EP0564316A1 - Method for continuous casting - Google Patents

Abstract

The invention applies to continuous casting of steel in a mould with cooled walls, which is driven in oscillatory movement with travel h and frequency f, for producing a product leaving the mould at a casting speed Vc, the metal being topped with a lubricant forming liquid slag, the downward speed of the ingot mould being greater than the casting speed Vc during a crust-forming time tN. According to the invention, without altering the nature of the lubricant, it is possible to adjust the casting speed Vc over a wide range in order to adapt to specified casting conditions, by acting in combination on the travel and on the frequency of the oscillations as a function of the chosen casting speed, so that, whatever the casting speed Vc, the rate Q of consumption of the lubricant and the crust-forming time tN are each held at a substantially constant optimum value over the entire adjustment range of the speed. <IMAGE>

Description

The subject of the invention is a process for continuously casting a molten metal which in particular makes it possible to vary the casting speed.

The technique of continuously casting a ferrous metal, to obtain a product such as a billet, a bloom or a slab, has been known and used for a long time. Generally, a continuous casting installation comprises an ingot mold or shell, consisting of a bottomless mold limiting a cavity open at its two ends and whose walls are cooled vigorously so that the molten metal poured into it upper orifice of the mold forms, along the cooled walls, a solidified crust thick enough at the level of the lower orifice to allow the continuous evacuation of a product limited by said solidified crust and the central part of which remains liquid solidifies progressively in a so-called secondary cooling device placed below the mold and in which are placed, in addition, extraction means, for example, rollers driven in. rotation, which allow the product to be pulled down at an adjustable speed which depends on the casting conditions.

Generally, the mold has a substantially vertical axis and the secondary cooling device, which forms a corset for guiding the product, is curved so as to bring the horizontally cast product horizontally, which facilitates the evacuation of the product and its cutting into. sections of a certain length. Generally, the axis of the mold has a curvature corresponding to that of the guide corset to facilitate the change of direction of the product.

It is necessary to avoid adhesion of the metal on the cooled walls of the mold which could cause tearing of the solid crust and breakthroughs.

This is why, from the start of the development of the continuous casting technique, it has been proposed to oscillate the ingot mold parallel to its rectilinear or curved axis. AT For this purpose, various well known devices are used. Generally, the mold is removably fixed on a table which is guided and animated by oscillating movements, for example by means of levers connected to an oscillation system. The latter can be, for example, an eccentric system giving the mold a sinusoidal movement. More recently, however, other oscillation systems have been proposed, for example with hydraulic control, which give wider possibilities for adjusting the oscillation movement and, for example, allow a square type speed diagram to be produced. , jagged or otherwise.

However, to avoid sticking of the solidified crust on the cooled walls, it is also necessary to lubricate them with a product capable of interposing between the crust and the wall, to promote sliding and improve the quality. of surface.

For some time, powdered products have been used as a lubricant which are poured onto the meniscus formed by the liquid metal at the top of the mold and melt in contact with the metal. It is advantageous to use products which, in addition to their lubricating power, fulfill the functions of a slag such as the absorption of inclusions.

The liquid slag thus formed at the contact of the metal meniscus descends along the cooled walls of the mold, forming a thin film between the wall and the solidified crust.

This descent of the slag along the walls is favored by the cyclic movement of oscillation of the ingot mold which comprises, at each cycle, a phase of descent of the ingot mold and a phase of ascent in the opposite direction of the product which continues to descend. It has long been known that it is necessary to adjust the oscillation movement of the mold so that it reaches, at the end of the descent, a speed greater than the speed of extraction of the product, which makes it possible to create a negative sliding effect for a certain period called "negative stripping time" or "healing time". It has been observed, in fact, that the liquid slag interposed between the cooled wall and the solidified crust is compressed for the duration of the negative sliding and then decompresses, which promotes the infiltration of the lubricant.

This results, however, in the formation of wrinkles or oscillation marks on the faces of the cast product, the depth of which depends on the nature of the metal, but also on the casting conditions and, in particular, on the stroke and the frequency of the oscillations. as well as the duration of the negative slip.

Furthermore, the quality of the lubrication also depends on the nature of the slag, in particular its viscosity, the dimensions of the product poured and the speed of extraction.

To improve the surface quality of the cast product, we seek to minimize as much as possible the depth of the oscillation wrinkles and we can act, for this, on a large number of parameters depending, in particular, on the nature of the metal and casting conditions.

It is recognized, however, that essentially the healing time must be reduced and, for this purpose, fairly high frequencies are usually used in conjunction with a reduced stroke, which further allows the inertial forces to be minimized and the risk of vibration of the oscillation mechanism. However, the infiltration of the lubricant is thus reduced, which increases the danger of sticking.

For each type of metal, it is possible to determine, at least empirically, the nature of the slag, in particular its viscosity and the optimal consumption which will allow, for a normal extraction speed, and up to the desired maximum speed, '' ensure good lubrication of the mold.

However, the product extraction speed cannot be kept constant or even limited to a narrow range. In fact, this speed already depends on the cross section of the product, the products of small section such as billets being cast at speeds higher than the casting speed of certain larger products such as blooms or slabs, the ratio can be of the order of double or triple.

Furthermore, for the same product, it may be necessary, in modern installations, to vary the extraction speed widely. For example, it is known that the molten metal is brought from the steelworks into pockets which are placed in turn above the installation, the empty pocket being replaced by a full pocket. To avoid discontinuity in casting during the replacement time of a ladle, the steel is not poured directly into the mold, but into an intermediate container which acts as a buffer and, moreover, can distribute the steel in several neighboring lines. However, the replacement of an empty pocket by a full pocket can be carried out with a delay exceeding the capacities of the intermediate container and, in this case, it is necessary to reduce the flow rate of the metal poured into the ingot mold and, consequently, the extraction speed.

However, if the extraction speed is varied, it is necessary, however, to maintain good lubrication of the walls and to maintain an optimal healing rate. For this, it is possible to act on the amplitude and / or the frequency of the oscillations as a function of the casting speed. However, in conventional machines, in which the oscillation is produced by eccentric, it is, in general, difficult to adjust the amplitude of the oscillations and, in any case, this adjustment can only be done when the the machine. In practice, therefore, until now it was customary to act only on the frequency of the oscillations in order to adapt the speed of the mold to the speed of casting.

Often the frequency is simply a linear function of the casting speed. In the attached Figure, for example, the variations of the frequency as a function of the casting speed have been shown which make it possible to determine, for each speed, the frequency which should be given to the oscillations, the stroke of oscillation being kept constant over the entire speed adjustment range. In the example shown, which corresponds to a classic case, the constant oscillation stroke is 6.5 millimeters and the frequency is linearly linked to the speed by the relation f = 100 V _c .

The average speed of the ingot mold during a cycle being V _m = 2 hf, the stripping ratio commonly called "NSR" and which is equal to V _m / V _c = 2 hf / V _c a therefore, for a stroke of 6.5 millimeters, a value of 1.3, which corresponds to a case frequently found in the industry.

On the other hand, we know that, for a sinusoidal movement of the ingot mold, the healing time or negative stripping time is: $${\text{t}}_{\text{NOT}}\text{=}\frac{\text{60}}{\text{π f}}\text{. Arc cos}\frac{{\text{V}}_{\text{vs}}}{\text{π fh}}$$

Figure 1b is a diagram showing the variations in the healing time t _N as a function of the values given at the casting speed and taking into account the corresponding frequency indicated in Figure la. It can be seen that, for relatively high casting speeds, greater than 1 meter / minute, the healing time is quite low, around 0.1 seconds, which makes it possible to minimize the depth of the oscillation wrinkles, in particular for steel grades characterized by a "ferritic potential" of the order of 1 and which tend to deep wrinkles with the consequence of a risk of formation of transverse cracks.

We see, however, that the low t _N values correspond to high frequencies, which increases the danger of sticking by decreasing the infiltration of the lubricant with increasing tendency to stick at high casting speeds. It is therefore necessary to adapt the viscosity of the slag to the casting speed.

Thus, in the example shown in Figures 1a and 1b, a powder is advantageously used by melting a slag whose viscosity at 1300 ° is: η₁ = 1.5 poise.

As indicated in the diagram, it is thus possible to pour under good conditions products of relatively small dimensions, for example billets of section 150 x 150 millimeters at speeds which can vary between 1.2 and 1.8 m / min.

= 6,0 poises. On peut ainsi couler des produits de dimensions relativement élevées, par exemple des blooms de section 240 x 240 mm à des vitesses pouvant aller de 0,4 à 0,8 m/min. On voit cependant sur le diagramme que le temps de strippage peut alors varier de 0,25 à 0,5 sec environ.On the other hand, for lower speeds, it will be necessary to use another powder making it possible to obtain at 1300 °, for example, a slag of viscosity η $\genfrac{}{}{0ex}{}{\text{''}}{\text{1}}$

= 6.0 poises. It is thus possible to pour products of relatively large dimensions, for example blooms of 240 x 240 mm section at speeds which can range from 0.4 to 0.8 m / min. However, it can be seen from the diagram that the stripping time can then vary from approximately 0.25 to 0.5 sec.

Such a result is therefore not entirely satisfactory, and yet it has been obtained by varying the quality of the slag for two speed ranges which, moreover, are quite limited.

The object of the invention is therefore to remedy such drawbacks by means of a new continuous casting process making it possible to vary the casting speed over a much wider range with the same slag.

In accordance with the invention, the nature of the lubrication product and its optimum consumption rate are first of all determined as a function of the nature of the metal and of the normal casting conditions and, without modifying the nature of the lubrication product, the casting speed Vc over a wide range to adapt to casting conditions determined, by acting jointly on the stroke and on the frequency of the oscillations as a function of the casting speed chosen, so that, for each casting speed V _c , the consumption rate Q of the lubrication product and the time healing t _N do not differ significantly each from an optimal value valid over the entire speed adjustment range.

According to an essential characteristic of the invention, the stroke and the frequency of the oscillations are adjusted differently over two speed ranges covering the wide desired adjustment range, respectively a range of high speeds which descends from the maximum casting speed to a critical speed V ′ and in which the oscillation stroke is kept constant while the oscillation frequency is an increasing function of the casting speed, and a range of low speeds which goes from the critical speed to a minimum speed and in which the oscillation frequency is kept substantially constant while the oscillation stroke is an inverse function of the casting speed, said critical speed being the speed to which one can descend by keeping the frequency constant and keeping an acceptable slip ratio V _m / V _c , V _c being the casting speed at a given instant and V _m being l at average speed of the mold during the cycle corresponding to this instant.

Preferably, in the low speed range, the amplitude of the oscillations is an inverse linear function of the casting speed and in the high speed range, the oscillation frequency is a direct linear function of the casting speed.

Q

étant le débit de consommation de laitier en kg par m2 de section de la lingotière,

h

la course des oscillations en mètres

f

la fréquence des oscillations en nombre de cycles par minute (cpm)

V_c

la vitesse de coulée en m/min

η

la viscosité du laitier en poises, à 1300°C environ

A

une constante

m

un nombre compris entre 0 et 1.

According to another essential characteristic of the invention, over a range of adjustment of the casting speed V _{c which} can range from approximately 0.3 m / min to 7 m / min or more, the stroke and the frequency of the oscillations are linked to the nature and rate of consumption of the lubrication product by relation: $${\text{Q = A (hfV}}_{\text{vs}}{\text{.η)}}^{\text{- m}}$$

Q

being the flow rate of slag consumption in kg per m2 of section of the mold,

h

the course of the oscillations in meters

f

the frequency of the oscillations in number of cycles per minute (cpm)

V _c

casting speed in m / min

η

the viscosity of the slag in poises, at around 1300 ° C

AT

a constant

m

a number between 0 and 1.

Particularly advantageously, the constants A and m of the preceding relation have values of the order of 0.5.

dans laquelle D, C et a sont des valeurs constantes dépendant de la nature du métal et des conditions de coulée.According to another characteristic, in the low speed range, the oscillation stroke is related to the casting speed V _c by the relation: $${\text{h = - DV}}_{\text{vs}}{}^{\text{at}}\text{+ C}$$

in which D, C and a are constant values depending on the nature of the metal and the casting conditions.

Furthermore, it is preferable that in the range of high speeds, the frequency of the oscillations is adjusted as a function of the casting speed Vc so as to always remain greater than a minimum frequency f '= 680 V _c / 2h.

In a particularly advantageous embodiment, the mold is animated with triangular type oscillations and the healing time t _N is maintained at a constant optimal value over the entire range of adjustment of the casting speed.

Preferably, the rate of consumption of the lubrication product is maintained, over the entire range of adjustment of the casting speed, at a substantially constant value of the order of 0.3 kg per m2 of section of the mold.

In a particularly advantageous embodiment of a continuous casting installation for placing in implementing the method according to the invention, the ingot mold is associated with force measurement sensors emitting a signal used for instant optimization of the parameters in a closed and self-regulating control loop.

However, the invention will be better understood from the following description of a practical example illustrated by the appended drawings.

Figures 1a and 1b are, as already indicated, diagrams illustrating examples of conventional casting and indicating respectively, as a function of the casting speed, the stroke and the frequency of oscillation in Figure 1a and, on Figure 1b, the healing time and the slag consumption rate.

Figures 2a and 2b are diagrams illustrating a practical example of embodiment of the invention, and respectively indicating, as a function of the casting speed, the values of the stroke and the oscillation frequency in Figure 2a and, on Figure 2b, the values of the healing time and the slag consumption rate.

h étant la course d'oscillation en mètres, f la fréquence en cycles par minute, V_c la vitesse de coulée en mètre par minute et η la viscosité à 1300°C en poise.After evaluating a large number of industrial evaluations, it was possible to establish an approximate and empirical function between the consumption Q of lubrication product, expressed in kg per m2 of cross section and the essential parameters of casting, this function being of the form: $${\text{Q = A (hf V}}_{\text{vs}}{\text{.η)}}^{\text{- m}}$$

h being the oscillation stroke in meters, f the frequency in cycles per minute, V _c the casting speed in meters per minute and η the viscosity at 1300 ° C in poise.

The temperature of 1300 ° C corresponds to the characteristic surface temperature of mild steels, that is to say about 200 ° C below the Solidus. For more alloyed grades, an adaptation of the viscosity value to a lower characteristic temperature would be necessary.

• . h entre 0,002 et 0,020 m
• . f entre 20 et 400 cpm et, de préférence, 25 à 200 cpm
• . V_c entre 0,3 et 7,0 m/min
• . η entre 0,1 et 20 poises.

This function is essentially empirical but it has been established that it could, in practice, be applied to the following range of different parameters:

• . h between 0.002 and 0.020 m
• . f between 20 and 400 cpm and, preferably, 25 to 200 cpm
• . V _c between 0.3 and 7.0 m / min
• . η between 0.1 and 20 poises.

In the most classic cases, the constants A and m are of the order of 0.5.

On Figure 1b which corresponds, as we have seen, to examples of conventional casting, with constant stroke and linear increase in frequency as a function of speed, we have indicated, on the one hand, the variation of the time of negative stripping t _N and, on the other hand, the values of the consumption flow rate Q, for two kinds of slag employed having, respectively, a viscosity of 1.5 poise for the relatively high speeds corresponding to the casting of billets of dimensions 150 x 150 millimeters and a viscosity of 6 poises for relatively low speeds corresponding to the pouring of blooms of dimensions 240 x 240 millimeters.

It can be seen that, for the casting of billets at speeds ranging from 1.2 to 1.8 m / min, the negative stripping time remains between 0.1 and 0.2 sec and the consumption of slag varies between 0, 4 and 0.3 kg / m2.

However, it has been observed that the optimal value for the consumption of slag powder was of the order of 0.3 kg / m2, the optimal healing time being 0.1 sec. for steel grades with a "ferritic potential" of the order of 1.

Consequently, for products with small sections and high casting speeds, the surface quality can be maintained satisfactory, the stripping time and the slag consumption being close to optimal values.

On the other hand, it can be seen that, even using a slag of high viscosity, for example, of the order of 6 poises, the healing time and the consumption of slag vary more strongly and deviate appreciably from the optimum values for the speeds low. There is therefore a risk of obtaining a very questionable surface quality at low speeds, despite the use of a high viscosity slag powder.

It will be seen, on the other hand, that the method according to the invention gives a very great operating flexibility to a continuous casting installation because it allows the casting speed to be regulated over a wide range without changing the nature of the lubrication product and in keeping healing time and consumption of this product close to optimal values, even at low speeds.

In FIG. 2a, the variations of the oscillation stroke h and of the oscillation frequency f are represented as a function of the casting speed chosen, which may vary, in the example shown, between 0.3 and 2 m / min.

In the example shown, a slag of viscosity η₂ = 3.5 poises was chosen.

Pour une telle course d'oscillation, cette loi de variation de la fréquence conduit, pour une vitesse maximale de coulée de 2 m/min, à un rapport de glissement "N S R" = 0,68 qui permet d'assurer le strippage négatif nécessaire pour une bonne action du lubrifiant, cette action pouvant, par exemple, être surveillée au moyen de capteurs qui indiquent les efforts appliqués sur la lingotière, par exemple des pesons ou des jauges de contrôle.In a first range of high speeds, the oscillation stroke is maintained, as previously, at a constant value, for example 4 mm. On the other hand, the frequency is modified linearly as a function of the speed, according to the relationship: $${\text{f = 70 V}}_{\text{vs}}\text{+ 30.}$$

For such an oscillation stroke, this frequency variation law leads, for a maximum casting speed of 2 m / min, to a slip ratio "NSR" = 0.68 which ensures the necessary negative stripping for a good action of the lubricant, this action can, for example, be monitored by means of sensors which indicate the forces applied to the mold, for example scales or control gauges.

As shown in Figure 2a, the oscillation frequency is a direct function of the speed and therefore increases with it but, in the chosen law of variations, the frequency always remains greater than the value leading to a minimum "NSR" ratio of 0.68, the line representative of the variations of the frequency f being above the line f 'represented in dotted lines and which corresponds to the equation f = 680 V _c / 2h.

Generally, the oscillation frequency can be adjusted over a wide range, for example, from 20 to 400 cycles per minute. However, it is preferable not to exceed 200 cpm to promote the longevity of the oscillation system.

According to one of the characteristics of the invention, the casting speed can be reduced by keeping a constant oscillation stroke and by lowering the frequency in proportion to the speed over a whole range of high speeds going from the maximum speed to a critical speed V ′ which is the speed to which one can descend by keeping the oscillation stroke constant and by maintaining a slip ratio "NSR" = Vm / V _c acceptable and, in the case shown, of 0, 68, the critical speed V 'being of the order of 1 m / min.

On the other hand, if we want to descend into a range of speeds lower than the critical speed V ', we then maintain the frequency of oscillations at a constant value which corresponds to the critical speed V' and which is of the order of 100 cycles per minute and the oscillation stroke h is adjusted according to a linear inverse function of the speed, which means that the oscillation stroke h increases in proportion to the lowering of the casting speed V _c .

dans laquelle D, C et a sont des valeurs constantes dépendant de la nature du métal et des conditions de coulée.Preferably, the oscillation stroke h is linked to the casting speed V _c , in the low range, by a relation of shape : $${\text{h = ± DV}}_{\text{vs}}{}^{\text{at}}\text{+ C}$$

in which D, C and a are constant values depending on the nature of the metal and the casting conditions.

In the case of casting shown in Figure 2a, we have seen that h is a linear function of V _c , a being therefore equal to 1.

Thus, by using the same slag of viscosity 3.5 poises, it was possible to pour products of different sections and in two speed ranges, respectively billets of section 150 x 150 millimeters over a range of speeds going from 1.2 to 1.8 m / min and blooms of 240 x 240 mm section on a speed range from 0.4 to 0.8 m / min.

We can thus compare the advantages provided by the invention compared to the classic example shown in Figures 1a and 1b.

It has already been indicated that an essential advantage lies in the use of the same slag of medium viscosity whereas, in the previous case, a slag of low viscosity was used for the billets and a slag of high viscosity for the blooms. This advantage is particularly important when it is desired to vary the section of the cast product, during casting, a change of slag then being very difficult.

Furthermore, the curve representing the variations in the healing time t _N has been indicated in FIG. 2b and it can be seen that it remains below the optimal value 0.1 sec over the whole range of high speeds and that, if it reaches higher values for low speeds, these values remain around 0.25 sec, which is very acceptable and much less than the healing time observed in Figure 1b.

But, on Figure 2b which also shows the representative curves of the consumption of Dairy Q, we see, in moreover, that, in both cases, the curves are substantially horizontal and that consumption Q is maintained over the entire speed range at a practically constant value and of the order of optimal consumption of 0.3 kg per m2. This possibility of maintaining consumption is also an important advantage of the invention.

It can therefore be seen that, without changing the nature of the slag, the invention makes it possible to vary the speed over a very wide range while maintaining the negative stripping time and the consumption of slag at values close to their optimal value, which allows ensure excellent surface quality.

To achieve, according to the invention, the adjustment of the oscillation stroke as a function of the speed, it is advantageous to control the oscillations of the ingot mold by means of a hydraulic drive system described, for example, in the patent French 86.03282 filed March 7, 1986 by the same Company or in document EP-A-0325.931. Such a system makes it possible, in fact, to very easily carry out a change of stroke during casting.

Furthermore, the curve t _N indicated above and shown in Figure 2b corresponds to the classic case of sinusoidal oscillations, but a hydraulic oscillation control system allows the shape of the speed variation diagram to be easily modified and oscillations to be carried out. rectangular or triangular.

In this case, the healing time can be set, over the entire speed setting range, to a constant value t ' _N equal to the optimal value of 0.1 / sec as shown in Figure 2b .

It can be seen that this advantage is particularly significant in the case of low speeds since it makes it possible to further reduce the healing time to the optimal value. However, the use of triangular oscillations is also interesting in the case of high speeds. Indeed, in the example shown where we start, for the critical speed V ′ = 1 m / min, of an oscillation frequency of 100 cpm, which corresponds to a total duration of the cycle of 0.6 sec, the ascent time of the ingot mold which is equal to t _P = t _c - t _N and which is 0.5 sec for the critical speed of 1 m / min, can be gradually reduced according to the increase in speed and the concomitant increase in frequency according to the law F = 70 V _c + 30, since t _N remains equal to the optimal value 0.1 sec.

Thus, over the high speed range, the time for the ingot mold to rise relative to the product can drop from 0.5 to 0.25 sec when the casting speed goes from 1 to 2 m / min.

It can be seen that the oscillation parameters can be perfectly adapted to the needs of surface quality and this way of operating decreases the vibrations and increases the longevity of the oscillation system.

The invention can therefore be applied, in general, to any continuous casting installation allowing adjustment of the oscillation stroke during casting and it is particularly advantageous in the case of triangular oscillations making it possible to produce a constant and optimal healing time.

Such a casting installation will preferably be equipped with sensors making it possible to measure the forces applied to the ingot mold and the signal of which can be used for instant optimization of the parameters in a closed and self-regulating control loop.

Of course, the invention is not only limited to the single embodiment which has just been described in detail and, depending on the nature of the steel and the casting conditions, it would be possible to cover other ranges of casting speed, using a slag of different viscosity.

In addition, provision has been made for the casting of billets for the range of high speeds and blooms for the range of low speeds, but the principles of the invention are applicable to all product sections, for example to the casting of slabs whose section can be varied during casting.

The reference signs, inserted after the technical characteristics mentioned in the claims, have the sole purpose of facilitating the understanding of the latter and in no way limit their scope.

Claims (14)

Process for the continuous casting of a molten metal in an ingot mold consisting of a bottomless mold with cooled walls and a substantially vertical axis, driven by oscillating movements over a stroke (h), parallel to the axis and to a frequency (f), for producing a product leaving the mold at a casting speed (V _c ), the metal being surmounted, in the ingot mold, by a fusible product in contact with it for the formation of a liquid slag capable of lubricating the cooled walls, the oscillations of the ingot mold being adjusted so that, during each oscillation cycle of duration (t _c ), the speed of the ingot mold down is greater than the casting speed (V _c ) during a healing time (t _N ), said casting speed (V _c ) being able to be modified to adapt to the casting conditions,
characterized by the fact that the nature of the lubrication product and its optimum consumption rate are determined first of all as a function of the nature of the metal and of the normal casting conditions and that, without modifying the nature of the lubrication product, the casting speed (V _c ) is _adjusted over a wide range to adapt to determined casting conditions, acting jointly on the stroke and on the frequency of the oscillations as a function of the chosen casting speed, such so that, for each casting speed (V _c ), the flow rate (Q) of consumption of the lubrication product and the healing time (t _N ) do not differ significantly, each of an optimal value valid over the entire speed setting range. Continuous casting method according to claim 1, characterized in that the stroke and the frequency of the oscillations are adjusted differently on two speed ranges covering the wide desired adjustment range, respectively a range of high speeds which descends from the maximum speed to 'at a critical speed (V') and in which the oscillation stroke is kept constant then that the oscillation frequency is an increasing function of the casting speed, and a range of low speeds which goes from the critical speed to a minimum speed and in which the oscillation frequency is kept substantially constant while the amplitude of the oscillations is a decreasing function of the casting speed, said critical speed being the speed to which one can descend by keeping the amplitude of oscillations constant and by maintaining an acceptable slip ratio (V _m / V _c ) , (V _c ) being the casting speed at a given instant and (V _m ) the average speed of the ingot mold during the cycle corresponding to this instant. Continuous casting method according to claim 2, characterized in that, in the range of low speeds, the oscillation stroke is an inverse linear function of the casting speed. Continuous casting method according to claim 2, characterized in that, in the range of high speeds, the frequency of the oscillations is a direct linear function of the casting speed. Continuous casting process according to one of Claims 1 to 4, characterized in that, over a setting range of the casting speed (V _c ) which can range from approximately 0.3 m / min to 7 m / min or more, the stroke and the oscillation frequency are linked to the nature and the rate of consumption of the lubrication product by the relation: $${\text{Q = (A) (hf Vc. Η)}}^{\text{- m}}$$

Q being the rate of slag consumption in kg per m2 of section of the ingot mold h the oscillation stroke in meters f the frequency of the oscillations in number of cycles per minute (cpm) V _c the casting speed in m / min η the viscosity of the slag in poises, at around 1300 ° C At a constant m a number between 0 and 1. Continuous casting method according to claim 5, characterized in that (A) and (m) have values of the order of 0.5. Continuous casting process according to one of the preceding claims, characterized in that, in the range of low speeds, the oscillation stroke (h) is related to the casting speed (V _c ) by a relation: $${\text{(h) = ± D. (V}}_{\text{vs}}{\text{)}}^{\text{at}}\text{+ C}$$

in which (D), (C) and (a) are constant values depending on the nature of the metal and the casting conditions. Continuous casting method according to one of the preceding claims, characterized in that, in the range of high speeds, the frequency of the oscillations is adjusted as a function of the casting speed Vc so as to always remain greater than a minimum frequency f '= 680 (V _c / 2h). Continuous casting method according to one of the preceding claims, characterized in that the ingot mold is provided with triangular oscillations and that the healing time t _N is maintained at a constant optimum value over the entire adjustment range of the casting speed. Continuous casting method according to one of the preceding claims, characterized in that the rate of consumption of the lubrication product is maintained, over the entire adjustment range of the casting speed Vc at a substantially constant speed of the order of 0.3 kg per m2 of section of the mold. Continuous casting method according to one of the preceding claims, characterized in that the oscillation frequency can range from 20 to 400 cycles per minute. Continuous casting method according to claim 11, characterized in that the oscillation frequency does not exceed 200 cycles per minute. Continuous casting method according to one of the preceding claims, characterized in that the healing time is maintained over the entire speed adjustment range at a substantially constant value of the order of 0.1 sec. for steel grades with a ferritic potential of the order of 1. Continuous casting method according to one of the preceding claims, characterized in that the ingot mold is associated with force measurement sensors emitting a signal used for instant optimization of the parameters in a closed and self-regulating control strip.

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