Tubes designed for welding, the ends must be perpendicular to the axis of the tube, without burrs. For resistance welding ends with suitable blanks obtained after cutting lathes, machining truboreznyh, saw a pendulum, followed by removing the burr drill with a diameter equal to the inner diameter of the pipe. Stripping of blank surfaces from dirt and rust is not required. The process of developing resistance welding technology is practically reduced to the choice of rational parameters of heat and precipitation, to ensure the achievement of equal strength of welded joints with the base metal, and the absence of defects in the welded joint. The required quality of welded joints is obtained by squeezing heated uniformly over the cross section edge products. The uniformity of heating is achieved by selecting the optimum welding conditions. Satisfactory formation of the joint can be obtained for different values of welding current and the duration of heating. Each diameter of the pipe corresponds to a range of welding currents within which ensured the formation of a satisfactory joint. The essential quality of welding has vliyanie.na current density in the product. At a current density of less than 0.5 A/mm2 high quality welds can be achieved in case of mechanical precipitation only when accumulated at the ends of the welded metal parts of the product has already begun to flow, ie, after the appearance of flowing liquid metal layer. At the same time to ensure the stability of the welding process is necessary to maintain the clearance between the workpiece, which can only be achieved by using tracking systems. At a current density of more than 0.5 A/mm2 mechanical sediment can be carried out in the presence of liquid products at the ends of a metal film without the appearance of flowing layer. This allows the heating of pipe ends at fixed relative to each other parts of the welded products, reduces the amount of planted metal, ie, reduces the magnitude of the internal and external burrs. Due to the fact that the heating is carried out at the fixed parts of the product, it becomes possible to simplify the design of the equipment by eliminating the complex tracking systems. If the power supply is not limited to, seek the upper limit of the welding current. Given a pre-rational power supply is the most efficient use of its power. On the uniformity of heating of the ends of the perimeter of the product significantly affects the rate of displacement of the arc. found that in the final stage of heating may be a local increase in the gap, the so-called digging. In the metal, where the digging occurred, a zone of low strength weld, or even lack of adhesion compounds. Cause of tearing is, apparently, the appearance of liquid metal drops, the speed of movement is much smaller than the velocity of the arc. Due to the speed difference between having a delay in the movement of the arc, leading to local melting of the ends and release of molten metal from the joint. One way of wresting control is a periodic change in the direction of rotation of the arc (reverse), which makes it possible for some time to disperse the liquid metal on the edges, not allowing him to collect in one place. However, reversal, especially in high-power modes, is malopodhodyaschim and could be hard to remedy. It was established experimentally that the combination of current density in the product of more than 0.5 A/mm2 arc moving with velocities of the order of 100-150 m / sec can eliminate digging, and to provide uniform heating of the edges. Based on this value is determined by the radial induction in the gap and magnetizing force excitation coils. Defining the parameters of the excitation coils (the number of turns, wire cross-section and current) are made on the basis of structural considerations and the way power coils (whether or arc by successive inclusion in the welding circuit). The magnitude of the specific efforts of precipitation during welding technology slightly higher compared to the contact welding, and is 8-10 kg/mm2 for mild steel. The optimal value of the installation of the gap between the welded parts of the products practically does not depend on the size of the welded products. For example, for pipes up to 100mm - the optimum size of this gap is 2 mm, and for pipe diameters from 100 mm to 300 mm -2,5-3. Deviations from the optimal size of the gap as to decrease (to 1.5 mm for pipe diameters up to 100 mm and 2 mm for pipe diameters 100 - 300 mm) and upward (up to 2.5 mm for pipe diameters up to 100 mm to 3.5 mm for pipe diameters of 100-300 mm) can lead to a breach of the stability of motion of the arc. Summary of welding modes, providing a satisfactory quality of welded joints in the fixed parts of the product in the process of heating, for pipe diameter 17-114mm of steel St20 STZ-listed in the table.
| The diameter of the pipe, mm | Wall thickness, mm | Welding current, A | Magnetizing force of the coil, and in- | The voltage on the arc, in | Duration of heating, s | Effort precipitation, kg |
| 17 | 2 | 200 | 1200 | 25-26 | 1.0 | 900 |
| 26.8 | 2.8 | 260 | 1400 | 25-26 | 1.8 | 1800 |
| 32 | 3.5 | 350 | 2400 | 25-26 | 2.0 | 2500 |
| 43.5 | 3.5 | 400 | 3000 | 26-27 | 2.3 | 3600 |
| 57 | 3 | 550 | 3600 | 26-27 | 4.2 | 4600 |
| 89 | 4 | 750 | 4500 | 27-29 | 5.5 | 8500 |
| 114 | 5 | 950 | 6000 | 28-30 | 9.0 | 15000 |
Electric Resistance Welding
Theory Fundamentals of Resistance Welding
Resistance Welding Technology
Equipment for Resistance Welding
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