JP2005257692A - Grinding method for roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize a grinding amount of a roll to enhance a roll unit consumption, and to enhance efficiency for grinding the roll, when grinding the roll with a surface damaged thermally and mechanically by rolling or the like. <P>SOLUTION: When grinding the roll 110 with the surface damaged thermally and mechanically, the surface of the roll 110 is brought into contact with a surface wave probe 10 via a film of a contact medium, before starting the grinding or in the midway of the grinding, while rotating the roll 110, so as to propagate a surface wave from the surface wave probe 10 and to remove a liquid in a portion where the surface wave is propagated out of the roll surface, a height of reflected wave from the thermally and mechanically damage portion existing or remaining on the surface of the roll 110 is measured therein, and the grinding amount hereinafter is set in response to the height of the reflected wave to be ground. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a metal cylindrical body such as a rolling roll or roller, particularly cracks present on the surface of the high-speed rolling steel made of high-speed tool steel whose surface is thermally and mechanically damaged due to rolling, and on the surface. The present invention relates to a roll grinding method using an ultrasonic flaw detection method for a cylindrical body surface, which is preferably applied when detecting defects such as surface waves.

  A rolling roll used for hot rolling of a metal plate is subjected to thermal and mechanical damage on the surface by rolling. Hereinafter, with reference to FIG. 24, the thermal and mechanical damage on the surface of the former work roll (hereinafter referred to as the finishing high stand roll) made of high-speed tool steel used for hot finish rolling will be described in detail. The thermal damage is caused by the high temperature of the material to be rolled before the finishing stand, and deep primary cracks K called heat cracks are generated perpendicular to the surface of the roll 100. The mechanical damage is due to shear stress due to rolling with the backup roll, and secondary cracks L are generated in the direction almost parallel to the roll surface starting from the heat crack K. In addition, a plurality of these cracks are connected to generate minute chips M on the roll surface. When this minute chip M is transferred to the material to be rolled, it becomes a surface defect of the material to be rolled, so that it is removed from the surface to a certain depth (hereinafter referred to as a certain amount), for example, by grinding with a grindstone, The roll is used again for rolling. After grinding, ultrasonic flaw detection using surface waves (referred to as surface wave flaw detection) is performed as seen in Patent Document 1.

  Specifically, a surface wave probe (probe) is brought into contact with the surface of a rotating roll through a film of a contact medium such as water, and the surface wave is directed in the direction opposite to the roll rotation direction from the surface wave probe. , And the film of the contact medium where the surface wave propagates on the roll surface is removed to detect defects existing on the roll surface or directly below the surface. If a defect is detected by this surface wave flaw detection, additional grinding is performed.

  As an apparatus to which the flaw detection method according to Patent Document 1 is applied, there is an ultrasonic flaw detection apparatus disclosed in Patent Document 2. This ultrasonic flaw detector includes a rotating means for rotating a cylindrical or columnar specimen to be inspected for surface defects in the circumferential direction, and an ultrasonic probe for detecting defects and the like with ultrasonic waves. And a holding unit that holds the probe so as to maintain a certain distance from the surface of the test material above the test material, and a medium liquid such as water serving as an ultrasonic transmission medium with the probe A water supply means for supplying between the test materials is provided. The holding portion has a copying portion that protrudes downward from the probe and smoothly contacts the surface of the test material, and the copying portion of the holding portion is brought into contact with the rotating test material. Keep the distance to the test material constant. Further, the water supply means is provided in the vicinity of the contact of the holding portion. This water supply means has an accommodating portion capable of temporarily storing the medium liquid guided to the vicinity of the probe from other places. This accommodating part is located in the vicinity of the probe, and has a plurality of water outlets at the bottom and an air vent hole penetrating to the outside at the top. Each of the plurality of water outlets is arranged in front of the traveling direction when the probe scans the surface of the test material by rotation of the test material, and is arranged so as to intersect the circumferential direction. From the front of the probe, the medium water in the housing portion is discharged between the probe and the surface of the test material.

JP-A-4-276547 JP 7-294493 A

  However, it has recently been clarified that the flaw detection method disclosed in Patent Document 1 has the following major problems when it is used to detect defects existing on the surface of a high-speed roll for a stand before and after finishing or directly under the surface. .

  That is, since the minute chip M shown in FIG. 24 does not occur without the secondary crack L, in order to prevent the generation of the minute chip M, only the secondary crack L may be removed by grinding. However, in the conventional ultrasonic flaw detection method, even after all the secondary cracks L are removed, a phenomenon in which a reflected wave with a large amplitude appears is observed. If grinding is performed until this reflected wave does not appear, removal is unnecessary. The remaining part of the next crack K is scraped off, and the roll basic unit deteriorates.

  This is because the ultrasonic flaw detection method using surface waves is highly sensitive to defects perpendicular to the roll surface, and even if all the secondary cracks L are removed, the remaining portions of the primary cracks K are detected. is there. Since the depth of the remaining portion of the primary crack K is considerably small, the amplitude of the reflected wave from the remaining portion of each primary crack K is small, but the remaining portion of the primary crack K is There are innumerable numbers on the roll surface, and there are also innumerable paths along which the surface waves propagate by ultrasonic flaw detection using surface waves. When a specimen (here, a roll) having such countless minute reflectors is flaw-detected using surface waves, the distance from the surface wave probe 10 is as shown in FIG. There is always a combination of minute reflectors having a difference of λ / 2. FIG. 25 illustrates this combination of minute reflectors, and the minute reflectors K1 to K4 correspond to this combination.

  When a region in which such minute reflectors K1 to K4 exist is flaw-detected using a narrow-band pulse having a pulse width of five times or more of the surface wave wavelength as in the prior art, it is caused by a long pulse. As shown in FIG. 26, small reflected waves overlap with each other in the same phase and interfere to increase the amplitude, resulting in a reflected wave having a large defect. That is, in the ultrasonic flaw detection using the surface wave of the high-speed roll for the hot finish rolling pre-stage stand, the flaw detection is performed using a narrow band pulse whose pulse width is 5 times the wavelength of the surface wave. The amplitude of the reflected wave from K is detected excessively. As a result, grinding is performed until the amplitude of the reflected wave from the primary crack K becomes smaller than a predetermined value, and the primary crack K is almost removed, so that the grinding amount becomes excessive and the roll basic unit deteriorates.

  It is also conceivable to raise the threshold value set for defect detection to such an extent that the primary crack K is not overdetected. However, if this threshold value is increased, the defect detection capability will be lowered, so that there is a risk that defects that should be detected such as cracks that exist alone (generated due to an accident during rolling) may be missed. .

  The problems of ultrasonic flaw detection described above do not exist only in primary cracks such as rolling rolls, but in general metal cylinders such as rollers, the crystal structure is rough and scattered waves are generated from the grain boundaries. In such a case, when flaw detection is performed using a conventional narrow-band pulse, high noise is generated by the same mechanism as the phenomenon already described, and therefore there is a similar problem.

  The depth of thermal and mechanical damage generated by rolling is the length of the rolled metal sheet, the rolling speed, the cooling conditions of the roll, and the material (even if it is a roll classified into the same material) There is a small difference in material due to the difference in method). Therefore, if this is removed by a fixed amount of grinding, the following problems occur.

  (1) When the thermal / mechanical load is small and the depth of thermal / mechanical damage is small, the surface of the roll is scraped off to an undamaged part (over grinding), and the grinding amount increases, Basic unit deteriorates.

  (2) If the thermal / mechanical load is large and the depth of thermal / mechanical damage is large, this will remain even after a certain amount of grinding, and defects will be detected during flaw detection. Necessary. However, since it is unclear how much thermal and mechanical damage remains, the additional grinding amount has to be the same as the initial grinding amount, which is usually too much grinding (over grinding), and the grinding amount As a result, the basic unit of roll deteriorates.

  (3) The grinding time of the roll becomes longer by the time required for the above overgrinding, and the efficiency of roll grinding is reduced.

  Further, in the ultrasonic flaw detector disclosed in Patent Document 2, no consideration is given to the relationship between the rotation speed of the test material and the required amount of the medium liquid, but the test material depends on the rotation speed of the test material. The amount of medium liquid that escapes between the probe and the surface of the test material changes, for example, when the rotational speed of the test material increases, the fluid escapes between the probe and the surface of the test material. The amount of liquid in the medium increases, the amount of liquid in the medium between the probe and the surface of the test material is insufficient, the transmission of ultrasonic waves to the test material may be poor, and surface defects may not be detected. . On the other hand, when the rotation speed of the roll is reduced, the excess medium liquid flows out in front of the probe, which may attenuate the surface wave and make it impossible to detect surface defects.

  The present invention has been made to solve the above-mentioned conventional problems. When grinding a roll whose surface is thermally and mechanically damaged by rolling or the like, the roll grinding amount is optimized by optimizing the grinding amount of the roll. It is another object of the present invention to provide a roll grinding method capable of improving the efficiency of roll grinding.

  In the present invention, when grinding a roll whose surface is thermally and mechanically damaged, the roll is rotated through a contact medium film on the surface of the roll before starting grinding or during grinding. The surface wave probe is brought into contact, the surface wave is propagated from the surface wave probe, and the liquid on the surface of the roll where the surface wave propagates is removed, so that the thermal / mechanical that exists or remains on the surface of the roll. The problem is solved by measuring the height of the reflected wave from the damaged portion and setting the subsequent grinding amount according to the reflected wave height to perform grinding.

As shown in FIG. 1, a surface wave probe 10 that can be used in the present invention is mainly composed of an ultrasonic transducer 10A, a damping material 10B, and a resin wedge 10C. when was the f _c, it has a frequency bandwidth of the surface wave and more 0.50f _c.

That is, now, assuming that the frequency spectrum of the surface wave transmitted and received by the surface wave probe 10 has a frequency distribution conceptually shown in FIG. 2, it is within −6 dB with respect to the peak value of the spectrum intensity (signal intensity). The frequency width (f _R −f _L ) of the range is defined as the frequency bandwidth, and the following equation (1) is established.

f _R −f _L ≧ 0.50 f _c (1)

Thus, the frequency band of the surface wave probe 10, and a more wideband 0.50f _c. The specific configuration of the surface wave probe 10 will be described. The ultrasonic vibrator 10A includes a vibrator having a low mechanical Q value, such as a lead niobate-based porcelain or the composite vibrator shown in FIGS. Or a vibrator that is easily mechanically damped even if the mechanical Q value is high, such as a lead titanate-based ceramic. Here, the mechanical Q value is a quantity representing the sharpness of resonance vibration, and the greater the Q value, the longer the vibration duration. The center frequency f _c of the surface wave to be transmitted and received, since the scattering noise by crystal grain boundaries and surface roughness of the material to be testing different, it is necessary to set an appropriate range. For example, in the case of a roll for rolling, 1 to 4 MHz is preferable.

  Further, as the damping material 10B, an object obtained by mixing and hardening a powder having a large specific gravity such as tungsten (metal) with an epoxy resin and the like is adhered to the back surface of the ultrasonic transducer 10A, thereby ultrasonic waves are obtained. The ultrasonic vibration generated in the vibrator 10A is braked. As the volume fraction of powder such as tungsten (metal) increases, the weight of the damping material increases, so that the damping effect of the vibration of the ultrasonic vibrator increases, and the pulse width of the ultrasonic pulse decreases.

By the ultrasonic transducer 10A and the damping member 10B with the material structure as described above, the frequency bandwidth 0.5f _c or more and a pulse width of the wavelength of the surface wave 2.5 times or less of the ultrasonic pulses Can be generated (transmitted).

Further, as shown in FIG. 1, the resin wedge 10C is brought into contact with the surface of the subject through the medium so that the ultrasonic vibration satisfies the following expression (2) and enters the subject. The normal surface S1 of the ultrasonic transmission / reception surface intersects with the incident angle θ _i with respect to the normal line S1 of the bottom surface, and the front surface of the ultrasonic transducer 10A (ultrasonic transmission / reception surface) on the inclined surface Is to be affixed. The wedge 10C itself is formed using, for example, a polystyrene resin, a polyimide resin, or the like having a small attenuation rate so as not to damage the short pulse waveform as described above.

θ _i = sin ⁻¹ (C _W / C _R ) (2)

Where C _{W is} the velocity of the ultrasonic wave in the resin wedge
C _R : velocity of surface wave in cylinder

FIG. 3 shows the result of investigating the relationship between the pulse width and the frequency bandwidth by fabricating the surface acoustic wave probe 10 with the center frequency f _c = 2 MHz having different frequency bandwidths by changing the material of the damping material. Is. However, here, frequency bandwidth indicates a time equal to the center frequency f _c as 100%.

  As can be seen from FIG. 3, when the frequency bandwidth is 50% or more, it is possible to generate a short pulse whose pulse width is 2.5 times or less of the wavelength of the surface wave. The surface wave pulse having a short pulse width generated in this way is applied to defect detection of a roll in which an infinite number of remaining primary cracks K exist. Also in this case, as described with reference to FIG. 25, there is always a combination of minute reflectors K1 to K4 whose distance from the surface wave probe 10 is λ / 2 when the wavelength of the surface wave is λ. .

Figure 4 is a said frequency bandwidth 0.70 F _c above, when the pulse width using a 1.5-fold and short ultrasonic pulses of a wavelength of the surface wave was testing a region where the micro reflectors are present These observation waveforms are shown and correspond to FIG. 26 of the conventional example.

  As shown in FIG. 4, since the pulse width is short, even if the reflected waves having a small amplitude from the remaining portion of the primary crack K overlap with each other in the same phase, the increase in the amplitude is small. That is, when the surface wave probe 10 of the present invention that can transmit and receive a surface wave pulse with a short pulse width is applied to defect detection of a roll in which an infinite number of remaining portions of the primary crack K exist, the remaining portion of the primary crack K It is possible to effectively prevent the amplitude of the reflected wave from increasing.

  FIG. 5 shows the reflected wave height from the primary crack K of the first work roll for hot finish rolling (pulse width / surface), using the surface wave probe having a center frequency of 2 MHz with different frequency bandwidth (different pulse width). The result of investigating the relationship with the wavelength of the wave) is shown. However, as a reference for the height of the reflected wave, the height of the reflected wave from the vertical drill hole having a diameter of 1 mm and a depth of 1 mm was taken, and the depth of the primary crack K was about 0.15 mm.

  In the figure, measured points A1, A2, and A3 correspond to the present invention, and a lead niobate-based ceramic is used as the ultrasonic transducer 10A constituting the surface wave probe 10, and further mixed with an epoxy resin as a damping material 10B. A damping material having a volume fraction of tungsten powder of 80%, 60%, and 40%, respectively, is used. B1 and B2 correspond to comparative examples, using PZT as the ultrasonic transducer 10A, and further using a damping material in which the volume fraction of tungsten powder mixed with the epoxy resin is 80% and 60% as the damping material 10B, respectively. Yes. C1 and C2 correspond to conventional examples, and PZT having slightly different mechanical Q values is used as the ultrasonic transducer 10A, and the damping material 10B is not used. Except for the above, the measurement was performed using substantially the same apparatus.

  FIG. 5 shows that the reflected wave height from the primary crack K decreases as the pulse width becomes shorter.

Next, materials suitable for the ultrasonic transducer 10A and the resin wedge 10C were examined in detail. As described above, the damping material 10B is obtained by mixing and hardening an epoxy resin with tungsten powder, and the volume fraction of the tungsten powder mixed with the epoxy resin is 80%, 60%, 40%, and 20%, respectively. . As the ultrasonic vibrator 10A, lead niobate-based porcelain, lead titanate-based porcelain, PZT, barium titanate, lithium niobate, 1-3 type composite vibrator (as shown in FIG. 6, a polymer made of epoxy resin or the like) A vibrator plate in which a large number of small columnar lead zirconate titanates (hereinafter referred to as PZT) 11B are placed on a material plate 11A, and a 0-3 type composite vibrator (as shown in FIG. Ceramic vibrator particles 11D are uniformly dispersed therein, 3-1 type composite vibrator (as shown in FIG. 8, lead zirconate titanate (PZT) plate 11E with many through holes In this case, an oscillator in which a polymer material 11F such as an epoxy resin is poured and hardened is selected, and a polyimide wedge, a polystyrene resin, an acrylic resin, a fluororesin is used as the resin wedge 10C. Select a resin, manufacture a surface wave probe, measure the frequency bandwidth and pulse width of the transmitted and received surface wave, and use the same primary work roll for hot finish rolling as the experiment shown in FIG. The reflected wave height from the crack K was investigated. The height of the reflected wave is taken as the height of the reflected wave from a longitudinal drill hole having a diameter of 1 mm and a depth of 1 mm, which is exactly the same as the experiment whose result is shown in FIG. FIG. 9 shows the experimental results when the volume fraction of tungsten powder in the damping material 10B is 80%, and FIG. 10 shows the experimental results when the volume fraction of tungsten powder in the damping material 10B is 60%. The experimental results when the volume fraction of tungsten powder in 10B is 40% are shown in FIG. However, although the case where the reflected wave height from the primary crack K is higher than -11 dB (the reflected wave height from the primary crack K is not 3 dB or more lower than that of the conventional probe) is deleted, the ultrasonic transducer is not used. The results for PZT are all shown for comparison as comparative examples. FIG. 12 shows the experimental results when the volume fraction of tungsten powder in the damping material 10B is 20%, and the reflected wave height from the primary crack K is higher than −11 dB. 9 to 11, in all cases, the ultrasonic vibrator 10A includes a lead niobate-based ceramic, a lead titanate-based ceramic, a 1-3 type composite vibrator, a 0-3 type composite vibrator, It can be seen that all 3-1 type composite vibrators can be used. The resin wedge 10B includes polyimide resin (ultrasonic attenuation constant at 2 MHz: 1.2 × 10 ² dB / m), polystyrene resin (ultrasonic attenuation constant at 2 MHz: 1.3 × 10 6). ² dB / m), acrylic resin (ultrasonic attenuation constant at 2 MHz: 1.8 × 10 ² dB / m), fluororesin (Teflon (registered trademark): ultrasonic attenuation constant at 2 MHz: 1.8 It can be seen that all of (× 10 ² dB / m) can be used. Therefore, the wedge material may have an ultrasonic attenuation constant of ² × 10 ² dB / m or less at ² MHz. Furthermore, comparing FIG. 9 to FIG. 11 with FIG. 12, it can be seen that the volume fraction of tungsten powder in the damping material 10B needs to be 40% or more.

  The inventors of the present invention conducted ultrasonic flaw detection of the former work roll for hot finishing rolling under substantially the same conditions using a surface wave probe having a pulse width of 5 times the wavelength of the surface wave, which has been conventionally used. Since it was confirmed that the reflected wave from the primary crack was reduced by 3 dB between the flaw detection performed after the grinding step one time before the final roll grinding and the flaw detection performed after the final grinding step. If the height of the reflected wave from the primary crack K can be reduced by 3 dB or more, the number of roll grinding steps can be reduced at least once. Whether or not the final roll grinding stage is to be performed is determined based on whether or not an actual measurement value measured after grinding has become a predetermined threshold value or less.

  Therefore, as shown in FIG. 5, the reflected wave height from the primary crack is reduced by 3 dB or more compared to the measured value C1 using a surface wave probe whose pulse width is 5 times the wavelength of the surface wave used in the past. If the pulse width of the surface wave probe from which the measured value can be obtained is 2.5 times or less of the wavelength of the surface wave, the difference between the measured value A3 and C1 is 3 dB. The number can be reduced more than once.

Furthermore, it can be said from FIG. 3 that the bandwidth of a surface wave probe capable of transmitting and receiving a surface wave whose pulse width is 2.5 times or less of the wavelength of the surface wave is appropriate to be 50% or more. Therefore, by setting the frequency bandwidth of the surface wave probe above 0.50F _c, it can be seen that the effect of reducing the role of the over-grinding caused by over-detection of the primary cracks. This is the basis for the frequency bandwidth of the surface wave probe 0.50F _c above.

As described above in detail, the frequency band width is more 0.50F _c, by using a surface wave probe pulse width is more than 2.5 times the wavelength of the surface wave, pulse width conventionally used surface Compared with the case of using a surface wave probe of about 5 times the wavelength of the wave (point C1 in FIG. 5) and the case of using the surface wave probe (points A1 to A3), the reflected wave height from the primary crack K is 3 It could be reduced by ˜6 dB or more.

  Similarly, the depth generated in the rolling roll in which the primary crack K having a depth of about 0.10 mm remains or the high speed roll in which the primary crack K having a depth of about 0.25 mm remains. When a 0.5 mm crack was detected, a surface wave probe with a pulse width of 1.5 times the wavelength of the surface wave had an S / N ratio of 10 dB of the reflected wave from the crack, and a pulse width of 2 of the wavelength of the surface wave. In the surface wave probe of 5 times, the S / N ratio of the reflected wave from the crack was 7 dB, whereas in the conventional surface wave probe whose pulse width is about 5 times the wavelength of the surface wave, The S / N ratio was about 4 dB. Therefore, according to the flaw detection method used in the present invention, the S / N ratio can be increased by about 3 to 6 dB as compared with the conventional method, and the defect detection capability can be greatly improved.

  Next, the ultrasonic vibrator 10A, the damping material 10B, and the resin wedge 10C shown in FIG. 1 are each a lead niobate-based porcelain, a damping material in which tungsten powder is mixed with epoxy resin at a volume fraction of 60%, Using an ultrasonic flaw detector provided with a surface wave probe 10 made of polyimide resin, flaw detection is performed on 500 pre-rolling work rolls for hot finish rolling, and reflected waves from primary cracks (heat cracks) are predetermined. We investigated the actual grinding amount until the level dropped below the same level. Using an ultrasonic flaw detector with a surface wave probe with a pulse width of about 5 times the wavelength of the surface wave, the same as the diameter grinding amount. According to the present invention, it was reduced to 0.2 mm from 0.33 mm in the conventional example investigated in (1).

  As described above, according to the flaw detection method used in the present invention, it is possible to reduce the grinding amount by 0.1 mm or more as compared with the prior art. Even in such a case, the degree of surface defects of the material to be rolled generated due to minute chips generated on the surface of the rolling roll was almost the same as before.

  The inventors use a high-speed roll having artificial defects, change the rotational speed of the high-speed roll, the transmission of ultrasonic waves from the probe to the roll surface is stable, and excess medium liquid FIG. 13 shows the result of examining the amount of medium liquid (water in this experiment) suitable for maintaining the height of the reflected wave from the artificial defect at a constant value without flowing out to the front of the probe. Show. If the amount of water is within the hatched range, the transmission of ultrasonic waves from the probe to the roll surface becomes stable. It has been found that the amount of the medium liquid needs to be increased as the rotation speed of the high-speed roll increases. Therefore, the rotational speed of the high-speed roll is measured by the rotational speed detecting means, and an appropriate amount is controlled by controlling the supply amount of the medium liquid using the flow rate control valve provided in the water supply means according to the rotational speed of the high-speed roll. Medium liquid can be supplied between the probe and the high-speed roll surface, so that the transmission of ultrasonic waves from the probe to the roll surface can be stably maintained, and excessive medium liquid can be detected. It is possible to prevent the flow out to the front of the touch element.

  The inventors used the surface wave probe to detect the reflected wave height from the thermally / mechanically damaged part and the remaining amount of the thermally / mechanically damaged part (when the reflected wave height falls below the defect detection threshold). Measure the height of the reflected wave from the thermally and mechanically damaged parts while grinding the rolls that were thermally and mechanically damaged by rolling in small increments. did. The result is shown in FIG. It is well understood that the remaining amount of the thermal / mechanical damaged part is reduced and the height of the reflected wave from the thermal / mechanical damaged part is also reduced. FIG. 15 shows the relationship between the grinding amount necessary to remove the thermal / mechanical damaged part and the reflected wave height from the thermal / mechanical damaged part, as shown in FIG. Therefore, if the reflected wave height from the thermally and mechanically damaged portion is measured by ultrasonic flaw detection using surface waves before starting grinding or in the middle of grinding, and the grinding amount is determined using the relationship shown in FIG. Optimal grinding is possible by preventing excessive grinding beyond the thermally and mechanically damaged part and uncut residue of the thermally and mechanically damaged part.

  In particular, the surface wave probe and the grinding wheel are moved to the place where the reflected wave height from the thermal / mechanical damaged part is the highest, and plunge grinding is performed while flaw detection is performed, and the thermal / mechanical damaged part is detected. It is possible to perform optimum grinding by obtaining a grinding amount at which the height of the reflected wave from is reduced to a predetermined level or less and grinding the remaining roll surface according to this grinding amount.

  That is, if ultrasonic flaw detection using surface waves is carried out before starting grinding or in the middle of grinding, the height of the reflected wave from the thermally and mechanically damaged part is the highest, as is apparent from the relationship of FIG. It can be identified that the remaining amount of the thermal / mechanical damaged portion is the largest. Therefore, as shown in FIG. 16, the position where the grindstone 62 of the roll grinding apparatus and the surface wave probe 10 are brought into contact with the rolling roll 110 (position in the axial direction of the roll) is matched, and thermal and mechanical damage is caused. The grindstone 62 of the roll grinding apparatus and the surface wave probe 10 are brought into contact with the place where the height of the reflected wave from the portion is the highest. Then, ultrasonic flaw detection using surface waves is performed, and if the rolling roll is plunge-ground until the reflected wave height from the thermally and mechanically damaged part falls below a predetermined threshold value, the grinding amount at this time is reduced from the entire surface of the rolling roll. This is the amount of grinding required to remove mechanical and mechanical damage. Therefore, grinding may be performed by setting the grinding amount of the remaining roll surface to the grinding amount.

  According to the flaw detection method used in the present invention, when ultrasonic flaw detection is performed using surface waves, it is possible to prevent over-detection of primary cracks and to prevent deterioration of the roll basic unit due to over grinding. Furthermore, the level of noise from primary cracks and crystal grain boundaries can be reduced, and the defect detection capability can be greatly improved.

  In particular, according to the present invention, when grinding a roll whose surface has been thermally and mechanically damaged by rolling, the subsequent grinding amount is set according to the height of the reflected wave from the thermal and mechanical damage. In this case, the amount of roll grinding can be optimized to improve the roll basic unit, and the efficiency of roll grinding can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 17 is a schematic side view showing a first embodiment of an ultrasonic flaw detector that can be used in the present invention.

  The ultrasonic flaw detector according to the present embodiment uses a rolling roll denoted by reference numeral 110 in the drawing as an object, and transmits and receives surface waves of the roll 110 and a roll rotating apparatus that rotates the roll 110 as a basic configuration. For supplying a contact wave (water) attached to the holder 12 between the surface of the roll 110 and the surface wave probe 10. Means (to be described later).

  As the roll rotating device, illustration is omitted in order to avoid complication of the drawing, but any known appropriate device can be used as long as it can rotate the rolling roll 110 to be inspected in the circumferential direction C thereof. Can be used.

The surface wave probe 10, the frequency bandwidth 0.50F _c above, so that the pulse width is capable of transmitting and receiving 2.5 times or less of the surface wave having a wavelength of the surface wave, the composition of the resonator type and damping material Is adjusted.

  In the surface wave probe 10, a state in which water (contact medium) is filled in a gap between the probe 10 and the surface of the rolling roll 110 that is the subject is formed, and ultrasonic waves are transmitted through the water to the roll 110. By transmitting the surface wave to the roll 110, the surface wave is propagated to the roll 110 and the reflected wave is received, whereby the surface defect of the rolling roll 110 can be detected.

  The probe holder 12 holding the surface wave probe 10 is attached to the lower part of a guide 16 that can slide in the vertical direction with respect to the fixed structure 14 positioned above the rolling roll 110. It is held by the part 18. The holding mechanism section 18 includes a pair of front and rear rollers, a total of four rollers 20, and the probe holder 12 is disposed between the rollers 20. And when flaw detection is performed, these four rollers 20 are in contact with the surface of the rolling roll 110 and rotate, thereby stabilizing flaw detection scanning.

  The fixed structure portion 14 is provided with a motor 14A for supplying power for raising and lowering the holding mechanism portion 18 along the guide 16 via a known transmission means (not shown), and an attachment base 14B thereof. ing.

  The fixed structure portion 14 can be scanned in the axial direction of the rolling roll 110 by scanning means (not shown), and thereby the surface wave probe 10 can be scanned in the axial direction of the rolling roll 110.

  The probe holder 12 is attached to a lower end of a rod-like body 12A that is loosely fitted to the holding mechanism portion 18 so as to be movable up and down, and a spring (not shown) interposed at a predetermined position around the rod-like body 12A. ) Is always supported in a downward direction in the drawing, that is, in a state of being pressed against the surface of the rolling roll 110 with an appropriate force.

  In the probe holder 12, in order to form a predetermined gap between the surface wave probe 10 and the rolling roll 110, a pair of copying rollers 22 projecting toward the rolling roll 110 below the surface wave probe 10. Is provided.

  FIG. 18 is an enlarged front view of this state, in which shafts 24 are provided on opposite sides of the probe holder 12 along the horizontal direction (roll axis direction), and the copying roller 22 is provided on both sides thereof. Are rotatably mounted. In this way, the scanning roller 22 pivotally supported by the probe holder 12 receives an appropriate pressing force from the spring, so that it always comes into contact with the surface of the rolling roll 110 during measurement. In the holder 12, the surface wave probe 10 is held so that a constant gap is always maintained between the surface wave probe 10 and the rolling roll 110.

  Further, in the surface wave probe 10, as shown in FIG. 19 in which the contours of the probe holder 12 and the copying roller 22 are omitted by two-dot chain lines, a water supply section (water supply means) 26 is provided therein. The water guided from the conduit 28 is once accommodated in the accommodating portion 26A, and is discharged from the discharge hole 26B provided at the bottom of the accommodating portion 26A, and there is no air bubble between the surface wave probe 10 and the rolling roll 110. A water layer can be formed. Since the water supply means may be configured using a conventionally known appropriate means, detailed description thereof is omitted.

  In FIG. 17, reference numeral 30 denotes a scraper that removes water supplied from the water supply unit 26 as described above so that the water remains on the roll surface and does not flow onto the propagation path of the surface wave.

  Since the ultrasonic flaw detector of the present embodiment has the above-described apparatus configuration, water serving as an ultrasonic propagation medium is supplied between the surface wave probe 10 and the surface of the rolling roll 110 that is the subject. The flaw detection operation can be performed easily and reliably while scanning the probe 10 on its surface.

  Using this embodiment, flaw detection is performed on 500 pre-rolling work rolls (high-speed rolls) for hot finish rolling, and the reflected waves from primary cracks called heat cracks are lowered to a predetermined level or lower. When the actual grinding amount was investigated, the actual grinding amount (diameter conversion) with a flaw detector using a surface wave probe having a pulse width of about 5 times the wavelength of the surface wave was 0.33 mm. However, in this embodiment, it was 0.20 mm, and it was confirmed that the grinding amount could be reduced by 0.1 mm or more compared to the conventional case. Even in this case, the occurrence of surface defects in the material to be rolled due to minute chips on the surface of the high-speed roll was not different from the conventional one.

  Next, referring to FIG. 20, a second embodiment of an ultrasonic flaw detector that can be used in the present invention and is suitable for flaw detection by scanning the surface wave probe 10 on the surface of a high-speed roll will be described. This will be described in detail.

  In the present embodiment, the rolling roll 110 is a high-speed roll, and the rotational speed of the high-speed roll is detected by the rotational speed detector 32 and sent to the flow rate control valve 34 provided in the water supply device. It is controlled to fit the range shown in FIG. The output of the surface wave probe 10 is input to the defect determination circuit 44 via the ultrasonic transmitter / receiver 40 and the gate circuit 42.

  The ultrasonic transmitter / receiver 40 supplies an electric pulse for transmitting a surface wave to the surface wave probe 10, amplifies a signal captured by the surface wave probe 10 to a level necessary for defect determination, and a gate circuit 42. Output to. The gate circuit 42 extracts a signal to be subjected to defect determination from the signal output from the ultrasonic transceiver 40 and outputs the signal to the defect determination circuit 44. The defect determination circuit 44 detects and outputs the amplitude of the signal output from the gate circuit 42, or compares the level of the signal with a predetermined threshold, and when the level of the signal is high, To detect surface defects.

  As in the first embodiment, the probe holder 12 includes a water supply unit 26 as shown in FIG. The water supply unit 26 has a flow rate according to the rotational speed (circumferential speed) of the rolling roll 110 by the flow rate control valve 34, and temporarily stores the water guided from the conduit 28 in the storage unit 26A. It discharges from the discharge port 26 </ b> B provided at the bottom, and forms a water-free layer between the surface wave probe 10 and the rolling roll 110.

  Since the other points are the same as those in the first embodiment, the same reference numerals are used and detailed description thereof is omitted.

  FIG. 21 shows the result of investigating the high speed roll having surface defects by changing the rotation speed from 25 rpm to 50 rpm with the apparatus of this embodiment, and investigating the relationship between the height of the reflected wave from the defect and the rotation speed. . If the apparatus of this embodiment is used, surface defects can be detected satisfactorily regardless of the rotation speed of the high-speed roll.

  Next, a third embodiment according to the present invention will be described in detail with reference to FIG.

  In the present embodiment, ultrasonic flaw detection using surface waves is performed before starting grinding or in the middle of grinding, and the height of the reflected wave from the thermally and mechanically damaged portion is measured, and then the grinding roll 60 is fed to the grinding device 60. The apparatus which transmits the setting value of grinding amount is shown. As the grinding device for the rolling roll, a conventionally known appropriate device may be used, and the illustration is omitted in order to avoid complication of the drawing.

  An ultrasonic flaw detector 50 is connected to the surface wave probe 10 to supply an electric pulse for transmitting a surface wave from the surface wave probe 10 to the surface wave probe 10, and a signal received by the surface wave probe 10 is received. Amplifies to a level suitable for defect determination. Furthermore, the ultrasonic flaw detector 50 uses the same gate circuit (not shown) as in the second embodiment to extract the reflected wave from the thermal and mechanical damage from the amplified signal and detect its height. To do. The height of the reflected wave from the thermal / mechanical damaged part detected by the ultrasonic flaw detector 50 is sent to the computer 52, and the thermal / mechanical damaged part is removed by referring to the relationship of FIG. The amount of grinding required to do this is required. The set value of the grinding amount thus obtained is sent to the grinding device 60 of the rolling roll, and grinding is performed using, for example, a grindstone.

  Since the other points are the same as those in the first and second embodiments, the same reference numerals are used and detailed description thereof is omitted.

  Using this embodiment, 200 pre-rolling work rolls for hot finish rolling were flawed and the amount of grinding was investigated. As a result, reflection waves from thermally and mechanically damaged parts, which have been conventionally performed, were investigated. The estimated value of the grinding amount by a method of repeating a certain amount of grinding until the height falls below a predetermined threshold (the grinding amount in the conventional method is estimated from the actual grinding amount value using this device for each roll) The diameter was 0.23 mm, which was also 0.18 mm, and it was confirmed that the grinding amount could be reduced by 0.05 mm or more compared to the conventional case.

  Next, a fourth embodiment according to the present invention will be described in detail with reference to FIG.

  In the present embodiment, a position detector 36 for detecting the position of the surface wave probe 10 in the roll axis direction is provided, and the computer 52 receives the position detector 36 from the position detector 36 in the roll axis direction. Rolling the part where the height of the reflected wave from the thermally and mechanically damaged part is the highest in ultrasonic flaw detection by surface waves that have been detected and sent before the start of grinding or in the middle of grinding A position on the roll is required. When performing grinding called plunge grinding, as shown in FIG. 16, the position where the surface wave probe 10 and the grindstone 62 are in contact with the rolling roll 110 (position in the axial direction of the roll) matches. The surface wave probe 10 is mechanically aligned and installed.

  Since other configurations are the same as those of the third embodiment, the same reference numerals are used and detailed description thereof is omitted.

  Hereinafter, the operation of this embodiment will be described in detail. First, the surface wave of the entire surface of the rolling roll is scanned by scanning the surface wave probe 10 in the axial direction of the rolling roll 110 while rotating the rolling roll 110 in the circumferential direction C before starting grinding or in the course of grinding. Is reflected by the computer 52 to which the height of the reflected wave from the thermal / mechanical damaged portion and the position detection signal of the surface wave probe 10 are input. The position on the rolling roll 110 where the wave height is highest is determined.

  Next, as shown in FIG. 16, the surface wave probe 10 and the grindstone 62 are moved to this position, and ultrasonic flaw detection by the surface wave is performed until the reflected wave height from the thermally and mechanically damaged portion falls below a predetermined threshold value. The plunge grinding of the rolling roll 110 is performed while performing the above, and the grinding amount at this time is obtained.

  The set value of the grinding amount thus obtained is input to the grinding device 60 for rolling rolls, and the remaining roll surface is ground.

  Using the apparatus of the present embodiment, 200 front work rolls for hot finish rolling were flawed and the results of grinding amount were investigated. Reflection from a thermally and mechanically damaged portion, which has been conventionally performed. The estimated value of the grinding amount in a method of repeating a certain amount of grinding until the wave height falls below a predetermined threshold was 0.24 mm in terms of diameter, but in this embodiment, it is also 0.19 mm, It was confirmed that the grinding amount could be reduced by 0.05 mm or more compared to the conventional case.

  Although the present invention has been specifically described above, the present invention is not limited to that shown in the above embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, the specific materials of the ultrasonic transducer 10A, the damping material 10B, and the resin wedge 10C, which are members constituting the surface wave probe, are not limited to those shown in the above embodiment, and have similar functions. Any material can be used.

  Moreover, although the case where water was used as a contact medium was shown in the said embodiment, you may use other liquids, such as oil.

  The application target of the present invention is not limited to a rolling roll, particularly a high-speed roll, and is not particularly limited as long as it is a cylindrical body such as a roller made of metal or the like.

Sectional drawing which expands and shows schematic structure of the surface wave probe which can be used by this invention Diagram for explaining frequency bandwidth of surface acoustic wave probe Diagram showing the relationship between the frequency bandwidth of the surface wave probe and (pulse width / surface wave wavelength) Explanatory drawing which shows the relationship between the observation waveform by the said surface wave probe, and the reflected wave from a micro reflector Diagram showing the relationship between the height of the reflected wave from the primary crack and (pulse width / surface wave wavelength) A perspective view showing a 1-3 type composite vibrator which is an example of a probe vibrator that can be used in the present invention. The perspective view which shows the 0-3 type composite vibrator | oscillator which is another example of the probe vibrator | oscillator which can be used by this invention A perspective view showing a 3-1 type composite vibrator which is still another example of a probe vibrator that can be used in the present invention. When the volume fraction of tungsten powder in the damping material is 80%, the vibrator material and the resin material of the surface wave probe, the frequency bandwidth of the surface wave, the pulse width, and the reflected wave from the primary crack Chart showing the relationship between height measurement results Similarly, the relationship between the vibratory material and the resin material of the surface wave probe, the measurement result of the frequency bandwidth of the surface wave, the pulse width, and the height of the reflected wave from the primary crack when 60% is shown. Chart Similarly, when the ratio is 40%, the relationship between the vibratory material and the resin material of the surface wave probe, the measurement result of the frequency bandwidth of the surface wave, the pulse width, and the height of the reflected wave from the primary crack is shown. Chart Similarly, the relationship between the vibratory material and the resin material of the surface wave probe and the measurement result of the frequency bandwidth of the surface wave, the pulse width, and the height of the reflected wave from the primary crack when it is 20% is shown. Chart Diagram showing results of investigation of roll rotation speed and appropriate amount of medium liquid The diagram which shows the relationship between the height of the reflected wave from a thermal and mechanical damage part, and the residual amount of a thermal and mechanical damage part for demonstrating the principle of this invention Similarly, a diagram showing the relationship between the amount of grinding required and the height of reflected waves from thermally and mechanically damaged parts Similarly, a perspective view showing the positional relationship between a grindstone and a surface wave probe in plunge grinding The side view which shows schematic structure of 1st Embodiment of the ultrasonic flaw detector which can be used by this invention The front view which expands and shows the probe holder part of 1st Embodiment Similarly, the principal part side view which fractures | ruptures and shows the water supply part with which the surface wave probe was equipped The side view which shows schematic structure of 2nd Embodiment of the ultrasonic flaw detector which can be used by this invention The diagram which shows the investigation result of the relationship between the height of the reflected wave from a defect, and a rotation speed when flaw detection is performed by changing the roll rotation speed in the second embodiment. The side view which shows schematic structure of 3rd Embodiment of the ultrasonic flaw detector which concerns on this invention. Similarly, the side view which shows schematic structure of 4th Embodiment Conceptual diagram for explaining cracks generated on the surface in the circumferential direction of a work roll for hot finish rolling Explanatory drawing showing the positional relationship between the surface wave probe and the minute reflector Explanatory diagram showing the relationship between the observed waveform by the conventional method and the reflected wave from the micro reflector

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Surface wave probe 10A ... Ultrasonic vibrator 10B ... Damping material 10C ... Resin wedge 12 ... Probe holder 14 ... Fixed structure part 16 ... Guide 18 ... Holding mechanism part 20 ... Roller 22 ... Copying roller 24 ... Shaft 26 ... Water supply Unit 28 ... Conduit 30 ... Scraper 32 ... Rotational speed detector 34 ... Flow control valve 36 ... Position detector 40 ... Ultrasonic transmitter / receiver 44 ... Defect determination circuit 50 ... Ultrasonic flaw detector 52 ... Computer 60 ... Grinding device 62 ... Whetstone 110 ... rolling roll

Claims (3)

When grinding rolls that have been thermally and mechanically damaged on the surface,
Before starting grinding or in the middle of grinding, while rotating the roll, the surface wave probe is brought into contact with the surface of the roll through the film of the contact medium, and the surface wave is propagated from the surface wave probe. Measure the height of the reflected wave from the thermal / mechanical damage that exists or remains on the surface of the roll by removing the liquid in the part where the surface wave propagates.
A roll grinding method, wherein grinding is performed by setting a subsequent grinding amount in accordance with the reflected wave height. In the roll grinding method according to claim 1, the surface wave probe and the grinding wheel are moved to a place where the reflected wave height from the thermally and mechanically damaged portion is the highest, and plunge grinding is performed while performing flaw detection, Find the grinding amount at which the reflected wave height from the thermally and mechanically damaged part is below the specified level.
A roll grinding method comprising grinding the remaining roll surface in accordance with the grinding amount.   3. The roll grinding method according to claim 1, wherein the roll is a rolling roll.

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