JPH066345B2 - Plastic pipe joint and its electric fusion connection method - Google Patents

Description

The present invention relates to a plastic pipe joint for electrically connecting a plastic pipe and a plastic pipe joint to each other, and an electric fusion connection method therefor.

[Conventional technology]

A general plastic pipe joint and a plastic pipe connected thereto are shown in FIG. 8 in a longitudinal sectional view. Figure 8 shows
The plastic pipe 2A and one end of the plastic pipe joint 100 are electrically fused and connected, and the other end of the plastic pipe joint 100 and the plastic pipe 2B are electrically fused and connected to each other to make the plastic pipe The state where the tube 2A and the tube 2B are connected is shown.

The plastic pipe joint 100 includes a pipe joint body 101, a heating wire 12, and two connector pins 13. The pipe joint body 101 is made of plastic and has an annular projection 14 formed on the inner peripheral surface of the through hole and in the axially intermediate portion. The heating wire 12 is embedded in the inner peripheral surface of the pipe joint body 101 in a coiled manner. The lower part of each of the two connector pins 13 is embedded in both ends of the pipe joint body 101, and is connected to each end of the heating wire 12. The upper portion of the connector pin 13 projects from the outer peripheral surface of the pipe joint body 101. A cylindrical protrusion 16 is formed around the connector pin 13 on the outer peripheral surface of the pipe joint body 101.

Next, the plastic pipe 2A and the plastic pipe 2B
The connection sequence between the and the plastic pipe fitting 100 will be described.

First, the plastic pipe 2A and the plastic pipe 2
Insert A into the through hole of the plastic pipe joint 100 from each end, and insert until it hits the protrusion 14. Next, a connector (not shown) is inserted into each connector pin 13 at both ends of the plastic pipe fitting 100. Through this connector, the heating wire 12 of the plastic pipe fitting 100
Pass a current through. This energization causes the heating wire 12 to generate heat,
The inner peripheral surface portion of the plastic pipe joint 100 and the outer peripheral surface portions of the insertion portions of the plastic pipes 2A and 2B are melted. After this melting, the energization is stopped and the components are cooled to bond them. After this, the connector is removed from the plastic pipe fitting 100 to complete these connections.

Conventionally, energization control in this connection has been performed as follows. That is, the temperature and the plastic pipe fitting 100
The control is such that the initial temperature on the surface of, for example, is measured, the energization time to the plastic pipe joint 100 is set by the measured temperature, and the energization is performed during this set time. An example of the relationship between this energization time and the initial temperature is shown in FIG. 9, and the initial temperature is changed from -10 ° C to 40 ° C at 5 ° C intervals of 10 ° C.
According to the stage, the energization time is 120 seconds when the initial temperature is from -10 ° C to 0 ° C, the energization time is 110 seconds when the initial temperature is from 0 ° C to 10 ° C, and 100 se when the temperature is from 10 ° C to 20 ° C.
c, 90 seconds at 20 ° C to 30 ° C, 80 seconds at 30 ° C to 40 ° C.

[Problems to be solved by the invention]

As described above, the energization control for setting the energization time to the plastic pipe joint has a problem that it is difficult to set the energization time.

The reason for this is that the setting of the energization time must be set not only by the initial temperature of the surroundings but also by the size of the plastic pipe joint, the plastic material, the temperature measurement position, and the error in the electrical resistance of the heating wire, There is a possibility that the optimum energization time may change depending on the error of the current value or voltage value and the accuracy of the temperature measuring device.

The object of the present invention is an electric fusion-bonding connection method between a plastic pipe joint and a plastic pipe, which is suitable for the connection method having no difficult energization time and having sufficient performance for connection, and this connection method. To provide a plastic pipe fitting, as well as a fusion plug and a thermocouple.

[Means for solving problems]

The present invention relates to a pipe joint main body made of a thermoplastic resin material, a heating wire embedded in an inner surface of the main body, and both ends of the heating wire, the lower part is embedded in the main body and the upper part is an outer peripheral surface of the main body. In the electrofusion-type pipe joint in which a more protruding connector pin and a recessed hole for fitting a sensor near the connector pin are formed, the distance from the bottom surface of the recessed hole of the main body to the embedded heating wire is The plastic pipe joint is characterized in that the distance is greater than the distance from the inner surface of the main body to the heating wire.

Further, the connection method is as follows: first, the plastic pipe is inserted into the plastic pipe joint; and second, a connector and a thermocouple that are fitted to the connector pin of the plastic pipe joint are connected to each other. A fusion plug consisting of a holder that holds it integrally is fitted and attached to the connector pin of the plastic pipe joint and the concave hole for the thermocouple, and thirdly, the plastic is inserted through the connector of the fusion plug. When an electric current is passed through the heating wire of the pipe joint to generate heat, and fourthly, the temperature rise is continuously measured by the thermocouple of the fusion plug and the result is displayed, and when the preset temperature is reached. 5th, after stopping the current to the plastic pipe fitting, measure the temperature drop with the thermocouple to remove the fusion plug from the plastic pipe fitting. The electric fusion-bonding connection method for a plastic pipe joint is characterized in that a detachable temperature is set in advance and a display is displayed when the temperature has dropped to the set temperature.

[Action]

The electric fusion-bonding connection method of the plastic pipe joint according to the present invention measures the temperature of the plastic pipe joint by using a thermocouple, and controls the energization of the plastic pipe joint based on this temperature. There is no difficult setting of energization time,
In addition, the connection method has sufficient performance for connection. In addition, the plastic pipe joint has a concave hole for the thermocouple, and the distance from the inner peripheral surface of the pipe joint body to the heating wire is a constant value for each size, and the distance from the bottom of the concave hole to the heating wire is Since the size is set to be slightly larger than the above distance and each size is set within a substantially constant range, the place where the thermocouple measures is the place where the resin does not melt, and the measured temperature is the fusion point of the plastic pipe joint. Since it is in a close place, the position suitable for energization control is measured.

〔Example〕

A plastic socket pipe joint according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a vertical cross-sectional view showing a state in which a fusion plug 3 is attached to one end of a plastic socket pipe joint 1 in an attempt to connect the plastic pipe 2A to one end of the plastic socket pipe joint 1.
The plastic pipe 2A is exactly the same as the plastic pipe 2A described in the section of the related art, and the plastic socket pipe joint 1 is almost the same as the plastic pipe joint 100 described in the section of the related art, and is different. The point is that the plastic socket pipe joint 1 of the present embodiment has a concave hole 15 for a thermocouple formed near a cylindrical projection 16 formed around the connector pin 13 of the socket pipe joint body 11. Therefore, the plastic socket pipe joint 1 is also symmetrical with respect to the middle in the axial direction. The connector pin 13, the cylindrical projection 16 and the concave hole 1 for the thermocouple shown in FIG.
5 is also provided at the other end of the plastic socket pipe joint 1, and the fusion plug 3 is attached to this other end. Also,
The plastic socket fitting 1 also comprises a socket fitting body 11, a heating wire 12 and two connector pins 13.

Here, the recessed hole 15 for the thermocouple of the plastic socket pipe joint 1 is a hole for inserting a thermocouple described later, and an electric wire wound around and embedded in the bottom surface and the inner peripheral portion of the socket pipe joint body 11. The distance from the outer diameter surface of the heating wire 12 is set to be slightly larger than the distance from the outer diameter surface of the heating wire 12 to the inner peripheral surface of the socket pipe joint body 11. The reason is that if it is too large, the temperature close to the outside air temperature will be measured as usual, and the accuracy will be poor. On the other hand, if it is too small, the temperature of the heating wire is almost measured, and the average temperature of the portion to be melted is not measured. In addition, since the heating wire may move and come into contact with the thermocouple during melting, it is not preferable that it is too small.

Actually, the desirable dimension is 0.6 to 1.8 mm between the bottom surface of the recessed hole 15 and the outer diameter surface of the heating wire 12 wound and embedded in the inner peripheral portion of the socket pipe joint body 11, and the outer diameter of the heating wire 12 is 0.4-0.6
It can be said that the distance from the outer diameter surface of the heating wire 12 to the inner peripheral surface of the socket pipe joint body 11 is about 0.5 to 0.6 mm.

Next, the fusion plug 3 will be described with reference to FIG. The fusion plug 3 is fitted and mounted in the connector pin 13 and the thermocouple recessed hole 15 of the plastic socket pipe joint 1, and the connector 31 fitted in the connector pin 13
A thermocouple 32, a holder 33 that integrally holds the connector 31 and the thermocouple 32, and a cap 34 of the holder 33. There are two fusion plugs 3, and each is connected to the wire 5. The connector 31 has a connector bush 311 having a hole for fitting with the connector pin 13, a bush case 312 covering the outer peripheral surface of the connector bush 311, and a connector bush 3
11 and the bush case 312 are connected to each other by a connecting pin 313.
It consists of The thermocouple 32 includes a thermocouple body 321 and
The thermocouple case 322 covers the thermocouple body 321.

The holder 33 holds the connector 311 and the thermocouple 32 in parallel and integrally, and the holder 33 and the connector 31 are detachable, and the holder 33 and the thermocouple 32 are detachable.
Is also removable. The holder 33 fits the upper part of the connector 31, and also fits the upper part and the middle part of the thermocouple 32. The lower part of the connector 31 in the holder 33 is not in contact with the connector 31 and there are gaps at equal intervals. The wire 5 is a power cable 54 and a lead wire 52.
And a protective tube 53 that covers the energizing cable 54 and the lead wire 52. The energizing cable 54 is connected to the upper portion of the connector bush 311 and is connected to the lead wire 52.
Is connected to the thermocouple body 321. The cap 34 is made of rubber, the lower part is fitted to the outer peripheral surface of the upper part of the holder 33, the upper part is fitted to the outer peripheral surface of the protective tube 53 of the wire 5, and the connection part between the energizing cable 54 and the connector bush 311 is covered. At the same time, the lead wire 52 and the thermocouple body 321
It covers the connection part with.

Next, the details of the thermocouple body 321 will be described. FIG. 2 shows a partial vertical sectional view of the thermocouple 321 and FIG. 3 is a sectional view taken along the line AA of FIG. The thermocouple 321 is a protective tube 32.
The thermocouple wires 324 and 3 are composed of five and two thermocouple wires 324 and 324 'and their connecting portions 323.
No. 24 'has no particular difference in material and shape from the conventional thermocouple wire.

The protection tube 325 is made of ceramics or ceramics, that is, made of a material that is electrically insulating and has a lower thermal conductivity than steel such as stainless steel. This shape is a cylinder, and two through holes 327 in the same direction as the axis of the cylinder are formed apart from each other.

The thermocouple wires 324 and 32 are inserted into the two through holes 327.
4'is passing. Two thermocouple wires 324 and 32
The 4'connecting portion 323 is located at the lowermost end of the protection tube 325 and is formed to connect the two through holes 327 to each other.
It is in 26. The thermocouple wire 324 and the wire 324 'are connected to each other and silver brazing and sintering are performed around the connection and fixed in the groove 56.

The lowermost surface of the connection part 323 brazed with silver becomes the surface of the silver brazing part. That is, the outer surface of the silver brazing portion is the lowermost outer surface of the connecting portion 323, and forms the lowermost outer surface of the thermocouple 321.

Since the thermocouple 321 of the embodiment described above is inserted into the thermocouple recess 15 of the plastic socket pipe joint 1, the temperature of the molten portion of the plastic socket pipe joint 1 itself is directly measured. Further, since the protective tube 325 is made of ceramics or ceramics having a low thermal conductivity, the amount of heat absorbed by the plastic socket fitting 1 is small and the measurement is not performed at a low temperature. Since the contact portion is the surface of the silver brazing portion, it is possible to measure the temperature with a fast response speed even when the temperature changes abruptly.

In the thermocouple 321 of the present embodiment, the protective tube 325 is made of ceramics or earthenware to reduce the absorption of the heat quantity of the plastic socket fitting 1, but in order to further reduce the heat quantity absorption, the thermocouple wires 324 and 324 are used. This effect is observed when the diameter of ′ is reduced.

However, the diameter of this wire is preferably about 0.1 mm to 0.2 mm, and if it is too thin, the difficulty of welding connection increases and the risk of disconnection also increases.

Further, reducing the outer diameter of the protective tube 325 is also effective in reducing the absorption of heat.

However, if it is too thin, problems will occur in strength, especially in the case of ceramics, and it tends to break. Therefore, as shown in FIG. 1, a protective case 322 may be integrally provided around the thermocouple 321. The material of the protective case 322 has a low thermal conductivity and is a ductile plastic for compensating the fragility of pottery. Is appropriate.

Next, the connection sequence between the plastic pipe 2A and the plastic socket pipe joint 1 will be described.

Further, the plastic pipe 2A is inserted into the through hole of the plastic socket pipe joint 1 until it hits a projection (not shown). Next, the fusion plugs 3 are fitted and attached to the respective connector pins 13 at both ends (only one end is shown) of the plastic socket pipe joint 1. At this time, the connector 31 of the fusion plug 3 is fitted to the connector pin 13, and the cylindrical projection 16 of the plastic socket pipe joint 1 is fitted in the gap between the lower portion of the connector 31 and the holder 33. Further, the thermocouple 321 is inserted into the thermocouple recessed hole 15 of the plastic socket pipe joint 1, and the thermocouple 321
The lower end of the lightly contacts the bottom surface of the concave hole 15 for the thermocouple. At this time, an elastic means such as a spring may be provided between the holder and the holder for light contact.

Next, an electric current is passed through the heating wire 12 of the plastic socket pipe joint 1 through the fusion plug 3 to generate heat, thereby melting the inner peripheral surface portion of the plastic socket pipe joint 1 and the outer peripheral surface portion of the insertion portion of the plastic pipe 2A. After this melting
Stop energizing, cool and connect them. Finally, the fusion plug 3 is removed from the plastic socket pipe joint 1 to complete the connection.

The energization control and the display at that time in the connection sequence described above will be described with reference to FIGS. 4 and 5. FIG. 4 is a front view showing the display surface of the control device main body 4, and the other ends of the two wires 5 each having one end connected to each of the two fusion plugs 3 are connected to the control device main body 4.

First, first, the energizing button of the control device body 4 is pressed to cause an electric current to flow through the plastic pipe joint 1 to generate heat. At this time, the temperature of the plastic socket pipe joint 1 is continuously measured by the thermocouple 32 of the fusion plug 3 at the same time when the energizing button is turned on, and is continuously displayed on the control device body 4.

Secondly, the maximum temperature due to the heat generation of the plastic socket fitting 1 is set in advance in the control device body 4, and the plastic socket fitting 1 is automatically heated when the temperature rises due to energization and reaches this set temperature. To stop energizing. At the same time, turn off the power button and turn on the cooling lamp. In addition, at this time, a signal such as a buzzer or a sound may be issued to indicate when the power supply is stopped.

Here, the set maximum temperature of the plastic socket pipe joint 1 is appropriately about 130 ° C. when the material of the plastic pipe joint 1 and the plastic pipe 2A is medium density polyethylene.

Thirdly, after the power supply to the plastic socket pipe joint 1 is stopped, this temperature drop situation is continuously measured and displayed,
A temperature at which the fusion plug 3 can be removed from the plastic socket pipe joint 1, that is, a temperature at which an external force does not affect the joining state of the fusion joint between the plastic pipe 2A and the plastic socket pipe joint 1. Set
When this set temperature is reached, this display, for example, a temperature display or a sound such as a buzzer or sound is given. In the case of the pipe 2A made of medium-density polyethylene and the socket pipe joint 1 made of medium-density polyethylene, this temperature is appropriately about 60 ° C. In the electric fusion-bonding connection method of the plastic socket pipe joint 1 and the plastic pipe 2A described above, when the initial outside air temperatures are -7 ° C, 22 ° C, and 38 ° C, respectively, the plastic socket pipe changes and changes with time. The temperature of the joint 1 is shown in FIG.

Next, the contents displayed on the display surface of the control device body 4 will be described in more detail with reference to FIG. Control device body 4
When the power switch is turned on, the fusion plug 3 is fitted into the plastic socket fitting 1, and the lamp shown in the figure is turned on. When this fitting and mounting are completed, the connection lamp lights up. Here, if the thermocouple 32, the heating wire 12, the energizing cable 54, the lead wire 52, etc. are broken, or if there is a poor connection, the abnormal disconnection lamp lights up and the connection lamp does not light up.

After lighting the connection lamp, press the energizing lamp switch, and this lamp switch lights up while energizing. At this time, when the energizing current is abnormally large or abnormally small, the abnormal lamp is turned on.

When the power supply is automatically stopped, the power supply lamp switch turns off and the cooling lamp lights up. Next, during cooling, when the temperature of the fusion plug 3 drops to a removable temperature, the cooling lamp is turned on, and the lamp shown in the figure removing the fusion plug 3 from the plastic socket fitting 1 is turned on. Here, if the lighting time is abnormally short or long while the energizing lamp switch is lighting or the cooling lamp is lighting, the abnormal time lamp is lit. If these abnormal lamps light up, press the emergency stop switch to
May turn off the power to.

Next, the temperature of the joint on the display surface of the control device body 4, the energizing rod-shaped lamps, and the cooling and detaching rod-shaped lamps will be described. In the column of the temperature of the joint, the bottom surface temperature of the concave hole 15 of the plastic socket pipe joint 1 measured by the thermocouple 32 of the fusion plug 3 is continuously displayed. Energization,
Each rod lamp for cooling and removing is, for example, 0, 1
It is a lamp that displays 0, 20 ... 80, 90, 100% in the form of a bar graph.

For example, during energization, at the start of energization, that is, the temperature other than energization is 20 ° C., and the set maximum temperature at which energization is stopped is 13
When the temperature is 0 ° C and the temperature is 75 ° C at some point during energization, the energized rod-shaped lamp at this point is (75/20) / (13
0-20) = 50% is displayed.

Next, during cooling, the temperature at the start of cooling, that is, the set maximum temperature range 130 ° C. at which energization is stopped, the set temperature at which the fusion plug 3 can be removed is 60 ° C., and the temperature at a certain point during cooling is 100 ° C. At ℃, the cooling rod lamp at this point is (130-100) / (130-60) = 42.9%
→ Display 40%. The detachable rod-shaped lamp has a detachable set temperature of 60 ° C., the final temperature, that is, the temperature at the start of measurement is 20 ° C., and the temperature at the time of detachment is 50 ° C., (60-50) / (60-20) = 25% → 30
Display%.

The temperature of the joint, the rod lamp for energizing, and the rod lamps for cooling and detaching described above indicate the stage at which electricity is being energized, cooling, or detachable. That is, for example, if it is a display only for turning on the energizing lamp during energization, there is no clue as to how long after this point the energization will end, but if there is such a display, there is an effect of roughly estimating.

In the electric fusion splicing connection method of the plastic socket pipe joint described above, a thermocouple was used for temperature measurement, but other than this, for example, a thermistor or resistance temperature detector, a temperature sensor capable of outputting the temperature by an electric signal. If

The plastic socket pipe joint 1 described above is a pipe joint that connects the plastic pipe 2A and the plastic pipe 2B in a straight line. Next, a plastic branch pipe joint 6 for branch-connecting the plastic pipe 2C will be described with reference to FIG. 6 and FIG. 7 which is a sectional view taken along line AA of FIG. The plastic pipe 2C has a through hole 21C that penetrates to the inner peripheral surface on the outer peripheral surface. The plastic branch pipe joint 6 includes a plastic branch pipe joint body 61, a heating wire 62, and two connector pins 63. The branch pipe joint body 61 has a shape obtained by dividing a cylinder in half in the axial direction, that is, a saddle portion 6 having a lower surface along the outer peripheral surface of the cylinder.
11 and a through hole 611 formed in the center of the saddle portion 611.
1 and a cylindrical main body portion 612 extending upward from the outer peripheral surface of the saddle portion 611 in the radial direction, and these are integrated. Here, the radial direction upper side of the saddle portion 611 is an upper side when the inner peripheral surface of the saddle portion 611, that is, the surface along the outer peripheral surface of the cylinder is the lower surface.

The saddle portion 611 has branch pipe joint bodies 6 at both ends in the radial direction.
1 is a projection 61 for temporarily fixing the plastic pipe 2C.
12 are formed. The cylindrical main body portion 612 has a joint portion, for example, a female screw 6121 at its upper end, and the plug 7 is screwed into the female screw 6121 so that it can be closed. Further, the cylindrical main body 612 may have a technique tube 6122 in this cylindrical intermediate portion, and may be branched and connected by connecting another technique (not shown) to the technique tube 6122.

The heating wire 62 is embedded by winding the lower surface of the branch pipe joint body 61, that is, the lower surface of the saddle portion 611 and the inner peripheral surface. The lower portions of the two connector pins 63 are connected to the respective ends of the heating wire 62, and are embedded in the axial ends of the saddle portion 611 of the branch pipe joint body 61. The upper portions of the two connector pins 63 project from the outer peripheral surface of the saddle portion 611. Here, the saddle part 6 of the connector pin 63
The protrusion from 11 and the area around the connector pin 63 of the saddle 611 are the same as those of the plastic socket pipe joint 1 described above. That is, the saddle part 611
Cylindrical protrusion 61 around the connector pin 63 on the outer peripheral surface of
13 and a concave hole 6114 for the thermoelectric body are formed.

Further, the same applies to the fusion plug and the thermocouple as in the case of the plastic socket pipe joint described above.

Next, the connection order and energization control of the plastic branch pipe joint 6 and the plastic pipe 2C will be described.

First, first, the lower surface of the plastic branch pipe joint 6 is placed on the outer peripheral surface of the plastic pipe 2C and temporarily fixed. At this time, it is necessary to align the through hole 6111 of the saddle portion 611 of the plastic branch pipe joint 6 with the through hole 21C of the plastic pipe 2C.

Hereinafter, the same method as the electric fusion-bonding connection method between the plastic socket pipe joint 1 and the plastic pipe 2A is used, that is, the fusion plug 3 described secondly before is connected to the connector pin 63 of the plastic branch pipe joint 6. And thermocouple recess 6
Then, the heating wire 62 of the plastic branch pipe joint 6 is supplied with current through the connector 31 of the fusion plug 3 to generate heat.

Fourthly, the temperature increase is continuously measured by the thermocouple 32 of the fusion plug 3, and the current is stopped when the maximum temperature due to the heat generation of the preset energization is reached. Give a signal that the

Fifthly, when the temperature drop is continuously measured by the thermocouple 32 after the electric current to the plastic branch pipe joint 6 is stopped and the temperature at which the fusion plug 3 can be removed is set and the temperature has dropped to this set temperature. Give a signal such as a buzzer or sound.

Sixth and finally, the fusion plug 3 is removed from the plastic branch pipe joint 6.

With the above, the electric fusion type connection between the plastic branch pipe joint 6 and the plastic pipe 2C is completed.

〔The invention's effect〕

The electric fusion-bonding connection method for plastic pipe joints according to the present invention has an effect that the difficult energization time is not set and the connection performance is sufficient. Further, in the electric fusion-bonding connection method for the plastic pipe joint of the present embodiment, since there is an indication of the time when the fusion plug can be removed, the removal is not too early or too late. Further, since there is a signal by the sound at the time of stopping the power supply and at the time of removal, the operator can know the signal without looking at the main body of the control device and the like, and the rough estimate of the time can be obtained. Furthermore, since the fusion plug has the connector and the thermocouple held integrally, they can be fitted and mounted at the same time. Further, since the concave hole for the thermocouple is provided, there is an effect that the temperature rise can be detected quickly.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a state in which a plastic pipe is inserted into a plastic pipe joint and a fusion plug is fitted and attached in one embodiment, and FIG. 2 is a partial vertical sectional view showing an embodiment of a thermocouple. Fig. 3, Fig. 3 is a sectional view taken along the line A-A in Fig. 2, Fig. 4 is a front view of the control device main body, and Fig. 5 is a diagram showing a temperature change after the start of energization of the plastic pipe joint. The figure shows a longitudinal sectional view showing a plastic pipe joint and a plastic pipe. Fig. 7 shows a sectional view taken along the line AA of Fig. 6. Fig. 8 shows a longitudinal sectional view of a conventional plastic pipe joint and a pipe. FIG. 9 is a diagram showing a conventional energization control. 1 ... Plastic pipe fitting 2 ... Plastic pipe 3
... fusion-bonding plug, 4 ... control device body, 5 ... wire, 6 ... plastic branch pipe joint.

Claims (5)

[Claims] 1. A pipe joint body made of a thermoplastic resin material, a heating wire embedded in an inner surface portion of the body, and both ends of the heating wire are connected to each other, a lower portion is embedded in the body and an upper portion is an outer periphery of the body. In the electric fusion-bonded pipe joint in which a connector pin protruding from the surface and a concave hole for fitting a sensor near the connector pin are formed, the distance from the bottom surface of the concave hole of the main body to the embedded heating wire Is larger than the distance from the inner surface of the main body to the heating wire, which is a plastic pipe joint. 2. The plastic pipe joint according to claim 1, wherein the distance from the bottom surface of the recessed hole to the heating wire is 0.6 to 1.8 mm. 3. The fusion plug energizing the connector pin according to claim 1, comprises a holder for integrally holding the thermocouple and the connector bush, and a cap for holding the lead wire of the thermocouple and the energizing gable. The thermocouple consists of a pair of thermocouple wires and an electrically insulating protective tube having a low thermal conductivity, and the pair of thermocouple wires are installed apart from each other in the protective tube, and these are connected together. A plastic pipe joint, characterized in that a portion is provided at the lowermost end of the protective pipe, and a part of the end face is made of a metal having a high thermal conductivity. 4. A method for connecting a plastic pipe joint and a plastic pipe according to claim 1 by electric fusion, wherein firstly, the plastic pipe joint is connected to the plastic pipe. Secondly, a fusion splicing plug consisting of a connector that fits into the connector pin of the plastic pipe joint, a thermocouple, and a holder that integrally holds these, and the connector pin of the plastic pipe joint. Thirdly, it is fitted and fitted into a concave hole for a thermocouple. Thirdly, an electric current is passed through the heating wire of the plastic pipe joint through the connector of the fusion plug to generate heat, and fourthly, the fusion plug. The temperature increase is continuously measured by the thermocouple of No. 3, and the result is displayed. When the preset temperature is reached, the current is stopped. After the current is stopped, measure the temperature drop with the thermocouple, set the temperature at which the fusion plug can be removed from the plastic pipe joint in advance, and display when the temperature has dropped to this set temperature. An electric fusion-bonding connection method for plastic pipe joints, characterized by: 5. A display according to claim 4, wherein a sound is emitted when the current to the plastic pipe joint is stopped and / or when the temperature drops to a removable set temperature of the fusion plug. An electric fusion-bonding connection method for plastic pipe joints, which is characterized in that