GB2196887A - Inclined continuous metal- casting plant - Google Patents

Abstract

An inclined continuous metal- casting plant comprising an inclined rectangular mould (1) resting on a narrow face, a secondary colling system (2), a drawing device (3) and a device (5) for cutting an ingot (4) into specified-size billets, all the above-said units being arranged one after another on a common processing axis in the ingot-forming direction. The angle of inclination of the horizontal is in the range from 20 DEG to 60 DEG . The mould cavity may have various shapes (Figs. 2-4, not shown.) <IMAGE>

Description

SPECIFICATION Inclined continuous metal-casting plant The invention relates to continuous casting of metal and, more particularly, to the inclined continuous metal-casting plants and can be used in ferrous and nonferrous metallurgy for casting mostly rectangular, or nearly rectangular (slab) ingots and shaped, e.g. beam type, billets.

Widely used in ferrous metallurgy are vertical continuous metal-casting plants, the prototype being the casting device of M. Dalen entitled "Water-cooled movable-bottom bowls for casting of metals" (Schwartzmeyer B. Continuous casting, Trsltd from German, Moscow, Metallurgizdat, 1962, pp.71-72) consisting of a movable bottom-pour ladle, a vertical ingot mould, a secondary air-cooling system in the form of an ingot temperature-equalizing chamber, power-driven withdrawal rolls for taking the ingot from the mould, and a shears for cutting the ingot into specified-size billets.

The vertical arrangement of all the plant units increases the height of the plant to 40-43 m. The construction of such plants calls for digging deep pits for the equipment, up to 25-27 m below the shop floor level, or for erecting high buildings. In both cases an increase in the height of the plants involves a sharp increase of capital outlays, complicates their operation and the process of casting.

Limitation of the plant height imposes, in turn, certain limitations on the casting rate or ingot section and, consequently impairs the plant output. It means that the vertical plants are unfit for casting large-volume melts e.g. from converters of 300-400-ton capacity since in this case the metal would have to be held for long in the laddle. Besides, the limited height of the plant also limits the length of a single billet.

The tendency towards reducing the plant height has led to devising the continuous metal casting plants with their component units arranged along a curvilinear axis (see, for example, "Continuous casting of steel". Papers of the International Conference, London, 1977. Trsltd from English. Moscow "Metallurgizdat", 1982, pp. 116-140). As compared with the vertical plants, these plants have additional devices for bending or unbending the ingots, since the ingot is formed here in a radial mould and in a secondary cooling system arranged along a curvilinear axis or, else, the straight ingqt is first bent in a special device (the so-colled vertical continuous metalcasting ingotbending plants). In both cases a curvilinear ingot is then unbent and brought to a horizontal position.

These plants are lower than the vertical ones; feature a higher casting rate since the ferrostatic pressure of the liquid metal does not limit this parameter; are capable of producing an ingot of an unlimited length; at an equal output they call for 3050% lower capital outlays; they facilitate the operation of the plant since the basic equipment is located above the shop floor level.

However, the inherent disadvantages of these plants include: complicated design due to a curvilinear outline of the secondary cooling system; necessity for the straightening mechanism and, in the case of a vertical ingot-bending plant, a pulling and bending mechanism; heavy loads on the equipment, causing frequent breakdowns (particularly of secondary cooling rollers and straighteningpulling device) and compelling the designers to increase the power and metal content of the entire plant; complicated adjustment of the equipment along the processing axis; necessity for maintaining a high surface temperature (up to 1000 C) which denies the possitility of increasing the cooling intensity and, consequently, the solidification rate; difficulties in uniform cooling of the ingot over the large-and small-radius faces in the secondary cooling system which involves a risk of producing a heterogeneous structure of the ingot; asymmetrical distribution of nonmetallic inclusions throughout the thickness of the ingot; single or double bending of the ingot which may bring about cracking, particularly in steels with a high sensitivity to red shortness which curbs down their casting rate by the necessity to complete solidification within the limits of a constant-radius curvature.

Horizontal continuous metal-casting plants are free from the disadvantages inherent in curvilinear continuous metal-casting plants.

Nevertheless, horizontal plants (cf. e.g., Horizontal Continuous Casting of Non-ferrous Steel at "Kove Steel" Works, "Iron and Steel Eng.", 1985, 62, No.10) are suitable only for casting ingots of small cross sections: square up to 110x 110 mm in cross section and round up to 180 mm in diameter casting being carried out from 30 to 50 ton ladles. This limitation is due to the presence of a junction unit between the metal-receiving unit and the mould, said joint having a low stabiiity.

Approaching most closely the herein-proposed invention in its technical essence is the inclined continuous-steel casting plant for making square billets (see "Continuous casting of steel" by M.S. Boychenko, V.S. Rutes, V.V.

Fulmacht, Moscow "Metallurgizdat", 1961, pp. 15-16, 61-64) comprising the successively arranged on the processing axis: inclined mould, secondary cooling system, intermediate roller bed, pulling stand in the form of a track mechanism wich pulls the ingot, curvilinear roller bed on which the ingot is bent for further movement in a horizontal direction, and a semiautomatic ingot-cutting device.

The inclined plant is of a small height which cuts down its construction costs considerably, simplifies the arrangement of the equipment and facilitates attendance.

However, this type of the continuous metalcasting plant failed to win wide industrial application through an extremely difficult delivery of metal into the mould by a sufficiently long pipelike refractory duct (charging bar) directed along the mould axis which renders control of metal flow, stable casting conditions and surface quality practically impossible. The assymmetrical structure of the ingot and unilateral segregation of nonmetallic inclusions throughout the thickness of the ingot prevent the inclined plant from casting slab billets in a traditional position on the wide face (as in radial and curvilinear plants). Due to a considerably lower ferrostatic pressure of the liquid metal in a small-height inclined plant the upper face of the ingot may cave in due to shrinkage.

Besides, at a longer solidification period there may occur concentration of nonmetallic inclusions and gas blisters under the upper face of the ingot which impairs the quality of metal.

The cardinal object of the invention resides in providing an inclined metal-casting plant with a low metal content ensuring the possibility of forming a high-quality rectilinear ingot.

This problem is solved by providing a continuous metal-casting plant comprising an inclined rectangular mould resting on a narrow face, a secondary cooling system, a drawing device for pulling the ingot out of the mould, and a device for cutting the ingot into specified-size billets, all the above-listed units being arranged one after another on a common processing axis in the ingot-forming direction.

This makes it possible to reduce considerably the metal content of the plant by dispensing with the equipment for bending and straightening the ingot, to cast very thick ingots at a high casting rate and to improve the quality of ingots by reducing the ferrostatic pressure of the liquid phase and eliminating the compulsory deformation.

It is practicable that the angle of the processing axis to the horizontal should range from 20 to 60 approximately.

This permits reducing the height of the plant and arranging the equipment above the shop floor level which cuts down considerably the metal content and capital outlays for the construction of the plant and facilitates working conditions and servicing of the processing equipment.

It is expedient that the internal surface of the upper face of the rectangular mould be maid outwardly convex.

This prevents the falling of the upper skin and formation of rippled surface and permits forming an ingot with a convex upper face devoid of surface defects.

Now the invention will be explained by way of example with reference to the appended drawings.

in which: Fig. 1 is a schematic diagram of the inclined continuous metal-casting plant according to the invention; Figs 2, 3, 4 are cross-sectional views of the mould for casting rectangular billets, beamshaped billets and billets with a convex upper face, according to the invention; Fig. 5 is the location of the metal meniscus with a mould inclined at 30 to the horizontal according to the invention.

The proposed inclined continuous metalcasting plant comprises the following units installed on a common rectilinear processing axis successively one after another; an inclined mould 1 resting on the narrow face, said mould being of a rectangular or nearly rectangular shape and located adjacent to a secondary cooling system 2 followed by a drawing device 3 for pulling the ingot 4 from the mould 1, and a device 5 for cutting the ingot 4 into specified-size billets (Fig. 1). Arranged above the mould 1 are pouring ladle 6 with a batching device 7 and an intermediate ladle 8 iwth a batching cup (not shown in Fig.1) linked with a vertically elongated refractory cup 9 for feeding metal below the level of melt in the inclined mould 1.The cross section of the mould 1 may be rectangular or nearly rectangular (Fig.2), or in the form of an I-beam (Fig.3) or rectangular with an outwardly convex face 10 (Fig.4).

The rectilinear processing axis of the plant rules out distortion of the ingot 4 to the moment of its final solidification, which improves the quality of the ingot 4 and broadens the nomenclature of the cast metal, increases the pouring rate, i.e. the plant capacity, and reduces the metal content due to elimination of the equipment for bending and straightening the ingot 4.

The angle to the horizontal of the rectilinear processing axis ranges from 20 to 60 which permits decreasing the height of the plant and installing the equipment above the shop floor level thereby reducing considerably the metal content and capital outlays for the construction of the plant at the same time facilitating the labour conditions and servicing of the plant equipment.

If the inclination angle of the plant is less than 20 , it becomes difficult to feed metal into the inclined mould 1 with the aid of a vertically-arranged elongated cup 9 because of a too small layer of molten metal above the lower face of the mould 1 and a strong development of meniscus. Conversely, the inclination angle of the processing axis exceeding 60 eliminates the advantages in reducing the height of the present plant in comparison with the vertical continuous metal-casting plants.

The arrangement of the rectangular mould 1 on the narrow face permits feeding metal into it below the melt level with the aid of elongated refractory cups 9 widely used nowadays. This also improves the quality of the ingot 4 due to a reduction of the quantity of nonmetallic inclusions because in this case the metal meniscus is considerably developed in the mould 1 and the velocity of metal movement on its surface in the mould 1 is considerably lower than it is in the radial and vertical moulds, all other conditions being equal. For example, with the processing axis inclined at 30 to the horizontal, the length a of the meniscus is twice the width b of the ingot 4 as shown in Fig.5; correspondingly, the surface area of the meniscus is twice iarger and the velocity of flows in the subsurface layers of metal in the mould 1 is reduced also two times.This extends the time of contact between metal and heat-insulating slag which covers the metal meniscus in the mould 1, thus favouring the conditions for migration (flotation) of nonmetallic inclusions and their assimilation by slag. The arrangement of the mould 1 on the narrow face also eliminates the limitations on the cross-sectional shape of the ingots 4, their nomenclature is by far greater than that shown in Figs 2 through 4, and their width is also increased.

The outwardly convex shape of the inner surface of the upper face 10 of the mould 1 is conducive to the forming of the convex self-supporting upper face of the ingot 4 which prevents the falling and rippling of the crust, cracking of the upper face of the ingot 4, formation of rolling laps and reduces the amount of side cuttings.

In contradistinction to the horizontal continuous metal-casting plants, the present plant has no junction unit between the metal-receiving unit and the mould. Therefore limitations as to the cross-section of the ingots cast and the amount of cast metal are overruled.

The herein-proposed inclined continuous metal-casting plant functions as follows. Metal is delivered from the pouring ladle 6 via the batching device 7 into the intermediate ladle 8 from which it is fed through the batching cup (not shown in Fig. 1) and a vertically-set elongated cup 9 under the metal level into the inclined mould 1 which rests on the narrow face. The well developed meniscus and the resultant comparatively low velocity of metal flows in the inclined mould 1 favours the conditions for flotation of nonmetallic inclusions and their assimilation by the heat-insulating slag covering the metal meniscus in the mould 1. This improves the quality of metal due to removal of non-metallic inclusions.

The shell of the ingot 4 formed in the mould 1 is capable of standing the ferrostatic pressure of metal and the pulling force. The ingot 4 is continuously drawn at a pre-se lected speed from the mould 1 through the secondary cooling system 2 where said ingot 4 is cooled by means of nozzles (not shown in Fig. 1) to a state of complete solidification.

The fully crystallized ingot 4 is cut into specified-size billets with the aid of the device 5 located after the drawing device 3.

When casting ingots with a small ratio of sides, the ingot can be bent into a horizontal plane after complete solidification thereof.

Inasmuch as inclined mould 1, secondary cooling system 2, drawing device 3 and device 5 for cutting the ingot 4 into specifiedsize billets are arranged along one rectilinear processing axis one after another, the ingot 4 is not deformed in the course of forming which improves its quality and does not limit the pouring rate thus stepping up the plant output.

When the ingot 4 is inclined on the narrow face and moves on a straight line this creates conditions for more optimum and uniform secondary cooling than in the radial and curvilinear plants which use various consumptions of water on the wide faces of the billet over the small and large radiuses.

The use of the inclined mould 1 with outwardly convex internal surface of the upper face 10 improves the quality of the ingot 4 due to elimination of falling and folding of the upper skin at the initial forming stage of the ingot shell and forming of its convex upper face which rules out the laps on the side edge during rolling and other surface defects.

A small height of the plant resulting from its inclined and rectilinear arrangement, no need for bending and straightening the ingot 4 lift the limitations on the casting speed, intensity of secondary cooling, provide prerequisites for uniform cooling and improvement of quality of metal at the same time reducing the metal content of the plant, facilitating the operation and servicing of the technological equipment.

The inclined arrangement of the rectangular mould on the narrow face and forming a continuous ingot on the rectilinear processing axis require no bending and straightening of the ingot and lift the limitations on the cross-sectional shape of the cast ingots and on the casting rate thus improving the quality of the ingots, broadenning the nomenclature of the cast metal, permitting the casting of rectangular (slab) ingots on inclined plants with a high productivity and soiving the problem of feeding metal into the mould from vertically-arranged elongated cups in a conventional manner as in vertical and curvilinear plants.

The inclination of the rectilinear processing axis at an angle ranging approximately from 20 to 60 to the horizontal, permits reducing the height of the plant and arranging the equipment above the shop floor level which cuts down the required metal content and the capital outlays for the construction of the plant at the same time facilitating the operation and servicing of the technological equipment.

The use of an inclined mould with an outwardly convex internal surface of the upper face improves the quality of the ingot by preventing the falling and rippling of the upper skin at the initial stage of forming the ingot shell and the ingot with a convex upper face which also prevents the formation of laps on the side edge in the course of rolling and of other surface defects.

Claims (6)

1. A continuous metal-casting process of the type in which molten metal is passed into one end of a cooled mould end a solidified ingot is pulled from out the other end end cut into billets: in which the common longitudinal axis of the mould and the emerging continuous ingot defines a straight line inclined to the horizontal, and the separation of the ingot into billets takes place generally at this lime.

2. Metal-casting plant comprising a straight longitudinally-extending mould open at each end and surrounded by cooling means, defining a longitudinal mould axis inclined to the horizontal; a drawing device to withdraw a continuous ingot from the open lower end of the mould; and a cutting device for separating billets from the continuous ingots withdrawn; in which the drawing device and cutting device are located to act generally on the defined inclined axis.

3. An inclined continuous metal-casting comprising an inclined mouldrectangular in cross-section resting on a narrower face; a secondary cooling system surrounding said mould; a drawing device for pulling a continuous ingot from the mould; and a device for cutting the ingot into specified-size billets; in which all the above-listed units are arranged one after another on a common processing axis in the inclined ingot-forming direction as defined by the inclined mould.

4. An inclined plant as claimed in Claim 2 or 3 wherein the angle of said axis to the horizontal ranges approximately from 20"C to 60"C.

5. An inclined plant as claimed in Claims 2, 3 or 4 wherein the internal surface of said mould is outwardly convex.

6. An inclined plant as claimed in any of claims 2 to 5 as described above with reference to the accompanying drawings.