Why Sand Collapse Occurs in Lost Foam Casting and V-Process Casting, and How to Prevent It

Sand collapse—commonly known as “mold collapse” or “flask collapse”—is a typical defect in lost foam casting and V-process casting.

Causes of Sand Collapse

1. Insufficient airflow with excessive instantaneous pressure

2. Uneven sand compaction

3. Intermittent pouring

4. Air leakage or external pressure counteracting internal negative pressure

5. Uneven refractory coating thickness

Solutions

1. Optimize airflow and pressure parameters
Set a reasonable airflow rate. The instantaneous pressure and airflow should be determined according to the size and volume of the casting to maintain stable negative pressure.

2. Ensure uniform vibration compaction
The vibration amplitude of the compaction table should be maintained within 1.0–1.5 mm, with uniform amplitude. Three-dimensional vibration parameters should be consistent to ensure uniform compaction of the entire sand mold.

3. Maintain stable and continuous pouring
Pouring must be steady and accurate, without interruptions. Intermittent pouring introduces air into the mold, which counteracts the negative pressure and leads to sand collapse.

4. Prevent air leakage
Air leakage must be strictly avoided. The upper sealing film should be firmly pressed and properly covered with sand to prevent molten metal splashing and burning through the plastic film, which would cause air leakage and result in mold collapse.

5. Ensure uniform coating thickness
The refractory coating layer must be uniform—neither too thin nor too thick locally. Uneven coating allows molten metal penetration into the sand, which can also cause sand collapse.