A MACHINE AND A METHOD FOR CASTING A METAL STRIP

Abstract: Thin metal strips, for example wide carbon steel strips, are cast in a single belt machine. The width of the molten metal on the belt is defined by side dams (12, 13) on the belt (11). The side dams have inwardly directed surfaces against the molten metal which makes the surface of the molten metal even also at its edges.

Description: A machine and a method for casting a metal strip This invention relates to a strip casting machine comprising a cooled and power driven endless belt with side dams, and a device for supplying molten metal to the upper side of a flat and substantially horizontal part ofthe endless belt. It relates also to a method of casting a metal strip. A single belt strip casting machine of this kind is described in WO 93/01015. When casting strips, there will usually be edge drops, that is the edges will be thinner, so that the edges must be cut away. It is an object ofthe invention to counteract edge drop and this is accomplished principally by having inwardly inclined side dams. Another object is to permit the casting of thinner strips than has been possible before. To these ends, the invention has been given the characteristics stated in the claims. The invention will be described with reference to the accompanying drawings. Figure 1 is a fragmentary perspective view ofa strip casting machine in accordance with the invention, Figure 2 is a fragmentary longitudinal section through a machine that is somewhat modified from the machine in Figure 1 , Figure 3 is a transverse section taken along line 2-2 in Figure 3, and Figure 4 is a schematic transverse section through a strip cast by a machine described, the width and thickness ofthe strip being not in scale. The machine shown in Figure 1 has a substantially horizontal, water cooled, and power driven belt 11 of a heat conductive material for example copper. The belt 11 has side dams 12, 13 which can be movable with the belt, but which can also be fixed. They can advantageously be movable laterally and fixed in various lateral positions so that strips of various width can be cast. Above the belt, there is a tundish 14 that functions as a distributor of molten metal. It has a number of ceramic nozzles distributed over the entire width ofthe belt so that they produce several separate jets that meet the belt 11 which moves as indicated by the arrow 15. The orifices should be so located that the molten metal flows out and solidifies as a cast thin continuous strip 29 on the substrate, that is, on the movable belt 11. A container 16, for example a furnace or a ladle, supplies a controlled flow of molten metal to the tundish/distributor 14. The flow out ofthe container 16 can be regulated in various conventional ways, for example by means ofa stopper rod or a sliding gate nozzle. The Figures 3 and 4 show a design which is somewhat modified from the design shown in Figure 1. The container is replaced by a rotatable tube 17 ofthe kind disclosed in WO 9301015. The level ofthe molten metal in the tube 17 is kept constant by means of a non-illustrated regulator that regulates the supply of molten metal to the tube 17. The tube 17 has an outlet 18 in the form ofa slot and the flow out ofthe tube can be regulated by turning ofthe tube 17 since such turning changes the ferrostatic pressure that drives the flow out through the slot 18. The tundish 14 has two fixed walls 20, 21 that slows down the flow in the tundish and make the flow laminar before it reaches orifices 22. The endless belt 1 1 is cooled by a large number of cooling nozzles 23 that eject water jets against the underside ofthe belt 1 1 so that the molten metal solidifies on the copper belt into a cast continuous strip. Since the endless belt 1 1 moves fast when the vertical and parallel jets 30 from the orifices 22 ofthe tundish meet the belt 11 and the molten metal does not wet the belt, the molten metal will not flow backwardly on the belt and a rear dam is therefore not necessary. The molten metal should flow out on the belt 11 into an even layer and the distance between the jets 30 must therefore not be too big. There is no contact between the tundish/distributor 14 and the belt 11 and the side dams 12, 13 ofthe belt, which is advantageous particularly when a casting is ended or if a casting goes wrong, since the molten metal cannot freeze on the machine and prevent it from being started again. The jets are shown vertical but they can also be inclined. Another tundish/distributor can quickly and easily be exchanged for the one on the machine when one wants to cast strips of another width or one wants to change to a casting process that needs other orifices or another number of orifices since the tundish is neither coupled to the endless belt 11 nor to the container 16 or 17. The number of orifices and their size need to be varied in relation to the combination of strip width, belt velocity, viscosity ofthe molten metal, and desired thickness ofthe strip. The side dams 13J4 are shown having inwardly inclined walls. A steel strip 29 is shown in Figure 1, which has been cast with the machine described. Because ofthe inward inclination ofthe side dams, the metal surface is horizontal along the lines in which solid matter (the dams), the molten metal, and gas (argon) meet. If the surfaces ofthe dams should instead be vertical, the surface would bend downwards at the edges since the molten metal does not wet the side dams. The inclined dams in combination with the supply of molten metal in the form of separate jets make the upper surface ofthe strip very even. It will also be possible to cast thinner strips when the influence ofthe surface tension is counteracted in this way. The inclination ofthe side walls ofthe dams 12,13 should be chosen so that it matches the angle of wetting in order to get a flat surface of the molten metal. It should be understood that the figures are schematic and fragmentary. A cover is for example not shown. Such a cover holding a protective atmosphere, e.g. argon, protects the free jets of molten metal and the free surface ofthe molten metal on the belt from being oxidised. The strip casting machine according to the invention can be made in different sizes and for various kinds of metals and alloys. It can for example be suited for fast casting of carbon steel in strip thicknesses down to 6 mm or less and for strip widths of up to 2 metres or more.

Claims: CLAIMS 1. A strip casting machine comprising a cooled and power driven endless belt (11) with side walls (12, 13) and a device (14) for supplying molten metal to the upper side of a flat and substantially horizontal part ofthe endless belt, characterised in that the side walls (12, 13) have inwardly inclined sides facing the melt 2. A machine according to claim 2, characterised in that the endless belt (11) has no rear wall and a distributor ( 14) is arranged with a plurality of orifices for pouring molten metal directly onto the belt 3 A machine according to claim 2, characterised in that the distributor (14) comprises a tundish (14) arranged to be supplied with a controlled flow of molten metal from a ladle (16) 4 A method of casting a metal strip by supplying molten metal to a cooled and power driven endless belt (1 1) while limiting the width ofthe molten metal by side walls (12, 13) on the belt, characterised in that one uses side walls (12, 13) which have inwardly inclined sides that face the melt and chooses an inclination that matches the angle of wetting so that the surface ofthe molten metal will be flat. 5. A method according to claim 4, characterised in that the molten metal is poured on to the belt in the form of a plurality of free streams (30) which are so close that the molten metal flows out to an even layer on the belt

Inventors: HOLMBERG ANDERS, HOLMGREN ALLAN, HOLMBERG, ANDERS, HOLMGREN, ALLAN
Applicants: HOLMBERG ANDERS, HOLMGREN ALLAN, MANNESMANN AG, HOLMBERG, ANDERS, HOLMGREN, ALLAN, MANNESMANN AKTIENGESELLSCHAFT
Application year: 1996
Main classification: B22D11
IPC codes: B22D11