PURPOSE: To provide a uniform temperature distribution along the direction of plate width by preventing concentration of eddy currents at the end of the plate width through the control of the current-carrying states of exciting coils.
CONSTITUTION: The exciting coils 5 of magnetic poles 3, 4 which are located in the same position along the direction of plate width are grouped. The longitudinally adjoining coils 5 of each group are disposed to produce magnetic flux 6 in opposite directions. The adjoining coils 5 of the adjoining groups also produce magnetic flux 6 in opposite directions. As a result, eddy currents extending in the direction of the arrow are produced around the magnetic flux 6. A switch for each group is turned on by the width of a thin plate 1, and electricity is not transmitted to those groups of coils 5 which are off the plate width. Thus the eddy currents flow through the entire thin plate 1 while describing a small group, and the concentration of the eddy currents at the ends of the plate width does not occur, resulting in a uniform temperature distribution. The cores of the magnetic poles that are off the width of the thin plate 1 are not magnetized, so voltage buildup and decrease in heating efficiency, both of which could be caused by the generation of magnetic flux, can be prevented.
TSURUSAKI KAZUYA
SEZE SHINJI
MIHARA KAZUMASA
FUJIOKA HIRONORI
