Flaw detection device and flaw detection method

Abstract

To provide a liquid immersion probe capable of performing a flaw detection inspection deep inside an object to be inspected in flaw detection.SOLUTION: A liquid immersion probe (52) includes a front face plate 64 that has a circular shape in plan view and is formed so that a surface facing an object to be inspected is formed as, a concave surface 68 that curves to gradually recesses toward a center. Defining a curvature radius of each of a first virtual tangent M1 and a second virtual tangent M2 which are perpendicular to each other at the center of the concave surface 68 and curve along the concave surface 68 as a first curvature radius R1 and a second curvature radius R2 respectively, the first curvature radius R1 and the second curvature radius R2 are different from each other. When ultrasonic waves (70, 72) oscillate in the solvent (24), the ultrasonic waves are focused at two points.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an immersion probe that oscillates ultrasonic waves, a flaw detection inspection device including the same, and a flaw detection inspection method using the same.

Background Art

[0002] For example, a turbine engine has a large number of members that rotate at high speed. This type of member is generally manufactured by subjecting a billet to forging or the like. Here, it is desirable that a member used in a harsh environment such as a constituent member of a turbine engine exhibits sufficient durability. In order to obtain such a member, it is conceivable to use a billet that does not have large defects inside. From the above viewpoints, a flaw detection inspection is performed on the billet prior to forging or the like. As a specific method thereof, immersion flaw detection inspection is exemplified.

[0003] In immersion flaw detection inspection, ultrasonic waves are oscillated from a probe to a billet immersed in water. When the diameter of the billet is large, in order to perform flaw detection deep inside near the center, as described in Patent Document 1, it may be necessary to use a plurality of probes that oscillate ultrasonic waves with different focal points. This is because ultrasonic waves with a longer focal length reach deeper inside the billet.

[0004] In addition, Patent Document 2 proposes a configuration of a probe that enables oscillation in two modes, an electric focusing mode and a time reversal mode. In this case, it is said that flaw detection from the inside to the surface of the billet is possible with a single probe by selecting the electric focusing mode for flaw detection of a relatively shallow part of the billet and the time reversal mode for flaw detection of a deep part.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] The technology described in Patent Document 1 uses four immersion probes. As the number of probes increases, the number of parts in the flaw detection inspection device also increases. Furthermore, it takes a long time to obtain information from all the probes. In other words, in this case, it is not easy to reduce costs, nor is it easy to shorten the inspection time.

[0007] On the other hand, the immersion probe described in Patent Document 2 has a complex structure. Moreover, even though it is a two-mode probe, it is not easy to emit ultrasonic waves across a wide wavelength range. Consequently, it is not easy to perform flaw detection deep inside large-diameter billets.

[0008] The present invention was made to solve the above-mentioned problems, and aims to provide a liquid immersion probe that has a simple configuration but can perform flaw detection deep inside an object under inspection, a flaw detection inspection device equipped with the same, and a flaw detection inspection method using the same. [Means for solving the problem]

[0009] To achieve the above objective, according to one embodiment of the present invention, a liquid immersion probe is provided which comprises a transducer that emits ultrasonic waves with a frequency of 10 MHz or higher to an object to be inspected immersed in a solvent, and which uses the ultrasonic waves to inspect whether or not there are defects in the object to be inspected, The device includes a front plate that is circular in plan view, and whose surface facing the object to be inspected is formed as a concave surface that curves so as to gradually become recessed towards the center. When the radii of curvature of the first and second virtual tangents, which are mutually orthogonal at the center of the concave surface and curve along the concave surface, are denoted as the first radius of curvature and the second radius of curvature, the first radius of curvature and the second radius of curvature are different, In the aforementioned solvent, the ultrasonic waves emitted from the transducer are focused at two points based on the difference between the first and second radii of curvature, providing an immersion probe.

[0010] According to another embodiment of the present invention, a flaw detection inspection apparatus comprising a storage tank for storing a solvent and an immersion probe for emitting ultrasonic waves to an object to be inspected immersed in the solvent, The immersion probe comprises a transducer that emits ultrasonic waves with a frequency of 10 MHz or higher to the object to be inspected, and a front plate that is circular in plan view and whose surface facing the object to be inspected is formed as a concave surface that curves so as to gradually become recessed towards the center. When the radii of curvature of the first and second virtual tangents, which are mutually orthogonal at the center of the concave surface and curve along the concave surface, are denoted as the first radius of curvature and the second radius of curvature, the first radius of curvature and the second radius of curvature are different, In the solvent, the ultrasonic waves emitted from the transducer are focused at two locations based on the difference between the first and second radii of curvature, while the ultrasonic waves that pass through the solvent and enter the object under inspection are focused at one location inside the object under inspection.

[0011] According to yet another embodiment of the present invention, in a flaw detection inspection method in which an object to be inspected is immersed in a solvent and an ultrasonic wave with a frequency of 10 MHz or higher is emitted from a transducer constituting a liquid immersion probe, and the presence or absence of defects in the object to be inspected is inspected by the ultrasonic wave, A flaw detection inspection method is provided using a liquid immersion probe that is circular in plan view, and whose surface facing the object to be inspected is formed as a concave surface that curves gradually toward the center, and which has a front plate in which the first and second radii of curvature are different, with the first and second radii of curvature being defined as the first and second radii of curvature, respectively, when the first and second radii of curvature are mutually orthogonal at the center of the concave surface and curve along the concave surface, and the ultrasonic waves emitted from the transducer in the solvent are focused at two locations based on the difference between the first and second radii of curvature, while the first and second radii of curvature are set to radii of curvature at which the ultrasonic waves that have passed through the solvent and entered the object to be inspected are focused at one location inside the object to be inspected. [Effects of the Invention]

[0012] According to the present invention, a dual-focus probe is employed as the immersion probe, which has two ultrasonic focus points (focal points). The focal length of the short-focus wave is extended by the lens effect of the object being inspected. As a result, the two focal points substantially coincide within the object being inspected. Therefore, it becomes easy to determine whether or not defects exist deep inside the object being inspected (perform flaw detection).

[0013] Therefore, it becomes possible to detect defects that were previously undetectable due to being below the detection limit of conventional technology. For this reason, for example, even in this invention, inspected objects that still do not show any defects can be selected as materials for components to be used in harsh environments. Such materials exhibit sufficient durability.

[0014] Furthermore, a dual-focus probe can be obtained by forming a concave surface on the front plate. This makes it possible to construct an immersion probe that can perform flaw detection deep inside the object being inspected, despite its simple configuration. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic perspective view of a flaw detection inspection device according to an embodiment of the present invention. [Figure 2] It is a schematic perspective view of an immersion probe constituting the flaw detection inspection device of FIG. 1. [Figure 3] FIG. 3A is a cross-sectional view of the main part along the Y direction of the immersion probe of FIG. 2, and FIG. 3B is a cross-sectional view of the main part along the Z direction. [Figure 4] It is a schematic explanatory diagram showing the focusing position of ultrasonic waves oscillated from the immersion probe of FIG. 2. [Figure 5] It is ultrasonic beam profile data showing the focusing range of ultrasonic waves with respect to the plane incident object at F1 and F2 in FIG. 4. [Figure 6] It is a schematic explanatory diagram showing a situation where the focal length is extended when the first wave is incident on the billet. [Figure 7] FIGS. 7A and 7B are schematic explanatory diagrams showing a situation where the second wave is incident on the billet. [Figure 8] FIG. 8A shows a state where an immersion probe different from the immersion probe of FIG. 2 faces the billet, and FIG. 8B is a schematic explanatory diagram showing a state where a reflected wave is generated due to a flaw. [Figure 9] It is a change diagram showing the relationship between the distance from the second probe (distance converted in water) when ultrasonic waves are incident on the billet and the ultrasonic beam profile data focused inside the billet. [Figure 10] It is a chart showing the relationship between the contrast FBH (circular planar flaw) and the diameter of the FBH for which it is possible to determine whether or not it exists. [Figure 11] It is a chart showing the evaluation of the characteristics as a dual-focus probe using immersion probes with various different first curvature radii and second curvature radii.

Embodiments for Carrying Out the Invention

[0016] The following describes in detail a preferred embodiment of the flaw detection inspection method according to the present invention, relating to the relationship between the immersion probe and the flaw detection inspection apparatus comprising it, with reference to the attached drawings. In the following, "front" refers to the side facing the object to be inspected, and "rear" refers to the opposite direction. For example, "front end of the immersion probe" means "the end of the immersion probe facing the object to be inspected."

[0017] First, a brief description of the billet 10 shown in Figure 1 will be provided. The billet 10, which is the object to be inspected, is cylindrical in shape, and in this case, the diameter D is set to 8 inches (203.2 mm). Furthermore, the billet 10 is manufactured by so-called powder metallurgy, which involves sintering powder of a heat-resistant nickel-based alloy. In other words, this billet 10 is made of a heat-resistant nickel-based alloy.

[0018] On the other hand, the flaw detection inspection device 20 is equipped with a storage tank 22. Water 24 is stored in the storage tank 22 as a solvent. As will be described later, ultrasonic waves propagate through the water 24 to reach the billet 10. Displacement guide rails 26a and 26b are laid on the upper surface of the storage tank 22.

[0019] A rotary table 28 for positioning and fixing the billet 10 is installed at the bottom of the storage tank 22. The rotary table 28 is rotatable under the action of a rotary motor (not shown) or the like, which is provided on the underside of the rotary table 28. On the upper surface of the rotary table 28, clamping guide rails 30a to 30c are laid, extending radially from the rotation center of the rotary table 28 and spaced approximately 120° apart from each other. Clamping claws 32a to 32c are slidably provided on each of the clamping guide rails 30a to 30c. Each clamping claw 32a to 32c moves synchronously along the clamping guide rails 30a to 30c under the action of a linear actuator (not shown).

[0020] The ends of the gripping claws 32a to 32c facing the billet 10 are formed as projections that protrude vertically upward. The billet 10 is gripped by the projections as the gripping claws 32a to 32c move closer to each other. This gripping positions and fixes the billet 10 in an upright position at the center of the rotary table 28. The billet 10 rotates in accordance with the rotation of the rotary table 28.

[0021] The flaw detection inspection device 20 further includes a movable part 36 attached to the storage tank 22. This movable part 36 has an X-movement stage 38, a Y-movement slider 40, and a Z-movement holder 42. The X-movement stage 38 straddles the displacement guide rails 26a and 26b and is displaced in the X direction along the displacement guide rails 26a and 26b under the action of a linear actuator (not shown). The X direction is the longitudinal direction of the storage tank 22.

[0022] The Y-movement slider 40 is engaged with the X-movement stage 38 and is displaced along the X-movement stage 38 (in the Y direction) by a linear actuator (not shown). In other words, the X-movement stage 38 guides the Y-movement slider 40 during this displacement. The Y direction is the width direction of the storage tank 22.

[0023] The Y-movement slider 40 is equipped with a ball screw 44 as an actuator for vertical displacement. The Z-movement holder 42 is displaced in the Z direction (height direction) along the ball screw 44 as the ball screw 44 is rotated by the screw rotation motor 46. Note that the X, Y, and Z directions in the following drawings correspond to the X, Y, and Z directions in Figure 1.

[0024] The Z-movement holder 42 is formed with a horizontal lower surface and an inclined upper surface that slopes upward as it moves away from the ball screw 44. Therefore, the Z-movement holder 42 has a trapezoidal shape, with one end through which the ball screw 44 passes being shorter and the other end that moves away from the ball screw 44 being longer. A retaining shaft 48 passes through the other end that moves away from the ball screw 44. Furthermore, a probe holder 54 that holds the first probe 50 and the second probe 52 is provided at the lower end of the retaining shaft 48. In other words, the Z-movement holder 42 holds the first probe 50 and the second probe 52 (both immersion probes) via the retaining shaft 48 and the probe holder 54.

[0025] The first probe 50 is a point-focusing probe used to perform flaw detection on the billet 10 in the region from the surface to a depth of 50 mm. The minimum size of detectable flaws decreases as the ultrasonic frequency increases. For this reason, the first probe 50 is selected to have a transducer capable of emitting ultrasonic waves 56 (see Figure 8A) at a frequency of 10 MHz or higher. The frequency of the ultrasonic waves 56 emitted by the transducer of the first probe 50 is, for example, 15 MHz, but it may also be 10 MHz. In the latter case, there is the advantage that the near-field limit distance is increased.

[0026] The first probe 50 is selected such that, in a preliminary test profile where the maximum amplitude of the reflected wave from a 0.4 mm diameter circular planar defect (Flat Bottom Hole, hereinafter also referred to as "FBH") in an internal defect type comparison test piece is set to 80% of the vertical axis scale, the maximum amplitude of the noise is less than 10%. In other words, the first probe 50 has a good signal-to-noise ratio (SNR). Therefore, based on the actual inspection profile using the first probe 50, it is possible to easily determine whether or not there are minute defects in the billet 10 up to a depth of 50 mm from the surface.

[0027] Next, the second probe 52, which serves as an immersion probe according to this embodiment, will be described. Figure 2 is a schematic perspective view of the second probe 52. This second probe 52 comprises a cylindrical casing 60, a vibrator 62 housed within the casing 60, and a front plate 64 that closes the front end opening of the casing 60. Electrodes and dampers are also housed within the casing 60, but these are not shown in the figures.

[0028] The transducer 62 is made of a piezoelectric material and emits ultrasonic waves by vibrating in response to the repeated application and deapering of voltage from the electrodes. In this case, the transducer 62 is capable of emitting ultrasonic waves with a frequency of 10 MHz or higher (typically 10 MHz). The transducer 62 is also capable of receiving ultrasonic waves that are reflected back to the transducer 62 from locations where defects exist within the billet 10, i.e., reflected waves.

[0029] Four tab-shaped stopper portions 66 are formed to protrude from the front end of the casing 60, and these tab-shaped stopper portions 66 are folded back toward the front panel 64. This prevents the front panel 64 from coming off the casing 60.

[0030] The front plate 64 attached to the front end of the casing 60 is circular in plan view. The front surface of the front plate 64 facing the object under inspection is formed as a concave surface 68 that gradually indents towards the rear, moving away from the object under inspection, as it approaches the center O. In other words, the concave surface 68 is curved throughout.

[0031] Here, the radius of curvature of the concave surface 68 in the Y direction and the radius of curvature in the Z direction are different. Specifically, if we define the first virtual tangent line M1 as a virtual tangent line passing through the center O and tangent to the curved surface of the concave surface 68 in the Y direction, and the second virtual tangent line M2 as a virtual tangent line tangent to the curved surface in the Z direction and perpendicular to the first virtual tangent line M1, and let the radii of curvature of these lines be the first radius of curvature R1 and the second radius of curvature R2, then R2 > R1. That is, as shown in Figure 3A, the curvature is large in the Y direction, resulting in a large degree of curvature. On the other hand, as shown in Figure 3B, the curvature is small in the Z direction, and therefore the degree of curvature is also small.

[0032] Therefore, when the billet 10 is not present in the water 24, as shown in Figure 4, the focal length of the ultrasonic waves spreading along the Y direction (hereinafter referred to as "first wave 70" for convenience) becomes F1, and the focal length of the ultrasonic waves spreading along the Z direction (hereinafter referred to as "second wave 72" for convenience) becomes F2, which is longer than F1. In other words, the focal points of the first wave 70 and the second wave 72 are different. Thus, the focal points of the ultrasonic waves in the second transducer 52 are two points based on the difference in the radii of curvature of the concave surface 68 in the Y and Z directions. As can be understood from this, the second transducer 52 is a bifocal transducer.

[0033] Figures 5A and 5B show the ultrasonic beam profile data when flat plate-shaped planar comparison test specimens are placed at F1 and F2, respectively. At F1, since the second wave 72 has not yet been focused, an echo extending in the Z direction is observed, corresponding to the diffusion of the second wave 72 at F1. On the other hand, at F2, the second wave 72 is focused, but the first wave 70, which was focused at F1, has diffused. Therefore, an echo extending in the Y direction is observed, corresponding to the diffusion of the first wave 70 at F2.

[0034] In contrast, when the first wave 70 is incident on the billet 10 in water 24, the focal length of the first wave 70 becomes F1', as shown in Figure 6. F1' is greater than the focal length F1 in the planar comparison test specimen. On the other hand, when the second wave 72 is incident on the billet 10 as shown in Figures 7A and 7B, the focal length F2' is approximately the same as the focal length F2 in the planar comparison test specimen. That is, no change is observed in the focal length of the second wave 72. Furthermore, as can be understood by comparing Figures 6, 7A, and 7B, the convergence points of the first wave 70 and the second wave 72 substantially coincide at point P. This point will be discussed later.

[0035] The first radius of curvature R1 and the second radius of curvature R2 are set based on the diameter (or radius of curvature) of the billet 10, the sound velocity ratio between the solvent water 24 and the heat-resistant nickel-based alloy material of the billet 10, the minimum beam width, etc., so that the convergence point (point P) of the first wave 70 and the second wave 72 exceeds the center of the diameter of the billet 10. An example of the first radius of curvature R1 is in the range of 150 to 200 mm, and an example of the second radius of curvature R2 is in the range of 450 to 500 mm.

[0036] The second probe 52, configured as described above, performs flaw detection inspection on the billet 10 over a range from a depth of approximately 35-40 mm to the diameter center (a depth of 4 inches = 101.6 mm from the surface). In other words, the flaw detection range of the first probe 50 and the flaw detection range of the second probe 52 partially overlap.

[0037] In this second transducer 52, in a preliminary test profile where the maximum amplitude of the reflected wave from a 0.4 mm diameter FBH in an internal defect type comparison test specimen is set to 80% of the vertical axis scale, the maximum noise amplitude is less than 10%, similar to the first transducer 50. In other words, the second transducer 52 also has a good signal-to-noise ratio. Therefore, based on the actual inspection profile using the second transducer 52, it is possible to easily determine whether or not there are minute defects in the billet 10 in the range from a depth of 50 mm to beyond the center of the diameter.

[0038] The flaw detection inspection device 20 further includes a computer 74. The display of this computer 74 shows the ultrasonic beam profile data, the actual inspection profile, and the like.

[0039] The second probe 52 (liquid immersion probe) and the flaw detection inspection device 20 according to this embodiment are basically configured as described above, and their effects will now be explained in relation to the flaw detection inspection method according to this embodiment.

[0040] To perform a flaw detection inspection on the billet 10, first, the billet 10 is positioned and fixed on the rotary table 28 (see Figure 1). That is, the billet 10 is placed in an upright position at the center of the rotary table 28. Then, under the action of the linear actuator, the gripping claws 32a to 32c are displaced so that they are directed toward the center of the rotary table 28. At this time, the gripping claws 32a to 32c are of course guided by the gripping guide rails 30a to 30c. The protrusions of the gripping claws 32a to 32c grip the lower end of the billet 10 from three sides, thereby positioning and fixing the billet 10 at the center of the rotary table 28. Note that if the test piece, including the billet 10, is self-supporting, there is no particular need to use the gripping claws 32a to 32c.

[0041] Next, the X-movement stage 38 is displaced along the displacement guide rails 26a and 26b under the action of a linear actuator. That is, the first probe 50 and the second probe 52 are brought closer to the billet 10. The X-movement stage 38 stops at a position where the first wave 70 and the second wave 72 emitted by the second probe 52 converge at a point (point P) slightly beyond the center of the diameter of the billet 10. Furthermore, the Z-movement holder 42 moves along the Z direction by the rotation of the ball screw 44, and the probe holder 54 faces the lower end of the billet 10 (see Figure 8A).

[0042] Then, the Y-movement slider 40 is displaced along the X-movement stage 38 under the action of the linear actuator. As a result, the first probe 50 faces the lower end of the billet 10. During or before / after this movement, the rotary table 28 is rotationally biased, and the billet 10 rotates integrally with it. In this state, ultrasonic waves 56 are emitted from the first probe 50.

[0043] The ultrasonic waves 56 propagate through the water 24 stored in the storage tank 22 and enter the billet 10 from the surface of the side circumferential wall, and from that surface proceed diametrically into the interior of the billet 10. Since the first transducer 50 is a point focusing transducer, as shown in Figure 8A, the ultrasonic waves 56 are focused within the billet 10 at a predetermined depth from the surface. This focusing position can be adjusted by setting the propagation distance of the ultrasonic waves 56 through the water 24. In this embodiment, the focusing position is set to a depth of approximately 50 mm from the surface. Then, as shown in Figure 8B, if a defect 76 exists between the surface and a depth of 50 mm, the ultrasonic waves 56 are reflected by the inner wall of the defect 76. The reflected wave 78 generated by this reflection is received by the transducer in the first transducer 50.

[0044] As described above, the first transducer 50 has a good signal-to-noise ratio, and as calculated based on equation (2) described later, it is possible to distinguish even a reflected wave 78 from an FBH with a diameter of 0.17 mm from noise. In other words, even if the defect 76 is of such extremely small size, an echo with a sufficient peak height is generated. Therefore, minute defects 76 can be easily detected. If no defect 76 is present, no echo is generated. Thus, whether or not a defect equivalent to 0.17 mm in diameter or less is present in the billet 10 can be determined by whether or not an echo is detected.

[0045] While ultrasonic waves 56 are emitted from the first probe 50, the rotary table 28 and the billet 10 continue to rotate together. The ball screw 44 also continues to rotate, and the Z-movement holder 42 gradually moves toward the upper end of the billet 10. Consequently, the trajectory of the point of incidence of ultrasonic waves 56 on the billet 10 becomes helical. In this way, the first probe 50 performs flaw detection on the billet 10 from the surface to a depth of 50 mm, covering the entire circumference of the billet 10 from the lower end to the upper end.

[0046] Next, a flaw detection inspection is performed on the billet 10 from a depth of 50 mm (actually, from a depth of about 35-40 mm) beyond the center of the diameter. For this purpose, the Z-movement holder 42 moves downward and the Y-movement slider 40 is slightly displaced, so that the second probe 52 faces the lower end of the billet 10, as shown in Figures 6, 7A, and 7B. Subsequently, ultrasonic waves (first wave 70, second wave 72) are emitted from the second probe 52.

[0047] Here, as shown in Figures 7A and 7B, the second wave 72 has a linear shape in a plan view with the viewpoint in the Z direction. Also, on the side wall of the billet 10, the portion into which the second wave 72 is incident extends along the Z direction. The curvature of this incident portion in a plan view is so small that it can be ignored, and it approximates a linear shape. For this reason, the second wave 72 is hardly affected by the so-called lens effect of the billet 10. Consequently, the second wave 72 converges at a point (point P) beyond the diameter center of the billet 10. The distance (focal length) of the second wave 72 from the second probe 52 to point P at this time is denoted as F2'. Note that the speed of sound in water 24 is about 1 / 4 the speed of sound in the heat-resistant nickel-based alloy that is the material of the billet 10. Therefore, F2' is about 4 times F2.

[0048] On the other hand, as shown in Figure 6, the first wave 70 has a roughly triangular shape in a plan view with the viewpoint in the Z direction, such that it diffuses on the second probe 52 side and the beam diameter narrows as it approaches the billet 10 side. Also, on the side circumferential wall of the billet 10, the portion into which the first wave 70 is incident extends along the circumferential direction of the billet 10. This incident portion is curved with a predetermined curvature. Therefore, the first wave 70 is affected by the lens effect of the billet 10. The distance (focal length) of the first wave 70 from the second probe 52 to the point of focus, i.e., point P, is defined as F1''.

[0049] When the first wave 70 is not affected by the lens effect, the distance from the second probe 52 to the focal point (focal length) F1'' of the first wave 70 is approximately 1 / 4 of F1. In contrast, when the first wave 70 is affected by the lens effect, the focal length increases; that is, F1' > F1''. Thus, when curvature is present in the incident portion, the focal length can be made longer than the original focal length due to the lens effect.

[0050] As described above, the first radius of curvature R1 and the second radius of curvature R2 (see Figure 2) of the concave surface 68 constituting the second transducer 52 are set so that the first wave 70 and the second wave 72 are focused at point P, which is approximately the same location within the billet 10. That is, F1' ≈ F2' (or F1' = F2') holds true. Thus, although there are two focal points of the ultrasonic waves emitted by the second transducer 52 in the water 24, there is only one focal point within the billet 10 (see Figures 6, 7A, and 7B). In short, it is possible to make the second transducer 52, which is a bifocal transducer, function as a point-focusing transducer.

[0051] Furthermore, as described above, the focal points of the first wave 70 and the second wave 72 are located beyond the center of the diameter of the billet 10. Therefore, flaw detection inspection of the billet 10 from a depth of 50 mm to beyond the center of the diameter can be performed using only the second probe 52. If a defect exists in this area, a reflected wave is generated as described above, and this wave is received by the transducer 62 inside the casing 60.

[0052] The second transducer 52 also has a good signal-to-noise ratio, and can distinguish even reflected waves from a 0.17 mm diameter FBH from noise. In other words, even with such extremely small defects, echoes with sufficient peak height are generated in the actual inspection profile. On the other hand, no echoes are generated when no defects are present. Thus, the presence or absence of echoes makes it possible to determine whether or not there are defects smaller than 0.17 mm in diameter deep inside the billet 10.

[0053] Similar to the flaw detection inspection using the first probe 50, the rotary table 28 and the billet 10 continue to rotate together while ultrasonic waves are being emitted from the second probe 52. In addition, the ball screw 44 continues to rotate, and the Z-movement holder 42 gradually moves toward the upper end of the billet 10. As a result, the trajectory of the ultrasonic wave incident on the billet 10 becomes helical, so that flaw detection inspection is performed on the billet 10 from a depth of 50 mm to its diameter, covering the entire circumference of the billet 10 from the lower end to the upper end.

[0054] As described above, according to this embodiment, a flaw detection inspection can be performed on the surface of an 8-inch diameter billet 10, extending beyond the diameter center, using only two probes, the first probe 50 and the second probe 52. Therefore, the number of probes can be reduced as much as possible. Consequently, the number of parts in the flaw detection inspection device 20 can be reduced, and capital investment can be lowered.

[0055] Furthermore, in flaw detection inspection, the number of probe scans (the number of times the probe moves in the Z direction) is equal to the number of probes. However, in this embodiment, as described above, the number of probes can be reduced to two, so the number of scans becomes two. This reduces the time required from the start to the end of the scan. In other words, this embodiment makes it possible to reduce the time required for flaw detection inspection.

[0056] Furthermore, to obtain the second probe 52, it is sufficient to fabricate a front plate 64 having a concave surface 68. This avoids the need for a complex structure for the second probe 52.

[0057] Billets 10 containing defects are not used as materials for obtaining components that require excellent durability under harsh operating environments, such as turbine engine components. In other words, according to this embodiment, only billets 10 in which the internal defects are smaller than the detection limit of the flaw detection inspection device 20 can be selected as materials for obtaining such components. Therefore, the production yield of components exhibiting excellent durability is improved.

[0058] The present invention is not particularly limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0059] For example, the diameter of the billet 10 may be set to something other than 8 inches. In this case, the first radius of curvature R1 and the second radius of curvature R2 of the concave surface 68 of the front plate 64, the distance from the second probe 52 to the billet 10, etc., should be set so that F1' and F2' roughly coincide, but exceeding the center of the billet 10's diameter.

[0060] Furthermore, solvents other than water 24 may be used. In addition, one or more other transducers may be used in combination with the first transducer 50 and the second transducer 52. [Examples]

[0061] [Example 1] A second probe 52 was fabricated, which housed a transducer 62 that emits ultrasonic waves at a frequency of 10 MHz within a casing 60, and had a front plate 64 with a first radius of curvature R1 of 180 mm and a second radius of curvature R2 of 480 mm. The outer diameter of the casing 60 was set to 25 mm. This second probe 52 was immersed in water 24 in a position where the first virtual tangent M1 was in the horizontal direction and the second virtual tangent M2 was in the height direction, and ultrasonic waves were emitted. As a result, the focal length F1 of the first wave 70 was 175 mm, and the focal length F2 of the second wave 72 was 400 mm.

[0062] Next, a plane comparison test specimen made of a heat-resistant nickel-based alloy was immersed in water 24, and ultrasonic waves were emitted from a second transducer 52, which was spaced approximately 50 mm apart, toward the plane comparison test specimen, and incident on the specimen so as to be approximately perpendicular to the surface of the plane comparison test specimen. Furthermore, the focal lengths of the first wave 70 and the second wave 72 were determined based on the collected ultrasonic beam profile data. Then, considering that the sound velocity ratio between water and the plane comparison test specimen is approximately 4, the water equivalent distance was calculated using the following equation (1).

number

[0063] According to the ultrasonic beam profile data, when the underwater equivalent distance was 160 mm, the echo shown in Figure 5A was obtained based on the diffusion of the second wave 72, and when it was 350 mm, the echo shown in Figure 5B was obtained based on the diffusion of the first wave 70. From these results, it can be seen that the second transducer 52 is a bifocal transducer with focal lengths of 160 mm and 350 mm in underwater equivalent distances.

[0064] Next, a billet-shaped comparison test specimen with a diameter of 8 inches and a 0.4 mm diameter FBH formed inside as a comparison defect was immersed in water 24, and ultrasonic waves were emitted from a second transducer 52, which was spaced approximately 50 mm apart, toward the billet-shaped comparison test specimen. The obtained ultrasonic beam profile data is shown in Figure 9, along with the underwater equivalent distance calculated using equation (1). From Figure 9, it can be seen that as the underwater equivalent distance approaches 350 mm, the echo approaches a point shape and its area decreases. From this, it is clear that the focal points of the first wave 70 and the second wave 72 are approximately coincident within the billet-shaped comparison test specimen, and that the underwater equivalent distance is 350 mm, which is the focal length.

[0065] Next, the sensitivity of the second transducer 52 to FBH was determined based on the following equation (2).

number

[0066] Furthermore, S npk is the maximum amplitude (maximum peak height) of the noise. In this case, the maximum amplitude of the noise was less than 10% of the maximum amplitude of the FBH with a diameter of 0.4 mm. Therefore, in equation (2), FBH# cal 1, S npk Substituting 10 into the equation, the value on the right-hand side of equation (2) is approximately 0.42. From this value, it can be seen that the second probe 52 can display an FBH with a diameter of 0.42 / 64 inches as an echo with an amplitude that ensures a signal-to-noise ratio of 3.0 dB in the actual inspection profile. Converting 0.42 / 64 inches to millimeters gives 0.17 mm.

[0067] These results show that, even with a relatively large billet 10 having a diameter of 8 inches, the second probe 52 can detect extremely fine defects corresponding to a 0.17 mm diameter FBH deep inside the billet 10. In other words, by using the second probe 52, it is possible to determine whether or not fine defects are present deep inside the billet 10.

[0068] [Example 2] A second probe 52 was fabricated, having a front plate 64 containing a transducer 62 that emits ultrasonic waves at a frequency of 10 MHz or 15 MHz within a casing 60. The characteristics of the bifocal probe were evaluated by using transducers 62 with different dimensions and varying the first radius of curvature R1 and the second radius of curvature R2. The frequency was 10-15 MHz and the dimensions of the transducer 62 were 15-25 MHz. m When the value is m, it is preferable to set the first radius of curvature R1 to 220-500 mm and the second radius of curvature R2 to 100-200 mm. The optimal results in this case are shown together in Figure 11.

[0069] Figure 11 shows that an excellent dual-focus probe can be obtained by appropriately setting the first radius of curvature R1 and the second radius of curvature R2. [Explanation of symbols]

[0070] 10...Billet 20...Flaw detection equipment 22...Storage tank 24...Water 28... Rotary table 32a~32c... Clamping jaws 36...Movable part 38...X-shaped moving stage 40...Y movement slider 42...Z movement holder 48...Holding axis 50...1st probe 52...Second probe 56...Ultrasonic 62...Resonator 64...Front plate 68...Concave surface 70...First wave 72... The second wave 74... Computers 76...scratch 78...reflected wave M1...First virtual tangent M2...Second virtual tangent

Claims

1. A flaw detection inspection apparatus comprising a storage tank for storing a solvent and an immersion probe for emitting ultrasonic waves towards an object to be inspected immersed in the solvent, The immersion probe comprises a transducer that emits ultrasonic waves with a frequency of 10 MHz or higher to the object under inspection, a casing that houses the transducer and has an opening at the end facing the object under inspection, and a front plate that is circular in plan view, and whose surface facing the object under inspection is formed as a concave surface that curves so as to gradually indent towards the center, and which closes the opening of the casing. When the radii of curvature of the first and second virtual tangents, which are mutually perpendicular at the center of the concave and curve along the concave, are denoted as the first radius of curvature and the second radius of curvature, the first radius of curvature and the second radius of curvature are different, A flaw detection inspection device wherein the ultrasonic waves emitted from the transducer and output from the front plate into the solvent are focused at two locations in the solvent, in which the object to be inspected is not immersed, based on the difference between the first radius of curvature and the second radius of curvature, while the ultrasonic waves that pass through the solvent and enter the object to be inspected are focused at one location inside the object to be inspected.

2. A flaw detection inspection apparatus according to claim 1, further comprising: a rotating table provided in the storage tank for holding the object to be inspected; and a movable part for moving the immersion probe at least along the height direction of the object to be inspected held on the rotating table.

3. A flaw detection inspection apparatus according to claim 1 or 2, comprising at least two immersion probes, wherein the at least two immersion probes each emit ultrasonic waves, and the focal points of these ultrasonic waves within the object under inspection are different from those of the other.

4. In a flaw detection inspection method in which an object to be inspected is immersed in a solvent, and ultrasonic waves with a frequency of 10 MHz or higher are emitted from a transducer constituting a liquid immersion probe, and the presence or absence of defects in the object to be inspected is inspected using the ultrasonic waves, A method for inspecting defects using a liquid immersion probe comprising: a casing that houses the transducer and has an opening at the end facing the object to be inspected; a front plate that is circular in plan view, with the surface facing the object to be inspected being formed as a concave surface that curves gradually toward the center to close the opening of the casing; and having a first virtual tangent and a second virtual tangent that are mutually orthogonal at the center of the concave surface and curve along the concave surface, wherein the radius of curvature of the first and second virtual tangents are different, and the ultrasonic waves emitted from the transducer and output from the front plate into the solvent are focused at two locations in the solvent where the object to be inspected is not immersed, based on the difference between the first and second radii of curvature, while the first and second radii of curvature are set to the radius of curvature at which the ultrasonic waves that have passed through the solvent and entered the object to be inspected are focused at one location inside the object to be inspected.

5. A flaw detection inspection method according to claim 4, wherein the object to be inspected is a cylindrical body with a diameter of 8 inches.

6. A method for inspecting defects according to claim 4 or 5, wherein the object to be inspected is made of a nickel-based alloy.

7. A flaw detection inspection method according to any one of claims 4 to 6, wherein at least two immersion probes are used, each having different focal points for the ultrasonic waves it emits within the object under inspection.

8. A method for inspecting defects according to any one of claims 4 to 7, wherein water is used as the solvent.

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