Hot-runner mold for injection molding

In a hot-runner device for injection molding, including:

• a hot-runner block having therein a first hot-runner passage, said hot runner block having therein a first outlet opening which provides fluid communication between said first hot-runner passage and a location external to said hot-runner block;
• an outer stem supported in said first hot-runner passage for movement between two positions in which an end thereof is respectively engaging and spaced from a portion of said hot-runner block which has said first outlet opening therein, said outer stem having therein a second hot-runner passage and having in said end thereof a second outlet opening which is aligned with said first outlet opening and which provides fluid communication between said second hot-runner passage and a location external to said outer stem, an outer surface of said outer stem in the region of said end thereof being spaced inwardly from an inner surface of said first hot-runner passage;
• an inner stem which is smaller in cross-sectional size than said second hot-runner passage and is supported in said second hot-runner passage for reciprocal movement relative to said hot-runner block and said outer stem between first and second positions in which said inner stem is respectively spaced from and obstructing fluid flow through each of said first and second openings, said inner stem being movable to a third position which is between said first and second positions and in which said inner stem is spaced from said first outlet opening but is obstructing fluid flow through said second outlet opening;
• means for selectively supplying respective moldable materials to said first and second hot-runner passages;
• and fluid actuated means for selectively effecting movement of said inner and outer stems relative to said hot-runner block and independently of each other;
• the improvement comprising wherein said fluid actuated means includes said hot-runner block having therein a first chamber, said first hot-runner passage opening into said first chamber at a location remote from said first outlet opening, includes said outer stem having on an end thereof remote from said second outlet opening a first piston which is movable within and slidably sealingly engages an inner surface of said first chamber and which has therein a second chamber, said second hot-runner passage opening into said second chamber at a location remote from said second outlet opening, includes said inner stem having thereon a second piston which is movable within and slidably sealingly engages an inner surface of said second chamber, and includes means for selectively supplying pressurized fluid to said first and second chambers in a manner effecting reciprocal movement of said first and second pistons therein;
• wherein said first piston has means for providing fluid communication between said first and second chambers on sides of said first and second pistons remote from said first and second outlet openings, and wherein said means for selectively supplying pressurized fluid to said first and second chambers includes first and second fluid passages which respectively communicate with said first chamber on opposite sides of said first piston, a circumferential groove provided in and encircling said first piston, an opening in said first piston which provides fluid communication between said circumferential groove and said second chamber on a side of said second piston nearest said first and second outlet openings, and a third fluid passage which communicates with said first chamber at a location which is aligned with said circumferential groove in said first piston in all operational positions of said first piston.