| 摘要 |
<p>This invention relates to an improved valve-gated injection molding mechanism illustrated in a multi-cavity arrangement. A vertical valve pin reciprocates in a central bore in a heater enclosed in the mold actuated by an air operated piston through a rocker arm to precisely control the opening and closing of a gate into a cavity through which pressurized molten plastic material is supplied from a molding machine. A titanium alloy seal is provided in an air space between the heater nozzle and the mold near the gate to reduce the quantity of molten plastic material flowing into the space thereby reducing the creation of cold slugs and problems on color changes. The lower portion of the valve pin is formed of a highly conductive material such as a beryllium-copper alloy to increase heat transfer to the lower tip of the valve pin. This reduces the resistance of the valve pin penetrating the cold slug in the gate area, which permits a reduction in the amount of force necessarily transmitted through the rocker arm, thus reducing wear of the mechanism and increasing its operating life span. Structure of the rocker arm valve pin and piston is provided which eliminates rotation of the valve pin or piston relative to the rocker arm during use. This enables bearing contact to be made between the valve pin, rocker arm and piston along transverse ridges, thereby reducing pivotal wear. The rocker arm pivots about a pivot pin, the ends of which are received in a pair of downwardly opening slots in the mold for ease of manufacture and assembly.</p> |
