Pressure casting flow system

#This invention relates to an improved alloy flow system for use in the pressure casting of alloys.

#In a number of recent patent applications, we have disclosed inventions relating to the pressure casting of alloys, utilising what is referred to as a controlled expansion port (or CEP). Those applications include PCT/AU98/00987, relating to magnesium alloy pressure casting and PCT/01/01058, relating to aluminium alloy pressure casting. They also include the further applications PCT/AU01/00595 and PCT/AU01/01290, as well as Australian provisional applications PR7214, PR7215, PR7216, PR7217 and PR7218 each filed on 23 Aug. 2001. These further applications relate variously to the pressure casting of magnesium, aluminium and other pressure castable alloys and to devices and apparatus for use in pressure casting of those alloys.

#As indicated, a CEP is utilised in the inventions of the above-identified patent applications. A CEP is a relatively short part of the alloy flow path which increases in cross-sectional area, from an inlet end to an outlet end of the CEP, such that alloy flowing through the CEP has a substantially lower flow velocity at its outlet end relative to the inlet end. The reduction in flow velocity is such that, in its flow through the CEP, the alloy undergoes a change in its state. That is, with molten alloy received from a pressurised source of supply to the inlet end of the CEP, the reduction in flow velocity from that attained at the inlet end to that at the outlet end is such that the state of the alloy changes from the molten state at the inlet end to a semi-solid or thixotropic state at the outlet end.

#In order that the invention may more readily be understood, description now is directed to the accompanying drawings, in which:

#FIG. 1 is a schematic representation of a two cavity mould arrangement, taken on the parting plane between fixed and movable mould parts, illustrating a first embodiment of the invention;

#FIG. 2 is a sectional view taken on line II of FIG. 1 and shown on an enlarged scale;

#With reference to FIGS. 1 and 2, there is represented therein two die cavities 10 and 11, defined by fixed mould half 12 and movable mould half 13 and each for use in producing a respective casting in a high pressure casting machine (not shown). Each of die cavities 10 and 11 is arranged to receive alloy from a pressurised supply of molten alloy of the machine, with alloy passing to each cavity by a common alloy feed system 14 according to a first embodiment of the present invention. The embodiment is one in accordance with the first form of the invention as described above.

#The alloy feed system 14 defines an alloy flow path which has a first part defined by nozzle 16, shown in more detail in FIG. 2, and a second part 18, referred to as a CEM as identified earlier herein, which extends between each cavity and across the outlet end of nozzle 16.

#In overall form and detail, nozzle 16 is in accordance with the invention of the above-mentioned patent application PCT/AU01/01290. As shown in FIG. 2, nozzle 16 includes an elongate annular housing 20 by which the first part of the metal flow path defines a bore comprising a runner 22 and, at the outlet end of the runner 22, a CEP 24. Housing 20 has its outlet end neatly received in an insert 26 of fixed mould half 12, while its inlet end abuts against a fitting 28 of platen 29. Around housing 20 there is an electric resistance coil 30 and, outside coil 30, a layer of insulation 32. Also, an insulating gap 34 is provided between insulation 32 and insert 26, except for a short distance at the outlet end of housing 20 where it is in metal to metal contact with insert 24, while gap 34 also extends between insulation 32 and fitting 28. As disclosed in PCT/AU01/01290, coil 30 and insulation 32 provide for control of heat energy level of housing 20 and the temperature of alloy flowing through runner 22 and CEP 24.