Atlas of Casting Defects
Positive
Faceted or pyramid like surface with a distinct ridgeline often associated with flash
N/A
Flat featureless surfaces
N/A
When a shell buckles, it only separates from the pattern. With prime coat lift, the shell also fractures, allowing the backup layers to fill the gap between the primary layer and the wax pattern
The bond strength of the primary layer to the wax patter is insufficient and the primary layer buckles (lifts) off the pattern. The bond strength can be insufficient for a number of reasons including stress on the primary layer as it shrinks during drying.
| Area | Possible Cause | Potential Correction |
|---|---|---|
| Wax | Temperature change in wax causes the wax to move and disrupt the primary layer bond. Wax pattern temperature not stable |
Ensure the wax pattern has stabilized in temperature before applying shell layers |
| Wax | Pattern cleaning inadequate. Poor adhesion of the primary coat to the wax pattern |
Increase etch strength or, time in etch. Reduce the time from etch to primary layer |
| Wax | Pattern cleaning inadequate. Poor adhesion of the primary coat to the wax pattern |
Increase etch strength or, time in etch. Reduce the time from etch to primary layer |
| Wax | Pattern flexing during dipping |
Add additional pattern supports |
| Shell | Large temperature change |
Control the dipping area to +/- 3 F |
| Shell | Dried too long |
Set a maximum dry time |
| Shell | Dried too short |
Insure the primary layer is completely gelled before applying backup layers |
| Shell | Poor prime coat wetting |
Confirm the prime slurry is wetting the pattern |
| Shell | Low adhesion binder |
Increase polymer level |
| Shell | Drying too fast (high pattern shrinkage & drying stress) |
Slow down (Increase) the drying by reducing airflow or increasing room humidity or reduce airflow |
| Shell | Pre-wet is lifting prime |
Eliminate pre-wet or reduce dry time between pre-wet and slurry application |
| Shell | Too much slurry on interior surfaces |
Decrease slurry viscosity or increase drain time |
| Shell | Too little slurry on interior surfaces |
Increase slurry viscosity or decrease drain time |
| Shell | Insufficient stucco on interior surfaces |
Don’t let slurry surface dry or over drain before stucco application |
| Shell | Primary slurry in poor condition |
Employ proper slurry controls |
| Shell | Soaking (saturating) the mold promotes lifting. Vibration too high |
Eliminate pre-wets. Vibration used during dipping can cause the primary coat to separate from the pattern |
| Shell | Pattern flexing during dipping |
Add additional pattern supports |
| Shell | Soaking (saturating) the mold promotes lifting |
Stucco molds immediately after slurry has drained |
| Shell | Pre-heat causes mold deformation |
Increase hold time between de-wax and pre-heat |
| Shell | Thermal expansion mismatches within the shell |
Change shell composition |
| Other (Mold design) | Pattern is too flat and featureless |
Add ribs or dimples to break up flatness and create features |
| Other | Pattern flexing during dipping |
Add additional pattern supports |