INGOT MOULD TO OBTAIN THIN SLABS

Abstract: Method to obtain thin slabs by continuous casting, whereby the ratio between the short side and the long side of the slabs is greater than 1:10, the thin slabs (13) being obtained by casting in an ingot mould (10), the slab (13) becoming detached during cooling from the ingot mould (10) independent­ ly and automatically owing to its geometric conformation being such that its long sides (12) diverge from each other. Ingot mould (10) for the continuous casting of thin slabs, in which the dimensional ratio between the short side (11) and the long side (12) of the mould is between 1:10 and 1:100, the mould (10) employing the above method, at least one of the long sides (12) having an outline that includes a substantial­ ly continuous enlargement of the section of the mould, starting from one of the short sides (11).

Description: This invention concerns an ingot mould to obtain thin slabs by continuous casting <according to the preamable of claim 1>. To be more exact, the invention concerns an ingot mould for the continuous casting of thin slabs, that is to say, suitable to cast slabs of which the ratio between their short side and long side is between 1:10 and 1:100. Methods and ingot moulds to produce slabs are known, as also are the problems linked thereto. The dimensional ratio between the short side and the long side of ingot moulds of a known type which can function properly does not exceed 1:10. In ingot moulds for thin slabs with which the invention is concerned, as a result of the dimensional ratio between the short side and the long side of the mould varying between 1:10 and 1:100, the solidifying material in the mould tends to slip on the wall of the mould. This slipping leads to the formation of cracks and clefts in the material of the slab. Moreover, the resulting material does not possess the desired homogeneity in its cross section. Furthermore, the extraction forces which have to be applied to the slab are such as to entail the risk of the peeling and breakage of the slab as it leaves the mould. Problems of a mechanical nature and also of a metallurgical type have therefore to be tackled, with the consequence that the thin slabs which can be produced with the present state of the art and which result therefrom comprise cracks, clefts, lack of homogeneity, etc. An ingot mould has been designed (EP-A-149734, DE-C-887990) which has an enlarged tapered conformation of its upper part, but this enlarged tapered conformation performs substantially only the purpose of enabling a casting plunger to be introduced; otherwise this introduction would be impossible as a result of the art employed by the patent applicant in question. So as to obviate such drawbacks and obtain a plurality of advantages which will be made clear in the following description, the present applicant has studied and tested a continuous casting ingot mould which is suitable to cast thin slabs, that is to say, suitable to cast slabs having a dimensional ratio of between 1:10 and 1:100 of their short side to their long side. According to the invention, the walls of the ingot mould are parallel to the lengthwise central axis of the ingot mould itself for a first lengthwise tract, while they diverge outwardly with a predetermined inclination relative to said axis for a second tract, which follows said first tract in the casting direction. According to the invention the ingot mould has, at least as regards one of its long sides, a conformation which becomes enlarged progressively from its short side towards the middle of that long side. This progressive enlargement enables a reduction in friction to be achieved as soon as the solidification period begins. This reduction in friction during solidification is obtained by exploiting the dimensional shrinkage taking place in the material itself. More generally, the idea of the solution of the invention provides for exploitation of the dimensional shrinkage occurring in the material during cooling so as to achieve an independent, automatic, progressive detachment of the cast solidifying thin slabs from the ingot mould. According to a variant the ingot mould may have a conformation whereby at least one whole long side is inclined. According to other variants the ingot mould will have a greater width at an intermediate position in one of the two halves of the long side of the mould. All these variants are such as will conform to the philosophy itself of the invention, whereby when solidification begins and even a very small shrinkage takes place, the section of the solidifying and therefore dimensionally shrinking slab tends to become detached independently and automatically from the ingot mould owing to the reciprocal geometry of the mould and slab, and this detachment is accentuated by the inclination of at least part of at least one long side of the mould and slab. The invention is therefore embodied with an ingot mould for the continuous casting of thin slabs having the features disclosed in claim 1. The dependent claims describe other forms of embodiment of the invention. The attached figures, which are given as a non-restrictive example, show some preferred embodiments of the invention as follows:- Fig.1 shows a cross section of an ingot mould having a rhombic conformation with the acute angles bevelled to form the short sides of the ingot mould itself; Fig.2 shows a cross section of an ingot mould formed with a plurality of rhombs having dimensions increasing progressively towards the centre of the mould; Fig.3 shows a cross section of an ingot mould having a lens-like conformation; Fig.4 shows a variant of Fig.3; Fig.5 shows a quadrangular conformation with one long side inclined in relation to the other long side; Fig.6 shows a cross section of an ingot mould with one long side substantially straight, whereas the other long side is cusp-shaped; Fig.7 shows a variant of Fig.6; Fig.8 shows the behaviour of the cooling mass during cooling within the ingot mould; Fig.9 shows an evolutive variant of the invention. In the figures an ingot mould 10 has short sides 11 and long sides 12. The short sides 11 are drawn straight in the figures but may actually be bevelled and/or radiused to merge with the long sides 12. In the working embodiments of Figs.1, 2, 3 and 6 at least one long side 12 has a substantially counterpart conformation on each side of a plane A-A passing along the centreline of the long side 12 and positioned vertically to the ingot mould. According to the variants of Figs.5 and 7 at least one long side 12 has a conformation that includes an enlargement offset from the centre of that side. This enlargement may affect a short side (Fig.5) or an intermediate position B-B on the long side 12, such intermediate position B-B being located in one half of that long side 12. Besides being inclined in relation to each other, the long sides may be made with a curved or partly curved development that produces the same effect. Other analogous and derived figures can be obtained very easily. Fig.8 makes evident the concept on which the invention is based. While cooling, the cast mass 13 tends to shrink continuously until it reaches a state of equilibrium. By shrinking or contracting, the cast mass 13 tends to produce a separation according to the arrows 14 from the sides 212, 112 and 11, being assisted in this result by the geometric conformation of the sides themselves. The modest inclination of the long sides 12 enhances the action of separation. According to the invention the inclination will be between 1: 50 and 1: 5, but advantageously from about 1: 10 to 1: in 20. The inclination of the long sides 12 in cooperation with the geometric configuration of the cooling mass 13 accentuates the separation effect. Even when it is very slight, this separation is enough to reduce the friction between the outer surface of the slab 13 and the inner surface of the ingot mould 10. This reduction in friction provides a plurality of advantages. It reduces the force needed for extraction of the slab; it avoids the superficial dragging effect due to the different speeds of the outer skin and the inside of the cooling slab 13; it prevents any lack of homogeneity which is not due to the material itself; it obviates the formation of cracks and clefts. According to the invention the ingot mould 10 has a uniform vertical conformation along an initial tract 15, whereas its remaining vertical tract 16 has a diverging bell-shaped conformation, thus producing a separation of the slab from the side wall of the mould and also a natural separation in the lower part of the mould.

Claims: Ingot mould (10) for continuous casting of thin slabs, in which the dimensional ratio between the short side (11) and the long side (12) of the casting material is comprised between 1:10 and 1:100, the geometrical conformation of a cross section of said ingot mould (10) being such that, starting from one of the short sides (11), at least one of the long sides (12) diverges outwardly relative to the central lengthwise axis of the ingot mould (10), characterised in that the walls (11,12) of said ingot mould (10) are parallel to said central lenghtwise axis for a first longitudinal tract (15), and they diverge outwardly with a predetermined inclination relative to said axis for a second tract (16), which follows said first tract (15) in the casting direction. Ingot mould (10) according to claim 1, characterised in that the inclination ratio of said walls (11,12) relative to said axis is comprised between 1:50 and 1:5. Ingot mould (10) according to claim 2, characterised in that said inclination ratio is comprised between 1:20 and 1:10. Ingot mould (10) according to anyone of the preceding claims, characterised in that said cross section has a substantially rhombic configuration. Ingot mould (10) according to anyone of claims 1 to 3, characterised in that at least one long side (12) diverges at least up to a median lenghtwise plan (A-A) of the ingot mould (10). Ingot mould (10) according to anyone of claims 1 to 3, characterised in that at least one of the long sides (12) diverges outwardly following a continuous curved path. Ingot mould (10) according to anyone of claims 1 to 3, characterised in that said cross section is formed by a broken line formed by a plurality of rhombs having dimensions increasing progressively towards the centre of the mould.

Inventors: FASANO, FULVIO
Applicants: DANIELI & C. OFFICINE MECCANICHE S.P.A.
Application year: 1988
Main classification: B22D11
IPC codes: B22D11