. Transactions. sirable to know the elongation of the alloy when cold, but it is ofgreater importance to determine the elongation at various temperaturesranging from the melting point of the alloy down to normal tem-perature. The reason for this becomes apparent when the physicalphenomena of the die-casting process are considered. Let us assumethat a ring 12 in. ( cm.) in diameter is to be die-cast in a metallicmold around a metallic core. As the molten metal strikes the moldit solidifies. Here a change of state occurs that is accompanied by 584 DIE CASTINGS AND THEIR APPLICATION TO THE W
. Transactions. sirable to know the elongation of the alloy when cold, but it is ofgreater importance to determine the elongation at various temperaturesranging from the melting point of the alloy down to normal tem-perature. The reason for this becomes apparent when the physicalphenomena of the die-casting process are considered. Let us assumethat a ring 12 in. ( cm.) in diameter is to be die-cast in a metallicmold around a metallic core. As the molten metal strikes the moldit solidifies. Here a change of state occurs that is accompanied by 584 DIE CASTINGS AND THEIR APPLICATION TO THE WAR PROGRAM a reduction in volume, commonly termed shrinkage. Unlike a sandcore, the metallic core is not compressible and retains its originalsize and form so that the shrinkage of the metal is converted into astretching action on the solidified casting. If the elongation of thealloy at that temperature is not high enough to withstand this stressthe casting will crack. In the usual die-casting practice it is not. Fig. 7.—Die-casting machine with vacuum applied diuectly to die. practical to remove the casting from the die at the solidification tempera-ture of the alloy. For example, the solidification temperature of thealuminum-copper alloys used in the die-casting process is approximately1150° F. (621° C). It has not been found practical to run the castingdies above a temperature of 500° F. (260° C), which means that the cast-ings are withdrawn from the dies at that temperature. It follows thatthe casting is subjected to another stretching stress after the casting hassolidified, due to the contraction in volume that must occur when acasting is cooled from a temperature of 1150° F. to 500° F. The writer has been unable to find any reliable method for determin-ing quantitatively the elongation of alloys at various methods have been suggested but they have proved of doubtfulvalue. The simplest way is to use the old method. Totest the alloy, a
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
