US3741277A - Process for continuously operating a continuous casting plant - Google Patents

Abstract

The invention relates to a process for continuous continuous casting of liquid metals wherein a series of melts are cast from ladles into an exchangeable tundish wherefrom the metal runs into a water-cooled mould via a casting tube extending into said mould. The tundish exchange is carried out by removing the worn tundish from casting position, moving a new, empty tundish above the mould in a manner that its casting tube extends in to the mould, driving a ladle containing hot liquid metal above the tundish and filling the new tundish when it is in casting position. While the tundish is being exchanged the casting level in the mould is lowered to a position below the outflow opening of the casting tube and is kept there until metal runs from the new tundish into the mould. This is preferably achieved by reducing the drawing out speed of the cast bar. By using an empty tundish it becomes possible to exchange the tundishes immediately. Furthermore, the yields and operational safety are greatly increased by the invention.

Description

United States Patent [191 Bachner et al.

[ June 26, 1973 [75] Inventors: Ernst Bachner; Walter Fortner, both of Linz, Austria [73] Assignee: Vereinigte Osterreichische Eisenund Stahlwerke Aktiengesellschaft, Linz, Austria [22] Filed: Dec. 13, 1971 [21] Appl. No.: 207,481

[30] Foreign Application Priority Data Soeda et al. 164/82 Primary Ezgq mine r-Robert D. Baldwin Attorney-Granville M. Brumbaugh, Arthur S. Tenser [5 7] ABSTRACT The invention relates to a process for continuous continuous casting of liquid metals wherein a series of melts are cast from ladies into an exchangeable tundish wherefrom the metal runs into a water-cooled mould via a casting tube extending into said mould. The tundish exchange is carried out by removing the worn tundish from casting position, moving a new, empty tundish above the mould in a manner that its casting tube extends in to the mould, driving a ladle containing hot liquid metal above the tundish and filling the new tundish when it is in casting position. While the tundish is being exchanged the casting level in the mould is lowered to a position below the outflow opening of the casting tube and is kept there until metal runsfrom the new tundish into the mould. This is preferably achieved by reducing the drawing out speed of the cast bar. By using an empty tundish it becomes possible to exchange the tundishes immediately. Furthermore, the yields and operational safety are greatly increased by the invention.

4 Claims, 3 Drawing Figures PAIENIED JUN 2 6 I975 F'IG.3

' FIG? E. i m vw PROCESS FOR CONTINUOUSLY OPERATING A CONTINUOUS CASTING PLANT The invention relates to a process for continuous casting of hot liquid metals, in particular steel, wherein a number of melts are successively cast from ladies into a tundish whence the metal is permitted to run into a water-cooled mould via a casting tube extending into it, whereupon the cast bar still having a liquid core is drawn out and further cooled in a secondary cooling zone, the tundish being exchangeable.

The patent and technical literature contains numerous proposals dealing with continuous continuous casting, which term refers to a method for casting a bar of indefinite length from any desired number of casting ladles, the tundish (distributor) being exchangeable as often as desired according to need. A plant destined for continuous continuous casting is described e.g., in the British Pat. specification No. l 212 918 and US. Pat. No. 3 552 902. This plant comprises two bearing arms each of which is rotatable around a vertical axis and carries a casting ladle, and at least one exchangeable tundish, both bearing arms independently of each other being rotatable from an initial position, the ladle feed position, into opposite directions to two operating positions; the tundish or the tundishes are likewise rotatable, namely from a resting position to the casting position. This arrangement is to enable continuous casting without interruption, even if disturbances should occur at one tundish, as e.g., at a stopper or outflow; in this case a tundish which is filled with hot liquid metal and ready for casting has to be brought without delay into casting position. Operation experience has shown that the metal supply to the mould must not be interrupted for longer than 30 seconds up to a maximum of 60 seconds when one tundish is exchanged for other. Because of the fact that casting tubes are used which are fixed to the tundishes and have to extend below the casting level in the mould, it is necessary to design the tundishes to be liftable and lowerable. When a tundish is exchanged, at first the ladle has to be removed from its operation position, then the tundish to be exchanged has to be lifted to a height at which the bottom margin of the casting tube lies above the upper margin of the mould, then the tundish to be exchanged has to be removed, the new tundish filled with liquid metal has to be lifted, moved into position above the mould'and then it has to be lowered into operation position, whereupon the metal supply into the mould may be resumed.

Obviously, this relatively complicated method is not free from disturbances, in particular because the steel tends to freeze although the refractory lining of the new tundish is pre-heated to a temperature of about l,0O C. As is well known, the steel is relatively cool in the lowermost zone of a casting ladle; it cools further off,

- when the tundish is being filled, within a short period,

because the temperature of the refractory lining of the tundish is about 500 C lower than that of the steel. The waiting time amounts to at least 1.5 min. until the tundish is filled and casting thus may be continued. Owing to these difficulties it is not surprising that until today it has not been possible to carry out a continuous continuous casting operation over an unlimited period of time, nor is it surprising that productivity and yields are rather low in the customary continuous casting plants. The invention is aimed at avoiding the described difficulties and at increasing operational safety in the exchange of the tundishes. In a process of the kind defined in the introduction the invention resides in that in an exchange of the tundish the tundish is moved away from the casting position and a new, empty tundish is positioned above the mould in a manner that its casting tube extends into the mould, whereupon a ladle containing hot liquid metal is moved above the tundish and the tundish is filled, wherein, when the new tundish is being brought into position, the casting level in the mould is brought to a position below the outflow opening of the casting tube and is kept so long in this position until the metal runs from the new tundish into the mould, whereupon the casting level in the mould is lifted again. I

Since, according to the invention, an empty tundish has to be used for the exchange, the outflow opening of the casting tube has to be kept free from liquid steel in the mould, until steel is delivered from the ladle into the tundish; this, however, is only possible when the tundish is sufflciently lowered, i.e., so far that the casting ladle may be brought into its operation position above the tundish. If the casting level were not lowered during the exchange, liquid steel would enter through the outflow opening into the casting tube and freeze there; then it would not be possible to continue casting.

According to a further feature of the invention for effecting the temporary change of the position of the casting level in the mould the drawing out speed of the cast bar is reduced and after the exchange of the. tundish increased again, a uniform drawing out speed of 0.1 to 0.2 'm./min. being preferably maintained while the tundish is being exchanged independently from the original drawing out speed and from the other casting conditions.

In order that the invention may be more fully understood details and advantages of the invention shall now be explained with reference to the accompanying schematical drawing.

FIG. 1 is a lateral view of the upper part of a continuous casting plant, partly in section; it shows how the metal is supplied to the mould.

. FIGS. 2 and 3 show the changes of the casting level in the mould during and after the exchange of a tundish.

In FIG. 1 numeral 1 denotes a stopper ladle, which is horizontally displaceable in direction of the double arrow; the ladle may be moved either on a bearing arm which is rotatable around a vertical rotation axis or on a carriage displaceable on a straight or circular path. Numeral 2 denotes a liftable, lowerable and horizontally displaceable tundish below the ladle 1, which is provided with a casting tube 3 having several outflow openings 4 spaced around the circumference of its lower end. The casting tube may be closed by a stopper (not shown) in customary manner, by means of which the metal supply into the mould can be controlled. Numeral 5 refers to a water-cooled continuous casting mould which oscillates in vertical direction, and from which a cast bar 6 with a solidified bar shell 7 and a liquid core 8 is drawn out; FIG. 1 does not show the device joined to the mould for guiding and drawing out the bar in which the bar is cooled until it is completely solidified, nor does it show the separating means by which it is severed into pieces. Numerals 9,10, l 1,12,13 denote horizontal planes; plane 9 is laid through the casting level of the liquid metal in the mould 5 in a position maintained during normal operation, i.e., when the tundish is not being exchanged, plane 10 is laid through the upper margin of the mould, plane 1 l is laid through the bottom margin of the casting tube 3 when the tundish is in normal operation position, plane 12 is laid through the bottom margin of the stopper ladle 1, and plane 13 is laid through the upper margin of the tundish 2 when it is in normal operation position. As a rule, the level difference between the planes 10 and 9 amounts to 50 mm and the level difference between planes 9 and 11 to from 100 mm to 150 mm, i.e., the outflow openings 4 lie below the casting level 9. The casting tube 3 is closed at its lower end and its outflow openings 4 are downwardly slanting by an angle of 25 to the horizontal line. The outflow openings 4 may also extend horizontally, or slant in upward direction. The distance between the planes 12 and 13 is kept as small as possible during operation, because otherwise, owing to the great fall height of the metal stream running from the stopper ladle 1, an undesired oxidation would take place as a result of the influence of the air as well as a strong erosion of the refractory lining of the tundish 2. Numeral 14 denotes a tundish which is in the reserve position; it has a casting tube 3' and outflow openings 4'; the stand-by tundish is, like the tundish 2, liftable, lowerable and horizontally displaceable in direction of the double arrows. The tundishes 2, 14 are movable by means of devices, not shown, e.g., rotatable arms or carriages. The empty tundish is in pre-heated condition and ready for being exchanged against the tundish 2. For this purpose the tundish 14 must be arranged above the mould sufficiently high so that the horizontal plane 15 laid through the lower margin of the casting tube 3' lies above the plane of the upper margin of the mould. The maximum lifting height of the tundish corresponds to the level difference between the planes l5 and 11 and in the present case amounts to 400 mm. The horizontal plane 16 laid through the upper margin of the tundish 14 lies above the plane 12, i.e., the casting ladle 1 cannot be moved above the tundish 14 in reserve position. When the tundishes are to be exchanged, at first the stopper ladle 1 is moved to the left from its operating position into a waiting position and then the tundish 2 is removed from its operating position; in doing so, it is not absolutely necessary, to lift the tundish 2 prior to the horizontal displacement perhaps to the levels or 16, respectively, but it is possible to break off the casting tube 3 which at this stage is already greatly worn, during the horizontal displacement and to remove later the broken piece from the mould hollow space.

As soon as the tundish 2 is removed, the casting level 9 is lowered by 100 to 150 mm to the position 17(FlG. 2). For this purpose, as soon as the tundish 2 is removed, preferably the drawing out speed of the cast bar which originally amounted to about 1.0 m./min. is reduced to 0.1 m./min.; the casting level thus sinks slowly, while the tundish 14 is brought into position above the mould 5 and then lowered. The tundish 14 is lowered at first only so far that the casting ladle 1 or a second casting ladle, not shown, may be moved above the tundish l4 and filling of the tundish may be started (FIG. 2). Providing for the plane through the bottom margin of the casting tube 3' to lie somewhat above the plane 17, as shown at 18, or 70 to 120 mm below the plane 9, will suffice. As soon as the steel issues from the openings 4' the tundish is lowered into the final operation position, in which the bottom margin of the casting tube 3 reaches plane 11 (FIG. 3). In this position, the casting tube 3 penetrates a layer of casting powder 19 on the casting level. The casting powder prevents the steel from solidifying while the metal supply to the mould is interrupted. As soon as the original position 9 of the casting level is reached again, the continuous casting drawing out speed is increased again to about 1.0 m./min. at which point the exchange of the tundish is completed. It is also possible to lower the casting level during the exchange of the tundish without altering the drawing out speed and then interrupt drawing out of the bar until the original casting level is reached again.

When the process according to the invention is applied on industrial scale, it does not lead to any casting disturbances within the continuous casting machine; the temporary lowering of the casting level by to mm in a continuous casting mould of 700 mm height does not cause a break-through of the continuous bar shell 7 below the mould 5. The connection of the liquid metal supplied after the temporary interruption of the metal supply to the mould with the liquid core 8 is uniform over the total bar cross section. Suitably an exchange of the tundish is carried out when a predetermined length of a bar section is reached; in other words: when the bar is severed, the separation cut is carried out in the area of connection where the metal coming from the old and new tundishes meet, which area may be discerned from the outside of the bar by a so-called set-off, which ordinarily occurs at any interruption of the metal supply to themould.

It is not absolutely necessary to lower the casting level until below the bottom margin of the casting tube, but it suffices to lower the casting level until below the bottom margin of the outflow openings 4'; it is essential that the casting tube 3 does not immerse so deep into the liquid core 8 that steel penetrates into the hollow space of the casting tube 3' and solidifies there, which would make it impossible to continue casting.

By applying the invention it is possible to cast absolutely free from disturbances an unlimited number of melts absolutely continuously to a single bar. Until now it was necessary to accept an interruption in casting of 30 to 60 minutes after each melt or at least after a small number of melts, in order to prepare the continuous casting machines for new casting so that the output performance of the continuous casting plant remained relatively poor. The yields which decrease in an undesirable manner with rising numbers of completely dead periods are increased when the invention is employed.

The fact that in the process according to the invention an empty tundish may be utilized in the tundish exchange apart from avoiding the disadvantages described in the introduction affords the additional advantage that the tundish may immediately be exchanged also if casting disturbances should occur suddenly, e.g., in case of a casting tube failure; in such a case, if necessary, also a tundish may be used that is not completely preheated because the metal gets from the casting ladle into the mould within the shortest period and thus cannot freeze in the tundish. In the operation method so far employed, in which a filled tundish was used, it was impossible to exchange the tundishes quickly, because the preparation time, that is the time used for filling and manipulation, was too long.

What is claimed is:

1. A process for continuously operating a continuous casting plant for hot liquid metals including steel, comprising casting a plurality of melts successively from ladles into exchangeable tundishes placed in a casting position in which the metal is permitted to run into a water-cooled continuous mould via respective tundish casting tubes extending into said mould and having at least one outflow opening submersed below casting level to form a cast bar,

drawing out the cast bar still having a liquid core,

and further cooling said bar in a secondary cooling zone,

intermediate exchanges of said tundishes being effected while continuous casting is carried on by the steps of moving a ladle from its operating position to a second position,

moving a first tundish away from casting position,

lowering the casting level in said mould to a position below said at least one outflow opening of a new empty tundish casting tube, and simultaneously positioning the new, empty tundish above said mould in a manner that its casting tube extends into the mould,

placing a ladle containing hot liquid metal above said new tundish and initiate filling of said new tundish, lowering said new tundish into its final operating position when the metal begins to run from said new tundish into said mould, and permitting the casting level in said mould to rise to an operating level.

2. The process set forth in claim 1, wherein lowering I independently from the drawing out speed originally applied and from other casting conditions.

3. The process set forth in claim 1, wherein the casting level is permitted to rise again by interrupting the drawing out of the cast bar.

I 4. The process set forth in claim 1, wherein said first tundish is removed from casting position by horizontal displacement only breaking off its casting tube against the inner mold wall.

Claims (4)

1. A process for continuously operating a continuous casting plant for hot liquid metals including steel, comprising casting a plurality of melts successively from ladles into exchangeable tundishes placed in a casting position in which the metal is permitted to run into a water-cooled continuous mould via respective tundish casting tubes extending into said mould and having at least one outflow opening submersed below casting level to form a cast bar, drawing out the cast bar still having a liquid core, and further cooling said bar in a secondary cooling zone, intermediate exchanges of said tundishes being effected while continuous casting is carried on by the steps of moving a ladle from its operating position to a second position, moving a first tundish away from casting position, lowering the casting level in said mould to a position below said at least one outflow opening of a new empty tundish casting tube, and simultaneously positioning the new, empty tundish above said mould in a manner that its casting tube extends into the mould, placing a ladle containing hot liquid metal above said new tundish and initiate filling of said new tundish, lowering said new tundish into its final operating position when the metal begins to run from said new tundish into said mould, and permitting the casting level in said mould to rise to an operating level.

2. The process set forth in claim 1, wherein lowering of the casting level in the mould to a position below the outflow opening of the new casting tube is accompanied by reducing the drawing out speed originally applied, and permitting the casting level in the mould to rise again is accompanied by increasing the drawing out speed again after the exchange of the tundish is carried out, a uniform drawing out speed of 0.1 to 0.2 m./min. being maintained while the tundish is being exchanged independently from the drawing out speed originally applied and from other casting conditions.

3. The process set forth in claim 1, wherein the casting level is permitted to rise again by interrupting the drawing out of the cast bar.

4. The process set forth in claim 1, wherein said first tundish is removed from casting position by horizontal displacement only breaking off its casting tube against the inner mold wall.

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