JPH05131547A - Method and device for welding fusion joint - Google Patents

Abstract

PURPOSE:To surely detect short of an electric heating coil embedded in an electrofusion joint and to execute power saving and to prevent welding failure in a welding device and a method wherein the electrofusion joint is used. CONSTITUTION:A pair of plastic pipes to be welded are inserted into a joint 10 wherein an electric heating wire is embedded in the inner circumferential part. These plastic pipes are welded by heating and melting the outer circumferential face thereof by the electric heating ware 12. In this case, when voltage output to the electric heating wire is lowered and inputted current is raised, the current to the electric heating wire is lowered.

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 when a pair of plastic pipes are butted and connected to each other, 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 electrothermal coil is embedded in the inner peripheral portion thereof. At the time of fusing, the electric heating coil is energized, and the outer circumferences of the pair of plastic tubes to be fused are heated and fused to butt-join the plastic tubes via a joint.

[0002]

2. Description of the Related Art Electrofusion joints are variously called pipe joints, T joints, elbow joints, saddle joints, etc. according to their shapes. In all of them, an electrothermal coil is embedded in the inner peripheral portion and inserted into the joint. The pair of plastic pipes (including a saddle) to be fused are directly heated by an electric heating coil to melt the outer peripheral surfaces of the pipes. When the outer peripheral portion of the melted plastic pipe is solidified after a lapse of a predetermined time, it is fixed to the inner peripheral surface of the joint, and thus the plastic pipes are connected to each other through the joint.

The quality of fusion, that is, the accuracy, is greatly influenced by the energization time of the electric heating coil, and therefore it is important to control the energization time accurately. The control of the energization time is based on the assumption that the electric power supplied to the electric heating coil is constant. In other words, even if the voltage or current fluctuates during the fusing work, the voltage or current should be controlled so that the electric power is constant. For example, the energization time may be the same as the set value without changing. Such control of the constant power supply method has been conventionally performed.

[0004]

By the way, as the melting of the plastic pipe progresses, the adjacent coil windings sometimes come into contact with each other to cause a short circuit. If heating is continued with the short-circuited, the joint will melt and become defective at the end. However, the joint is expensive and it is fatal that the yield is reduced. In addition, even if it does not melt until it melts thickly, the inner peripheral side of the joint cannot be seen, so it cannot be found even if the fusion state is incomplete.
There is a problem that defective products cannot be checked. When a plastic pipe is used for a gas pipe or a water pipe, it cannot be overlooked because it causes gas leakage or water leakage.

When a short circuit occurs, the voltage drops temporarily. Therefore, theoretically, a short circuit can be detected 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 is apt to fluctuate as is well known, so the method of detecting a voltage drop will detect a short even if not short-circuited. .. This can also be understood more clearly, for example, assuming that the generator is also connected to other loads. In other words, when another load is started, the power supply voltage drops for a moment, so that even if the fusion work is perfectly normal, if only the voltage drop is detected as a parameter, it is judged as a short circuit.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to realize a fusing device and method capable of reliably detecting a short circuit of a heating wire during fusing work in order to solve the above problems. .. In order to achieve the above object, according to the fusion joint control method of the present invention, a pair of plastic pipes to be fused are fitted into the joint in which the heating wire is embedded in the inner peripheral portion,
When the plastic tube is fused by heating and melting the outer peripheral surface with a heating wire, when the output voltage to the heating wire drops and the input current rises, the current flowing to the heating wire is reduced. ..

According to the fusion joint control device of the present invention, a voltage detector for detecting the output voltage to the heating wire,
It is structurally characterized in that it has a current detector that detects an input current, and a control device that reduces a current flowing 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, so that the current increases according to Ohm's law. Therefore, the short circuit of the heating wire can be surely detected by simultaneously detecting the voltage drop and the current increase. On the other hand, when the load other than the fusion device is started as described above, the voltage drops, but in that case, the current also drops, so this is not erroneously detected as a short circuit.

When a short circuit is detected, the controller reduces the current supplied to the heating wire (power save) to keep the power constant. As a result, the heat fusion work can be continued without changing the preset energization time. As a result, even if the heating wire is short-circuited during the tentative or fusion work, the joint itself can ensure a predetermined fusion performance, and thus can be used as a good product and the yield can be improved.

[0010]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 shows the basic configuration of the present invention. In the figure, a pair of plastic pipes P1 and P2 are inserted into the electrofusion joint 10 with their ends abutting against each other. The electrofusion joint 10 has an electrothermal coil 12 which is connected to an external output terminal (connector) 16 by a connecting wire 14 on the inner peripheral portion thereof. The connector 16 is connected to an AC power source (outlet or generator) through the control device 24 by the external connector 18. 26 is a connection plug to an AC power supply. The controller 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 (output current of the control device 24) to the electric heating coil 12 and the output voltage V are the current detector 22 and the current detector 22, respectively.
The detection signals SI and S detected by the voltage detector 20
V is input to the controller 24. At the time of fusion bonding, the external connector 18 is connected to the connector 16 of the joint 10 and the plug 26 is connected to a power source (not shown), and then the controller 2
When the start switch (4) (not shown) 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, etc. of the connected pipes P1 and P2. As a result, the outer peripheral portions of the heated and melted plastic pipes P1 and P2 adhere 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 fusion work.

If, for example, the electrothermal coil 12 is short-circuited at the time t0 shown in FIG. 2 during fusing, the resistance I becomes small, and the current I increases according to Ohm's law, as described above. At the same time, the rectifying / smoothing circuit 28 (automatic voltage adjusting device) delays in response to a momentary drop and then returns to the initial constant voltage. On the other hand, the current remains rising. Therefore,
If this state is left as it is, a high current continues to flow in the electric heating coil 12, and the plastic tubes P1 and P2 are overheated and overmelted, resulting in a defective product.

Therefore, in the present invention, the "short circuit occurrence" is detected by capturing the above instantaneous voltage drop that occurs at the same time as the current increase at the time of short circuit, and when the short circuit occurs, power saving, that is, by lowering the current (power Is maintained at a constant value), and the fusion work is continued as it is 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 or not the current I becomes larger than a predetermined current value Ir. Similarly, step 3
In 03, the voltage detector 20 changes the voltage V to a predetermined voltage value V.
It is detected whether it is lower than r. The reference current value Ir and the voltage value Vr are values for not detecting a current or voltage fluctuation (noise) during normal work. 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 saving) at time t1 shown in FIG. As a result, the electric power is kept constant even when the coil 12 is short-circuited, and therefore the fusion work can be continued as it is for the initial set time without changing the energization time.

[0015]

As described above, according to the present invention,
It is possible to reliably detect a short circuit of the electrothermal coil during the fusion work, and even if a short circuit occurs, a power save will be performed, otherwise a defective or defective fusion product will result. The joint can be made a good product, and the yield of the joint can be significantly improved. In addition, it is possible to prevent the defective joint from being used as a gas pipe or a water pipe, which greatly contributes to safety.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part of a fusion bonding device according to the present invention.

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

FIG. 3 is a diagram showing a flow chart of a fusion welding control device according to the present invention.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A joint (10) having a heating wire embedded in an inner peripheral portion thereof.
When a plastic tube is fused by inserting a pair of plastic tubes to be fused into the inside and heating and melting the outer peripheral surface with the heating wire (12), the output voltage to the heating wire drops and the input current is A method for controlling a fusion splicer, characterized in that a current flowing through a heating wire is reduced when the temperature rises. 2. A joint (10) having a heating wire embedded in an inner peripheral portion thereof.
In a device in which a pair of plastic tubes to be fused are fitted and the outer peripheral surface is heated and fused by a heating wire (12) to fuse the plastic tubes, a voltage detector for detecting an output voltage to the heating wires (20), a current detector (22) for detecting an input current, and a control device (24) including an automatic voltage regulator for decreasing the input current to the heating wire when the output voltage decreases and the input current increases. A fusion-bonding device for fusion-bonding joints.