EP2358919B1 - Device for controlling the introduction of several metals into a cavity designed to melt said metals - Google Patents

Description

The present invention relates to a device for controlling an introduction of several metals into a cavity adapted to a melting of said metals according to the preamble of claim 1.

The invention relates mainly to the metal coating by dipping rolled steel strips in continuous scrolling, and in particular to the control of the chemical analysis of the coating.

The metal coating by dipping continuously rolled steel strips is a known technique which essentially comprises two variants, that in which the strip coming out of an annealing furnace slopes obliquely into a bath of liquid metal coating and is deflected vertically. upwards by a roll immersed in said liquid metal. The other variant is to deflect the strip vertically upwards at its outlet from the oven and then to scroll in a vertical channel containing magnetically levitated liquid metal.

In both cases, the purpose of the operation is to create on the surface of the steel strip a continuous and adherent deposit of metal coating.

At its exit from the liquid metal, the strip drives on both sides a liquid film which is dewatered, by electromagnetic or gas-blowing devices, until it is reduced to the desired thickness. The wrung liquid film is then cooled until solidification. The consumption of coating metal by deposition on both sides of the strip is compensated by the addition of ingots in the bath of liquid metal. In known manner, these ingots are brought to the liquid bath by chain conveying devices and are introduced into the liquid metal bath manually or automatically on a given instruction from a bath level measurement. More or less sophisticated devices, like the one described in WO2007137665 or JP05186857A , have been proposed to make the introduction of ingots in the bath more precise, in particular to avoid their sudden fall as in KR20040057746A .

Metal coatings, such as those used for example in galvanizing generally use an alloy of at least two different metals like zinc and aluminum. Depending on the titration of the alloy to be deposited on the strip, it is necessary to feed the coating bath ingots of suitable composition. This can be done by supplying particular titration ingots but, as a general rule, ingots of standard composition (for example some without alloying elements and others with a fairly high percentage of alloying elements) are used. alternatively introduced in a sequence to ensure, on average, the required titration on the band. The document KR20020053126 describes such an ingot feeding system based on a calculation of daily consumption.

But, depending on the type of coating used, the amount of an alloying element referred to in the coating may be different from that actually consumed. This is typically the case of galvanizing with aluminum alloy zinc. Indeed, in contact with the liquid mixture occurs a dissolution of the iron from the steel strip which, for one part, participates in the formation on the surface of the strip of a combination layer of about 0.1μ of compound Fe ₂ Al ₅ Zn _x and, for another part, diffuses towards the bath of liquid mixture as long as the Fe ₂ Al ₅ Zn _x layer is not formed continuously. The Fe ₂ Al ₅ Zn _x layer serves as a support for the protective layer of zinc, whereas the dissolved iron will contribute to forming in the liquid mixture precipitates composed of Fe, Al and Zn called "mattes" or "dross". On the other hand, the steel elements immersed in the bath, such as a stainless steel bottom roller and its support arms, also undergo a dissolution of the iron in the bath which also participates in the formation of dross. As the aluminum content in these compounds is greater than that of the deposited alloy layer, the total consumption of aluminum is slightly greater than that which would be strictly necessary for the deposition of an alloy layer on both sides of the alloy. the band. The necessary aluminum content must therefore be determined from the sum of the aluminum consumptions in the coating, in the Fe ₂ Al ₅ Zn _x combination layer formed on the surface of the strip and in the dross.

However, many factors such as the immersion time (therefore, all things being equal the speed of travel of the band), the temperature of the bath, the amount of dross formed, etc. lead to more or less significant variations in the consumption of aluminum for the same content referred to in the deposit.

The ingot supply systems based solely on the theoretical consumption of alloying elements in the coating layer are therefore insufficient and, on the other hand, the estimates of additional consumption in the Combination layers and drosses remain very imprecise because based on static operating data of the facilities and theoretical kinetics of Fe ₂ Al ₅ Zn _x formation under these static operating conditions. In most cases the ingot feed is based on the operator experience, supported by regular chemical analyzes of samples taken from the liquid bath. Certain continuous measurement techniques based on electrochemical sensors such as that described in the document US5,256,272 are also implemented despite the fragility and unreliability of these measuring devices.

Some improvements have however been envisaged to improve this situation, for example KR20040057746 suggests to directly measure the aluminum content of the bath "at regular intervals" in order to regulate a rate of introduction of ingots grading 20% of aluminum alternately with pure zinc ingots. This alternative remains however imperfect because the discontinuous measurement of the aluminum content associated with the response time required for the implementation, as a function of the measurement results, and the fusion of ingots without or with 20% of aluminum, besides its management difficulty over time, does not make the method more accurate than the theoretical calculation.

An alternative for better continuous dosing of the zinc content as the first coating metal and especially that of aluminum as the second alloy metal is described by several devices in WO2008 / 105079 . A first device has two separate tanks respectively containing zinc and aluminum in liquid form, that is to say each of their liquid temperatures is above the melting temperature of zinc and aluminum, that is 420 ° C for zinc and ~660 ° C for aluminum. These two liquid metals are then introduced into the coating cavity (a temperature around 460 ° C where, due to the large differences and temperature gradients between the liquid metals and the coating liquid bath, large quantities of dross are inevitably A second device provides for the introduction of zinc and aluminum in the form of web-like solid metals which are unwound in the coating bath at controlled flow rates and grades at required levels and bath level. temperature gradients are inevitable, since at least the pure aluminum must be heated at least ~ 660 ° C just before its introduction in the coating bath so that it can mix in the bath in liquid form. Finally, a third device provides that the two separate tanks with respectively zinc and liquid aluminum flow into an intermediate reservoir where a large amount of dross is formed due to excessive temperature gradients. The advantage of this latter device is to be able to isolate the coating bath dross in the intermediate bath, however, need to be evacuated frequently because of their dense formation. Generally, these devices therefore suffer from the presence of too large temperature gradients, conducive to such a strong formation of dross annoying and therefore inevitably having significant losses of metal useful tape coating. This disadvantage therefore imposes unnecessary additional costs of overconsumption of metals useful for the coating as well as highly restrictive environmental aspects of massive reprocessing of dross formed.

According to this observation, the present invention proscribes methods or devices involving high temperature gradients and should be based on a use of metal ingot or metal alloy to bring to fusion.

Thus, an object of the present invention is to provide a device for controlling an introduction of several metals in the form of ingots in a cavity adapted to a melting of said metals for which temperature gradients of the metals introduced and the contents of the cavity. are minimal.

A device is thus described by the content of claim 1.

A set of subclaims also has advantages of the invention.

• un premier métal est introduit sous forme d'au moins un premier lingot à forte teneur dudit premier métal,
• un deuxième métal est introduit sous forme d'au moins un deuxième lingot constitué d'un alliage du premier métal et du deuxième métal,

la méthode selon l'invention prévoit que :

• la teneur en deuxième métal du deuxième lingot est choisie dans une gamme de teneurs significatives pour assurer un débit global visé de fusion cumulée des lingots,
• la gamme de teneurs significatives est choisie dans un intervalle limité de valeurs séquentiellement croissantes de façon à minimiser des écarts entre des températures de fusion des lingots.

From a method of controlling an introduction of several metals into a cavity adapted for melting said metals in order to coat a steel strip by dipping with said metals in the form of liquid metal, for which

• a first metal is introduced in the form of at least a first ingot to strong content of said first metal,
• a second metal is introduced in the form of at least a second ingot consisting of an alloy of the first metal and the second metal,

the method according to the invention provides that:

• the second metal content of the second ingot is chosen from a range of significant levels to ensure an overall target flow of cumulated merge ingots,
• the range of significant contents is selected within a limited range of sequentially increasing values so as to minimize differences between ingot melting temperatures.

The cavity here is a conventional or magnetic levitating coating crucible, or a melting crucible of said auxiliary ingots to the coating crucible. In the context of galvanizing the steel strip for which the control method according to the invention is implemented, the first metal is zinc and the second metal is mainly aluminum. The present invention is however not limited to these two metals as well as to alloys of these unique metals depending on the type of coating chosen. More importantly, on the one hand, thanks to the use of alloy ingots where for example one of the two metals would have required a high melting temperature, the overall melting temperature of the ingot remains lower thanks to the presence of other metals of the alloy.

In addition, if the range of significant contents is chosen as previously described, it is possible to have a homogeneous and continuous range of ingot melting temperatures in this content range, even if one or more ingots are immersed or removed in the cavity. Thus, strong temperature gradients at the introduction of ingots into the cavity are advantageously avoided.

Analogously to the second ingot, at least a third ingot of the alloy type of the second ingot and having a significant content of second or other metal can of course be introduced into the cavity, its content being distinct from that of the second ingot in the selected range of significant grades. In the same way, several distinct ranges of significant contents can be implemented in order to be able to obtain a greater dynamic of variation of contents if need be. If large differences between the contents of several ranges are required, it is possible to arrange these ranges by using at least one ingot having an intermediate content between these ranges. Thus again, because of the differences in contents thus reduced, any sudden variation in melting temperature required will advantageously be damped.

Given the differences between the required melting temperatures of one of the ingots in the form of an alloy of at least the first and second metals and an imposed temperature of the bath in the cavity, second metal content intervals are ideally squared. in the ranges according to the invention around at least one eutectic point of an equilibrium diagram of the alloy of said ingots (said diagram representing the melting temperature of the alloy of each ingot as a function of the percentage of the metals of alloy of said ingot). Indeed, particularly in the vicinity of the eutectic point, the alloy firstly has a minimum required melting temperature lower than that of each metal component and therefore much closer to the bath temperature. It is thus possible to maintain the temperature differences in a minimal range while being able to modify the ranges of significant contents in a limited range framing the eutectic point. To do this, ingots corresponding to these sequentially increasing ranges are introduced or withdrawn from the bath.

By way of example, for a dip galvanization of a steel strip, the first metal is Zn zinc and the second metal is Al aluminum and the significant range of contents is chosen in aluminum content ranges. around the eutectic point of the equilibrium diagram of the Zn-Al alloy: corresponds to a minimum melting temperature for a Zn-Al alloy (for example: 4.5% of Al allowing a melting point of 390 ° C.).

Types of ingots at various levels used for the main types of galvanizing coatings such as for such a Zn-Al alloy are known and can be so calibrated according to the ranges of significant levels as the invention provides.

By way of example, for a galvanization of conventional type, a range named "GI" provides an aluminum content in an interval of [0; 1%] (or more likely [0; 10%]). This meets a "ASTM B852-07" standard for which ranges of significant content can be selected by providing ingots having an aluminum content of 0.25, 0.35, 0.45, 0.55, 0.65, 0.75 or 1%. In case of additional and occasional need of aluminum, it is possible to extend the previous range by means of additional ingots with higher content and meeting other standard such as "ASTM B860-07" presenting 4, 5, or 10% of aluminum or conversely to use a pure zinc ingot.

Other types of galvanization under predefined standards provide lower intakes for the aluminum content (range named "GA" providing an aluminum content in an interval of [0; 1%]) and the invention can provide intervals significant grades at limited intervals that meet other standards such as "ASTM B852-07". In this case, the invention can provide that at least one of the ingots may comprise pure zinc, such as an ingot known under the ASTM standard.

Alloys, for example under the trademark GALFAN®, also have higher aluminum content ranges [4.2-6.2%] (and sometimes [0; 10%]) which may be potentially exploitable within the meaning of the invention to define ranges of significant contents higher than usual contents, while remaining in a limited neighborhood of the eutectic point of the Zn-Al equilibrium diagram.

In summary for this example, if the first metal is zinc and the second metal is aluminum, the significant range of contents is predominantly selected in aluminum content ranges of [0.10%] and minor way in higher grade intervals.

A range with significant contents can therefore advantageously be chosen from at least one range of concentration values related to limited variations in the melting temperature of the equilibrium diagram of an ingot alloy, ideally by choosing the values of said staggered intervals in the vicinity of the eutectic point of the ingot alloy.

• une introduction active du premier et d'au moins un des deuxièmes lingots (alliages) est contrôlée en fonction d'une mesure de chaque teneur des métaux, finalement liquides dans la cavité et/ou solides sur la bande revêtue,
• afin de choisir lequel des deuxièmes lingots pour l'introduction, au moins une teneur en deuxième métal du deuxième lingot est d'une part sélectionnée dans la gamme de teneurs significatives pour assurer un débit global visé de fusion cumulée des lingots afin de maintenir un niveau constant de métal liquide dans la cavité,
• d'autre part, un débit global effectif de fusion cumulée des lingots dans la cavité est mesuré et mis en relation avec les teneurs mesurées de chaque métal dans la cavité afin de déterminer un débit partiel effectif de fusion de chaque lingot,
• en cas d'écart du débit global effectif et du débit global visé, au moins un des débits partiels effectifs de chaque lingot est réadapté pour compenser cet écart en modifiant une hauteur immergée d'introduction d'au moins un des lingots dans la cavité.

The method also provides that:

• an active introduction of the first and at least one of the second ingots (alloys) is controlled according to a measurement of each content of the metals, finally liquid in the cavity and / or solids on the coated strip,
• in order to choose which of the second ingots for the introduction, at least a second metal content of the second ingot is firstly selected in the range of significant grades to ensure an overall target flow of cumulated merger ingots to maintain a level constant liquid metal in the cavity,
• on the other hand, an overall effective cumulative melting flow of the ingots in the cavity is measured and related to the measured contents of each metal in the cavity in order to determine an effective partial melting flow of each ingot,
• in the event of deviation from the effective overall flow rate and the overall flow rate targeted, at least one of the effective partial flows of each ingot is readapted to compensate for this difference by modifying a submerged depth of introduction of at least one of the ingots into the cavity.

A very fine regulation of the ingot melting can thus be obtained, without, again, successive introductions of bullion with steep rates and / or partial contents too far apart are involved.

comprenant une teneur visée en deuxième métal (Al%x) dans le revêtement liquide et une teneur respective en deuxième métal (Al%1, ..., Al%n) de chacun d'une pluralité (n) de deuxièmes lingots, ladite teneur respective étant comprise dans la gamme de teneurs significatives,
et le débit global visé (Qx) de métal liquide neuf nécessaire pour maintenir constant le niveau de métal liquide dans la cavité, ledit débit global visé (Qx) étant également compensé par la somme de débits partiels de fusion simultanée (Q1, ..., Qn) de la pluralité (n) de deuxièmes lingots.Said connection between the total effective cumulative melting flow of the ingots and the contents the measured contents of each metal is effected in that a partial melting flow of each of the ingots simultaneously introduced is established so as to maintain an equality of equilibrium (A) such that: $$\mathrm{al}\%\mathrm{x}*\mathrm{Qx}=\left[\left(\mathrm{al}\%1*\mathrm{<figure-callout\; id="1"\; label="Q"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q</figure-callout>}1\right)+...+\left(\mathrm{al}\%\mathrm{not}*\mathrm{qn}\right)\right]$$

comprising a second metal target content (Al% x) in the liquid coating and a respective second metal content (Al% 1, ..., Al% n) of each of a plurality (n) of second ingots, said respective content being within the range of significant levels,
and the overall target flow rate (Qx) of new liquid metal necessary to keep the level of liquid metal constant in the cavity, said overall target flow rate (Qx) being also compensated by the sum of partial flow rates of simultaneous melting (Q1, ... , Qn) of the plurality (n) of second ingots.

In the same way as the second metal, at least one third metal may also be introduced into the cavity in the form of an ingot alloy compound, of the type of the second or third ingot mentioned above. The previous equality can thus be applied to this third metal taking into account the flow rates / partial contents of said third metal. It would be the same for any other additive metal of the type of the second metal, like the aluminum stated above. Also, in the same way as the first metal, at least one additional metal can be introduced into the cavity in the form of a high-grade ingot of said complementary metal.

The invention proposes a device for implementing the aforementioned method. This device is more particularly described using an exemplary embodiment and application provided using a figure described:

1: Device according to the invention for the control of an introduction of several metals in a cavity adapted to a melting of said metals

• un organe de mesure (21) du niveau (20) de métal liquide provenant de la fusion des lingots dans la cavité,
• au moins un organe de mesure de teneurs (22, 23) des métaux issus de la fusion des lingots,
• un calculateur (4) recevant des valeurs de mesures de niveau et de teneurs issus des organes de mesure (21, 22, 23), délivrant des valeurs effectives de débits de fusion globale et partielle selon chaque métal et adaptant lesdites valeurs effectives à des valeurs corrigées selon une égalité d'équilibre prédéfini,
• un contrôleur (5) auquel sont fournies les valeurs corrigées de débit et délivre des consignes de correction,
• un organe de variation (9) d'une hauteur d'introduction d'au moins un et donc de chacun des lingots dans la cavité où se produit la fusion, ledit organe de variation étant commandé par les consignes de correction du contrôleur pour l'introduction ou le retrait des lingots.

Figure 1 thus presents a device for implementing the method described for the control of an introduction of several metals (Zn, Al, ...) in the form of ingots (10, 11) in a cavity (2, 3) adapted to a melting said metals to coat a steel strip (1) by dipping with said metals in the form of liquid metal, for which the cavity is a conventional coating crucible (2) (Including, for example, a deflector bottom roller (6) of intracavity strip and a vertical deflection roller (7) above the cavity) or a magnetically levitated crucible, or a melting auxiliary crucible (3) said ingots connected by a channel (8) to a coating pan (2), and comprising:

• a measuring member (21) for the level (20) of liquid metal resulting from the melting of the ingots in the cavity,
• at least one member for measuring the contents (22, 23) of the metals resulting from the melting of the ingots,
• a calculator (4) receiving level and content measurement values from the measuring elements (21, 22, 23), delivering effective values of overall and partial melting rates for each metal and adapting said actual values to values corrected according to a predefined equilibrium equilibrium,
• a controller (5) to which the corrected rate values are provided and provides correction instructions,
• a variation member (9) with a height of introduction of at least one and therefore of each of the ingots in the cavity where the melting occurs, said variation member being controlled by the correction instructions of the controller for the introduction or withdrawal of ingots.

The ingots are thus arranged and driven by the variation member (9) in correlation with the significant ranges of contents in order to avoid any difference in the melting temperature of the ingots.

The equal equilibrium (A) can therefore be taken into account in the controller (5) which, as a function of the correction setpoint, defines an appropriate sequence for introducing one or more ingots in compliance with the conditions imposed by a range chosen within a limited range of sequentially increasing values so as to minimize differences between ingot melting temperatures.

The content measuring device (22, 23) may comprise a Laser Induced Breakdown Spectrocopy (LIBS) type laser spectrometer or at least one electrochemical sensor adapted to the measurement of one of the metals involved. It is possible to place at least one of these measuring members at the level of the liquid metal (case 22) and / or at the level of the coated strip (case 23) as a function of the desired liquid mixture contents or final coating properties.

The level measuring member (21) may be a float on the surface of liquid metal for example at the liquid metal transfer channel from the auxiliary melting crucible (3) to the coating crucible ( 2), a radar or optical level measuring means of said liquid metal surface.

Claims (3)

1. Device for implementing a method for controlling the introduction of a plurality of metals into a cavity (2, 3) designed to melt said metals in the form of ingots (10, 11) in order to dip-coat a steel strip (1) with said metals in the form of molten metal, wherein the cavity is a conventional or magnetically levitated coating pot (2), or an auxiliary pot (3) for melting said ingots, and comprising:

   - a measuring device (21) for measuring the level of molten metal resulting from the melting of the ingots in the cavity,

   - at least one measuring device (22, 23) for measuring the contents of the metals resulting from melting of the ingots,

   - a computer (4) receiving level and content measurement values from measuring devices (21, 22, 23) supplying actual overall and partial rates of melting according to each metal, and adapting said actual values to corrected values according to a predefined equality of equilibrium,

   - a controller (5) which is supplied with corrected flow values and issues correction instructions,

   characterised by

   - a device (9) for varying the introduction height of at least one of the ingots into the cavity, said variation device being controlled by correction instructions from the controller for the introduction or withdrawal of the ingots.
2. Device according to claim 1, wherein the content measuring device comprises a LIBS type laser spectrometer or at least one electrochemical sensor.
3. Device according to claim 1 or 2, wherein the level measuring device (MN) is a float on the molten metal surface, a radar or an optical means of measuring the level of said molten metal surface.

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