一.问题的提出 我厂生产的R175A型柴油机缸体结构复杂,平均壁厚为5mm,材质为HT20—40灰口铸铁,须作气密性试验,不允许有渗漏、气孔及非金属夹杂等缺陷。在生产中出现的主要问题有(1)在薄壁处出现大量白口,机械加工困难;(2)由于在配砂、造型、熔化、浇注等方面控制不当产生的气孔 A problem raised I plant R175A diesel engine cylinder structure is complicated, the average wall thickness of 5mm, made of HT20-40 gray cast iron, to be for air tightness test, does not allow leakage, porosity and non-metallic inclusions Other defects. The main problems in production are: (1) a large number of white splats appear at the thin wall and the machining is difficult; and (2) the pores generated due to improper control in sand preparation, molding, melting and pouring