Metal Penetration

Metal Breakout or PenetrationMetal penetration or breakout presents as an irregular metal formation; typically in slots, holes, passages or tight areas. This defect indicates that the metal "broke out", or penetrated the ceramic shell. This is usually due to the fact that the shell is typically too weak (due to structure or dryness) to adequately hold the metal in the desired shape. This defect is often referred to as "birdnesting" when it appears in corners.

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


Area

Cause

Cure

Wax

 

 

Shell

  1. Weak spots in the ceramic shell due to difficulty of buildup in details.
  2. Improper shell build in the detail area.
  3. Insufficient or poor shell drying.
  4. Excess slurry and/or stucco left behind.
  1. Use thinner coats to strengthen detail. Consider using ceramic cores.
  2. Use prewet, intermediate slurries and finer stuccos until the detail is adequately built.
  3. Allow extra dry time on these parts, especially during early shell coats.
  4. Improve draining and/or blow off excess stucco between coats.
  5. Use core material or preformed core to built deep pockets or slots.

Metal

 

 

Other

  1. Rapid depressurization of autoclave.
  1. Depressurize from maximum pressure to atmospheric gradually over about 2 minutes (evaluate autoclave operating parameters).

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