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Closed loop control of the induction heating process using miniature magnetic sensors

United States Patent

May 20, 2003
View the Complete Patent at the US Patent & Trademark Office
Sandia National Laboratories - Visit the Intellectual Property Management and Licensing Website
A method and system for providing real-time, closed-loop control of the induction hardening process. A miniature magnetic sensor located near the outer surface of the workpiece measures changes in the surface magnetic field caused by changes in the magnetic properties of the workpiece as it heats up during induction heating (or cools down during quenching). A passive miniature magnetic sensor detects a distinct magnetic spike that appears when the saturation field, B.sub.sat, of the workpiece has been exceeded. This distinct magnetic spike disappears when the workpiece's surface temperature exceeds its Curie temperature, due to the sudden decrease in its magnetic permeability. Alternatively, an active magnetic sensor can measure changes in the resonance response of the monitor coil when the excitation coil is linearly swept over 0-10 MHz, due to changes in the magnetic permeability and electrical resistivity of the workpiece as its temperature increases (or decreases).
Bentley; Anthony E. (Tijeras, NM), Kelley; John Bruce (Albuquerque, NM), Zutavern; Fred J. (Albuquerque, NM)
Sandia Corporation (Albuquerque, NM)
10/ 207,424
July 29, 2002
FEDERALLY SPONSORED RESEARCH The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation.