GB678035A - Improvements in processes for precision castings - Google Patents

Abstract

678,035. Moulding processes; mould materials. ROLLS-ROYCE, Ltd. March 16, 1951 [March 17, 1950], No. 6777/50. Class 83 (i). [Also in Group V] In a method for the precision casting of hollow articles, more particularly blades for internal combustion turbines made of a high melting-point metal, an insert of fired waterbound clay refractory is first supported in a die while a wax pattern is formed around it and is then supported in a flask, while the pattern is invested by the refractory mould material so that after melting out the wax, the insert remains as a part of the mould and after casting the article, may be removed therefrom by mechanical means. The insert is cast in a two-part plaster of Paris mould a, a<SP>1</SP> Fig. 1, having a filling opening d and an internal cavity with a central part c and end portions c<SP>1</SP> to form projections e on the insert. A suitable refractory for forming the insert comprises bentonite 1-5 per cent, pipe clay 1-10 per cent, china clay 10-60 per cent, flint powder 10-60 per cent, molochite 5-50 per cent, sodium carbonate less than 1 per cent, sodium silicate less than 1 per cent and water as required. Another suitable refractory comprises ball clay 4.5-5.5 per cent, pipe clay 11-12 per cent, china clay 15-17.5 per cent, flint powder 30-40 per cent, sodium silicate and sodium carbonate 0.125-0.250 per cent and water 26-35 per cent. Before the refractory has completely set, the mould may be inverted to allow some of the material to run out from the centre, thus leaving a hollow insert which is fired at up to 1000‹ C. The insert is then supported in a two-part die by its end projections while wax is injected to form the pattern around the insert. The insert is then supported at one end in a wax block g, Fig. 3, on the base h<SP>1</SP> of a flask h, a block of wax g<SP>1</SP> being inserted between the block g and the pattern f<SP>4</SP> in order to support the latter and to form a runner when the wax is melted out. The pattern and insert are invested with the mould material from a funnel j, and the wax melted out to leave the insert as part of the mould. After casting, the mould is broken away from the article and the insert destroyed as by sand-blasting.