate by calculation. (Crystal structure), volume change due to heat, etc. are estimated, and based on this estimation result, the linear absorption coefficient of radiation is calculated according to a preset calculation formula, and the plate thickness of the steel plate is measured using this calculation result. A method for measuring the thickness of a steel sheet by radiation, which comprises: