WO1993007305A1 - Enclosures and installations for line galvanising cut lengths of metallurgical products - Google Patents

Abstract

An enclosure (3, 10) for line galvanising cut lengths of metallurgical products (1) such as tubes, angles, sections, sheets or similar from a vertical or horizontal continuous casting line (2) comprises, at least at its end at which the treated metallurgical products (1) are discharged, a solenoid valve consisting of a mobile multiphase inductor winding (7, 16) capable of surrounding a fixed hollow armature (9, 14) arranged so that the metallurgical products (1) leaving the said continuous casting line (2) can pass through it, the said inductor winding (7, 16) being capable of longitudinal movement with respect to the said hollow armature (9, 14) depending on whether or not a product to be treated is present at its centre. The invention also describes an alternative embodiment of this enclosure, and an installation including said enclosures.

Description

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ENCLOSURES AND FACILITIES FOR THE ONLINE GALVANIZATION OF DISCONTINUOUS METALLURGICAL OBJECTS

The present invention relates to a set of enclosures and installations for the in-line galvanization of discontinuous metallurgical objects, such as profiles, tubes and the like. The enclosures and the proposed installations can in particular be arranged at the outlet of a continuous casting line, vertical or horizontal, of steel semi-finished products.

It is known that the treatment of metallurgical products obtained, in the steel industry, by horizontal or vertical continuous casting techniques, must most often be reprocessed on the surface by galvanizing with zinc, aluminum or from other protective alloys. However, no steel plant is known where the galvanizing line is installed at the outlet of the continuous casting line. As a result, the steel products leaving a continuous casting line are first cooled, before being later reheated to be hot-dip galvanized in autonomous installations, for example by soaking in an alloy bath molten liquid metal contained in an enclosure, or, according to the technique notably described in patent FR-2 323 772, by in-line galvanization. In the latter case, well suited to the treatment of angles and profiles, the metallurgical products pass through a bath of a molten metal alloy, contained in an enclosure provided with two aligned inlet and outlet orifices, the level said bath being maintained at a vertical level higher than that of said orifices, so that the products to be coated are completely submerged when they pass through said enclosure. According to the present invention, a new type of sealed galvanizing enclosure is proposed, provided with inlet and outlet orifices aligned on the axis of travel of the products to be covered, this type of enclosure comprising, at least at its end placed on the side of the outlet of the treated metallurgical objects, an electromagnetic valve constituted by a polyphase inductive winding capable of surrounding a fixed hollow armature, arranged to be crossed by metallurgical objects exiting from the continuous casting line, said inductive winding being able to be displaced longitudinally with respect to said induced hollow so that:

on the one hand, when no metallurgical object enters the galvanizing enclosure, said inductor winding surrounds said armature so as to prevent any leakage of the metal or of the metallic coating alloy out of said enclosure,

- on the other hand, when a metallurgical object leaves said continuous casting line and enters the galvanizing enclosure, said inductive winding surrounds only said object which, while then undergoing, by the play of magnetomotive forces acting at its surface, a wiping effect of the coating deposited on its surface inside said enclosure, prevents any leakage of the metal or the metallic alloy of coating from said enclosure.

In a second variant, entirely equivalent to this first variant, the hollow armature is movable and the inductor winding of the electromagnetic valve, placed at least at the outlet of the galvanizing enclosure, is fixed, their relative displacements being identical to those described above, with the same results on the sealing of said enclosure.

These enclosures can in particular be arranged at the outlet of a continuous casting line, vertical or horizontal, of steel semi-finished products.

In the application of such a device in the case of vertical .continuous casting, it is understood that the galvanizing enclosure can be arranged vertically; under the effect of gravity, the metal or the molten metal alloy of the coating bath may, in fact, only leak downwards, and it is therefore sufficient to arrange a single valve electromagnetic sealing at the exit of this enclosure.

On the other hand, in the application of the same device in the case of horizontal continuous casting, the galvanizing enclosure will normally comprise an electromagnetic valve at each of its ends, at least the outlet valve comprising a hollow armature, fixed or mobile according to the variant of execution chosen; indeed, an enclosure arranged horizontally can leak through its two ends, even if it is true, moreover, that the movement of metallurgical objects to be treated through this enclosure promotes, due to the driving forces acting on the galvanizing bath, its watertightness at the entrance. Other characteristics and advantages of the present invention will emerge more clearly from the description which follows of two installations for in-line galvanization arranged at the outlet of a continuous casting line, respectively vertical and horizontal, these installations being given by way of 'nonlimiting examples with reference to the accompanying drawings in which:

- Figures 1 to 3 are views in longitudinal section of an in-line galvanizing installation arranged at the outlet of a vertical continuous casting line of steel tubes or profiles, showing the successive stages in the operation of the installation according to that a tube or the like enters the galvanizing enclosure (FIG. 1), passes through this enclosure (FIG. 2), then leaves it (FIG. 3), - FIGS. 4 to 6 are views in longitudinal section of an installation galvanizing line arranged at the outlet of a horizontal continuous casting line, showing the successive stages of the operation of the installation depending on whether a tube or the like enters the galvanizing enclosure (FIG. 4), passes through this enclosure (FIG. 5), then comes out (figure 6). The variant shown in FIGS. 1 to 3 relates to the in-line galvanization of metallurgical objects 1 leaving a vertical continuous casting line 2, which is shown in dashed lines in the figures. In the embodiment shown, a vertical galvanizing enclosure 3 is arranged in the extension of the outlet of said objects 1, so as to galvanize them, for example with zinc, immediately after their forging; for this purpose, the enclosure 3 comprises: - a vertical tubular body 4 having an inlet orifice 5 and an outlet orifice 6 aligned to allow the passage, through the enclosure 3, of the objects 1 to be covered, for example a continuous wire, a rod, a bar, a profile, an angle iron or even a tube, of iron or steel;

a polyphase inductor winding 7 surrounding the tubular body 4 at its outlet orifice 6, this winding 7 being electrically connected to a polyphase current source 8 of adjustable intensity, so as to create a sliding field oriented from the bottom towards the top of the tubular body 4; when a metal or a molten metal alloy is introduced into the enclosure 3, the latter is thus pushed back towards the interior of the tubular body 4, under the effect of magnetohydrodynamic forces opposing its flow out of said enclosure 3.

According to the present invention, the tubular body 4 of the enclosure 3 can be moved concentrically with respect to a vertical hollow armature 9, of a material with high magnetic permeability; this armature 9 is intended to concentrate the lines of the sliding magnetic field which is generated by the inductor winding 7 when the latter is crossed by its polyphase current. When this armature 9 is thus introduced coaxially in the middle of the outlet orifice 6 of the tubular body 4 (see FIG. 1), the efficiency of the magnetic field is considerably improved and, in this situation, the electromagnetic valve thus formed by the combination of armature 9 and inductor winding 7 is susceptible to completely stop the gravity flow of the metal or of the molten metal alloy being in the enclosure 3. Conversely, this efficiency decreases when the tubular body 4, and therefore the enclosure 3, is moved, so that the outlet 6 no longer surrounds the armature 9; in this situation, if nothing is done, the molten metal or alloy can leak out of enclosure 3.

These two situations correspond to the two phases of the galvanizing process, namely, respectively, to the absence or the presence of a metallurgical object 1 to be covered through the tubular body 4 of the enclosure 3. The galvanizing cycle of an object 1 is then the following: - when an object 1 leaves the continuous casting line 2, a detection system not shown in the figures causes the triggering of a device for moving the tubular body 4 and the winding inductor 7 downwards, relative to the hollow armature 9 which we have chosen to leave fixed, this movement taking place until said tubular body 4 is completely disengaged from said armature 9 (see FIG. 2);

- The object 1 therefore firstly crosses the hollow armature 9, the role of which is clearly understood, then arrives with a still high temperature at the level of the inlet orifice 5 of the tubular body 4 containing the metal or the coating metal alloy; by entering the enclosure 3, and in accordance with the teachings of patent FR-2 323 772, the object 1 is immediately covered with a layer of protective metal;

the lower end of the object 1 thus travels coaxially in the middle of the tubular body 4, over a length imposed by the physical galvanizing conditions (thickness of the coating, speed of travel), until reaching the outlet orifice 6 where the inductor winding 7 acts against the forces of gravity, to retain in the enclosure 3 the metal or the molten metal alloy. This confining effect of galvanizing bath in the enclosure 3, which had been greatly reduced due to the withdrawal of the armature 9, is then again considerably increased due to the presence of the metallurgical object of steel or iron located in the middle of the inductor winding 7. In addition, the magnetohydrodynamic processes involved contribute to "wiping" of the object 1, that is to say to the regulation of the thickness of the coating deposited; in this regard, the means for controlling the intensity of the current supplied by the polyphase current source 8 provides the means for carrying out this "wiping" in a perfectly controlled manner;

- finally, slightly before the upper end of the object 1 emerges from the outlet orifice 6 of the tubular body 4, and depending on the vertical speed of the object 1 and the length of the enclosure 3, we acts on the means of vertical displacement of said enclosure 3 to raise the tubular body 4 around the fixed armature 9, so that when said object 1 comes completely out of enclosure 3, said armature 9 is returned to the middle of the inductor winding 7 and again provides total sealing at the bottom of said enclosure 3 (see FIG. 3).

This cycle is repeated as soon as another object 1 is detected at the output of the continuous casting line 2.

It will be observed that, in the phases of the method described above, it is of course not necessary to completely disengage the hollow armature 9 from the interior of the tubular body 4; in particular, it is entirely possible to provide that only the inductor winding 7 moves in a reciprocating movement around the tubular body 4 which, in this case, is kept fixed relative to the hollow armature 9. In the latter case, the armature 9 is taken of a length not going completely up to the exit of the enclosure 3, which allows the metal or the molten metal alloy contained in the tubular body 4 to follow the progress or the vertical regression of the inductor winding 7 along said tubular body 4; in these conditions :

- when the inductor winding 7 is in the low position, the sliding magnetic field acts on the metallurgical product 1 only to wipe it and prevent any leakage outside the enclosure 3 (galvanizing situation comparable to that of FIG. 2),

- When the inductor winding 7 is in the high position, the sliding magnetic field acts on the hollow armature 9 (situation comparable to Figures 1 and 3).

Of course, the exterior and interior geometries of the hollow armature 9 are adapted to the cross section of the metallurgical objects 1 to be treated as well as to that of the tubular body 4. In addition, the respective sizes of the hollow armature 9 and of the objects 1 having to transit there are calculated to, on the one hand, avoid any contact or friction between them, and on the other hand, to ensure that, from the point of view of the inductive winding 7, the energy to be supplied for maintain the bath of molten metal or metal alloy in the enclosure 3 is substantially identical, whether when said armature 9 is in the middle of the outlet orifice 6 of the tubular body 4, or whether when object 1 passes through said orifice 6. According to another characteristic of the invention, the tubular body 4 is made from a material preferably not wettable by metal or the molten metal alloy necessary for galvanization; for example, the tubular body 4 may be covered internally with a ceramic material. Likewise, it is obvious to a person skilled in the ordinary art that the tubular body 4 must be permeable to the magnetic field, at least at its outlet orifice 6, so as to allow the sliding field generated in its center by the inductor winding 7 can propagate, depending on the operating phase of the installation, to the hollow armature 9 or to the metallurgical object 1 passing through said outlet orifice 6. It will also be noted that a conventional heating device, for example by electromagnetic induction or by Joule effect, is arranged around the tubular body 4 to keep the metal or the molten metal alloy at a temperature above its melting temperature.

Furthermore, according to a preferred embodiment of the present invention, the part of the installation connecting the outlet of the continuous casting line 2 and the inlet orifice 5 of the tubular body 4 of the galvanizing enclosure 3 is maintained under a controlled atmosphere of a neutral or slightly reducing gas. The enclosure 3 can itself preferably be placed under a controlled atmosphere, as well as its output. This gaseous protection makes it possible to avoid any surface oxidation of the objects 1 before they are covered with their protective coating.

Finally, it is desirable to vigorously cool the objects 1 covered at their exit from the galvanizing enclosure 3; this makes it possible to very quickly stop the growth of the intermetallic layers forming at the interface between the protective coating and the iron or steel constituting metallurgical objects 1. This cooling is also necessary for the completion of all the forging processes by continuous casting. It will also be noted that, according to the process implemented according to the invention, any chemical or mechanical pickling by shot blasting, as well as any possible fluxing, become useless before the galvanizing operations; this provides considerable advantages on the quality of the coating obtained, on the one hand, and, on the other hand, on the elimination of the risks of embrittlement of the objects 1 by chemical attack due to acids (embrittlement by hydrogen of the water of dissolution of pickling acids normally used before any galvanizing).

In a second variant of the invention which will now be described with reference to Figures 4 to 6, we chose to equip a continuous casting line 2 horizontal with an in-line galvanizing installation comprising an enclosure 10 which is arranged horizontally. In this case, the absence of gravity effect - helping to eliminate the sealing problems at the level of the inlet orifice 5 of the tubular body 4 of a vertical galvanizing enclosure, such as the enclosure 3 (Cf. figure 1 to 3) - must be compensated by the arrangement, on the side of the inlet orifice 11 of the tubular body 12 of the horizontal enclosure 10:

- Either an electromagnetic valve formed by an inductor winding 13 surrounding a hollow armature 14, of a material with high magnetic permeability, for the passage of metallurgical objects 1 to be covered, this inductor winding 13 being electrically connected to a current source polyphase of adjustable intensity, so as to create a sliding field oriented towards the inside of said tubular body 12.

- Or a device closing the enclosure 10 on the side of its inlet orifice 11; this second case, if it actually provides the economy of the inductor winding 13 and of its electrical supply, leads to subjecting the relative displacements of the tubular body 12 and of the hollow armature 14. Furthermore, it is clear that, to keep the bubble of molten metal or metal alloy inside the galvanizing enclosure 10, a second electromagnetic valve should be arranged around the outlet orifice 15 of said enclosure 10, this valve comprising a inductor winding 16 capable of surrounding the hollow armature 14, this inductor winding 16 being electrically connected to a polyphase current source 17 of adjustable intensity, so as to create a sliding field oriented towards the interior of said tubular body 12. On will also observe that there is a sealing problem between the hollow armature 14 and the metallurgical product 1 on the side of the outlet orifice 15 of the enclosure 10. In fact, except to move the enr only inductor 16 in the same direction as the metallurgical product 1 as the latter passes through the enclosure 10 (see FIG. 5) - which allows the sliding magnetic field generated by said winding 16 to come loop on said product 1, and therefore to seal the enclosure 10 downstream -, it would be advisable:

- Or to lower the intensity of said sliding magnetic field to prevent the metal or the molten metal alloy from being forced back into the annular space left free between the inner wall of the hollow armature 14 and the metallurgical product 1, source d '' a metal or alloy leak upstream of enclosure 10,

- Or to move the hollow armature 14 to obtain, in the middle of the inductor winding 16, a less intense force field which then repels less the metal or the molten alloy in said annular space.

In all cases, the risk that the leakage of metal or alloy upstream of the enclosure 10 is too great is not negligible, and, according to a characteristic complementary to the present invention, it is thus provided to arrange upstream of the enclosure 10, namely on the side of the inlet orifice 11 of the tubular body 12, a means of producing a back pressure capable of acting against the discharge of metal or metallic alloy melted in the annular space of the hollow armature 14 and of the metallurgical product 1 being covered and wiped. Preferably, this means of production, not shown in the figures, delivers a flow of a neutral gas simulating a gravitational effect of the molten metal comparable to that acting to prevent the backflow of the metal upward into the vertical galvanizing enclosure. 3 of the first variant of the invention (see Figures 1 to 3).

As the metallurgical product 1 leaves the galvanizing enclosure 10, the inductor winding 16 is brought back around the hollow armature 14 so that, when said product 1 emerges completely from the outlet orifice 15, the sealing of the enclosure 10 is perfectly ensured downstream.

Of course, all the additional characteristics of the installation specifically adapted to the case of vertical continuous casting can be reproduced in the case of horizontal continuous casting, namely the maintenance of metallurgical products 1 under a neutral or slightly reducing atmosphere, as well as their rapid cooling after galvanizing.

Claims

1 - Enclosure (3, 10) for the in-line galvanization of discontinuous metallurgical objects (1), such as tubes, angles, profiles, sheets or the like, leaving a vertical continuous casting line (2) or horizontal, characterized in that it comprises, at least at its end placed on the outlet side of the metallurgical objects (1) treated, an electromagnetic valve constituted by a polyphase inductive winding (7, 16) movable, capable of surrounding a fixed hollow armature (9, 14), arranged to be crossed by metallurgical objects (1) leaving said continuous casting line (2), said inductor winding (7, 16) being able to be displaced longitudinally with respect to said hollow armature ( 9, 14) so that: - firstly, when no metallurgical object (1) is present at the outlet orifice (6, 15) of said galvanizing enclosure (3, 10), said inductor winding (7, 16) surrounds said hollow armature (9, 14) so as to prevent any leakage of the metal or of the coating metal alloy from said enclosure (3, 10), - on the other hand, when a metallurgical object (1) leaves said continuous casting line (2) and reaches the outlet orifice (6, 15) of said galvanizing enclosure (3, 10), said inductor winding (7, 16) surrounds only said metallurgical object (1) which, while preventing leakage of metal or of molten metal alloy outside the enclosure (3, 10), is subjected, by the play of magnetomotor forces acting at its surface, a wiping effect of the coating deposited by contact with said metal or said molten metal alloy. 2 - Enclosure (3, 10) for the in-line galvanization of discontinuous metallurgical objects, such as tubes, angles, profiles, sheets or the like, leaving a continuous vertical or horizontal casting line, characterized in that that it comprises, at least at its end placed on the side of the outlet of the objects metallurgical treated, an electromagnetic valve constituted by a fixed polyphase inductor winding, capable of surrounding a movable hollow armature, arranged to be crossed by metallurgical objects leaving the continuous casting line, said hollow armature being able to be displaced longitudinally with respect to said winding inductor so that: on the one hand, when no metallurgical object is present at the outlet orifice of said galvanizing enclosure, said inductor winding surrounds said armature so as to prevent any leakage of the metal or of the metallic alloy coating outside said enclosure, - on the other hand, when a metallurgical object leaves said continuous casting line and reaches the outlet orifice of said galvanizing enclosure, said inductor winding surrounds only said metallurgical object. 3 - Enclosure (3) for galvanizing according to any one of claims 1 or 2, characterized in that it comprises: - a vertical tubular body (4) having an inlet orifice (5) and an outlet orifice (6) aligned to allow the passage, through the enclosure (3), of the objects (1) to be covered, - a polyphase inductor winding (7) surrounding said tubular body (4) at its outlet orifice (6), this inductor winding (7) being electrically connected to a polyphase current source (8) of adjustable intensity, so as to create a sliding field oriented from the bottom to the top of said tubular body (4), - A vertical hollow armature (9), of a material with high magnetic permeability, intended to concentrate the lines of the sliding magnetic field, generated by the inductor winding (7) when the latter is placed concentrically around said armature (9). 4 - Enclosure (10) for galvanizing according to any one of claims 1 or 2, characterized in that it comprises: - a vertical tubular body (12) having an inlet orifice (11) and an outlet orifice (15) aligned to allow the passage, through the enclosure (10), of the objects (1) to be covered, - a polyphase inductor winding (16) surrounding said tubular body (12) at its outlet orifice (15), this inductor winding (16) being electrically connected to a polyphase current source (17) of adjustable intensity, so as to create a sliding field oriented towards the inside of said tubular body (12), - A horizontal hollow armature (14), of a material with high magnetic permeability, intended to concentrate the lines of the sliding magnetic field, generated by the inductor winding (16) at the outlet of said enclosure (10). 5 - enclosure (10) for galvanizing according to claim 4, characterized in that it comprises a polyphase inductive winding (13) surrounding said tubular body (12) at its inlet orifice (11), this inductive winding (13) being electrically connected to a polyphase current source of adjustable intensity, so as to create a sliding field oriented towards the inside of said tubular body (12). 6 - enclosure (10) for galvanizing according to claim 4, characterized in that it comprises a device closing said enclosure (10) on the side of the inlet orifice (11) of the tubular body (12). 7 - enclosure (10) for galvanizing according to any one of claims 4 to 6, characterized in that, on the side of the inlet orifice (11) of the tubular body (12), there is arranged a means of production of a back pressure capable of acting against the discharge of molten metal or metal alloy into the annular space separating the hollow armature (14) and the metallurgical product (1) being covered and wiped. 8 - enclosure (10) for galvanizing according to claim 7, characterized in that the means for producing a counterpressure delivers a flow of a neutral gas intended to simulate a gravitational effect of the molten metal which is comparable to that acting to prevent the backflow of said molten metal upwards into a vertical galvanizing enclosure. 9 - Installation for the in-line galvanization of discontinuous metallurgical objects (1), such as tubes, angles, profiles, sheets or the like, leaving a continuous casting line (2) vertical or horizontal, comprising, at the outlet of said continuous casting line (2), a galvanizing enclosure (3, 10) according to any one of claims 1 to 8. 10 - Installation for galvanizing according to the preceding claim, characterized in that the part of the installation connecting the outlet of the continuous casting line (2) and the inlet orifice (5, 11) of the tubular body (4 , 12) of the galvanizing enclosure (3, 10) is maintained under a controlled atmosphere of a neutral or slightly reducing gas. 11 - Installation for galvanizing according to any one of claims 9 or 10, characterized in that the galvanizing enclosure (3, 10), as well as its outlet, are maintained under a controlled atmosphere of a neutral or slightly reducing gas . 12 - Installation for galvanizing according to any one of claims 9 to 11, characterized in that means are provided for vigorously cooling the metallurgical objects (1) at their exit from the galvanizing enclosure (3, 10).