Liquid metal flow in moulds with off-set sprue

Two different geometries of sprue/runner junctions have been investigated for their effects on the flow behaviour of molten aluminium alloys during mould filling. In the present work, three-dimensional computer simulations of mould filling for (i) conventional in-line and (ii) sprue off-set relative to the runner (i.e. the sprue located at the side of the runner), have been carried out and compared with real-time X-ray radiographic observation experiments. The example modelled is the cast plate which was adopted in the Benchmark test,¹⁰ where the conventional sprue/ runner junction presented an ingate velocity in the range 0.5 to 0.7 m/s, generally above the critical value 0.5 m/s in which surface turbulence phenomena were clearly observed, in agreement with the prediction. In contrast, it was shown that the ingate velocity when the sprue was sited offset relative to the runner is in the range 0.3 to 0.4 m/s, reducing surface turbulence in the casting cavity itself, although some initial surface turbulence at the sprue/runner junction was noted. Experimental studies including 3-point bend tests demonstrate greater strength and consistency, illustrating the overall reduction in damage for the castings produced with the off-set sprue.