FR2512364A1 - METHOD AND DEVICE FOR CASTING STEEL TO THE DIMENSIONS OF SLABS - Google Patents

Abstract

IN A PROCESS FOR THE CONTINUOUS CASTING OF STEEL TO THE DIMENSIONS OF THE SLABS WITH AN INSTALLATION WHERE THE BAR IS GUIDED FOLLOWING A CIRCLE ARC PATH R EXTENDING OVER A QUARTER OF A CIRCUMFERENCE, THEN THEN IN A STRAIGHT LINE, L 'LIQUID STEEL BEING SPILLED IN THE UPPER OPEN END OF A VERTICAL LINGOTIER, TO AVOID SWELLING OF THE SKIN OF THE BAR AND THE APPEARANCE OF CURRENTS INSIDE THE CORE OF LIQUID METAL IN THE AREA OF THE TIP EXTREME OF THIS CORE, WE CHOOSE THE INCLINATION A OF THE RIGHT-LINE GUIDANCE OF THE BAR IN RELATION TO THE HORIZONTAL DEPENDING ON THE THICKNESS OF IT, AS WELL AS ITS DESCENT SPEED IN THE LINGOTIER AND THE COOLING CONDITIONS THEY -MEMES, SO THAT THE TIP OF THE LIQUID CORE IS HELD AT ABOUT THE SAME HEIGHT AS THE LEVEL OF THE MELTED METAL IN THE LINGOTIER, AND THAT THE BAR ITSELF IS COMPLETELY SOLIDIFIED IN THE PLANE CORRESPONDING TO THIS LEVEL .

Description

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  The present invention relates to a process for the casting of steel to the dimensions of slabs. It also relates to a device

  for the implementation of this process.

  We know that to obtain slabs in continuous casting, we use installations of the type in an arc of a circle. The molten metal is poured from above into a mold produced in rectilinear or curved form, which can be arranged vertically or in an orientation. oblique and in which it partially solidifies The bar thus obtained, and which is still internally liquid, is then guided in an apparatus in the form of an arc of a circle, to be straightened after having traversed a quarter of circumference therein and to continue thus its course in the horizontal direction The ferrostatic pressure which reigns inside the bar results in deformations of the external part

  or skin thereof, between the support elements of the aforementioned device.

  More particularly in the area of final solidification, the liquid currents linked to it cause segregation towards the end or tip of the core which is not yet solidified It is known to reduce the swelling of the bar in this area by applying it particular means of additional direct cooling, or also of reducing the flow of the still liquid metal by a light rolling of the bar towards its point of final solidification; it is also possible to obtain an improvement of the structure by the effect

  of a magnetic field However, it was not possible to achieve

  sufficient segregation, so that a problem remains to be solved here. Thus, processes of the kind in question have limits from the point of view of the quality of the product since too much cooling of the bar can lead to superficial cracks, and too pronounced lamination of interior cracks. The invention aims to avoid these drawbacks and at the same time to establish a method and a device which eliminate the swelling of the skin of the bar with the flows which are linked to it inside.

  of the liquid core thereof in the vicinity of its tip.

  According to the invention, in a continuous casting installation of steel to the dimensions of the slabs, with curved guide of the bar extending over more than a quarter of circumference, then then in a straight line, the steel being poured in the liquid state in the upper end of a mold placed substantially vertically and open at the top, to avoid swelling of the skin of the

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  bar and the appearance of currents inside the liquid metal core in the region of the extreme point thereof, one chooses according to the thickness of the cast bar, the inclination of the guide straight from the bar with respect to the horizontal, as well as its rate of descent into the ingot mold and that the cooling conditions such that the tip of the liquid core of the said bar is maintained approximately at the same height as the level of the molten metal in the mold, and the bar itself is completely

  solidified in the geometric plane corresponding to this level.

  The invention also relates to a device for implementing the above method, of the type comprising a mold for continuous casting of the steel open in the upward direction, a guide of the casting bar extending over more than one quarter of a circumference, a straightening assembly of the bar followed by a rectilinear guide system for the latter, which device is remarkable in that, starting from the mold, the guide of the bar extends in an arc of a circle, over more than a quarter of a circumference to arrive at an angle "with respect to the vertical, and in that after this arc, the straightening assembly of the bar is arranged so that the rectilinear part which is connected thereto end

  upward in a horizontal plane intersecting the mold.

  In the manufacture of tubes by continuous casting without the use of

  tion of a mandrel, it is known to guide the bar in an arc from 180 to 270, thanks to which the liquid fraction extends along a half-circumference in the manner of a system of communicating vessels, the skin which remains around this fraction constituting the tube to be obtained Here, however, the problem of segregation indicated above does not arise because the residual liquid fraction withdraws from

inside the tube.

  The advantages of the process according to the invention consist in that in the vicinity of the critical point of the end of the liquid core of the

  bar, the skin is not subjected to the action of ferrostatic pressure

  that This pressure acts in a disadvantageous way in two respects Firstly, it results in imposing on the central part of the support rollers on the one hand a mechanical load and on the other hand a simultaneous thermal load due to the contact with the surface of slab These rollers are thus caused to bend In extreme cases their bending exceeds the elastic limit of the metal so that one arrives at a creep of their constituent material and consequently in a permanent deformation That leads to corresponding deformations of the

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  bar section The flows thus caused determine segregation. Furthermore, the skin of the bar swells between the successive support rollers under the effect of ferrostatic pressure. This process is repeated several times towards the tip of the liquid core and

  also causes unfavorable steel flow.

  The advantages of the proposed process will be explained below a

using an example.

  A continuous casting installation with a radius of 10.50 m has a ferrostatic pressure of 7.3 bar at the tip of the liquid core. For a spacing of 500 mm between the rollers and for a slab width of 2000 mm, the skin receives between two successive rollers a load of 73 Mp and this same load applies to the rollers themselves It is it which can be reduced to zero thanks to the

process according to the invention.

  There is schematically shown in Fig 1 an embodiment.

  In a continuous casting installation with a radius of

  8.0 m a slab 250 mm thick is poured at a speed of 1.5 m / min.

  With usual secondary cooling, the solidification constant 1/2

  is 24 mm min, while the corresponding time is 27.1 min.

  Under these conditions the length of the liquid core would be 40.1 m.

  The angle CX would be deduced from the formula L 8 f (90 + oc) 1 R 180 tg o expression in which O This is equal to about 17 in this case, while R denotes the radius of the installation and L the length of l 's liquid soul. Likewise, installations could be provided as a function of the bending radius of the bar, the thickness of the slab, the casting speed and the intensity of the cooling. In the event of a change in conditions, it is possible to adjust the obliquity of the

  path of the bar by acting on the corresponding angle of inclination.

  It should also be understood that the foregoing description

  has been given only by way of example and that it in no way limits the field of the invention from which one would not depart by replacing the

  execution details described by all other equivalents.

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R E V E N D I CA T IO N S

  1 Process for the continuous casting of steel to the dimensions of the slabs in an installation with curved guide of the bar extending over more than a quarter of circumference, followed by a straight line path, the steel being poured at the liquid state in the upper end of an ingot mold open at the top and disposed substantially vertically, characterized in that the inclination of the rectilinear guide is chosen as a function of the thickness of the casting bar -this relative to the horizontal, as well as its rate of descent into the mold and that the cooling conditions, so that the tip of the liquid core of said bar is maintained at approximately the same height as the level of the molten metal in the ingot mold and that the slab itself is fully solidified in a geometric plane

corresponding to this level.

  2 Device for implementing the method according to the claim

  cation 1, of the type comprising a continuous casting mold open in the upward direction, a guide of the casting bar extending over more than a quarter of circumference, a straightening assembly of this bar followed by a straight guide of that -ci, characterized in that starting from the mold, the guide of the bar extends over more than one

  quarter of circumference to arrive at an angle OC relative to the ver-

  ticale, and in that after this arc, the straightening assembly of the bar is arranged so that the rectilinear guide part which connects to it ends in an upward direction in a horizontal plane

cutting the mold.

  3 Device according to claim 2, characterized in that the rectilinear guide portion of the bar is constituted in the known manner by pairs of facing rollers extending on the

width thereof.

  4 Device according to all of claims 2 and 3,

  characterized in that the inclination angle Os of the bar guide

  is adjustable and can therefore be adapted to the casting conditions.