1- ! I • !-.< T or K\ 1'ANSIo.N ON SHKINRACIK, KTC. ^(jl
The 4i open-sand " method of easting test bars affords the means of making eomparative tests under varied conditions and ^'ives an excellent opportunity to observe eharaeteristie pbenoinenaat the moment of solidification, etc. In casting test bars of hard iron, a pronounced shrinkage alon^* the upper surface is often noticed during the period of expansion; and often before expansion is over there may be seen through shrink-holcs at tlu* hottest part of the bar (namely, at the point where it was poured,) that the interior is still liquid, showing that it is not necessary that the whole body of the casting shall solidify before expansion takes place. In this phenomenon, we perceive also the simultaneous action in the casting of two opposite tendencies, shrinkage ^'om^ on in some parts, while expansion is occurring in others.
It is the general impression anion^ moulders and founders that the hollei the iron is poured, the more it will shrink, that is, the more the casting will require to be "'fed." This is an error into which the. moulder has fallen by reason «»f thr longer time occupied in the eooliiu* or shrinkage of the "hot"-poured metal, and <onsrqttrnt!y the longer period of "feeding." The t»tal addition of iron required in the " feeding-heads" is no x'lvattM" with "hot" than with "dull"-poured iron, unless the "hot "-poured metal has more largely penetrated, fused or strained the walls of the mould.
Numerous experiments have failed to show me any elTec-t produced upon the total expansion by changes in the temperature of the metal when poured. Such an eflVet would not he naturally expected, since the expansion begins only with solidification, and the temperature of solidification, it is reasonable to say, isU Citut