EP0004690A1 - Method and device for the continuous casting of metal - Google Patents

Abstract

In a continuous casting machine (1) having a molding cavity (8) delimited by a pair of movable belts (2, 3) and a pair of lateral dams (6, 7), the casting is controlled according to a signal which is created by subjecting a photosensitive element (23) to radiation transmitted to it by an optical system (17) housed outside the cavity (8) and aiming at the border between the cast metal (11) and the part, not covered by the metal (11), of one of the lateral dams (7). The sensitivity of the photosensitive element (23) is mainly in the visible spectrum and is low for infrared radiation.

Description

• - on coule le métal fondu à l'entrée d'une cavité de moulage délimitée par une courroie mobile inférieure, une courroie mobile supérieure et une paire de barrages latéraux refroidis, le métal solidifié sortant de cette cavité par une sortie,
• - on crée un signal fonction du niveau du métal fondu à l'entrée de ladite cavité, et
• - on contrôle la coulée en fonction de ce signal.

The present invention relates to a casting process. continues from a metal which

• the molten metal is poured at the entrance to a molding cavity delimited by a lower moving belt, an upper moving belt and a pair of cooled lateral dams, the solidified metal leaving this cavity by an outlet,
• a signal is created which is a function of the level of the molten metal at the entrance to said cavity, and
• - the casting is controlled as a function of this signal.

A continuous casting process of this kind is known according to French patent application No. 75-00243.

According to this known method, several signals are created which are functions of the level of the molten metal at the entrance to said cavity by means of heat detectors held against the moving belts.

It is therefore used, according to this known method, two series of heat detectors to create the signals and a necessarily complicated processing and control device, since it must process a relatively large number of signals.

The choice of this complicated and therefore costly solution results from the prejudice that it is impossible to determine by optical means the level of the molten metal bath with sufficient precision to allow effective and sufficiently precise control of the casting.

However, it has been found according to the present invention that a control of the casting on the basis of a signal created optically is feasible in practice, even in the method of the type determined above according to which the molten metal is cast in a mold cavity delimited by two belts and a pair of cooled side dams.

To this end, according to the invention, the above-mentioned signal is created by subjecting a photosensitive element to radiation transmitted to it by an optical system housed outside the cavity and targeting an area of one of the lateral barriers, this area being located on either side of the border between the cast metal and the part of this barrier not covered by the metal and the sensitivity of the photosensitive element being essentially in the visible spectrum and being low for infrared radiation.

The three conditions are necessary so that the signal created responds in a sufficiently faithful manner to the variations in the level of the liquid at the entrance of the cavity and can be of sufficient intensity to control the pouring so as to maintain said level between acceptable lower and upper limits.

If the sensitivity of the element is not mainly located in the visible spectrum and is not low for infrared radiation, the efficiency of the optoelectronic device is not sufficient, as will be demonstrated with respect to the example described below.

If the photosensitive element is not subjected to radiation through an optical system housed in outside the cavity but for example by means of a quartz rod housed at the very entrance of the molding cavity, this system, more particularly the quartz rod, is then necessarily close to the surface of the metal cast and a jet of molten metal entering the mold cavity; it is then easily soiled by metal splashes and thus becomes unfit for the transmission of radiation.

If the optical system does not target the area of one of the lateral barriers located on either side of the border between the cast metal and the part of this barrier not covered by the metal, the variations in signal intensity are too low to allow effective casting control based on this signal.

Indeed, the cavity is normally supplied by a set of two chutes having a fairly high inertia, which means that the control requires the detection of a relatively small change in the level of the metal poured into the cavity. This control is only reliable thanks to the discharge by the upper belt of the molten metal along the lateral dams at the entrance of the cavity. This backflow gives rise to greater changes in the coverage of the lateral dams by the molten metal than would be the case if one were only to take into account the rise and fall of the horizontal level of the molten metal.

This effect, combined with the fact that the difference in visible radiation emitted by the molten metal on the one hand and by the relatively cold lateral barrier on the other hand is significant, makes it possible to carry out a rigorous control of the casting based on a signal produced. by a photosensitive element which is under the influence of the radiation of a field located on the border of the molten metal and of the part of a side barrier not covered by. molten metal.

It should be noted that it is known to subject a photosensitive element, by means of an optical system housed outside a cavity and targeting a field situated on either side of the border between the surface of the metal. flow and a wall of the cavity, to a radiation produced in this field, this photosensitive element being capable of producing a signal as a function of the radiation and the control of the flow being made as a function of this signal. A control of this kind is known according to American patents No. 3,459,949 and No. 3,838,727. However, it follows from the text of American patent n ° 3,838,727 and from the publication "Modern technique - June 1976 - pages 44-47" describing the practical applications of the process according to American patent n ° 3,459,949. 'act of processes applying to the casting of steel in vertical molds with fixed walls. It is however not possible to apply without further means of controlling the casting according to these prior patents when the molding cavity is delimited by two movable walls and a pair of cooled side dams.

A controlled continuous casting of non-ferrous metals melted in a molding cavity delimited by movable walls is known according to the American patent n ° 2,246,907. On the one hand it is not a matter of pouring into a cavity of the kind determined above. On the other hand, the transmission of radiation to the photosensitive element takes place via a quartz rod, which has the disadvantage already described above.

The invention relates not only to the casting method determined above, but also to an apparatus for carrying out this method.

• - un moule essentiellement composé :
  • d'une première courroie sans fin mobile dont le brin supérieur constitue une surface porteuse pour la coulée,
  • - d'une seconde courroie sans fin mobile dont le brin inférieur constitue une surface délimitante supérieure pour la coulée, et
  • - de deux barrages latéraux, ces courroies et ces barrages latéraux déterminant une cavité de moulage présentant une entrée et une sortie,
• - de moyens de refroidissement des barrages latéraux,
• - un dispositif d'alimentation en métal fondu débouchant à l'entrée de la cavité de moulage,
• - un élément capable de produire un signal qui est fonction du niveau du métal fondu à l'entrée de la cavité, et
• - un moyen commandé par le signal et contrôlant la coulée.

The invention relates more particularly to a continuous metal casting apparatus comprising;

• - a mold essentially composed:
  • a first endless moving belt whose upper strand constitutes a load-bearing surface for casting,
  • - a second movable endless belt, the lower strand of which constitutes an upper delimiting surface for casting, and
  • - two lateral dams, these belts and these lateral dams determining a molding cavity having an inlet and an outlet,
• - means for cooling the side dams,
• a device for supplying molten metal opening at the entrance to the molding cavity,
• - an element capable of producing a signal which is a function of the level of the molten metal at the entrance to the cavity, and
• - a means controlled by the signal and controlling the pouring.

According to the invention the element capable of producing the signal is a photosensitive element capable of producing a signal which is a function of received radiation and whose sensitivity is essentially in the visible spectrum and is low for infrared radiation, a system optical system being housed outside the cavity and targeting an area of one of the lateral dams situated on either side of the border between the cast metal and the part of this dam not covered by the metal, this optical system transmitting the radiation received to the photosensitive element.

Other details and particularities of the invention will emerge from the description of a casting process continuous of a metal and an apparatus for its implementation according to the invention, given below by way of nonlimiting example and with reference to the accompanying drawings.

• FIG. 1 is an overall view of an apparatus according to the invention, showing part of a casting machine in operation, the feed device of this machine, an optoelectronic device detecting the level of the metal cast in this machine, and a level adjustment device associated with this detector device.
• Figure 2 is a plan view of part of the apparatus of Figure 1 showing the casting machine and the optoelectronic device.
• Figure 3 is a perspective view of the inlet end of the casting machine of Figure 1, made looking from a location above the level and obliquely opposite the inlet of this machine.
• FIG. 4 is an enlarged view of the part circled in dotted lines in FIG. 3.
• FIG. 5 represents on a larger scale a vertical section made along the axis of the opto-electronic device of FIG. 1.
• Figure 6 is a sectional view along line VI-VI of Figure 5.
• FIG. 7 is a sectional view along line VII-VII of FIG. 5.
• FIG. 8 is a sectional view along line VIII-VIII of FIG. 5.
• Figures 9, 10 and 11 show on a larger scale a detail of the image formed in the optoelectronic device of la.figure 5, when it is pointed in Figure 4, for different levels of the cast metal.
• FIG. 12 represents the image formed in the optoelectronic device of FIG. 5, when the metal is at its normal level.
• FIG. 13 represents a vertical section made along the axis of a variant of the optoelectronic device of FIG. 5.

FIG. 14 is a front view on a larger scale of a part of the device of FIG. 13.

In the different figures, the same reference notations designate identical elements.

The apparatus shown comprises a continuous casting machine 1 of the type with twin belts. Such a machine comprises an upper mobile endless belt 2 and a lower mobile endless belt 3.

The upper belt 2 is driven by rollers not shown in the direction of arrow 4, and the lower belt 3 in the direction of arrow. 5. Two endless mobile lateral barriers 6 and 7 are located partly between the lower strand of the upper belt 2 and the upper strand of the lower belt 3. Each of the lateral dams 6 and 7 consists of a large number of blocks of metal strung on an endless ribbon. These side dams 6 and 7 define with the upper belt 2 and with the lower belt 3 a cavity or molding area 8 between an inlet 9 and an outlet not shown, this molding area being inclined 15 ° downward from the inlet towards the exit. In this molding zone, the upper strand of the lower belt 3 constitutes a supporting surface for casting, and the lower strand of the upper belt 2, an upper delimiting surface for casting. The movement of the belts 2 and 3 causes that of the movable barriers 6 and 7. These movable dams therefore move with the belts 2 and 3 in the direction of the arrow 10 from the inlet 9 towards the not shown outlet of the molding zone 8. In this molding zone, the movable lateral barriers 6 and 7 are carried by the lower belt 3. These lateral dams return outside the molding zone 8 from the outlet (not shown) to the inlet 9.

Cooling of the molten metal in the molding zone 8 is carried out by spraying a coolant on the one hand on the belts 2 and 3, as described in American patents No. 3,036,348 and No. 3,041,686 , and on the other hand on the lateral dams 6 and 7, outside of the molding zone 8, as described in American patents n ° 3,865,176 and n ° 3,955,615. Each of the lateral dams 6 and 7 therefore constitutes a movable wall of the molding cavity 8, this movable wall being cooled before being brought into contact with the molten metal.

In the molding zone 8, the distance between the belts 2 and 3 is 6 cm and that between the lateral dams 6 and 7 is 12 cm.

Liquid copper 11, which is at a temperature of approximately 1120 ° C., is introduced into inlet 9 of the molding cavity 8 using a chute 12, which in turn is supplied with liquid copper 11 through the taphole 13 of the chute 14, the flow rate of which is adjusted using the stopper 15 During its passage through the molding cavity 8.of the machine 1, the liquid copper 11 gradually solidifies and leaves the not shown outlet of the machine 1 in the form of an endless bar with a cross section of 12 x 6 cm. We sink at a speed of about 13 meters per minute.

When looking into the inlet 9 of the casting machine 1 in operation, from a place located above the level and obliquely opposite the inlet so that one sees the submerged molding face of one of the two lateral dams 6 and 7 in the liquid copper 11, for example the molding face 16 of the lateral dam 7, it can be seen that the liquid copper 11, following its discharge by the upper belt 2, moves to the right along face 16 when the level of copper 11 rises, and to the left when the level drops, as shown in Figure 4, in which N denotes the normal level, L a level too low and H too high a level.

We now replace the human eye with the optoelectronic device 17. This is located about 4.5 meters from entrance 9, about 1.75 meters above the level of this entrance and 1 meter from the median plane X - X of the casting machine 1.

The optoelectronic device 17 comprises a tube 18 provided with a biconvex objective 19 having a focal distance of 650 mm and a tube 20 provided with a mat glass 21, a diaphragm 22, a photosensitive element 23 and a support 24 for the photosensitive element 23, this support having a guide groove 25.

The objective 19 is fixed at 26 and the mat glass 21 at 27. The tube 20 can slide in the tube 18 and be fixed there using the screw 28. The diaphragm 22, the photosensitive element 23 and its support 24 form an assembly 29, which can slide in the tube 20 and be fixed there using the screw 30. The tube 18 is fixed on a movable pointing support 31. On the mat glass 21 are drawn a rectangle 32 of 5 x 1 mm and two markers 33. In the diaphragm 22 is made a rectangular opening 34 of 5 x 1 mm, which coincides with the rectangle 32 of the mat glass 21, when the assembly 29 is fixed in the tube 20 against the mat glass 21 using the screw 30, the end of the latter being housed in the guide groove 25.

The device 17 is pointed at the part of the machine 1, which is surrounded by dotted lines in FIG. 3, so that the right half of the rectangle 32 is illuminated by the liquid copper 11 when it is at its normal level N , as shown in FIG. 9, in which 35 denotes the illuminated fraction of the rectangle 32, and 36 denotes the dark fraction, the latter corresponding to a part of the molding face 16 which is black. At this time, a lowering of the copper level below the N level will decrease the illuminated fraction of the rectangle 32 (Figure 10) and an increase in the level of. copper above level N will increase the illuminated fraction of rectangle 32 (figure 11).

To point the device 17, remove the assembly 29 and look at the mat glass 21, on which appears the reverse image of the targeted part of the machine 1. This image is brought into focus by sliding the tube 20 in the tube 18, and tube 20 is fixed when a clear image has been obtained. The tube 18 is then pointed so as to obtain the above-mentioned result, that is to say the image of Figure 12. To facilitate the pointing can be made two marks (not shown) on a fixed part (not shown) of the casting machine 1, with which must coincide the marks 33 of the mat glass 21 to ensure a clean pointing. Once the device 17 is properly pointed, the assembly 29 is replaced.

The photosensitive element 23 is a resistance to cadmium sulphide, which has a sensitive surface 37 of 5 × 1 mm coinciding with the rectangular opening 34 formed in the diaphragm 22; this diaphragm 22 serves to screen the light reflections on the mat glass 21. The resistance to CdS 23 has a maximum sensitivity between 500 and 650 nanometers, that is to say in the visible spectrum.

The CdS resistance 23 is connected by the wires 38 and 39 to the adjustment circuit 40. It is supplied via a series resistor 41 by a stabilized current source 42. Changes in resistance at 23 cause changes in the current I. The voltage across the resistor 41 therefore depends on the resistance changes at 23, that is to say the light intensity or the copper level. The voltage obtained across the resistor 41 is leveled a little using the capacitor 43 to eliminate the wave motion of the copper, and introduced into the regulator 44 of the PID type. This controls via the valves of the hydraulic system 45, the movement of the piston of the cylinder 46 which is connected to the stopper 15 by the rods 47 and 48. The cylinder 49 is a follower cylinder, which is mounted in series with the cylinder 46 This cylinder 49 is connected to a potentiometer 50, which returns the position of the cylinder 49 and therefore that of the cylinder 46 in the form of an electrical signal to the regulator 44.

In the apparatus described above, the opto-electronic device 17 has an efficiency of 70%, which means that if a current I of 100 units is measured when the copper level is raised to that the rectangle 32 is just fully illuminated, only a current I of 30 units is measured when the level of the copper is lowered until the rectangle 32 is just completely dark.

When the resistance to CdS 23 is replaced in the device described above by a photosensitive element of silicon, the sensitivity of which is essentially in the infrared (between 700 and 1000 nanometers), the efficiency of the optoelectronic device drops - notwithstanding the fact that the liquid copper is at a temperature of approximately 1120 ° C and the molding face 16 at a temperature of only approximately 130 ° C - at 20%, which no longer allows the casting to be regulated, given that 'at this moment the influence of disturbing signals of all kinds becomes too great.

A variant 51 of the optoelectronic device 17 comprises a cylindrical chamber 52, provided with a biconvex objective 53, a semi-transparent mirror in an inclined position 54, an eyepiece 55, a diaphragm 56 and a resistance to CdS 57. On the eyepiece 55 is drawn a rectangle 58 and in the diaphragm 56 is made a rectangular opening 59. The diaphragm 56 is housed so that its opening 59 receives via the lens 53 and the mirror 54, the radiation emitted by the target field through the objective 53, the mirror 54 and the rectangle 58 of the eyepiece 55.

This device 51 can be easily constructed from a conventional optical pyrometer. Indeed, we only have to modify the shape of the figure on the eyepiece and the opening in the diaphragm, this shape being round in a conventional optical pyrometer, and replacing the photosensitive element, the latter being particularly sensitive to infrared radiation in a conventional optical pyrometer.

It should be understood that the invention is in no way limited to the embodiment described above and that many modifications can be made without departing from the scope of this patent.

Thus, for example, the resistance to CdS 19 can be replaced by any photosensitive element (photoconductive element, photovoltaic element, photodiodes, etc.), which, optionally provided with a filter absorbing the infrared rays, reacts in substance only on visible light.

Instead of making the signal produced by the photosensitive element act on the device for supplying molten metal to the casting machine, this signal can also be made to act on the device controlling the rate of casting, that is to say the speed of the mold walls of the casting machine.

It should also be understood that the expression "cool the movable wall before bringing it into contact with the molten metal" covers both the action which consists in projecting a refrigerant fluid on the movable wall as well as the action which consists in making simply pass the movable wall through a relatively cold environment such as the ambient atmosphere.

Also, the movable side dams 6 and 7 can be replaced by stationary dams and provided inside with means allowing a coolant to circulate there.

Claims (7)

1. Process for the continuous casting of a metal according to which - the molten metal (11) is poured into the inlet (9) of a mold cavity (8) delimited by a lower moving belt (3), an upper moving belt (2) and a pair of cooled side dams ( 6 and 7), the solidified metal leaving this cavity (8) via an outlet, a signal is created which is a function of the level of the molten metal (11) at the input (9) of said cavity (8), and - the flow is controlled as a function of this signal, characterized in that the above-mentioned signal is created by subjecting a photosensitive element (23 or 57) to radiation transmitted to it by an optical system (17 or 51) housed outside the cavity and targeting an area of one of the aforementioned lateral dams, this area being located on either side of the border between the cast metal (11) and the part of this dam (7) not covered by the metal (11) and the sensitivity of the photosensitive element (23 or 57) being essentially in the visible spectrum and being low for infrared radiation. 2. Method according to claim 1, characterized in that molten metal is poured (11) whose temperature is less than about 1200 ° C. 3. Method according to claim 2, characterized in that molten copper is poured. 4. Continuous metal casting apparatus comprising: - a mold essentially composed: - a first movable endless belt (3) whose upper strand constitutes a load-bearing surface for casting, - a second mobile endless belt (2), the lower strand of which constitutes an upper delimiting surface for casting, and - two lateral dams (6 and 7), these belts (2 and 3) and these lateral dams (6 and 7) determining a molding cavity (8) having an inlet (9) and an outlet, - means for cooling the side dams (6 and 7), - a supply device (12, 13, 14, 15) of molten metal (11) opening at the inlet (9) of the molding cavity (8), - an element capable of producing a signal which is a function of the level of the molten metal (11) at the inlet (9) of the cavity (8), and - a means controlled by the signal and controlling the pouring,
characterized in that the element capable of producing the signal is a photosensitive element (23 or 57) capable of producing a signal which is a function of received radiation and whose sensitivity is essentially in the visible spectrum and is low for the infrared radiation, an optical system (17 or 51) being housed outside the cavity (8) and targeting an area of one of the lateral dams situated on either side of the border between the cast metal (11) and the part of this barrier (7) not covered by the metal (11), this optical system (17 or 51) transmitting the received radiation to the photosensitive element (23 or 57). 5. Apparatus according to the preceding claim, characterized in that the optical system (17) comprises a lens (19) forming an optical image on a mat glass (21) and a diaphragm (22) disposed between this glass (21) and the photosensitive element (23). 6. Apparatus according to the preceding claim, characterized in that the mold and the mat glass (21) include pins (33). 7. Apparatus according to claim 4, characterized in that the optical system (51) comprises a lens (53) and a pointing eyepiece (55), the lens (53) converging by. through an inclined semi-transparent mirror (54), housed between the objective (53) and the eyepiece (55), the radiation received by the optical system (51) on a diaphragm (56) disposed between this mirror (54) and the photosensitive element (57).

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