Both, the Croning process and the Hot-Box process require hot pattern equipment, and thus the energy to cure the binders. Ashland Chemical, a US Company, has introduced the Cold-Box process into mass production of cores in 1968; the cores of resin aggregates are cured without heating – in a cold core box (US Patent, 1966). The system was originally introduced as Ashland Cold-Box Process, now is referred to as Phenolic Urethane Cold Box process (PUCB). The process combines the advantages of the CO2 and the Hot-Box processes. From the CO2 process, it takes a similar sequence of curing at the room temperature using gaseous catalyst (controlled hardening), causing almost instant curing of the moulding aggregate. It also takes the benefits of the organic binders from the Hot-Box process, especially their superior shakeout features.
The principle of the process is that the resin-based moulding aggregate is compacted in an unheated core box by shooting, and then a catalyst applied as a vapour is transmitted through the moulding aggregate, producing rapid hardening within the core box or on the pattern plate. The amine catalyst is a slightly volatile, strongly odorous liquid which is corrosive (pH = 10) and, moreover, inflammable, and its vapours are explosive. The enclosed systems are therefore required for the vapour curing stage. After being shot into the core box (A), the core is purged by the catalyst vapour prepared in the generator (B). The gassing time is usually a few seconds. Since the catalyst vapour forms an explosive mixture with air, the carrier gas for the curing vapour is either nitrogen or carbon dioxide. The whole system is hermetically sealed, the used vapours are fed to the neutralizer (C) where they are incinerated or neutralized in phosphoric acid. More preferably, a chemical scrubber with H2SO4 is used to obtain the amine for reuse. The catalyst vapour cycle is followed by an air purge cycle that forces the amine gas through the aggregate mass to remove residual amine from the hardened core. The cured core is ready for ejection from the core box within 20–30 seconds after shooting.
Principle of Ashland cold box process;
A) core box assembly, B) gas generator, C) neutralizer / regenerator;
1 – core, 2 – corebox with input and output channel system, 3 – liquid amine catalyst,
4 – control air, 5 – carrier gas / purge air, 6 – spray nozzle, 7 – chemical scrubber, 8 – incineration of amine residues