JP3315153B2 - Cavitation jet nozzle - Google Patents

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 the residual stress of a work such as a steel material. The present invention relates to a technique in which a water jet accompanied with cavitation collides with the surface of the work in water, thereby causing an excessive force in the tension direction. The present invention relates to a structure of a cavitation jet nozzle in which a surface where a stress remains is treated until a compressive stress is applied.

[0002]

2. Description of the Related Art Residual stress in a weld or the like, which causes stress corrosion cracking, is caused by shot blast in which a steel ball is blown by air current, sand blast using sand particles or garnet particles, or cryoblast using ice particles. A peening treatment is performed to improve the residual stress from the tensioning direction (the direction in which the crack is expanded) to the compression direction. Such a peening technique is widely used at the time of processing various mechanical structures or parts as a measure for improving residual stress.

[0003] However, there are many structures that must be peened even in such an environment where the blast operation cannot be performed. For example, a special heat exchanger or reaction tank filled with water, or a welded portion of an offshore structure is all in water, and the work of removing water is almost physically or economically impossible.

[0004] Recovering blast particles from water is a very difficult task. If ice particles are used, collection is unnecessary, but the construction cost is too high and there is not much economic merit.

The use of high-speed water jets is known as a unique processing, mining or cleaning technique. Attempts have been made by Westinghouse to utilize this technique for improving stress (see Japanese Patent Application Laid-Open No. 62-63614). ). Peening with a water jet also has the advantage of preventing the local temperature rise due to the water cooling effect.

[0006] However, this is an operation in the atmosphere in which the axial dynamic pressure of the water jet can be effectively used, and there is no guarantee that this technology can be developed as it is as a submerged water jet. In water, the decay of the jet axial dynamic pressure is quite fast. This is because the diffusion is fast because the liquid phase is the same as the resistance of the surrounding water. In order to obtain shaft power as high as that of a gas-phase water jet in water, an ultra-high pressure generator is required, resulting in a very disadvantageous technology in terms of cost.

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

[0008]

FIG. 9 shows a typical structure of a nozzle used for general water jet processing. The purpose of this nozzle is to narrow the water jet into a beam in the gas phase. Even if the nozzle is used for the water jet as it is, the strength of the cavitation (Intensity)
ity) is not enough.

The reason is that the submerged water jet is not so turbulent that bubble nuclei in the jet water are not excited until they reach active cavitation.

In the drawing, reference numeral 801 denotes a nozzle body;
Reference numeral 802 denotes high-pressure supply water, 803 denotes a central axis, 804 denotes a jet port, 805 denotes a constricted portion (diameter contraction portion), and 806 denotes a high-pressure water supply channel.

FIG. 10 schematically shows the state of cavitation in a high-speed water jet in water. The nozzle used here is intended to sharpen the narrowing of the diameter contraction portion 904 of the nozzle as compared with the example shown in FIG. 9 and to give a stronger depressurizing effect to disturb the jet and promote the cavitation. A cavitation is generated in the ejection holes 903 (905), and a cavitation cloud 906, which is a mass of fine cavitation bubbles, is generated. The cavitation cloud 906 splits downstream, and at the time of the splitting, a bead-shaped vortex cavitation 907 resulting from turbulence (vortex) in the jet is generated. The vortex cavity 907 has a property of generating an extremely large impact pressure on a solid surface and severely eroding and damaging the solid material. In other words, if the generation of the vortex cavity 907 is active, the residual stress on the surface of the steel material can be efficiently improved.

In the drawing, reference numeral 901 denotes a nozzle body;
902 is high-pressure supply water, 908 is the disappearance of the cavitation cloud, 909 is coarse bubbles, and 910 is ambient water.

The jet from the nozzle whose structure is shown in FIG. 9 has a weak turbulence, and the generation of a vortex cavity useful for peening is inactive.

Incidentally, Japanese Patent Laid-Open No. 60-1688 shown in FIG.
The nozzle disclosed in Japanese Patent Publication No. 54 is a nozzle developed for various operations in water, and the use of cavitation is declared.

In the drawings, reference numeral 1001 denotes a nozzle body, 1002 denotes an orifice portion, 1003 denotes a conical opening,
1004 is a conical cavity, 1005 is a piping member, 1006
Denotes a high-pressure jetting device, and 1007 denotes an object to be jet-processed.

JP-A-61-8184 shown in FIG. 12 is an invention for removing contaminants by the action of cavitation generated in a submerged water jet.

In the figure, 1101 is a water tank, 11
02 is a part to be cleaned, 1103 is a nozzle, 1103a is a nozzle tip, 1104 is water, and 1105 is a pipe.

SUMMARY OF THE INVENTION An object of the present invention is to provide a structure of a cavitation jet nozzle which makes turbulence of a jet more active and is suitable for promoting cavitation in view of the above problems. is there.

[0019]

In order to solve the above-mentioned problems, the present invention provides a nozzle having the following structure intended to promote cavitation.

At the tip of the nozzle to which high-pressure water is supplied from the pump, that is, immediately upstream of the ejection hole, a cavity (internal circulation chamber) in which a strong circulation vortex is formed is provided to prevent the water jet from the ejection hole into the water. Gives a strong (not uniform in the radial direction of the jet) strong turbulence. The technique of providing a cavity (internal circulation chamber) for creating such a circulation vortex in a nozzle can be applied to a single-hole nozzle having a single ejection hole or a multi-hole nozzle having a large number of ejection holes. It is.

[0021]

The strong circulation vortex generated in the hollow internal circulation chamber according to the present invention remarkably amplifies the turbulence of the water jet ejected from the ejection hole. Since the high-pressure water is supplied to the hollow internal circulation chamber through the connecting narrow tube as the primary pressure reducing nozzle (primary cavitator), the cavitation in the internal circulation chamber is caused by a sudden change in the flow field accompanied by the pressure reduction. appear. Since the injection pressure is applied to the internal circulation chamber, the cavitation in the chamber is not so severe.

This cavitation also amplifies the turbulence of the water jet jetted from the jet port. Since the circulating flow in the internal circulation chamber is a kind of restricted (spatially constrained) jet, the turbulence becomes uneven in the circumferential direction in the circulation chamber.

The amplification of disturbance as described above significantly promotes cavitation. As a phenomenon, the division of the cavitation cloud (see FIG. 10) becomes active, and the vortex cavitation having a strong impact property appears at a high frequency. In this way, the peening efficiency is greatly improved.

To describe the characteristics of the jet hydrodynamically, the potential core is shortened due to the strong energy dissipation in the orifice, and the entrain begins in the immediate vicinity of the orifice. Such a jet characteristic can be said to be extremely advantageous for promoting the cavitation, since the active entrain creates a strong shear force due to the turbulent vortex.

[0025]

FIG. 3 is a schematic view showing the flow in a cavitation jet nozzle according to the present invention.

As the high-pressure water 302, the injection nozzle body 301
The water supplied to the tubing communicates with the communication capillary (primary cavitator) 30
3 is sharply squeezed upstream and becomes a contraction flow 304, and is led into a communication thin tube (primary cavitator) 303. In the communication thin tube (primary cavity) 303, a cavity is generated due to the reduced pressure and a sudden change in the flow field (a cavity generation point 305). However, since the pressure in the internal circulation chamber 306 on the downstream side is high, this cavitation is not necessarily developed, and is a type of sporadic fine bubbles.

The communicating thin tube (1)
The water flow blown into the internal circulation chamber 306 from the next cavity 303 creates a considerably strong circulation vortex 307 in the internal circulation chamber 306. The circulation vortex 307 is accompanied by strong anisotropic turbulence, and the ejection holes (secondary cavitator) 3
From 09, the turbulence of the cavitation jet 311 blown into the surrounding water 313 is greatly amplified. Due to the violent turbulence created in this way, the potential core in the cavitation jet 311 disappears. On the other hand, the cavitation jet 31
The entrainment flow rate into 1 increases.

Thus, the cavitation jet 3
No. 11 is a state in which the disturbance is significantly developed. The turbulence in the cavitation jet 311 first stimulates the bubble nuclei in the water by the pressure fluctuation to promote the excitation. Therefore, the disturbance activates the cavitation. In addition, the vortex turbulence in the cavitation jet 311 generates a vortex cavitation that generates a strong impact pressure on the solid surface. As a result of the synergistic effect of the above-described operations, the turbulence inside the cavity jet 311 becomes active, and the cavity is remarkably amplified.

In the drawing, reference numeral 308 denotes a contraction, 310
Indicates a location where severe cavitation occurs, and 312 indicates entrainment of ambient water.

As described above, the injection pressure is increased indiscriminately, or the communication capillary (primary cavitator) 303 is increased.
When the squeezing (ratio of the cross-sectional area of the opening) of the nozzle and the ejection hole (secondary cavitator) 309 is increased, the cavitation becomes active, but the pressure loss due to the reduction of the opening cross-sectional area and the bubble lock due to the generation of the cavitation bubble. Therefore, the injection flow rate may be reduced.

As shown in FIG. 4, the structure of the nozzle and the injection conditions may be set in consideration of the characteristics of both the cavitation intensity and the pressure loss.

FIG. 7 shows the impact pressure of a group of cavitation bubbles generated in a cavitation jet for a cavitation jet nozzle (FIGS. 1 and 2) according to the present invention and a nozzle (FIG. 9) according to the prior art. The characteristics of occurrence are compared as a change with respect to the distance (stand-off) Z between the nozzle and the workpiece.

The pressure at which the cavitation jet was generated was determined by placing a pressure-sensitive paper beside the cavitation jet. The generated pressure tends to increase and reach a peak with respect to the standoff under a condition of small Z, and then rapidly decrease.

The use of the nozzle according to the present invention (FIGS. 1 and 2) produces a higher pressure in the tested region than the nozzle according to the prior art (FIG. 9), ie, a peening nozzle. It can be seen that this is suitable.

In order to confirm the performance as a peening nozzle, underwater peening is actually performed under the same conditions (in order to compare only the effects of the nozzle structure, the conditions of injection pressure, standoff or water quality are the same). Carried out in
The effect of improving residual stress was investigated. The result is shown in FIG.

The magnitude of the residual stress was expressed dimensionlessly using the magnitude of the residual stress in the stretching direction -1 (the absolute value of the magnitude was 1) before peening (X) as a reference. In the method using the conventional nozzle (Y), the stress on the compression side is improved up to +0.4, but when the nozzle according to the present invention is used (Z), the residual stress can be significantly improved up to +1.4. I understand.

FIG. 1 is a sectional view showing the structure of a cavitation jet nozzle embodying the present invention.

This cavitation jet nozzle is
The high pressure water supply gun 3, the intermediate plate 2, and the injection nozzle main body 1 are arranged in this order from the upstream part. The fixture 12 is for fixing the nozzle body 1 and the high-pressure water supply gun 3 with the intermediate plate 2 sandwiched therebetween, and is a cap nut type component.

The high-pressure water 4 is supplied through a high-pressure water supply channel 5 opened at the center of the high-pressure water supply gun 3, and is guided to a communicating thin tube (primary cavitator) 8 opened in the intermediate plate 2.

Reference numeral 6 denotes a central axis of the high-pressure water flow path, 7 denotes an enlarged portion of the high-pressure water flow path, 9 denotes an internal circulation chamber, 10 denotes an ejection hole (secondary cavitator), and 11 denotes a central axis of the ejection hole.

As shown in FIG. 2, four communicating thin tubes (primary cavitators) 8 are opened at equal intervals of 90 ° in the circumferential direction of the intermediate plate 2. The communication thin tube (primary cavitator) 8 has a role of rapidly reducing the pressure of the high-pressure water 4 to cause cavitation and a role of causing strong turbulence in the liquid. An injection nozzle body 1 having an internal circulation chamber 9 is connected downstream of the intermediate plate 2. An ejection hole (secondary cavitator) 10 is opened at the center of the ejection nozzle body 1, that is, on the processing target surface side. The internal circulation chamber 9 of the injection nozzle body 1 has a role of creating a strong vortex therein and giving a violent turbulence to the liquid.

Assuming that the diameter of the communicating thin tube, the diameter of the internal circulation chamber, and the diameter of the ejection hole are d ₁ , d _C, and d ₂ , respectively, the preferable conditions for setting the dimensions are: 1.6 <(d _C / d ₁ ) ² <30. (1) 3.0 <(d _C / d ₂ ) ² <48 (1) More desirably, 8.0 <(d _C / d ₁ ) ² <24 (2) 16 <(d _C / d ₂ ) ² <32 (2)

When it is difficult to set the dimensions under the condition of the expression (2) due to the manufacturing cost and the structural limitation of the atomizer,
Even if the dimensions are determined within the range of the expression (1), it is possible to secure performance equal to or higher than the standard. If d ₁ and d ₂ are too small with respect to the inner diameter d _C of the internal circulation chamber 9, the cavitation in the internal circulation chamber 9 becomes active, but the pressure loss may increase due to the so-called bubble lock due to the blockage due to the filling of bubbles. There is. In this way, since two different conditions, that is, the characteristic that is desired to be positive (cavitation) and the characteristic that is desired to be reduced (pressure loss) are to be combined, it is necessary to properly select a range suitable for actual construction.

FIG. 4 shows the respective aperture ratios (d ₂ / d ₁ ).
² schematically illustrates the change characteristics of the cavitation strength I (Intensity) and the pressure loss ΔP with respect to ² and (dc / d ₂ ) ² . As the aperture ratio increases, both the pressure loss ΔP and the cavitation strength I increase. In particular, the pressure loss ΔP has a characteristic of rapidly increasing from a certain opening ratio condition.

Therefore, as shown in the figure, the actual construction conditions may be set in a range where ΔP is not too high, but in a common range where the strength of the cavitation can be as strong as possible. Formula (1) or (2)
The preferred dimensional range of the aperture ratio represented by the equation is determined as described above.

FIGS. 5 and 6 show the structure of a cavitation nozzle according to another embodiment.

FIG. 5 is a cross-sectional view passing through the central axis 406 of the high-pressure water flow path, and FIG. 6 is a view of the outer surface in front of the nozzle from the surface to be processed.

The difference from the previous embodiment (FIGS. 1 and 2) is that a plurality of ejection holes (secondary cavitators) 410 are opened on the surface to be processed of the ejection nozzle body 401.
Therefore, the nozzle according to this embodiment is of a large capacity type (having a large injection flow rate). Vent hole (secondary cavitator) 41
Reference numeral 0 denotes an opening that extends outward at an angle θ with respect to the central axis 406 of the high-pressure water flow path.

Also in this embodiment, the cavitation jet nozzle is constituted by the injection nozzle main body 401, the intermediate plate 402, the high-pressure water supply gun 403, and the fixture 412 for assembling these components.

The conditions for setting the combination of the diameter d _{1 of} the communicating thin tube, the diameter dc of the internal circulation chamber, and the diameter d ₂ of the ejection hole are determined from the equations (1) and (2) in the same manner as in the previous embodiment. Such a large-capacity nozzle is used when it is intended to improve the residual stress on the surface of a large steel material by one peening.

In the drawing, reference numeral 404 denotes high-pressure water;
5 is a high pressure water supply channel, 406 is a high pressure water channel central axis, 40
Reference numeral 7 denotes an enlarged portion of a high-pressure water flow path, 408 denotes a communicating thin tube (primary cavitator) 409, an internal circulation chamber, and 411, a central axis of the ejection hole.

The present invention utilizing the collision pressure due to the high-speed water flow in the water and the collapse pressure of the bubbles due to the cavitation can be applied as a method for improving the residual stress of members constituting various devices. In general, in improving residual stress, it is much more preferable to perform normal temperature treatment without applying heat, that is, without transformation of a metal structure. The present invention is also advantageous from this point, and can be applied to the improvement of the stress of the pressure-resistant member of the boiler. Also, considering that it is underwater work,
It can also be applied to the repair of marine structures and ships.

On the other hand, on the bottom of the ship below sea level,
Shells, algae and other small creatures attach to them and cause considerable flow resistance when traveling. The method according to the invention makes it possible to remove these deposits while traveling in seawater by providing nozzles on the ship. In this way,
Once the deposits could be removed in the seawater, a series of operations saying that a ship was put in a dock, pumped water out of the dock, discarded contaminated water containing the deposits, and then put seawater back in the dock were all necessary. This will be omitted, and ship maintenance will be more economical. In addition, the on-board removal technique is particularly advantageous for special high-speed boats having a long interval to a port call. 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 can be summarized as follows.

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

(2) Since beads for blasting are not used, labor for collecting or discarding them can be omitted.

(3) Since the peening is performed in water, the temperature of the peening portion does not locally increase, and the temperature of the target structure can be kept low and more uniform. (4) Peening in water eliminates noise measures.

(5) Due to the construction in water, there is no need to worry about the disposition of the droplets (splashing droplets).

(6) Since the cavitation is actively generated in the underwater jet, 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 costs (initial costs) and construction operation costs (running costs) can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a view in the direction of aa 'of FIG. 1;

FIG. 3 is a schematic diagram showing a mechanism of generation of a cavitation jet in a cavitation nozzle.

FIG. 4 is a characteristic diagram showing characteristics of cavitation performance and pressure loss.

FIG. 5 is a longitudinal sectional view of a cavitation jet nozzle according to another embodiment of the present invention.

6 is a view in the direction of bb 'in FIG. 5;

FIG. 7 is a characteristic diagram showing the effect of the present invention.

FIG. 8 is a characteristic diagram showing the effect of the present invention.

FIG. 9 is a longitudinal sectional view of a nozzle according to a conventional example.

FIG. 10 is a schematic view showing a splitting mechanism of a cavitation jet.

FIG. 11 is a configuration diagram showing an example of the prior art.

FIG. 12 is a schematic diagram showing another example of the prior art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection nozzle main body 2 Intermediate plate 3 High-pressure water supply gun 4 High-pressure water 5 High-pressure water supply flow path 6 High-pressure water flow path central axis 7 High-pressure water flow path expansion part 8 Communication thin tube (primary cavitator) 9 Internal circulation chamber 10 Spout hole (2) Next cavitator) 11 Central axis of vent hole 12 Fixture

──────────────────────────────────────────────────続 き Continuing on the front page (72) Koichi Kurosawa, Inventor 3-1-1, Sachimachi, Hitachi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Kunio Enomoto 502, Kandatecho, Tsuchiura-shi, Ibaraki Co., Ltd. (56) References JP-A-60-168554 (JP, A) JP-A-63-50699 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B24C 1 / 10 B05B 1/34 B24C 5/04 C21D 7/04

Claims (3)

(57) [Claims] 1. A water jet supplied from a high pressure pump through a high pressure water supply channel in a cavitation jet nozzle in which high pressure water supplied from a high pressure pump is jetted at high speed from a nozzle to collide with a workpiece in the water. Through a communicating narrow tube as a primary cavitator, which is one or more primary depressurizing nozzles having a reduced flow passage cross-sectional area than the high-pressure water supply flow passage, a hollow cylindrical tube having a larger flow sectional area than the communicating thin tube.
Into the internal circulation chamber, and open at the tip of this internal circulation chamber.
A jet nozzle for jetting high-speed water into a surrounding water from an orifice smaller than a cross-sectional area of the cylindrical internal circulation chamber . 2. The method according to claim 1, wherein the cross-sectional area of the flow passage of the internal circulation chamber is 1.6 times or more 30 times the cross-sectional area of the flow passage of the communicating narrow tube.
A cavitation jet nozzle characterized by being set to less than twice. 3. The cavitation jet nozzle according to claim 1, wherein the cross-sectional area of the flow path of the internal circulation chamber is set to be at least 3 times and less than 48 times the cross-sectional area of the ejection hole.