374,450. Dental flasks ; casting- apparatus ; moulding indiarubber and artificial resin. JOANNIDES, C., 88, Fenchurch Street, London. Nov. 2, 1928, Nos. 31995/28 and 26547/29. [Class 87 (ii).] Comprises improvements in apparatus for the production of dentures from thermoplastic material by the injection process designed to avoid contamination of the mould and the detrimental action of steam upon the rubber in the mould ; to expedite the heating of the mould ; and to avoid overheating of the material in the injecting-device. The flask is isolated from the water used for heating and scouring and means is provided to prevent steam from entering the mould; and the injector is separately heated and is placed in operative position after the mould has been scoured and drained. The apparatus is also constructed that scouring, injection and vulcanization or hardening may be performed without removing the flask. As shown in Fig. 1, the apparatus comprises a boiler 10 formed with a recess 12 to receive the flask 14 of substantially the same shape. A spring 55 presses the flask against the inner face of a cover 20 closing the recess. The flask is formed with openings 33 registering with openings 33a in the cover and the cover is recessed at 54 to form an annular space to which steam may be admitted from the boiler by opening a valve 26, Fig. 2. The boiler is also furnished with a pressure reducing valve 52 which is opened during the scouring operation. Water is introduced into the boiler through an inlet 51, Fig. 1, inset to determine the filling level. The inlet is closed by a plug 51a which may carry an electric heating element 56 ; or the boiler may be heated by a gas burner 46. As shown, the openings 33 are disposed one above the other to facilitate draining of the mould. The scouring attachment comprises a member 60, adapted to be clamped to the cover 20 by a screw 67, furnished with horizontal tubes 57 terminating in nozzles 58 adapted to enter the openings 33 and fitted with rubber packing rings 59 to form steamtight joints. The upper tube 57 terminates in a branch tube 61 adapted to be connected by a hose 62 to a valve 63 communicating with the water space in the boiler ; the lower tube terminates in a vertical draining limb 65. In use, the flask containing the wax model invested in plaster and dried, is inserted into the recess 12 and the cover 20 is closed and the scouring attachment 60 is placed in position. Owing to the proximity of the walls of the flask and those of the recess 12, the mould is rapidly heated, and heating is assisted by admitting steam through the valve 26 to the space 54. The upper flask opening 33 is at or near the centre of the flask and communicates with the model through a wax or metal spine 50 ; the lower opening is near the extremity. After melting of the wax, the hose 62 is connected to the tube 61 and the valve 63 is opened to admit water from the boiler for scouring, the pressure-reducing valve being first opened. Scouring is continued until steam flows through the mould and outlet 65 after which the valve 63 is closed and the hose 62 is disconnected. The valve 52 is then closed and heating continued to ensure complete draining and drying of the mould ; if desired, air, preferably hot, may be forced through the mould. Injection is then effected by replacing the attachment 60 by the injector 84, Fig. 3, which is of.the type described in Specification 374,470, and has been previously heated to a degree sufficient to permit the screw 85 to rotate easily. The base rubber is supplied in strip form from a reel, as described in Specification 374,471, mounted upon a stud 90c. To avoid overheating of the rubber, the mould should be heated to a temperature below the melting- point of sulphur, the proper temperature being determined by a test injection. As shown, the injector is not subjected to the direct heat of the boiler. When the rubber exudes from the lower opening 33, injection is stopped and the injecting device is removed. Closing-plugs 34, 35, Fig. 4, having internal, spring-actuated, counter plugs, are then inserted into the openings 33a and, after allowing excess rubber to escape, are screwed home to seal the openings 33. Before the plugs are completely closed, the valve 26 is opened to admit steam to the space 54 and drive out air ; the plugs are then closed and the temperature of the boiler raised to complete vulcanization. After vulcanization, the valve 26 is closed and the cover 20 is removed to allow the flask 14 to be withdrawn. Instead of effecting the vulcanizing operation in the apparatus, the flask may be removed after injection, the openings 33 being closed by plugs 119, Fig. 9, carried by a clamp 121, and transferred to a separate vulcanizer. To facilitate removal of the finished denture from the flask, a press 102, Fig. 6, is provided. This press may also be used to apply and withdraw the cover 116, Fig. 9. The openings 33a, Figs. 1 and 3, are coarsely threaded so that the injector may be quickly inserted and withdrawn, and are of equal size so that injection may be effected through either opening. In the modified apparatus shown in Fig. 3, the openings 33a are formed through the wall of the boiler. For artificial resin, injection is effected through the lower opening, and in place of the closing-plugs, the flask openings are closed by a slide 96 which is forced down bv a screw 98 in the cover 20. In this modification, the valve 26 is formed as a screwed plug adapted to be operated by an oppositelythreaded member 27. Fig. 4 shows a further modification of the apparatus adapted to receive a two-part flask 14 which is partly packed by hand. The two parts of the flask are forced together by springs 24 on the cover 20 and are locked by spring clamps 15. In this modification the openings 33a are at the same level and draining of the mould is effected by blowing and evaporation. When large numbers of dentures are required, each flask is scoured by hot water from a separate supply, e.g. by water passed through a serpentine coil heated by a suitable burner; and each flask, after injection is transferred to a separate vulcanizer. To avoid repeated filling of the boiler, the flask while in the apparatus, may also be scoured by water from an external supply. To avoid damage of the flask openings by the closing plugs, such openings may be formed in removable bushes of sulphur-resisting material, e.g. stainless steel, nickel-chrome, &c.