The invention concerns a unique and advantageous clamping mechanism for a hot-runner manifold system used for injection molding. A fastener connection is provided between the hot-runner manifold block and the mold plate of the product mold for the injection-molding system. A sprue bushing is situated in the mold plate in tight fluid communication with the hot-runner manifold. Clamping members located on both sides of the hot-runner manifold are screwed into the mold plate and secure the manifold to the mold plate.
Hot-runner manifold systems are well known and are used to convey the synthetic-material melt, plastified by heating, into a plurality of individual sprue bushings positioned in mold plates of the injection-molding system. The manifolds keep the plastic material in a fluid condition while the material flows from the injection machine nozzle through the sprue bushings and into the mold cavity. Hot-runner manifold systems provide for use of a plurality of sprue bushings and multi-cavity molds and thus allow increased manufacture of more products.
The sprue bushings are inserted into recesses or bores in the mold plate. The top or inlet ends of the sprue bushings are positioned and sealed against the lower surface of the hot-runner manifold block. (The lower surface is also called the "underside" of the manifold block. In addition, the "top side" of the hot-runner manifold means the external side of the hot-runner manifold block, which lies opposite the lower surface and the sprue bushings.)
Known hot-runner manifolds commonly contain pairs of lugs which protrude on opposite sides of the block and which accommodate clamping screws. In order to produce such hot-runner manifold blocks, the external contours, including the externally protruding lugs, are machined from a larger block of metal material. This requires considerable expenditure of labor and waste of material.
Since the hot-runner manifolds are heated, they undergo thermal expansion when in operation, while the sprue bushings inserted into the injection-molding mold plate typically maintain their position. Such thermal expansion, depending on the dimensions of the hot-runner manifold block, may be relatively large, for example on the order of 3 mm. This causes twisting and distortion of the clamping screws inserted in the lateral lugs. Furthermore, the thermal expansion causes an increase in the surface pressure between the hot-runner manifold and the sprue bushings. This may cause the bushing to be forced into the bottom surface (under side) of the hot-runner manifold and cause surface damage (erosion) on the sealing surface.
Consequently, it is an object of the present invention to provide a clamping mechanism for hot-runner manifold systems which is an improvement over known fastening mechanisms. It is another object of the present invention to provide a clamping mechanism for hot-runner manifold systems which permits thermal expansion of the manifolds without adverse effects on the clamping screws and/or the sprue bushings.