Numerical Analyses of End and Riser Effects on Solidification Directionality of Plate Castings for Alloys and Pure Metals

Abstract

  The riser effects on solidification directionality of plate castings for alloys and pure metals were numerically examined by heat transfer and solidification simulation. The influencing factors as well as the relation to the end effects were also investigated. Numerical results showed that the riser effects have the same magnitude relation as the end effects except for the cases of pure aluminum or pure copper castings with sand molds. There were also tendencies for both greater riser effects and greater end effects to be obtained by higher mold temperatures or higher superheats. One of the main factors influencing the riser effects as well as the end effects was b_castH^*/b_mold (b_cast and b_mold : thermal diffusivity of casting and mold, respectively, H^* : dimensionless latent heat). For the cases of pure aluminum or pure copper castings with sand molds, significantly smaller riser effects were however obtained due to the synergistic effects of the dimensionless solidification temperature range, ΔT^* and temperature diffusivity of casting, α_cast. The ΔT^* and α_cast change not only solidification behavior but also the solidification time of the riser part and/or the balance of the solidification time between the plate and riser part. These may affect the thermal conduction from the riser part to the plate part. In addition, most of the experimental rules or results about the riser-effective range could be explained on the basis of the riser effects. The above findings indicate that the effect due to the heat transfer caused by the riser is an important factor for the formation of the sound range.