DC welding. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / welding equipment

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I propose a CT scheme that allows welding at direct current using electrodes for alternating current, direct current and stainless steel electrodes.

Industrial machines designed for direct current welding generate direct current with a pulsation of 400 ... 800 Hz, which improves the welding technology. The higher the DC ripple frequency, the better the welding.

The proposed circuit (Fig. 1) makes it possible to obtain a DC pulsation frequency of 100 Hz, which is inferior to industrial designs, but has a great advantage over PTs designed for AC welding. This scheme allows you to adjust the welding current down to zero, which simplifies the technology of welding thin objects.

For welding ordinary and stainless steels with stainless electrodes, it is necessary to increase the welding current voltage, since the resistance of stainless steels is higher than the others.

It is difficult to weld with stainless electrodes at a voltage of 45 ... 60 V, the electrodes heat up, poorly "hold" the arc, "stick". Therefore, in the proposed circuit, the voltage on the secondary winding is increased to 80 V.

The power of the ST is calculated by a voltage of 80 V, in the secondary winding of the ST - by the diameter of the welding electrode (see RE8 / 2000). To obtain a constant welding current in the circuit, a full-wave rectification of the alternating current of the secondary winding of the ST is used. The rectifier bridge consists of two thyristors and two diodes. A third winding has been introduced to control thyristors. Changing the amplitude of the control voltage using the resistor R3 on the control electrodes of the thyristors changes their opening phase. The earlier the thyristors open, the greater the welding current and vice versa. The shape of the welding current pulses obtained using the proposed scheme does not affect the quality of welding.

The total resistance of the resistor R3 must be selected so that the welding current, if possible, is smoothly regulated from zero to maximum. The control winding must be phased and connected according to the diagram. If the welding current is not adjustable, it is necessary to swap the ends of the third winding on the diodes VD1 and VD4.

In the absence of powerful diodes, they can be replaced by thyristors of the same type that are designed for control. This replacement is shown in Fig. 2

To improve the welding current control characteristics, a capacitor C3 can be connected in parallel with the resistor R1. The circuit does not have temperature compensation, therefore, after several minutes of operation, it is necessary to reduce the welding current to a small extent.

For a rectifier bridge, you can use power thyristors and diodes with an operating current of 100 A or more and a voltage of 100 V or more. The types of thyristors and diodes are not given, since there are a lot of old and new modifications (for example, see RA5/2000, p. 35).

Thyristors, like diodes, are mounted on appropriate radiators designed for each type of thyristors and diodes. In case of self-manufacturing of a double-rod type magnetic circuit, the width of the magnetic circuit plates is limited by the presence of existing plates.

Magnetic circuit plates can be cut from large sheets of large industrial transformers. The length of large and small plates will depend on the window of the magnetic circuit.

The dimensions of the magnetic circuit window depend on the dimensions of the CT coils. Coil dimensions can be calculated by specifying the number of turns in the coil layer. Knowing the thickness and width (or the diameter of the wire in insulation), you can calculate the dimensions of the coils. Due to the loose fit of the turns in the coil, it is necessary to divide the obtained results of the dimensions by the fill factor - 0,7 ... 0,8, one should also take into account the thickness of the insulation between the layers of the coils and the body insulation.

Coils 3A and 3B can be wound on one of the coils of the secondary winding in two wires ? 0,6 ... 1 mm or separately in one wire on each coil of the secondary winding.

If you remove the output from the 2 A coil, then when switching the rectifier bridge to this output, the device can be used to start the car. Although the power of the CT should be enough for the cutting mode, it is possible to make a tap in the 1A coil and by switching the power to this tap, increase the cutting power for a short time. If necessary, weld on alternating current, connect the welding circuit to the terminals "K" of coil 2A and "50 V" on coil 2B. The voltages for which the winding coils are designed are indicated in the diagram.

Author: B. N. Dubinin

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