Buckling

BucklingBuckling2Buckling presents as a pyramid-like bump or lump (usually with a sharp peak) that appears on the surface of the casting. This defect indicates that the shell shrinks and loses adhesion to the wax pattern and buckles outward during the drying process. This is especially prevalent on primary coats and flat surfaces; indicating that the primary coat moved away from the wax pattern.

The causes of this defect are evident in the wax and shell portions of the process. To cure these causes, R&R recommends taking the following actions.


Area

Cause

Cure

Wax

  1. Inadequate pattern cleaning. The wax pattern was not washed properly and the first slurry coat could not adhere properly to the wax pattern.
  2. Temperature change in wax.
  1. Check pattern cleaner, change as required. Use non-silicone mold release. Improve pattern washing technique, ensuring that the release agent is removed from the pattern and the pattern wash is still effective.
  2. Make sure wax temperature has stabilized before dipping.

Shell

  1. Dried too fast.
  2. Dried too long.
  3. Low adhesion binder.
  4. 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.
  5. Temperature change in drying area.
  1. Slow down drying – reduce airflow and RH.
  2. Set maximum dry time for primary coats.
  3. Use different binder with improved wax adhesion.
  4. Check/add wetting agent. Use a high quality primary binder with good wetting/adhesion characteristics that is resistant to drying stresses. Polymer-containing binders reduce the propensity of colloidal silica to contract and flake as it dries.
  5. Control drying room temperature to ±3°F (±-16.1°C).

Metal

   

Other

   

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