Apparatus And Method For Use In Casting Of Metals And/Or Metal Alloys

Abstract

An apparatus and method is disclosed for forming an item in a mould using a casting process, typically a counter gravity casting system. Heating assembly, transfer assembly and mould filling assembly can be used in combination. The transfer assembly includes apparatus and method for removing sedimentation from the liquid metal and/or metal alloy received from the heating assembly and extracting the same prior to the metal and/or metal alloy reaching the mould filling assembly at which the same is supplied to fill a cavity of a mould and which, once filled, can be slid to a location to cool and thereby make available the mould filling assembly for the next mould to be filled. This apparatus and method provide an efficient, high throughput system, along with high quality cast items.

Claims

1. Apparatus for use in the casting of metal and/or metal alloy, said apparatus comprising: a heating assembly in which the metal and/or metal alloy is changed into a substantially liquid state; a mould filling assembly in which the metal and/or metal alloy is moved into a mould to be cast; and a transfer assembly to transfer the metal and/or metal alloy by allowing the material to flow between the heating assembly and the mould filling assembly and said transfer assembly allows for sedimentation of one or more bi-films in the metal and/or metal alloy during transfer and wherein the transfer assembly includes a launder and means to create a portion in the launder which allows the one or more bi-films an opportunity to separate from the flow of the metal and/or metal alloy and settle in a vessel or sump from which a bi-film sediment is extracted.

2. Apparatus according to claim 1 wherein said transfer assembly allows for a passive degassing of said metal and/or metal alloy during passage of the same through the transfer assembly in a molten, liquid condition.

3. (canceled)

4. (canceled)

5. Apparatus according to claim 1 wherein the heating assembly is provided in a form of a dry hearth melter from which the liquid metal and/or metal alloy is transferred in a molten liquid condition via the transfer assembly to the mould filling assembly.

6. Apparatus according to claim 5 wherein metal and/or metal alloy charge materials are preheated as they move down a shaft of the heating assembly by heat from a heating means moving up the shaft so as to form a counter flow heat exchanger.

7. Apparatus according to claim 5 wherein the metal and/or metal alloy charge material is melted on a hearth and runs down a slope and into a holding bath of the heating assembly while oxide skin on the charge material remains on the hearth.

8. Apparatus according to claim 1, wherein the mould filling assembly includes a mould for forming an item to be cast from the metal and/or metal alloy, a crucible furnace to which the liquid metal and/or metal alloy is supplied from the transfer assembly, and a pump to move the metal and/or metal alloy into a cavity in the mould to fill the same.

9. (canceled)

10. Apparatus according to claim 8 wherein the liquid metal and/or metal alloy flows through a riser tube and into the mould cavity placed above the same.

11. Apparatus according to claim 1 wherein the mould filling assembly includes a casting platen on which the mould is located and when the mould is filled with the metal and/or metal alloy, the mould is slid along the casting platen to a location to cool and solidify the metal and/or metal alloy and thereby free up the mould filling assembly to receive a new, empty mould.

12. Apparatus according to claim 1 wherein extraction of the bi-film sediment from the vessel or sump is via a riser tube, to an end of which is applied a vacuum to draw up the bi-film sediment through the riser tube.

13. Apparatus according to claim 1 wherein a bubble lift mechanism is used to remove the bi-film sediment from the vessel or sump by imparting bubbles into molten material and which rise and move through a riser tube and carry a flocculant volume of sedimentation along with flow from the molten material.

14. Apparatus according to claim 12 wherein material which is emitted from a top of the riser tube is directed into a mould to solidify.

15. (canceled)

16. Apparatus according to claim 1 wherein the launder includes an elongate channel at a predetermined height so as to minimise any fall of liquid flow from the heating assembly.

17. Apparatus according to claim 16 wherein the transfer assembly includes heating means to maintain a temperature of the molten material as it passes along said elongate channel.

18. Apparatus according to claim 1 wherein the apparatus includes dosage means to allow dosage of elements into the liquid material, the elements promote sedimentation prior to location of extraction of sedimentation.

19. Apparatus according to claim 18 wherein the dosage means includes a wire formed of an aluminium based alloy containing one or more elements which form compounds with aluminium and which nucleate and grow on bi-films.

20. Apparatus according to claim 1 wherein a portion of the launder allows for separation of the one or more suspended bi-films in the liquid metal and/or metal alloy material and the sediment of the one or more bi-films separates from the flow and settles in a vessel or sump to concentrate the bifilm sediment at a location from where the bifilm sediment can be extracted.

21. Apparatus for use in a counter gravity casting process, said apparatus comprising: a mould filling assembly including a mould with a cavity therein, a furnace in which a metal and/or metal alloy in a liquid state is located, a passage in a form of a riser tube connecting the furnace to the cavity to allow liquid metal to pass therealong and into the mould cavity when an ingate of the mould is in register with the riser tube, and wherein a support surface is provided and located so as to be substantially level with an interface between the ingate of the mould and the riser tube such that after filling of the mould cavity to a desired extent, a supply of liquid metal is closed off and the mould is moved by a sliding action from a position in register with the riser tube across the support surface to a position thereon which is sufficiently remote from the riser tube to allow a further mould to then be placed in connection with the riser tube.

22. Apparatus according to claim 21 wherein the supply of liquid metal and/or metal alloy is cut off by operation of a valve which is located at an end of the riser tube which opposes the end at which the interface with the mould is located.

23. Apparatus according to claim 21 wherein the furnace provides a reservoir of the metal and/or metal alloy and a pump is provided which allows control of pressure of a supply of the liquid metal and/or metal alloy to the riser tube and mould cavity.

24. Apparatus according to claim 21 wherein cooling apparatus is provided and/or the support surface is of a form so as to encourage solidification of the liquid metal and/or metal alloy in the filled mould, at least adjacent to the mould ingate and to a sufficient extent to then allow the filled mould to be lifted clear from the support surface as a subsequent step.

25-26. (canceled)

27. A method of casting a metal and/or metal alloy item including a heating assembly, a mould filling assembly and a transfer assembly to transfer liquid metal and/or metal alloy from the heating assembly to the mould filling assembly, said method including the steps: heating the metal and/or metal alloy charge in the heating assembly to a substantially liquid state, passing the liquid material along a launder channel of the transfer assembly to a furnace of the mould filling assembly, inducing movement of the liquid metal and/or metal alloy into the mould via one or more riser tubes to fill the mould, and wherein during flow of the liquid metal and/or metal alloy along the transfer assembly, sedimentation of one or more bi-films in the metal and/or metal alloy occurs in at least a portion of the launder channel and collecting the sedimentation separated from the metal and/or metal alloy material flow in a vessel or sump and extracting said bi-film sediment from the vessel or sump.

28. The method according to claim 27 wherein a rate of sedimentation is increased by causing heavy precipitates to form on an outer, wetted surfaces of the one or more bifilms, by adding heavy elements into solution in the liquid metal and/or metal alloy.

29. The method according to claim 27 wherein the method includes aligning an ingate of the mould with an orifice of a riser tube of the mould filling assembly via which liquid metal and/or metal alloy is supplied from a furnace in the mould filling assembly to the mould via a pump.

30. The method according to claim 29 wherein the orifice is substantially coincident in a horizontal plane with an adjacent substantially horizontal support surface and along which the mould, when filled, is slid to a cooling location.

31. The method according to claim 29 wherein the liquid metal and/or metal alloy is provided at a first level in the riser tube, and pressure applied to the liquid metal and/or metal alloy is increased to move the same to a second level which is in the cavity in the mould and then stopping the liquid metal supply and when the cavity of the mould is filled sliding the mould sideways on the support surface to a sufficient extent to move the mould clear of the riser tube and retaining the mould in contact with the support surface until at least the liquid metal and/or metal alloy located in the cavity adjacent the ingate solidifies.

32. (canceled)

33. The method according to claim 31 wherein the first level of the liquid metal and/or metal alloy is substantially level with the support surface and the second level is substantially at a top of the mould cavity.

34. The method according to claim 27 wherein the support surface is formed of a cooling heat conducting material and/or cooling means are operated to cool the support surface.

35-38. (canceled)

Description

[0079] Specific embodiments of the invention are now described with reference to the accompanying drawings wherein:

[0080] FIGS. 1a-b illustrate counter gravity system apparatus in accordance with one embodiment of the invention in side elevation and plan;

[0081] FIGS. 2a-e illustrate apparatus in accordance with one embodiment of the invention prior to the commencement of use of the same;

[0082] FIG. 3 illustrates the apparatus components in accordance with one embodiment of the invention;

[0083] FIG. 4 illustrates the apparatus in accordance with one embodiment in plan and subsequent to the filling of a first mould and in-use to fill a second mould;

[0084] FIGS. 5a-e illustrate one embodiment of the transfer assembly in accordance with the invention;

[0085] FIGS. 6a-h illustrate views of one embodiment of the pump of the mould filling assembly;

[0086] FIGS. 7a-g illustrate views of a replaceable insert for the pump of FIGS. 6a-h; and

[0087] FIGS. 8a-f illustrate a component for use with the furnace of the mould filling assembly in accordance with one embodiment of the invention.

[0088] Referring firstly to FIGS. 1a and b there is illustrated a casting system in accordance with one embodiment of the invention. In this embodiment the system is a counter gravity casting system.

[0089] The system includes a heating assembly 2 in the form of a dry hearth tower which includes a flue 4 which allows gases to pass up through the descending charge, pre-heating the charge efficiently as a counter-flow heat exchanger. The use of the dry hearth 6 melting provides an advantage over crucible or bath melting because the primary oxide skins on the charge materials can be separated completely from the metal. The oxide skins remain on the sloping hearth 6 and are scraped off periodically. The molten metal and/or metal alloy, free from the primary oxides which would normally have been present, enters the refining system. Typically the dry hearth melter can maintain the melt level 8 constant to within a few millimetres and feed-back from the monitor of the metal level can be used to match the melting rate to the casting rate.

[0090] The transfer assembly 26 includes a launder or channel to allow the flow of the liquid metal and/or metal alloy from the heating assembly 2 to the mould filling assembly 12 in the direction of arrow 14. Along the launder there is provided a portion 16 which acts as an oxide sediment pump (OSP) 16 to allow sedimentation of oxide bifilms from the liquid metal and/or metal alloy in a controlled manner, together with extraction via a pump 18.

[0091] As the liquid metal and/or metal alloy flows, traversing over the top of a sump or vessel 20, the rate of descent of bifilms ensures that the larger, heavier bifilms have sufficient time to sink through the overlying flow and be captured by entering the sump or vessel 20. Their rate of descent can be controlled by the rate of addition of heavy alloy addition. The vacuum assisted pump 18 periodically lifts the sediment (the concentrated oxide and liquid aluminium mixture) out of the sump or vessel 20 and into a pigging ingot so that the cast sediment, is provided in a uniquely convenient ingot form to facilitate the recovery of the entrained aluminium.

[0092] In one embodiment the OSP channel or launder can be split into two channels or launders so reducing the metal speed by half and doubling the time for sedimentation. This also facilitates the blocking off of one channel for cleaning or maintenance without stopping production.

[0093] The relatively shallow depth of the channel or channels 10 will allow for passive degassing by the counter-directional flow of dry nitrogen above the melt.

[0094] Furthermore, as the system has no moving parts, requires zero human intervention, and all the processes are ‘passive’ i.e. occur naturally without intervention the efficiency and implementation of the apparatus is significantly improved with regard to conventional apparatus.

[0095] Typically the liquid metal and/or metal alloy is kept molten by overhead electrical elements 24 which extend along the length of the channel or channels 10. The temperature is designed to be low from the heating assembly 2 and through the transfer assembly 26 to maximise sedimentation and degassing efficiencies, reduce energy consumption, and extend refractory life.

[0096] Filters 22 can be introduced as required to filter materials from the metal and/or metal alloy prior to the same reaching the mould filling assembly 12.

[0097] The mould filling assembly 12 includes a pump 28 and the liquid metal and/or metal alloy is introduced via the opening of a valve in the base of the pump body. The body is then pressurised to raise the metal up the riser tube 30 and into the mould. A non-return system keeps the melt at the top of the riser tube 30 ready for the next mould (avoiding falling back to avoid the generation of oxides in the riser tube).

[0098] In one embodiment the volume of the body 32 of the pump 28 is approximately only 1 percent of the volume of a low pressure furnace, so that very little pressurising gas is required to operate the pump. Oxidation inside the pump can therefore be avoided relatively economically by the use of the completely inert argon gas. The casting pressures are typically only in the region of 0.2-0.4 bar providing a further economy in the use of argon. Fill time can be programmed to suit.

[0099] The small pump chamber or cavity 34 also means that the pump is responsive so a ‘fill profile’ can be generated for castings if necessary. Combined with modelling flow software it would be possible to know when to speed up or to slow down the rate of fill to reduce the generation of oxides for castings with complex internal geometry which is a significant improvement.

[0100] Typically, in this embodiment, a pump of 20-30 kg capacity is suspended in a crucible furnace 36 of a required capacity, such as in the range 300-500 kg aluminium. Electrical resistance heating elements surrounding the crucible permit the raising of the metal temperature to an appropriate casting temperature just prior to casting.

[0101] The ability to slide the filled mould casting as will be subsequently described, off the riser tube 30 in, for example the direction of arrow 38 and along the casting platen 40 onto an adjacent support surface has major advantages over current systems and the sliding action allows the cast metal in the mould cavity to start the cooling process ‘off-line’ and frees up the riser tube 30 within only a few seconds for the next casting mould to be placed over the same.

[0102] The casting platen 40 is typically formed of steel and is the surface on which moulds are cast and is flush with the top of the riser tube and the pump 28 is suspended from the platen. Below the casting platen 40 there is provided a production system which can be arranged to provide ultra-clean liquid metal and/or metal alloy and deliver it into moulds in a controlled and repeatable flow avoiding damage to the liquid.

[0103] Above the casting platen 40 the user is free to adapt the type of mould and mould handling facilities as they require. One such process employs a vacuum assisted investment block moulding technique for very thin wall precision castings that has been adapted to a counter gravity filling process.

[0104] Alternatively, a design involving permanent steel dies is possible for the manufacture of automotive wheels and when compared to current systems, increased quality, reduced production costs and higher production rates seem achievable. The current practice is roughly a wheel every 3-4 minutes with a scrap rate varying between 10-18%. With good mechanical handling for the dies above the platen, a reasonable estimation is that a rate of casting a wheel every 1-2 minutes is achievable with practically zero scrap. The use of a carousel for the steel dies could produce a defect and scrap free 25 kg casting every 30-40 seconds.

[0105] Furthermore the same apparatus can be used for the filling of sand moulds.

[0106] Embodiments of the respective assemblies of the system are now described and it should be appreciated that the assemblies below the casting platen can be used to advantage in combination or independently and in conjunction with further types of assemblies above the casting platen which may be conventionally available.

[0107] With respect to the heating assembly 2 then, in operation, when the charge materials which are to be used to form the liquid metal alloy are placed in the heating assembly heating means in the melter heat the charge materials and heating gases which are created pass in the direction of arrow 100 upwardly through the shaft and thereby heat the charge materials as they pass downwardly through the shaft in the direction of arrow 101 to reach the dry hearth 6 which transforms the charge materials into a liquid molten form. The molten material then runs down the slope 103 and into a holding bath 8 with the skin of the charging material which remains after the liquification of the same remaining on the hearth 6. After a period of time, such as for example, an hour or more, the accumulating pile of oxide skins are removed from the hearth 6 and into a dross bin. This is in contrast to common melting procedures which use baths or crucibles which necessarily mix the highly deleterious oxide skins of the charge into the liquid metal. The dry hearth melting technique effectively segregates the major oxide content, the primary oxide skins on the charge from the melt and with the skins moving to dross bin and the molten material progressing in a different direction.

[0108] Turning now to the FIGS. 1a-b and 5a-e the liquid metal and/or metal alloy transfer assembly 26 is illustrated in greater detail. The molten metal alloy moves from the furnace heating assembly 2 into the transfer assembly 26 and moves along channels 10 and preferably at a uniform height so as to avoid any fall of the material and allow the distribution of the molten material to the required locations in the foundry.

[0109] The launder transfer system also includes the overhead electrical resistance element heater 24 to maintain the temperature of the molten material and maintain the same in the liquid condition whilst, at the same time, ensuring that the temperature of the same is as low as can be practically allowed, whilst preventing solidification. The reason for keeping the temperature as low as possible is to provide several benefits which are; the improved degassing of the molten material from hydrogen gas, particularly if a dry gas is flowed counter current over its surface and secondly, the precipitation of second phases onto bi-films occurs more efficiently at lower additions of sedimenting elements, thirdly, the extension of refractory life, and fourthly, the saving of energy.

[0110] At the oxide sedimentation pump location 16, a proportion of the bi-films and their suspension in the molten material will detrain and settle out and can be effectively caught by the system at the base vessel 20. However, it is found that the natural rate of settling is relatively low due to the near neutral buoyancy of the bi-films in the molten material. Thus, in order to enhance the rate at which bi-films settle, prior to entering the detrainment station, the molten material is dosed by a continuous wire feed 105 of elements which will promote sedimentation. The wire feed is, in this embodiment, an aluminium based alloy containing one or more elements which form heavy intermetallic compounds and which deposit and grow on bi-films when, as in this embodiment the molten material is a liquid aluminium alloy. The wire can be fed from, for example a similar apparatus as is used to feed welding wire and the wire feed promotes the controlled sedimentation to occur depending on the flow rate of the molten material.

[0111] In one embodiment titanium (Ti) can be added to enhance the rate of sedimentation of bifilms from the liquid metal. The elimination of oxide bifilms down to perhaps a size of 10 um is dependent on a number of factors including (i) the cleanness of the charge material; (ii) the melting rate; (iii) the level of alloy additions; (iv) the temperature.

[0112] As the dosed molten material enters the sedimentation portion 16 of the launder, the tendency is for the molten material to continue its horizontal flow as indicated by arrow 107 and to traverse the upper level of the sedimentation volume because of the slightly favourable temperature gradient resulting from the overhead heating causing the upper layers of liquid in the launder to be slightly lower density. The horizontal flow distance across the top of the sedimentation volume is targeted to give adequate time for bi-films above a maximum size to settle out of the flow. For instance, a flow time of one minute across the unit might result in the descent of bi-films by at least 100 mm thereby allowing them to escape the horizontal flow stream and reach the largely stagnant liquid below at the vessel 20. This eliminates bi-films of a certain size, corresponding for instance to the elimination of all bi-films down to a 5 micrometres diameter, whereas a 10 minute traverse time would eliminate bi-films down to perhaps 1 micrometre diameter. These elimination dimensions will depend on the concentration of the dosing alloy, the speed of the molten metal across vessel 20, and the temperature of the liquid.

[0113] In a continuous flow regime, such as is required for DC casting, a continuous flow through the sedimentation unit could also be subject to the same logic requiring length of time, lowness of temperature and concentration of dopant to effect a useful cleaning action down to an acceptable maximum size of oxide bi-film defect.

[0114] Typically, the sedimentation vessel 20 is shaped to concentrate the sediment at a point of maximum concentration and at that point, the sediment is sucked out by a bubble lift or vacuum pump (OSP) 18 shown in more detail in FIGS. 5a-e. The molten material enters the OSP assembly 18 at the entry 137 and at which typically the wire 105 is located. The molten material passes into the sedimentation vessel 20 at which tubes 138 conveying inert gas are located to provide gas down into the sedimentation volume at a sufficient rate so as to create intermittent bubbles and preferably forms bubbles at a conveniently high point in a riser tube 140 because bubbles created low down in the riser tube expand as they rise, finally filling the whole tube and continuing to accelerate, lifting the flocculent by means of a vacuum.

[0115] The result is an exit of sediment in an accelerated manner which is effectively uncontrolled. To better control the lifting action, the bubble tubes 138 are gradually lowered into place so that controlled, trauma free movement of the sediment from the molten material in the sedimentation volume is achieved.

[0116] The bubbles from the exit 139 of the tubes 138 then rise up the respective coaxial outer riser tubes 140 and as they do so the bubbles act as a piston so as to move the contents of the riser tubes 140 with the flow of the bubbles in the direction of arrows 141 to the exit 142 and into dross bins 144. Once primed, each bubble will lift up what is in the tube above it and suck in more oxides and sediment from the bottom of the sediment vessel 20. Typically the shape of the exit 142 will be chamfered and has the effect of pushing the oxides and sediment clear from the exit and therefore allows the same to be clear for the next bubble and entrained sediment.

[0117] Typically the larger the gap between the respective inner tube 138 and outer riser 140 tube, then the greater amount of sediment which can be removed by each bubble from the molten material.

[0118] The bubble generation rate and/or frequency and the provision of specific types of wire feed can be electronically linked to the required flow rate of the molten material as dictated by, for example, the furnace and/or required casting rate. Typically the higher the flow rate then the more additions of wire material and removal of sedimentation is required.

[0119] Also, the inner diameter of the riser tube may be increased to counter the effect of a bubble, or agglomeration or bubbles, ejecting liquid and sediment from the exit 142. The lifting action of the bubbles to provide a discreet pulsing action therefore assists the flow of the flocculant volume of sediment. The gas involved is required to be an inert gas such as argon.

[0120] Alternatively, instead of a tube with an exit 142 from which bubbles are released with the sediment, a porous plug is provided in the base of the sedimentation vessel 20 and the riser tube 140 is adjustable so as catch the bubbles emerging from the porous plug.

[0121] Alternatively to the provision of dross bins, it may be advantageous to cast the sediment into ingots near the top of the riser tube and so that instead of dross bins, ingot moulds are provided to be filled, and then the ingots can be moved away and stacked and this can, in one embodiment be performed in an automated manner. In this embodiment, then in place of an overflowing chute to carry away the sediment from the top of the riser tube, the riser tube connects directly with an ingot mould, causing sediment to fill the mould in a counter gravity manner and when the mould is filled, the mould and its solidifying sediment is moved away to be replaced by a new mould and so on. In one embodiment, the mould can be handled and emptied by a robot which may also perform the stacking operation and therefore not require any human intervention.

[0122] In an alternative example of the apparatus in accordance with the invention instead of the use of a bubble lift to extract sediment, a vacuum lift is used which has the advantage of increased control, avoiding the possible instability caused by the uncontrolled expansion of the bubble during its rise. The vacuum lift once again has the benefit of few moving parts. It can also be connected to an ingot casting station, in which newly formed ingots of sediment are cast, and can be transported away and stacked by robot.

[0123] In one embodiment, the sedimentation collection process can be used in series to further perform a cleaning effect on the molten material in stages. Although this embodiment might suggest that the same benefit could be gained by enlarging the sedimentation pump, effectively lengthening the distance which the liquid metal flows over the top of the sedimentation volume and so lengthening the time available for sedimentation, such an embodiment is not recommended in at least certain instances. This can be because the sediment requires walls at some angle of repose in the region of 45 degrees, thereby necessarily forming a sedimentation volume deeper than approximately 0.5 metre. Most furnaces containing liquid aluminium are limited to approximately this depth because of the danger of leakage. With increasing depth beyond 0.5 metre, it is widely accepted that the danger of leakage becomes unacceptable.

[0124] After the molten material has traversed the sedimentation stage 16 on the transfer assembly it is necessary to ensure that the metal does not suffer any further entrainment affect whereby fresh bi-films would be created.

[0125] Thus it is ensured that after the liquid metal has traversed the sedimentation pump 18, the metal is never poured, but continues its horizontal flow along channels 10, to the mould filling assembly and then finally transported counter-gravity into the moulds as will be described to manufacture cast products.

[0126] Referring now to FIGS. 2a-e and 3, there is illustrated in a schematic manner a mould filling assembly 12 in accordance with one embodiment of the invention and the apparatus includes a supply of liquid metal 104, such as a holding furnace 36 which retains the metal at a sufficient temperature so as to be held in a liquid state. A pressurised means such as a pump 28 allows the liquid metal to be supplied to a riser tube 30 in the liquid state and to pass upwardly in the direction of arrow 110 through the riser tube. The riser tube has an outlet or orifice interface 112 which is provided for the selective location with an ingate 114 of a mould 116 which has a cavity 118 which is to be filled with the liquid metal and/or metal alloy.

[0127] The apparatus further includes a support surface in the form of the casting platen 40 and the surface may be formed of a relatively “cool” material such as steel which is sufficiently hardwearing to withstand the sliding action of the moulds 116 thereacross. In one embodiment, the surface of the casting platen 40 are acted upon by a cooling medium applied to its underside which is supplied from a cooling medium source, such as cool water or air so as to assist in maintaining the said support surfaces 40 in a relatively cool low temperature condition.

[0128] FIG. 2a illustrates the mould 116 having been placed in position on the casting platen with its ingate 114 aligned with the riser tube 30 and in connection with a gasket seal which can be formed of a compressible ceramic fibre and held in place, if necessary, by being partially recessed into the mould so that the ingate 114 of the mould 116 is connected to the orifice interface 112 of the riser tube 30 as shown. The liquid metal 104 is pressurised to a pressure P1 by the pump 28 which is just enough to provide the liquid metal 104 at a level L1 which is substantially level with the support surface 40 or a few millimetres below the same.

[0129] The condition of the pump 28 is then changed to increase the pressure of the liquid metal 104 to P2 which causes the level of the liquid metal to rise upwardly as indicated by arrow 128 to level L2 as shown in FIG. 2b so that the liquid metal 104 fills the cavity 118 of the mould. When the mould cavity is filled a valve 130 which until this point has been open, is closed so retaining the liquid metal 104 at height L2 and isolating the mould 116 from the pump 28.

[0130] As the mould 116 cavity 118 is now full of liquid metal 104 and is now isolated from the pump 28 and is in the condition shown in FIG. 2c, the mould 116 can then be slid sideways as indicated by the arrow 132 in FIG. 2d, so as to remove the ingate 114 from the orifice interface 112 of the riser tube 30 and the ingate 114 is maintained in contact with the support surface 40 as the sliding movement occurs. Any imperfections in the base of the mould can be accommodated and mitigated by the provision of the ceramic fibre gasket around the mould ingate 114, which acts to seal the sliding interface. Also, no liquid metal spurts from the open orifice of the riser tube 30 as the level of the liquid metal 104 in the riser tube 30 remains at L1 and cannot rise while the valve 130 remains closed. During the closure of the valve 130 the pump 28 may be recharged with liquid metal 104 from the holding furnace 36.

[0131] The mould 116 is then continued to be slid in the direction of arrow 132 until the mould 116 reaches a position which is sufficiently remote or removed from the orifice 112 so that the orifice is then free and can be subsequently reused by the placement of a new mould 116′ which is slid into position as indicated by arrow 138 as shown in FIG. 2e so as to bring the ingate 114′ into connection with the riser tube 30 and the cycle of steps is repeated to fill that mould 116′ and so on with successive moulds

[0132] FIG. 4 illustrates a plan view of the casting platen 40 which has located thereon the mould 116 which has been filled as described with regard to FIGS. 2a-e so that this first mould 116 can be retained in position on the surface 40 for as long a period of time as required so that the cooling effect of the casting platen 40 solidifies the liquid metal 104 in the cavity 118 to a sufficient extent so that the first mould 116 can subsequently be removed from the casting platen 40 without any risk of loss of metal which may cause damage to the casting therein or harm to personnel. While this mould 116 is cooling, the ingates 114′ of subsequent mould 116′ and then ingate 114″ of mould 116″ have been connected, in sequence, to the orifice interface 112 of the riser tube and the liquid metal 104 introduced into the same using the method as described and without delay as the orifice 112 and surrounding casting platen 40 is quickly cleared for use. As the process steps are repeated for successive moulds, the moulds 116′, and 116″ are shown as having also been slid as indicated by arrows 134 and 136 respectively to locations on the casting platen 40 and a fourth mould 116′″ is shown in connection with the orifice interface 112 and is in the process of being filled.

[0133] It will therefore be appreciated that at any given time, there may be one, two or further moulds all cooling on the casting platen 40 while subsequent moulds are being filled. As a result, the productivity time using this process, is significantly improved so that for example, with minimal moving parts, and minimal loss of liquid metal and costs, a typical cycle time for a 1-2 kg mould casting is estimated to comprise:

[0134] 5 seconds for the siting of the mould over the riser tube

[0135] 5 seconds for the filling of the mould

[0136] 5 seconds for the actuating slide and pressure reduction and opening of valve V

[0137] So that a total of 15 seconds is the estimated cycle time. For castings which are larger, typically up to approximately 200 kg, the filling time would be increased but only extending the cycle time to perhaps 30-40 seconds.

[0138] Turning now to FIGS. 6a-8f there are illustrated components utilised in the mould filling assembly 12 which are now described in detail.

[0139] In the pump 28 illustrated in FIGS. 6a-h there is shown a pump body 32 which may be of height which is selected to suit the desired capacity of the particular pump.

[0140] In addition, the length of the riser tube 30 and valves 44, 46 need to be provided of a length to match that of the selected pump body 32 and all of the other components of the pump 28 can be common and regardless of the particular capacity of the pump. Filter 48 is bonded to an insert 50 of the pump and the filter 48 prevents ingress of oxides into the pump body 32 and the filter 52 protects the valves 44, 46 from oxide debris and prevent the same from settling on the valve seats. A baffle box 54 is located in the body 32 by pins from the interior of the pump body in order to minimise any leaks to externally of the pump and the working melt level of the liquid metal and/or metal alloy is 10 mm lower than face 56 of the baffle.

[0141] When the pump is out of use or requires cleaning the insert 50 can be removed and if necessary replaced by moving the same as indicated by arrow 54 in FIG. 6c into the main cavity 34 of the pump body, typically using a hydraulic press. The insert includes a tunnel 58 therein which, in this embodiment is toroidal in shape, and allows the flow of the liquid metal from the main cavity 34, through the tunnel and into the riser tube 30 from where the liquid metal and/or metal alloy move upwardly towards the casting platen 40 and the mould located thereon to thereby flow into the mould cavity to fill the same.

[0142] The tunnel and the components of the insert are shown in greater detail in FIGS. 7a-g and it will be seen that the tunnel includes a tapered post 60 to allow the liquid metal and/or metal alloy to enter the tunnel with reduced turbulence.

[0143] The tunnel 58 floor can have upon it a textured surface, this textured surface is designed to snag and hold any bi-films that have entered the pump.

[0144] The riser tube 30 lower end has a filter directly below it, such that any metal that wants to pass into the riser tube 30 from the tunnel 58, has to go through the filter. This is to trap and snag any bi-films that have made it this far into the pump.

[0145] The upper face 62 of the insert includes the interface 64 with the riser tube 30 lower end and the interfaces 66,68 with the respective in valve 46 and out valve 44 of the pump.

[0146] In FIGS. 8a-f there is illustrated a component for use with the furnace 36 of the mould filling assembly, and into which furnace the liquid metal or metal enters from the channel 10 of the transfer assembly 26 in the direction of arrow 72. In accordance with this embodiment the component 70 is elongate and is formed of a refractory material and is attached to the inner wall 74 of the furnace 36 adjacent the entrance 76. The component has a lip or wall 78 which is located above the height of the base of the entrance 76 and hence prevents overflow of the liquid metal and/or metal alloy into the crucible 36 before the level of the liquid metal and/or metal alloy in the crucible reaches the height of the base of the channel 10 and hence reduces the possibility of the generation of oxides in the liquid metal and/or metal alloy in the crucible. This therefore encourages the priming of the liquid metal and/or metal alloy in the crucible from the bottom of the furnace 36. The component can also be provided with a pour formation 80 passing to the bottom of the furnace to further direct the flow of the liquid metal and/or metal alloy. Furthermore, the component can be left in place, as even once the priming from the bottom of the furnace has been achieved and the furnace is full and overflows the melt level would be the same height and so there would be no drop-off of the liquid metal and/or metal alloy on the other side. It is also envisaged that the melt rate of the dry hearth melter assembly 2 can be controlled to match the hole in the component 70.

[0147] It should also be appreciated that the size and capacity of the pump 28 which is used can be altered to suit the size of castings required. For example, if the castings are typically 3 kg, the melt rate 200 kg/h, a 20 kg pump can be used which has the potential to deliver about 1000 kg/h. However alternatively a larger pump, for example, with a 40 kg capacity can be used which would yield for instance 20 kg castings filled in approximately 10 seconds, giving approximately 100 castings/h, requiring a melt rate of 2000 kg/h. The size of the pump can be increased to 200 kg shot size. However, of course, for such large castings, the numbers of such castings per day is usually limited

[0148] The apparatus and method as herein described provides an optimum casting package for most mould types, providing superior casting quality and the reliability of a system with few moving parts, low energy consumption, efficient use of metal and low-cost replaceable consumables.

[0149] The system requires a minimal labour input beyond an operator in charge of melting and periodic primary oxide removal, and an operator to monitor the oxide pump and casting station whilst at the same time reducing the conventional scrap rate of between 10-18% to near zero with oxide-depleted metal and controlled, non-turbulent filling, for any foundry using this technology.

[0150] Furthermore there is a significant potential for improved properties of the cast alloy. A sufficiently high ductility will allow, for the first time, an acceptance of the necessary accompanying loss of some of the ductility by the addition of higher levels of alloys to increase strength. A high and reliable ductility (elongation to failure) will allow users of the technology to enter into markets that have traditionally been a no-go area for castings. The cast material which is created as a result of use of the system, is expected to have a high thermal and electrical conductivity as a result of the absence of bifilms. The bifilm populations generally present in cast Al alloys, acting as a population of cracks, cause the heat to travel via circuitous, lengthy routes, because it cannot cross the ‘air gap’ of the cracks. In contrast, of course, in ultra-clean metal, heat or electrons will flow efficiently in straight lines, offering minimal resistance to flow.