SO2 hardened furan resins

This process uses furan resins, which contain about 80 % furfliryl alcohol. Both resins polymerise under acid conditions. These resins need to be mixed with the sand and with oxidising agents, such as organic peroxides or hydrogen peroxide. The reaction between these peroxides and the injected sulphur dioxide then generates sulphuric acid, which causes a rapid polymerisation. The gassing period is always followed by a purging period, the purpose of which is to remove the excess unreacted sulphur dioxide from the mass of sand. 

4 SO2 hardened epoxy/acrylic (free radical curing) 

The gassing period is always followed by purging with the same inert gas that was used for curing, the purpose of which is to remove the unreacted excess sulphuric dioxide from the sand mass. 

The silicate generally used is sodium silicate, defined by its concentration (dry solid content) and modulus (silica soda ratio Si02/Na20). This modulus ranges from 2.0 to 2.8, the most common being 2.0 to 2.3. This silicate is mixed with the sand at a concentration of between 2 to 4 %. Shake-out and de-coring additives are commonly used and are usually pre-mixed with the silicate. 

Curing occurs by gassing with carbon dioxide, due to its sUghtly acidic character. The C02-ratio should not exceed 1 to 2 % of the mass of sand, with a gassing time in the range of 10 to 60 seconds. The cured moulds and cores do not require pinging. 

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SO2 hardened epoxy/acrylic (free radical curing). As for gassing and purging, collection and treatment are described in the SO2 hardened furan resins section. The best gassing conditions for achieving cores with good characteristics require ... 

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