How can you tell whether cavities in a casting are due to po

How can you tell whether cavities in a casting are due to porosity or shrinkage?

Solution

a) By the average size and distribution. Porosity is something that would be distributed randomly thru out, and may be having entrained gas.

b) the shrinkage occurs at the top and boundaries. Usually there is a central part where the density is also different.

Shrinkage also involves local fracture, the boundaries of these pores would be irregular.,