Electrofusion joints

Abstract

To provide an electrofusion joint capable of electrically fusing a plastic pipe to be connected not simultaneously at both of right and left sockets but by each of right and left sockets.SOLUTION: In an electrofusion joint, a going path in which spiral advances in a going path direction from an opening portion side of the electrofusion joint to an opening portion side at an opposite side of the opening portion and a return path in a direction reverse to the going path direction, are formed by means of one heating wire in a fusion portion. The going path in the fusion portion includes: a first area at an axial central portion in the fusion portion in which pitches of the spiral shape are formed by the same pitch (F(n)-F(n+1)=13.0 mm (n=0-3)); and a second area excluding the central portion in which the pitches of the spiral shape are formed by the pitches which are twice the same pitch in maximum (F(4)-F(5)=16.5 mm (turn portion T)). In the return path in the fusion portion, both of the first area and the second area have the same pitch (R(n)-R(n+1)=13.0 mm (n=0-6: including turn portion)).SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an electric fusion joint used for connecting plastic pipes, and particularly to an electric fusion joint having a structure in which an electric heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe.

Background Art

[0002] Electric fusion joints are usually manufactured by an injection molding method, and an electric heating wire is embedded in the inner peripheral portion of a joint body made of a thermoplastic resin such as polyethylene or polybutene. Such electric fusion joints are sometimes called EF (ElectroFusion) joints, EF sockets, etc. As such an electric fusion joint, mainly for large-diameter electric fusion joints, a joint having a structure in which a concave groove is provided by cutting in a spiral shape along the inner surface of a pipe made of a thermoplastic resin, and an electric heating wire is inserted into this concave groove, has been provided. Although the manufacturing method of the electric fusion joint of this structure is simple, the manufacturing difficulty in terms of mounting the electric heating wire so as not to float up from the groove has been pointed out as a problem. In view of such problems, Japanese Patent No. 5035672 (Patent Document 1) discloses an electric fusion joint having a structure in which an electric heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe, in which the electric heating wire does not float up from the concave groove due to temperature changes in the storage environment, and no voids occur at the fusion interface with the plastic pipe.

[0003] The electrofusion joint disclosed in Patent Document 1 comprises a thermoplastic resin tube into which a plastic tube is inserted, a U-shaped groove formed on the inner circumference of the resin tube in a spiral shape with a small spiral pitch and a large spiral pitch, tongue-shaped portions formed on both sides of the groove opening, and a heating wire inserted into the groove, wherein the width of the groove is formed to be the same as or slightly narrower than the diameter of the heating wire, the depth of the groove is deeper than the diameter of the heating wire, the groove portion with a small spiral pitch is shallower than the groove portion with a large spiral pitch, the heating wire inserted into the groove portion with a small spiral pitch is embedded in the groove with resin including the molten tongue-shaped portion, and the heating wire inserted into the groove portion with a large spiral pitch is pressed into the groove by the pressed tongue-shaped portion. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5035672 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the electrofusion joint disclosed in Patent Document 1, as described in paragraphs 0016 to 0018 of Patent Document 1, is manufactured through three steps: first, a thermoplastic resin sleeve is prepared and a U-shaped groove is formed on its inner surface by helical cutting; second, a pressing tool is pressed and moved along the groove to deform the side wall and form a burr-like tongue-shaped portion protruding from the inner surface; and third, an electric heating wire is inserted along the entire length of the groove. As a result, the manufacturing cost tends to be high.

[0006] Furthermore, the electrofusion joint disclosed in Patent Document 1 is merely a joint for connecting two plastic pipes in series, as described in paragraph 0009 of Patent Document 1. More specifically, the inner circumferential surface of the sleeve is divided into a left fusion section that melts and fuses the surface of a plastic pipe inserted from the left, a right fusion section that melts and fuses the surface of a plastic pipe inserted from the right, a left winding end between the left fusion section and the left connector pin (terminal pin), a right winding end between the right fusion section and the right connector pin (terminal pin), and a connecting section between the left fusion section and the right fusion section. A groove is formed continuously from the left winding end to the right winding end, and a single continuous electric heating wire is installed within it. In other words, because it is assumed that plastic pipes will be fused to the left and right sockets of the electrofusion joint simultaneously, a single continuous electric heating wire is wound on the inner surface of the joint in the same direction from left to right (or right to left).

[0007] In such a structure, there are several problems: (1) Even if plastic pipes are fused to both the left and right sockets, they must be fused simultaneously, making it impossible to fuse them one at a time; (2) It is not possible to fuse a plastic pipe to one of the sockets, rather than both, and connect it to the other socket using another connection method (making it impossible to realize a single-socket type electrofusion joint); and (3) Generally, in the case of a double-socket, as described in (1) above, fusion must be done simultaneously, requiring twice the fusion energy of a single-socket, and as the diameter (size) increases, the required power (generator) becomes very large. Furthermore, the problems in (1), (2), and (3) above can be solved by arranging the left and right heating wires independently without providing a connecting section, but in that case, one of the two terminal pins placed in the two locations on the left and right will be placed on the central side in the axial direction of the electrofusion joint. In this case, since the terminal pins are installed in through-holes that penetrate the sleeve of the electrofusion joint, there is a problem that if the terminal pins are installed on the central side of the electrofusion joint, it may lead to water leakage due to these through-holes. For this reason, a total of four terminal pins must be placed, two on each of the two locations on the left and right, so as not to affect watertightness.

[0008] However, the electrofusion joint disclosed in Patent Document 1 is merely a joint for connecting two plastic pipes in series and simultaneously. Therefore, Patent Document 1 does not describe or suggest a method of independently arranging the left and right heating wires without providing such a connecting section, and arranging a total of four terminal pins, two on each side. The present invention was developed in view of the above-mentioned problems, and its objective is to provide an electrofusion joint having a structure in which an electric heating wire is fitted into a groove formed on the inner circumference of a thermoplastic resin pipe, which can electrofusion the plastic pipe to be connected to one of the left and right sockets at a time (either both left and right are electrofused, or only one side is electrofused and the other is not), and which can electrofusion without increasing manufacturing costs and without affecting watertightness. [Means for solving the problem]

[0009] To achieve the above objective, the electrofusion joint according to the present invention employs the following technical means. In other words, the electrofusion joint according to the present invention is an electrofusion joint comprising a fusion portion in which a heating wire is inserted into a spirally formed notched groove on the inner circumferential surface of a thermoplastic resin pipe into which a resin pipe to be connected is inserted, wherein the fusion portion is provided on at least one end side in the axial direction of the electrofusion joint so as to be energized for the heating wire, and in the fusion portion, a forward path in which the spiral progresses in the forward path direction from the opening side of the electrofusion joint to the opening side opposite the opening side and a return path in the opposite direction to the forward path are formed by a single heating wire, and the fusion portion is characterized in that both the forward path and the return path include a first area in the axial center of the fusion portion in which the spiral pitch is formed at the same pitch, and a second area other than the center in which the spiral pitch is formed at a pitch up to twice that of the same pitch.

[0010] Preferably, the second area can be configured to include a switching portion from the outbound path to the return path. More preferably, the pitch of the switching portion can be configured to be equal to or greater than the same pitch. More preferably, the switching portion can be configured to be formed as a semicircle with a diameter larger than half of the same pitch. More preferably, the switching portion can be configured to be formed as a semicircle with a diameter of 150% or more of half of the same pitch. [Effects of the Invention]

[0011] According to the present invention, an electrofusion joint is provided that has a structure in which an electric heating wire is fitted into a recess formed on the inner circumference of a thermoplastic resin pipe, and that the plastic pipe to be connected can be electrofused to one of the left and right sockets at a time, rather than simultaneously to both the left and right sockets (it is also acceptable for both sides to be electrofused, or for only one side to be electrofused and the other side not to be electrofused), and that electrofusion can be performed without increasing manufacturing costs and without affecting watertightness. [Brief explanation of the drawing]

[0012] [Figure 1] (A) a side view and (B) a front view of an electrofusion joint according to an embodiment of the present invention, wherein (C) is a cross-sectional view indicated by arrow 1C, (D) is a cross-sectional view indicated by arrow 1D, (E) is a cross-sectional view indicated by arrow 1E, and (F) is a cross-sectional view indicated by arrow 1F. [Figure 2] Figure 1 is a perspective view (part 1: forward path) illustrating the manufacturing method of the electrofusion joint shown. [Figure 3] Figure 1 is a perspective view (part 2: return path) illustrating the manufacturing method of the electrofusion joint shown in Figure 1. [Figure 4] Figures 2 and 3 show (A) a front view (part 1: forward path) and (B) a front view (part 2: return path) to illustrate the relationship between the cutting tool used in the manufacturing method of the electrofusion joint shown in Figures 2 and 3 and the electrofusion joint (in this case, the sleeve before processing). [Figure 5] Figures 2 and 3 show (A) to (E) plan views and (F) to (I) perspective views of the specialized cutting tools used in the manufacturing method of electrofusion joints. [Figure 6] Figure 5 shows (A) to (C) perspective views and (D) a front view to illustrate the dimensions of each part of the specialized cutting tool. [Figure 7] This diagram illustrates the (A) forward winding and (B) return winding of the electrofusion joint 100. [Figure 8] This diagram illustrates the (A) forward winding and (B) return winding of the electrofusion joint 200. [Figure 9] This diagram illustrates the (A) forward winding and (B) return winding of an electrofusion joint in a comparative example. [Figure 10] (A)-(B) Plan view, (C) Installation procedure diagram, and (D)-(E) Connection component diagrams are provided to illustrate the terminal pins of the electrofusion joint. [Modes for carrying out the invention]

[0013] Hereinafter, an electrofusion joint and a method for manufacturing an electrofusion joint according to an embodiment of the present invention will be described with reference to Figures 1 to 10. In Figures 1 to 10, the same components are denoted by the same reference numerals and have the same function, so they may not be described repeatedly. Here, the electrofusion joint according to the embodiment of the present invention is mainly an electrofusion joint of medium to large diameter (for example, an inner diameter of 300 mm or more), and this electrofusion joint has a structure manufactured by a manufacturing method characterized by cutting a spiral groove (for example, the cross-sectional shape of this groove is a V-shaped groove, as the cutting blade of the special cutting tool described later is V-shaped when viewed from the direction along the inner circumference) along the inner surface (sometimes described as the inner circumferential surface) of a resin pipe (sometimes described as a pipe material or sleeve) made of thermoplastic resin, and simultaneously fitting an electric heating wire into this groove. Furthermore, the electrofusion joint according to the embodiment of the present invention may be a double-receiving type with electric heating wires independently provided on the left and right, or a single-receiving type with electric heating wires provided on only one side, but in the following description it will be described as a double-receiving type. In other words, the electrofusion joint according to this embodiment does not have a connecting portion like that in Patent Document 1 on the central side in the axial direction, and instead has the left and right heating wires independent, with a total of four terminal pins arranged in two places on the left and right ends of the electrofusion joint. Because it does not have through holes (holes that penetrate the outer and inner surfaces of the sleeve) for providing terminal pins on the central side, it has the characteristic of not affecting watertightness.

[0014] In addition, as the electric fusion joint according to this embodiment, although the electric fusion joints 100 and 200 are shown in FIG. 1, these are two types of electric fusion joints with different winding structures (structures manufactured by winding methods with different start positions S and / or end positions E of the winding and different winding pitches). The electric fusion joint having the winding structure shown in FIG. 7 is the electric fusion joint 100 shown in FIG. 1, and the electric fusion joint having the winding structure shown in FIG. 8 is the electric fusion joint 200 shown in FIG. 1. Note that the electric fusion joint having the winding structure shown in FIG. 9 pertains to a comparative example.

[0015] Furthermore, although it is an example, by adopting the winding structure shown in any of FIGS. 7 to 8, using the dedicated cutting tool shown in FIGS. 5 to 6 and the manufacturing method shown in FIGS. 2 to 4, along the inner peripheral surface of the pipe material (sleeve), and a spiral groove formed by the forward path from the end side to the central side and the return path from the central side to the end side of the sleeve is cut and provided by the cutting edge of the dedicated cutting tool, and at the same time an electric heating wire is inserted (embedded, buried) into the groove, and then the terminal pin shown in FIG. 10 is surely connected to the inserted electric heating wire, and the electric fusion joint shown in FIG. 1 is completed.

[0016] <Overall Structure of Electric Fusion Joint> First, the overall structure of the electric fusion joint manufactured as described above will be described. As shown in FIGS. 1(A) and 1(B), the electric fusion joint 100 (having the winding structure shown in FIG. 7) and the electric fusion joint 200 (having the winding structure shown in FIG. 8) according to this embodiment, as an example, in the case of a nominal diameter of 250 (the electric fusion joint corresponding to the outer diameter of the resin pipe of the connection partner being 315 mm), it has an inner diameter of 317 mm, an outer diameter of 400 mm, and an axial length of 300 mm, and has a hollow cylindrical shape. In the following, when describing the absolute values of numerical values for the electric fusion joint 100 etc. including the dedicated cutting tool 1000, even if not noted, they are the numerical values for this electric fusion joint with a nominal diameter of 250 (inner diameter 315 mm). In the following, there may be cases where the electric fusion joint 100 and the electric fusion joint 200 are described by taking the electric fusion joint 100 as a representative. And an electric heating wire 300 is spirally embedded in its inner peripheral surface.

[0017] In other words, the electrofusion joint 100 has a fusion section in which a heating wire 300 is inserted into a spirally formed notched groove on the inner circumferential surface of a thermoplastic resin pipe (pipe material, sleeve) into which the resin pipe to be connected is inserted. This fusion section is provided on at least one (here both) axial end side of the electrofusion joint 100 so that current can be passed through the heating wire 300 (via terminal pin 2000). In this fusion section, the forward path, in which the spiral progresses from the opening side of the electrofusion joint 100 to the opening side on the opposite side of the opening, and the return path in the opposite direction to the forward path are both formed by a single heating wire 300.

[0018] More specifically, as shown in Figures 1(C) to 1(F), the electrofusion joint 100 is equipped with a terminal pin 2000 (S side) at the start position S side (forward path start side) and a terminal pin 2000 (E side) at the end position E side (return path end side) of one heating element 300 on each side. This terminal pin 2000 is a metal processed product, and its detailed structure will be described later, but it is equipped with a structure that ensures reliable connection with the heating element 300. In the electrofusion joint 100, the terminal pins 2000 are positioned at the same circumferential position but offset in the axial direction at the start position S side and the end position E side. In contrast, the terminal pins 2000 in the electrofusion joint 200 are positioned at approximately the same axial position but offset in the circumferential direction at the start position S side and the end position E side. In all electrofusion joints, to avoid affecting watertightness, (since the electrofusion joint according to this embodiment is a double-receiving type) a total of four terminal pins, two on each of the left and right sides, are arranged on the end side of the electrofusion joint (not on the axial center side). To position the terminal pins 2000 in this manner, the winding structure, as shown in Figures 7 and 8, comprises a forward winding, a turn section T, and a return winding.

[0019] The electrofusion joint 100 is equipped with an indicator 3000, which is an injection-molded part, corresponding to the positions of the left and right heating wires 300. When electrofusion is performed by supplying power to the heating wires 300 via the terminal pins 2000, the indicator 3000 rises, allowing confirmation that electrofusion is taking place.

[0020] <Method for manufacturing electrofusion joints> The electrofusion joint 100 according to this embodiment, which has the winding structure described above, is embedded in the inner circumferential surface of the electrofusion joint by a manufacturing method for electrofusion joints described below with reference to Figures 2 to 4, such that a single heating element 300 comprises a forward winding, a turn section, and a return winding. The special cutting tool 1000 used in the manufacturing method for electrofusion joints described below is shown in Figures 5 to 6.

[0021] The manufacturing method for the electrofusion joint 100 according to this embodiment includes a joint setting step of setting the electrofusion joint (here, not a finished electrofusion joint but a hollow cylindrical pipe material (sleeve), although this parenthetical notation may not be mentioned below) on a lathe so as to rotate; a tool setting step of setting a dedicated cutting tool (dedicated cutting tool 1000 shown in Figures 2 to 6) on the lathe; and a fusion joint forming step of moving the dedicated cutting tool 1000 in the axial direction while bringing it into contact with the inner circumferential surface of the electrofusion joint, and rotating the electrofusion joint to form a fused portion. The fusion joint formation step includes a groove cutting step in which a notch groove is cut into the inner circumferential surface using the push-cutting blade 1200 provided on the dedicated cutting tool 1000; a heating wire insertion step in which the heating wire 300 is inserted into the notch groove from the heating wire supply hole 1210 provided on the dedicated cutting tool 1000 (more specifically, the heating wire 300 inserted from the heating wire introduction hole 1110 provided on the body portion 1100 of the dedicated cutting tool 1000 is discharged from the heating wire supply hole 1210 provided on the push-cutting blade 1200 of the dedicated cutting tool 1000 and inserted into the notch groove); and a heating wire fixing step in which the notch groove into which the heating wire 300 is inserted is pressed together with the heating wire 300 using the pressing guide 1300 provided on the dedicated cutting tool 1000 to fix the heating wire 300 in the notch groove. In the tool setting step, the dedicated cutting tool 1000 is set on the lathe so that a switching step can be performed in which the orientation of the dedicated cutting tool 1000 in the inner circumferential direction is reversed by 180 degrees to switch from the forward path to the return path (forming the turn section T described later). The heating wire supply section may be described as being formed by the heating wire introduction hole 1110, the heating wire supply hole 1210, and the communication holes provided inside the dedicated cutting tool 1000 that connect these holes, with the same diameter (d1 described later), or these same diameter d1 may be represented as the diameter of the heating wire supply hole 1210.

[0022] In the joint setting step described above, the lathe on which the electrofusion joint is set is preferably a general-purpose lathe or an NC (Numerical Control) lathe. Furthermore, as shown in the relationship between the dedicated cutting tool 1000 and the electrofusion joint in the forward path shown in Figure 4(A), and the relationship between the dedicated cutting tool 1000 and the electrofusion joint in the return path shown in Figure 4(B), the dedicated cutting tool 1000 has a structure that faces the inner circumferential surface of the rotating electrofusion joint, in the order of the cutting blade 1200, the heating wire supply hole 1210, and the pressing guide 1300, and it is preferable that the direction from the heating wire introduction hole 1110 (inlet) to the heating wire supply hole 1210 (outlet) of the dedicated cutting tool 1000 is the same direction as the direction in which the electrofusion joint rotates.

[0023] Furthermore, as shown in Figure 2(C), it is preferable that the fusion joint formation step further includes a switching step in which the dedicated cutting tool 1000 moves in the axial direction (stops parallel movement) and the rotation of the electrofusion joint is stopped (stops rotation), thereby reversing the direction of the dedicated cutting tool 1000 in the inner circumferential direction by 180 degrees and switching from the forward path to the return path (forming the turn section T described later). Referring to Figure 2, the fusion joint formation step in this manufacturing method will be explained separately as forward winding formation and return winding formation.

[0024] As shown in Figure 2(A), the special cutting tool 1000 is positioned at the starting position S of the forward path, and the special cutting tool 1000 is brought into contact with the inner circumferential surface of the electrofusion joint and started to move axially (parallel movement), while simultaneously starting the rotation of the electrofusion joint (here, clockwise rotation when viewed from the opening on the left). By bringing the special cutting tool 1000 into contact with the inner circumferential surface of the electrofusion joint and starting the parallel movement of the special cutting tool 1000 and the rotation of the electrofusion joint in this way, the forward winding 300F begins to be embedded into the inner circumferential surface of the electrofusion joint from the starting position S.

[0025] By controlling the parallel movement speed of the special cutting tool 1000 and the rotation speed of the electrofusion joint to form the forward winding shown in Figures 7 and 8, the forward winding 300F (specifically, either the forward winding in Figure 7(A) or Figure 8(A)) is formed as shown in Figure 2(B). Furthermore, as shown in Figure 2(C), once the forward winding 300F shown in Figures 7-8 is formed until the dedicated cutting tool 1000 reaches the end position of the forward path (the starting position of the semicircle of the turn section T), a switching step is executed. At this time, the parallel movement of the dedicated cutting tool 1000 and the rotation of the electrofusion joint are stopped, and the direction of the dedicated cutting tool 1000 in the inner circumferential direction is reversed by 180 degrees to form the turn section T for switching from the forward path to the return path.

[0026] Next, as shown in Figure 3(A), the special cutting tool 1000, located at the start position of the return path (the end position of the semicircle of the turn section T), is brought into contact with the inner circumferential surface of the electrofusion joint and is moved axially (parallel movement in the opposite direction to the forward path), and the electrofusion joint is started to rotate (here, rotated counterclockwise when viewed from the left opening). By bringing the special cutting tool 1000 into contact with the inner circumferential surface of the electrofusion joint in this way, the parallel movement of the special cutting tool 1000 (parallel movement in the opposite direction to the forward path, bringing the special cutting tool 1000 closer to the start position S) and the rotation of the electrofusion joint (reverse rotation to the forward path) are started, causing the return winding 300R to begin to be embedded in the inner circumferential surface of the electrofusion joint from the end position of the turn section T.

[0027] By controlling the parallel movement speed of the special cutting tool 1000 and the rotation speed of the electrofusion joint to form the return winding shown in Figures 7 and 8, a return winding 300R (specifically, the return winding shown in either Figure 7(B) or Figure 8(B)) is formed as shown in Figure 3(B). Furthermore, as shown in Figure 3(C), once the dedicated cutting tool 1000 reaches the end point of the return path (end position E), the return winding 300R shown in Figures 7 and 8 is formed, and a single heating element is embedded in the inner surface of the electrofusion joint from the start position S through the turn section T to the end position E, as the forward winding 300F, the turn section T, and the return winding 300R.

[0028] <Structure of specialized blades> The structural features of the special cutting tool 1000 used in the manufacturing method of the electrofusion joint described above will be explained in detail below with reference to Figures 5 and 6. As described above, the dedicated cutting tool 1000 has a structure that faces the inner circumferential surface of the rotating electrofusion joint, in the order of the cutting blade 1200, the heating wire supply hole 1210, and the pressing guide 1300. Furthermore, the shape of the cutting blade when viewed from the direction along the inner circumferential surface (the direction shown in Figures 5 to 6) is approximately V-shaped, and the tip of the approximately V-shape contacts the inner circumferential surface to cut the notch groove. Here, as shown in Figures 5 and 6, if the axial length of the dedicated blade 1000 is the blade width A, the axial width of the press guide 1300 is the press guide width E, and the wire diameter of the heating element 300 is the diameter d2, then it is preferable that the blade width A and the press guide width E are 10 times or more the diameter d2.

[0029] For an electrofusion joint with a nominal diameter of 250, the blade width A and the press guide width E were set to 10 mm as described above. However, the load on the dedicated blade 1000 was large when embedding the heating wire 300 by pressing and when making a U-turn (when forming the turn section T), causing deformation and damage to the pressing blade 1200. Therefore, to improve strength, the blade width A and the press guide width E were set to 15 mm. Here, these blade width A and press guide width E may vary depending on the nominal diameter of the electrofusion joint, but in this invention, attention is paid to the relationship with the diameter d2, which is the wire diameter of the heating wire 300 embedded in the inner circumferential surface of the electrofusion joint. Generally, a diameter d2 of about 0.7 mm to 1.1 mm is preferably used. In the case of 0.7 mm, A=E=15 mm and d2=0.7 mm, so 15 / 0.7=21.42. In the case of 1.1 mm, A=E=15 mm and d2=1.1 mm, so 15 / 1.1=13.64. In both cases, it is preferable that the blade width A and the presser guide width E are 10 times or more the diameter d2.

[0030] Furthermore, if the length in the inner circumferential direction from the cutting blade 1200 to the press guide 1300 is distance G, and the wire diameter of the heating element 300 is diameter d2, then it is preferable that the blade width A and the press guide width E are at least four times the diameter d2. When comparing distances G of 2 mm and 5 mm for an electrofusion joint with a nominal diameter of 250 mm, the shorter distance is undesirable because the embedding position of the heating wire 300 is shallower (the embedding position is closer to the inner surface of the joint and the heating wire is visible and not hidden), while the longer distance is preferable because it has a greater pressing effect (the heating wire is not visible and is hidden). Here, these distances G may change depending on the nominal diameter of the electrofusion joint, but in this invention, we focus on the relationship with the diameter d2, which is the wire diameter of the heating wire 300 embedded in the inner circumferential surface of the electrofusion joint. As mentioned above, if the diameter d2 is 0.7 mm and 1.1 mm, in the case of 0.7 mm, G = 5 mm and d2 = 0.7 mm, so 5 / 0.7 = 7.143, and in the case of 1.1 mm, G = 5 mm and d2 = 1.1 mm, so 5 / 1.1 = 4.545, and in both cases, it is preferable that the distance G is 4 times or more the diameter d2.

[0031] Furthermore, it is preferable that the angle α of the roughly V-shaped tip of the cutting blade 1200 is less than 80 degrees. When comparing an angle α of 80 degrees and 40 degrees for the cutting blade 1200 with an electrofusion joint of nominal diameter 250, a larger angle α is undesirable because it increases the groove width during U-turn (when the turn portion T is formed), causing the heating wire 300 to lift out of the groove and easily detach from it (this problem does not occur when the angle α is small). Therefore, in the present invention, it is preferable that the upper limit of this angle α is 80 degrees. Furthermore, it is preferable that the width of the cutting blade 1200 in the axial direction, on the side opposite to the tip, is defined as the cutting blade width B, and the height of the roughly V-shaped cutting blade 1200 is defined as the cutting blade height C, such that the cutting blade width B ≤ cutting blade height C × 0.75.

[0032] Regarding the approximately V-shaped tip bevel angle (angle α) of the cutting blade 1200, considering it from a different perspective, the following conclusion can be drawn. For an electrofusion joint with a nominal diameter of 250, in order to prevent the problem of the groove width becoming large during a U-turn (when the turn portion T is formed), causing the heating wire 300 to lift out of the groove and easily come off, it is preferable in this invention that the cutting blade width B ≤ cutting blade height C × 0.75. Furthermore, if the width of the cutting blade 1200 in the axial direction, on the side opposite to the tip, is defined as the cutting blade width B, the height of the roughly V-shaped cutting blade 1200 is defined as the cutting blade height C, and the diameter of the heating wire 300 is defined as diameter d2, then it is preferable that the cutting blade width B is 2.8 times or less the diameter d2, and the cutting blade height C is 3.6 times or more the diameter d2.

[0033] Regarding the approximately V-shaped tip bevel angle (angle α) of the push-cut blade 1200, considering it from another perspective, we can conclude the following. As mentioned above, in order to avoid the problem of the groove width becoming larger during U-turns (when the turn portion T is formed) for an electrofusion joint with a nominal diameter of 250, causing the heating wire 300 to lift out of the groove and easily come off, the value may vary depending on the nominal diameter of the electrofusion joint. However, in this invention, we focus on the relationship between the external dimensions of the push-cut blade 1200 (push-cut blade width B and push-cut blade height C, where B=3mm and C=4mm for a nominal diameter of 250) and the diameter d2 of the heating wire 300 embedded in the inner circumferential surface of the electrofusion joint. As mentioned above, if the diameter d2 is 0.7 mm and 1.1 mm, then in the case of 0.7 mm, B / d2 = 3 / 0.7 = 4.285 (4.3: rounded up) and C / d2 = 4 / 0.7 = 5.714 (5.7: rounded down), and in the case of 1.1 mm, B / d2 = 3 / 1.1 = 2.727 (2.8: rounded up) and C / d2 = 4 / 1.1 = 3.636 (3.6: rounded down). It is preferable that the cutting blade width B is 2.8 times the diameter d2 or less, and the cutting blade height C is 3.6 times the diameter d2 or more.

[0034] Furthermore, if the length of the cutting blade 1200 in the inner circumferential direction is the cutting blade length D, and the wire diameter of the heating element 300 is the diameter d2, then it is preferable that the cutting blade length D is 10 times or less the diameter d2. For an electrofusion joint with a nominal diameter of 250 mm, it is assumed that the shorter the cutting blade length D, the lower the load during U-turns (when forming the turn section T). However, since shortening the blade length reduces the rigidity of the cutting blade 1200, it is preferable to maintain a length of about 6 to 7 mm. Here, the cutting blade length D may vary depending on the nominal diameter of the electrofusion joint, but in this invention, we focus on the relationship with the diameter d2, which is the wire diameter of the heating wire 300 embedded in the inner circumferential surface of the electrofusion joint. As mentioned above, if the diameter d2 is 0.7 mm and 1.1 mm, in the case of 0.7 mm, D = 6 to 7 mm and d2 = 0.7 mm, so 8.57 (= 6 / 0.7) to 10 (= 7 / 0.7), and in the case of 1.1 mm, 5.45 (= 6 / 1.1) to 6.36 (= 7 / 1.1), and in both cases, it is preferable that the cutting blade length D is 10 times or less the diameter d2.

[0035] Furthermore, it is preferable that the diameter of the heating element supply section (more specifically, the diameters of the heating element introduction hole 1110 and the heating element supply hole 1210, and the communication holes provided inside the dedicated blade 1000 that connect these holes, which are the same diameter and may be represented by the diameter of the heating element supply hole 1210) be diameter d1, and the wire diameter of the heating element be diameter d2, with diameter d1 being at least twice the diameter d2.

[0036] Here, the relationship (difference, clearance) between diameter d1 and diameter d2 basically holds the same for electrofusion joints with different nominal diameters. Regarding diameter d2, which is the wire diameter of the heating wire 300, when the difference between diameter d1, which is the diameter of the heating wire supply section in the dedicated blade 1000, and diameter d2, which is the wire diameter of the heating wire 300, is about 0.4 mm, the resistance when the heating wire 300 passes through the dedicated blade 1000 is large and breakage of the heating wire was confirmed (diameter d1: 1.5 mm, diameter d2: 1.1 mm). When a clearance of about 0.8 mm was secured as the difference (diameter d1 - diameter d2) (diameter d1: 1.5 mm, diameter d2: 0.7 mm), breakage of the heating wire 300 was not confirmed. From these results, it is preferable to secure a clearance equivalent to the diameter d2, which is the wire diameter of the heating wire 300.

[0037] <Winding structure> The characteristics of the winding method used in the above-described method for manufacturing electrofusion joints and the characteristics of the winding structure of the electrofusion joints manufactured by this method will be described in detail below with reference to Figures 7 to 9. Figures 7 and 8 are diagrams illustrating the winding structures of electrofusion joints 100 and 200 according to this embodiment, and Figure 9 is a diagram illustrating the winding structure of an electrofusion joint according to a comparative example for comparison with them. Furthermore, in the winding structures in Figures 7 and 8, the position of the turn section T (the pitch of the turn section T) can be appropriately changed (within the range that satisfies the conditions shown below) depending on the operating status of the electrofusion joint manufacturing apparatus according to this embodiment.

[0038] As described above, in the fusion portion of the electrofusion joint, a total of four terminal pins 2000 are arranged on the end side (not the axial center side) of the electrofusion joint, two on each side. Therefore, the electrofusion joint 100 has a winding structure in which a single heating element 300 is embedded by a winding method in which a spiral progresses in the forward direction from the opening side of the opening to the opposite side of the opening, and a return direction in the opposite direction to the forward direction passes through a turn section T. This winding structure has the following features.

[0039] The fusion joint of an electrofusion joint includes, in both the forward and return paths, a first area in the axial center of the fusion joint where the helical pitch is formed at the same pitch, and a second area other than the center where the helical pitch is formed at up to twice the pitch of the same pitch. More specifically, the area of ​​the fusion joint of the electric fusion joint is divided into a first area in the axial center of the fusion joint and a second area including the start position S and end position E of the heating wire 300 and the turn section T, excluding the first area which is the central part. The spiral winding pitch in the first area is formed at the same pitch, while the spiral winding pitch in the second area is formed at up to twice the pitch of the same pitch in the first area.

[0040] As shown in Figure 9, when the winding pitch of the second area is approximately 3 to 5 times that of the first area, the heating element 300 tends to move outward during fusion, leading to overhang outside the electrical fusion joint and a tendency for short circuits to occur due to contact between the heating element and the forward / return winding. On the other hand, when the change in the winding pitch of the second area is small compared to that of the first area (the winding pitch of the second area is the same as the same pitch of the first area, or up to twice the same pitch of the first area), overhang of the heating element 300 and short circuits tend to be less likely to occur. For this reason, it is preferable to keep the winding pitch of the second area to be the same as (including the same) to about twice that of the winding pitch of the first area.

[0041] As shown in Figures 7 to 9, this is just one example of an electrofusion joint with a nominal diameter of 250, but the winding pitch is divided into the first area and the second area and is shown below. As shown in the forward winding of Figure 9(A), which is the winding structure of the electrofusion joint relating to the comparative example, the forward processing pitch is F(n)~F(n+1)=9.0mm (n=1~5) in the first area and F(0)~F(1)=14.5mm and F(6)~F(7)=20.5mm (turn section T) in the second area. Since the winding pitch of the second area (here, F(6)~F(7)=20.5mm (turn section T)) is 2.3 times the same pitch of the first area (here, F(n)~F(n+1)=9.0mm (n=1~5)), the winding pitch of the second area is not the same as the same pitch of the first area, and is at most twice as bad as the same pitch of the first area.

[0042] Furthermore, as shown in the return winding in Figure 9(B), the return winding pitch is R(n)~R(n+1)=9.0mm (n=1~5) in the first area, and R(0)~R(1)=35.0mm and F(6)~F(7)=15.0mm (turn section T) in the second area. Because the winding pitch of the second area (here, R(0)~R(1) = 35.0mm) is 3.9 times that of the same pitch in the first area (here, R(n)~R(n+1) = 9.0mm (n=1~5)), the winding pitch of the second area is not the same as that of the same pitch in the first area, and is at most twice as bad as that of the same pitch in the first area.

[0043] In the winding structure shown in Figure 9, the heating element 300 tends to move outward during fusion, leading to a tendency for it to protrude outside the electrical fusion joint and for short circuits to occur due to contact between the heating elements in the forward and return circuits. Next, as shown in the forward winding of Figure 7(A), which is the winding structure of the electrofusion joint 100 according to this embodiment, the forward processing pitch is F(n)~F(n+1)=13.0mm (n=0~3) for the first area and F(4)~F(5)=16.5mm (turn section T) for the second area, and the winding pitch of the second area satisfies (the same pitch as the first area, or) up to twice the same pitch as the first area.

[0044] Furthermore, as shown in the return winding in Figure 7(B), the return winding processing pitch satisfies the following conditions: the first and second areas have R(n)~R(n+1)=13.0mm (n=0~6: including the turn portion), and the winding pitch of the second area is the same as (or up to twice as) the same pitch of the first area. Furthermore, as shown in the forward winding of Figure 8(A), which is the winding structure of the electrofusion joint 200 according to this embodiment, the forward processing pitch is such that the first and second areas have a pitch of F(n)~F(n+1)=13.0mm (n=0~5: including the turn portion), and the winding pitch of the second area is the same as (or up to twice as) the same pitch of the first area.

[0045] Furthermore, as shown in the return winding in Figure 8(B), the return winding pitch is such that the first area is R(n)~R(n+1)=13.0mm (n=0~4), the second area is R(5)~R(6)=14.5mm (turn section T), and the winding pitch of the second area satisfies the condition that it is (same as the same pitch as the first area, or) up to twice the same pitch as the first area. Unlike the winding structure shown in the comparative example in Figure 9, the winding structures shown in Figure 7 and Figure 8 did not show a tendency for the heating wire 300 to easily move outward during fusion, resulting in overhang outside the electrofusion joint or short circuits due to contact between the heating wires in the forward and return paths.

[0046] Furthermore, as mentioned above, the second area, which is divided into the first and second areas, includes the transition section (turn section T) from the outbound to the return route. Furthermore, it is preferable that the pitch of this switching section (turn section T) is equal to or greater than the pitch of the first area. In the case of an electrofusion joint with a nominal diameter of 250, as an example, the pitch of the switching section (turn section T) is 16.5 mm relative to the same pitch of 13.0 mm in the first area, as shown in the forward winding of Figure 7(A), 13.0 mm relative to the same pitch of 13.0 mm in the first area, as shown in the return winding of Figure 7(B), 13.0 mm relative to the same pitch of 13.0 mm in the first area, as shown in the forward winding of Figure 8(A), and 14.5 mm relative to the same pitch of 13.0 mm in the first area, as shown in the return winding of Figure 8(B). Thus, the pitch of the switching section (turn section T) satisfies the requirement that it is greater than or equal to the same pitch of the first area.

[0047] As mentioned above, the winding structure in Figure 9 is undesirable because the winding pitch of the second area is the same as the same pitch as the first area, or does not satisfy the condition of being at most twice the same pitch as the first area. The pitch of the switching section (turn section T) in Figure 9 is 20.5 mm compared to the same pitch of 9.0 mm in the first area, as shown in the forward winding in Figure 9(A), and 15.0 mm compared to the same pitch of 9.0 mm in the first area, as shown in the return winding in Figure 9(B). Thus, the pitch of the switching section (turn section T) satisfies the condition that it is at least the same pitch as the first area. Therefore, if the winding structure in Figure 9 is changed so that the winding pitch of the second area is the same as the same pitch as the first area, or satisfies the condition of being at most twice the same pitch as the first area, it is possible to eliminate the tendency for the heating element 300 to easily move outward during fusion, which can lead to overhang outside the electric fusion joint and short circuits due to contact between the heating elements of the forward and return paths, thereby realizing a desirable winding structure.

[0048] The switching section (turn section T) is preferably formed as a semicircle with a diameter larger than half the same pitch in the first area. The switching section (turn section T) is preferably formed as a semicircle with a diameter of 150% or more of half of the same pitch in the first area. It is preferable.

[0049] In the case of an electrofusion joint with a nominal diameter of 250, as an example, the diameter of the semicircle of the switching portion (turn portion T) is 10.0 mm relative to the same pitch of 13.0 mm in the first area, as shown in the forward winding of Figure 7(A) for the first area, 10.0 mm relative to the same pitch of 13.0 mm in the first area, as shown in the return winding of Figure 7(B) for the first area, 10.0 mm relative to the same pitch of 13.0 mm in the first area, as shown in the forward winding of Figure 8(A) for the first area, and 10.0 mm relative to the same pitch of 13.0 mm in the return winding of Figure 8(B) for the first area, satisfying the requirement that the switching portion (turn portion T) is a semicircle with a diameter larger than half of the same pitch in the first area, and a semicircle with a diameter of 150% or more of half of the same pitch in the first area.

[0050] Furthermore, as mentioned above, the winding structure in Figure 9 is undesirable because the winding pitch of the second area is the same as the same pitch as the first area, or does not satisfy the condition that it is at most twice the same pitch as the first area. The diameter of the semicircle of the switching portion (turn portion T) in Figure 9 is 10.0 mm relative to the same pitch of 9.0 mm in the first area, as shown in the forward winding in Figure 9(A), and 10.0 mm relative to the same pitch of 9.0 mm in the first area, as shown in the return winding in Figure 9(B). The switching portion (turn portion T) satisfies the condition that it is a semicircle with a diameter larger than half the same pitch in the first area, and a semicircle with a diameter of 150% or more relative to half the same pitch in the first area. Therefore, regarding the winding structure in Figure 9, if the winding pitch of the second area is changed to be the same as the same pitch of the first area, or up to twice as large as the same pitch of the first area, it is possible to eliminate the tendency for the heating element 300 to move outward during fusion, which can lead to overhang outside the electrical fusion joint and short circuits due to contact between the heating elements in the forward and return paths, thereby achieving a desirable winding structure.

[0051] <Terminal pin structure> The structural features of the terminal pin 2000 that constitutes the electrofusion joint described above will be explained in detail below with reference to Figure 10. As described above, the electrofusion joint according to this embodiment does not have a connecting portion like that in Patent Document 1 on the central side in the axial direction, and instead has four terminal pins 2000 arranged in two places on the left and right ends of the electrofusion joint, with the left and right heating wires independent. Because it does not have through holes (holes that penetrate the outer and inner surfaces of the sleeve) for providing terminal pins on the central side, it has the characteristic of not affecting watertightness. These terminal pins 2000 are provided by cutting a spiral groove with the push-cutting blade 1200 of a dedicated cutting tool 1000, and at the same time the heating wire is fitted into the groove (after the process shown in Figures 2 and 3), the terminal pins 2000 shown in Figure 10 and the heating wire fitted into the inner surface are securely connected. Thus, the terminal pins 2000 of the electrofusion joint according to this embodiment have a structure that securely connects to the heating wire 300 embedded in the inner surface.

[0052] The terminal pin 2000 shown in Figure 10(A) and the terminal pin 2100 shown in Figure 10(B) are both terminal pins provided in the electrofusion joint according to this embodiment, but differ in the shape of the groove provided at the end 2030 on the heating element 300 side, which encloses the heating element 300 along its longitudinal direction. The terminal pin 2000 shown in Figure 10(A) has a groove 2032 without a taper, while the terminal pin 2100 shown in Figure 10(B) has a tapered groove 2132. This is the only difference between the terminal pins 2000 and 2100. Figure 10(C) shows the procedure for creating a hole for inserting the terminal pin and the procedure for inserting the terminal pin into the hole and enclosing the heating element 300 in the groove provided at the end 2030 on the heating element 300 side, thereby ensuring a secure connection between the terminal pin and the heating element 300. Note that terminal pins 2000 and 2100 may sometimes be described using terminal pin 2000 as a representative example.

[0053] The terminal pin 2000 is a roughly cylindrical, conductive (copper, lead, etc., may be used as the material for the terminal pin) inserted into a hole drilled in the outer surface of a thermoplastic resin pipe (pipe material, sleeve) so as to reach the heating element 300, and is used to supply electricity to the heating element 300 from an external power source. The end 2030 of the terminal pin 2000 on the heating element 300 side (more specifically, the lower end face of the roughly cylindrical shape) is provided with a groove 2032 (a tapered groove 2132 in the case of terminal pin 2100) that encloses the heating element 300 along the longitudinal direction of the heating element 300, and a mark indicating the direction of the groove 2032 (or tapered groove 2132) is placed at a position on the outer surface of the thermoplastic resin pipe opposite the end of the terminal pin 2000, where it is visible from the outer surface of the thermoplastic resin pipe when the terminal pin and the heating element are in contact. In this case, the mark indicates the direction of the groove 2032 (or tapered groove 2132) and is visible from the outer surface of the thermoplastic resin tube when the terminal pin 2000 (or terminal pin 2100) and the heating element 300 come into contact, thus ensuring that the heating element 300 is reliably enclosed within the groove 2032 (or tapered groove 2132).

[0054] Preferably, this mark is a marker groove 2012 located on the outer peripheral end 2010 (more specifically, the upper end face of a roughly cylindrical shape) and oriented in the same direction as the groove 2032 (or tapered groove 2132). In this case, as shown in Figures 10(A) and 10(B), the groove 2032 (or tapered groove 2132) and the marker groove 2012 are oriented in the same direction, and the marker groove 2012 is visible from the outer peripheral surface of the thermoplastic resin tube when the terminal pin 2000 (or terminal pin 2100) and the heating element 300 come into contact, thereby ensuring that the heating element 300 is reliably enclosed within the groove 2032 (or tapered groove 2132).

[0055] The cross-sectional shape of the tapered groove 2132 is preferably an inverted V-shape, where the groove width on the groove opening side is wider than the groove width at the groove bottom. This makes it possible to more reliably prevent poor electrical contact when the heating element 300 and the terminal pin 2000 are connected and fused by soldering. As described above, the terminal pins 2000 shown in Figure 10(A) and 2100 shown in Figure 10(B) are substantially cylindrical in shape and conductive. The end 2030 (lower end face) on the heating element 300 side has a groove 2032 (or tapered groove 2132) that encloses the heating element 300 along its longitudinal direction. A marker groove 2012 is provided on the outer surface side of the thermoplastic resin tube opposite to the end 2030, at a position visible from the outer surface of the thermoplastic resin tube when the terminal pin and the heating element are in contact (end 2010 (upper end face)), in the same direction as the groove 2032 (or tapered groove 2132). Furthermore, a flange 2020 is provided in the intermediate portion between the end 2010 (upper end face) and the end 2030 (lower end face) to prevent detachment.

[0056] The installation procedure for the terminal pin 2000 with this configuration will be explained with reference to Figure 10(C). In the procedure described below, steps (C1) to (C3) are performed before winding formation, and steps (C4) to (C5) are performed after winding formation (after the processes shown in Figures 2 and 3). The dimensions of each part are based on an electrofusion joint with a nominal diameter of 250 as an example. (C1) A hole with a diameter corresponding to the size (diameter) of the flange 2020 is drilled from the outer surface to the inner surface of the electrofusion joint 100. At this time, the depth of the hole is determined according to the position of the flange 2020. For example, if the maximum diameter of the flange 2020 is 10.5 mm, a hole with a diameter of 10 mm is drilled. Also, if the lowest end of the flange 2020 is 15 mm from the upper end face of the terminal pin 2000, a hole with a depth of 18 mm is drilled.

[0057] (C2) Stop the drill at the depth determined in (C1) above and chamfer the outer surface around the hole. For example, chamfer by 2 mm. (C3) Drill a hole in the electrofusion joint 100 from the outer surface toward the inner surface, with a diameter corresponding to the size (diameter) of the terminal pin 2000 below the flange 2020. For example, if the size (diameter) below the flange 2020 is 5mm to 6mm, drill an 8mm diameter hole through to the inner surface. Steps (C4) and (C5) that follow are post-winding processes as shown in Figures 2 and 3. (C4) Insert the terminal pin 2000 into the through hole. At this time, visually confirm the mark groove 2012 and insert the terminal pin 2000 into the through hole so that the groove 2032, which is provided in the same direction as the mark groove 2012, encloses the heating wire 300 (so that the groove 2032 encloses the heating wire 300 with the longitudinal direction of the heating wire 300 parallel to the mark groove 2012).

[0058] (C5) With the terminal pin 2000 inserted into the through hole and the heating element 300 enclosed in the groove 2032, the heating element 300 is soldered to connect the terminal pin 2000 and the heating element 300. Thus, the heating element 300 enclosed in the groove 2032 (or tapered groove 2132) and the terminal pin 2000 (or terminal pin 2100) are connected by soldering (this is just one example). However, the present invention is not limited to such soldering connections, and the following connections can be adopted. These connections other than soldering will be explained with reference to Figures 10(D) and 10(E). Although Figures 10(D) and 10(E) show the connection between the heating element 300 and the terminal pin 2100, the terminal pin 2000 may be used instead of the terminal pin 2100.

[0059] As shown in Figures 10(D) and 10(E), in the tapered groove 2132, it is preferable that the terminal pin 2100 and the heating element 300 are joined by a conductive connecting member having a shape that matches the shape of the tapered groove 2132 or the shape of the heating element 300, which then contacts and joins the terminal pin 2100 and the heating element 300. As such connecting members, as shown in Figure 10(D), the connecting member 2210 may have a hollow portion that encloses the cross-sectional shape of the vertical plane in the longitudinal direction of the heating element 300 and may be a substantially hollow cylindrical shape that matches the groove width, or as shown in Figure 10(E), the connecting member 2220 may have a substantially rectangular prism shape that matches the groove width. Terminal pin 2100 is preferable to terminal pin 2000 because, once the connecting members 2210 and 2220 are fitted into the tapered groove 2132, they are less likely to come out of the tapered groove 2132.

[0060] <Effects of the above-described embodiment> The method for manufacturing an electrofusion joint and the electrofusion joint having the above-described configuration provide the following effects. (1-1) By attaching a dedicated cutting tool to a general-purpose conventional lathe or NC lathe and rotating the sleeve, the heating wire can be installed (embedded) on the inner surface. This eliminates the need for injection molding equipment and dedicated heating wire winding equipment, making it possible to install and fix the heating wire. In particular, while injection molding required a dedicated mold for each size, the method for manufacturing electrofusion joints according to this embodiment makes it possible to manufacture electrofusion joints that match the sleeve diameter of the base material relatively easily. (1-2) By cutting a notch in the inner circumference of the sleeve with a cutting blade and inserting the heating wire while advancing a special cutting tool along the inner circumference, the heating wire can also be fixed when it passes through the press guide. As a result, grooving, heating wire installation, and fixing can be done in a single process. This makes it possible to shorten the manufacturing time. (1-3) Because the height of the cutting blade and the diameter and position of the holes through which the heating wire passes inside the dedicated cutting tool can be changed relatively easily, the embedding depth of the heating wire on the inner surface of the electrofusion joint and the diameter of the heating wire can be adjusted arbitrarily and relatively easily. (1-4) Because the shape of the cutting blade can be changed relatively easily to a shape other than a "approximately V-shape," such as a "conical shape," it is possible to reduce the resistance acting on the cutting blade when the winding pitch of the heating wire is greatly changed or the winding direction is drastically changed (such as when reversing by 180° to form a turn section T).

[0061] (2) In the electrofusion joint according to this embodiment, the area of ​​the fusion section is divided into a first area in the axial center of the fusion section and a second area including the start and end positions of the heating wires other than the first area which is the center, as well as the turn section. A winding structure is adopted in which the spiral winding pitch in the first area is formed at the same pitch, and the spiral winding pitch in the second area is at most twice the pitch of the same pitch in the first area. In other words, unlike the general winding structure in electrofusion joints, the winding pitch near the joint inlet (end) and the turn section (second area) is not larger than that of the central part of the fusion section (first area), but is kept at most twice as large (in order to keep the winding pitch small), so that the heating wires do not move outward during fusion, and it is less likely that they will protrude outside the electrofusion joint, and that short circuits due to contact between the heating wires in the forward and return paths will not occur. Furthermore, even if it does not significantly affect the quality of the joint, reducing the protrusion of the heating wire from the electrofusion joint improves the appearance. Also, when winding the heating wire, if the winding pitch is large, the load acting on the cutting blade of the specialized cutting tool increases because the force is applied in an oblique direction. By keeping the winding pitch the same or not exceeding twice that of the specialized cutting tool, wear and deformation of the cutting blade can be suppressed.

[0062] (3) When inserting the terminal pin into the hole (during driving), the terminal pin may rotate, preventing the heating wire from fitting into the groove, making it impossible to reliably connect the terminal pin to the heating wire. However, by adding a mark (mark groove) indicating the direction of the groove in a position visible from the outer surface of the electrofusion joint, it is possible to check whether the terminal pin is rotating during insertion, and the heating wire can be reliably contained within the groove. In addition, by connecting the terminal pin to the heating wire by means other than soldering, it is possible to more reliably avoid situations where the solder comes off during energization and the electrofusion process is interrupted. As a result, by reliably connecting the terminal pin and the heating wire, it is possible to prevent fusion problems at the construction site.

[0063] As described above, according to the electrofusion joint and the method for manufacturing the electrofusion joint according to this embodiment, an electrofusion joint is provided that has a structure in which a heating wire is fitted into a groove formed on the inner circumference of a thermoplastic resin pipe, and that the plastic pipe can be electrofused to one of the left and right sockets at a time (either both left and right are electrofused, or only one side is electrofused and the other is not), without increasing manufacturing costs or affecting watertightness, thereby providing a more reliable connection between the terminal pin and the heating wire.

[0064] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Industrial applicability]

[0065] The present invention is particularly preferable in that it provides an electrofusion joint having a structure in which a heating wire is fitted into a groove formed on the inner circumference of a thermoplastic resin pipe, and allows for electrofusion of the mating plastic pipe to be connected to one of the left and right sockets at a time (either both left and right are electrofused, or only one side is electrofused and the other is not), without increasing manufacturing costs or affecting watertightness, and with more reliable connection between the terminal pin and the heating wire. [Explanation of Symbols]

[0066] 100 Electric Fusion Joints 200 Electric Fusion Joints 300 heating wire 300F Outbound winding 300R return winding 1000 Specialized Blades 1100 Body part 1110 Heating wire introduction hole 1200 Cutting blade 1300 Pressing Guide 1600 Housing joint 2000 Terminal pins 3000 indicators

Claims

1. An electrofusion joint comprising a fusion section in which a heating wire is inserted into a spirally formed notched groove on the inner circumference of a thermoplastic resin pipe into which the resin pipe to be connected is inserted, wherein the resin pipe can be electrofused one socket at a time rather than both sockets simultaneously, The fusion portion is provided on both the left and right sides of the axial end of the electrofusion joint, independently, so as to be able to conduct electricity to the heating element. In the fusion portion, a forward path in which a spiral progresses from the opening side of the electric fusion joint to the opposite side of the opening, and a return path in the opposite direction to the forward path, are formed by a single heating wire. The electrofusion joint is provided with terminal pins on the forward start side and return end side of the single heating element, with two terminal pins each on the left and right end sides of the receiving sockets, and each electrofusion joint is provided with a total of two heating elements and a total of four terminal pins, and the axial central part of the electrofusion joint is not provided with heating elements or terminal pins. The fusion joint is characterized in that, in both the forward and return paths, it includes a first area in the axial center of the fusion joint where the helical pitch is formed at the same pitch, and a second area in the fusion joint other than the center where the helical pitch is formed to be up to twice as large as the same pitch and at a minimum the same pitch.

2. The electrofusion joint according to claim 1, characterized in that the second area includes a switching portion from the forward path to the return path.

3. The electrofusion joint according to claim 2, characterized in that the pitch of the switching portion is equal to or greater than the same pitch.

4. The electrofusion joint according to claim 2 or 3, characterized in that the switching portion includes a semicircle with a diameter larger than half of the same pitch.

5. The switching portion includes a semicircle with a diameter of 150% or more compared to half of the same pitch. The electrofusion joint according to claim 4, characterized in that...

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