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High-frequency welding finned tube

How does high-frequency welding finned tube work?

The high-frequency welding finned tube use the skin effect and proximity effect of the high-frequency current to heat the outer surface of the steel strip and the steel tube while the steel strip is wound around the steel pipe, until the plastic state or melting, a certain pressure on the wound steel strip Complete welding next.

This high-frequency welding is actually solid-phase welding. Compared with inlaying, brazing (or integral hot-dip galvanizing) and other methods, it is excellent in terms of product quality (high welding rate of fins, up to 95%), productivity, and degree of automation.

High-frequency welding uses solid resistance heat as an energy source. The resistance heat generated by the high-frequency current in the workpiece during welding heats the surface of the welding zone of the workpiece to a molten or near plastic state, and then applies (or does not apply) upsetting force to achieve metal bonding.

Therefore, it is a solid phase resistance welding method. High-frequency welding can be divided into contact high-frequency welding and induction high-frequency welding according to the way that high-frequency current generates heat in the workpiece.

When contacting high-frequency welding, high-frequency current is introduced into the workpiece through mechanical contact with the workpiece. During induction high-frequency welding, the high-frequency current generates an induction current in the workpiece through the coupling effect of the induction coil outside the workpiece.

High-frequency welding is a highly specialized welding method, and special equipment should be equipped according to the product. High productivity, welding speed up to 30m / min. Mainly used for welding longitudinal or spiral seams when making pipes.

The contents of the two major effects of high-frequency current in high-frequency welding are:

Skin effect: When a conductor is fed with alternating current, the current distribution on the conductor cross-section is uneven, the current density gradually increases from the center of the conductor to the surface, and most of the current only flows along the surface of the conductor.

The lower the resistivity of the conductor, the greater the magnetic permeability, and the higher the frequency of the current, the more significant the skin effect.

Proximity effect: When high-frequency currents flow in opposite directions in two conductors or in a reciprocating conductor, the current will concentrate on a special physical phenomenon that flows on the adjacent side of the conductor.

High-frequency welding usually uses a current frequency range of 300 to 450kHz, and sometimes a frequency as low as 10kHz

 

Murphy high frequency finned tube scaled

 

High-frequency welding fin characteristics

  1. Due to the fast welding speed and the strong self-cooling effect of the weldment, not only is the heat-affected zone small, but it is also not easy to oxidize, so the structure and performance of the weld is very good.
  2. Anti-corrosion performance, wear resistance, low contact thermal resistance, high stability, anti-ashing ability.
  3. Large heat exchange area.

High-frequency welding type

There are two types of high-frequency welding: high-frequency resistance welding and high-frequency induction welding.

High-frequency resistance welding: use rollers or contactors as electrodes to introduce high-frequency current into the workpiece, suitable for continuous longitudinal seam butt welding and spiral lap seam welding of tubes, welding of boiler finned tubes and spiral fins of heat exchangers.The outer diameter of the weldable pipe is 1200 mm, the wall thickness is 16 mm, and the thickness of the ventral pole of the I-beam can be welded 9.5 mm. The productivity is very high.

High-frequency induction welding: the induction coil is used to heat the workpiece, which can weld small-diameter tubes with an outer diameter of 9 mm and thin-wall tubes with a wall thickness of 1 mm. Commonly used for longitudinal seam welding of small and medium diameter steel pipes and brass tubes, but also for girth welding, but the power loss is greater than high-frequency resistance welding.

The main parameters that affect the quality of high-frequency welding are the frequency, power, forming an angle of the workpiece, extrusion force, the distance between the electrode (or induction coil), and the extrusion roller, and the welding speed.

The main equipment includes high-frequency power supply, workpiece forming equipment, and extrusion machinery. High-frequency welding has stable quality, high productivity, and low cost. It is suitable for high-efficiency automatic production lines and is an advanced method for producing seamed pipes.

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