Electrofusion joints

Abstract

To provide an electrofusion joint in which the strength of the electrofusion socket is appropriately improved. [Solution] The electrofusion joint 10 comprises a joint body 12 having an electrofusion socket 16 and a heating wire 20 embedded in the electrofusion socket. The heating wire has an effective heating wire portion 50 that is spirally provided near the inner circumferential surface of the electrofusion socket 16 in the fusion zone 40, and a reinforcing portion 52 that is spirally provided at a predetermined radial distance from the inner circumferential surface of the electrofusion socket in the cold zone 42 at the axial rear, so as not to melt the inner circumferential surface of the electrofusion socket during fusion.

Description

Technical Field

[0001] The present invention relates to an electric fusion joint, and particularly to an electric fusion joint having an electric fusion receiving port in which a cold zone is formed, for example.

Background Art

[0002] An example of a conventional electric fusion joint is disclosed in Patent Document 1. The elbow-type EF joint of Patent Document 1 is made of a thermoplastic resin, and has an elbow-shaped joint body mainly composed of straight pipe portions (electric fusion receiving ports) on both sides and a curved pipe portion therebetween, and a heating wire disposed on the inner peripheral side thereof. This heating wire is composed of an embedded portion (effective heating wire portion) wound around the inner peripheral surface of each straight pipe portion and a connecting portion connecting the ends of the respective embedded portions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As shown in Figure 9, in a conventional general electrofusion joint 100, the electrofusion socket 102 has cold zones 108 and 110 formed on the back and front sides of the fusion zone 106 in which the heating wire 104 is spirally embedded, in order to prevent molten resin from overflowing during fusion. Since the cold zones 108 and 110 are not fused with other pipe members 112, if the inside of the piping is under high pressure or pulsating water pressure, the strength of the cold zone 108 at the back of the electrofusion socket 102 may be insufficient, and damage (cracks) may occur in the electrofusion socket 102. In particular, in the case of elbow-type electrofusion joints that form bends in piping, thrust forces generated by centrifugal force from water flow and water pressure imbalances can deform (vibrate) the inner portion 114 of the electrofusion socket 102. This deformation increases the likelihood of damage occurring at the end 116 on the fusion zone 106 side of the cold zone 108 in the inner part, where stress tends to concentrate. To increase the strength of the electrofusion socket 102, it is conceivable to increase the wall thickness of the electrofusion socket 102 or reinforce it from the outside with a separate component. However, this would increase the amount of material or components used, leading to higher costs. It would also increase the weight, worsening the ease of installation.

[0005] Therefore, the primary objective of this invention is to provide a novel electrofusion joint.

[0006] Another object of this invention is to provide an electrofusion joint that can adequately improve the strength of the electrofusion socket. [Means for solving the problem]

[0007] The first invention is an electrofusion joint comprising a synthetic resin joint body having an electrofusion socket, and a heating wire embedded in the electrofusion socket, wherein the heating wire has an effective heating wire portion spirally provided near the inner circumferential surface of the electrofusion socket in a fusion zone formed in the axial center of the electrofusion socket, and a reinforcing portion spirally provided at a predetermined radial distance from the inner circumferential surface of the electrofusion socket in a cold zone formed in the axial depth of the electrofusion socket, so as to prevent the inner circumferential surface of the electrofusion socket from melting during fusion.

[0008] In the first invention, the electrofusion joint comprises a joint body made of synthetic resin having an electrofusion socket. A heating wire is embedded in the electrofusion socket. This heating wire has an effective heating wire portion and a reinforcing portion. The effective heating wire portion is spirally provided near the inner circumferential surface of the electrofusion socket in the fusion zone formed in the axial center of the electrofusion socket. The reinforcing portion is spirally provided at a predetermined radial distance from the inner circumferential surface of the electrofusion socket in the cold zone formed in the axial depth of the electrofusion socket, so as to prevent the inner circumferential surface of the electrofusion socket from melting during fusion. In other words, the reinforcing portion is a part that does not contribute to the fusion joint and functions as a reinforcing member of the electrofusion socket.

[0009] According to the first invention, since a portion of the heating element is used as a reinforcing member, the strength of the electrofusion socket can be appropriately improved while suppressing increases in cost and weight, and consequently, damage to the electrofusion socket can be reliably prevented.

[0010] The second invention is dependent on the first invention, and the predetermined distance at which the reinforcing portion is radially separated from the inner circumferential surface of the electrofusion socket is set to a size of 1.2 mm or more and 3.5 mm or less.

[0011] The third invention is dependent on the first or second invention, wherein the predetermined distance at which the reinforcing portion is radially separated from the inner circumferential surface of the electrofusion socket is set to a size of 1.8 times or more and 7.0 times or less the diameter of the heating wire.

[0012] The fourth invention is dependent on the first or second invention, and the reinforcing portion is provided to extend substantially the entire axial length of the cold zone.

[0013] The fifth invention is subordinate to the fourth invention, and the reinforcing portion has a larger spiral pitch than the effective heating wire portion.

[0014] The sixth invention is dependent on the first or second invention, and the reinforcing portion is provided at the end of the cold zone on the fusion zone side.

[0015] The seventh invention is dependent on the sixth invention, and the reinforcing part has a smaller helix pitch than the effective heating wire part.

[0016] The eighth invention is dependent on the first or second invention, and the inner diameter of the helix of the reinforcing part gradually increases from the connecting part with the effective heating wire part toward the axially inner side of the electric fusion joint.

[0017] The ninth invention is dependent on the first or second invention, and the inner diameter of the helix of the reinforcing part is enlarged stepwise at the connecting part with the effective heating wire part.

[0018] The tenth invention is dependent on the first or second invention, and the joint body has electric fusion joints formed at both axial ends respectively and a curved pipe part formed at the axial center part.

Advantages of the Invention

[0019] According to this invention, since a part of the heating wire is used as a reinforcing member, while suppressing an increase in cost and weight, the strength of the electric fusion joint can be appropriately improved, and thus breakage of the electric fusion joint can be surely prevented.

[0020] The above object, other objects, features, and advantages of this invention will become clearer from the detailed description of the embodiments below with reference to the drawings.

Brief Description of the Drawings

[0021] [Figure 1] It is a front view showing an electric fusion joint which is an embodiment of this invention. [Figure 2] It is a plan view showing the electric fusion joint of FIG. 1. [Figure 3] It is a cross-sectional view showing a cross section of the electric fusion joint on line III-III of FIG. 2. [Figure 4] It is a cross-sectional view showing a cross section of the electric fusion joint on line IV-IV of FIG. 1. [Figure 5] It is an enlarged cross-sectional view showing an enlarged cross section of the electric fusion joint portion of the electric fusion joint of FIG. 1. [Figure 6]It is a diagram showing a state where a pipe member is electrically fusion-bonded to an electrical fusion joint receiving port of FIG. 1. [Figure 7] It is a cross-sectional view showing an electrical fusion joint of another embodiment of this invention. [Figure 8] It is an enlarged cross-sectional view showing an enlarged cross-section of an electrical fusion joint receiving port portion of FIG. 7. [Figure 9] It is a diagram showing a state where a pipe member is electrically fusion-bonded to an electrical fusion joint receiving port of a conventional electrical fusion joint.

Mode for Carrying Out the Invention

[0022] Referring to FIGS. 1 and 6, an electrical fusion joint 10 according to an embodiment (first embodiment) of this invention includes a joint body 12 having an electrical fusion joint receiving port 16. Another pipe member 200 made of synthetic resin is electrically fusion-bonded to the electrical fusion joint receiving port 16. The electrical fusion joint 10 of this embodiment is an elbow-type electrical fusion joint (EF elbow) that electrically fusion-bonds pipe members 200 to each other in a direction intersecting each other to form a bent pipe.

[0023] The use and diameter of the pipe constructed using the electrical fusion joint 10 are not particularly limited, but the electrical fusion joint 10 is preferably used for connecting synthetic resin pipes made of polyethylene with a nominal diameter (inner diameter) of 20 mm to 150 mm for water supply or gas use. Hereinafter, an electrical fusion joint 10 with a nominal diameter of 75 mm of the joint body 12 will be exemplified and described.

[0024] As shown in FIGS. 1-5, the electrical fusion joint 10 includes a joint body 12 formed of a polyolefin-based synthetic resin such as polyethylene and polybutene. The joint body 12 includes a curved pipe portion 14 and electrical fusion joint receiving ports 16 extending from both ends of the curved pipe portion 14, respectively. That is, the joint body 12 has two electrical fusion joint receiving ports 16 formed at both axial ends and a curved pipe portion 14 formed at the axial center portion. In this embodiment, the curved pipe portion 14 is curved at an angle of 45 degrees, and the two electrical fusion joint receiving ports 16 extend (open) in a direction intersecting each other at an angle of 45 degrees.

[0025] The electrofusion socket 16 is the part that receives the end of the pipe member 200 (see Figure 6) to be connected. A stopper 18 is formed at the far end of the electrofusion socket 16. In this embodiment, the annular stopper 18 is formed by reducing the diameter of the inner circumferential surface at the far end of the electrofusion socket 16 in a stepped manner. However, the stopper 18 may be a plurality of protrusions formed at predetermined intervals in the circumferential direction. When connecting the end (insertion port) of the pipe member 200 to the electrofusion socket 16, the insertion length of the pipe member 200 into the electrofusion socket 16 is determined by the tip of the pipe member 200 abutting against the stopper 18.

[0026] Furthermore, a heating wire 20 is embedded in the vicinity of the inner circumferential surface of the electrofusion socket 16, extending in a spiral shape. In this embodiment, electrofusion sockets 16 are formed at both ends of the joint body 12, but the heating wires 20 provided in these two electrofusion sockets 16 are continuous and consist of a single metal wire. The diameter of the heating wire 20 is, for example, 0.3 mm to 0.8 mm, and in this embodiment, it is 0.42 mm. The specific configuration of the heating wire 20 will be described later.

[0027] The end of the heating wire 20 is connected to a power connection terminal 22 that protrudes from the top of the tip of the electrofusion socket 16. When the power connection terminal 22 is connected to a power source and current is passed through the heating wire 20, heat is generated. This heat heats and melts the resin at the joint surface between the electrofusion socket 16 and the pipe member 200, thereby fusing the electrofusion socket 16 and the pipe member 200 together. Furthermore, an indicator 24 is formed on the top of the electrofusion socket 16, on the axial side of the power connection terminal 22. The indicator 24 is for indicating that the joint surface between the electrofusion socket 16 and the pipe member 200 has fused (or the progress of the fusion).

[0028] Furthermore, a base portion 26 is formed on the bottom of the outer circumferential surface of the joint body 12. The base portion 26 has a flat bottom surface 26a (lower surface) that contacts the mounting surface such as the ground. The base portion 26 can also be formed on the bottom of the outer circumferential surface of the electrofusion socket 16, but it is preferable to form it on the bottom of the outer circumferential surface of the curved pipe portion 14. By providing such a base portion 26, the electrofusion joint 10 can be stably mounted on the mounting surface.

[0029] The method for manufacturing the electrofusion joint 10 is not particularly limited, but for example, the electrofusion joint 10 can be manufactured by injection molding. Briefly, the electrofusion joint 10 in this embodiment is manufactured by spirally winding a heating wire 20 around the outer circumference of an inner core which will become the inner layer 30, setting this inner core in a mold, and then injection molding an outer layer 32 onto its outer circumference.

[0030] In the electrofusion socket 16 of such an electrofusion joint 10, cold zones 42 and 44 are formed on both sides of the axial direction of the fusion zone 40, where the inner circumferential surface of the electrofusion socket 16 is melted by the heating element 20. That is, the electrofusion socket 16 has a fusion zone 40 formed in the axial center, as well as a first cold zone 42 formed in the axial rear and a second cold zone 44 formed in the axial front. The cold zones 42 and 44 are parts where the inner circumferential surface of the electrofusion socket 16 does not melt during fusion, and are necessary to prevent molten resin from flowing out from the gap between the electrofusion socket 16 and the pipe member 200.

[0031] As mentioned above, conventional electrofusion sockets may have insufficient strength in the cold zone (first cold zone) formed in the axial depth. In particular, in the case of elbow-type electrofusion joints, the effects of thrust force and stress concentration caused by centrifugal force and water pressure imbalance due to water flow become significant, increasing the likelihood of damage occurring at the end of the first cold zone on the fusion zone side (see Figure 9). For this reason, a technology that can appropriately improve the strength of electrofusion sockets is desired.

[0032] Therefore, in this embodiment, by using a portion of the heating wire 20 as a reinforcing member of the electrofusion socket 16, the strength of the easily damaged part of the electrofusion socket 16 can be appropriately improved while suppressing increases in cost and weight. Specifically, the heating wire 20 is extended spirally into the first cold zone 42 to prevent melting of the inner circumferential surface of the electrofusion socket 16, and this extended portion that does not contribute to the fusion joint (reinforcement portion 52, described later) is used as a reinforcing member of the electrofusion socket 16. The configuration of the heating wire 20 will be described in detail below.

[0033] As shown in Figures 3 to 5, the heating element 20 has an effective heating element portion 50 provided in the fusion zone 40 formed in the axial center of the electrofusion socket 16, and a reinforcing portion 52 provided in the first cold zone 42 formed in the axial rear of the electrofusion socket 16.

[0034] The effective heating element portion 50 is the part that melts the inner circumferential surface of the electrofusion socket 16 during fusion, and is provided in a spiral shape near the inner circumferential surface of the electrofusion socket 16. However, the effective heating element portion 50 does not need to be completely embedded in the resin, and a part of it (the inner circumferential part of the spiral) may be exposed on the inner circumferential surface of the electrofusion socket 16. In this embodiment, the predetermined distance t1 at which the effective heating element portion 50 is radially separated from the inner circumferential surface of the electrofusion socket 16 (i.e., the wall thickness of the electrofusion socket 16 inside the spirally wound effective heating element portion 50) is 0.7 mm. Also, in this embodiment, the spiral pitch P1 of the effective heating element portion 50 is 2.2 mm.

[0035] The reinforcing portion 52 is spirally arranged at a predetermined radial distance t2 from the inner surface of the electrofusion socket 16 so that the inner surface of the electrofusion socket 16 does not melt during fusion. The predetermined distance t2 from the inner surface of the electrofusion socket 16 (i.e., the thickness of the electrofusion socket 16 inside the spirally wound reinforcing portion 52) is preferably 1.2 mm to 3.5 mm. Furthermore, the predetermined distance t2 is preferably 1.8 to 7.0 times the diameter of the heating element 20. In addition, the number of turns of the reinforcing portion 52 is preferably 2 to 4 turns (i.e., approximately 720° to 1440°).

[0036] Furthermore, in this embodiment, the reinforcing portion 52 is provided so as to extend over substantially the entire axial length of the first cold zone 42, and the axial rear end of the reinforcing portion 52 (the axial center end of the joint body 12) extends to a position further rear than the stopper 18. Moreover, in this embodiment, the spiral pitch P2 of the reinforcing portion 52 is set to be larger than the spiral pitch P1 of the effective heating wire portion 50, and is 6.2 mm. By making the pitch P2 larger (wider), the first cold zone 42 can be reinforced in a balanced manner over its entire axial length without excessively increasing the number of turns of the heating wire 20.

[0037] Furthermore, in this embodiment, the inner diameter of the spiral of the reinforcing portion 52 gradually increases from the connection portion with the effective heating wire portion 50 toward the axial rear side of the electrofusion socket 16 (towards the axial center side of the joint body 12). In other words, the predetermined distance t2 gradually increases toward the axial rear side of the electrofusion socket 16. In this embodiment, the predetermined distance t2 is 1.3 mm in the axial front portion of the electrofusion socket 16 and 2.2 mm in the axial rear portion of the electrofusion socket 16. Also, in this embodiment, the predetermined distance t2 is 1.8 times the diameter of the heating wire 20 in the axial front portion of the electrofusion socket 16 and 4.2 times the diameter of the heating wire 20 in the axial rear portion of the electrofusion socket 16.

[0038] Furthermore, the heating wires 20 provided in the two electrofusion sockets 16 are made of a single metal wire as described above, and the axial rear end of the reinforcing portion 52 of the heating wire 20 provided in one electrofusion socket 16 and the axial rear end of the reinforcing portion 52 of the heating wire 20 provided in the other electrofusion socket 16 are connected by a connecting portion 54 embedded in the curved pipe portion 14.

[0039] Furthermore, at the connection point between the effective heating element section 50 and the reinforcing section 52, the effective heating element section 50 and the reinforcing section 52 cannot be strictly separated, and there is a transition point where the connection point switches from the effective heating element section 50 to the reinforcing section 52. In this embodiment, the connection point (transition point) between the effective heating element section 50 and the reinforcing section 52 is formed such that the inner diameter of the spiral gradually expands as it moves towards the axial rear side of the electrofusion socket 16. Therefore, although the fusion zone 40 may expand slightly towards the axial rear side, it has almost no effect on the actual axial length of the fusion zone 40 (and consequently, the design fusion strength).

[0040] As shown in Figure 6, when the end of the pipe member 200 is inserted into the electrofusion socket 16 of the electrofusion joint 10 and the heating wire 20 is passed through it, the resin at the joint surface between the electrofusion socket 16 and the pipe member 200 is heated and melted in the fusion zone 40, and the electrofusion socket 16 and the pipe member 200 are fused together. On the other hand, in the cold zones 42 and 44, the inner circumferential surface of the electrofusion socket 16 is not melted and remains unfused to the pipe member 200.

[0041] In piping formed using the electrofusion joint 10 in this manner, even if thrust force is generated due to centrifugal force from water flow or water pressure imbalance, the deformation (vibration) of the inner portion 70 of the electrofusion socket 16 is suppressed because the first cold zone 42 is reinforced by the reinforcing portion 52 of the heating element 20 along substantially its entire axial length. This prevents stress caused by this deformation from concentrating at the end 72 on the fusion zone 40 side of the first cold zone 42, thereby preventing damage to the electrofusion socket 16.

[0042] As described above, according to this embodiment, since a portion of the heating wire 20 is used as a reinforcing member, the strength of the electrofusion socket 16 can be appropriately improved while suppressing increases in cost and weight. Therefore, damage to the electrofusion socket 16 can be reliably prevented.

[0043] Next, with reference to Figures 7 and 8, an electrofusion joint 10 of another embodiment (second embodiment) of the present invention will be described. In this second embodiment, the arrangement of the reinforcing portion 52 differs from that of the first embodiment described above. In the following description, parts common to the above embodiments will be given the same reference numerals, and redundant explanations will be omitted or simplified.

[0044] As shown in Figures 7 and 8, the reinforcing portion 52 of this second embodiment is provided at the end 72 of the first cold zone 42 on the fusion zone 40 side. In other words, the end 72 of the first cold zone 42 on the fusion zone 40 side, where stress due to deformation is likely to concentrate, is reinforced intensively by the reinforcing portion 52.

[0045] Furthermore, in this embodiment, the spiral pitch P2 of the reinforcing portion 52 is set smaller than the spiral pitch P1 of the effective heating wire portion 50. This pitch P2 may be the same size as pitch P1, but it is preferable that it be between 0.7 and 0.9 times the size of pitch P1. In this embodiment, the pitch P2 is 1.6 mm, which is set to 0.73 times the size of pitch P1. By making the spiral pitch P2 of the reinforcing portion 52 smaller (narrower), the end 72 of the first cold zone 42 can be reinforced more effectively. Note that the heating wire 20 (effective heating wire portion 50) in the fusion zone 40 becomes foreign matter in the fusion bonding, so if the effective heating wire portion 50 is arranged with a small pitch P1, there is a risk that the fusion strength will decrease. In contrast, the reinforcing portion 52 provided in the first cold zone 42 is not related to the fusion strength, so it is possible to set the pitch P2 smaller within a range where the heating wires 20 do not short-circuit with each other.

[0046] In piping formed using the electrofusion joint 10, even if thrust force is generated due to centrifugal force from water flow or water pressure imbalance, the end 72 on the fusion zone 40 side of the first cold zone 42, where stress due to pipe deformation tends to concentrate, is reinforced intensively by the reinforcing part 52, thus preventing damage to the electrofusion socket 16.

[0047] In this second embodiment, as in the first embodiment, the strength of the electrofusion socket 16 can be appropriately improved while suppressing increases in cost and weight. Therefore, damage to the electrofusion socket 16 can be reliably prevented.

[0048] In the embodiments described above, the inner diameter of the spiral at the connection point (transition point) between the effective heating element section 50 and the reinforcing section 52 is gradually increased, but it may also be increased in a stepped manner. That is, the diameter of the spiral of the reinforcing section 52 may be increased in a stepped manner at the connection point with the effective heating element section 50. Furthermore, after the diameter of the spiral of the reinforcing section 52 has been increased at the connection point with the effective heating element section 50, the inner diameter of the spiral may be the same or approximately the same along its entire axial length.

[0049] Furthermore, in the first embodiment described above, the reinforcing portion 52 is provided so as to extend over substantially the entire axial length of the first cold zone 42, and in the second embodiment described above, the reinforcing portion 52 is provided at the end 72 on the fusion zone 40 side of the first cold zone 42, but these can also be combined. That is, the reinforcing portion 52 may be provided so as to extend over substantially the entire axial length of the first cold zone 42, and the pitch P2 of the spiral of the reinforcing portion 52 may be made smaller at the end 72 on the fusion zone 40 side of the first cold zone 42. In other words, the reinforcing portion 52 may have a tightly wound portion with a small pitch P2 provided at the end 72 on the fusion zone 40 side of the first cold zone 42, and a coarsely wound portion with a large pitch P2 provided on the axially inner side of the tightly wound portion.

[0050] In the above-described embodiments, 45-degree elbow-type electrofusion joints were used as examples, but the electrofusion joints according to this invention may also be 22.5-degree elbow-type, 90-degree elbow-type, or the like. Furthermore, this invention is not limited to elbow-type electrofusion joints, but can be applied to any shape of electrofusion joint, such as cheese-type, socket-type, or single-socket type, as long as it has an electrofusion socket with a cold zone formed therein.

[0051] Furthermore, the specific numerical values ​​and configurations mentioned above are merely examples and can be modified as needed according to product specifications and other requirements. [Explanation of Symbols]

[0052] 10 ... Electrofusion joints 12 ... Fitting body 14...Bent pipe section 16 ... Electrofusion socket 20…Heating wire 40... Fusion splicing zone 42...First cold zone (cold zone at the far end of the axial direction) 50 ... Effective heating element section 52 ...Reinforcement 54 ...Wataribe 100 ... Conventional electrofusion joints 200 ... Other pipe components

Claims

1. A synthetic resin joint body having an electrofusion socket, and The aforementioned electrofusion socket is equipped with an electric heating wire embedded in it, The aforementioned heating element is In the fusion zone formed in the axial center of the electrofusion socket, an effective heating element is provided spirally near the inner circumferential surface of the electrofusion socket, and An electrofusion joint having a spirally arranged reinforcing portion at a predetermined radial distance from the inner circumferential surface of the electrofusion socket, in a cold zone formed in the axial depth of the electrofusion socket, so as to prevent the inner circumferential surface of the electrofusion socket from melting during fusion.

2. The electrofusion joint according to claim 1, wherein the predetermined distance at which the reinforcing portion is radially separated from the inner circumferential surface of the electrofusion socket is 1.2 mm or more and 3.5 mm or less.

3. The electrofusion joint according to claim 1 or 2, wherein the predetermined distance at which the reinforcing portion is radially separated from the inner circumferential surface of the electrofusion socket is 1.8 times or more and 7.0 times or less the diameter of the heating wire.

4. The reinforcing portion is provided so as to extend substantially the entire axial length of the cold zone, as described in claim 1 or 2.

5. The electric fusion joint according to claim 4, wherein the reinforcing portion has a larger spiral pitch than the effective heating wire portion.

6. The reinforcing portion is provided at the end of the cold zone on the fusion zone side, as described in claim 1 or 2.

7. The reinforcing portion has a smaller spiral pitch than the effective heating wire portion, as described in claim 6.

8. The electrofusion joint according to claim 1 or 2, wherein the reinforcing portion has an inner diameter that gradually increases as it moves from the connection portion with the effective heating wire portion toward the axial rear side of the electrofusion socket.

9. The electrofusion joint according to claim 1 or 2, wherein the reinforcing portion has a stepped increase in diameter at the connection point with the effective heating wire portion.

10. The electrofusion joint according to claim 1 or 2, wherein the joint body has electrofusion sockets formed at each of the axial ends and a curved pipe portion formed in the axial center.

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