INDUCTIVE HEATING DEVICE

Abstract: An inductive heating device in which a plurality of heating coils (1) are selectively connected to a phase lag compensating matching board (4) provided with capacitors (3), the heating coils (1) being used to heat inductively a workpiece. A plurality of output terminals (10 to 15) are provided on the matching board (4) connected directly to a common current collecting line (8). Preferably, connections are also provided directly between adjacent ones of the output terminals. With the arrangement of the invention, the power line voltage drop is minimized thereby decreasing power losses.

Description: INDUCTIVE HEATING DEVICE The present invention relates to an inductive heating device in which current supply is effected selectively to inductive heat.ing coils. A conventional inductive heating device of the same general type to which the invention pertains is shown in Fig. 1. In Fig. 1, reference numeral 1 designates a plurality of heating coils, 2 switches for selectively activating the heating coils, 3 power-factor enhancing capacitors forming a paral-lel resonance circuit for compensating for the lag power factors of the heating coils 1, 4 a matching board on which the capacitors 3 are mounted, 5 a power source for supplying electrical power to the input terminal 6 of the matching board 4, 7 current supplying lines for supplying current to the heating coils 1, 8 a common current line provided on the matching board, and 9 an output terminal. In this heating-device, workpieces to be heated (not shown) are placed inside the heating coils. A process ing cycle of loading a workpiece, heating the workpiece, cooling the workpiece and loading another workpiece is employed. In order to increase the percentage of time of utilization of the power source and the processing ability of the device, it is necessary to provide plural heating coils 1 For this purpose, switches 2 are provi ded to selectively swith the heating coils 1, with one switch being closed to connect a single coil to the matching board at any time. If, however, heating coils 1 having, for example, a diameter of 500 to 3000 mm and a length of 500 to 5000 m are provided and current is suppled to one heating coil at a time, sometimes it is impossible to supply current effectively to the heating coil which is farthest from the matching board 4 because of power transmission losses caused by power line voltage drops. The invention mitigates the above-described drawback accompanyi.ng a conventional inductive heating device by returning power losses. According to the invention there is provided an inductive heating device in which a plurality of heating coils 1 are selectively connected to a matching board 4 provided with at least one capacitor 3 for inductive heating of a workpiece, chracterized in that a plurality of output terminals 10 to 15 are provided on said matching board 4 for respective ones of said heating coils 1 , said output terminals being connected directly to said at least one capacitor. An inductive heating coil arrangement is provided in which a common current collecting line which collects the currents of various capacitors serves as a current supply line for supplying current to the plural heating coils, thereby decreasing the power line voltage drop. Fig. 1 is a digram showing the arrangement of a conventional inductive heating device, and Fig. 2 is a diagram showing the arrangement of an inductive heating device according to the invention. The invention will be described with references to Fig. 2. In Fig. 2, reference numerals 1 through 6 and 8 designate components identified by the same reference numerals as in Fig. 1. Reference numerals 10 through 15 designate output terminal pairs which are provided on the matching board 4 and are connected to the current collecting line 8. The pairs of output terminals 10 through 15 are connected through the switches 2 to corresponding ones of the heating coils 1. In the conventional device, the common current collecting line 8 merely functions to collect the currents from the various capacitors 3. On the other hand, in the device of the invention, the common current collecting line 8 serves as the current supplying lines (which are also provided in the conventional device) because a plurality of output terminals 10 through 15, each of which can be selectively connected to a separate one of the heating coils 1, are provided on the matching board 4. Preferably, connections are also provided directly between adjacent ones of said output terminals, i.e. one line of terminal pair 10 would be connected to the corresponding line 11 and so on. In a case where large currents flow in the device, connecting bus bars can be employed instead of the switches 2. Not only is a separate common current supplying line for the heating coils eliminated, but also the voltage drops between the power source and the various coil input terminals are decreased and equalized. In addition, the space needed for installation of the device is reduced.

Claims: CLAIMS: 1. An inductive heating device in which a plurality of heating coils (1) are selectively connected to a matching board (4) provided with at least one capa citor (3) for inductive heating of a workpiece, characterized in that a plurality of output termin als (10 to 15) are provided on said matching board (4) for respective ones of said heating coils (1), said output terminals being connected directly to said at least one capacitor. 2. The inductive heating device of claim 1 further characterized by connecting means connected direct ly between adjacent ones of said output terminals (10 to 15). 3. The inductive heating device of claim 1 or 2 charac terized in that a common current collecting line (8) is provided on said matching board (4), each of said output terminals (1o to 15) being directly connected to a most closely adjacent point on said common current collecting line (8).

Inventors: HOSHIKAWA, TORU C/O TOYO TANSO CO., LTD., OSAKI, YOSHIHIKO C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA, TOYO TANSO CO., LTD.
Application year: 1982
Main classification: H05B6
IPC codes: H05B6