Abstract
(1) In the report of mold sand binders (report 2nd), since the heating time interval was fixed, we could not know how the strength of binder will change according to heating time interval. Therefore, this time we examined the change of strength according to heating time interval with fixed heating temperature.
In our test, first of all, we added 5% (weight percent) of various kinds of binders and baked these test piece at the optimum baking temperature. Then, we heated the surface of the test pieces to 1350°C for the respective period of time. We dropped Hgadrops on these heated surfaces and obtained the strength by the quantity of exfoliating sand grains of these pieces.
According to this result, there are two types of relation between the influence of heating time interval on the quantity of exfoliating sand grains :
I. In cases quantity of exfoliation sand grains increases with the prolongation of the heating time interval.
II. In cases quantity of exfoliation sand grains increases up to some degree of heating time interval but decreases when it goes beyond that period.
(2) In this report, we examined the change of strength according to adding condition : colloid and powder of same binders. According to this result, it seems that the strength of mold using colloid binder is stronger than powder binder. (M. T.)
