The present invention broadly relates to continuous casting and, more specifically, pertains to a new and improved method and apparatus for continuously casting metal in a mold chamber having cooled rotating walls.
Generally speaking, the present invention relates to a method of continuously casting metal, in particular steel, in the form of strips or thin slabs, wherein the molten metal is poured, with the aid of a feed means, between four cooled walls rotating in the direction of casting. The circumferential surface of a casting drum or roll cools a first broad side of the strip or slab forming in the mold chamber, a second cooled wall cools the other broad side of the strip or slab being formed, and two narrow side walls, which are moved with the first or second cooled wall, cool the narrow sides of the substantially rectangular strip or slab being formed. One of the two broad side walls extends between the narrow side walls. The invention also concerns an apparatus for performing the method. This apparatus comprises at least two cooled walls movable in a predetermined direction of casting, a feed means, a first cooled wall of said at least two cooled walls forming a first broad side cooling wall of a mold chamber, and a second cooled wall of said at least two cooled walls having a recess substantially complementary to a cross-section of the cast strand and forming a second broad side cooling wall and two narrow side cooling walls of said mold chamber.
In the continuous casting of metals, in particular steel, in the form of thin broad strips, high casting rates are necessary for the production capacities required in large scale industrial operations. In this connection, considerable difficulties arise in feeding the molten metal in a uniform manner into a broad shallow mold in which the metal solidifies at least at its surface. For solving these problems, continuous casting installations have been developed wherein the molten metal is passed between two rotating drums or between one rotating drum and a circulating belt and is allowed to solidify while in contact with the cooled walls defined by these elements. In such systems, the cooled walls move in synchronism with the strand so that it is prevented from translating in relation to the cooling walls.
The French Pat. No. 2,091,851, granted Jan. 21, 1972, discloses a method for the continuous casting of substantially rectangular steel strip. The molten metal is poured between two rotating casting drums, use being made of a ceramic feed means. A first casting drum has a depression in its circumferential surface and forms a broad or wide side and two narrow sides of a mold chamber. The second casting drum which, over the length of the mold chamber, extends or engages between the narrow sides of the first casting drum, forms the second broad or wide side of the mold chamber. These four cooled walls, which move in the direction of casting, form a mold which, because of its rotary movement, essentially travels with the strand.
Instead of two rotary drums, a single drum and a circulating belt may also be employed. To achieve a high casting capacity, a high speed movement of the drums is necessary on the one hand, and a relatively great length of mold chamber in the direction of casting is required on the other. With a long mold chamber, as required for reliably and safely achieving a high rate of casting, it is possible, by the appropriate choice of drum diameter in relation to the thickness of strip to be cast, to create a correspondingly large gap between the cooled broad sides at the ingate or pouring inlet side. This is advantageous as regards the feed of disadvantages arise as regards the narrow sides. Since the mold chamber, between the broad sides and beginning at the ingate or pouring inlet side, narrows continuously down to a gap corresponding to the thickness of the strand, solidification of the narrow sides of the strand must be initially inhibited if their deformation is to be avoided between the mutually approaching drum walls. Furthermore, the recess in one of the casting drums would have to be very deep. A gap of a certain width for preventing friction, wear et cetera or for accommodating thermal expansion is unavoidable between the mutually engaging roller and narrow side walls. In this known casting method it is therefore not possible to prevent molten steel from penetrating into this gap and it becomes solidified in the form of adhering burrs, sometimes called "feathers" or "brows", lying parallel to the narrow sides. These burrs or "feathers" are joined to the simultaneously forming skin on the broad side of the strip. They prevent shrinkage or detachment from the drum which normally occurs upon cooling of the broad side. This leads to defects in the strand and in particular to cracks or even metal breakouts which require immediate interruption of the casting operation.