This invention relates generally to injection molding and more particularly to multi-cavity thermal gated injection molding apparatus to coinject melt from two or more melt sources having a melt distribution plate mounted between the common manifold and the nozzle leading to each gate.
Coinjection of more than one type of melt is known in the art, as shown in U.S. Pat. Nos. 3,894,823 to Hanning which issued July 15, 1975, 4,373,886 to Hehl which issued Feb. 25, 1983, 4,657,496 to Ozeki et al. which issued Apr. 14, 1987 and 4,717,324 to Schad et al. Which issued Jan. 5, 1988. Thermal gated apparatus having heating and cooling in a cavity forming insert separate from the nozzle as shown in the applicant's Canadian patent application serial number 2,030,287 filed Nov. 19, 1990 entitled "Injection Molding Apparatus having Separate Heating Element in the Cavity Forming Insert".
While the above coinjection systems show each melt passage having only a single channel, the applicant's German patent application serial numbers P40 32499.0 entitled "A Method of Producing a Multi-Component Injection Moulded Part and a Multi-Cavity Injection Moulding System", P40 32500.8 entitled "A Method of Producing a Multi-Component Injection Moulded Part and a Multi-Cavity Injection Moulding System", P40 32508.3 entitled "An Injection Nozzle" and P40 32509.1 entitled "An Injection Nozzle for an Injection Moulding System and a Method of Producing the Same", all filed Oct. 12, 1990 show valve gated coinjection molding systems having an outer passage which extends through a pair of spaced channels in each nozzle. In order to thermal gate larger volumes of materials, it is preferable to have a heated cavity forming insert separate from each nozzle, and that each outer melt passage have more than two channels. However, it is also necessary to maintain balanced melt flow, avoid dead spots and minimize shear stress.