EP0677345A1 - Method and apparatus for twin roll continuous casting - Google Patents

Abstract

A method is claimed for the continuous casing of thin metal products between rolls, according to which the molten metal is cast in a casting space (3) defined by the cylindrical walls of two rolls (1,2) with parallel axes. These rolls are counter rotated and internally cooled. Two fixed lateral closing walls (4) are placed against the front end surfaces of the rolls. A lubricant is spread on these front surfaces (5) to lubricate the interfaces between the rolls and the walls and the solidified product is extracted in a direction (F) essentially perpendicular to a plane containing the axes of the rolls. A system (18, 19) is provided to measure one or more parameters representing the rubbing or sealing conditions of the roll-wall interfaces and the quantity of lubricant is regulated as a function of the values of these measured parameters in order to remove the lubricant and thus provoke a temporary more rapid erosion of the closing walls. The device used to put this method into service is also claimed. <IMAGE>

Description

The present invention relates to the continuous casting of thin metallic products, in particular steel, according to the continuous casting technique between two counter-rotating cylinders, and more particularly the management of contact and lubrication between the front ends of such cylinders and the walls. lateral closure, applied against these front ends, to delimit the casting space defined between the cylinders.

Known installations for continuous casting between cylinders comprise two cylinders with horizontal and parallel axes, internally cooled, rotated in opposite directions, and spaced from each other by a distance corresponding to the desired thickness of the cast product. .

During casting, the molten metal is poured into the casting space, defined between the cylinders, solidifies on contact with them, and is extracted downwards, during their rotation in the form of a thin strip. . To contain the molten metal, lateral sealing walls are pressed against the front ends of the cylinders. Such lateral closure walls are commonly made of refractory material, at least in their part brought into contact with the molten metal.

It is necessary to seal between the cylinders and the lateral closure walls. For this, the walls are pressed against the ends of the cylinders, and to reduce the induced friction, the interface between cylinder and closure wall is lubricated. A known method of lubrication consists in depositing a lubricating material on the front surfaces of the cylinders. This deposit is for example carried out by applying to these surfaces a solid rod of a lubricant, comprising for example boron nitride or graphite.

But it sometimes happens that the contact between the closing wall and the cylinder is not regular enough. especially at the start of casting, due to irregularities in the surface of the closure walls, or their positioning which is not perfectly perpendicular to the axes of the rolls.

The regularity of the contact can also be destroyed, during casting, by metal infiltrations or tearing of the refractory material from the obturation walls, in the contact zone.

These infiltrations or tears can catch on the front surfaces, or edges, of the cylinders. To prevent these snagging from causing damage to the refractory material of the closure walls, during the rotation of the cylinders, provision has also been made to use scrapers or brushes to remove these snagging from the front surfaces of the cylinders.

A problem which remains is that if metal infiltrations cling to the edges of the cylinders or to the obturation walls, or if these hollow out locally following tearing of their constituent materials, or simply following their wear, closure wall - cylinder contact is not regular over the entire length of the contact arc, which affects sealing and may cause further infiltration.

The present invention aims to solve these problems, and aims in particular to ensure perfect sealing between cylinders and lateral closure walls permanently during casting by managing the wear of said closure walls.

With these objectives in view, the invention relates to a process for the continuous casting of metals between cylinders, according to which molten metal is poured into a casting space defined by the cylindrical walls of two cylinders with parallel axes, counter-rotating and internally cooled, and two fixed lateral closure walls placed against the front end surfaces of the cylinders, and a lubricant is deposited on these front surfaces to lubricate the cylinder-closure wall interfaces, and the solidified product is extracted in an extraction direction substantially perpendicular to the plane containing the axes of the cylinders, characterized in that the quantity of lubricant supplied to each of these interfaces, either periodically or in the event of deterioration of the friction or sealing conditions at the cylinder-closure wall interface.

By reducing, which can go as far as eliminating, the lubricant supplied to the interface, the friction between cylinders and obturation walls is increased. This results in wear of the closure wall in the zone of contact with the cylinder, which can be assimilated to running in of this wall on the front surface of the rotating cylinder, which leads to re-establishing good contact and good bearing of the cylinder on the closure wall over the entire area thus worn, and therefore to a return to good sealing conditions, by eliminating metal snagging or refractory tearing.

When the reduction or elimination of lubricant is carried out periodically, its effect is of a preventive type. In this case, there is then periodically a limited erosion of the lateral obturation walls which eliminates any beginning of possible snagging, and thus avoids an increase in these snagging, which would lead to repelling them. obturating walls by moving them away from the cylinders and therefore further deteriorating the seal, and therefore increasing infiltration and the risks of metal snagging on the refractory of said walls. Likewise, in the event of a small localized removal of the refractory in the contact area, the voluntary erosion of this area, over its entire surface, tends to suppress the digging caused by the removal, and therefore avoids that 'it is only growing.

The same erosion mechanism intended to correct the harmful effects of metal infiltrations and snagging, or of refractory tearing, is used in the case where the reduction or removal of lubricant is controlled in response to a measured variation d '' a parameter representative of the friction or sealing conditions at the cylinder - closure wall interface.

According to a first variant, the quantity of lubricant deposited is varied as a function of the force exerted on the closure wall in the direction of extraction. In this case, variations in the force measured are representative of variations in the friction conditions of the cylinders on the closure wall considered, these variations in friction being themselves indicative of a disturbance (infiltration, attachment or tearing) to the interface.

According to another variant, the quantity of lubricant deposited is varied as a function of the position of the closure wall relative to the front surfaces of the cylinders, measured in the direction of the axes of the cylinders. In this case, the displacement of the closure wall is indicative of an attachment of infiltrated metal between said wall and the cylinder, this attachment having the effect of moving the closure wall away from the front surface of the cylinder.

According to yet another variant, the quantity of lubricant deposited is varied as a function of parameters characteristic of the vibrations induced in the closure wall during casting. As in the first variant above, variations in the vibration regime of the closure wall are indicative of variations in the friction conditions, themselves indicative of disturbances at the interface.

According to a first method, to adjust the quantity of lubricant supplied to the interface, the bearing force of a solid stick of lubricant applied to each of the front faces of the cylinders is varied.

According to a preferred method, a stick of lubricant is applied permanently and with a substantially constant force to each of the front faces of the cylinders, and to reduce the quantity of lubricant supplied to the interface, the lubricant deposited is removed by means of a scraper or brush. This method has the advantage of obtaining a faster effect of the reduction or elimination of lubricant, because it effectively removes the lubricant located on the front surface of the cylinder, as soon as the scraper and / or the brush are put into service, while the first method can leave lubricant on the front surface of the cylinder for several turns of the latter before the consumption of lubricant, which occurs naturally in operation, leads to its effective reduction or elimination.

The invention also relates to a continuous casting device between cylinders, comprising two counter-rotating cylinders with parallel axes, defining between them a casting space, delimited by two lateral closure walls, fixed and placed against the front surfaces of end of the cylinders, means for depositing a lubricant on said front surfaces, means for measuring one or more parameters representative of the friction or sealing conditions at the cylinder-closure wall interface, characterized in that 'It includes means for reducing the quantity of lubricant supplied to said interface when the value or values of this or these parameters indicate a degradation of said friction or sealing conditions.

Preferably, the adjustment means comprise a scraper or a brush associated with each of the front surfaces, and means for switching the scraper or the brush on or off to remove the lubricant present on said front surfaces.

• un capteur d'effort pour mesurer l'effort exercé sur la paroi d'obturation dans la direction perpendiculaire au plan contenant les axes des cylindres et/ou,
• un capteur de déplacement pour mesurer les déplacement de la paroi d'obturation latérale, dans une direction parallèle aux axes des cylindres et/ou,
• un accéléromètre, permettant de mesurer des paramètres caractéristiques du régime vibratoire de la paroi d'obturation, ces vibrations résultant, comme on le comprend aisément, d'un phénomène de broutage dû au fait que les parois d'obturation ont tendance à gripper contre les chants des cylindres, lorsque les conditions de frottement se dégradent, ou varient de manière aléatoire.

The measurement means may in particular include:

• a force sensor for measuring the force exerted on the closure wall in the direction perpendicular to the plane containing the axes of the cylinders and / or,
• a displacement sensor for measuring the displacements of the lateral closure wall, in a direction parallel to the axes of the cylinders and / or,
• an accelerometer, making it possible to measure parameters characteristic of the vibratory regime of the obturation wall, these vibrations resulting, as is easily understood, from a chattering phenomenon due to the fact that the obturation walls tend to seize against the edges of the cylinders, when the friction conditions deteriorate, or vary randomly.

The implementation of these different measuring means, and the exploitation of the signals which they supply, for controlling the means for adjusting the quantity of lubricant will be easily carried out by a person skilled in the art, according to the characteristics specific to each installation, to manage, during casting, the wear of the sealing walls.

Other characteristics and advantages of the invention will appear in the description which will be given of a continuous casting installation between a cylinder of thin steel strips, in accordance with the invention, and of its method of implementation;

• la figure 1 est une vue frontale schématique partielle de l'installation de coulée.
• la figure 2 est une demi-vue d'une paroi d'obturation latérale lorsqu'un accrochage de métal coulé se produit,
• la figure 3 est une vue en coupe selon la ligne III-III de la figure 2,
• la figure 4 est une vue similaire à celle de la figure 2, après une suppression momentanée de lubrification,
• la figure 5 et une vue en coupe selon la ligne V-V de la figure 4,
• la figure 6 est une représentation graphique de l'évolution dans le temps de la position d'une paroi d'obturation, lors du démarrage de l'installation, et lorsque un accrochage de métal se produit,
• la figure 7, est une vue d'un moyen de lubrification des surfaces frontales des cylindres, selon la flèche F1 de la figure 1,
• la figure 8 est une vue d'un racleur placé entre l'une des dites surfaces frontales, selon la flèche F2 de la figure 1,
• la figure 9 est une vue d'une brosse rotative agissant sur l'une des dites surfaces frontales, selon la flèche F3 de la figure 1.

Reference is made to the appended drawings in which:

• Figure 1 is a partial schematic front view of the casting installation.
• FIG. 2 is a half-view of a lateral closure wall when an entanglement of cast metal occurs,
• FIG. 3 is a sectional view along line III-III of FIG. 2,
• FIG. 4 is a view similar to that of FIG. 2, after a temporary suppression of lubrication,
• FIG. 5 and a sectional view along the line VV of FIG. 4,
• FIG. 6 is a graphical representation of the evolution over time of the position of a closure wall, when the installation starts, and when a metal catching occurs,
• FIG. 7 is a view of a means of lubrication of the front surfaces of the cylinders, according to the arrow F1 in FIG. 1,
• FIG. 8 is a view of a scraper placed between one of said front surfaces, according to arrow F2 in FIG. 1,
• FIG. 9 is a view of a rotary brush acting on one of said front surfaces, according to arrow F3 in FIG. 1.

The installation for continuous casting of thin strips of steel, shown diagrammatically in the drawing in FIG. 1, comprises two casting rolls 1, 2, of horizontal and parallel axes, spaced by a distance corresponding to the thickness of the bandaged. The molten metal is poured into the casting space 3 defined between the cylinders 1,2. These are internally cooled and rotated in opposite directions, so that, during casting, the steel strip is pulled down, in the direction indicated by arrow F.

The pouring space is delimited by fixed walls 4 for lateral closure, applied against the front surfaces 5 of the cylinders by pressure means 20, such as springs or jacks, in a manner known per se. The walls 4 have, on the side of the casting space, a central part 6 of refractory material, preferably thermally insulating, bordered by two strips 7 which extend, according to a curvature corresponding to that of the cylinders, over the entire height of the wall 4.

These bands 7, also called inserts, are made of a refractory material having good qualities of resistance to abrasion wear. The external radius of curvature of these bands 7 is slightly greater than the external radius of the cylinders, so that a part 7 ′ of the bands 7 projects beyond the periphery of the cylinders and is, during casting, in contact with the cast metal. Therefore, it is therefore the remaining part 7 '' of each strip 7 which is in rubbing contact with the corresponding front face of each cylinder, to ensure the sealing of the casting space.

In accordance with the invention, the installation comprises means 8 for depositing a lubricant on the front surfaces 5, shown diagrammatically in FIG. 1, and shown in more detail in FIG. 7, in a preferred embodiment. These means comprise, for each front face of the cylinders, a solid rod of lubricant 9, such as for example boron nitride or graphite, guided in a tubular support 10 fixed on the structure 11 of the installation. The rod 9 is pushed against the front surface 5 of the cylinder 1 by a pressure means such as a spring 12, or a jack. In the variant shown, the spring 12 presses the lubricating stick 9 on the front surface 5, permanently and with a substantially constant force throughout the casting. During the rotation of the cylinder, lubricant is therefore deposited and distributed over the entire circumferential part of the front surface 5 of the cylinder 1, and can be brought by this rotation, to the contact interface between this surface and the part 7 '' of the insert 7 of the closure wall 4, to ensure lubrication.

The installation also includes means for adjusting the quantity of lubricant supplied to the interface, comprising, associated with each front surface 5 of the cylinders, a scraping system 13 and a rotary brush 14, driven in rotation by a motor 15.

The scraping system, shown in more detail in FIG. 8, comprises a blade-shaped scraper 16 which can be applied in contact with the front surface 5, or distant from it, by a jack 17, or a means of equivalent movement control.

The brush 14 can, similarly, be applied with a controlled force against the front surface 5, or be removed from it, by equivalent displacement means, not shown.

The installation also includes means 18 for measuring the position in the axial direction of the cylinders, for the closure wall 4, with respect to the front surface 5. These measurement means make it possible to determine the variations in position of the wall shutter, and therefore give information on the operating conditions of the installation at the level of the cylinder - shutter wall interface, in particular on the sealing of the casting space at this interface. For example, when cast metal infiltrates between the cylinder and the obturation wall and forms a solidification 21 which adheres to the obturation wall 4, the presence of this attachment pushes the wall against the force exerted by the pressure means 20, creating a clearance at the interface, detrimental to the seal, and detectable by the displacement measurement means 18.

We will now describe, in relation to FIG. 6, a casting process according to the invention, making it possible to manage the wear of the closure wall during of casting. The plot 30 of Figure 6 shows the position of the closure wall 4, relative to the general structure of the installation, as a function of time. Part 31 of line 30 corresponds to the start of casting, during which a progressive displacement of the closure wall 4 is observed, the result of relatively rapid wear of the refractory material constituting the insert 7. This period corresponds to a lapping of the insert by friction of the cylinder during its rotation, until the two surfaces are in intimate contact which ensures a good seal. In the absence of any disturbance, the friction and sealing conditions at the interface stabilize, the lubrication being ensured by the regular supply of lubricant resulting from the deposit made by friction of the lubricant stick 8 on the front surface 5 of the cylinder. The lubricant becomes embedded in the roughness hollows of this surface, this roughness being of the order of 5 to 20 μm. The wear regime of the closure wall is then stabilized at very slow wear; and the closing wall practically does not undergo any more displacement (part 32 of the layout).

When a disturbance occurs, for example a catch 21 of metal on the closure wall, the latter is pushed back. The measurement means record this decline (part 33 of the plot 30). In response to this reversing signal, the scraper 13 and the brush 14 are put into service, that is to say that they are pressed against the front surface 5 of the cylinder, and remove therefrom the lubricant deposited by the stick 9. This results in an immediate reduction in lubrication, therefore an increase in friction, which has the effect of eliminating the hooking by abrasion and of causing a greatly increased wear of the closure wall 4, which results in by moving it (part 34 of the plot 30) beyond its previous speed position.

After a predetermined time, or when the displacement thus caused of the closure wall has reached a predetermined value, the brushes and / or scrapers are put out of service. The supply of lubricant to the interface is thus again ensured, which avoids continuing wear of the insert 7, and makes it possible to return to stabilized operating conditions with continuous tight contact at the interface.

It is thus possible to manage the wear of the closure wall by putting the brushes or scrapers on or off.

The regulation of this wear by the means described above can be associated with a modulation of the forces of application of the wall against the cylinders by the pressure means 20, according to each situation: start of casting, stabilized regime, or incident.

The temporary reduction or elimination of lubrication of the interface can also be carried out by eliminating the application of the stick 9 on the front surface of the cylinder.

The invention makes it possible in particular to avoid using for the inserts a material of the self-lubricating type, for example with a high content of boron nitride, a less resistant and more expensive material, by ensuring the lubrication of the cylinder-wall interface. sealing via the front surfaces of the cylinders, instead of ensuring this lubrication by the inserts themselves.

The invention is not limited to the device method described above by way of example. In particular, the deposition of lubricant on the front surfaces of the cylinders can also be carried out by other means than the rods described above, for example by systems for applying liquid or pasty lubricant, spraying liquid or pulverulent lubricant, etc. ... Also, the relative provision of the means of lubrication 8, brush 14, closure wall 4 and scraper 13, shown in FIG. 1 in this order according to the direction of rotation of the cylinders, can be modified; the lubrication means 8 being able in particular to be placed between the brush and the closure wall, the effect of brushing being then still remarkable because the lubricant deposited after brushing is in a reduced quantity compared to what would occur without no brushing.

Likewise, scrapers which, being placed downstream of the obturation wall in the direction of rotation, also ensure the elimination of possible metal snagging on the edges of the cylinders, can also be placed upstream, but after the means of lubrication, and in addition to or instead of brushes.

Furthermore, means other than the displacement measurement means described above can be used to measure parameters representative of the friction or sealing conditions at the cylinder - closure wall interface.

In particular, it is possible to use means for measuring the force exerted on the closure wall 4, in the direction of extraction (arrow F) of the cast product, for example a load cell 19 placed under said closure wall. . The load cell 19 therefore serves to measure the force exerted on the wall 4 resulting from the friction of the cylinders 1, 2 in rotation on this wall, this force depending on the friction conditions and therefore in particular the force of application of the wall 4 on the cylinders, in the direction of the two axes, of the effective contact surface, and of the lubrication conditions.

Variations in the measured force are representative of modifications of the friction conditions at the interface, which can be caused either by abnormal localized wear of the wall. shutter, or tearing of its material, or also infiltration of cast metal and metal snagging on said wall.

It is also possible to measure the force exerted downwards on each closure wall 4 by two force sensors disposed respectively on the sides of the wall. This arrangement makes it possible to know, in addition to the total force, the forces caused by the friction of each cylinder on said wall, independently of one another, and thus to better appreciate at which cylinder-wall interface occurs the degradation of the friction and sealing conditions, and therefore of being able to act predominantly at the level of the interface concerned.

In addition to the means for measuring the force exerted on the closure wall downwards, it is possible to use sensors measuring the force exerted on the wall in the direction of the axes of the cylinders, and thus complete the knowledge of the conditions of friction at the cylinder-wall interface.

It is also possible to use an accelerometer linked to each of the obturation walls, the signal supplied by the latter, filtered and analyzed, making it possible to detect the appearance of galling of the cylinders on the obturation walls, signs of disturbances to the interface between these and the cylinders, and therefore making it possible to act accordingly on the quantity of lubricant supplied to this interface.

It is also possible, in addition to or in place of the implementation of the means for reducing or eliminating the lubricant supplied to the interface in response to the detection of a disturbance, to carry out this implementation cyclically throughout casting.

It is then possible to vary the quantity of lubricant supplied to the interface between a maximum value and a zero value according to a predetermined regular periodicity, so as to act preventively to avoid the appearance or amplification of disturbances.

Claims (12)

Process for the continuous casting of thin metallic products between cylinders, according to which molten metal is poured into a casting space (3) defined by the cylindrical walls of two cylinders (1, 2) with parallel axes, counter-rotating and internally cooled, and two fixed side walls (4) placed against the front end surfaces of the cylinders, and a lubricant is applied to these front surfaces (5) to lubricate the cylinder-end wall interfaces, and the product is extracted solidified in an extraction direction (F) substantially perpendicular to the plane containing the axes of the cylinders, characterized in that the quantity of lubricant supplied to each of these interfaces is reduced either periodically or in the event of degradation of the friction conditions or seal at the cylinder-shutter interface. Method according to claim 1, characterized in that the quantity of lubricant supplied to the interface is varied between a maximum value and a zero value according to a predetermined regular periodicity. Method according to claim 1, characterized in that the quantity of lubricant deposited is varied as a function of the force exerted on the closure wall (4) in the direction of extraction (F). Method according to claim 1, characterized in that the quantity of lubricant deposited is varied as a function of the position (d) of the closure wall (4) relative to the front surfaces (5) of the cylinders, measured in the direction of cylinder axes. Process according to claim 1, characterized in that the quantity of lubricant deposited is varied function of parameters characteristic of the vibrations induced in the closing wall during casting. Method according to one of the preceding claims, characterized in that, to adjust the quantity of lubricant supplied to the interface, the bearing force of a solid stick (9) of lubricant applied to each of the front faces is varied 5) cylinders. Method according to one of the preceding claims, characterized in that, in order to regulate the quantity of lubricant supplied to the interface, a stick (9) of lubricant is applied permanently and with a substantially constant force to each of the front faces of the cylinders , and to reduce the quantity of lubricant supplied to the interface, the lubricant deposited is removed by means of a scraper (13) or a brush (14). Continuous casting device between cylinders, comprising two cylinders (1, 2) counter-rotating with parallel axes, defining between them a casting space (3), delimited by two lateral closing walls (4), fixed and placed against the surfaces frontal (5) end of the cylinders, means (8) for depositing a lubricant on said front surfaces, means (18, 19) for measuring one or more parameters representative of the friction or sealing conditions at the cylinder-shutter wall interface, characterized in that it includes means for reducing the quantity of lubricant supplied to said interface when the value or values of this or these parameters indicate a degradation of said friction conditions or sealing. Device according to claim 8, characterized in that the adjustment means comprise a scraper (13) or a brush (14) associated with each of the front surfaces (5), and means for switching the service on or off. scraper or brush to remove the lubricant present on said front surfaces. Device according to claim 8, characterized in that the measuring means comprise, for each closure wall, a force sensor (19) for measuring the force exerted on the closure wall in the direction perpendicular to the plane containing the axes of the cylinders. Device according to Claim 8, characterized in that the measuring means comprise, for each closure wall, a displacement sensor (18) for measuring the displacement of the lateral closure wall, in a direction parallel to the axes of the cylinders . Device according to claim 8, characterized in that the measuring means comprise, for each closure wall, an accelerometer.

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