负压消失模铸造白色缺陷的预防

Study on Preventing White Defects of Negative Pressure EPC

运用流体力学原理,计算出负压消失模铸造在充型时直浇道上端会出现较大的真空度,因而很容易把沿途的干砂吸入直浇道带进铸型中形成白色缺陷。预防措施:对较大的铸件可用流钢砖或树脂砂、水玻璃砂制成的直浇道镶插进浇道杯下部,对中小铸件可把直浇道与浇口杯制成一体,在其上一边刷涂料一边缠绕玻璃丝布,或把浇口杯下部100 mm^150 mm的直浇道周围的干砂换上50 mm厚的自硬砂包覆起来,或用泡沫塑料切割成8 mm^12 mm厚的挡砂套(其上刷好涂料)围封在浇口杯和直浇道的连接处进行浇注,可以减少铸件的白色缺陷。

Calculation using the principle of fluid dynamics shows that vacuum degree in the top area of sprue during filling of the negative pressure EPC is quite high. Therefore some dry sand is easy to be absorbed into the sprue and brought into mold cavity leading to white defects. For big castings, such defects can be avoided by inserting sprue made from brick, resin-sands or sodium silicate bonded sand into sprue basin. For small to medium castings, using coated and glass fiber cloth wound one piece of sprue and pouring cup instead of separated sprue and pouring cup, or changing the 100-150 mm deep dry sand of sprue below the pouring cup to no-bake sand, or placing coated plastic foam round the junction of sprue and pouring cup to block sand can reduce the white defects.