The ferrite is generally used as impedance magnetic core in high-frequency welding, which can effectively improve welding speed and quality and reduce energy loss.

When high frequency welder has a high frequency current in induction coil through, will produce a high frequency flux in the coil, the high frequency magnetic flux induced eddy current in the welded pipe welding will melt weld, using a magnet can greatly improve the magnetic flux of induction line circle, so as to greatly improve the weld pipe of induction electromotive force, the purpose of increasing welding power.

When high-frequency induction welding technology is used to produce welded tubes, an impedance device needs to be placed in the inner cavity of the welded tube blank to change the distribution of induced current in the tube blank, as shown in Figure 1.  Placing the impedance device in a suitable position can make the induced current gather on the fusion surface of the welded pipe, so as to improve the efficiency of induction welding; If the placement scheme of impedance device is not appropriate, it will not only reduce the welding efficiency of welded pipe, but even make the product quality problems.

Here we combine some experience in the production process of impeder installation and in production should pay attention to the tubing problem to make a summary:  

A.  Mounting position of the impeder (Ferrite bar).  

The installation position of ferrite has an important effect on whether it can fully play its function.  According to the law of electromagnetic induction, the installation position of the ferrite bar should follow the following principles: one end of the ferrite bar should exceed the induction coil, and the part beyond the induction coil should be appropriately long (about the length of one coil).  Specifically, if ferrite bar is long enough, the midpoint of the coil can be taken as the center position of the ferrite, so that one end of the ferrite is 3-4 mm beyond the center line of the extrusion roll, and the other section is a longer distance beyond the induction coil.  If the ferrite  bar is not long enough, the center of the ferrte should be appropriately moved towards the heating zone to ensure that one end of the ferrite bar exceeds the center line of the extrusion roll, but care should be taken to ensure that the other end of the ferrite must exceed the induction coil.

B.  Installation of impedance device (ferrite bar).  

The magnetic bar should be firmly installed first to avoid vibration in the welding process. The position of installation should be so that the axis of the magnetic bar is consistent with the rolling center line, and the ferrite bar as close to the solder joint as possible.  

C.  Water cooling problems.  

Water cooling is an important problem in high frequency straight seam welded pipes. The purpose is to keep each part of the magnetic bar at a low and constant temperature in the high-frequency welding process, so that the magnetic bar has a high permeability and remain unchanged.  In order to achieve this goal, we must pay attention to two problems: one is to have enough water flow, which requires enough water pressure and appropriate large water cross sectional area.  Second, it should have high heat dissipation efficiency.  Even if the water flow is very high, if the heat dissipation efficiency of the magnetic rod is very low, it still cannot reach the purpose of water cooling.

D.  Some problems should be paid attention to in the production process.  

1).  When installing the impedance device, the front end shall not exceed the center line of the extrusion roll too far, generally controlled between 3-4mm.

2).  In the production process, the position of the ferrite bar and whether it is taken away or broken should be checked regularly, and the wire drawing or sundries hanging on the magnetic bar should be removed frequently.