Sand expansion defects

These defects belong to the group of mold-based casting defects (see mold-based casting defect) which can occur due to thermal expansion of the molding base material (see Sand expansion) under the influence of the casting heat.

Especially with quartz sand, the transformation of the α quartz into the β quartz (see Quartz) leads to a considerable increase in volume and associated strong compressive stresses which can lead to sand expansion defects such as scabbing and rat tails.

Fig. 1 shows the expansion behavior of different molding base materials.

 

  • Figure: Thermal expansion of different molding base materials:1) Quartz sand, 2) Feldspar, 3) Chromite sand, 4) Andalusite, 5) Fireclay, 6) Cerabeads, 7) Zircon sand
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