The spalling defect caused from the delamination of shell layers in ceramic molds is a significant source of casting scrap and rework. Spalling occurs due to poor adhesion of one or more layers in a ceramic shell. The layer where delamination occurs has traditionally been difficult to isolate because no measurement technique has been widely utilized.
Traditional efforts to solve this defect typically involve changes to the shell building process that cannot be evaluated until castings are completed. Process changes without evidence to indicate that the defect will be eliminated are risky. The foundry can lose time, material and potentially process control without seeing any impact on spalling defect reduction. Implementing a measurement technique earlier in the shell building process can reduce these risks.
This paper focuses on a method to measure the weakest adhesion point of a ceramic shell sample. This test has been used to isolate ceramic shell construction variables that effect intercoat adhesion of ceramic shell layers. Utilizing this method, a foundry can optimize the slurry shell building process to reduce the potential for spalling defects on their castings. This test can be employed on a small scale without the need to jeopardize standard production.