Cavitation treatment method

Abstract

The purpose of the present invention is to provide a cavitation treatment method for performing cavitation treatment on a side surface of an object hole of an object. A cavitation treatment method includes: immersing an object (10a) having an object hole (20a) having an axis (23) and a side surface (22) and a nozzle (102) having a spout (102a) in a treatment liquid (104); and spraying a jet (C1) of the processing liquid (104) containing cavitation bubbles in a spraying direction, the spraying direction being inclined with respect to the axis (23) when viewed from a direction orthogonal to the axis (23), and the spraying direction being inclined with respect to a normal line (32) descending from the nozzle (102a) toward the side surface (22) when viewed from the direction of the axis (23).

Description

Technical Field

[0001] The invention relates to a cavitation treatment method for performing cavitation treatment on the surface of an object. Background Art

[0002] In the past, cavitation treatment was performed on metal objects (Japanese Patent No. 6872929). In cavitation treatment, a jet of fluid containing cavitation bubbles (bubbles) is made to collide with the object, and the surface of the object is treated by the impact force when the cavitation bubbles collapse. Through cavitation treatment, compressive residual stress can be applied to the surface of the object.

[0003] Objects to be subjected to cavitation treatment have various shapes and sizes. In order to perform appropriate cavitation treatment, it is necessary to make the jet collide with the surface of the object in an appropriate manner according to the conditions of the object. Summary of the invention

[0004] An object of the present invention is to provide a cavitation treatment method for performing cavitation treatment on the side surface of a target hole of a target object.

[0005] One aspect of the present invention is a cavitation treatment method, comprising:

[0006] immersing an object having an object hole having an axis and a side surface and a nozzle having a nozzle opening in a treatment liquid; and

[0007] A jet of the treatment liquid containing cavitation is ejected along a jet direction, wherein the jet direction is inclined relative to the axis when viewed from a direction orthogonal to the axis, and is inclined relative to a normal line descending from the nozzle toward the side when viewed from the direction of the axis.

[0008] A substantially circular shape refers to shapes that are similar to a circle, such as an ellipse or a regular polygon with an obtuse inner angle, in addition to a circle. In addition, among these shapes, there may be shapes with some deformations such as concave-convex, crooked, etc. The shape of the cross section of the object hole is, for example, a shape obtained by reducing a circle, an ellipse, a regular decagon, a regular icosagon, or a regular polygon with more than ten sides in one of the vertical and horizontal directions. The shape of the cross section of the object hole may also be deformed in the direction of the axis. For example, a portion of the cross section of the object hole may also be reduced in the direction of the axis. Preferably, the cross-sectional shape of the object hole changes continuously in the direction of the axis.

[0009] The axis of the object hole passes, for example, through the center of gravity of the cross section. The object hole can also be produced by additive manufacturing.

[0010] The jet is made to travel along the side, and the area where the jet passes through is cavitated.

[0011] During the cavitation treatment, the object and the nozzle are immersed in the treatment liquid stored in the tank. In the treatment liquid, a jet of the treatment liquid is ejected from the nozzle toward the object. The treatment liquid is, for example, water. The treatment liquid may also be a treatment liquid in which an abrasive is mixed with water. The abrasive may also be turbid in the treatment liquid stored in the tank.

[0012] The object is made of metal. Examples of the metal constituting the object are heat-resistant alloys, aluminum alloys, magnesium alloys, titanium, titanium alloys, and steel. Examples of the object are mechanical parts, medical equipment parts, and medical instruments. Examples of mechanical parts are piping, valves, piping joints, and aerospace parts. Examples of medical instruments are surgical implants. Examples of aerospace parts are aircraft engine parts, other aircraft parts, rocket engine parts, spacecraft parts, satellite parts, and rocket piping. The object can also be manufactured by additive manufacturing.

[0013] The target hole of the object may be a hole having a bottom surface. The target hole may be a hole penetrating the object. The target hole may be a hole extending in a straight line with a straight axis. The target hole may be a hole extending in a curved line with a curved axis.

[0014] The object hole may also extend in the up-down direction. The object hole may also extend in the horizontal direction. The object hole may also extend in a direction inclined relative to the up-down direction or the horizontal direction. In the case where the object hole extends in a curved manner, the direction of the axis of the opening of the object hole may be in any direction. The object hole may also be a hole without branches. The object hole may also be a hole with branches. The inner diameter of the object hole is, for example, greater than 24 mm.

[0015] The nozzle orifice diameter of the nozzle is, for example, 0.5 mm to 3 mm, and the jet pressure of the jet is, for example, 10 MPa to 200 MPa.

[0016] The inclination angle of the jet direction with respect to the axis is, for example, 5 degrees or more and less than 90 degrees, and preferably 15 degrees to 75 degrees.

[0017] The nozzle can be moved along the axis. For example, the nozzle can also be moved from the upstream side of the flow of the jet to the downstream side. The nozzle can also be moved from the downstream side of the flow of the jet to the upstream side. The axis parallel to the axis also includes the axis itself. That is, the nozzle can also rotate around the axis. The nozzle can also rotate around an axis that is different from the axis and parallel to the axis. The nozzle can also be inserted into the object hole from the beginning of the cavitation treatment. The nozzle can also be located outside the object hole at the beginning of the cavitation treatment and then moved and inserted into the object hole.

[0018] The cavitation process may be performed on the entire side surface of the target hole. The cavitation process may be performed on a part of the side surface of the target hole.

[0019] According to the cavitation treatment method of the present invention, it is possible to perform cavitation treatment on the side surface of the target hole of the target object. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a cavitation treatment device according to a first embodiment.

[0021] Figure 2 This is an axial cross-sectional view of the nozzle portion and the object according to the first embodiment.

[0022] Figure 3 yes Figure 2 Cross-sectional view along line III-III.

[0023] Figure 4 It is an explanatory diagram of the region subjected to cavitation treatment in the first embodiment.

[0024] Figure 5 This is an illustration of a band area.

[0025] Fig. 6A This is a diagram showing an example of the cavitation process in the first embodiment.

[0026] Figure 6B It is an explanatory diagram of the rotation of the nozzle in the first embodiment.

[0027] Fig. 7A This is a diagram showing an example of the cavitation process in the first embodiment.

[0028] Figure 7B It is an explanatory diagram of the movement of the nozzle in the first embodiment.

[0029] Fig. 8A This is a diagram showing an example of the cavitation process in the first embodiment.

[0030] Figure 8B It is an explanatory diagram of the movement of the nozzle in the first embodiment.

[0031] Fig. 9 It is an axial cross-sectional view of the object of the second embodiment.

[0032] Explanation of symbols

[0033] 10a, 10b Object

[0034] 20a, 20b Object holes

[0035] 22 Side

[0036] 23 Axis

[0037] 32 Normals

[0038] 102 Nozzle

[0039] 102a Nozzle

[0040] 104 Treatment fluid

[0041] C1 Jet DETAILED DESCRIPTION

[0042] <First Embodiment>

[0043] The cavitation treatment device used in the cavitation treatment method of the first embodiment is described. Figure 1 As shown, the cavitation treatment device 100 includes a tank 101, a nozzle 102, a mounting table 103, a supply pipe 105, and a high-pressure fluid supply source (not shown). The cavitation treatment device 100 performs cavitation treatment on an object 10a.

[0044] The tank 101 stores a treatment liquid 104. The treatment liquid 104 is, for example, water. The tank 101 may include a device for circulating the stored treatment liquid 104.

[0045] The supply pipe 105 is, for example, a straight pipe extending in the up-down direction. The processing liquid 104 supplied from the high-pressure fluid supply source passes through the inside of the supply pipe 105 .

[0046] The nozzle 102 is connected to the lower end of the supply pipe 105. Figure 2 As shown, the nozzle 102 has a nozzle 102a. The nozzle 102 ejects a jet C1 of the treatment liquid 104 from the nozzle 102a. The details of the ejection direction of the jet C1 will be described later. The treatment liquid 104 is supplied to the nozzle 102 from a high-pressure fluid supply source through a supply pipe 105. The jet C1 contains many cavitation bubbles. The nozzle 102 and the supply pipe 105 can move in three axial directions: horizontal direction (front-back direction and left-right direction) and up-down direction. The nozzle 102 rotates integrally with the supply pipe 105. The nozzle 102 rotates around the rotation axis 30. The central axis of the supply pipe 105 can be consistent with the rotation axis 30. The control device (not shown) controls the ejection speed (pressure) of the jet C1, the movement of the nozzle 102 and the supply pipe 105 in the three axial directions, and the rotation. The nozzle diameter (inner diameter) of the nozzle 102 is, for example, 0.5 mm to 3 mm.

[0047] like Figure 2 as well as Figure 3 As shown, in the cavitation treatment method of this embodiment, the object 10a is a straight tube. Figure 2 yes Figure 3 II-II line cross-sectional view of the object 10a. The object 10a has an object hole 20a. The object hole 20a has an axis 23. The axis 23 of the object hole 20a is also the axis of the object 10a. The object hole 20a is circular in cross section and extends in a straight line. That is, the axis 23 of the object hole 20a is a straight line. The axis 23 of the object hole 20a is consistent with the central axis of the object hole 20a.

[0048] The object hole 20a has openings at both ends. The first opening portion 21 of the object hole 20a is located at the top. The second opening portion (not shown) of the object hole 20a is located at the bottom. The object hole 20a has a cylindrical side surface 22. The inner diameter D1 of the object hole 20a is larger than the outer diameter of the nozzle 102. The inner diameter D1 of the object hole 20a is larger than the rotation diameter D2 of the nozzle 102. Therefore, the nozzle 102 can be inserted into the object hole 20a and rotated. The inner diameter of the object hole 20a may not change along the direction of the axis 23. The inner diameter of the object hole 20a may also change along the direction of the axis 23.

[0049] In the cavitation treatment method of this embodiment, the rotation axis 30 of the nozzle 102 is aligned with the axis 23 of the target hole 20a. Here, a straight line parallel to the injection direction of the jet C1 and passing through the center of the nozzle 102a is used as the jet center line 31. Figure 2 As shown, the jet center line 31 is inclined relative to the axis 23 of the object hole 20a (the rotation axis 30 of the nozzle 102). At this time, the acute angle formed by the jet center line 31 and the axis 23 is set to the first inclination angle α. That is, the injection direction of the jet C1 is inclined at the first inclination angle α relative to the axis 23 of the object hole 20a. The first inclination angle α is, for example, greater than 5 degrees and less than 90 degrees, preferably 15 degrees to 75 degrees. In addition, the jet center line 31 does not intersect with the axis 23 and is located in a twisted position. Therefore, the first inclination angle α is defined as the angle between the parallel lines of the jet center line 31 and the axis 23 that intersect at any point.

[0050] like Figure 2 , Figure 3 As shown, the jet centerline 31 intersects the line 23a parallel to the axis 23. Figure 2 In the figure, the parallel line 23a is located further back than the axis 23 in the direction perpendicular to the paper surface. Figure 2 Therefore, in fact, the first inclination angle α is relative to Figure 2 The angle at which the paper surface is tilted on the plane.

[0051] like Figure 3 As shown, when viewed from the direction of the axis 23, the jet center line 31 intersects the normal line 32 relative to the side surface 22 of the target hole 20a from the nozzle 102a. The normal line 32 is a straight line that passes through the center of the nozzle 102a and is orthogonal to the tangent line of the side surface 22. The jet center line 31 is inclined relative to the normal line 32. At this time, the acute angle formed by the jet center line 31 and the normal line 32 is set to the second inclination angle β. That is, the injection direction of the jet C1 is inclined at the second inclination angle β relative to the normal line 32 descending from the nozzle 102a to the side surface 22 of the target hole 20a. The second inclination angle β is, for example, not less than 1 degree and not more than 10 degrees.

[0052] like Figure 1 As shown, the mounting platform 103 mounts and fixes the object 10a. The mounting platform 103 fixes the object 10a with fasteners such as bolts and clamps, or clamps the object 10a to fix it. The mounting platform 103 can move in the up and down direction. Thus, the object 10a can be moved in and out of the groove 101. The control device controls the movement of the mounting platform 103 in the up and down direction.

[0053] The cavitation treatment device 100 can inject the jet C1 to any position of the object 10a from any distance.

[0054] In this embodiment, the cavitation treatment is performed on the entire surface of the side surface 22 of the target hole 20a. Thus, the effect of the cavitation treatment is imparted to the entire surface of the side surface 22 of the target hole 20a.

[0055] The steps of the cavitation treatment method of the present embodiment performed by the cavitation treatment apparatus 100 are as follows.

[0056] First, the treatment liquid 104 is stored in the tank 101 . The amount of the treatment liquid 104 stored is an amount that can immerse the object 10a to a sufficient depth. The sufficient depth is, for example, 300 mm to 500 mm. At this time, the nozzle 102 and the mounting table 103 are located above the liquid surface of the treatment liquid 104 .

[0057] Next, the object 10a is placed and fixed on the mounting table 103. The object 10a is fixed in a posture where the first opening 21 of the target hole 20a faces upward.

[0058] Next, the mounting table 103 is moved downward, and the object 10 a and the mounting table 103 are immersed in the processing liquid 104 stored in the tank 101 .

[0059] Next, the nozzle 102 is moved in the horizontal direction so that the nozzle 102 is located above the opening 21 of the target hole 20a. At this time, the rotation axis 30 of the nozzle 102 is aligned with the axis line 23 of the target hole 20a.

[0060] Next, the nozzle 102 is moved downward and immersed in the treatment liquid 104 stored in the tank 101. Then, the distance between the nozzle 102 and the opening 21 of the target hole 20a is set to a distance suitable for cavitation treatment. The opening 21 is the upper end of the area where the cavitation treatment is performed. The distance suitable for cavitation treatment is, for example, a distance of about 40 to 100 times the nozzle diameter of the nozzle 102. For example, if the nozzle diameter of the nozzle 102 is 1 mm, the distance between the nozzle 102 and the opening 21 is preferably 40 mm to 100 mm.

[0061] Next, the high-pressure fluid supply source is activated, and the jet C1 is ejected from the nozzle 102. The jet C1 enters the interior of the target hole 20a from the opening 21 of the target hole 20a.

[0062] Next, the nozzle 102 is rotated around the rotation axis 30 (the axis line 23 of the target hole 20a) as needed. Also, the nozzle 102 is moved downward and inserted into the target hole 20a as needed.

[0063] like Figure 2 as well as Figure 3 As shown in FIG. 1 , the jet C1 ejected in the above-mentioned direction advances while rotating in a spiral shape inside the target hole 20a. The trajectory 40 of the jet C1 is a spiral shape along the side surface 22 with the axis 23 of the target hole 20a as the center. The trajectory 40 of the jet C1 is a line drawn on the side surface 22 by the center of the jet C1 as the jet C1 advances. Figure 4 As shown, on the side surface 22, a spiral band-shaped region B1 of a predetermined width centered on the trajectory 40 of the jet C1 is cavitated.

[0064] However, the shape of the band-shaped area B1 varies depending on various conditions. The various conditions refer to, for example, the ejection direction of the jet C1 (the first inclination angle α, the second inclination angle β), the diameter of the target hole 20a, the ejection speed (pressure) of the jet C1, etc. Figure 4 as well as Figure 5 As shown, the shape of the band-shaped region B1 refers to, for example, the length L1 along the trajectory 40, the width w centered on the trajectory 40, the pitch p of the spiral described by the trajectory 40, etc. As the jet C1 advances, the cavitation bubbles contained in the jet C1 collapse. Therefore, the length L1 of the band-shaped region B1 is limited.

[0065] In addition, during the cavitation treatment, the intensity of the cavitation treatment varies depending on the distance from the nozzle 102 along the trajectory 40, as the cavitation bubbles grow and collapse in the jet C1. The intensity of the cavitation treatment refers to, for example, the intensity of the compressive residual stress imparted, the density or depth of the pits formed on the surface. Therefore, when performing the cavitation treatment, the strongest treatment is performed at a point where the distance from the nozzle 102 is the most suitable distance, and the intensity of the treatment becomes weaker as the distance from this point increases. For the direction orthogonal to the trajectory 40, the intensity of the treatment also becomes weaker as the distance from the trajectory 40 increases. Here, the area where the required intensity treatment is performed is set as the strip area B1. As shown in FIG. Figure 5 As shown in FIG. 1 , a peripheral region S1 where the processing strength is insufficient is generated around the band-shaped region B1. Figure 5 In the figures other than FIG. 104 , the peripheral region S1 is not shown, and only the band-shaped region B1 is shown. The intensity of the cavitation treatment also varies (is not uniform) inside the band-shaped region B1 , and treatment unevenness occurs according to the distance from the nozzle 102 .

[0066] Depending on the conditions, the entire side surface 22 may be cavitated simply by ejecting the jet C1 from the nozzle 102. For example, this type of treatment applies when the vertical length of the target hole 20a is sufficiently short or the diameter of the target hole 20a is sufficiently short.

[0067] On the other hand, depending on the conditions, only the jet C1 ejected from the nozzle 102 may not cavitate the entire side surface 22. Fig. 6A As shown in FIG. 4 , sometimes the length L1 of the band-shaped area B1a is less than one turn of the spiral, and only a portion of the circumferential direction of the side surface 22 is cavitated. For example, the case where the diameter of the target hole 20a is large and the length L1 of the band-shaped area B1a is shorter than one turn of the trajectory 40 belongs to this type of treatment. In this case, the nozzle 102 is rotated around the axis 23 of the target hole 20a while the jet C1 is ejected. As a result, as shown in FIG. Figure 6B As shown, the new band-shaped area B1b is subjected to cavitation treatment. The new band-shaped area B1b becomes a different area from the band-shaped area B1a before the nozzle 102 is rotated according to the direction of the nozzle 102 (the injection direction of the jet C1). In this way, by rotating the nozzle 102, the entire surface of the side surface 22 (the entire circumference) is subjected to cavitation treatment.

[0068] like Fig. 7A As shown in FIG. 1 , sometimes the strip-shaped area B1a at a certain point is separated from the strip-shaped area B1a at points around the side surface 22 from the point, and only a part of the strip-shaped area B1a is cavitated. For example, the case where the pitch p of the spiral described by the trajectory 40 is longer than the width w of the strip-shaped area B1a belongs to this case. In this case, the nozzle 102 is moved downward while the jet C1 is ejected. That is, the nozzle 102 is moved along the axis 23 of the target hole 20a. As a result, as shown in FIG. Figure 7B As shown, the new band-shaped area B1b is subjected to cavitation treatment. The new band-shaped area B1b is a different area from the band-shaped area B1a before the nozzle 102 is moved, depending on the position of the nozzle 102 in the vertical direction. In this way, by moving the nozzle 102, the cavitation treatment is performed on the entire surface of the side surface 22. In addition, in this case, by rotating the nozzle 102, the cavitation treatment may also be performed on the entire surface of the side surface 22.

[0069] like Fig. 8A As shown, sometimes the length L1 of the strip-shaped area B1a is short, and only a portion of the upper side of the side surface 22 is cavitated. For example, it is applicable to a case where the length of the target hole 20a in the vertical direction is longer than the length L2 in the direction of the axis 23 when the strip-shaped area B1 is wound along the trajectory 40. In this case, the nozzle 102 is moved downward while the jet C1 is ejected. At this time, the nozzle 102 can also be inserted into the target hole 20a. Thus, as Figure 8BAs shown, the new band-shaped area B1b is subjected to cavitation processing. The new band-shaped area B1b is different from the band-shaped area B1a before the nozzle 102 is moved, depending on the vertical position of the nozzle 102. In this way, by moving the nozzle 102, the entire surface of the side surface 22 is subjected to cavitation processing.

[0070] When the above-mentioned various conditions overlap, the nozzle 102 may be rotated and moved at the same time. Furthermore, the nozzle 102 may be rotated or moved without considering the above-mentioned various conditions.

[0071] In this way, the jet C1 is ejected from the nozzle 102, and the nozzle 102 is rotated or moved as needed, so that the side 22 is subjected to cavitation treatment. Here, when the jet C1 is ejected in a direction orthogonal to the axis 23 of the target hole 20a, the jet C1 that collides with the side 22 goes around the side 22 and returns to the point of initial collision. Then, the jet C1 ejected from the nozzle 102 collides with the returning jet C1, hindering the cavitation treatment of the point. In the present embodiment, the jet C1 advances while rotating in a spiral shape. Therefore, the rotating jet C1 and the jet C1 that collides with the side 22 do not collide. Therefore, the cavitation treatment based on the jet C1 is not hindered.

[0072] By rotating the nozzle 102 , the circumferential treatment unevenness inside the band-shaped region B1 can be reduced. By moving the nozzle 102 along the axis 23 , the treatment unevenness inside the band-shaped region B1 in the direction of the axis 23 can be reduced.

[0073] In addition, the order of each process of the cavitation treatment method of this embodiment is not limited to the above order. For example, the treatment liquid 104 may be stored in the tank 101 after the stage 103 or the nozzle 102 is moved. The nozzle 102 may also be moved in the horizontal direction after moving in the downward direction. The nozzle 102 may also be moved in the horizontal direction and in the downward direction at the same time.

[0074] <Second Embodiment>

[0075] A cavitation treatment method according to the second embodiment will be described. In this embodiment as well, substantially the same cavitation treatment apparatus 100 as that of the first embodiment is used.

[0076] like Fig. 9As shown, in the cavitation treatment method of this embodiment, the object 10b is a curved tube. The object 10b has an object hole 20b. The object hole 20b has an axis 23. The object hole 20b is circular in cross section and has a linearly extending portion and a curved extending portion. The object hole 20b has an upstream straight portion 201, a curved portion 202, and a downstream straight portion 203. The upstream straight portion 201 extends in the up-down direction. The curved portion 202 curves in the horizontal direction from the lower end of the upstream straight portion 201. The downstream straight portion 203 extends in the horizontal direction from the front end of the curved portion 202. The axis 23 of the object hole 20b has a straight portion and a curved portion, similar to the object hole 20b itself.

[0077] The target hole 20b has openings at both ends. The target hole 20b has a first opening 21 in the upstream straight portion 201. The first opening 21 opens upward. The target hole 20b has a second opening (not shown) in the downstream straight portion 203. The second opening opens in the horizontal direction.

[0078] The target hole 20b has a cylindrical side surface 22. The inner diameter of the target hole 20b is larger than the outer diameter of the nozzle 102. The inner diameter of the target hole 20b is larger than the rotation diameter of the nozzle 102. Therefore, the nozzle 102 can be inserted into the target hole 20b and rotated. The inner diameter of the target hole 20b may not change along the axis 23. The inner diameter of the target hole 20b may also change along the axis 23.

[0079] In the present embodiment, the cavitation process is performed on the entire side surface 22 of the target hole 20b.

[0080] The process of the cavitation treatment method of this embodiment is substantially the same as the process of the cavitation treatment method of the first embodiment. The jet C1 is ejected from the nozzle 102, and the nozzle 102 is rotated or moved as needed to perform cavitation treatment on the side 22. The trajectory 40 of the jet C1 is a spiral shape centered on the axis 23 of the target hole 20b and along the side 22. In the curved portion 202, the jet C1 advances while rotating spirally along the side 22. In addition, the supply pipe 105 can be bent, and in the curved portion 202, the nozzle 102 can also move along the curved axis 23.

[0081] The present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the main purpose of the present invention, and all technical matters included in the technical ideas recorded in the claims become the objects of the present invention. Although the above-mentioned embodiments show preferred examples, those skilled in the art can implement various alternatives, corrections, variations or improvements according to the contents disclosed in this specification, which are included in the technical scope recorded in the attached claims.

Claims

1. A cavitation treatment method, characterized in that: include: Immersing an object (10a, 10b) having an object hole (20a, 20b) having an axis (23) and a side surface (22) and a nozzle (102) having a nozzle opening (102a) in a treatment liquid (104); and A jet (C1) of the treatment liquid (104) containing cavitation bubbles is ejected along a jet direction, wherein the jet direction is inclined relative to the axis (23) when viewed from a direction orthogonal to the axis (23), and the jet direction is inclined relative to a normal (32) descending from the nozzle (102a) toward the side (22) when viewed from the direction of the axis (23).

2. The cavitation treatment method according to claim 1, characterized in that: The cross section of the object holes (20a, 20b) is substantially circular.

3. The cavitation treatment method according to claim 1 or 2, characterized in that: The nozzle (102) is rotated about an axis parallel to the axis (23).

4. The cavitation treatment method according to any one of claims 1 to 3, characterized in that: The nozzle (102) is moved along the axis (23).

5. The cavitation treatment method according to any one of claims 1 to 4, characterized in that: The nozzle (102) is inserted into the object hole (20a, 20b).

6. The cavitation treatment method according to any one of claims 1 to 5, characterized in that: The inclination angle (α) of the injection direction relative to the axis (23) is greater than 5 degrees and less than 90 degrees.

7. The cavitation treatment method according to any one of claims 1 to 6, characterized in that: When viewed from the direction of the axis (23), the inclination angle (β) of the injection direction relative to the normal line (32) is not less than 1 degree and not more than 10 degrees.

8. The cavitation treatment method according to any one of claims 1 to 7, characterized in that: The jet (C1) is made to move along the side surface (22), and a cavitation treatment is performed on the area of ​​the side surface (22) through which the jet (C1) passes.

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