JP7684876B2 - Electric fusion joint - Google Patents

Description

The present invention relates to electric fusion joints.

Conventionally, electric fusion joints have been known as joints for connecting plastic pipes such as gas pipes and water and sewer pipes. For example, an electric fusion joint has a cylindrical socket into which a plastic pipe is inserted, and a coil-shaped heating wire is embedded near the inner surface of the socket. When electricity is passed through the heating wire to heat the part close to the heating wire for a predetermined period of time, the inner surface of the socket and the outer surface of the plastic pipe are fused together.

In the electric fusion process, kinks (twisting, twisting, etc.) may occur due to thermal expansion of the heating wire. If kinks occur during current flow, the heating wires are likely to come into contact with each other and cause a short circuit, which may result in poor fusion.
Patent Document 1 proposes a method of covering an electric heating wire with an insulating film made of polyimide or the like so as to prevent a short circuit even if the electric heating wires come into contact with each other.

Japanese Patent Application Publication No. 4-347094

However, the method of Patent Document 1 has a problem in that the manufacturing cost increases.
The present invention provides an electric fusion joint in which kinking of the heating wire is unlikely to occur.

The present invention has the following aspects.
[1] An electric fusion joint having a joint body with a cylindrical socket portion and a coiled heating wire embedded in the inner peripheral surface of the socket portion, wherein the heating wire has a ring stiffness A expressed by the following formula 1 of ^2.3 x ^10-3 kgf/mm or more, where R (unit: mm) is the inner winding diameter of the heating wire, E (unit: kgf/mm2) is the Young's modulus, and d (unit: mm) is the wire diameter.
A = E I / R ³ ... Equation 1
I = π · d ⁴ / 64 ... Equation 2

The present invention provides an electric fusion joint that is less likely to kink the heating wire.

1 is a front view showing an example of an electric fusion joint according to the present invention. FIG. 1 is a schematic diagram showing an example of an X-ray image of an electric fusion joint in which a kink has occurred in the heating wire. 1 is a graph showing the results of an example and a comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a front view, partially in cross section, of an electric fusion joint 1 according to the present embodiment. The electric fusion joint 1 according to the present embodiment has a joint body 2 and a heating wire 4.
The joint body 2 is cylindrical and has openings at both ends. A positioning protrusion 2b protruding inward from an inner peripheral surface 2a is located at the center in the pipe axis Q direction, and on both sides of the protrusion 2b are cylindrical sockets 3. A plastic pipe (not shown) is inserted into the socket 3 during electrical fusion.

The socket portion 3 has a heating wire 4 embedded in the inner peripheral surface 2a of the joint body 2. In the direction of the tube axis Q, the region where the heating wire 4 exists is the heated region. Between the heated region and the opening of the joint body 2, and between the heated region and the positioning protrusion 2b, are cold regions where the heating wire 4 does not exist.
The heating wire 4 is in the form of a coil that runs along the inner circumferential surface 2a and is present in the vicinity of the inner circumferential surface 2a. The value of (R-r), which represents the difference between the inner winding diameter R of the heating wire 4 and the inner diameter r of the socket portion 3, is, for example, 0.1 to 5 mm, preferably 0.2 to 4 mm, and more preferably 0.2 to 3 mm.
The inner diameter r of the socket portion 3 can be designed depending on the application of the electric fusion joint 1. If the inner diameter r of the socket portion 3 is large, kinking of the heating wire 4 is likely to occur during electric fusion, and application of the present invention is therefore highly effective.

The distance between the coiled heating wires 4 in the direction of the tube axis Q (not including the thickness of the heating wire) is preferably, for example, 0.5 to 3 mm, and more preferably 0.5 to 2 mm. When the distance between the wires is not uniform, it is expressed as an average value.
The total number of turns of the heating wire 4 can be set according to the length of the heating region in the tube axis Q direction.

A pair of terminal pins 11 protruding radially outward from the outer circumferential surface of both ends of the joint body 2 in the pipe axis Q direction are present. The terminal pins 11 are electrically connected to the heating wire 4. When a cable connector of a current-carrying device (not shown) is attached to the terminal pins 11 and electricity is applied to the heating wire 4, the heating wire 4 generates heat.
An indicator 12 is present on the outer peripheral surface of the heating region. The indicator 12 is formed integrally with the bottom surface of a recess 12a that is recessed in the radial direction of the joint body 2. When the heating wire 4 generates heat with a plastic pipe inserted into the socket portion 3 of the joint body 2, the resin around the heating wire 4 melts and thermally expands. When sufficient pressure is applied to the fusion portion between the socket portion 3 and the plastic pipe, the indicator 12 bulges outward in the radial direction. When the indicator 12 is exposed from the recess 12a, it can be determined that the fusion has been performed properly.

The joint body 2 is made of a thermoplastic resin composition. An example of a thermoplastic resin composition is a resin composition mainly composed of polyolefin. In this specification, "a resin composition mainly composed of polyolefin" means a resin composition containing 50 mass% or more of polyolefin. For example, a resin composition made of one or more types of polyolefin, or a resin composition containing one or more types of polyolefin and additives as required, can be mentioned.
The thermoplastic resin contained in the resin composition constituting the joint body 2 may be one type or two or more types. Specific examples include polybutene resin, high density polyethylene resin, medium density polyethylene resin, polypropylene resin, etc.
The melting point of the resin composition constituting the joint body 2 is preferably 120 to 135°C, and more preferably 125 to 130°C.

The heating wire 4 is made of a material that generates heat when electricity is passed through it. Materials with high electrical resistance are preferably used. Examples include nichrome wire, iron-chromium alloy wire, copper wire, copper-nickel alloy wire, iron-nickel alloy wire, manganese wire, copper-nickel-manganese alloy wire, nickel-chromium alloy wire, and chromel wire.

When the inner winding diameter of the heating wire 4 is R (unit: mm), the Young's modulus is E (unit: kgf/mm ² ), and the wire diameter is d (unit: mm), the ring rigidity A represented by the following formula 1 is 2.3×10 ^-3 kgf/mm or more.
A = E I / R ³ ... Equation 1
I = π · d ⁴ / 64 ... Equation 2
I in the formula 1 is the second moment of area (unit: mm ⁴ ) expressed by the formula 2.
For example, the material (Young's modulus E) and wire diameter d of the heating wire 4 are designed according to the inner winding diameter R (unit: mm) of the heating wire 4 so that the ring rigidity A has a desired value.

If the ring rigidity A of the heating wire 4 is 2.3×10 ⁻³ kgf/mm or more, it is possible to prevent kinking of the heating wire 4. The ring rigidity A is preferably 5.0×10 ⁻³ kgf/mm or more, and more preferably 1.0×10 ⁻² kgf/mm or more. There is no particular upper limit to the ring rigidity A.

The electric fusion joint 1 can be manufactured by a known method. For example, a core mold corresponding to the inner shape of the joint body 2 is prepared, and the heating wire 4 is wound in a coil shape on the outer surface of the core mold. The electric fusion joint 1 can be manufactured by a method of injection molding a resin composition into the space between an outer mold corresponding to the outer shape of the joint body 2 and the core mold around which the heating wire 4 is wound.
Alternatively, the joint body 2 can be manufactured by a method of molding the inner layer member and the outer layer member, the boundary being the surface on which the heating wire 4 exists. For example, the inner layer member is first molded by injection molding, and the heating wire 4 is wound in a coil shape on its outer surface. The inner layer member wound with the heating wire 4 is placed in a mold, the outer layer member is molded by injection molding, and the inner layer member and the outer layer member are integrated together, thereby manufacturing the electric fusion joint 1.

In this embodiment, the shape of the electric fusion joint 1 is a socket, but this is not limited to this and any shape with a cylindrical receiving port can be used in the same way. Examples include a tee, elbow, etc.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.
(Example)
A socket-type electric fusion joint 1 shown in Figure 1 was manufactured. The joint body 2 was made of a resin composition (melting point 130°C) containing high-density polyethylene resin as the main component.
The obtained electric fusion joint 1 and a resin pipe were joined by electric fusion. The resin pipe was made of a resin composition (melting point 130° C.) mainly composed of high density polyethylene resin. The outer diameter of the resin pipe was selected to correspond to the nominal diameter of the electric fusion joint 1.
After the electric fusion, an X-ray inspection was performed to observe the electric heating wire and check whether or not a kink had occurred. Figure 2 is a schematic diagram showing an X-ray image of an electric fusion joint in which a kink had occurred in the electric heating wire. Reference numeral 20 indicates the portion in which a kink had occurred.
The results of investigating whether or not kinking occurred for various electric fusion joints 1 with different dimensions are shown in Figure 3. In Figure 3, the horizontal axis represents the inner diameter r of the socket part of the joint, and the vertical axis represents the ring rigidity A. ○ represents an example where kinking did not occur, and × represents an example where kinking occurred.
As shown in the results in FIG. 3, when the ring rigidity A of the heating wire was 2.3×10 ⁻³ kgf/mm or more, kinking did not occur.

Reference Signs List 1 Electric fusion joint 2 Joint body 2a Inner peripheral surface 2b Positioning projection 3 Socket portion 4 Heating wire

Claims (1)

A joint body having a cylindrical socket portion and a coil-shaped heating wire embedded in an inner peripheral surface of the socket portion,
The electric fusion joint has a ring rigidity A represented by the following formula 1 of 2.3 x 10-3 kgf/mm or more, where R (unit: mm) is the inner winding diameter of the heating wire, E (unit: kgf/ ^mm2 ) is the Young's modulus, ^and d (unit: mm) is the wire diameter.
A = E I / R ³ ... Equation 1
I = π · d ⁴ / 64 ... Equation 2

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