Welding machine from LATR. Scheme, description

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Welding machine from LATR. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / welding equipment

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I am sure: not a single artisan, homely owner will refuse from a compact and at the same time quite reliable, cheap and easy-to-manufacture "welder". Especially if he finds out that this apparatus is based on an easily upgradeable 9-ampere (familiar to almost everyone from school physics lessons) laboratory autotransformer LATR2 and a home-made thyristor mini-regulator with a rectifier bridge. They allow not only to safely connect to a 220V AC household lighting network, but also to change Uw on the electrode, which means choosing the desired welding current value.

Operating modes are set using a potentiometer. Together with capacitors C2 and C3, it forms phase-shifting chains, each of which, triggering during its half-cycle, opens the corresponding thyristor for a certain period of time. As a result, adjustable 1-20 V are on the primary winding of the welding T215. Transforming in the secondary winding, the required -Us make it easy to ignite the arc for welding on alternating (terminals X2, X3) or rectified (X4, X5) current.

Rice. Fig. 1. Welding transformer based on the widely used LATR2 (a), its connection to the circuit diagram of a self-made adjustable machine for welding on alternating or direct current (b) and a voltage diagram explaining the operation of the transistor arc burning mode controller (click to enlarge)

Resistors R2 and R3 shunt the control circuits of thyristors VS1 and VS2. Capacitors C1, C2 reduce to an acceptable level of radio interference that accompanies the arc discharge. In the role of the light indicator HL1, signaling the inclusion of the device in the household electrical network, a neon lamp with a current-limiting resistor R1 is used.

To connect the "welder" to the apartment electrical wiring, a conventional plug X1 is applicable. But it is better to use a more powerful electrical connector, which is commonly called "Euro plug-Euro socket". And as the SB1 switch, the VP25 "bag" is suitable, designed for a current of 25 A and allowing you to open both wires at once.

As practice shows, it does not make sense to install any kind of fuses (anti-overload machines) on the welding machine. Here you have to deal with such currents, if exceeded, the protection at the network input to the apartment will definitely work.

For the manufacture of the secondary winding, the casing-enclosure, the current-collecting slider and the mounting fittings are removed from the base LATR2. Then, on the existing 250 V winding (127 and 220 V taps remain unclaimed), reliable insulation is applied (for example, from varnished fabric), on top of which a secondary (lowering) winding is placed. And this is 70 turns of an insulated copper or aluminum bus, having a diameter of 25 mm2. It is acceptable to make the secondary winding from several parallel wires with the same overall cross section.

Winding is more convenient to carry out together. While one, trying not to damage the insulation of adjacent turns, carefully stretches and lays the wire, the other holds the free end of the future winding, preventing it from twisting.

The upgraded LATR2 is placed in a protective metal casing with ventilation holes, on which a circuit board made of 10 mm getinaks or fiberglass is placed with an SB1 batch switch, a thyristor voltage regulator (with resistor R6), a light indicator HL1 for turning on the device in the network and output terminals for welding on an alternating (X2, X3) or direct (X4, X5) current.

In the absence of a basic LATR2, it can be replaced with a home-made "welder" with a magnetic circuit made of transformer steel (core cross section 45-50 cm2). Its primary winding should contain 250 turns of PEV2 wire with a diameter of 1,5 mm. The secondary one is no different from the one used in the modernized LATR2.

At the output of the low-voltage winding, a rectifier unit with power diodes VD3-VD10 is installed for DC welding. In addition to these valves, more powerful analogues are quite acceptable, for example, D122-32-1 (rectified current - up to 32 A).

Power diodes and thyristors are installed on radiators-heat sinks, the area of each of which is at least 25 cm2. The axis of the adjusting resistor R6 is brought out of the casing. A scale with divisions corresponding to specific values of direct and alternating voltage is placed under the handle. And next to it is a table of the dependence of the welding current on the voltage on the secondary winding of the transformer and on the diameter of the welding electrode (0,8-1,5 mm).

Of course, self-made electrodes made of carbon steel "rolled wire" with a diameter of 0,5-1,2 mm are also acceptable. Blanks 250-350 mm long are covered with liquid glass - a mixture of silicate glue and crushed chalk, leaving the 40-mm ends unprotected, which are necessary for connecting to the welding machine. The coating is thoroughly dried, otherwise it will begin to "shoot" during welding.

Although both alternating (terminals X2, X3) and direct (X4, X5) current can be used for welding, the second option, according to welders, is preferable to the first. Moreover, polarity plays an important role. In particular, when applying a "plus" to the "mass" (the object being welded) and, accordingly,

connecting the electrode to the terminal with a minus sign, the so-called direct polarity takes place. It is characterized by the release of more heat than with reverse polarity, when the electrode is connected to the positive terminal of the rectifier, and the "mass" to the negative. Reverse polarity is used when it is necessary to reduce heat generation, for example, when welding thin sheets of metal. Almost all the energy released by the electric arc goes to the formation of a weld, and therefore the depth of penetration is 40-50 percent greater than with a current of the same magnitude, but with direct polarity.

And a few other very important features. An increase in the arc current at a constant welding speed leads to an increase in the penetration depth. Moreover, if the work is carried out on alternating current, then the last of these parameters becomes 15-20 percent less than when using direct current of reverse polarity. The welding voltage has little effect on the depth of penetration. But the width of the seam depends on Uw: with increasing voltage, it increases.

Hence an important conclusion for those involved in, say, welding when repairing a car body made of sheet steel: the best results will be obtained by welding with direct current of reverse polarity at a minimum (but sufficient for stable arcing) voltage.

The arc must be kept as short as possible, the electrode is then consumed evenly, and the penetration depth of the welded metal is maximum. The seam itself is clean and strong, practically devoid of slag inclusions. And from rare splashes of the melt, which are difficult to remove after the product has cooled, you can protect yourself by rubbing the near-weld surface with chalk (the drops will roll off without sticking to the metal).

The arc excitation is carried out (after applying the corresponding -Usv to the electrode and "mass") in two ways. The essence of the first is in a light touch of the electrode on the parts to be welded, followed by its removal by 2-4 mm to the side. The second method is reminiscent of striking a match on a box: sliding the electrode over the surface to be welded, it is immediately taken away for a short distance. In any case, you need to catch the moment of the arc and only then, smoothly moving the electrode over the seam formed right there, maintain its calm burning.

Depending on the type and thickness of the metal to be welded, one or another electrode is selected. If, for example, there is a standard assortment for a St3 sheet 1 mm thick, electrodes with a diameter of 0,8-1 mm are suitable (this is what the design under consideration is mainly designed for). For welding work on 2 mm rolled steel, it is desirable to have both a more powerful "welder" and a thicker electrode (2-3 mm).

For welding jewelry made of gold, silver, cupronickel, it is better to use a refractory electrode (for example, tungsten). Metals that are less resistant to oxidation can also be welded using carbon dioxide protection.

In any case, work can be performed both with a vertically located electrode, and tilted forward or backward. But sophisticated professionals say: when welding with a forward angle (meaning an acute angle between the electrode and the finished seam), more complete penetration and a smaller width of the seam itself are provided. Backward welding is recommended only for lap joints, especially when dealing with profiled steel (angle, I-beam and channel).

An important thing is the welding cable. For the device in question, copper stranded (total cross section is about 20 mm2) in rubber insulation is the best fit. The required quantity is two one and a half meter segments, each of which should be equipped with a carefully crimped and soldered terminal lug for connection to the "welder". For direct connection to the "mass" they use a powerful crocodile clip, and with the electrode - a holder resembling a three-pronged fork. You can also use the car "cigarette lighter".

You also need to take care of your personal safety. When arc welding, try to protect yourself from sparks, and even more so from splashes of molten metal. It is recommended to wear loose-fitting canvas clothing, protective gloves and a mask that protects the eyes from the harsh radiation of the electric arc (sunglasses are not suitable here).

Of course, we must not forget about the "Safety regulations when performing work on electrical equipment in networks with voltages up to 1 kV". Electricity does not forgive carelessness!

Author: M.Veviorovsky

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