Industrial electric heating furnaces – Induction furnace device – Coreless
Patent
1999-11-12
2000-12-19
Hoang, Tu Ba
Industrial electric heating furnaces
Induction furnace device
Coreless
373156, 219653, H05B 622
Patent
active
061635626
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an induction heating device to raise the temperature of metals with a view to melting or hot working them, said device comprising at least one cavity defined by a ladle designed to receive the metals to be brought up to a temperature greater than or equal to their melting point or by an oven designed to receive the billets of metal to be brought up to a temperature which is lower than their melting point, this temperature being determined to forge the metals, along with induction heating means for said ladle or said oven.
BACKGROUND OF THE INVENTION
Induction heating devices are well known in the field of metal melting, forging billets of metal with a view to hot machining them, metal or alloy working or smelting. Nevertheless, in known devices, the induction coil(s) are wound around the cavity receiving the metal and are usually cooled by a water-cooling circuit. There is a possible risk of leaks in the cooling circuit, which is totally prohibited when working with molten metals. Furthermore, the efficiency achieved with this configuration generally does not exceed 40 to 60%. This efficiency is proportional to the ratio of the inductor's surface area and the surface area of the stack. What is more, the magnetic field created by the induction coils is an open field. Consequently, the losses are significant and amount to around 1/3 of the total power applied.
In this field of application, the main technical constraints to be taken into account are as follows: standards and European directives (CENELEC and DG5), metal be avoided).
Other induction heating devices have attempted to provide a solution to the first problem posed. Some devices are described in the publications DE-C-266 566, US-A-1 834 725 and BE-A-351 671 and comprise at least two yokes arranged around the cavity receiving the metal to be heated, which are L-shaped or C-shaped, so that the ends converge toward the inside of said cavity. Each yoke bears an electric coil creating a magnetic field which closes through said cavity. An improvement to this type of construction is described in the publication DE-C-277 870 which provides for three yokes, the coils of which are fed individually and phase-shifted in order to create a rotary field. In all these embodiments, all the magnetic fields are radial, which means that the lines of electric flux cross the cavity's axis and cross right through it axially. These magnetic fields create an induction current limited to the periphery of said cavity and generate an increase in the temperature of the metal in this zone with the remainder of the metal being heated by conduction. The efficiency of these various devices and even the one providing for a rotary field, remains very low, as the effective part of the field using for heating purposes is small.
SUMMARY OF THE INVENTION
The present invention proposes to overcome the drawbacks of the prior art and meet the requirements of current standards by means of an induction heating device which makes it possible to achieve efficiency in the region of 80 to 95%, with smaller induction boxes, a higher power factor (cos .phi.0.8 instead of 0.05 or 0.1) and requiring less electric energy consumption. Furthermore, the present invention makes it possible to speed up the temperature rise and therefore the melting or hot machining of the metal, thus also favoring energy savings. The energy savings achieved by the present invention are such that a return on investment within about two years can be envisaged, which is very appreciable in commercial terms.
The aim is achieved by a device such as the one described in the preamble and characterized in that the induction coils are fitted in the same direction so that their north pole is located on one side of the cavity and their south pole on the opposite side, in that they are arranged so as to generate null magnetic field zones arranged alternately between non null field zones spread out on the periphery of the cavity, the non null field zones each comprising a
REFERENCES:
patent: 1834725 (1931-12-01), Northrup
patent: 1879360 (1932-09-01), Linnhoff
patent: 5090022 (1992-02-01), Mortimer
Hoang Tu Ba
Internova International Innovation Company B.V.
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