EP0692330B1 - Process and installation for continuous casting thin metallic products between rolls - Google Patents

Abstract

Molten metal is poured into a casting space bounded by the cylindrical surfaces of two counter-rotating rolls (1,1') and two lateral retaining walls (3), and a thin solidified prod. is extracted from this space. A measured thrust is exerted on the retaining walls (3) parallel to the roll axes, in order to press them against the roll faces (11). The drag on each retaining wall in the direction of the casting motion is measured. The measured values of thrust and drag are used to derive a quantity which is indicative of the friction conditions in the contact zone between the retaining walls and cylinder faces. This quantity is compared with a predetermined value, and the comparison result is used for control of casting parameters. <IMAGE>

Description

The present invention relates to the continuous casting of thin metallic products, in particular of thin steel strips, 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 lateral closure walls, 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 strip. thin. To contain the molten metal, the 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 therefore necessary to seal between the cylinders and the lateral closure walls. For this, these end walls are pressed against the ends of the cylinders and, to reduce the friction induced during the rotation of the cylinders, lubrication of the cylinder - end wall interface is usually provided, by adding a consumable lubricant or by use, at this interface, of a self-lubricating material.

• aux déformations géométriques des cylindres et des parois d'obturation, en particulier en début de coulée, provoquées par les dilatations des divers éléments de l'installation,
• aux efforts exercés sur ces éléments, notamment les efforts exercés sur les parois d'obturation, dans la direction des axes des cylindres, par le métal coulé, et qui tendent à écarter les dites parois d'obturation des cylindres,
• à l'usure des parois d'obturation, ou des chants des parois refroidis des cylindres, qui n'est pas toujours régulière sur toute la surface des zones en contact,
• aux éventuelles amorces d'infiltration de métal coulé entre paroi d'obturation et cylindre, qui tendent à les écarter l'une de l'autre.

However, the effective achievement of this seal and its conservation throughout the casting presents many difficulties, due in particular to:

• to the geometric deformations of the cylinders and of the closure walls, in particular at the start of casting, caused by the expansions of the various elements of the installation,
• to the forces exerted on these elements, in particular the forces exerted on the closure walls, in the direction of the axes of the cylinders, by the cast metal, and which tend to separate said closure walls from the cylinders,
• the wear of the sealing walls, or the edges of the cooled walls of the cylinders, which is not always regular over the entire surface of the areas in contact,
• to possible primers for the infiltration of metal poured between the closure wall and the cylinder, which tend to separate them from one another.

• réguler l'effort de pression des parois d'obturation contre le chant des cylindres pour le maintenir dans une fourchette de valeur donnée,
• réguler la position des parois d'obturation pour assurer un jeu minimal entre ces parois et les cylindres,
• mesurer ce jeu et réguler en conséquence l'effort de pression.

In an attempt to ensure this seal as well as possible, and to avoid infiltration of metal poured between the cylinders and the obturation walls, several methods are already known which consist respectively in:

• regulate the pressure force of the closure walls against the edge of the cylinders to keep it within a given value range,
• regulate the position of the closure walls to ensure minimum clearance between these walls and the cylinders,
• measure this play and regulate the pressure force accordingly.

None of these methods has proved satisfactory, or at least sufficient, to ensure sealing throughout the casting, since it is only possible to measure the resulting forces. acting on the closure wall, or a general position of this wall, without being able to take account of the forces or punctual games located on small areas of the interfaces.

It has also been proposed to solve this problem by causing controlled wear of the closure wall, by friction of the cylinders against it, and this throughout the casting. Thus, the aim is to constantly regenerate the shutter wall - cylinder interface, so as to best standardize the contact conditions over the entire surface of this interface. Thus, the document EP-A-546,206 describes a method according to which, before the start of the casting, the closure walls are strongly pressed against the rolls, in order to carry out a sort of running-in of the latter by abrasion by the edges of the cylinders, then this pressure is reduced and, during casting, we continue to move the closing walls towards the cylinders at a predetermined speed to continually ensure the continuation of voluntary wear and thus try to maintain regular contact over the entire surface of the interfaces.

However, this method does not take into account random variations in the contact conditions that may occur during casting, and leads to significant wear of the closure walls, even when the contact conditions are satisfactory and would not require causing such wear.

The documents JP-A-04224052 and JP-A-63248547 propose to take into account parameters reflecting the friction which is exerted between the cylinders and the obturation walls for the management of the application of the obturation walls or the lubrication of cylinder-shutter interfaces. However, the means proposed only make it possible to obtain an overall evaluation of the friction between a closure wall and the cylinders on which it rests.

The present invention therefore aims to solve the problems mentioned above and to improve the management of the contact between the closure walls and the cylinders, while avoiding significant wear of said closure walls. More particularly, the invention aims to improve knowledge of the actual state of contact between the closure walls and the cylinders, permanently during casting, in order to be able to act accordingly on the means for applying pressure and positioning of the closure walls against the cylinders.

With these objectives in view, the invention relates in particular to a process for the continuous casting of thin metallic products between two counter-rotating cylinders, according to which molten metal is poured into a casting space defined by the cylindrical walls of said cylinders and two lateral obturation walls and the solidified thin product is extracted in an extraction direction, there is exerted on said obturation walls a thrust force in a direction parallel to the axes of the cylinders, to apply them against the front ends of the walls cylindrical, and the said force is measured, characterized in that in order to evaluate the state of the contact between the closing walls and the cylindrical walls constantly during the casting, the driving forces exerted on each closing wall are measured according to the direction of extraction, this measurement being carried out for each closure wall at the level of each cylinder, and deduced from the measured values ées of the pressure and drive forces, a quantity representative of the friction conditions at each of the contact surfaces of the sealing walls - cylindrical walls, the value of said quantity is compared to a predetermined set value, and at least one casting parameter is adjusted as a function of the result of this comparison in order to bring this quantity back to the set value.

The method according to the invention therefore makes it possible to much better know the actual state of the contact between the closure walls and the cylinders, since it adds to the measurements, already known, of the thrust force exerted on said wall, and of its position, a measure of a quantity representative of the friction conditions, for example a coefficient of friction. This allows you to appreciate the variations in the friction of the surfaces in contact with respect to a reference, for example in the state before the introduction of the cast metal into the casting space. Knowledge of friction, in combination with that of the position of the closure wall and the thrust force exerted on it, makes it possible, for example, to assess a variation in the effective contact surface, which may be due to irregular wear of the refractory, to an infiltration of metal poured between cylinder and closure wall, or to a positioning of the latter not parallel to the front surface of a cylinder. We can also appreciate a possible insufficient lubrication. It therefore becomes possible to react, manually or automatically, to correct these faults, taking into account their causes, by acting on certain casting parameters, such as the thrust force on the closure wall, the position of that -this, or the cylinder clamping force, their speed, etc.

• deux cylindres ayant des axes de rotation parallèles et des parois cylindriques refroidies, disposés symétriquement par rapport à un plan médian d'extraction, et entraînés en rotation de sens contraire,
• deux parois d'obturation latérales disposées contre les extrémités frontales des dites parois cylindriques,
• des moyens de poussée pour appliquer les dites parois d'obturation contre les parois cylindriques avec un effort de poussée, et
• des moyens de mesure de l'effort de poussée,

   caractérisé en ce qu'il comprend des moyens de mesure de l'effort de frottement exercé sur chacune desdites parois d'obturation par chacun desdits cylindres lors de leur rotation.The subject of the invention is also a device for continuous casting between cylinders of thin metallic products, comprising:

• two cylinders having parallel axes of rotation and cooled cylindrical walls, arranged symmetrically with respect to a median plane of extraction, and driven in rotation in opposite directions,
• two lateral closure walls disposed against the front ends of said cylindrical walls,
• thrust means for applying said closure walls against the cylindrical walls with a thrust force, and
• means for measuring the thrust force,

characterized in that it comprises means for measuring the friction force exerted on each said closure walls by each of said cylinders during their rotation.

Preferably, the means for measuring the friction force comprise, for each closure wall, two force sensors for measuring the friction forces exerted on said closure wall by each of the cylinders. Thus, it is possible to further improve the knowledge of the state of the closure wall-cylinder contact, by separately assessing this state at the level of each cylinder.

According to a particular arrangement, the force sensors are situated respectively on either side of said median plane and the closure wall is supported, in the direction of extraction, only by two support means placed respectively towards the ends lateral of said wall, and said force sensors are located in said support means.

This arrangement allows a simple embodiment of the device, the said support means can for example be dynamometric axes fixed horizontally on the holding structure and adjusting the position of the closure wall, and on which said wall is simply hung.

Other characteristics and advantages will appear in the description which will be given by way of example of a device according to the invention, of continuous casting between cylinders of thin steel strips, and of its implementation.

• la figure 1 est une vue schématique partielle en coupe d'un dispositif de coulée,
• la figure 2 est une vue frontale de la paroi d'obturation et de son support.

Reference is made to the appended drawings in which:

• FIG. 1 is a partial schematic view in section of a casting device,
• Figure 2 is a front view of the closure wall and its support.

In the drawing of Figure 1, we see the end of one of the cylinders 1, 1 ', of the installation and a assembly 2 for applying a closure wall 3 against the edge 11 of the cylinders. This assembly 2 is itself supported, in a manner known per se, on a frame 4 of the casting installation.

The assembly 2 comprises a main carriage 5, guided in translation along the direction of the axes of the cylinders, on the frame 4. The movement of the principal carriage is controlled by a jack 6 which makes it possible to adjust the position of the assembly 2, and therefore the closure wall 3, relative to the cylinders 1, as well as applying the wall 3 against the edge of the cylinders with an adjustable force.

The main carriage 5 carries a secondary carriage 7 guided horizontally on said main carriage 5, and therefore movable transversely to the direction of the axes of the cylinders, by a jack shown schematically at 8, to adjust the transverse position of the closure wall 3 compared to the cylinders.

The secondary carriage has at its upper part two pins 9, 9 'which extend horizontally, in the direction of the axes of the cylinders, and are arranged symmetrically with respect to the longitudinal median plane P of the installation.

The closure wall 3, made of refractory material, is held on a support plate 10 comprising two ears 12 at its upper part.

Each of the ears has a bore 13, 13 ', which engages on a pin 9, 9'.

One of the pins 9 is engaged practically without play in the corresponding bore 13, while the other bore 13 'is produced in the form of a horizontal oblong hole, so as to allow differential expansion between the support plate 10 and the secondary carriage 7 without clamping the pins 9, 9 '.

Thus, the closure wall 3 and its support 10 are simply suspended on the pins 9, 9 ', which include means for measuring the forces exerted on them, transverse to their axes. In practice, the pins 9, 9 ′ constitute dynamometric axes, making it possible to measure the forces exerted on them by the support 10, these forces resulting from the weight of the support 10 and closure wall assembly, from the effect d 'drive down the wall 3 by the cast metal, and especially the friction of this wall against the edges of the cylinders, during their rotation.

Furthermore, the support 10 abuts by its rear face, in the direction of the axes of the cylinders, against other dynamometric axes 14, 14 ', 14' 'fixed on the secondary carriage 7, and which constitute measuring means of the horizontal force of application of the wall 3 against the cylinders. Two of these dynamometric axes 14, 14 'are arranged in the upper part of the assembly 2, on either side of the plane P, and the third dynamometric axis 14' 'is located towards the lower end of this assembly.

The support 10 therefore has three support zones, arranged in a triangle, and the various aforementioned dynamometric axes thus make it possible to evaluate the distribution of the thrust forces of the wall 3 against the cylinders, as much in the vertical direction (axes 9, 9 '), only in the horizontal direction (axes 14, 14', 14 ''). We can thus measure the value of the component of this thrust force relative to each cylinder separately, and by combining it with the value of the force measured by the dynamometric axis 9, 9 'located on the corresponding side, evaluate a coefficient specific friction at each of the shutter wall - cylinder interfaces.

• F_V1 la force verticale mesurée par l'axe dynamométrique 9,
• F_V2 la force verticale mesurée par l'axe dynamométrique 9',
• F_H1 la force horizontale mesurée par l'axe dynamométrique 14,
• F_H2 la force horizontale mesurée par l'axe dynamométrique 14',
• F_H3 la force horizontale mesurée par l'axe dynamométrique 14'',
• F_V la force verticale de friction exercée sur la paroi d'obturation et
• F_H la force d'application globale de la paroi contre les cylindres,

   on a $$\begin{array}{c}\begin{array}{c}{\text{F}}_{\text{V}}{\text{= F}}_{\text{V1}}{\text{+ F}}_{\text{V2}}\\ {\text{F}}_{\text{H}}{\text{= F}}_{\text{H1}}{\text{+ F}}_{\text{H2}}{\text{+ F}}_{\text{H3}}\text{.}\end{array}\end{array}$$

So if we call

• F _V1 the vertical force measured by the dynamometric axis 9,
• F _V2 the vertical force measured by the dynamometric axis 9 ',
• F _H1 the horizontal force measured by the dynamometric axis 14,
• F _H2 the horizontal force measured by the dynamometric axis 14 ',
• F _H3 the horizontal force measured by the dynamometric axis 14 '',
• F _V the vertical friction force exerted on the closure wall and
• F _H the overall application force of the wall against the cylinders,

we have $$\begin{array}{c}\begin{array}{c}{\text{F}}_{\text{V}}{\text{= F}}_{\text{V1}}{\text{+ F}}_{\text{V2}}\\ {\text{F}}_{\text{H}}{\text{= F}}_{\text{H1}}{\text{+ F}}_{\text{H2}}{\text{+ F}}_{\text{H3}}\text{.}\end{array}\end{array}$$

As F _H3 is the force of application of the closing wall, in the lower part of the wall, it can decompose into a force kF _H3 of application on the cylinder 1 and a force (1 - k) F _H3 of application on the other cylinder 1 ′, k varying from 0 to 1 depending on whether the bottom of the obturation wall rests only on one cylinder, only on the other, or on both at the same time, k representing the distribution of F _H3 between the two cylinders.

The comparison of F _H1 and kF _H3 to F _H2 and (1 - K) F _H3 gives an image of the states of application of the sealing wall against each of the cylinders. The orders of magnitude of the coefficients of friction of the obturation wall against each of the cylinders expressed $$\begin{array}{c}\begin{array}{c}\text{through}\frac{{\text{F}}_{\text{V1}}}{{\text{F}}_{\text{H1}}{\text{+ kF}}_{\text{H3}}}\text{for cylinder 1}\\ \text{and}\frac{{\text{F}}_{\text{V2}}}{{\text{F}}_{\text{H2}}{\text{+ (1-k) F}}_{\text{H3}}}\text{for cylinder 1 '}\end{array}\end{array}$$

The dynamometric axes 9, 9 ', 14, 14', 14 '' are connected to calculation and regulation means 15, which can either display data representative of these friction coefficients, to indicate possible anomalies to the operator and allow him to remedy them by acting on various parameters of the casting, either acting directly on these parameters, for example on the force of application of the wall 3 against the cylinders by acting on the supply pressure of the cylinder 6 or on the position of the wall with respect to the edge of the cylinders, by controlling an adequate movement of the said cylinder.

The device also includes position sensors 16, schematically represented in FIG. 2, for example placed at the level of the support 10, and preferably arranged in a triangle, like the dynamometric axes 14, 14 ', 14' '. These sensors make it possible to detect displacements of the support 10 of the wall 3, either with respect to a fixed reference, or with respect to the edges of the cylinders, or both, and this independently for the different zones of the obturation wall. .

These sensors thus make it possible to detect and evaluate either an overall displacement of the support in the direction of the axes, or an inclination of the wall relative to the normal reference plane, perpendicular to the axes of the cylinders. These displacements can be in the direction of a distance from the cylinders, which occurs for example if cast metal infiltrates between the wall 3 and the edge of a cylinder, and tends to spread them apart. These displacements can also be in the direction of an approximation towards the cylinders, for example following a wear of the refractory material of the wall 3, leading to a momentary reduction in the bearing force of this wall on the cylinder located in the side where the wear has occurred and a reaction in response from the jack 6 which moves the assembly 2 until said support force returns to a sufficient level.

In view of the above example, it will already have been understood the advantage of being able to simultaneously measure the position of the support of the wall 3 relative to a fixed mark, or directly the position of this wall relative to the cylinders, and the force corresponding to the pressure exerted by the wall 3 on one or other of the cylinders.

By adding a measurement of the vertical forces exerted during casting on said wall 3, it further improves the knowledge that one can have of the state of contact between wall and cylinder, and this also for each cylinder.

For example, at a constant bearing force of the wall on the edge of a cylinder, measured by one of the dynamometric axes 14, 14 ', 14' ', an increase in the vertical force measured by a dynamometric axis 9, 9 ', may be indicative of a lubrication defect.

By measuring the vertical forces and the bearing force of the wall 3, we can deduce a coefficient of friction at the interface between the wall and one of the cylinders, and therefore the horizontal component of the friction force which s '' adds to the spreading force of the cylinders generated by the cast metal, and by measuring the total clamping force of the cylinders, i.e. the force exerted to keep them at the right distance one of the other, we can deduce by difference the part of this force corresponding precisely to the force generated by the cast metal, which is an indicator of the solidification state of the cast product.

The combination of these different measures therefore makes it possible to obtain a great deal of additional information on the state of the wall-cylinder contact and to correct the parameters of the casting accordingly to maintain the casting installation in an optimal state, allowing that observed beginnings of degradation are quickly corrected and before these degradations become irremediable and cause the casting to stop.

In particular, it will be possible, either manually or automatically, to adjust the pressure force of the closure wall on the cylinders, or the position of this wall, as a function of the variations in friction coefficients detected.

To further improve the knowledge of the state of wall-cylinder contact, it is also possible to place a vibration sensor on the closure wall, or its support, an increase in detected vibrations also being indicative of a degradation of the state of this contact.

It should also be noted that, even if the closure wall and its support are not articulated with respect to the intermediate carriage or to assembly 2, the inevitable functional clearances in this assembly result in said wall and its support may undergo limited rotations from their general plane which is theoretically perpendicular to the axes of the cylinders. This also makes it possible to prevent a significant clearance being created for example between the wall and one of the cylinders, following a more pronounced wear on the side of this cylinder than on the other. For such a case, under the force of the thrust exerted by the jack 6, the wall 3 will be applied against the cylinders while being slightly oblique. An increased thrust force will then lead to an increase in friction preferentially on the side where the wear was less, and to a preponderant wear on this side, tending to bring the wall in a normal orientation of its general plane, precisely perpendicular to the axes of the axes. cylinders. The same effect could occur in the case where the wear is more pronounced downward than upward of the closure wall.

The invention is not limited to the particular arrangements of the devices, nor to the modes of implementation described previously by way of example.

In particular, the number and arrangement of the various force and / or displacement sensors can be modified without departing from the scope of the invention.

Claims (11)

1. Method for continuous casting of thin metal products between two counter-rotatory rolls, according to which molten metal is poured into a casting space defined by the cylindrical walls of the said rolls (1, 1'') and two lateral closure walls (3) and the solidified thin product is extracted in an extraction direction, a thrust force is exerted on the said closure walls in a direction parallel to the axes of the rolls, in order to apply them against the front ends (11) of the cylindrical walls, and the said force is measured, characterized in that, in order to evaluate the closure wall/cylindrical wall contact state continuously during casting, the drive forces exerted on each closure wall in the extraction direction are measured, this measurement being carried out for each closure wall at each roll, and a quantity, representative of the friction conditions at each of the closure wall/cylindrical wall contact surfaces is deduced from the measured values of the pressure forces and of the drive forces, the value of the said quantity is compared with a predetermined set-point value, and at least one casting parameter is adjusted as a function of the result of this comparison in order to return this quantity to the set-point value.
2. Method according to Claim 1, characterized in that the said pressure force is adjusted as a function of the values of the measured quantity representative of the friction conditions.
3. Method according to Claim 1, characterized in that the position of the closure wall is adjusted as a function of the values of the measured quantity representative of the friction conditions.
4. Method according to Claim 1, characterized in that the said quantity representative of the friction conditions is the coefficient of friction.
5. Device for continuous casting of thin metal products between rolls, including:

   - two rolls (1, 1') having parallel axes of rotation and cooled cylindrical walls, which rolls are arranged symmetrically with respect to a median extraction plane (P) and are driven in rotation in opposite senses,

   - two lateral closure walls (3) arranged against the front ends (11) of the said cylindrical walls,

   - thrust means (6) for applying the said closure walls against the cylindrical walls with a thrust force, and

   - means (14, 14', 14'') for measuring the thrust force, characterized in that it comprises means (9, 9') for measuring the friction force exerted on each of the said closure walls by each of the rolls during their rotation.
6. Device according to Claim 5, characterized in that the means for measuring the friction force include, for each closure wall, two force sensors (9, 9') for measuring the friction forces exerted on the said closure wall by each of the rolls.
7. Device according to Claim 6, characterized in that the force sensors (9, 9') are situated respectively on either side of the said median plane (P).
8. Device according to Claim 7, characterized in that the closure wall (3) is supported, in the extr action direction, only by two support means (9, 9') placed respectively towards the lateral ends of the said wall, and the said force sensors are situated in the said support means.
9. Device according to one of Claims 5 to 8, characterized in that it furthermore includes position sensors (16) for measuring the position of the closure walls (3) with respect to the front ends (11) of the cylindrical walls.
10. Device according to one of Claims 5 to 9, characterized in that each closure wall includes a vibration sensor.
11. Device according to one of Claims 5 to 10, characterized in that the means for measuring the thrust force include, for each closure wall, force sensors (14, 14') arranged on either side of the median plane (P) in order to measure the thrust force at each cylinder.

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