JPH05288671A - Measuring method by infrared spectroscopy method for surface of steel plate - Google Patents

Abstract

PURPOSE:To obtain the measuring method for the roughness (roughness and waviness) of the surfaces of various kinds of steel plates. CONSTITUTION:Infrared rays in an s-polarized light state (the polarized light orthogonal to a plane formed of incident light and the surface of a steel plate) is cast on the surface of a steel plate, and the reflected spectrum of the infrared rays is obtained. The reflectivity at the specified wave number in the reflected spectrum of the infrared rays is obtained. The roughness of the surface of the steel plate is estimated based on the correlation with the reflectivity and the roughness (roughness and waviness) of the surface of the steel plate, which are obtained beforehand.

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 roughness of a steel sheet surface (roughness and waviness), and is required to have workability and sharpness of paint for automobiles and household electric appliances. It is applied to the field.

[0002]

2. Description of the Related Art The requirements for steel sheets used for automobiles and household electric appliances have expanded to fields such as corrosion resistance as well as workability and paint clarity, among which paint clarity is a consumer hobby. Together with diversification, its importance is increasing.

It is the roughness (roughness and waviness) of the steel sheet surface that controls the paint clarity and workability, and in order to control this, steel manufacturers put a pattern on the roll with a laser or electric discharge, In this way, steel sheets with appropriate surface roughness are manufactured by temper rolling at. Regardless of which method is used, it is important to control the roughness of the steel sheet surface.If the roughness is low, there are obstacles such as die scuffing during press working, while if the roughness is high, The coating clarity deteriorates. Therefore, it is necessary to control the surface roughness within a certain range at the steel sheet manufacturing site.

The roughness of the surface of the steel sheet can be measured by a contact method in which a tip having a sharp tip is brought into contact with the surface for scanning to measure the roughness, and a method of irradiating the surface with light to measure the intensity of reflected light. A non-contact method (optical method) for measuring roughness based on a change or a change in focus attached to a surface is widely used.

Since the measuring accuracy of the contact method depends on the polar radius of the tip of the stylus, it is difficult to measure the roughness of about 0.1 μm or less, and the measuring accuracy is low. Further, since it is a local measurement, there is a drawback that the error is large even if the number of times of measurement is increased. Therefore, the non-contact method is currently being replaced.

Since the non-contact method uses light as a medium, it has higher sensitivity than the contact method. However, since the absorption of light by a substance existing on the surface to be measured, such as a lubricating oil or an anticorrosive oil, causes a large error in the measured value, it is difficult to apply it unless the surface is clean. For example, JP-A-62-21
No. 11 discloses, as a surface roughness meter using reflected light, a device for measuring roughness from the ratio of specular reflected light and scattered reflected light. However, in this device, since the reflected light is attenuated by dirt such as oil on the measurement surface, when it is applied to a sample such as a steel plate surface coated with lubricating oil or rust-preventing oil, there is a drawback that the error becomes large.

As described above, the method of measuring the surface roughness of the steel sheet currently used is said to be highly accurate, simple and quick, which is required at the manufacturing site, and is not affected by the lubricating oil or rust preventive oil on the surface of the steel sheet. Does not meet the requirements.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art, to prevent the roughness of the steel sheet surface from being obstructed by the lubricating oil or rust preventive oil present on the steel sheet surface, and to simply, quickly and with high accuracy. There is a point to provide.

[0009]

According to the present invention, an infrared reflection spectrum is obtained by injecting infrared light in the s-polarized state (polarized light perpendicular to the plane formed by the incident light and the normal to the steel plate surface) to the roughness of the steel plate surface. It is a method of measuring the roughness at a specific wave number in the infrared reflection spectrum, and measuring the roughness of the surface of the steel sheet based on the correlation between the reflectance and the roughness that is obtained in advance.

The features of the present invention are that the reflection behavior of infrared light is affected by the roughness of the steel plate surface, and that the electric field strength of the standing wave formed on the steel plate surface by the reflection of infrared light is its polarization. It depends on the state.

When a general infrared spectrophotometer is used, the reflection behavior of infrared light on the surface of the steel sheet is affected by the roughness of the steel sheet. When the roughness is small, the reflectance is large and the roughness becomes large. The reflectance tends to decrease. That is, since there is no surface roughness, for example, infrared light incident on a mirror-finished surface is reflected at the same reflection angle as the incident angle and reaches the detector, the decrease in reflectance is due to the reflectance specific to the metal. Controlled only by. On the other hand, when the surface has roughness, the reflection angle of the incident infrared light has various values and is not necessarily the same as the incident angle, so that the ratio of the reflected light reaching the detector decreases. When the surface roughness is low, this reduction rate has a narrow distribution centered around the value equal to the incident angle, so the amount of infrared light that reaches the light receiving part of the detector is relatively large. , The reflectance is high. On the other hand, when the surface roughness is large, the distribution of the reflection angle has a wide distribution centered on the value equal to the incident angle, so the amount of infrared light reaching the light receiving part of the detector is small and the reflectance is It gets lower.

Infrared light in the p-polarized state, s-
The characteristics of the infrared reflection spectrum when the light source is infrared light in a polarized state or ordinary infrared light that does not selectively use the polarization component will be described.

Infrared light in the p-polarization state The reflection behavior of infrared light on a metal surface depends largely on the polarization state, and is in the p-polarization state (parallel to the plane formed by the incident light and the normal to the steel plate surface). When (polarized) infrared light is incident on the surface of the steel sheet at a large angle of 50 ° or more, a standing wave having a large electric field intensity is formed vertically on the surface of the steel sheet due to the interference between the electric field of the incident light and the electric field of the reflected light. As a result, the infrared absorption spectrum of the components that oscillate perpendicularly to the steel plate surface in the vibration mode of the infrared active substances such as rust preventive oil and lubricating oil existing on the steel plate surface is detected with high sensitivity. Light undergoes the effect of reducing the reflectance due to the roughness of the steel plate surface.

Infrared light of s-polarization state When infrared light of s-polarization state (polarization perpendicular to the plane formed by the incident light and the normal to the steel plate surface) is incident on the steel plate surface, the electric field and reflected light of the incident light Of the standing wave cancels each other on the surface of the steel sheet, and the electric field strength of the standing wave becomes almost zero. As a result, the infrared absorption spectra of infrared active substances such as lubricating oil and rust preventive oil on the surface of the steel sheet are not detected, but the effect of reducing the reflectance due to the roughness of the surface of the steel sheet is received.

Normal Infrared Light Normal infrared light used in general infrared spectroscopy is p
It contains a polarized component and an s-polarized component. Therefore, when normal infrared light is incident on the surface of the steel sheet, p-
Since a standing wave is formed perpendicularly to the steel plate surface by the polarized component, the infrared absorption spectrum of infrared active substances such as rust preventive oil and lubricating oil existing on the steel plate surface is detected, and at the same time, it depends on the roughness of the steel plate surface. Receives the effect of reducing the reflectance.

As described above, when normal infrared light (including both p-polarized light and s-polarized light) or infrared light in the p-polarized state is used as incident infrared light for measuring the roughness of the steel sheet surface, Since the reflection spectrum is affected not only by the roughness of the steel plate surface but also by the contamination of the surface with rust-preventing oil, lubricating oil, etc., the accuracy of roughness measurement is reduced. On the other hand, s-
When polarized infrared light is incident, it is hardly affected by dirt such as lubricating oil on the steel plate surface, and the reflection spectrum is affected only by the roughness of the steel plate surface. It is higher than when infrared light or normal infrared light is used.

When infrared light in the s-polarized state is used, the interference between the incident infrared light and the reflected infrared light occurs at any incident angle, and the oscillating electric field strength of the standing wave on the surface of the steel sheet is always almost zero. The incident angle may be any angle.

According to the present invention, the infrared reflection spectra of steel sheets of various roughness whose roughness is previously measured by a contact type or non-contact type roughness meter are measured by infrared reflection using infrared light in the s-polarized state. Method, the relationship between the reflectance at a specific wave number and the roughness is determined in advance, and the relationship is used as a calibration curve to measure the roughness of the surface of the steel sheet of unknown roughness as the reflectance of infrared light in the s-polarized state. It is estimated from.

[0019]

EXAMPLE In this example, IR810 manufactured by JASCO Corporation was used as an infrared spectrophotometer, and the incident angle of infrared light in the s-polarized state was 70 °. The IR 810 is a dispersion type infrared spectrophotometer, but the same result can be obtained with a Fourier transform type infrared spectrophotometer. In terms of sensitivity, the Fourier transform type is higher than the dispersion type, so the Fourier transform type is recommended for thin film measurement.

Centerline average roughness (Ra) and filtered centerline waviness (Wca) of a cold-rolled steel sheet which is a standard sample for preparing a calibration curve.
Is shown in Table 1. Ra was measured under the condition that the high cutoff value was 0.8 mm. Also, Wca is a low cutoff value of 0.8.
mm and the high cutoff value was 8 mm. In each measurement, Surfcom 550A manufactured by Tokyo Seimitsu Co., Ltd., which is a contact type roughness meter, was used.

FIG. 1 shows an infrared reflection spectrum obtained by entering infrared light in the p-polarization state and an infrared reflection spectrum obtained by entering infrared light in the s-polarization state. In Figure 1, p
-It is shown that the absorption by the lubricating oil on the surface, which was observed under the condition of using the polarized infrared light, was not observed at the incidence of the s-polarized infrared light. It can be seen that the surface roughness can be measured with high accuracy when used.

The infrared reflectance spectrum of s-polarized light incident on the standard sample was measured to obtain the reflectance at 3800 cm ^-1 . Table 2 shows the reflectance of each standard sample. In this example, the reflectance was measured at 3800 cm ^-1 , but in principle, there is no problem with any wave number.

FIG. 2 shows the relationship between Ra and reflectance. FIG. 2 shows that a good linear relationship with a correlation coefficient r = 0.990 holds between Ra and the reflectance. FIG. 3 shows the relationship between Wca and reflectance. FIG. 3 shows that a good linear relationship with a correlation coefficient r = 0.996 holds between Wca and the reflectance. Therefore, the infrared reflection spectrum of an unknown steel plate is s-
Ra and Wca can be measured by using FIG. 2 and FIG. 3 as a calibration curve by measuring using infrared light in a polarized state and determining the reflectance at 3800 cm ⁻¹ .

An attempt was made to apply this method to the measurement of a cold rolled steel sheet in which Ra and Wca are actually unknown. Infrared reflection spectrum was measured by an infrared reflection method using s-polarized infrared light, 3800c
When Ra and Wca were estimated from the reflectance of m ⁻¹ , Ra
The values of 0.54 μm and Wca = 0.46 μm were obtained. This value is a value obtained by the contact method Ra = 0.53 μm, W
It shows a good agreement with ca = 0.47 μm.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

INDUSTRIAL APPLICABILITY The present invention makes it possible to estimate the roughness of the surface of various steel plates simply, quickly and with high accuracy without being affected by the lubricating oil, rust preventive oil, etc. existing on the steel plate surface. .. Therefore, it is possible to manage the image clarity and lubricity of steel sheets for automobiles and steel sheets for home appliances.

[Brief description of drawings]

FIG. 1 is an infrared reflection spectrum of a steel plate surface measured using infrared light in a p-polarization state and infrared light in a s-polarization state.

FIG. 2 is a center line average roughness of a cold rolled steel sheet as a standard sample and 3 of infrared reflection spectra measured by using s-polarized infrared light.
The figure which showed the relationship of the reflectance of 800 cm- ¹ .

[Fig. 3] Filter center line waviness and s- of a cold rolled steel sheet of a standard sample
The figure which showed the relationship of the reflectance of 3800 cm < ^-1 > of the infrared reflection spectrum measured using the polarized infrared light.

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[Procedure amendment]

[Submission date] May 11, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

[0019]

EXAMPLE In this example, IR810 manufactured by JASCO Corporation was used as an infrared spectrophotometer, and the incident angle of infrared light in the s-polarized state was 70 °. The IR 810 is a dispersion type infrared spectrophotometer, but the same result can be obtained with a Fourier transform type infrared spectrophotometer. In terms of sensitivity, the Fourier transform type is higher than the dispersive type, so the Fourier transform type is recommended for measuring minute roughness .

Claims (1)

[Claims] 1. An infrared reflection spectrum is measured by injecting infrared light in the s-polarized state (polarized light perpendicular to the plane formed by the incident light and the normal to the steel plate surface) to the surface of the steel plate and measuring the infrared reflection spectrum. Obtain the reflectance at a specific wave number in the reflection spectrum, based on the correlation between the reflectance and the roughness obtained in advance, by infrared spectroscopy of the steel sheet roughness, characterized by measuring the roughness of the steel sheet surface Measurement method.