JP2008232765A - Device of inspecting flaw in the vicinity of surface using back scattered radiation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flaw inspection device capable of surely determining the presence of flaws in the vicinity of the surface of target of inspection, such as, casting by utilizing back scattered radiation, without requiring high radiation energy. <P>SOLUTION: The device is constituted so as to provide a rotary table 2 for holding the inspection target W to rotate it in front of the irradiation direction of the radiation from a radiation generating source 1 and includes a radiation detector 4 for detecting the back scattered radiation from the inspection target W on the rotary table 2 through a collimator 3 and a reconstitution operator 6 for reconstituting a CT image using the output of the radiation detector 4. The back scattered radiation data is collected by rotating the rotary table 2 within an angle range of 180°, while the inspection target W is arranged on the rotary table 2 so that the center of the inspection region A thereof almost coincides with the condensing point of the collimator 3 and the rotary axis R of the rotary table 2 passes through the inspection region A to be subjected to the reconstitution of a tomographic image. By this method, the presence of the flow in the vicinity of the surface of the inspection target W can be inspected using radiation of energy of a degree reaching the inspection region A in the vicinity of the surface of the inspection target W, without transmitting the radiation through the inspection target W. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for inspecting the presence or absence of defects near the surface of an inspection object such as a casting or an aluminum die cast product using radiation such as X-rays, gamma rays, or neutrons, and more specifically, depending on the inspection object. The present invention relates to a defect inspection apparatus that constructs a tomographic image of an inspection region near the surface using backscattered radiation.

  Non-destructive inspection of internal defects such as voids, cracks and voids in casting materials such as castings and aluminum die-cast products improves reliability, safety, and yield of final products. The place that contributes to

Conventionally, for such non-destructive inspection of casting materials, radiation fluoroscopes that transmit X-rays, gamma rays, neutrons and other radiation to the casting material and image the intensity of the transmitted radiation, and further inspection A tomographic image of the casting material is obtained by reconstructing the transmitted radiation data captured at every predetermined minute angle while rotating the target casting material around an axis along a direction orthogonal to the radiation transmission direction. A radiation CT apparatus has been used (see, for example, Patent Document 1).
JP-A-7-12759

  Incidentally, casting materials such as cast iron are materials that are difficult to transmit radiation such as X-rays, gamma rays, and neutrons, and very high energy radiation is required to transmit thick cast iron.

  Taking the case of X-rays as an example, an X-ray tube voltage of about 200 kV is required for inspection of cast iron having a thickness of 15 mm in the X-ray transmission direction. Incidentally, the tube voltage of a fluoroscope for a human body is usually 100 kV or less. Therefore, an X-ray fluoroscopic apparatus and an X-ray CT apparatus using cast iron as an inspection object are expensive and require a complicated system.

  On the other hand, in the case of a material such as cast iron, the voids, cracks, or voids present in the center of the material are hardly problematic in strength, but rather are in the vicinity of the casting surface (the surface of the casting immediately after casting). Defects such as cracks and voids are a major problem. The reason for this is that, in general, in many cases, a cast product finally cuts a surface layer portion including a casting surface to obtain a final product. However, as shown in FIG. If there are defects such as cracks C or voids S, as shown in FIG. 2 (B), the defects are exposed on the surface of the product by cutting the surface layer portion, resulting in surface defects of the final product, This is because manufacturing costs such as processing are wasted.

  Although the defects near the casting surface could be confirmed with a conventional radioscopy apparatus or radiation CT apparatus, as described above, high-energy radiation is required, and an apparatus that can be more easily inspected is desired.

  The present invention has been made in view of such circumstances, and does not require high radiation energy, and reliably determines the presence or absence of defects near the surface of an inspection object such as a casting using backscattered radiation. The problem is to provide a device that can be used.

  In order to solve the above problems, the defect inspection apparatus near the surface using the backscattered radiation of the present invention uses the backscattered radiation obtained by irradiating the inspection object with the radiation, An apparatus for inspecting for the presence or absence of a defect, which is arranged in front of a radiation source and a radiation irradiation direction from the radiation generation source, holds an inspection object, and is centered on an axis orthogonal to the radiation irradiation direction. Provided between a rotary table for rotating the inspection object, a radiation detector for detecting backscattered radiation from the inspection object on the rotation table, and the radiation detector and the inspection object on the rotation table. And a reconstruction calculation device for constructing a tomographic image of the inspection object along a plane orthogonal to the rotation axis using the output from the radiation detector, and the inspection object In the state where the center of the inspection area substantially coincides with the condensing point of the collimator and is arranged on the rotation table so that the rotation axis passes through the inspection area, the rotation table is within about 180 °. Rotating within an angular range, the reconstruction computing device is characterized by constructing a tomographic image of the examination region using backscattered radiation data obtained within the rotational angular range (claim 1). .

  Here, in the present invention, the collimator can suitably employ a configuration (Claim 2) that is arranged so that the condensing point is substantially located on the rotation axis.

  Further, in the present invention, the X-ray detector is a two-dimensional detector, and the collimator has a structure in which openings are provided in cone cones at different angles from a condensing point. 3) is possible.

  Alternatively, in the present invention, the X-ray detector is a one-dimensional detector, and the collimator has a structure in which apertures are radially formed at different angles from a condensing point. 4) is also possible.

  Examples of the radiation used in the present invention include X-rays, gamma rays, and neutron rays.

  The present invention utilizes backscattered radiation in which radiation incident on a material is scattered backward by interaction with the material, and detects defects near the surface of the inspection object without requiring high radiation energy. It is what.

  That is, as shown in FIG. 3, when the radiation r is incident on the substance m, the radiation is scattered in the forward and backward directions with a certain probability in addition to transmitting the substance m. This backscattering occurs with a certain probability even if the radiation has low energy. Therefore, if this backscattered radiation is used, it is not necessary to use radiation having such a high energy that can pass through the inspection object for the inspection of the presence or absence of defects near the surface.

  Taking X-rays as an example, as shown in FIG. 4A, as described above, a tube voltage of 200 kV is required to transmit 15 mm of cast iron, but for example, a 100 kV X-ray tube The X-rays generated under the voltage cannot pass through the cast iron of that thickness, as shown in FIG. 5B, and reach a depth of about 5 mm from the surface and stop there. However, this X-ray reaches the vicinity of the casting surface, that is, about 1 mm to several mm from the surface and includes the final surface cutting region, and is then scattered stochastically there.

  In order to selectively detect the radiation scattered backward, in the present invention, a collimator is provided in front of the incident surface of the radiation detector. This collimator is arranged so that its condensing point substantially coincides with the center of the inspection target area, and openings are provided in a single row radial shape or cone radial shape from the condensing point that substantially coincides with the center of the inspection target region of the inspection target object. A radiation absorbing material having a different structure is used. As this radiation absorbing material, for example, tungsten or the like can be suitably used for X-rays, and degraded uranium or the like having a higher shielding ability than tungsten can be suitably used for gamma rays, and neutrons can be absorbed by neutrons. A material containing boron or lithium can be preferably used.

  In addition, in order to obtain data for constructing a tomographic image, the rotation axis of the rotary table needs to exist in the inspection target area, and preferably the center of the inspection target area and the rotation axis substantially coincide with each other. The rotating table is rotated in the state to detect the backscattered radiation.

  When there is no defect such as a void, crack, or void in the inspection target region near the surface of the inspection target, the inspection target region A interacts as shown in FIG. On the other hand, as shown in FIG. 2B, when there are defects D such as voids, cracks or voids in the inspection target area A, these defects D are voids. Since there is no substance that causes interaction, there is no backscattering of radiation from the defect D. Accordingly, when the defect D as described above is in the inspection target region, the intensity of the backscattered radiation is reduced as compared with the case where there is no defect D.

  Then, when the inspection object is placed on a rotary table, the intensity data of the backscattered radiation as described above is collected at a certain angle by rotating the rotary table, and the CT image is reconstructed using the collected data. As a result, a backscattered radiation CT image is obtained.

  In the present invention, the collection range of the backscattered radiation intensity data, that is, the rotation range of the rotary table for CT imaging is limited to about 180 ° or less. This is, for example, the surface of the inspection object. With the vertical direction as a reference, it is rotated approximately 90 ° or less counterclockwise and approximately 90 ° or less clockwise.

The reason why the rotation angle range of the rotary table at the time of CT imaging is limited to about 180 ° or less is as follows.
1. The apparatus of the present invention images backscattered radiation due to defects near the surface of the inspection object. If the state shown in FIG. 6A is a rotation angle of 0 °, +90 as shown in FIG. CT imaging is performed by rotating within the range of 90 ° from −90 ° as shown in FIG. 5C. The rotation center of the rotary table is in the inspection area A set near the surface of the inspection object W. Preferably, CT imaging is performed in a state where the center of the inspection area A and the rotation center R substantially coincide with each other so that R enters. In such imaging, if the inspection object W is rotated beyond 180 ° as shown in FIG. 6D, the inspection region near the surface to be inspected with respect to the radiation incident position of the inspection object W. It can be assumed that A is separated and the incident radiation does not reach the inspection region A and no backscattering occurs, or even if it occurs, the backscattering radiation does not reach the detector. This is because it is negligible.

  2. If the inspection object is rotated beyond about 180 °, the inspection object W may cause physical interference with the radiation source S or the like as shown in FIG.

  3. Due to recent advances in CT technology, it is possible to obtain a good CT image even if a rotation angle of the object at the time of CT imaging is limited to about 180 ° or less.

  4). By attaching an angle limit of approximately 180 ° or less, the region of the inspection region near the surface of the inspection object can be brought as close as possible to the radiation port of the radiation source, thereby increasing the geometric magnification of the radiation image. You can also. For this reason, it is also possible to acquire an enlarged CT image.

  Therefore, in the present invention, the rotation angle range of the rotary table at the time of CT imaging is set to approximately 180 ° or less to the extent that backscattered radiation from the vicinity of the surface of the inspection object can be ignored and / or inspection. To the extent that the object does not interfere with the radiation source and / or to obtain a good CT image even if angle restriction is applied, and / or to bring the vicinity of the surface of the inspection object as close as possible to the radiation emission port It is to the extent that it can be done.

  According to the present invention, defects existing near the surface of a cast product such as cast iron or aluminum die casting are detected by backscattered radiation without using high-energy radiation. A destructive CT inspection can be performed.

In addition, while preventing physical interference between the object to be inspected and the radiation source, the part near the surface to be inspected can be brought as close as possible to the radiation outlet, thereby increasing the geometric magnification of the radiation image. And an enlarged CT image can be acquired.
And by realizing the presence or absence of defects near the surface of the cast product by CT image using such backscattered radiation, the surface defect of the final product after cutting near the surface is detected in advance, Cutting costs can be reduced.

  Moreover, although the presence or absence of the defect of the surface vicinity was able to be confirmed even with the conventional radioscopy apparatus and CT apparatus, the high energy radiation is required and the apparatus which can be test | inspected more easily by this invention is implement | achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic plan view showing a mechanical configuration and a block diagram showing a system configuration.

  The apparatus includes an X-ray generation source 1 mainly composed of an X-ray tube, a rotary table 2 on which an inspection object W is mounted to give rotation, and an X scattered back from the inspection object W on the rotation table 2. A collimator 3 that selectively transmits rays and shields other X-rays, an X-ray detector 4, and a computer 6 that performs CT calculation and the like are mainly configured.

  The computer 6 captures the output of the X-ray detector 4 via the image data capturing circuit 7 and displays a CT image reconstructed by CT calculation on the display 8. The computer 6 also controls the drive of the rotary table 2 and the X-ray generation source 1 through a driver or an X-ray controller (none of which are shown), and includes operations such as a keyboard, a mouse, or a joystick. Various commands can be given by operating the unit 9.

  The X-ray detector 4 is a two-dimensional (panel) detector in this example, and the collimator 3 is made of, for example, tungsten or the like, which easily absorbs X-rays, and has a plurality of cone-shaped openings at different angles. In the formed structure, the positional relationship between the two is set so that the apex of each cone-shaped opening, which is the light condensing point, is approximately located on the rotation axis R of the turntable 2. In the X-ray generation source 1, a part of the tip on the X-ray emission port side passes through an opening 4 a provided at the center of the X-ray detector 4 and protrudes toward the rotary table 2.

  The inspection object W is, for example, a cast iron product, and the purpose of the inspection is whether or not there is a defect such as a void, a crack, or a void on the surface of the final product after cutting the cast surface. The inspection object W is rotated about the rotation axis R while being mounted on the rotary table 2, but the inspection area A in the vicinity of the surface is substantially located on the rotation axis R of the rotation table 2. Thus, it is used for CT imaging in a state mounted on the rotary table 2.

  Since the X-ray energy from the X-ray generation source 1 described above, that is, the tube voltage of the X-ray generation source 1 only needs to reach the inspection region A in the vicinity of the surface of the inspection object W, for example, 100 kV can do.

  When performing CT imaging, the inspection object W is mounted on the rotary table 2 as described above, and the rotary table 2 is rotated within a range of about 180 ° or less while irradiating the X-rays from the X-ray generation source 1. Then, the X-ray intensity data from the X-ray detector 4 is fetched into the computer 6 which fetches every minute angle set in advance. The X-rays incident on the X-ray detector 4 at the time of CT imaging are those in which the X-rays irradiated on the inspection object W are back-scattered by the inspection object W and pass through the collimator 3. Accordingly, the X-rays incident on the X-ray detector 4 become X-rays scattered back from the region near the condensing point of the collimator 3, that is, the inspection region A, in the inspection object W. As clarified in the description of FIG. 5 described above, if there are defects such as voids, cracks, or voids in the inspection region A, the substance that interacts with X-rays is lacking there. Backscattered X-rays are not generated from these defects, and the backscattered X-ray intensity is weaker than when these defects are not present.

  In the computer 6, a backscattered X-ray CT image of the inspection region A is constructed and displayed on the display unit 8 by reconstruction calculation using the backscattered X-rays from the inspection region A thus captured. From this CT image, it is possible to inspect the presence or absence of defects such as voids, cracks or voids in the inspection area A.

  Here, in the above embodiment, an example in which a two-dimensional detector is used as the X-ray detector 4 has been shown, but a one-dimensional detector may be used. In this case, the collimator 3 does not need to have a cone radial shape, and may have a structure in which openings having different angles are formed in a single row radial shape.

The radiation used in the present invention is not limited to X-rays as described above, and gamma rays and neutron rays can be used. In the case of using gamma rays, an isotope such as cobalt 60 (Co ⁶⁰ ) is used as a radiation source, depleted uranium or the like is used as a collimator material, and a gamma ray detector using a sodium iodide (NaI) scintillator as a detector. Can be used.

In the case of using a neutron beam, a neutron beam source using a small nuclear reactor is used as a radiation source, a material containing boron or lithium is used as a scintillator material, and boron trifluoride (BF ₃ ) is used as a detector. A neutron detector such as a counter may be used.

In the configuration diagram of the embodiment of the present invention, a schematic diagram showing a mechanical configuration and a block diagram showing a system configuration are shown together. It is explanatory drawing of the internal defect which becomes a problem in materials, such as cast iron. It is explanatory drawing of the backscattering of the radiation by a substance. When cast iron is used as an inspection object, it is an explanatory diagram of a difference in necessary tube voltage between the case where an image is obtained by transmitting X-rays and the case where backscattering is used. It is explanatory drawing of the difference in backscattered radiation when there are no defects, such as a void, a crack, or a void, in a test | inspection area | region, and these defects. It is explanatory drawing of the reason which makes the rotation angle range of a turntable substantially 180 degrees or less in this invention. It is explanatory drawing of the advantage in the case of making the rotation angle range of a turntable into about 180 degrees or less in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray generation source 2 Rotary table 3 Collimator 4 X-ray detector 4a Aperture 6 Computer 7 Image data capture circuit 8 Display 9 Operation part A Inspection area R Rotating shaft W Inspection object

Claims (4)

An apparatus for inspecting the presence or absence of defects near the surface of an object to be inspected using backscattered radiation obtained by irradiating the object to be inspected,
A radiation source, a rotary table disposed in front of the radiation direction from the radiation source, holding the inspection object, and rotating the inspection object around an axis perpendicular to the radiation irradiation direction; and A radiation detector for detecting backscattered radiation from the inspection object on the turntable, a collimator provided between the radiation detector and the inspection object on the turntable, and an output from the radiation detector And a reconstruction calculation device for constructing a tomographic image of the inspection object along a plane orthogonal to the rotation axis using
In the state where the inspection object is arranged on the rotary table so that the center of the inspection area substantially coincides with the condensing point of the collimator and the rotation axis passes through the inspection area. And the reconstruction calculation device constructs a tomographic image of the examination region using backscattered radiation data obtained within the rotation angle range. Defect inspection equipment near the surface using backscattered radiation.   2. The defect inspection apparatus near the surface using backscattered radiation according to claim 1, wherein the collimator is arranged so that a condensing point thereof is substantially located on the rotation axis.   2. The radiation detector according to claim 1, wherein the radiation detector is a two-dimensional detector, and the collimator has a structure in which openings are provided in a cone radial shape at different angles from a condensing point. Defect inspection equipment near the surface using backscattered radiation.   2. The radiation detector according to claim 1, wherein the radiation detector is a one-dimensional detector, and the collimator has a structure in which openings are radially formed in a row at different angles from a condensing point. Defect inspection equipment near the surface using backscattered radiation.

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