[0001] The present invention relates to an inductive heating device in which current supply
is effected selectively to inductive heating coils.
[0002] 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 parallel 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.
[0003] In this heating-device, workpieces to be heated (not shown) are placed inside the
heating coils. A processing 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 l. For this purpose, switches
2 are provided to selectively swith the heating coils 1, with one switch being closed
to connect a single coil to the matching board at any time.
[0004] If, however, heating coils 1 having, for example, a diameter of 500 to 3000 mm and
a length of 500 to 5000 mm 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.
[0005] The invention mitigates the above-described drawback accompanying 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.
[0006] 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.
[0007] 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.
[0008] In a case where large currents flow in the device, connecting bus bars can be employed
instead of the switches 2.
[0009] 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.
[0010] In addition, the space needed for installation of the device is reduced.
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 capacitor (3) for inductive
heating of a workpiece, characterized 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.
2. The inductive heating device of claim 1 further characterized by connecting means
connected directly between adjacent ones of said output terminals (10 to 15).
3. The inductive heating device of claim 1 or 2 characterized 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).
