JP3355294B2 - Nozzle setting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of setting a nozzle used for water jet peening using a water jet.
In the technology for peening or cleaning the surface of an object using high-speed water jets in water,
Regarding the setting method .

[0002]

2. Description of the Related Art Water jet peening (WJ)
P) is a technique in which high-pressure water is jetted from a nozzle at high speed in water, and a submerged water jet accompanied by vigorous cavitation collides with an underwater structure to improve the residual stress of the structure.

[0003] This WJP is used for stress corrosion cracking (SC) in a pressure vessel (RPV) of a light water reactor type reactor or a structure inside the reactor.
There is strong interest as a technology that can eliminate the factor C). In addition, WJP is effective not only for improving residual stress but also for cleaning in a furnace (removal of oxide scale where radioactive substances are concentrated).

In an ideally large space, as shown in FIG. 14, at a predetermined standoff distance (linear distance between the nozzle 1 and the processing target surface 7) × _S , a so-called “target” welding in WJP construction is performed. The submerged water jet 4 with cavitation impinges on the part 8 at a right angle. In this case, nozzle 1
Is orthogonal to the processing target surface 7. In the figure, 2 indicates high-pressure water, 6 indicates ambient water, and 26 indicates a collision jet.

[0005] However, complicated shaped structures in the reactor,
Moreover, in order to construct a welded portion in a narrow portion, the underwater water jet 4 accompanied by cavitation must obliquely collide with the processing target surface 7 as shown in FIG. In the figure, 5 is a narrow space, and θs is a collision angle.

The underwater water jet 4 with cavitation is:
The impact pressure generated during the rapid collapse of numerous cavitation bubbles upon impact has a strong mechanical effect on the material and improves residual stress. However, in the case of making the collision obliquely, the collision jet 26 flowing along the processing target surface 7 after the collision becomes
Since it is not axially symmetric with respect to the central axis 3, the phenomenon related to peening is complicated.

In FIG. 15, the effect of peening is not maximized at the intersection of the center axis 3 of the submerged water jet 4 with cavitation and the processing surface 7, that is, the collision center 9. This is because (1) flow distribution in the flow direction of the impinging jet,
This is the result of a combination of complex phenomena such as (2) the development of cavitation in the free jet before collision and the collision jet after collision, and (3) the supply of bubble nuclei at the interface of the collision jet.

In the high-speed water jet in the gas phase shown in FIG. 16, the split water drops only obliquely collide with the surface 7 to be processed, and the role of the repelling impinging jet 26 is small, and the phenomenon is simple. In the figure, 5 is a columnar water jet, and 16 is a water droplet.

[0009]

As described above, when a jet is obliquely collided with a WJP construction such as a narrow portion, it is necessary to maximize the effect on a target, that is, a portion where the stress state is desired to be most improved. It is necessary to optimize the direction of the nozzle. Improper peening, such as improper positioning of the nozzle or jetting direction of the jet, results in misalignment, resulting in insufficient stress improvement effects, and time is spent on construction and the injection pressure must be increased unnecessarily. Significantly reduces construction efficiency.

This is a difference from the jet in the gas phase (see FIG. 16), and is a characteristic of the phenomenon in the underwater jet. In other words, if the characteristics of the underwater water jet are skillfully used, the effect of improving the residual stress can be maximized.

An object of the present invention is to overcome the disadvantages of the prior art described above, when colliding a jet stream obliquely to processed surface, it is possible to set the nozzle to the optimum direction nozzles
It is to provide a setting method of the file.

[0012]

This onset bright in order to achieve the above object, according to the Invention The generation of by jetting high pressure water from the nozzle in water
Water jet with cavitation impinges on the surface to be machined
When performing stress improvement processing on the surface to be machined
The center of impact, which is the intersection of the center axis of the jet and the surface to be machined, is stress
It is on the upstream side of the part to be improved, and the water jet is
Set the nozzle so that it collides obliquely with the surface to be machined.
In the method of setting a nozzle to be set, the center of the water jet is
The collision angle θs, which is the angle between the axis and the surface to be machined, is
The larger the distance between the collision center and the part where the stress
The shorter the distance δ and the smaller the collision angle θs,
The distance δ is set to the collision angle θs so that δ becomes longer.
It is characterized by setting according to .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the point of intersection between the central axis of the jet jetting from the nozzle and the surface to be processed, ie, the collision center of the jet, is located upstream of the point where the stress state is to be most improved, ie, the target of the object to be processed. Install the nozzle so that it comes to the side (nozzle side). Thus, the distance of shifting the collision center from target to the upstream side, depending on the inclination angle theta _S is sandwiched angle between the workpiece and the jet, a longer distance to shift as the inclination angle theta _S is small, the inclination angle The attitude of the nozzle is set such that the shift distance becomes shorter as θ _S approaches 90 ° (right angle). The relationship between the inclination angle θ _S and the distance by which the collision center is shifted from the target will be described later.

By doing so, the residual stress improvement amount Δσ (compressive residual stress after the construction—tensile residual stress before the construction) is maximized on the target on the surface to be processed, and the construction efficiency is extremely high. Peening can be performed.

First, an outline of the present invention will be described. Underwater, a high-speed water jet obliquely colliding with the surface to be machined,
The angle becomes obtuse on the downstream side of the jet from the collision center, and vortex cavitation (Vortex ca) occurs downstream of the impingement jet.
visitation). This phenomenon is very important from the viewpoint of peening, but is particularly remarkable when the jet region of the second peak collides with the surface to be processed.

Therefore, in the present invention, the region of the impinging jet where the vortex cavitation develops most coincides with the target portion for processing. Some types of cavitation are also generated in high-speed water jets in water, but strong impact pressure is generated especially during rapid collapse of vortex cavitation bubbles. This vortex cavitation plays a major role in improving the residual stress from the tensile direction to the compressive direction.

In short, the present invention makes the most of the effect of peening by making use of the development process of the vortex cavitation of the impinging jet that flows down on the surface to be worked after the collision when the jet collides obliquely with the surface to be worked. It is to try to make it.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a processing method using a water jet according to a first specific example.

In the surface 7 to be machined in this specific example, it is the weld 8 that most strongly wants to improve the stress, which is the target of machining. The high-pressure water 2 is jetted from the nozzle 1 and becomes a submerged water jet 4 with cavitation and collides with the processing target surface 7.

The collision angle θ _S is determined by the relationship between the center axis 3 and the surface 7 to be machined.
It is an acute angle. The collision center 9, which is the intersection of the central axis 3 of the submerged water jet 4 with cavitation and the processing target surface 7, is shifted upstream by a distance δ from the welded portion 8, that is, in a direction closer to the nozzle 1. Shifting the position by a distance δ is a feature of the present invention.

FIG. 2 is a schematic view of a processing method using a water jet according to a second specific example. This specific example is an example in which the collision angle θ _S is larger than that of the first specific example shown in FIG. If there is room in the processing space, the collision angle θ _S can be made closer to 90 ° in this way.

In this specific example, the distance δ between the welded portion 8 and the collision center 9 which is the target of the peening process is shorter than the distance δ when the collision angle θ _S is small in FIG. Thus, it is also a feature of the present invention to vary the distance δ in the proper technique in accordance with the impact angle theta _S.

FIG. 3 is a schematic view of a processing method using a water jet according to a third specific example. This embodiment is greatly inclined nozzle 1 is an example of a construction to reduce the impact angle theta _S. In the construction of a narrow part, such inclination is not rare. When the collision angle θ _S is small as described above, the distance δ between the collision center 9 and the target welded portion 8 is as shown in FIG.
2 is longer than the distance δ in the specific example of FIG.

[0024] In FIGS. 1 to 3, stand-off distance x _s is the linear distance between the nozzle 1 and the collision center 9 are both assumed to be the second peak corresponds (see Fig. 8).

The distance δ from which the collision center 9 is displaced from the target (welded portion 8) is determined by the following method with respect to the collision angle θ _S.

Δ = αx _S (cos θ _S ) ² (1) In the above equation, the coefficient α is set to 0.033 <α <0.233 (2) , 0.04 <α <0.09 (3)

By setting these conditions, the effect of peening can be maximized. The above (1) to (3)
Is derived from the results of systematic experiments. In still (1), x _S is the standoff distance corresponding second peak.

FIG. 4 is a sectional view showing an example of a nozzle used in peening according to the present invention. The high-pressure water 2 is guided through a high-pressure water supply flow path 10, decompressed and accelerated by a radially contracting portion (restriction portion) 11, and is ejected from an ejection hole 12 to form an underwater water jet accompanied by cavitation. An account counter 13 is provided at the outlet of the outlet 12.
This is to prevent the shape of the jet from being collapsed due to erosion at the outlet of the jet hole 12 to prevent the jet from being biased.

The nozzle shown in FIG. 5 is provided with a conical enlarged cavity 14 at the outlet end of the jet hole 12 in the nozzle 1 shown in FIG. By providing the enlarged cavity portion 14 in this manner, a circulating vortex is generated between the jet immediately after the ejection from the ejection hole 12 and the inner wall of the enlarged cavity portion 14, and the action of the vortex causes a pressure fluctuation, thereby promoting the turbulence of the jet flow. Cavitation grows vigorously.

FIG. 6 shows the collision angle θ _S and the above (1) to (5).
From the relationship of the equation (3), the result of the residual stress improvement amount Δσ in the construction example in which the shift δ is set (distribution 2 of residual stress improvement amount)
5) is shown.

The residual stress improvement amount Δσ was determined by subtracting the tensile residual stress before the application from the compressive residual stress after the application. Central axis 3 of submerged water jet 4 with cavitation
From the collision center 9, which is the intersection of the
Δσ becomes the maximum at a position shifted only by. From this, it is recognized that the method of determining the shift δ of the intersection according to the collision angle θ _S according to the present invention is extremely effective.

FIG. 7 shows an example of a construction in which the collision angle θ _S is made small and the jet is considerably inclined to cause collision.
Is the impinging jet.

In this case, as is clear from the relationship of the equation (1), the collision angle θ _S is smaller than in the example of FIG. Δσ which is the effect of improving residual stress
Was also maximized at a position shifted by δ from the collision center 9.

By embodying the present invention from the above two examples, the effect of maximizing the peening efficiency was proved.

Next, in a region on the obtuse angle side (downstream side) of the jet colliding obliquely, the residual stress improvement amount Δσ becomes larger than that on the acute angle side (upstream side), and at the intersection of the center of the jet and the processing surface. downstream of impinging jet range than collisions central describes why delta sigma to peak.

This is basically because secondary collision cavitation develops in the collision jet downstream from the collision center 9 due to the collision. In particular, on the obtuse side of the impinging jet, there are several possible mechanisms for the development of cavitation, and a combination of these mechanisms should have occurred.

FIG. 9 is a schematic diagram for explaining that the flow distribution of the impinging jet 17 differs between the obtuse angle side and the acute angle side.

The obtuse angle turn flow Q of the impinging jet 20 on the obtuse angle side
₂ is greater than the acute angle turn flow to Q ₁ impinging jet 19 acute side. Obviously, the obtuse-angled impinging jet 20 having a large flow rate has abundant cavitation bubble nuclei, active cavitation, and a large peening effect. 24 indicates a collision center.

FIG. 10 schematically illustrates the concept of linking to a region where vortex cavitation develops due to shear turbulence at the jet interface.

At the interface of the underwater water jet 4 with cavitation, a vortex cavitation development region 18 originating from the interface shear layer is generated. When the inclined jets collide with each other, the processing target surface 7 obliquely cuts the vortex cavitation development region 18 as illustrated. On the obtuse angle side, the region where the vortex cavitation greatly develops flows on the processing target surface 7 as a collision jet, so that the peening effect also increases.

FIG. 11 schematically illustrates a mechanism in which cavitation develops in a shear layer region on the processing target surface 7 triggered by a collision.

In the obtuse turn collision jet 20 downstream of the collision center 9, a shear layer 21 develops on the surface 7 to be processed. Cavitation grows due to the strong shear vortices generated here. The collision is the trigger
Time delay for cavitation to grow sufficiently 22
Is the shift δ of the intersection in FIGS. 1 to 3, 6 and 7.
It is considered to be equivalent to

FIG. 12 schematically illustrates the mechanism by which the obtuse-angled impinging jet 20 that contacts the surrounding water 6 on a wide surface flows more bubble nuclei from the surrounding water through the interface of the jet. Indicates the inflow of bubble nuclei.

In an actual phenomenon, it is considered that a plurality of mechanisms described above are combined. For the reasons described above, by using the region generated downstream of the collision center of the obtuse angled collision jet for processing, the amount of stress improvement at the portion where the effect of improving residual stress is desired to be maximized can be maximized.

Up to this point, an example has been described in which the jet is ejected obliquely downward and collides with the upwardly facing work surface. Conversely, the jet flow may be ejected obliquely upward and obliquely onto the downwardly facing work surface. The method of realization is exactly the same.

FIG. 13 is a view showing a state in which
FIG. 3 schematically illustrates a processing method in a case where an underwater water jet 4 accompanied by cavitation is jetted and collided obliquely upward from a nozzle 1. Collision angle is θ _S , standoff distance x _S
Corresponds to the second peak.

The intersection point of the center axis 3 of the submerged water jet 4 with cavitation and the processing target portion 7, that is, the collision center 9 is shifted by a distance δ to the upstream side of the welded portion 8 where the strongest construction is to be performed (shift of the intersection point). . This distance δ is the collision angle θ
Set according to the method described above according to _S.

However, in the case of such upward injection, buoyancy is generated, so that the inflow 23 of bubble nuclei slightly increases as compared with the case shown in FIG. That is, the bubble nuclei in the surrounding water 6 form the submerged water jet 4 with cavitation.
Cavitation will be further promoted as more is supplied.

[0049]

The effects obtained by implementing the present invention are summarized as follows.

(1) When the nozzle is installed obliquely with respect to the workpiece and the jet is inclined to collide with the jet, the stress improvement effect can be maximized at the target where the stress state is desired to be most improved.

(2) Due to the effect of (1), the peening effect in the construction of the narrow part is improved, and the peening construction can be completed in a short time.

(3) Due to the effect of the above (1), the strength of the structural material in the narrow portion is increased, and the soundness of the structure in terms of strength is improved. For example, fatigue strength is increased and stress corrosion cracking (SCC) can be prevented.

(4) As described in the above (1), peening can be performed only by making the nozzle oblique or by using a nozzle in which the jet flows obliquely. There is no need to use it, and the reliability of the construction increases because a simple nozzle is used.

[Brief description of the drawings]

FIG. 1 is a schematic view of a processing method using a water jet according to a first specific example of the present invention.

FIG. 2 is a schematic view of a processing method using a water jet according to a second specific example of the present invention.

FIG. 3 is a schematic view of a processing method using a water jet according to a third specific example of the present invention.

FIG. 4 is a sectional view showing a first example of a nozzle to be used.

FIG. 5 is a sectional view showing a second example of a nozzle to be used.

FIG. 6 is a first measurement example of the residual stress distribution, and is an explanatory diagram showing a result of improvement of the residual stress by the method of the present invention.

FIG. 7 is a second measurement example of the residual stress distribution, and is an explanatory diagram showing a result of improvement of the residual stress by the method of the present invention.

FIG. 8 is a schematic diagram showing an impact pressure distribution in a jet axis direction.

FIG. 9 is a schematic view showing a first example of a mechanism considered to be a basis of an effect produced by the present invention.

FIG. 10 is a schematic diagram showing a second example of a mechanism considered to be a basis of an effect produced by the present invention.

FIG. 11 is a schematic diagram showing a third example of a mechanism considered to be a basis of an effect produced by the present invention.

FIG. 12 is a schematic view showing a fourth example of a mechanism considered to be a basis of an effect produced by the present invention.

FIG. 13 is a schematic view of a processing method using a water jet according to a fourth specific example of the present invention.

FIG. 14 is a schematic view showing an example of a conventional processing method using a water jet.

FIG. 15 is a schematic diagram illustrating an example of a processing method using a water jet when a nozzle is inclined.

FIG. 16 is a schematic diagram showing an example of jet processing in a gas phase.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle 2 High-pressure water 3 Central axis 4 Underwater water jet with cavitation 6 Ambient water 7 Surface to be processed 8 Welded part 9, 24 Collision center 10 High-pressure water supply channel 11 Diameter contraction part 12 Spout hole 13 Counterbore part 14 Conical Mold expansion cavity 17, 26 Collision jet 19 Acute angle collision collision jet 20 Obtuse angle collision collision jet 23 Inflow of bubble nucleus 25 Distribution of residual stress improvement Xs Standoff distance θs Collision angle δ Shift of intersection

Continuing on the front page (72) Inventor Koichi Kurosawa 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Eisaku Hayashi 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Hitachi, Ltd.Hitachi Plant (72) Inventor Kunio Enomoto 502, Kandate-cho, Tsuchiura-city, Ibaraki Pref.Hitachi Machinery Research Institute, Ltd. (56) References JP-A-7-328858 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B24C 1/10 C21D 7/04

Claims (4)

(57) [Claims] 1. Generated by injecting high pressure water from a nozzle in water
Water jet with cavitation
When performing stress improvement processing on the surface to be machined by
The collision center, which is the intersection of the center axis of the water jet and
Upstream of the area where the force is to be improved,
The nozzle so as to collide obliquely with the surface to be processed
In the method for setting a nozzle, the angle between the central axis of the water jet and the surface to be processed is defined.
As the collision angle θs increases, the collision center and the stress
The distance δ to the part to be improved is short, and the collision angle θs is small.
So that the distance δ becomes longer.
Nozzles characterized by being set according to the collision angle θs
How to set the file . 2. The nozzle setting method according to claim 1, wherein the distance δ between the collision center and the portion where the stress is to be improved.
Δ = αxs (cos θs) ² where θs: collision angle (narrow angle side), xs: stand-off distance, α: coefficient The condition of coefficient α is selected within the range of 0.033 <α <0.233. Nozzle setting method
Law . Te 3. A setting method odor nozzle according to claim 2 wherein <br/>, the condition of the coefficient alpha, 0.04 <alpha setting of the nozzle, characterized in that it selected in the range of <0.09 How . 4. The nozzle according to claim 2 or 3 ,
In setting method, to select the stand-off distance xs, in a region than the first peak following minimum value of the impact pressure distribution is formed downstream of the nozzle corresponding to the area of the second peak is the downstream region Nozzle setting characterized by
How .