FR2649340A1 - METHOD AND DEVICE FOR CONTINUOUS CASTING BETWEEN CYLINDERS OF THIN METAL PRODUCTS FOR DIRECT COLD ROLLING - Google Patents

Abstract

According to this method, molten metal is cast between two rolls (1, 2) with parallel axes, driven in rotation in opposite directions and whose walls are cooled. Use is made of at least one roll whose generatrix is curved and whose diameter is slightly smaller in its axially central part than towards its ends, and the metal is kept in contact with the wall of the said roll over an arc which is longer in the said central part than towards the said ends. To this end, the casting device comprises a riser (3) whose lower edge (33) of the longitudinal walls (31) is in contact with the walls of the said rolls at the top of the nip (5) between the latter, and the line (35, 35') of contact of the lower edge of the longitudinal wall of the riser with this roll is curved so that the length of the arc of the surface (6, 7) of this roll between the said line and the said nip is greater towards the middle of the said longitudinal wall than over its edges.

Description

1 2649340

  METHOD AND DEVICE FOR CONTINUOUS CASTING BETWEEN

  CYLINDERS OF THIN METAL PRODUCTS

DIRECT COLD ROLLING

  The present invention relates to casting between rolls of thin metal products, such as in particular strips or sheets of steel. This type of casting is intended to obtain by casting thin products which can then be directly

cold rolled.

  In roll casting installations, the liquid metal is poured into a casting space defined by the portions of the cylindrical walls of the rolls located above the plane passing through the parallel axes of said rolls, and by end walls also called small faces or side walls, generally fixed, substantially perpendicular to the axes of the cylinders. During casting, the liquid metal gradually solidifies on contact with cooled cylindrical walls of the rolls forming solidified skins which are driven by the rotating rollers and meet at the neck, that is to say - at the said plane passing through the axes of the cylinders, to form

  the finished product that is continuously extracted down.

  In some cases, these installations also include a kind of fixed riser consisting of two longitudinal walls in sealing contact with the cylinders and two end walls extending upwards said small faces or being integral parts thereof. This extension will subsequently be designated by the term "flyweight" by analogy with the portion overcoming the mold or mold and intended to contain the withdrawal weight.

  in fixed mold casting or casting plants.

  This "flyweight" has the particular function, in the case of casting between cylinders, to delimit the cylinder surface on which the solidification of the cast metal takes place, and thus to ensure the regularity of this solidification, whatever the level metal in the weight. In addition, the meniscus of the liquid metal is not in contact with the walls of the cylinders and the risk of entrainment of the

  impurities floating on the meniscus is thus greatly reduced.

  In any case, many problems remain in obtaining a product that can be subsequently directly cold rolled. Indeed one of the desired characteristics for a flat product to be cold rolled is to present a slight transverse bulge. It is known that this initial bulge, for example of the order of a few tens of micrometers for a sheet of a few millimeters thick, makes it possible to obtain, after rolling, a sheet of constant thickness or at least of adequate cross-sectional area. a flat or hollow blank is not acceptable by the laminators. The main problem that the present invention proposes to solve is therefore to obtain a product resulting from casting which

present this bulge.

  With this object in view, the subject of the invention is a process for continuous casting between rolls in which liquid metal is poured between two cylinders of parallel axes driven in rotation in direction.

  opposite and whose walls are cooled.

  According to the invention, this method is characterized in that at least one cylinder whose generator is curvilinear and whose diameter is slightly smaller in its axially median part than at its ends, and the metal is maintained in contact with the wall of said cylinder on a longer arc in said portion

  median only towards said ends.

  As will be understood, the method consists in increasing the contact time of the metal with the cooled cylinder wall in the axially median zone thereof with respect to the contact time in the end zones, so as to form a solidified skin thicker towards the middle than on its edges and thus to obtain at the level of the neck between the cylinders a solidified product in all its transverse section and having the desired slight bulge, this curved

  corresponding to the "hollow" of the surface of the cylinder.

  The inventors have indeed found experimentally that the contact time, and therefore the length of the contact arc, of the metal on the cylinder has a considerable influence on the thickness of the solidified skin. Thus, for example, for a cast product having a final thickness of 2 mm and a contact arc length of 600 mm, all things being equal, a variation of 50 mm of this arc length can induce a variation of solidified skin thickness of about 50g m. The inventors have therefore imagined using this property to obtain the desired bulge by adapting the length of the contact arc between the cylinder and the metal at a certain distance from the vertical median plane perpendicular to the axes of the rolls, depending on the thickness. the product sought at that distance measured from the longitudinal axis of the product, or

  in other words, depending on the "hollow" of the surface of the rolls.

  The invention also relates to a cylinder casting device comprising two cylinders having cooled walls and a flyweight whose lower edge of the longitudinal walls is substantially in contact with the walls of said cylinders, above the neck between them. . This device is characterized in that at least one of the cylinders has a curvilinear generatrix and a slightly smaller diameter in its median part than at its ends, and in that the line of contact of the lower edge of the longitudinal wall of the flyweight with this cylinder is curved so that the length of the arc of the surface of this cylinder between said line and said neck is greater towards the middle of said wall

longitudinal only on its edges.

  According to a particular disposition of the invention, said longitudinal wall of the weight is generally flat and has at its lower edge a chamfer more accentuated towards the middle of said

wall only towards its edges.

  According to another arrangement, said longitudinal wall of the weight has a concavity directed towards the inside of the weight. As will probably have already been understood, these arrangements make it possible to ensure in a simple and practical manner the implementation of the method according to the invention described above, to the extent of course when the casting is maintained the level of liquid metal at

  above said contact line flyweight-cylinder.

  The invention will be better understood and other characteristics and

  benefits will emerge from reading the description that is going to be

  as an example of a device according to the invention.

  Reference is made to the accompanying drawings in which: - the figure is a schematic representation in perspective, partially torn off, of a casting device between rolls with flyweight; FIGS. 2a and 2b are sections perpendicular to the axes of the cylinders respectively at the ends and in the middle of the device; - Figure 3 is a view similar to that of Figure 1 in the case of a variant; Figures 4a and 4b are sections of the product respectively obtained in the case of the use of two and a single wall of the shaped weight according to the invention. It is specified that in the figures the "hollows" of the cylinders and the bulges of the product obtained have been deliberately exaggerated to facilitate the understanding of the invention, being well noted that in reality these hollows and bulges are of the order of ten

micrometers.

  FIG. 1 shows a continuous casting installation between cylinders comprising two cylinders 1 and 2 surmounted

a feeder 3.

  The cylinders 1, 2 are slightly in "hollow", that is to say that their generatrices 11, 12 are not absolutely straight but slightly curved, - with an arrow corresponding substantially to the value of the curved desired for the cast product. They are rotated in the opposite direction, according to the arrows 13, and their walls are cooled. It is specified that the hollow of the cold rolls may be slightly different, generally greater, than said desired convex product, in order to compensate hot their possible diameter variations due to the expansion, during''staging thermal regime. beginning of casting, dilation whose effects are not generally

  perfectly identical throughout the length of the cylinders.

  The feeder made of refractory material comprises two longitudinal walls 31 parallel to the axes of the rolls and whose lower edge 33 is kept in contact with the rolls with the least possible functional clearance possible, and two end walls 32 which also constitute in the example shown the end walls closing the casting space 4 further defined by the portion of the surfaces of the rolls above the neck 5 located at the plane

  horizontal P passing through the axes of said cylinders.

  According to the invention, the lower edge of said longitudinal walls 31 comprises a chamfer 34 of increasing importance from the ends towards the middle of said longitudinal walls 31. As a result, the line of contact 35 of each longitudinal wall with the corresponding cylinder is curve and the chamfer 34 is concave. This chamfer is clearly visible in the drawings of FIG. 2 -5 where FIG. 2a shows a section of the longitudinal wall 31 at one of its ends and FIG. 2b a section of this wall towards its center. It is clearly seen that the arc 6 on which the cast metal is in contact with the cooled wall of the cylinder towards its center, is longer than the corresponding arc 7 towards its ends. During casting, the liquid metal is poured into the maselotte and fills the casting space 4. The level of liquid metal is regulated to be maintained above the contact line 35 between the flyweight and cylinder. During the rotation of the rolls, and because of these differences in contact arc length, the contact time of the metal with the cylinder wall is greater towards its middle, which leads to a greater solidified skin thickness at center of the product only on its edges. The skins meet at the neck 5 and form the final product having the desired bulge, as shown in Figure 4a. In this figure, the product 8 has been represented as consisting of two convex zones 8 ', 8' ', each coming from the skins formed on each cylinder, and it will of course be understood that there is no real

  discontinuity between these two areas in the finished product.

  FIG. 4b similarly shows a section of the product resulting from an installation according to another embodiment of the invention in which only one cylinder is recessed and only the longitudinal wall of the counterweight adjacent to this cylinder presents the chamfer described above, the second cylinder then having rectilinear generatrices and the corresponding longitudinal wall of the flyweight being flat to the line of contact with said second cylinder. In this case, the skin 9 'formed on this second cylinder is of constant thickness over its entire width, only the skin 9 "having an extra thickness towards its middle. <br /> <br /> <br /> Because of the small real crown, this asymmetry will have practically no impact. influence on the finished product 9 which will present a convex equivalent to the product 8, to the extent of course o the "hollow" of the first cylinder and the corresponding bevel of the longitudinal wall of the weight have been increased accordingly, that is- This embodiment has the advantage of having to perform hollow machining only on a single cylinder, as well as the chamfer on a single cylinder.

  Longitudinal wall of the weight.

  Theoretically the lower edge 33 of the longitudinal wall 31 should also have a curvature corresponding to the "hollow" of the cylinder to maintain a constant functional clearance over its entire length between said wall and the cylinder. However, this "hollow" is virtually very low, even if said lower edge is straight, which S facilitates the manufacture of the weight, there is little risk of infiltration of the liquid metal by the said game. has already been explained, the variation of solidified thickness required to ensure the desired curvature of the cast product and the uniform solidification of the product at the neck 5, requires a significant variation in the length of the contact arc on which

  the skin is solidified.

  As an example, are given below chamfer values, in an experimental installation for the 2 mm band casting necessary to obtain a curvature of the band of the order

50 / m.

  Chamfer on two Chamfer on a single wall Wall length 300 mm 600 mm 300 mm 600 mm contact arc Chamfer value 12.2 mm 24.4 mm 24.7 mm 49.4 mm The invention is not not limited to the device described above by way of example. We can also use a feeder as shown in Figure 3, the longitudinal walls 31 'have a concavity directed towards the even casting space over the entire height of said walls. In other words, in this variant, the longitudinal walls of the flyweight do not have a chamfer at their lower edges, but it is the general curvature of

  these walls which determines a curved line 35 'contact flyweight

  cylinder and thus the variation of the desired arc length of contact.

Claims (4)

  1) Method of continuous casting between rolls in which liquid metal is poured between two cylinders (1, 2) of parallel axes rotated in opposite directions and whose walls are cooled, characterized in that at least one cylinder is used whose generator is curvilinear and whose diameter is slightly smaller in its axially central part than towards its ends, and the metal is kept in contact with the wall of said cylinder on an arc   longer in said middle portion than toward said ends.   2) A casting device between cylinders comprising two cylinders (1, 2) having cooled walls and a flyweight (3) whose lower edge (33) of the longitudinal walls (31) is substantially in contact with the walls of said cylinders above the collar (5) therebetween, characterized in that at least one of the cylinders has a curvilinear generatrix and a slightly smaller diameter in its axially central part than at its ends, and that the contact line (35, 35 ') on the lower edge of the longitudinal wall of the weight with this cylinder is curved so that the arc length of the surface (6, 7) of this cylinder between said line and said neck is greater towards the middle of said wall longitudinal only on its edges.   3) Device according to claim 2, characterized in that said longitudinal wall (31) of the feeder is generally flat and has at its lower edge a chamfer (34) more accentuated   towards the middle of said wall only towards its edges.   4) Device according to claim 2, characterized in that said longitudinal wall of the weight has a concavity   directed towards the inside of the weight.