Advantages

Welding with high-frequency currents is most often used for the manufacture of electric welded stainless steel pipes of small and medium diameters. Such welding has a number of advantages:

- Making pipes from a variety of steel grades - alloyed, high-alloy, carbon, as well as non-ferrous metals, on the same welding equipment
- Minimum power consumption.
- It is possible to achieve high welding speed - up to 2-2,5 m/s without loss of weld quality.
- Use of the initial blanks of different materials and getting sufficiently strong weld.
All this is achieved due to the significant concentration of current on the edges of the welded metal, which heats a very thin layer of metal. At a frequency of 450 kHz the depth of edge heating at 20 °C is 0.05 mm. At the loss of magnetic properties (after 723 °C for steel) the depth increases to 0,9 mm at the same frequency and up to 2 mm at 70 kHz. Fast welding and low energy consumption are achieved due to the rapid heating of thin metal layers. Edges of the workpiece are heated either by contact or induction welding.

Contact method

The maximum current that is concentrated on the surface of the edges causes rapid heating. When the edges are brought closer together by the rollers compressing the weld, forming a welding gauge, the current density increases. At the point where the edges converge, the temperature is maximum. Convergence of the heated edges and compression leads to the formation of the weld. If the diameter of the stainless steel pipe is minimal, the bypass current heats the entire perimeter, which leads to the need to increase the input power for welding. The disadvantage of contact current input is that the workpiece can only be used with a high surface finish. Even in this case, contact wear, vertical edge oscillations, surface changes are inevitable and lead to a violation of the welding mode, reduced productivity. There can be burns on the surface of the pipe.

Induction method

Eddy currents in the metal are excited with the help of ring inductors. External inductors are installed along the diameter of the stainless steel pipe, and if the pipe is thicker than 200 mm, internal inductors are also installed. The induction currents are concentrated at the ends of the edges. The higher the magnetic permeability, the higher the current strength and heating of the steel. Advantages and disadvantages. The induction method is good because regardless of the surface of the workpiece, it provides a stable supply of energy, as well as high quality of the weld. This advantage has made the induction method the most popular. TESA inductors can be powered using both lamp-based generators (up to 450 thousand Hz) and machine-based generators (10 thousand Hz). When welding pipes made of steel and nickel alloys up to Ø 100 mm, select a frequency of 450 kHz, brass alloys - 70 kHz. When welding steel pipes, Ø>200 mm, with walls of 6-20 mm reduce the frequency to 10 kHz for deeper heating. The welding speed is reduced to 0.5-1 m/s in order to bring the heating to the melting point of the weld. The presence of oxides, in particular refractory ones, requires power up to 1600 kW for welding medium-diameter pipes. The possibility to use different high-frequency welding modes is one of the important advantages of this method, which is applicable to both alloyed steels and non-ferrous metals.

Grat

High-frequency welding leads to the formation of both external and internal burr up to 60% of the pipe wall thickness. This is considered a significant disadvantage. Outer burr is removed with the help of a burr remover, which is installed in the line of the mill. The formation of internal burr is prevented by shaping the edges, either by cutting or rolling and burning. This achieves a higher quality and expands the field of application of the finished tubes. Internal grate cutters with one cutter for continuous cutting are the most applicable. But the need for frequent change of cutters and stops for this mill, makes their use only in the production of limited batches of high quality pipes reasonable.

Buy, price

Company Evek GmbH sells stainless steel rolled products at the best price. It is formed taking into account technological features of production and does not include additional costs. With us you can buy a variety of products in bulk for large-scale production. We also offer good terms for retail buyers. On our site you will find all the necessary information. Orders are fulfilled in a very short time. Wholesale customers are offered discounts.