A new differential dilatometer for the determination of volume changes during solidification

Abstract

In recent years, the practical requirements of the metal industries have made it necessary to study the factors which govern the production of good castings. One of the most important of these factors is the change of volume which accompanies solidification. The experimental methods which have hitherto been used to determine this change have given discordant results, and it has seemed desirable to devise a new method, less liable to error. The new form of volumenometer which is the subject of this paper is intended to eliminate most of the errors inherent in the older methods. It has been applied to the measurement of the volume changes of two eutectic alloys, those of lead and tin and of tin and bismuth, the former of which contracts during solidification, whilst the latter shows a distinct expansion. The results indicate that the method is trustworthy. Previous Methods of Measurement . The older methods, which have been used for the experimental determination of the changes in volume, associated with the change in state of bodies, may be divided into the following classes:— ( a )The coefficients of expansion of the solid and liquid, over limited ranges of temperature, are measured and the volume change occurring at the melting point is found by extrapolation. The coefficient of expansion of the solid is found either by direct measurement of the linear expansion or deduced from measurements derived from some hydrostatic method in which Archimedes’ Principle is employed. The expansion of the liquid melt is inferred from observations on some dilatometric or hydrostatic method.