JP2517946Y2 - Electric resistance welding equipment - Google Patents

Description

The present invention relates to an electric resistance welding apparatus, and more particularly to an electric resistance welding apparatus equipped with a protection circuit for preventing continuous current flow in the primary side circuit of a welding transformer. The present invention relates to resistance welding equipment.

(Prior Art) An electric resistance welding apparatus, in which an electric current is caused to flow through a contact portion of a member to be joined, is heated by resistance heat generated here, and is welded by applying pressure, has been widely used from the past (Japanese Patent Laid-Open Publication No. Sho. 62-34683).

FIG. 4 is a circuit diagram showing a welding power source circuit in a conventional electric resistance welding apparatus, 1 is an earth leakage breaker, 2 is a welding timer conductor, 3 is a welding transformer, and 4 is a welding gun.
The earth leakage circuit breaker 1 includes a through-type current transformer (ZCT) 7 having primary windings 5 and 6 made of wire conductors.
When a large current flows due to a ground fault, inter-phase short circuit or overload in the subsequent circuits, a voltage is induced in the secondary winding 8 of the current transformer 7. Reference numeral 9 denotes an amplifier, and since the voltage induced in the secondary winding 8 of the current transformer 7 is minute, this voltage is amplified by the amplifier 9 via the sensitivity switching device 10, and the electromagnetic circuit is output by the output of this amplifier 9. The circuit breaker 11 is excited to operate. 12 is a voltage switching device, 13 is a trip display button, and 14 is a test button. By pressing this test button 14 to short-circuit the contacts 15 and 16, the amplifier 9 excites the circuit breaker 11 to cut off the leakage current. The device 1 can be operated.

The welding timer conductor 2 includes a thyristor stack 17 arranged in the primary side circuit of the welding transformer 3 and a thyristor stack so that an electric current is intermittently applied to the primary side circuit.
It is composed of a control circuit (not shown) for controlling the device 17. The welding transformer 3 is a transformer that reduces the 440V AC voltage to about 40V.

FIG. 5 (A) is a timing chart showing an intermittent energization state when performing a normal welding operation using the electric resistance welding apparatus having the above-described configuration. One energization time is 60 Hz power supply. At 13 to 25 Hz, it is a short time of less than 1/2 second, and the longest time cannot exceed 1 second. Between each energizing time, there is a non-energizing time of 30 to 120 Hz for moving the welding spot.

By the way, in the electric resistance welding apparatus as shown in FIG. 4, considering, for example, a case where the SCR stack 17 in the welding timer conductor 2 fails and becomes conductive, the winding capacity of the welding transformer 3 is large. Therefore, in that case, no voltage is generated in the secondary winding 8 of the current transformer 7, and thus the energized state is maintained for a long time as shown in FIG. 5 (B). As a result, the insulation is destroyed by the burnout of the welding timer conductor 2 or the welding transformer 3, and finally the current transformer 7 senses in the form of an interphase short circuit or a ground fault, and the earth leakage breaker 1 is activated for the first time. It causes inconvenience.

(Object of the Invention) Therefore, an object of the present invention is to provide an electric resistance welding apparatus capable of interrupting the current when a failure occurs in the primary side circuit of the welding transformer 3 and the current may flow for a long time. And

(Structure of the Invention) The present invention applies a current intermittently flowing in the primary side circuit of a welding transformer to a primary winding of a current transformer in response to intermittently repeating a predetermined short time welding operation. To the primary side circuit of the welding transformer by operating the circuit breaker based on the voltage induced in the secondary winding of the current transformer when the current flowing through the primary winding becomes excessive. In an electric resistance welding device configured to cut off the energization of the electric power source, a detection unit for detecting intermittent energization in the primary side circuit, and set at each energization start time point in response to the energization detection by the detection unit The timer has a predetermined set time longer than each energization time of intermittent energization in the primary side circuit of the welding transformer, and the set time is set in the primary side circuit. If current flows until the time elapses, the above circuit interruption And it is configured to actuate the vessel.

(Effect of the Invention) According to the present invention, when a current flows longer than the primary side circuit of the welding transformer and each energization time of intermittent energization in the primary side circuit, the set time of the timer elapses. As the circuit breaker is activated by this timer, if the SCR in the welding timer conductor is damaged or short-circuited, current will flow in the primary circuit of the welding transformer because the earth leakage breaker will not operate. The continuing drawbacks can be eliminated, and as a result, burnout of the welding transformer or heating of the earth leakage breaker can be prevented.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram in the case where the continuity prevention means according to the first embodiment of the present invention is added to the earth leakage breaker, and the earth leakage breaker 1 itself has the same structure as that shown in FIG. Therefore, the same reference numerals are allotted to corresponding members, and duplicate description will be omitted. In FIG. 1, a power line 18 connected to the primary winding 6 of the current transformer 7 is provided with a current transformer (CT) 19 for detecting the presence or absence of energization in the power line 18, A timer 21 is connected to the secondary winding 20 of the current transformer 19. This timer 21 is shown in FIG.
Each energization time of intermittent energization as shown in
Longer than 25Hz length, eg 120Hz length (2 seconds)
Is a timer with a set time of
It is set for each of t1, t2, t3, and so on.
It is reset every 1 ', t2', t3 ', .... An electromagnetic relay 22 that is activated when the set time of the timer 21 is finished is provided. The contacts 23 and 24 of the electromagnetic relay 22 are connected in parallel with the contacts 15 and 16 of the test button 14, and when the electromagnetic relay 22 is activated, it is as if the test button 14 was pressed. The earth leakage breaker 1 can be operated. Therefore, for example, when the SCR stack of the welding timer conductor 2 in FIG. 4 is short-circuited and continuous energization occurs in the primary side circuit of the welding transformer 3, as shown in FIG.
The operation of 21 can surely stop the power supply after 2 seconds.

Next, FIG. 2 is a circuit diagram in the case where the continuity prevention means according to the second embodiment of the present invention is added in the earth leakage breaker as in the first embodiment. Also in this embodiment, the first embodiment is also shown. Similarly to the above, the current transformer 19 is provided in the primary side circuit of the welding transformer 3, and the timer 21 similar to that of the first embodiment is connected to the secondary winding 20 thereof. However, in this embodiment, the output of the timer 21 is output. Is supplied to the amplifier 9 through the sensitivity switching device 10, and the amplifier 9 excites the circuit breaker 11 to operate based on the output of the timer 21. It is apparent that the same effects as those of the first embodiment can be obtained by this embodiment as well.

Further, FIG. 3 is a circuit diagram of a third embodiment of the present invention in which the current transformer 19 and the timer 21 of the continuation prevention means are provided outside the earth leakage breaker 1. In this embodiment, the contacts 15, 16
Instead of the test button 14 for short-circuiting
Electromagnetic test button 25, which can also be activated electromagnetically by
Is attached to the earth leakage breaker 1. According to this embodiment,
It is clear that the same effects as those of the first and second embodiments described above can be obtained.

[Brief description of drawings]

1 to 3 show the first embodiment of the electric resistance welding apparatus according to the present invention.
-Circuit diagram showing essential parts of the third embodiment, FIG. 4 is a circuit diagram showing a welding power supply circuit in a conventional electric resistance welding apparatus, and FIG.
The figure is a timing chart for explaining the present invention. 1 ... Leakage breaker 2 ... Welding timer conductor 3 ... Welding transformer, 4 ... Welding gun 7 ... Current transformer, 9 ... Amplifier 10 ... Sensitivity switching device, 11 ... Circuit breaker 12 ... Voltage switching device, 14 ... Test button 17 ... Thyristor stack 19 ... Current transformer, 21 ... Timer 25 ... Electromagnetic test button

Claims (1)

(57) [Scope of utility model registration request] 1. A current flowing intermittently in a primary side circuit of a welding transformer is caused to flow through a primary winding of a current transformer in response to intermittently repeating a predetermined short time welding operation, and When the current flowing through the primary winding becomes excessive, the circuit breaker is operated based on the voltage induced in the secondary winding of the current transformer to cut off the power supply to the primary side circuit of the welding transformer. In the electric resistance welding apparatus configured to perform the above, a detection unit for detecting intermittent energization in the primary side circuit, and a predetermined set time longer than each energization time of intermittent energization in the primary side circuit And a timer which is set at each start point of energization in response to the energization detection by the detecting means and operates the circuit breaker when a current flows in the primary side circuit until the set time elapses. And an electrical resistance characterized by Welding equipment.