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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Welding - optional. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / welding equipment With the help of our design circle at school, seven years ago we manufactured and tested several welding transformers (ST). They work in such a way that they do not cause any complaints from anyone. That is why I would like to offer options for their calculation and manufacture to everyone for whom a welding transformer is not a whim, but a vital necessity. Moreover, getting a ready-made ST is often the problem of problems. Yes, and their dimensions are significant (as, indeed, the cost).
As you know, electric welding is carried out at a voltage of 40-60V and a current of 50 A to 300 A, depending on the electrodes used and the thickness of the metals being welded. Based on this, it is possible to determine the power P (in watts) of the transformer: P \u2d IU, where I is the current strength in amperes, and U is the voltage in volts. Depending on the power P, the cross-sectional area S (in cmXNUMX) of the magnetic circuit is also selected. This is done according to the formula: S=P^0,5. And already by the value of S, the number of turns w per 1V of voltage is determined: w=50/S Knowing the required voltages U1 and U2, it is easy to calculate the number of turns of the primary w1 and secondary w2 windings: w1=wU1, w2=wU2. After that, the cross section of the wires of the windings is determined. In this case, it should be taken into account that the current density in the welding transformer winding made of copper, during normal cooling, should be no more than 5 A/mm2.
Based on these calculations and experimental data, we have come to the following conclusions. In order for the transformer to develop the required power, it is advisable to choose a cross section of its magnetic circuit of 50 cm2 (a further increase in S threatens to increase in size and weight). In this case, the primary winding should contain 260 turns of copper wire or bus with a cross section of 7-10 mm. In such a winding, taps are made from 140, 160, 180, 200, 220, 240 turns. By connecting a network to them, it is possible to adjust the current over a wide range (from 50 A to 250 A). The secondary winding must contain 40-50 turns of a copper bus with a cross section of at least 25 mm. But if "hard" operation (with high currents) is supposed, then the cross section here must be increased by 5-10 mm2. Moreover, to increase the efficiency of the transformer, it is better to wind the first 10-15 turns here over the primary winding, and the rest - on the second half of the core. For wider possibilities for adjusting the current, it is possible to make a tap in the secondary winding from about the 30th turn. An original and compact welding transformer with high efficiency is obtained if an iron package (set) from ... the stator of a burned-out electric motor is used as a magnetic circuit. To do this, for a failed electric motor with suitable dimensions, the case is broken, the winding is removed. Leave only a package of iron, smoothing the sharp corners well. Having wrapped the iron with a keeper tape, the windings are wound, based on the same calculations and data on the number of turns that we have given above. That is, the primary winding should contain 260 turns. Moreover, she makes taps starting from the 140th turn, every 20 turns. The secondary winding has 40-50 turns. There are three options for winding such a transformer. The primary winding is performed using a shuttle, and the secondary winding is carried out taking into account the rigidity of the tire. In the case when the winding II is evenly distributed along the magnetic circuit, the efficiency is maximum, and the current can be increased to 350 A. When preparing the toroidal core, it is best, if possible, to bore the grooves where the motor windings lay on a lathe. And some more advice. In the manufacture of the apparatus, it is necessary to carefully isolate the windings from each other and between the layers with a keeper tape, followed by impregnation of all this with bituminous varnish. In the primary circuit, a fuse and a switch for the number of turns should be taken into account. The simplest version of the latter is shown in the illustration. It must be remembered that in the primary circuit, the current ranges from 8 A (at 260 turns mode) to 25 A (at 140 turns mode). Therefore, the device must be connected to the network with a wire with a cross section of at least 7-10 mm2. The cable of the secondary network is connected through an adapter block using end caps (see Fig.), which are easy to make from a copper tube. And from a steel tube, an electric holder is made by do-it-yourselfers. It is usually not easy for a novice welder to master the work with a welding machine: the arc is not the right one. There is no need to despair, however. The first and simplest way to start an arc is by sliding the electrode to the metal being welded. Reminds me of the process of lighting a match. Having excited the arc, the electrode is smoothly removed from the metal at a distance of 2-5 mm. And welding is done.
We know from ourselves: it is difficult to keep the electrode at a minimum distance. But this should be achieved, since at a high position of the electrode, when it is easier to hold the arc, the quality of the weld is much worse. And the near-weld zone itself is splashed with molten metal and slag. The second method of excitation of the welding arc is more complicated. The electrode here is brought almost vertically to the place of welding and, after a light touch, is immediately taken up. To obtain a smooth weld, it is necessary to combine three electrode movements simultaneously. The first is its continuous and uniform movement down as it burns. The essence of the second is in the movement of the electrode along the welding board. Moreover, the electrode should be tilted in the direction of movement, at an angle of 15-30° to the axis perpendicular to the plane of welding. The normal speed of movement of the electrode is considered to be the one at which a seam bead is formed. The width of the latter is approximately 1,5 of the electrode diameter. The third is the oscillatory movement of the electrode across the seam ("zigzag" or "spiral"). Allows for a wider bead and better edge melting. Moreover, the width of the roller here sometimes reaches two or three diameters of the electrode. You can study the welding technology in more detail in the special literature. Read, comprehend, train - and the welding arc will be obedient to you. In conclusion, it is useful, I think, to recall the need to comply with safety regulations. Before turning on the welding machine, it must be inspected and cleaned of dust and dirt. Do not forget also that inclusion in the network without grounding is unacceptable. And all changes in the operating mode should be performed at idle or even with the device turned off. In no case should electric welding be performed in damp, unventilated rooms, during precipitation. Fire safety measures must be strictly observed. The presence of fuels and lubricants is strictly prohibited. Naturally, damage to the device must not be allowed. All malfunctions in it must be eliminated immediately. Remember also that if the vehicle is being welded, then it must also be grounded. You need to work in overalls, in a place equipped with ventilation, which is turned on 5-10 minutes before the start of work. Make sure that the welding cable is not too long. And its cross section must correspond to the strength of the current. Light filters must also be selected according to the strength of the current. Moreover, if the latter is 15-30 A, they use C3 type filters. C4 is used at 30-60 A. At an arc current of 60-150 A, C5 filters are indispensable. And C6 and C7 are used, respectively, at 150-275 A and 275-350 A. Finally, one more rule. Welding of pressure vessels is strictly prohibited. We recommend using a paste with the following formula for coating electrodes: liquid glass - 1 l, chalk - 0,5 kg, wood ash - 1 kg. The thickness of the coating should be 0,15-0,25 mm. Dry it for 12-20 hours. Authors: V.Mishiev, N.Ivanov, Essentuki For those who are not new to the manufacture of conventional "rod" welding transformers, I strongly recommend switching to another, more complex (but interesting and promising) type using a tape magnetic circuit. After all, the advantages of the latter are obvious.
Firstly, it is absolute noiselessness in operation (there is no buzz). Secondly, there is efficiency, high efficiency. Since the magnetizing force in tape magnetic circuits is 4-5 times greater than in conventional (type-setting), by reducing the cross section ((Dd) * b / 2) of the magnetic circuit, it is possible to significantly reduce the mass of the transformer itself. For example, my 25 kg CT allows you to freely cook steel with a "five". I took the material for tape magnetic circuits from discarded current transformers (CT = 35 kV). They are set to MB = 35 kV. Winding data for ST in this case will be:
I recommend welding with this transformer at direct current. But we need at least the simplest "bridge" rectifier on the VD-200. Moreover, it is desirable to connect the "positive" output here to the electrode holder through a choke (see figure). The latter is wound on the magnetic circuit from the magnetic starter II - III size with a copper bus S = 35 mm2 until the "window" is filled (10-15 turns). This will make it easier to strike and maintain the arc. Literature
Author: S.Babichev, Balakleya
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