The main process parameters of high-frequency straight seam welded pipes manufactured by high frequency welded pipe equipment include welding heat input, welding pressure, welding speed, size of opening angle, position and size of induction coil, position of impedance, etc. These parameters have a great impact on improving the product quality, production efficiency and unit capacity of high-frequency welded pipes. Matching various parameters can make manufacturers obtain considerable economic benefits.

3.Welding speed

The welding speed is also one of the main parameters of the welding process of the high frequency welded pipe equipment. It is related to the heating system, the deformation speed of the weld and the crystallization speed of the metal atoms. For high-frequency welding, the welding quality improves with the welding speed, because the shortening of the heating time narrows the width of the edge heating zone and shortens the time for metal oxide formation; if the welding speed is reduced, not only the heating zone becomes wider, That is, the heat-affected zone of the weld becomes wider, and the width of the melting zone changes with the change of the input heat, and the internal burr formed is also larger. The width of the fusion line under different welding speeds is shown in Figure 5. It can be seen from the figure that a more ideal welding seam can be obtained when the welding speed is higher under the same extrusion amount.

Fig.5 Width of fusion line at different welding speeds

During low-speed welding, it is difficult to weld due to the reduction of the corresponding input heat. At the same time, due to the influence of the edge quality of the board and other external factors, such as the magnetism of the resistor, the size of the opening angle, etc., it is easy to cause a series of defects. Therefore, during high-frequency welding, the fastest welding speed should be selected for production according to the specifications of the product under the conditions allowed by the capacity of the unit and the high frequency welded pipe equipment.

4.Open corners

The opening angle, also known as the welding V angle, refers to the angle between the edge of the strip before the squeeze roll, as shown in Figure 6. Usually the opening angle varies between 3° and 6°, and the size of the opening angle is mainly determined by the position of the guide roller and the thickness of the guide sheet. The size of the V angle has a great influence on the welding stability and welding quality.

Figure 6 Schematic diagram of high frequency induction welding V corner

When the V angle is reduced, the strip edge distance will be reduced, so that the proximity effect of the high frequency current can be strengthened, which can reduce the welding power or increase the welding speed and improve the productivity. If the opening angle is too small, it will lead to early welding, that is, the welding point will be squeezed and fused before reaching the maximum temperature, which will easily form defects such as inclusions and cold welding in the weld, reducing the quality of the weld. Although the power consumption is increased when the V angle is increased, it can ensure the stability of the strip edge heating under certain conditions, reduce the loss of edge heat and reduce the heat affected zone. In the actual production of high frequency welded pipe equipment, in order to ensure the quality of the weld, the V angle is generally controlled at 4° to 5°.

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