Sizing Ferrite Rods for ERW Pipe Welding

Hrm... the theory of ferrite rod in ERW pipe production. Sorry for the basic nature of my response, but I'm not sure what level of knowledge you have or what exactly you are looking for in regards to ferrite "parameters." However, I am going to use industry-specific terms to the HF Induction Welding Industry which you should know since you are in the industry.

So...

In induction welding, the high-frequency magnetic field from the induction coil induces an alternating current in the open seam tube.

The current will travel around both the diameter and along the vee-angle. Since we are welding, we want the current to travel along the vee-angle in order to heat the edges of the strip, and not the body of the tube/pipe.

To redirect the current along the vee-angle, an impeder is placed inside the tube at the location of the induction coil.

The impeder is used to increase the impedance of the ID of the tube/pipe. The greater the impedance, the larger percentage of the current will travel along the vee-angle, the more efficient the welding process will be.

Impeders are generally made from ferromagnetic materials, such as ferrite. When induction welding was first developed ferrite was made from nickel zinc materials. However, the technology has improved and manganese zinc materials are now used.

Ferrites performance is not linear to the curie point, so cooling is important. The important "parameters" of ferrite for induction welding are:

high curie temperature

high saturation flux density (gauss)

stability through operating temperature range

dissipation at your welder operating frequency

The length of your impeder should be 3.5 times the induction coil length (or the induction coil inside diameter) and should pass the contact point of the vee-angle by about an 1/8 of an inch.

The diameter of the impeder should be as large as possible inside the tube, but general practice sizes it at around 75% of the tube OD... this varies with wall thickness.

The ferrite should be incased to protect it as any cracks in the material will reduce its efficiency.

So, these are the basic parameters of ferrite in the Induction Welding process of the tube and pipe industry. Hope it was of some use.

JavaHead