JPS5940145Y2 - DC arc welding machine - Google Patents

Description

[Detailed description of the invention] The invention uses a thyristor to both rectify the output current and adjust the output voltage by controlling the conduction angle and phase of the thyristor, and has constant voltage characteristics or external characteristics close to it.
This invention relates to a DC arc welding machine that automatically feeds a consumable wire and performs welding primarily in the short-circuit transition region.

FIG. 1 is an example of a DC arc welding machine using a thyristor.

In the figure, 1 is the primary winding of the main transformer.

2a and 2b are secondary windings of the main transformer, and each phase voltage U of this secondary winding 2a.

v, w have a phase difference of 120 degrees from each other, and each phase voltage u', v'w' of the secondary winding 2b also has a phase difference of 120 degrees from each other.

Moreover, the secondary winding 2a. The neutral points of 2b are connected,
The winding directions are such that U and u', v, VW, and W' have opposite polarities, so in the end, u, v, w,
u', v', and w' have a phase difference of 60° each, and this is shown in a vector diagram as shown in Figure 2.

Thyristors 3a to 3f have their anodes connected to the respective phases of the secondary windings 2a and 2b of the main transformer, and thyristors 3a, 3b, and 3e are connected to the secondary winding 2a.
The cathodes of the group are connected together, and the thyristor 3d is also connected to the secondary winding 2b.

The cathodes of groups 3e and 3f are connected, and two windings 4a are connected at a neutral point N between these two thyristor groups to make the magnetic coupling as close as possible.

An interphase reactor with 4b is connected.

A DC reactor 5 is connected to the neutral point N of the windings 4a and 4b of the interphase reactor, and a welding load is applied between the DC reactor 5 and the neutral point of the secondary windings 2a and 2b of the main transformer. 6 are connected to form a so-called Sanwa double star rectifier circuit with an interphase reactor.

Conventionally, in this type of DC arc welding machine, in order to reduce the pulsation component of the rectified waveform, to control the short-circuit current value during short-circuit transition welding, and to reduce the amount of spatter generated, the following methods are used: Figure 3, in which the DC reactor 5 is connected to the secondary DC circuit, shows short-circuit transition when the wire feed rate is set to - and constant by this type of DC arc welding machine with constant voltage characteristics. The welding current waveform during welding is shown.

In the figure, OP is a current waveform when the inductance of the DC reactor 5 is small, the time t1 leading to arc regeneration is short, and the current value ■1 during arc regeneration is a dog.

For this reason, the molten pool is blown away during arc regeneration, resulting in a large amount of spatter.

If the inductance of the DC reactor 5 is increased, the current waveform becomes like OQ, and the time t2 until arc regeneration is reached.
becomes longer than tl, and the current value during arc regeneration ■2 becomes ■1
become smaller.

Therefore, spatter during arc regeneration is reduced.

However, if the inductance of the DC reactor 5 is further increased to make the current waveform like an OR, the time t3 until arc regeneration becomes longer, and the current value (3) during arc regeneration becomes smaller.

For this reason, the lack of current during arc regeneration causes insufficient pinching force during short circuits, making it difficult to regenerate the arc, reducing the number of short circuits during welding, making it impossible to obtain a uniform beat, and causing poor arc start. As mentioned above, in conventional DC arc welding machines of this type, it is necessary to connect an appropriate accelerator to the secondary circuit, and a DC reactor is usually connected to the DC circuit.

However, the reactor in a DC circuit generally has a saturation phenomenon unless it has an air core, so the amount of girder accelerator differs depending on whether the current value is large or small. There is a drawback that when the current is small, the amount of the girdle is too large, and if the optimum gluing axle is connected when the current is small, the amount of the reactor is insufficient when the current is large.

The present invention looses the magnetic coupling between the two windings of the interphase reactor so that the two windings also act as a DC inductance, which is equivalent to connecting a DC reactor separately to the secondary DC circuit. The feature is that the effect is given to the interphase reactor.

The details of the present invention will be explained below with reference to the drawings.

FIG. 4 shows the operating principle of the current equalization effect of the interphase reactor, and 4a and 4b are the windings of the interphase reactor connected at the neutral point N.

Winding wire 4a. If the magnetic coupling between the windings 4b and 4b is dense and complete as in the past, then among the currents flowing from the windings 4a and 4b to the neutral point N, if the current ia flowing from the winding 4a is Assuming that the current i flowing from 4d is larger, the magnetic flux φ due to the difference current (ia-i(1))
As shown in the vector diagram of FIG. 5, an electromotive force e is generated, thereby generating a circulating current 18, which reduces ia and increases i, so that 1a=i.

When 1a=i, the magnetic flux φ is demagnetized and only a small resistance drop occurs.

Conventionally, this type of interphase reactor has two cores arranged on the same iron core 7 so that the magnetic coupling is tight, as shown in FIGS. 6 and 7, in order to improve current distribution. Winding wire 4a
, 4b is wound.

Fig. 6 shows a conventional example in which two windings 4a and 4b are wound simultaneously on the same core 7, and Fig. 7 shows a central part of an outer iron core 7 having three parallel cores. This is a conventional example in which two windings 4a and 4b are wound simultaneously.

In either case, the magnetic coupling between the two windings is kept close,
It was designed and manufactured with the primary consideration given to the original current distribution effect of the interphase reactor.

Now, in FIG. 4, if the magnetic coupling between the windings 4a and 4b is weak, leakage occurs in the magnetic flux φ, and the electromotive force e
decreases, and the circulating current i8 also decreases, so 18=ib does not hold.

Therefore, ia and i flow into the neutral point N without being completely divided evenly.

At this time, the difference current (ia-ib) passes through the winding 4a without being affected by the leakage magnetic flux and flows into the neutral point N.
The winding 4a operates as a DC inductance with respect to the difference current (ia-i6).

Similarly, when the current i is larger than ia, the winding 4b operates as a DC inductance with respect to the difference current (i6-ia).

Of course, if the magnetic coupling is made even looser and the magnetic coupling between the windings 4a and 4b is completely eliminated, both windings will act as only DC inductances for the currents i, ..., i6. However, it does not perform the current equalization function as an interphase reactor.

In this way, in order to operate the interphase reactor as a DC inductance without significantly impairing the current distribution effect as an interphase reactor, the inductance between the two windings does not have to be extremely loose. Since it is proportional to the square of the number of turns and the cross-sectional area of the iron core, it is sufficient to increase the number of turns and the cross-sectional area of the iron core in the two windings.

That is, by making the core of the interphase reactor into a core type having two parallel cores with the same cross-sectional area, and separately winding the two windings of the phase reactor around the two parallel cores of the core core, By making the magnetic coupling between the two windings loose and adjusting the cross-sectional area of the iron core and the number of turns of the winding, the appropriate value of inductance can be used as a welding machine without practically impairing the current distribution effect of the interphase reactor. The necessary inductance can be obtained.

FIG. 8 shows an embodiment of the interphase reactor of the present invention.

7 is the iron core of the interphase reactor, and 4a and 4b are windings connected at the neutral point N.

The winding 4a and the winding 4b are wound separately on both legs of the iron core 7, so that the magnetic coupling is loose.

According to the experimental results, the cross-sectional area of the iron core 7 is 4 cm x 6
cm = 24 cnf, and the number of turns of the windings 4a and 4b was about 40 turns, and good welding results could be obtained without connecting a separate DC reactor.

As described above, the present invention makes the magnetic coupling between the two windings of the interphase reactor loose to the extent that the current distribution effect of the interphase reactor is not practically impaired, and the current generated by the difference between the currents flowing through the two windings is generated. By giving leakage to the magnetic flux, both windings are operated as an inductance with respect to the difference current between the currents flowing through both windings by an amount corresponding to the leakage magnetic flux,
The number of turns of both windings and the cross-sectional area of the iron core are adjusted so that the inductance is the same as that of the DC reactor, which was conventionally connected separately to the secondary DC circuit. This allowed it to double as a DC reactor.

Therefore, according to the present invention, since the inductance that was present in conventional DC circuits is provided in the interphase reactor that operates in AC, there is no saturation phenomenon and it is possible to provide an appropriate amount of inductance in the range of small to large currents. In addition, since there is no need to connect a DC reactor, the circuit configuration can be simplified, and the number of electrical connections in large current circuits, which are particularly unreliable, can be reduced, improving the reliability of equipment and making the equipment more economical. , the quality effect is also large.

Furthermore, when a separate DC reactor is provided, there is an advantage that the DC reactor can be made smaller.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a general DC arc welding machine using a Sanwa double star rectifier circuit with an interphase reactor, and Figure 2 is a vector of the secondary winding of the main transformer in a three-phase double rectifier circuit. Figure 3 is a welding current waveform diagram, Figure 4 is a diagram of the operating principle of the interphase reactor, Figure 5 is a vector diagram of the interphase reactor, and Figures 6 and 7 are schematic diagrams showing structural examples of conventional interphase reactors. 8 are perspective views of one embodiment of an interphase reactor used in the DC arc welding machine of the present invention. 1... Primary winding of main transformer, 2a, 2b...
...Same secondary winding, 3a, 3b, 3c,
3d, 3e. 3f...thyristor, 4a, 4b...
Winding wire, 6...Welding load, 7...Iron core.

Claims (1)

[Scope of utility model registration request] In a DC arc welding machine equipped with a three-phase double star rectifier circuit using an interphase reactor, in which a silisk is connected between the secondary winding of the main transformer and the welding load, the phase-to-phase reactor is connected to two windings. This is achieved by separately winding the windings on both legs of the iron core so that the magnetic coupling between the wires is weak, and by providing inductance to these two windings, this interphase reactor can also be used as a DC reactor. A DC arc welding machine featuring: