A control pin ( 12 ) for controlling the flow of liquid metal in a casting process includes an elongate body member ( 34 ), the body member being made at least partially of a composite ceramic material that includes a fibrous reinforcing material embedded within a ceramic matrix. The body member ( 34 ) is preferably hollow and includes a wear-resistant tip ( 36 ) at one end.
1. A control pin adapted to control the flow of liquid metal in a casting process, the control pin comprising an elongate body member and a wear-resistant tip at one end of the elongate body member, the body member and the wear resistant tip being made of different materials the body member being made at least partially of a laminated composite ceramic material that comprises multiple layers of a reinforcing fabric embedded within a cast ceramic matrix, and the wear-resistant tip being made of a wear-resistant ceramic material.
2. A control pin according to claim 1 , wherein the reinforcing fabric comprises a woven reinforcing fabric.
3. A control pin according to claim 1 , wherein the reinforcing fabric is made of glass.
4. A control pin according to claim 1 , wherein the composite ceramic material comprises between 2 and 25 layers of reinforcing fabric.
5. A control pin according to claim 4 , wherein the composite ceramic material comprises between 4 and 10 layers of reinforcing fabric.
6. A control pin according to claim 1 , wherein the matrix material is selected from the group consisting of fused silica, alumina, mullite, silicon carbide; silicon nitride, silicon aluminium oxy-nitride, zircon, magnesia, zirconia, calcium silicate, boron nitride, aluminium nitride and titanium diboride, and mixtures of these materials.
7. A control pin according to claim 1 , wherein the matrix material is calcium based.
8. A control pin according to claim 1 , wherein the matrix material comprises calcium silicate and silica.
9. A control pin according to claim 1 , wherein the matrix material comprises Wollastonite and colloidal silica.
10. A control pin according to claim 1 , wherein the control pin comprises a non-stick surface coaling.
11. A control pin according to claim 10 , wherein the coating comprises boron nitride.
12. A control pin according to claim 1 , wherein the elongate body member is substantially cylindrical.
13. A control pin according to claim 1 , wherein the elongate body member is at least partially hollow.
14. A control pin according to claim 13 , wherein the elongate body member has a circumferential wall having a wall thickness in the range 1–10 mm.
15. A control pin according to claim 1 , wherein the wear-resistant tip is inserted at least partially into one end of the elongate body member.
16. A control pin according to claim 1 , wherein the elongate body member and the wear-resistant tip have complementary locking formations.
17. A control pin according to claim 16 , wherein the complementary locking formations comprise complementary recesses on the elongate body member and the wear-resistant tip, which are filled with an adhesive or cement.
18. A control pin according to claim 1 , wherein the wear-resistant tip is made of a material selected from the group consisting of fused silica, alumina, mullite, silicon carbide, silicon nitride, silicon aluminium oxy-nitride, zircon, magnesia, zirconia, calcium silicate, boron nitride, aluminium titanate, aluminium nitride and titanium diboride.
19. A control pin according to claim 1 , wherein the wear-resistant tip is made of a material having a density in the range 1800–3000 kg/m 3 .
20. A control pin according to claim 19 , wherein the wear-resistant tip is made of a material having a density in the range 1900–2500 kg/m 3 .
21. A control pin according to claim 1 , wherein the control pin has a length in the range 200–1000 mm.
22. A control pin according to claim 1 , wherein the control pin has a diameter in the range 20–75 mm.