Atlas of Casting Defects
Negative
Small discrete positives which appear like grains of sand. When severe, the positives are closely clustered and the surface feels like sandpaper
N/A
Near gates, heavy sections or slow to cool sections of the casting
Burn-in, burn on, pimpling, stucco penetration, rough surface
Visual Inspection
Metal penetrates into the primary layer during casting. Pinholes or air pockets in the primary layer fill with metal during casting
OR
Stucco penetrates the primary surface and traps an air pocket against the wax
| Area | Possible Cause | Potential Correction |
|---|---|---|
| Shell | Stucco particles too large |
Change shell code, use finer stucco on the first few shell layers |
| Shell | Incomplete slurry mixing |
Insure the slurry is completely mixed before using in production |
| Shell | Foaming in slurry |
Insure air is not being sucked into the slurry by the mixer. Conduct antifoam test and adjust if necessary |
| Shell | Primary slurry instability (micro-gelling) refractory solids) |
Conduct gel test on binder solution. Replace slurry if bad |
| Shell | Prime slurry layer too thin |
Increase slurry viscosity or reduce slurry drain time. Modify drain orientation. Double dip the mold in the slurry. Increase the pre-wet drain time or orientation |
| Shell | Reaction with primary coat contaminants |
Ensure rusting or corrosion of the mixing equipment is not occurring. Remove iron contamination with magnets |
| Shell | Drain time too long before stucco application |
Optimize drain time. Train operators or adjust robot program |
| Shell | Rainfall sander too high above pattern |
Raise pattern in relation to sand fall |
| Shell | Non-uniform sand delivery from rain rainfall equipment |
Maintain or adjust equipment |
| Shell | Improper air flow in fluid bed |
Reduce air flow as needed, keep bed clean. Maintain sufficient flow to avoid having to force patterns into bed |
| Foundry | High ferrostatic pressure |
Reduce the height of the mold. Reduce the vacuum level. Reduce the spinning speed (centrifugal casting) |
| Foundry | Casting cooling rate too slow |
Speed up casting cooling, insure cast molds are not too close together. If penetration localized to hot spots, improve radiant heat loss by lengthening gates or increasing the spacing between adjacent parts |
| Foundry | Oxidized metal |
Improve melting and casting process to pre |
| Foundry | Metal temperature too hot |
Reduce metal temperature |