Requirements of an environment protection concerning limitation of volatile substances
emission are forcing changes of several technologies applied in foundry practice. In the
first place the application of technologies using easily evaporating substances, including
alcohols, is limited. Restrictions concern alcohol protective coatings, which are substituted
by water coatings. Ethyl silicate, ceramic sands binding agent, is successively substituted by
colloidal silica in investment casting technology.
Drying and the following hardening of layers produced with using binders dissolved in
water solutions is a much slower process than the one with alcohol as a solvent. In some
processes, as e.g. at drying protective coatings on moulds and cores, these drying procedure
can be accelerated either by warming the mould (core) or by blowing warmed air. However,
such solution is not possible in the case of the investment casting technology, since mould
warming could cause deformation of a wax model. In the transitory period, and that is the
actual situation concerning this technology, the alternate building of layers: one with the
colloidal binder and the next with ethyl silicate is applied in several industrial plants. This
procedure accelerates the drying process, but can not be considered the final solution.