Pressurised feeding systems

Abstract

Pressurised feeding is by no means new. Whitworth patented a method for pressurising steel in refractory lined ingot moulds in the mid 1800s, while accounts of pressurising aluminium castings during solidification appeared in the 1930s, and the pressurisation of risers in steel and iron castings surfaced in the 1950s. It is appropriate to distinguish between cases where the whole casting and rigging has been pressurised and those where the feeder heads alone were pressurised. Generally speaking, pressurising the whole casting has not proved especially effective. Early experiments with aluminium involved top pouring of moulds contained in an autoclave. The considerable height through which the metal fell undoubtedly mitigated results. Furthermore, since the alloys were of a non-skin forming variety (i.e. long freezing range) the puncture of the partially solidified surface led to further property degradation.Work of Watmough and Berry in the US in 1961, repeated by Irani and Kondic at Birmingham published eight years later, employed aluminium sand cast bars with pressurised feeder heads surrounded by stout insulating sleeves. The results of both sets of experiments with long-freezing range alloys, showed excellent promise in terms of reducing dispersed porosity. During the nineties Fischer-Disa picked up this concept and successfully implemented it on a production basis for both aluminium and ductile iron. Most recently MSU in collaboration with US metal casters has applied the technique to tilt-poured permanent moulding (gravity-die casting). The results of this recent work will be described in detail.