INJECTION MOULDING

1390912 Injection moulding BRITISH UNITED SHOE MACHINERY CO Ltd 15 May 1972 [15 May 1971] 15139/71 Heading B5A In a method of injection moulding, e.g. shoe soles, after completion of injection, a plug P (Fig. 2) is inserted into the sprue bore 22 which leads to the mould cavity, to prevent escape of moulding material from the bore 22. In a first embodiment (Fig. 2) injection is effected through a passage 12 in an injection head 10 and an aperture 38 in a slide member 36, a purging member 13 being retracted beyond an inlet port (not shown) extending into the passage 12 from a mixing chamber. On completion of injection, the purging member 13 is advanced to the position seen in Fig. 3 (not shown) thereby ejecting residual material from the passage 12 into the aperture 38 and bore 22. The slide 36 is then moved to bring a second aperture 40 into line with the passage 12 and bore 22, the aperture 40 containing a plug P left from the preceding injection operation. By advancing the member 13 to the position seen in Fig. 4 (not shown) the plug P is pushed into the bore 22. The next injection is effected through the aperture 40, and partly soldified material (P1) remaining in the aperture 38 is used for the plug. In a second embodiment (Fig. 7) the slide 36 of the first embodiment is replaced by a generally circular member 86 which has a plurality of apertures 90 and is rotatable on a shaft 88. A plurality of mould assemblies are provided, part of one being shown at 70 with its sprue bore 72. A mixing chamber 74 is connected through a port 75 to an injection passage 62 containing a purging member 63. Operation is similar to the first embodiment but the member 86 rotates through #th of a revolution where eight mould assemblies are provided. In a third embodiment (Fig. 9) the plug P 2 which is inserted into the sprue bore 122 is punched out of a ribbon R of resilient expanded plastics material by a purging member 113. This member 113 is a close fit in the injection passage 112 which is connected by a port 125 to a mixing chamber (not shown). Injection is effected through the hole in the ribbon R formed during the preceding injection operation. The ribbon is moved forwards by automatic feeding means. In a fourth embodiment (Fig. 10) pre-formed plugs P 3 slide from a hopper 195 down a raceway 194 and are fed by loading mechanism 196 into one of a plurality of apertures 190 in a circular member 186. The member 186 is rotated automatically to bring the apertures 190 in t