The reasons for the shrinkage porosity, burnt-on sand and sand inclusion of the iron castings
The shrinkage porosity of iron castings refers to the small and incoherent shrinkage cavity, which is gathered in one or more places. The crystalline grain is thick and big, and there will be small holes between each grain. There will be water percolation when doing the hydraulic testing. When it comes to the shrinkage porosity defects of iron casting, it is important to reduce the thermal center as far as possible to minimize the pouring temperature and pouring speed.
The burnt-on sand defect of iron casting means that on the surface of the casting, all or part is covered with a layer of metal (or metal oxide) and sand (or paint) composition(or chemical compound), which will cause the surface roughness of the casting. At this time, it needs to pay attention to reducing the sand clearance, appropriately reducing the metal pouring temperature and improving the refractoriness of molding sand or core sand.
There is a layer of metal nodule or sheet on the surface of the iron casting defect, and there is a layer of moulding sand between the metal nodule and the casting. When facing this defect, it is necessary to strictly control the properties of molding sand or core sand, improve the gating system, and make the metal liquid flow stable. The large plane casting should pay attention to casting on the lean.
The cold shut defect of the iron castings also means that there is a gap that is not fully fused on the casting, which is the crater. Its boundary is very smooth and evasive.
Facing the cold shut defect of the iron castings, we should increase the pouring temperature and pouring speed and improve the gating system. It can’t cut off when pouring. The misrun defects of iron casting are due to the fact that the metal liquid is not fully filled with mold cavity, and the pouring temperature and pouring speed should be increased.It can’t cut off and the leak-out should be prevented.