Electric heating – Inductive heating – Specific inductor configuration
Patent
1997-02-27
1998-04-28
Leung, Philip H.
Electric heating
Inductive heating
Specific inductor configuration
219677, 336 57, 336 62, 373154, H05B 642
Patent
active
057447845
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a low-loss induction coil for heating and/or melting metallic materials, the coil having windings formed by lengths of hollow tubing and carrying a coolant.
Induction coils of the abovementioned type and consisting of hollow conductors made of copper are known. The induction current is carried through these hollow conductors, while a fluid coolant, e.g. water, flows through the interior of the hollow conductors. Increased energy losses occur in the end zones of induction coils designed in this manner, since the transverse magnetic fields occurring to an increased extent there induce eddy currents in the hollow conductor made of copper.
It is known from EP 0,240,099 A2 to carry the induction current solely through a plurality of individual conductors which run parallel to one another, are insulated from one another, and are combined to form braids. In this case, the cross section of the individual conductors is dimensioned such that no significant eddy currents can occur in the end regions of such induction coils.
Compared to the induction coils made of hollow conductors, these induction coils have the disadvantage that their manufacture and also the measures required to guarantee sufficient cooling are more complex and more expensive. Despite the electrically insulating means surrounding them, e.g. lacquer or insulation tubing, the individual conductors or braids must have a good thermal contact with the coolant.
A further disadvantage of the current transport through braids, i.e. through a large number of individual conductors, results from the spatial distribution of the current density thus caused. Since each individual conductor carries current, the current density is distributed approximately uniformly over the cross section of the braid, and the mean distance between the induction current and the metallic material being heated is thus determined approximately by the braid center. In contrast, in the case of hollow conductors, the current density is concentrated on the part of the cross section of the hollow conductor facing the inside surface of the induction coil. With the same inside radius of the coil, the mean distance between the induction current and the metallic material being heated is thus higher in one braid coil, as a result of which here the losses caused by this distance are greater at the same time.
The object of the present invention is to provide an induction coil of the type mentioned at the beginning, which reduces the losses over the entire coil length in an efficient and cost-effective manner.
In an induction coil of the type mentioned at the beginning, this object is achieved according to the invention in that a current-carrying element in the form of at least one braid consisting of insulated individual conductors is provided in the windings in at least one of the end zones of the induction coil, and that the remaining windings are designed as hollow conductors and are each electrically connected to the current-carrying element.
In such a coil, the advantages of the coil constructions combined with one another here come into effect.
In the end zones, the current is carried through braids, as a result of which losses due to transverse magnetic fields are avoided to a great extent. Moreover, it has been shown empirically that, when braid conductors are used, the active zone of the coil is longer than when hollow conductors are used. The reason for this is presumably a lower permeability of the braid windings to transverse magnetic fields, since here the current density is distributed uniformly over the cross section of the braid. In contrast, in the case of hollow conductors, the current density can concentrate on partial zones of the cross section, as a result of which other zones remain virtually currentless and thus provide gaps for transverse magnetic fields to pass through.
In the central zone of the coil where the induced magnetic field has no significance in the radial direction, the simple and cost-effective construction variant with t
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patent: 2457843 (1949-01-01), Strickland, Jr.
patent: 3260792 (1966-07-01), Kreisel
patent: 3809846 (1974-05-01), Baumgartner et al.
patent: 5391863 (1995-02-01), Schmidt
patent: 5430274 (1995-07-01), Couffet et al.
patent: 5461215 (1995-10-01), Haldeman
Leung Philip H.
Otto Junker GmbH
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