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不锈钢铸件缩松的原因有哪些

发布时间:2018-04-12点击量:84

不锈钢铸件缩松的原因有多种:由于不锈钢铸件断面过厚,造成补缩不良形成缩孔。不锈钢铸件壁厚不均匀,在壁厚部分热节处产生缩孔或缩松。 由于不锈钢铸孔直径太小形成铸孔的砂芯被高温金属液加热后,长期处于高温状态,降低了不锈钢铸孔表面金属的凝固速度,同时,砂芯为气体或大气压提供了信道,导致了孔壁产生缩孔和绣松。 不锈钢铸件的凹角圆角半径太小,使尖角处型砂传热能力降低,凹角处凝固速度下降,同时由于尖角处型砂受热作用强,发气压力大,析出的气体可向未凝固的金属液渗入,导致铸件产生气缩孔。熔炼方面的原因:不锈钢 液体金属的含气量太高,导致在不锈钢铸件冷却过程中以气泡形式析出,阻止邻近的液体金属向该处流动进行补缩,产生缩孔或缩松。 当灰铸铁碳当量太低时,将使铁水凝固时共晶石墨析出量减少,降低了石墨化膨胀的作用,使凝固收缩增加,同时也降低铁水的流动性。认而降低铁水的自补缩能力,使铸件容易产生缩孔或缩松。 当铁水含磷量或含硫量偏高时,磷是扩大凝固温度范围的元素,同时形成大量的低熔点磷共晶,凝固时减少了补缩能力。硫是阻碍石墨化的元素,硫还能降低铁水的流动性。同时,铁水氧化严重,也降低液体金属的流动性,使铸件产生缩孔或缩松。 孕育铸铁或球墨铸铁在浇注前用硅铁等孕育剂进行孕育处理时,如果孕育不良,将导致铁水凝固时析出大量的渗碳体,从而使凝固收缩增加,产生缩孔的局部必然会出现缩松.产生的机理是一样的,铸件在凝固的过程中,最后冷却部位得不到补缩即会产生.There are many reasons for the shrinkage of stainless steel castings: due to the excessive thickness of the stainless steel castings, the shrinkage is bad and the shrinkage cavity is formed. The wall thickness of stainless steel castings is uneven, and shrinkage cavity or porosity is formed at the hot part of the wall thickness. As the diameter of the stainless steel is too small, the sand core formed by the casting hole is heated by high temperature metal liquid for a long time, and it is in a high temperature state for a long time, which reduces the solidification speed of the metal on the surface of the stainless steel casting hole. At the same time, the sand core provides the channel for gas or atmospheric pressure, resulting in the shrinkage and embroidery of the hole wall. The angular radius of the concave angle of the stainless steel castings is too small to reduce the heat transfer ability of the molding sand and the solidification speed at the concave corner. At the same time, the gas pressure is strong and the gas can be permeated into the non solidified metal fluid because of the sharp corner of the molding sand. The reason for melting is that the gas content of the stainless steel liquid metal is too high, which causes the precipitation of the stainless steel castings in the form of bubbles in the cooling process, and prevents the adjacent liquid metal from flowing to the place to make up, resulting in shrinkage or shrinkage. When the carbon equivalent of gray cast iron is too low, the precipitation of eutectic ink will be reduced, the effect of graphitization expansion is reduced, the solidification shrinkage is increased, and the fluidity of molten iron is also reduced. It is believed that the self shrinking ability of molten iron can be reduced, resulting in shrinkage or porosity. When the phosphorus content or sulfur content of molten iron is high, phosphorus is an element that expands the range of solidification temperature, and forms a large number of low melting point phosphorus eutectic, which reduces the filling capacity. Sulfur is a hindrance to graphitization, and sulfur can also reduce the fluidity of molten iron. At the same time, the oxidation of molten iron is serious, which also reduces the fluidity of liquid metal and causes shrinkage or porosity of castings. When inoculating cast iron or spheroidal graphite cast iron before pouring with ferrosilicon and other inoculants for inoculation, if the inoculation is bad, a large number of carburized carburized bodies will be precipitated when the molten iron is solidified, which makes the shrinkage of the solidification increase, and the part of the shrinkage will inevitably shrink. The mechanism is the same, the casting is cooled in the solidification process. When the parts are not made up, they will come into being.

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