Casting process performance is generally understood as […]
Casting process performance is generally understood as a combination of those properties that are most prominent in mold, crystallization and cooling processes. Fluidity, shrinkage, air tightness, casting stress, inspiration. These properties depend on the composition of the alloy, but also with the casting factors, alloy heating temperature, the complexity of the mold, pouring mouth system, gate shape and so on.
Liquidity refers to the ability of the alloy liquid to fill the mold. The size of the fluid determines whether the alloy can cast complex castings. The eutectic alloy is the best in aluminum alloy. There are many factors that affect the liquidity, mainly the composition, temperature and alloy liquid metal oxides, metal compounds and other pollutants in the solid particles, but the external fundamental factors for the casting temperature and pouring pressure (commonly known as pouring head) The level of.
Shrinkage is one of the main features of cast aluminum alloys. Generally speaking, the alloy from the liquid pouring to solidification, until the cold to room temperature, is divided into three stages, respectively, liquid shrinkage, coagulation shrinkage and solid shrinkage. The shrinkage of the alloy has a decisive effect on the quality of the casting, which affects the size of the casting, the generation of stress, the formation of cracks and the size of the change. Usually casting shrinkage is divided into body shrinkage and line shrinkage, in the actual production of the general application of line shrinkage to measure the shrinkage of the alloy.
Casting alloy liquid from pouring to solidification, in the final solidification of the place there will be macroscopic or microscopic contraction, this shrinkage caused by the macroscopic shrinkage of the naked eye can be seen, and divided into concentrated shrinkage and dispersion of shrinkage. Concentrated shrinkage holes are large and concentrated, and distributed in the casting at the top or thick section of the hot section. Dispersed shrinkage morphology is scattered and small, most of the distribution in the casting axis and hot parts. It is difficult to see that the macrophages are mostly distributed in the grain boundary or between dendrites of dendrites. Shrinkage and loosening are one of the major defects in casting, due to the fact that liquid shrinkage is greater than solid shrinkage. Production found that the smaller the scope of solidification of cast aluminum alloy, the more likely to form a concentrated shrinkage, the wider the scope of solidification, the more likely to form a decentralized shrinkage, therefore, in the design must make the casting aluminum alloy in line with the principle of solidification, The shrinkage of the liquid during solidification to solidification should be supplemented with the alloy solution, which is concentrated and loose in the external riser. For the easy to produce loose loose aluminum alloy castings, riser set more than the number of concentrated shrinkage, and easy to produce loose place to set the cold iron, increase the local cooling speed, so that the same time or rapid solidification.
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