PURPOSE: To prevent deterioration of strength of a lead portion of a thin wire heater coil for a high voltage by twisting the lead portion of the heater coil, followed by primary and secondary energizing/heating treatments, so as to obtain an oxide film at the surface thereof, and remarkably reducing heat generation in the lead portion.
CONSTITUTION: A heater wire rod made of, for example, an Fe-Cr-Al alloy and having a diameter of 0.29mm is turned by 560 times thereby forming a coil portion 10 having an outer diameter of 8mm and a length of 125mm. The coil portion 10 is backed at 800°C for 60 minutes inside an electric furnace, thus producing an oxide of Cr excellent in anticorrosion at the surface thereof. The end portion of the coil portion 10 is drawn out for duplication, followed by twisting at a pitch of 2mm, thus forming a lead portion 11. The coil portion 10 is put into a glass tube 2 at a length of 140mm while being separated from a coil, followed by a primary energizing/heating treatment at 400V for 15 seconds, thereby obtaining a alumina oxide film having an electric insulating characteristic at the surface of the wire rod. Subsequently, the coil portion 10 is contracted in the axial direction, followed by a secondary energizing/ heating treatment at 350V for 3 seconds.
TAKEMOTO MASAYUKI
KONO AKIO
