JPH0647665A - Cavitation injection nozzle - Google Patents

Abstract

PURPOSE:To improve the surface stress condition of an under-water structure by setting a cover surrounding a cavitation jet to a nozzle to open toward the surface of a steel material to be a processing object. CONSTITUTION:Inside a cover 7 set to a nozzle, a turbulant circulation whirlpool 206 of a strong anisotropy is generated between the cover inner wall and a cavitation jet 205, and the bubbles and the bubble cores in the cavitation jet 205 are utilized to the peening repeatedly, so as to improve the peening efficiency. And a whirlpool with a strong anisotropy and disturbed turbulantly gives a strong turbulance also to the cavitation jet 205, and excites the bubble cores in the water, so as to expedite the cavitation. In this cavitation expediting, an array of bubbles 207 resulting from whirlpools, which is the type of generating a prominent shock pressure in the jet when the jet hits a substance surface 207, is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for reducing residual stress of a work such as steel, and by causing a water jet accompanied by cavitation to collide with the surface of the work in water, an excessive stress in the tensile direction is generated. The present invention relates to the structure of a cavitation injection nozzle that is intended to process the remaining surface until a compressive stress acts.

[0002]

2. Description of the Related Art The surface stress of an existing structure having a potential corrosion that causes stress corrosion cracking is caused by a shot blast in which a steel ball is blown by the force of an air flow, a sand blast using sand grains,
A peening process such as cryoblast using ice particles is performed to improve the stress from the tensile direction (direction of expanding the crack) to the compression direction.

Such a peening technique is widely used in processing various mechanical structures or parts as a measure against residual stress.

However, there are many structures that must be peened by all means in such an environment where the blast operation is not possible. For example, in a special heat exchanger or reaction tank in a water-filled state, or in a welded portion of an offshore structure, work for removing water is physically or economically impossible. Also, recovering blast particles from water is a very difficult task. If ice particles are used, recovery is not necessary, but economical merits are hard to come out.

The use of high-speed water jet is known as a unique processing, mining, or cleaning technique, and an attempt to utilize it for improving surface stress was made by Westinghouse Electronics Co., Ltd. (Japanese Patent Laid-Open No. 62-6).
3614 publication). Peening with a water jet has the merit of preventing a local temperature rise due to the water cooling effect.

However, this is for the work in the atmosphere in which the axial dynamic pressure of the water jet can be effectively utilized, and there is no guarantee that this technique can be directly deployed as an underwater water jet. In water, the damping of the jet axial dynamic pressure is fairly fast. This is due to the fast diffusion due to the same liquid phase as the resistance of the surrounding water. In order to obtain an axial dynamic pressure similar to that of a gas-phase water jet in water, an ultrahigh pressure generator is required, which is a very disadvantageous technique in terms of cost.

On the other hand, in the underwater water jet, cavitation occurs due to the shearing action of the jet and the surrounding water. If cavitation is promoted and the crushing action of a large amount of bubbles can be effectively utilized, there is a possibility that a peening effect similar to a water jet in a gas phase can be achieved at a low injection pressure.

FIG. 9 shows a typical structure of a nozzle used for general water jet processing. This nozzle is intended to squeeze a water jet into a beam in the gas phase, and even if it is used as it is for an underwater water jet, active cavitation is unlikely to occur. The reason is that the squeezing angle θ of the diameter contracting portion 705 is small (less than 20 °),
This is because the pressure reducing action in this squeezing is too gentle and the bubble nuclei are not easily excited.

Reference numeral 701 in the drawing denotes a nozzle body, and 702.
Is a high pressure supply water, 703 is a central axis, 704 is a high pressure water supply flow path, and 706 is an ejection hole.

A prior art nozzle shown in FIG.
No. 0-168554) is a nozzle developed for various operations in water, and the use of a cavitation is claimed.

In the figure, 1001 is a nozzle body, 10
02 is an orifice part, 1003 is a conical opening part, 1004
Is a conical hollow portion, 1005 is a piping member, 1006 is a high-pressure ejection device, and 1007 is an ejection processing object.

The example shown in FIG. 13 is intended to remove contaminated deposits by the action of the cavitation generated in the underwater jet (Japanese Patent Laid-Open No. 61-8184).

In the figure, 1101 is a water tank, 1102 is a part to be cleaned, 1103 is a nozzle, 1103a is a nozzle tip, 1103b is an ejection hole, 1104 is water, 1105 is a pipe line.

[0014]

As described above, although the technology for effectively utilizing the cavitation is being developed,
The most important for the generation of cavitation is the continuous supply of cavitation nuclei.

FIG. 10 is a schematic representation of a cavitation jet which is jetted from the nozzle 801 at high speed.

Reference numeral 802 in the drawing is high pressure supply water, and 803
Is an ejection hole, 804 is a diameter contraction portion, 805 is a cavity generation portion, 806 is a cavity cloud, 807
Is a vortex thread cavitation, 808 is a disappearance portion of the cavitation cloud, 809 is coarse bubbles, and 810 is ambient water.

Due to the turbulence caused by such intense cavitation, many bubble nuclei in the water jetted from the nozzle 801 or the ambient water 810 are excited.

As shown in FIG. 11, even when the cavity jet 903 collides with the surface 904 to be processed, the bubbles or bubble nuclei in the rebounding jet 905 are lifted by buoyancy.

In the figure, 901 is a nozzle, 902 is high pressure water, 906 is a bubble flow rising by buoyancy, 907 is a large bubble formed by coalescence, and 908 is ambient water.

As described above, the floating of the cavity bubbles or the bubble nuclei in the excited state causes the bubbles that should be effectively used for peening to escape. If the cavitation bubble is reused or the bubble nucleus in the excited state is repeatedly given a trigger, the peening efficiency should be improved.

An object of the present invention is to promote cavitation and improve residual stress on the surface of steel material.

[0022]

In order to achieve the above object, the present invention employs the following method.

A cover is installed on the nozzle between the ejection hole of the nozzle and the surface to be processed so as to gently surround the cavity jet ejected from the nozzle. A gap is provided between the tip of the cover and the surface to be machined so that a part of the rebounding jet generated by colliding with the surface to be machined escapes to the periphery in the radial direction. When the surface to be processed has a curved shape, the tip end surface of the cover has an opening shape corresponding to this. Further, the cover can be applied to a multi-port nozzle having a large number of ejection holes by expanding the shape toward the end.

[0024]

[Operation] Inside the cover installed in the nozzle, turbulent circulation vortices with strong anisotropy are formed between the inner wall of the cover and the cavitation jet, and bubbles and bubble nuclei in the cavitation jet are repeatedly used for peening. , The peening efficiency is improved.

Further, in the inside of the cover, the vortex with strong anisotropy and intense turbulence also gives strong turbulence to the jet jet of the cavity, which excites bubble nuclei in the water and promotes the cavity. The promotion of cavitation is to create a vortex-derived bubble row of a type that generates a striking impact pressure when colliding with a solid surface inside the jet flow.

Due to the synergistic action of the above two effects, a jet flow in which the cavitation is significantly developed is created inside the cover, and as a result, the peening performance is improved.

[0027]

1 shows a structure of a cavitation injection nozzle according to an embodiment of the present invention as a sectional view through a central axis 4.

At the tip of the nozzle body 1 where the ejection hole 6 opens, a cavity jet ejected from the ejection hole 6 (see FIG. 1).
A cover 7 is provided so as to surround 0). There is a gap 9 between the tip of the cover 7 and the surface 8 to be machined so that a part of the rebounding jet generated by the collision jet jet colliding with the surface 8 to be machined is discharged to the outside of the cover 7. .

In the figure, 2 is high-pressure water, 3 is a high-pressure water supply channel, and 5 is a diameter contracting portion (squeezing portion).

The inner diameter D _{C of the} cover 7 is the hole diameter D of the ejection hole 6.
_It is set to be in the range of at least 20 times and less than 80 times _n , more preferably 30 times or more and less than 55 times. The cover 7 is
In order to more forcibly form the circulation vortex created by the collision jet flow colliding with the surface 8 to be processed, a space of at least 30 times the ejection hole diameter D _n or more is required. The diameter of Kiyabiteshiyon jet, since the spread 10 times the hole diameter D _n of ejection holes 6, if Estimate the vortexes around Kiyabiteshiyon jet spread equal to Kiyabiteshiyon jet, the inner diameter D _C of the cover 7 of the jet holes 6 pore diameter It _means that 30 times or more of D _n is necessary. If D _C is unreasonably large, the circulation vortex around the jet of the cavitation becomes weak, which is equivalent to not providing the cover 7.

The distance (gear) L _C between the tip of the cover 7 and the surface 8 to be machined is 0.2 times or more the distance (standoff) L _P between the tip of the nozzle body 1 and the surface 8 to be machined. 6
It is set to less than twice, preferably less than 0.5 times. If L _C is too large, most of the water and bubbles in the cavitation jet will bounce off from the gap between the cover 7 and the surface 8 to be processed and escape as a jet.

On the other hand, if L _C is too small, that is, if the gap between the tip of the cover 7 and the surface 8 to be machined is too small, the flow rate injected from the ejection holes 6, the circulating flow rate in the cover 7, and the cover 7 are The amount of leak from the gap between the surfaces 8 to be machined becomes unbalanced, and the cover 7 is in a closed state in which water and air bubbles are excessively filled, and a proper jet jet cannot be generated.

The shape of the cover 7 attached to the tip of the nozzle is the same as or similar to the shape of the surface 8 to be processed.

FIGS. 4 (a) and 4 (b) show the shape of the cover when peening a flat processed surface.
The cover 30 is provided so as to correspond to the flat processing target surface 303.
The tip of 2 is finished in a flat shape.

Reference numeral 301 in the drawing denotes a nozzle body, 304
Is a jet hole, 305 is a central axis, 306 is a high-pressure water supply channel,
307 is high-pressure water.

FIGS. 5A and 5B show the shape of the cover when the surface of the cylindrical object surface 403 is peened. The cover 402 is fitted to the cylindrical surface shape and size.
The tip of is also made into a substantially cylindrical opening surface.

Reference numeral 401 in the drawing denotes a nozzle body, 404
Is a jet hole, 405 is a central axis, 406 is a high-pressure water supply flow path,
407 is high-pressure water.

As described above, if the shape of the tip opening surface of the cover and the shape of the surface to be peened are matched, the flow rate of the rebounding jet flow escaping from the gap between the cover and the surface to be peened becomes substantially uniform in the circumferential direction of the cover. , The cavitation jet does not tilt extremely inside the cover.

The present invention can be applied not only to a nozzle having a single ejection hole, but also to a porous nozzle.

FIG. 6 shows a cross-sectional structure of the multi-hole nozzle in which the ejection holes 505 face a little outside. Further, FIG. 7 is a structural diagram of the same perforated nozzle as viewed from the downstream side to the upstream side. A jet flow dividing member so that an independent circulation vortex 510 is generated for each cavity jet 507 generated from each ejection hole 505, that is, a circulation vortex 510 generated in each cavity jet 507 does not interfere with an adjacent circulation vortex 510. 508 is provided. In this specific example, since there are four ejection holes 505, the jet flow dividing member 5
The inside of the cover 506 is divided into four by 08.

In this multi-hole nozzle, since the ejection holes 505 face outward, the cover 506 also adopts a shape that widens toward the downstream side.

Reference numeral 501 in the drawing denotes a nozzle body, 502
Is a high-pressure water supply channel, 503 is a high-pressure water supply channel, 504 is a high-pressure water branch channel, 509 is a surface to be processed, and 511 is a rebounding jet discharged from the cover 506.

FIG. 2 is a sectional view showing the phenomenon in the cavity injection nozzle according to the present invention, which passes through the central axis 203. A circulation vortex 206 is formed around the cavitation jet 205, and the bubbles and bubble nuclei in the cavitation jet 205 are circulated and reused, so that the strength of the cavitation is amplified. Coarse air bubbles 209 that collide with the surface 207 to be processed and become larger by being coalesced are discharged from between the tip of the cover 204 and the surface 207 to be processed, and float in the surrounding water 208.

FIG. 3 is a view of the phenomenon in the nozzle cover 204 as seen from the downstream side. The circulation vortex 206 is
Cover 204 (or cavitation jet 205)
Occur at unequal intervals in the circumferential direction of. The circulation vortex 206 is
Although six pieces are drawn in this figure, there may be two or three pieces.
The generation of the circulating vortices at unequal intervals indicates that strong anisotropic turbulence is generated in the cover 204.

Such an anisotropic turbulence violently disturbs the cavity jet 205, triggers the bubble nuclei in the liquid, and promotes the chain chain. In short, the present invention is a combined effect of two functions of (I) the circulation use of the cavity bubble 211 and the bubble nucleus by the circulation vortex generated in the cover 204, and (II) the excitation of the bubble nucleus in the liquid in the jet jet of the anisotropic jet. Therefore, the cavitation is promoted and the peening efficiency is improved.

Reference numeral 201 in the drawing denotes a nozzle body, 202
Is an ejection hole, and 210 is a rebounding jet.

FIG. 8 shows the peening effect by using the nozzle according to the present invention based on the stress improvement result. Before peening, use the dimensionless notation-1.
Although there was 22 residual stress in the tensile direction, the stress was improved in the compression direction up to +1.08 by peening with the cavity injection nozzle according to the present invention.
If the surface stress of the steel material is in a compressed state, cracks are less likely to be generated, and the growth of existing cracks is suppressed.

It can be said that the stress improving effect of using the nozzle according to the present invention is much larger than that obtained by the usual water jet treatment.

The present invention utilizing the collision pressure due to a high-speed water flow in water and the bubble collapse pressure due to cavitation can be applied as a residual stress improving method for members constituting various devices.

Generally, in improving the stress, it is much preferable to perform the normal temperature treatment without applying heat, that is, without the transformation of the metal structure. From this point as well, the present invention is advantageous and can be applied to the residual stress of the pressure resistant member of the boiler.
Further, when considering underwater work, it can be applied to marine structures and ships.

In addition, the present invention can be applied to the excavation work of seabed rocks related to port construction. Compared with the underwater blasting method using dynamite, it can be said that it is a safe and detailed method.

On the other hand, at the bottom of the ship below sea level,
Although shellfish, algae, and other small organisms attach and give rise to considerable flow resistance during travel, the means according to the invention make it possible to remove these deposits in seawater.

Thus, if it is possible to remove the attached organisms in seawater, (I) put the ship in the dock, (II) pump out the water from the dock, and (III) discard the contaminated water containing the attached substances, Furthermore, the series of operations (IV) that seawater is re-entered into the dock will be omitted, and the conservation of ships will be made more economical. It is preferable from the viewpoint of marine environmental protection if the amount of the special paint used for preventing the deposit is reduced.

[0054]

The effects of the present invention are as follows.

(1) The surface stress state of an underwater structure can be efficiently improved.

(2) Since beads for blasting are not used, the trouble of collecting or discarding them can be saved. Therefore, it becomes an economical operation.

(3) Since peening is carried out in water, the temperature of the peening portion does not rise locally and the temperature of the target structure can be kept low and even.

(4) Since peening is performed in water, the noise level can be reduced.

(5) Due to the peening in water, it is not necessary to worry about the end of the droplets (scattering droplets).

(6) Since the cavitation generated in the submerged water jet is effectively used, a predetermined effect can be obtained at a relatively low pressure. An ultra-high pressure water supply system (pump, piping, valve, etc.) is not required, and equipment cost (initial cost) and operation cost (running cost) can be suppressed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a cavitation injection nozzle according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a flow phenomenon in the cavity injection nozzle according to the embodiment of the present invention.

FIG. 3 is a schematic view of a flow phenomenon in the cavity injection nozzle according to the embodiment of the present invention as viewed from the downstream side.

FIG. 4 is a view showing the shape of a cover when peening a flat processed surface.

FIG. 5 is a view showing a shape of a cover when peening a surface of a cylindrical processing target surface.

FIG. 6 is a cross-sectional view of a multi-hole nozzle whose ejection holes face slightly outward.

FIG. 7 is a view of a multi-hole nozzle whose ejection holes face slightly outward, viewed from the downstream side.

FIG. 8 is an explanatory diagram of experimental results showing the effect of the present invention.

FIG. 9 is a vertical cross-sectional view of a nozzle according to a conventional example.

FIG. 10 is a schematic diagram showing a phenomenon of a cavitation jet in a conventional nozzle.

FIG. 11 is a schematic view showing a problem of the conventional injection method.

FIG. 12 is a vertical cross-sectional view of a nozzle according to another conventional example.

FIG. 13 is a vertical cross-sectional view of a nozzle according to still another conventional example.

[Explanation of symbols]

 1 Nozzle body 2 High-pressure water 3 High-pressure water supply channel 4 Central axis 5 Diameter contraction part 6 Jet hole 7 Cover 8 Surface to be processed 9 Gap 205 Cavitation jet 206 Circulating vortex 208 Ambient water 209 Coarse bubbles 210 Bounce jet 211 Cavitation bubble 303 Processing target surface 403 Cylindrical processing target surface 508 Jet dividing member 510 Circulating vortex

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Kurosawa, 3-1-1, Saiwaicho, Hitachi, Ibaraki Prefecture Hitachi Ltd. Hitachi factory (72) Inventor, Kunio Enomoto, 502, Kamimachi, Tsuchiura, Ibaraki Company Hiritsu Seisakusho Mechanical Research Center

Claims (4)

[Claims] 1. A cavitation injection nozzle that improves the surface stress state of a workpiece by injecting water supplied from a high-pressure pump into the water at high speed from the nozzle in water and colliding it with the workpiece in the water. A cavitation injection nozzle characterized in that a cover surrounding a cavitation jet ejected into water and accompanied by cavitation is installed in the nozzle so as to open toward the surface of the steel material to be processed. 2. The cage injection nozzle according to claim 1, wherein the inner diameter of the cover is set to be 20 times or more and less than 80 times the diameter of the ejection hole of the nozzle. 3. The method according to claim 1, wherein a gap is provided between the tip of the cover installed on the nozzle and the surface of the steel material to be processed, and the distance between the nozzle and the surface of the steel material to be processed is A cavity injection nozzle characterized in that it is configured to be 0.2 times or more and less than 0.6 times the interval. 4. The cage injection nozzle according to claim 3, wherein the shape of the opening at the tip of the cover is configured to match or be similar to the shape of the surface to be processed.