In the process of casting production, the traditional technology is generally designed according to the theory of sequential solidification and simultaneous solidification. In the production practice of iron castings, it is found that it is sometimes difficult to achieve the ideal effect by using the above two theories. In this regard, Professor Wei Bing of Xi’an University of technology put forward the theory of proportional solidification. Once the theory was put forward, it was widely used in the casting production of iron castings and achieved satisfactory casting results. The essence of the theory is the concept of limited feeding. It is considered that at a certain moment of solidification, some parts of any iron casting are shrinking, some parts have entered the graphitization expansion, the time is at the same time, and the molten iron is interlinked; At this time, expansion and shrinkage can offset each other. The shrinkage value shown by the casting is actually the net result of expansion and shrinkage offset. The principle is shown in the figure.
Point a is the beginning of cavity filling; Point B is the cavity filling; Point C is the end time of casting solidification; Point D is the maximum value of graphitization expansion rate; The curved triangle ABC is the total shrinkage of the casting; The curved triangle ADC is the graphitization expansion of the casting; The curved triangle ab’p is the net shrinkage of the casting, which is called the apparent shrinkage of the casting; Point P is the equilibrium point, and the corresponding time is the time when the shrinkage is equal to the expansion of the casting. At this time, the shrinkage is zero, which is the end time of riser feeding.
It can be seen from the figure that for iron castings, the riser only needs to feed the castings in AP period, while the traditional theory thinks that the castings must be fed in AC period, so the riser feeding time required by the proportional solidification theory is greatly shortened.
In the casting process design of pancake iron castings, the proportional solidification theory can solve the problems of shrinkage cavity and porosity at the root of riser in traditional casting process, and greatly improve the qualified rate of castings; At the same time, the process yield and utilization rate of hot metal can be improved.