Although the anti shrinkage factor is a factor that must be considered in the casting process, recently, with the market demand for casting performance is higher and higher. Therefore, when designing the anti shrinkage process of castings, the use performance of castings, such as mechanical properties of castings, must be considered.
But in fact, when it comes to the mechanical properties of castings, there are often problems that conflict with the anti shrinkage factors of castings. This requires that the advantages and disadvantages of some anti shrinkage process factors, especially metallurgical factors, should be weighed when designing the anti shrinkage process of castings, which is also a focus of this paper.
In the process of designing the casting to be processed, it is necessary for designers to prevent the defects of shrinkage cavity and porosity. Generally speaking, sequential solidification is the basic process principle to prevent casting from producing shrinkage cavity and porosity. However, the principle of equilibrium solidification proposed by Zhang Ruifen, senior engineer of zhycasting, etc., has also been paid more and more attention.
Following the principle of “sequential solidification” and realizing the sequential solidification of iron castings, three conditions must be met:
① The solidification time of molten iron in riser must not be less than that of casting;
② There should be enough molten iron in the riser to feed the casting;
③ During casting solidification, there is always a feeding channel connected with riser, and there is enough expansion angle of feeding channel.
In order to meet the above conditions, a subsidy is used near the riser neck to make the hot spot close to the riser realize the sequential solidification smoothly; the cold iron can also be used to eliminate the influence of the hot spot far away from the riser to strengthen the sequential solidification.
The effect of riser on the heat interference of castings is also considered in the corresponding equilibrium solidification. Compared with the former, there is a distinct argument that the solidification time of molten iron in riser should not be later than that of casting. According to this argument and considering the thermal interference of riser, the placement and size selection of riser and chill are obviously different from the process design based on the principle of sequential solidification. Therefore, in the actual process design, according to the actual situation of castings, it is very important to select the above process principles.