Atlas of Casting Defects
Positive
Island of surplus metal often associated with flash at the casting edge. The edge of the defect has the appearance of a coastline
Sharp corners adjacent to flat or featureless surfaces
Primary coat buckle, investment penetration
With prime coat lift, the shell also fractures, allowing the backup layers to fill the gap between the primary layer and the wax pattern. When a shell buckles, it only separates from the pattern.
During shell building, the primary coat cracks and lifts off the pattern. Subsequent slurry layers penetrate and fill the gap between the pattern and the primary coat. This defect is a close cousin to buckle
| Area | Possible Cause | Potential Correction |
|---|---|---|
| Wax | Wax pattern temperature not stable |
Ensure the wax pattern has stabilized in temperature before applying shell layers |
| Shell | Poor adhesion of the prime coat to the wax pattern |
Increase the etch strength or etch time. Reduce the time from etch to 1st layer application |
| Shell | Large temperature drop when applying 2nd layer |
Increase the room humidity |
| Shell | Large temperature variation during prime coat drying |
Maintain +/- 3 F in the dipping and drying area |
| Shell | Drying too long |
Shorten the dry time |
| Shell | Drying too fast (large pattern shrinkage) |
Increase the room humidity or reduce airflow |
| Shell | Primary coat binder is gelled |
Test the primary coat binder to determine if it is gelled |
| Shell | Uneven primary coating thickness giving rise to variable rates of drying |
Modify the draining technique to produce a more uniform slurry coverage |
| Shell | Slurry dry out on sharp edges |
Shorten the draining time, increase the humidity in the shell dipping area |
| Shell | Poor adhesion and elasticity properties of the primary slurry |
Green strength additives in the primary slurry becoming unstable or ineffective |