Conclusions
The thermal conductivity of moulding sands with binders,
which are broadly applied at making medium and large cast-ings, is very poorly known. Binders decomposition at a rela-tively low temperature renders measuring difficult and several
investigation methods are not suitable for investigating mould-ing sands being in such state. The developed, new methodol-ogy of investigating the moulding sands conductivity – by
means of the steady heat flow – allows to study this group of
sands. The performed tests allowed determining the thermal
conductivity in the range up to approximately 450C. The
minimum of the conductivity value at a relatively low temper-ature, (approximately 300-350C) is probably related to the
binder pyrolysis and heat emissivity, which disturbs and slows
down the heat flow from the casting into the mould.
It was pointed out in investigations, that the conductivi-ty increase can be achieved by introducing such additions as
graphite or steel shot into moulding sands. A low conductivity
of moulding sands with organic binders can prevent obtaining
a fine structure castings. The conductivity assessment under
conditions of an unsteady heat flow leads to similar conclu-sions. Moulding sands with organic binders reveal the lowest
conductivity at a temperature slightly above 300C. A much
better conductivity characterises moulding sands with inor-
357
ganic binder – water glass. The difference is specially visible
at higher temperatures, above 500600C.
A conductivity increase at the compaction degree increas-ing (which measure is the apparent density) is observed in all
kinds of moulding sands.