Cold-box amine hardened phenolic urethane

The chemistry of this polyurethane based process is very similar to the polyurethane eold-setting one, e.g. it involves a phenolic resin and an isocyanate (MDI). Only the eatalyst is different here a tertiary amine is used, such as triethylamine (TEA), dimethylethylamine (DMEA), dimethylisopropylamine (DMIA) or dimethylpropylamine (DMPA). The amine is applied as a vapour, using compressed air, nitrogen or CO2 as a carrier gas. Both resin and isocyanate are in solution in aromatic and/or polar solvents that have high boiling points. Contamination by water must be strictly avoided as it reacts strongly with isocyanate and weakens the binder. 

The amine is delivered either by a generator, in which a supporting gas, preferably inert, is saturated with amine vapours, or by an injector, which measures out just the right amoimt of amine required for the operation, this latter being carried to the sand by compressed air or gaseous nitrogen. The addition rate for the binder varies from 1.0 to 2.0 % based on the sand weight, with resin and isocyanate in a 50 50 ratio. 

The amine is just a catalyst and is not consumed in the reaction. After curing, it remains in the sand of the mould or core and has to be purged. The purging period currently lasts 10 to 15 times longer than the injection of the amine. The amount of amine required for curing is about 0.05 % based on the sand weight, but typically 0.10 to 0.15 % is used. 

In a variant of the process called the Cold-box Plus process the corebox is heated to 40 - 80 °C using circulating hot water. This yields cores with even better mechanical properties, but results in higher interval times. 

---