A cold-setting process is based on the ambient-temperature hardening of a binder after it is combined with reagent or catalyst, introduced as liquids during the aggregate mixing. Curing of the binder system begins immediately after all components are combined. For a period of time after the initial mixing, the moulding aggregate is workable and flowable to allow the filling of the core or the moulding box. After an additional time period, the moulding aggregate cures to the point where it can be removed from the box. The time difference between filling and stripping of the box can range from a few minutes to several hours, depending on the binder system used, curing agent and its amount, a base aggregate type and its temperature.
The cold setting processes are characterized by two important parameters: bench life and strip time. The bench life is a time interval until the moulding aggregate retains its moulding properties and must be processed after preparation. It is defined as the time needed for the moulding aggregate to reach the strength value of 7 kPa. The strip time is a time interval until the moulding aggregate reaches the handling strength, when the core can be removed from core box, or the mould separated from pattern plate. The handling strength is defined as 140 kPa. The ratio of the bench life to the strip time characterizes the behaviour of the mixture. The closer this ratio to 1, the more suitable the bounding system for the foundry purposes. The best ratio is exhibited by the polyurethane-based cold-set system, so-called PEP-Set, which achieves almost ideal moulding properties.
There are a lot of individual cold-setting binder systems, whether organic or inorganic. There is the classification of some of the more important self-setting binder systems:
- Acid Catalysed systems:
- furan resins,
- phenolic resole resins (Gisag Cold-Box).
- Ester-Cured systems:
- alkaline phenolic resin (Alphaset, Novaset),
- sodium silicate – an inorganic alternative.
- Phenolic urethane system (PUN) – phenol novolac resin + polyisocyanate (hardener) + amine catalyst (Pep-Set);
- Alkyd-Oil-Urethane system – low cost, but post-cure is required.