Method for manufacturing a core and tube for forming a socket.

Abstract

This invention provides a method for manufacturing socket-forming cores and pipes that can improve casting quality. [Solution] The core (3) for forming the socket extends along the axial direction toward the back of the pipe from the position (100x) which will be the end of the pipe of the socket (100b), and has a weir portion (33) at the extended tip that is raised radially inward of the pipe (100), and the weir portion (33) has a protruding portion (34) that extends beyond the boundary position (100s) between the socket (100b) and the straight portion (100a) to a position that becomes part of the straight portion (100a).

Description

Technical Field

[0001] The present invention relates to a core for forming a socket and a method for manufacturing a pipe.

Background Art

[0002] For centrifugally casting a cast iron pipe, molten metal is poured into a centrifugal casting mold frame, and the mold frame is rotated at high speed around the axial center of the centrifugal casting mold frame.

[0003] Incidentally, a ductile cast iron pipe generally has a socket with a larger diameter than the pipe body at one end thereof. Correspondingly, the centrifugal casting mold frame (hereinafter sometimes simply referred to as a mold frame) is also provided with a socket forming portion having a larger diameter than the inner diameter of other portions at one end thereof. In addition, the inner peripheral surface of the socket of a ductile cast iron pipe generally has a complicated shape, and so-called cores such as sand cores are used to form such an inner peripheral surface of the socket.

[0004] The core is formed in a cylindrical shape, and on the outer periphery thereof, there are formed an uneven portion for forming a groove on the inner circumference of the socket and a diameter-expanded portion for forming the inner depth of the socket. The core is supported by a core ring in a core setter, and when the core ring is mounted on the mold frame, the core is inserted into the socket forming portion of the mold frame and set concentrically. Besides sand cores, cores made of heat-resistant metal as disclosed in Patent Document 1 are also known.

[0005] An example of the metal core disclosed in Patent Document 1 is shown in Fig. 11. The core 100 in Fig. 11 has a structure bulging in the diameter-reducing direction at the end portion on the inner depth side of the socket. Hereinafter, this bulging portion is referred to as a weir portion 200. An end face 201 on the inner depth side of the socket in the weir portion 200 is located at the boundary between the socket 501 and the straight portion 502, and part of the molten metal flowing from the spigot side is blocked by this end face 201.

Prior Art Literature

Patent Literature

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-164953 [Overview of the project] [Problems that the invention aims to solve]

[0007] There is a difference in wall thickness between the socket and the straight section. When there is a difference in wall thickness during casting, it can cause a difference in the time it takes for the cast iron to cool and solidify, potentially leading to casting defects such as shrinkage cavities. The inventors of the present invention have found that similar casting defects can occur even when casting using the core described in Patent Document 1 (core 100 in Figure 11), and have investigated casting methods to improve casting quality, leading to the completion of the present invention.

[0008] One embodiment of the present invention provides a socket-forming core and a pipe manufacturing method that can improve casting quality. [Means for solving the problem]

[0009] To solve the aforementioned problems, a socket-forming core according to one aspect of the present invention is a socket-forming core used when manufacturing a pipe having a straight section and a socket by centrifugal casting, wherein the socket-forming core extends along the axial direction toward the back of the pipe from a position that will be the pipe end of the socket, and has a weir portion that is raised radially inward of the pipe at the extended tip, and the weir portion protrudes beyond the boundary between the socket and the straight section to a position that becomes part of the straight section.

[0010] According to the above configuration, the weir section protrudes beyond the boundary between the socket and the straight section to a position where it becomes part of the straight section. Therefore, the contact between the protruding portion and the molten metal increases the cooling rate of the molten metal in the portion corresponding to the protruding portion compared to the conventional method (where the molten metal is exposed to the atmosphere and naturally cooled). As a result, the shape is formed before shrinkage cavities occur, thus suppressing the occurrence of shrinkage cavities compared to the conventional method, and providing a socket-forming core that can improve the casting quality of pipes.

[0011] In one aspect of the present invention, the core for forming a socket may be configured such that the wall thickness in the weir portion becomes thinner along the axial direction toward the back of the pipe.

[0012] According to the above configuration, it is possible to prevent the weir section from tilting towards the cast pipe after casting.

[0013] Furthermore, in order to solve the above-mentioned problems, a pipe manufacturing method according to one aspect of the present invention is a pipe manufacturing method for manufacturing a pipe having a straight section and a socket by centrifugal casting, comprising: a placement step of arranging a socket-forming core, which has a weir portion that is raised radially inward of the pipe at a tip portion that extends along the axial direction toward the back of the pipe from a position that will be the pipe end of the socket, and the weir portion protruding beyond the boundary position between the socket and the straight section to a position that becomes part of the straight section, in a centrifugal casting mold; and a pouring step of pouring molten metal between the centrifugal casting mold and the socket-forming core.

[0014] According to the above configuration, the molten metal poured between the centrifugal casting frame and the socket-forming core in the pouring step comes into contact with the protruding portion of the weir of the socket-forming core. In this way, the contact between the protruding portion and the molten metal increases the cooling rate of the molten metal in the portion corresponding to the protruding portion compared to the conventional method (where the molten metal is exposed to the atmosphere and naturally cooled). As a result, the shape is formed before shrinkage cavities occur, so the occurrence of shrinkage cavities can be suppressed compared to the conventional method, and pipes with higher casting quality can be manufactured. [Effects of the Invention]

[0015] According to one aspect of the present invention, it is possible to provide a socket-forming core and a pipe manufacturing method that can improve casting quality. [Brief explanation of the drawing]

[0016] [Figure 1]It is a view of a pipe manufactured using a centrifugal casting machine provided with a socket forming core which is one embodiment of the present invention, and is a side view with a part being a cross-sectional view. [Figure 2] It is a partial cross-sectional view of a centrifugal casting machine provided with a socket forming core which is one embodiment of the present invention. [Figure 3] It is an enlarged cross-sectional view of the portion B enclosed by the broken-line frame shown in Fig. 2. [Figure 4] It is a view showing the flow of a pipe manufacturing method according to an embodiment of the present invention. [Figure 5] It is a view showing the effect on the inner circumferential surface of the socket of a pipe achieved by the socket forming core of Embodiment 1. [Figure 6] It is a partially enlarged view of a socket forming core of Embodiment 2 which is another embodiment of the present invention. [Figure 7] It is a partially enlarged view showing a modified example of the socket forming core shown in Fig. 6. [Figure 8] It is a partially enlarged view showing a modified example of the socket forming core shown in Fig. 6. [Figure 9] It is a partially enlarged view showing a modified example of the socket forming core shown in Fig. 6. [Figure 10] It is a view showing the effect on the inner circumferential surface of the socket of a pipe achieved by the socket forming core of Embodiment 2. [Figure 11] It is a view showing the prior art. MODE FOR CARRYING OUT THE INVENTION

[0017] [Embodiment 1] [Pipe centrifugally cast] First, a pipe 100 centrifugally cast according to the present embodiment will be described with reference to Fig. 1. In Fig. 1, for convenience of explanation, a part is a cutaway view, and the hatched portion represents the cut surface of the pipe 100.

[0018] As shown in Figure 1, the pipe 100 has a socket 100b at one end and a spigot 100c at the other end. Between the socket 100b and the spigot 100c, there is a straight section 100a that extends in a nearly straight line and has an inner diameter that is nearly constant along the pipe axis XC. The spigot 100c has an inner diameter that is nearly constant along the pipe axis XC, and since this diameter is the same as the inner diameter of the straight section 100a, it can be included as part of the straight section 100a.

[0019] The socket 100b has a shape for inserting the spigot of another pipe. Furthermore, an annular groove 100n is formed on the inner circumferential surface of the socket 100b for attaching a locking ring to prevent the pipe 100 from detaching when connected to another pipe. The socket 100b and the spigot 100c allow the pipe 100 to be connected to another pipe.

[0020] Examples of pipes 100 with the above configuration include well-known ductile iron pipes used as earthquake-resistant pipes for water supply, etc. However, the pipes are not limited to these.

[0021] In this embodiment, a configuration used when manufacturing a pipe 100 with the above configuration by centrifugal casting in a pipe manufacturing line will be described. Below, a centrifugal casting machine for centrifugal casting of the pipe and a socket-forming core provided in the centrifugal casting machine will be described.

[0022] [Centrifugal casting machine] Figure 2 is a cross-sectional view of a centrifugal casting machine 1 equipped with a socket-forming core, which is one embodiment of the present invention. Figure 2 is a vertical cross-sectional view including the pipe axis XC, just like Figure 1. For the sake of explanation, Figure 2 shows the state in which the socket 100b and straight section 100a of the pipe are formed by the centrifugal casting machine 1.

[0023] The centrifugal casting machine 1 comprises a metal frame 2 (centrifugal casting metal frame), a core 3 for forming a socket, and a drive roller 4.

[0024] The metal frame 2 is supported horizontally on the drive roller 4, allowing it to rotate at high speed around its central axis. With the socket-forming core 3 inserted into the socket-forming portion 21 of the metal frame 2, molten metal is poured into the metal frame 2 to form the pipe 100 by centrifugal force.

[0025] [Core for forming socket] The socket-forming core 3 is supported by a coring ring 5, and is configured to be inserted into the socket-forming portion 21 of the metal frame 2 and set concentrically when the coring ring 5 is mounted on the metal frame 2. There are no particular restrictions on the structure of the coring ring 5 or the manner in which the coring ring 5 and the socket-forming core 3 are connected. In addition, the coring ring 5 and the socket-forming core 3 may be integrated into a single structure as shown in Figure 2, in which case the socket-forming core may be directly mounted on the metal frame 2.

[0026] The socket-forming core 3 is formed in a cylindrical shape and extends along the axial direction toward the back of the pipe from position 100x, which is the end of the pipe socket. Here, Figure 2 also shows a three-dimensional coordinate system of XYZ, with the direction along the pipe axis XC as the Y axis. The positive Y axis is defined as the direction toward the back of the pipe. The Z axis is the vertical direction, and the XY plane is defined as the horizontal plane. The axis (central axis) of the metal frame 2 and the axis (central axis) of the socket-forming core 3 can be considered to be coaxial with the pipe axis XC.

[0027] On the outer circumferential surface of the extension portion of the socket-forming core 3 that extends axially toward the back of the pipe, there are irregularities 31 formed to create an annular groove 100n (Figure 1) that is formed on the inner circumferential surface of the socket 100b. The socket-forming core 3 also has a weir portion 33 at the tip of the extension portion that is raised radially inward of the pipe. Here, "radially inward of the pipe" means the direction from a certain position in a virtual plane perpendicular to the pipe axis XC (central axis) toward the pipe axis XC.

[0028] Figure 3 is an enlarged view of the dashed-line-enclosed portion B shown in Figure 2. As shown in Figure 3, the weir portion 33 is raised radially inward in the pipe at the tip portion that extends along the axial direction toward the back of the pipe in the receiving-mouth forming core 3. Here, "raised" means that it is raised higher than the region 6 adjacent to the weir portion 33 in the portion of the receiving-mouth forming core 3 that extends along the axial direction toward the back of the pipe, and this region refers to the surface that extends along the axial direction toward the back of the pipe from the position 100x which is the pipe end in the receiving-mouth forming core 3. On the outer circumference of this region 6, there is a groove-forming portion 30 with uneven surfaces 31.

[0029] As shown in Figure 3, the weir section 33 protrudes beyond the boundary position 100s between the receiving opening 100b and the straight section 100a, to a position where it becomes part of the straight section 100a. This protruding portion is referred to as the projection 34.

[0030] There are no particular restrictions on the length of the projection 34 in the direction towards the back of the pipe (positive Y-axis direction); it is sufficient that it extends beyond the boundary position 100s to the straight section 100a. The projection 34 and the weir section 33 are provided around the entire circumference of the tip of the receiving-mouth forming core 3.

[0031] The socket-forming core 3, configured in this way, is combined with the metal frame 2, and molten metal is poured inside to form the tube 100 by centrifugal force. The rotation is continued for a while to cool and solidify the molten metal. The tube manufacturing method in which the tube is manufactured by centrifugal casting in this embodiment will be explained below with reference to Figure 4.

[0032] [Pipe manufacturing method] Figure 4 is a diagram showing the flow of the pipe manufacturing method of this embodiment. The pipe manufacturing method S10 of this embodiment includes a placement step S11 and a pouring step S12. Each step will be described below.

[0033] In the placement step S11, the socket-forming core 3 described above is placed in the metal frame 2. The socket-forming core 3 is centered using a well-known method so that its central axis is coaxial with the central axis of the metal frame 2, and then the socket-forming core 3 is fixed to the metal frame 2 via the coring ring 5 (Figure 2).

[0034] In the pouring step S12, molten metal is poured between the metal frame 2 and the socket-forming core 3 formed in the arrangement step S11. In the pouring step S12, after pouring the molten metal, the metal frame 2 and the socket-forming core 3 are rotated around their central axis, and the tube 100 is formed by the centrifugal force accompanying the rotation.

[0035] When removing the cast tube from the metal frame 2 after casting the tube by centrifugal force, the coring 5 is pulled out from the socket of the metal frame 2, the cast tube 100 is pulled out from the metal frame 2 with the socket-forming core 3 still attached, and then the socket-forming core 3 is destroyed and removed from the socket 100b. For this reason, the socket-forming core 3 is made of a material that can be discarded each time it is formed, like a sand core. However, the socket-forming core 3 may be made of a heat-resistant metal to allow for repeated use, so that the socket-forming core 3 can be removed from the cast tube 100 at an appropriate time. As a removal mechanism, the socket-forming core 3 may be configured to move radially inward. If it can be reused, it does not need to be discarded each time it is formed, like a sand core.

[0036] With the socket-forming core 3 described above, the protrusion 34 provided in the weir portion 33 allows contact between the protrusion 34 and the molten metal. This differs from the conventional method in which the molten metal is exposed to the atmosphere and naturally cools. Furthermore, with the socket-forming core 3 described above, the cooling rate of the molten metal in the portion between the protrusion 34 and the metal frame 2 can be increased compared to the conventional method. As a result, the shape of the boundary position 100s between the socket 100b and the straight portion 100a and its adjacent regions (the adjacent region on the socket 100b side and the adjacent region on the straight portion 100a side) is formed before shrinkage cavities occur. In other words, with the socket-forming core 3, the occurrence of shrinkage cavities is suppressed compared to the conventional method, and a pipe 100 with high casting quality can be manufactured.

[0037] The casting quality of the tube 100 centrifugal cast using the socket-forming core 3 and metal frame 2 of this embodiment will be explained with reference to Figure 5. Figure 5 is an image of a portion of the inner surface of the socket 100b of the centrifugal cast tube 100. The area to be imaged corresponds to the dashed framed portion of the tube 100 shown in the upper part of Figure 5. Note that the centrifugal casting conditions and tube materials are the same as those of previous models, so their explanation is omitted here.

[0038] As shown in Figure 5, no shrinkage cavities have formed on the inner circumferential surface of the socket 100b of the pipe 100 at the boundary position 100s between the socket 100b and the straight section 100a, and in the adjacent area on the straight section 100a side. This is because the weir section 33 has a protruding portion 34, and contact between the protruding portion 34 and the molten metal is achieved, which increases the solidification speed of this contact area and changes the final solidification point from the surface of the contact area to the inside of the pipe, thereby suppressing the occurrence of depressions (shrinkage cavities).

[0039] Furthermore, since the protruding portion 34 and the weir portion 33 are provided around the entire circumference of the tip of the receiving-mouth forming core 3, the solidification rate is uniform at each part of the circumference, and the occurrence of depressions (sink cavities) in the target area caused by uneven solidification rates between target areas can be suppressed.

[0040] Furthermore, since the molten metal poured into the space between the metal frame 2 and the protruding portion 34 forms a pool, even if there is a tendency for shrinkage cavities, the structure of the tube formed in that portion by the rising molten metal (the boundary position 100s and the adjacent region on the straight portion 100a side) can be made denser.

[0041] Here, the outer surface of the protruding portion 34 that is positioned opposite the inner surface of the metal frame 2 may have a gently sloping surface that approaches the pipe axis XC towards the back of the pipe. Having such a sloping surface results in a configuration where the space between the metal frame 2 and the protruding portion 34 is widely open towards the back of the pipe, making it easier for molten metal to be poured into this space without gaps. This allows for good formation of the pipe wall in that portion.

[0042] [Embodiment 2] Other embodiments of the present invention will be described below. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated. This embodiment will be described below with reference to Figure 6.

[0043] Figure 6 is an enlarged cross-sectional view corresponding to the enclosed area B in Figure 2 shown in Embodiment 1, and corresponds to Figure 3. The receiving-mouth forming core 3A of this embodiment differs from the weir portion 33 of Embodiment 1 in that the shape of the weir portion 33A is different.

[0044] The core 3A for forming the socket shown in Figure 6 has a weir section 33A in which the wall thickness decreases along the axial direction toward the back of the pipe. This differs from the weir section 33 of Embodiment 1, in which the wall thickness is almost constant along the axial direction toward the back of the pipe, including the protruding section 34.

[0045] The wall thickness referred to here is the thickness in the radial direction. As shown in Figure 6, the wall thickness of the weir section 33A decreases continuously up to the tip of the protruding section 34A located at the tip. In other words, the surface of the weir section 33A facing the pipe axis XC is an inclined surface that is tilted with respect to the pipe axis XC. Furthermore, the weir section 33A is part of the inner circumferential surface of the socket-forming core 3A and can be described as having a tapered shape.

[0046] The socket-forming core 3A is made of sand cores. The socket-forming core 3A, made of sand cores, tends to become structurally brittle when heated by contact with molten metal during centrifugal casting. In particular, the tip of the socket-forming core 3A has a large difference in wall thickness on either side of the boundary position 100s, which makes it prone to uneven temperature distribution, and consequently the core itself tends to collapse. In this regard, the weir section 33A has a shape in which the wall thickness decreases along the axial direction toward the back of the pipe. Therefore, even if the weir section 33A collapses during or immediately after casting, the thin wall on the protruding section 34A side makes it less likely for the sand cores that constituted the protruding section 34A to collapse onto the inner surface of the cast pipe 100 (the inner surface of the straight section 100a), a phenomenon known as core collapse.

[0047] Therefore, the socket-forming core 3A has the advantage of being less prone to core tilting, and even if core tilting does occur, it is on a smaller scale, and there is also the advantage that the burden of removing the tilted core that adheres to the inner surface of the pipe by grinding is reduced.

[0048] [Modified example 1 of weir section 33A] The shape of the weir section 33A in Figure 6 is not the only configuration that can suppress the occurrence of core collapse, as seen in the receiving-port forming core 3A of this embodiment described above. The following are some modified examples of the weir section 33A.

[0049] Figure 7 is an enlarged cross-sectional view showing a modified example, corresponding to the view of the area around the weir section 33A in Figure 6. Unlike the weir section 33A, the weir section 33B in Figure 7 does not have a shape where the wall thickness decreases along the axial direction toward the back of the pipe. Instead, although the wall thickness of the protruding portion 34B gradually decreases toward the tip of the protruding portion 34, the wall thickness of the weir section 33B other than the protruding portion 34B is constant.

[0050] Even in the weir section 33B shown in Figure 7, the thinness of the protruding section 34B makes it less likely for the sand cores that constituted the protruding section 34B to collapse (core collapse) toward the inner surface of the cast pipe 100 (the inner surface of the straight section 100a).

[0051] [Modified example 2 of weir section 33A] The following are further modifications of the weir section 33A. Figure 8 is an enlarged cross-sectional view showing modification 2, and corresponds to the view of the area around the weir section 33A in Figure 6. Unlike the weir section 33A, the weir section 33C in Figure 8 does not have a shape in which the wall thickness is thinned along the axial direction toward the back of the pipe, but rather has a step recessed radially outward at the tip of the protruding section 34C.

[0052] In other words, the stepped weir section 33C has a smaller radial inward protrusion at the protruding section 34C. Alternatively, the weir section 33C can be described as having a portion where the wall thickness decreases towards the tip.

[0053] Furthermore, the wall thickness is constant in the weir section 33C, except for the protruding section 34C.

[0054] [Modified example 3 of weir section 33A] The following are further modifications of the weir section 33A. Figure 9 is an enlarged cross-sectional view showing modification 3, which corresponds to the view of the area around the weir section 33A in Figure 6. Unlike the weir section 33A, the weir section 33D in Figure 9 does not have a shape in which the wall thickness continuously thins along the axial direction toward the back of the pipe, but rather the protruding section 34D has a curved recessed shape in cross-sectional view.

[0055] Even in the weir section 33D shown in Figure 9, the protruding section 34D is thinner, so even if the weir section 33D collapses, the sand cores that made up the protruding section 34D are less likely to collapse (core collapse) toward the inner surface of the cast pipe 100 (the inner surface of the straight section 100a).

[0056] Furthermore, the wall thickness is constant in the portion of the weir section 33D other than the protruding portion 34D.

[0057] According to the socket-forming core 3A of this embodiment and the socket-forming cores 3B, 3C, and 3D of each modified example described above, similar to the socket-forming core 3 of Embodiment 1, the protrusions 34A, 34B, 34C, and 34D provided on the weir portions 33A, 33B, 33C, and 33D can increase the cooling rate of the molten metal in the portion between the protrusions and the metal frame 2. As a result, the occurrence of shrinkage cavities can be suppressed, and a pipe 100 with high casting quality can be manufactured.

[0058] The casting quality of the tube 100 centrifugal cast using the socket-forming core 3A and metal frame 2 (Figure 2) of this embodiment will be explained with reference to Figure 10. Figure 10 corresponds to Figure 5 shown in Embodiment 1. Like Figure 5, Figure 10 is an image of a part of the inner surface of the socket 100b of the centrifugal cast tube 100. The area to be imaged corresponds to the dashed framed portion of the tube 100 shown in the upper part of Figure 10. Note that the centrifugal casting conditions and tube materials are the same as before, so their explanation is omitted here.

[0059] As shown in Figure 10, no shrinkage cavities have formed on the inner circumferential surface of the socket 100b of the pipe 100 at the boundary position 100s between the socket 100b and the straight section 100a, and in the adjacent area on the straight section 100a side. This is because the weir section 33A has a protruding portion 34A, and contact between the protruding portion 34A and the molten metal is achieved, which increases the solidification speed of this contact area and changes the final solidification point from the surface of the contact area to the inside of the pipe, thereby suppressing the occurrence of depressions (shrinkage cavities).

[0060] Furthermore, as shown in Figure 10, the adjacent region on the straight section 100a side of the boundary position 100s between the receiving opening 100b and the straight section 100a does not have an uneven shape along the circumference and has a relatively smooth surface. This indicates that so-called core tilting has not occurred.

[0061] In this embodiment and its modifications, as in Embodiment 1, the solidification rate at the boundary position 100s between the receiving end 100b and the straight portion 100a, and in the adjacent region on the straight portion 100a side, is uniform at each part of the circumference, thus suppressing the occurrence of unevenness. Furthermore, since the molten metal poured into the space between the metal frame 2 and the protruding portion 34A forms a pool, even if there is a tendency for shrinkage cavities, the riser can make the structure of the tube formed in that part (the boundary position 100s and the adjacent region on the straight portion 100a side) denser.

[0062] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0063] 1. Centrifugal casting machine 2. Gold frame (centrifugally cast gold frame) 3, 3A, 3B, 3C, 3D Core for socket formation 4 drive rollers 5. Coring 21 Socket forming part 30 Groove forming part 31 Uneven part 33, 33A, 33B, 33C, 33D Weir 34, 34A, 34B, 34C, 34D protrusion 100 tubes 100a Straight part 100b socket 100n annular groove 100s boundary position XC tube shaft (shaft)

Claims

1. A socket-forming core used when manufacturing a tube having a straight section and a socket by centrifugal casting, The core for forming the socket is made of sand cores and extends along the axial direction toward the back of the pipe from the position that will become the pipe end of the socket, and has a weir portion that is raised radially inward at the extended tip of the pipe. The weir portion is formed as part of the sand core and protrudes beyond the boundary between the receiving opening and the straight portion to a position where it becomes part of the straight portion. The wall thickness in the aforementioned weir section is formed to become thinner along the axial direction toward the back of the pipe. A core for forming a socket, characterized by the above features.

2. A method for manufacturing a pipe having a straight section and a socket by centrifugal casting, A core for forming a socket, comprising a sand core having a weir portion that rises radially inward along the tip of the socket, extending along the axial direction toward the back of the pipe from the position that will be the end of the socket, wherein the weir portion protrudes beyond the boundary between the socket and the straight portion to a position that becomes part of the straight portion, the weir portion is formed as part of the sand core, and the wall thickness of the weir portion is formed to become thinner along the axial direction toward the back of the pipe, is placed in a centrifugal casting mold as an arrangement step, A pouring step of pouring molten metal between the centrifugal casting frame and the core for forming the socket, including, A method for manufacturing pipes characterized by the following features.

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