A polyethylene pipe electrofusion welded joint

Abstract

This invention relates to the field of electrofusion welding technology, and more particularly to an electrofusion welding joint for polyethylene pipes. The joint includes: a main body with two symmetrically mounted connectors at both ends, each connector containing a positive electrode and a negative electrode; an annular groove on the inner side of the main body, into which a polyethylene welding sleeve is fitted; a protruding ring at the center of the inner wall of the welding sleeve; a spirally distributed resistance wire coaxially laid inside the welding sleeve, the resistance wire embedded within the sleeve wall; wires extending in the same direction from both ends of the resistance wire outwards from the welding sleeve, connected to the positive and negative electrodes respectively; and several uniformly spaced heat-resistant insulating rods embedded within the welding sleeve, the heat-resistant insulating rods extending axially along the resistance wire and fixedly connected to the outer surface of each turn of the resistance wire; the resistance wire has a rectangular cross-section, its inner surface parallel to the inner surface of the welding sleeve. This invention provides uniform heating.

Description

Technical Field

[0001] This invention relates to the field of electrofusion joint technology, and more particularly to an electrofusion welding joint for polyethylene pipes. Background Technology

[0002] Polyethylene pipes have become widely used in urban gas transmission and distribution systems due to their excellent sealing performance, corrosion resistance, high toughness, light weight, and long service life. In pipeline laying projects, it is necessary to reliably connect a large number of pipes of different specifications, and capacitor-electrode welding is currently one of the most common connection methods.

[0003] This connection method primarily relies on an electrofusion joint. The ends of the two polyethylene pipes to be connected are inserted into the welding sleeve of the electrofusion joint. The welding sleeve contains spirally distributed resistance wires. During welding, electricity is applied to the resistance wires, generating heat due to the Joule effect. This heat is transferred to the inner wall of the welding sleeve via thermal conduction, melting it and fusing it with the outer wall of the polyethylene pipes, thus achieving a permanent connection between the pipes.

[0004] However, because the embedded resistance wire typically has a circular cross-section, the distance between the outer surface of the resistance wire and the inner surface of the welding sleeve is not uniform. This distance gradually increases from the center of the resistance wire's cross-section towards both sides. This uneven gap distribution directly leads to uneven heating of the inner surface of the welding sleeve.

[0005] During the welding process, the area of ​​the welding sleeve directly below the center of the resistance wire has the smallest gap, the shortest heat conduction path, and the most concentrated heat flow, resulting in the highest heat absorption density. This area is highly susceptible to overheating, leading to "over-welding." Over-welding causes degradation of the polyethylene material, breaking down molecular chains, resulting in excessive melting and a sharp decrease in viscosity. Furthermore, the increased fluidity of the molten material can cause misalignment of the resistance wire, further exacerbating the instability of the weld quality.

[0006] Conversely, in the regions on either side of the center of the resistance wire, the increased gap leads to a decrease in heat flux density, and the inner surface of the welding sleeve may not reach the ideal melting temperature and state, easily resulting in a "cold weld." Cold welding results in insufficient material fusion, preventing effective intermolecular diffusion and entanglement at the joint, creating potential weak points that severely affect the strength and sealing reliability of the connection joint.

[0007] Therefore, there is an urgent need for a new technical solution to address the technical challenge of coexisting over-soldering and cold soldering caused by uneven heating. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide an electrofusion welded joint for polyethylene pipes that heats uniformly.

[0009] This invention provides an electrofusion welded joint for polyethylene pipes, comprising:

[0010] The main body has two connectors symmetrically installed at both ends, and a positive electrode and a negative electrode are respectively provided in the connectors;

[0011] The inner side of the main body is provided with an annular groove, and a polyethylene welding sleeve is engaged in the groove.

[0012] A protruding ring is provided at the center of the inner wall of the welding sleeve;

[0013] The welding sleeve is coaxially laid with spirally distributed resistance wires, which are embedded in the sleeve wall. Both ends of the resistance wires are led out of the welding sleeve in the same direction and connected to the positive and negative electrodes respectively.

[0014] The welding sleeve is also embedded with several heat-resistant insulating rods arranged at uniform intervals. The heat-resistant insulating rods extend axially along the resistance wire and are fixedly connected to the outer side of each turn of the resistance wire.

[0015] The resistance wire has a rectangular cross-section, and its inner surface is parallel to the inner surface of the welding sleeve.

[0016] As a further technical solution, a limiting groove is provided on the inner side of the heat-resistant insulating rod, and the resistance wire is snapped into the limiting groove;

[0017] The limiting groove is positioned in a spiral shape, and the radial outer side and the two axial sides of each turn of the resistance wire are in contact with the limiting groove.

[0018] As a further technical solution, the heat-resistant insulating rod has outward protrusions at both ends; the top of the protrusions has a groove, and the extension direction of the groove is perpendicular to the heat-resistant insulating rod.

[0019] As a further technical solution, the heat-resistant insulating rod is a ceramic insulating rod.

[0020] As a further technical solution, the specific connection structure between the heat-resistant insulating rod and the resistance wire is as follows: the side of the groove is first metallized;

[0021] The material used for metallizing the groove can be one of the following two cases: one is that the metallizing material of the groove is the same as the material of the resistance wire, and then it is fixed by welding;

[0022] The second is:

[0023] The metallized material of the groove is different from that of the resistance wire, and they are connected and fixed by brazing.

[0024] As a further technical solution, the welding sleeve includes an inner fusion layer and an outer base layer. The fusion layer is used to melt and fix the polyethylene pipe. The resistance wire is located inside the fusion layer, and part of the heat-resistant insulating rod is located in the fusion layer and the other part is located in the base layer.

[0025] As a further technical solution, the spacing between two adjacent turns of the resistance wire is a, and the distance between the inner surface of the resistance wire and the inner surface of the molten sleeve is b, where a = 2b.

[0026] As a further technical solution, the distance between the connection between the molten layer and the substrate layer and the outer wall of the resistance wire is set as c, where c ≥ 1.5a;

[0027] The thickness of the heat-resistant insulating rod is set to be greater than the sum of c and the thickness of the resistance wire.

[0028] As a further technical solution, the long side of the resistance wire cross-section is flush with the inner surface of the welding sleeve; the long side of the resistance wire cross-section is more than twice the length of the short side.

[0029] As a further technical solution, the inner and outer surfaces of the heat-resistant insulating rod are both arc-shaped, and this arc is concentric with the resistance wire; the length of the limiting groove wall is kept consistent. Compared with the prior art, the polyethylene pipe electrofusion welding joint of the present invention has the following beneficial effects:

[0030] (1) The heat-resistant insulating rod is non-conductive, which will not interfere with the current transmission and heating of the resistance wire during the welding process, ensuring that the welding process is carried out stably according to the designed electrical parameters, and avoiding abnormal heating or welding defects caused by additional conductive paths.

[0031] (2) The heat-resistant insulating rod has a high melting point and will not melt at high welding temperatures. It can always maintain the solid support of the resistance wire, maintain the relative position and structural stability of the resistance wire and the welding sleeve, avoid the displacement of the resistance wire due to the melting of the heat-resistant insulating rod, and ensure the reliability of the welding.

[0032] (3) The heat-resistant insulating rod is fixedly connected to the resistance wire. Multiple evenly distributed heat-resistant insulating rods act as a sturdy support, providing support to the resistance wire from multiple directions, enhancing the structural stability of the resistance wire in the welding sleeve, effectively resisting various stresses and external interferences during the welding process, so that the resistance wire will not be misaligned in the axial and radial directions.

[0033] (4) The cross-section of the resistance wire is set to be rectangular, and the distance between it and the inner side of the welding sleeve is uniform. The heat conduction path is consistent, so that the inner side of the welding sleeve is heated evenly and the melting speed is consistent. This avoids over-welding and cold welding problems caused by local overheating or overcooling, and improves the quality of the welded joint.

[0034] (5) The structural reinforcement of the heat-resistant insulating rod and the uniform heating characteristics of the rectangular resistance wire work together to ensure stable heat transfer along the circumferential and axial directions of the welding sleeve during welding. The inner wall material of the welding sleeve can achieve consistent and sufficient melting throughout the welding area, promoting the full diffusion and entanglement of polyethylene molecular chains, thereby forming a dense and high-strength fusion interface. This not only significantly improves the sealing performance and long-term service reliability of the joint, but also reduces the risk of pipeline failure due to welding defects. Attached Figure Description

[0035] Figure 1 This is a front sectional view of the present invention;

[0036] Figure 2 yes Figure 1 Enlarged view of point A in the middle;

[0037] Figure 3 yes Figure 1 Enlarged view of point B in the middle;

[0038] Figure 4 This is a schematic diagram of the connection structure between the resistance wire and the heat-resistant insulating rod;

[0039] Figure 5 yes Figure 4 Enlarged view of point C in the middle;

[0040] Figure 6 This is a front view of the heat-resistant insulating rod, showing only a portion of it;

[0041] Figure 7 yes Figure 6 Sectional view of DD;

[0042] In the figure: 1. Welding sleeve; 2. Resistance wire; 3. Heat-resistant insulating rod; 4. Limiting groove; 5. Protrusion; 6. Polyethylene pipe; 7. Protruding ring; 8. Main body; 9. Groove; 11. Melting layer; 12. Substrate layer; 13. Slot; 81. Connector; 82. Positive electrode; 83. Negative electrode. Detailed Implementation

[0043] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0044] An embodiment of the present invention discloses an electrofusion welding joint for polyethylene pipes, such as... Figure 1-4 As shown, the adjacent connecting ends of two polyethylene pipes 6 are connected together, including a main body 8. Two connectors 81 are symmetrically installed at both ends of the main body 8. A positive electrode 82 and a negative electrode 83 are respectively provided in the connectors 81, and the positive electrode 82 and the negative electrode 83 are respectively connected to the two ends of the power supply.

[0045] The inner side of the main body 8 is provided with an annular groove 9, and a polyethylene welding sleeve 1 is engaged in the groove 9. The connecting end of the polyethylene pipe 6 is inserted into the welding sleeve 1, wherein a protruding ring 7 is provided at the center of the inner wall of the welding sleeve 1, and the connecting end of the polyethylene pipe 6 abuts against the protruding ring 7 to achieve installation limitation.

[0046] The welding sleeve 1 is internally fitted with spirally distributed resistance wires 2, which are completely embedded within the sleeve wall and integrally injection molded. Both ends of the resistance wires 2 extend outwards from the welding sleeve 1 in the same direction, connecting to the positive electrode 82 and the negative electrode 83, respectively. When the resistance wires 2 are energized, electrical energy is converted into heat energy, which melts the connection surface between the welding sleeve 1 and the polyethylene pipe 6. Under high temperature and pressure, the molten material in the interface molten zone undergoes molecular chain diffusion and entanglement. After natural cooling, the welding sleeve 1 and the polyethylene pipe 6 are firmly and tightly bonded together, resulting in a welded joint with sufficient strength and a safe and reliable weld.

[0047] The welding sleeve 1 is also embedded with several heat-resistant insulating rods 3 evenly spaced along the circumference of the welding sleeve 1. In this embodiment, there are two heat-resistant insulating rods 3, which are made of ceramic. The heat-resistant insulating rods 3 extend axially from the resistance wire 2 and are fixedly connected to the outer side of each turn of the resistance wire 2. To improve the connection stability between the heat-resistant insulating rods 3 and the resistance wire 2, a limiting groove 4 is provided on the inner side of the heat-resistant insulating rod 3, and the resistance wire 2 is engaged in the limiting groove 4. Moreover, the limiting groove 4 is spirally positioned, and the radial outer side and both axial sides of each turn of the resistance wire 2 are in contact with the limiting groove 4. This arrangement increases the contact area between the resistance wire 2 and the heat-resistant insulating rod 3, and the limiting groove 4 limits the position of each turn of the resistance wire 2, resulting in higher positional stability of the resistance wire 2.

[0048] The heat-resistant insulating rod 3 has outwardly protruding protrusions 5 at both ends to increase the contact area between the heat-resistant insulating rod 3 and the welding sleeve 1, thereby improving their bonding strength. Figure 5 and Figure 6 As shown, the top of the protrusion 5 is provided with a groove 13, which is used to further increase the bonding force between the heat-resistant insulating rod 3 and the welding sleeve 1. Moreover, the extension direction of the groove 13 is perpendicular to the heat-resistant insulating rod 3. During injection molding, the injection material will flow into the groove 13, thereby forming resistance to the movement of the heat-resistant insulating rod 3 in the length direction, thereby further preventing the resistance wire 2 from axially misaligning.

[0049] Among them, such as Figure 7As shown, both the inner and outer surfaces of the heat-resistant insulating rod 3 are arc-shaped; both the inner and outer surfaces of the heat-resistant insulating rod 3 are concentric with the resistance wire 2. This configuration ensures that the distance between the bottom of the limiting groove 4 and the outer wall of the heat-resistant insulating rod 3 remains consistent, and the length of the groove wall of the limiting groove 4 also remains consistent, resulting in a uniform mass distribution in the portion of the heat-resistant insulating rod 3 with the limiting groove 4. The consistent length of the groove wall of the limiting groove 4 also ensures a uniform force distribution between the limiting groove 4 and the resistance wire 2, thereby improving the engagement stability between the limiting groove 4 and the resistance wire 2.

[0050] The specific connection structure between the heat-resistant insulating rod 3 and the resistance wire 2 is as follows: the side of the groove 9 is first metallized, and the metallized material is the same as that of the resistance wire 2, and then fixed by welding. Alternatively, it can be metallized with a different material than the resistance wire 2 and then connected and fixed by brazing.

[0051] The heat-resistant insulating rod 3 has the following advantages: First, the non-conductive nature of the heat-resistant insulating rod 3 will not interfere with current transmission and heating of the resistance wire 2 during welding, ensuring that the welding process proceeds stably according to the designed electrical parameters and avoiding abnormal heating or welding defects caused by additional conductive paths; Second, the high melting point of the ceramic material means it will not melt at the high welding temperature, maintaining solid support for the resistance wire 2 and preserving the relative position and structural stability of the resistance wire 2 and the welding sleeve 1, preventing displacement of the resistance wire 2 due to melting of the heat-resistant insulating rod 3, and ensuring the reliability of the welding; Third, the heat-resistant insulating rod 3 is fixedly connected to the resistance wire 2, and the multiple evenly distributed heat-resistant insulating rods 3 act as a sturdy support, providing support for the resistance wire 2 from multiple directions, enhancing the structural stability of the resistance wire 2 within the welding sleeve 1, effectively resisting various stresses and external forces during the welding process, and preventing the resistance wire 2 from misaligning axially and radially.

[0052] The resistance wire 2 has a rectangular cross-section, and its inner surface is parallel to the inner surface of the welding sleeve 1. This arrangement ensures that the distance between the resistance wire 2 and the inner surface of the welding sleeve 1 is uniform, and the heat conduction path is consistent. This results in uniform heating of the inner surface of the welding sleeve 1 and a consistent melting rate, avoiding over-welding or under-welding problems caused by local overheating or under-cooling, and improving the quality of the welded joint.

[0053] Among them, such as Figure 4As shown, the spacing between two adjacent turns of the resistance wire 2 is set as 'a', and the distance between the inner surface of the resistance wire 2 and the inner surface of the welding sleeve 1 is 'b', where a = 2b. This proportional relationship ensures that the heat generated by the resistance wire 2 in both the axial and circumferential directions can be transferred to the inner surface of the welding sleeve 1 with a consistent heat flux density. Since the resistance wire 2 has a rectangular cross-section and its inner surface is parallel to the inner surface of the welding sleeve 1, this specific spacing of a = 2b ensures that the heat received by any unit area on the inner surface of the welding sleeve 1 during the welding process is relatively uniform, thus achieving the ideal melting temperature simultaneously. This fundamentally eliminates the phenomenon of simultaneous localized "over-welding" and "cold welding" caused by uneven gaps in traditional circular resistance wires 2.

[0054] The long side of the resistance wire 2's cross-section is flush with the inner surface of the welding sleeve 1, and the long side of the resistance wire 2's cross-section is more than twice the length of its short side. This structure has the following advantages: while keeping the cross-sectional area of ​​the resistance wire 2 unchanged, changing the circular cross-section to a rectangular cross-section with an aspect ratio greater than 2:1 essentially reshapes the originally concentrated "point-like" heat source into a "strip-like" heat source extending along the inner wall of the welding sleeve 1. When the long side of this rectangle is parallel and flush with the inner surface of the welding sleeve 1, it means that the core heating area of ​​the resistance wire 2 is maximized and uniformly close to and covered on the inner wall surface of the welding sleeve 1 that needs to be melted. This completely changes the problem of uneven gap between the traditional circular resistance wire 2 and the inner wall of the welding sleeve 1 caused by the cross-sectional shape, allowing the heat flow to be conducted to the inner wall of the welding sleeve 1 in a wider and more uniform area, thereby eliminating the inherent defect of overheating (over-welding) in the central area and insufficient heat (cold welding) in the side areas from the perspective of heat source shape.

[0055] The resistance wire 2 is positioned close to the inner side of the welding sleeve 1; the welding sleeve 1 consists of an inner molten layer 11 and an outer base layer 12; the molten layer 11 is used for melting and fixing to the polyethylene pipe 6; the resistance wire 2 is located within the molten layer 11. For example... Figure 3As shown, at the connection between the molten layer 11 and the base layer 12, the distance between this connection and the outer wall of the resistance wire 2 is set to c, where c ≥ 1.5a. This allows the thickness of the heat-resistant insulating rod 3 to be greater than the sum of c and the thickness of the resistance wire 2, ensuring that part of the heat-resistant insulating rod 3 is located in the molten layer 11 and the remaining part in the base layer 12. The advantages of this arrangement are: First, by placing the resistance wire 2 directly within the molten layer 11 near the inner side of the welding sleeve 1, the distance heat is transferred from the resistance wire 2 to the inner wall of the welding sleeve 1 (i.e., the welding surface) is significantly shortened. This reduces heat loss during the transfer process, improves thermal efficiency, and allows heat to act more quickly and concentratedly on the molten layer 11 area that needs to be melted. Second, during the welding process, only the inner molten layer 11 is heated to a molten state and fuses with the outer wall of the polyethylene pipe 6 to be joined. The outer substrate layer 12 remains solid, serving as the structural framework of the entire joint 81. This effectively prevents the welding sleeve 1 from deforming or collapsing due to overall softening during welding heating, ensuring the dimensional stability and structural strength of the electrofusion joint 81 during welding. Third, part of the heat-resistant insulating rod 3 is located in the molten layer 11, while the remaining part is embedded and fixed in the unmelted substrate layer 12. This design allows the heat-resistant insulating rod 3 to play a crucial fixing role during welding, ensuring not only its positional stability but also preventing the resistance wire 2 from changing position.

[0056] Compared to existing technologies, the advantages of this invention are: the structural reinforcement of the heat-resistant insulating rod 3 and the uniform heating characteristics of the rectangular resistance wire 2 work together to ensure stable heat transfer along the circumferential and axial directions of the welding sleeve 1 during welding. The inner wall material of the welding sleeve 1 can achieve consistent and sufficient melting throughout the welding area, promoting the full diffusion and entanglement of polyethylene molecular chains, thereby forming a dense, high-strength fusion interface. This not only significantly improves the sealing performance and long-term service reliability of the joint 81, but also reduces the risk of pipeline failure due to welding defects.

[0057] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0058] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrofusion welded joint for polyethylene pipes, characterized in that, include: The main body has two connectors symmetrically installed at both ends, and a positive electrode and a negative electrode are respectively provided in the connectors; The inner side of the main body is provided with an annular groove, and a polyethylene welding sleeve is engaged in the groove. A protruding ring is provided at the center of the inner wall of the welding sleeve; The welding sleeve is coaxially laid with spirally distributed resistance wires, which are embedded in the sleeve wall. Both ends of the resistance wires are led out of the welding sleeve in the same direction and connected to the positive and negative electrodes respectively. The welding sleeve is also embedded with several heat-resistant insulating rods arranged at uniform intervals. The heat-resistant insulating rods extend axially along the resistance wire and are fixedly connected to the outer side of each turn of the resistance wire. The resistance wire has a rectangular cross-section, and its inner side is parallel to the inner side of the welding sleeve. The welding sleeve includes an inner fusion layer and an outer base layer. The fusion layer is used to melt and fix the polyethylene pipe. The resistance wire is located inside the fusion layer, and part of the heat-resistant insulating rod is located in the fusion layer and the other part is located in the base layer.

2. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The inner side of the heat-resistant insulating rod is provided with a limiting groove, and the resistance wire is snapped into the limiting groove; The limiting groove is positioned in a spiral shape, and the radial outer side and the two axial sides of each turn of the resistance wire are in contact with the limiting groove.

3. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The heat-resistant insulating rod has outward protrusions at both ends; the top of the protrusions has a groove, and the extension direction of the groove is perpendicular to the heat-resistant insulating rod.

4. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The heat-resistant insulating rod is a ceramic insulating rod.

5. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The specific connection structure between the heat-resistant insulating rod and the resistance wire is as follows: the side of the groove is first metallized. The material used for metallizing the groove can be one of the following two cases: one is that the metallizing material of the groove is the same as the material of the resistance wire, and then it is fixed by welding; The second is: The metallized material of the groove is different from that of the resistance wire, and they are connected and fixed by brazing.

6. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The distance between two adjacent turns of the resistance wire is a, and the distance between the inner surface of the resistance wire and the inner surface of the molten sleeve is b, where a = 2b.

7. The polyethylene pipe electrofusion welded joint according to claim 6, characterized in that, The distance between the junction of the molten layer and the substrate layer and the outer wall of the resistance wire is set as c, where c ≥ 1.5a; The thickness of the heat-resistant insulating rod is set to be greater than the sum of c and the thickness of the resistance wire.

8. The polyethylene pipe electrofusion welded joint according to claim 1, characterized in that, The long side of the resistance wire cross-section is flush with the inner surface of the welding sleeve; the long side of the resistance wire cross-section is more than twice the length of the short side.

9. The polyethylene pipe electrofusion welded joint according to claim 2, characterized in that, The inner and outer surfaces of the heat-resistant insulating rod are both arc-shaped, and this arc is concentric with the resistance wire; the length of the limiting groove wall is kept consistent.

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