抄録
In author's foundry there have been produced grey iron castings of 100 to 1,000 kg in weight for machine tool and internal combusion engine by using skin dried sand molds. For this skin drying synthetic sand which had been formerly used was found to be unfit, because it caused scab defects particularly when the weight of castings was heavier than 400 to 500 kg. to eliminate shch defects Na-bentonite, alpha starch and various cushioners are mixed with molding sand. Skin drying is made by using hot air of 270°C for 0.5 to 2 hours. The depth of skin thus dried ranges from 15 to 45 mm. For mdding facing sand is specially prepared. In reclamation of sand new sand is added to the used sand at a ratio of about 5%. of casting defects caused due to molding sand blow holes rank first, amounting for 27%, and sands rank second.
