GB332194A - Method and apparatus for making dental castings and molds for the same - Google Patents

Abstract

332,194. Meyer, F. S. April 0, 1929. Moulding processes ; patterns ; flasks; moulds.- In order to compensate for contraction during solidification of dental castings of gold, such as inlays and crowns, the plaster mould is made of a harder plaster than usual and at an elevated temperature so that the wax pattern is expanded. The wax model is carried by sprue former 12<c> adjustably secured in a chuck 11 of a recess former 10<a>, having a groove 10<b> filled with wax &c. to make a water-tight joint with the mould-ring. Mould materials. - The model is first coated with plaster of Paris containing 10 to 55 per cent of silica by means of a 'brush, the former 10<a> being rasped to eliminate bubbles from this coating I. The mould-ring 13, having a rib or groove 13<a>, is then heated and placed in position and filled with previously prepared fluid plaster containing a large proportion of silica and at a temperature of 110‹ to 125‹ F. The whole is then subjected to a temperature of about 110‹ to 130‹ F. and the plaster allowed to harden. The formers 10<a>, 12<c> are then removed and the mould is clamped by a flanged ring 16, Fig. 6, to a vessel 14 filled with water which is slowly heated until it boils the steam and water forcing the wax of the pattern out and into a trough 18. The mould is then dried at 300‹ F., preceded by a short period at 700‹ to 900‹ F. if desired, and cast without cooling. Treating mould materials.-Fig. 8 shows an oven for carrying out the process having an electric heater 26 for the 'vessel 14, an electrically heated chamber A at the higher temperature, a chamber B heated indirectly, and a top plate C for lower temperatures for drying, heating flasks, keeping fluid plaster o hot &c. The sprue former may comprise nested rod and tubes, that of the required size being slid out for use.