| 摘要 |
In forming a metal-casting mould, an intimate mixture of a finely divided refractory material and a binder consisting of a liquid alkali metal silicate and a soluble solid alkali metal silicate in admixture is applied, to a casting-defining surface and then rigidified by application of a gas such as carbon dioxide. In preferred mixtures, an organic compound such as glycerine or sucrose is included, the refractory material constitutes 90-97% by weight of the mixture, the liquid alkali metal silicate constitutes 60 to 99% by weight of the binder and has a silica to alkali metal oxide molar ratio within the range 1,55 : 1, to 3,41 : 1,0, and the solid alkali metal silicate has a silica to alkali metal oxide molar ratio between 3,41 : 1,0 and 1,0 : 2,0. According to an example, a silicate binder composition consisting of 90% liquid sodium silicate (1 Na2O : 2,48 SiO2) containing 46,6% solids and 10% powdered anhydrous sodium metasilicate was prepared by adding the solid silicate to the liquid silicate; the resultant silicate mixture had an Na2O : SiO2 ratio of 1 : 2,07 and a solids content of 51,94%. The compressive strength of a two inch square cube of a sand-silicate mixture prepared by admixing 95% fine and -5% silicate mixture, after exposure to carbon dioxide for 10 seconds was 172 p.s.i; a similarly proportioned sand-silicate mixture employing a silicate binder consisting of 100% liquid sodium silicate had a compressive strength of 55 p.s.i. Specification 847,477 is referred to. |
