Abstract: The air-impact molding machine (flask size: 600 mm × 450 mm× 390 mm) and apparatus (size of sample pipe: (φ50 mm×120/250 mm) are used to study the influence of the molding sand on the compaction. The curve of wet compressing strength changing with compactability has a maximum value in 32% compactability. The wet compressing strength increases with the content of bentonite and the increase rate is great in lower bentonite content. The core the powder coal, heavy oil, dead clay and the less the atarch, the greater the wet compressing strength. The above experimental results are analyzed and combining the speciality of air-impact molding the principles of choosing molding sand for air-impact molding are suggested.

Key words: Air- impact moulding, Bentonite, Compactability, Molding sand