JP3173826B2 - Fusion joint method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion joint used for butt-connecting a pair of plastic pipes, and more particularly to a fusion method and apparatus using such a fusion joint. Such a fusion joint is generally called an electrofusion joint, and an electric heating coil is embedded in an inner peripheral portion thereof. At the time of fusion, a current is supplied to an electric heating coil, and the outer circumferences of a pair of plastic pipes to be fused are heated and melted to butt and join the plastic pipes via a joint.

[0002]

2. Description of the Related Art Electrofusion joints are variously referred to as pipe joints, T joints, elbow joints, saddle joints, etc., depending on their shapes. In each case, an electrothermal coil is embedded in the inner periphery and inserted into the joint. The pair of plastic tubes (including saddles and the like) to be fused are directly heated by an electric heating coil to melt the outer peripheral surfaces of the tubes. When the outer peripheral portion of the melted plastic pipe solidifies after a predetermined time has passed, it is fixed to the inner peripheral surface of the joint, and thus the plastic pipes are connected to each other via the joint.

[0003] The quality of fusion, ie, the accuracy, is greatly affected by the time of energization of the electric heating coil. Therefore, it is important to accurately control the energization time. The control of the energization time is based on the assumption that the power supplied to the electric heating coil is constant. In other words, even if the voltage or current fluctuates during the welding operation, it is necessary to control the voltage or current so that the supplied power remains constant. In this case, the energization time may be set to the set value without being changed. Such control of the constant power supply method has been conventionally performed.

[0004]

As the melting of the plastic tube progresses, the adjacent coil windings come into contact with each other, sometimes causing a short circuit. If heating is continued with a short circuit, the joint will eventually melt and become a defective product. However, joints are expensive, and a decrease in the yield is fatal. Also, even if it does not melt until it melts, the inner peripheral side of the joint cannot be seen, so even if the fusion state is incomplete, it can not be found,
There is a problem that a defective product cannot be checked. When a plastic pipe is used for a gas pipe or a water pipe, it causes gas leakage or water leakage and cannot be overlooked.

When a short circuit occurs, the voltage temporarily drops. Therefore, a short circuit can be detected theoretically by detecting this voltage drop. However, when, for example, a generator is used as the power source of the fusion device, the output voltage of the generator easily fluctuates as is well known. . This can also be more clearly understood, for example, assuming that the generator is also connected to another load. In other words, when the other load starts, the power supply voltage drops for that moment. For this reason, even if the welding operation is completely normal, if only the voltage drop is detected as a parameter, it is determined that a short circuit has occurred.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a welding apparatus and a method capable of reliably detecting a short circuit of a heating wire during a welding operation in order to solve the above-mentioned problems. . To achieve the above object, according to the method for controlling a fusion joint according to the present invention, a pair of plastic pipes to be fused are fitted into a joint in which a heating wire is embedded in an inner peripheral portion,
When the plastic pipe is fused by heating and melting its outer peripheral surface with a heating wire, the output voltage to the heating wire decreases and the input current to the heating wire decreases when the input current increases. .

Further, according to the fusion joint control device of the present invention, a voltage detector for detecting an output voltage to a heating wire,
It is characterized by comprising a current detector for detecting an input current, and a control device for reducing the current supplied to the heating wire when the output voltage decreases and the input current increases.

[0008]

When the heating wire is short-circuited, the voltage instantaneously drops, but at the same time, the resistance also drops. Therefore, the current increases according to Ohm's law. Therefore, the short-circuit of the heating wire can be reliably detected by detecting the voltage drop and the current rise simultaneously. On the other hand, when a load different from the fusing device is started as described above, the voltage drops, but in that case, the current also drops, so that this is not erroneously detected as a short circuit.

When a short circuit is detected, the control device reduces the current supplied to the heating wire (power save) to keep the power constant. As a result, the heating and fusing operation can be continued without changing the preset energizing time. As a result, even if the heating wire is short-circuited during the provisional operation and the fusing operation, the joint itself can secure a predetermined fusing performance, and therefore can be used as a non-defective product and the yield can be improved.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows the basic configuration of the present invention. In the figure, a pair of plastic tubes P1 and P2 are inserted into the electrofusion joint 10 with their ends facing each other. The electrofusion joint 10 has an electrothermal coil 12 connected to an external extraction terminal (connector) 16 by a connection wire 14 at an inner peripheral portion thereof. The connector 16 is connected to an AC power supply (outlet or generator) via a control device 24 by an external connector 18. 26 is a connection plug to an AC power supply. The control device 24 has a known rectifying / smoothing circuit 28 for AC / DC conversion, and supplies a predetermined DC current to the electric heating coil 12 of the electrofusion joint 10.

The input current I (the output current of the control device 24) and the output voltage V to the electric heating coil 12 are determined by the current detector 22,
The detection signals SI and S are detected by the voltage detector 20.
V is input to the control device 24. Upon fusion, the external connector 18 is connected to the connector 16 of the joint 10, the plug 26 is connected to a power supply (not shown), and then the control device 2
When the start switch (not shown) of No. 4 is started, the power supply current is supplied to the electric heating coil 12 of the joint 10. The current supply is stopped after a predetermined energization time determined according to the diameters, materials, and the like of the connected pipes P1, P2. As a result, the outer peripheral portions of the heated and melted plastic pipes P1 and P2 are fixed to the inner peripheral surface of the joint after being left for a predetermined time (self-cooling), and the plastic pipe P
1, P2 are connected to each other via a joint 10. The above is a normal welding operation.

If, for example, the electric heating coil 12 is short-circuited at the time t0 shown in FIG. 2 during the fusion, the current I increases according to Ohm's law because the resistance is reduced as described above. At the same time, the voltage instantaneously drops due to the response delay of the rectifying / smoothing circuit 28 (automatic voltage regulator), and then returns to the initial constant voltage. On the other hand, the current remains elevated. Therefore,
If this state is left, a high current continues to flow through the electric heating coil 12, and the plastic tubes P1, P2 are overheated and overmelted, resulting in defective products.

Therefore, in the present invention, the occurrence of a short circuit is detected by detecting the instantaneous voltage drop that occurs simultaneously with the rise of the current during a short circuit. When a short circuit occurs, the power is saved, that is, the current is reduced. Is maintained at a constant value), and the welding operation is to be continued for a predetermined energizing time.

FIG. 3 shows a flowchart of the control device of the present invention. In the figure, first, in step 301, the current detector 22 detects whether the current I has become larger than a predetermined current value Ir. Similarly, step 3
03, the voltage V is set to a predetermined voltage value V by the voltage detector 20.
It is detected whether it has fallen below r. The reference current value Ir and the voltage value Vr are values for preventing current or voltage fluctuation (noise) during normal operation from being detected. If I ≧ Ir and V ≦ Vr in steps 301 and 303, the process proceeds to step 305, where the current I is reduced to the original value (power save) at time t1 shown in FIG. As a result, even when the short-circuit of the coil 12 occurs, the electric power is kept constant, so that the welding operation can be continued for the initial set time without changing the energizing time.

[0015]

As described above, according to the present invention,
Shorting of the electric heating coil during the welding operation can be reliably detected, and if a short circuit occurs, performing a power save will otherwise result in a defective or defective fused product. The quality of the joint can be improved, and the yield of the joint can be significantly improved. Further, the possibility that the defective joint is used as a gas pipe or a water pipe can be prevented, which greatly contributes to safety.

[Brief description of the drawings]

FIG. 1 is an illustrative sectional view of a main part of a fusion device according to the present invention.

FIG. 2 is a diagram showing voltage and current changes when a heating wire is short-circuited in the fusing apparatus shown in FIG. 1;

FIG. 3 is a diagram showing a flowchart of a control device for a fusing operation in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Joint 12 ... Electric heating coil 16, 18 ... Connector 20 ... Voltage detector 22 ... Current detector 24 ... Control device

Continuation of front page (72) Inventor Tadanori Mato 3-15-11 Joto, Kofu City, Yamanashi Prefecture Inside Kofu Meidensha Co., Ltd. (56) References JP-A-1-120325 (JP, A) JP-A-2-130131 (JP) JP-A-62-116128 (JP, A) JP-A-2-196630 (JP, A) JP-A-3-128450 (JP, A) JP-A-4-319077 (JP, A) 4-334438 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 65/00-65/82

Claims (2)

(57) [Claims] A joint (10) having a heating wire embedded in an inner peripheral portion thereof.
When a pair of plastic tubes to be fused is inserted into the inside and the outer peripheral surfaces thereof are heated and melted by a heating wire (12), when the plastic tubes are fused, the output voltage to the heating wire decreases and the input current decreases. A method for controlling a fusion joint, comprising reducing a current supplied to a heating wire when the temperature rises. 2. A joint (10) in which a heating wire is embedded in an inner peripheral portion.
A voltage detector for detecting an output voltage to a heating wire in a device for fusing a plastic tube by fitting a pair of plastic tubes to be fused therein and heating and melting the outer peripheral surfaces thereof by a heating wire (12). (20) a control device (24) including a current detector (22) for detecting an input current, and an automatic voltage regulator for reducing the input current to the heating wire when the output voltage falls and the input current rises A fusion-bonding apparatus for a fusion joint, comprising: