抄録
The thin and extended projection on the castings, i.e. “selfcooling fin”, absorbs heat from the cast body so rapidly that the freezing time is sufficiently reduced. The thinner and more widely extended fin is found to be more effective to a degree, but the critical size of the fin may be neccessarily decided not only on the technical and economical bases but also on the problem of heat flow.
Chilling effect of the fin was observed on the case of the bar castings of pure aluminium. The results obtained were as follows. The fin 2.5-4.0mm. in thickness and 15-20 times in width is found to be most successful, while the optimum size of the bar castings is t/D=0.08-0.16. The freezing time of the castings is shortened by 45-50% in this condition. The cooling curves obtained in the center of the castings and at the joints and ends of the fins during solidification are suitable evidences for the phenomenon above noted. These fins have a generous cooling effect and are able to substitute for the conventional chill.
The application of the fins to promote directional solidification is also described. The fins properly arranged expand the sound areas and prevent formation of the hot spots in the heavy sections. The fins on the tin bronze castings are not so effective but ones on the high-strength yellow brass casting are so effective as they substitute for the cast iron chill 7-9mm. in thickness. A consideration is also turned toward the combined use of the several fins on the high-strength yellow brass and aluminium bronze castings. It is found that the most successful distance between each fin is approximately 20mm.
