Atlas of Casting Defects
Positive
Gradual thickening of the casting wall. May have finning in the area of the bulge. May not be detectable by the naked eye but can be caught by gauging.
N/A
Parallel surfaces, deep holes, or slots. Adjacent patterns on assembly. Large flat featureless surfaces
Bulging, bulging cracking, bulging overheating, shell bulge
Shell bulge generally has a more rounded surface
Permanent defection of
the mold wall either during
dewaxing or casting.
| Area | Possible Cause | Potential Correction |
|---|---|---|
| Wax | Patterns too close causing premature bridging |
Use spacers during assembly to produce consistent pattern spacing |
| Shell | Shell too thin |
Add shell layers or add stiffening feature |
| Shell | Mold hot strength too low (mold creeping during casting cooling) |
1) Increase refractoriness of the shell 2) Ensure optimal SiO2 levels in the backup slurry 3) Ensure uniform mold thickness |
| Shell | Slurry not wetting out area |
1) Use vacuum dipping or re-orient pattern. 2) Use a thinner slurry |
| Shell | Slurry/stucco not getting into area |
Use a “poured core” |
| Shell | Stucco not getting into area |
1) Rainfall, hand pour or re-orient pattern 2) If bridging in slots or holes, use a finer stucco or make sure hole is open prior to applying subsequent dips until sufficient slurry/stucco has been applied |
| Shell | Slurry is being washed away when subsequent coats are applied |
Ensure sufficient intra-coat dry time and conditions for hard to dry areas of the mold |
| Shell | Green strength of the shell is too low to withstand dewaxing |
1) Increase the dry time between each layer 2) Apply additional coats 3) Increase final dry time 4) Redesign assembly to permit a more rapid heat transfer to all parts of mold 5) Vent pattern cavities 6) Check dewax process for optimal performance and that it is in control |
| Shell | Deformation during dewaxing |
See “Finning” |
| Foundry | Solidification time too long |
Decrease metal temperature, decrease mold temperature, speed casting cooling rate |
| Foundry | Ferrostatic pressure too high |
Reduce vacuum level, reduce spinning rate (centrifugal) |
| Foundry | Ferrostatic pressure too high |
Reduce the metal height above the part |