GB2120587A

GB2120587A - Improvements in or relating to vessels such as tundishes

Info

Publication number: GB2120587A
Application number: GB08214757A
Authority: GB
Inventors: Alan Hey; Joseph William Cudby
Original assignee: K S R INTERNATIONAL Ltd
Current assignee: K S R INTERNATIONAL Ltd
Priority date: 1982-05-20
Filing date: 1982-05-20
Publication date: 1983-12-07
Also published as: ZA827992B

Abstract

The tundish (10) has at least one outlet (13 or 14) for melt to exit the tundish after negotiating a barrier suspended in the tundish, the barrier being a monolithic concrete dam (18 or 19) having an edge, e.g. its bottom edge (21), spaced from a tundish wall, e.g. its bottom (22), for the melt to pass to the outlet (13 or 14). The dam (18 or 19) has an internal passage (24, 25) for feeding gas to ejectors (28) comprising groups of refractory capillary tubes (29) in the bottom edge (21) of the dam, so that gas can be bubbled into the melt as it traverses the dam. By using an inert gas, inclusions in the melt can be swept away from the outlet (13 or 14), and by using a reactive gas the composition of the melt can be controlled. <IMAGE>

Description

SPECIFICATION Improvements in or relating to vessels such as tundishes The present invention relates to tundishes or intermediate vessels in the pouring of molten metals, for instance in continuous casting procedures. More particularly, the invention is directed to procedures and tundishes wherein gas is introduced for treating the melt, for example to remove inclusions therefrom or to reduce the amount thereof in the melt.

According to the present invention, there is provided a tundish or intermediate vessel for use in the teeming of molten metals, wherein a dam or weir therein serves to hinder flow of molten metal towards an outlet of the tundish, the dam or weir having an edge spaced from an adjacent surface of the tundish for the flow of molten metal to the outlet, and wherein the dam or weir has an internal gas passage and ejectors in or adjacent its said edge for ejecting gas into the said metal flow, the ejectors comprising capillary bores.

The invention also provides a method of teeming molten metal in a casting operation, wherein the melt is teemed into a tundish and is discharged from an outlet therefrom after flowing past a dam or weir in the tundish, and a gas is ejected into the melt as it crosses the dam or weir to carry inclusions in the melt to the melt surface, and thus away from the outlet, or otherwise to treat the melt before it is discharged from the outlet, the gas being ejected from gas nozzles carried by the dam or weir and fed with gas by means of an internal gas passage in the dam or weir.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: Fig. 1 is a transverse cross-sectional view through an intermediate teeming vessel in the form of a tundish embodying this invention, and Fig. 2 is a longitudinal cross-sectional view through the tundish of Fig. 1 , taken on the line Il-Il in Fig. 1.

The vessel 10 is an open-topped tundish having a metal shell 11 and refractory brick inner lining 1 2. The illustrated tundish is of the double-outlet form but could have but one outlet instead of a plurality thereof. The outlets 13, 14 are of generally conventional nature, as is the tundish itself, and the following description will therefore omit details with which the addressee will be familiar.

Molten metal is poured into the tundish 10 in the vicinity of the middle thereof, as indicated by the arrow 1 6. To reach the outlets 13, 14, the melt has to negotiate respective dams or weirs 18, 1 9. As shown in the drawings, the dams 18, 1 9 are suspended by resting on the side walls 20 of the tundish, so as to depend into the melt. The dams 18, 1 9 extend fully across the tundish. Each dam 18, 19 has one edge, its bottom 21, spaced from the adjacent bottom 22 of the tundish. Melt flowing to one or other of the outlets 13, 14 is therefore constrained to flow through the restricted spaces between the dams and the tundish bottom 22.

The dams 1 8, 19 are monolithic members comprising cementitious castings made from refractory concrete. The concrete can involve a hydraulic or chemical binding system, e.g. a phosphate binding system. The dam castings can be reinforced by known techniques. Each dam is designed to eject gas into the melt as the latter crosses the dam in its passage to the associated outlet 13 or 14.

Both dams 1 8, 1 9 possess an internal gas passage indicated generally at 24. Gas is piped to each of the dams and down a first, vertical section of the passage 24 to a second, horizontal section thereof. The latter section is enlarged to form a plenum 25 which extends adjacent the dam bottom 21 along substantially the whole length thereof. Gas fed from an external source into the dams is admitted to the melt by ejectors 28 each comprising a group or plurality of downwardlyextending capillary bores 29.

Dam 1 8 has the capillary bores 29 formed by refractory capillary tubes cast in groups in situ in the dam casting.

Dam 19, however, has the capillary bores 29 provided in perforated refractory plugs 30 secured in seatings 31 in the bottom 21 of the dam. The seatings 31 open to the plenum 25 and are holes in the bottom 21, sized and shaped to suit the plugs 30 which may be cemented in place.

Alternatively, the plugs 30 could be secured by casting the dam 1 9 thereabout. Each perforated plug 30 is traversed by refractory capillary tubes defining the bores 29. The plugs can be cementitious bodies formed from a refractory concrete having the capillary tubes cast in situ therein.

Capillary tubes similar to or of the type used for thermocouple sheathing are convenient to use, those made from recrystallised alumina being suitable for steel teeming operations. Multihole thermocouple sheathing, having e.g. six bores, could well be employed.

The capillary bores 29 should be of a size allowing free passage of gas. They should not be so large, however, that metal is likely to enter and block them. Bores of the order of 0.5 to 0.6 mm in diameter can be used, but the invention is not restricted to such a size.

In the illustrated construction, there will be a tendency for more gas to enter the melt from those ejectors 28 closer to the gas admittance end 32 of the passage 24 than from those ejectors further therefrom. A more even distribution of gas into the metal flow beneath the dams 18, 1 9 can be attained by increasing the ejector gas flow areas the further the ejectors are from the gas admittance end 32. The gas flow area of an ejector 28 is determined by the number and sizes of its capillary bores 29. Variation of these two parameters will enable the designer readily to attain desired gas flows from the ejectors 28.

Formation of the passage 24 and its plenum section 25 can be accomplished in any convenient way. For instance, they can be fabricated from metal tubing having apertures at the locations desired for the ejectors 28. Plastics or cardboard tubing could be used instead. A disappearing-core casting technique could also be used. A disappearing-core, which could comprise wax or a wax/cotton mixture, is meited or burned away when the dam is brought to service temperature.

The method of teeming according to the invention involves pouring the molten metal into a tundish and discharging it from the outlet 13 or 14 thereof after the melt has flowed past the weir or dam 18 or 19. Gas is blown into the melt as it passes the dam 1 8 or 19 by gas ejection nozzles carried by the dam, and is fed thereto by means of its internal gas passage 24. Normally an inert gas will be used, to sweep inclusions in the melt to the melt surface 33. The melt discharged from the tundish will be of depleted inclusion content, therefore. A reactive gas could be used, however, to control the chemical composition of the discharged melt. Oxidising, carbonic and nitrogenous gases could be used, for instance, to influence the oxygen, carbon and nitrogen contents of the melt.

The illustrated arrangement constrains the melt to flow beneath the dams. The dams could be arranged otherwise, for instance to require the melt to pass between them and one or other of the sides of the vessel. In such a case, the ejectors will blow the gas towards the adjacent tundish side.

In a modification of the illustrated embodiment, the ejectors are located adjacent rather than in the bottom edge of the dams. The capillary bores then open to the side walls of the dams and may be horizontally disposed or inclined to the vertical, as desired.

In a further modification, each ejector comprises but one capillary bore, and the or each dam then possesses a row of single-bore ejectors in or adjacent the said edge. The ejectors may, but need not necessarily, be equally spaced along the dam.

Claims

1. A tundish or intermediate vessel for use in the teeming of molten metals, wherein a dam or weir therein serves to hinder flow of molten metal towards an outlet of the tundish, the dam or weir having an edge spaced from an adjacent surface of the tundish for the flow of molten metal to the outlet, and wherein the dam or weir has an internal gas passage and ejectors in or adjacent its said edge for ejecting gas into the said metal flow, the ejectors comprising capillary bores.

2. A tundish according to claim 1, wherein each capillary bore is of a size allowing free passage of gas therethrough and preventing entrance of molten metal therein.

3. A tundish according to claim 2, wherein each capillary bore has a diameter of the order of half a millimetre.

4. A tundish according to claim 1, 2 or 3, wherein the ejectors possess gas flow areas which increase the further the ejectors are from a gas admittance end of the gas passage.

5. A tundish according to any of claims 1 to 4, wherein the dam or weir is a cementitious casting and the ejectors are formed by groups of refractory capillary tubes cast in situ therein.

6. A tundish according to any of claims 1 to 4, wherein the dam or weir is a cementitious casting and the ejectors are formed by perforated refractory plugs secured in seatings in the dam or weir which open to the said gas passage.

7. A tundish according to claim 6, wherein each plug is traversed by a plurality of refractory tubes defining the capillary bores.

8. A tundish according to claim 7, wherein each plug is a cementitious casting having the tubes cast in situ.

9. A tundish according to any of claims 1 to 8, wherein the dam or weir is spaced from the bottom of the tundish such that metal is constrained to flow thereunder in its motion towards the outlet, and the ejectors are located in the bottom edge of the dam or weir.

10. A tundish substantially as herein described with reference to and as shown in the accompanying drawings.

11. A method of teeming molten metal in a casting operation, wherein the melt is teemed into a tundish and is discharged from an outlet therefrom after flowing past a dam or weir in the tundish, and a gas is ejected into the melt as it crosses the dam or weir to carry inclusions in the melt to the melt surface, and thus away from the outlet, or otherwise to treat the melt before it is discharged from the outlet, the gas being ejected from gas nozzles carried by the dam or weir and fed with gas by means of an internal gas passage in the dam or weir.

12. A method of teeming molten metal substantially as herein described with reference to the accompanying drawings.