Abstract: An induction heating apparatus and related temperature control circuitry and method of controlled heating of a workpiece at two temperature levels. The apparatus and method utilizes a temperature sensing device, adjustable reference temperature circuitry utilizing a voltage dividing circuit triggered by a timing circuit to heat the workpiece to a first predetermined temperature, dwell at the predetermined temperature for an amount of time governed by the timing device and continue heating the workpiece to a second predetermined desired temperature. The method and circuitry being particularly useful in heating a laminar structure where a ferromagnetic material is coated with a surface of nonconducting, nonferromagnetic material, such as paint.

Abstract: Disclosed is an induction heating apparatus wherein the tank circuit and heater coil are combined in a single unit which is separated from the power supply. A coil forms both the inductance element of a tuned circuit and the primary winding of a current transformer. The inductance element is associated with a secondary winding formed by a metal sheet of material wrapped about the inductance element and can form both the capacitance of the tuned circuit and the secondary winding of the current transformer. A heat transfer unit is connected directly to the secondary winding formed by the single turn of sheet material and is used to provide inductive heating to a work surface to which thermally activated adhesives are to be secured. The induction heating unit is formed as a hand-held portable gun and includes the electronic circuitry in a rear body portion of the gun and the heat transfer unit forms a nosepiece for the gun so that precise local areas can be heated.