JP2011245582A - Cavitation generating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cavitation generating apparatus that can shorten a length along the injection direction of a cavitation jet and that can perform cavitation peening even in a part with a narrow space for execution.SOLUTION: A low pressure water jetting means 11 is composed of a water stream adjusting tank 21 in which supplied low pressure water flows in and a low pressure jetting hole 23 which, in communication with the water stream adjusting tank 21, can jet the supplied low pressure water nearly vertically to the supplied direction. A high pressure nozzle 13 is arranged along the center axis of the low pressure jetting hole 23 and, for the purpose of surrounding the circumference with the low pressure water jetted from the low pressure jetting hole 23, is configured to jet high pressure water in the same direction as the jetting direction of the low pressure water from the low pressure jetting hole 23 to generate cavitation air bubbles. Along the circumference of the opening inside the water stream adjusting tank 21 of the low pressure jetting hole 23, there is installed a rectifying wall 12 in a manner projecting toward the inside of the water stream adjusting tank 21.

Description

  The present invention relates to a cavitation generator.

  As shown in FIG. 6, the conventional cavitation generator uses a concentric nozzle to inject a low-pressure water (low-speed water) jet into the atmosphere and inject a high-pressure water (high-speed water) jet into the center thereof. An aerial cavitation jet is generated. The cavitation generating device is suitably used as a device for cavitation peening because a peening effect can be obtained by the collapse impact force of the generated cavitation bubbles of the generated air cavitation jet. It has been demonstrated that cavitation peening using this cavitation generator can improve the fatigue strength of metallic materials such as stainless steel, and can introduce compressive residual stress to prevent stress corrosion cracking (for example, Patent Documents 1 to 5, see Non-Patent Documents 1 to 3.

  In power plants and chemical plants, suppression of stress corrosion cracking of piping and the like is an urgent issue. In order to suppress the stress corrosion cracking, the best solution is to reduce the tensile residual stress that causes the stress corrosion cracking or to make the tensile residual stress a compressive residual stress. In general, shot peening, ultrasonic peening, laser peening, cavitation peening and the like are used to introduce compressive residual stress.

  However, when used in a plant, laser peening cannot be applied because water cannot be stored on the outer periphery of the piping of the plant. Also, shot peening and ultrasonic peening are difficult to construct while the plant is in operation because there is a risk of ignition or ignition due to collision of shots. Although it is possible to prevent ignition and ignition by stopping the operation of the plant, the economic loss is great. On the other hand, since cavitation peening can introduce compressive residual stress only with water, there is no risk of ignition or ignition even when used during plant operation. For this reason, practical application of cavitation peening is desired in plants.

JP-A-8-257998 Japanese Patent No. 2894450 Japanese Patent No. 2957976 JP 2000-202326 A JP 2003-62492 A

H. Soyama, “Introduction of Compressive Residual Stress Using a Cavitating Jet in Air”, Trans. ASME, J. Eng. Mater. Technol., 2004, 126, p.123-128 H. Soyama, “High-Speed Observation of a Cavitating Jet in Air”, Trans. ASME, J. Fluids Eng., 2005, 127, p.1095-1101 H. Soyama, “Improvement of Fatigue Strength by Using Cavitating Jets in Air and Water”, Journal of Materials Science, 2007, 42, p.6638-6641

  In the conventional cavitation generating device as shown in FIG. 6, it is necessary to rectify the low-pressure water (low-speed water) jet in order to generate the air cavitation jet, and the nozzle length is about 30 times the nozzle diameter. Met. For this reason, there existed a subject that the site | part with a narrow space for constructions, such as the piping welding part vicinity with a concern about stress corrosion cracking in a plant, cannot be processed. In the example shown in FIG. 6, since the length of the nozzle is about 60 cm, it was not possible to process a part where the space for construction is narrower. Also, if the nozzle is shortened, the concentric low-pressure water (low-speed water) jet flows in an uneven manner, so air is sucked from the portion where the flow is small and becomes mere bubbles instead of cavitation, and the peening effect cannot be obtained. .

  The present invention has been made paying attention to such a problem, and can shorten the length of the cavitation jet along the jet direction, and can perform cavitation peening even in a narrow space for construction. The object is to provide a cavitation generator.

  In order to achieve the above object, a cavitation generator according to the present invention comprises low pressure water injection means having low pressure injection holes capable of injecting supplied low pressure water in a direction substantially perpendicular to the supply direction, and the low pressure water High-pressure water is injected in the same direction as the low-pressure water injection direction from the low-pressure injection hole so as to be surrounded by the low-pressure water injected along the central axis of the injection hole and injected from the low-pressure injection hole. A high-pressure nozzle capable of generating cavitation bubbles, and the low-pressure water jetted from the low-pressure nozzle is configured to flow substantially evenly around the high-pressure water jetted from the high-pressure nozzle. Features.

  The cavitation generator according to the present invention is preferably used as a device for cavitation peening in a plant or the like. In the cavitation generator according to the present invention, the high pressure water injected from the high pressure nozzle arranged along the central axis of the low pressure injection hole of the low pressure water injection means is in the same direction as the injection direction of the low pressure water injected from the low pressure injection hole. In addition to being jetted, the low-pressure water is configured to surround the high-pressure water and flow almost evenly, so that cavitation bubbles due to the high-pressure water can be generated even in the atmosphere.

  At this time, since the low-pressure water supplied to the low-pressure water injection means is injected from the low-pressure injection holes in a direction substantially perpendicular to the supply direction, the length of the device in the direction along the injection direction of the cavitation jet is reduced. Can be shortened. For this reason, even if it is a site | part with a narrow space for constructions, such as the piping welding part vicinity which a stress corrosion crack is a concern in a plant etc., an apparatus can be installed and cavitation peening can be performed. Thereby, the compressive residual stress by cavitation peening can be introduce | transduced into those parts, and the stress corrosion cracking of those parts can be prevented.

  Further, the cavitation generating device according to the present invention sufficiently surrounds the collision surface of the cavitation bubble with low-pressure water and pressurizes the work surface and the surface to be cleaned with the collision pressure of the low-pressure water, thereby increasing the crushing impact force of the cavitation bubble. High processing ability. For this reason, processing time can be shortened. Further, since the treatment can be performed only with water, there is no risk of ignition or ignition even when used during operation of a plant or the like, and the safety is high.

  In the cavitation generating apparatus according to the present invention, it is preferable that the low-pressure water injection means has a water flow adjusting tank into which the supplied low-pressure water flows, and the low-pressure jet hole communicates with the water flow adjusting tank. In this case, since the low-pressure water supplied to the low-pressure water injection means flows into the water flow adjusting tank and temporarily stays there, even if the low-pressure water changes the flow direction and is injected from the low-pressure injection hole, It can be made to flow almost uniformly around the high-pressure water sprayed from the high-pressure nozzle.

  Furthermore, the cavitation generating apparatus according to the present invention has a rectifying wall provided so as to protrude toward the inside of the water flow adjusting tank along the peripheral edge of the opening inside the water flow adjusting tank of the low pressure injection hole. Is preferred. In this case, the effect of retaining the low-pressure water supplied to the low-pressure water jetting means in the water flow adjusting tank can be enhanced by the rectifying wall, and the influence of the low-pressure water supply direction can be reduced. For this reason, the low-pressure water injected from the low-pressure injection holes can flow more evenly around the high-pressure water.

  In the cavitation generating apparatus according to the present invention, the water flow adjusting tank has an internal space of a predetermined height along the injection direction of the low-pressure water from the low-pressure injection hole, and the rectifying wall is the water flow adjusting tank It is preferable to have a height of 1/4 to 3/4 of the predetermined height. In this case, the uniformity of the low-pressure water flowing around the high-pressure water can be particularly increased.

  ADVANTAGE OF THE INVENTION According to this invention, the length along the injection direction of a cavitation jet can be shortened, and the cavitation generator which can perform cavitation peening even in the site | part with a narrow space for construction can be provided.

It is a longitudinal section showing a cavitation generating device of an embodiment of the invention. It is a longitudinal cross-sectional view which shows the modification in case there is no rectification | straightening wall of the cavitation generator of embodiment of this invention. It is a graph which shows the residual stress introduce | transduced by the cavitation generator of embodiment of this invention. It is a graph which shows the depth distribution of the residual stress introduce | transduced by the cavitation generator of embodiment of this invention. It is the longitudinal cross-sectional view which shows the height H of the rectification wall of the cavitation generator of embodiment of this invention, (b) It is a graph which shows the residual stress introduce | transduced when changing the height of a rectification wall. It is a longitudinal cross-sectional view which shows the conventional cavitation generator.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 5 show a cavitation generating apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the cavitation generator 10 includes a low-pressure water injection unit 11, a rectifying wall 12, and a high-pressure nozzle 13.

  As shown in FIG. 1, the low-pressure water injection means 11 has a water flow adjusting tank 21 having a rectangular parallelepiped outer shape and a rectangular parallelepiped space inside. The water flow adjusting tank 21 is formed so that the inner wall surface is parallel to the outer surface of the low-pressure water injection means 11. The low-pressure water injection unit 11 has a supply port 22 communicating with the water flow adjusting tank 21 on one end surface 11a. The low-pressure water injection means 11 has a low-pressure injection hole 23 that passes through one inner wall 21 a of the water flow adjusting tank 21 and opens on one side surface. The low-pressure injection hole 23 has a circular cross section and a central axis that is perpendicular to the outer surface of the low-pressure water injection unit 11. The low pressure injection hole 23 is formed so that the hole diameter gradually increases from the outer surface of the low pressure water injection means 11 toward the inside of the water flow adjusting tank 21.

  The low-pressure water injection means 11 can supply low-pressure water from the supply port 22 to the water flow adjusting tank 21. The low-pressure water injection means 11 is supplied with low-pressure water flowing from the supply port 22 toward the back of the water flow adjusting tank 21. The low-pressure water injection means 11 can inject low-pressure water supplied to the water flow adjusting tank 21 from the low-pressure injection hole 23. The low pressure water injection means 11 is configured to inject from the low pressure injection hole 23 in a direction substantially perpendicular to the supply direction of the low pressure water. The water flow adjusting tank 21 forms an internal space having a predetermined height along the injection direction of the low-pressure water from the low-pressure injection hole 23.

  The low-pressure water injection unit 11 has a high-pressure supply hole 24 on the inner wall 21 b of the water flow adjusting tank 21 on the opposite side to the low-pressure injection hole 23. The high-pressure supply hole 24 extends from the one end surface 11 a of the low-pressure water injection means 11 provided with the supply port 22 toward the back of the water flow adjustment tank 21 through the inner wall 21 b of the water flow adjustment tank 21. It extends to a position intersecting with the central axis, where it is bent vertically toward the low pressure injection hole 23 and penetrates the water flow adjusting tank 21.

  As shown in FIG. 1, the rectifying wall 12 is provided along the periphery of the opening on the inner side of the water flow adjusting tank 21 of the low pressure injection hole 23. The rectifying wall 12 is provided so as to protrude toward the inside of the water flow adjusting tank 21. The rectifying wall 12 has an inner wall surface formed by extending the shape of the low-pressure injection hole 23, and is formed so that the inner diameter gradually increases toward the inside of the water flow adjusting tank 21. Further, the rectifying wall 12 has a height that is ½ of the height of the water flow adjusting tank 21 along the injection direction of the low-pressure water from the low-pressure injection hole 23.

  As shown in FIG. 1, the high-pressure nozzle 13 is elongated and has a high-pressure water introduction hole 25 in the center. The high pressure nozzle 13 is disposed along the central axis of the low pressure injection hole 23 so that the high pressure water introduction hole 25 is coaxial with the low pressure injection hole 23. The high-pressure nozzle 13 has a tip portion 13 a disposed inside the low-pressure injection hole 23, and is provided so as to cut through the inside of the water flow adjusting tank 21 along the injection direction of the low-pressure water from the low-pressure injection hole 23. The high pressure nozzle 13 is provided so that the high pressure water introduction hole 25 communicates with the high pressure supply hole 24 of the low pressure water injection means 11.

  The high-pressure nozzle 13 is formed such that the outer surface of the distal end portion 13a gradually increases in diameter from the distal end surface 13b toward the distal end side. The high pressure nozzle 13 is formed so that the outer surface of the tip end portion 13 a is substantially parallel to the wall surface of the low pressure injection hole 23. The high-pressure nozzle 13 has a high-pressure injection port 26 having an inner diameter smaller than that of the high-pressure conduit 25 at a position slightly retracted from the tip surface 13 b inside the high-pressure conduit 25.

  The high-pressure nozzle 13 can inject the high-pressure water supplied from the high-pressure supply hole 24 from the high-pressure injection port 26. The high-pressure nozzle 13 injects high-pressure water in the same direction as the low-pressure water injection direction from the low-pressure injection hole 23 so that the periphery of the high-pressure water is surrounded by the low-pressure water. Thereby, the high pressure nozzle 13 can generate cavitation bubbles.

  In the specific example shown in FIG. 1, the low-pressure injection hole 23 has an opening diameter of 20 to 30 mm on the outer surface side of the low-pressure water injection unit 11. The high pressure nozzle 13 has an outer diameter of the tip surface 13b of 12 to 16 mm. The height of the water flow adjusting tank 21 along the injection direction of the low-pressure water from the low-pressure injection hole 23 is about 30 mm.

Next, the operation will be described.
The cavitation generator 10 is preferably used as a device for cavitation peening in a plant or the like. In the cavitation generator 10, the high-pressure water injected from the high-pressure nozzle 13 is surrounded by the low-pressure water injected from the low-pressure injection hole 23 and is injected in the same direction as the low-pressure water. At this time, since the low-pressure water supplied to the low-pressure water injection means 11 flows into the water flow adjusting tank 21 and temporarily stays there, even if the low-pressure water changes the flow direction and is injected from the low-pressure injection hole 23, the injected low-pressure water The water can be made to flow almost evenly around the high-pressure water jetted from the high-pressure nozzle 13. Further, since the rectifying wall 12 can enhance the retention effect in the water flow adjustment tank 21 of the low-pressure water and reduce the influence of the low-pressure water supply direction, the low-pressure water injected from the low-pressure injection hole 23 is It can be made to flow more evenly around the high pressure water. As a result, the cavitation generator 10 can effectively generate cavitation bubbles by high-pressure water even in the atmosphere.

  The cavitation generator 10 injects the low-pressure water supplied to the low-pressure water injection means 11 from the low-pressure injection holes 23 in a direction substantially perpendicular to the supply direction, so that the cavitation generator 10 has a direction along the injection direction of the cavitation jet. The length can be shortened. For this reason, even if it is a site | part with a narrow space for constructions, such as the piping welding part vicinity which a stress corrosion crack is a concern in a plant etc., an apparatus can be installed and cavitation peening can be performed. Thereby, the compressive residual stress by cavitation peening can be introduce | transduced into those parts, and the stress corrosion cracking of those parts can be prevented.

  In the specific example shown in FIG. 1, the length of the device in the direction along the injection direction of the cavitation jet can be shortened to about three times the nozzle diameter (about 6 to 9 cm). This is 1/6 to 1/10 in length compared to the conventional one shown in FIG. Thus, even in the vicinity of a welded part of a pipe such as a plant, cavitation peening can be performed if the space for construction is about 6 cm.

  Further, since the cavitation generating device 10 sufficiently surrounds the collision surface of the cavitation bubbles with low-pressure water and pressurizes the work surface and the surface to be cleaned with the collision pressure of the low-pressure water, the crushing force of the cavitation bubbles may be increased. It has high processing capability. For this reason, processing time can be shortened. Further, since the treatment can be performed only with water, there is no risk of ignition or ignition even when used during operation of a plant or the like, and the safety is high.

  As shown in FIG. 2, the cavitation generator 10 does not have to include the rectifying wall 12. Even in this case, since the water flow adjusting tank 21 provides the retention effect of the low-pressure water, the low-pressure water injected from the low-pressure injection hole 23 flows evenly around the high-pressure water injected from the high-pressure nozzle 13 to some extent. It is possible to generate cavitation bubbles due to high-pressure water even in the atmosphere.

[Effect of cavitation peening]
An experiment was conducted to examine the effect of cavitation peening by the cavitation generator 10. In the experiment, the cavitation generator (with the rectifying wall) shown in FIG. 1 and the cavitation generator (without the rectifying wall) shown in FIG. 2 were used. In the experiment, the pressure of the high-pressure water injected from the high-pressure nozzle 13 is 20 MPa, the pressure of the low-pressure water injected from the low-pressure injection hole 23 is 0.08 MPa, and the distance between the test piece for peening and the tip surface 13 b of the high-pressure nozzle 13 ( The standoff distance) was 25 mm.

  Stainless steel (JIS SUS316L) was used as a test piece, and the residual stress on the surface of the test piece when the treatment time per unit length was changed was measured with an X-ray diffractometer. The measurement results are shown in FIG. As a result of the experiment, as shown in FIG. 3, it was confirmed that compressive residual stress can be introduced by cavitation peening of the cavitation generator shown in FIGS. In addition, it was confirmed that the compressive residual stress introduced was larger and the peening effect was higher when the rectifying wall 12 was present than when the rectifying wall 12 was not present. In particular, when the rectifying wall 12 is present, it has been confirmed that a compressive residual stress of 300 MPa or more can be introduced when the processing time per unit length is about 2 s / mm or more.

  Next, the residual stress with respect to the depth from the surface of the test piece was measured when stainless steel (JIS SUS316L) was used as the test piece and the treatment time per unit length was 1 s / mm. The measurement results are shown in FIG. In FIG. 4, the residual stress at each depth was measured by an X-ray diffractometer while electrolytically polishing the test piece. Further, as comparison data, the stress was measured even when cavitation peening was not performed (unprocessed) and is shown in FIG.

  As a result of the experiment, as shown in FIG. 4, when there is no rectifying wall 12, compressive residual stress can be introduced to a depth of about 70 μm from the surface of the test piece. It was confirmed that compressive residual stress can be introduced from the surface of the piece to a depth of 250 μm or more. In addition, it was confirmed that the compressive residual stress can be introduced more deeply in the case where the rectifying wall 12 is present than in the case where the rectifying wall 12 is not present, and the peening effect is high.

  Next, an aluminum plate was used as a test piece, and the amount of erosion when cavitation peening was performed at the same position for 10 minutes was measured. The measurement results are shown in Table 1. As a result of the experiment, as shown in Table 1, it was confirmed that the test piece was eroded and a cavitation peening effect was obtained by the cavitation generator shown in FIGS. In addition, it was confirmed that the amount of erosion was greater and the peening effect was higher when the rectifying wall 12 was present than when the rectifying wall 12 was not present.

[Height of rectifying wall 12]
An experiment was conducted to examine the effect of cavitation peening on the height of the rectifying wall 12 of the cavitation generator 10. In the experiment, the cavitation generator shown in FIG. 1 was used. As shown in FIG. 5 (a), the height of the rectifying wall 12 is represented by H being 1/2 of the height of the water flow adjusting tank 21 along the direction of low pressure water injection from the low pressure injection hole 23. In the experiment, the pressure of the high-pressure water injected from the high-pressure nozzle 13 is 20 MPa, the pressure of the low-pressure water injected from the low-pressure injection hole 23 is 0.08 MPa, and the distance between the test piece for peening and the tip surface 13 b of the high-pressure nozzle 13 ( The standoff distance) was 25 mm.

  Stainless steel (JIS SUS316L) was used as a test piece, and the residual stress on the surface of the test piece when the treatment time per unit length was changed was measured with an X-ray diffractometer. The measurement was performed for three cases where the height of the rectifying wall 12 was 0.5H, 1.0H, and 1.5H. The measurement result is shown in FIG. As a result of the experiment, as shown in FIG. 5B, it was confirmed that compressive residual stress can be introduced by cavitation peening regardless of the height of the rectifying wall 12. Compared to the case where the rectifying wall 12 in FIG. 3 is not provided, it was confirmed that the compressive residual stress introduced is high and the peening effect is high regardless of the height of the rectifying wall 12. In particular, when the height of the rectifying wall 12 is 1.0H, the introduced compressive residual stress is larger and the peening effect is higher than when the height of the rectifying wall 12 is 0.5H and 1.5H. It was confirmed.

DESCRIPTION OF SYMBOLS 10 Cavitation generator 11 Low pressure water injection means 12 Rectification wall 13 High pressure nozzle 21 Water flow adjustment tank 22 Supply port 23 Low pressure injection hole 24 High pressure supply hole 25 High pressure water supply hole 26 High pressure injection port

Claims (4)

Low-pressure water injection means having low-pressure injection holes capable of injecting the supplied low-pressure water in a direction substantially perpendicular to the supply direction;
The high-pressure water is disposed in the same direction as the low-pressure water injection direction from the low-pressure injection hole so as to be surrounded by the low-pressure water injected along the central axis of the low-pressure injection hole and injected from the low-pressure injection hole. A high-pressure nozzle capable of generating cavitation bubbles by jetting,
The low-pressure water jetted from the low-pressure jet holes is configured to flow almost uniformly around the high-pressure water jetted from the high-pressure nozzle.
A characteristic cavitation generator.   2. The cavitation generation according to claim 1, wherein the low-pressure water injection unit includes a water flow adjusting tank into which the supplied low-pressure water flows, and the low-pressure jet hole communicates with the water flow adjusting tank. apparatus.   3. The cavitation according to claim 2, further comprising a rectifying wall provided so as to protrude toward the inside of the water flow adjusting tank along a peripheral edge of an opening on the inside of the water flow adjusting tank of the low pressure injection hole. Generator. The water flow adjustment tank has an internal space of a predetermined height along the injection direction of the low-pressure water from the low-pressure injection hole,
The rectifying wall has a height of ¼ to ¾ of the predetermined height of the water flow adjusting tank,
4. The cavitation generator according to claim 3, wherein

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