JPH11133005A - Surface wave probe for inspection of roll and method for setting incident angle thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable transmission and reception of surface waves with high efficiency even in the presence of a difference in materials of rolls and improve a signal to noise ratio (S/N) of reflection waves from defects, by setting an incident angle of ultrasonic waves to satisfy a specific formula. SOLUTION: A surface wave probe for inspection of rolls comes in touch with a surface of a rotating roll via a medium, which comprises an ultrasonic vibrator 40 and a wedge 41 bringing ultrasonic waves into the surface of the roll with an incident angle θi. The surface wave probe is arranged to propagate surface waves in a direction opposite to a rotational direction of the roll, thereby detecting defects present on the roll surface immediately below the roll surface. The incident angle θi of ultrasonic waves is set to satisfy an equation θi=sin<-1> (CW/CRav) wherein CW is a speed of ultrasonic waves in the wedge 41; and CRav is an average value of speeds of surface waves of each roll to be inspected. The incident angle θi is an angle to a vertical plane orthogonal to the roll surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection for inspecting defects such as cracks existing on the surface of a roll such as a high-speed tool steel roll, generally called high-speed tool roll, or just below the surface with a surface wave. The present invention relates to a surface acoustic wave probe for roll inspection to be applied and an incident angle setting method thereof.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No.
An ultrasonic flaw detection method using a surface wave as disclosed in Japanese Patent No. 276547 is used. That is, the surface wave probe is brought into contact with the surface of the roll, which is a rotating cylindrical body, via a couplant, and the surface wave is propagated from the surface wave probe in a direction opposite to the roll rotation direction. This is a method of detecting defects existing on the surface of the roll or directly below the surface while removing the couplant from the portion where the wave propagates.

The above-mentioned surface acoustic wave probe comprises at least an ultrasonic oscillator and a wedge for causing ultrasonic waves to be incident on the roll surface at an angle θi. The incident angle θi is expressed by the following equation (1) using the law of refraction. Set to satisfy. ^{θi = sin -1 (CW / CR} s) ... (1) where, CW: the ultrasonic velocity in the wedge, CR _s: surface wave velocity of a general steel. Here, the incident angle θi is an angle with respect to a vertical plane perpendicular to the roll surface.

[0004]

However, recently, it has been found that when a surface flaw of a roll is inspected using the above-mentioned surface acoustic wave probe, a sufficient S / N ratio cannot be obtained in a detection signal. . Therefore, the present inventors paid attention to the difference in the material caused by the difference in the method of manufacturing the high-speed roll, and examined how the difference in the material affects the surface flaw detection described above. Then, as shown in Table 1, it was found that the surface wave velocity of each roll made of a different material varies considerably depending on the material.

[0005]

[Table 1]

It has also been found that the surface wave velocity at high speed rolls is significantly different from the surface wave velocity of general steel, 2980 m / sec. The transmission and reception of the surface wave to and from the roll surface by the surface acoustic wave probe is performed at an angle of refraction of 90 degrees with respect to the incident angle θi using the refraction phenomenon expressed by the above equation (1). Therefore, when the speed of the surface wave differs depending on the roll material as shown in Table 1, it is necessary to change the incident angle according to the speed of each surface wave. Otherwise, the transmission and reception efficiency of the surface wave will be reduced.

However, at present, a surface acoustic wave probe is manufactured by determining an incident angle θi based on a surface acoustic wave velocity of 2980 m / sec in general steel. Actually, as shown in Table 1, the surface wave velocity in each high-speed roll is significantly different from the surface wave velocity in general steel. Although the surface wave velocity varies, the difference is not taken into account at all in the design of the incident angle θi. Therefore, the incident angle θi greatly differs from an appropriate value for transmitting and receiving the optimal surface wave.

[0008] The inspection of high speed rolls is usually carried out on or near a roll grinding facility. Such mechanical equipment often generates a large electric noise from a motor, an inverter, and the like, and a large electric noise is often superimposed on a flaw detection signal using a surface wave. Then, in the high-speed roll inspection, since the transmission / reception efficiency of the surface wave described above has already been reduced, the height of the reflected wave of the defect is reduced, and therefore the ratio of the amplitude of the defect reflected wave to the electric noise. The S / N ratio is reduced, and the defect detection ability is reduced.

Further, even if an incident angle θi is determined in accordance with the surface wave velocity of a high-speed roll of a specific material, and a surface wave probe is manufactured, the value of the surface wave velocity is, for example, as shown in Table 1.
If the speed is adjusted to either the minimum or maximum value of the surface wave velocity such as 3090m / sec or 3180m / sec, the material has the maximum or minimum value of the surface wave velocity and vice versa. In this case, the transmission / reception efficiency of the surface wave is reduced and the defect detection capability is reduced, and the problem cannot be solved.

[0010] Further, replacing the surface acoustic wave probe with an optimum one for each roll of a different material results in a time loss in operation and is not practical. The purpose of the present invention is
In high-speed ultrasonic inspection of high-speed rolls using surface waves,
Even if the roll material is different due to the difference in manufacturing method, the surface wave can be transmitted and received with high efficiency, and the S /
An object of the present invention is to provide a roll inspection surface acoustic wave probe capable of increasing the N ratio and a method of setting an incident angle thereof.

[0011]

According to the present invention, at least an ultrasonic vibrator and a wedge which makes an ultrasonic wave incident on the roll surface at an incident angle θi are brought into contact with the surface of the rotating roll via a medium. In a roll inspection surface wave probe that is disposed so as to propagate a surface wave in a direction opposite to the rotation direction of the roll and detects a defect existing immediately below the surface of the roll, an incident angle θi of the probe is as follows: The above problem was solved by setting to satisfy the expression 2).

Θi = sin ⁻¹ (CW / CRav) (2) where CW is the ultrasonic velocity in the wedge, and CRav
Is the average value of the surface wave velocity of each roll to be inspected. Here, the incident angle θi is an angle with respect to a vertical plane perpendicular to the roll surface. Further, the medium is in contact with the surface of the rotating roll via a medium, and is composed of at least an ultrasonic vibrator and a wedge that causes ultrasonic waves to be incident on the roll surface at an incident angle θi, in a direction opposite to the rotation direction of the roll. As a method of setting an incident angle of a roll inspection surface wave probe that is arranged so as to propagate a surface wave and detects a defect existing immediately below the surface of the roll, the incident angle θi satisfies the above expression (2). The above problem was solved by setting as follows.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave probe 4 according to the present invention.
As shown in FIG. 1, is composed of at least an ultrasonic transducer 40 and a wedge 41 made of resin or the like. As the ultrasonic vibrator 40, a piezoelectric vibrator such as a lead niobate porcelain, a lead titanate porcelain, a lithium niobate porcelain, a barium titanate porcelain, or a lead zirconate titanate porcelain is used.

The wedge 41 is made of an acrylic resin, a polystyrene resin, a polyimide resin, or the like.
The incident angle θi is given so that the ultrasonic wave from 40 satisfies the expression (2) and is incident as a surface wave on the surface of the roll as the test material. An embodiment of the present invention will be specifically described based on FIG. The surface acoustic wave probe 4 of the present invention is applied to an ultrasonic flaw detector having a function of supplying a medium such as water, which is a propagation medium of ultrasonic waves, between the surface acoustic wave probe 4 and the surface of the roll 110 as an object. In particular, rolls 110 such as high-speed rolls
It is suitable for scanning and moving the surface acoustic wave probe 4 on the surface of the surface to perform flaw detection.

The ultrasonic flaw detector is provided with a rotating means (not shown) for rotating the roll 110, a probe holder 10 for holding the surface wave probe 4 and a medium supply means (not shown), and a copying roller for copying the roll surface. 11, 2
The probe holder 10 is made to follow the roll surface at 1 and 22 to maintain a proper constant gap between the roll surface and the probe. A scraper 50 that removes a medium on the roll surface that is an obstructive factor for flaw detection, a guide 70 on which the probe holder holding mechanism 20 and the scraper 50 are attached and guides them vertically to the roll surface,
The probe holder holding mechanism 20 is guided vertically along the guide 70 by a motor 31 along a roll surface. As a method of transmitting the power of the motor 31, any suitable means such as a conventionally well-known gear may be used, and illustration and description thereof are omitted here.

The medium for flaw detection is supplied by medium supply means 60 attached to the probe holder 4 on the upstream side with respect to the roll rotation direction as shown in FIG. The medium supply means 60 includes a medium conduit 61, a medium accommodating portion 62, and a medium discharge hole 63, and supplies a medium without bubbles under the surface acoustic wave probe 4. The adhesion of the medium to the surface of the roll is a hindrance to flaw detection in surface flaw detection, and is thus removed using a scraper as described above.

The probe holder 10 is attached to the tip of a rod 25 which is loosely fitted to the probe holder holding mechanism 20 so as to be slidable up and down. A spring (not shown) is provided at an appropriate position around the rod 25, and is always provided. The probe holder 10 is urged downward. The probe holder 10 is provided with the surface acoustic wave probe 4 described above.

[0018]

2 and 3 show a surface acoustic wave probe according to the present invention and FIG.
5 is a graph showing the results of measuring artificial defects processed into five types of rolls shown in Table 1 using various types of conventional surface acoustic wave probes. FIG. 2 is a graph in which the echo height of the reflected wave of the artificial defect is measured, and FIG. 3 is a graph in which the S / N ratio of the reflected wave of the artificial defect is measured.

The artificial defect is 1 mm on each roll surface.
φ, 1mm depth drilled holes are used. Here, the wedge of the surface acoustic wave probe is made of polystyrene resin (CW = 2340 m / sec). The following three types of surface acoustic wave probes were prepared as described above.

Probe F: Averages the surface wave velocities of five types of rolls of interest, and conforms to θi calculated from the average value CRav and the ultrasonic velocity CW of the polystyrene resin using equation (2). Surface wave probe configured as follows. That is, θi = 48.1 degrees. 3 is a surface wave probe of the present invention. Probe G: a surface wave probe configured to conform to θi calculated from the surface wave velocity of roll number # 4 in Table 1 and the ultrasonic velocity of the polystyrene resin. That is, θi = 4
9.2 degrees. It is a conventional surface acoustic wave probe.

Probe H: velocity of surface wave on general steel
(2980 m / sec) and a surface acoustic wave probe configured to match θi calculated from the ultrasonic velocity of polystyrene resin. That is, θi = 51.7 degrees. 9 shows another conventional surface acoustic wave probe. 2 and 3 that the probe F of the present invention has a high echo height and high S regardless of the type of roll.
It was confirmed that the / N ratio could be obtained stably.

Here, the vertical axis in FIG. 2 shows the echo height of the reflected wave when the artificial defect of roll number # 1 is detected by the surface wave probe F as 0 dB. Next, a total of 20 surface defects, four for each of the five types of rolls shown in Table 1, were sampled from actual rolls, and the S / N ratio of the reflected waves from those surface defects was measured. FIG.
Serial numbers are assigned to the 20 surface defects, and the numbers are plotted on the horizontal axis and the S / N ratio is plotted on the vertical axis.

Here, the above-described three types of probes F, G and H are applied to the surface acoustic wave probe. FIG. 6 also confirms that the probe F of the present invention can stably detect a flaw even at an actual surface defect at a high S / N ratio.

[0024]

By applying the present invention to the ultrasonic inspection method for rolls using surface waves, it is possible to transmit and receive surface waves with high efficiency despite the difference in roll material due to the difference in manufacturing method. The flaw detection can be performed without exchanging the surface wave probe, and the S / N ratio of the defect reflected wave can be increased with the common surface wave probe.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a surface acoustic wave probe according to the present invention.

FIG. 2 is a graph showing the results of measuring the reflected wave heights of artificial defects processed into five types of rolls using the probe of the present invention and a conventional probe.

FIG. 3 shows the S / S of the reflected wave of an artificial defect processed into five types of rolls using the probe of the present invention and the probe of the conventional method.
It is a graph which shows the result of having measured N ratio.

FIG. 4 is a front view showing an example of an ultrasonic inspection apparatus to which the surface acoustic wave probe of the present invention is applied.

FIG. 5 is a cross-sectional view showing only a surface acoustic wave probe and a medium supply unit for describing a medium supply method according to the present invention.

FIG. 6 is a graph showing, as an S / N ratio, a result of flaw detection inspection of 20 surface defects using a probe of the present invention and a probe of a conventional method.

[Explanation of symbols]

 4 Surface acoustic wave probe 10 Probe holder 20 Probe holder holding mechanism 40 Ultrasonic transducer 41 Wedge 50 Scraper 110 Roll

Claims (2)

[Claims] 1. A wedge that contacts a surface of a rotating roll via a medium and that causes at least an ultrasonic vibrator and an ultrasonic wave to be incident on the roll surface at an incident angle θi;
A roll surface acoustic wave probe for detecting defects existing directly under and above the roll surface, wherein the incident angle θi is set so as to satisfy the following equation: . Note θi = sin ^-1 (CW / CRav) where CW: Ultrasonic velocity in the wedge CRav: Average value of the surface wave velocity of each roll to be inspected, where the incident angle θi is perpendicular to the roll surface Angle with the plane. 2. A wedge, which is in contact with the surface of a rotating roll via a medium, and at least causes an ultrasonic transducer and ultrasonic waves to be incident on the roll surface at an incident angle θi.
A method for setting an incident angle of a roll inspection surface wave probe for arranging a surface wave in a direction opposite to a rotation direction of the roll and detecting a defect existing immediately below the surface of the roll. A method for setting an incident angle of a roll inspection surface wave probe, wherein the angle θi is set so as to satisfy the following expression. Note θi = sin ^-1 (CW / CRav) where CW: Ultrasonic velocity in the wedge CRav: Average value of the surface wave velocity of each roll to be inspected, where the incident angle θi is perpendicular to the roll surface Angle with the plane.