Method for forming constriction in cylindrical member

Abstract

Provided is a method for forming a constriction in a cylindrical member with which it is possible to form the constriction having a thickness of a designed value without local fluctuation. This method has a constriction formation step for forming the constriction by sequentially pressing, between a mandrel and a mandrel head, a first processing roller and a second processing roller against the outer circumferential surface of the cylindrical member that is rotating, the first and the second processing rollers being capable of rotating the cylindrical member on a rotation axis parallel to the cylinder axis and having mutually-different outer circumferential shapes. The difference between the diameter of the first processing roller and the diameter of the second processing roller is 10 mm or less.

Description

Method for forming a constriction on a cylindrical member

[0001] The present invention relates to a method for forming a constriction on the outer peripheral surface of a cylindrical member.

[0002] For example, as a power storage system, development of a sodium-sulfur battery (hereinafter referred to as a NaS battery), which is a secondary battery using the reaction between sodium and sulfur, is in progress. This NaS battery has, for example, a β-alumina solid electrolyte tube inserted inside a cylindrical positive electrode container made of aluminum or the like, sulfur filled in the space between the positive electrode container and the β-alumina solid electrolyte tube, and sodium filled inside the β-alumina solid electrolyte tube.

[0003] And, for example, in a high-temperature environment of 300 °C or higher, the ionic conductivity of the β-alumina solid electrolyte is increased, and sodium and sulfur are reversibly reacted through the solid electrolyte, so that charging and discharging are repeatedly performed.

[0004] When such a NaS battery repeatedly charges and discharges, for example, as the temperature changes between 100 °C and 300 °C, the internal pressure of the positive electrode container also fluctuates greatly. As a damper for absorbing such fluctuations in the internal pressure of the positive electrode container, a constriction (recess) extending in the circumferential direction is formed on the outer peripheral surface of the cylindrical positive electrode container. By forming such a constriction, it is possible to prevent the positive electrode container from being damaged when it expands, for example, in the longitudinal direction.

[0005] Conventionally, when forming a constriction on the outer peripheral surface of a cylindrical member such as the positive electrode container of a NaS battery, a cylindrical mandrel is inserted inside the cylindrical member, and then a processing roller that rotates together with the cylindrical member is pressed against the outer peripheral surface of the rotating cylindrical member and pushed in the radial direction to form a constriction, which is a long groove recessed so as to extend in the circumferential direction of the cylindrical member (see, for example, Patent Documents 1 and 2).

[0006] Japanese Patent Application Laid-Open No. 8-132145, Japanese Patent No. 3429658

[0007] However, with conventional methods for forming constrictions in cylindrical members, there was a concern that the thickness of the constricted area would not match the design value depending on the difference in diameter between the two processing rollers, resulting in localized thickness fluctuations. When the thickness of the constricted area fluctuates locally, there is a risk of cracks or deformation occurring when stress is applied to the constricted area.

[0008] This invention was proposed in view of the above-mentioned problems, and aims to provide a method for forming a constriction in a cylindrical member that can form a constriction with a thickness as specified in the design value and without localized thickness fluctuations.

[0009] To solve the above problems, the following means are proposed for forming a constriction in a cylindrical member according to one embodiment of the present invention. (1) A method for forming a constriction in a cylindrical member according to embodiment 1 of the present invention is a method for forming a constriction in a cylindrical member that is hollow cylindrical in shape and is recessed inward along the circumferential direction, comprising: a clamping step of clamping the cylindrical member between a first clamp equipped with a cylindrical mandrel inserted into the hollow interior from one open end of the cylindrical member and a second clamp equipped with a cylindrical mandrel head inserted into the hollow interior from the other open end of the cylindrical member; a rotation step of rotating the cylindrical member together with the first clamp and the second clamp around a cylindrical axis; and a constriction forming step of sequentially pressing a first processing roller and a second processing roller, which have different outer peripheral shapes and are rotatable around a rotation axis parallel to the cylindrical axis of the cylindrical member, against the outer peripheral surface of the rotating cylindrical member between the mandrel and the mandrel head to form the constriction, wherein the difference between the diameter of the first processing roller and the diameter of the second processing roller is 10 mm or less.

[0010] (2) Embodiment 2 of the present invention is the method for forming a constriction in a cylindrical member according to Embodiment 1, wherein the outer diameter of the cylindrical member is in the range of 75 mm or more and 95 mm or less.

[0011] (3) Embodiment 3 of the present invention is the method for forming a constriction in a cylindrical member according to Embodiment 2, wherein the diameter of the first processing roller is 110 mm ± 100 mm and the diameter of the second processing roller is 110 mm ± 100 mm.

[0012] (4) Embodiment 4 of the present invention is the method for forming a constriction in a cylindrical member according to Embodiment 2, wherein in the constriction forming step, the rotational speed of the cylindrical member is 230 rpm or more and 250 rpm or less.

[0013] (5) Embodiment 5 of the present invention is a method for forming a constriction in a cylindrical member according to any one of embodiments 1 to 4, wherein the insertion length of the mandrel into the cylindrical member is longer than that of the mandrel head.

[0014] (6) Embodiment 6 of the present invention is a method for forming a constriction in a cylindrical member according to any one of embodiments 1 to 5, wherein the cylindrical member is made of a metal including aluminum.

[0015] (7) Embodiment 7 of the present invention is a method for forming a constriction in a cylindrical member according to any one of embodiments 1 to 6, wherein a fitting member that can be fitted onto the mandrel head is formed on the surface of the mandrel facing the mandrel head.

[0016] (8) Embodiment 8 of the present invention is a method for forming a constriction in a cylindrical member according to any one of embodiments 1 to 7, wherein the cylindrical member in which the constriction is formed is a battery case for a sodium-sulfur battery.

[0017] According to the present invention, it is possible to provide a method for forming a constriction in a cylindrical member that is capable of forming a constriction with a thickness as specified in the design value and without localized thickness fluctuations.

[0018] This is a cross-sectional view showing an example of a NaS battery in a charged state. This is a perspective view showing an example of a constriction forming apparatus used in the method for forming a constriction in a cylindrical member according to this embodiment. This is a schematic configuration diagram of the constriction forming apparatus (cylindrical member processing apparatus) when viewed from the side. This is a plan view illustrating the sizes of the first processing roller and the second processing roller. This is a flowchart showing the method for forming a constriction in a cylindrical member according to one embodiment of the present invention in steps. This is an explanatory diagram showing a jig for inserting a mandrel. This is a cross-sectional view showing (a) a constriction (intermediate formed body) formed by the first processing roller and (b) a constriction formed by the second processing roller.

[0019] The following describes a method for forming a constriction in a cylindrical member according to one embodiment of the present invention, with reference to the drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may be enlarged for convenience to make the features of the present invention easier to understand, and the dimensional ratios of each component may not be the same as in reality.

[0020] [Sodium-Sulfur Battery (NAS Battery)] First, we will describe a sodium-sulfur battery (NAS battery), which is an example of the application of a constricted cylindrical member formed by the method for forming a constriction in a cylindrical member according to one embodiment.

[0021] Figure 1 is a cross-sectional view showing an example of a NaS battery in a charged state. The NaS battery 50 comprises a positive electrode container 53 made of a constricted cylindrical member, a solid electrolyte tube 55 housed inside the positive electrode container 53, and an outer container (battery container) 51 that houses the positive electrode container 53 and the solid electrolyte tube 55.

[0022] An annular insulating member 57 is positioned on the upper part of the positive electrode container 53, and this annular insulating member 57 is fitted between the inner circumferential surface of the positive electrode container 53 and the outer circumferential surface of the solid electrolyte tube (sodium housing) 55. An electrode cap 59 is positioned on top of this annular insulating member 57. In other words, in this embodiment, the electrode cap 59 is positioned at the opening of the positive electrode container 53, thereby creating an airtight seal inside the positive electrode container 53.

[0023] When the NaS battery 50 is charged, the solid electrolyte tube 55 is filled with pure sodium (metallic sodium) 65. A sulfur electrode 67, made of graphite felt impregnated with sulfur, is placed in the space between the positive electrode container 53 and the solid electrolyte tube 55. A positive electrode terminal 61 is connected to the upper end of the positive electrode container 53, and a negative electrode terminal 62 is placed on the electrode cap 59.

[0024] The positive electrode container 53 can be any cylindrical member with a constriction, manufactured by the method for forming a constriction in a cylindrical member of this embodiment, described later, with one open end closed. A constriction 53a is formed near the open end, with a recess that curves inward (towards the center) encircling the outer surface.

[0025] The positive electrode container 53 may be entirely made of, for example, an aluminum alloy. The outer casing (battery container) 51 covering the outer surface of the positive electrode container 53 is made of, for example, nickel-containing stainless steel. The solid electrolyte tube (sodium housing) 55 is made of β-alumina. Furthermore, the annular insulating member 57 is made of α-alumina, and the electrode cap 59 is made of aluminum or the like. In addition, the positive electrode terminal 61 and the negative electrode terminal 62 are made of aluminum or the like.

[0026] In this configuration, the NaS battery 50 is designed so that charging and discharging occur when sodium (Na) filled inside the solid electrolyte tube 55 and sulfur (S) placed outside the solid electrolyte tube 55 react through the solid electrolyte tube 55 made of β-alumina.

[0027] That is, 2Na + XS → Na ２ S Ｘ (Discharge), Na ２ S Ｘ →The reversible reaction of 2Na + XS (charge) allows for repeated charging and discharging. Here, sodium polysulfide (Na) is produced by the reaction. ２ S Ｘ The sodium 65 will be present inside the sulfur electrode 67 as described above. Therefore, in the discharge state, there is no sodium 65 inside the solid electrolyte tube 55, resulting in a hollow state, while in the charge state, the inside of the solid electrolyte tube 55 is filled with sodium 65.

[0028] The positive electrode container 53 of such a NaS battery 50 is subjected to stress that causes it to expand and contract along its longitudinal direction (vertical direction in Figure 1) due to the charging and discharging process described above and changes in the external temperature environment. Therefore, the constriction 53a acts as a damper that allows for this expansion and contraction of the positive electrode container 53 due to temperature changes, thereby preventing damage to the positive electrode container 53.

[0029] The following describes one embodiment of a method for forming a constriction in a cylindrical member that can be suitably used as a positive electrode container for a NaS battery as described above. Figure 2 is a perspective view showing an example of a constriction forming apparatus (cylindrical member processing apparatus) used in the method for forming a constriction in a cylindrical member of this embodiment. Figure 3 is a schematic configuration diagram of the constriction forming apparatus (cylindrical member processing apparatus) viewed from the side.

[0030] The constriction forming device (cylindrical member processing device) 10 comprises a first clamp 11, a second clamp 12, and a processing roller device 19.

[0031] The first clamp 11 includes a work stopper 13 that contacts one end We1 of the cylindrical member W during processing and biases the cylindrical member W toward the second clamp 12, a rotatable cylindrical mandrel 14 extending from one end We1 of the cylindrical member W, and a mandrel stopper 15 that adjusts the position of the mandrel 14 along a direction perpendicular to the cylindrical axis of the mandrel 14.

[0032] The second clamp 12 includes a mandrel head (core metal) 16, a workpiece stopper 17 that contacts the other end We2 of the cylindrical member W during processing and biases the cylindrical member W toward the first clamp 11, and a rotating device (motor) 18 that rotates the workpiece stopper 17.

[0033] During the necking process, the cylindrical member W is held between the first clamp 11 and the second clamp 12. Then, by rotating the work stopper 17 with the rotating device (motor) 18, the cylindrical member W, whose other end We2 is in contact with the work stopper 17, rotates around its cylindrical axis.

[0034] Furthermore, a fitting projection (fitting member) 21 is formed at the center of the circular end face of the mandrel 14 facing the mandrel head 16. Also, a recess 22 capable of receiving the fitting projection 21 is formed at the center of the circular end face of the mandrel head 16 facing the mandrel 14.

[0035] During the necking process, the ends of the mandrel 14 and the mandrel head 16 come into close proximity, and the fitting of the fitting projection 21 and the recess 22 prevents misalignment of the central axes of the mandrel 14 and the mandrel head (core metal) 16.

[0036] Furthermore, in this embodiment, the mandrel 14 is formed to be longer in the direction of the cylindrical axis than the mandrel head 16. The ratio of the lengths of the mandrel 14 and the mandrel head 16 in the direction of the cylindrical axis is adjusted according to the position where a constriction is formed in the cylindrical member W. That is, the position where the mandrel 14 and the mandrel head 16 face each other is the position where a constriction is formed in the cylindrical member W.

[0037] The processing roller device 19 consists of a first processing roller 24 and a second processing roller 25, which have different outer circumference shapes, and a sliding base 26 that supports the first processing roller 24 and the second processing roller 25. The first processing roller 24 and the second processing roller 25 are driven rollers that move by contacting the outer circumference Wf of a rotating cylindrical member W. The first processing roller 24 and the second processing roller 25 may also be configured to be rotated by a rotating means such as a motor.

[0038] The first processing roller 24, for example, forms a constriction (intermediate forming body) on the cylindrical member W such that the cross section perpendicular to the circumferential direction is, for example, trapezoidal (see Figure 7(a)). The second processing roller 25 further constricts the trapezoidal constriction (intermediate forming body) formed by the first processing roller 24, so that the cross section perpendicular to the circumferential direction is, for example, trapezoidal with a curved bottom (see Figure 7(b)).

[0039] Thus, in the constriction forming device 10 of the present embodiment, by sequentially pressing the first processing roller 24 and the second processing roller 25 having different outer peripheral shapes against the outer peripheral surface Wf of the rotating cylindrical member W, a constriction having a target cross-sectional shape is formed on the cylindrical member W.

[0040] The sliding pedestal 26 of the constriction forming device 10 slides in a direction orthogonal to the cylindrical axis of the cylindrical member W. Thereby, the first processing roller 24 and the second processing roller 25 are moved between a neutral position where neither the first processing roller 24 nor the second processing roller 25 contacts the outer peripheral surface Wf of the cylindrical member W, a first processing position where only the first processing roller 24 contacts the outer peripheral surface Wf of the cylindrical member W, and a second processing position where only the second processing roller 25 contacts the outer peripheral surface Wf of the cylindrical member W.

[0041] FIG. 4 is a plan view for explaining the sizes of the first processing roller and the second processing roller. The diameter (outermost diameter) φ1 of the first processing roller 24 and the diameter (outermost diameter) φ2 of the second processing roller 25 are formed such that the difference in their diameters is 10 mm or less between the first processing roller 24 and the second processing roller 25.

[0042] For example, when the diameter of the first processing roller 24 is 150 mm, the second processing roller 25 may be formed such that the diameter is in the range of 140 mm to 160 mm.

[0043] Furthermore, for example, when the outer diameter of the cylindrical member is 75 mm or more and 95 mm or less, while satisfying the condition that the difference in diameter between the diameter φ1 of the first processing roller 24 and the diameter φ2 of the second processing roller 25 described above is 10 mm or less, the diameter φ1 of the first processing roller is preferably 110 mm ± 100 mm, and the diameter φ2 of the second processing roller is preferably 110 mm ± 100 mm.

[0044] Thus, by appropriately maintaining the diameters of the first processing roller 24 and the second processing roller 25, it becomes possible to form the constriction according to a predetermined design dimension in the constriction forming step of the constriction forming method for the cylindrical member described later.

[0045] In the constriction forming device 10 of this embodiment, by controlling the holding time at the processing positions of the first processing roller 24 and the second processing roller 25 and the circumferential length in contact with the cylindrical member W, a constriction with the desired dimensions can be accurately formed on the outer peripheral surface of the cylindrical member W.

[0046] FIG. 5 is a flowchart showing step by step the method for forming a constriction on a cylindrical member according to an embodiment of the present invention. In the method for forming a constriction on a cylindrical member of this embodiment, the constriction forming device (cylindrical member processing device) 10 having the above-described configuration is used.

[0047] First, the mandrel 14 and the mandrel head 16 having a diameter smaller than the inner diameter of the cylindrical member W, which is the workpiece, by 10% or less in diameter are set in the constriction forming device 10.

[0048] The cylindrical member W may have, for example, an outer diameter in the range of 75 mm or more and 95 mm or less, a thickness in the range of 1.0 mm or more and 2.0 mm or less, and a length in the range of 400 mm or more and 600 mm or less. In this embodiment, a cylindrical member W made of an aluminum alloy having an outer diameter of 85 mm, a thickness of 1.3 mm, and a length of 500 mm is used.

[0049] Next, the mandrel 14 is inserted into the hollow interior from the open end on the one end We1 side of the cylindrical member W. When inserting the cylindrical member W onto the mandrel 14, it is preferable to attach an insertion jig 29 to the tip of the mandrel 14, for example, as shown in FIG. 6. By using such an insertion jig 29, the mandrel 14 can be smoothly guided into the hollow portion of the cylindrical member W, and damage to the mandrel 14 can be prevented.

[0050] Next, the mandrel head 16 is inserted into the hollow interior from the open end on the other end We2 side of the cylindrical member W. As a result, the fitting protrusion 21 of the mandrel 14 fits into the recess 22 of the mandrel head 16 inside the cylindrical member W. The opposing portions of the mandrel 14 and the mandrel head 16 become the positions for forming constrictions on the cylindrical member W.

[0051] Then, by biasing the mandrel stopper 15 and the workpiece stopper 17, respectively, at one end We1 and the other end We2 of the cylindrical member W, the cylindrical member W is clamped between the first clamp 11 and the second clamp 12 (clamping step S1).

[0052] Next, the rotating device (motor) 18 is operated to rotate the cylindrical member W around its cylindrical axis via the work stopper 17 (rotation process S2). In this rotation process S2, by maintaining an appropriate clearance between the inner surface of the cylindrical member W and the outer surface of the mandrel 14 and the outer surface of the mandrel head 16, it is possible to prevent the cylindrical member W from rotating eccentrically with respect to the mandrel 14.

[0053] The rotational speed of the cylindrical member W from the rotational process S2 to the next constriction formation process S3 can be set to a range of, for example, 230 rpm or more and 250 rpm or less. In this embodiment, the rotational speed of the cylindrical member W is set to 240 rpm.

[0054] Next, a constriction is formed in the cylindrical member W at a predetermined constriction formation position (constriction formation step S3). At this time, the constriction formation position of the cylindrical member W should be set in a range of 10 mm to 100 mm along the length direction of the cylindrical member W from the open end on the other end We2 side of the cylindrical member W (the other open end). Such a constriction formation position is determined by the formation position of the constriction 53a in the positive electrode container 53 of the NaS battery 50 in Figure 1.

[0055] In the constriction formation process S3, first, the sliding base 26 of the constriction formation device 10 is slid to move the first processing roller 24 to a position where it contacts the outer circumferential surface Wf of the cylindrical member W. As a result, the first processing roller 24 rotates in response to the rotation of the cylindrical member W. In this embodiment, the constriction formation position by the first processing roller 24 and the second processing roller 25 is set to a position 34 mm from the other end We2 of the cylindrical member W.

[0056] Then, the sliding base 26 is slid further, pressing the first processing roller 24 toward the inside of the cylindrical member W at a predetermined processing rate. As a result, a constriction (intermediate forming body) V1 is formed on the cylindrical member W, such that the cross section perpendicular to the circumferential direction is, for example, trapezoidal, as shown in Figure 7(a).

[0057] Next, the sliding base 26 is slid in the opposite direction to the processing direction of the first processing roller 24, thereby separating the first processing roller 24 from the cylindrical member W. Next, the second processing roller 25 is moved to the position where the constriction (intermediate forming body) V1 of the cylindrical member W is formed. As a result, the second processing roller 25 rotates in a manner driven by the rotation of the cylindrical member W.

[0058] Then, the sliding base 26 is slid further and placed on top of the constriction (intermediate formation) V1 formed by the first processing roller 24, and the second processing roller 25 is pressed against it at a predetermined processing rate. As a result, a constriction V2 is formed in the cylindrical member W, as shown in Figure 7(b), with a cross section perpendicular to the circumferential direction, for example, forming a trapezoid with a curved bottom.

[0059] When forming a constriction on the circumferential surface of such a cylindrical member W, a first processing roller 24 and a second processing roller 25 are used, which are formed such that the difference in their diameters is 10 mm or less. For example, the diameter (outermost diameter) φ1 of the first processing roller 24 is 150 mm, and the diameter (outermost diameter) φ2 of the second processing roller 25 is 150 mm ± 10 mm or less.

[0060] When a first processing roller 24 and a second processing roller 25 are pressed against the circumferential surface of a cylindrical member W rotating at a constant speed, for example, 240 rpm, each will rotate in response to the pressure, but the rotational speed increases as the diameter decreases. When the difference in rotational speed between the first processing roller 24 and the second processing roller 25 becomes large, the resistance during processing will also differ significantly between the first processing roller 24 and the second processing roller 25.

[0061] If there is a large difference in resistance during processing, the thickness (wall thickness) of the final constriction V2 may fluctuate locally, making it difficult to form the constriction V2 as designed.

[0062] Therefore, as in this embodiment, by using a first processing roller 24 and a second processing roller 25 formed such that the difference in their diameters is 10 mm or less, the difference between the processing resistance when the constriction (intermediate formation) V1 is formed by the first processing roller 24 and the processing resistance when the constriction V2 is formed by the second processing roller 25 can be reduced, making it possible to form a constriction V2 with the thickness as designed. The constriction V2 thus formed does not have large localized variations in thickness, and the occurrence of defects such as cracks and buckling when external stress is applied can be prevented.

[0063] Furthermore, for example, when the outer diameter of the cylindrical member is 75 mm or more and 95 mm or less, it is preferable that the diameter φ1 of the first processing roller 24 be in the range of 110 mm ± 100 mm, and the diameter φ2 of the second processing roller 25 be in the range of 110 mm ± 100 mm. By setting the diameters (outer diameters) of the first processing roller 24 and the second processing roller 25 within this range, the first processing roller 24 and the second processing roller 25 can be rotated at a speed suitable for stable necking.

[0064] In this embodiment, the constriction of the cylindrical member W is formed in two stages using the first processing roller 24 and the second processing roller 25. However, the method is not limited to this, and the constriction can also be formed in multiple stages using three or more processing rollers. In this case as well, by keeping the diameter difference between the multiple processing rollers to 10 mm or less, it is possible to form a constriction on the cylindrical member as designed, without large local variations in thickness.

[0065] As described above, according to the method for forming a constriction in a cylindrical member of this embodiment, by forming a constriction using a first processing roller 24 and a second processing roller 25 formed such that the difference in their diameters is 10 mm or less, the difference in processing resistance between the two processing rollers is reduced, making it possible to form a constriction on the circumferential surface of the cylindrical member W as designed, without large local variations in thickness.

[0066] Although one embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0067] According to the present invention's method for forming a constriction in a cylindrical member, a cylindrical member can be obtained in which a constriction is formed with high precision and minimal error when forming a constriction along the circumferential direction of the cylindrical member. A cylindrical member with such a constriction can be preferably used in a battery container equipped with a buffer function that allows for thermal expansion and contraction. Therefore, it has industrial applicability.

[0068] 10... Narrowing device (cylindrical member processing device) 11... First clamp 12... Second clamp 13, 17... Work stopper 14... Mandrel (core metal) 15... Mandrel stopper 16... Mandrel head (core metal) 18... Rotating device (motor) 19... Processing roller device 24... First processing roller 25... Second processing roller 26... Sliding base W... Cylindrical member V1... Narrowing (intermediate forming body) V2... Narrowing

Claims

1. A method for forming a constriction in a cylindrical member, wherein the cylindrical member has a hollow cylindrical shape and the constriction is formed inward along the circumferential direction, comprising: a clamping step of clamping the cylindrical member between a first clamp equipped with a cylindrical mandrel inserted into the hollow interior from one open end of the cylindrical member and a second clamp equipped with a cylindrical mandrel head inserted into the hollow interior from the other open end of the cylindrical member; a rotation step of rotating the cylindrical member together with the first and second clamps around a cylindrical axis; and a constriction forming step of sequentially pressing a first processing roller and a second processing roller, which have different outer peripheral shapes and are rotatable around a rotation axis parallel to the cylindrical axis of the cylindrical member, against the outer peripheral surface of the rotating cylindrical member between the mandrel and the mandrel head to form the constriction, wherein the difference between the diameter of the first processing roller and the diameter of the second processing roller is 10 mm or less.

2. The method for forming a constriction in a cylindrical member according to claim 1, wherein the outer diameter of the cylindrical member is in the range of 75 mm or more and 95 mm or less.

3. The method for forming a constriction in a cylindrical member according to claim 2, wherein the diameter of the first processing roller is 110 mm ± 100 mm, and the diameter of the second processing roller is 110 mm ± 100 mm.

4. The method for forming a constriction in a cylindrical member according to claim 2, wherein in the constriction forming step, the rotation speed of the cylindrical member is 230 rpm or more and 250 rpm or less.

5. The method for forming a constriction in a cylindrical member according to any one of claims 1 to 4, wherein the insertion length of the mandrel into the cylindrical member is longer than that of the mandrel head.

6. The method for forming a constriction in a cylindrical member according to any one of claims 1 to 4, wherein the cylindrical member is made of a metal including aluminum.

7. A method for forming a constriction in a cylindrical member according to any one of claims 1 to 4, wherein a fitting member that can be fitted onto the mandrel head is formed on the surface of the mandrel facing the mandrel head.

8. The method for forming a constriction in a cylindrical member according to any one of claims 1 to 4, wherein the cylindrical member having the constriction formed is a battery case for a sodium-sulfur battery.

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