Electrical fusion joint

Abstract

To avoid troubles occurring during construction or difficulty in transportation in an electro fusion joint.SOLUTION: An electro fusion joint 250 includes a fusion part in which a heating wire 300 is inserted into a cut groove spirally formed on an inner peripheral surface of a thermoplastic resin pipe into which a resin pipe to be connected thereto is inserted. The fusion part is provided on at least one of axial ends (both ends in this example) of the electro fusion joint 250 so as to be able to energize the heating wire 300 (via a terminal pin). At the fusion part, an outward path in which the spiral proceeds in an outward direction from the opening side of the electro fusion joint 250 to the opening side opposite to the opening and a return path provided in a reverse direction are formed by one heating wire 300. The electro fusion joint 250 includes recessed parts 252, in each of which the inner peripheral surface is recessed, on the inner peripheral surface at the opening side relative to the fusion part.SELECTED DRAWING: Figure 14

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 a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe.

Background Art

[0002] An electric fusion joint is usually manufactured by an injection molding method, and a heating wire is embedded in the inner peripheral portion of a joint body made of a thermoplastic resin such as polyethylene or polybutene. Such an electric fusion joint may be called an EF (ElectroFusion) joint, an EF socket, or the like. 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 spirally by cutting along the inner surface of a pipe made of a thermoplastic resin, and a heating wire is inserted into the concave groove has been provided. Although the manufacturing method of the electric fusion joint having this structure is simple, the manufacturing difficulty in mounting the heating wire so as not to float out of 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 a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe, in which the heating wire does not float out of the concave groove due to temperature changes in the storage environment, and no voids are generated at the fusion interface with the plastic pipe.

[0003] The electric fusion joint disclosed in this Patent Document 1 includes a thermoplastic resin tube into which a plastic tube is inserted, a U-shaped concave groove formed spirally on the inner peripheral surface of the resin tube with a small spiral pitch portion and a large spiral pitch portion, a tongue-shaped portion formed on both side surfaces of the concave groove opening, and a heating wire inserted into the concave groove. The width of the concave groove is formed to be the same as or slightly narrower than the diameter of the heating wire, the depth of the concave groove is formed to be deeper than the diameter of the heating wire, and the concave groove portion with a small spiral pitch is formed to be shallower than the concave groove portion with a large spiral pitch. The heating wire inserted into the concave groove portion with a small spiral pitch is embedded in the concave groove with the melted resin including the tongue-shaped portion, and the heating wire inserted into the concave groove portion with a large spiral pitch is pushed into the concave groove by the pressed tongue-shaped portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the electric fusion joint disclosed in this Patent Document 1, as described in paragraphs 0016 to 0018 of Patent Document 1, after preparing a thermoplastic resin sleeve and forming a U-shaped concave groove spirally on its inner peripheral surface by cutting, while pressing a pressing tool and moving it along the concave groove to deform the side wall to form a burr-like tongue-shaped portion flying out from the inner peripheral surface, and then inserting a heating wire over the entire length of the concave groove, it is manufactured through three steps. Therefore, the manufacturing cost tends to be high.

[0006] Moreover, the electric fusion joint disclosed in this 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 peripheral surface of the sleeve is divided into a left fusion part that melts and fuses the surface of the plastic pipe inserted from the left, a right fusion part that melts and fuses the surface of the plastic pipe inserted from the right, a left winding end between the left fusion part and the left connector pin (terminal pin), a right winding end between the right fusion part and the right connector pin (terminal pin), and a bridging part between the left fusion part and the right fusion part. The concave groove is continuously formed from the left winding end to the right winding end, and a single continuous heating wire is installed therein. That is, on the premise that plastic pipes are simultaneously fused to the left and right receiving ports of the electric fusion joint, a single continuous heating wire is wound in the same direction from left to right (or from right to left) on the inner surface of the joint.

[0007] In such a structure, there are the following problems: (1) Even if plastic pipes are fused and connected to both the left and right receiving ports, they must be fused simultaneously and cannot be fused one by one on each side; (2) It is not possible to fuse and connect a plastic pipe to only one of the left or right receiving ports (either the left or the right) and connect the plastic pipe or the like to the other receiving port by another connection method (a single-receiving-type electric fusion joint cannot be realized). Furthermore, the problems (1) and (2) above can be solved by arranging the left and right heating wires independently without providing a bridging part. In that case, however, one of the two terminal pins arranged in two places on the left and right will be arranged on the central part side in the axial direction of the electric fusion joint. In this case, since the terminal pin is installed in a through hole that penetrates the sleeve of the electric fusion joint, if the terminal pin is installed on the central part side of the electric fusion joint, there is a problem of the possibility of leading to water leakage due to this through hole. Therefore, a total of four terminal pins, two on each of the left and right, must be arranged so as not to affect the water tightness.

[0008] However, since the electric fusion joint disclosed in Patent Document 1 is only a joint for connecting two plastic pipes of a connection partner in series and simultaneously, Patent Document 1 does not disclose or suggest anything about arranging a total of four terminal pins, two by two, at two locations on the left and right, without providing such a crossing portion and independently of the left and right heating wires. In particular, when the terminal pins arranged in this way are connected to an external power source to supply power to the heating wires and the resin pipe (resin pipe) of the connection partner and the electric fusion joint are electrically fused, if the clearance between the resin pipe and the electric fusion joint is small, or if the electrical energy applied (supplied) by the electric fusion is large, the resin will be excessively melted, leading to problems during construction. Such electric fusion joints also have the problem that they are difficult to carry during handling (during production and construction) because they have no handles. However, Patent Document 1 does not disclose or suggest anything about such problems themselves or solutions to these problems.

[0009] The present invention has been developed in view of the above problems, and its object is to provide an electric fusion joint having a structure in which a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe, and capable of electrically fusing a plastic pipe of a connection partner to one of the left and right receiving ports, not both at the same time (even if both left and right are electrically fused, only one of the left and right needs to be electrically fused and the other does not need to be electrically fused), thereby avoiding troubles or difficulties during construction and enabling electric fusion.

Means for Solving the Problems

[0010] To achieve the above object, the electric fusion joint according to the present invention takes the following technical means. That is, the electric fusion joint according to the present invention is an electric fusion joint provided with a fusion part in which a heating wire is inserted into a notch groove formed in a spiral shape on the inner peripheral surface of a thermoplastic resin tube into which a resin tube of a connection partner is inserted. The fusion part is provided on at least one end side in the axial direction of the electric fusion joint so as to be able to energize the heating wire. In the fusion part, a forward path in which the spiral progresses in the forward path direction from the opening side of the electric fusion joint to the opening side on the opposite side of the opening and a return path in the direction opposite to the forward path direction are formed by a single heating wire, and the inner peripheral surface on the opening side of the fusion part is provided with a recess in which the inner peripheral surface is recessed.

[0011] Preferably, the recess can be configured to be provided over the entire circumference of the inner periphery. More preferably, the recess can be configured to also serve as a handle of the electric fusion joint.

Advantages of the Invention

[0012] According to the present invention, there is provided an electric fusion joint having a structure in which a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin tube, and the plastic tube of the connection partner can be electrically fused not simultaneously to both the left and right receiving ports but one by one to the left and right receiving ports (even if both the left and right are electrically fused, only one of the left and right may be electrically fused and the other may not be electrically fused), and an electric fusion joint that can avoid troubles or transportation difficulties during construction and can perform electric fusion can be provided.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 14

Mode for Carrying Out the Invention

[0014] Hereinafter, an electric fusion joint and a method for manufacturing the electric fusion joint according to an embodiment of the present invention will be described with reference to FIGS. 1 to 10. In these FIGS. 1 to 10, the same components are denoted by the same reference numerals and their functions are also the same, so there may be cases where they will not be repeatedly described. Here, the electric fusion joint according to the embodiment of the present invention is mainly an electric fusion joint for medium to large diameters (for example, an inner diameter of 300 mm or more). This electric fusion joint has a spiral groove (as an example, the cross-sectional shape of this groove is a V-groove because the cutting edge of a dedicated cutting tool to be described later is V-shaped when viewed from the direction along the inner peripheral surface) provided by cutting on the inner surface (which may be described as the inner peripheral surface) of a resin pipe (which may be described as a pipe material or a sleeve) made of a thermoplastic resin, and at the same time, an electric heating wire is inserted into this groove. Further, the electric fusion joint according to the embodiment of the present invention may be of a double-receiving type in which electric heating wires are provided independently on the left and right, or a single-receiving type in which electric heating wires are provided only on one side of the left and right. However, in the following, it will be described as a double-receiving type. That is, the electric fusion joint according to the present embodiment does not provide a bridging portion as in Patent Document 1 on the central portion side in the axial center direction, and the electric heating wires on the left and right are independent, and a total of four terminal pins, two on each of the left and right ends of the electric fusion joint, are arranged. Since it does not have a through hole (a hole penetrating the outer peripheral surface and the inner peripheral surface in the sleeve) for providing a terminal pin on the central portion side, it has the feature of not affecting the watertightness.

[0015] Also, as the electric fusion joint according to the present embodiment, FIGS. 1 shows electric fusion joints 100 and 200. These are two types of electric fusion joints having different winding structures (structures manufactured by winding methods in which the start position S and / or the end position E of the winding are different, and the winding pitch is different). 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 relates to a comparative example.

[0016] 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 using 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 a forward path from the end side to the central side and a 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. At the same time, after an electric heating wire is inserted (embedded, buried) into the groove, 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.

[0017] <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 an outer diameter of 315 mm of the resin pipe of the connection partner), 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 including the dedicated cutting tool 1000, etc., even if not noted, they are the numerical values for the electric fusion joint with this 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 representing the electric fusion joint 100. And an electric heating wire 300 is spirally embedded in its inner peripheral surface.

[0018] That is, this electric fusion joint 100 includes a fusion part in which an electric heating wire 300 is inserted into a notch groove formed in a spiral shape on the inner peripheral surface of a thermoplastic resin pipe (pipe material, sleeve) into which the resin pipe of the connection partner is inserted. This fusion part is provided on at least one (here both) end side in the axial direction of the electric fusion joint 100 so as to be energizable to the electric heating wire 300 (via the terminal pin 2000). In this fusion part, a forward path in which the spiral progresses in the forward path direction from the opening side of the electric fusion joint 100 to the opening side on the opposite side of the opening and a return path in the direction opposite to the forward path direction are formed by one electric heating wire 300.

[0019] More specifically, as shown in FIGS. 1(C) to 1(F), the electric fusion joint 100 includes a terminal pin 2000 (S side) on the start position S side (forward path start side) of one electric heating wire 300 on each of the left and right sides, and a terminal pin 2000 (E side) on the end position E side (return path end side). This terminal pin 2000 is a metal processed product, and although its detailed structure will be described later, it has a structure that is surely connected to the electric heating wire 300. Note that the terminal pins 2000 in the electric fusion joint 100 are at the same position in the circumferential direction and are displaced in the axial direction on the start position S side and the end position E side. In contrast, the terminal pins 2000 in the electric fusion joint 200 are arranged at substantially the same position in the axial direction and are displaced in the circumferential direction on the start position S side and the end position E side. In any of the electric fusion joints, in order not to affect the waterproofness, (since the electric fusion joint according to the present 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 (not the axial center side) of the electric fusion joint. In order to arrange the terminal pin 2000 at such a position, as shown in FIGS. 7 to 8, the winding structure includes a forward path winding, a turn portion T, and a return path winding.

[0020] The electric fusion joint 100 includes an indicator 3000 in which an injection molded product is embedded, corresponding to the positions of the left and right electric heating wires 300. At the time of electric fusion when power is supplied to the electric heating wire 300 via the terminal pin 2000, it is possible to confirm that the electric fusion has been performed by the indicator 3000 bulging.

[0021] <Manufacturing method of electric fusion joint> The electric fusion joint 100 according to the present embodiment having the above-described winding structure is embedded in the inner peripheral surface of the electric fusion joint so that one electric heating wire 300 includes a forward path winding, a turn portion, and a return path winding, by the manufacturing method of the electric fusion joint described below with reference to FIGS. 2 to 4. Note that a dedicated cutting tool 1000 used in the manufacturing method of the electric fusion joint described below is shown in FIGS. 5 to 6.

[0022] The manufacturing method of the electric fusion joint 100 according to this embodiment includes a joint setting step of setting a lathe to rotate an electric fusion joint (here, it is a hollow cylindrical pipe (sleeve) rather than a completed electric fusion joint, but the parentheses may not be described hereinafter), a tool setting step of setting a dedicated tool (dedicated tool 1000 shown in FIGS. 2 to 6) on the lathe, and a fusion part forming step of moving the dedicated tool 1000 axially while bringing it into contact with the inner peripheral surface of the electric fusion joint and rotating the electric fusion joint to form a fusion part. And this fusion part forming step includes a groove cutting step of cutting a notch groove on the inner peripheral surface with a cutting blade 1200 provided on the dedicated tool 1000, an electric heating wire insertion step of inserting an electric heating wire 300 into the notch groove from an electric heating wire supply hole 1210 provided on the dedicated tool 1000 (more specifically, discharging the electric heating wire 300 inserted from an electric heating wire introduction hole 1110 provided in the body part 1100 of the dedicated tool 1000 from the electric heating wire supply hole 1210 provided on the cutting blade 1200 of the dedicated tool 1000 and inserting the electric heating wire 300 into the notch groove), and an electric heating wire fixing step of pressing the notch groove into which the electric heating wire 300 is inserted together with the electric heating wire 300 by a pressing guide 1300 provided on the dedicated tool 1000 to fix the electric heating wire 300 in the notch groove. Here, in the tool setting step, the dedicated tool 1000 is set on the lathe so that a switching step of reversing the inner circumferential direction of the dedicated tool 1000 by 180 degrees and switching from the forward path to the return path (forming a turn part T described later) can be executed. In addition, the electric heating wire supply part may be described as being formed with the same diameter (d1 described later) formed by the electric heating wire introduction hole 1110, the electric heating wire supply hole 1210, and a communication hole provided inside the dedicated tool 1000 connecting these holes, or these same diameters d1 may be described by representing the diameter of the electric heating wire supply hole 1210.

[0023] Here, in the above-described joint setting step, the lathe on which the electric fusion joint is set is preferably a general-purpose lathe or an NC (Numerical Control) lathe. Further, as shown in the relationship between the dedicated cutting tool 1000 and the electric fusion joint in the forward path shown in FIG. 4(A) and the relationship between the dedicated cutting tool 1000 and the electric fusion joint in the return path shown in FIG. 4(B), the dedicated cutting tool 1000 has a structure facing the inner peripheral surface of the rotating electric fusion joint in the order of the cutting edge 1200, the heating wire supply hole 1210, and the pressing guide 1300. It is preferable that the direction from the heating wire introduction hole 1110 (entrance) to the heating wire supply hole 1210 (exit) provided in the dedicated cutting tool 1000 is the same as the direction in which the electric fusion joint rotates.

[0024] Also, as shown in FIG. 2(C), it is preferable that the fusion part forming step further includes a switching step of moving (parallel movement stop) the dedicated cutting tool 1000 in the axial direction and stopping the rotation (rotation stop) of the electric fusion joint, reversing the direction in the inner circumferential direction of the dedicated cutting tool 1000 by 180 degrees, and switching from the forward path to the return path (forming the turn part T described later). Referring to FIG. 2, the fusion part forming step in this manufacturing method will be described separately for the forward path winding formation and the return path winding formation.

[0025] As shown in FIG. 2(A), the dedicated cutting tool 1000 is positioned at the start position S of the forward path, and while bringing the dedicated cutting tool 1000 into contact with the inner peripheral surface of the electric fusion joint, the movement in the axial direction (parallel movement) is started, and at the same time, the rotation of the electric fusion joint (here, clockwise rotation when viewed from the left opening) is started. By starting the parallel movement of the dedicated cutting tool 1000 and the rotation of the electric fusion joint while bringing the dedicated cutting tool 1000 into contact with the inner peripheral surface of the electric fusion joint in this way, the forward path winding 300F starts to be embedded in the inner peripheral surface of the electric fusion joint from the start position S.

[0026] If the parallel movement speed of the dedicated cutting tool 1000 and the rotation speed of the electric fusion joint are controlled so as to form the forward path winding shown in FIGS. 7 to 8, the forward path winding 300F (specifically, the forward path winding in either FIG. 7(A) or FIG. 8(A)) is formed as shown in FIG. 2(B). Furthermore, as shown in FIG. 2(C), when the dedicated cutting tool 1000 reaches the end position of the forward path (the starting position of the semicircle of the turning portion T) and the forward path winding 300F shown in FIGS. 7 to 8 is formed, a switching step is executed. At this time, the parallel movement of the dedicated cutting tool 1000 and the rotation of the electric fusion joint are stopped, and the direction of the dedicated cutting tool 1000 in the inner circumferential direction is reversed by 180 degrees to form a turning portion T for switching from the forward path to the return path.

[0027] Next, as shown in FIG. 3(A), while bringing the dedicated cutting tool 1000 at the start position of the return path (the end position of the semicircle of the turning portion T) into contact with the inner circumferential surface of the electric fusion joint, the movement in the axial direction (parallel movement in the reverse direction of the forward path) is started, and the rotation of the electric fusion joint (here, rotation counterclockwise as viewed from the left opening) is started. In this way, while bringing the dedicated cutting tool 1000 into contact with the inner circumferential surface of the electric fusion joint, the parallel movement of the dedicated cutting tool 1000 (parallel movement in the reverse direction of the forward path so as to approach the dedicated cutting tool 1000 to the start position S) and the rotation of the electric fusion joint (reverse rotation of the forward path) are started, and the return path winding 300R starts to be embedded in the inner circumferential surface of the electric fusion joint from the end position of the turning portion T.

[0028] When the parallel movement speed of the dedicated cutting tool 1000 and the rotation speed of the electric fusion joint are controlled so as to form the return path winding shown in FIGS. 7 to 8, the return path winding 300R (specifically, the return path winding in either FIG. 7(B) or FIG. 8(B)) is formed as shown in FIG. 3(B). Furthermore, as shown in FIG. 3(C), when the dedicated cutting tool 1000 reaches the end point (end position E) of the return path and the return path winding 300R shown in FIGS. 7 to 8 is formed, one heating wire is embedded in the inner circumferential surface of the electric fusion joint as the forward path winding 300F, the turning portion T, and the return path winding 300R from the start position S through the turning portion T to the end position E.

[0029] <Structure of the dedicated cutting tool> The structural features of the dedicated cutting tool 1000 used in the above-described method for manufacturing an electric fusion joint will be described in detail below with reference to FIGS. 5 to 6. As described above, the dedicated cutting tool 1000 has a structure that faces the inner peripheral surface of the rotating electric fusion joint in the order of the cutting blade 1200, the heating wire supply hole 1210, and the pressing guide 1300. Further, the shape of the cutting blade as viewed from the direction along the inner peripheral surface (the direction shown in FIGS. 5 to 6) is substantially V-shaped, and the tip side of the substantially V-shaped blade abuts against the inner peripheral surface to cut the notch groove. Here, as shown in FIGS. 5 to 6, taking the axial length of the dedicated cutting tool 1000 as the tool width A, the axial width of the pressing guide 1300 as the pressing guide width E, and the wire diameter of the heating wire 300 as the diameter d2, it is preferable that the tool width A and the pressing guide width E are 10 times or more the diameter d2.

[0030] For the electric fusion joint with a nominal diameter of 250, the above-mentioned tool width A and pressing guide width E were set to 10 mm. However, due to the large load on the dedicated cutting tool 1000 during the embedding and U-turn (formation of the turn portion T) of the heating wire 300 by pressing, the cutting blade 1200 was deformed and damaged. Therefore, for the purpose of improving strength, the tool width A and the pressing guide width E are set to 15 mm. Here, although these tool width A and pressing guide width E may vary depending on the nominal diameter of the electric fusion joint, in the present 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 peripheral surface of the electric fusion joint. This diameter d2 is generally preferably used in the range of about 0.7 mm to 1.1 mm. In the case of 0.7 mm, A = E = 15 mm, d2 = 0.7 mm, and 15 / 0.7 = 21.42. In the case of 1.1 mm, A = E = 15 mm, d2 = 1.1 mm, and 15 / 1.1 = 13.64. In both cases, it is preferable that the tool width A and the pressing guide width E are 10 times or more the diameter d2.

[0031] Furthermore, taking the length in the inner peripheral surface direction from the cutting blade 1200 to the pressing guide 1300 as the distance G and the wire diameter of the heating wire 300 as the diameter d2, it is preferable that the tool width A and the pressing guide width E are 4 times or more the diameter d2. When comparing the distance G at 2 mm and 5 mm for an electric fusion joint with a nominal diameter of 250, the shorter distance results in a shallower embedding position of the heating wire 300 (the embedding position is closer to the inner surface of the joint and the heating wire can be visually confirmed and not hidden), which is not preferable. The longer distance has a greater pressing effect (the heating wire cannot be visually confirmed and is hidden), which is preferable. Here, although these distances G may vary depending on the nominal diameter of the electric fusion joint, in the present 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 peripheral surface of the electric fusion joint. As described above, when the diameter d2 is 0.7 mm and 1.1 mm, in the case of 0.7 mm, G = 5 mm, d2 = 0.7 mm, and 5 / 0.7 = 7.143. In the case of 1.1 mm, G = 5 mm, d2 = 1.1 mm, and 5 / 1.1 = 4.545. In both cases, it is preferable that the distance G is more than 4 times the diameter d2.

[0032] Furthermore, regarding the tip opening angle of the substantially V-shaped tip of the cutting blade 1200 as the angle α, this angle α is preferably less than 80 degrees. When comparing the angle α of the cutting blade 1200 at 80 degrees and 40 degrees for an electric fusion joint with a nominal diameter of 250, the larger the angle α, the larger the groove width during U-turn (when forming the turn portion T), and the heating wire 300 is likely to protrude from the groove and come off the groove, which is not preferable (since such problems do not occur when the angle α is smaller). In the present invention, it is preferable that the upper limit of this angle α is 80 degrees.

[0033] Furthermore, regarding the width in the axial direction of the cutting blade 1200, which is the width on the side opposite to the tip side, as the cutting blade width B, and the height of the substantially V-shaped cutting blade 1200 as the cutting blade height C, it is preferable that the cutting blade width B ≤ the cutting blade height C × 0.75. Regarding the tip opening angle (angle α) of the substantially V-shaped tip of the cutting blade 1200 of the cutting blade 1200, considering from another perspective, the following judgment can be made. For an electric fusion joint with a nominal diameter of 250, in order not to cause the problem that the groove width during U-turn (when forming the turn portion T) becomes large and the heating wire 300 protrudes from the groove and easily comes off the groove, in the present invention, it is preferable that the cutting blade width B ≤ the cutting blade height C × 0.75. Furthermore, taking the axial width of the cutting blade 1200 on the side opposite to the tip side as the cutting blade width B, the height of the substantially V-shaped cutting blade 1200 as the cutting blade height C, and the wire diameter of the heating wire 300 as the diameter d2, 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.

[0034] Regarding the tip opening angle (angle α) of the substantially V-shaped cutting blade 1200 of the cutting blade 1200, considering from another perspective, the following judgment can be made. As described above, from the perspective of not causing the problem that the groove width increases during a U-turn (when forming the turn portion T) and the heating wire 300 floats out of the groove and is likely to come off the groove for an electric fusion joint with a nominal diameter of 250, although it may vary depending on the nominal diameter of the electric fusion joint, in the present invention, attention is paid to the relationship between the outer dimensions of the cutting blade 1200 (the cutting blade width B and the cutting blade height C, where B = 3 mm and C = 4 mm for a nominal diameter of 250) and the wire diameter of the heating wire 300 embedded in the inner peripheral surface of the electric fusion joint, which is the diameter d2. As described above, when the diameter d2 is 0.7 mm or 1.1 mm, in the case of 0.7 mm, B / d2 = 3 / 0.7 = 4.285 (4.3: rounded up), 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), C / d2 = 4 / 1.1 = 3.636 (3.6: rounded down). 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.

[0035] Furthermore, taking the length of the inner peripheral surface direction of the cutting blade 1200 as the cutting blade length D and the wire diameter of the heating wire 300 as the diameter d2, it is preferable that the cutting blade length D is 10 times or less the diameter d2. For an electric fusion joint with a nominal diameter of 250, it is assumed that the cutting blade length D should be as short as possible so that the load during a U-turn (when forming the turning part T) is reduced. However, if it is made too short, the rigidity of the cutting blade 1200 will decrease, so it is preferable to ensure a length of about 6 to 7 mm. Here, although the cutting blade length D may vary depending on the nominal diameter of the electric fusion joint, in the present invention, attention is paid to the relationship with the wire diameter d2 of the heating wire 300 embedded in the inner peripheral surface of the electric fusion joint. As described above, when the diameter d2 is 0.7 mm or 1.1 mm, in the case of 0.7 mm, D = 6 to 7 mm, d2 = 0.7 mm, and 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). In either case, it is preferable that the cutting blade length D is 10 times or less the diameter d2.

[0036] Furthermore, taking the diameter of the heating wire supply part (more specifically, the diameter of the heating wire introduction hole 1110, the heating wire supply hole 1210, and the communication hole provided inside the dedicated cutting tool 1000 connecting these holes, which are of the same diameter and may be represented by the diameter of the heating wire supply hole 1210) as diameter d1 and the wire diameter of the heating wire as diameter d2, it is preferable that the diameter d1 is 2 times or more the diameter d2.

[0037] Here, regarding the relationship (difference, clearance) between the diameter d1 and the diameter d2, the same relationship basically holds for electric fusion joints with different nominal diameters. Regarding the diameter d2, which is the wire diameter of the heating wire 300, when the difference between the diameter d1, which is the diameter of the heating wire supply part in the dedicated cutting tool 1000, and the 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 cutting tool 1000 is large and the breakage of the heating wire is confirmed (diameter d1: 1.5 mm, diameter d2: 1.1 mm). When a clearance of about 0.8 mm is ensured for these differences (diameter d1 - diameter d2) (diameter d1: 1.5 mm, diameter d2: 0.7 mm), the breakage of the heating wire 300 is not confirmed. From these facts, it is preferable to ensure a clearance equivalent to the diameter d2, which is the wire diameter of the heating wire 300.

[0038] <Winding Structure> Regarding the characteristics of the winding method used in the above-described method for manufacturing an electric fusion joint and the characteristics of the winding structure of the electric fusion joint manufactured by the manufacturing method, a detailed description will be given below with reference to FIGS. 7 to 9. FIGS. 7 and 8 are diagrams for explaining the winding structures of the electric fusion joints 100 and 200 according to the present embodiment, and FIG. 9 is a diagram for explaining the winding structure of an electric fusion joint according to a comparative example for comparison with them. Further, in the winding structures in FIGS. 7 and 8, the position of the turn portion T (the pitch of the turn portion T) can be appropriately changed according to the operating conditions of the manufacturing apparatus for the electric fusion joint according to the present embodiment (within a range satisfying the conditions shown below).

[0039] As described above, in the fusion portion of the electric fusion joint, in order to arrange a total of four terminal pins 2000, two at each of the left and right positions, on the end side (not the axial center portion side) of the electric fusion joint, a winding structure in which one heating wire 300 is embedded by a winding method in which a forward path in which a spiral advances in the forward path direction from the opening side of the electric fusion joint 100 to the opening side on the opposite side of the opening and a return path in the opposite direction of the forward path direction pass through the turn portion T is provided. This winding structure has the following characteristics.

[0040] The fusion portion of the electric fusion joint includes a first area at the axial center of the fusion portion where the spiral pitch is formed at the same pitch for both the forward path and the return path, and a second area other than the central portion where the spiral pitch is formed at a pitch that is at most twice the same pitch. More specifically, the area in the fusion portion of the electric fusion joint is divided into a first area at the axial center of the fusion portion and a second area including the start position S and the end position E of the heating wire 300 and the turn portion T other than the first area which is the central portion. The spiral winding pitch in the first area is formed at the same pitch, and the spiral winding pitch in the second area is formed at a pitch that is at most twice the same pitch in the first area.

[0041] With respect to the winding pitch of the first area, as shown in FIG. 9, when the winding pitch of the second area is about 3 to 5 times that of the first area, the heating wire 300 tends to move outward during fusion welding, and there is a tendency that the heating wire may protrude outside the electric fusion joint or a short circuit may occur due to the contact of the heating wire in the forward and return paths. On the other hand, when the change in the winding pitch of the second area with respect to the winding pitch of the first area is small (the winding pitch of the second area is the same as the same pitch of the first area, or at most 2 times the same pitch of the first area), there is a tendency that the heating wire 300 is less likely to protrude or short-circuit. Therefore, it is preferable to suppress the winding pitch of the second area to be equal (including the same) to about 2 times the winding pitch of the first area.

[0042] Although it is an example because it is the case of the electric fusion joint with a nominal diameter of 250 shown in FIGS. 7 to 9, the winding pitch is divided into the first area and the second area and is shown below. As shown in the forward winding of FIG. 9(A) which is the winding structure of the electric fusion joint according to the comparative example, the forward processing pitch is such that the first area is F(n)~F(n + 1)=9.0 mm (n = 1~5), and the second area is F(0)~F(1)=14.5 mm and F(6)~F(7)=20.5 mm (turn part T). Since the winding pitch of the second area (here F(6)~F(7)=20.5 mm (turn part T)) is 2.3 times the same pitch of the first area (here F(n)~F(n + 1)=9.0 mm (n = 1~5)), the winding pitch of the second area is not the same as the same pitch of the first area and does not satisfy even at most 2 times the same pitch of the first area.

[0043] Also, as shown in the return winding of FIG. 9(B), the return processing pitch is such that the first area is R(n)~R(n + 1)=9.0 mm (n = 1~5), and the second area is R(0)~R(1)=35.0 mm and F(6)~F(7)=15.0 mm (turn part T). Since the winding pitch of the second area (here 35.0 mm of R(0)~R(1)) is 3.9 times the same pitch of the first area (here 9.0 mm of R(n)~R(n + 1) (n = 1~5)), the The winding pitch is not the same as the same pitch in the first area and does not satisfy up to twice the same pitch in the first area at most.

[0044] In the winding structure shown in FIG. 9, when fusing, the heating wire 300 tends to move outward easily, and there is a tendency that the heating wire protrudes outside the electric fusion joint or a short circuit occurs due to the contact of the heating wire in the forward and return paths. Next, as shown in the forward winding of FIG. 7(A) which is the winding structure of the electric fusion joint 100 according to the present embodiment, the forward processing pitch is such that the first area is F(n)~F(n + 1)=13.0 mm (n = 0~3), the second area is F(4)~F(5)=16.5 mm (turn portion T), and the winding pitch of the second area satisfies (the same as the same pitch in the first area, or) up to twice the same pitch in the first area at most.

[0045] Also, as shown in the return winding of FIG. 7(B), the return processing pitch is such that the first area and the second area are R(n)~R(n + 1)=13.0 mm (n = 0~6 including the turn portion), and the winding pitch of the second area satisfies the same as the same pitch in the first area (or up to twice the same pitch in the first area at most). Furthermore, as shown in the forward winding of FIG. 8(A) which is the winding structure of the electric fusion joint 200 according to the present embodiment, the forward processing pitch is such that the first area and the second area are F(n)~F(n + 1)= 9 .0 mm (n = 0~5 including the turn portion), and the winding pitch of the second area satisfies the same as the same pitch in the first area (or up to twice the same pitch in the first area at most).

[0046] Also, as shown in the return winding of FIG. 8(B), the return processing pitch is such that the first area is R(n)~R(n + 1)= 9 .0 mm (n = 0~4), the second area is R(5)~R(6)=14.5 mm (turn portion T), and the winding pitch of the second area satisfies (the same as the same pitch in the first area, or) up to twice the same pitch in the first area at most. In the winding structures shown in these Figures 7 and the winding structure shown in Figure 8, unlike the winding structure according to the comparative example shown in Figure 9, when fusing, the heating wire 300 is less likely to move outward, and there is no tendency for the heating wire to protrude outside the electric fusion joint or for a short circuit (short) to easily occur due to contact between the heating wires in the forward and return paths.

[0047] Also, as described above, the second area divided into the first area and the second area includes a switching portion (turn portion T) from the forward path to the return path. Furthermore, it is preferable that the pitch of this switching portion (turn portion T) is equal to or greater than the same pitch in the first area. In the case of an electric fusion joint with a nominal diameter of 250, although it is an example, the pitch of the switching portion (turn portion T) is 16.5 mm with respect 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 with respect to the same pitch of 13.0 mm in the first area as shown in the return winding of Figure 7(B), 9 .0 mm with respect to 9 .0 mm, and as shown in the return winding of Figure 8(B), 9 .0 mm with respect to 14.5 mm, and the pitch of the switching portion (turn portion T) satisfies the condition of being equal to or greater than the same pitch in the first area.

[0048] Note that, as described above, the winding pitch in the second area is the same as the same pitch in the first area or is not preferably less than the maximum of twice the same pitch in the first area. The pitch of the switching portion (turn portion T) in FIG. 9 showing a winding structure that is not preferable is 20.5 mm with respect to the same pitch of 9.0 mm in the first area as shown in the forward winding of FIG. 9(A), and 15.0 mm with respect to the same pitch of 9.0 mm in the first area as shown in the return winding of FIG. 9(B). The pitch of the switching portion (turn portion T) satisfies the condition of being equal to or greater than the same pitch in the first area. Therefore, with respect to the winding structure in FIG. 9, if the winding pitch in the second area is changed to be the same as the same pitch in the first area or to satisfy a maximum of twice the same pitch in the first area, it is possible to eliminate the tendency for the heating wire 300 to easily move outward during fusion and for protrusion outside the electric fusion joint or short circuit (short) due to contact between the forward and return heating wires to easily occur, and a preferable winding structure can be realized.

[0049] The switching portion (turn portion T) is preferably formed as a semi-circle with a diameter larger than half of the same pitch in the first area. The switching portion (turn portion T) is preferably formed as a semi-circle with a diameter of 150% or more with respect to half of the same pitch in the first area. is preferable.

[0050] In the case of an electric fusion joint with a nominal diameter of 250, although it is an example, the diameter of the semi-circle of the switching portion (turn portion T) is 10.0 mm with respect to the same pitch of 13.0 mm in the first area as shown in the forward winding of FIG. 7(A), 10.0 mm with respect to the same pitch of 13.0 mm in the first area as shown in the return winding of FIG. 7(B), 10.0 mm with respect to the same pitch of 9 .0 mm in the first area as shown in the forward winding of FIG. 8(A), and the same pitch in the first area as shown in the return winding of FIG. 8(B) 9It is 10.0 mm with respect to 0.0 mm, and the switching portion (turn portion T) satisfies being a semi - circle with a diameter larger than half of the same pitch in the first area and a semi - circle with a diameter 150% or more of half of the same pitch in the first area.

[0051] As described above, in FIG. 9 showing a winding structure that is not preferable in that the winding pitch of the second area is the same as the same pitch of the first area or does not satisfy up to twice the same pitch of the first area at most, the diameter of the semi - circle of the switching portion (turn portion T) is 10.0 mm with respect to the same pitch of 9.0 mm in the first area as shown in the forward winding of FIG. 9(A), and 10.0 mm with respect to the same pitch of 9.0 mm in the first area as shown in the return winding of FIG. 9(B). The switching portion (turn portion T) satisfies being a semi - circle with a diameter larger than half of the same pitch in the first area and a semi - circle with a diameter 150% or more of half of the same pitch in the first area. Therefore, for the winding structure in FIG. 9, if the winding pitch of the second area is changed so as to satisfy being the same as the same pitch of the first area or up to twice the same pitch of the first area at most, it is possible to eliminate the tendency that the heating wire 300 is likely to move outward during fusion and there is a risk of the heating wire protruding outside the electric fusion joint, and a short - circuit (short) is likely to occur due to the contact of the heating wire in the forward and return paths, and a preferable winding structure can be realized.

[0052] <Terminal pin structure> Regarding the structural features of the terminal pin 2000 constituting the above - mentioned electric fusion joint, it will be described in detail below with reference to FIG. 10. As described above, the electric fusion joint according to the present embodiment does not provide a bridging portion such as that in Patent Document 1 on the central portion side in the axial center direction, but rather separates the left and right heating wires and arranges a total of four terminal pins 2000, two on each of the left and right ends of the electric fusion joint. Since it does not have a through hole (a hole penetrating the outer peripheral surface and the inner peripheral surface of the sleeve) for providing a terminal pin on the central portion side, it has the characteristic of not affecting the watertightness. These terminal pins 2000 are provided with spiral grooves cut by the cutting edge 1200 of the dedicated tool 1000, and after inserting the heating wires into the grooves (after the steps shown in FIGS. 2 and 3), the terminal pins 2000 shown in FIG. 10 are surely connected to the heating wires inserted into the inner peripheral surface. Thus, the terminal pins 2000 included in the electric fusion joint according to the present embodiment have a structure that is surely connected to the heating wire 300 embedded in the inner peripheral surface.

[0053] The terminal pin 2000 shown in FIG. 10(A) and the terminal pin 2100 shown in FIG. 10(B) are both terminal pins included in the electric fusion joint according to the present embodiment, and are provided at the end 2030 on the heating wire 300 side, and the shapes of the grooves that enclose the heating wire 300 along the longitudinal direction of the heating wire 300 are different. The terminal pin 2000 shown in FIG. 10(A) has a groove 2032 without a taper, and the terminal pin 2100 shown in FIG. 10(B) has a tapered groove 2132 with a taper. This is the only difference between the terminal pin 2000 and the terminal pin 2100. Also, FIG. 10(C) shows the procedure for providing a perforation for inserting the terminal pin and the procedure for inserting the terminal pin into the perforation and enclosing the heating wire 300 in the groove provided at the end 2030 on the heating wire 300 side to surely connect the terminal pin and the heating wire 300. Note that the terminal pin 2000 and the terminal pin 2100 may be described by representing them with the terminal pin 2000.

[0054] This terminal pin 2000 is inserted into a hole drilled so as to reach the heating wire 300 from the outer peripheral surface of a thermoplastic resin tube (pipe material, sleeve), and has a substantially cylindrical shape for supplying electricity from an external power source to the heating wire 300 and has conductivity (for example, copper, lead, etc. can be used as the material of the terminal pin). At the end 2030 on the heating wire 300 side of the terminal pin 2000 (this end 2030 is more specifically the lower end surface of a substantially cylindrical shape), a groove 2032 (a tapered groove 2132 in the case of the terminal pin 2100) that encloses the heating wire 300 along the longitudinal direction of the heating wire 300 is provided. A mark indicating the direction of the groove 2032 (or the tapered groove 2132) is provided at a position on the outer peripheral surface side of the thermoplastic resin tube on the side opposite to the end of the terminal pin 2000 where the terminal pin and the heating wire are in contact and is visible from the outer peripheral surface of the thermoplastic resin tube. In this case, this mark indicates the direction of the groove 2032 (or the tapered groove 2132), and since it is visible from the outer peripheral surface of the thermoplastic resin tube when the terminal pin 2000 (or the terminal pin 2100) and the heating wire 300 are in contact, the heating wire 300 can be surely enclosed in the groove 2032 (or the tapered groove 2132).

[0055] This mark is preferably a mark groove 2012 provided at the end 2010 on the outer peripheral surface side (this end 2010 is more specifically the upper end surface of a substantially cylindrical shape) and having the same direction as the groove 2032 (or the tapered groove 2132). In this case, as shown in FIGS. 10(A) and 10(B), the groove 2032 (or the tapered groove 2132) and the mark groove 2012 are in the same direction, and since the mark groove 2012 is visible from the outer peripheral surface of the thermoplastic resin tube when the terminal pin 2000 (or the terminal pin 2100) and the heating wire 300 are in contact, the heating wire 300 can be surely enclosed in the groove 2032 (or the tapered groove 2132).

[0056] The cross-sectional shape of the tapered groove 2132 is preferably a substantially inverted V-shaped shape in which the groove width on the groove opening side is wider than the groove width at the groove bottom. This can more reliably prevent poor conduction when the heating wire 300 and the terminal pin 2000 are connected and fused by soldering. As described above, the terminal pin 2000 shown in Fig. 10(A) and the terminal pin 2100 shown in Fig. 10(B) have a substantially cylindrical shape and are conductive. At the end 2030 (lower end face) on the side of the heating wire 300, a groove 2032 (or tapered groove 2132) that encloses the heating wire 300 along the longitudinal direction of the heating wire 300 is provided. At a position on the outer peripheral surface side of the thermoplastic resin tube on the side opposite to this end 2030, at a position where the terminal pin and the heating wire are in contact and visible from the outer peripheral surface of the thermoplastic resin tube (end 2010 (upper end face)), a mark groove 2012 in the same direction as the groove 2032 (or tapered groove 2132) is provided. Further, a retaining flange 2020 is provided at an intermediate portion between the end 2010 (upper end face) and the end 2030 (lower end face).

[0057] The installation procedure of the terminal pin 2000 having such a configuration will be described with reference to Fig. 10(C). In the procedure described below, (C1) to (C3) are carried out before the winding formation, and (C4) to (C5) are carried out after the winding formation (after the steps shown in Figs. 2 and 3). Also, for each part dimension, an electrical fusion joint with a nominal diameter of 250 is taken as an example.

[0058] (C1) Drill a hole with a diameter corresponding to the size (diameter) of the flange 2020 from the outer peripheral surface to the inner peripheral surface of the electrical fusion joint 100. At this time, the depth of the hole is determined according to the position of the flange 2020. For example, a hole with a diameter of 10 mm is drilled for the maximum diameter of the flange 2020 being 10.5 mm. Also, a hole with a depth of 18 mm is drilled for the lowermost end of the flange 2020 being at a position 15 mm from the upper end face of the terminal pin 2000. (C2) Stop the drill at the depth determined in (C1) above, and chamfer the periphery of the hole on the outer peripheral surface. For example, chamfer it by 2 mm.

[0059] (C3) Drill a hole with a diameter corresponding to the size (diameter) below the flange 2020 of the terminal pin 2000 from the outer peripheral surface to the inner peripheral surface of the electric fusion joint 100. For example, when the size (diameter) below the flange 2020 is 5 mm to 6 mm, drill a hole with a diameter of 8 mm through to the inner peripheral surface. (C4) and (C5) hereafter are the processes after the winding process shown in FIGS. 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 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 and the mark groove 2012 being parallel).

[0060] (C5) In the terminal pin 2000 inserted into the through hole with the heating wire 300 enclosed in the groove 2032, solder the heating wire 300 to connect the terminal pin 2000 and the heating wire 300. In this way, the heating wire 300 enclosed in the groove 2032 (or the tapered groove 2132) and the terminal pin 2000 (or the terminal pin 2100) are connected by soldering (although it is an example). However, the present invention is not limited to such connection by soldering, and the following connections can be adopted. The connection other than this soldering will be described with reference to FIGS. 10(D) and 10(E). Note that FIGS. 10(D) and 10(E) describe the connection between the heating wire 300 and the terminal pin 2100, but it may be the terminal pin 2000 instead of the terminal pin 2100.

[0061] As shown in FIGS. 10(D) and 10(E), for the joining of the terminal pin 2100 and the heating wire 300 in the tapered groove 2132, it is preferable that a connecting member having conductivity with a shape matching the shape of the tapered groove 2132 or the shape of the heating wire 300 abuts against the terminal pin 2100 and the heating wire 300 and is joined. As such a connecting member, as shown in FIG. 10(D), the connecting member 2210 may have a substantially hollow cylindrical shape that encloses the cross-sectional shape of the heating wire 300 in a plane perpendicular to the longitudinal direction thereof and matches the groove width, or, as shown in FIG. 10(E), the connecting member 2220 may have a substantially prismatic shape that matches the groove width. Note that it is preferable that the terminal pin 2100 is more difficult to come out of the tapered groove 2132 than the terminal pin 2000 when the connecting members 2210 and 2220 are fitted into the tapered groove 2132.

[0062] <The effects of the above-described embodiments> According to the method for manufacturing an electric fusion joint and the electric fusion joint having the above-described configuration, the following effects can be obtained. (1-1) By attaching a dedicated cutting tool to a general-purpose ordinary lathe or NC lathe and rotating the sleeve, the heating wire can be installed (embedded) on the inner peripheral surface without using injection molding equipment and dedicated heating wire winding processing equipment, enabling the installation and fixing of the heating wire. In particular, in the case of injection molding, a dedicated mold for each size was required, but according to the method for manufacturing an electric fusion joint according to the present embodiment, it is possible to relatively easily manufacture an electric fusion joint that matches the sleeve diameter of the base material. (1-2) By notching the inner peripheral surface of the sleeve with a cutting blade and advancing the dedicated cutting tool along the inner peripheral surface while inserting the heating wire, the heating wire can be fixed when passing through the pressing guide, enabling grooving, heating wire installation, and fixing in a single process. As a result, the manufacturing time can be shortened. (1-3) Since it is possible to relatively easily change the height of the cutting blade, the passing hole diameter and position of the heating wire in the dedicated cutting tool, it is possible to arbitrarily and relatively easily adjust the embedding depth of the heating wire on the inner peripheral surface of the electric fusion joint and the heating wire diameter. (1-4) Since it is possible to relatively easily change the shape of the cutting blade to a "conical shape" or the like other than the "substantially V-shaped", it is possible to suppress the resistance acting on the cutting blade when greatly changing the winding pitch of the heating wire or extremely changing the winding direction (such as forming a turn portion T by inverting 180°).

[0063] (2) In the electric fusion joint according to this embodiment, the area in the fusion part is divided into a first area at the axial center of the fusion part and a second area including the start and end positions of the heating wire and the turn part other than the first area which is the center part thereof. 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 same pitch in the first area. That is, in the general winding structure of the electric fusion joint, the winding pitch near the joint inlet (end part) and the turn part (second area) is not larger than that in the central part of the fusion part (first area), and is at most twice. Therefore (in order not to increase the winding pitch), when fusing, it is difficult for the heating wire to move outward, and it is also difficult for the electric fusion joint to protrude outward, and there is a tendency that a short circuit due to contact between the forward and return heating wires is unlikely to occur. Further, even when it does not greatly affect the joining quality, suppressing the protrusion of the heating wire from the electric fusion joint leads to an improvement in appearance. Also, when winding the heating wire, when the winding pitch becomes large, the load acting on the cutting blade of the dedicated tool increases because the force acts in an oblique direction. By making the winding pitch the same or not exceeding twice, it also leads to suppressing wear and deformation of the cutting blade of the dedicated tool.

[0064] (3) When inserting the terminal pin into the hole (when driving it in), there was a case where the terminal pin rotated and the heating wire could not fit into the groove, so the terminal pin could not be surely connected to the heating wire. However, because a mark (mark groove) indicating the direction of the groove is provided at a position visible from the outer peripheral surface of the electric fusion joint, it is possible to confirm the presence or absence of rotation of the terminal pin during the insertion of the terminal pin, and the heating wire can be surely included in the groove. Also, by connecting the terminal pin to the heating wire other than by soldering, it is possible to more surely avoid a situation where the solder comes off during energization and the electric fusion process is interrupted. As a result, since the terminal pin and the heating wire can be surely connected, it is possible to prevent fusion troubles at the construction site.

[0065] The embodiments described above should be considered illustrative in all respects and not restrictive. The scope of the present invention includes all changes within the meaning and scope equivalent to the claims, for example, the following three modifications can be cited. As a first modification, a terminal pin 2300 having structural features different from the terminal pin 2000 constituting the above-described electric fusion joint will be described in detail below with reference to FIG. 11. In the following description of the terminal pin 2300 according to this modification, the same reference numerals are given to the configurations common to the terminal pin 2000 or the terminal pin 2100 shown in FIG. 10, and detailed descriptions thereof will not be repeated here. The terminal pin 2300 shown in FIG. 11(A) is used in combination with the connection pin 2400 shown in FIG. 11(B), and has a structure that is securely connected to the heating wire 300 inserted (embedded) in the notch groove formed spirally on the inner peripheral surface of the thermoplastic resin tube (pipe material, sleeve).

[0066] In this modification example, as a structure for securely connecting the terminal pin 2300 to the heating wire 300, a terminal pin 2300 having a substantially cylindrical shape and conductivity (for example, copper, lead, etc. can be used as the material of the terminal pin) provided in a through hole (synonymous with through - hole) drilled from the outer peripheral surface of a thermoplastic resin tube (pipe material, sleeve) to reach the heating wire 300, for supplying electricity from an external power source to the heating wire 300, and a connecting pin 2400 having conductivity for connecting the terminal pin 2300 and the heating wire 300 are included. The connecting pin 2400 is formed by bending a metal piece, and includes a hollow cylindrical portion 2410 that fits into the substantially cylindrical shape on the terminal pin 2300 side, and a crimping portion 2430 that crimps the heating wire 300 on the heating wire 300 side. Note that the size (diameter) and length of the hollow cylindrical portion 2410 of the connecting pin 2400 correspond to the size (diameter) and length of the substantially cylindrical portion 2330 of the terminal pin 2300 so that the hollow cylindrical portion 2410 of the connecting pin 2400 can be fitted into the substantially cylindrical portion 2330 of the terminal pin 2300. Further, the tip of the substantially cylindrical portion 2330 is provided with a taper 2332 to more easily insert the connecting pin 2400 into the terminal pin 2300.

[0067] And the crimping portion 2430 of the connecting pin 2400 is formed by folding back the metal piece at the end on the heating wire 300 side of the connecting pin 2400, and crimping the heating wire 300 inserted between the folded - back metal pieces (as shown by the black - painted arrow in (D3) of FIG. 11(D), using a crimping tool or an electrician's pliers, etc.). Also, although not limited, this connecting pin 2400 can adopt a receptacle terminal as shown in the plan view of FIG. 11(B) and the perspective view of (D1) of FIG. 11(D). Here, this connecting pin 2400 (although not limited, here it is a receptacle terminal) has a shape in which a metal piece (metal thin plate) is bent and continuously formed, cut by a dotted line, and the hollow cylindrical portion 2410 and the crimping portion 2430 are connected by a connecting portion 2420 as shown in (B1) of FIG. 11(B).

[0068] The connection procedure between the terminal pin 2300 and the heating wire 300 using the connection pin 2400 having such a configuration will be described with reference to FIG. 11(C). Note that since (C1) to (C3) are the same as those in FIG. 10 described above, they will not be repeatedly described here. (C4) Insert the terminal pin 2300 into the through hole. By this time or after this, as a crimping step, as shown in (D1) to (D3) of FIG. 11(D), the end of the heating wire 300 inserted into the notch groove formed spirally on the inner peripheral surface of the thermoplastic resin tube (pipe material, sleeve) is crimped to the crimping portion 2430 of the connection pin 2400. At this time, as described above, the heating wire 300 inserted between the folded metal pieces is caulked (using a crimping tool or an electrician's pliers as shown by the black arrow in (D3) of FIG. 11(D)) and crimped.

[0069] (C5) As a connection step, the hollow cylindrical portion 2410 of the connection pin 2400 to which the end of the heating wire 300 is crimped to the crimping portion 2430 is fitted (as shown by the gray arrow) to the substantially cylindrical portion 2330 of the terminal pin 2300, so that the terminal pin 2300 and the heating wire 300 are connected through the connection pin 2400 in the through hole. In this way, the hollow cylindrical portion 2410 of the connection pin 2400 to which the end of the heating wire 300 is crimped to the crimping portion 2430 is fitted to the substantially cylindrical portion 2330 of the terminal pin 2300, and the end of the heating wire 300 is surely connected to the terminal pin 2300 without using soldering or the like.

[0070] As a second modification, a terminal pin 2500 having structural features different from those of the terminal pins 2000 and 2300 constituting the above-described electric fusion joint will be described in detail below with reference to FIG. 12. Note that in the following description of the terminal pin 2500 according to this modification, the same reference numerals are given to the configurations common to the terminal pin 2000 or 2100 shown in FIG. 10 and the terminal pin 2300 shown in FIG. 11, and the detailed description thereof here will not be repeated. The terminal pin 2500 shown in Fig. 12(A) is used in combination with the connecting cylinder 2600 shown in Fig. 12(B), and has a structure that is securely connected to the heating wire 300 inserted (embedded) into the notch groove formed spirally on the inner peripheral surface of the thermoplastic resin pipe (pipe material, sleeve).

[0071] In this modification, as a structure for securely connecting the terminal pin 2500 to the heating wire 300, a through hole (synonymous with through hole) drilled so as to reach the heating wire 300 from the outer peripheral surface of the thermoplastic resin pipe (pipe material, sleeve), and provided with a substantially cylindrical shape and conductivity for supplying electricity from an external power source to the heating wire 300 (using copper, lead, etc. as the material of the terminal pin is an example), the terminal pin 2500, and a connecting cylinder 2600 having conductivity for connecting the terminal pin 2500 and the heating wire 300 are included. The terminal pin 2500 includes a substantially cylindrical portion 2530, and a side groove 2530S along the central axis of the substantially cylinder, which is a groove corresponding to the diameter of the heating wire 300, is provided on the curved surface of the substantially cylindrical portion 2530. The connecting cylinder 2600 is formed by bending a metal piece into a substantially cylindrical shape. The terminal pin 2500 enclosing the heating wire 300 in the side groove 2530S is inserted into the substantially cylindrical portion of the connecting cylinder 2600, and the heating wire 300 is pressed against the terminal pin 2500. In addition, the size (diameter) and length of the substantially cylindrical shape of the connecting cylinder 2600 correspond to the size (diameter) and length including the heating wire 300 enclosed in the side groove 2530S so that the heating wire 300 can be inserted into the substantially cylindrical portion 2530 of the terminal pin 2500 enclosing the heating wire 300 in the side groove 2530S and the heating wire 300 can be pressed against the terminal pin 2500. Further, the tip of the substantially cylindrical portion 2530 is provided with a taper 2532 to more easily insert the connecting cylinder 2600 into the terminal pin 2500.

[0072] And the groove enclosing such a heating wire 300 is preferably provided as an end face groove 2530E on the end face of the substantially cylinder on the heating wire 300 side of the substantially cylindrical portion 2530 in addition to the side groove 2530S provided on the curved surface of the substantially cylinder of the substantially cylindrical portion 2530 in the terminal pin 2500. In addition, the connecting cylindrical body 2600 can adopt a crimp terminal or a terminal obtained by processing a crimp terminal. Here, as an example of the crimp terminal, a terminal called a bare crimp terminal for copper wire defined in JIS C 2805 can be cited. Here, in the case of a crimp terminal such as a round crimp terminal, a Y-shaped crimp terminal, or a rod-shaped crimp terminal, for example, as shown in (B2) of FIG. 12(B), the dotted line portion of such a crimp terminal (the round portion in the case of a round crimp terminal, the Y-shaped portion in the case of a Y-shaped crimp terminal, and the rod-shaped portion in the case of a rod-shaped crimp terminal) is cut and processed into only the crimp portion. In the case of a crimp terminal called a crimp sleeve, since it does not originally have the dotted line portion shown in (B2) of FIG. 12(B), it can be used without processing. In this way, a crimp terminal or a terminal obtained by processing a crimp terminal can be adopted as the connecting cylindrical body 2600.

[0073] The connection procedure between the terminal pin 2500 and the heating wire 300 using the connecting cylindrical body 2600 having such a configuration will be described with reference to FIGS. 12(C) and 12(D). Since (C1) to (C3) are the same as those in FIG. 10 described above, they will not be repeatedly described here. (Pre-process of C4) As an inclusion step, the end of the heating wire 300 inserted into the notch groove formed spirally on the inner peripheral surface of the thermoplastic resin pipe (pipe material, sleeve) is included in the groove (side groove 2530S, or side groove 2530S and end face groove 2530E) of the terminal pin 2500. At this time, as shown by the gray-painted arrow in (D1) of FIG. 12(D), the end of the heating wire 300 is included in the groove by winding it around the substantially cylindrical portion 2530 of the terminal pin 2500. Next, as shown by the gray-painted arrow in (D2) of FIG. 12(D), the substantially cylindrical portion 2530 of the terminal pin 2500 with the heating wire included in the groove is inserted into the substantially cylindrical connecting cylinder 2600 to press-connect the heating wire 300 to the terminal pin 2500. At this time, although not limited, for example, as shown by the black-painted arrow in (D3) of FIG. 12(D), it is also preferable to press-connect the heating wire 300 to the terminal pin 2500 by caulking using a crimping tool or an electrician's pliers, etc. However, in the present invention, the substantially cylindrical portion of the connecting cylinder 2600 is inserted into the terminal pin 2500 with the heating wire 300 included in the side groove 2530S, and the heating wire 300 is only press-connected to the terminal pin 2500, so that the terminal pin 2500 and the heating wire 300 are surely connected.

[0074] (C4)(C5) As a connection step, the terminal pin 2500 with the end of the heating wire 300 included in the groove (side groove 2530S, or side groove 2530S and end face groove 2530E) of the terminal pin 2500 crimped by the connecting cylinder 2600 is inserted into the through hole as shown by the gray-painted arrows in (C4) and (C5) of FIG. 12(C), and the terminal pin 2500 and the heating wire 300 are connected via the connecting cylinder 2600 in the through hole.

[0075] In this way, the heating wire 300 included in the groove (side groove 2530S, or side groove 2530S and end face groove 2530E) of the terminal pin 2500 and the connecting cylinder 2600 are press-connected, and the end of the heating wire 300 is surely connected to the terminal pin 2500 without using soldering or the like. Regarding the step of inserting and press - fitting the connection cylinder 2600 into the terminal pin 2500 in which the heating wire 300 is enclosed in the groove (side groove 2530S, or side groove 2530S and end - face groove 2530E), the present invention does not exclude performing it in the through - hole as shown in (C4) of FIG. 11(C) in the same manner as in the second modification example. That is, in the through - hole, the substantially cylindrical portion of the connection cylinder 2600 may be inserted into the terminal pin 2500 in which the heating wire 300 is enclosed in the side groove 2530S so that the heating wire 300 is press - fitted to the terminal pin 2500.

[0076] <Third Modification Example: Inner Peripheral Surface Structure of Electric Fusion Joint (Opening Side and Central Side)> As a third modification example, an electric fusion joint 250 having structural features of the inner peripheral surface other than the fusion part in the above - described electric fusion joint will be described in detail below with reference to FIGS. 13 and 14. The winding structure of the electric fusion joint 250 according to this modification example is obtained by cutting two turns of the return path in the winding structure of the electric fusion joint 100 shown in FIG. 7 (with the same processing pitch and T diameter), and arranging it in a position that is substantially the same in the axial direction and shifted in the circumferential direction on the start - position S side and the end - position E side like the winding structure of the electric fusion joint 200 shown in FIG. 8 (different from the winding structure of the electric fusion joint 100 shown in FIG. 7). Since the other winding structures of the electric fusion joint 250 are the same as the winding structures of the electric fusion joint 100 shown in FIG. 7 or the electric fusion joint 200 shown in FIG. 8, the same reference numerals are given in FIGS. 13 and 14, and detailed descriptions thereof will not be repeated here.

[0077] Note that the structural features (recess 252, protrusion 254) of the electric fusion joint 250 according to this modification example, which will be described in detail below, other than the fusion part of the inner peripheral surface, do not mean that they cannot be applied to the electric fusion joint 100 and the electric fusion joint 200. Instead, they can be applied to electric fusion joints including the electric fusion joint 100, the electric fusion joint 200, and the electric fusion joint 250 that have a fusion part.

[0078] As shown in FIGS. 13 and 14, this electric fusion joint 250 (similar to the electric fusion joints 100 and 200) includes a fusion part in which a heating wire 300 is inserted into a notch groove formed spirally on the inner peripheral surface of a thermoplastic resin tube (pipe material, sleeve) into which a resin tube of a mating part is inserted. This fusion part is provided on at least one (here, both) end side in the axial direction of the electric fusion joint 250 so that the heating wire 300 can be energized (via a terminal pin 2000 or the like).

[0079] In this fusion part, a forward path in which the spiral progresses in the forward path direction from the opening side of the electric fusion joint 250 to the opening side opposite to the opening and a return path in the direction opposite to the forward path direction are formed by a single heating wire 300. And, as a structural feature other than the fusion part on the inner peripheral surface of the electric fusion joint 250, a concave part 252 with a recessed inner peripheral surface is provided on the inner peripheral surface on the opening side with respect to the fusion part. And this concave part 252 is provided over the entire circumference of the inner periphery. Furthermore, this concave part 252 also serves as a handle of the electric fusion joint 250. By adopting such a configuration, the following problems can be solved.

[0080] (A) When the resin tube (resin pipe) of the mating part and the electric fusion joint 250 are electrically fused, if the clearance between the resin pipe and the electric fusion joint 250 is small, or if the electrical energy applied (supplied) by the electric fusion is large, the resin may be excessively melted. In such a case, there may occur a problem that the excessively melted resin leaks from between the resin pipe of the mating part and the end face of the electric fusion joint 250, resulting in a poor appearance. With respect to such a problem, since the concave part 252 with a recessed inner peripheral surface is provided on the opening side (here, both ends) of the inner peripheral surface of the electric fusion joint 250, the excessively melted resin can be filled in this concave part 252 so as not to generate resin leaking from the end face of the electric fusion joint 250, or the amount of resin leaking can be reduced. (B) When handling the electric fusion joint 250 (during production and construction), there may be a problem that it is difficult to carry because the electric fusion joint 250 has no handle. To address such a problem, a concave portion 252 with a sunken inner peripheral surface is provided on the opening side (here, both ends) of the inner peripheral surface of the electric fusion joint 250. As a result, it becomes possible to place a jig or a finger in a concave shape, and the workability of carrying can be improved.

[0081] Furthermore, this electric fusion joint 250 includes a convex portion 254 (in a rib shape) with a protruding inner peripheral surface on the inner peripheral surface on the central side of the electric fusion joint 250 in the axial direction relative to the fusion portion. And this convex portion 254 is provided over the entire circumference of the inner periphery. With such a configuration, the following problems can be solved.

[0082] When the resin pipe (resin pipe) of the connection partner and the electric fusion joint 250 are electrically fused, if the clearance between the resin pipe and the electric fusion joint 250 is small, or if the electrical energy applied (supplied) by the electric fusion is large, the resin may be excessively melted. In this case, the melted resin may flow from the end face of the resin pipe of the connection partner (the side inserted into the electric fusion joint 250) toward the central side in the axial direction of the electric fusion joint 250, or the heating wire of the fusion part may be pushed out from the notch groove by the melted resin, causing the heating wire 300 to be exposed. As a result, it may become impossible or difficult to insert the resin pipe from the opposite side, resulting in problems. To address such problems, a convex portion 254 with a protruding inner peripheral surface is provided on the inner peripheral surface of the electric fusion joint 250 on the central side in the axial direction from the fusion part. This enables the excessively melted resin to be blocked from flowing to the opposite side (the side where the resin pipe is not inserted) beyond this convex portion 254 (it can be blocked by the rib-shaped convex portion 254), and even if the heating wire 300 pops out from the notch groove, it can be prevented from flowing to the opposite side (the side where the resin pipe is not inserted) (it can be blocked by the rib-shaped convex portion 254). Therefore, the flow of the melted resin and / or the heating wire 300 from the central side of the electric fusion joint 250 to the opening side on the opposite side can be suppressed, making it possible to insert the resin pipe from the opening on the opposite side and preventing troubles during the insertion of the resin pipe at the construction site.

[0083] As described above, according to the electric fusion joint and the method for manufacturing the electric fusion joint according to the present embodiment including the modified example, there is provided an electric fusion joint having a structure in which a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe. The plastic pipe is inserted into one of the left and right sockets at a time instead of both at once (even if both the left and right are for electric fusion, only one of the left and right needs to be for electric fusion and the other does not have to be for electric fusion). This can ensure the connection between the terminal pin and the heating wire more reliably without increasing the manufacturing cost and without affecting the watertightness, avoiding troubles or difficulties during construction, and providing an electric fusion joint that can be electrically fused.

[0084] It should be noted that the embodiments including the modified examples disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Industrial Applicability

[0085] The present invention is preferably applicable to an electric fusion joint having a structure in which a heating wire is inserted into a concave groove formed in the inner peripheral portion of a thermoplastic resin pipe, and can electrically fuse a plastic pipe to be connected to only one of the left and right receiving ports at a time (even if both the left and right are electrically fused, it does not matter if only one of the left and right is electrically fused and the other is not), without increasing the manufacturing cost and without affecting the watertightness, making the connection between the terminal pin and the heating wire more reliable, and avoiding troubles or difficulties during construction. This is particularly preferable in terms of being able to provide such a joint.

Explanation of Signs

[0086] 100 Electric fusion joint 200 Electric fusion joint 250 Electric fusion joint 300 Heating wire 300F Forward winding 300R Return winding 1000 Special tool 1100 Body part 1110 Heating wire introduction hole 1200 Cutting blade 1300 Pressing guide 1600 Housing joint 2000, 2300, 2500 Terminal pins 3000 Indicator

Claims

1. An electric fusion joint having a fusion part in which a heating wire is inserted into a notch groove formed spirally on the inner peripheral surface of a thermoplastic resin tube into which a resin tube of a connection partner is inserted, The fusion part is provided on at least one end side in the axial direction of the electric fusion joint so that the heating wire can be energized, In the fusion part, a notch groove of a forward path in which the helix advances in the forward path direction from the opening side of the electric fusion joint to the opening side opposite to the opening, a notch groove of a turn part in which the forward path is reversed by 180 degrees on the opposite opening side, and a notch groove of a return path in the direction opposite to the forward path direction are formed by inserting one heating wire into one continuous notch groove, The inner peripheral surface on the opening side of the fusion part is provided with a recess in which the inner peripheral surface is recessed, The turn part is formed as a semi-circle having a diameter larger than half of the spiral pitch of the forward path or the return path at the axial center of the fusion part. The electric fusion joint is characterized by this.

2. The electric fusion joint according to claim 1, wherein the recess is provided over the entire circumference of the inner periphery.

3. The electric fusion joint according to claim 1 or claim 2, wherein the recess also serves as a handle of the electric fusion joint.

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