Application of Cenospheres for high temperature alloy castings
Alumino-silicate cenospheres can be used in mould and shell materials for high temperature alloy castings, but they must be treated as a specialized lightweight refractory filler, not just a simple “add-on” to standard silica sand.
As a refractory filler in ceramic shells (investment moulds), alumino-silicate materials are well established and are often combined with colloidal silica binders; optimized Al2O3/SiO2 ratios (e.g. 60/40) improve hot strength and thermal shock resistance.
Replacing a fraction of dense refractories with cenospheres can reduce shell/mould density and thermal conductivity, which may decrease heat extraction rate and thermal gradients into the mould, sometimes beneficial for hot-spot control and thermal insulation around thin sections.
Nevertheless, keep in mind that cenospheres are hollow and significantly weaker than dense refractory grains; in cementitious systems, increasing cenosphere content reduces compressive and bending strength markedly and increases porosity. So In sand moulds, cenospheres are better used as a controlled, small percentage addition in a carefully formulated refractory or insulating “facing” or backing mix, rather than bulk replacement of silica sand in contact with critical thin walls.
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