The judgment of multiple hot spots is to judge the number, size and position of hot spots that may be separated in the solidification process of castings according to the judgment basis, and then calculate the shrinkage and feeding on these basis. Multi hot spot judgment is what we often say to judge the condition of feeding channel during casting solidification, so as to determine the shrinkage of each hot spot and the location and size of shrinkage cavity.
The previous prediction of shrinkage casting defects mainly focused on calculating the total shrinkage of all risers, and then evenly distributing the shrinkage to each riser. Although this method is simple, it has many disadvantages. For example, it can not deal with the situation of bright and dark risers well. Therefore, some casting researchers, such as Jia Baoqian and Kang Jinwu, put forward a multi heat node method based on this method, that is, carry out specific analysis and research according to the actual situation of each riser, mainly by analyzing the solidification of castings to simulate the temperature field, Realize different feeding of each isolated hot joint. The schematic diagram of isolated hot joint is shown in figure. It can be seen from the figure that three regions are formed in the solidification process of the casting: region I where the solid rate FS is less than the critical flow solid rate FSC, region II where the solid rate FS is greater than the critical flow solid rate FSC and less than 1, and region III which has been completely solidified. The critical flow solid rate FSC. That is, the maximum solid rate that can flow when the solid phase and liquid phase exist together, and its value is generally between 0.5 and 0.8. Among the three regions, region I is a region that can flow, and region II is a region that cannot flow but does not completely solidify. The isolated region separated by solid phase in the feeding channel formed during casting solidification is called hot spot, in which both region I and region II can be called hot spot.