Electric heating – Metal heating – Of cylinders
Patent
1991-03-14
1993-01-12
Leung, Philip H.
Electric heating
Metal heating
Of cylinders
219 1071, 219 1079, H05B 644
Patent
active
051792583
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an induction furnace for heating and temperature homogenization in hot-rolling of thin steel strips produced by continuous casting and already subjected to a preliminary rolling step.
It is generally known to use M.F. induction furnaces in steel industry. These furnaces are used, although not widely, as an alternative to the gas furnaces for heating of the slabs having a thickness of more than about 100 mm, whereas the use with strips having a thickness of less than about 30 mm is limited to a thermal treatment of the edges in order to oppose the natural cooling which, being greater than in the central zones, causes such a temperature decrease as to produce possible cracks at the strip edges. However this induction treatment of the edges is accomplished by means of C-shaped inductors which enclose, like sliding shoes, only the fringe areas of the strip during the forward movement and certainly cannot be considered true and actual induction furnaces.
On the contrary the induction furnaces for slabs comprise a row of inducing coils having a substantially toroidal shape, within which the slab is caused to move forward in sequence, between one coil and the other there being provided driven and/or idle rollers for feeding said slab. These coils have a size that in the direction of movement are in the order of about 900 mm.
On the other hand plants are provided at present for the continuous production of steel strip by the continuous casting method in order to have as final product the so-called "coil" or steel plates cut at prefixed lengths, wherein it is required that strips in an intermediate step of hot-rolling are heated with contemporaneous temperature homogenization in induction furnaces for reaching the required temperature in the final steps of rolling. In this respect reference should be made to the Italian Patent Application No. 20752 A/88, the PCT Application DE-88-00628 and German Patent Application No. P-3840812.0.
In this respect the adoption of known induction furnaces, already used for the slabs, cannot however give the expected results due to the fact that inconveniences would occur, being caused e.g. to the strip stumbling and possible hitting against the coils owing to its lower rigidity with respect to the slabs having a greater thickness. Furthermore the strip requires for temperature homogenization that in certain zones, possibly not always the same but such as to be localized at each time, the heating has to be stronger with a greater concentration of flux lines. As a matter of fact this is not required by the slabs, since the temperature is more homogeneous due to the greater thickness.
Therefore it is an object of the present invention to provide an induction furnace for steel strips from continuous casting having a thickness of less than 30 mm, as they have been already partially hot-rolled so as to heat homogeneously the strip up to the required temperature for the subsequent steps of rolling completion without facing the above-mentioned drawbacks.
The induction furnace according to the invention comprises an array of coils, each of which is embedded in an inductor unit, separately fed by one or more frequency converter and successively crossed by the strip being supported and driven through pairs of rollers between each coil and the subsequent one, the size of each coil in the forward direction of the strip being less than 500 mm, there being also provided flux concentrating devices which are distributed in pairs on each inductor, at least at one upper or lower side with respect to the plane defined by the strip itself.
According to a preferred embodiment of the invention the flux concentrating devices are mounted movable in a transverse direction to the strip and preferably also perpendicularly to the strip itself for a better distribution of power in the areas where a stronger heating is required. These and additional objects, advantages and characteristics of the induction furnace according to the invention will be clear to the persons skilled in t
REFERENCES:
patent: 3444346 (1969-05-01), Russell et al.
patent: 4185183 (1980-01-01), Kamimoto
patent: 4357512 (1982-11-01), Nishimoto et al.
patent: 4795872 (1989-01-01), Hagisawa et al.
patent: 4891484 (1990-01-01), Waggott et al.
Arvedi Giovanni
Gosio Giovanni
Arvedi Giovanni
Leung Philip H.
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