what is gas hole in sand casting defects?
Sand casting is a means of producing rough metal castings using a mold usually made from sand formed around a replica of the object to be cast that is removed once the sand has been compacted.
A gas hole is a defect in the casting that occurs due to trapped gases and dirty metal. Gases get trapped due to hard ramming or improper venting. These defects also occur when excessive moisture or excessive gas forming materials are used for mould making.