Chromite sand has excellent veining resistance. It is one of the mainstream special base sands in the foundry industry to solve veining defects.
Core Principle
Root cause of veining: At 573°C, quartz in silica sand undergoes crystal phase transformation with sharp volume expansion. This causes thermal stress cracking on the surface of sand cores, and molten metal penetrates the cracks to form veining.
Advantages of chromite sand:
- No crystal phase transformation and very low thermal expansion coefficient. It maintains stable volume at high temperatures without abrupt expansion like silica sand, greatly reducing the tendency of sand core thermal cracking at the source.
- Its thermal conductivity is much higher than silica sand. It dissipates heat rapidly and reduces temperature difference and thermal stress inside and outside the sand core to further inhibit crack formation.
- A dense solid sintered layer forms between particles at high temperatures. Even if tiny cracks occur, it can block the penetration of molten metal and stop the second stage of veining formation.
Application Notes
It is widely used for complex internal cavity sand cores, hot spot areas and facing sand (engine blocks / cylinder heads, valves, steel castings). It is often used to partially replace silica sand instead of the whole core to control costs.
Comparison: Veining resistance ranking: Cerabeads > Chromite sand > Olivine sand > Silica sand. Chromite sand has far better veining resistance than silica sand, but slightly weaker than cerabeads.
Chromite sand delivers good veining resistance. With low thermal expansion, no quartz phase transformation and high thermal conductivity, it effectively suppresses veining in resin bonded sand cores. It is a proven material for eliminating veining defects on internal cavities.