Pyramid-like bump or lump (usually with a sharp peak) that appears on the surface of the casting
Indicates that the shell shrinks and loses adhesion to the wax pattern and buckles outward during the drying process
Especially prevalent on primary coats and flat surfaces; indicating that the primary coat moved away from the wax pattern
Causes of this defect are evident in the wax and shell portions of the process; to cure, R&R recommends taking the following actions:
Inadequate pattern cleaning.
The wax pattern was not washed properly and the first slurry coat could not adhere properly to the wax pattern.
Temperature change in wax.
Make sure wax temperature has stabilized before dipping.
Dried too fast.
Slow down drying – reduce airflow and RH.
Dried too long.
Set maximum dry time for primary coats.
Low adhesion binder.
Use different binder with improved wax adhesion.
Poor/low wetting agent.
The primary binder is not wetting the wax pattern sufficiently (low quality primary binder with poor wetting characteristics). As the layer dries, it experiences stress and contracts or flakes.
Temperature change in drying area.
Control drying room temperature to ±3°F (±-16.1°C).