GB2202172A

GB2202172A - Improvements in continuous casting apparatus

Info

Publication number: GB2202172A
Application number: GB08803345A
Authority: GB
Inventors: Robert Wilson
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-02-12
Filing date: 1988-02-12
Publication date: 1988-09-21
Also published as: GB8803345D0; GB8703231D0

Abstract

The apparatus comprises a melt chamber (2), a feed conduit (3) for the continuous passage of molten metal out of the melt chamber (2), cooling means (6, 7) for receiving the molten metal from said feed conduit and solidifying same, means (10) for withdrawing the solidified metal from the cooling means, and means (5) for applying pressure to the molten metal in the melt chamber (2) in order to urge molten metal through the feed conduit (3) to the cooling means (6, 7), said feed conduit (3) extending from the melt chamber (2) at a location adjacent the base thereof. An alternative embodiment to that shown provides for supply of the molten metal to a horizontally disposed cooling means and containment of the apparatus within an outer, pressure vessel with insulated walls (Fig. 3, not shown). <IMAGE>

Description

IMPROVEMENTS IN CASTING FURNACES This invention relates to improvements in casting furnaces, particularly but not exclusively, for continuous casting of most ferrous metals or alloys such as stainless steels, high alloy special steels and cast irons; also non-ferrous metals such as silver, aluminium, gold, beryllium, cadmium, chromium, cobalt, copper, indium, magnesium, manganese, molybdenum, nickel, lead, palladium, platinum, rhodium, silicon, tin, tantalum, titanium, vanadium, tungsten, zinc and alloys based thereon.

Previously proposed furnaces commonly comprise a crucible, a die-carrier into which interchangeable dies or moulds may be inserted and a feed channel interconnecting the crucible and the die or mould when inserted into the die carrier. An example of such a furnace is described in British Patent No. 1,328,399.

Such previously proposed arrangements have a disadvantage in that the metal, on its passage from the crucible to the die or mould, travels along a conduit made up of a number of interconnecting components thereby necessitating adequate seals between adjacent components to prevent molten metal squeezing therebetween. Also such previously proposed apparatus such as that described in aforementioned British Patent No. 1,328,399 have required the application of a vacuum in order to lift metal by suction upwards through a feed tube of graphite to a cooling zone. Such a vacuum or suction method requires the employment of specially designed and relatively expensive apparatus.

It has also previously been proposed to utilise a vacuum melting pressurised continuous casting process in which a casting furnace is supplied with metal which is melted therein. Gas pressure is then applied to the surface of the molten metal in the furnace to force the molten metal up a tubular mould located above and adjacent the molten metal surface and in which mould it solidifies and is drawn off as a solid metal rod. During this process the mould has to be maintained in a constant relationship relative to the upper surface of the molten metal in the furnace and consequently the casting furnace has to be continuously moved upwardly as the level of the molten metal in the furnace is lowered due to the molten metal being drawn off.

The necessity of effecting such upward movement of the furnace is a significant disadvantage.

An objection of the present invention is to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided apparatus for the continuous casting of metal comprising a melt chamber, a feed conduit for the continuous passage of molten metal out of the melt chamber, cooling means for receiving the molten metal from said feed conduit and solidifying same, and means for withdrawing the solidified metal from the cooling means, said apparatus being characterised in that means is provided for applying pressure to the molten metal in the melt chamber in order to urge molten metal through the feed conduit to the cooling means, said feed conduit extending from the melt chamber at a location adjacent the base thereof.

The present invention also allows high refractory metals which may be aggressive to graphite, to be conveniently transferred via a suitable refractory ceramic tube or channel to the casting die or mould directly from a suitable ceramic crucible thus avoiding any possible contact of the molten metal and graphite. The furnace will however operate equally well on an all-graphite system and has in fact many applications particularly in precious metals and copper based alloys.

The design of the furnace and casting unit of the invention is primarily for upward casting but can equally be applied to horizontal casting. The system is described for casting from one outlet but can equally well operate with two or more outlets from either vertical upwards or horizontal die.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional view of a first embodiment of continuous casting furnace in accordance with the invention in which the furnace operates in a vertical delivery mode; Fig. 2 is a plan view of the line A-A of Fig. 1; and Fig. 3 is a fragmentary vertical sectional view of the upper part of a second embodiment of the invention arranged to operate in the horizontal delivery mode.

Referring to Figs. 1 and 2, a continuous casting furnace comprises a graphite crucible body 1 provided with an alumina (A1203) or other ceramic liner or secondary crucible 2. Extending vertically upwardly from adjacent the base of the melting chamber defined by the crucible 2 is a boron nitride or other suitable ceramic feed tube or channel 3. A graphite top sealing plate 4 closes the top of the crucible 2 and a gas entry pipe 5 extends into the bowl of the crucible from the exterior of plate 4.

The feed tube 3 extends upwards from a location spaced from but close to the base of crucible 2 and passes through a sealed aperture in sealing plate 4 before extending through a graphite die holder 6 surrounded by die cooling tubes 7.

As the melt passes up the bore of tube 3, it solidifies in the vicinity of the solidus/liquidus interface designated generally by the reference numberal 8. Above the interface 8, a solid, continuously cast rod 9 is formed which is engaged by and drawn at a predetermined rate from the die holder 6 by rotatable withdrawal rolls 10 in a pulsing action.

The sealing plate 4 is secured to the crucible holder 1 by means of a plurality of retaining bolts 11 through the intermediary of a gas tight seal 12.

A charging gate 13 extends in a gas-tight manner through the sealing plate 4 to enable solid metal to be charged into the casting furnace.

In use of the apparatus, for example in casting typical high nickel chromium alloy with solidus around 14000C and liquidus around 14400C with a liquid metal density of 7.47 gm/cm3, solid metal is first fed into the casting furnace through a charging gate 13. The solid metal is melted in the sealed melting chamber of crucible 2 by any suitable means and a low positive pressure slightly exceeding atmospheric is then applied to the surface of the melt by introducing an inert gas, preferably argon, through gas entry pipe 5. The applied positive gas pressure must be sufficient to convey liquid metal up the tube 3 to the point of solidification within the cooled die holder 6.

In the second embodiment shown in Fig. 3, the same components are given the same reference numerals as in the embodiment described in Figs. 1 and 2 and the method of operation is substantially the same. In the embodiment of Fig. 3, however, the vertical ceramic feed tube 3 terminates at a location spaced from but close to the base of crucible 2 and discharges into a horizontal passage 14 which extends through graphite die holder 6 and from which passage the solid cast rod 9 is drawn. In this embodiment the casting furnace and cooled die holder are enclosed within an outer steel case 15 provided with an internal heat insulating layer 16. Also the junction between the upper end of vertical tube 3 and horizontal passage 14 is suitably sealed at 17.Although in this embodiment as shown in Fig. 3, positive gas pressure is applied to the surface of the melt through gas supplied through pipe 5, it should be noted that such positive gas pressure can be applied in other ways. For example, the outer steel case 15 can be pressurised which in turn causes this pressure to be applied to the surface of the melt in the melting chamber in order to urge molten metal up the feed tube 3 to the cooled die, the die being the only outlet to atmosphere. It will be understood that in this arrangement the sealing plate 4 can be omitted or provided with a suitable aperture which will permit access of the pressurised gas to the surface of the molten metal in the melt chamber.

In both of the embodiments described above the arrangement has advantages in that the ceramic feed tube 3 is a very simply constructed die providing no possibility of metal leak from this simple high temperature plumbing which has substantially no seals.

Due to the fact that the feed tube 3 extends downwardly in the crucible 2 and terminates close to the base thereof, this enables continuous withdrawal of the molten material without any relative movement between the co-operating feed tube 3 and its associated crucible 2.

Die changing to provide differing rod profiles or cross-sections is simplified and can be carried out with liquid metal in the crucible. Such die changing can be effected by reducing the applied gas pressure to atmospheric pressure and thus allowing metal in the feed tube 3 to flow back into the main melt chamber leaving the die face of liquid metal. The casting surface is then cooled down for die removal.

It will be further appreciated that charging of cold metal can be made through the gas tight gate valve 13 without interrupting a casting run. Also, the above embodiments specify the preferable use of boron nitride for the die feed tube 3. Boron nitride is a ceramic which is unaffected by a significant number of metals and can operate to at least 1700 C.

In the above described embodiments, the applied gas pressure should be maintained throughout the casting run at a level sufficient to satisfy the dynamic requirements of the metal or alloy system employed and also should preferably be sufficient to cast all or nearly all of the metal from the crucible 2 to the end of the conduit formed by the feed tube 3.

Modifications can be made to the embodiments described above. For example, the bore of the die or dies can be of any desired profile and more than one outlet from the casting die can be provided. Also, by using a multichambered crucible system, the apparatus and process of the invention can be plumbed to supply two or more metals or alloys to a continuous casting die assembly.

If the apparatus is to be used with metals which are compatible with graphite and e.g. precious metals where loss of metal cannot be tolerated, the apparatus can be of a simplified form in which the ceramic crucible 2 is eliminated and the melt chamber is formed by the graphite outer body 1. In this case the feed tube 3 is also of graphite.

Any suitable pressurising gas can be used apart from argon so long as the gas is compatible with the metal or alloys being cast. Nitrogen could, for example, be used.

Claims

1. Apparatus for the continuous casting of metal comprising a melt chamber, a feed conduit for the continuous passage of molten metal out of the melt chamber, cooling means for receiving the molten metal from said feed conduit and solidifying same, and means for withdrawing the solidified metal from the cooling means, said apparatus being characterised in that means is provided for applying pressure to the molten metal in the melt chamber in order to urge molten metal through the feed conduit to the cooling means, said feed conduit extending from the melt chamber at a location adjacent the base thereof.

2. Apparatus as claimed in claim 1, in which the melt chamber is provided with a cover which sealingly closes same, said cover being provided with inlet means for supplying the chamber with metal and with a pressurised gas.

3. Apparatus as claimed in claim 1, in which the melt chamber is surrounded by an outer casing and means is provided for pressurisation of the interior of the casing and for enabling transmission of that pressure to the surface of molten metal contained in the melt chamber.

4. Apparatus as claimed in any of claims 1 to 3, in which the feed conduit comprises a feed tube which extends downwardly into the melt chamber to terminate at a location close to but spaced from the base of the melt chamber.

5. Apparatus as claimed in claim 4, in which the feed tube is of ceramic material.

6. Apparatus as claimed in claim 5, in which the ceramic material is boron nitride.

7. Apparatus as claimed in any preceding claim, in which the cooling means comprises a die holder having at least one passage therethrough for molten metal from the feed conduit, and cooling elements in said die holder for solidifying the metal therein.

8. Apparatus as claimed in claim 7, in which the die holder is interchangeable to enable production of solidified rods of differing cross-section.

9. Apparatus as claimed in claim 7 or 8 in which the die holder has two or more passages therethrough for molten metal.

10. Apparatus as claimed in any preceding claim in which the melt chamber has a ceramic lining.

11. Apparatus for the continuous casting of metal, substantially as hereinbefore described with reference to Figs. 1 and 2, or Fig. 3 of the accompanying drawings.