Plastic injection molding system with multiple tip torpedo heater

A plastic injection molding system comprising a mold having first passageway means into which a fluid plastic flow stream is introduced, said first passageway means communicating with a sprue passageway, said sprue passageway, being formed by a cylindrical bore with tapered opposite ends communicating with respective small diameter gates through which fluid plastic material is directed;

• means defining mold cavities in communication with said gates;
• a composite torpedo heater comprising an elongated metal casing having an exposed outer cylindrical surface with tapered, pointed tips at opposite outmost ends thereof;
• means supporting said torpedo heater concentrically in said sprue passageway bore with said tips each in closely adjacent relation to one of said gates and with said outer exposed casing surface and said bore defining an unobstructed annular fluid plastic flow passageway about each said tip and a portion of said casing adjacent said tip and substantially along the entire length of said casing through which fluid plastic material is directed at an elevated temperature;
• said annular flow passageway having a radial width defined by the distance between the outer perimeter of said casing and the inner perimeter of the cylindrical bore that is less than the diameter of said casing;
• said casing being formed with an internal bore at the location of each said tip;
• said casing having an outer diameter of about twice the diameter of said casing bore so as to define a thick casing wall about the bore,
• electrical heating means disposed in the bore of each said tip;
• said heating means comprising a core with a resistance wire disposed thereon and heat transmitting material surrounding the wire and core, said heat transmitting material being compacted about the resistance wire and core for filling all air voids therebetween and effecting efficient heat transfer;
• means existing said casing intermediate the ends thereof for electrically coupling said heating means to a power source for enabling heating of said heating means and heat conduction outwardly through said thick casing wall for heating fluid plastic material directed through said annular flow passageway and over said tips to a desired temperature independent of temperature conditions external to said casing;
• and
• means for regulating the temperature of said heating means and thus the temperature of said tips and fluid plastic material directed through said annular flow passageway and over said tips.