Influence of Welding Frequency on High-frequency Welded Pipe

Welding is critical to the quality of high-frequency welded pipes, and the frequency of high frequency welding has a great impact on welding, because the high-frequency's frequency affects the distribution of current within the steel plate.

The impact of high or low selected frequency of welding mainly acts on affecting the size of the weld heat affected zone. From the welding efficiency, pipe manufacturers should use a higher frequency as far as possible. 100KHz high-frequency current can penetrate 0.1mm ferrite steel, but 400KHz can only penetrate 0.04mm, which means that the current density distribution on the surface of the steel plate of the latter is nearly 2.5 times higher than the former.

In the production practice, pipe manufacturers generally choose 350KHz ~ 450KHz frequency when welding carbon steel material. When welding alloy steel material, and welding more than 10mm thick steel plate, pipe manufacturers can use 50KHz ~ 150KHz low frequency, because the skin effect of chromium, zinc, copper, aluminum and other elements contained by the alloy steel has some differences from steel.

Now, foreign high-frequency equipment manufacturers have mostly used solid-state high-frequency new technology, after setting a frequency range, it will aromatically track and adjust frequency according the thickness of the material, the unit speed, etc when welding.

High Frequency Welding

High Frequency (HF) or Radio Frequency (RF) welding is the joining of materials by supplying HF energy in the form of an electromagnetic field (27.12 MHz) and pressure to the material surfaces to be joined. A generator produces the energy. The tool used to supply the

energy is called an electrode. The electrical energy causes the molecules within the material to start moving, which generates heat that causes the material to soften and thereby fuse together. No outside heat is applied. It is instead generated within the material. After cooling the welded surface under maintained pressure, the material is fused and a weld has been created. The weld seam can be at least as strong as the surrounding material – or even stronger.

Four important factors that affect the final weld result are pressure, welding effect, welding time and cooling time. These parameters can be adjusted and combined in different ways to achieve the optimal welding result for a specific material.

The material most commonly used with HF welding is PVC (polyvinyl chloride), sometimes called vinyl and PU (Polyurethane). The material can be thick or thin, reinforced or coated. It can also be plain, coloured or patterned.

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