JPH0412260A - Detecting method for surface flaw of metallic member - Google Patents

Abstract

PURPOSE:To detect a surface flaw with high accuracy without spoiling quality by a simple equipment by heating the surface of a metallic member by a high frequency current and detecting a distribution of radiation energy of radiated medium infrared rays of specific wavelength by an infrared camera. CONSTITUTION:When a metallic member 1 presses through in a high frequency induction coil 2, radiation energy is radiated from the surface of the member 11 by a high frequency current which is subjected to frequency control by an inverter 3, there fore, an infrared image is photographed by four sets of infrared cameras 4 placed immediately behind the coil 2. The camera can detect radiation energy of medium infrared rays of 3 - 5 mum wavelength, an infrared image of a detection object from the member 1 is formed in many semiconductor image pickup elements placed two-dimensionally, and a video signal corresponding to photodetecting intensityu is outputted to a data processing panel 5 by an electronic scan. By setting the detection wavelength of the camera 4 to 3 - 5 mum, a fluctuation of photodetecting infrared-ray intensity caused by a variation of infrared emissivity scarcely occurs, therefore, even if the surface of the member 1 does not become a wetting state, an SN ratio is high, and an output which can discriminate enough a surface flaw is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting surface flaws on metal members.

[Conventional technology]

For example, infrared flaw detection has been known as a method for detecting the presence or absence of surface flaws in rolled metal members. This method involves passing a metal member through a high-frequency induction coil to excite a high-frequency induced current on the surface of the metal member to induction heat the surface of the metal member. The temperature detection output at the scratched area changes greatly in a pulse-like manner to detect the scratch.

However, the infrared camera conventionally used in this infrared flaw detection method is one made by ELKEM, which uses a mercury-cadmium chill light as a detection element, and its detection wavelength detects electromagnetic waves in the far-infrared region of 8 to 12 μm. there were. However, infrared flaw detection, which is carried out by exclusively detecting electromagnetic waves in the far-infrared region, can detect changes in infrared emissivity due to scale adhesion to the surface of metal parts or differences in surface gloss. There was a problem that it became difficult to detect surface scratches. Therefore, in the infrared flaw detection method disclosed in JP-A No. 58-85146, the emissivity is made uniform by spraying liquid (water) onto the surface of the metal member being detected to moisturize the surface. Efforts are being made to improve the signal-to-noise ratio and make detection easier.

[Issues with conventional technology]

However, when the surface of a metal member is moistened with a liquid as described in item 1, detection errors will occur if the metal member is not evenly moistened. In addition, it takes a lot of man-hours to dry it after inspection, and if the drying is incomplete, there is a risk that the quality will be affected.

[Failure to solve the problem]

The present invention aims to solve the above problems, and involves heating the surface of a metal member with a high-frequency current and detecting the distribution of mid-infrared radiation energy with a wavelength of 3 to 5 μm emitted from the surface using an infrared camera. This is a characteristic feature.

〔Example〕

FIG. 1 shows a system diagram of a surface flaw detection device that uses a long rectangular steel material as the material to be inspected. In the figure, reference numeral 1 denotes a metal member to be inspected, and the metal member 1 is moved at a constant speed in the direction of the arrow by the drive of a roller j general feeding device (not shown). 2 is a high frequency induction coil through which a high frequency current whose frequency is controlled by an inverter 3 is passed through the coil 2, and a metal member 1 is passed through the coil 2.
pass

Immediately after the coil 2, four infrared cameras 4 are installed so as to face each surface of the metal member 1.

5 is a data processing board for processing video signals obtained from the outside line cameras 4, and 6 is a control board.

FIG. 2 shows a graph of the intensity of radiant energy generally emitted from the surface of an object. As shown in this graph, any object with a temperature emits electromagnetic waves with an intensity corresponding to the surface temperature, and as the temperature rises, the radiated energy increases. However, when the temperature is low, as shown in the figure, there is no radiation of short wavelengths. On the other hand, FIG. 3 shows a graph showing the infrared transmittance in the atmosphere. As shown in the graph, the infrared transmittance in the atmosphere varies greatly depending on the wavelength. And in the far infrared region, the wavelength is 8 to 1.
High transmittance at 3 μm, wavelengths 3 to 5 in the medium-speed infrared region
The transmittance in μm is generally high, and when these wavelengths pass through the atmosphere, they are absorbed by the main components of the atmosphere (H□O, CO2, etc.) and are therefore called the atmospheric window.

However, in the present invention, the infrared camera 4 has wavelengths of 3 to 3.
An infrared camera capable of detecting mid-infrared radiation energy of 5 μm is used. Infrared rays of this wavelength have high transmittance through the atmosphere and are also emitted from objects with relatively low temperatures (300K or higher). Then, an infrared image of the detected object is formed through a lens through an infrared camera 4 in which a large number of semiconductor image sensors are two-dimensionally arranged, and a charge (BiL image signal) generated in accordance with the intensity of the received infrared light is electronically scanned. The data is sequentially outputted to the data processing board 5.

By the way, according to Blank's radiation law, the wavelength λ, the absolute temperature T, and the radiant energy E have the following relationship.

Since the present invention detects mid-infrared rays with a wavelength λ of 3 to 5 μm, λ-4 μm is substituted into the above equation (1) and compared with the conventional detection wavelength of λ-10 μm in the far infrared region. Therefore, T=290 K (17゛c), Tm
Table 1 shows the radiant energy E calculated at 2O3K (27°C).

Table 1 In other words, at λ-4μm, the rate of change in radiant energy for a temperature difference of 10°C is 0.47610.718 = 0.66, whereas for λ-10μm, the rate of change in radiant energy for a temperature difference of 10°C is 0. .84510.992 #01
It becomes 85.

Expressing this in a simplified form, △T4=56j! ogE2/E △T1o=141 j! It becomes ogEz/E.

Table 2 calculates the temperature change when the emissivity changes by 0.1, assuming that E is the radiant energy when it is a black body (emissivity 1.0).
become that way.

Table 2 In other words, at a wavelength of 10 μm, the surface temperature of the detected object is 8.2
Even if the emissivity increases by 0.1 °C, the radiant energy remains the same, so the infrared camera will only detect the same temperature.However, at a wavelength of 4 μm, the surface temperature of the object to be detected is 3.3 °C. Even if the emissivity decreases by 0.1, the radiant energy increases and the infrared camera can detect the temperature change. In other words, by setting the wavelength to 4 μm, the influence of the emissivity of the detected object on the radiant energy can be reduced.

For this reason, the infrared camera 4 that detects radiant energy with a wavelength of 3 to 5 μm has little variation in the received infrared intensity due to changes in the infrared emissivity of the surface of the metal member 1, and for this reason, the surface of the metal member 1 does not have to be kept in a wet state. It also has a high signal-to-noise ratio and can provide an output that can sufficiently identify surface flaws.

〔Effect of the invention〕

As described above, according to the method for detecting surface flaws on metal members of the present invention, surface flaws can be detected without wetting the metal member with water, etc. This method has the advantageous effect that the equipment can be simplified without requiring a drying device, there is no risk of deteriorating the quality of the metal member, and that surface flaws can be detected with high precision with little risk of misdetection.

[Brief explanation of drawings]

The drawings show an embodiment of the method for detecting surface flaws on metal members according to the present invention, and FIG. 1 is a system diagram of the detection device, and FIG. 2 is a graph showing the intensity of radiant energy from the surface of an object.
FIG. 3 is a graph showing infrared transmittance in the atmosphere. 1... Metal member, 2... High frequency induction coil, 4...
・Infrared camera.

Claims (1)

[Claims] A method for detecting surface flaws on a metal member, comprising heating the surface of the metal member with a high-frequency current, and detecting the distribution of mid-infrared radiation energy with a wavelength of 3 to 5 μm emitted from the surface using an infrared camera.