Industrial electric heating furnaces – Induction furnace device – For furnace regulating
Patent
1996-10-07
1999-03-30
Hoang, Tu Ba
Industrial electric heating furnaces
Induction furnace device
For furnace regulating
373146, 373148, 373151, 363 71, H05B 606
Patent
active
058898123
DESCRIPTION:
BRIEF SUMMARY
This application is a national filing under 35 U.S.C. .sctn. 371 and priority is claimed herein pursuant to 37 C.F.R. .sctn. 1.78 and 35 U.S.C. .sctn. 119 from copending International Application No. PCT/DE95/00175 filed on Feb. 10, 1995 and which designated the United States of America at the time of filing.
DESCRIPTION
The present invention relates to a process for the operation of coreless induction smelting or holding furnaces, in which in melting operation, at an induction frequency of .gtoreq.100 Hz, there results a slight stirring motion in the melt, and in the melting or holding operation, at an induction frequency lowered by a maximum of 50%, but always .gtoreq.50 Hz, there results a greater stirring motion in the melt, as well as to an electrical switching unit for coreless induction melting and holding furnaces with an induction frequency in the range from mains frequency to medium frequency which exhibit at least one single- or multi-part induction coil positioned around a furnace crucible, as well as an electrical voltage supply device with a frequency transformer or converter.
Known from DE-PS 27 48 136 is a coreless induction crucible furnace that can be operated both with the mains frequency and with a higher frequency. This kind of furnace is chiefly operated with a medium frequency in order to rapidly melt the metal introduced in solid condition to the melting crucible. If, on the other hand, the already molten metal is vigorously stirred and slag or alloy treatments are performed with the melt, a lower frequency, e.g., the mains frequency, is primarily used.
A disadvantage of this known induction melting and holding furnace, and the process used to operate it, rests in the fact that two different power mains must be available to perform the assigned function, specifically, operation in two frequency ranges. The expense in terms of apparatus is therefore high, since practically two separate switching facilities must be employed.
Also requiring two supply facilities with different frequencies is the solution according to British patent no. 508 255 (FIG. 9). Here, an induction coil consisting of two partial coils is simultaneously attached to one feed device of lower frequency and one of higher frequency. In addition to the high expense associated with the subject matter of the first referenced patent, the British patent has a further disadvantage in that each mains must be protected with a special filter so that the frequency of either mains does react negatively on the other.
The goal of the present invention, therefore, is to indicate a process for the operation of a furnace of the generic type in which only a slight degree of increased technical expense makes operation with several frequencies possible, where the additional expenses are cost-effective and can be realized in a small space.
This goal is achieved by the process according to the invention in that at least one capacitor, switched in parallel with the induction coil(s), is provided which, together with the induction coil(s), forms an electrical resonant circuit, and in that during the transition from melting operation, involving only slight stirring movement in the melt, to the melting or holding operation, involving a greater degree of stirring movement, or during the reverse transition, the capacitor capacitance and/or the inductance present in the resonant circuit are increased or decreased.
Furthermore, the process according to the invention may provide that the capacitance and/or the inductance of the resonant circuit can be increased or decreased by at least 1/3 its given total.
It has proven to be expedient and sufficient to increase the capacitance or the inductance by at least the indicated amount.
An even more intensive melting bath mixture can be obtained by increasing or reducing the capacitance and/or inductance of the resonant circuit by twice its total value.
Secondary claims 4 to 6 contain particularly advantageous methods for implementing the process according to the invention. It has proven to be particul
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Hoang Tu Ba
Otto Junker GmbH
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