Defect characteristics and detection methods
It is an open hole or a dark hole embedded with molding materials on the surface or inside of the casting. It can be found in all parts of the casting after box cleaning or X-ray fluoroscopy and machining.
Causes of formation
- The bonding strength of sand mold, sand core or coating is not enough, and it is scattered into the alloy liquid
- Because the core head and the mold core seat are crushed during assembly or the joint surface of the mold is crushed after the box is closed
- The strength of dry sand mold decreases due to too long stay time and damp
- The compactness of the mold or core is uneven, some parts are tight, some parts are loose
- When the sand mold or core is burnt during baking, the adhesive loses bonding effect or is damaged artificially (cracks, etc.) but not found
Prevention methods and remedial measures
- Improve the quality of sand mold and sand core
- Before mold assembly, check the core to see if there are cracks and other defects
- When the core is put into the mold for assembly, the size shall be checked with the measuring tools such as the sample plate to prevent the core from being damaged due to the mismatch and bulge
- Eliminate or reduce special protrusions and sharp corners on the mold
- Make the compactness of sand mold and sand core even and reach the appropriate compactness
- Strictly control the baking temperature of sand mold and core to prevent over burning of sand mold and core
- If the retention time of the mold before pouring is less than or equal to 4h and more than 4h, the mold shall be disassembled and baked or scrapped with blowtorch again