For high frequency welding of stainless steel tubes with a diameter up to 16 mm may experience technological difficulties. So, shunt the current around the perimeter of the pipe increases, but due to the reduction of the length of the perimeter reduced the concentration of current at the edges. The parameters of the inductor and rolls welding stands are not allowed to bring them enough to significantly reduce the resistance of the edges, thereby reducing the current on the circular path and increasing its concentration on the edges. A reduction in the size of the magnetic core can cause overheating and breakages.
In the production of stainless steel welded pipes 12X18H10T Ø 5−32 mm, applying a direct current welding by resistance method. The method consists in the heating of the edges using heat from the passage of high currents through the joints reduced edges. Due to the rough surface they have a high resistance. Current is supplied to the rotating edges of the contact electrodes. Heating edges, and welding them occurs during advancement of the workpiece through the welding gun. Diagram of the current supply is such that is suitable for the production of pipes with Ø> 12 mm. At smaller diameters significantly increased shunt current, which leads to a decrease in welding voltage, and the temperature rise around the perimeter of the pipe does not allow with sufficient force to compress the seam for a solid connection.
Constant welding current gives a very smooth inner Burr with a height of 0,15−0,25 mm, which cannot be achieved by high frequency welding. Calibration of the split washers and the forming rolls to create the conditions when the internal burrs shall not exceed 0.15 mm. Due to this, these pipes are in some cases can replace the more expensive seamless pipe, manufactured by cold rolling and, for example, in the pressure oil line of cars.
The most commonly by welding, a constant current is made of pipe Ø 10−20 mm with a wall thickness of 0,7−1 mm Tube is produced from the cold strip. The welding speed reaches 1.2 m/s. Pipe of smaller diameter is produced by cold reduction and a total reduction of up to 50%. So TESA 5−16 installing pressure-reducing-stretching mill with drive 9 and 8 non-alternating two-roll mill stands. Finished pipe Ø 5 to 12 mm is wound into coils, and pipes with large diameter is cut to length.
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