Patent Publication Number: US-9427803-B2

Title: Alloy casting apparatus

Description:
This is a national stage of PCT/AU2005/001315 filed 1 Sep. 2005 and published in English. 
     FIELD OF THE INVENTION 
     This invention relates to alloy casting apparatus. 
     BACKGROUND TO THE INVENTION 
     There is a need for a versatile gravity casting apparatus which is well suited to the needs of foundries for economical production of high integrity components. The present invention is directed to meeting that need and, in particular, to provide casting apparatus useful in the production of castings of magnesium alloys. 
     GENERAL SUMMARY OF THE INVENTION 
     The casting apparatus provided by the present invention has a reversibly pivotable assembly which enables gravity flow and feeding of alloy in a casting operation. The assembly includes an alloy supply vessel, in the form of a reservoir pot, retort or tank, a furnace in which the vessel is contained, and a die with which the vessel is in communication. The assembly is tiltable in one direction about a substantially horizontal axis to enable the flow of alloy to at least one die cavity defined by the die and in the opposite direction to prevent that flow. 
     The apparatus can be adapted or suitable for use with any gravity castable alloy. However, it is particularly suited for use with magnesium and magnesium alloys, herein collectively referred to as magnesium alloy. This is because the apparatus enables particular issues involved in handling and casting molten magnesium alloy to be accommodated. Thus, while the invention can have wider application, it principally is described herein with reference to magnesium alloy. 
     The casting apparatus according to the present invention has a supply vessel for holding a supply of alloy, a furnace in which the vessel is contained and in which the vessel is heatable to maintain the supply of alloy at a suitable casting temperature, a die mounted laterally outwardly from the vessel and on or in relation to the furnace, a conduit providing communication between the vessel and the die, and means for reversibly tilting an assembly including the furnace, the vessel and the die about a substantially horizontal axis to enable or prevent the flow of the alloy from the vessel to a die cavity defined by the die. 
     In the apparatus, the means for reversibly tilting the assembly may be capable of operating in at least the first of two possible modes. The first of the two modes is able to be used for operation of the apparatus in a number of repeated casting cycles. In the first mode, the assembly is tiltable between a first, non-casting position it occupies on completion of one cycle and before commencement of the next cycle and in which the flow of alloy from the vessel to the die is prevented, and a second, casting position enabling flow from the vessel to the die. The second mode is able to be used on completion of a casting run or to enable maintenance or repair of the apparatus. In the second mode, the assembly is tiltable to a third storage position which is beyond the non-casting position in a direction away from the casting position. When the assembly is in the storage position alloy retained in the conduit during pivoting in the first mode is able to drain back into the vessel. 
     The vessel may be able to hold a volume of molten alloy which is substantially larger than the volume of alloy consumed in a casting cycle. Preferably the vessel is able to receive fresh alloy as required to maintain an upper free surface of the alloy at a substantially constant level relative to the vessel when the assembly is in the non-casting position. However, the alloy surface may vary from a constant level within a relatively narrow range. The magnitude of that range can vary with the size of the apparatus, but can for example be not more than about ±30 mm, such as about ±15 mm of a desirable level. Alloy may be supplied to the vessel from a larger holding furnace, adjacent to the apparatus, such as by a syphon action. Alternatively, alloy may be added to the vessel from time to time, when necessary between successive cycles, such as by adding solid alloy to be melted in the vessel. 
     The positions to which the assembly is tiltable may be attained by pivoting to fixed angular positions. This includes each of the three positions detailed above, as well as a fourth position detailed later herein. However there can be benefit in the assembly being able to be tilted from the non-casting position to the casting position through an angle which increases sufficiently in successive casting cycles to achieve a substantially uniform pressure head for each cycle. That is, the increase in tilting angle can be designed to allow for the loss of molten metal in each casting cycle. Of course there are limits to the number of cycles over which increased tilting angle is practical before it is necessary to increase the volume of alloy in the vessel. 
     In one form, the conduit has a first end at the vessel at a location which most preferably is below the level of alloy in the vessel when the assembly is in the non-casting position. The arrangement is such that a pressure head of molten alloy above that location is able to be maintained during pivoting of the assembly in the first mode and such that the pressure head of alloy increases as the assembly tilts from the non-casting to the casting position. With the assembly in the casting position, the pressure head reaches a maximum, with the level of alloy in the vessel sufficiently above the highest point in the die cavity to ensure complete die cavity fill. 
     From the location from which the conduit extends, the conduit passes away from the vessel, and laterally through a wall of the furnace and outwardly to a second end at the die. The conduit communicates with the die, at least in preferred forms of the invention, in a manner enabling alloy to flow upwardly in, and fill, the die cavity under the pressure head of alloy established in the vessel when the assembly is in the casting position. While not essential, it is preferable that the conduit communicates with the die cavity at a location which, with the assembly in the non-casting position, is directly below the die cavity. In any event, the die most preferably is located laterally outwardly from the vessel and at a height such that, with the assembly in its non-casting position and the die open, the level of alloy in each of the vessel and the conduit is in the same horizontal plane extending adjacent to the second end of the conduit and a fixed part of the die. 
     The conduit preferably is relatively long. The first part of the conduit within the furnace is heated by the furnace, thereby reducing the risk of excessive cooling of the alloy in flowing to the die. The second part of the conduit between the furnace and the die preferably is protected from excessive cooling. For this protection, the conduit can be of a refractory thermal insulating material, or the second part can be provided with an insulation sleeve. However the second part of the conduit, particularly where it is of a suitable metal such as steel, preferably is heated, such as by provision of an electric resistance coil around the second part. 
     The conduit may have a main part of its length from the first end which, in extending through and outwardly from the furnace, also is inclined downwardly relative to the assembly when in the non-casting position. The main part may, for example, be inclined at an angle of from about 5° to 15° from the horizontal. From the end of main part remote from the vessel, the conduit has a shorter part which extends upwardly to the die such as substantially vertically. The relative lengths of the main and shorter parts, and the angle at which the main part is inclined downwardly from the horizontal, are such that a relatively small angle of pivoting is necessary to enable the assembly to pivot between the non-casting and casting positions. The angle of pivoting may, for example, be from about 15° to 30°, such as from about 20° to 25°. The shorter part may extend upwardly from the main part at an acute angle which substantially corresponds to the complement of the angle at which the main part is inclined from the horizontal. Alternatively, the conduit may have an intermediate part providing a curved transition from the main part to the shorter part. 
     The location at which the conduit extends from the vessel preferably is such as to facilitate use of a relatively small angle of pivoting between the non-casting and casting positions. As indicated above, that location most preferably is below the level of alloy in the vessel when the assembly is in the non-casting position. The vessel most preferably has an upstanding wall from which the conduit extends, with the wall preferably at not more than a small angle to the vertical with the assembly in the non-casting position. Thus, as the assembly pivots from that position, the pressure head of alloy above the location from which the conduit extends is able to increase substantially as the assembly pivots to the casting position. Also, to maximise this effect, the axis about which the assembly is pivotable may be horizontally spaced beyond the centre-line of the vessel, in a direction away from that location, such that the spacing between the axis and the location is significant relative to the length of the major part of the conduit. The spacing may, for example, be at least about 40% of that length, but preferably is in excess of about 50% of that length. 
     In one convenient form, the vessel comprises a trough which is U-shape in cross-sections perpendicular to the pivot axis. In that form, the conduit extends from one of opposite side walls defined by the U-shape, while the pivot axis is offset towards or, if required beyond, the other one of those walls. A vessel of that form may have a respective upwardly extending wall at each end, with those walls extending transversely with respect to the pivot axis, such as substantially vertically. In that, or in other forms, the vessel most preferably has a cover which enables maintenance, if required, of a protective atmosphere over the surface of the alloy. The cover may have an openable port through which fresh alloy is able to be supplied to the vessel. Alternatively, a syphon pipe may extend through the cover to enable maintenance of the level of alloy in the vessel by a syphon action. 
     The vessel may have a transverse baffle or partition which divides the interior of the vessel into two chambers or sections. Where the vessel is a trough as described above, the transverse baffle may be intermediate of and, for example, about mid-way between the end walls. The conduit is able to extend from a first one of the chambers or sections, while fresh alloy is able to be supplied to the second chamber or section. The baffle has openings therethrough, or openings are defined between an edge of the baffle and a base surface of the vessel such that fresh alloy supplied to the second chamber is able to flow through to the first chamber from which the conduit extends. The arrangement is such that solid lumps of alloy are able to be present in the second, charging chamber without impeding alloy flowing from the first, casting chamber to the conduit during a casting operation. 
     In one embodiment of the apparatus according to the invention, the die has a lower part by which the die is mounted on or in relation to the furnace, and an upper part which is moveable relative to the furnace for opening and closing the die. In that embodiment, the die is provided with supply means for supplying protective cover gas to the die cavity for protecting the surface of molten alloy, at the second end of the conduit, when the die is open. The supply means preferably is operable to provide protective gas to the die for flow into the die cavity on solidification of alloy therein and just prior to tilting of the assembly from the casting position to the non-casting conditions. The arrangement is such that, as molten alloy retracts from the die, a resultant reduction in pressure at the second end of the conduit enables protective gas to flow into the second end of the conduit. As will be appreciated, the protective gas is supplied at a slight positive pressure, enabling its flow into the die cavity and into the second end of the conduit. Flow of the protective gas within the die cavity to the conduit is facilitated by the inherent shrinkage of a product being cast providing a slight clearance between the surface of the product and the die surfaces defining the die cavity. 
     Preferably the cover gas is able to flow into the die cavity along one or more channels formed in one or each of the die parts at the parting plane. The gas may be supplied to the outer periphery of surfaces of the die parts between which the parting plane is defined. In one convenient form, the gas is supplied from a convenient source of supply to a chamber which extends around that periphery, and is able to flow from the chamber to the die cavity along a plurality of passageways defined, for example, at the parting plane of the die. 
     As the assembly is tilted to the casting position, alloy flowing into the die cavity displaces air and protective gas. Thus, fresh protective gas needs to be supplied to the die in each casting cycle. The apparatus preferably includes means for timing the supply of protective gas as appropriate, in response to relevant operating parameters. 
     The means for supplying protective cover gas preferably includes a system of passages which provide communication between a supply port of the die, to which the gas can be supplied from a source, and the die cavity. The system of passages also enables gas in the die cavity on commencing a casting operation to be purged by molten alloy flowing into the die cavity, with the purged gas discharging from the passages via a discharge port. Respective valves can be operable to close one of the ports when the other of the ports is open. 
     If the die remains open for a prolonged period of time, it is desirable to supply cover gas to the die end of the conduit. This may be by means of a supply hose, gun, spray can or the like. 
    
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       In order that the invention may more readily be understood, reference is made to the accompanying drawings, in which: 
         FIG. 1  is a sectional view through a casting apparatus according to the present invention, showing the apparatus in a non-casting position; 
         FIG. 2  corresponds to  FIG. 1 , but shows the apparatus in a casting position; 
         FIG. 3  shows, on an enlarged scale, part of the apparatus shown in  FIG. 2 ; 
         FIG. 4  is similar to  FIG. 3 , but shows part of a control system in a slightly modified arrangement; 
         FIG. 5  is an enlarged, exploded perspective view of part of the arrangement of  FIG. 4 ; 
         FIG. 6  shows, on an enlarged scale, a further part of the apparatus shown in  FIGS. 1 and 2 ; 
         FIG. 7  is a perspective view of a component shown in  FIG. 6 ; 
         FIG. 8  schematically illustrates a mechanism for releasing the component of  FIG. 7 ; 
         FIG. 9  is a cut-away perspective view of a part of the apparatus shown in  FIGS. 1 and 2 ; 
         FIGS. 10 to 13  provide schematic representation of a furnace as described with reference to  FIGS. 1 and 2 , but in four different respective positions; and 
         FIGS. 14 to 16  show respective views of an alternative to the control system shown in  FIGS. 4 and 5 . 
     
    
    
     With reference to  FIGS. 1 and 2 , the apparatus  10  shown therein has an assembly  12  which includes a supply vessel  14  for holding a supply of molten alloy  15  and a furnace  16  in which vessel  14  is contained and heatable for maintaining alloy  15  at a casting temperature. The assembly  12  further includes a die  18  mounted on or in relation to furnace  16 , laterally outwardly from one side of vessel  14 , and a conduit  20  providing communication between vessel  14  and die  18 . 
     The assembly  12  is mounted so as to be tiltable on a substantially horizontal axis “X” which extends normal to the views depicted in  FIGS. 1 and 2 . To enable this, a trunnion  22  projecting from each end of furnace  16  is journalled in a respective one of a pair of stanchions  24  secured to base B. Also, at each end of furnace  16 , there is a respective hydraulic ram  26  which is extendable and retractable for tilting of assembly  12 . 
     The vessel  14  is in the form of a relatively short trough defined by a U-shaped peripheral plate  28  and opposite end walls  30 . Also, intermediate of end walls  30 , vessel  14  has a transverse baffle on partition  29  which has openings  31  and is more fully described below. The conduit  20  has a main part  32  which extends from one side wall  34  of plate  28 , through an adjacent side wall  36  of furnace  16 , to a position spaced below die  18 . From the outer end of part  32 , conduit  20  has a shorter upwardly extending part  38  providing communication with die  18 . As best seen in  FIG. 6 , the inner end of conduit parts  32  is connected to an annular flange  40  provided on a connector  42  of vessel  14 . The flange  40  is abutted by a similar flange  44  of conduit  20 , while the flanges  40  and  44  are secured together by a clamp device  45  described in more detail below. 
     The die  18  has a lower part  46  and an upper part  48 . The part  46  is mounted on or in relation to furnace  16 . In the somewhat schematic representation of  FIGS. 1 and 2 , part  46  is depicted essentially as mounted on the upper end of part  38  of conduit  20 . However, a more typical arrangement would be for furnace  16  to have a side bracket or apron on which part  46  is supported, as schematically depicted at  49 . The upper part  48  is able to be moved between the position shown in  FIG. 2 , in which the parts  46  and  48  define a die cavity  50  (see  FIG. 3 ), and the raised position shown in  FIG. 1 . For this movement, apparatus has upstanding guides  52  on the upper ends of which a hydraulic ram  54  is mounted. The ram  54  is retractable and extendable for raising and lowering of die part  48  relative to die part  46 . 
     The vessel  14  is designed to hold a volume of molten alloy  15  such that, with assembly  12  in the non-casting position shown in  FIG. 1 , the free surface of alloy  15  is above the location of at which connector  42  provides communication between vessel  14  and conduit  20 . From that location, part  32  of conduit  20  extends outwardly and downwardly with respect to vessel  14 . The arrangement is such that, with assembly  12  in the non-casting position, and the die  18  open (so that the outer end of conduit  20  is at atmospheric pressure), the free surface of alloy  15  in conduit  20  is just below die  18 . With retraction of the hydraulic ram  26 , assembly  12  is able to be tilted on axis X, clockwise with respect to the views shown in  FIGS. 1 and 2 , to bring assembly  12  to the casting position shown in  FIG. 2 . However prior to this tilting, ram  52  is extended to move upper die part  48  down to engage lower die part  46  and thereby close die  18  in readiness for a casting operation. 
     As assembly  12  is tilted from the non-casting position of  FIG. 1  to the casting position of  FIG. 2 , the location at which conduit  20  extends from vessel  14  drops further below the surface of alloy  15  in vessel  14 . The pressure head above that location increases to a maximum at the casting position. Also, the outer end of conduit  20  and the closed die  18  are lowered relative to the free surface of alloy  15  in vessel  14 . As a consequence, alloy is caused to flow into conduit  20  under the influence of gravity and, from conduit  20  into the die cavity  50 . The top of cavity  50  is below the surface of alloy in vessel  14  to an extent in the casting position that a substantial pressure head “H” exists above the cavity  50 . Thus, die cavity fill is able to be achieved under a significant pressure which ensures completion of filling and a measure of shrinkage offset. 
     Due to the length of main part  32  of conduit  20 , it is sufficient for assembly  12  to be tilted through only a relatively small angle in establishing the pressure head H on moving from the non-casting position to the casting position. The angle may be for example, from about 15° to 30°, such as from about 20° to 25°. The attainment of a substantial pressure head is assisted by the downward inclination of conduit  20  relative to vessel  14  with assembly  12  in the non-casting position, and the bent or dog-leg form of conduit  20  resulting from its mutually inclined parts  32  and  38 . Development of the pressure head also is assisted by axis X being spaced beyond the centre-line of vessel  14  in a direction away from the side of vessel  14  from which conduit  20  extends, as well as by conduit  20  extending from a relatively upright portion of sidewall  34  of plate  28 . 
     At least when casting with magnesium alloy, a protective atmosphere most preferably is provided in vessel  14  and, when die  18  is open, in the outlet end of conduit  20 , in order to prevent oxidation and a risk of combustion of the alloy. In vessel  14 , the volume above alloy  15  is relatively easily protected. Suitable protective gases are more dense than air and, hence, relatively easily retained, while retention of the gas is assisted by provision of a lid  55  covering vessel  14 . With alloy in the upper end of part  38  of conduit  20 , the matter is less straight forward. However, an arrangement as illustrated in  FIGS. 3 to 5  is found to provide a beneficial result. 
       FIG. 3  shows the die  18  just prior to the commencement of tilting of assembly  12  from the non-casting position. Thus, the die  18  is closed.  FIG. 4  shows the situation after return of assembly  12  to the non-casting position, just prior to opening of die  18  for release of a casting  56  from die cavity  50 . 
     As shown in  FIGS. 3 to 5 , each lower and upper die parts  46  and  48  has a respective peripheral flange  58  and  60 . In  FIG. 3 , the flange  60  of die part  48  has a down-turned outer rim  62 , while a seal  64  is fitted around a groove  65  in the lower edge of rim  62  for bearing against the upper face of flange  58  of part  46 . In  FIGS. 4 and 5 , the flange  58  of part  46  has an upturned outer rim  62 , while a seal  64  for bearing against the upper edge of rim  62  is fitted around a groove  65  in the lower face of flange  60  of part  48 . The arrangement is such that, with die  18  closed to bring parts  46  and  48  into contact on parting plane P, the flanges  58  and  60  form a manifold  66 . In manifold  66 , a chamber  68  is defined around the periphery of die parts  46  and  48  and through which plane P extends. Around the die cavity  50 , chamber  68  and cavity  50  are in communication by a plurality of slots  70  formed in the surface of at least one of parts  46  and  48 —in part  46 , in the arrangement illustrated—to define thin passageways  71  between cavity  50  and chamber  68 . 
     Manifold  66  includes at least one connector  72  which communicates with chamber  68 . Connector  72  is connectable to a supply line  74  by which protective cover gas is able to be supplied to chamber  68 . Also, manifold  66  includes at least one connector  75  through which gas is able to discharge from chamber  68  for collection via discharge line  76 . 
     As previously indicated, the surface of alloy  15  in conduit  20 , with assembly  12  in the non-casting position and die  18  open, is just below die  18 . This remains the case on closing die  18 , prior to tilting from that position, as illustrated in  FIG. 3 . As the assembly  12  is tilted to the casting position, the alloy rises in conduit  20 , enters the die via inlet sprue  78  and flows into and fills die cavity  50 . In the processes of obtaining die cavity fill, the alloy displaces gas present in the outlet end of conduit  20  and in cavity  50 . The displaced gas passes along passageways  71  to chamber  68 . From chamber  68 , the displaced gas is discharged via line  76 . To enable this, a valve  80  in line  76  is opened, while a valve  82  in line  74  is closed. The valves  80  and  82  preferably are solenoid valves. 
     On solidification of a casting  56  produced by die cavity fill in tilting to the casting position, alloy solidifies back from the casting to a narrow neck at the inlet to sprue  78 . On completion of this solidification the assembly  12  is returned to the non-casting position. As the assembly is tilted away from the casting position, still molten alloy in conduit  20  is drawn back toward vessel  14 , tending to create a void between the surface of molten alloy in conduit  20  and solidified alloy in sprue  78 . 
     Prior to the commencement of tilting from the casting position, valve  80  is closed and valve  82  is opened. With opening of valve  82 , protective gas is supplied into chamber  68 , and the protective gas is able to pass via passageways  71  and the die cavity  50 , into the end of conduit  20 . This is enabled by the shrinkage of alloy in cavity  50  on solidification providing a sufficient slight clearance around the resultant casting  56  for the flow of protective gas from passageways  71 , around the casting  56  and sprue metal to conduit  20 . Also, the protective gas necessarily is supplied at a pressure in excess of atmospheric pressure for its supply into chamber  68  while, as indicated, retracted alloy in conduit  20  tends to create a reduction in pressure is generated in conduit  20 . 
     When assembly  12  is returned to the non-casting position, the valve  82  is closed. The die part  48  then is raised and the casting is removed. However, even though the die  18  is open, the protective gas is able to be sufficiently retained in the end of conduit  20  due to it being more dense than air. The gas thus is able to protect the upper surface of alloy in conduit  20  from oxidation during the relatively short interval between casting cycles. 
     In addition to being operable to tilt assembly  12  between the casting and non-casting positions, ram  26  is able to be operated to tilt assembly  12  to a storage position. For this, ram  26  is extended to an extent greater than necessary to return assembly  12  from the casting to the non-casting position. That is, assembly  12  is tilted anti-clockwise, relative to the views of  FIGS. 1 and 2  beyond the non-casting position of  FIG. 1 . The angle through which the assembly  12  is tiltable from the non-casting to the storage position needs to be sufficient to enable all alloy in conduit  20  to flow back into vessel  14 . 
     The storage position is able to be used on completion of a casting campaign. Alloy which solidifies in the vessel  14  is able to be remelted by heat energy input from furnace  16 . However, alloy should not be permitted to solidify in conduit  20 , due to difficulty in remelting it. Tilting of assembly  12  to the storage position enables avoidance of solidification of alloy in conduit  20 . 
     Tilting to the storage position also can be used in the event of a failure of vessel  14  which allows molten alloy to drain into furnace  16 . As shown, furnace  16  has a drainage port  84  which, with assembly  12  in the storage position, enables molten alloy to be drained into a chamber  86  mounted along the side of furnace  16  remote from die  18 . The chamber  86  may be provided with flux  87  suitable for forming a slag with molten alloy. As the chamber  86  is able to remain relatively cool, the flux may be kept in plastic bags which melt on contact with the alloy to release their contents. The sloping base  88  facilitates draining of alloy into chamber  86 . 
     Conduit  20  may necessitate removal for service or replacement from time to time. This is facilitated by clamp device  45  and the arrangement shown in  FIG. 6 . As shown in  FIG. 6 , the faces of flanges  40  and  44  interfit due to flange  44  having a recessed seat  89  and flange  40  having a projecting central hub  90 . A corrugated gasket  91  is provided between seat  89  and hub  90 , and the flanges  40  and  44  are urged together by device  45  to achieve a seal at gasket  91 . 
     Each flange  40  and  44  has a tapered outer side face. The device  45  has an opposed pair of clamp members  92  and  93 , each of which defines a semi-circular groove in which flanges  40  and  44  are able to seat. The lower member  92  has a parallel pair of threaded rods  94  projecting therefrom, and through holes in the upper member  93 . Above member  93 , a compression spacer tube  95  is fitted on each rod  94  such that a nut  96  tightened on the rod  94 , down onto the tube  95 , draws the members  92  and  93  together. The groove in each of members  92  and  93  has tapered sides which bear against tapered sides of flanges  40  and  44 . Thus, tightening the nuts  96  or rods  94  serves to force the flanges  40  and  44  firmly together to grip gasket  91 . 
     As shown in  FIGS. 1 and 2 , the upper ends of rods  94  and tubes  95  project through the tops of furnace  16 . Thus, nuts  96  readily are able to be tightened or released, as required. Also, as best seen in  FIG. 7 , the upper member  93  has a rod  97  which projects upwardly between rods  94 . The rod  97  serves as a handle for use in manoeuvring device  45 . However, as shown in  FIG. 8 , a nut  98  can be provided on the threaded upper end of rod  97 , after positioning a heavy sleeve  99  on rod  97 , with the arrangement being operable as an impact hammer for use in separating members  92  and  93  after loosening nuts  96 . 
     With reference to  FIG. 9 , the perspective view of vessel  14  shown therein is cut-away to show baffle  29 . The baffle is shaped to conform to the inner U-shaped surface of plate  28 , and is secured in position by welding to plate  28 . Baffle  29  is substantially parallel to and located mid-way between end walls  30  of vessel  14 . Thus, the interior of vessel  24  is divided into a first chamber  14   a  from which conduit  20  extends, and a second chamber  14   b . Fresh alloy is able to be supplied to the chamber  14   b  and, to maintain the molten alloy in chamber  14   a  at a required level, the holes  31  are provided in baffle  29  to enable alloy to flow from chamber  14   b  to chamber  14   a . Baffle  29  has an upper edge which, relative to assembly  12  in the non-casting position, has a substantially horizontal mid-section  29   a  and, at each end of the mid-section  29   a , an outwardly and upwardly inclined end section  29   b . The required level of alloy in vessel  14  is such that it is below the mid-portion of  29   a  with the assembly  12  in the non-casting position and below a respective end portion  29   b  with assembly  12  in each of the casting and storage positions. 
     With reference to each of  FIGS. 10 to 13 , the apparatus  110  shown therein is very similar to the apparatus  10  of  FIGS. 1 and 2 . The structure of and casting operations with apparatus  110  generally will be understood from the description of  FIGS. 1 and 2 . To the extent that it is necessary to refer to components of the apparatus  110 , they have the same reference numeral as the corresponding components of apparatus  10 , plus  100 . However, staunchens and a ram corresponding to staunchens  24  and ram  26  of  FIGS. 1 and 2  have been omitted for simplicity of illustration. 
       FIGS. 11 and 12  show the apparatus  110  respectively in a non-casting position corresponding to that of  FIG. 1  and a casting position corresponding to that of  FIG. 2 . Thus, in  FIG. 11 , the assembly  112  is in the non-casting position, ready for movement to the casting position shown in  FIG. 12 . The aspects of operation in movement between these positions are essentially as described in relation to  FIGS. 1 and 2 . 
       FIG. 10  shows the apparatus  110  after having been moved from the casting position of  FIG. 12  to the non-casting position of  FIG. 11 , and then beyond the non-casting position to a park or storage position. In the latter position, which may be assumed for example at the end of a casting campaign, the main part  132  of conduit  120  is inclined upwardly from vessel  114  such that it is slightly above horizontal. As a consequence, alloy  115  has drained back from the lower die part  146  of open die  118 , and from conduit  120 , into vessel  114 . 
       FIG. 13  shows the assembly  112  in an emptying position. The assembly is moved to this position from the park or storage position of  FIG. 10 , by tilting the assembly through the non-casting position of  FIG. 11  and to and beyond the casting position of  FIG. 12 . However, prior to leaving the park or storage position, the conduit  20  is modified. This can be by a number of different arrangements. In a first arrangement, the clamp device  145  is loosened to enable the conduit  120  to be removed, after which it is replaced by another conduit  120   a . As shown in  FIG. 13 , conduit  120   a  is straight and provides an in-line continuation of connector  142  of vessel  114 . The arrangement is such that, as assembly  112  is tilted to its emptying position, alloy is able to discharge from vessel  114  to be received in a suitable receptacle  100 . In  FIG. 13 , assembly  112  is shown part-way to its emptying position. Assembly  112  needs to tilt further beyond the casting position of  FIG. 12  to reach the emptying position in which all alloy in vessel  114  is able to discharge into receptacle  100 . 
     In a second arrangement, illustrated in  FIG. 12 , the end of the main part  132  remote from connector  142  has a removable cap  101 . When it is required to empty vessel  114 , cap  101  is removed with the assembly  112  in the park position of  FIG. 10 , and an in-line short conduit  102 , shown in broken outline in  FIG. 12 , then is fitted. As a further variant,  101  denotes a valve member to which conduit  102  can be attached. The valve member  101  enables conduit  102  to be fitted with assembly in any position, with the valve member  101  being adjustable between positions in which it prevents or enables flow through conduit  102 . 
       FIGS. 14 to 16  show an alternative to the arrangement of  FIGS. 4 and 5 , both in respect of the form of the die and the system for distributing protective gas and displacing atmospheric gas. Parts of the arrangement of  FIGS. 14 to 16  which correspond to those of  FIGS. 4 and 5  have the same reference numeral, plus  100 . 
       FIG. 14  shows a part sectional view of a die  118  having lower and upper die parts  146  and  148  and, between parts  146  and  148  when the die  118  is closed, a peripheral die body assembly  102 . The parts  146  and  148  with body assembly  102  together define a die cavity  150 . Thus, rather than there being a parting plane at which parts  146  and  148  meet, each of parts  146  and  148  meets a respective surface of body assembly  102 . 
     The body assembly  102  includes a plurality of elongate members  103 , of which part of one is shown in each of  FIGS. 15 and 16 . The members  103  have mitered ends at which adjacent members  103  meet. Also the members  103  define a flow system which enables the supply of protective gas to and the purging of atmospheric gas from the die cavity  150 . 
     In the upper and lower surfaces  103   a  of each member  103 , there is defined a longitudinal groove  104  adjacent to the outer face  103   b . From each groove  104 , a plurality of shallow, but relatively wide channels  105  extend to the inner, die cavity defining face  103   c . A bore  106  provides communication between each groove  104 , while an inlet port  107  at the outer face  103   b  communicates with bore  106 . With the die closed, as shown in  FIG. 14 , each groove  104  and its channels  105  are covered by the adjacent one of die parts  146  and  142 , to define longitudinal passage  104   a  and shallow passages  105   a , respectively. The arrangement is such that gas is able to flow from a gas flow line partly shown at  108 , through port  107  to passage  104   a  and then, via passages  105   a , into the die cavity  150 , or from cavity  150  in the reverse direction for discharge through line  108 . 
     At one mitered end  103   d  of each member  103 , each end  103   d  of each alternate member  103 , or each end  103   d  of each member  103 , there is a similar facility for gas flow. Thus, as shown in  FIGS. 15 and 16 , there is a vertical groove  109  adjacent to the outer face  103   b  and a plurality of shallow, but relatively wide channels  111  which extend from the groove  109  to the inner face  103   c . A port  113  communicating with groove  109  enables a flow of gas to or from the die cavity  150 . With the die closed, the opposed ends of adjacent members  103  abut so that the groove  109  and channels  111  provide a passageway between the die cavity  150  and port  113 . 
     The arrangement is similar to that described reference to  FIGS. 4 and 5 . Thus, the flow system for at least one member  103  may have its gas flow line  108  connected to a source of supply of protective cover gas to be supplied to the die cavity when required, with at least one other member  103  having its line  108  enabling discharge of gas from a cavity  150  when required. In this case, the facility for gas flow at mitered ends  103   d  may be inter-connected with the system for flow in line  108 . A number of arrangements are possible, although the overall requirement is that the die cavity  150  is able to be purged of gas by incoming alloy, and to receive protective gas, when required. 
     A number of significant practical benefits of the casting apparatus of the present invention will be understood from the description with reference to the drawings. Thus, apparatus significantly extends the capability, and reduces the cost, of permanent mold casting for a wide range of components, including high-performance components. Also, the apparatus enables low capital, tooling and running costs, while it is amendable to electric resistance heating. The apparatus has a small machine footprint, while it can avoid the need for ladling through the air, and requires no applied pressure to fill the die cavity. The apparatus enables a high yield of cast metal, typically about 95%. 
     The casting apparatus is found to enable production of high-integrity castings which can be heat treatable and weldable. Castings with complex internal shapes are possible, using sand cores. The apparatus is suitable for small to large production quantities for a wide range of products for the automotive and other industries. 
     Castings (produced with apparatus according to the invention) are found to have excellent finish out of the die, with no flow lines or discolouration and good overall cosmetic appearance. The castings have excellent surface detail and definition, and are free of misruns. Also, machined castings display good, bright finish. The measured tensile properties for castings produced with the apparatus are found to equal or exceed comparable reported properties for gravity permanent mold-cast alloy, such as AZ-91. 
     The apparatus of the present invention enables cycle times which are faster than equivalent magnesium gravity permanent mould castings, with no risers needed. Also, the cycle times are significantly faster than equivalent aluminium gravity permanent mold castings. Additionally, consumable costs generally are low, such as with protective cover gas, while commercially available die coat can be used. Casting wall thicknesses are typical of permanent mold casting. Also, labour costs can be kept to a low level. 
     Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.