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铸件夹砂又名结疤,北方俗称起皮子,南方叫起夹子。其特征为铸件表面上有金属夹杂和包含型砂或渣等所形成的片状或瘤状物,这种凸出铸件的疙瘩凿去后,铸件局部表面上即呈现凹陷的沟槽或凹塘。铸件夹砂缺陷一般都发生于潮模铸造。是铸件报废的常见缺陷之一。国内外铸造工作者在向夹砂斗争的长期实践中,积累了很多宝贵而丰富的经验,很值得学习和研究。一、铸件产生夹砂的原因近代夹砂理论认为,产生夹砂的机理为:在浇注过程中砂型表面受高温金属液的热力作用,表面层水份向里迁移,使表面形成干燥层,而内部产生一层高湿度、低强度的弱砂带;同时砂子被加热发生相变,产生体积膨胀。当膨胀应力大于弱砂带强度时,该层产生滑动,就使表面干燥层弯曲、变形,与弱砂带脱离而突起。使表面破裂被液体金属渗入,就产
Casting sand, also known as scarring, commonly known as the northern skin, called the South clip. The utility model is characterized in that there are metal inclusions on the surface of the casting and sheet or nodules formed by molding sand or slag. After the knots of the protruding casting are chiselled, concave grooves or concave pits are formed on the local surface of the casting. Sand casting defects generally occur in the tide casting. Casting scrap one of the common defects. The foundry workers at home and abroad have accumulated a great deal of valuable and rich experience in the long-term practice of sand-holding struggle, which is worth studying and studying. First, the reasons for sand casting sand production Modern grip theory that the sand produced by the mechanism: in the casting process by the high temperature molten metal surface of the liquid heat, the migration of surface moisture to the surface to form a dry layer, and Internal produce a layer of high humidity, low strength of the weak belt; the same time the sand was heated phase change, resulting in volume expansion. When the expansion stress is greater than the strength of the weak belt, the layer slippage causes the surface dry layer to bend, deform, and protrude from the weak belt. Make surface rupture liquid metal infiltration, on the production