原砂中SiO_2含量较低,在混碾时易破碎和粉化,而在激热和激冷时较不易碎。使用SiO_2较低的原砂可以减轻铸铁件表面的化学粘砂和“原生机械粘砂,”减少结疤缺陷,但是容易形成烧结的砂壳。如果铸件较厚或浇注温度较高,应设法防止破壳混入回用砂中使型破性能恶化和使铸件形成“次生的机械粘砂”。 The lower the original SiO_2 content in the sand, crushing and crushing in the mixed grind, and less vulnerable to heat and chilling. Using lower SiO 2 virgin sand can reduce chemical sticking sand and “native mechanical sticking sand” on the surface of the cast iron to reduce scarring defects but easily form a sintered sand shell. If the castings are thick or the pouring temperature is high, try to prevent the shell from mixing back into the sand to deteriorate the performance of the castings and to make the castings “secondary mechanical sticky sand.”