EP0913218B1 - Method and installation for casting thin strips on one roll or between two rolls - Google Patents

Abstract

Metal strip production, in a continuous caster with one or two rolls with near-surface cooling channels, involves continuous spot measurement of the roll surface temperature in a free air zone and determination of the moment at which the measuring zone is opposite a channel for evaluating coolant circulation in the channel. An Independent claim is also included for a single or twin roll continuous strip caster, in which the above process is carried out.

Description

The invention relates to the continuous casting of metals in the form of strips. metallic by direct solidification of liquid metal on one or between two cylinders rotated.

The cylinders used on the casting installations implementing this process generally consist of a core ensuring the mechanical resistance of the cylinder and its drive in rotation, and by a ferrule surrounding this heart. This ferrule is made a material that is a good conductor of heat, such as copper or one of its alloys. It's at its contact that the poured liquid metal should solidify, and it should therefore be energetically internally cooled. For this purpose, a cooling fluid, generally water, flows under pressure inside channels drilled in the thickness of the shell, in parallel to the axis of the cylinder. These channels are connected at their ends to supply conduits and return formed, for example, in the heart of the cylinder. The channel section of cooling and their distribution in the shell are determined so as to ensure sufficient fluid flow to ensure sufficient heat extraction from the liquid metal, as well as a homogeneous distribution of the cooling on the around the cylinder. Such cylinders are described, in particular, in documents EP-A-0 428 464, EP-A-0 499 562 and EP-A-0 650 789.

Usually, at least for cylinders used on casting plants steel strips, the cooling channels have a diameter of the order of 10 to 15 mm. This diameter can be increased, up to approximately 20 mm, if rods are inserted which, in reducing the useful section of these enlarged channels, make it possible to confine the flows in portions of the channels close to the outer surface of the shell. Compared to the use of free channels of smaller diameter, such an arrangement, described in the document EP-A-0 499 562, makes it possible to increase the heat exchange surface between the fluid and the ferrule as well as the ease of drilling the channels, without requiring change the speed and flow of the coolant.

The homogeneity of the cooling of the ferrule is all the better as the distance separating two neighboring channels is lower, therefore the number of channels is higher. AT this effect, the number of channels to be provided in the shell depends in particular on the diameter of the cylinder, which can be of the order of 500 to 1500 mm. In practice, a number of 100 to 200 channels is usual.

Homogeneous cooling of the shell is a necessary condition for the tape is free from defects. In particular, if a canal gets blocked partially or completely during casting, the external surface of the shell present on the width of the cylinder an abnormally high temperature facing this channel. Solidification tape is not done as quickly as it should be, and this gives locally on the surface of the strip a brittleness which can cause the appearance of cracks cross. Blockage of a canal may occur due to progressive scaling of the channels if the cooling water is insufficiently demineralized, or of an accumulation of various impurities which it brought there. When such a blockage occurs while driving to a very strong local increase in the temperature of the shell, and that we cannot remedy, it becomes necessary to stop the pouring to avoid irreversible deterioration of the shell. This is an expensive piece, which is important to keep in good condition as long as possible.

The object of the invention is to provide operators operating a machine continuous casting of bands on a cylinder or between two cylinders a means of controlling during casting the good condition of the cooling channels of each of the cylinders.

To this end, the invention relates to a process for manufacturing thin strips metallic by solidification of liquid metal on the surface of a rotating cylinder or between the surfaces of two cylinders with horizontal axes rotated in opposite directions, the or said cylinders each comprising in the vicinity of their surface a multiplicity of channels through which a coolant flows, characterized in that, for each of said rotating cylinders, its temperature is punctually continuously measured surface in an area where its surface is in the open air, we determine the moments at which said measurement zone is opposite one of said channels, and from this measurement is deduced assessment of the quality of the circulation of said cooling fluid in said channel.

The subject of the invention is also an installation for continuously casting strips metallic by solidification of liquid metal on the surface of a rotating cylinder or between the surfaces of two cylinders with horizontal axes rotated in opposite directions, the or said cylinders each comprising in the vicinity of their surface a multiplicity of channels traversed by a cooling fluid, characterized in that it comprises, for each of said cylinders, at least one instrument for continuously measuring its temperature surface in a point measurement area where said surface is in the open air, means for determining the moments at which said measurement zone faces one of said channels and to identify this channel, and means for deducing, from the measurements and previous determinations, information representative of the quality of the circulation of the cooling fluid in said channel.

As will be understood, the invention consists in continuously measuring the temperature of the surface of the ferrule parading in front of a measuring instrument such as an optical pyrometer, to put the measurement at all times in relation to the angular position of the cylinder, and to give the possibility to warn operators when it is observed over several laps of consecutive cylinder an abnormally high temperature of the shell surface for a given angular position of the cylinder corresponding to the presence of a channel cooling below the measurement area. This high temperature is considered a partial or total blockage index of the cooling channel located opposite the zone of the ferrule concerned.

• la figure 1 qui montre schématiquement en coupe transversale une installation de coulée continue de bandes métalliques entre deux cylindres selon l'invention;
• la figure 2 qui montre des courbes représentatives d'un exemple de mesures de la température de surface d'un des cylindres, réalisées sur l'installation selon l'invention lors de deux tours consécutifs dudit cylindre.

The invention will be better understood on reading the description which follows, referring to the following appended figures:

• Figure 1 which shows schematically in cross section an installation for continuous casting of metal strips between two cylinders according to the invention;
• FIG. 2 which shows curves representative of an example of measurements of the surface temperature of one of the cylinders, carried out on the installation according to the invention during two consecutive turns of said cylinder.

The continuous casting installation of thin metal strips shown in the Figure 1 conventionally comprises two cylinders 1, 1 'with horizontal axes kept close from each other and rotated in opposite directions by means not shown. Their lateral surfaces 2, 2 'define, where they face each other, a sealed casting space 3 laterally by refractory walls 4 (only one of which is visible in FIG. 1) pressed against the ends of the cylinders 1, 1 '. Above the cylinders 1, 1 'is a distributor 5 containing the liquid metal 6 to be cast, which is, for example, steel or copper. A pouring nozzle 7 brings the liquid metal 6 into the casting space 3 from distributor 5. The cylinders 1, 1 'each consist of a core 8, 8' rigid on which act the means for rotating the cylinders 1, 1 ', and by a ferrule 9, 9' fixed rigidly on the core 8, 8 '. It is this ferrule 9, 9 ', made of a good conductive material heat such as copper or a copper alloy, which solidifies the metal liquid 6 present in the casting space 3. For this purpose, it has in its thickness a number "N" of cooling channels 10, 10 ′ traversed by a fluid such as water, arranged parallel to the axis of the cylinder 1, 1 ', and connected by their ends to means for supplying and evacuating the cooling fluid, integrated into the core 8, 8 ′ (not shown in Figure 1). Channels 10, 10 'are independent of each other. For more details concerning the design of cylinders 1, 1 ', reference may be made in particular to the documents cited in the preamble to the request and which describe (non-limiting) examples of such designs. In contact with the cooled ferrules 9, 9 ' form solidified skins 11, 11 ′ of metal which, in the example shown (as is generally the case during steel casting), meet at neck 12, i.e. at the level where the cylinders 1, 1 'are closest to each other, to form a strip 13 fully solidified.

According to the invention, a means is placed opposite each of the cylinders 1, 1 ' fixed point measurement of the surface temperature "T" of its shell 9, 9 'in an area where this ferrule 9, 9 'is exposed to the open air (i.e. it is not in contact with the metal), preferably mid-width of cylinder 1, 1 '. As shown, this means of temperature measurement can be constituted in particular by an optical pyrometer 14, 14 ' which has the advantage of practicing contactless measurement. A means of measuring the contact temperature, such as a thermocouple, would theoretically be acceptable, but would have the disadvantage of wearing out during casting, or even deteriorating the surface of the ferrule 9, 9 '. In addition, the heat given off by the friction of the thermocouple against the ferrule 9, 9 'would distort the result of the measurement. The result of this point measurement of the surface temperature "T" carried out on each shell 9, 9 'is continuously transmitted to processing units 15, 15 'each assigned to one of the cylinders 1, 1'. These units of treatment also receive from the devices for rotating the cylinders 1, 1 'information on the angular position of the cylinders 1, 1'. This information allows determine when the point area for measuring surface temperature "T" of the shell 9, 9 'is plumb with a cooling channel 10, 10', and also which channel of rank "n" (n being between 1 and N) it is, with respect to a channel of rank 1 taken arbitrarily as a reference. It is thus possible for the processing units 15, 15 'to gather the information making it possible to trace the curves 16, 17 of FIGS. 2a and 2b, and possibly to trace them on screens 18, 18 ′ for the operators in charge the operation of the installation.

• la température superficielle "T" de la virole 9, 9' dans la zone considérée a oscillé généralement autour d'une valeur moyenne T_moy; elle était légèrement inférieure à T_moy dans les zones situées sensiblement face à la plupart des canaux de refroidissement 10, 10' et légèrement supérieure à T_moy entre lesdites zones; ces hétérogénéités tolérables de la température superficielle "T" de la virole 9, 9' sont dues à la plus ou moins grande distance des zones considérées par rapport aux canaux 10, 10';
• mais dans des zones encadrant l'aplomb des canaux de rang "n" et "n+3", la température "T" a pris une valeur nettement supérieure à T_moy; cela est l'indice que dans ces deux canaux, la circulation du fluide de refroidissement ne s'effectuait plus normalement au moment de la mesure, à la suite d'un bouchage partiel ou total de leur section.

The curve of FIG. 2a partially represents a curve 16 plotted from the data collected by one of the processing units 15, 15 '. This curve 16 shows on the ordinate the temperature "T" of the shell 9, 9 'measured punctually continuously by the pyrometer 14, 14' during a complete revolution of row "x" of the corresponding cylinder 1, 1 '. Using the data transmitted by the device for rotating the cylinder 1, 1 'on the angular position of the cylinder 1, 1', it is possible to determine when the measured temperature T corresponds to that of a zone. the ferrule 9, 9 ′ situated at the base of a cooling channel 10, 10 ′ of given rank. It is thus possible to graduate the axis of the abscissas of FIG. 2a with the rows of the cooling channels 10, 10 'in question. In the example shown in FIG. 2a, curve 16 shows that during this turn of row "x":

• the surface temperature "T" of the shell 9, 9 'in the zone generally oscillated around an average value T _av; it was slightly less than T _avg in the zones situated substantially opposite most of the cooling channels 10, 10 ′ and slightly greater than T _avg between said zones; these tolerable heterogeneities of the surface temperature "T" of the shell 9, 9 'are due to the greater or lesser distance of the zones considered with respect to the channels 10, 10';
• but in zones framing the plumb of the channels of rank "n" and "n + 3", the temperature "T" has taken a value much higher than T _avg ; this is the indication that in these two channels, the circulation of the cooling fluid was no longer carried out normally at the time of the measurement, following a partial or total blockage of their section.

• que la température moyenne T_moy autour de laquelle oscillait normalement la température superficielle "T" de la virole 9, 9' lors du tour de rang "x+1" n'a pas été très sensiblement différente de ce qu'elle était au tour de rang "x";
• que la température "T" mesurée à l'aplomb du canal de rang "n" a encore augmenté, et que face à des canaux voisins de rangs "n-1" et "n+1", la température "T" a commencé également à devenir anormalement élevée; cela est l'indice que dans l'espace de temps séparant les deux mesures, la circulation du fluide de refroidissement dans le canal de rang "n" ne s'est pas améliorée, et que l'effet de ce défaut dans le refroidissement de la virole 9, 9' se faisait sentir sur une plage de largeur croissante;
• et que la température "T" mesurée à l'aplomb du canal de rang "n+3" est revenue à une valeur plus proche de T_moy; cela est l'indice que dans l'espace de temps séparant les deux mesures, la circulation du fluide de refroidissement dans le canal de rang "n+3" s'est améliorée, par exemple parce que les impuretés qui la gênaient lors du tour de rang "x" ont pu être entraínées par le courant de fluide refroidissant.

The curve 17 in FIG. 2b is equivalent to the curve 16 in FIG. 2a, but it is drawn for the turn of row "x + 1" of the same cylinder 1, 1 '. Compared to curve 16 plotted for the previous round of rank "x", we note:

• than the average temperature T _av normally oscillated around which the surface temperature "T" of the shell 9, 9 'during the revolution of rank "x + 1" was not significantly different from what it was in round of rank "x";
• that the temperature "T" measured above the channel of rank "n" has further increased, and that facing neighboring channels of rows "n-1" and "n + 1", the temperature "T" has started also to become abnormally high; this is the indication that in the space of time separating the two measurements, the circulation of the cooling fluid in the channel of rank "n" has not improved, and that the effect of this defect in the cooling of the ferrule 9, 9 'was felt over a range of increasing width;
• and that the temperature "T" measured above the channel of rank "n + 3" has returned to a value closer to T _avg ; this is the indication that in the space of time separating the two measurements, the circulation of the coolant in the channel of rank "n + 3" has improved, for example because the impurities which obstructed it during the turn of rank "x" may have been entrained by the flow of cooling fluid.

Provision may be made for the processing unit 15, 15 'to trigger an alarm signaling the abnormal operation of a channel 10, 10 'as soon as the temperature "T" of the shell 9, 9' measured at its height exceeds a predetermined value which is considered not to be not be permanently exceeded under penalty of deterioration of the shell 9, 9 '. We can also plan to calculate after each revolution of cylinder 1, 1 'the average of temperatures "T" which have been measured facing the N channels 10, 10 ′, and to trigger a alarm if one or more of these temperatures "T" exceed this average by, for example, 20 ° C or higher. Alternatively, to avoid triggering as much as possible unjustified alarms in the event of only temporary blockage of a channel 10, 10 ', we can also provide that the processing unit 15, 15 ′ stores the results of the measurements made during several consecutive turns. The alarm is only triggered if a temperature "T" deemed excessive (in absolute value, or by comparison with the temperatures "T" measured elsewhere during the same turn) below a channel 10, 10 'given a was observed during, for example, 5 consecutive rounds.

The following table 1 illustrates by an example the form that data collection can take and the conclusions that it is possible to draw as to the advisability, at a given moment, of triggering an alarm signaling that a specific channel is obstructed in a durable and dangerous way for the good condition of the shell. The cylinder concerned has 200 channels; the data presented was collected during 7 consecutive rounds. We have chosen to trigger an alarm when the surface temperature of the cylinder measured above a given channel during a given turn has, during 5 consecutive turns, exceeded by at least 20 ° C the average temperature measured in the 200 channels during the corresponding lap. In Table 1, the temperatures deemed abnormally high according to this criterion and which can therefore contribute to the triggering of an alarm, are entered in bold type.

In this example, it was measured directly above channel 25 for 5 turns consecutive (63 to 67) a temperature more than 20 ° C higher than the average temperature measured during each of the corresponding turns. As a result, an alarm was triggered at the end of round 67 to signal a probable at least partial blockage of the channel 25. The fact that the measured temperature increased continuously between turns 61 and 67 is the indication that this blockage is likely to worsen and deteriorate definitively the cylinder if the casting continues under these conditions. However, plumb of channel 28, an excessive temperature was only measured during 3 consecutive turns, at after which the temperature returned to a normal level. This is an indication that the blockage of channel 28 which could have caused this temperature increase did not persisted, and therefore it was useless to raise an alarm because of him.

For more security, one can plan to install opposite each cylinder 1, 1 'a plurality of pyrometers 14, 14 '(or other means for measuring temperature). We can thus hope to detect blockages of channels 10, 10 'with better accuracy.

Of course, without departing from the spirit of the invention, other methods of treatment collected data could be used, provided that it allows us to conclude with good reliability, from the measured temperatures, that the coolant does not not flow properly in a given channel, and that it can be harmful for the integrity of the shell and also for the quality of the casting strip.

When an alarm has been triggered, operators can choose to interrupt the casting to avoid deterioration of the shell, especially since, as we have said, the blockages of cooling channels can lead to the appearance of faults prohibitions on the solidified strip which make it unnecessary to continue casting. If they have any the possibility, operators can also launch actions to try to unblock the concerned channel (s), for example a large and sudden increased coolant pressure. The processing units of data can be directly connected to the bodies allowing to control this unclogging action, so as to trigger them without operator intervention when they are necessary.

The invention has been described in the case of its application to the casting of strips thin metal between two cylinders. But it is clearly transposable to case of the casting of metal strips on a single cylinder. Likewise, it can be applied to casting machines where the cooling channels would be provided not to inside the ferrule, but between the ferrule and the cylinder core, or even to machines where the cylinders would not have a separate ferrule from the heart, but a single part. The main thing is that the cylinder (s) have channels near their surface. fluid flow, and that the influence of each channel on the local surface temperature of the cylinder can be discriminated.

Claims (5)

1. Process for manufacturing thin metal strip by the solidification of liquid metal on the surface of a rotating roll or between the surfaces of two rolls having horizontal axes and rotating in opposite directions, the said roll or rolls each having, near their surface, a multiplicity of channels through which a coolant circulates, characterized in that, for each of the said rotating rolls, its surface temperature is continuously measured at a discrete point in an area where its surface is in the open air, the moments when the said measurement area lies opposite one of the said channels is determined and an assessment as to the quality of the circulation of the said coolant in the said channel is deduced from the said measurement.
2. Process according to Claim 1, characterized in that the said assessment as to the quality of the circulation of the said coolant in the said channel is deduced from a plurality of measurements of the surface temperature of the roll in line with the said channel which are carried out during several consecutive revolutions of the roll.
3. Plant for the continuous casting of metal strip (13) by the solidification of liquid metal (6) on the surface of a rotating roll or between the surfaces (2, 2') of two rolls (1, 1') having horizontal axes and rotating in opposite directions, the said roll or rolls (1, 1') each having, near their surface (2, 2'), a multiplicity of channels (10, 10') through which a coolant circulates, characterized in that it comprises, for each of the said rolls (1, 1'), at least one instrument for the continuous measurement of its surface temperature in a discrete measurement area where the said surface (2, 2') is in the open air, means for determining the moments when the said measurement area lies opposite one of the said channels (10, 10') and for identifying this channel (10, 10'), and means (15, 15') for deducing, from the above measurements and determinations, information representative of the quality of the circulation of the coolant in the said channel (10, 10')
4. Plant according to Claim 3, characterized in that the said instrument for measuring the surface temperature of the roll is a non-contacting measurement instrument such as an optical pyrometer (14, 14').
5. Plant according to Claim 3 or 4, characterized in that said means (15, 15') for deducing information representative of the quality of the circulation of the coolant in the said channel (10, 10') are connected to means for carrying out actions aimed at improving the said circulation.

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