http://fluxtrol.com Chapter 5: Magnetic Flux Control for Induction Heating Systems Includes: Magentic Flux Concentrators, Process Improvements, Production Efficiencies, Simulation and Design.

1. Chapter V. Basics of Magnetic Flux Control in Induction Systems

3. Concentrator Effect Magnetic flux concentration is one of the types of flux control, which also includes shielding, deviation or other magnetic field modification. Application of C-shaped concentrator to coil tubing results in dramatic reduction (elimination) of external magnetic field, in higher power in the part under the coil face (for the same coil current) and in reduction of power outside of the coil face zone. On the other side the C-shaped concentrator pushes the coil current to its face reducing the cross-section of current flow. Losses in the coil grow. When concentrator is properly applied its benefits overcome this effect. Power distribution on the part surface

4. Electrodynamic Forces In induction heating processes Electrodynamic forces usually play a negative role causing coil and part vibration. Vibration can generate harmful noise and also reduce coil lifetime. Electrodynamic forces are distributed between the system components. At high frequency forces are applied to the coil component surfaces. The coil copper face always experiences repulsion from the workpiece. The concentrator poles experience attraction to the workpiece. Resulting force applied to the coil may be either attractive or repulsive (more typical). For the same workpiece power, the electrodynamic forces become lower with higher frequency. Electrodynamic forces vary in time. Electrodynamic forces applied to the coil copper and concentrator poles. Workpiece is a magnetic steel with a locally austenitized (non-magnetic) zone under the coil face.

12. Example of Magnetic Core Influence on Parameters of I.D. Coil With the same pipe power, application of core reduced coil current from 2000 A to 900 and corresponding reactive power from 65.8 to 30.2 kVAr. Electrical efficiency of the coil increased from 69% to 84%. Coil head voltage remained almost the same (5% increase) Flux 2D program

17. Example: Single-Shot Coil with Fluxtrol 50 Fluxtrol 50 concentrators (yellow) are placed in strategic areas of the coil Concentrators are mechanically attached to copper while good thermal contact provided by glue

21. Results: Coil Current Demand vs. Permeability Concentrator reduces current demand 40 - 50% at permeability 40 - 50 compared to permeability 1 (air). Notice: very small improvement at higher permeability for all studied cases 3500 Permeability Magnetic part Non-magnetic part

22. Results: Total Power vs. Permeability Concentrator reduces power demand 25 - 30% at permeability 20 - 40. Notice: no improvement at higher permeability for all studied cases Permeability Magnetic part Non-magnetic part

24. Results: Coil Current Demand vs. Permeability 3500 Concentrator reduces current demand 40 - 50% at permeability 40 - 60 compared to bare coil (Mu =1); very small improvement takes place at higher permeability for all studied cases

25. Results: Total Power vs. Permeability Concentrator reduces power demand 25 - 30% at permeability 20 – 40; almost no improvement at higher permeability for all studied cases Experiments confirm these theoretical conclusions