ON THE SHRINKAGE COEFFICIENT OF DIE CASTINGS AND GRAVITY CASTINGS

In the previous paper on the shrinkage formula of die casting and gravity casting, we explained the nature of shrinkage, and said that it must differ in the case of the casting with cores from that of the casting without cores.In this paper we tried to ascertain whether the shrinkage formula was corret or not and whether the nature of shrinkage deduced from the formula was in accord with the results of the experiment.This experiment showed that the shrinkage coefficient of castings is nearly the same as the one inferred from the shrinkage formula.But in some castings slight differences were visible. The cause of these differences is not yet found.The nature of shrinkage coefficient which we came to know was:(1) On the casting with cores.(A) Shrinkage coefficient varied according to the temperature of each die and casting.In the early process of casting when the temperature of die and casting was low, shrinkage coefficient was small, and later as the temperature rose coefficient also became large, and in the last stage it became nearly constant.(B) Shrinkage coefficent was influenced by the shots number per hour.(C) Casting temperature did not give direct influence upon the shrinkage coefficient, but generally shrinkage coefficent became larger with raising the casting temperature.(D) Shrinkage coefficient differed according to the surface condition of the dies, that is, it was small in the earliest period but after about 10 thousand shots it became larger, because the die cavity surface was covered with oil and an oxidation film.(E) Shrinkage coefficient varied in every part of the same casting because the temperature of a die or a casting differed according to each part of the die or casting.And the products could not have exactly the same figure of the die.(2) On the casting without cores.Shrinkage coefficient became linearly small in proportion to the rise of die temperature and was not influenced by the casting temperature.