FR2717410A1 - Method and device for continuous casting between rolls - 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.

Description

Method and device for continuous casting between rolls

  The present invention relates to the continuous casting of thin metal products, in particular steel, according to the technique of continuous casting between two counter-rotating rolls, 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 define the casting space defined between the cylinders. Known continuous roll casting installations comprise two cylinders of horizontal and parallel axes, internally cooled, driven in rotation in the opposite direction, 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 in contact with them, and is extracted towards the

  low, when rotating in the form of a thin band.

  To contain the molten metal, side closure walls are pressed against the front ends of the rolls. Such side closure walls are currently made of refractory material, at least in their part brought to be in contact with the

molten metal.

  It is necessary to seal between the cylinders and the side closure walls. For this, the walls are pressed against the ends of the cylinders, and to reduce the induced friction, the cylinder interface wall-closing is lubricated. A known method of lubrication is to deposit a lubricant material on the front surfaces of the rolls. This deposit is for example made by applying to these surfaces a solid bar of a lubricant, comprising

  for example boron nitride or graphite.

  But it happens that the contact between the closure wall and cylinder is not sufficiently regular, especially at the beginning of casting, due to irregularities in the surface of the closure walls, or their positioning not perfectly perpendicular to the

axes of the cylinders.

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

  shutter, in the contact zone.

  These infiltrations or tearing can catch on the frontal surfaces, or songs, of the cylinders. To prevent these clashes from causing deterioration of the refractory material of the closure walls, during the rotation of the rolls, it has also been planned to use scrapers or brushes to remove these snaps from the front surfaces of the shutters.

cylinders.

  A problem that remains is that if metal infiltrations cling to the edges of the cylinders or walls of fillings, or if they are digging locally due to tearing of their constituent materials, or simply following their wear, the shutter wall contact - cylinders is not smooth over the entire length of the contact arc, which impairs the seal and may cause

new infiltrations.

  The present invention aims to solve these problems, and is particularly intended to ensure a perfect seal between cylinders and side closure walls permanently during casting.

  managing the wear of said shutter walls.

  With these objectives in mind, the subject of the invention is a process for the continuous casting of metals between rolls, according to which molten metal is poured into a casting space defined by the cylindrical walls of two cylinders of parallel axes, counter-rotating and cooled internally, and two fixed side closure walls placed against the end faces of the cylinders, and is deposited on these front surfaces a lubricant to lubricate the cylinder-wall interfaces shutter, and the solidified product is extracted in a extraction direction substantially perpendicular to the plane containing the axes of the cylinders, characterized in that the quantity of lubricant brought into each of these interfaces is reduced either periodically or in case of deterioration of the conditions

  friction or sealing at the cylinder-interface

shutter wall.

  By the reduction, which can go as far as the suppression, of the lubricant brought to the interface, the friction between cylinders and walls of fillings is increased. This results in wear of the closure wall in the area of contact with the cylinder, which can be likened to a break-in of this wall on the front surface of the rotating cylinder, which leads to restore good contact and good range of the cylinder on the closure wall over the entire area thus used, and thus a return to good sealing conditions, by removing metal snaps or the

refractory tears.

  When the reduction or removal of lubricant is carried out periodically, its effect is preventive. In this case, there is then periodically caused limited erosion of the lateral closure walls which eliminates any start of possible clashes, and thus avoids an increase in these clashes, which would lead to pushing the closing walls away from the cylinders and therefore to further deteriorate the seal, and thus to increase infiltration and the risk of clashes of metal on the refractory walls. Similarly, in the case where a small localized tearing of the refractory has occurred in the contact zone, the deliberate erosion of this zone, over its entire surface, tends to suppress the excavation caused by

  the tearing off, and thus prevents it from growing.

  The same erosion mechanism intended to correct the harmful effects of infiltrations and clinging of metal, or of refractory tearing, is used in the case where the reduction or suppression of lubricant is controlled in response to a measured variation of a parameter representative of the friction conditions or

  sealing at the cylinder interface - shutter wall.

  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 extraction direction. In this case, variations in the measured force are representative of variations in the friction conditions of the rolls on the closure wall

  considered, since these variations in friction are themselves

  same indicators of a disturbance (infiltration,

  hanging or tearing) at the interface.

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

  shutter the front surface of the cylinder.

  According to 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 amount of lubricant supplied to the interface, the support force of a solid rod of lubricant applied is varied.

  on each of the end faces of the rolls.

  According to a preferred method, a lubricant rod is permanently applied and with a substantially constant force on each of the end 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 removal of lubricant, because it effectively removes the lubricant on the front surface of the cylinder, as soon as the scraper and / or the brush are put into operation, while the first method can leave lubricant on the front surface of the cylinder for several turns of the cylinder before the consumption of lubricant, which occurs naturally in operation, does not lead to

  effective reduction or suppression.

  The subject of the invention is also a device for continuous casting between rolls, comprising two counter-rotating cylinders of parallel axes, defining between them a casting space, delimited by two lateral closing walls, fixed and placed against the front surfaces of each other. end of the cylinders, and means for depositing a lubricant on said front surfaces, characterized in that it comprises means for measuring one or more parameters representative of the friction or sealing conditions at the cylinder-wall interface shutter, and means for adjusting the quantity of lubricant supplied to said interface in

  depending on the value of this or these parameters.

  Preferably, the adjustment means comprise a scraper or a brush associated with each of the front surfaces, and means for putting the scraper or the brush into service or out of order in order to remove the lubricant present on said front surfaces. The measuring means can comprise in particular: 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 displacement. of the lateral closure wall, in a direction parallel to the axes of the cylinders and / or - an accelerometer, for measuring characteristic parameters of the vibratory regime of the closure wall, these vibrations resulting, as is easily understood, grazing phenomenon due to the fact that the closure walls tend to seize against the edges of the cylinders, when the conditions of

  friction are degraded, or vary randomly.

  The implementation of these different measuring means, and the exploitation of the signals they provide, for controlling the means for adjusting the amount of lubricant will be easily achieved by the skilled person, depending on the specific characteristics of each installation, to manage, during casting, the wear of

shutter walls.

  Other features and benefits of

  the invention will appear in the description that will be

  made of a continuous casting installation between the cylinder of thin strips of steel, in accordance with the invention, and of its method of implementation; Reference is made to the accompanying drawings, in which: FIG. 1 is a diagrammatic front view;

  partial of the casting installation.

  FIG. 2 is a half-view of a lateral closure wall when a latching of cast metal occurs; FIG. 3 is a sectional view along the line III-III of FIG. 2; FIG. 4 is a view similar to that of FIG. 2, after a momentary suppression of lubrication,

  - Figure 5 and a sectional view along line V-

  V of Figure 4, - Figure 6 is a graphical representation of the evolution over time of the position of a closure wall, when starting the installation, and when a metal snap occurs, - FIG. 7 is a view of a means for lubricating the front surfaces of the rolls, along arrow F1 of FIG. 1; FIG. 8 is a view of a scraper placed between one of said end surfaces, according to FIG. arrow F2 of FIG. 1; FIG. 9 is a view of a rotating brush acting on one of said front surfaces, according to FIG.

arrow F3 of FIG.

  The continuous casting installation of thin strips of steel, shown schematically in the drawing of FIG. 1, comprises two casting rolls 1, 2 of horizontal and parallel axes spaced a distance corresponding to the thickness of the gang. 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 extracted downwards, in the direction indicated by the arrow F. The casting space is delimited by fixed side-sealing walls 4 applied against the front surfaces 5 of the rolls by pressure means 20,

  such as springs or cylinders, in a manner known per se.

  The walls 4 have, on the side of the casting space, a central portion 6 of refractory material, preferably thermally insulating, bordered by two strips 7 which extend in a curvature corresponding to that

  cylinders, over the entire height of the wall 4.

  These strips 7, also called inserts, are made of a refractory material having good abrasion-resistant qualities. The outer radius of curvature of these strips 7 is slightly greater than the outer radius of the rolls, so that a portion 7 'of the strips 7 protrudes from the periphery of the rolls and is, during casting, in contact with the cast metal. Therefore, it is the remaining portion 7 "of each strip 7 which is in rubbing contact with the corresponding front face of each cylinder, for

  seal the casting space.

  According to the invention, the installation comprises means 8 for depositing a lubricant on the front surfaces 5, shown diagrammatically in FIG. 1, and shown in greater detail in FIG. 7, in a preferred embodiment variant. These means comprise, for each end face of the rolls, a solid lubricant rod 9, such as for example boron nitride or graphite, guided in a tubular support 10 fixed on the structure 11 of the installation. The stick 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 bears the lubricant rod 9 on the front surface 5, permanently and with a substantially constant force throughout the casting. During the rotation of the cylinder, lubricant is deposited and distributed over the entire circumferential portion 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 portion 7 " of the insert 7 of the closure wall 4, for in

ensure lubrication.

  The installation also comprises 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 brush

  rotary 14, driven in rotation by a motor 15.

  The scraping system, shown in greater detail in FIG. 8, comprises a scraper 16 in the form of a blade that can be applied in contact with or away from the front surface 5 by a jack

  17, or equivalent displacement control means.

  The brush 14 may similarly be applied with a controlled force against the front surface 5, or removed therefrom, by means of

  equivalent displacement, not shown.

  The installation also comprises means 18 for measuring the position in the axial direction of the rolls, of the closure wall 4, with respect to the front surface 5. These measuring means make it possible to determine the variations in position of the wall shutter, and therefore give indications on the operating conditions of the installation at the interface cylinder - wall shutter, in particular on the sealing of the casting space at this interface. For example, when cast metal infiltrates between the cylinder and the closure wall and forms a solid bonding 21 adhering to the closure wall 4, the presence of this attachment pushes the wall against the wall force exerted by the pressure means 20, creating a play at the interface, harmful to the seal, and detectable by the measuring means of

displacement 18.

  We will now describe, in connection with Figure 6, a casting process according to the invention for managing the wear of the closure wall during casting. The plot 30 of FIG. 6 represents the position of the closure wall 4, with respect to the general structure of the installation, as a function of time. The portion 31 of the trace 30 corresponds to the beginning of casting, during which there is a gradual movement of the closure wall 4, resulting from a relatively rapid wear of the refractory material constituting the insert 7. This period corresponds to a lapping the insert by rubbing 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 conditions of friction and sealing at the interface stabilize, the lubrication being ensured by the regular supply of lubricant resulting from the deposit made by friction of the lubricant rod 8 on the front surface 5 of the cylinder. The lubricant is embedded in the roughness hollows of this surface, this roughness being of the order of 5 to 20 gm. The wear rate of the closure wall is then stabilized at a very slow wear; and the closure wall is practically no longer subjected to

displacement (part 32 of the layout).

  When a disturbance occurs, for example a

  hooking 21 of metal on the closure wall, that

  it is pushed back. The measuring means record this decline (part 33 of the trace 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 from it the lubricant deposited by the rod 9. This results in an immediate reduction of the lubrication and therefore an increase in the friction, which has the effect of eliminating the abrasive fixing and causing a greatly increased wear of the closure wall 4, which results in by moving it (part 34 of the

  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 decommissioned. The supply of lubricant to the interface is thus again ensured, which avoids further wear of the insert 7, and allows to return to stabilized operating conditions with a

  continuous waterproof contact at the interface.

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

or scrapers.

  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 rolls by the pressure means 20, depending on each situation:

  start of casting, steady state, or incident.

  The reduction or temporary suppression of lubrication of the interface can also be achieved by removing 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 self-lubricating type material, 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. shuttering through the front surfaces of the rolls, at the

  instead of ensuring this lubrication by the inserts themselves

  same. 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 achieved by means other than the rods described above, for example by liquid or pasty lubricant application systems, liquid or powdery lubricant spray, etc. ... Also, the relative arrangement of the lubrication means 8, brush 14, closure wall 4 and scraper 13, shown in Figure 1 in this order in the direction of rotation of the cylinders, can be modified; the lubricating means 8 can in particular be placed between the brush and the closure wall, the effect of the brushing is then still remarkable because the lubricant deposited after brushing is in reduced amount relative to this

  which would occur without any brushing.

  Similarly, scrapers which, being placed downstream of the closure wall in the direction of rotation, also ensure the elimination of any metal clashes on the edges of the cylinders, can also be placed upstream, but after the lubrication means, and in addition to or instead of the brushes. Moreover, other means than the displacement measuring means described above can be used to measure parameters representative of the friction or sealing conditions at the interface.

cylinder - shutter wall.

  In particular, it is possible to use means for measuring the force exerted on the closure wall 4, in the extraction direction (arrow F) of the cast product, for example a load cell 19 placed under the said closure wall. . The load cell 19 thus 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 on the application force of the wall 4 on the cylinders, in the direction of their axes, the surface

  effective contact, and lubrication conditions.

  Variations in the measured effort are representative of changes in the friction conditions at the interface, which can be caused either by abnormal localized wear of the closure wall, or tearing of its material, or also by infiltration of the metal cast and clashes

of metal on the said wall.

  We can also measure the force exerted down on each closure wall 4 by two force sensors respectively disposed 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 the said wall, independently of one another, and thus to better appreciate which cylinder-wall interface occurs. degradation of the friction and sealing conditions, and therefore to be able to act as

  predominantly at 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 to complete the knowledge of the conditions of the friction at the cylinder-wall interface. It is also possible to use an accelerometer linked to each of the closure walls, the signal supplied by it, filtered and analyzed, making it possible to detect the occurrence of galling of the cylinders on the closure walls, signs of disturbances to the shutter. interface between them and the cylinders, and therefore to act accordingly on the amount of lubricant brought to this interface. It is also possible, in addition to or instead of implementing means for reducing or removing the lubricant supplied to the interface in response to the detection of a disturbance, to proceed with this implementation.

  cyclically throughout the casting.

  It is then possible to vary the amount 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 the disturbances.

Claims (12)

  1. A method of continuous casting of thin metallic products between rolls, in which molten metal is poured into a casting space (3) defined by the cylindrical walls of two cylinders (1, 2) of parallel axes, counter-rotating and cooled internally, and two fixed lateral sealing walls (4) placed against the end end faces of the rolls, and on these front surfaces (5) a lubricant is deposited for lubricating the cylinder-closure wall interfaces, and the solidified product in a direction of extraction (F) substantially perpendicular to the plane containing the axes of the rolls, characterized in that the quantity of lubricant brought into each of these interfaces is reduced either periodically or in case of deterioration of the conditions   friction or sealing at the cylinder-interface shutter wall.   2. Method according to claim 1, characterized in that the amount of lubricant brought to the interface between a maximum value and a zero value is varied.   according to a predetermined regular periodicity.   3. Method according to claim 1, characterized in that the amount of lubricant deposited is varied as a function of the force exerted on the closure wall.   (4) in the extraction direction (F).   4. Method according to claim 1, characterized in that the amount of lubricant deposited is varied as a function of the position (d) of the closure wall (4) with respect to the front surfaces (5) of the rolls,   measured in the direction of the axes of the cylinders.   5. Method according to claim 1, characterized in that the amount of lubricant deposited is varied according to characteristic parameters of the vibrations.   induced in the closure wall during casting.   6. Method according to one of the claims   characterized in that, to adjust the amount of lubricant supplied to the interface, the support force of a solid rod (9) of lubricant applied to each of the end faces (5) is varied. cylinders.   7. Method according to one of the claims   preceding, characterized in that to adjust the amount of lubricant supplied to the interface is applied permanently and with a substantially constant force on each of the end faces of the cylinders, a rod (9) of lubricant, and to reduce the amount of lubricant brought to the interface, we remove the lubricant   deposited by means of a scraper (13) or a brush (14).   8. Device for continuous casting between rolls, comprising two counter-rotating cylinders (1, 2) of parallel axes, defining between them a casting space (3), delimited by two lateral sealing walls (4), fixed and placed against the end surfaces (5) of the ends of the cylinders, and means (8) for depositing a lubricant on said front surfaces, characterized in that it comprises means (18, 19) for measuring one or more parameters representative of the friction or sealing conditions at the cylinder-closure wall interface, and means for adjusting the amount of lubricant supplied to said interface by   depending on the value of this or these parameters.   9. Device according to claim 8, characterized in that the adjusting means comprise a scraper (13) or a brush (14) associated with each of the front surfaces (5), and means for putting into operation or out service of the scraper or brush to remove the   lubricant present on said front surfaces.   10. 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 plan containing the axes of the cylinders.   11. 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 shutter wall, an accelerometer.