The induction method of Field Heat Treatment uses Coaxial Cables to transfer power to either a liquid-cooled copper braided hoses or solid copper coil wrapped around the material to be heated to create a magnetic field. As the electrical current is pushed through the conductor it creates a magnetic field. The magnetic field excites the molecules in the material, which creates heat that radiates from the center of the material outward in all directions.
For certain applications a coil can be created in a “Probe” type format. In this instance the coil is created to be placed as close to the surface of the material, to be heated, as possible, but does not actually wrap around. Examples of this are seen in Bolt Heating and Induction Brazing applications.
The Control Unit for an induction system is typically allows you to alter the percentage of power output. The depth of the magnetic field can also be adjusted by adjusting the induction frequency. It should be noted that it is possible to heat non-ferrous materials with the proper equipment.
Induction Heating Systems are not new to the industry and have been being used for over 30 years. In recent years a small 35kva induction heating system has become commercially available the market place, and has considerable limitations to its abilities when compared to the larger 65-200 Kva Induction Heating Units that are used by the Field Heat Treatment Contractors and Service Companies.
Induction units are most often singularly controlled outputs. Some systems proclaim to be Dual Output while they are actually in fact operating in a parallel system and averaging the output from multiple thermocouple points. If the system is truly Dual Output is could heat to different masses of steel at independently controlled rates.
Induction Heating Systems are great for Stud / Nut Removal, Induction Brazing, Turbine Rotor De-Stacks, Retaining Ring Removal, High Temperature Field Heat Treatment applications like Solution Annealing. It should be noted that compared to Electrical Resistance, Induction Heating Systems are far more complicated in terms of on board electronics and they required a more skilled personnel to operate them.
While Induction Heating Systems have been utilized for Welding Pre-heat applications due to their ability to heat quickly, they have been found to be considerably less accurately controlled when compared to Electrical Resistance Equipment. For P-91/ P-15E materials where, Minimum Pre-Heat, Maximum Interpass and PWHT temperature tolarances are critically important, Induction Heating Systems are less than ideal.