The design of the welding source for semi-automatic welding with a thyristor regulator. Scheme, description

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Electric welding. The design of the welding source for semi-automatic welding with a thyristor regulator. Encyclopedia of radio electronics and electrical engineering

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Basic electrical diagram

On fig. 18.20 shows a circuit diagram of a welding source with a thyristor controller for semi-automatic welding.

The source is powered by a single-phase network 220 V, 50 Hz. The basis of the source is the welding transformer T1. It galvanically separates the mains and the welding circuit, and also reduces the mains voltage to the value required to power the welding arc.

Alternating voltage from the secondary winding of the transformer T1 is fed to the input of a controlled full-wave rectifier VD7, VD8, VS3, VS4, with which the welding voltage is adjusted. To maintain the arc in the pauses of the rectified voltage, a special two-winding choke L1 is used.

The design of the welding source for semi-automatic welding with a thyristor regulator
Rice. 18.20. Schematic diagram of the welding source

Additionally, the source for semi-automatic welding includes specialized units for controlling the supply of shielding gas and welding wire, which are powered by a constant voltage of 24 V. A constant voltage of 24 V is obtained using a separate low-power transformer T2 and a full-wave rectifier VD1-VD4.

Diodes VD3, VD4, together with thyristors VS1, VS2, form a controlled rectifier, with which the wire feed speed is adjusted. Control of the on state of the source is carried out using the LED HL1.

Source control node performed on relay K2. The source is turned on by pressing the button S2, which is located on the holder. At the same time, relay K1 is activated and, with its contact K1.1, connects the supply motor M2 to the output of the controlled rectifier VD3, VD4, VS1, VS2.

Contact K1.3 turns on the gas valve K2, which supplies shielding gas to the welding zone. Through contact K1.2 from the output of the rectifier VD1-VD4, the rectified pulsating voltage is supplied to the power outputs (1,5) of the control units A1 and A2.

With control unit A1 the wire feed speed is controlled, and with the help of block A2 the welding voltage is set.

After power is applied, the control units Al, A2 begin to form control pulses, which, through terminals 3, 4, arrive at the control electrodes of the thyristors and open them.

From the output of the controlled rectifier VD7, VD8, VS3, VS4, the voltage through the primary winding of the inductor L₁ enters the welding holder. From the output of the controlled rectifier VD3, VD4, VS1, VS2, the voltage through the closed contact K1.1 is supplied to the armature of the motor M2.

The motor unwinds the welding wire from the spool, pushes it into the hose holder channel, and welding begins. The welding current depends on the wire feed speed, which is usually adjustable from 0,1 to 10-15 m/min.

Each output voltage of the source corresponds to a certain current, and hence the wire feed speed, for which it is possible to obtain a stable arc burning process. The feed rate depends on the voltage applied to the motor armature M2, which is controlled by the control unit A1.

Unlike the source described earlier, little power is dissipated on the thyristors of the controlled rectifier, which facilitates the temperature regime of the entire device, and also increases its reliability. Since the welding voltage is turned on/off using a controlled rectifier VD7, VD8, VS3, VS4, there is no need to use a special electromagnetic starter, which also favorably affects the overall reliability of the source.

The welding process continues as long as the S2 button on the welding holder is pressed. Release button S2 to stop welding. In this case, the button contacts open and de-energize the relay coil K1.

Relay K1 with its contacts Kl.l, K1.2 and K1.3 turns off the wire feed, turns off the output voltage of the source and the gas valve. To prevent inertial rotation of the feed motor after de-energizing, its anchor circuit is short-circuited by a normally closed contact K1.1.

Details

Diodes VD7, VD8 type D151-125 and thyristors VS3, VS4 type T161-160 are installed on standard aluminum radiators of type 0151 or on any other radiators with an area of 250-300 cm2.

Diode VD10 type D112-25 is mounted on a radiator type O111 or any other having an area of 100-150 cm2.

As a transformer T2, you can use any transformer 220/27 V with a power of 150-200 VA. You can use a ready-made transformer type OSM-0,16.

Relay K1 - type RP21 or similar, with a 24 V DC coil.

As the motor M2 of the feeder, you can use any motor power. 60-100 W for a voltage of 24 V, for example, the motor from the windshield wiper drive of a KamAZ car.

Welding transformer design

Since the source uses a transformer having a rod core, the winding is wound on two identical frames, where each of the windings can be assembled from two series or parallel sections.

Primary winding The transformer contains 340 turns and is wound with enamelled copper wire:

or 2,2 mm if the sections are connected in series;
or 1,45 mm if the sections are connected in parallel.

Secondary winding the transformer contains 48 turns and is wound with an aluminum bus with a cross section:

or 36 mm2 if the sections are connected in series;
or 18 mm2 if the sections are connected in parallel.

Council. Before winding, the frame should be strengthened by planting it on a wooden mandrel. The hole intended for fitting onto the core should be 1,5-2 mm larger than the core, which will allow you to subsequently assemble the transformer without any problems.

First, the primary winding is wound, and then the secondary. After winding each layer of wire, the winding should be compacted with light blows of a wooden hammer. If the transformer is made in artisanal conditions, then each layer of the wire must be coated with an impregnating varnish.

As the interlayer insulation 0,5 mm thick pressboard is used. For the secondary winding, an aluminum rectangular busbar of a suitable section is taken. In extreme cases, you can remove a round core of a suitable cross section from an electrical cable. In this case, the plastic insulation must be removed from the wire, and then tightly wrapped with keeper tape or thin cotton fabric, previously cut into strips 20 mm wide.

After winding and impregnation, the transformer should be dried. The temperature and drying time are determined by the brand of impregnating varnish used.

The transformer core is made of plates of cold-rolled transformer steel 35 mm wide and 0,35 mm thick (cold-rolled steel, in contrast to hot-rolled steel, which has an almost black color, has a white color). You can use sheet steel from a decommissioned transformer of a transformer substation.

The existing iron is first cut into strips 35 mm wide, then cut into fragments 95 and 179 mm long. Burrs on the edges of chopped iron must be removed with a needle file or fine file. The core is assembled "overlapping" with possibly smaller gaps at the joints of individual sheets. The design of the transformer core is shown in fig. 18.21.

The design of the welding source for semi-automatic welding with a thyristor regulator
Rice. 18.21. Welding transformer core structure

Choke design

Two winding choke L₁ wound on a standard Ш-shaped tape core ШЛ32х50. Primary winding contains 18 turns of an aluminum bus with a section of 36 mm2. Secondary winding wound with copper enameled wire with a diameter of 1,45 mm.

When assembling, it is necessary to insert spacers 1 mm thick (total gap 2 mm) from textolite or other non-magnetic and non-conductive material into the joints of the core.

Source connection

To connect the primary winding of the transformer to the ~220 V network, it is necessary to use a cable with a copper core with a cross section of at least 2,5 mm2 and a 25 A power socket with a grounding knife, which must be connected to the transformer core and to the protective casing. In this case, the grounding contact of the socket must be reliably grounded.

The positive pole of the source is usually brought out to a specialized connector designed to connect a hose holder. The S2 button located on the holder is connected through the same connector.

The negative pole of the output voltage of the source must be connected to a brass stud with a diameter of 10 mm, mounted on a dielectric heat-resistant panel, which is attached to the protective casing of the source. Soft copper wires with a cross section of 16-25 mm2 can be used as welding ends.

Author: Koryakin-Chernyak S.L.

See other articles Section welding equipment.

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