Hot sprue bushing with interchangeable tip having multiple edge gates

A hot sprue bushing for transporting plasticized material from injection nozzles to the edges of mold cavities while controlling the temperature thereof, said hot sprue bushing comprising:

• at least one heating cartridge;
• an elongated body of given length having arranged in order along its length a head, a stem, and a tip end, said head having a reference seating surface which faces said tip end and a rear surface facing opposite said tip end, said elongated body having a through bore passing from end to end through said head, stem, and tip thereof for transporting plasticized material through at least a portion of said elongated body from said head toward said tip end thereof, said elongated body having at least one nonthrough bore extending alongside said through bore, in heat conducting relationship with respect thereto, and receiving said heating cartridge for controlling the temperature of plasticized material as it travels along said through bore, said nonthrough bore having a length which extends from said head rear surface, through said head and said stem and into said tip end by a predetermined distance, said length of said nonthrough bore being shorter than said given length of said elongated body, said through bore being counterbored a given depth near said tip end of said elongated body, said body being fabricated of a material with a predetermined heat capacity and coefficient of thermal conductivity to provide it with a predetermined mass and heat transfer capability;
• and
• a tip fitted into said counterbore of said elongated body so that part of said tip is in heat conducting relationship with respect to said elongated body while its remaining parts are thermally isolated therefrom, said tip being releasably mateable with said elongated body and having a flow bore which is adapted to communicate with said through bore of said elongated body to receive plasticized material from it, said tip including a plurality of branch flow channels that communicate with said flow bore thereof and terminate in openings for edge gating with a plurality of mold cavities, said tip being fabricated of a material that has a thermal mass less than that of said body material and a coefficient of thermal conductivity substantially higher than that of said elongated body material so that said elongated body acts as a constant temperature source with respect to said tip so as to transfer heat to said tip at said portion thereof in thermal contact therewith to heat said tip and maintain said tip at temperatures for plasticizing material without requiring heating apart from that supplied to said body by said heating cartridge.