Critical Fraction Solid Time records the time, in minutes, for each part of the casting to reach the Critical Fraction Solid Point. This is the point at which the alloy is solid enough that liquid feed metal can no longer flow. Therefore, for judging directionality of solidification, and whether any isolated areas have formed within the casting that cannot be fed by risers, Critical Fraction Solid Time is generally a better indication than Solidification Time. Plotting Critical Fraction Solid Time gives a good indication of whether any contraction that forms will be able to be fed by liquid feed metal within the risers or feeders.

 

 

The areas that appear as isolated pools of molten metal will not be able to receive feed metal from the risers if any contraction should occur during cooling and solidification.

 

This plot is interpreted in the same manner as Solidification Time. That is, you want a good progression from the edges of the casting, in towards the riser contacts, and out into the risers themselves.

 

In cast irons, which may have an expansion component to solidification, an isolated area shown in this plot MAY not exhibit shrinkage. The Material Density function should also be checked to verify the formation of shrinkage. See Unit 22 for MDF information.

 

 

For most alloys, you are looking for a good progression of solidification, from the edges of the casting, out through the riser contacts and into the risers. If any area becomes isolated, it is an area that will be prone to shrinkage.