Ingot mould system

An apparatus (10) for casting metal ingots comprises a series of ingot moulds (12) mounted along an endless conveyor (11) which is arranged to be driven around spaced-apart rotatable members (15) and (17). A molten metal supplying device (20) has a discharge member for supplying molten metal to empty moulds (12) moving along an upper run (14) of the conveyor (11) from a supply end (16) to a discharge end (18) of the upper run (14) of the conveyor (11). A casting hood (13) overlies at least a portion of the moulds (12) on the upper run (14) of the conveyor (11). Adjacent moulds (12) of the portion of moulds are closely contiguous during passage beneath the casting hood (13) whereby passage of protective gas between said adjacent moulds is minimized. The casting hood (13) and the portion of moulds (120) form a substantially gas-tight enclosure above the portion of moulds (12) into which gas can be introduced. The enclosure houses the discharge member of the molten metal supplying device (20).

FIELD OF THE INVENTION 
 The present invention relates to an improved method and system for ingot 
 mould casting of metals. More particularly, the present invention relates 
 to an apparatus for casting metal ingots, a mould for use in the 
 apparatus, a method which utilises the apparatus, and metal cast by the 
 method. 
 BACKGROUND OF THE INVENTION 
 The use of an ingot mould to cast molten metals is common practice. Casting
 of metals under an inert or protective gas atmosphere also is well known 
 and is essential in the case of some metals such as magnesium. 
 In casting metals in ingot moulds, a system which is frequently used has a 
 series of moulds mounted along an endless conveyor by which the moulds are
 presented in turn to a molten metal supply or distribution device. The 
 conveyor, which may comprise endless chains or belts, passes around 
 longitudinally spaced cogs, sprockets or the like, by which drive is 
 imparted to the conveyor. The series of moulds is mounted on the conveyor 
 so as to be in an upright orientation when presented to the supply or 
 distribution device on an upper run of the conveyor. Typically the moulds 
 are inverted in turn as each passes around a cog, sprocket or the like at 
 a discharge end of the conveyor, such that the then sufficiently 
 solidified ingot therein is able to drop from its mould. 
 With such a conventional conveyor system, it is difficult to restrict 
 adequately the amount of air ingress to the atmosphere above the moulds 
 and/or the amount of inert or protective gas atmosphere that leaks between
 moulds or otherwise is lost. Of course, it is possible to house the entire
 system in a leakproof enclosure, and to have the molten metal supply or 
 distribution device within the enclosure. However, this substantially 
 increases overall capital costs, and gives rises to several practical 
 difficulties in operation, not the least of which is difficulty of access 
 to the system in the event of a malfunction, particularly where the inert 
 or protective gas is toxic. 
 SUMMARY OF THE INVENTION 
 In a first aspect, the present invention provides an apparatus for casting 
 metal ingots comprising: 
 a series of ingot moulds mounted along an endless conveyor which is 
 arranged to be driven around spaced apart rotatable members; 
 a molten metal supplying device having a discharge member for supplying 
 molten metal to empty moulds moving along an upper run of the conveyor 
 from a supply end to a discharge end of the upper run of the conveyor;. 
 a casting hood overlying at least a portion of the moulds on the upper run 
 of the conveyor and being in slideable sealing engagement with the portion
 of the moulds, adjacent moulds of the portion of moulds being closely 
 contiguous during passage beneath the casting hood whereby passage of gas 
 between said adjacent moulds is minimised, the casting hood and the 
 portion of moulds forming a substantially gas tight enclosure above the 
 portion of moulds, the enclosure housing the discharge member of the 
 molten metal supplying device; and 
 gas introduction means for introducing gas into the enclosure. 
 In a second aspect, the present invention provides a method for casting 
 molten metal utilising an apparatus according to the first aspect of the 
 present invention, the method comprising the steps of driving the series 
 of ingot moulds around the spaced apart rotatable members, introducing gas
 into the enclosure to establish and maintain an atmosphere of the gas 
 within the enclosure, and supplying molten metal from the discharge member
 to successive moulds moving below the casting hood. 
 In a third aspect, the present invention provides a metal cast by a method 
 according to the second aspect of the present invention. 
 Preferably, the spaced apart rotatable members comprise longitudinally 
 spaced cogs, sprockets or the like. Preferably, sides of said adjacent 
 moulds are substantially normal to the direction of movement of the moulds
 along the upper run of the conveyor. Preferably, the casting hood is 
 mounted above, and extends along, the upper run and along each side of the
 conveyor. 
 The moulds may be of rectangular form in plan view. While this is not 
 necessarily the case, particularly in relation to the cavity of each for 
 casting an ingot, such form will be assumed for ease of description. In 
 line with that assumption, it will be further assumed that each mould is 
 of similar form and dimensions and that each has a rectangular open top 
 bounded by substantially parallel sides which are substantially 
 perpendicular to the length of the conveyor, and a respective end which 
 extends along each side of the conveyor. However, it is to be noted that 
 these further assumptions also do not necessarily apply. 
 On the upper run of the conveyor, successive moulds may be closely 
 contiguous along adjacent sides of the open top of each. The arrangement 
 may be such that the adjacent sides simply abut at opposed surfaces 
 thereof. Alternatively, the adjacent sides may interfit or interlock. In 
 each case, the adjacent sides preferably conform to close tolerances, so 
 as to minimise the gap between the successive moulds and, hence, the 
 extent to which inert or protective gas atmosphere provided above the 
 moulds is able to escape during movement of the moulds along the upper 
 run. However, whether abutting, interfitting or interlocking, it is 
 necessary that successive moulds are closely contiguous on the upper run 
 of the conveyor in a manner which enables their separation as each mould 
 reaches and moves around the discharge end of the conveyor. 
 In accordance with a fourth aspect of the present invention, a mould may 
 comprise a substantially rectangular base, a pair of end walls and first 
 and second side walls, the end walls and side walls extending upwardly and
 outwardly from the base, the side walls being longer than the end walls 
 and the first side wall being taller than the second side wall, the first 
 side wall having an outwardly extending first side wall lip having a 
 concave underside and the second side wall having an outwardly extending 
 second side wall lip having a convex upperside, the first and second side 
 wall lips being arranged such that when two of the moulds are placed 
 horizontally beside one another the concave underside of the first side 
 wall lip of a first of the two moulds sits atop the convex upperside of 
 the second side wall lip of a second of the two moulds whereby passage of 
 gas between the first side wall of the first mould and the second side 
 wall of the second mould is minimised. 
 In one arrangement, each side of the open top of each mould is defined by 
 an outwardly turned lip, one of which is slightly higher than the other. 
 The higher lip of one of successive moulds, for example the leading lip in
 the direction of movement along the upper run, can overlap the lower lip 
 of the other of the successive moulds. The lips may be arcuate in sections
 parallel to that direction, such that a convex upper surface of the lower 
 lip is received under a concave lower surface of the upper lip. Where of 
 such arcuate form, the lips may have a radius of curvature which 
 facilitates separation of the leading one of the successive moulds when it
 reaches the discharge end of the conveyor. Also, in that arrangement, the 
 higher lip preferably is at substantially the same height as the ends of 
 the open top such that, in being received over the lower lip of the next 
 successive mould, it is neatly received between the ends of the open top 
 of that next mould. 
 The casting hood may be of elongate form in plan view. Also, it may have a 
 respective side structure along each side of the conveyor by which it is 
 in slideable sealing engagement with at least a plurality of successive 
 moulds on the upper run, and a cover which extends between the side 
 structures, above these moulds. That sealing engagement may be provided 
 along ends of the open top of each of the moulds, and preferably is of a 
 tongue and groove type. In one form, each of those ends has a groove 
 therein into which an edge of the respective side structure is received. 
 Each groove preferably is defined in an upper surface of its end. However,
 a converse arrangement is possible, in that each end of the open top of 
 each mould may define a rib which is received in a groove of the 
 respective side structure, with each rib preferably defined on an upper 
 surface of its end. 
 With each of the tongue and groove types of sealing engagement, the 
 engagement preferably is substantially continuous along the length of the 
 conveyor along which the casting hoods extends. Thus, where grooves are 
 defined in the ends of the open top of each mould, the grooves in adjacent
 ends of successive moulds preferably are substantially aligned and in 
 close end-to-end relation. Similarly, where each end defines a rib, the 
 ribs of adjacent ends of successive moulds preferably are substantially 
 aligned and in close end-to-end relation. In each case, the tongue and 
 groove type of engagement provides a form of labyrinth seal which creates 
 a tortuous path acting to minimise gas loss from within, or ingress of 
 ambient air to, the space within the casting hood, above moulds therein. 
 As will be appreciated, each mould cools somewhat after releasing an ingot 
 cast therein on passing around the discharge end of the conveyor, and 
 during its return via the supply end of the conveyor to the filling 
 position. On reaching the filling position and receiving molten metal, 
 each mould will be heated. The system thus needs to allow for thermal 
 expansion and contraction of the moulds during such cooling and heating. 
 Such allowance may be provided by the side structures of the casting hood.
 In one form providing such allowance, at least that part of each side 
 structure which provides slideable sealing engagement with the moulds is 
 resilient and able to flex to accommodate thermal expansion and 
 contraction of the moulds. At least that part of the side structure may be
 formed of a suitable heat resistant cloth, with this material preferably 
 being used with a tongue and groove type of seal in which the groove is 
 defined by the moulds. In an alternative form, that part of each side 
 structure which provides slideable sealing engagement with the moulds may 
 be relatively rigid, and made, for example, of a suitable metal, but able 
 to move to accommodate the thermal variation by being able to adjust 
 laterally of the conveyor in sealing relationship with an associated part 
 of its side arrangement. 
 It also will be appreciated that moulds moved by the conveyor along the 
 upper run will undulate somewhat, despite manufacture to the closest 
 tolerances and despite the moulds being closely contiguous. It therefore 
 is desirable that the slideable sealing engagement between the moulds and 
 side structures of the casting hood be able to accommodate this. Thus, 
 where for example, that engagement is of a tongue and groove type, with 
 the grooves opening vertically, the depth of the engagement within the 
 grooves can be sufficient to allow for variation in height of successive 
 moulds due to any undulations. 
 As described to this stage, the casting hood will be understood as being of
 a form in which the space above successive moulds on the upper run of the 
 conveyor is closed by side structures of the hood, and a cover which 
 extends between the sides. The hood also is adapted for the supply of 
 inert or protective gas to that space so to substantially comprise the 
 atmosphere therein. Additionally, the hood is adapted to enable the 
 casting of molten metal therein in each of the successive moulds, as each 
 mould reaches a filling position. Moreover, the casting hood has an inlet 
 structure and an outlet structure spaced along the conveyor, by which it 
 engages moulds moving along the upper run to minimise ingress of ambient 
 air to and loss of atmosphere from the space enclosed by the hood. 
 Each of the inlet and outlet structures of the casting hood preferably 
 comprises an airlock. Where this is the case, each structure may comprise 
 a longitudinally spaced pair of wall members, each joined to the cover and
 extending between and joined to the side structures. A lower edge of each 
 wall of the pair bears against the top of successive mould passing 
 thereunder. Preferably, the spacing between the walls of each pair exceeds
 the spacing between the sides of each mould so as to maximise retention of
 sealing integrity at each end of the casting hood. The walls of each pair 
 may be adapted to resiliently engage the top of successive moulds. For 
 this purpose, the walls may be formed of flexible, heat resistant cloth, 
 so as to resiliently bear against the top of successive moulds. 
 Alternatively, the walls may be rigid, but have a lower edge formed of 
 such fabric so as to provide resilient engagement with the moulds. 
 The casting hood may be adapted for the supply of inert or protective gas 
 to the space therein by having a gas supply conduit extending to the hood 
 from a source of supply of the gas. The conduit may simply communicate 
 with the space, such as through a side structure or the cover of the hood.
 However, the conduit preferably communicates with at least one 
 distribution duct of the hood which extends longitudinally therein and has
 a plurality of outlets from which the gas can be discharged into the 
 space. The gas preferably is supplied to the space so as to maintain the 
 atmosphere therein at a slight overpressure sufficient to prevent the 
 ingress of ambient air. 
 The inert or protective gas preferably is supplied to the space such that 
 the gas substantially comprises the atmosphere within the casting hood. By
 way of example, the inert gas may be nitrogen, argon, or a mixture of 
 nitrogen and argon and the protective gas may be a dilute sulphur 
 hexafluoride/dry air mixture, a dilute sulphur hexafluoride/carbon dioxide
 mixture, a dilute sulphur hexafluoride/dry air/carbon dioxide mixture, or 
 a sulphur dioxide/dry air mixture. Where the inlet and outlet structures 
 comprise airlocks, the gas preferably is supplied to that part of the 
 space between those structures, as well as to the part of the space 
 between the pair of walls of at least the inlet structure. As will be 
 appreciated, each mould approaching the inlet structure will have ambient 
 air in its cavity, and the inert or protective gas supplied in the airlock
 comprising that structure most preferably is directed so as to flush the 
 ambient air from successive moulds, prior to each mould passing in turn 
 beyond the airlock. 
 The casting hood may be adapted to enable the casting of molten metal 
 therein, in each of successive moulds, in a variety of ways. Preferably 
 the molten metal is supplied to the casting hood, from a source of supply,
 via a supply pipe which communicates with a molten metal distribution 
 device located within the hood at a pouring position. The distribution 
 device may comprise a discharge head which defines an outlet end of the 
 supply pipe. In this case, the supply of molten metal may be controlled so
 as to be terminated for an interval between completion of filling of each 
 mould in turn, when in a filling position, and the arrival of the next 
 following mould at that position. However, the distribution device may be 
 continuously operable and comprise, for example, a rotatable casting wheel
 member having a plurality of spouts which are operable in turn for filling
 successive moulds at the filling position. 
 Over at least an inlet part and an outlet part of its length, the casting 
 hood may be relatively shallow, so as to minimise the volume of inert or 
 protective gas required to provide the atmosphere therein. Where the metal
 distribution device comprises a discharge head, the hood may be of similar
 shallow form over its full length. However, where the distribution device 
 is of larger form, such as a rotatable casting wheel member, the height of
 the casting hood at the region of the filling position for moulds may be 
 large so as to define a chamber adjacent the filling position, in which 
 the discharge device is housed and operable.

DETAILED DESCRIPTION OF THE DRAWINGS 
 Referring firstly to FIG. 1, the system 10 comprises a horizontally 
 disposed conveyor 11 having ingot moulds 12 mounted thereon and a casting 
 hood 13 mounted over a plurality of the moulds 12 on an upper run 14 of 
 conveyor 11. 
 Conveyor 11 comprises endless chains or an endless belt which passes around
 a first rotatable member 15 at a supply end 16 of the conveyor 11 and a 
 second rotatable member 17 at a discharge end 18 of the conveyor 11. 
 Members 15 and 17 comprise cogs, sprockets or the like; one of which is 
 driven so as to cause conveyor 11 to move successive moulds 12 from the 
 supply end 16 to the discharge end 18, along the upper run 14, and then to
 return the moulds 12 along a lower run 19 to the supply end 16. 
 Hood 13 extends longitudinally above the upper run 14 over a plurality of 
 moulds 12 thereon. The longitudinal extent of hood 13 is such that it has 
 an inlet end 13a downstream of the supply end 16 and an outlet end 13b 
 upstream from the discharge end 18. The length of conveyor 11 between 
 supply end 16 and inlet end 13a may be relatively short. However, the 
 length of conveyor 11, from outlet end 13b to the discharge end 18 needs 
 to be such that molten metal poured into successive moulds 12 via a molten
 metal supply line 20 between ends 13a and 13b is able to solidify 
 sufficiently before the moulds 12 pass around the discharge end 18 and are
 inverted to discharge ingots. 
 Hood 13 has a respective side wall structure 21 above each side of conveyor
 11, a top cover 22 which extends between the top edge of each side wall 
 structure 21, an inlet structure 24 at inlet end 13a and an outlet 
 structure 25 at outlet end 13b. These features of hood 13 will be 
 subsequently described in more detail. However, it is to be appreciated 
 that hood 13 substantially encloses a space above moulds 12 as they pass 
 from inlet end 13a to outlet end 13b. Also, hood 13 has a connector means 
 (not shown) which is connectable to a source of pressurised inert or 
 protective gas and is adapted for discharge of the gas within hood 13. 
 Referring now to FIGS. 2-6, each mould 12 is of elongate rectangular form, 
 with a leading side wall 26, a trailing side wall 27 and end walls 28 
 which are inclined upwardly and slightly outwardly with respect to a base 
 29 for ease of discharge of an ingot cast therein. Moulds 12 are disposed 
 with their side walls 26 and 27 extending laterally across conveyor 11, 
 and with each end wall 28 adjacent and extending along a respective side 
 of conveyor 11. 
 In each mould 12, the leading side wall 26 is of substantially the same 
 height as end walls 28, although the trailing side wall 27 is of slightly 
 lesser height. Also, each side wall 26 and 27 and each end wall 28 has an 
 outwardly extending lip or flange, respectively designated lips 26a, 27a 
 and 28a. The lips 26a and 27a are of arcuate cross-section with the form 
 of leading lip 26a defining a concave lower surface 30 (see FIGS. 4 and 5)
 which is substantially complimentary to a convex upper surface 31 of 
 trailing lip 27a. As best illustrated in FIGS. 4 and 5, the leading lip 
 26a extends over the trailing lip 27a of a preceding mould 12. For this 
 arrangement, the length of the leading lip 26a is such that it is able to 
 be neatly received between the end walls 28 of the preceding mould 12. 
 Successive moulds 12 on the upper run 14 thus interfit or interlock, so as
 to be closely contiguous. This preferably is such that, for moulds 12 
 below hood 13, loss of inert or protective gas between successive moulds 
 is able to be minimised, due to surfaces 30 and 31 being closely adjacent 
 or in contact. 
 The relationship between overlapped lips 26a and 27a of adjacent moulds 12 
 is such that the adjacent moulds 12 are able to separate on passing around
 the supply and discharge ends 16 and 18 respectively of conveyor 11. On 
 passing fully around ends 16 and 18, the lips 26a and 27a resume their 
 overlapping relationship. 
 The gas sealing may be improved by providing sealing means between adjacent
 moulds 12 (see FIG. 5). The sealing means may take a variety of forms 
 including a compressible seal 32 which extends longitudinally along the 
 end 27b of trailing lip 27a and which is arranged to compress and provide 
 a gas tight seal adjacent to the junction of the leading wall 26 and the 
 leading lip 26a of the following mould as the moulds 12 move about first 
 rotatable member 15 and approach inlet end 13a of the hood 13. The gas 
 tight seal between adjacent moulds 12 then remains intact as the moulds 12
 move along the upper run 14 of conveyor 11. Alternatively, the sealing 
 means may take the form of a longitudinal spring steel gasket 33 which is 
 affixed to upper surface 31 of trailing lip 27a and which is arranged to 
 compress and bridge between surfaces 30 and 31 to provide a gas tight seal
 between adjacent moulds 12 during their passage along the upper run 14 of 
 conveyor 11. As with compressible seal 32, spring steel gasket 33 forms 
 the gas tight seal between adjacent moulds 12 as they move about first 
 rotatable member 15 and approach inlet end 13a. 
 The end wall lips 28a are flat and horizontally disposed and have a pair of
 apertures 34 (see FIG. 2) by which moulds 12 are secured to conveyor 11. 
 The pair of apertures 34 receive bolt and nut 35 (see FIG. 6) by which a 
 horizontally disposed arm 36 of an angle bracket 37 is secured to the 
 underside of lip 28a. A vertically disposed arm 38 of angle bracket 37 is 
 welded to a link 39 of the conveyor 11. 
 Additionally, each end wall lip 28a has a groove 40 formed in its upper 
 surface which is parallel to the direction of travel of the conveyor 11. 
 The groove 40 of each lip 28a is positioned such that, as moulds 12 are 
 moved along the upper run 14 of conveyor 11, each groove 40 is 
 longitudinally aligned and in close end-to-end relationship for successive
 moulds 12. The grooves 40 enable substantial sealing with hood 13 along 
 each side of conveyor 11. 
 As shown most clearly in FIG. 6, each side wall structure 21 of hood 13 is 
 of two part form, comprising an upper square section tubular member 42 and
 an elongate bracket 44 of angle section. Each member 42 and bracket 44 is 
 continuous along substantially the full length of hood 13 between inlet 
 end 13a and outlet end 13b. However, each member 42 is closed at each end.
 Each bracket 44 has a horizontally disposed flange 44a on which its tubular
 member 42 rests, and a vertically disposed flange 44b which extends from 
 the inner edge of flange 44a. To maintain bracket 44 in relationship to 
 its tubular member 42, the tubular member 42 has secured to its lower side
 an inturned flange 42a which extends laterally below the flange 44a. The 
 arrangement is such that bracket 44 is able to adjust laterally with 
 respect to member 42, while a labyrinth seal is maintained therebetween by
 flange 42a. 
 As moulds 12 pass under hood 13 via inlet end 13a, the lower edge of flange
 44b is received in a respective groove 40 of each mould 12. This 
 relationship is maintained until the mould 12 passes beyond the outlet end
 13b of hood 13. A resultant tongue-and-groove coupling between brackets 44
 and moulds 12 provides a gas seal therebetween, with the tolerances and 
 depth of engagement allowing for undulation of moulds 12 during their 
 movement. Also, the ability of brackets 44 to move laterally relative to 
 tubular members 42 allows for thermal variation in the dimensions of 
 moulds 12. 
 Cover 22 of hood 13 comprises a metal plate which bridges and rests on the 
 respective tubular members 42. A seal preferably is provided therebetween 
 by a suitable gasket (not shown), as this allows for relative thermal 
 expansion and contraction. 
 At one or more locations along the length of hood 13 there is provided a 
 transverse square section pipe 45 which bridges and extends beyond tubular
 members 42 for introducing gas into the space defined by hood 13 above 
 moulds 12. For this purpose pipe 45 has a connector (not shown) for 
 receiving gas from a pressurised source (not shown) and is closed at each 
 end. Pipe 45 is mounted on a side support structure 46 at each side of 
 conveyor 11 with pipe 45 and, hence, side wall structures 21 being 
 maintained at a constant height. Pipe 45 and members 42 are in 
 communication via a port 47 defined by aligned apertures in each. Around 
 each port 47, pipe 45 is welded to each member 42 to provide a gas tight 
 seal. Also, along each member 42, there is a series of holes 48 by which 
 the interior of each member 42 is in communication with the space defined 
 by hood 13 above moulds 12. The arrangement is such that inert or 
 protective gas is able to be supplied from the pressurised source to pipe 
 45 and then to tubular members 42 via ports 47. From the tubular members 
 42 the gas is discharged within hood 13 via holes 48 so as to comprise the
 atmosphere within hood 13. The gas is supplied at a sufficient pressure so
 that the atmosphere within hood 13 is at a slight overpressure thus 
 preventing the ingress of ambient air. However, the overpressure should be
 kept to a minimum so as to avoid undue loss of the gas from system 10. 
 Each of inlet structure 24 and outlet structure 25 comprises an airlock 
 defined by a transverse pair of walls 50 (FIGS. 1 and 6). In each of 
 structures 24 and 25, the longitudinal spacing between the walls 50 
 preferably exceeds the spacing between leading side wall 26 and trailing 
 side wall 27 of each mould 12. Also each wall 50 is sealed against top 
 cover 22 and each side wall structure 21, respectively across the full 
 transverse and vertical extent of hood 13. Walls 50 are of a substantially
 gas impervious, flexible and heat resistant cloth, and bear against the 
 upper edges of moulds 12 passing thereunder. The walls 50 thus provide a 
 gas seal at both the inlet end 13a and outlet end 13b of hood 13. In this 
 regard, ambient air and water vapour resulting from cooling of the moulds 
 after discharge of ingots will be taken into the inlet end 13a by 
 successive empty moulds 12. However, each mould 12 in turn initially will 
 be between the pair of walls 50 of inlet structure 24 and, as tubular 
 members 42 discharge inert or protective gas between those walls 50 via 
 holes 48, as well as between inlet and outlet structures 24 and 25, the 
 ambient air and water vapour will be displaced by the gas before each 
 mould 12 in turn passes under the second, innermost one of the walls 50. A
 similar functioning occurs with the walls 50 of the outlet end structure 
 25, although there is less need for a double wall arrangement in this 
 case. 
 Between its inlet and outlet structures 24 and 25, hood 13 has a length 
 accommodating a plurality of successive moulds 12 thereunder. At an 
 intermediate position along that length, system 10 includes a molten metal
 filling station (not shown) below which each mould 12 is presented in turn
 to receive a quantity of molten metal to be cast therein. The filling 
 Station may comprise a supply line 20 (see FIG. 1) which extends through 
 hood 13 and is adapted at an outer end 52 to receive molten metal from a 
 suitable source (not shown) for discharge via a discharge head (not shown)
 into a mould 12 within hood 13. In such a case, hood 13 may be of 
 substantially constant height throughout, as shown. Alternatively, the 
 filling station may comprise a casting wheel member 52 such as shown in 
 simplified schematic form in FIG. 4 which is rotatable to supply molten 
 metal to each of successive moulds 12 via a respective one of a plurality 
 of spouts. In the latter case, it may be necessary for hood 13 to have 
 inlet and outlet end portions of substantially uniform height and an 
 intermediate portion of increased height in which the casting wheel member
 is housed for rotation. 
 An ingot mould casting system as shown in FIGS. 1 to 6 has been 
 successfully used for the casting of magnesium ingots, using a dilute 
 sulphur hexafluoride (SF.sub.6)/dry air gas mixture as a protective cover 
 gas. The system was found to function efficiently, restricting the amount 
 of ambient air ingress and minimising the amount of SF.sub.6 that was lost
 from the system. Published data suggests a lowest rate of cover gas 
 consumption of 0.7 kg/tonne of magnesium cast. However, with operation 
 with the system of the present invention, it has been found that this 
 consumption level can be reduced by at least 50%. At current prices for 
 SF.sub.6 (AU$60/kg), this would result in a saving of over AU$1,26M for a 
 60000 tonnes per year casting operation. 
 While the invention has particular application in ingot mould casting of 
 magnesium, it also is applicable with benefit to the casting of other 
 metals. Recent unpublished work has suggested that if aluminium were cast 
 under an inert gas, a substantial reduction or complete elimination of 
 dross formation may be possible. Dross presently needs to be skimmed from 
 the top of a solidifying aluminium ingot to provide a clean, flat surface 
 to enable efficient, automated ingot stacking. From experience with the 
 system of the present invention, the problem of dross formation and the 
 resultant need for skimming might be avoided with use of the system for 
 casting aluminium under an inert gas. The system of the present invention 
 may also have application for the casting of other metals, such as lead.