Defect characteristics and remedy of honeycomb in sand casting

Defect characteristics and detection methods

A wormhole or loose hole appearing in the thick part of a casting or in the transition part of a thick thin wall. Appearance inspection and X-ray fluoroscopy can be found evenly.

Causes of formation

The gas producing material in the mold interacts with the alloy liquid to produce a great deal of gas pressure. After the thin wall around the thick part has solidified, the gas breaks through the thick part which is still in the liquid state with great pressure, and then the part gradually solidifies and crusts

Prevention methods and remedial measures
  1. Improve the permeability of sand mold: ① Use molding sand with good air permeability. ② More air holes should be set up at the corner of the cavity which finally enters the alloy liquid. ③ Strictly control the humidity, tightness and uniformity of sand mold
  2. Adopt molding sand, core sand and bonding material with low gas generation
  3. Use dry sand mold for pouring if necessary
  4. Set and place appropriate chill according to the shape of the casting at the honeycomb hole to improve the solidification speed of this part
  5. Or increase the riser for air outlet and feeding at this position
  6. When using hygroscopic material as core binder, if the core is kept for more than one day and night, it shall be dried again before assembling sand mold
  7. The assembled sand mold shall be poured within 4h after assembly and shall not be placed on the hot bottom plate to avoid moisture absorption