| 摘要 |
Silica sand is coated with low-alkalinity sodium silicate and treated with NaOH to produce a dry free-flowing sand that requires a minimum time (1/2-3 mins) when gassed with CO2. The water of hydration is kept to 10-20% of the maximum, and the weight of coating is only 1-2% of the weight of sand. Gassing is done at a pressure of 0.035-0.15 kg/cm2 through a rubber sheet with holes in it, and vented through holes in the pattern and bottom plate. By the use of a low alkalinity binder, the mould is easier to release from the pattern and the reduced gassing time allows greater productivity from one pattern. Temperature rise on gassing is no more than 5 degrees and the mould has good shelf life and stability before casting. |
