对于大多数发动机的供油、泠却和制动系的主要壳体类铸件,都有一个重要的要求:腔壁必须具有气密性。然而,即使采用完善的铸造工艺也难以避免疏松和其它铸造缺陷,要得到致密铸件是极其困难的。统计资料表明,此类壳体由于气密性差而报废的铸件数可多达20％～70％。实践证明,如果通过自出浸渗,内外加压或真空负压等方法将这些铸件渗以有机液体(聚酯类树脂)或无机溶剂(碱性金属硅酸 For the majority of engine fueling, cooling and braking system of the main shell castings, there is an important requirement: the cavity wall must be air tightness. However, it is extremely difficult to obtain dense castings even if it is difficult to avoid looseness and other casting defects even with a well-established casting process. Statistics show that such cases due to poor air tightness and the number of castings can be as much as 20% to 70%. Practice has proved that if by self-infiltration, internal and external pressure or vacuum and other methods of these castings seepage into the organic liquid (polyester resin) or inorganic solvents (alkaline metal silicate