JP2007111700A - Method for producing bottle-neck shell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a bottle-neck shell for large-sized pressure vessel, in which the defective thickness is prevented by restraining the shrinkage of a material at a boundary part between the bottle-neck part and a straight cylindrical shell and the yield of a product is improved at a low cost. <P>SOLUTION: In the method for producing the bottle-neck shell, a notch is formed on the outer peripheral surface of a ringed blank and the bottle-neck part is integrally formed at the end part of the cylindrical shell part by forging for widening the diameter while rotating this blank between a core metal and an anvil, wherein this notch is formed so that the ratio of the distance L<SB>1</SB>from the end surface Ea at the bottle-neck part side of the blank to the other surface Eb of the blank from the notch to the thickness T becomes ≥7.0 at the position of ≤0.28 of the whole length L<SB>0</SB>of the blank. The forging for widening the diameter is performed so that a forging widening ratio S satisfies the formula (1) S=(1/b)×(δ<SB>1u</SB>/L<SB>1</SB>)×(L<SB>0</SB>/L<SB>1</SB>)<SP>2</SP>, by bringing the anvil into contact with the outer peripheral surface of the blank from the notch to the end surface Eb. Wherein, b is a material dependent constant, and δ<SB>1u</SB>is the permissible upper limit of the forging for widening diameter ratio. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an aperture shell of a large-sized ring member for a pressure vessel having a cylindrical end portion apertured for joining hemispherical end plates.

  In a large pressure vessel such as a reactor for chemical equipment or a nuclear pressure vessel, a hemispherical end plate is joined to a mouth restricting portion provided at an end portion of a straight cylindrical shell (straight shell) of the main body portion. Conventionally, when the diameter of the hemispherical end plate is greatly different from the outer diameter of the cylindrical shell of the main body, a ring is formed between the hemispherical end plate 7 and the right cylindrical shell 8 as shown in FIG. The intermediate members called Dutchman 9 having different shapes and different outer diameters are joined together. However, in this joining method in which the intermediate member is interposed, the weld line is increased and the manufacturing cost is increased. Therefore, by forming the Dutchman 9 and the straight cylindrical shell 8 integrally, as shown in FIG. There has been a demand for a mouth shell having a mouth portion 8a formed therein.

  For example, in Patent Document 1, as shown in FIGS. 12A and 12B, when forging while rotating a forged member having a cylindrical shape between a mandrel 10 and an anvil 11, A method of forging a large ring for a large ring in which a step portion 13 is provided in the gold 10 and the end portion of the forged material 12 is lowered into the step portion 13 during forging. Is disclosed.

  Moreover, in patent document 2, as shown to Fig.13 (a), the hollow frustoconical long diameter different diameter ring interposed between the right cylindrical part of a large-sized wall pressure vessel and a hemispherical end plate is shown. First, a mandrel 15 fitted with a different diameter sleeve 14 matched to the inner shape of the deformed ring is supported by a mandrel support 16 and a forging material 17 having a thickness difference is suspended from the different diameter sleeve 14. While the forging material 17 is sequentially rotated by the hole expanding anvil 18, the mandrel 15 and the different diameter sleeve 14, the large diameter portion 17 a is subjected to hole expansion forging, and the ring 19 restrains the expansion of the small diameter portion 17 b. Next, as shown in FIG. 13 (b), the anvil 18 is replaced with an anvil 18a provided with an inclined portion 20 and a convex portion 21, and the forging material 17 is anvil. 18a and different diameter sleeve 14 continue forging and forging How to form is disclosed.

Further, in Patent Document 3, as shown in FIGS. 14A and 14B, mouth drawing is performed by causing a die 23 for mouth drawing having a taper on the inner surface to act on the end of the forged ring member 22. At this time, the forging ring member 22 placed on the table 24 on the press bed is subjected to mouth drawing by thinning the forming end region of the forging ring member 22 or performing notch processing in the circumferential direction of the region. A mouth-drawing molding method is disclosed in which a press anvil 26 acts through a plate 25 for uniformly reducing the working die 23.
Japanese Patent Publication No.55-24378 Japanese Examined Patent Publication No.57-46938 Japanese Unexamined Patent Publication No. Sho 63-317231

  However, in the case of forming the squeezed portion by the forging method disclosed in Patent Document 1, a thinning due to the shrinkage occurs at the boundary between the squeezed portion 12a and the cylindrical shell portion 12b. In particular, in the case of providing a mini skirt portion that protrudes short for container support over the outer periphery of the end portion of the cylindrical shell portion 12a, it is necessary to increase the surplus in order to prevent the occurrence of the above-mentioned lack of thickness, Forging process design becomes difficult. Further, in the forging method disclosed in Patent Document 2, since the angle of the anvil 18a and the inclined portion 14a of the different diameter sleeve is particularly important, an anvil and a different diameter sleeve are required in accordance with the conical long different diameter ring of the product. This increases the manufacturing cost. Furthermore, in the mouth-drawing molding method disclosed in Patent Document 3, the mouth-drawing portion is not formed by expanding and forging the cylindrical shell portion (main body portion), but by press working using the mouth-drawing forming die 23. In order to form, like the case of patent document 2, the shaping die for aperture drawing matched with the forge ring of a product is needed, and a manufacturing cost increases by the press load becoming large.

  Accordingly, an object of the present invention is to provide a large pressure that can prevent the occurrence of thinning by suppressing the shrinkage of the material at the boundary portion between the mouthpiece portion and the right cylindrical shell, and improve the product yield at a low cost. It is to provide a method for producing a mouth-opening shell for a container.

  In order to solve the above problems, the present invention employs the following configuration.

That is, the manufacturing method of the mouth-opening shell according to claim 1 includes a step of machining a notch on the outer peripheral surface of the ring-shaped material, and diameter-enlarging forging while rotating the ring-shaped material between the core metal and the anvil. By doing so, a mouth-drawing shell manufacturing method in which a mouth-drawing portion is integrally formed at the end of the cylindrical shell, wherein the thickness of the ring-shaped material is T, the total length is L ₀ , The distance from one end face Ea to the notch where the mouthpiece portion of the material is formed is L ₁ , the distance from this notch to the other end face Eb is L ₂ , and the thickness of the cylindrical shell after diameter expansion forging is t. When the allowable upper limit amount is δ _1u and the reduction ratio is S, the notch position is L ₂ / L on the outer peripheral surface in a range where L ₁ / L ₀ is 0.28 or less from the end face Ea. Formed to satisfy T ≧ 7.0, from the notch to the end face Eb Contacting the anvil the material peripheral surface, rolling reduction S, characterized in that the diameter increases forging so as to satisfy the following first formula.
S ≦ (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (1)
Here, the rolling reduction (thickness reduction rate) S = ((T−t) / T × 100 (%)), b is a constant depending on the material, and the allowable upper limit δ _1u is the target throttle amount δ ₁ + the machining margin Mu on the outer peripheral surface side of the aperture stop portion.

FIGS. 1A and 1B show the cross-sectional shapes in the longitudinal direction of the ring-shaped material 1 and the apertured shell 2 after diameter expansion forging, respectively. As shown in FIG. 1 (a), the distance L ₁ from the end face Ea, the V-shaped notches 3 of the depth h, the inner wall surface of one of which as a perpendicular to the central axis of the ring-shaped material And continuously formed on the outer peripheral surface thereof. The distance L ₁ from the end surface Ea of the V-shaped notch 3 is a distance in the central axis direction from the end surface Ea to the groove bottom of the V-shaped notch 3. In FIG. 1B, δ ₁ indicates a drawing amount, and δ ₂ indicates a taper amount of the outer peripheral surface of the cylindrical shell portion 2a that can be generated depending on forging conditions. That is, the amount of restriction δ1 is ½ of the diameter difference between the outer diameter D _2a at the end A of the aperture stop _2b and the outer diameter D _2b at the end B of the cylindrical shell 2a (= (D _2b −D _2a ) / 2), and the taper amount δ ₂ is 1/2 of the difference in diameter between the outer diameters D _2b and D _2c at both end portions B and C of the cylindrical shell portion 2a (= (D _2c −D _2b ) / 2). When the cylindrical shell portion 2a is not tapered, the throttle amount δ1 is equal to the outer diameter of the cylindrical shell portion 2a (D _2b = D _2c ) and the end portion A (end surface Ea) of the mouth throttle portion 2b. the half of the diameter difference between the D _2a.

A ring-shaped material (FIG. 1 (a)) having the dimensions shown in Table 1 is made of lead whose deformation behavior at room temperature is similar to the deformation behavior in the hot temperature range of steel, and FIG. The results of forming the mouthpiece shell 2 shown in b) are shown in FIGS. FIG. 2 is a plot of the taper δ ₂ / L ₂ of the outer peripheral surface of the cylindrical shell portion 2 a against the rolling reduction S. FIG. 3 is a plot of the inclination (gradient) θ ₂ for each ring-shaped material obtained in FIG. 2 against the shape parameter L ₂ / T of the diameter-enlarged forged portion of the ring-shaped material. From FIG. 3, if the shape parameter L ₂ / T of the ring-shaped material is 7.0 or more, preferably θ ₂ is zero if it is 7.6 or more, that is, δ ₂ / T is zero. It can be seen that no taper occurs on the outer peripheral surface of the cylindrical shell portion 2a. This is because when the ratio of the reduction region (L2) to the wall thickness T is 7.0 or more, the ring-shaped material becomes a deformation state close to a plane strain state in which the longitudinal elongation hardly occurs. This is because the influence of the portion 2b on the cylindrical shell portion 2a is small enough to be ignored.

FIG. 4 is a plot of the taper δ ₁ / L1 of the mouth restricting portion 2b against the rolling reduction S at the position of each notch 3 shown in Table 1. FIG. 5 is a plot of the throttle amount gradient (gradient) θ ₁ (= δ ₁ / (L ₁ × S)) obtained from FIG. 4 against the position parameter L ₁ / L ₀ of the notch 3. From FIG. 5, it can be seen that the aperture amount inclination θ ₁ (= δ ₁ / (L ₁ × S)) and the position parameter L ₁ / L _{0 of the} notch 3 have the relationship of the expression (3).
δ ₁ / (L ₁ × S) = 0.32 × (L ₁ / L ₀ ) ² ------------ (3)
From the equation (3), the reduction ratio S necessary for obtaining the target throttle amount δ ₁ can be obtained by the equation (4).
S = 1 / 0.32 × (L ₀ / L ₁ ) ² × (δ ₁ / L ₁ ) ---------- (4)
Therefore, in order to obtain the aperture value [delta] ₁ of the target is reduction ratio S, it is necessary to satisfy the equation (5).
S = (1 / b) × (δ ₁ / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (5)
Here, b is a material specific value determined by the material, and b = 0.32 when lead is used as the ring-shaped material in the above-mentioned diameter expansion forging experiment.

The squeezed shell is subjected to machining as shown in FIG. 6 after forming a squeezed portion by the above-described diameter-enlarged forging, and becomes a squeezed shell product. Therefore, the allowable upper limit drawing amount δ _1u is δ _1u = δ ₁ + Mu, where Mu is the machining margin of the outer peripheral surface of the mouth restrictor 2b. By substituting this δ _1u into δ ₁ in equation (5), the allowable upper reduction ratio S _U is
S _U = (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------ (6)
Therefore, the rolling reduction S needs to be equal to or lower than the allowable upper rolling reduction S _U (S ≦ S _U ) and needs to satisfy the expression (1).
S ≦ (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (1)
The diaphragm amount [delta] _1L lower limit to be acceptable, when the white machining of the inner peripheral surface of the mouth aperture portion 2b and M _L, the δ _1L = δ ₁ -M _L. By substituting this δ _1L into δ ₁ in equation (5), the allowable lower limit rolling reduction S _L is
S _L = (1 / b) × (δ _1L / L ₁ ) × (L ₀ / L ₁ ) ² ------------ (7)
Therefore, the rolling reduction S needs to be equal to or more than the allowable lower rolling reduction S _L (S ≧ S _L ), and it is necessary to satisfy the equation (8).
S ≧ (1 / b) × (δ _1L / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (8)
In this way, the taper is not generated in the cylindrical shell portion, the mouth aperture forgings shell aperture amount [delta] ₁ is formed of the target is obtained. In addition, the constant b of the formula (1) can be easily determined by conducting a diameter expansion forging experiment whose experimental conditions are shown in Table 1 with respect to the material of the ring-shaped material provided for the mouthpiece shell. . Further, the target drawing amount δ ₁ can be set in consideration of the finished shape of the mouth-drawing shell and the machining margins on the outer peripheral side and the inner peripheral side of the finished product with the enlarged diameter forged.

The manufacturing method of the mouth-opening shell according to claim 2 includes a step of processing a notch on the outer peripheral surface of the ring-shaped material, and forging the diameter-enlarging while rotating the ring-shaped material between the core metal and the anvil. The manufacturing method of the mouthpiece shell in which the mouthpiece portion is formed integrally with the end portion of the cylindrical shell, where the wall thickness of the ring-shaped material is T, the overall length is L ₀ , and the outer diameter is D _2. The distance from one end face Ea to the notch where the mouthpiece portion of the ring-shaped material is formed is L ₁ , the distance from this notch to the other end face Eb is L ₂ , and the thickness of the cylindrical shell after diameter-enlarged forging When the thickness is t, the allowable upper limit amount is δ _1u , and the reduction ratio is S, the position of the notch is on the outer peripheral surface where L ₁ / L ₀ is in the range of 0.33 or less from the end face Ea. is formed so as to satisfy _L 2 /T<7.0, the end face from said notch The material peripheral surface to b contacting the anvil, rolling reduction S, characterized in that the diameter increases forging so as to satisfy any of the following first equation and the second equation.
S ≦ (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (1)
S ≦ a × (L ₀ / L ₁ ) × (D ₂ / L ₁ ) ------------------------- (2)
Here, a and b are constants depending on the material, and the allowable upper limit δ _1u is the target squeeze amount δ ₁ + the machining margin Mu on the outer peripheral surface side of the aperture squeeze portion.

FIG. 7 shows the taper δ ₂ / L ₂ of the cylindrical shell part, the notch position parameter L ₁ / L ₀ representing the aperture area, the parameter L ₁ / D ₂ representing the constraint strength of the mouth area, and It is plotted against the product of the rolling reduction S, (L ₁ / L ₀ ) × (L ₁ / D ₂ ) × S. The mathematical formula in the figure shows a functional expression (regression formula) of δ ₂ / T and (L _{1 /} L ₀ ) × (L _{1 /} D ₂ ) × S. From FIG. 7, when (L ₁ / L ₀ ) × (L ₁ / D ₂ ) × S ≦ 0.1185 or less, δ ₂ / L ₂ is zero, and the outer peripheral surface of the cylindrical shell portion 2 a is tapered. It turns out that it does not occur. Therefore, if the reduction ratio S is selected so as to satisfy the above expressions (1) and (2), the target throttle amount δ ₁ can be obtained without generating a taper on the outer peripheral surface of the cylindrical shell portion 2a. I understand that. It should be noted that the constant a in the above equation (2) can also be easily determined by conducting a diameter-forging experiment whose experimental conditions are shown in Table 1 for the material of the ring-shaped material used for the aperture shell. Can do.

  According to the present invention, a notch is formed on the outer peripheral surface of the ring-shaped material, and the ring-shaped material is subjected to diameter expansion forging while rotating between the core metal and the anvil, so that the end of the cylindrical shell portion is apertured. When manufacturing a mouthpiece shell in which the part is formed integrally, the position range where the notch is processed is clarified, the outer peripheral surface of the cylindrical shell part is not tapered, and the boundary with the mouthpiece part is lacking. The diameter forging conditions for obtaining the target drawing amount without damaging are clarified, so that a forged product can be obtained at a lower cost and with less machining margin than conventional press working. Forging process design that can improve the product yield can be easily performed.

  Embodiments of the present invention will be described below with reference to FIGS. 8 to 10.

FIG. 8 shows a state in which a ring-shaped material 1 having a total length L ₀ and a wall thickness T for a pressure vessel such as Cr—Mo steel is set between a core metal 4 and an anvil 5. The ring-like blank 1, for the improvement of the internal organization, in advance, pre-expanded diameter forging is subjected along its entire length L _0. The ring-shaped material 1 is positioned at a distance L ₁ along the axial direction from one end face Ea where the aperture stop is formed, that is, L ₁ / L ₀ ≦ 0.28 and L ₂ / T ≧ A V-shaped notch 3 is machined along the outer peripheral surface at a position satisfying 7.0. A step 6 is provided at the end of the cored bar 4 on the side of the squeezed portion 2b so as not to restrain the squeezed portion 2b during diameter expansion forging. Moreover, anvil 5, so as not to pressure the mouth aperture portion 2b, and is formed to a width of forging an outer circumferential surface of the distance L ₂ from the notch 3 of the ring-shaped material 1 to the other end face Eb. Then, as shown in FIG. 9, in order to obtain the target drawing amount δ ₁ while rotating the ring-shaped material 1 between the core metal 4 and the anvil 5, the reduction ratio S () satisfying the above equation (1). = (T−t) / T × 100 (%)) until diameter expansion forging is performed.

In this way, if the outer peripheral surface of the ring-shaped material 1 excluding the mouthpiece 2b is pressed against the anvil 5 and subjected to diameter expansion forging, the forging line of the notch 3 is divided as shown in FIG. underfill does not occur due to material shrinkage of the boundary between the mouth aperture portion 2b and the cylindrical shell portion 2a by the action of, and the target throttle amount [delta] ₁ is obtained without taper occurs on the outer peripheral surface. For this reason, a forged finished product of the mouthpiece shell 2 having a small machining cost with a simple process design is obtained, and the product yield is improved.

  FIG. 10 shows the finished shape of the mouth-drawn shell 2 that has been subjected to machining such as cutting on the forged finished product of the mouth-drawn shell 2 shown in FIG. 9 and finished in the shape shown by the broken line in FIG. 2 shows a hemispherical end plate 7 attached to a container, and a container-supporting miniskirt portion 2c is formed at the end of the cylindrical shell portion 2a so as to protrude short over the outer periphery thereof. As shown in FIGS. 8 and 9, the ring-shaped material 1 provided with the notch 3 is subjected to diameter-forging to reduce the machining allowance with a simple process design and with less machining allowance. A forged finished product of the shell 2 is obtained, and the product yield is improved.

The reduction ratio for obtaining the target throttle amount δ ₁ without the occurrence of thinning due to material shrinkage at the boundary between the mouth throttle portion 2b and the cylindrical shell portion 2a and without the occurrence of taper on the outer peripheral surface is as follows: It can also be realized by selecting a rolling reduction S that satisfies both the above formulas (1) and (2). As conditional expression taper does not occur in a cylindrical shell portion 2a, due to the use of (2), the position for machining a notch 3, in consideration of the outer diameter D ₂ of the ring-like material 1, or ring-shaped material 1 can be determined in consideration of the size of 1 and an appropriate notch position can be easily determined even in the case of a larger ring-shaped material.

  The notch 3 is desirably provided at a depth of at least 5% of the wall thickness of the mouth restrictor 2b in order to suppress the shrinkage of the material and prevent the lack of thickness. Further, the shape of the notch 3 is not necessarily limited to the V shape.

(A) It is explanatory drawing which shows the cross-sectional shape of the longitudinal direction of a ring raw material. (B) It is explanatory drawing which shows the cross-sectional shape of the longitudinal direction of the aperture_diaphragm | restriction shell after diameter expansion forging. It is an explanatory diagram plotting the outer circumferential surface of the taper (δ _{2 /} L ₂₎ the reduction ratio of the cylindrical shell portion of the mouth aperture shell. The cylindrical shell portion of the taper of Fig. _{2 (δ 2 / L 2)} , is an explanatory diagram plotting the ring-shaped material shape parameter (L 2 _{/ T).} FIG. 6 is an explanatory diagram in which the taper δ ₁ / L ₁ of the mouth restrictor is plotted against the rolling reduction S for each notch position shown in Table 1. It is an explanatory view showing the relationship between the mouth aperture aperture amount inclination theta ₁ of the shell _{(= δ 1 / (L 1} × S)) and notch position parameter _(L 1 / L _0). It is explanatory drawing which shows typically the target drawing amount of the diameter forging finishing goods, and its tolerance | permissible_range. FIG. 5 is an explanatory diagram in which a taper δ ₂ / L ₂ of a cylindrical shell portion is plotted with respect to a diameter forging parameter F. It is explanatory drawing which shows the state which set the ring-shaped raw material between the metal core 4 and the anvil 5 at the time of diameter expansion forging. It is explanatory drawing which shows the state in which the aperture part was formed by diameter expansion forging. It is explanatory drawing which shows the finishing shape of a mouth-drawing shell. (A) It is explanatory drawing which showed typically the structure which joins a hemispherical end plate and a cylindrical main-body part using an intermediate member. (B) It is explanatory drawing which shows the integrated aperture diaphragm shell which provided the aperture diaphragm part in the edge part of a cylindrical main-body part. (A), (b) It is explanatory drawing which shows the method of manufacturing a caliber shell by the diameter expansion forging of a prior art. (A), (b) It is explanatory drawing which shows the method of manufacturing a squeezed shell by the diameter expansion forging of another prior art. It is explanatory drawing which shows the method of manufacturing a mouth-opening shell by the press molding of a prior art.

Explanation of symbols

1: Ring-shaped material 2: Mouth aperture shell 2a: Cylindrical shell portion 2b: Mouth aperture portion 2c: Mini skirt portion 3: Notch 4: Core metal 5: Anvil 6: Stepped portion 7: End plate 8: Straight cylindrical shell 9 : Dutchman

Claims (2)

There is a step of processing a notch on the outer peripheral surface of the ring-shaped material, and the ring-shaped material is subjected to diameter forging while rotating between the metal core and the anvil, so that the mouth restrictor is formed at the end of the cylindrical shell. A manufacturing method of a mouthpiece shell formed integrally, wherein the thickness of the ring-shaped material is T, the total length is L ₀ , and a notch is formed from one end face Ea on which the mouth-shaped mouthpiece portion of the ring-shaped material is formed. L ₁ , the distance from this notch to the other end face Eb, L ₂ , the wall thickness of the cylindrical shell after diameter-enlarged forging t, the allowable upper limit amount δ _1u , and the reduction ratio S, the position of the notch is formed on the outer peripheral surface where L ₁ / L ₀ is in the range of 0.28 or less from the end face Ea so as to satisfy L ₂ /T≧7.0. The anvil is brought into contact with the outer peripheral surface of the material up to the end surface Eb, and the rolling reduction S is Mouth aperture method for manufacturing a shell, characterized in that the diameter increases forging so as to satisfy the first equation below.
S ≦ (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (1)
Here, the rolling reduction (thickness reduction rate) S = ((T−t) / T × 100 (%)), b is a constant depending on the material, and the allowable upper limit δ _1u is the target throttle amount δ ₁ + the machining margin Mu on the outer peripheral surface side of the aperture stop portion. There is a step of processing a notch on the outer peripheral surface of the ring-shaped material, and the ring-shaped material is subjected to diameter forging while rotating between the metal core and the anvil, so that the mouth restrictor is formed at the end of the cylindrical shell. A manufacturing method of a mouthpiece shell formed integrally, wherein the ring-shaped material has a wall thickness T, an overall length L ₀ , an outer diameter D ₂ , and a ring-shaped material mouth restrictor is formed. The distance from one end face Ea to the notch is L ₁ , the distance from this notch to the other end face Eb is L ₂ , and the thickness of the cylindrical shell after the diameter expansion forging is t. When δ _1u and the _rolling reduction ratio are S, the position of the notch is such that L ₂ /T<7.0 is satisfied on the outer peripheral surface where L ₁ / L ₀ is within 0.33 or less from the end face Ea. The anvil is formed in contact with the outer peripheral surface of the material formed from the notch to the end surface Eb. Mouth aperture method for manufacturing a shell, characterized in that the reduction ratio S is, the diameter increases forging so as to satisfy any of the following first equation and the second equation.
S ≦ (1 / b) × (δ _1u / L ₁ ) × (L ₀ / L ₁ ) ² ------------- (1)
S ≦ a × (L ₀ / L ₁ ) × (D ₂ / L ₁ ) ------------------------- (2)
Here, a and b are constants depending on the material, and the allowable upper limit δ1u is the target squeeze amount δ ₁ + the machining margin Mu on the outer peripheral surface side of the aperture squeeze portion.

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