EP0013218B1 - Induction heating apparatus for flat metallurgical products - Google Patents

Description

The subject of the present invention is an installation for the induction heating of metallurgical products according to the preamble of claim 1.

Document DE-A-1 176 773 discloses an oven of this type which includes a coil-shaped inductor and transport means which, in order not to pass through the coil, comprise at least one frame with two rails extending beyond ends of the coil driven in a cyclic movement and cooperating with fixed rails or belonging to a second frame.

This provision has many limitations. It only allows the treatment of small products, because the frame is only supported at its ends. It is only applicable to products having a length and a height of the same order, the coil having to be roughly circular for the field to be homogeneous. It is not adaptable to the height of the products, the fractions of the coil being fixed relative to each other.

The oven according to document FR 2 328 170 is similar to the previous one, the first frame having a longitudinal reciprocating movement and cooperating with support rods passing through the coil and driven in a vertical reciprocating movement. This oven has the same drawbacks as the previous one. In addition, it requires two mobile mechanisms and the support rods must remain small in order not to create field heterogeneities.

The present invention aims to provide an installation of this type that better meets those previously known to the requirements of practice, in particular in that the above drawbacks are eliminated and in that the installation makes it possible to treat flat metallurgical products of very large dimensions, such as slabs, continuously.

This result is achieved thanks to the provisions defined in the characterizing part of claim 1. The advantages obtained are in particular the following: very wide and very heavy products can be treated, because the inductors are flat and horizontal, parallel to the large faces some products. The products rest by gravity on the supports at a distance from the lower inductor which is constant and can be chosen at the optimum value. The two inductors being independent, their distance can be adjusted to the thickness of the part and it can be much less than the width. The means of transport can pass through the lower inductor without difficulty, the windings having long parts parallel to the length of the oven, that is to say in the direction of movement.

Flat inductors have already been proposed, but for treating parts on edge (FR-A 2 339 316) or by placing the product on the lower inductor after having raised the upper inductor (GB patent 1,513,241). The skilled person has never considered moving large metallurgical products, such as slabs, on a dish, probably because he thought it impossible to do so because of the importance of the masses to be lifted and moved. from means passing longitudinally through the oven and the need for close points of support for the products, except in areas where they are very hot and therefore have a low resistance to bending.

The inventor has devised a provision which overcomes what the person skilled in the art seemed to regard as an impossibility, since the technique had remained in a prior art represented by very old documents, such as DE-A 1 176 773 dating back to 1954. Furthermore, this approach implied that the inventor appreciated the advantages of moving large flat metallurgical products in a continuous induction furnace of dimensions adapted to those of the products by keeping the latter flat.

• - la figure 1 est un schéma de principe, en coupe suivant un plan longitudinal, de l'ensemble de l'installation;
• - la figure 2 est une coupe schématique suivant la ligne II-II de la figure 1 ;
• la figure 3, similaire à la figure 2, montre une variante de réalisation.

The invention will be better understood on reading the following description of an installation which constitutes a particular embodiment given by way of non-limiting example. The description refers to the accompanying drawings, in which:

• - Figure 1 is a block diagram, in section along a longitudinal plane, of the entire installation;
• - Figure 2 is a schematic section along the line II-II of Figure 1;
• Figure 3, similar to Figure 2, shows an alternative embodiment.

For clarity, the scale has not been respected in Figures 1 to 3.

The installation shown schematically in Figures 1 and 2 is intended for the treatment of slabs. The oven proper, of which only a fraction is shown in FIG. 1, is associated with a feed table 10 with side members and a table with unloading rollers 12 on which the slabs are brought by pinch rollers 11. Several ovens can obviously be arranged side by side, the roller tables 12 of all the ovens supplying the same distribution carriage to the rolling mills circulating on paths transverse to the furnace. In the installation described, the products circulate in the oven in the direction of their great length.

The oven 9 advantageously comprises an envelope tunnel 13 intended to limit losses thermal. The lower part of the envelope 13 can constitute a deck 14.

The casing 13 contains two inductors 16 and 17 intended to provide sliding electric fields in the longitudinal direction of the furnace. The lower inductor 17 is fixed and carried by the platform 14. It is located below the path traveled by the slabs 15. It is protected from the heat radiated by these slabs by an insulating lining 18, for example made of refractory bricks. The inductor 16, which can be suspended from the envelope or carried by tie rods passing through it, has a similar constitution. The suspension tie rods are advantageously carried by a mechanism making it possible to modify the height of the inductor 16, so as to give the air gap between the inductor 16 and the product 15, an optimal value.

The oven is provided with means for supporting the advancement of the slabs 15. In the embodiment illustrated in FIGS. 1 and 2, these means are constituted by a pilgrim-type conveyor of conventional constitution. This conveyor comprises fixed support feet 19 carried by the platform 14 and distributed longitudinally at sufficiently close intervals to avoid any bending of the slabs. It also has movable feet 20 fixed to a spar 21 placed under the tunnel envelope and to which a mechanism, not shown, allows the movement indicated by the arrow f in FIG. 1 to be imparted and the reverse movement. It can be seen that the movable feet 20 make it possible to advance the slab step by step with a determined advance step.

The feet 20 and 19 being in contact with the products at high temperature must be made of suitable material. In practice, materials at least partially non-magnetic will advantageously be used in the portion of the oven where the temperature does not reach the Curie point. It will often be convenient to constitute these feet, throughout the length of the furnace, in refractory material at least in the part in contact with the products 1 5.

When the products to be treated are standard metallurgical products, the width of which hardly exceeds two meters, two longitudinal rows are sufficient. 20 feet apart for example by one meter. Etane given that the resistance to bending and to creep of metallurgical products decreases when the temperature increases, it will often be advantageous to reduce the interval between two successive feet in the hottest zones: one can for example use a spacing of several mothers in the entry zone of the furnace where the metal is at moderate temperature, and go down to a value of the order of a meter in the hottest zones.

Despite the thermal insulation of the inductors 16 and 17, it will often be necessary to cool them. For this, it will be possible for example to provide the upper inductor 16 with a network of circulation tubes of a refrigerant which penetrates through the casing and leaves it by conduits 22. A pulsed suction may be provided to evacuate the hot air above the inductor 17 in a pulsed manner. This suction will at the same time eliminate any scale that may have formed. The envelope tunnel 13 will usually be made of sheet metal internally lined with refractory. It could constitute an enclosure the sealing of which is sufficient to maintain in the oven the conditioning atmosphere necessary for the treatment of certain special steels.

Support devices other than the pilgrim pitch conveyor shown in FIGS. 1 and 2 can be used. In the alternative embodiment shown in FIG. 3 (where the members corresponding to those of FIGS. 1 and 2 have the same reference number assigned of index a), the support means consist of two rows of discs 20a of which only the upper parts pass through the lower inductor 17a. The discs 20a are wedged in pairs on drive shafts 21a placed below the tunnel and, consequently, are shielded from the action of the high temperatures prevailing in the oven.

The drive mechanisms of the shafts are advantageously provided to make it possible to give the discs a back-and-forth movement in the event of the rolling stop leading to the products remaining in place, in order to avoid any deformation. The control mechanisms of the rollers 20a situated in the terminal part of the oven are, for their part, advantageously provided for discharging the products, after heating, at high speed, which makes it possible to dispense with the pinch rollers 11 or organs of other types necessary in most cases for extraction.

The advantages of the installation appear immediately: the length of the oven is used in full, so that it can be reduced; the products remain permanently flat; the thermal efficiency can be very high given the adjustment possibilities which do not exist in the case of induction furnace with annular inductors; the heating curves can be perfectly adapted to the different shades of metal to be treated.

By way of example, it can be indicated that three installations of the kind defined above are sufficient to supply slabs of 250 × 1500 mm, 14 m in unit length, to a train of continuous strip rolling mills producing 6,000,000 tonnes per year. Each of the three installations requires an installed capacity of around 100 MW. For slabs with a current thickness of approximately 250 mm, the inductors can be supplied at the network frequency.

Claims (9)

1. Apparatus for induction heating of metallurgical products, comprising a tunnel provided with means for induction heating of the products located along the tunnel and means for progressively advancing the products along the tunnel and for supporting said products independently of the heating means, characterized in that the heating means comprise a flat inductor (16) located above the path of the products and a flat inductor (17) located under the path and traversed by the movable elements (20 or 20a) of the advance means for longitudinally moving the products and provided for wide metallurgical products (15), such as slabs, to rest flat of the advance means.

2. Apparatus according to claim 1, characterized in that the flat inductors are polyphase inductors.

3. Apparatus according to claim 1, characterized in that only the level of that inductor (16) which is located above the path of the product is adjustable.

4. Apparatus according to claim 1, 2 or 3, characterized in that the support or advance means consist of a pelgrim step conveyor having feet (20) supporting the products and passing through the inductor (15) located under the path of the products.

5. Apparatus according to claim 4, characterized in that the feet are actuated by a mechanism located out of the tunnel.

6. Apparatus according to claim 4 or 5, characterized in that the feet at least partially consist of non magnetic refractory material.

7. Apparatus according to claim 1, 2 or 3, characterized in that the support and advance means consist of disks projecting through that inductor which is located under the path of the products and carried by drive shafts located under the tunnel.

8. Apparatus according to any one of claims 1-7, characterized in that the support means (20, 20a) are disposed in two parallel rows, symetrical with respect to the median plane of the tunnel and have a spacing which is smaller in the zones where the products are at the highest temperature.

9. Apparatus according to any one of claims 1-8, characterized in that it is fractionated into several successive sections, provided with separate temperature regulating means which control the power dissipated in inductor sections in the successive sections.

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