Coil-based method for preparing electrofusion fittings and electrofusion fittings

Abstract

The present invention discloses a preparation method of an electrofusion fitting based on a coil and an electrofusion fitting. This method improves the fixing method of the resistance coil in the electrofusion fitting, forms an injection molding model of the electrofusion fitting based on the coil, and selects appropriate time parameters based on the welding process, improving the development efficiency of the electrofusion fitting and ensuring that when the electrofusion fitting is assembled with other pipes, the resistance coil is not easily displaced, does not easily leak wires, and is not easily damaged.

Description

Technical Field

[0001] The present invention relates to the technical field of electrofusion pipe fittings, and particularly to a preparation method and electrofusion pipe fittings based on a coil. Background Art

[0002] Electrofusion pipe fittings refer to a kind of plastic (such as polyethylene) pipe fittings that can be melted by the temperature generated by an electric current to achieve connection. Electrofusion pipe fittings can perform electrofusion connection on plastic pipes with different melt indexes, and can adapt to complex and narrow construction environments. In addition, the weld joints formed by using electrofusion pipe fittings have a high safety factor. Therefore, electrofusion pipe fittings are widely used in the field of pipe connection. However, in the related art, the resistance coil is usually fixed inside the pipe fitting by an injection molding heat fixation method or a numerically controlled machine tool mechanical placement method, and a part of the resistance coil is exposed outside, which is not only easy to oxidize, but also easy to squeeze the resistance wire during pipe assembly, so that leakage, wire breakage or short circuit problems are likely to occur during the application process, affecting the use of electrofusion pipe fittings. In addition, the connection terminals of the electrofusion pipe fittings in the related art and the coil usually adopt a cold contact method, and the risk of poor contact and loose contact is relatively high. There are large differences in the welding time parameters of electrofusion pipe fittings of the same specification in the market. And currently, the verification of the time parameters of electrofusion pipe fittings will cause irreversible damage to the products, resulting in high verification test costs, long cycles and low efficiency for the time parameters. Summary of the Invention

[0003] To solve at least to some extent the above deficiencies, the present invention provides a preparation method and electrofusion pipe fittings based on a coil.

[0004] The preparation method of the electrofusion pipe fittings based on a coil provided by the present invention includes: establishing a mathematical model of the coil based on the key parameters of the electrofusion pipe fittings, namely the length of the melting zone, the length of the cooling zone, the linear distance parameter from the inner wall surface of the electrofusion pipe fitting to the outer wall surface of the coil, and the number of turns of the coil, simulating and selecting the welding time parameter of the electrofusion pipe fitting based on the electrothermal conversion characteristics of the coil, and placing the coil in the polyethylene material body to manufacture the electrofusion pipe fitting, and then verifying the compliance of the time parameter. The specific steps are as follows:

[0005] Taking the center point of the coil as the coordinate origin to construct a coordinate system, and constructing a mathematical model equation based on the coil:

[0006] X = A * cos(θ * 360 * N);

[0007] Y = A * sin(θ * 360 * N);

[0008] Melting zone: Z = L * θ ± B;

[0009] Cooling zone: Z = B * θ;

[0010] Wherein: A = (dn + D) / 2 + T, where dn is the inner diameter of the electrofusion fitting, D is the diameter of the resistance wire forming the coil, T is the linear distance from the inner wall surface of the electrofusion fitting to the outer wall surface of the coil, N is the number of turns of the coil, the coil sequentially has a first melting zone, a cooling zone, and a second melting zone in its axial direction, L is the length of the first melting zone or the second melting zone, B is half of the length of the cooling zone, and 0 ≤ θ ≤ 1.

[0011] Form a coil based on the mathematical model equation.

[0012] Envelop the guide sleeve based on the formed coil to form an insert combination.

[0013] Form an injection-moldable model of the electrofusion fitting based on the insert combination, simulate the energy demand relationship during the electrofusion fitting welding process, and select the time parameters for electrofusion welding based on the electrothermal conversion characteristics of the coil.

[0014] Manufacture the electrofusion fitting according to the injection-moldable model of the coil, and thermoset the coil in the polyethylene material body.

[0015] Optionally, A is greater than or equal to the diameter of the pipe fitting that mates with the electrofusion fitting; and / or L is greater than or equal to the minimum value specified in Chinese national standard GB15558.2.

[0016] Optionally, B is greater than 5 cm.

[0017] Optionally, it further includes performing performance tests on the electrofusion fitting, and the performance tests include peel tests and hydrostatic tests for welding at normal temperature, high temperature, or low temperature.

[0018] Optionally, it further includes detecting the distribution of the coil in the polyethylene material body of the electrofusion fitting.

[0019] Optionally, the guide sleeve is a tubular structure, and the outer diameter of the guide sleeve is A.

[0020] Optionally, the guide sleeve has a first enveloping zone, an intermediate zone, and a second enveloping zone. The first melting zone envelops the first enveloping zone, the second melting zone includes the second enveloping zone, and the cooling zone envelops the intermediate zone.

[0021] Optionally, simulating the energy demand relationship during the electrofusion fitting welding process includes: based on the resistance property of the coil, the material property of the polyethylene material body, and the output energy supply of the electrofusion welder, simulate the change of the temperature field in the welding area over time, and select the time parameters for welding.

[0022] Optionally, the electrofusion fitting includes two terminal posts, and both ends of the coil are thermoset in the two terminal posts respectively.

[0023] Another embodiment of the present invention also provides an electrofusion fitting prepared by the preparation method in any of the above embodiments.

[0024] The present invention provides a preparation method for an electrofusion fitting based on a coil, which improves the fixing method of the resistance coil in the electrofusion fitting, forms an injection molding model of the electrofusion fitting based on the coil, and selects appropriate time parameters based on the welding process, improving the development efficiency of the electrofusion fitting and ensuring that when the electrofusion fitting is assembled with other pipes, the resistance coil is not easily displaced, not easily leaked, and not easily damaged.

[0025] Those skilled in the art will better understand the above and other objects, advantages, and features of the present invention from the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings. Brief Description of the Drawings

[0026] Some specific embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings in an exemplary but non-limiting manner. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0027] Figure 1 is a front view of the coil in an embodiment of the present invention.

[0028] Figure 2 is a structural diagram of the coil in an embodiment of the present invention.

[0029] Figure 3 is a structural diagram of the insert combination in an embodiment of the present invention.

[0030] Figure 4 is a model diagram of the guide sleeve in an embodiment of the present invention.

[0031] Figure 5 is a perspective view of the electrofusion fitting in an embodiment of the present invention.

[0032] Figure 6 is a schematic diagram of the cooperation between the electrofusion fitting and other pipes in an embodiment of the present invention.

[0033] Figure 7 is a simulation experiment diagram of the electrofusion fitting in an embodiment of the present invention.

[0034] Figure 8 is a material property diagram of the copper coil in an embodiment of the present invention.

[0035] Figure 9 is a material property diagram of the polyethylene material body in an embodiment of the present invention.

[0036] Figure 10 is a schematic diagram of the state of loading the coil with a load.

[0037] Reference numerals:

[0038] Electrofusion fitting 100, coil 1, first melting zone 11, cooling zone 12, second melting zone material 13, polyethylene material body 2, guide sleeve 3, first envelope zone 31, intermediate zone 32, second envelope zone 33, pipe 4, terminal post 5. Detailed implementation manners

[0039] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0040] In order to solve problems such as resistance coil wire leakage, short circuit and open circuit of electrofusion fittings, the present invention proposes a preparation method of an electrofusion fitting based on a coil, and an electrofusion fitting prepared by this preparation method. The present invention improves the fixing method of the resistance coil in the electrofusion fitting, forms an injection molding model of the electrofusion fitting based on the coil, and selects appropriate time parameters based on the welding process, improves the development efficiency of the electrofusion fitting, and ensures that when the electrofusion fitting is assembled with other pipes, the resistance coil is not easy to shift, not easy to leak wire, and not easy to break.

[0041] As Figures 1-9 shown, the preparation method of the electrofusion fitting 100 based on the coil 1 provided by the present invention, the coil 1 is the resistance coil, which is formed by helically winding the resistance wire, and the preparation method includes the following steps:

[0042] Step 1: Construct a coordinate system with the center point of the coil 1 as the coordinate origin, and construct a mathematical model equation of the melting zone based on the coil 1. The center point of the coil 1 refers to the midpoint of its central axis, and the mathematical model equation is as follows:

[0043] X = A * cos(θ * 360 * N);

[0044] Y = A * sin(θ * 360 * N);

[0045] Melting zone: Z = L * θ ± B;

[0046] Cooling zone: Z = B * θ;

[0047] Wherein: The units of X, Y, and Z are all millimeters. A = (dn + D) / 2 + T, where dn is the inner diameter of the electrofusion fitting 100, with the unit of millimeter; D is the diameter of the resistance wire of the construction coil 1, with the unit of millimeter; T is the straight-line distance from the inner wall surface of the electrofusion fitting 100 to the outer wall surface of the coil 1, with the unit of millimeter; N is the number of turns of the coil 1, which is equal to the straight-line length of the resistance wire divided by the average pitch; The coil 1 successively has a first melting zone 11, a cooling zone 12, and a second melting zone 13 along its axial direction. Both the first melting zone 11 and the second melting zone 13 are melting zones. L is the length of the first melting zone 11 or the second melting zone 13, with the unit of millimeter. B is half of the length of the cooling zone 12, with the unit of millimeter. The spiral turns of the coil 1 are mainly concentrated in the first melting zone 11 and the second melting zone 13. The cooling zone 12 only serves to connect the first melting zone 11 and the second melting zone 13 and does not play a role in melting and heating. During welding, the temperatures of the first melting zone 11 and the second melting zone 13 are relatively high, while the temperature of the cooling zone is relatively low; 0 ≤ θ ≤ 1, and θ is a parameter for the lengths of the melting zone and the cooling zone to change with the resistance wire pitch and the inner diameter of the electrofusion fitting 100.

[0048] Step 2: As Figure 1 and Figure 2 shown, construct the model of the coil 1 based on the mathematical model equation of the coil 1 in Step 1;

[0049] Step 3: As Figure 3 and Figure 4 shown, perform an envelope of the guiding sleeve 3 based on the coil 1 in Step 2 to form an insert combination as shown in Figure 3 . The envelope of the coil 1 on the guiding sleeve 3 means that the coil 1 is sleeved on the guiding sleeve 3, and the guiding sleeve 3 supports and fixes the coil 1 so as to form an injection molding model based on this insert combination in subsequent steps;

[0050] Step 4: As Figure 5 shown, form an injection-moldable model of the electrofusion fitting 100 based on the insert combination in Step 3, and simulate the energy demand relationship during the welding process of the electrofusion fitting 100, and select the time parameter. Due to the non-adjustability of thermal fixation, it is necessary to simulate the use performance of the electrofusion fitting and select appropriate time parameters;

[0051] Step 5: Manufacture the electrofusion fitting 100 according to the injection-moldable model in Step 4, and thermally fix the solid coil 1 in the polyethylene material body 2 to form the electrofusion fitting 100.

[0052] It should be noted that the time parameter selected in step 4 refers to the fusion time between the electrofusion fitting 100 and the pipe 4, that is, the heating time for the electrofusion fitting 100 to complete the electrofusion connection. When electrofusing the electrofusion fitting 100 and the pipe 4, the electrofusion fitting 100 is energized within a specific heating time to make the coil 1 release heat, so as to complete a stable electrofusion connection between the electrofusion fitting 100 and the pipe 4, avoiding unstable connection due to too short fusion time or excessive melting of the polyethylene material body 2 of the electrofusion fitting 100 due to too long fusion time, which affects the connection relationship.

[0053] The selection of the time parameter is related to the material properties of the polyethylene material body 2 of the electrofusion fitting 100, the resistance characteristics of the coil 1, etc. The preparation method of the electrofusion fitting 100 based on the coil 1 in the present invention is to utilize the electrical characteristics of the coil 1, etc., to confirm the most reasonable fusion time. Compared with the current common technical solution of conducting post-tests on the prepared electrofusion fitting 100 to find out the fusion time, this method first simulates appropriate time parameters based on the coil 1, and then can prove the rationality of the selected time parameter through verification, with higher development efficiency, shorter cycle and lower cost. Under a certain voltage condition (for example, 39.5 volts is selected according to national standards or market general standards), the coil is raised to a certain temperature and kept constant to prevent the polyethylene material from carbonizing. The research based on the coil is to find the time range in which the polyethylene material is best melted and does not carbonize under the change of multi-parameter conditions. Figure 10 It is a schematic diagram of the state of loading the coil. The correlation between the coil and the relevant parameters of the electrofusion fitting under different condition loads is studied through simulation.

[0054] The preparation method of the electrofusion fitting provided by the present invention conducts an overall design of the electrofusion fitting based on the electrical characteristics of the coil. According to the relevant parameter boundary conditions in the standard, a mathematical model equation of the coil is established, and the time parameter is selected for the welding process simulation. The coil is thermally fixed in the polyethylene material body, with a firm and reliable structure. The coil is not easy to loosen, so the problem of poor contact will not occur. At the same time, the coil is not easy to be squeezed and damaged, and the problems of open circuit or short circuit are not easy to occur. During the process of forming the insert assembly by enclosing based on the coil, the coil is not easy to be damaged. Even if the coil is damaged, it can be directly observed and revised in time. Therefore, the electrofusion fitting prepared according to the preparation method of the electrofusion fitting provided by the present invention has excellent performance stability.

[0055] The diameter D of the resistance wire forming the coil 1 is related to the resistance and thermoelectric characteristics of the resistance wire. The diameter of the resistance wire of the coil 1 can be selected optimally according to needs. In addition, the straight-line distance T from the inner wall surface of the electrofusion fitting 100 to the outer wall surface of the coil 1 can be selected optimally according to needs.

[0056] The produced electrofusion fittings shall ensure that the coil and the seal do not shift during assembly.

[0057] Optionally, the electrofusion fittings may be electrofusion sleeves, electrofusion elbows, electrofusion reducers, electrothermal fusion tees and other electrofusion fittings.

[0058] Preferably, the parameter A in the mathematical model equation in the above step 1 is greater than or equal to the diameter of the pipe 4 that mates with the electrofusion fitting 100. As Figure 6 shown, when the electrofusion fitting 100 is sleeved on the pipe 4 such that A is greater than or equal to the diameter of the pipe 4, it can prevent the pipe 4 from squeezing the electrofusion fitting 100 and causing deformation of the electrofusion fitting 100, thereby avoiding deformation or even breakage of the coil 1, and reducing the risk of the coil 1 breaking or short - circuiting.

[0059] Preferably, L is greater than or equal to the minimum value specified in the Chinese national standard GB15558.2. In this standard, different nominal diameters correspond to different minimum values of L. For example, when the nominal diameter is 32 mm, the minimum value of L is 10 mm; when the nominal diameter is 75 mm, the minimum value of L is 12 mm, and so on.

[0060] Preferably, B is greater than 5 cm, that is, the length of the cooling zone 12 is greater than 10 cm.

[0061] Preferably, the material of the coil 1 is copper, that is, the coil 1 is a copper coil. Further, high - purity copper or copper - nickel alloy is selected to make the coil 1. The copper coil can achieve stable heat transfer at 140 °C - 270 °C, has excellent thermal conductivity and specific heat capacity, and also has extremely high heat - shock resistance, and can work in a high - temperature environment of 220 °C and below for a long time.

[0062] Preferably, the material of the polyethylene material body 2 is polyethylene.

[0063] Optionally, in the step of simulating the energy demand relationship during the welding process of the electrofusion fitting 100, the output power of the selected electrofusion welder can be 3.5 kW, and the output electric pressure can be 39 - 40 V to simulate the welding environment under actual working conditions.

[0064] In some embodiments, as Figure 3 and Figure 4 shown, the guide sleeve 3 is a tubular structure, and the outer diameter of the guide sleeve 3 is A.

[0065] As Figure 4 shown, the guide sleeve 3 has a first envelope area 31, an intermediate area 32 and a second envelope area 33. As Figure 3 shown, the first fusion zone 11 envelopes the first envelope area 31, the second fusion zone 13 includes the second envelope area 33, and the cooling zone 12 envelopes the intermediate area 32.

[0066] A = (dn + D) / 2 + T, where dn is the inner diameter of the electrofusion fitting, D is the diameter of the resistance wire, and T is the distance from the inner wall of the electrofusion fitting to the outer wall of the resistance coil; L is the length of the first fusion zone 11 or the second fusion zone 13. In the Figure 3 and Figure 4 illustrated embodiment, the lengths of the first fusion zone 11 and the second fusion zone 13 are equal, both being L; B is half of the intermediate cooling zone. As Figure 4 shown, the length of the cooling zone is 2B; L1 is the distribution length of the resistance wire in the first fusion zone 11 or the second fusion zone 13, and L2 is the distribution length of the resistance wire in the intermediate zone 32.

[0067] Step 4 specifically includes designing a working model of the electrofusion fitting 100 based on the insert combination, i.e., an injection molding model, and simulating the energy demand relationship during the welding process of the electrofusion fitting 100. Simulating the energy demand relationship during the welding process of the electrofusion fitting specifically includes: based on the resistance property of the coil 1, the material property of the polyethylene material body 2, and the output energy supply of the electrofusion welder, simulating the change of the temperature field in the welding area over time, and selecting the welding time parameters.

[0068] In step 5, the polyethylene material is thermoformed and the coil 1 is firmly fixed, effectively realizing the position positioning of the coil 1.

[0069] As Figure 5 shown, the electrofusion fitting 100 includes two terminal posts 5, and both ends of the coil 1 are thermally fixed in the two terminal posts 5 respectively.

[0070] In some embodiments, the method for preparing an electrofusion fitting based on a coil further includes detecting the distribution of the coil 1 in the polyethylene material body 2 of the prepared electrofusion fitting 100 to detect whether the distribution of the coil 1 in the actually prepared electrofusion fitting 100 is consistent with the designed coil 1, so as to test the reliability of the preparation method. Optionally, X-ray fluoroscopy detection or other methods can be used for detection.

[0071] In some embodiments, the method for preparing an electrofusion fitting based on a coil further includes performing performance tests on the prepared electrofusion fitting 100. The performance tests include peel tests and hydrostatic tests for welding at normal temperature, high temperature, or low temperature.

[0072] The following describes a specific embodiment provided by the present invention.

[0073] In this specific embodiment, the material property of the copper coil 1 is as Figure 8 shown, and the thermal property of the polyethylene material of the polyethylene material body 2 is as Figure 9 shown.

[0074] Taking the center point of the coil 1 as the coordinate origin to construct a coordinate system, and constructing a mathematical model equation based on the coil 1. The mathematical model equation is as follows:

[0075] Fusion zone:

[0076] x = 46.5 * cos(θ * 360 * 16)

[0077] y = 46.5 * sin(θ * 360 * 16)

[0078] z = 32 * θ ± 15 Cooling zone:

[0079] x = 46.5 * cos(θ * 360 * 0.5)

[0080] y = 46.5 * sin(θ * 360 * 0.5)

[0081] z = 15 * θ.

[0082] Based on the above model equations, a model of coil 1 as shown in Figure 1 and Figure 2 can be formed;

[0083] Based on the model of coil 1, loading is carried out, and an insert is placed to form an insert combination as shown in Figure 3 ;

[0084] The formed insert combination is transformed into an injection-moldable model of electrofusion fitting 100 as shown in Figure 5 . The relationship between the temperature field and time during the welding process of electrofusion fitting 100 is simulated, and the time parameters 205 seconds, 200 seconds, and 196 seconds shown in the following table are selected;

[0085] Insert injection molding production is carried out to form electrofusion fitting 100;

[0086] Check the distribution of resistance coil 1 in electrofusion fitting 100;

[0087] Perform performance tests on the prepared electrofusion fitting 100, including peel tests and hydrostatic tests for welding at normal temperature, high temperature, or low temperature. And the energy of the electrofusion welder is basically consistent with the energy selected in the simulation test. The electrofusion welder is a voltage-type electrofusion welder with an output effective voltage of 39 - 40 volts.

[0088] The electrofusion fitting 100 prepared in this embodiment passes the relevant peel and hydrostatic tests required by national standard GB15558.2 and GIS standard, as shown in the following table:

[0089]

[0090] The present invention discloses a preparation method of an electrofusion fitting based on a coil. By analyzing the problems of short circuit and open circuit that easily occur in electrofusion fittings in related technologies, according to the boundary principle of electrofusion fittings in relevant standards and the market adaptability criterion of electrofusion fittings to electrofusion welding machines, a coil parameter model equation (coil design) is constructed. A coil envelope guide sleeve and an insert combination form an injection molding model, and the welding process of the electrofusion fitting is simulated to complete the selection of time parameters, and finally the electrofusion fitting is prepared. The implementation method of the electrofusion fitting based on the coil in the present invention effectively solves the problems of oxidation of the resistance coil of the electrofusion fitting, short circuit and open circuit of the electrofusion fitting, and improves the quality of the electrofusion fitting product and the development efficiency of the new electrofusion fitting product.

[0091] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing an electrofusion fitting based on a coil, characterized in that, it includes: establishing a mathematical model of the coil based on the key parameters of the electrofusion fitting, namely the melting zone length, the cooling zone length, the linear distance parameter from the inner wall surface of the electrofusion fitting to the outer wall surface of the coil, and the number of turns of the coil, simulating and selecting the welding time parameter of the electrofusion fitting based on the electrothermal conversion characteristics of the coil, and placing the coil in the polyethylene material body to manufacture the electrofusion fitting, and then verifying the compliance of the time parameter. The specific steps are as follows: Taking the center point of the coil as the coordinate origin to construct a coordinate system, and constructing a mathematical model equation based on the coil: X = A * cos(θ * 360 * N); Y = A * sin(θ * 360 * N); Melting zone: Z = L * θ ± B; Cooling zone: Z = B * θ; Where: A = (dn + D) / 2 + T, dn is the inner diameter of the electrofusion fitting, D is the diameter of the resistance wire for constructing the coil, T is the linear distance from the inner wall surface of the electrofusion fitting to the outer wall surface of the coil, N is the number of turns of the coil, the coil sequentially has a first melting zone, a cooling zone and a second melting zone in its axial direction, L is the length of the first melting zone or the second melting zone, B is half of the length of the cooling zone, 0 ≤ θ ≤ 1, Forming the coil based on the mathematical model equation; Enveloping the guiding sleeve based on the formed coil to form an insert combination; Forming an injection-moldable model of the electrofusion fitting based on the insert combination, simulating the energy demand relationship during the electrofusion welding process of the electrofusion fitting, and selecting the time parameter of the electrofusion welding based on the electrothermal conversion characteristics of the coil; Manufacturing the electrofusion fitting according to the injection-moldable model of the coil, and thermosetting the coil in the polyethylene material body; Simulating the energy demand relationship during the electrofusion welding process of the electrofusion fitting includes: simulating the change of the temperature field in the welding area over time based on the resistance property of the coil, the material property of the polyethylene material body, and the output energy supply of the electrofusion welder, and selecting the time parameter of the welding.

2. The method for preparing an electrofusion fitting based on a coil according to claim 1, characterized in that, A is greater than or equal to the diameter of the pipe fitting that mates with the electrofusion fitting; L is greater than or equal to the minimum value specified in Chinese national standard GB15558.

2.

3. The method for preparing an electrofusion fitting based on a coil according to claim 1, characterized in that, B is greater than 5 cm.

4. The method for preparing an electrofusion fitting based on a coil according to claim 1, characterized in that, it further includes performing performance tests on the electrofusion fitting, and the performance tests include peel tests and hydrostatic tests for welding at normal temperature, high temperature or low temperature.

5. The method for preparing an electrofusion fitting based on a coil according to claim 1, characterized in that, it further includes detecting the distribution of the coil in the polyethylene material body of the electrofusion fitting.

6. The method for preparing an electrofusion fitting based on a coil according to claim 1, characterized in that, the guiding sleeve is a tubular structure, and the outer diameter of the guiding sleeve is A.

7. The method for preparing an electrofusion fitting based on a coil according to claim 6, characterized in that, The guiding sleeve has a first enveloping area, an intermediate area, and a second enveloping area. The first melting area envelops the first enveloping area, the second melting area envelops the second enveloping area, and the cooling area envelops the intermediate area.

8. The method for preparing a coil-based electrofusion fitting according to claim 1, wherein, the electrofusion fitting includes two terminal posts, and both ends of the coil are thermoset within the two terminal posts respectively.

9. An electrofusion fitting, wherein, it is prepared according to the method for preparing a coil-based electrofusion fitting according to any one of claims 1-8.

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