The prediction criteria of shrinkage porosity and shrinkage cavity of iron castings have been studied and developed for many years, from the initial qualitative criteria such as temperature field pyrolysis method, G / root R method (R is the temperature gradient and R is the solidification rate), to the later quantitative criteria such as multiple isolated region solution pool method, equivalent liquid level shrinkage method and multi heat saving shrinkage and replenishment method. In the current commercial software, considering the problems of accuracy and calculation, the position of interval shrinkage can be predicted accurately by using g / root r criterion.
(1) Temperature gradient method. The possible location of shrinkage cavity is predicted by the temperature gradient at the end of solidification. Calculate the temperature gradient of each unit and the G at the end of solidification of each point on the casting section, where the unit with G ≤ 2-3 ° C / cm is the location where shrinkage casting defects may occur.
(2) G / root R is improved on the basis of temperature gradient method, which considers the alloy, size and shape of castings. When the value of the casting unit is less than a critical value after using the G / root r criterion, the unit is the unit that may have shrinkage casting defects. The set of these possible shrinkage units represents the distribution range of shrinkage. In order to determine the critical parameter value for predicting shrinkage porosity and shrinkage cavity casting defects.