Inorganic binder system
A composition for making cores and a process for metal casting, the composition comprising: a particulate refractory material; an inorganic binder comprising at least one alkali metal silicate; a pozzolanic additive; and a lustrous carbon former. The process includes forming a core from the composition and assembling a mould comprising the core and supplying molten metal.
1. A composition for making a core for use in a metal casting process, the composition comprising:
a particulate refractory material;
0.5 wt % to 5 wt % of an inorganic binder comprising one or more of sodium silicate, potassium silicate, lithium silicate, or a combination thereof;
0.1 wt % to 2 wt % of a pozzolanic additive, comprising one or more of silica fume, fused silica, pyrogenic silica, and micro-silica; and
0.1 to 1.5 wt % of a lustrous carbon former,
wherein said weight percentages are relative to the weight of the particulate refractory material.
2. The composition according to claim 1 , for making a core for use in a ferrous metal casting process, and wherein the lustrous carbon former is a strong lustrous carbon former, wherein the strong lustrous carbon former has a lustrous carbon content of at least 15%.
3. The composition according to claim 2 , wherein the strong lustrous carbon former comprises one or more of: asphalt; hydrocarbon resin; polystyrene; and gilsonite.
4. The composition according to claim 1 , for making a core for use in a non-ferrous metal casting process, and wherein the lustrous carbon former is a weak lustrous carbon former, wherein the weak lustrous carbon former has a lustrous carbon content of less than 15%.
5. The composition according to claim 4 , wherein the weak lustrous carbon former comprises one or more of: graded coal, coal dust, and seacoal.
6. The composition according to claim 1 , wherein the particulate refractory material comprises sand.
7. A core formed from the composition of claim 1 .
8. A process for producing a metal article by metal casting, the process comprising:
(i) mixing a composition according to claim 1 to form a mixture;
(ii) moulding and hardening the mixture to produce a core in the shape of an internal cavity of the article;
(iii) assembling the core with a mould for metal casting, such that the mould and the core together define a casting cavity;
(iv) supplying molten metal into the mould cavity until the mould cavity is filled;
(v) cooling and solidifying the molten metal to form the article.
9. The process of claim 8 , for producing a ferrous metal article by ferrous metal casting, wherein;
step (iv) is carried out at a temperature of at least 1000° C.
10. The process of claim 8 , for producing a non-ferrous metal article by non-ferrous metal casting, wherein;
step (iv) is carried out at a temperature of less than 1200° C.