鋳鉄の金型鋳造組織とエヤーギャップの形成について

  To study the effect of air gap formation on the structure of permanent mold cast iron, flat plates having 20mm thickness were poured into the metallic mold with mold ratio 4. The temperature at the both sides of plate, of which one was free but the other was fixed to the metallic mold by means of two machine screws, were measured with P_t-P_tR_h thermocouples. The air gap formed at the free side was measured with a dial gauge. These tests were performed by means of experimental designs, selecting factors and lewels are as follows ; Sc : 0.86 (3.11%C, 1.95%Si) 0.93 (3.30%C, 2.20%Si) 1.10 (3.97%C, 2.05%Si) Preheating temperature of metallic mold : 150°C, 350°C, Thickness of coating (soot) : 0.1mm, 0.3mm, Inoculation : uninoculated, inoculated. </br>  Irons were melted in a Tamman furnace with alumina crucible and were poured at about 1400°C. Their chemical composition was adjusted by the addion of steel. As the inoculant 0.3%Ca-Si (50%Si) was added to the molten metal in the crucible. </br>  Fig. 1 illustrates schematically the cooling and the schrinkage curves obtained in our tests, δ_A, δ_B and δ_C being respectively the size of air gap at the beginning of eutectic reaction, at the end of eutectic reaction and the beginning of eutectoid reaction.</br>  The conclusions obtained are as follows : </br>    (1) The thinner the thickness of soot and the lower the preheating temperature of the metallic mold are prepared, the lager the air gap δ_A at the beginning of the eutectic reaction becomes, because more rapid cooling rate produces a large degree of undercooling of the eutectic temperature. Sc and inoculation have little effect on the air gap δ_A and δ_B. The air gap δ_C at the beginning of the eutectoid reaction increases with the decrease of Sc, of soot thickness and of mold temperature. The expansion δ_A-δ_B, which is due to the preciptaion of graphite during the eutectic reaction, is markedly influenced by Sc. </br>    (2) The main factors having the large influeces on the cooling rate of the casting are the preheating temperture of mold and the thickness of soot, and in this study (high mold ratio) the latter effect is as remarkable as reported in the preceeding paper ⁽¹⁾.</br>    (3) A factor having the most remarkable influences on the structure and the hardness of casting is Sc, so then the choice of Sc may be of importance in the parmanent mold casting. </br>    (4) At the condition of low coolng rate, the casting with Sc 0.86 may be casted without chilling tendency. </br>    (5) The inocalation ts useful to avoid the chill formation in the casting with low Sc. </br>    (6) The air gap formation has a little influencees on the cooling rate, the structure and the hardness of casting.